Dissertationen zum Thema „CO2 chemical absorption“

I detta arbete studeras absorption av växthusgasen koldioxid (CO2) i ammoniaklösning. Målet med arbetet är att undersöka hur väl teknik med vegetabilisk olja kan förhindra avdunstning av ammoniaklösning vid absorptionen och på så vis främja grön kemi. En jämförelse görs sedan med en mer beprövad teknik med nedkylning. Därefter undersöks vilka salter som fälls ut vid absorptionen vid de båda teknikerna samt olika koncentration ammoniak (NH3). Genom att blanda ammoniak, etanol (C2H5OH) och vatten (H2O) i olika förhållanden i ett absorptionstorn erhölls den absorberande lösningen. CO2 i gasform fördes sedan in i reaktorn. I genomförda experiment gav teknik med vegetabiliskt oljemembran samma eller lägre materialförlust av ammoniaklösning som teknik med nedkylning. Högre halt av etanol innebar sänkt löslighet av ammoniumsalter vilket gav större utfällning av salter i utförda experiment. Detta kan observeras genom att jämföra kristallvikten i utförda experiment. Kristallerna analyserades med röntgendiffraktion (XRD). Salterna kunde identifieras genomatt jämföra erhållet resultat med standardprov från litteratur. Dock fanns avvikelser mellanresultatet och standardprov, vilket gjorde analysen svårtolkad.

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.

Following the climate change mitigation target in Paris agreement, the global warming has to be limited to 2.0°C above the preindustrial levels. One of the potential methods is carbon capture and storage (CCS), which can significantly reduce the CO2 emissions from the vast point sources such as power plants, industries, and natural gas processes. The CCS covers four steps which are capture, conditioning, transport, and storage. For the capture part, post-combustion capture is easier to implement based on today’s technologies and infrastructure compared with pre-combustion and oxy-fuel combustion captures, since the radical changes in the structure of the existing plant are not required. To design and operate different CCS processes, the knowledge of thermo-physical properties of the CO2 mixtures is of importance. In this thesis, the status and progress of the studies related to the impacts of the uncertainty in thermo-physical properties on the design and operation of the CCS processes were reviewed. The knowledge gaps and the priority of property model development were identified. According to the identified knowledge gaps in the review, the impacts of thermo-physical properties which are the density, viscosity, and diffusivity of the gas and liquid phases, and the surface tension and heat capacity of the liquid phase on the design of the absorber column for the chemical absorption using aqueous monoethanolamine were quantitatively analyzed. An in-house rate-based absorption model was developed in MATLAB to simulate the absorption process, and the sensitivity study was done for each property. An economic evaluation was also performed to further estimate the impacts of the properties on the capital cost of the absorption unit.  For column diameter of the absorber, the gas phase density shows the most significant impacts; while, the liquid phase density and viscosity show the most significant impacts on the design of the packing height and also the capital cost of the absorption unit. Therefore, developing the flue gas density model and liquid phase density and viscosity models of the aqueous solvents with CO2 loading should be prioritized.
Enligt Parisavtalets mål för klimatförändringar ska den globala uppvärmningen begränsas till 2.0° C över förindustriella nivåer. En av de potentiella metoderna är avskiljning och lagring av koldioxid (CCS), som avsevärt kan minska CO2-utsläppen från stora punktkällor såsom kraftverk, industrier och naturgasprocesser. CCS omfattar fyra steg som är avskiljning, konditionering, transport och lagring. Avskiljning genom efterförbränning är lättare att genomföra baserat på dagens teknik och infrastruktur jämfört med avskiljning före förbränning och genom oxybränsle förbränning, eftersom radikala förändringar av de befintliga anläggningars struktur inte behövs. För att utforma och driva olika CCS processer, är kunskap om termofysikaliska egenskaperna hos CO2 blandningarna av stor betydelse. I denna avhandling har status och framsteg för studier rörande effekterna av osäkerheten i termofysikaliska egenskaper på konstruktion och drift av CCS processer granskats. Kunskapsluckor och prioritering av utveckling av modeller för egenskaperna identifierades. Enligt de i översynen identifierade kunskapsluckorna, har effekterna av de termofysikaliska egenskaperna densitet, viskositet och diffusivitet av gas- och vätskefaserna, och ytspänningen och värmekapacitet av vätskefasen på utformningen av absorptionskolonnen för kemisk absorption med användning av vattenhaltig monoetanolamin analyserats kvantitativt. En hastighetsbaserad absorptionsmodell har utvecklats i MATLAB för simulering av absorptionsprocessen och känslighetsanalys gjordes för varje egenskap. En ekonomisk utvärdering genomfördes också för att ytterligare uppskatta effekterna av egenskaperna på kapitalkostnaden för absorptionsenheten. För bestämning av diametern av absorbatorns kolonn visar gasfasens densitet den mest betydande inverkan; medan vätskefasens densitet och viskositeten visar den mest betydande inverkan på utformningen av fyllmaterialets höjd och även kapitalkostnaderna för absorptionsenheten. Därför bör utveckling av modeller för rökgasens densitet och vätskefasens densitet och viskositet för det vattenbaserade lösningsmedlet med absorberad CO2 prioriteras.
VR CCS Project

Les procédés de captage de CO2 par absorption chimique engendrent une importante pénalité énergétique sur la production électrique des centrales à charbon, constituant un des principaux verrous technologiques au déploiement de la filière. L'objectif de cette thèse est de développer et valider une méthodologie à même d'évaluer précisément le potentiel d'un procédé de captage aux amines donné. La phénoménologie de l'absorption chimique a été étudiée en détail et représentée par des modèles à l'état de l'art. Le modèle e-UNIQUAC a été utilisé pour décrire les équilibres chimiques et de phases des solutions électrolytiques et les paramètres du modèle ont été régressés pour quatre solvants. Un modèle hors-équilibre a été utilisé pour représenter le transfert couplé de matière et de chaleur, accéléré par les réactions chimiques. Les modèles ont été validés avec succès sur des données expérimentales d'un pilote industriel et d'un pilote de laboratoire. L'influence des phénomènes sur les efficacités de séparation a été explicitée afin d'isoler les phénomènes les plus impactants. Une méthodologie a alors été proposée pour évaluer la pénalité énergétique, incluant les consommations thermiques et électriques, liée à l'installation d'un procédé de captage sur une centrale à charbon supercritique. Une méthode d'estimation du coût de l'électricité est proposée pour quantifier les dépenses opératoires et d'investissement d'un tel procédé. L'environnement de simulation et d'évaluation de procédés obtenu a ensuite été couplé à une méthode d'optimisation afin de déterminer les paramètres opératoires et les dimensions des équipements maximisant les performances énergétiques et économiques
CO2 capture processes by chemical absorption lead to a large energy penalty on efficiency of coal-fired power plants, establishing one of the main bottleneck to its industrial deployment. The objective of this thesis is the development and validation of a global methodology, allowing the precise evaluation of the potential of a given amine capture process. Characteristic phenomena of chemical absorption have been thoroughly studied and represented with state-of-the-art models. The e-UNIQUAC model has been used to describe vapor-liquid and chemical equilibria of electrolyte solutions and the model parameters have been identified for four solvents. A rate-based formulation has been adopted for the representation of chemically enhanced heat and mass transfer in columns. The absorption and stripping models have been successfully validated against experimental data from an industrial and a laboratory pilot plants. The influence of the numerous phenomena has been investigated in order to highlight the most limiting ones. A methodology has been proposed to evaluate the total energy penalty resulting from the implementation of a capture process on an advanced supercritical coal-fired power plant, including thermal and electric consumptions. Then, the simulation and process evaluation environments have been coupled with a non-linear optimization algorithm in order to find optimal operating and design parameters with respect to energetic and economic performances

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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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

Deux polymères modèles de natures chimiques opposées, le poly(oxyde d'éthylène) et le polystyrène, ont été fractionnés par un mélange supercritique CO2/solvant (solvant : éthanol, acétone, tétrahydrofurane), en fonction de leurs masses molaires, à température constante et à pression variable. Les expériences de fractionnement ont été réalisées sur des échantillons linéaires et sur des polymères à architecture ou de structure chimique plus complexes (polymères en étoile, dendrimères, macrocycles, copolymères à blocs). La solubilité de ces polymères dans les mélanges supercritiques CO2/solvant ainsi que la sélectivité de ces milieux ont été évaluées. L'influence des paramètres, pression, température, nature chimique et quantité de solvant a été étudiée. Enfin, nous avons mené une étude spectroscopique afin de mieux comprendre l'organisation microscopique des systèmes polystyrène//CO2/éthanol. Parallèlement, une modélisation thermodynamique des équilibres de phases, par la méthode SAFT, a été initiée.

In Canada, coal-fired power plants are the largest anthropogenic point sources of atmospheric CO₂. The most promising near-term strategy for mitigating CO₂ emissions from these facilities is the post-combustion capture of CO₂ using MEA (monoethanolamine) with subsequent geologic sequestration. While MEA absorption of CO₂ from coal-derived flue gases on the scale proposed above is technologically feasible, MEA absorption is an energy intensive process and especially requires large quantities of low-pressure steam. It is the magnitude of the cost of providing this supplemental energy that is currently inhibiting the deployment of CO₂ capture with MEA absorption as means of combatting global warming. The steam cycle of a power plant ejects large quantities of low-quality heat to the surroundings. Traditionally, this waste has had no economic value. However, at different times and in different places, it has been recognized that the diversion of lower quality streams could be beneficial, for example, as an energy carrier for district heating systems. In a similar vein, using the waste heat from the power plant steam cycle to satisfy the heat requirements of a proposed CO₂ capture plant would reduce the required outlay for supplemental utilities; the economic barrier to MEA absorption could be removed. In this thesis, state-of-the-art process simulation tools are used to model coal combustion, steam cycle, and MEA absorption processes. These disparate models are then combined to create a model of a coal-fired power plant with integrated CO₂ capture. A sensitivity analysis on the integrated model is performed to ascertain the process variables which most strongly influence the CO₂ energy penalty. From the simulation results with this integrated model, it is clear that there is a substantial thermodynamic advantage to diverting low-pressure steam from the steam cycle for use in the CO₂ capture plant. During the course of the investigation, methodologies for using Aspen Plus® to predict column pressure profiles and for converging the MEA absorption process flowsheet were developed and are herein presented.

Alors que les besoins énergétiques mondiaux continueront d’être satisfaits par des sources d’énergie fossiles, une solution viable pour réduire les émissions de CO2 serait de mettre en œuvre des technologies de captage du carbone. Le captage du CO2 par absorption dans des solvants aminés fait partie des technologies les plus avancées mises en œuvre sur les unités de post-combustion. Son application reste néanmoins limitée aux grandes sources ponctuelles, et les petites sources restantes difficiles à décarboner. Récemment, le chauffage microondes a gagné en popularité en raison de ses caractéristiques de sélectivité, de nature volumétrique et de facilité de contrôle ; d'autre part, les contacteurs à membrane sont des contacteurs gaz-liquide prometteurs en raison de leur compacité, de leur flexibilité opérationnelle et de leur facilité d'évolutivité par rapport aux colonnes à garnissage. Dans ce travail, nous explorons le fonctionnement de la désorption chimique lors d'un contacteur à membrane à fibres creuses par chauffage par micro-ondes.Une compréhension complète des interactions entre les champs microondes et les phénomènes de transfert est essentielle pour la conception, le fonctionnement et l’optimisation corrects d’un équipement à l’échelle industrielle. Ainsi, les taux de désorption du CO2 ont été étudiés expérimentalement à l'échelle locale d'une seule fibre millimétrique, placée dans une cavité micro-onde monomode. La modélisation numérique de la fibre a permis de visualiser les gradients de température formés à l'intérieur du solvant, et les taux de désorption locaux correspondants. En parallèle, une unité à l'échelle prototype a été conçue pour la désorption du CO2 à l'échelle d'un module à fibres creuses sous des champs microondes. À cette fin, nous avons conçu une cavité sur mesure pour abriter un module à membrane de telle manière que la désorption du CO2 aurait lieu simultanément avec le chauffage électromagnétique
As global energy needs will continue to be met by fossil-fuel based sources, a viable solution to reduce CO2 emissions would be to implement carbon capture technologies. CO2 capture by absorption in amine solvents ranks among the most advanced technologies to be implemented on post combustion units. Still, its application is remains constrained large point sources with small sources remaining difficult to decarbonize. Recently, microwave heating has gained in popularity due to its characteristics of selectiveness, volumetric nature, and ease of control; on the other hand, membrane contactors are promising gas-liquid contactors due to their compacity, operational flexibility, and ease scalability in comparison to packed columns. In this work we explore the operation of chemical desorption when a hollow fiber membrane contactor by microwave heating.A comprehensive understanding of the interactions of microwave fields and transfer phenomena is essential for the correct design, operation, and optimization of an industrial scale equipment. Hence CO2 desorption rates were experimentally studied at the local scale of a single millimetric fiber, placed in a mono-mode microwave cavity. Numerical modeling of the fiber allowed the visualization of the temperature gradients formed inside the solvent, and the corresponding local desorption rates. In parallel, a prototype-scale unit was designed for the desorption of CO2 at the scale of a hollow fiber module under microwave fields. To this end we designed a custom-design cavity was made to house a membrane module in such a manner that CO2 desorption would take place simultaneously with electromagnetic heating

Objetivo deste trabalho foi o de caracterizar e estudar o processo de transferência de massa da absorção de CO2 em soluções aquosas de aminas em coluna recheada operando em pressão atmosférica. Com este objetivo, construíram-se dois equipamentos, sendo um constituído de coluna em escala laboratório com recheio estruturado e outro de uma coluna em escala piloto com recheio randômico. Empregou-se a absorção de CO2, diluído em ar, em solução de NaOH, para a determinação da área interfacial efetiva. Os coeficientes globais de transferência de massa foram determinados para a absorção de CO2, diluído em ar, em diferentes soluções aquosas absorvedoras a base de aminas, a saber: 25% em massa de MEA, MEA-MDEA nas concentrações mássicas 5% MDEA 25% MEA, 10% MDEA 20% MEA e 15% MDEA 15% MEA. Constatou-se uma forte correlação entre a proporção da solução MDEA-MEA e o coeficiente global de transferência de massa. O planejamento dos ensaios em coluna piloto foi realizado com o emprego de simulador de processos, para a verificação hidrodinâmica da coluna e especificação das vazões de gás e de solução absorvente. Compararam-se, também, os resultados obtidos experimentalmente com os previstos pela simulação, no caso da absorção em MEA.
The aim of the present work was to characterize and study the mass transfer process of the CO2 absorption into single and blended alkanolamines in a packed column under atmospheric pressure. For this purpose, two systems were built, one of the columns is a laboratory structure packed column and the other is a pilot random packed column. The absorption of CO2 into NaOH was performed to determine the effective mass-transfer area and the overall mass-transfer coefficient. The absorption performance was evaluated in terms of the overall mass-transfer coefficient for the absorption of CO2 in air into single and blended alkanolamines: MEA 25% wt, and MEA-MDEA mixtures, MEA-MDEA (25% /5% wt), MEA-MDEA (20% /10% wt) and MEA-MDEA (15% /15% wt). The CO2 absorption performance of MEA-MDEA mixture has a high correlation with the proportion MEA-MDEA. Experimental series were designed employing a process simulator for the hydrodynamic checking and determination of gas and liq flow rates. Comparison of the experimental data and simulation results was made for the absorption into MEA.

Les dispositifs à micro/mini-canaux suscitent un vif intérêt pour l'absorption chimique efficace du CO₂ dans le cadre du captage de CO2. Cette thèse de doctorat vise à caractériser et à étudier le processus de transfert de masse à travers l’écoulement diphasique accompagné de réactions chimiques dans les mini-canaux, ainsi qu'à concevoir et développer de nouveaux absorbeurs de CO₂ miniaturisés avec des structures optimisées vis-à-vis de leurs performances d'absorption. Tout d'abord, la dynamique des bulles dans un mini-canal droit en T a été observée par moyen optique, montrant que la réaction chimique supprime la fragmentation des bulles mais favorise leur rétrécissement. Ensuite, le champ de vitesse et le champ de concentration de CO₂ dans le liquide ont été déterminés respectivement par la PTV et la colorimétrie sensible au pH, permettant le développement d'un modèle de transfert de masse de cellule unitaire modifié, intégrant les effets de la recirculation du flux et de la réaction chimique. En outre, une structure de chicane en spirale a été intégrée dans le mini-canal, d’où une amélioration significative du transfert de masse avec une faible augmentation des pertes de charge. Enfin, sur la base de cette stratégie d'intensification, une conception innovante d'absorbeur de CO₂ multicanaux intégrés, caractérisée par des unités parallèles de minicanaux croisés en double hélice conjuguée (Codohec), a été proposée. Un module à l'échelle du laboratoire de cette conception a été réalisé et ses performances d'absorption ont été évaluées de manière exhaustive, mettant en évidence divers avantages tels qu'un coefficient de transfert de masse élevé, une consommation d'énergie acceptable, un taux d'élimination élevé et une grande capacité de traitement du CO₂. Les résultats de cette thèse pourraient fournir de nouvelles perspectives sur les mécanismes de transport sousjacents du transfert de masse gaz-liquide accompagné de réactions chimiques et contribuer à la conception et à l'optimisation d'absorbeurs de CO₂ miniaturisés hautement efficaces pour des applications industrielles
Micro/minichannel devices show great interests for their potential in efficient CO2 chemical absorption in the context of the carbon capture. This PhD these aims to characterize and investigate the transport mechanisms involved in chemical reactionaccompanied two-phase mass transfer in minichannel, and to design and develop novel miniaturized CO2 absorbers featuring intensified structures and optimized absorption performances. Firstly, bubble dynamics within a T-junction straight minichannel were optically observed, showing that the chemical reaction tends to suppress bubble breakup while promoting its shrinkage. Then, the velocity field and CO2 concentration field in the liquid slug were determined using PTV and pH-sensitive colorimetry, respectively, permitting the development of a modified unit-cell mass transfer model that incorporates the effects of flow recirculation and chemical reaction. Further enhancement was achieved by embedding a spiral distributed baffle structure into the minichannel, leading to a significant increase in mass transfer coefficient with only a minor rise in pressure drop. Finally, building on this intensification measure, a novel design for an integrated multichannel CO2 absorber was proposed, featuring paralleling units of conjugated double-helix cross minichannels (Codohec). A lab-scale module of this design was realized, and its absorption performance was comprehensively evaluated, highlighting various advantages including a high mass transfer coefficient, acceptable energy consumption, high remove rate, and large CO2 treatment capacity. These findings may provide new insights into the underlying transport mechanisms of chemical reaction-accompanied gas-liquid mass transfer and contribute to the design and optimization of highly efficient miniaturized CO2 absorbers for industry applications

La thèse étudie le vaporeformage catalytique du méthane avec captage de CO2. Les catalyseurs bi-fonctionnels choisis se composent de nickel, efficace en vaporeformage, de CaO pour la sorption de CO2 et d'aluminate de calcium (Ca12Al14O33) pour permettre une bonne dispersion du métal et de CaO. La méthode de synthèse privilégiée était la méthode d'autocombustion assisté par microondes. Le rapport Ca/Al a été optimisé et un large excès de CaO est nécessaire (75%CaO ; 25%Ca12Al14O33) pour la sorption de CO2. Le reformage du méthane est total dès 650 °C (H2O/CH4 de 1 ou 3) et la sélectivité en hydrogène de 100% durant 7h ou 16h selon les conditions opérationnelles, validant le concept de vaporeformage du méthane assisté par l'absorption de CO2.

La réduction des émissions de CO2 anthropique est un des enjeux majeurs du 21eme siècle pour de nombreux pays. De nombreux procédés sont développés pour le captage du CO2, parmi lesquels l'absorption gaz-liquide par contacteur membranaire. L'utilisation d'une membrane permet d'intensifier le transfert grâce à une aire interfaciale développée 2 à 10 fois plus élevée (1000 à 5000 m2.m-3) que celle d'une colonne d'absorption (procédé de référence). Deux types de fibres sont étudiées : microporeuses et composites. Dans une partie expérimentale, l'influence de la nature des matériaux, des paramètres géométriques et opératoires sur les propriétés de transfert de matière et sur la stabilité des performances de captage des contacteurs membranaires est étudiée. Les résultats obtenus pour des durées d'expérimentation courte (dizaine d'heures de temps de contact), sont en adéquation avec les résultats présents dans la littérature. Bien que l'ajout d'une peau dense à un support poreux constitue une résistance supplémentaire au transfert de matière, une étude dédiée, effectuée sur des temps de contact importants (plusieurs centaines d'heures), a permis pour la première fois de valider le concept de résistance au mouillage des fibres à peau dense, comparativement aux fibres microporeuses (PP et PTFE). Dans une partie modélisation, une étude comparative d'approches mathématiques de complexité croissante a été menée. Un seul paramètre ajustable a été délibérément retenu : le coefficient de transfert de matière dans la membrane (km). Cette étude a estimé des valeurs de km obtenues par ajustement des données expérimentales dans la plage de données rapportées dans la littérature (10-2 à 10-5 m.s-1). Cependant, l'hypothèse d'une valeur caractéristique du km qui dépend du régime de fonctionnement est posée et commentée. Cette approche diffère singulièrement des travaux rapportés dans la littérature, qui postulent le plus souvent une valeur unique pour un matériau membranaire donné. Dans ces conditions, l'intérêt des fibres composites, qui présentent une valeur constante et vraisemblablement prédictible du coefficient de transfert membranaire de par leur résistance aux phénomènes de mouillage, apparaît comme particulièrement prometteur pour intensifier les procédés de captage du CO2 en post-combustion par absorption gaz-liquide.

Orientadores: Marco Aurelio Zezzi Arruda, Fabio Augusto
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: Este trabalho de Tese visa acoplar a fibra, empregada em microextração em fase sólida (SPME, do inglês solid phase microextraction), ao espectrômetro de absorção atômica com forno de grafite (GF AAS, do inglês graphite furnace atomic absorption spectrometer), visando reter espécies organometálicas volatilizadas nas etapas de secagem e pirólise do GF AAS. O elemento escolhido para avaliar o acoplamento SPME-GF AAS foi o Sn. Primeiramente, a concentração total de Sn foi determinada, utilizando a amostragem em suspensão como estratégia, uma vez que na avaliação da distribuição dos compostos organoestânicos por SPME-GF AAS, a concentração total de Sn seria efetuada a partir de uma suspensão. Para a otimização do método foram avaliados os seguintes parâmetros: solução de preparo da suspensão, e efeito da temperatura de pirólise e atomização. A mistura contendo HF 10 % (v/v) e HNO3 1 % (v/v) foi escolhida para preparar a suspensão, a composição Mg(NO3)2 + NH4H2PO4 apresentou resultados apropriados para ser utilizada como modificador químico convencional, e 1000 e 2200 °C foram as temperaturas ótimas para a pirólise e a atomização, respectivamente. Devido ao efeito de matriz, foi utilizada a técnica de adição de analito para a quantificação de Sn em suspensões de sedimento marinho e de rio, em que os limites de detecção e quantificação calculados foram de 1,5-2,6 e 4,5- 7,6 µg g, respectivamente. Para avaliar o acoplamento SPME-GF AAS, visando à retenção das espécies organoestânicas (butiltricloroestanho, dibutildicloroestanho e tributilcloroestanho) foi utilizada, primeiramente, uma suspensão de sedimento. A suspensão foi sonicada e, em seguida, uma alíquota foi injetada no forno de grafite do GF AAS juntamente com o reagente de derivação (tetraetilborato de sódio - NaBEt4). A programação do forno de grafite foi aplicada e a fibra de SPME foi introduzida no atomizador. Após a retenção das espécies de interesse na fibra, a mesma foi conduzida ao cromatógrafo a gás (CG) para a separação e detecção dos analitos. Os parâmetros instrumentais do CG foram previamente estudados, visando a melhor separação das espécies de interesse. Esses estudos foram realizados utilizando o modo de extração por headspace e SPME (HS-SPME, do inglês headspace-solid phase microextraction). Em relação aos estudos envolvendo suspensões de sedimento no acoplamento proposto SPME-GF AAS, alguns parâmetros foram avaliados frente à retenção das espécies de interesse; entre eles pode-se citar o tipo de fibra, a concentração do reagente de derivação e o pH da reação. Melhores resultados foram observados para a fibra PDMS/DVB, utilizando uma concentração de 0,2 % (m/v) de NaBEt4 para a etilação das espécies de interesse, sendo a reação realizada em pH 5,0. Entretanto, baixa eficiência de retenção (< 20 %) das espécies de interesse em suspensão de sedimento, foi obtida utilizando-se o acoplamento SPME-GF AAS, quando comparada à extração por HS-SPME. Dessa forma, foi realizada uma extração das espécies de interesse das amostras de sedimento, utilizando a energia ultrassônica, anteriormente à sua aplicação no acoplamento proposto SPME-GF AAS. Nesta etapa do trabalho, a temperatura do forno de grafite e o tempo de exposição da fibra de SPME no forno de grafite foram otimizados, visando à máxima eficiência de retenção das espécies de interesse no acoplamento SPME-GF AAS. Os melhores resultados foram observados para temperaturas do forno de grafite de 90 °C, com 986 s de tempo de exposição da fibra no atomizador. Por fim, foram realizados experimentos visando determinar a concentração total de Sn, e reter suas espécies organometálicas simultaneamente, na fibra de SPME, utilizando o acoplamento SPME-GF AAS.
Abstract: The goal of this Thesis was coupling the solid phase microextraction (SPME) to graphite furnace atomic absorption spectrometer (GF AAS) for extracting the organometallic species volatilized in the drying and pyrolysis steps of the GF AAS. For evaluating the SPME-GF AAS coupling, Sn was then chosen. Firstly, the total Sn concentration using the slurry sampling strategy was determined, once in the evaluation of the organotin compounds by SPME-GF AAS, the total Sn concentration would be obtained from a slurry solution. Some parameters were evaluated, such as the nature of the solution to prepare the slurry, and pyrolysis and atomization temperatures effects. The mixture of 10 % (v/v) HF plus 1 % (v/v) HNO3 was chosen to prepare the sediment slurries, the Mg(NO3)2 plus NH4H2PO4 was appropriated as conventional chemical modifier, and the values of 1000 and 2000 °C was used as pyrolysis and atomization temperatures, respectively. The analyte addition was used in the Sn determination in sediment (marine and river) samples by slurry sampling due to matrix effects. The detection and quantification limits were calculated as 1.5-2.6 and 4.5-7.6 µg g, respectively. For evaluating the SPME-GF AAS coupling in the extraction of organotin species (butyltrichloride, dibutyldichloride, and tributylchloride), a sediment slurry was firstly used. For this task, the slurry was sonicated and an aliquot of this solution plus the derivatization reagent (sodium tetraethylborate ¿ NaBEt4) were introducted consecutively into the graphite furnace of the GF AAS. Then, the graphite furnace program was applied, and the SPME fiber was exposed into the furnace. After the extraction of organotin species by SPME-GF AAS, the analytes were separated and detected by gas chromatography (GC). Before this procedure, instrumental parameters of the GC were studied. For this task, it was used the conventional extraction by HSSPME (headspace-solid phase microextraction). Related to studies of SPME-GF AAS coupling, employing slurry sampling, some parameters, such as fiber coating, derivatization reagent concentration, pH of the reaction, among others, were evaluated. Satisfactory results were obtained using the PDMS/DVB fiber in the presence of 0.2 % (m/v) NaBEt4 and pH 5.0. However, low extraction efficiency (< 20 %) was obtained, using the SPME-GF AAS coupling for organotin species extraction from sediment slurries, when comparing to HS-SPME extractions. Then, the extraction of organotin species from sediment samples, using the ultrasonic energy was carried out, before the sample introduction into the SPME-GF AAS coupling. In this step, the graphite furnace temperature and the fiber exposure time in the atomizer were optimized. The better results were noted when 90 °C as the graphite furnace temperature was used, and 986 s was attributed as the fiber exposure time into the atomizer. Additionally, the determination of total Sn concentration, and the extraction of organotin species in the SPME fiber, using the SPME-GF AAS coupling, was simultaneously carried out.
Doutorado
Quimica Analitica
Doutor em Ciências

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Coal-fired power plants are the largest anthropogenic point sources of CO2 emissions worldwide. About 40% of the world's electricity comes from coal. Approximately 49% of the US electricity in 2008 and 23% of the total electricity generation of Canada in 2000 came from coal-fired power plant (World Coal Association, and Statistic Canada). It is likely that in the near future there might be some form of CO2 regulation. Therefore, it is highly probable that CO2 capture will need to be implemented at many US and Canadian coal fired power plants at some point. Several technologies are available for CO2 capture from coal-fired power plants. One option is to separate CO2 from the combustion products using conventional approach such as chemical absorption/stripping with amine solvents, which is commercially available. Another potential alternative, membrane gas separation, involves no moving parts, is compact and modular with a small footprint, is gaining more and more attention. Both technologies can be retrofitted to existing power plants, but they demands significant energy requirement to capture, purify and compress the CO2 for transporting to the sequestration sites. This thesis is a techno-economical evaluation of the two approaches mentioned above along with another approach known as hybrid. This evaluation is based on the recent advancement in membrane materials and properties, and the adoption of systemic design procedures and optimization approach with the help of a commercial process simulator. Comparison of the process performance is developed in AspenPlus process simulation environment with a detailed multicomponent gas separation membrane model, and several rigorous rate-based absorption/stripping models. Fifteen various single and multi-stage membrane process configurations with or without recycle streams are examined through simulation and design study for industrial scale post-combustion CO2 capture. It is found that only two process configurations are capable to satisfy the process specifications i.e., 85% CO2 recovery and 98% CO2 purity for EOR. The power and membrane area requirement can be saved by up to 13% and 8% respectively by the optimizing the base design. A post-optimality sensitivity analysis reveals that any changes in any of the factors such as feed flow rate, feed concentration (CO2), permeate vacuum and compression condition have great impact on plant performance especially on power consumption and product recovery. Two different absorption/stripping process configurations (conventional and Fluor concept) with monoethanolamine (30 wt% MEA) solvent were simulated and designed using same design basis as above with tray columns. Both the rate-based and the equilibrium-stage based modeling approaches were adopted. Two kinetic models for modeling reactive absorption/stripping reactions of CO2 with aqueous MEA solution were evaluated. Depending on the options to account for mass transfer, the chemical reactions in the liquid film/phase, film resistance and film non-ideality, eight different absorber/stripper models were categorized and investigated. From a parametric design study, the optimum CO2 lean solvent loading was determined with respect to minimum reboiler energy requirement by varying the lean solvent flow rate in a closed-loop simulation environment for each model. It was realized that the success of modeling CO2 capture with MEA depends upon how the film discretization is carried out. It revealed that most of the CO2 was reacted in the film not in the bulk liquid. This insight could not be recognized with the traditional equilibrium-stage modeling. It was found that the optimum/or minimum lean solvent loading ranges from 0.29 to 0.40 and the reboiler energy ranges from 3.3 to 5.1 (GJ/ton captured CO2) depending on the model considered. Between the two process alternatives, the Fluor concept process performs well in terms of plant operating (i.e., 8.5% less energy) and capital cost (i.e., 50% less number of strippers). The potentiality of hybrid processes which combines membrane permeation and conventional gas absorption/stripping using MEA were also examined for post-combustion CO2 capture in AspenPlus®. It was found that the hybrid process may not be a promising alternative for post-combustion CO2 capture in terms of energy requirement for capture and compression. On the other hand, a stand-alone membrane gas separation process showed the lowest energy demand for CO2 capture and compression, and could save up to 15 to 35% energy compare to the MEA capture process depending on the absorption/stripping model used.