The competitive sorption of CO2 and CH4 with regard to the release of methane from coal

It is generally acknowledged that beds of hard coals are an important medium with regard to their capacity to act as a reservoir for mine gases. At present, in Poland, the problem of extracting "coal-based methane" is at the stage of prospective investigation and the search for optimum extraction procedures under the specific conditions existing in this country. During the extraction of coal, methane is liberated by the desorption of CH4 contained in the micropores of the coal, prior to which its release is hindered by sorption forces and the restricted and small dimensions of the transport paths. The aim of these investigations is to determine the thermodynamic conditions for the release of CH4 from the coal microstructure by means of displacement sorption with CO2. The paper presents a study of the sorption/desorption kinetics and equilibrium states with displacement of sorbate gases, as well as the expansion/contraction of coal accompanying the sorption processes. It was found that the total equilibrium content of the mixture of gases in coal, desorption of the mixture of gases and the composition of the desorbed gas depend mainly upon the type of coal and on the initial equilibrium composition of the gas during desorption, The composition of the gaseous phase, in equilibrium with the adsorbed phase., does not reflect the composition of the sorbed phase. (C) 2002 Elsevier Science B.V. All rights reserved.