Gas separation in microporous materials: A computational study of the influence of structural features on the selectivity

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In this project, computational chemistry techniques are employed to evaluate the potential of different microporous materials (zeolites, metal-organic frameworks, nanoporous molecular crystals) for adsorption-based gas separation applications. A particular emphasis is put on a detailed analysis of the role of specific interaction sites, such as extra-framework cations, coordinatively unsaturated metal sites, or functional groups, in conjunction with confinement to micropores. The investigation addresses different gas mixtures that are of relevance for industrial processes, for example in the removal of carbon dioxide from flue gases or from natural gas, or in the separation of alkane/alkene mixtures.The project follows a hierarchical approach: Firstly, grand-canonical Monte Carlo (GCMC) simulations using empirical interaction parameters are carried out for a wide variety of candidate materials, permitting an initial estimation of the adsorption selectivity. A more thorough GCMC study of the separation properties is then carried out for the most interesting systems that were identified in this screening. The relationships between the observed separation behaviour and the structural properties of the material (specific interaction sites, pore size, pore topology) are analyzed in detail. In the following, quantum-chemical calculations are carried out to develop a better understanding of the interactions between specific sites and adsorbed molecules. Molecular dynamics calculations are performed to analyze the impact of these sites on the diffusion of guest molecules. In the final part of the project, the adsorption properties of hypothetical zeolites are predicted. Due to their structural versatility, these systems are particularly well suited for a systematic study of the influence of the pore topology.