Influence of activated carbon in zeolite X/activated carbon composites on CH4/N2 adsorption separation ability

Abstract

A series of zeolite X/activated carbon composites with different ratio of zeolite X and activated carbon were prepared, which were adjusted by adding solid pitch powder and silicon dioxide as additional carbonaceous and silica source, respectively. The corresponding modified samples were obtained by treatment with the ammonium chloride solution. CH4 and N2 adsorption isotherms on all composites were determined within the pressure of 0–100 kPa at 298 K, and fitted with Henry model and Freundlich model. The results showed the adsorption separation abilities for CH4 and N2 were strongly influenced by activated carbon content, micropore structure and surface properties. The increase of activated carbon content increased the BET surface area, micropore surface area and micropore volume, leading to an enhanced CH4 adsorption capacity and CH4/N2 adsorption selectivity. Compared with the unmodified composites, the modified composites showed higher CH4/N2 adsorption selectivity, and CH4 adsorption capacity decreased slightly, which can be attributed to the reduction of the micropore structure parameters, the surface basic amount and basic strength. Furthermore, the modified composite HAX-3 presented the highest CH4/N2 selectivity of 3.4, and high CH4 adsorption capacities, which is favorable for application in pressure swing adsorption processes.