Дисертації з теми "CO2 capture and utilization"

In this PhD thesis, different types of hybrid organic-inorganic materials were studied as solid sorbents for the carbon dioxide capture, in order to give additional hints to the comprehension of phenomena playing an important role in CO2 adsorption processes. In the first part, hybrid organic-inorganic SBA-15 silicas functionalized with variable amount of amino groups were studied aiming to evaluate the influence of the different basic species on CO2 capture ability. Afterwards, it was decided to study the influence of siliceous support properties on the adsorption process. For this purpose, silica-based materials with different structure, morphology and particle size were selected and tested in the same experimental conditions, aiming to understand the effect of their physico-chemical properties on the CO2 adsorption. On one side MCM-41 silica-based materials with different particle diameter, passing from micrometric to nanometric scale, were considered, in order to study the size effect of the support on the adsorption properties. Furthermore, the effect of the porosity was evaluated by using as adsorbent a non-porous material (Stöber silica) and comparing the obtained results with those of MCM-41-based materials. Finally, the possible use of silica-based materials as catalyst for the carbon dioxide transformation into more useful products was studied. In particular, heterogeneous Cu-based catalyst supported on SiO2 have been studied as for the promotion of hydrogenation reaction of CO2 to formic acid.

As mankind attempts to halt climate change and global warming, large-scale carbon dioxide (CO2) capture, utilization and storage (CCUS) technologies are viewed as an indispensable approach to curb CO2 emission. This thesis focused on better understanding CO2-amine interactions during adsorption, while developing in parallel covalently immobilized polyethylenimine (PEI) adsorbents for CO2 adsorption. In addition, catalyst reusability issues reported in the synthesis of cyclic carbonates (CCs) from CO2 and epoxides using metal-free supported immobilized quaternary ammonium salts are addressed, while developing new organosilicas for the synthesis of CCs. The reaction between CO2 and amine was investigated at the gas-solid interface in an attempt to provide a unified CO2-amine interaction both in adsorption and absorption. A combination of density functional theory calculations and experimental data (FTIR and 13C NMR) showed that the formation of the zwitterion intermediate often reported in the literature is highly unlikely, instead a six-atom centered zwitterion mechanism involving the “assisting” effect of water, amine or other functional groups was found to be more feasible due to its lower activation energy. Moreover, evidence was provided to suggest that under humid conditions, bicarbonate and carbonate are formed from the reaction between water and CO2, and not the widely reported carbamate hydrolysis. With a goal of minimizing the leaching of amines on PEI-impregnated adsorbents, PEI was covalently immobilized on mesoporous aluminosilica using 3-glycidoxypropyltrimethoxysilane or 3-triethoxysilylpropyl isocyanate as linkers. The resultant materials were found to be more resistant to leaching (in ethanol) and degradation (air at 100 oC) compared to their impregnated counterparts. Further enhancement in oxidation stability was achieved by covalently grafting epoxide-functionalized PEI onto mesoporous aluminosilica. CO2 uptake over amine-containing adsorbents is widely reported to be enhanced in the presence of moisture. However, the same cannot be said for other adsorbents, such as, carbonaceous and zeolite-based materials, and most MOFs. In a soon to be submitted review manuscript, a comprehensive analysis on the role of water on CO2 uptake (equilibrium and kinetics), material structure and regeneration over a wide range of adsorbents is presented. As for CO2-epoxides fixation to cyclic carbonates, a quaternary ammonium salt supported on SBA-15 was used to investigate the observed literature trend between product yield and substrate type with catalyst reuse. Under mild reaction conditions (1.0 MPa CO2, 100 oC and 4 h), 1,2-butylene carbonate was obtained in high yields (> 95%) over 5 cycles as the substrate is easy to activate and the product can be completely removed from the catalyst surface due to its low boiling point. Nonetheless, using styrene oxide led to decrease in yield over reuse cycles, mainly because styrene carbonate crystals were trapped on the catalysts surface (13C MAS NMR and TGA data), thereby blocking access to active sites. By extensively washing all spent catalysts in acetone and using chromatographic grade SiO2 as support material, styrene carbonate was obtained in very good yield (> 93%) over five cycles. Finally, novel quaternary ammonium iodide-based organosilicas, grouped into disordered, ordered and periodic mesoporous organosilicas, were prepared and tested for the cycloaddition of CO2 to epoxide to yield cyclic carbonates. Under mild reaction conditions (0.5 MPa CO2, 50 oC and 10 – 15 h) catalysts with the ordered mesoporous organosilicas structure were found to be more active owing to their larger surface area and pore volume, enhancing the accessibility of active sites by epoxides.

El continu increment en l'ús de les energies renovables i els objectius per a la reducció de les emissions de diòxid de carboni (CO2) requereixen canvis significatius tant a nivell tècnic com a nivell normatiu. La captura i utilització de diòxid de carboni (CCU, per les sigles en anglès) és un mètode eficaç per aconseguir la mitigació del CO2 i al mateix temps mantenir de forma segura els subministraments d'energia. Si bé la demanda a la reducció de les emissions de CO2 està augmentant, l'eficiència energètica i el cost dels processos de captura de CO2 segueixen sent un factor limitant per a les aplicacions industrials. En el present treball s'estudia l'ús del procés d'adsorció per oscil·lació de pressió i buit (VPSA, per les sigles en anglès) amb adsorbents d'alta selectivitat per separar el CO2 dels gasos de combustió, com un mètode alternatiu al procés d'absorció tradicional amb amines. Es realitza un estudi preliminar mitjançant Anàlisi Tèrmica per determinar la capacitat d’adsorció i el comportament cíclic de la captura de CO2 per deu adsorbents comercials, inclosos els tamisos moleculars de carboni (CMS) i les zeolites. L'anàlisi es va fer amb CO2 pur, N2 pur i mescles dels dos gasos en la proporció 15%/85% que correspon a la composició d’un gas de combustió normal; s’usen les zeolites comercials 13X, 5A, 4A sense i amb aglomerants i tres tamisos moleculars de carboni (CMS) en l’interval de pressió de 0 a 10 bar i a 283K, 298K, 232K i 323 K de temperatura. Els resultats s’han ajustat amb els models Toth, Sips i Dual Site Langmuir (DSL). Es va realitzar una selecció entre deu adsorbents comercials per a la captura de CO2, inclosos els tamisos moleculars de carbó (CMS, per les sigles en anglès) i les zeolites. Es van determinar les propietats texturals, la capacitat d'adsorció i el comportament cíclic dels adsorbents per comparar el seu comportament a la separació del diòxid de carboni del nitrogen. Posteriorment, es van mesurar les isotermes d'adsorció d'un sol component en la balança de suspensió magnètica a quatre temperatures diferents (283, 298, 232 i 323 K) i en un ampli marge de pressions (de 0 a 10 bara). Les dades sobre les isotermes de components purs es van correlacionar utilitzant els models Toth, Sips i Dual Site Langmuir (DSL). Es van dissenyar i construir tres unitats de laboratori per realitzar l'experimentació del procés VPSA. La primera unitat es va usar per a la producció i el control de mescles gasoses de CO2 i N2 a una pressió màxima de 9 bara. En la segona unitat es van dur a terme la determinació dels equilibris d'adsorció amb una barreja de composició semblant a la dels gasos de combustió (15/85% de CO2/N2 v/v). Amb el programa Aspen Adsorption® es va simular el sistema experimental, obtenint que les prediccions del model DSL reprodueixen suficientment bé els resultats experimentals de les corbes de ruptura i els perfils de temperatura en el llit fix. A més, es van fer estudis dinàmics per avaluar les zeolites 5ABL i 13XBL usant el procés VPSA discontinu per a la separació CO2 de N2. La unitat dos es va dotar d'un sistema de control amb una interfície PLC que facilita la seva operació i automatització, usant una estratègia de control desenvolupada en aquest treball. En base als resultats obtinguts amb la unitat dos, tant experimentals com simulats, es va trobar que la zeolita 13XBL era la més adequada per al procés VPSA proposat. Els resultats experimentals es van emprar per alimentar el disseny de la unitat dos a Aspen Adsorption® i validar el model usat que al seu torn es va utilitzar per realitzar un disseny complet d'experiències de dos factors (26) en configuració continua. La tercera unitat experimental consta de tres columnes d'adsorció on es va incloure l'estratègia de control desenvolupada per la unitat dos i es va incloure la recirculació dels corrents rics en N2 i CO2. Es van dur a terme tres experiments del procés VPSA cíclic de 8 passos canviant els paràmetres de control del procés automatitzat i usant la zeolita 13XBL com adsorbent. Es va aconseguir satisfer els objectius en termes puresa de CO2 (> 80%) i consum energètic (<2.5 kWh/kgCO2). Sobre la base dels resultats experimentals i simulats, es va realitzar una demostració a escala pilot de la captura de CO2 del gas de combustió d'una caldera de vapor en una planta industrial a situada a la província de Barcelona.La planta pilot de captura de CO2 consta d'un procés de pretractament dels gasos de combustió, una unitat VPSA acoblada amb una unitat de deshumidificació i una aplicació industrial per a l'ús del CO2. A la unitat de pretractament, els gasos de combustió es van refredar de 70ºC a 25ºC i es van desnitrificar. A la unitat de deshumidificació, es va eliminar el vapor d'aigua del gas desnitrificat mitjançant adsorció sobre alúmina. Posteriorment, es va emprar el procés VPSA de vuit passos amb tres columnes usant zeolita 13XBL, en la qual es va obtenir un corrent enriquit de CO2 de 85 a 95% de puresa de CO2, amb una recuperació del 48 a 56%, una productivitat de 0,20-0,25 gCO2/(gads·h) i un consum energètic de 1.48 kWh/kgCO2. El CO2 recuperat es va usar per reemplaçar l'ús d'àcids minerals en l'etapa de regulació del pH de la planta de tractament d'aigües residuals existent a la fàbrica. Per tant, el procés desenvolupat és una alternativa efectiva per separar el CO2 dels punts d'emissió de gasos de combustió industrial i utilitzar el CO2 recuperat com a matèria primera per a aplicacions industrials. L'ús de CO2 capturat en aquestes fonts d'emissió té dos avantatges clars. D'una banda, es van reduir les emissions de CO2 a la atmosfera. De l'altra, va permetre reutilitzar i transformar un contaminant ambiental en compostos neutres.
El continuo incremento en el uso de las energías renovables y los objetivos para la reducción de las emisiones de dióxido de carbono (CO2) requieren cambios significativos tanto a nivel técnico como a nivel normativo. La captura y utilización de dióxido de carbono (CCU, por sus siglas en inglés) es un método eficaz para lograr la mitigación del CO2 y al mismo tiempo mantener de forma segura los suministros de energía. Si bien la demanda en la reducción de las emisiones de CO2 está aumentando, la eficiencia energética y el costo de los procesos de captura de CO2 siguen siendo un factor limitante para las aplicaciones industriales. En el presente trabajo se estudia el uso del proceso de adsorción por oscilación de presión y vacío (VPSA, por sus siglas en inglés) con adsorbentes de alta selectividad para separar el CO2 de los gases de combustión, como un método alternativo al proceso de absorción tradicional con aminas. Se realizó una selección entre diez adsorbentes comerciales para la captura de CO2, incluidos los tamices moleculares de carbón (CMS, por sus siglas en inglés) y las zeolitas. Se determinaron las propiedades texturales, la capacidad de adsorción y el comportamiento cíclico de los adsorbentes para comparar su comportamiento en la separación del dióxido de carbono del nitrógeno. Posteriormente, se midieron las isotermas de adsorción de un solo componente en la balanza de suspensión magnética a cuatro temperaturas diferentes (283, 298, 232 y 323 K) y en un amplio margen de presiones (de 0 a 10 bara). Los datos sobre las isotermas de componentes puros se correlacionaron utilizando los modelos Toth, Sips y Dual Site Langmuir (DSL). Se diseñaron y construyeron tres unidades de laboratorio para realizar la experimentación del proceso VPSA. La primera unidad se usó para la producción y el control de mezclas gaseosas de CO2 y N2 a una presión máxima de 9 bara. En la segunda unidad se llevaron a cabo las mediciones de los equilibrios de adsorción con una mezcla de composición semejante a la de los gases de combustión (15/85% de CO2/N2 v/v). Con el programa Aspen Adsorption® se simuló el sistema experimental, obteniendo que las predicciones del modelo DSL reproducen suficientemente bien los resultados experimentales de las curvas de ruptura y los perfiles de temperatura en el lecho fijo. Además, se hicieron estudios dinámicos para evaluar las zeolitas 5ABL y 13XBL usando el proceso VPSA discontinuo para la separación CO2 de N2. La unidad dos se dotó de un sistema de control con una interfaz PLC que facilita su operación y automatización, usando una estrategia de control desarrollada en este trabajo. En base a los resultados obtenidos con la unidad dos y su simulación, se encontró que la zeolita 13XBL era la que la más adecuada para el proceso VPSA propuesto. Los resultados experimentales se usaron para alimentar el diseño de la unidad dos en Aspen Adsorption® y validar el modelo usado que a su vez se utilizó para realizar un diseño completo de experiencias de dos factores (26) en configuración discontinua. La tercera unidad experimental consta de tres columnas de adsorción donde se incluyó la estrategia de control desarrollada para la unidad dos y se incluyó la recirculación de las corrientes ricas en N2 y CO2. Se llevaron a cabo tres experimentos en el proceso VPSA cíclico de 8 pasos cambiando los parámetros de control del proceso automatizado y usando la zeolita 13XBL como adsorbente. Se logró satisfacer los objetivos en términos pureza de CO2 (>80%) y consumo energético (<2.5 kW·h/kgCO2). Sobre la base de los resultados experimentales y simulados, se realizó una demostración a escala piloto de la captura de CO2 del gas de combustión de una caldera de vapor en una planta industrial situada en la provincia de Barcelona. La planta piloto de captura de CO2 consta de un proceso de pretratamiento de los gases de combustión, una unidad VPSA acoplada con una unidad de deshumidificación y una aplicación industrial para el uso del CO2. En la unidad de pretratamiento, los gases de combustión se enfriaron de 70ºC a 25ºC y desnitrificaron. En la unidad de deshumidificación, se eliminó el vapor de agua del gas desnitrificado mediante adsorción con alúmina. Posteriormente, se empleó el proceso VPSA de ocho pasos con tres columnas usando zeolita 13XBL, en la que se obtuvo una corriente enriquecida de CO2 de 85 a 95% de pureza de CO2, con una recuperación del 48 a 56%, una productividad de 0.20 a 0.25 gCO2/(gads٠h-) y un consumo energético de 1.48 kWh/ kgCO2. El CO2 recuperado se usó para reemplazar el uso de ácidos minerales en la etapa de regulación del pH de la planta de tratamiento de aguas residuales existente en la fábrica. Por lo tanto, el proceso desarrollado es una alternativa efectiva para separar el CO2 de los puntos de emisión de gases de combustión industrial y utilizar el CO2 recuperado como materia prima para aplicaciones industriales. El uso de CO2 capturado en estas fuentes de emisión tiene dos ventajas claras. Por un lado, redujeron las emisiones de CO2 a la atmósfera. Por otro lado, permitió reutilizar y transformar un contaminante ambiental en compuestos neutros.
The continuously increasing share of renewable energy sources and European Union targets for carbon dioxide (CO2) emission reduction need significant changes both on a technical and regulatory level. Carbon dioxide capture and utilization (CCU) is an effective method for achieving CO2 mitigation while simultaneously keeping energy supplies secure. While the demand for reduction in CO2 emissions is increasing, the improvement of energy-efficiency and the cost of CO2 capture processes remains a limiting factor for industrial applications. The present work studies the Vacuum Pressure Swing Adsorption process (VPSA) using high selectivity adsorbents for separating CO2 from flue gas as an alternative method to the traditional absorption process with amines. A screening analysis for CO2 capture was conducted on ten commercial adsorbents, including carbon molecular sieves (CMS) and zeolites. The textural properties, the adsorption capacities and the adsorbent cyclic behaviors were determined to compare their performance in the context of CO2 separation from nitrogen (N2). Subsequently, the single component adsorption isotherms were measured in a magnetic suspension balance at four different temperatures (283, 298, 232 and 323 K) and over a large range of pressures (from 0 to 10 bara). Data on the pure component isotherms were correlated using the Toth, Sips and Dual Site Langmuir (DSL) models. Three laboratory units were designed and built to perform the VPSA experiments. The first was used for the production and control of CO2 and N2 gas mixtures at a maximum pressure of 9 bara. Adsorption equilibrium measurements with a mixture that resembles the composition of combustion gases (15/85% CO2/N2 v/v) were obtained using the second unit that was built. Afterwards, the Aspen Adsorption® program was used to simulate the experimental system, where the predictions of the DSL model agree with the breakthrough curves and the temperature profiles of the experimental fixed bed results. In addition, dynamic studies were performed to evaluate the zeolites 5ABL and 13XBL using a discontinuous VPSA process for the CO2 separation of N2. The process was automated and operated with a PLC interface, using a control strategy developed in this work. Based on the comparison results of the zeolites, it was found that the 13XBL zeolite was the one most suitable for the proposed VPSA process. The experimental results were verified by numerical simulations in the Aspen Adsorption® software and the validated model was used to perform a two-factor complete design of experiments (26) using 13XBL simulations in a discontinuous configuration. The third experimental unit was built with three adsorption columns which included the developed control strategy and the recirculation of N2 and CO2 rich streams. Three experiments were carried out using zeolite 13XBL as an adsorbent for the proposed 8-step VPSA cyclic process by changing the control parameters of the automated process. Through the experiments, the objectives were achieved in terms of CO2 purity (> 90%) and energy consumption (> 2.5 kWh/kgCO2). Based on the experimental and simulated results, a pilot-scale demonstration plant for CO2 capture from flue gas in an existing industrial boiler in a Spanish company was carried out. The pilot-scale CO2 capture plant consisted of a pre-treatment process for flue gases, a VPSA unit coupled with a dehumidification unit and an industrial application for the use of CO2. In the pretreatment unit the flue gases were cooled from 70°C to 25°C and then denitrified. In the dehumidification unit, the water vapor was removed from the denitrified gas by adsorption with alumina. Subsequently, the three columns’ eight-step VPSA process developed with zeolite 13XBL was used. The results were a product purity of 85 to 95% of CO2, a recovery of 48 to 56%, a productivity of 0.20 to 0.25 gCO2/(gads٠h) and an energy consumption of 1.48 kWh/kgCO2. The recovered CO2 was then used to replace the use of mineral acids in the pH regulation stage of the existing wastewater treatment plant. Therefore, it is concluded that the developed process is an effective alternative to separate the CO2 from the emission points of industrial combustion gases and to use the recovered CO2 as raw material for industrial applications. The use of CO2 captured in these emission sources has two clear advantages. On the one hand, it reduces the CO2 emissions to the atmosphere. On the other hand, it allows the reuse and transformation of an environmental pollutant into neutral compounds.

Carbon capture, utilization and storage (CCUS) in confined saline aquifers in sedimentary formations has the potential to reduce the impact of fossil fuel combustion on climate change by storing CO2 in geologic formations in perpetuity. At PT conditions relevant to CCUS, CO2 is less dense than the pre-existing brine in the formation, and the more buoyant CO2 will migrate to the top of the formation where it will be in contact with cap rock. A typical cap rock is clay-rich shale, and interactions between shales and CO2 are poorly understood at PT conditions appropriate for CCUS in saline formations. In this study, the interaction of CO2 with clay minerals in the cap rock overlying a saline formation has been examined, using Na-rich montmorillonite as an analog for clay-rich shale. Attenuated Total Reflectance -- Fourier Transform Infrared Spectroscopy (ATR -FTIR) was used to identify potential crystallographic sites (AlAlOH, AlMgOH and interlayer space) where CO2 could interact with montmorillonite at 35"C and 50"C and from 0-1200 psi.  Analysis of the data indicates that CO2 that is preferentially incorporated into the interlayer space, with dehydrated montmorillonite capable of incorporating more CO2 than hydrated montmorillonite. No evidence of chemical interactions between CO2 and montmorillonite were identified, and no spectroscopic evidence for carbonate mineral formation was observed.  Further work is needed to determine if reservoir seal quality is more likely to be degraded or enhanced by CO2 - montmorillonite interactions.
Master of Science

The anthropogenic carbon dioxide (CO2) emission into the atmosphere, mainly through the combustion of fossil fuels, has resulted in a balance disturbance of the carbon cycle. Overwhelming scientific evidence proves that the escalating level of atmospheric CO2 is deemed as the main culprit for global warming and climate change. It is thus imperative to develop viable CO2 capture and sequestration (CCS) technologies to reduce CO2 emissions, which is also essential to avoid the potential devastating effects in future. The drawbacks of energy-cost, corrosion and inefficiency for amine-based wet-scrubbing systems which are currently used in industry, have prompted the exploration of alternative approaches for CCS. Extensive efforts have been dedicated to the development of functional porous materials, such as activated carbons, zeolites, porous organic polymers, and metal-organic frameworks (MOFs) to capture CO2. However, these adsorbents are limited by either poor selectivity for CO2 separation from gas mixtures or low CO2 adsorption capacity. Therefore, it is still highly demanding to design next-generation adsorbent materials fulfilling the requirements of high CO2 selectivity and enough CO2 capacity, as well as high water/moisture stability under practical conditions. Metal-organic frameworks (MOFs) have been positioned at the forefront of this area as a promising type of candidate amongst various porous materials. This is triggered by the modularity and functionality of pore size, pore walls and inner surface of MOFs by use of crystal engineering approaches. In this work, several effective strategies, such as incorporating 1,2,3-triazole groups as moderate Lewis base centers into MOFs and employing flexible azamacrocycle-based ligands to build MOFs, demonstrate to be promising ways to enhance CO2 uptake capacity and CO2 separation ability of porous MOFs. It is revealed through in-depth studies on counter-intuitive experimental observations that the local electric field favours more than the richness of exposed nitrogen atoms for the interactions between MOFs and CO2 molecules, which provides a new perspective for future design of new MOFs and other types of porous materials for CO2 capture. Meanwhile, to address the water/moisture stability issue of MOFs, remote stabilization of copper paddlewheel clusters is achieved by strengthening the bonding between organic ligands and triangular inorganic copper trimers, which in turn enhances the stability of the whole MOF network and provides a better understanding of the mechanism promoting prospective suitable MOFs with enhanced water stability. In contrast with CO2 capture by sorbent materials, the chemical transformation of the captured CO2 into value-added products represents an alternative which is attractive and sustainable, and has been of escalating interest. The nanospace within MOFs not only provides the inner porosity for CO2 capture, but also engenders accessible room for substrate molecules for catalytic purpose. It is demonstrated that high catalytic efficiency for chemical fixation of CO2 into cyclic carbonates under ambient conditions is achieved on MOF-based nanoreactors featuring a high-density of well-oriented Lewis active sites. Furthermore, described for the first time is that CO2 can be successfully inserted into aryl C-H bonds of a MOF to generate carboxylate groups. This proof-of-concept study contributes a different perspective to the current landscape of CO2 capture and transformation. In closing, the overarching goal of this work is not only to seek efficient MOF adsorbents for CO2 capture, but also to present a new yet attractive scenario of CO2 utilization on MOF platforms.

Accelerated carbonation is a new C02 storage method under development as a  solutionfor climatechangecausedbyanthropogenicactivities.Inacceleratedcarbonationanalkalinesourcesuch as minerals or industrial resid ues react with carbon dioxide in a presence of slightly acidicsolution to produce stable solid carbonates. There are varieties of accelerated carbonation routes,which differ in process condition. The aim of this study was to evaluate  and  compare  the potential of a slurry route process and a wet route process for the carbonation of basicoxygenfurnace slag using the C02 emitted by a conventional natural gas power plant. For this pmpose alife cycle assessment (LCA) study was performed based on principles and guidelines provided byISO 14040:2006 and routines and data provided by the SimaPro V8 software  package.Thematerial and energy requirements for each of the steps involved in the carbonation process, i.e.pre-treatment of raw material, C02 compression, transportation, carbonation step, after-treatmentand landfill, were calculated and included in the LCA study. The slurry and wet route resulted innet C02 reduction of 87.4% and 72.3% respectively. However, a positive contribution to otherenvironmental issues was observed with the wet route  leading to higher  impact mainly due  tohigh heating requirement. An exception was the contribution of the slurry route  to  abioticresource depletion, which was higher for the slurry route due to high water  requirement.  Ageneral conclusion was that the electricity consumption is the  main  cause  ofenvironmentalissues. Sensitivity analyses showed that the environmental impacts are dependent on thetransp01iation distance and electricity source, while no dependence was observed with respect toconstruction of the carbonation plant.

This thesis work contains an overview of potential alternative options to couple formate produced from CO2 with other coupling partners than formate itself. Ultimately, the intent is to produce high value chemicals from CO2 at a high selectivity and conversion, whilst keeping the required utility of electrons in the electrochemical CO2 conversion at a minimum. To select and find new coupling partners, a framework was developed upon which a broad variety of candidates were assessed and ranked. A multi-stage process was used to select first potential classes of molecules. For each class, a variety of commercially available compounds was analysed in depth for its potential suitability in the reaction with the active carbonite intermediate. This analysis has shown that a wide variety of factors come into play and especially the reactivity of the hydride catalyst poses a mayor challenge. The three major potential classes of compounds suitable for the coupling are carbon oxides (CO2 & CO), and aldehydes. As a second step the remaining options were ranked to identify which compound to test first. In this ranking the reactants sustainability, ease of commercial operation and commercial attractiveness of the compound were considered. The highest-ranking compounds that proposed the highest potential are CO2, benzaldehyde and para-formaldehyde. In proof-of-principle experiments CO2 could successfully be incorporated in the form of carbonate, oxalate and potentially formate. The overall incorporation efficiency based on the hydride consumption was shown to be 50%. It is suggested to continue this work with mechanistic studies to understand the reaction in detail as, based on further gained knowledge, the reaction can then be optimized towards optimal CO2 incorporation in the form of oxalate.

Carbon dioxide from biogas production is currently considered to be without value and isbecause of this released into the atmosphere in the biogas upgrading process. The residualgas is a potential carbon source and can create value in the biogas manufacturing process.By finding a suitable value-creating process that utilizes carbon dioxide, it can be possibleto provide both economic and environmental incentives for companies to develop theiroperations. This project explored the possibility to create value from this CO2. Through anevaluation of the technical maturity of CCU technologies, a recommendation could be givenat the end of the project. An analysis of technical barriers, such as pollutants in the gas, aswell as barriers in the form of competence and corporate culture were examined in orderto provide a reasoned recommendation. The project mapped which value-creating systemswould be suitable for biogas producers in a Swedish context. This included established methaneand carbon dioxide upgrading techniques currently in use and suitable CCU techniquesthat can interact with the selected upgrading processes and serve as value creators. Based onthis survey, it was then possible to identify common, critical variables for these systems. Thereafter,a recommendation of an appropriate CCU technology could be given depending onthe CO2 composition produced. One conclusion from the study was that carbon dioxide concentrationsfrom the residual gas was often high (approx. 97-98 %) and did not contain anycorrosive or toxic components, and that this largely depends on how the digestion reactor ishandled in the production process. Thus, questions were raised about what the actual limitationsof the CCU are, as they did not seem to be technical. CCU techniques that proved to beof particular interest were pH regulation of sewage plants, CO2 as a nutrient substrate for thecultivation of microalgae, and manufacturing of dry-ice for refrigerated transports. All of thesetechnologies currently have a sufficiently high degree of technical maturity to be installedalready today. Other CCU techniques, such as "’Power to gas”, require a high CO2 concentrationand were discarded as the literature review did not suggest the economic potential forthem as they require additional CO2 upgrading steps. Instead, CCU techniques were chosenthat could be implemented directly with the existing CO2 quality. Furthermore, it was concludedthat one reason why CCU technologies have not been widely implemented is internalbarriers between distributors and manufacturers (or users) of CCU technologies. Thus, theuse of carbon dioxide from biogas production and implementation of CCU technologies canbe promoted by eliminating barriers in companies, such as a lack of both knowledge andfinancial incentives.
Koldioxid från biogasproduktion betraktas i dagsläget som utan värde och släpps ut i atmosfärenvid uppgradering av biogas. Restgasen är en potentiell kolkälla och kan vara värdeskapandeför biogasprocessen. Genom att finna en lämplig värdeskapande process som utnyttjarkoldioxid går det att ge både ekonomiska och miljömässiga incitament till företag att utvecklasin verksamhet. I detta projekt undersöktes möjligheten att skapa värde av denna CO2.Genom en utvärdering av den tekniska mognadsgraden hos CCU-tekniker kunde en rekommendationges vid projektets slut. En analys av tekniska hinder, såsom föroreningar i gassammansättningen,såväl som hinder i form av kompetens och företagskultur undersöktes för attkunna ge en motiverad rekommendation. I projektet kartlades vilka värdeskapande systemsom skulle passa för biogasproducenter i en svensk kontext. Detta inkluderade etableradeuppgraderingstekniker för metan- och koldioxid som används i dagsläget. I projektet undersöktesäven lämpliga CCU-tekniker som kan samverka med de valda uppgraderingsprocessernaoch och agera värdeskapande. Utifrån denna kartläggning kunde det sedan anges vilkagemensamma, kritiska variabler som finns för dessa system. Därefter kunde en rekommendationav lämplig CCU-teknik ges beroende på den producerade CO2 sammansättningen. Enslutsats i projektet var att koldioxid från restgasen ofta var av hög koncentration (ca. 97-98 %)och ej innehöll några korrosiva eller toxiska komponenter, och att detta till stor del beror påhur rötkammaren är hanterad i produktionsprocessen. Således väcktes frågor kring vilka defaktiska begränsningarna för CCU är, då de inte torde vara tekniska. CCU-tekniker som visadesig vara av särskilt intresse var pH-reglering av avloppsverk, CO2 som näringssubstratför odling av mikroalger, samt tillverkning av kolsyreis för kyltransporter. Samtliga dessatekniker har tillräckligt hög teknisk mognadsgrad för att kunna installeras i dagsläget. AndraCCU-tekniker, såsom ”Power to gas”, kräver en hög CO2-koncentration och avfärdades dålitteraturstudien inte talade för den ekonomiska potentialen i dessa eftersom de kräver ytterligareuppgraderingssteg för CO2. Således valdes istället CCU-tekniker som skulle gå attimplementera direkt med den befintliga CO2 kvalitén. Vidare drogs slutsatsen att en anledningtill att CCU-tekniker inte har blivit vida implementerade till stor del är interna hindermellan distributörer och tillverkare (eller utnyttjare) av CCU-tekniker. Således kan användandetav koldioxid från biogasproduktion och implementering av CCU-tekniker främjasgenom att eliminera hinder hos företag. I projektet yttrade sig detta som bristande ekonomiskaincitament och okunskap. Ett ökat användande av CCU-tekniker kan också uppnås genomatt införa lagar och regler som begränsar användandet av föråldrade tekniker som drivs avfossila bränslen, och som kan ersättas av klimatvänliga CCU-tekniker.

CO2 global emissions exceed 30 Giga tonnes (Gt) per year, and the high atmospheric concentrations are detrimental to the environment. In spite of efforts to decrease emissions by sequestration (carbon capture and storage) and repurposing (use in fine chemicals synthesis and oil extraction), more than 98% of CO2 generated is released to the atmosphere. With emissions expected to increase, transforming CO2 to chemicals of high demand could be an alternative to decrease its atmospheric concentration. Transportation fuels represent 26% of the global energy consumption, making it an ideal end product that could match the scale of CO2 generation. The long-term goal of the study is to transform CO2 to liquid fuels closing a synthetic carbon cycle. Synthetic fuels, such as diesel and gasoline, can be produced from syngas (a combination of CO and H2) by Fischer Tropsch synthesis or methanol synthesis, respectively. Methanol can be turned into gasoline by MTO technologies. Technologies to make renewable hydrogen are already in existence, but CO is almost exclusively generated from methane. Due to the high stability of the CO2 molecule, its transformation is very energy intensive. Therefore, the current challenge is developing technologies for the conversion of CO2 to CO with a low energy requirement. The work in this dissertation describes the development of a recyclable, isothermal, low-temperature process for the conversion of CO2 to CO with high selectivity, called Reverse Water Gas Shift Chemical Looping (RWGS-CL). In this process, H2 is used to generate oxygen vacancies in a metal oxide bed. These vacancies then can be re-filled by one O atom from CO2, producing CO. Perovskites (ABO3) were used as the oxide material due to their high oxygen mobility and stability. They were synthesized by the Pechini sol-gel synthesis, and characterized with X-ray diffraction and surface area measurements. Mass spectrometry was used to evaluate the reducibility and re-oxidation abilities of the materials with temperature-programmed reduction and oxidation experiments. Cycles of RWGS-CL were performed in a packed bed reactor to study CO production rates. Different metal compositions on the A and B site of the oxide were tested. In all the studies, La and Sr were used on the A site because their combination is known to enhance oxygen vacancies formation and CO2 adsorption on the perovskites. The RWGS-CL was first demonstrated in a non-isothermal process at 500 °C for the H2-reduction and 850 °C for the CO2 conversion on a Co-based perovskite. This perovskite was too unstable for the H2 treatment. Addition of Fe to the perovskite enhanced its stability, and allowed for an isothermal and recyclable process at 550 °C with high selectivity towards CO. In an effort to decrease the operating temperature, Cu was incorporated to the structure. It was found that Cu addition inhibited CO formation and formed very unstable oxide materials. Preliminary studies show that application of this technology has the potential to significantly reduce CO2 emissions from captured flue gases (i.e. from power plants) or from concentrated CO2 (adsorbed from the atmosphere), while generating a high value chemical. This technology also has possible applications in space explorations, especially in environments like Mars atmosphere, which has high concentrations of atmospheric carbon dioxide.

The object of this PhD work is the study of innovative, composite and nanostructured polymeric materials for membrane-based separation and removal of CO2 from gaseous streams. The research on gas separation membranes, in the last two decades was largely devoted to the synthesis and fabrication of new, multiphasic materials, such as copolymers, composite materials bearing fillers dispersed in the polymeric matrix, or functionalized materials having selective functional groups attached to the polymer backbone. The materials investigated in this thesis can be divided in three classes: copolyetherimides: copolymers formed by a glassy polyimide phase, composite membranes, commonly defined as Mixed Matrix Membranes, functionalized materials obtained by chemically attaching amine moieties to a polymeric backbone for the instauration, in appropriate operative conditions, of the facilitated transport mechanism of CO2. All the above materials have the advantage that their transport properties, in terms of solubility, diffusivity and thus of gas permeability and selectivity, can be tuned and adjusted for the practical purpose. To this end, in this work, an experimental campaign devoted to the measurement of transport properties will be supported by a modeling approach on the continuous scale, for better understanding mass transport properties and the influence of material formulation on them, and develop easily accessible models for the prediction of materials behavior.

The object of this PhD work is the study of innovative, composite and nanostructured polymeric materials for membrane-based separation and removal of CO2 from gaseous streams. The research on gas separation membranes, in the last two decades was largely devoted to the synthesis and fabrication of new, multiphasic materials, such as copolymers, composite materials bearing fillers dispersed in the polymeric matrix, or functionalized materials having selective functional groups attached to the polymer backbone. The materials investigated in this thesis can be divided in three classes: copolyetherimides: copolymers formed by a glassy polyimide phase, composite membranes, commonly defined as Mixed Matrix Membranes, functionalized materials obtained by chemically attaching amine moieties to a polymeric backbone for the instauration, in appropriate operative conditions, of the facilitated transport mechanism of CO2. All the above materials have the advantage that their transport properties, in terms of solubility, diffusivity and thus of gas permeability and selectivity, can be tuned and adjusted for the practical purpose. To this end, in this work, an experimental campaign devoted to the measurement of transport properties will be supported by a modeling approach on the continuous scale, for better understanding mass transport properties and the influence of material formulation on them, and develop easily accessible models for the prediction of materials behavior.

Coal is the most common fossil resource for power production worldwide and generates 40% of the worlds total electricity production. Even though coal is considered a pollutive resource, the great amounts and the increasing power demand leads to extensive use even in new developed power plants. To cover the world's future energy demand and at the same time limit our effect on global warming, coal fired power plants with CO2 capture is probably a necessity. An Integrated Gasification Combined Cycle (IGCC) Power Plant is a utilization of coal which gives incentives for CO2 capture. Coal is partially combusted in a reaction with steam and pure oxygen. The oxygen is produced in an air separation process and the steam is generated in the Power Island. Out of the gasifier comes a mixture of mainly H2 and CO. In a shift reactor the CO and additional steam are converted to CO2 and more H2. Carbon dioxide is separated from the hydrogen in a physical absorption process and compressed for storage. Hydrogen diluted with nitrogen from the air separation process is used as fuel in a combined cycle similar to NGCC. A complete IGCC Power Plant is described in this report. The air separation unit is modeled as a Linde two column process. Ambient air is compressed and cooled to dew point before it is separated into oxygen and nitrogen in a cryogenic distillation process. Out of the island oxygen is at a purity level of 95.6% and the nitrogen has a purity of 99.6%. The production cost of oxygen is 0.238 kWh per kilogram of oxygen delivered at 25°C and 1.4bar. The oxygen is then compressed to a gasification pressure of 42bar. In the gasification unit the oxygen together with steam is used to gasify the coal. On molar basis the coal composition is 73.5% C, 22.8% H2, 3.1% O2, 0.3% N2 and 0.3% S. The gasification temperature is at 1571°C and out of the unit comes syngas consisting of 66.9% CO, 31.1% H2, 1.4% H2O, 0.3% N2, 0.2% H2S and 0.1% CO2. The syngas is cooled and fed to a water gas shift reactor. Here the carbon monoxide is reacted with steam forming carbon dioxide and additional hydrogen. The gas composition of the gas out of the shift reactor is on dry basis 58.2% H2, 39.0% CO2, 2.4% CO, 0.2% N2 and 0.1% H2S. Both the gasification process and shift reactor is exothermal and there is no need of external heating. This leads to an exothermal heat loss, but parts of this heat is recovered. The gasifier has a Cold Gas Efficiency (CGE) of 84.0%. With a partial pressure of CO2 at 15.7 bar the carbon dioxide is easily removed by physical absorption. After separation the solvent is regenerated by expansion and CO2 is pressurized to 110bar to be stored. This process is not modeled, but for the scrubbing part an energy consumption of 0.08kWh per kilogram CO2 removed is assumed. For the compression of CO2, it is calculated with an energy consumption of 0.11kWh per kilogram CO2 removed. Removal of H2S and other pollutive unwanted substances is also removed in the CO2 scrubber. Between the CO2 removal and the combustion chamber is the H2 rich fuel gas is diluted with nitrogen from the air separation unit. This is done to increase the mass flow through the turbine. The amount of nitrogen available is decided by the amount of oxygen produced to the gasification process. Almost all the nitrogen produced may be utilized as diluter except from a few percent used in the coal feeding procedure to the gasifier. The diluted fuel gas has a composition of 50.4% H2, 46.1% N2, 2.1% CO and 1.4% CO2. In the Power Island a combined cycle with a gas turbine able to handle large H2 amounts is used. The use of steam in the gasifier and shift reactor are integrated in the heat recovery steam generator (HRSG) in the steam cycle. The heat removed from the syngas cooler is also recovered in the HRSG. The overall efficiency of the IGCC plant modeled is 36.8%. This includes oxygen and nitrogen production and compression, production of high pressure steam used in the Gasification Island, coal feeding costs, CO2 removal and compression and pressure losses through the processes. Other losses are not implemented and will probably reduce the efficiency.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1985.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Bibliography: leaf 150.
by David Earl DeLucia.
M.S.

L'augmentation des émissions de dioxyde de carbone force l'implémentation de différentes stratégies de réduction des émissions de CO2 qui peuvent être divisées en deux groupes principaux: (i) Le captage du carbone et stockage (CCS) and (ii) le captage du carbone et utilisation (CCU). Un des procédés convertissant le CO2 en un produit à valeur ajoutée est le reformage à sec du méthane (DRM). Cependant le procédé de DRM n'a pas été commercialisé en raison de la forte endothermicité de la réaction et par manque de catalyseur actif, stable et bon marché à ce jour. Les matériaux possédant des propriétés bénéfiques pour la réaction de DRM et pouvant inclure les composants catalyseurs désirés à savoir Ni, MgO et Al2O3 sont les hydrotalcites. L'objectif principal de cette thèse est d'évaluer la performance catalytique de différents systèmes catalytiques à base d'hydrotalcite contenant du nickel lors de DRM. Cette thèse a été divisée en trois parties: (i) l'influence de l'introduction de nickel dans un système catalytique à base d'hydrotalcite, (ii) l'évaluation de la teneur en nickel des couches de brucite de l'hydrotalcite sur les propriétés catalytiques du matériau et (iii) l'évaluation de l'effet des promoteurs Ce et/ou Zr. Afin de répondre à ces problématiques, plusieurs catalyseurs à base d'hydrotalcite ont été synthétisés par la méthode de co-précipitation. Les propriétés physico-chimiques des matériaux préparés ont été évalués au moyen d'analyse élémentaire (XRF ou ICP-MS), XRD, FTIR, N2-sorption à basse température, H2-TPR, CO2-DPT, TEM, expériences SEM et TG. Les matériaux ont ensuite été testés dans la réaction de DRM à 550, 650 et 750°C
The growing emissions of carbon dioxide forced implementation of different CO2 emissions reduction strategies, which may be divided into two main groups: (i) carbon capture and storage (CCS) and (ii) carbon capture and utilization (CCU) technologies. The latter approach allows to recycle CO2. One of the processes that converts CO2 into added-value products is dry reforming of methane (DRM). The DRM process has not yet been commercialized due to the high endothermicity of the reaction and lack of cheap, active and stable catalysts.The materials which have beneficial properties in DRM reaction and may include desired catalysts components i.e. Ni, MgO and Al2O3 are hydrotalcites. The main goal of this PhD thesis was to evaluate catalytic performance of different hydrotalcite-based catalytic systems containing nickel in methane dry reforming process. This PhD was divided into three parts: (i) the comparison of the influence of nickel introduction into HTs-based catalytic system, (ii) the evaluation of wide range of nickel content in hydrotalcite brucite-like layers on materials catalytic properties and (iii) the evaluation of the effect of Ce and/or Zr promoters. In order to address these issues a number of different hydrotalcite-based catalysts was synthesized by co-precipitation. The physico-chemical properties of the prepared materials were evaluated by means of elemental analysis (XRF or ICP-MS), XRD, FTIR, low temperature N2 sorption, H2-TPR, CO2-TPD, TEM, SEM and TG experiments. The materials were subsequently tested in the DRM reaction. Most of catalytic tests were carried out at 550°C, but higher temperatures (650 and 750°C) were also studied

Det är välkänt att klimatförändringar på grund av global uppvärmning är en av de största kriserna som hotar jorden. Det är en enorm utmaning för mänskligheten att minska koldioxidutsläppen, den främsta orsaken till global uppvärmning. Enkelt genomförbara åtgärder är inte tillräckliga och teknik för att ta bort koldioxid från atmosfären anses nödvändig för att temperaturökningen inte ska överstiga de 1,5 °C som anges i Parisavtalet. Direkt infångning av koldioxid från luft (vanligen kallad direkt luftinfångning, (Eng. Direct air capture - DAC)) är en ny teknik som kan ta bort koldioxid direkt från atmosfären. För närvarande är denna metod dyr; upp till 1000 USD per ton avlägsnad koldioxid. Denna höga kostnad beror främst på den relativt låga koldioxidkoncentrationen i luften, vilket leder till att en stor anläggning behövs för att fånga upp gasen och därmed stora investeringar. Tekniken är mycket energiintensiv, antingen elektrisk eller termisk, och för att göra en direkt infångning effektivare, måste anläggningen drivas med energi som inte har några eller mycket låga koldioxidutsläpp. Energin på Island är billig och dess produktion innebär ett mycket lågt koldioxidavtryck. Syftet med arbetet i denna avhandling är att utforska om metoden för direkt infångning av koldioxid från luft kommer att vara en mer genomförbar metod än koldioxidinfångning från punktkällor (eng. point source - PS) på Island på grund av god tillgång till billig och ren energi. Lärandekurvan för direkt luftfångning studerades tillsammans med scenarier för metodens tekniska utveckling. Tre olika fall med punktkällor på Island studerades för jämförelse. Två olika direkta luftinfångningstekniker analyserades också, en som drivs av en stor mängd elektricitet och en som drivs mestadels av termisk energi. Det resulterade i att i bästa fall, där inlärningshastigheten är hög och tekniska förbättringar är signifikanta, så skulle produktionskostnaden för direkt luftinfångning (levelized cost of energy, LCOC) vara lägre än motsvarande för infångning från en punktkälla. Energikostnaden påverkar LCOC för DAC idag men med teknisk utveckling förväntas energibehovet minska och därför kommer energikostnadens påverkan att bli lägre. Det är dock fortfarande viktigt, med tanke på bidraget till att minska globala uppvärmningen, att energin som driver DAC-anläggningen har ett lågt koldioxidavtryck, vilket kan garanteras på Island. Tvärtom, om inlärningshastigheten för DAC-tekniken är låg och inga tekniska förbättringar sker i lösningsmedel eller sorbenter, är och kommer DAC-tekniken att bli dyrare än infångning från punktkällor om båda anläggningarna finns på Island. En hög inlärningshastighet och teknikutveckling är beroende av trycket att nå målen i Parisavtalet. Det är därför mycket viktigt för DAC att efterfrågan på koldioxidinfångning ökar. Dessutom har DAC mer potential att påverka klimatförändringarna eftersom DAC kan vara en kolnegativ teknik om den kombineras med permanent lagring av koldioxid. PS-avskiljningen kan endast vara en kolneutral teknik och detta om den kombineras med permanent lagring av koldioxid.
It is well known that climate change due to global warming is one of the greatest crises facing the Earth. It is a huge challenge for mankind to reduce CO2 emissions, the major cause of global warming. Mitigation measures are not enough. Technologies to remove the CO2 from the atmosphere are considered necessary, so the temperature rise does not exceed 1.5°C as stated in the Paris Agreement. Direct air capture (DAC) is a new technology that can remove carbon dioxide directly from the atmosphere. Currently, this method is expensive, up to 1000 USD per ton CO2 removed. This high cost is mostly due to the relatively low concentration of CO2 in the ambient air, leading to a large unit to capture the gas and therefore high capital investment. The technology is very energy-intensive, either electrical or thermal, and to make direct air capture more efficient the plant needs to be powered with energy that has no or very low CO2 emissions. The energy in Iceland is low cost and its production has a very low carbon footprint. This thesis aims to find out if the direct air capture method will be more feasible than a point source CO2 capture in Iceland due to good access to low-cost and clean energy. The learning curve for direct air capture was studied along with scenarios for its technological development. Two different direct air capture technologies were analyzed, one that is powered by a large amount of electricity and one powered mostly by thermal energy. Three different point source cases in Iceland were studied for comparison. For the best-case scenario, where the learning rate is high and technological improvements are significant, the levelized cost of direct air capture is lower than levelized cost of point source capture. The cost of energy affects the levelized cost of direct air capture today but with technical development, the energy needed is expected to go down, and therefore the effect of energy cost will be lower.  However, it is still important, concerning contribution to reducing global warming, that the energy powering the direct air capture plant has a low carbon footprint, which can be assured in Iceland. On the contrary, if the learning rate of the direct air capture technology is low and no technical improvements occur in solvents or sorbents the direct air capture technology is and will be more expensive than point source capture considering both located in Iceland. The high learning rate and development in technology are dependent on the pressure to reach the goals of the Paris Agreement. It is therefore vital for direct air capture that the demand for carbon removal measures is enhanced due to pressure to reach the Paris Agreement goals. Furthermore, direct air capture has more potential to affect climate change than point source capture as direct air capture can be a carbon-negative technology if coupled with the permanent storage of CO2. The point source capture can only be a carbon-neutral technology if coupled with the permanent storage of CO2.

To mitigate the global greenhouse gases (GHGs) emissions, carbon dioxide (CO2) capture and storage (CCS) has the potential to play a significant role for reaching mitigation target. Oxy-fuel combustion is a promising technology for CO2 capture in power plants. Advantages compared to CCS with the conventional combustion technology are: high combustion efficiency, flue gas volume reduction, low fuel consumption, near zero CO2 emission, and less nitrogen oxides (NOx) formation can be reached simultaneously by using the oxy-fuel combustion technology. However, knowledge gaps relating to large scale coal based and natural gas based power plants with CO2 capture still exist, such as combustors and boilers operating at higher temperatures and design of CO2 turbines and compressors. To apply the oxy-fuel combustion technology on power plants, much work is focused on the fundamental and feasibility study regarding combustion characterization, process and system analysis, and economic evaluation etc. Further studies from system perspective point of view are highlighted, such as the impact of operating conditions on system performance and on advanced cycle integrated with oxy-fuel combustion for CO2 capture. In this thesis, the characterization for flue gas recycle (FGR) was theoretically derived based on mass balance of combustion reactions, and system modeling was conducted by using a process simulator, Aspen Plus. Important parameters such as FGR rate and ratio, flue gas composition, and electrical efficiency etc. were analyzed and discussed based on different operational conditions. An advanced evaporative gas turbine (EvGT) cycle with oxy-fuel combustion for CO2 capture was also studied. Based on economic indicators such as specific investment cost (SIC), cost of electricity (COE), and cost of CO2avoidance (COA), economic performance was evaluated and compared among various system configurations. The system configurations include an EvGT cycle power plant without CO2 capture, an EvGT cycle power plant with chemical absorption for CO2 capture, and a combined cycle power plant. The study shows that FGR ratio is of importance, which has impact not only on heat transfer but also on mass transfer in the oxy-coal combustion process. Significant reduction in the amount of flue gas can be achieved due to the flue gas recycling, particularly for the system with more prior upstream recycle options. Although the recycle options have almost no effect on FGR ratio, flue gas flow rate, and system electrical efficiency, FGR options have significant effects on flue gas compositions, especially the concentrations of CO2 and H2O, and heat exchanger duties. In addition, oxygen purity and water/gas ratio, respectively, have an optimum value for an EvGT cycle power plant with oxy-fuel combustion. Oxygen purity of 97 mol% and water/gas ratio of 0.133 can be considered as the optimum values for the studied system. For optional operating conditions of flue gas recycling, the exhaust gas recycled after condensing (dry recycle) results in about 5 percentage points higher electrical efficiency and about 45 % more cooling water consumption comparing with the exhaust gas recycled before condensing (wet recycle). The direct costs of EvGT cycle with oxy-fuel combustion are a little higher than the direct costs of EvGT cycle with chemical absorption. However, as plant size is larger than 60 MW, even though the EvGT cycle with oxy-fuel combustion has a higher COE than the EvGT cycle with chemical absorption, the EvGT cycle with oxy-fuel combustion has a lower COA. Further, compared with others studies of natural gas combined cycle (NGCC), the EvGT system has a lower COE and COA than the NGCC system no matter which CO2 capture technology is integrated.
QC 20111123

A dynamic one-dimensional homogeneous model for a packed bed sorption-enhanced water-gas shift (SEWGS) reactor has been developed, describing the non-isothermal, non-adiabatic and non-isobaric operation of this type of reactor. The model was developed to describe a SEWGS reactor designed to work under operating conditions and syngas feeds encountered in a coal-fed Integrated Gasification Combined Cycle power plant utilizing an oxygen-fed gasifier. Different from previous integration designs reported in literature, the feasibility of leaving out the conventional high-temperature water-gas shift (WGS) reactor upstream of the SEWGS reactor has been investigated. The reactor was assumed to be packed with a mixture of K2CO3-promoted hydrotalcite CO2 adsorbent and commercial high-temperature FeCr-based water-gas shift catalyst pellets. Utilizing the reactor model, a mathematical modelling framework for the operation of eight SEWGS reactors in a SEWGS cycle has been developed. This system model accounts for all the necessary interactions between the reactors during the SEWGS cycle, including the exchange of mass in the feed, rinse, equalization and repressurization steps. In contrast to available open literature, the mathematical framework describes in detail how the necessary switches in the boundary conditions for the reactors have been realized.Simulations of several SEWGS cycles were carried out. The results were compared with experimental and modelling data from literature. Due to inconsistencies in the parameters and implementation of the model in the simulation software employed, results were in most aspects quantitatively not comparable to results from literature. However, the qualitative trends and physical mechanisms expected were observed and confirmed by the model. The temperatures in the reactors reached an unacceptable high level with respect to the tolerable operating conditions of the catalyst and adsorbent. It is planned to continue the work on the model, and implementing it within a full power plant model to investigate the effects of changes in the power production and thus the required amount of syngas to be treated.

The purpose of this thesis was to examine different technologies, which enhances the CO2 partial pressure in the flue gas from the natural gas combined cycle. A base case has been created as a reference for comparison of the other cycles. The base case includes a MEA capture plant with a reboiler duty of 3,6 MJ/kg CO2. To simulate the process in this thesis HYSYS and GT PRO have been used as simulation tools. The thesis has also looked into ways of extracting steam from the steam cycle to be used in the reboiler. The chosen extraction point was the crossover between the intermediate-pressure turbine and the low-pressure turbine, the steam was saturated with water from the low-pressure boiler and have a pressure and temperature of 3,6 bar and 140 °C into the reboiler. Four different technologies have been evaluated in this thesis; a natural gas combined cycle with the use of exhaust gas recycle and, three elevated pressure cycles; post-compression CO2 capture, post-expansion CO2 capture, and tail-end CO2 capture. These processes have been compared against each other with regards to the net plant efficiency, absorber size at the capture plant, and the technological maturity. The most promising of these technologies is the natural gas combined cycle with exhaust gas recycle and the tail-end CO2 capture processes, with respectively 52 % and 51,7 % net plant efficiency. The smallest absorber size is achieved by the use of post-compression CO2 capture, with a diameter of 2,9 m and a height of 10,5 m. The elevated pressure cycles have also been tested with the use of MDEA as solvent in the capture plant. By use of elevated pressure and MDEA the reboiler duty was reduced to 2 MJ/ kg CO2.

Carbon capture and storage technologies are necessary to start lowering greenhouse gas emissions while continuing to utilize existing thermal power generation infrastructure. Calcium looping is a promising technology based on cyclic calcination/carbonation reactions which utilizes limestone as a sorbent. Steam is present in combustion flue gas and in the calciner used for sorbent regeneration. The effect of steam during calcination on sorbent performance has not been extensively studied in the literature. Here, experiments were conducted using a thermogravimetric analyzer (TGA) and subsequently a dual-fluidized bed pilot plant to determine the effect of steam injection during calcination on sorbent reactivity during carbonation. In a TGA, various levels of steam (0-40% vol.) were injected during sorbent regeneration throughout 15 calcination/carbonation cycles. All concentrations of steam were found to increase sorbent reactivity during carbonation. A level of 15% steam during calcination had the largest impact. Steam changes the morphology of the sorbent during calcination, likely by shifting the pore volume to larger pores, resulting in a structure which has an increased carrying capacity. This effect was then examined at the pilot scale to determine if the phase contacting patterns and solids heat-up rates in a fluidized bed were factors. Three levels of steam (0%, 15%, 65%) were injected during sorbent regeneration throughout 5 hours of steady state operation. Again, all levels of steam were found to increase sorbent reactivity and reduce the required sorbent make-up rate with the best performance seen at 65% steam.

Ionic liquids (ILs) are molten salts at temperatures below 100 °C or at room temperature, achieving this by possessing ions that pack weakly, preventing the formation of a stable crystal lattice. The very low or non-existent volatility of the liquids is one of the most important reasons for why ILs are explored for carbon dioxide (CO2) capture, along with interesting properties such as thermal stability, nonflammability and tunability for high CO2 solubility. It is therefore important to understand, at a molecular level, the structure and properties of ILs. The work presented in this thesis employs classical molecular dynamics (MD) simulations to investigate ILs at varying temperature and varying loadings of CO2. Initially, the interatomic potentials or force field (FF) that can be used to simulate ILs are researched, before choosing two: The Generalised Amber FF (GAFF) and Canongia Lopez and Padua FF (CL&PFF). After a comparison of densities and structures resultant, further validation on the CL&PFF is reported. Subsequently, a phosphonium based IL, [P66614][NTf2], is investigated in a pure state at varying temperatures, to compare with experimental data. We study the density, structure and diffusion of the system, in terms of cation, anion and ion pair. We reinforce the results of our initial FF comparison, as the density is calculated to a high degree of accuracy compared with experiment. We continue to describe the influence of temperature on the structure and dynamics, comparing with experimental data where available. Finally, we considered the IL’s reported CO2 solubility and explored different loadings of CO2 in the IL system. We observe significant changes in IL structure and diffusion with even small loadings of CO2, along with interesting CO2 interactions and diffusion. Following on from this, we detail the initial modelling of a phosphonium based superbase ionic liquid, with a combination of FFs and scaling of atomic charges to better detail the diffusivity of the IL. Thus, in this thesis, we present ILs as a media that offers significant performance benefits when compared to traditional organic solvents for carbon capture. Additionally, we confirm the suitability of MD simulations for the accurate description and elucidation of structural and diffusive properties of ILs.

CO2 capture and storage (CCS) is estimated to reduce 14% of the global CO2 emissions in the 2 °C scenario presented by the International Energy Agency. Moreover, post combustion capture is identified as a potential method for CO2 capture from industry since it can be easily retrofitted without disturbing the core industrial process. Among the post-combustion capture methods, absorption using mono-ethanol amine (MEA) is the most mature technology that has been demonstrated at plant scale. However, using chilled ammonia process as a post combustion capture technology in a cement industry can reduce 47% energy penalty for CO2 capture when compared to the conventional MEA absorption method.  Hence, the current project aims at analyzing the chilled ammonia process when integrated with steel and ammonia plants. Key performance indicator like specific primary energy consumption per kilogram of CO2 avoided (SPECCA) is estimated and compared with MEA absorption method. Firstly, chilled ammonia process (CAP) for cement plant was used as reference case. Then, CAP for steel and ammonia processes was optimized by the means of the decision variables affecting the capture and energy efficiency. The energy consumption per kg CO2 captured and SPECCA was lower for the higher CO2 concentration in the flue gas. Results for SPECCA were 3,56, 3,52 and 3,61 MJ/kg CO2 for cement, steel, and ammonia plants, respectively.

This dissertation describes the design and optimization of a CO2-capture unit using aqueous amines to remove of carbon dioxide from the flue gas of a coal-fired power plant. In particular we construct a monolithic model of a carbon capture unit and conduct a rigorous optimization to find the lowest solvent regeneration energy yet reported. Carbon capture is primarily motivated by environmental concerns. The goal of our work is to help make carbon capture and storage (CCS) a more efficient for the sort of universal deployment called for by the Intergovernmental Panel on Climate Change (IPCC) to stabilize anthropomorphic contributions to climate change, though there are commercial applications such as enhanced oil recovery (EOR). We employ the latest simulation tools from Aspen Tech to rigorously model, design, and optimize acid gas systems. We extend this modeling approach to leverage Aspen Plus in the .NET framework through Microsoft's Component Object Model (COM). Our work successfully increases the efficiency of acid gas capture. We report a result optimally implementing multiple energy-saving schemes to reach a thermal regeneration energy of 1.67 GJ/tonne. By contrast, the IPCC had reported that leading technologies range from 2.7 to 3.3 GJ/tonne in 2005. Our work has received significant endorsement for industrial implementation by the senior management from the world's second largest chemical corporation, Sinopec, as being the most efficient technology known today.
Ph. D.

The Ca-looping cycle is a chemical process that alternates capture and release of CO2 using a Ca-based sorbent which can be applied to hydrogen production by steam reforming. Adding sorbent particles to the reformer achieves nearly pure hydrogen with higher yields via the ‘sorption enhancement’ effect. The major disadvantage is deactivation of the sorbent following multiple cycles and suggested solutions have been incorporation of inert material and regeneration by hydration. This work investigates Ca-based sorbents with a focus on their use for steam reforming of liquid feedstock. Thermodynamic analysis was used to understand the equilibrium of the steam reforming of three different feedstocks with and without CaO as the sorbent. Addition of sorbent significantly increased the H2 yield and the H2 molar fraction for all three feedstocks. Inert material was incorporated into CaO and CaO derived from Ca-D-gluconate. The resulting sorbents were investigated using thermogravimetric analysis (TGA) and a bench scale reactor in combination with X-ray diffraction (XRD) and N2 adsorption. Incorporation resulted in a reduction in pores in the 50-100 nm size range and caused self-reactivation behaviour over multiple cycles. The capture capacity and morphology of the sorbent was altered by the CaO precursor but XRD spectra were not. In situ XRD coupled with Rietveld refinement yielded new insights into the mechanism of Ca-based carbonation and sorbent stability. Agreement between in situ XRD and TGA data was found for carbonation of CaO and Ca(OH)2, and the mechanism of CO2 capture in partially hydrated CaO was investigated. Ca(OH)2 formed CaCO3 without the CaO intermediate, and anisotropic diffraction peak broadening was observed in the partially hydrated sorbent. Steam reforming of ethanol and glycerol with and without a Ca-based sorbent was investigated using a novel reactor featuring a nichrome resistance wire with a heating element/catalyst double function. Wire morphology had significant impact on feedstock conversion and the activity of the wire could be increased using a redox pretreatment which caused the formation of chromium oxides on the wire surface. The addition of sorbent by coating resulted in CO2 capture but not sorption enhancement. The coating also hindered water gas shift and eroded with time on stream.

In this project, composite membranes containing nanoparticles of polydopamine PDA (dopamine polymer) will be manufactured and characterized in view of their use for the separation of CO2. Polysulfone will be used as a polymer matrix support while poly(vinyilalcohol) has been chosen as selective layer material. The work will first focus on the optimization of the manufacturing parameters of nano composite membranes and then on the influence of the integration of PDA nanoparticles in the polymeric support at different concentrations. The final objective is to test the material properties, with particular reference to the separation performances of the membranes produced, and critically comment on the results obtained.

Chemical looping combustion (CLC) is a new concept for fuel energy conversion with CO₂ capture. In CLC, fuel combustion is split into seperate reduction and oxidation processes, in which a solid carrier is reduced and oxidized, respectively. The carrier is continuously recirculated between the two vessels, and hence direct contact between air and suel is avoided. As a result, a stoichiometric amount of oxygen is transferred to the fuel by a regenerable solid intermediate, and CLC is thus a varient of oxy-fuel combustion. In principle, pure CO₂ can be obtained from the reduction exhaust by condensation of the produced water vapor. The termodynamic potential and feasibility of CLC has been studied by means of process simulatons and experimental studies of oxygen carriers. Process simulations have focused on parameter sensitivity studies of CLC implemented in 3 power cycles; CLC-Combined Cycle, CLC-Humid Air Turbine and CLC-Integrated Steam Generation. Simulations indicate that overall fuel conversion ratio, oxidation temperature and operating pressure are among the most imortant process parameters in CLC. A promising thermodynamic potentail of CLC has been found, with efficiencies comparable to, - or better than existing technologies for CO₂ capture. The proposed oxygen carrier nickel oxide on nickel spinel (NiONiA1) has been studied in reduction with hydrogen, methane and methane/steam as well as oxidation with dry air. It has been found that at atmosphereic pressure and temperatures above 600° C, solid reduction with dry methane occurs with overall fuel conversion of 92%. Steam methane reforming is observed along with methane cracking as side reactions, yealding an overall selectivity of 90% with regard to solid reduction. If steam is added to the reactant fuel, coking can be avoided. A methodology for long term investigation of solid chemical activity in a batch reactor is proposed. The method is based on time variables for oxidaton. The results for NiONiA1 do not rule out CLC as a viable alternative for CO₂ capture, but long term durability studies along with realistic testing of the carrier in a continuous rig is needed to firmly conclude. For comparative purposes a perovskite was synthesized and tested in CLC, under similar conditions as NiONiA1. The results indicate that in a moving bed CLC application, perovskites have inherent disadvantages as compared to simpler compounds, by virtue of low relative oxygen content.

Summary:This thesis presents the technology qualification plan for the integrated gasification combined cycle power plant (IGCC) with carbon dioxide capture based on DNV recommendations. Objectives of the thesis work were development of a qualification plan, heat balance, material balance and performance characteristics for IGCC with CO2 capture. GT PRO software by thermoflow was used for the development of heat balance, material balance and performance characteristics of power plant.IGCC with pre-combustion capture is a process of generating power with very low CO2 emissions. The IGCC process gasifies coal to a syngas, converts the CO to CO2 in the shift reactors, separates the CO2 in the capture subsystem, and the resulting fuel is used for the gas turbine (GT) in a combined cycle setup. A comparison is also made between the enriched air blown gasification combined cycle power plant with CO2 capture and shell gasification combined cycle power plant with CO2 capture. For the case of this thesis, technology qualification steps obtained from DNV guidelines are implemented on the enriched air blown integrated gasification power plant with CO2 capture. First step of the technology qualification was to establish a qualification basis for the IGCC power plant with CO2 capture. In this step detailed process description of power plant is done in order to define what technology should do and what its functional requirements are?Next step of the technology qualification was technology assessment. The main purpose of this step was to divide the IGCC power plant with CO2 capture into manageable elements that involve the aspects of new technology and identify key challenges and uncertainties associated with those novel elements.Threat assessment was the third step in the technology qualification. Risks and failure modes associated with the commercialization of IGCC with CO2 capture are identified by applying risk assessment techniques like (Failure Mode Effect & Criticality Analysis (FMECA) and Hazard and Operability Analysis (Hazop). Analysis of variance was used in order to give priority to more critical failure modes.Faiure modes like surge problem of gas turbine,fouling,metal dusting and tube vibration for the heat exchanger, deactivation of catalyst for shift reactor, maldistribution of the solvent for the absorber, contaminated supply of steam to steam turbine have been identified.Qualification plans were developed for the identified failure modes of concern obtained from FMECA and Hazop analysis .The main objective of this step was to select qualification activities that adequately address the identified failure modes of concern with respect to its risk and determination of sufficient performance margins. Activities like integration of gas turbine to air separation unit, chemical treatment of water in order to avoid contaminated supply of water to HRSG and contaminated supply of steam to steam turbine, better understanding of distributor design and packing development for the absorber were suggested.After the selection of these qualification activities, execution of selected qualification activities was done in a systematic manner to document performance margins for the failure modes of concern.Last step of the technology qualification plan was concept improvement. The objective of the concept improvement step was to implement improvements that have been found necessary or beneficial during the failure mode identification and risk ranking or in the performance assessment.The focus of this work was to reduce uncertainties in these parameters in order to improve the confidence in the IGCC power plant with CO2 capture.

Direct capture of CO2 from ambient air is a developing technology, which is capable of removing CO2 directly from the atmosphere. Moreover, this technology is independent from sources of CO2 emissions. Hence, it can be set up at locations where pure stream of CO2 is needed such as in enhanced oil recovery. In this research, the performance of pelletized and natural limestone for CO2 capture from air in a fixed bed is studied. To compare the performance of sorbents for air capture, the effects of particle type (natural limestone and pelletized limestone), particle size (250-425 µm and 425-600 µm), gas flowrate (0.5 L/min and 1 L/min), and relative humidity, on the breakthrough time, breakthrough shape, and the global reaction rate are examined. Moreover, carbonation decay of sorbents over series of capture and regeneration cycles is studied. If the inlet stream (air) is humidified at 50% relative humidity, but the lime sorbents are not pre-hydrated, an axially non-uniform carbonated bed results. This phenomenon is due to the partial carbonation of sorbents at the first layers of the bed. While there is a competition between CO2 and water to react with CaO, partial carbonation reaction on the surface of the sorbents not only prevents further hydration, but also decreases the reaction rate at the surface. However, in comparison with a dry system where relative humidity was negligible and sorbents were not pre-hydrated, the observed carbonation conversion was higher. The best results were seen from experiments with pre-hydrated sorbents and humidified inlet stream. The smaller sorbent particles had a better performance (sharper breakthrough curve and longer breakthrough time) due to their greater surface area. A gas-solid reaction model was fitted to the breakthrough curves. Since at the beginning of carbonation there is no resistance of the product layer, it can be assumed that the process is reaction controlled. While after formation of the product layer (CaCO3), it becomes diffusion controlled. Results from fitted data also confirmed these conclusions. Moreover, each of sorbent went through 9 cycles and after each cycle the carbonation conversion of the sorbents was measured by TGA and the surface area by BET.

Two coal-fired power plants with CO2 capture by Pressure Swing Adsorption (PSA) havebeen modeled and simulated. The two power plants considered were IntegratedGasification Combined Cycle (IGCC) and conventional Pulverized Coal Combustion (PCC). Amathematical model of the PSA process for each of the power plants was developed and thegoal was to evaluate the feasibility of PSA as a technology for decarbonisation. Theperformance with CO2 capture by PSA was compared to a reference plant without CO2capture and to a power plant with CO2 capture by absorption, which is considered as thebenchmark technology. The size and number of the PSA columns were estimated todetermine the footprint.For the PCC power plant, the PSA model was a two-stage process consisting of a front and a tail stage. Two-stages mean that it consisted of two consecutive PSA processes. The front stage was a three-bed, five-step Skarstrom process with rinse. The tail stage was a two-bed, five-step Skarstrom process with pressure equalization. Zeolite 5A was used as adsorbent. For a specified capture rate of 90.0 %, the process achieved a purity of 96.4 % and a specific power consumption of 1.3 MJ/kgCO2. The net plant efficiency dropped 16.6 percentage points from 45.3 % to 28.7 % when introducing CO2 capture by PSA. In comparison, the PCC plant using absorption achieved a net plant efficiency of 33.4 %. The results indicate that the current state of the art PSA technology for decarbonisation as an alternative to absorption is not realistic for PCC power plants.For the IGCC power plant, the PSA model was a seven-bed, twelve-step Skarstromconfiguration with four pressure equalization steps using activated carbon as adsorbent. The process achieved a purity of 87.8 % and a capture rate of 86.3 % with negligible power consumption. The PSA process did not satisfy the performance targets of 90 % recovery and 95.5 % purity, and due to the low purity it is uncertain whether or not transport and storage of CO2 is at all feasible. The net plant efficiency dropped 12.5 percentage points from 47.3 % to 34.8 %. In comparison the IGCC plant with absorption achieved a net plant efficiency of 36.4 %. The results showed that PSA as a capture technology for IGCC power plants could not perform quite as well as absorption. However, PSA as a capture technology could have a potential if the purity could be increased, and is therefore more promising than PSA for PCC power plants.

This thesis work presents an evaluation of various processes for reducing CO2 emissions from natural-gas-fired combined cycle (NGCC) power plants. The scope of the thesis is to focus mainly on post-combustion chemical absorption for NGCC. For the post-combustion capture plant, an important interface is the steam extraction from the steam turbine in order to supply the heat for solvent regeneration. The steam extraction imposes a power production penalty. The thesis includes analysis and comparison between several chemical absorption processes configurations integrated with NGCC. The objectives of the present work were to use thermodynamic analysis on various chemical absorption process configurations to evaluate, quantify and justify improved design of NGCC with post-combustion CO2 capture. The thermodynamic evaluation of the processes gave insight to the detailed distribution of process irreversibilities and supports the state-of-the-art process configuration with the lowest energy penalty due to addition of CO2 capture to the power plant. The reference power plant without CO2 capture has a power production of 384 MW and a net electric efficiency of 56.4% (LHV) with CO2 emissions of ≈ 362 g CO2/ net kWh electricity. The power plant design was carried out using the computational tool GTPRO. The aim of the CO2 capture plant was to remove 90% of the CO2 emissions present in the flue gas. To assess and analyse the various chemical absorption process configurations, the UniSim Design software was used, which contains the Amines Property Package. This special property package has been designed to aid the modelling of alkanolamine treating units in which CO2 is removed from gaseous streams. The downstream compression of the captured CO2 was also simulated using UniSim Design. The investigated process configurations were comprised of chemical absorption process with absorber inter-cooling, split-flow process and lean vapour recompression (LVR) process. Several design parameters were modified for each of the process configurations to achieve low energy consumption and consequently low work demand. The inter-cooling of the absorber column led to increased solvent rich loading. Consequently, the solvent circulation rate and reboiler energy requirement was decreased. In the split-flow configuration, due to splitting of the rich solvent into two streams, the amount of rich solvent entering the bottom section of the stripper was reduced. Therefore, less reboiler energy was required to remove CO2 from the solvent to reach the same solvent lean loading as of the reference chemical absorption process. In the configuration with lean vapour recompression (LVR), the lean solvent stream was utilised as a low temperature heat source in order to add exergy input in the form of steam to the stripper column and thus reduce the reboiler duty. The reboiler duty for the CO2 capture was decreased from 3.74 MJ/kgCO2 in the reference chemical absorption process to 2.71 MJ/kgCO2 for the case of LVR with absorber inter-cooling. The net electric efficiency of the reference process with CO2 capture was calculated to 49.5% (LHV). With the improved process design, the highest net power plant efficiency was calculated to 50.2 % (LHV) for the case of LVR with absorber inter-cooling. Moreover, exergy analysis was performed to identify the irreversibilities associated with the integration of power plant with various CO2 capture and compression processes. Particularly, the second law of thermodynamics was used as a tool to evaluate and quantify the reduction of energy penalty associated with CO2 capture for each process modification. Defining the work input for a theoretical reversible CO2 capture process as the minimum required work was functional step in characterising the difference of the work input of theoretical reversible processes and the real irreversible processes. Exergy efficiency of the reference chemical absorption process was calculated to 21.3 % versus 25 % for the case of LVR with absorber inter-cooling. Through exergy balance for every CO2 capture process configuration, the exchange of exergy content of material and energy streams was assessed. Using the combination of power plant efficiency and exergy analysis as tools, a pre-combustion reforming combined cycle (IRCC) process with chemical absorption CO2 capture process was investigated. A rational efficiency of 43.8% was achieved, which indicates the share of input exergy utilised for work production by the power cycle in addition to the exergy of the pure compressed CO2 stream. The highest amount of irreversibility was contributed by the gas turbine and mainly by the combustor. The irreversibility which is inherent in the combustion process corresponded to a large fraction of original exergy of the fuel. This could be partially compensated by increase the preheating of the fuel supplied to the combustor. Also preheating the inlet streams to auto-thermal reactor (ATR) was found advantageous in decreasing the ATR irreversibilities.

The increase in the anthropogenic greenhouse gases has severely damaged the environment in terms of pollution and global climate change. It is capturing the carbon dioxide from the present and future power plants that could save the climate. The post-combustion CO2 capture system using amine wet scrubbing is investigated in detail for natural-gas fired power plant from pilot-scale to commercial-scale level. The research work is focused on the investigation of the different innovative modifications to the micro gas turbine (MGT) including exhaust gas recirculation (EGR), steam injection and humid air turbine. The process models are developed for both MGT and pilot-scale amine-based CO2 capture plant. The MGT model is tuned and validated with extensive experimental data at different part load conditions for base case, CO2, steam and simultaneous CO2 and steam injection to the default MGT. The thermodynamic behaviour, emissions, system efficiency and the sensitivity of the base case MGT for ambient conditions are explored. The robust model is extended for EGR, steam injection and humid air turbine system models; and process system performance comparison for the different modifications is assessed for possible recommendation. In addition, the impact of the operating conditions and locations of the EGR on the performance of the MGT is also analysed. Further, the effect of the enhanced CO2 on the extensively validated pilot-scale amine-based CO2 capture plant integrated with MGT is examined. In addition, the sensitivity analysis of the pilot-scale amine-based CO2 capture model is studied to quantify the effect of the operating parameters on the system performance and to estimate the optimum operating envelope. The EGR at 55 % resulted in a 20.5 % decrease in specific reboiler duty from the pilot-scale amine-based CO2 capture plant at the CO2 capture rate of 90 % for monoethanolamine at 30 wt. % aqueous solution. Furthermore, a techno-economic process design and/or scale-up of the commercial-scale amine-based CO2 capture system to service about 650 MWe of the natural gas-fired power plant system with and without EGR is investigated for varying EGR percentage. Finally, thorough comparative potential for the natural gas, coal, biomass fired and co-firing of coal and biomass power plants integrated with CO2 capture and CO2 compressions system are explored for different cases of each power plant. The biomass firing resulted in about 40 % increase in fuel flow rate for the constant heat input case while it resulted in 30 % derating of the power output for the constant fuel flow rate case. The comparative potential of gas-CCS, coal-CCS and BECCS has shown that the NGCC with EGR resulted in the least efficiency penalty on integration with CO2 capture and compression system due to the higher net efficiency. However, coal and biomass fired power plant resulted in the least specific losses per unit of the CO2 capture on integration with CO2 capture and compression system due to the higher specific CO2 capture.

The potential impact of carbon dioxide as a major source of global warming has led to extensive research in order to mitigate the greenhouse effect. In this work, four adsorbents were synthesized and studied. The adsorbents were obtained by grafting and sol-gel of amino-containing molecules such as bis[3-(trimethoxysilyl)propyl]amine as monoamine and [3-(2-aminoethylamino)propyl]- trimethoxysilane as diamine on the surface of silica gel. CO2 passed through adsorbents at room temperature for its capture, then desorbed at moderate heating, and stored in the form of insoluble BaCO3. The adsorbent synthesized by sol-gel synthesis was found to be more efficient due to its high content of amino groups. A demonstration experiment on reversible adsorption of CO2 on mesoporous modified silica gel was developed. This experiment visualizes a technology of post-combustion CO2 sequestration from industrial emission gases and its storage.

Le reformage de CH4, qui fait partie des technologies de valorisation du CO2, est considéré comme une voie intéressante pour la production de gaz de synthèse. Les hydroxydes à double couche (HDC) contenant du Ni, Al2O3, MgO ont des propriétés prometteuses. Le dopage par Y, Zr ou Ce a également montré une influence positive sur l’activité catalytique. L’objectif de cette thèse était donc d’évaluer des HDC Ni/Mg/Al dopés par Y, et Zr ou Ce dans la réaction de reformage à sec du méthane (DRM), l’oxydation partielle du méthane (POM), l’oxydation partielle combinée au reformage du méthane (CRPOM) et le tri-reformage du méthane (TRM). Les catalyseurs ont été caractérisés par XRD, XRF, N2-sorption, TPR-H2, TPD-CO2, chimisorption d’H2, TEM, HRTEM, TGA et spectroscopie Raman et testés en TPSR de 600 à 850 °C et à 700 °C pendant 5h. En DRM, en présence de Y, la dispersion de Ni et la SBET ont augmenté. La co-imprégnation de Zr et Y a conduit à une meilleure stabilité due à la formation d’une phase YSZ. L'addition de Zr et Y par co-précipitation a permis d’augmenter la dispersion de Ni et la basicité totale. En reformage « oxydant », HTNi et HTNi-Y2.0 ont été testés. En POM, HTNi et HTNi-Y2.0 sont actifs et stables avec H2/CO≈2.0. En CRPOM, on observe une conversion plus élevée de CH4, mais moins importante pour le CO2 comparée au DRM. L'ajout d'O2 dans le mélange réactionnel a donc contribué à l'élimination du carbone. La formation de carbone est limitée avec un rapport CO2/H2O=1 (TRM). Cependant, avec CO2/H2O = 0,5, une grande quantité de C est toujours présente et la stabilité structurelle de HTNi-Y2.0 est influencée négativement lorsque la périclase est transformée en hydroxyde
Reforming of methane, belonging to the Carbon Capture and Utilization technologies, is considered an attractive route for syngas production. Double-layered hydroxides (DLHs) with Ni, Al2O3, MgO components were reported to have promising properties. Promotion with yttrium, zirconium or cerium also positively influence the catalytic performance. Thus, the goal of this PhD thesis was to evaluate the catalytic behavior of Ni/Mg/Al DLHs promoted with Y, and Zr or Ce in dry reforming of methane (DRM), partial oxidation of methane (POM), partial oxidation combined with methane reforming (CRPOM), and tri-reforming of methane (TRM). The catalysts were characterized by XRD, XRF, N2 sorption, TPR-H2, TPD-CO2, H2 chemisorption, TEM, HRTEM, TGA and Raman spectroscopy and tested in TPSR from 600 to 850°C, and at 700°C for 5h. In DRM, the Y promotion increased Ni dispersion and SBET, especially with 2 wt.%. Zr and Y co-impregnation resulted in the YSZ phase formation leading to better stability. The Zr and Y introduction during co-precipitation step increased the Ni dispersion and the total basicity, similarly as for Ce and Y promoted materials. In the oxidative reforming, HTNi and HTNi-Y2.0 were tested. In POM, both were active and stable with H2/CO≈2.0. CRPOM tests showed higher CH4 conversion, but lower for CO2 as compared to DRM. Addition of O2 in the gas feed greatly contributed to the C removal. The carbon formation was inhibited when CO2/H2O=1 during TRM tests. However, with CO2/H2O=0.5, a high amount of C was formed, and the structural stability of Y-catalyst was negatively influenced as periclase was transformed into hydroxides

This work considers the value of flexible power provision from natural gas-fired combined cycle (NGCC) power plants operating post-combustion carbon dioxide (CO2) capture in low carbon electricity markets. Specifically, the work assesses the value of the flexibility gained by varying CO2 capture levels, thus the specific energy penalty of capture and the resultant power plant net electricity export. The potential value of this flexible operation is quantified under different electricity market scenarios, given the corresponding variations in electricity export and CO2 emissions. A quantified assessment of natural gas-fired power plant integrated with amine-based post-combustion capture and compression is attempted through the development of an Aspen Plus simulation. To enable evaluation of flexible operation, the simulation was developed with the facility to model off-design behaviour in the steam cycle, amine capture unit and CO2 compression train. The simulation is ultimately used to determine relationships between CO2 capture level and the total specific electricity output penalty (EOP) of capture for different plant configurations. Based on this relationship, a novel methodology for maximising net plant income by optimising the operating capture level is proposed and evaluated. This methodology provides an optimisation approach for power plant operators given electricity market stimuli, namely electricity prices, fuel prices, and carbon reduction incentives. The techno-economic implications of capture level optimisation are considered in three different low carbon electricity market case studies; 1) a CO2 price operating in parallel to wholesale electricity selling prices, 2) a proportional subsidy for low carbon electricity considered to be the fraction of plant electrical output equal to the capture level, and 3) a subsidy for low carbon electricity based upon a counterfactual for net plant CO2 emissions (similar to typical approaches for implementing an Emissions Performance Standard). The incentives for variable capture levels are assessed in each market study, with the value of optimum capture level operation quantified for both plant operators and to the wider electricity market. All market case studies indicate that variable capture is likely to increase plant revenue throughout the range of market prices considered. Different market approaches, however, lead to different valuation of flexible power provision and therefore different operating outcomes.

This thesis gives a detailed evaluation of the integration of power plants and post-combustion CO2 capture based on absorption. The study looks at natural gas combined cycles and pulverized coal power plants. Also the absorption process has been evaluated separately, aiming at reducing energy requirements in the capture process. In the first part of the thesis a theoretical part was given on fundamentals of CO2 capture by absorption, power generation, and process integration. Based on this theory, several case studies were defined for each of the three main processes. Simulation models were built accordingly and investigated. Simulation results from the capture process showed that there was a reboiler energy saving potential of 29% and 27% for NGCC and PC plant, respectively, when including vapor compression and absorption intercooling in the capture process. Another interesting observation made was reduced cooling duty in the overhead condenser of the stripper when applying vapor compression.Analysis of steam extraction from the NGCC plant showed it was possible to cover 1 MJ/kg CO2 directly from the HRSG. This steam can be provided directly from the LPB. For duties above 1 MJ/kg CO2 a secondary extraction point was required. In this study the IP/LP crossover was considered the most appropriate point to extract the remaining steam. The efficiency penalty when integrated with the different CO2 capture cases ranged from 7-8%, giving a net plant efficiency of 49.6-50.5%. At part load it was shown that the LPT should be throttled in order to secure constant pressure at the extraction point.For the PC plant the feedwater heat system showed potential in terms heat recovery in the return stream from the capture process. By integrating the return stream with FWH2, energy savings of 11.9% compared to the base case plant were found. Also it was found that the IP/LP crossover pressure should be set to 4.5 bar, since the IPT has the highest efficiency and therefore power production in this unit should be maximized. The final results for the PC plant efficiency range from 30-31.7% and the percentual efficiency penalty was 10-11.7% for the four capture case studies. As was the case for the NGCC plant, the LPT should be throttled when operating at part load.

Capture and storage from fossil fuel fired power plants is drawing increasing interest as a potential method for the control of greenhouse gas emissions. An optimization and technical parameter study for a CO2 capture process of the flue gas of a commercial gas power plant, based on absorption/desorption process with MEA solutions, using HYSYS with the Amine Property Package fluid package, has been performed. The optimization has aimed to reduce the energy requirement for solvent regeneration, by investigating the effects of circulation rate, cross-flow heat exchanger minimum approach, desorber operating pressure and the absorber diameter. In addition, an economic evaluation including investment cost has been performed for the first three parameters.Major energy savings can be realized by optimizing the desorber pressure and the solvent circulation rate. The circulation rate will have a clearly defined optimal point, while for the desorber pressure the temperature will be a limiting factor. A too high temperature may lead to amine degradation and corrosion problems. The cross-flow heat exchanger minimum temperature approach will not affect the energy consumption significantly. An optimum absorber column diameter was not found, but the column should be designed with a diameter large enough to prevent flooding through the column. A too large diameter will not favour the energy consumption very much, and other factors will be more decisive when the column diameter is chosen.

To deal with the threat of climate change, many technologies should be investigated, and power generation through an IRCC with CO2 capture is one alternative. However, capturing CO2 has a negative effect on the efficiency of the process as it requires a lot of energy. In this work, we try to reduce the energy consumption of an IRCC process with CO2 capture by developing a tool for finding the optimal process design with extensive heat integration.The design of an IRCC process involves many parameters which interfere in complex relationships. In this report, an MINLP model is established for optimizing important parameters simultaneously. The model relies on metamodeling based on process simulations in Aspen HYSYS to approximate difficult correlations, combined with a more direct approach for modeling computationally easier parts of the process.A general model for heat recovery targeting is developed for the heat integration optimization, and implemented as a part of the full IRCC optimization model.The global solver BARON is used for solving the problem, together with a relaxation procedure based on pinch analysis insights, and optimal solutions are usually found within several hours.The optimized IRCC process reaches a net electric efficiency of 49.97 %, assuming maximum heat integration, with only 1 % of the cooling and heating demands to be covered by utilities. The accuracy of the model is relatively good when compared to process simulations, but a less idealistic version of the IRCC should be designed based on the results to confirm the capability of the model.

We show experimentally that CO2 intercalates into the interlayer spaceof the synthetic smectite clay Li-fluorohectorite (LiFh). The intercalationoccurs for a range of conditions in terms of pressure (5 bar to 20 bar) andtemperature (-20'C to 5'C). The mean basal spacing of the clay layersin LiFh intercalated by CO2 is found to be approximately 12.0 Å.We observe that the dynamics depends on the pressure, with a higherintercalation rate at increased pressure. Even under pressure of 20 bar,intercalation of CO2 is slower than H2O intercalation in fluorohectoritesby orders of magnitude.In situ observations show that LiFh is able to retain CO2 in the interlayerspace at room temperature, and the CO2 only starts leaving the clay attemperatures exceeding 30'C. Hydrated and CO2-intercalated clays areindistinguishable by use of X-ray diffraction alone. The difference in behaviorat higher temperatures is used as an additional confirmation thatintercalation of residual water is not the cause of the observed swelling.Furthermore, we report a new intercalation state corresponding to intercalationof more than one layer of CO2 into the interlamellar space, andhave also observed changes in the intercalation state of a monohydratedLiFh sample under exposure to CO2.We believe that the findings, concerning both intercalation and deintercalation,could be relevant for application of clays related to capture, transportor storage of CO2.

Carbon capture and storage technologies are required in order to reduce greenhouse gas emissions, while continuing to utilize existing fossil-fueled power generation stations. Of the many developing post-combustion CO2 capture technologies, calcium looping appears promising due to its high thermal efficiency, technical feasibility at commercial-scale, and low sorbent cost. Calcium looping has now been performed at the larger-scale, but there is still a significant quantity of information about sorbent performance, the fate of trace pollutant emissions (specifically SO2 and HCl), dual fluidized bed operating configurations, and impact of realistic operating conditions that still needs to be determined. Based on an economic analysis of the process, three key parameters serve to have the largest potential economic impact: (1) the sorbent deactivation rate, (2) the Ca/C molar ratio, and (3) the rate of sorbent attrition. Therefore, a series of bench-scale, pilot-scale, and continuous pilot-scale testing were conducted to not only explore these parameters from an improvement standpoint, but accurately determine them under conditions expected at the commercial-scale. The presence of HCl did not have a significant impact on sorbent performance provided that steam is present during calcination, although issues with downstream corrosion could be a factor. High CO2 partial pressures during calcination, coupled with high temperatures and the presence of SO2, resulted in dramatically lower cyclic carbonation conversions and a reduced high CO2 capture efficiency regime. Continuous pilot-scale testing generated realistic, and more detrimental, values for sorbent carrying capacity, Ca/C molar ratio, sorbent make-up rates, and rate of sorbent elutriation, that can now be utilized for techno-economic evaluations and scale-up of the technology.

Carbon Capture and Storage has large a potential to mitigating the CO2 emissions caused by fossil fuel powered power plants. CCS reduces the energy efficiency of the plant and increases the demand on chemicals and infrastructure. It is though not only the direct emissions from the power plants that have an impact on the environment. The entire supply chain of the power plant has an impact, and it is therefore necessary to evaluate the entire life cycle of the plant. This thesis consists of a full process LCA of post-combustion absorption based carbon capture and storage (CCS) technologies for both coal power plants and natural gas power plants. The assessed CCS technologies are based on the solvents MEA, MDEA and chilled ammonia. MEA is the most commonly used solvent in post-combustion capture, while MDEA and chilled ammonia represents novel CCS technologies that are still under development. It was shown that a 90% capture rate was possible for all of the assessed capture technologies. It was further shown that the total global warming potential (GWP) could be decreased with above 60%. 90% reduction is not possible because of indirect emissions in the supply chain. The reduction in GWP comes at a cost of decreasing energy efficiency, which further leads to an increase in consumption of materials and infrastructure. This causes the non-GHG related impacts to increase, compared to a base scenario without CCS. CCS technology based on MDEA was calculated to be the technology with the lowest impact, mainly because it has the lowest energy requirement. Chilled ammonia was assessed as the technology with the largest impacts. The reason for this is that the chilling process is very energy intensive and therefore decreases the efficiency more, compared to the other technologies assessed. Also the large emissions of ammonia have a large impact on the acidification potential and the marine eutrophication potential.

In the CO2 capture from power generation, the energy penalties for the capture are one of the main challenges. Nowadays, the post-combustion methods have energy penalties lower than the oxy-combustion and pre-combustion technologies. One of the main disadvantages of the post-combustion method is the fact that the capture of CO2 at atmospheric pressure requires quite big equipment for the high flow rates of flue gas, and the low partial pressure of the CO2 generates an important loss of energy.The Allam cycle presented for NETPOWER gives high efficiencies in the power production and low energy penalties. A simulation of this cycle is made together with a simulation of power plants with pre-combustion and post-combustion capture and without capture for natural gas and for coal.The simulations give lower efficiencies than the proposed for NETPOWER. For natural gas the efficiency is 52% instead of the 59% presented, and 33% instead of 51% in the case of using coal as fuel. Are brought to light problems in the CO2 compressor due the high flow of CO2 that is compressed until 300bar to be recycled into the combustor.

The objectives of this master thesis have been to model and simulate oxy-combustion CO2 capture in a cement plant. The model developed is a process simulation of the calcination process with varying degree of air in-leakage, where heat is supplied by combustion in an oxygen rich environment, followed by capture of the CO2. The further gas separation after H2O condensation to achieve the required CO2 quality was evaluated. In addition to the process simulations, a review of literature related to oxy-combustion CO2 capture and cement production was performed, and an engineering evaluation of the necessary modifications to the cement plant conducted.A simulation model was built in Aspen HYSYS, and student Jelmer de Winter’s project work was utilized as a starting point. The model was developed with the aim to achieve results comparable to a process model constructed by the European Cement Research Academy (ECRA) in 2009. The goal was to capture as much of the CO2 as possible, and to achieve a CO2 purity of minimum 95 mol-% after the CO2 Compression and Purification Unit (CPU).CO2 purity in the dry flue gas of ~85 mol % was achieved, with a CO2 capture rate up to 96.4 %. Five different air in-leakages (2, 4, 6, 8 and 10 % of total flue gas flow) were tested. The results showed that the CO2 concentration in the flue gas decreased with increasing degree of air in-leakage. The decrease in CO2 concentration causes an increase of the power consumption of the CO2 CPU of ~2.6 % per percentage point of air in-leakage, and the CO2 capture rate was also reduced when the air in-leakage increased. These results agree well with results from previous oxy-combustion studies, and show the importance of minimizing air in-leakages in the cement plant.If oxy-combustion capture is to be utilized at a cement plant, some process modifications and additional equipment is required. An Air Separation Unit (ASU) is needed to provide almost pure oxygen for the combustion process. A Compression and Purification Unit (CPU) is also required, in order achieve the necessary CO2 purity and transport conditions. When using oxy-combustion technology, both the material conversion in the cement kiln system and the operational specifications of the overall process are different from those in conventional kiln operation. However, research made by ECRA in 2012 showed that the negative impacts of oxy-combustion on the product quality seem to be negligible.Other necessary process modifications when retrofitting with oxy-combustion are news design of the kiln burner and the clinker cooler in the cement plant. In addition, prevention of excessive air in-leakage by improving sealing locations at the cement plant is necessary, as the simulation results show. This is possible e.g. by waste gas flushed systems, or by an improved maintenance of inspection doors and similar devices. The CPU is up to a certain point capable of handling changes in the flue gas composition at short-term inspections; however it limits its efficiency.

Current extreme weather events are evidence of the global climate change and its effects on the environment. Although natural gas is a "greener" fuel compared to solid fuels, its continuous uncontrolled use will increase further the atmospheric CO2 emissions above sustainable levels. Natural gas fired power plants equipped with a carbon capture plant can serve as a short, and medium, term solution to mitigate global warming. Several research studies have shown that post-combustion capture technology is a readily available option to reduce drastically the CO2 emissions. However, its associated energy demand for separating CO2 from the other exhaust gases is high and needs to be reduced. Therefore, recirculating part of the exhaust gases to the inlet of gas turbine combustors increases significantly the exit CO2 concentration which is the driving force of the capture plant. This fundamental study focuses on the implications of the addition of CO2 on fuel-lean natural gas non-premixed flames. The thermal and chemical effects of adding CO2 in the air stream on the flame chemistry, properties, stability and the formation of pollutant emissions represent the main aim of the present study. Two experimental campaigns were performed in this study and in-flame, post-flame and exit measurements of major and minor combustion species and the flame temperature are performed utilising an in-house built combustion chamber. Experimental results concluded that CO2 has a considerable impact on the combustion process even at relatively low dilution levels. However, the effects of the dilution can be controlled in a beneficial way for the efficiency of the combustion systems. Furthermore, the assessment of the performance of a 1D numerical model on predicting the implications of the addition of CO2 on the flame chemistry was part of this study. The numerical results concluded that robust complex combustion models are needed to examine CO2-diluted combustion systems and it is evident that detailed chemical reaction mechanisms are as necessary as the inclusion of the interaction between turbulence and chemistry.

In this study, activated carbons (ACs) were synthesized and tested as CO2 sorbents. In-house ACs were prepared starting both from a traditional biomass (i.e. oak wood) and from an unconventional macroalgal seaweed (i.e. Laminaria hyperborea). In addition to this, a biomass-derived commercial AC was studied as a sorbent on which polyethylenimine (PEI) was impregnated. Biochars were produced both by pyrolysis at 800 °C and by hydrothermal carbonization (HTC) at 250 °C. Pyrolysis chars generally had higher fixed carbon and lower volatile content compared to hydrochars. Moreover, seaweed-derived chars exhibited significantly larger ash content than that measured for oak wood-based chars. Pyrolyzed and HTC-treated biomass were then activated either by physical (CO2) or chemical (KOH) treatment. Limited texture development of the biochars was observed after CO2 activation, yet this treatment proved to be more suitable for the creation of narrower micropores. By contrast, KOH activation, followed by HCl washing, led to a more dramatic texture enhancement (but to lower narrow micropore volumes) and higher purity of the ACs due to a significant demineralization of the chars. The morphology of all materials was examined by Scanning Electron Microscopy (SEM) which revealed the creation of larger pores after KOH activation, whereas chars and CO2-ACs generally showed an undeveloped porous matrix along with particles anchored onto the carbon structure. Furthermore, Energy-Dispersive X-ray spectroscopy (EDX) analyses corresponding to the SEM micrographs proved that these particles were inorganic. In particular, Ca compounds predominated in oak wood-based samples. For macroalgae-derived materials, a significant proportion of alkali (i.e. Na, K), alkaline-earth (i.e. Ca, Mg) metal ions and Cl was detected, along with high levels of Cl. Conversely, reduced or negligible levels of inorganic fractions were detected for all KOH-ACs, which confirmed that demineralization occurred upon HCl washing. The identity of inorganic species was revealed by X-Ray Diffraction (XRD) patterns. In particular, calcium oxalate and Ca(OH)2 were identified in oak wood chars, whereas CO2-activated derivatives had CaCO3 as their main crystalline phase. For macroalgae-based materials, KCl and NaCl were found to be the dominant crystalline phases. In addition, MgO was also identified in pyrolyzed seaweed and in its CO2-activated counterpart. By contrast, a partial or total lack of crystalline phases was found for all KOH-ACs, thus offering further evidence of the loss of inorganic species after HCl rinsing. The intrinsic alkalinity of biomass-derived chars and CO2-ACs was corroborated by the great amount of basic surface groups, whose number was lower for KOH-ACs. CO2 sorptions by chars and ACs were initially measured at T=35 °C, PCO2=1 bar, and Ptot=1 bar by using Thermogravimetric Analysis (TGA). Sorbents showing promising behaviour were then tested for capture of CO2 under simulated post-combustion conditions (T=53 °C, PCO2=0.15 bar, and Ptot=1 bar). Unmodified ACs showed relatively high sorption capacity (up to 70mg CO2∙g-1) at higher partial pressure and lower temperature. Nonetheless, the ACs’ sorption capability dramatically decreased at lower partial pressure and higher temperature. However, the biomass feedstocks included in this work proved to be advantageous precursors for sustainable synthesis of CO2-selective sorbents under post-combustion conditions. In particular, Ca(OH)2 and MgO intrinsically incorporated within the raw materials enabled production of highly basic “CO2-philic” sorbents without applying any chemical modifications. The best virgin ACs also exhibited fast adsorption kinetics, excellent regeneration capacity and good durability over ten Rapid Temperature Swing Adsorption (RTSA) cycles. On the other hand, the CO2 uptake of optimally-PEI modified commercial AC was up to 4 times higher than that achieved by the best performing unmodified AC. PEI impregnation was optimized to maximize post-combustion uptakes. In particular, the influence of various parameters (i.e. PEI loading, stirring time of the PEI/solvent/AC mixture, solvent type and sorption temperature) on the post-combustion capture capacity of the PEI-modified ACs was assessed. Interestingly, longer agitation engendered efficient dispersion of the polymer through the porous network. Additionally, a more environmentally friendly (i.e. aqueous) impregnation enabled uptakes nearly as large as those attained when the impregnation solvent was methanol, despite using lower amounts of polymer and shorter impregnation runs. In addition, when measuring uptakes under simulated post-combustion conditions but at 77 °C, optimization of aqueous PEI impregnation led to a sorption capacity larger than those achieved by the best performing PEI-loaded ACs impregnated using methanol as solvent. The use of an oak wood-derived carbon support or monoethanoloamine (MEA) as impregnating agent did not lead to any significant improvement of the CO2 sorption capacity. On the other hand, tetraethylenepentamine (TEPA)-impregnated AC slightly outperformed the optimally-PEI loaded sorbent, but the use of PEI was preferred because of its thermal stability. The addition of glycerol to the PEI/solvent/AC blend resulted in lower CO2 uptakes but moderately faster adsorption/desorption kinetics along with comparable “amine efficiency”. In addition, PEI-loaded AC showed larger CO2 uptakes and faster kinetics than those attained, for comparison purposes, by Zeolite-13X (Z13X). Furthermore, amine-containing ACs were found to be durable and easy to regenerate by RTSA at 120 °C. This CO2 desorption required ca. one third of the energy needed to regenerate a 30% MEA solution (i.e. the state of the art capture technique), thus potentially implying a lower energy penalty for the PEI-based technology in post-combustion power plant. Overall, at higher partial pressure of carbon dioxide, textural properties were the dominant parameter governing CO2 capture, especially at lower temperatures. This CO2 physisorption appeared to be governed by a combination of narrow microporosity and surface area. In contrast, at increased temperature and lower partial pressure, basic (alkali metal or amine-containing) functionalities were the key factor for promoting selective chemisorption of CO2.

Biogas encompassing mainly CO2/CH4 mixture has gained increased attention as a renewable energy source over the last years, mainly due to its contributions to greenhouse gas (GHG) abatement. However, this gaseous stream has been undervalued owing to its high CO2 content. Capturing endogenous CO2 from biogas broadens its utilisation as a substitute for natural gas. High energy consumption of traditional CO2 capture technologies has led to an opportunity to develop an alternative technique for large-scale carbon capture. Employing an anion exchange membrane (AEM)-based electrochemical cell for CO2 removal from gas mixtures is a new strategy based on the pH-gradient generated during redox reactions. This technology offers significant practical advantages owing to near-ambient temperature and pressure operating conditions. To open avenues for development research on the electrochemically-driven CO2 capture technique, key principles and features of all major methods for CO2 capture in the literature were summarised as part of this thesis. While to date the (AEM)-based electrochemical cells have received eminent fame for their application in CO2 capture, there are still major enhancement researches required to enhance the technology maturity and reduce costs. In this thesis, the aim was to determine the viability of this CO2 capture system as an alternative to conventional technologies for biogas upgrading. In this context, the main research chapters are summarised as follows: Firstly, a CO2 absorption column was integrated with an alkaline water electrolyser for biogas upgrading. After scrubbing CO2 in an aqueous absorption column, the resulting bicarbonate solution was fed through the cathode of an anion exchange membrane (AEM)-based electrolyser. With bicarbonate being the dominant anion, it migrates proportionally to the electron flow to the anode from where it is released together with anodic oxygen (O2). The proposed system allows electrochemically-assisted scrubbing and stripping of CO2 without the addition of chemicals. Coulombic efficiency calculations showed that the theoretical electron/carbon ratio of 1 (1 e/ 1 HCO3-) can be achieved by using a pH of 9 while using a traditional pH of around 13 results in more electrons and hence more energy requirement for electrochemical CO2 removal. As predicted from electrochemical stoichiometry, the system optimisation demonstrated that operating the integrated system at pH=9 results in the lowest energy requirement, even though the CO2 absorption rate in the absorbent pH= 13 was about three times higher than that at pH= 9. Results of this study suggest that integrated (AEM)-based alkaline water electrolyser and CO2 absorption column offer a low energy approach for the capture and removal of CO2 from biogas (0.25 to 0.92 kWh/kg CO2). This could potentially reduce the energy demand for CO2 separation from biogas by about 50% compared to the most energy-efficient technologies that are currently available. Recovery of absorbed CO2 on the anode side of the alkaline membrane diminishes the O2 content in the anodic gas stream. Given this high purity electrolytic O2 has a growing industrial interest in diverse applications such as biological wastewater treatment processes we designed and developed an innovative three-chamber electrochemical cell configuration capable of capturing CO2 and recovering it in an intermediate chamber enabling concomitant anodic high-purity oxygen generation. Our prototype successfully demonstrated that CO2 recovery can be separated from the anodic O2 gas stream by adding a cation exchange membrane (CEM) to the cell. A concise model was also developed to accurately predict the polarisation characteristic of the designed electrochemical cell by considering the numerical coefficient for the Tafel equation and ohmic losses. Next to the regeneration of spent alkaline solution for CO2 removal from biogas using an alkaline water electrolyser, the generated high-purity electrolytic O2 from the three-chamber electrochemical cell can be used as a valuable by-product in various industrial processes to improve the energy efficiency of the system. Our strategy to cut down the cost of electrochemically-driven CO2 removal was the effective utilisation of high-purity O2 in the aeration process of a wastewater treatment plant. The high-purity electrolytic O2 can be used to substitute the air in the conventional activated sludge process. To determine the benefit of switching from air to oxygen-enriched air or pure oxygen, an analytical model was derived to simulate the dynamic behaviour of a single bubble rising in stagnant water. This study explored the influence of operation parameters such as bubble diameter, and bubble release depth on gas-liquid mass transfer. The predicted results suggested that replacing air with high-purity oxygen in the aeration process of the conventional activated sludge can offset up to 30% of the energy required for water electrolysis. A greater advantage could be obtained by using the generated high-purity oxygen in the aeration system of industries with higher dissolved oxygen requirements such as the aquaculture industry. Finally, co-mixing electrolytic H2 generated during electrochemical biogas upgrading and CH4 may not be desirable and present some challenges such as the increased probability of ignition and material degradability. In this scenario, electrolytic H2 could be recycled from the cathode to the anode side to replace the kinetically sluggish oxygen evolution reaction (OER). The technical and economic aspect of the H2 recycling cell to generate the pH gradient required for capturing and stripping CO2 was explored. The experimental results showed that the H2 recycling cell enables CO2 capture with a minimum electrochemical work of 0.19 kWh/kg CO2, which is 30% lower than the alkaline water electrolyser system where anodic OER limits the energy efficiency of the process. The main conclusion drawn from this study is that the electrochemical-driven CO2 capture systems have the potential to reduce energy costs associated with the regeneration of spent alkaline absorbents in biogas upgrading systems.

The enormous anthropogenic emission of carbon dioxide is most likely one of the main reasons for the global warming and the climate change problems ([1], [2], [3]). Considering the continuing and progressively growing utilization of fossil fuels, mainly in the power generation sector where fossil fuel-based combustion and gasification power plants are predominant, the development and implementation of processes that avoid the associated CO2 emissions must be urgently identified. Carbon dioxide capture and storage, commonly termed CCS, represents a range of technologies oriented to affordably and efficiently sequester carbon dioxide from these sources and would be a possible mid-term solution to mitigate the emissions of CO2 into the atmosphere ([4]). However, the costs (especially in terms of penalties in the power plants efficiency) associated with the current industrially available CO2 capture techniques, such as amine-based scrubbing, are prohibitively high, thus making the development of new CO2 sorbents an highly important research challenge. Among several strategies currently under investigation, calcium oxide (CaO), readily obtained through a calcination stage of naturally occurring calcium carbonate (CaCO3), has been proposed as an alternative CO2 solid sorbent that could significantly reduce the costs of carbon dioxide capture systems. The technique, widely discussed in the literature and recently reviewed by several authors ([5], [6], [7] and [8]), is based on the reversible reaction CaO (s) + CO2 (g) ↔ CaCO3 (s) and is applied through cyclic stages of carbonation and of calcination, offering a number of advantages. However, a few issues, including especially the decline of sorbent capacity when they are cycled through multiple CO2 capture-and release stages, still call into question its widespread deployment on industrial applications. The improvement of this technology and the development of new calcium-based solid sorbents are currently a matter of study and, despite the apparent simplicity of the chemistry involved, several aspects of the carbonation reaction and its kinetics are still not clearly understood. The determination of the surface reaction kinetic parameters is one of the open disputes. Several contributions investigating the carbonation reaction and its kinetics have reported thus far activation energies varying in a range of about 20 ÷ 30 kJ/mol ([9], [10]) and 70 ÷ 80 kJ/mol ([11], [12], [13], [14]); a few authors otherwise asserted that the carbonation reaction has a zero-activation energy ([15], [16]). These values were estimated from CaO conversion versus time profiles obtained from CO2 absorption analysis carried out in a wide range of operating conditions in terms of carbonation temperatures and CO2 partial pressures and hence, the observed uncertainty in the mentioned activation energies is reasonably related to the quality of the experimental data. The accuracy of the experimental data is a questionable matter especially when the data are obtained through the thermo-gravimetric approach because, as well known, TGA experiments are typically affected by mass transfer limitations. The external diffusion is particularly important because it weighs on the gas (CO2) diffusion towards the solid sorbent (CaO) surface that is essential to support the carbon dioxide mole consumption due to the chemical reaction. Even though several strategies can be applied to reduce the external mass diffusion during the CaO carbonation studied in a TGA system (typically increasing the gas flow rates), evidences of a complete removal of such resistance cannot be easily provided. In fact, the typical circumstance that at high gas flow rates the conversion versus time curves can show no changes when increasing the gas flow rate does not imply that the external mass diffusion resistance is eliminated, but only that such resistance cannot be further reduced in the TGA geometry and operating conditions used. Indeed, the local velocities reached around/inside a TGA crucible (especially above the sorbent particles contained in a common sample holder) could be low even when the average velocity in the furnace is increased by increasing the gas flow rate, so that the local velocities around/inside a TGA crucible cannot be increased enough to compensate the very high consumption rate of CO2 due to the fast carbonation surface reaction. Therefore, alternative method has to be studied in order to measure CaO conversion versus time profile actually not limited by the external mass diffusion, and to check the validity of the thermo-gravimetric data currently available. A second aspect concerns the structural properties characterizing the solid sorbent particles and how such properties can affect the CO2 absorption performances of CaO. Since, CaO-CO2 is a typical gas-solid reaction, it is most likely that specific surface and pore volume distribution can affect the reaction kinetics of CaO sorbent particles, as well as their absorption capacity. Several studies have been carried out to comprehend the carbonation reaction and kinetics in terms of these structural properties (porosity, specific surface, structural parameter, or the whole pore size distribution) through the development and application of random pore/grain models ([15], [17], [10], [13], [18], [19]). Most of these contributions related the transition from the fast regime to the slow product-layer diffusion controlled regime, characterizing the CaO carbonation, to the filling of small pores and/or to the development of a critical carbonate layer, and focused the attention on the impact of the pore size distribution on the critical CaCO3 product layer thickness, for which an unambiguous value or a direct measure has not been anyway proposed. Additionally, even though CaO and CaCO3 are crystalline species and their crystalline structures could reasonably affect both the carbonation reaction kinetics and mechanism, very few contributions have been focused thus far to study their impact on the carbonation reaction, insomuch as the influence of CaO/CaCO3 crystalline domain sizes on the carbonation reaction with CaO-based solid sorbents has never been investigated. The research project summarized in this work of thesis has been focused on the investigation of the CaO carbonation reaction with the goal of clarifying these unresolved aspects. Sorbent samples were first characterized by thermo-gravimetric analysis (TGA). CaO particles, directly produced in the TGA apparatus through stages of thermal decomposition in N2 atmosphere (temperature range from 650°C and 900°C), were tested to investigate their reactivity in the CO2 capture process, aiming at identifying the absorption specific rates, and confirming as common TGA analysis are reasonably affected by physical limitations, mainly mass transfer resistances. The TGA unit was fed with gas consisting of pure carbon dioxide or of a N2/CO2 mixture so that different CO2 partial pressures were used within a range of 0.05 and 1 bar while carbonation temperatures were varied from 450°C up to 650°C. Some CaO sorbent samples were also preliminary prepared through a stage of calcination realized in a separate muffle furnace. Different operating conditions in terms of calcination temperatures (especially 900°C) and residence times at high temperature (from few minutes up to some hours) were used in order to produce CaO sorbent samples with different structural properties, mainly in terms of porosity and specific surface area. In fact, these factors, which are closely related to the sorbent modifications due to high temperature treatments, reasonably affect the carbonation reaction. Specific surface area measurements by N2 adsorption were performed to complete the characterization of the samples by means of BET analysis. The samples were afterwards tested during CO2 absorption processes carried out in the TGA unit under a gas flow of pure carbon dioxide (total pressure of 1 bar). Based on CaO conversions and the corresponding reaction rates measured, a simple reaction mechanism was applied to determine the kinetic parameters. An activation energy of about 45 kJ/mol was estimated, but it was reasonably associated to apparent kinetic rates. Moreover, the relationship between variation of the specific surface and porosity due to sintering and their effect on the carbonation reaction were not clearly quantify because of the uncertainty of the experimental data obtained, caused by the mass-transfer limitations that affected the TGA experiments. The X-ray powder diffraction technique was therefore applied since it can provide an alternative method to the thermo-gravimetric analysis for studying the CaO-CO2 reaction. X-ray diffraction experiments were carried out (in collaboration with the Department of Geosciences at the University of Padova) to determine the structural changes of the sorbent samples (namely phase evolution and crystallite size modifications) as a function of temperature and CO2 partial pressure. Several tests were performed using a high temperature reaction chamber, with a controlled gas inlet composition, both during the thermal decomposition (calcination/regeneration) and during the absorption processes. Calcination experiments, carried out in a N2 atmosphere (total pressure = 1 bar) and a temperature range varying between 650 and 950°C, allowed to observe that, after the complete decomposition of calcium carbonate precursor, the average crystallite size of CaO domains formed (approximately of 40 nm) considerably changes, when kept for long residence times at high temperatures. We also verified that even a low concentration of CO2 in the calcination atmosphere promotes CaO crystal size growth during the CaCO3 thermal decomposition and significantly increases the size of the nascent CaO crystalline domains. After the preparation stage of thermal decomposition, carbonation experiments using fresh calcines directly produced within the reaction chamber were performed. It was observed that differences in the crystallite size of the CaO samples apparently influence the solid sorbent reactivity in the following CO2 capture process. At the same carbonation isotherm (temperatures applied were in the range of 400-650°C), with a CO2 partial pressure of 1 bar, samples with a larger CaO crystal size (at the beginning of carbonation) showed a lower overall carbon dioxide absorption capacity, suggesting that the carbonation reaction (kinetics) could be affected by initial CaO sorbent particle crystallite size. Unfortunately, the low time resolution provided by the available standard laboratory instrumentation was not sufficient to obtain detailed information about the transformations occurring in the sample particles, especially during the initial very fast stage of the carbonation reaction, whereas the surface chemical reaction should reasonably occur with negligible effects of the product layer diffusion. Therefore, in-situ synchrotron radiation X-ray powder diffraction (SR-XRPD), performed at the Advanced Photon Source (APS) facilities of the Argonne National Laboratory, was finally applied to investigate the CaO carbonation reaction more in detail. A set of CO2 absorption experiments were conducted in a high temperature reaction capillary with a controlled atmosphere (CO2 partial pressure of 1 bar), in the temperature range between 450°C and 750°C using CaO based sorbents obtained by calcination of commercial calcium carbonate. The evolution of the crystalline phases during CO2 uptake by the CaO solid sorbents was monitored for a carbonation time of 20 min as a function of the carbonation temperature and of the calcination conditions. The Rietveld refinement method was applied to estimate the calcium oxide conversion during the reaction progress and the average size of the initial (at the beginning of carbonation) calcium oxide crystallites. The measured average initial carbonation rate (in terms of conversion time derivative) of 0.280 s-1 (± 13.2% standard deviation) is significantly higher than the values obtained by thermo-gravimetric analysis and reported thus far in the scientific literature. Additionally, a dependence of the conversion versus time curves on the initial calcium oxide crystallite size was observed and a linear relationship between the initial CaO crystallite size and the calcium oxide final conversion was identified. The evolution of the CaCO3 crystalline phase during the CaO carbonation was also investigated by means of the same technique. Maximum sizes of the calcium carbonate crystalline domains were observed in the CaCO3 crystallite size versus time curves, (specifically during the first rapid stage of the carbonation) and were identified as the average values of the critical CaCO3 product layer thickness. A relationship between this parameter and the corresponding calcium oxide conversion (at which the transition to the second slow reaction stage occurs), as well as a dependence of the carbonate product layer thickness with the initial CaO particle porosity, were found. Finally, CaCO3 critical product layer thicknesses were used to estimate the initial specific surface areas of the CaO sorbent particles afterwards utilized to calculate the kinetic parameters of the intrinsic surface carbonation reaction. A reaction rate constant of 1.89 × 10-3 mol/m2 s, with zero-activation energy, has been obtained.
Negli ultimi anni, l’interesse riguardo al problema del riscaldamento globale è cresciuto notevolmente. La comunità scientifica è concorde sul fatto che i cambiamenti climatici osservati nel mondo sono correlati alle emissioni di gas serra, in modo particolare quelle di biossido di carbonio, che sono incrementate rapidamente in seguito allo sviluppo tecnologico ed industriale ([1], [2], [3]). Il settore principalmente coinvolto nelle emissioni di CO2 è l’industria per la generazione di energia, dove gli impianti di combustione e gassificazione che sfruttano combustibili fossili sono predominanti e contano ancora oggi per più di un terzo di tutte le emissioni antropogeniche di CO2. Se si considera la continua e progressiva crescita nell’utilizzo di questi combustibili in tale settore, lo sviluppo e l’implementazione di processi caratterizzati da ridotte (se non assenti) emissioni di CO2 sono questioni che devono essere urgentemente affrontate. La cattura e lo stoccaggio dell’anidride carbonica, comunemente denominato CCS (dall’inglese Carbon dioxide Capture and Storage), rappresenta l’insieme delle tecnologie orientate appunto a separare l’anidride carbonica dalle correnti gassose industriali (oltre che al trasporto e allo stoccaggio della stessa in formazioni geologiche o nel fondo degli oceani in modo tale da isolarla dall’atmosfera a lungo termine) in modo efficiente ed economicamente conveniente, e rappresenta una possibile soluzione a breve termine per mitigare le emissioni di CO2 nell’atmosfera ([1], [4]). Tuttavia, i costi associati alle tecniche di cattura della CO2 ad oggi disponibili (come ad esempio i processi basati su lavaggi con solventi amminici) sono proibitivamente alti (soprattutto in termini di penalizzazioni nell’efficienza energetica degli impianti di produzione di energia), e rendono quindi lo sviluppo di nuovi sorbenti per la cattura del biossido di carbonio una sfida molto importante nel panorama della ricerca scientifica. Tra le diverse strategie attualmente investigate, l’ossido di calcio (CaO), facilmente ottenuto attraverso trattamenti termici di calcinazione del carbonato di calcio ampiamente disponibile e diffuso in natura, si presta come un sorbente solido particolarmente interessante/promettente che potrebbe ridurre in modo significativo i costi associati ai processi di cattura dell’anidride carbonica. La tecnica della cattura della CO2 attraverso sorbenti solidi a base di ossido di calcio è ampiamente discussa in letteratura e recentemente è stata riassunta da alcuni autori ([5], [6], [7], [8]). Essa fa riferimento alla reazione reversibile CaO (s) + CO2 (g) ↔ CaCO3 (s) e dovrebbe essere applicata attraverso cicli di calcinazione e carbonatazione, offrendo diversi vantaggi. Tuttavia, alcune problematiche, tra cui il progressivo declino nella capacità di cattura che tali sorbenti evidenziano all’aumentare del numero di cicli di assorbimento/desorbimento, ne mettono ancora in discussione l’utilizzo diffuso in applicazioni di scala industriale. La ricerca di miglioramenti e lo sviluppo di nuovi sorbenti solidi sono quindi una materia di studio attuale e, nonostante l’apparente semplicità della reazione chimica coinvolta, diversi aspetti riguardanti la carbonatazione del CaO non sono stati definitivamente chiariti. La determinazione dei parametri cinetici intrinseci della reazione di carbonatazione è una delle questioni aperte. La qualità della stima della costante cinetica della reazione superficiale (necessaria per progettare i reattori per la carbonatazione) dipende dall’accuratezza dei dati sperimentali (nello specifico delle curve di conversione vs. tempo) i quali, in tutti i contributi disponibili in letteratura, sono ottenuti (al meglio delle conoscenze dell’autore) tramite un approccio termo-gravimetrico ([15], [11], [12], [9], [10], o [21]). Tuttavia, è noto che misure TGA possono essere affette da limitazioni legate a resistenze al mass transfer, specialmente per quanto riguarda la diffusione esterna, per cui è ragionevolmente discutibile se i risultati finora riportati in letteratura siano realmente espressione della cinetica intrinseca oppure, diversamente, riproducano soltanto una cinetica di assorbimento della CO2 apparente. Un altro aspetto rilevante è la dipendenza della reazione di carbonatazione dalle proprietà strutturali del sorbente. Finora, diverse ricerche hanno focalizzato l’attenzione sull’impatto della porosità e della superficie specifica, o ancora sull’impatto della distribuzione della dimensione dei pori rispetto la reazione di carbonatazione e alla sua cinetica ([15], [17], [10], [13], [18], o [19]). Anche se la superficie specifica e la distribuzione della dimensione dei pori sono parametri probabilmente rilevanti nella determinazione della cinetica di una tipica reazione gas-solido come la carbonatazione del CaO, l’impatto delle dimensioni dei domini cristallini che formano le fasi di ossido di calcio e di carbonato sulle prestazioni dei sorbenti sono informazioni non ancora disponibili in letteratura quando ci si riferisce alla reazione di carbonatazione. Il progetto di ricerca riassunto in questo lavoro di tesi è stato quindi focalizzato sullo studio della reazione di carbonatazione del CaO e sulla caratterizzazione dei sorbenti a base di ossido di calcio, con l’obiettivo di chiarire questi aspetti emersi dalla letteratura, ancora poco risolti. Dopo avere affrontato il problema del surriscaldamento globale e aver riassunto le inequivocabili evidenze scientifiche riguardanti i cambiamenti climatici già discusse in dettaglio nei report dell’Intergovernmental Panel of Climate Change (IPCC) ([1], [2], [3] ), nel Capitolo 1 sono delineate le cause di tali cambiamenti ed la CCS viene presentata come una delle possibili strategie di mitigazione delle emissioni di CO2, focalizzando l’attenzione sullo stato dell’arte in merito alle tecnologie CCS attualmente investigate. Successivamente, viene presentata la tecnologia della cattura dell’anidride carbonica realizzata attraverso l’utilizzo di sorbenti solidi a base di ossido di calcio. Nel Capitolo 2 vengono quindi discussi gli aspetti fondamentali riguardanti la reazione di carbonatazione del CaO, descrivendo la sua termodinamica e il tipico comportamento caratterizzato da due differenti fasi di reazione ovvero, una parte iniziale veloce, controllata nei primi istanti dalla reazione chimica alla superficie, seguita da una seconda fase più lenta, controllata dalla diffusione della CO2 attraverso lo strato di carbonato di calcio prodotto. Altresì, nel capitolo sono riportate considerazioni sugli aspetti irrisolti riguardanti la reazione di carbonatazione riscontrati in letteratura, come la caratterizzazione/misura del critical product layer thickness, il quale determina la transizione tra i due regimi di reazione menzionati, ed il problema della stima dei parametri cinetici intrinseci della carbonatazione. Infine, sono proposti i principali risultati dell’investigazione preliminare condotta attraverso l’applicazione dell’approccio termo-gravimetrico. Campioni di sorbente (i.e. particelle di ossido di calcio) direttamente prodotti in TGA tramite decomposizioni termiche di CaCO3 commerciale, in atmosfera di N2 (range di temperatura tra i 650°C e i 900°C), sono state testate per analizzare la loro reattività nella fase di cattura del biossido di carbonio, con l’obiettivo di identificare le velocità di assorbimento specifiche e confermare come i tradizionali esperimenti in TGA siano affetti da limitazioni fisiche, specialmente resistenze legate a fenomeni di mass transfer. Questi esperimenti sono stati condotti alimentando un classico strumento TGA sia con CO2 pura, sia con miscele N2/CO2 in modo da variare la pressione parziale di anidride carbonica in un intervallo compreso tra 0.05 bar e 1 bar, e imponendo isoterme a diverse temperature di carbonatazione, fissate tra i 450°C e i 650°C. Alcuni campioni di sorbente sono stati anche preparati attraverso fasi di calcinazione realizzate separatamente in un forno a muffola. Diverse condizioni operative sono state utilizzate in termini di temperature di calcinazione (principalmente 900°C) e tempi di residenza a tali temperature (da pochi secondi a qualche ora), in modo da produrre particelle di ossido di calcio caratterizzate da differenti proprietà strutturali, specialmente in termini di porosità e superficie specifica. Infatti, tali fattori, che sono strettamente legati alle modificazioni strutturali alle quali questi sorbenti sono soggetti per effetto dei trattamenti termici ad alta temperatura, ragionevolmente influenzano la reazione di carbonatazione. Per completare la caratterizzazione dei sorbenti così prodotti si sono eseguite dapprima misure di superficie specifica attraverso adsorbimento di N2 e analisi BET, e in seguito se n’è testata la capacità di assorbimento di CO2 in TGA con flussi di anidride carbonica (pressione totale di 1 bar). Sulla base dei profili di conversione e delle corrispondenti velocità di reazione, un semplice modello cinetico ([9]) è stato utilizzato per determinare i parametri della cinetica intrinseca. Anche se ragionevolmente associabile ad una cinetica di reazione apparente, un’energia di attivazione di circa 45 kJ/mol è stata stimata. A seguito dell’incertezza sui dati sperimentali ottenuti e connessi a limitazioni legate a fenomeni di mass transfer, la tecnica di diffrazione ai raggi X su polveri è stata quindi applicata come metodo alternativo all’analisi termo-gravimetrica nello studio della reazione tra CaO e CO2. In particolare, nel Capitolo 3 è riportata una piccola descrizione dei principali fondamenti teorici alla base di questa tecnica; successivamente sono discussi i principali risultati raccolti durante una fase di studio realizzata in collaborazione con il dipartimento di Geoscienze dell’Università di Padova. Esperimenti di diffrazione in–situ sono stati condotti per determinare le variazioni strutturali che interessano i sorbenti solidi (in modo particolare, l’evoluzione nel tempo delle fasi cristalline (i.e. composizione) e le variazioni nelle dimensioni dei domini cristallini che caratterizzano le fasi stesse) in funzione della temperatura e della pressione parziale di anidride carbonica. Diversi esperimenti sono stati eseguiti usando una camera di reazione, applicata ad un diffrattometro da laboratorio, che ha permesso di controllare la composizione gassosa del sistema sia durante la fase di decomposizione/rigenerazione, sia durante il processo di assorbimento, nonché la temperatura del materiale testato. Esperimenti di calcinazione sono stati condotti anche qui in atmosfera di N2 (pressione totale di 1 bar) e in un intervallo di temperature tra i 650°C e i 950°C, ed hanno permesso di osservare che dopo la decomposizione completa del carbonato di calcio usato come precursore le dimensioni medie dei domini cristallini di CaO di neo formazione (approssimativamente nell’ordine dei 40 nm) cambiano considerevolmente quando il materiale è mantenuto ad alte temperature per lunghi tempi di permanenza. Inoltre, si è verificato che anche piccole concentrazioni di CO2 nell’atmosfera nella quale è condotta la fase di decomposizione favoriscono l’accrescimento dei cristalliti di ossido di calcio, tanto che le dimensioni dei nascenti domini cristallini di CaO risultano notevolmente aumentate rispetto al caso di calcinazioni condotte in atmosfera inerte. Prove di carbonatazione hanno invece evidenziato che differenze nella dimensione iniziale (ovvero, all’inizio della carbonatazione) dei domini cristallini di ossido di calcio apparentemente sembrano influenzare la reattività del campione di sorbente solido durante il processo di assorbimento della CO2: a parità d’isoterma di carbonatazione (temperature tra i 450°C e i 650°C), con pressioni parziali di CO2 di 1 bar, campioni costituiti da cristalliti più grandi hanno infatti mostrato una capacità di assorbimento della CO2 più bassa raggiungendo, al termine di esperimenti di carbonatazione nell’ordine dei 120 min, conversioni inferiori. Altresì, questa evidenza rimane confermata anche all’aumentare del numero di cicli di calcinazione/carbonatazione. Purtroppo, la bassa risoluzione temporale caratterizzante la strumentazione di laboratorio disponibile non è stata sufficiente per ottenere informazioni dettagliate sulle trasformazioni che avvengono nella struttura cristallina delle particelle di sorbente, soprattutto durante la fase iniziale (molto veloce) della carbonatazione laddove la reazione alla superficie (i.e. cinetica intrinseca) ragionevolmente ha luogo con trascurabili effetti di diffusione attraverso il product layer di carbonato. Per approfondire la caratterizzazione della carbonatazione del CaO attraverso la diffrazione dei raggi X si è pertanto scelto di incrementare le potenzialità della tecnica con l’utilizzo della radiazione da sincrotrone. Nel Capitolo 4 sono presentati i risultati sulla caratterizzazione della reazione tra CaO e CO2 ottenuti da esperimenti di diffrazione ai raggi X in-situ condotti in collaborazione con le strutture dell’Advanced Photon Source (APS) presso l’Argonne National Laboratory (Argonnne, IL, U.S.A). Un set di esperimenti di cattura della CO2 è stato completato utilizzando un sistema con capillare riscaldato appositamente sviluppato ([20]) per condurre prove di diffrazione da polveri controllando l’atmosfera di reazione (pressioni parziali di CO2 di 1 bar) e la temperatura (tra i 450°C e i 750°C), per seguire l’evoluzione delle fasi cristalline di CaO e CaCO3 durante il processo di carbonatazione di particelle di ossido di calcio prodotte per decomposizione termica di carbonato di calcio commerciale. Il metodo di raffinamento Rietveld è stato poi applicato sia per quantificare la conversione dell’ossido di calcio durante il procedere della reazione, sia per stimare la dimensione media dei domini cristallini di CaO all’inizio della carbonatazione. Dai profili di conversione è stata valutata una velocità media iniziale della carbonatazione (espressa in termini di derivata della conversione rispetto al tempo) pari a 0.280 s-1 (deviazione standard di ± 13.2%) che è risultata significativamente più alta rispetto ai valori ottenuti da analisi termo-gravimetriche e riportati finora in letteratura ([9], [15] o [12]). E’ stata inoltre osservata una dipendenza dei profili di conversione rispetto al tempo dalla dimensione iniziale dei cristalliti di ossido di calcio, come pure è stata identificata una relazione lineare tra questa grandezza e la conversione finale. Analogamente, anche l’evoluzione del carbonato di calcio durante la fase di assorbimento della CO2 è stata monitorata: dimensioni massime dei domini cristallini di CaCO3 sono state osservate nei profili del crystallite size del carbonato in funzione del tempo (in particolare durante la prima rapida fase della reazione), e sono state identificate come i valori medi del critical product layer thickness. Una relazione tra questo parametro e le corrispondenti conversioni dell’ossido di calcio, alle quali si può ragionevolmente associare la transizione alla seconda fase caratteristica della carbonatazione (i.e. regime controllato dalla diffusione della CO2 attraverso lo strato di prodotto), è stata individuata, come anche tra il critical product layer thickness e la porosità iniziale delle particelle di sorbente. Infine, i valori individuati sono stati usati per stimare la superficie specifica iniziale delle particelle di CaO utilizzate negli esperimenti di carbonatazione; tali superfici sono quindi state usate nella stima dei parametri cinetici intrinseci della reazione di carbonatazione, ottenendo una costante di reazione pari a circa 1.89 × 10-3 mol/m2 s, con energia di attivazione nulla.

The thermodynamic properties of CO2-mixtures are essential for the design and operation of CO2 Capture and Storage (CCS) systems. A better understanding of the thermodynamic properties of CO2 mixtures could provide a scientific basis to define a proper guideline of CO2 purity and impure components for the CCS processes according to technical, safety and environmental requirements. However the available accurate experimental data cannot cover the whole operation conditions of CCS processes. In order to overcome the shortage of experimental data, theoretical estimation and modelling are used as a supplemental approach.   In this thesis, the available experimental data on the thermodynamic properties of CO2 mixtures were first collected, and their applicability and gaps for theoretical model verification and calibration were also determined according to the required thermodynamic properties and operation conditions of CCS. Then in order to provide recommendations concerning calculation methods for engineering design of CCS, totally eight equations of state (EOS) were evaluated for the calculations about vapour liquid equilibrium (VLE) and density of CO2-mixtures, including N2, O2, SO2, Ar, H2S and CH4.   With the identified equations of state, the preliminary assessment of impurity impacts was further conducted regarding the thermodynamic properties of CO2-mixtures and different processes involved in CCS system. Results show that the increment of the mole fraction of non-condensable gases would make purification, compression and condensation more difficult. Comparatively N2 can be separated more easily from the CO2-mixtures than O2 and Ar. And a lower CO2 recovery rate is expected for the physical separation of CO2/N2 under the same separation conditions. In addition, the evaluations about the acceptable concentration of non-condensable impurities show that the transport conditions in vessels are more sensitive to the non-condensable impurities and it requires very low concentration of non-condensable impurities in order to avoid two-phase problems.   Meanwhile, the performances of evaporative gas turbine integrated with different CO2 capture technologies were investigated from both technical and economical aspects. It is concluded that the evaporative gas turbine (EvGT) cycle with chemical absorption capture has a smaller penalty on electrical efficiency, while a lower CO2 capture ratio than the EvGT cycle with O2/CO2 recycle combustion capture. Therefore, although EvGT + chemical absorption has a higher annual cost, it has a lower cost of electricity because of its higher efficiency. However considering its lower CO2 capture ratio, EvGT + chemical absorption has a higher cost to avoid 1 ton CO2. In addition the efficiency of EvGT + chemical absorption can be increased by optimizing Water/Air ratio, increasing the operating pressure of stripper and adding a flue gas condenser condensing out the excessive water.
QC 20100819