Effect of activated carbon treatment on methane adsorption

Abstract

Compressed natural gas (CNG) is currently being implemented in transportation by vehicle in Thailand. However, comparing to other fuels e.g. gasoline or diesel, energy density in CNG system is much less and therefore a vehicle is required to re-fill more often at service station. To increase the capacity of natural gas storage, increasing volume of storage tank or increasing gas pressure are possible way but both way required changing some or whole equipment. Another possible way is using adsorbent apply into CNG storage tank. In this experiment, the volumetric method was used under up to 4.5 MPa at constant temperature of 40°C. Two activated carbons from indigenous source derived from coconut shell and eucalyptus, and two commercial activated carbons were as an adsorbent to adsorb 99.999% methane. Furthermore, to improve adsorption capacity of untreated adsorbent, increasing surface area and increasing hydrophobic characteristic of sample were investigated. All three untreated activated carbon samples were pretreated (1) by soaking into acid/base solution to remove trace metal and to increase their surface area (2) by mixing with liquid hydrocarbon to increase the hydrophobicity. After treatment process, treated samples were characterized by SEM and surface area analyzer. The surface area of adsorbent strongly affects the amount of methane adsorbed.