Competitive Adsorption of Methane and Carbon Dioxide on Different Activated Carbons

Abstract

Adsorbed natural gas (ANG) is one of natural gas storage technologies, in which natural gas is adsorbed by a high porosity adsorbent material at relatively low pressure and room temperature with high methane capacity and low cost. Carbon-based materials, like activated carbons, are promising as an ANG storage adsorbent because of high surface area, high porosity, and high volumetric storage capacity. In this research, the adsorption capacity of single and binary component of CH4 and CO2 was investigated by using activated carbons including coconut shell activated carbon (CSAC), palm shell activated carbon (PSAC), and coal-based activated carbon (CBAC) in a packed bed column at room temperature. The composition ratio of single component of CH4 and CO2 was fixed at 20 vol% of the total feed gas, and the composition ratios of binary component of CH4 and CO2 were fixed at 14.6 : 5.4, 10.0 : 10.0, and 5.0 : 15.0 vol% of the total feed gases, respectively. The result of single component adsorption showed that all activated carbons exhibited preferential adsorption for CO2 in relation to CH4. It can be seen from binary component adsorption that the adsorbed amount increased with increased CO2 composition, while the amount of CH4 adsorbed decreased, indicating competition for adsorption sites and preferential adsorption of CO2 over CH4. In terms of the adsorption capacity of binary component, the methane selectivity was CSAC > PSAC > CBAC for the whole composition ratios of CH4 and CO2.