A COMPARISON OF THEORETICAL AND EMPIRICAL EXPANSION OF COALS IN THE HIGH-PRESSURE SORPTION OF METHANE

Empirical data on coal expansion due to high pressure sorption of methane were compared with the linear expansion ratio predicted on the basis of the theoretical dual sorption model. The model is based on a thermodynamical treatment of the sorption process, viewed as consisting of absorption and adsorption subprocesses, with a submicroporous and heterogeneous copolymeric nature of coal being assumed. While regarding the expansion of coal as a result of the absorption subprocess only, this model may be used to evaluate the theoretical linear expansion ratio. Three coal-methane systems have been examined. Coals with different degrees of metamorphism (wt% C (daf): 80.9, 86.5, 92.4) were used. Sorption and expansion measurements were carried out at 298 K, over the pressure range 0.5-4.5 MPa. Very good agreement of theoretical and empirical values was found in the lower pressure range. Differences observed in the higher pressure range suggest compression of pores was significant.