Mohamed, Amro Mamoon Osman (2018-05). CO2 Selective Metal Organic Framework ZIF-8 Modified Through IL Encapsulation: A Computational Study. Master's Thesis.
Nano-scale porous solids are alternate candidates for COv2 handling towards the development of materials for post-combustion COv2 capture with low energy demands and milder operating conditions. Zeolitic imidazolate framework-8 (ZIF-8) is one of the most investigated Metal Organic Frameworks (MOFs) for separation of gas mixtures. In this work, we investigate a new approach of tailoring MOF separation efficiency, by confining pairs of three different ionic liquids (ILs) in the cages of ZIF-8 (IL@ZIF-8). ILs comprising 1-butyl-3-methylimidazolium cation [bmim+] and three distinct anions, bis(trifluoromethylsulfonyl)imide [Tfv2N-], tricyanomethanide [TCM-], and tertracyanoborate [B(CN)v4-], were used in this study. Molecular force fields, previously developed by Economou and co-workers for both the ZIF-8 framework and the ILs, are used in the molecular simulations of these systems. Monte Carlo simulations, employing an appropriate set of constraints, are utilized for the calculation of sorption of COv2/CHv4 and COv2/Nv2 mixtures. The results show an increase of the COv2 sorption compared to pristine ZIF-8 due to the presence of the IL, which increases the COv2 selectivity and capacity dramatically. Recently reported experiments agree with our findings. Moreover, we explore how COv2 selectivity and capacity vary with IL composition in the IL@ZIF-8 complex, as a mean to define an optimum IL composition in terms of the separation efficiency. As a result of the pore volume reduction in the structure, a tradeoff between capacity and selectivity is present. Therefore, a sorbent selection parameter that combines working capacity and equilibrium selectivity proposed by Range and Yang, alongside a regenerability factor, are used to further determine the best sorbent among other known materials. The regenerability factor is adopted to reflect the fractional percentage of adsorption sites that are available for regeneration
Economou, Ioannis Senior Associate Dean for Academic Affairs and Graduate Studies, Texas A&M at Qatar