Adsorption of Gases in Microporous Organic Molecular Crystal, a Multiscale Computational Investigation

Abstract

The grand canonical Monte Carlo (GCMC) method and high-level first-principle calculations are performed to investigate the role of a constrained channel of microporous organic molecular crystal in separating H2 from binary mixtures containing N2, CH4, or CO2. GCMC simulations show that the selectivity of N2, CH4, or CO2 over H2 is in the order of N2/H2 < CH4/H2 < CO2/H2, which is consistent with the order of isosteric heats of adsorption. Particularly at low pressure the selectivity is very high because CO2, CH4, or N2 initially occupies the preferential site in the channel with less sites left for H2. In addition, dispersion corrected density functional theory (DFT-D) is introduced to study the interaction energies and structural properties of the conjugated channel and gases. By comparing with the benchmark data of the coupled-cluster calculations with singles, doubles, and perturbative triple excitations [CCSD(T)] estimated at the complete basis set (CBS) limit, the proper functional is selected. The first-principle calculations confirm that the heterogeneous channel can hold CO2, CH4, or N2 much stronger than H2, suggesting the microporous organic molecular crystal is a good candidate for potential hydrogen purification.