Carbon dioxide and methane competitive adsorption on coconut shell activated carbon

Abstract

The use of natural gas as a fuel in natural gas vehicles (NGVs) has become an attractive alternative to gasoline and diesel fuels because of its inherent clean burning characteristics. In adsorbed natural gas (ANG), natural gas is adsorbed by a porous adsorbent material at a relatively low pressure with similar methane capacity as compared to commercially compressed natural gas (CNG). Carbon-based adsorbents, like activated carbon, could provide high adsorption capacity and delivery due to its high specific surface area and high volumetric storage capacity. In this research, the adsorption capacity of methane was investigated using coconut shell activated carbon (CSAC) as an adsorbent in a packed bed column at room temperature (25°C). Binary mixtures of methane and carbon dioxide (10, 20, and 30 vol% of CO2) were used. Furthermore, to improve adsorption capacity of adsorbent, increasing surface area and increasing hydrophobic characteristic of sample were investigated. The CSAC was treated (1) by soaking into acid/alkali solution to increase their surface area (2) by mixing with methyl ester sulfonate (MES) solution to increase the hydrophobicity. BET, SEM and FTIR techniques were used to characterize the adsorbents. The composition of methane and carbon dioxide adsorption was determined by GC. Results showed that carbon dioxide significantly affects the adsorption of methane. The breakthrough time of carbon dioxide is longer than that of methane, and the methane roll up increases with the increase in the concentration of carbon dioxide because carbon dioxide is more selectively adsorbed on all adsorbents than that of methane.