S.P. NANDI , P.L. WALKER, JR
Two techniques have been used to study the diffusion of methane in American coals of rank varying from low volatile matter anthracite to high volatile content bituminous. Diffusion of methane out of coal at sub-atmospheric pressures has been studied using a constant pressure apparatus. Diffusion of methane into coal at elevated pressures has been studied using a constant volume apparatus. Diffusion in the micropore system is activated, the activation energy varying from 3.5 kcal/mol* for low volatile matter anthracite to about 7.0 kcal/mol for bituminous coals. This suggests that the average size of the accessible micropores in the anthracites is larger than that in the bituminous coals.