The detrimental effects of rising CO₂ levels on the global climate have made carbon abatement technologies one of the most widely researched areas of recent times. In this thesis, we first present a techno-economic analysis of a novel approach to directly capture CO₂ from air (Air Capture) using highly selective adsorbents. Our process modeling calculations suggest that the monetary cost of Air Capture can be reduced significantly by identifying adsorbents that have high capacities and optimum heats of adsorption. The search for the best performing material is not limited to Air Capture, but is generally applicable for any adsorption-based separation. Recently, a new class of nanoporous materials, Metal-Organic Frameworks (MOFs), have been widely studied using both experimental and computational techniques. In this thesis, we use a combined quantum chemistry and classical simulations approach to predict macroscopic properties of MOFs. Specifically, we describe a systematic procedure for developing classical force fields that accurately represent hydrocarbon interactions with the MIL-series of MOFs using Density Functional Theory (DFT) calculations. We show that this force field development technique is easily extended for screening a large number of complex open metal site MOFs for various olefin/paraffin separations. Finally, we demonstrate the capability of DFT for predicting MOF topologies by studying the effect of ligand functionalization during CuBTC synthesis. This thesis highlights the versatility and opportunities of using multiscale modeling approach that combines process modeling, classical simulations and quantum chemistry calculations to study nanoporous materials for adsorptive separations.

Dans le cadre de la recherche de procédés d'absorption gaz-liquide intensifiés, cette étude vise au développement des contacteurs membranaires pour la capture du CO₂ en post combustion, comparativement aux colonnes garnies. Les contacteurs à membranes fibres creuses microporeuses permettent un transfert de matière élevé mais sont confrontés à des problèmes de mouillage entraînant une dégradation importante des performances dans le temps. Notre but est de concevoir des fibres composites constituées d'une structure microporeuse et d'une peau dense fine et fortement perméable au CO₂ afin d'établir une barrière au passage du liquide et de limiter la résistance au transfert de matière. Pour cela, nous avons sélectionné des polymères super vitreux comme le PTMSP et le Téflon AF2400 qui se caractérisent par une très forte perméabilité au CO₂ et une bonne compatibilité chimique avec la MEA (liquide d'absorption de référence). Les fibres composites ont été réalisées par un procédé de recouvrement conduisant à une faible épaisseur de peau dense (1 à 2 microns). Des modules à fibres composites ont été testés pour séparer un mélange CO₂/N2 avec une solution aqueuse de MEA. Les fibres composites présentent des efficacités de capture similaires à celles des fibres microporeuses mais assurent en plus le maintien des conditions de non mouillage. Des simulations, reposant sur une modélisation 2D du transfert de matière, ont permis de prédire les performances des contacteurs membranaires à fibres composites dans des conditions plus proches de la réalité industrielle et ont mis en évidence un facteur d’intensification pouvant aller jusqu’à 6 par rapport aux colonnes garnies / The present work aims to explore the intensification of gas-liquid absorption processes. This study is applied to post combustion CO₂ capture by means of membrane contactors in comparison to packed columns. Microporous hollow fiber membrane contactors lead to high mass transfer but wetting problems are likely to occur and result in tremendous deterioration in performances with time. Our objective is to develop composite hollow fibers based on a microporous structure and a thin dense layer highly permeable to CO₂, in order to create a real barrier to liquid penetration and to limit mass transfer resistance. Super glassy polymers as PTMSP and Teflon AF2400 were selected for their extremely high CO₂ permeability and their chemical resistance to MEA (reference absorption liquid). Composite hollow fibers were made by coating and the dense layers obtained are thin (1 to 2 microns). Composite hollow fiber membrane contactors were tested for the separation of a CO₂/N2 mixture with an aqueous solution of MEA. Capture ratios achieved by composite hollow fibers are similar to those measured for microporous membranes and the dense layer prevents from wetting problems. Simulations based on 2D modeling of the mass transfer, show that the performances of composite hollow fiber membrane contactors, under operating conditions close to the industrial case, can lead to an intensification factor up to 6 compared to packed columns