Effect of Surface Area and Micropore Volume of Activated Carbons from Coal by KOH, NaOH and ZnCl2 Treatments on Methane Adsorption

This paper investigates the methane adsorption characteristics of activated carbons produced from coal by activation with KOH, NaOH and ZnCl2 treatments at different agent to coal ratios (1: 1-6: 1) and temperatures (600-800 degrees C) under N-2 flow. CH4 adsorption capacities and desorption behaviors of the activated carbons were examined at 0 degrees C and 25 degrees C. The relationship between CH4 adsorption characteristics and surface properties of activated carbons, such as BET surface area determined by N-2 adsorption at -196 degrees C, and micropore volume determined by CO2 adsorption at 0 degrees C were investigated. Optimal results for CH4 adsorption at 0 degrees C and 25 degrees C were obtained for the activated carbon samples obtained with KOH treatment at 800 degrees C at 4: 1 ratio, as 2.67 and 1.12 mmol/g, respectively. The results have shown that CH4 adsorption increased proportionally with micropore volume of activated carbons, whereas BET surface area does not exhibit an exact consistency. CH4 adsorption-desorption isotherms at 25 degrees C have shown that an increase in mesopore formation caused a decrease in adsorption; but allowed desorption to be reversible. Higher methane adsorption capacities were obtained from activated carbons produced from coal by various treatments in this study than most of the reported results in literature at the similar conditions, indicating the suitability of the evaluated materials for industrial applications of methane storage.