Adsorption and separation of CH4/H2 in MIL-101s by molecular simulation study

Abstract

MIL-101s offer potential application for CH4/H2 adsorption separation owing to its high porosity and excellent chemical stability. In this work, the grand canonical Monte Carlo method was employed to study the adsorption and separation of CH4/H2 on a novel series of MIL-101s materials, such as MIL-101, MIL-101_NDC and new constructed MIL-101_R7-BDC. The simulation results showed that CH4 was preferentially adsorbed over H2 in all MIL-101s. The adsorption capacities of pure CH4 and H2 on MIL-101_NDC were much higher than that in the other two MIL-101s, due to its largest Sacc (accessible surface area) and Vp (pore volume). The adsorption-site results suggested that the super-tetrahedras were the main adsorption site for CH4 molecules in all studied MIL-101s. Moreover, the additional benzene rings in MIL-101_R7-BDC introduced several new CH4 adsorption sites which were close to the edge of large and small cages. Finally, we found that MIL-101_R7-BDC had the highest CH4 selectivity. CH4 selectivity of MIL-101s was significantly affected by Δqst (adsorption heat) and Sacc (accessible surface area) in terms of different organic ligands.