Adsorption Isotherm and Kinetic Study of Methane on Palm Kernel Shell-Derived Activated Carbon

Activated carbon (AC) was synthesized from palm kernel shell (PKS) using different activating agents, i.e., steam, carbon dioxide (CO2), and CO2-steam, in order to analyze the impact of activating agents on the pore opening of AC. In this study, AC produced from PKS was found to have great potential as an adsorbent for methane storage. The different molecular diffusivity and reactivity of the combination of CO2 and steam succeeded in producing AC with the highest burn-off of 78.57%, a surface area of 869.82 m2/g, a total pore volume of 0.47 cm3/g, and leading to maximum methane gas adsorption capacity of 4.500 mol/kg. All types of ACs exhibited the best fit with the Freundlich isotherm model, with the correlation coefficient (R2) ranging from 0.997 to 0.999, indicating the formation of multilayer adsorption. In addition, the adsorption kinetic data for all ACs followed the pseudo-first-order model showing that the rate of adsorption was dependent on both the adsorbent and the adsorbate and was governed primarily by physical adsorption between the pore surface and methane gas. The results of intraparticle diffusion model indicated that the adsorption of methane was affected by both pore diffusion and exterior layer diffusion due to the different adsorption rates.