Tailoring biomass-based activated carbon for CH4 storage by combining chemical activation with H3PO4 or ZnCl2 and physical activation with CO2

Abstract

Coconut shell-based activated carbons intended for CH4 storage were prepared by chemical activation with H3PO4 or ZnCl2 and/or physical activation with CO2. Efforts were focused to establish relationships among the activation procedure, the textural and physical-chemical properties of the resulting materials and their volumetric CH4 uptake. The best results were achieved by using the combination of a relatively soft chemical activation with H3PO4 or ZnCl2, just the sufficient to minimize the presence of macropores originated from the botanical structure of the precursor, followed by physical activation with CO2 to develop a narrow pore size distribution mainly located around the optimum pore diameter/width for CH4 storage. This combined methodology permitted to obtain excess volumetric CH4 adsorption capacities as high as 94, 148 and 145 V/V for granular, powdered/compressed and monolithic carbons, respectively. The corresponding total CH4 storing capacities were estimated to be 102, 165 and 163 V/V. It is worthy to highlight that the precursor was a low cost and abundant agricultural by-product, which is very important for large-scale applications such as gas transportation and gas storage in vehicular fuel tanks.