Improved CO₂/CH₄ Separation Performance in Negatively Charged Nanoporous Graphene Membranes

Abstract

We propose a negatively charged nanoporous graphene (NPG) membrane which presents an improved separation performance of CO2/CH4 gas mixtures. The CO2 permeance and the selectivity of CO2 molecules over CH4 molecules both increase after adding negative partial charges on each carbon atom. The CO2 permeance can increase from 6.81 × 105 GPU for the neutral NPG membrane up to 5.65 × 106 GPU for a partial charge of −0.125 e, and the selectivity increases correspondingly from 10.4 to 42.8. The improved separation performance can be attributed to the relatively enhanced adsorption of CO2 molecules and weakened adsorption of CH4 molecules on the graphene surface at high partial charges. The enhanced adsorption of CO2 molecules can enhance their permeation abilities by improving the surface contributions, especially on the molecular deliverability from surface to pore area for permeation. The weakened adsorption of CH4 molecules can weaken the permeation abilities of themselves due to the limited surface contributions and simultaneously improve the CO2 permeance by abating their blocking effects for the permeation of CO2 molecules. Meanwhile, the enhanced adsorption layer on the graphene surface can further enhance the net CO2 permeance by preventing the permeated molecules from moving back to the feed side.

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