Efficient separation of He/CH4 mixture by functionalized graphenylene membranes: A theoretical study

Abstract

In this work, we prepared two types of functionalized pore on pristine graphenylene membrane to study and compare the He/CH4 separation performance employing molecular dynamics (MD) simulation. The gas molecules transport through the membranes was monitored during the simulations. The results indicated that methane molecules cannot pass through the membranes under applied conditions, while helium molecules simply penetrate through, which verifies the ultrahigh selectivity of helium over methane molecules. The maximum helium permeance of about 1 × 107 GPU was obtained through the functionalized graphenylene membrane at room temperature, which is much higher than graphenylene membrane. As a consequence, the functionalized graphenylene membrane can supply both high permeance and selectivity for helium separation. The van der Waals (vdW) interactions between gas molecules and the surface of the membrane was also investigated. We further conducted the potential of mean force (PMF) calculations to study the permeation of gas molecules across the membrane. Although methane molecules, due to more powerful interactions between them and the surface of the membrane, adsorb on the membrane surface, face higher energy barrier near the membrane nanopore. In reality, adsorption prefers methane molecules on the membrane surface, while diffusion favors helium over methane molecules through the nanopores. The functionalized graphenylene membrane is expected to be able to be employed as a promising membrane for a highly efficient helium purification system.