Designing new amine functionalized metal-organic frameworks for carbon dioxide/methane separation

Amine functionalized materials have drawn researcher's increasing attention to carbon dioxide/methane separation. The kinds or modification densities of amine groups have significant impacts on the adsorption and separation efficiency of carbon dioxide/methane system. In this work, grand canonical Monte Carlo (GCMC) simulations were employed to study the adsorption and separation of carbon dioxide/methane 50:50 mixture by five different metal-organic frameworks (MOFs), the unmodified MIL 53(Al) and four amine functionalized (NH2, (NH2)4, NHCO, CH2CONH2) MIL-53(Al) MOFs. It was found that although original MIL 53 had the best adsorption amount, its separation efficiency is not very high. The carbon dioxide/methane separation factor of (NH2)4 amine functionalized MIL-53 is the best in five MOFs. Moreover, the predicted separation performance of NH2 and NHCO functionalized MIL-53 also surpass that of the original one. However, the predicted separation performance of CH2CONH2 modified MIL-53 is not so good, both its carbon dioxide/methane separation factor and adsorption amount are lower than those of the original one. The geometric effect and energetic effect are analyzed to explain the difference of separation efficiency. This work shows that a rational design of functionalized MOF is a feasible way to improve the carbon dioxide/methane separation efficiency and to provide helpful information for future MOF preparation and applications.