Effect of pressure and temperature on diffusion of CO2 and CH4 into coal from the Lorraine basin (France)

Abstract

Abstract Adsorption kinetics of CO 2 and CH 4 from a high volatile bituminous coal of the Lorraine basin (north-east of France) were studied at 0.1 MPa and 5.0 MPa in a range of temperatures from about 283.15 K to 333.15 K. Kinetic measurements were performed using a gravimetric experimental set-up, which allows measurement of gas density. Sorption equilibrium is reached faster for CO 2 than CH 4 . The differences are mainly due to the physico-chemical parameters of both gas molecules and their coal-interactions. The pressure-dependence of diffusion parameters in coals was shown. Increasing gas pressure decreases the equilibrium time. For example, the CO 2 equilibrium time is about 15 h at 5 MPa and about 40 h for 0.1 MPa. The study of kinetic sorption at different temperatures suggested that the diffusion of gases into coal is activated for CO 2 and CH 4 . The effective diffusion, D e , and the diffusion coefficient, D , estimated from modelling experimental data by assuming Fickian and unipore diffusion, increased with increasing temperature. The diffusion coefficient was estimated at about 10 − 12 m 2 s − 1 . Assuming Arrhenius' law, the activation energy of CO 2 adsorption was rather low, about 18 kJ mol − 1 compared to the one of CH 4 , about 34 kJ mol − 1 .