Dissertations / Theses on the topic 'N2 capture and conversion'

El canvi climàtic causat per l'augment del contingut de CO2 a l'atmosfera està causant gran preocupació avui dia. La constant necessitat de generació d'energia verda ens va inspirar a desenvolupar un sistema fotosintètic artificial. El sistema funciona com un full, on el CO2 es capta directament de l'aire a través dels porus de la membrana i passa als següents compartiments per convertir-se finalment en metanol o altres hidrocarburs i serà utilitzat com a combustible. L'objectiu principal del treball és revelar la influència dels contactors de membrana basats en polisulfona sobre la taxa de captura de CO2 atmosfèric mitjançant absorció química en solucions aquoses. Les membranes de làmines planes que varien en morfologia es van preparar per precipitació i es van sotmetre a caracterització de morfologia interna i de la superfície. La membrana de polisulfona es va modificar amb una sèrie d'additius coneguts per l'afinitat de CO2, com ara: nenopartículas de ferrita, carbó activat i enzims. A més, la compatibilitat entre les membranes i la solució absorbent es va avaluar en termes de mesures d'inflament i angle de contacte. A més, es van realitzar estudis preliminars sobre la conversió de CO2 capturada en combustibles amb l'ús d'una unitat electroreductora. Els estudis van mostrar que el sistema basat en polisulfona té una assimilació de CO2 superior en comparació amb el rendiment d'un full. A més, els millors resultats es van obtenir utilitzant una membrana en blanc i sense modificar, el que proporciona un baix cost de producció. A més, es va aconseguir la conversió de bicarbonat a àcid fòrmic, donant un començament prometedor per millorar en el treball futur.
El cambio climático causado por el aumento del contenido de CO2 en la atmósfera está causando gran preocupación hoy en día. La constante necesidad de generación de energía verde nos inspiró a desarrollar un sistema fotosintético artificial. El sistema funciona como una hoja, donde el CO2 se capta directamente del aire a través de los poros de la membrana y pasa a los siguientes compartimentos para convertirse finalmente en metanol o otros hidrocarburos y sera utilizado como combustible. El objetivo principal del trabajo es revelar la influencia de los contactores de membrana basados en polisulfona sobre la tasa de captura de CO2 atmosférico mediante absorción química en soluciones acuosas. Las membranas de láminas planas que varían en morfología se prepararon por precipitación y se sometieron a caracterización de morfología interna y de la superficie. La membrana de polisulfona se modificó con una serie de aditivos conocidos por la afinidad de CO2, tales como: nenopartículas de ferrita, carbón activado y enzimas. Además, la compatibilidad entre las membranas y la solución absorbente se evaluó en términos de medidas de hinchamiento y ángulo de contacto. Además, se realizaron estudios preliminares sobre la conversión de CO2 capturada en combustibles con el uso de una unidad electroreductora. Los estudios mostraron que el sistema basado en polisulfona tiene una asimilación de CO2 superior en comparación con el rendimiento de una hoja. Además, los mejores resultados se obtuvieron utilizando una membrana en blanco y sin modificar, lo que proporciona un bajo costo de producción. Además, se logró la conversión de bicarbonato a ácido fórmico, dando un comienzo prometedor para mejorar en el trabajo futuro.
The climate change caused by the increased CO2 content in the atmosphere is raising a lot of concern nowadays. The constant need for sustainable green energy generation inspired us to develop an artificial photosynthetic system. The system works as a leaf, where CO2 is captured directly from air through the membrane pores and passes to the next compartments to be finally converted to methanol or other hydrocarbons and to be further used as fuel in fuel cells. The main scope of the work is to reveal the influence of polysulfone -based membrane contactors on atmospheric CO2 capture rate by chemical sorption into absorbent aqueous solutions. Flat sheet membranes that vary in morphology were prepared by immersion precipitation and undergo internal morphology and surface characterization. The polysulfone membrane was modified with a number of additives known for the CO2 affinity such as: ferrite nenoparticles, activated carbon and enzymes. Moreover, the compatibility between membranes and absorbent solution was evaluated in terms of swelling and contact angle measurements. Additionally, preliminary studies concerning the captured CO2 conversion to fuels were performed with use of electro-reductive unit. Studies showed that the polysulfone based system has superior CO2 assimilation compared to a leaf performance. Moreover, the best results were obtained using blank and unmodified membrane, providing a low production cost. Furthermore, the conversion of bicarbonate to formic acid was achieved, giving a promising start to be improved in future work.

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.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 234-253).
Carbon capture, utilization, and storage (CCUS) technologies have a central role to play in mitigating rising CO₂ emissions and enabling sustainable power generation. Most industrially mature CCS technologies based on amine chemisorption are highly energy-intensive, consuming up to 30% of the power generating capacity of the plant in order to thermally regenerate the sorbents for continued capture. Moreover, the released CO₂ must additionally be compressed and stored permanently, which adds additional energy penalties and potential risks of release. To address these challenges, this thesis develops a new strategy for integrating CO₂ capture and conversion into a single process stream.
Such an approach, which employs CO₂ in the captured state as the reactant for subsequent electrochemical reactions, eliminates the need for energetically-intensive sorbent regeneration and CO₂ release between capture and utilization steps while potentially providing new solutions for the storage challenge. In the first part of this thesis, a proof-of-concept demonstration of combined CO₂ capture and conversion within a Li-based electrochemical cell is presented. To develop this system, new electrolyte systems were first designed to integrate amines (used in industrial CO₂ capture) into nonaqueous electrolytes. The resulting systems were found to be highly effective in both capturing and activating CO₂ for subsequent electrochemical transformations upon discharge of the cell.
This activity was particularly well-demonstrated in solvents such as DMSO where CO₂ normally is completely inactive, in which the amine-modified electrolytes containing chemisorbed CO₂ were found to enable discharge at high cell voltages (~2.9 V vs. Li/Li⁺) and to high capacities (> 1000 mAh/gc), converting CO₂ to solid lithium carbonate. Formation of a densely-packed, solid phase product from CO₂ is not only logistically attractive because it requires less storage space, but also eliminates the costs and safety risks associated with long-term geological storage of compressed CO₂. In addition, the conversion process generates electricity at point-of-capture, which may help to incentivize integration of the technology with existing point-source emitters. While promising, this initial system exhibited several challenges including slow formation of the active species in solution.
To address this, a suite of experimental and computational methods were employed to elucidate the influence of the electrolyte on electrochemical reaction rates. Reduction kinetics were found to be influenced by alkali cation desolvation energetics, which favors larger alkali cations such as potassium. Through further development, amine-facilitated CO₂ conversion was also demonstrated to be transferrable to other amine- and solvent- systems, opening a potentially large design space for developing improved electrolytes. Furthermore, the effect of operating temperature was investigated to evaluate the potential of this technology to integrate with practical CO₂ capture needs. While higher temperatures (40°CLastly, CO₂ discharge activity as a function of electrolyte composition was also investigated in non-amine electrolytes for rechargeable Li-CO₂ batteries. In these systems, increased availability of the Li⁺ cation was found to be critical for supporting CO₂ activation and sustaining discharge to high capacities.Overall, the central advance of this thesis is the successful demonstration of using amine sorbents in an electrochemical context to activate new modes of CO₂ reactivity, establishing the feasibility of integrated CO₂ capture-conversion. This work not only provides a new reaction platform, but also proposes post-combustion storage concepts of CO₂ in solid phases that simultaneously achieve permanent CO₂ fixation and power delivery.
by Aliza Khurram.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering

This thesis reports an investigation into carbon dioxide capture and catalysis in several target metal-organic frameworks (MOFs) and porous organic polymers (POPs). In chapter 2, a series of Zr-MOFs were synthesised for potential applications in carbon capture and storage. In the first instance, a novel Zr-based MOF was constructed exclusively from the monocarboxylate ligand formate. Despite the low surface area, the new material exhibited a high affinity for CO2 over nitrogen at room temperature. In addition, the water-stable Zr–tricarboxylate series of frameworks, exhibited tunable porosity by virtue of systematic modulation of the chain length of the monocarboxylate ligand. Last but not least, defect concentrations and their compensating groups have been systematically tuned within UiO-66 frameworks by using modified microwave-assisted solvothermal methods. Both of these factors have a pronounce effect on CO2 and H2O adsorption at low and high pressure. Chapter 3 focuses on the development of a rapid and efficient microwave-assisted solvothermal method for a series of zirconium oxide based MOFs known as MIL-140s. Combined experimental and computational studies have revealed the interplay between the framework pore size and functionality on the CO2 adsorption performance of MIL-140 frameworks. The potential for CO2 photocatalysis in POPs was also explored in chapter 4. A POP with free 2,2’-bipyridyl sites was prepared via Sonogashira-Hagihara coupling and catalytically active moieties ([(α-diimine)Re(CO)3Cl]) were introduced using a post-synthesis metalation method. Thereafter, the Re-containing porous organic polymer was tested for the photocatalytic reduction of CO2. After an induction period, Re-POP produced CO at a stable rate, unless soluble [(bpy)Re(CO)3Cl] (bpy = 2,2´-bipyridine) was added. This provides some of most convincing evidence to date that [(α-diimine)Re(CO)3Cl] catalysts for photocatalytic CO2 reduction decompose via a bimetallic pathway.

Microporous metal organic frameworks (MOFs) are a novel class of materials formed through self-assembly of inorganic and organic structural building units (SBUs). They show great promise for many applications thanks to record-breaking internal surface areas, high porosity as well as a wide variety of possible chemical compositions. Molecular simulation has been instrumental in the study of MOFs to date, and this thesis work aims to validate and expand upon these efforts through two distinct computational MOF investigations. Current separation technologies used for CO2/N2 mixtures, found in the greenhouse gas-emitting flue gas generated by coal-burning power plants, could greatly benefit from the improved cost-effective separation MOF technology offers. MOFs have shown great potential for CO2 capture due to their low heat capacities and high, selective uptake of CO2. To ensure that simulation techniques effectively predict quantitative MOF gas uptakes and selectivities, it is important that the simulation parameters used, such as force fields, are adequate. We show that in all cases explored, the force field in current widespread use for N2 adsorption over-predicts uptake by at least 50% of the experimental uptake in MOFs. We propose a new N2 model, NIMF (Nitrogen in MoFs), that has been parameterized using experimental N2 uptake data in a diverse range of MOFs found in literature. The NIMF force field yields high accuracy N2 uptakes and will allow for accurate simulated uptakes and selectivities in existing and hypothetical MOF materials and will facilitate accurate identification of promising materials for CO2 capture and storage as well as air separation for oxy-fuel combustion. We also present the results of grand canonical and canonical Monte Carlo (GCMC and canonical MC), DFT and molecular dynamics (MD) simulations as well as charge density analyses, on both CO2 and N,N-dimethylformamide adsorbed in Ba2TMA(NO3) and MIL-68(In), two MOFs with non-equivalent inorganic structural building units. We demonstrate the excellent agreement found between our simulation results and the solid-state NMR (SSNMR) experiments carried out by Professor Yining Huang (Western University) on these two MOFs. Molecular simulation enables discoveries which complement SSNMR such as the number, distribution and dynamics of guest binding sites within a MOF. We show that the combination of SSNMR and molecular simulation forms a powerful analytical procedure for characterizing MOFs, and this novel set of microscopic characterization techniques allows for the optimization of new and existing MOFs.

Since the industrial revolution, the consumption of fossil fuels has been rapidly increasing to cater for the needs of an ever growing world population. The annual 30 billion tonnes of carbon dioxide released into the atmosphere cannot be absorbed by the natural carbon cycle alone unless it is supported by an anthropogenic one. The potential hazards of sequestering carbon dioxide has seen the exploration of multifunctional solid state materials as candidates to capture carbon dioxide and convert it into commercially viable chemicals; however, the high energy penalty associated with the reduction of carbon dioxide requires a catalyst to lower the activation energy. The redox active salen metal complex has found applications in both chemical and electrochemical catalysis. This thesis reports the design and synthesis of discrete salen metal complexes and their incorporation into Metal Organic Frameworks (MOFs) and Porous Organic Polymers (POPs) for the capture of carbon dioxide and its electrochemical conversion. The investigations reported in this thesis uncover a number of important insights into the mechanisms of redox activity in salen metal complexes en route to their immobilisation into solid state materials. Not only does this study pave the way towards the further design of redox active salen based multifunctional materials, but it also aids in a means to understand the factors that govern their rich chemistry.

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.

This work of thesis deals with the micro-textural properties characterization of calcium oxide as CO2 capture solid sorbent, that strongly influence the carbonation reaction step performances. The investigation of the sorbent micro-structure was carried out by means of both in-situ and ex-situ techniques, varying the precursor (CaCO3) activation conditions and sintering effects on the final sorbent pore network. X-ray diffraction and N2-adsorption techniques were used to identify correlations between the sorbent micro-textural properties and the average sorbent crystallite size, by considering completely calcined calcium carbonate samples under vacuum conditions and varying the high temperature (800-900°C) heating step period. With the aim to investigate the high temperature and time dependent phenomena, as pore generation, sintering processes and pore closure, in-situ X-ray small angle scattering techniques were carried out for the first time to investigate the sorbent micro-structure evolution during calcite decomposition and the CaO carbonation reaction. Firstly, preliminary ex-situ measurements were performed at the Advanced Photon Source facilities of the Argonne National Laboratory to test the X-ray small angle scattering technique capabilities to investigate high porous samples, such as completely calcined CaCO3 and partially carbonated CaO-based sorbents, and successful results were obtained, providing a detailed quantitative description of the sorbent micro-structure. Therefore, for the first time in-situ time-resolved X-ray small angle scattering tests were carried out to investigate the sorbent micro-textural properties generation during the CaCO3 calcination reaction and their evolution during the CaO carbonation reaction. Two different sets of experiments were considered, by performing CaCO3 calcination reactions below 800°C in pure nitrogen and at high temperatures (800°C and 900°C) in presence of CO2 (from 1% up to 50% in balance with N2) in the reaction atmosphere. Afterwards, CaO carbonation tests were performed at 550°C with 0.5% of CO2 in balance with N2. Because of the non-catalytic gas-solid nature of the CaO carbonation reaction, a modified random pore model was proposed in order to represent both the reaction kinetics and the sorbent micro-structure evolution over the reaction. In addition, a computation fluid dynamic study on a thermo-gravimetric analyzer was performed to quantify the external mass transfer effects on the kinetics of the CaO carbonation reaction.
Il presente lavoro di tesi è incentrato sulla caratterizzazione delle proprietà micro-texturali dell’ossido di calcio impiegato come sorbente solido per la cattura della CO2, le quali hanno un ruolo cruciale per quanto concerne le prestazioni del sorbente durante lo stadio di carbonatazione. Lo studio della micro-struttura del sorbente è stata condotta attraverso tecniche di natura in-situ ed ex-situ, variando le condizioni di attivazione del precursore (CaCO3) e gli effetti del sintering sulla struttura finale della matrice porosa. Tecniche come la diffrazione ai raggi X e l’adsorbimento con N2 sono state impiegate per identificare correlazioni tra le proprietà micro-strutturali del sorbente e la rispettiva dimensione media delle cristalliti, andando a considerare campioni completamente calcinati di carbonato di calcio in vuoto e variando le condizioni di alta temperatura (800-900°C) durante la fase di riscaldamento. Con l’obiettivo di studiare quei particolari fenomeni che avvengono ad alta temperatura e che presentano una marcata dipendenza dal tempo, come la generazione della struttura porosa del sorbente, i processi di sintering e la chiusura dei pori in fase di carbonatazione, la tecnica di small angle X-ray scattering in-situ è stata per la prima volta applicata allo studio dell’evoluzione delle proprietà micro-strutturali del sorbente sia durante la fase di calcinazione, sia durante la carbonatazione del CaO. Inizialmente, test preliminari di natura ex-situ sono stati condotti all’Advanced Photon Source dell’Argonne National Laboratory per testare le capacità di analisi della tecnica di small angle scattering ai raggi X nel caratterizzare campioni ad elevata porosità, come quelli ottenuti dalla completa calcinazione del CaCO3 e quelli parzialmente carbonatati. Eccellenti risultati sono stati ottenuti da questi test, i quali hanno fornito una descrizione quantitativa estremamente dettagliata della micro-struttura dei sorbenti analizzati. Perciò, per la prima volta test di small angle scattering ai raggi X di natura in-situ sono stati effettuati per analizzare la generazione delle proprietà micro-texturali del sorbente durante la fase di calcinazione del CaCO3 e, successivamente, la loro evoluzione durante la fase di carbonatazione del CaO. Due principali set di esperimenti sono stati condotti: calcinazioni di CaCO3 al di sotto di 800°C in atmosfera di puro N2; calcinazioni di CaCO3 ad alta temperatura (800°C e 900°C) in presenza di CO2 (da un minimo di 1% fino ad un massimo di 50%) nell’ambiente di reazione. Successivamente, test di carbonatazione del CaO sono stati effettuati a 550°C e con 0.5% di CO2. A causa della natura non catalitica della reazione di carbonatazione del CaO, un nuovo modello basato sul random pore model è stato proposto al fine di rappresentare non solo la cinetica di reazione, ma anche l’evoluzione della micro-struttura del sorbente durante la carbonatazione. Infine, uno studio fluidodinamico computazionale su un’apparecchiatura per l’analisi termo gravimetrica è stato effettuato per poter quantificare gli effetti del mass transfer esterno sulla cinetica di carbonatazione del CaO.

In the present work, the deviations in the solubility of CO2, CH4, and N2 at 30 °c in the mixed gases (CO2/CH4) and (CO2/N2) from the pure gas behavior were studied using the dual-mode model over a wide range of equilibrium composition and pressure values in two glassy polymers. The first of which was PI-DAR which is the polyimide formed by the reaction between 4, 6-diaminoresorcinol dihydrochloride (DAR-Cl) and 2, 2’-bis-(3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The other glassy polymer was TR-DAR which is the corresponding thermally rearranged polymer of PI-DAR. Also, mixed gas sorption experiments for the gas mixture (CO2/CH4) in TR-DAR at 30°c took place in order to assess the degree of accuracy of the dual-mode model in predicting the true mixed gas behavior. The experiments were conducted on a pressure decay apparatus coupled with a gas chromatography column. On the other hand, the solubility of CO2 and CH4 in two rubbery polymers at 30⁰c in the mixed gas (CO2/CH4) was modelled using the Lacombe and Sanchez equation of state at various values of equilibrium composition and pressure. These two rubbery polymers were cross-linked poly (ethylene oxide) (XLPEO) and poly (dimethylsiloxane) (PDMS). Moreover, data about the sorption of CO2 and CH4 in liquid methyl dietahnolamine MDEA that was collected from literature65-67 was used to determine the deviations in the sorption behavior in the mixed gas from that in the pure gases. It was observed that the competition effects between the penetrants were prevailing in the glassy polymers while swelling effects were predominant in the rubbery polymers above a certain value of the fugacity of CO2. Also, it was found that the dual-mode model showed a good prediction of the sorption of CH4 in the mixed gas for small pressure values but in general, it failed to predict the actual sorption of the penetrants in the mixed gas.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Mit der Arbeit werden braunkohlegefeuerte IGCC-CCS-Kraftwerke gesamtheitlich beschrieben, deren Potenziale erarbeitet und mit ASPEN Plus™ sowie EBSILON® Professional simulativ abgebildet. Es kann gezeigt werden, dass ausgehend von Basiskonzepten braunkohlegefeuerter IGCC-CCS-Kraftwerke mit verschiedenen Potenzialen zum gegenwärtigen Stand der Technik sowie dem im Jahr 2025 Wirkungsgradsteigerungen sowie prozesstechnische Vereinfachungen möglich sind. Als Potenziale werden dabei verringerte Braunkohletrocknung, konservativere Annahmen der technologischen Auslegung als auch Modifizierungen der CO-Konvertierung, sowie für das Jahr 2025 konservative Annahmen und innovative Potenziale untersucht. Ausgangspunkt bildet eine Analyse von bestehenden und zukünftig erwarteten Prozesskomponenten braunkohlegefeuerter IGCC-CCS-Kraftwerke unter Berücksichtigung von drei unterschiedlichen Vergasungsverfahren (nach Siemens, nach Shell und dem HTW-Verfahren).

Carbon dioxide (CO2) has long been regarded as the major greenhouse gas, which leads to numerous negative effects on global environment. The capture and separation of CO2 by selective adsorption using porous materials proves to be an effective way to reduce the emission of CO2 to atmosphere. Porous organic polymers (POPs) are promising candidates for this application due to their readily tunable textual properties and surface functionalities. The objective of this thesis work is to develop new POPs with high CO2 adsorption capacities and CO2/N2 selectivities for post-combustion effluent (e.g. flue gas) treatment. We will also exploit the correlation between the CO2 capture performance of POPs and their textual properties/functionalities. Chapters Two focuses on the study of a group of porous phenolic-aldehyde polymers (PPAPs) synthesized by a catalyst-free method, the CO2 capture capacities of these PPAPs exceed 2.0 mmol/g at 298 K and 1 bar, while keeping CO2/N2 selectivity of more than 30 at the same time. Chapter Three reports the gas adsorption results of different hyper-cross-linked polymers (HCPs), which indicate that heterocyclo aromatic monomers can greatly enhance polymers’ CO2/N2 selectivities, and the N-H bond is proved to the active CO2 adsorption center in the N-contained (e.g. pyrrole) HCPs, which possess the highest selectivities of more than 40 at 273 K when compared with other HCPs. Chapter Four emphasizes on the chemical modification of a new designed polymer of intrinsic microporosity (PIM) with high CO2/N2 selectivity (50 at 273 K), whose experimental repeatability and chemical stability prove excellent. In Chapter Five, we demonstrate an improvement of both CO2 capture capacity and CO2/N2 selectivity by doping alkali metal ions into azo-polymers, which leads a promising method to the design of new porous organic polymers.

abstract: The large-scale anthropogenic emission of carbon dioxide into the atmosphere leads to many unintended consequences, from rising sea levels to ocean acidification. While a clean energy infrastructure is growing, mid-term strategies that are compatible with the current infrastructure should be developed. Carbon capture and storage in fossil-fuel power plants is one way to avoid our current gigaton-scale emission of carbon dioxide into the atmosphere. However, for this to be possible, separation techniques are necessary to remove the nitrogen from air before combustion or from the flue gas after combustion. Metal-organic frameworks (MOFs) are a relatively new class of porous material that show great promise for adsorptive separation processes. Here, potential mechanisms of O2/N2 separation and CO2/N2 separation are explored. First, a logical categorization of potential adsorptive separation mechanisms in MOFs is outlined by comparing existing data with previously studied materials. Size-selective adsorptive separation is investigated for both gas systems using molecular simulations. A correlation between size-selective equilibrium adsorptive separation capabilities and pore diameter is established in materials with complex pore distributions. A method of generating mobile extra-framework cations which drastically increase adsorptive selectivity toward nitrogen over oxygen via electrostatic interactions is explored through experiments and simulations. Finally, deposition of redox-active ferrocene molecules into systematically generated defects is shown to be an effective method of increasing selectivity towards oxygen.
Dissertation/Thesis
Masters Thesis Chemical Engineering 2019

Carbon dioxide is a viable resource, if used as a raw material for bioprocessing. It is abundant and can be collected as a byproduct from industrial processes. Globally, photosynthetic organisms utilize around 6’000 TW (terawatt) of solar energy to fix ca. 800 Gt (gigaton) of CO2 in the planets largest carbon-capture process. Photosynthesis combines light harvesting, charge separation, catalytic water splitting, generation of reduction equivalents (NADH), energy (ATP) production and CO2 fixation into one highly interconnected and regulated process. While this simplicity makes photosynthetic production of commodity interesting, yet photosynthesis suffers from low energy efficiency, which translates in an extensive footprint for solar biofuels production conditions that store < 2% of solar energy. Electron transfer processes form the core of photosynthesis. At moderate light intensity, the electron transport chains reach maximum transfer rates and only work when photons are at appropriate wavelengths, rendering the process susceptible to oxidative damage, which leads to photo-inhibition and loss of efficiency. Based on our fundamental analysis of the specialized tasks in photosynthesis, we aimed to optimize the efficiency of these processes separately, then combine them in an artificial photosynthesis (AP) process that surpasses the low efficiency of natural photosynthesis. Therefore, by combining photovoltaic light harvesting with electrolytic water splitting or CO2 reduction in combination with microbiological conversion of electrochemical products to higher valuable compounds, we developed an electro-microbial carbon capture and conversion setups that capture CO2 into the targeted bioplastic; polyhydroxybutyrate (PHB). Based on the type of the electrochemical products, and the microorganism that either (i) convert products formed by electrochemical reduction of CO2, e.g. formate (using inorganic cathodes), or (ii) use electrochemically produced H2 to reduce CO2 into higher compounds (autotrophy), three AP setups were designed: one-pot, two-pot, and three-pot setups. We evaluated the kinetic (microbial uptake and conversion, electrochemical reduction) and thermodynamics (efficiencies) of the separate processes, and the overall process efficiency of AP compared to photosynthesis. We address the influence of several parameters on efficiencies and time-space yields, e.g. salinity, pH, electrodes, media, partial pressures of H2 and CO2. These data provide a valuable basis to establish a highly efficient and continuous AP process in the future.

Dissertação de Mestrado Integrado em Engenharia do Ambiente apresentada à Faculdade de Ciências e Tecnologia
A captura e armazenamento de carbono (CAC) e a captura e utilização de carbono (CCU) são consideradas internacionalmente como potencial medidas de mitigação para a redução de emissões atmosféricas de dióxido de carbono geradas em grandes fontes industriais. Este estudo incide sobre uma análise teórica das várias opções das tecnologias de CAC e CCU, e uma parte experimental sobre a carbonatação mineral utilizando um resíduo industrial alcalino, os grits, formados durante o processo Kraft na produção de pasta de papel. A parte experimental do estudo foi realizada no Centro de Investigação para os Processos Químicos e Produtos da Floresta (CIEPQPF) do Departamento de Engenharia Química da Universidade de Coimbra.Foi adotada a via de carbonatação mineral indireta composta por duas etapas: a etapa de extração de cálcio e a etapa de carbonatação originando um precipitado de carbonato de cálcio. Numa primeira abordagem foram analisados quatro possíveis solventes de extração (HNO3, CH3COOH, NaOH e o NH4Cl), de forma a determinar qual dos solventes teria um melhor desempenho na fase de extração de cálcio dos grits. De entre os quatro solventes apenas o HNO3 e o CH3COOH se destacaram com eficiências de remoção de 79,4 e 73,2 %, respetivamente, depois de 2 horas de operação a 30 oC. Testes cinéticos com os dois solventes demonstraram que inicialmente a cinética de dissolução do resíduo era muito rápida, estabilizando após 60 minutos. O HNO3 teve um melhor desempenho sobretudo nas eficiências registadas, contudo como é um ácido de natureza corrosiva e com custos associados elevados, optou-se pelo CH3COOH como solvente de extração de Ca dos grits. Um planeamento Box-Behnken com três fatores (temperatura, concentração da solução de CH3COOH e razão sólido/líquido, S/L(g/L)) com três níveis foi utilizado para determinar as condições ótimas da etapa de extração. A partir da análise estatística dos resultados, tendo como base o diagrama de Pareto, foi possível determinar quais os fatores que mais influenciam a extração de Ca. A concentração de ácido acético e a razão sólido-líquido foram os únicos fatores que demonstraram resultados com significância estatística, contribuindo positivamente e negativamente para a eficiência de extração de Ca, respetivamente. As análises baseadas na metodologia da superfície de resposta e função de “desirability” permitiram encontrar as condições ótimas: concentração de ácido de 2M, temperatura de 45ºC e razão sólido/líquido de 30g/L com uma eficiência de extração de cerca de 77 %.Na segunda etapa, foram realizadas experiências de carbonatação para a precipitação de carbonato de cálcio, fazendo reagir o licor rico em cálcio, obtido na etapa de extração sob condições ótimas, com uma corrente gasosa de CO2 num reator de pressão feito de inox. Essas experiências foram planeadas de acordo o projeto do tipo Box-Behnken com dois fatores (temperatura e pressão no interior do reator). A análise estatística dos resultados demonstrou que a única variável com significado estatístico era o efeito quadrático da temperatura, contribuindo negativamente para a eficiência de carbonatação. Deste modo, conclui-se que os intervalos de variação dos fatores selecionados não permitiram obter a variabilidade desejada para a eficiência de carbonatação. Contudo, foi possível obter condições ótimas de 30ºC e 30 bar, com eficiências de carbonatação na ordem dos 74 %, correspondendo uma capacidade de sequestro de CO2 de cerca de 460 kg CO2 /ton de grits.
The carbon capture and storage (CCS) and carbon capture and utilization (CCU) have been considered internationally as potential measures to reduce the atmospheric emissions of carbon dioxide by large industrial sources.This study focuses on a theoretical analysis of the several options given by the CCS and CCU, and experimental work of mineral carbonation using an alkaline industrial waste, the grits, formed during the Kraft process in the production of paper pulp. The experimental tests were carried out at Chemical Process Engineering and Forest Products Research Centre (CIPQPF), Department of Chemical Engineering of University of Coimbra. The route of the indirect mineral carbonation was adopted, composed by two steps: first the extraction of calcium from the grits and second the precipitation of calcium carbonate. In a first approach, four possible extraction solvents were analyzed (HNO3, CH3COOH, NaOH and NH4Cl) to determine which solvent exhibited the best performance of the extraction of Ca from the grits. Among them, only HNO3 and CH3COOH have shown significant results with extraction efficiencies of 79.4 and 73.2%, respectively, after 2 h at 30 oC. Kinetic tests conducted with the two solvents demonstrated that initially the rate of the extraction process of Ca was very fast, stabilizing after 60 minutes. Since the nitric acid is a corrosive acid and with high associated costs, the acetic acid was selected for dissolution of grits and extraction of calcium. A Box-Behnken design with three factors (temperature, concentration of CH3COOH solution and solid/liquid ratio) having three levels was used to determine the optimal conditions of the extraction step. From the Pareto chart, it was possible to conclude that the acetic acid concentration and the solid-liquid ratio were the factors that demonstrated results with a significant statistical level, contributing positively and negatively to the efficiency of Ca extraction, respectively. The analysis based on the response surface methodology and the desirability functions allowed to found the following optimal conditions: acetic acid concentration of 2M, solid/liquid ratio of 30 g/L and temperature of 45ºC with an efficiency approximately of 77%. In the second step, carbonation experiments for the precipitation of CaCO3 were performed contacting the Ca-rich liquor, obtained from the extraction step operated under optimal conditions, with a flux of pure CO2 gaseous in a stainless inox reactor. These experiments were planned according to a Box-Behnken design with two factors (temperature and the pressure inside the reactor) at three levels. The statistical analysis of the results demonstrated that the only variable with a significant statistical level was the quadratic effect of the temperature, contributing negatively to the carbonation efficiency. Therefore, the ranges of the levels selected for the 2 factors do not produced a desired variability in the carbonation efficiencies. However, the response surfaces and desirability functions led to optimal conditions of 30 ºC and 30 bar, reaching a carbonation efficiency of 74%, corresponding a CO2 sequestration capacity of 460 kg CO2/ton of grits.

Dupla diplomação UTFPR
Nowadays, several research and development efforts are devoted to find processes that can mitigate global warming. This phenomenon is caused by anthropogenic emissions of greenhouse gases, such as carbon dioxide and methane. In this way, adsorption processes are a promising alternative for capturing and separating greenhouse gases because it presents a lower energy cost, compared to other methods, and especially for the possibility of regenerating the adsorbent material without generating by-products. In addition, adsorption processes can be used for upgrading natural gas, a fuel with a low emission of carbon dioxide per kilowatt of energy produced. Thus, the main objective of this work was the development of an adsorption simulator to study the separation of CO2/CH4/N2 mixtures in a fixed bed including the conceptual design of a cyclic pressure swing adsorption (PSA) process for CO2 capture and purification. In order to achieve this objective, a mathematical model has been developed to describe the adsorption of mixtures in a fixed bed solved through numerical methods available in the literature. The numerical implementation was performed in MATLAB® simulation environment. The implemented model was tested and validated by simulating numerical examples of fixed bed adsorption available in the literature. Also, the model was used to fit experimental data collected at LSRE/CIMO-IPB concerning the CO2 adsorption in a fixed bed containing Activated Carbon derived from a municipal solid waste compost (AC-MSW). It was found, that the non-isothermal fixed bed adsorption model developed accurately described the experimental data. Finally, the thermodynamic and kinetic data collected from the best AC-MSW studied material was used to design a conceptual PSA unit using the numerical model and simulator developed. The conceptual PSA process was designed to capture carbon dioxide in a real post-combustion stream with data supplied by Persian Gulf Star Oil Company (PGSOC). Process performance parameters of the conceptual PSA simulated, indicate that is possible to achieve between 9.5-25% purity and high recovery of CO2 (above 87%) with the AC-MSW material, depending on the purge to feed ratio.
Atualmente, grandes esforços em pesquisa e desenvolvimento são destinados à busca de processos que possam mitigar o aquecimento global. Esse fenômeno é ocasionado por emissões antropogênicas de gases de efeito estufa, como o dióxido de carbono e o metano. Diante deste problema, o processo de adsorção é uma alternativa promissora para a captura e separação de gases do efeito estufa por apresentar menor custo energético, comparado a outros métodos, e especialmente, pela possibilidade de regenerar o material adsorvente sem gerar subprodutos. Além disso, a adsorção pode ser utilizada na purificação do gás natural, um combustível com baixa emissão de dióxido de carbono por kilowatt de energia produzida. Assim, o principal objetivo deste trabalho foi desenvolver um simulador do processo de adsorção para o estudo da separação de misturas CO2/CH4/N2 em leito fixo incluindo um projeto conceitual do processo cíclico de adsorção por oscilação de pressão (PSA) para captura e purificação de CO2. Para alcançar este objetivo, um modelo matemático que descreve a adsorção de misturas em leito fixo foi desenvolvido e resolvido aplicando-se métodos numéricos disponíveis na literatura. A implementação numérica foi realizada no ambiente de simulação MATLAB®. O modelo implementado foi testado e validado simulando exemplos numéricos disponíveis na literatura. Além disso, o modelo foi ajustado aos dados experimentais coletados no LSRE/CIMO-IPB sobre a adsorção de CO2 em leito fixo contendo Carbono Ativado derivado de compostos de resíduos sólidos urbanos (AC-MSW). Constatou-se que o modelo não isotérmico de adsorção em leito fixo descreveu com boa precisão os dados experimentais. Por fim, os dados termodinâmicos e cinéticos coletados do melhor material estudado de AC-MSW foram utilizados para projetar uma unidade conceitual PSA utilizando o modelo numérico desenvolvido. A unidade conceitual PSA foi projetado para capturar dióxido de carbono de um fluxo real de gases pós-combustão, com dados fornecidos pela empresa Persian Gulf Star Oil Company (PGSOC). Os parâmetros de desempenho do processo PSA simulado indicam que com o AC-MSW é possível obter uma pureza entre 9.5-25% e alta recuperação de CO2 (acima de 87%), dependendo da relação entre a purga e a alimentação.

Ever increasing anthropogenic emissions of greenhouse gas carbon dioxide (CO₂) are considered as the main driving force behind climate change on Earth. Despite the incentives surrounding carbon-free energy, it will take decades until significant market penetration is achieved. In the meantime, while carboneous fossilized energy sources continue to dominate the energy blend and worldwide energy demand is continuously increasing, carbon capture and storage (CCS) can offer an immediate solution to fight climate change. Several high temperature CO₂ capture technologies are under development (e.g. chemical looping of calcium sorbents is predicted to provide zero emission energy from coal). Calcium sorbents must be recycled given its natural state in the Earth's crust as calcium carbonate. Looping raises concerns about the energy intensive sorbent regeneration and ultimate fate of the separated CO₂ as well as the degradation of the sorbent material. Unlike their Ca-based counterparts, Mg-bearing sorbents, derived from silicate minerals and industrial wastes, can act as combined carbon capture and storage media in various energy conversion systems. The magnesium carbonate formed during the carbon mineralization process is recognized as the most safe and permanent method to store anthropogenic CO₂. Despite the benefits of Mg carbon mineralization, the reactions experience limitations in terms of kinetics and overall conversion, depending on the reaction system, and the mechanisms are not well understood, especially at high temperature and pressure conditions. Mg(OH)₂ carbonation in the slurry phase is known to occur spontaneously and recent results show improved gas-solid carbonation with comparable materials in the presence of H₂O vapor. The pathways of H₂O enhanced gas-solid Mg(OH)₂ carbonation were investigated at elevated temperatures and CO₂ pressures (up to 400 °C and 15 atm). Attributed to the fast formation of hydrated carbonate intermediates, carbonation conversion showed dramatic increase with increasing H₂O loading. Still, carbonation of Mg(OH)₂ in a gas-solid system has largely demonstrated limited reaction kinetics and overall conversion. The gas-solid limitations and the enhanced effect of steam motivated an in-depth study of slurry phase Mg(OH)₂ carbonation. The literature lacked an investigation of Mg(OH)₂ slurry carbonation at elevated temperature, thus this study examined carbonation at moderate temperature and CO₂ pressure (up to 200 ºC and 15 atm). The reaction conditions responsible for hydrated and anhydrous carbonate product phases were evaluated and carbonate formation kinetics were investigated. Reaction temperature was found to be the dominant parameter driving the formation of specific carbonate phases. Anhydrous carbonate is most desirable from a carbon storage perspective, due to its magnesium efficiency, omission of additional crystal waters and thermodynamic stability; therefore solution additives were investigated for their role in bypassing formation of metastable intermediates. The use of MgCO₃ seed particles gave the best result, producing 100% anhydrous carbonate at 150 ºC where it was not observed previously. After the detailed study of Mg(OH)₂ carbonation in both gas-solid and slurry arrangements, its integration with an energy conversion process, the water gas shift reaction (WGSR), was explored to increase the sustainability of carboneous energy sources. The removal of CO₂ by the carbonation reaction enhanced hydrogen yield of the WGSR as the equilibrium of the gas phase reaction was shifted towards products. Unexpectedly, a side reaction was exposed, which converted CO to aqueous formate ion and limited the overall production of hydrogen. Overall, this study explored the fundamental chemistry relating to carbonate phase formation mechanisms and kinetics during the carbonation reaction of Mg(OH)₂ in various reactor systems.

In order to address the global challenges of climate change caused by the increasing concentration of carbon dioxide (CO2), Carbon Capture, Utilization and Storage (CCUS) has been proposed as a promising strategy in carbon management. In parallel with the target of zero emission in fossil-fired power plants, negative emission has also drawn a great deal of attention in other chemical sectors, including cement making and steel production industries. Thanks to the recent reduction in the cost of renewable energy sources, such as wind and solar, a paradigm shifting concept has emerged to directly convert the captured carbon into chemicals and fuels. In this way, decarbonization in various chemical sectors can be achieved with a reduced carbon footprint. A variety of carbon dioxide conversion pathways have been investigated, including thermochemical, biological, photochemical, electrochemical and inorganic carbonation methods. Electrochemical conversion of carbon dioxide has been thoroughly investigated with great progress in electrocatalysts and reaction mechanisms. However, fewer studies have been taken to tackle the constraint of the low solubility of CO2 in conventional aqueous electrolytes. In an effort to improve the solubility of CO2, various novel electrolytes have been designed with a higher uptake of CO2 and a compatibility with electrochemical conversion, including Nanoparticle Organic Hybrid Materials (NOHMs)-based fluids. NOHMs are a unique liquid-like nanoscale hybrid material, comprising of polymers grafted onto nanoparticles (e.g., silica). NOHMs have demonstrated an excellent thermal stability and a high chemical tunability. Two types of NOHMs with ionic bonding (I) between the polymers and nanoparticles were selected in this study: NOHM-I-PEI incorporating polyethylenimine polymer (PEI) and NOHM-I-HPE consisting of polyetheramine polymer (HPE), illustrative of two modes of carbon capture (e.g., chemisorption and physisorption). The NOHMs-based fluids were synthesized with different secondary fluids and salt to tune the viscosity and conductivity. As the first liquid hybrid solvent system for combined carbon capture and conversion, the physical, chemical and electrochemical properties of NOHMs-based fluids were systematically investigated. It was found that NOHMs-based aqueous fluids have exhibited a lower specific heat capacity than that of the 30 wt.% monoethanolamine (MEA) solvents. In addition, upon CO2 loading, the increase in specific heat capacity and the reduction of the viscosity of the NOHM-I-PEI based aqueous fluids can be attributed to the formation of intra-molecular hydrogen bonds. The different chemistries of the two NOHMs can be reflected by the viscosity-based mixing behavior. The smaller critical concentration and the higher intrinsic viscosity of NOHM-I-HPE based aqueous fluids implied a more significant contribution of viscosity to the system by the addition of NOHM-I-HPE. The viscosity of NOHM-I-HPE (30 wt.%) in water was measured to be 395 cP, an order of magnitude higher than that of NOHM-I-PEI (30 wt.%) in water, which was determined to be 22.6 cP. It was also discovered that the addition of N-methyl-2-pyrrolidone (NMP) has resulted in a dramatic increase of the viscosity of NOHM-I-PEI based aqueous fluids, hypothesized to be due to a possible formation of a complex between NMP and NOHM-I-PEI. On the other hand, the presence of 0.1 M potassium bicarbonate (KHCO3) salt greatly reduced the viscosity of NOHM-I-HPE based aqueous fluids. The electrochemical properties of NOHMs-based fluids were also characterized and an excellent electrochemical stability has been demonstrated. The conductivities of NOHMs-based fluids witnessed an unexpected enhancement from the corresponding untethered polymer-based solutions. At 50 wt.% loading, the conductivity was 15 mS/cm for NOHM-I-PEI based aqueous fluids doped by 1 M bis(trifluoromethylsulfonyl)amine lithium salt (LiTFSI), while it was 0.91 mS/cm for PEI based aqueous solutions. Even after the viscosities of the two solutions were converted to the same value, there was still a large gap between the conductivities of the NOHMs-based fluids and polymer-based fluids. The relative tortuosity of ion transport in NOHMs-based fluids compared to untethered polymer-based solutions was less than 1. This result was indicative of a shorter pathway of ion transport in NOHMs-based fluids than in polymer-based fluids. Thus, it is suggested that in addition to a viscosity effect, unique multi-scale structures were also formed, enabling an enhanced ion transport in the NOHMs-based fluids. With this hypothesis, ultra-small-angle X-ray scattering (USAXS) technique was utilized to construct the structures of NOHMs morphology in secondary fluids, from agglomerates at large scale to aggregates at mid-scale, and to the interparticle distance at small scale. The sizes of the aggregates and the interparticle distance were highly tunable by varying the concentrations of NOHMs, and the types of NOHMs and secondary fluids. For example, the aggregate size was (32.30 ± 0.3) nm and (153.9 ± 1.5) nm for 50 wt.% loading of NOHM-I-PEI and NOHM-I-HPE in mPEG, respectively. This hierarchical structure was hypothesized to give ions unique channels and pathways to migrate, resulting in the surprising conductivity enhancement. Cryogenic electron microscopy (CryoEM) was also employed to image such multi-scale fractal structures. The diffusion behavior under this hierarchical structure was studied subsequently. To our surprise, in certain NOHMs-based fluids, such as 10 wt.% NOHM-I-HPE in water at 25℃, the diffusion coefficient of water was 3.43×(10)^(-9) m2/s, higher than that of deionized water, 2.99×(10)^(-9) m2/s. This is evident of the channels created by NOHMs in the secondary fluids to allow faster local diffusion of water and ions. Meanwhile, the diffusion coefficient of NOHM-I-HPE was higher with the presence of 0.1 M KHCO3 salt compared to the salt-free case in water. Though counter-intuitive, this was because salt would interact with the ionic bonding sites of NOHMs, facilitating the dynamic hopping of polymers on the nanoparticle surface, and thus improving the fluidity of the NOHM-I-HPE based aqueous fluids. This investigation of multi-scale structures and diffusion behavior of NOHMs-based fluids was insightful in understanding how the ions move in the system, and in explaining the enhanced conductivity of NOHMs-based fluids compared to the corresponding untethered polymer-based solutions. It is believed that ions move in two regions of the NOHMs-based fluids, the NOHMs-rich region and secondary fluids-rich region, in the mechanisms of translational movement, and coupled and decoupled ion migration with structural relaxation of NOHMs and secondary fluids. With the understanding of the fundamental properties and the construction of hierarchical structures, the carbon capture performance was evaluated for NOHMs-based fluids. The carbon capture behavior can be tuned by the concentration of NOHMs, and the presence of salt and physical solvents. The carbon capture kinetics was determined by both the amount of the capture material and the viscosity of the fluids. It was determined that 30 wt.% NOHM-I-PEI based aqueous fluids exhibited an optimal balance between capture capacity and sorption kinetics. As the concentration of NOHMs further increased, the elevated viscosity of the system limited the mass transfer of carbon capture. It was also found that salt induced a minimal impact on carbon capture in the initial 100 min for 5 wt.% NOHMs loading, but would negatively impact the capture capacity and kinetics at higher NOHMs loadings. Meanwhile, the addition of physical solvent (NMP) reduced carbon capture capacity and kinetics. Various existing forms of CO2 have been identified in NOHMs-based fluids, including carbamate, bicarbonate, and physisorbed CO2. Carbamate came from the reaction between CO2 and the amine functional groups on NOHM-I-PEI. Physisorbed CO2 was identified as the electroactive species for electrochemical conversion of CO2. In the combined carbon capture and conversion experiments using 5 wt.% NOHM-I-HPE based aqueous electrolyte, carbon monoxide (CO) production was enhanced on polycrystalline silver by 60%, and selectivity was changed on a pyridinic-N doped carbon-based electrode, in comparison with conventional 0.1 M KHCO3 electrolyte. The roles of NOHMs in carbon capture and conversion were also explored. The addition of NOHMs was able to improve the solubility of CO2 with a tunable pH change. It is hypothesized that NOHMs can complex with the electrochemical reaction species,CO2 (CO2^-), and this complex formation can be tunable by the concentration and types of NOHMs. In the end, an alternative approach of utilizing NOHMs-based fluids has also been proposed through encapsulation. The encapsulation of NOHMs-based fluids has enabled a higher specific surface area for CO2 uptake, and an enhancement in capture kinetics has been observed compared to the non-encapsulated NOHMs-based fluids. In summary, a novel nanoscale hybrid solvent system has been developed for combined carbon capture and conversion. The insight into the chemistry of this hybrid solvent system is not beneficial to the advancement in carbon capture and conversion, but it is also enlightening for the interdisciplinary development of various areas involving nanoscale hybrid materials.

The increasing CO2 level in the atmosphere, mostly attributed to anthropogenic activities, is overwhelmingly accepted to be the main greenhouse gas responsible for climate change. Combustion of fossil fuel is claimed to be the major cause of excess CO2 emission into the atmosphere, but human society will still rely heavily on fossil fuel for energy and feedstock supplements. In order to mitigate the environment-energy crisis and achieve a sustainable developing mode, Carbon Capture, Utilization and Storage (CCUS) is an effective method and attracts considerable interests. Rather than conventional aqueous amine-based liquid absorbent, e.g. the toxic, corrosive and energy intensive monoethanolamine (MEA), solid adsorbents are preferable for CO2 capture. CO2 utilization via CO2 conversion to fuel or other value-added products is favored over CO2 storage. Also it is preferred that no transportation of captured CO2 is required. Capturing and converting CO2 to fuel, such as synthetic natural gas or CH4 is particularly useful if it is produced at the site of CO2 generation. The converted CO2 can then be recycled to the inlet of the power plant or integrated into existed fuel infrastructure eliminating any transportation. This thesis presents a study of the development, performance and characterizations of a newly discovered (second generation) dual functional material (DFM) for CO2 capture and catalytic conversion to methane in two separated steps. This material consists of Ru as the methanation catalyst and “Na2O” obtained from Na2CO3 hydrogenation as the CO2 adsorbent, both of which are deposited on the high surface area γ-Al2O3 support. The Ru, “Na2O” DFM captures CO2 from O2- and steam-containing flue gas at temperature from 250 °C to 350 °C in step 1 and converts it to synthetic natural gas (CH4) at the same temperature with addition of H2 produced from excess renewable energy (solar and/or wind energy) in step 2. The heat generated from methanation drives adsorbed CO2 to Ru by spillover from the adsorption sites and diffuse to Ru for methanation. This approach utilizes the heat in the flue gas for both adsorption and methanation therefore eliminating the need of external energy input. The second generation DFM was developed with a screening process of solid adsorbent candidates. Initial adsorption studies were conducted with powdered samples for CO2 capture capacity, methanation capability, and resistance to an O2-containing simulated flue gas feed. The new composition of DFM was then prepared with tablets for future industrial applications and scaled up to 10 grams suitable for testing in a fixed bed reactor. Parametric and 50-cycle aging studies were conducted in a newly constructed scaled-up fixed bed reactor using 10 grams of DFM tablets in the simulated flue gas atmosphere for CO2 capture. With the presence of O2 in CO2 feed gas for step 1, the Ru catalyst is oxidized but must be rapidly reduced in step 2 to the active metallic state. Parametric studies identified 15% H2 is required for stable operation with no apparent deactivation. The parametric plus 50-cycle aging studies demonstrated excellent stability of the second generation DFM. A kinetic study was also conducted for the methanation step using powdered DFM but prepared via the tablet method to minimize any mass transfer and diffusion influence on the methanation rate. An empirical rate law was developed with kinetic parameters calculated. The methanation rate of captured CO2 is highly dependent on H2 partial pressure (approaching a reaction order of 1) while essentially zero reaction order of CO2 coverage was determined. The kinetic study highlights the importance of H2 partial pressure on the methanation process. Characterizations were conducted on the ground fresh and aged (underwent parametric and aging studies) DFM tablets. BET surface area, H2 chemisorption, X-ray diffraction (XRD) pattern, transmission electron microscopy (TEM) images and scanning transmission electron microscope- energy dispersive spectroscopy (STEM-EDS) mapping were utilized to study the material changes between fresh and aged samples. From fresh to aged, similar BET surface area was measured, improved both Ru and “Na2O” dispersion, and decreased Ru cluster size was observed while no definitive proof of the nature of the sodium species was obtained via XRD. The second generation DFM containing 5% Ru, 6.1% “Na2O” / Al2O3 was shown to possess the capability of capturing CO2 from O2-containing simulated flue gas and subsequent methanation with addition of H2 produced from excess renewable energy (or from chemical processes) with twice the CO2 and CH4 capacity relative to the first generation DFM. Activity, selectivity and stability has been demonstrated for the second generation DFM. We envision swing reactors to be utilized commercially where the flue gas feed for step 1 and H2 for step 2 are throttled alternatively between each reactor for continuous operation.

Atmospheric CO2 concentrations are at their highest level on record. Scientific evidence has demonstrated a direct correlation between the rise of CO2 levels and an increase of the global median temperature (~1°C higher than compared to the pre-industrial revolution times) due to the greenhouse gas effect. The change in climate due to this rapid increase of CO2 levels is already negatively affecting our ecosystem and lives, with unpredictable consequences in the future. The main source of anthropogenic CO2 emissions is attributed to the combustion of fossil fuels for energy production and transportation. Global indicators signal that carbon-intensive fuels will continue to be utilized as a main energy source despite the rising implementation of renewable energy sources. In order to curb CO2 emissions, several carbon dioxide capture, utilization and sequestration (CCUS) technologies have been suggested. The current state-of-the-art CO2 capture technology utilizes toxic and corrosive aqueous amine solutions that capture CO2 at room temperature but require heating above the water boiling point temperatures to separate CO2 from the amine solution; the latter of which is to be recycled. Once the CO2 is purified, it is necessary to transport it to its sequestration site or an upgrading processing plant. These are complicated schemes that involve many energy-intensive and costly processes. To address the shortcomings of these technologies, we propose a Dual Function Material (DFM) that both captures CO2 and catalytically converts it to methane in-situ. The DFM consists of a catalytic metal intimately in contact with an alkaline metal oxide supported on a high surface area carrier. The process operates within the flue gas at 320°C for both CO2 capture and methane generation upon the addition of renewable H2. The catalyst is required to methanate the adsorbed CO2 after the capture step is carried out in an O2 and steam-containing flue gas. Ruthenium, rhodium, and nickel are known CO2 methanation catalysts, provided they are in the reduced state. All three were compared for performance under DFM flue gas conditions. Ni is a preferred methanation catalyst based on price and activity; however, its inability to be reduced to its active state after experiencing O2-containing flue gas during the capture step was an outcome determined in this thesis. The performance of a variety of alkaline adsorbents (“Na2O”, CaO, “K2O” and MgO) and carriers (Al2O3, CeO2, CeO2/ZrO2 (CZO), Na-Zeolite-X (Na-X-Z), H-Mordenite Zeolite (H-M-Z), SiC, SiO2 and ZrO2-Y) were also studied. Selection of the best materials was based on CO2 capture capacity, net methane production and hydrogenation rates that were evaluated with thermogravimetric analysis and in fixed bed reactor tests. Rh and Ru DFMs were effective methanation catalysts with Ru being superior based on capture capacity, hydrogenation rate and price. Ru remained active towards methanation even after exposure to O2 and steam-containing simulated flue gas. Alkaline adsorbents, in combination with reduced Ru, were tested for adsorption and methanation. Ru – “Na2O”/Al2O3 DFMs showed the highest rates for methanation although CaO is also a reasonable candidate with slightly lower methanation kinetics. To date, we have demonstrated that -Al2O3 is the most suitable carrier for DFM application relative to other materials studied. The Ni-containing DFM, pre-reduced at 650°C, was highly active for CO2 methanation. However, the hydrogenation with 15% H2/N2 is completely inactive after exposure to O2 and steam, in a flue gas simulation, during the CO2 capture step at 320oC. This thesis reports that small amounts of precious metal (≤ 1% Pt, Pd or Ru) enhance the reduction (at 320°C) and activation of Ni-containing DFM towards methanation even after O2 exposure in a flue gas. While ruthenium is most effective, Pt and Pd all enhance reduction of oxidized Ni. Another objective of this thesis was to investigate whether a portion of the Ru, at its current loading of 5%, could be replaced with less expensive Ni while maintaining its performance. The findings show that the main advantage of the presence of Ni is a small increase in CO2 adsorption and increase in methane produced, at the expense of a lower methanation rate. Extended cyclic aging studies corroborate the stable performance of 1% Ru, 10% Ni, 6.1% “Na2O”/Al2O3. Characterization methods were used to monitor physical and chemical changes that may have occurred during aging studies. Measurements of the BET surface area, H2 chemisorption, XRD pattern, TEM images and STEM-EDS mapping were utilized to study and compare the structural and chemical changes between fresh and aged Ru doped Ni DFM samples. While similar BET surface areas were observed for the fresh and aged samples, some redispersion of the Ru and Ni sites was confirmed via H2 uptake and the observed decreases in Ru and Ni cluster size in the aged sample in comparison to the fresh. XRD patterns confirm an almost complete disappearance of the NiOx and RuOx species and the appearance of catalytically active Ru0 and Ni0 peaks on the aged sample compared to the fresh one. Further details of these methods, findings and conclusions are described in this thesis.

博士
國立臺灣師範大學
化學系
104
Using various nano clusters to catalyze different chemical reactions is one of the many important research issues in recent years. The N2 bond cleavage is the rate-limiting step in the synthesis of ammonia, and ruthenium is a catalyst well known for this reaction. Both of double-icosahedral Ru19 (DI-Ru19) and twinned truncated octahedral Ru79 (t-TO-Ru79) clusters have been investigated to catalyze the adsorption and dissociation of dinitrogen on the active valley-like (stepped) region in Ru19 and Ru79. On the DI-Ru19 cluster, our results show that the valley-like region of Ru19 cluster could dissociate N2 with the lowest reaction barrier 0.78 eV；which on the t-TO-Ru79 cluster, our results demonstrate that dissociating the N-N bond of a N2 molecule on the valley-like region of t-TO Ru79 cluster has a even much lower reaction barrier, 0.27 eV. By using electronic analysis, we found that the adsorbed N2 molecule is parallel to the close-packed Ru atoms on a valley-like active site in both of Ru19 and Ru79, causing much amount of charge transfer from the d orbital of Ru atoms to the 2π* orbital to produce this small barrier. Nickel hydroxide clusters and graphene oxide (GO) composites are novel nanomaterials in the application of electrochemical catalysts. In this work, we calculated the energy of Ni4 adsorbed on saturated hydroxyl graphene oxide (hGO), which formed a Ni4(OH)3 cluster on the hydroxyl graphene oxide (Ni4(OH)3/hGO) and released 4.47 eV. We subsequently studied the oxidation of CO on the Ni4(OH)3/hGO system via three mechanisms –Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and carbonated mechanisms. Our results show that the activation energy for oxidation of the first CO molecule according to the ER mechanism is 0.14 eV, much smaller than that with LH (Ea = 0.65 eV), or with carbonated (Ea = 1.28 eV) mechanisms. The barrier of oxidation of the second CO molecule to CO2 with the ER mechanism increases to 0.43 eV, but still less than that via LH (Ea = 1.09 eV), indicating that CO could be effectively oxidized through the ER mechanism on the Ni4(OH)3/hGO catalyst. Zinc Oxide was an efficient catalyst for the aldol or Knoevenagel condensation reaction and could also be applied as the sensor for detecting ethanol. Here we have investigated the adsorption and C-C coupling reactions of ethanol and acetaldehyde on a (ZnO)12 cluster. First, with only two acetaldehyde molecules as reactants, the major product would be the 3-hydroxylbutanal formed by C-C coupling reaction via Zimmerman–Traxler model of aldol mechanism. Second, while with only two ethanol molecules, there is no product formed spontaneously, either acetaldehyde from ethanol dehydrogenation nor butanol by C-C coupling reaction of two ethanol molecules. Third, with coadsorption of one acetaldehyde and one ethanol molecules on (ZnO)12 cluster, the major product would be 2-buten-1-ol formed via C-C coupling reaction, in which the mechanism is similar to the aldol mechanism. These results demonstrate that the reactivity of C-C coupling reactions between ethanol and acetaldehyde on (ZnO)12 cluster depend on the concentration of acetaldehyde molecules.

Mit der Arbeit werden braunkohlegefeuerte IGCC-CCS-Kraftwerke gesamtheitlich beschrieben, deren Potenziale erarbeitet und mit ASPEN Plus™ sowie EBSILON® Professional simulativ abgebildet. Es kann gezeigt werden, dass ausgehend von Basiskonzepten braunkohlegefeuerter IGCC-CCS-Kraftwerke mit verschiedenen Potenzialen zum gegenwärtigen Stand der Technik sowie dem im Jahr 2025 Wirkungsgradsteigerungen sowie prozesstechnische Vereinfachungen möglich sind. Als Potenziale werden dabei verringerte Braunkohletrocknung, konservativere Annahmen der technologischen Auslegung als auch Modifizierungen der CO-Konvertierung, sowie für das Jahr 2025 konservative Annahmen und innovative Potenziale untersucht. Ausgangspunkt bildet eine Analyse von bestehenden und zukünftig erwarteten Prozesskomponenten braunkohlegefeuerter IGCC-CCS-Kraftwerke unter Berücksichtigung von drei unterschiedlichen Vergasungsverfahren (nach Siemens, nach Shell und dem HTW-Verfahren).:1 Einleitung und Zielsetzung 2 Grundlagen und Methodik 2.1 IGCC und CCS 2.2 Gewählte Randbedingungen 2.3 Untersuchte Konzepte 2.4 Grundlagen der Konzeptbewertung 2.4.1 Energetische Analyse 2.4.2 Exergetische Analyse 2.4.3 Kohlenstoffbilanz 2.5 Verfahrenstechnische Simulationswerkzeuge 3 IGCC-CCS-Kraftwerksprozess 3.1 Vergasung 3.1.1 Reaktionen 3.1.2 Fluiddynamische Klassifizierung 3.1.3 Vergasungstechnologien 3.1.4 Flowsheet Simulation der Vergasungstechnologien 3.1.5 Vergleich der abgebildeten Vergasungstechnologien 3.2 Vergasungsstofftrocknung und -aufbereitung 3.2.1 Technologie der Vergasungsstofftrocknung und -aufbereitung 3.2.2 Flowsheet Simulation der Vergasungsstofftrocknung und -aufbereitung 3.3 Sauerstoffbereitstellung 3.3.1 Technologie der kryogenen Luftzerlegung 3.3.2 Flowsheet Simulation der kryogenen Luftzerlegung 3.3.3 Potenziale 3.4 Gaskonditionierung 3.4.1 Kühlung, Entstaubung und Spurstoffentfernung 3.4.2 CO-Konvertierung 3.4.3 CO2- und H2S-Abtrennung 3.4.4 H2S-Aufbereitung 3.4.5 CO2-Verdichtung und -Speicherung 3.4.6 Reingaskonditionierung 3.5 Stromerzeugung im GuD-Prozess 3.5.1 Technologie des GuD-Prozesses 3.5.2 Flowsheet Simulation des GuD-Prozesses 3.5.3 Potenziale 3.6 Gesamtkonzepte für IGCC-CCS-Kraftwerke zum gegenwärtigen Stand der Technik 3.7 Betrachtungen zu Strängigkeit und Verfügbarkeit der Gesamtkonzepte für IGCC-CCS-Kraftwerke zum gegenwärtiger Stand der Technik 4 Konzeptstudien 4.1 Konservative Annahmen zum gegenwärtigen Stand der Technik 4.2 Verringerte Braunkohletrocknung zum gegenwärtigen Stand der Technik 4.3 Modifizierte CO-Konvertierung zum gegenwärtigen Stand der Technik 4.3.1 Quenchkonvertierung 4.3.2 Isotherme katalytische CO-Konvertierung 4.3.3 Kombination von Quenchkonvertierung und isothermer katalytischer CO-Konvertierung 4.4 Konservative Annahmen zum Stand der Technik im Jahr 2025 4.5 Innovatives Potenzial zum Stand der Technik im Jahr 2025 5 Zusammenfassung