Studies on the competitive sorption of CO2 and CH4 on hard coal

This paper presents the results of studies on the competitive sorption using the gas mixtures CO2-CH4 on hard coal from a Polish coal mine. The experiments were conducted at an original research stand under isobaric conditions, for the pressure values of 1, 2, 5, 10 bar, and at the temperature of 313 K. The value of the effective diffusion coefficient D-e grew along with the content of CO2 in the gas mixture, while for the sample saturated with pure CO2 the value of D-e was higher than in the sample saturated with pure CH4 by more or less one order of magnitude. The Langmuir and Langmuir-Freundlich sorption isotherms were determined. It was observed that an increase in the sorption corresponding to the filling of monolayers in both isotherms occurred along with a growth of the CO2 concentration in the gas mixture. The total pore volume increased by 19.0-29.7% in a sample saturated with pure CO2 as compared to a sample saturated with pure CH4. Pore distribution was similar. At the same time, in the sample saturated with CO2, the pore volume was higher than in the case of other samples for almost entire diameter range.