Methane adsorption by activated carbons: comparison among coconut-, palm-, and bituminous coal based activated carbons

Abstract

Consumption of natural gas as a vehicular fuel has continuously increased in Thailand. Compressed natural gas (CNG) is natural gas which is compressed and stored under high pressure ~3,600 psi. To increase the travel distance per fill up, the storage capacity needs to be enhanced. It has been suggested that a porous material such as activated carbon can adsorb natural gas, and thus, increase the capacity of natural gas storage. Therefore, this research focuses on methane adsorption using several types of commercial activated carbon, such as activated carbons derived from coconut shell, palm shell, and bituminous coal with different iodine number; and coconut-based activated carbon by chemical activation process. Methane adsorption was measured by a volumetric apparatus under the pressure up to 1,000 psia at temperatures of 35, 40, and 45 °C. In addition, the physical properties of activated carbons were characterized by BET surface analysis, and Field Emission Scanning Electron Microscope (FE-SEM). The surface area, micropore volume, total pore volume, and average pore diameter played an important role in methane adsorption. A higher surface area of activated carbons led to greater methane adsorption capacity (mmol/g).