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 meth ane were compared with the linear expansion ratio predicted on the bas is of the theoretical dual sorption model. The model is based on a the rmodynamical treatment of the sorption process, viewed as consisting o f absorption and adsorption subprocesses, with a submicroporous and he terogeneous copolymeric nature of coal being assumed. While regarding the expansion of coal as a result of the absorption subprocess only, t his model may be used to evaluate the theoretical linear expansion rat io. Three coal-methane systems have been examined. Coals with differen t degrees of metamorphism (wt% C (daf): 80.9, 86.5, 92.4) were used. S orption and expansion measurements were carried out at 298 K, over the pressure range 0.5-4.5 MPa. Very good agreement of theoretical and em pirical values was found in the lower pressure range. Differences obse rved in the higher pressure range suggest compression of pores was sig nificant.