Molecular Simulations of Binary Gas Mixture Transport and Separation in Slit Nanopores

We propose a new method to simulate the gas mixture transport and separation in slit nanopores. The method is based on the random removal of molecules from the permeate side in the dual control volume-grand canonical molecular dynamics (DCV-GCMD) method. Each step in the random removal is independent of the previous steps. The conventional method, DCV-GCMD, simulates the gas mixture in control volumes based on the chemical potential of each component, in which the gas compositions have to be known in advance and kept constant. However, the transport process affects the composition of the produced gas mixture due to selective adsorption in the nanopores. This process has been modeled iteratively in the literature. We propose an alternative method to calculate the composition in the permeate side directly; in our approach, the computational efficiency is improved by an order of magnitude compared to the iterative method. Transport of gas mixtures of CH4/He and CO2/CH4 is investigated in graphene, graphite, and tetrahedral-octahedral-tetrahedral (TOT) structure slit pores. Pore width is the dominant factor in the species separation. The solid substrates and surface roughness have a pronounced effect on gas separation. The average pressure may have a pronounced effect when the pore width is less than 1.00 nm.