Influence of heat-treatment on the selective adsorption of CO2 in a model natural gas over molecular sieve carbons Original Research Article

The kinetically selective adsorption of CO2 in CH4 was studied using three commercially available molecular sieve carbons. All as-received carbons examined in this study exhibited poor kinetic selectivity. However, heat-treatment at around 1273 K significantly improved the kinetic selectivity of one carbon (K-MSC) with the least decrease of adsorptive capacity of CO2. No improvement was obtained with other two carbons. The heat-treatment at 1273 K removed oxygen functional groups on the surface of K-MSC and significantly increased the degree of graphitization. The extent of graphitization of the other carbons remained unchanged by heat-treatment. The increasing degree of graphitization caused shrinkage of K-MSC and controlled the slit width of the pores. Higher temperature of the heat-treatment further increased the kinetic selectivity but markedly reduced the adsorptive capacity because of too much shrinkage, owing to excess graphitization. Heat-treatment at 1273 K enhanced the hydrophobicity of the carbon surface and reduced the inhibition of CO2 adsorption by water in the relative humidity range of 0–50%. At higher humidity, the effect was minimal as condensation on the pore wall occurred. Removal of oxygen functional groups by heat-treatment appears favorable for improving this kind of selectivity.