COAL ADSORPTION CAPACITY MEASUREMENTS USING CARBON DIOXIDE AT SUB-CRITICAL AND SUPERCRITICAL CONDITIONS

摘要

This paper presents the quantification of the adsorption capacity of coal samples using Carbon Dioxide at varying pressure and temperature conditions. The experimental method employed the Gibbs volumetric approach, carried out on both dry and moist coal sample. Experimental results indicated a slight decrease in the adsorbed amount within the vicinity of the critical point (i.e. 7-8 MPa) which was then followed by a monotonous increase on the adsorbed amount. Such a trend was apparent for isotherms at other temperature conditions, with the 35 ℃ isotherm exhibiting the highest increase. Test results further showed that temperature increase and moisture content have negative effects on the sorption capacity especially at high pressure conditions. Comparison of pure CO_2, N_2 and CH_4 isotherms also verified that CO_2 is much adsorbed on the coal's surface relative to the other gases. Binary sorption measurement further indicated that increasing concentrations of either N_2 or CH_4 in a mixture causes the amount of adsorbed CO_2 to decrease, due to competition for adsorption sites.