Adsorption of methane on dry coal at elevated pressure

Methane equilibrium adsorption isotherms were determined on Illinois No.6 (Herrin seam), Oklahoma Hartshorne, Pennsylvania Pittsburgh, and Virginia Pocahontas No.3 United States coal seams, using a volumetric method and an equation of state for methane: the amount of methane adsorbed on crushed and dried coal was measured as a function of pressure. Isotherms were measured at 30 °C for the Illinois coal and at 0, 30 and 50 °C for the others. Most measurements were made to 150 atm pressure, but a few to 240 atm. The data were correlated by the Langmuir and the Polanyi adsorption models. The methane—coal system, uncorrected for adsorbate density, adhered well to the Langmuir model up to 150 atm pressure, but Polanyi behaviour could not be demonstrated satisfactorily, with or without a correction for adsorbate density. Monolayer volumes at 30 °C from the Langmuir equation were 28, 24, 19 and 20cm³ (STP)/g coal respectively for the four coals studied (the range for several investigators was 13 to 39 cm³/g and for the Langmuir constant b 0.03 to 0.23 atm^?1). Isosteric heats of adsorption at zero coverage and 30 °C were 4.2, 2.4 and 5.3 kcal/mol for the Hartshorne, Pittsburgh and Pocahontas coals, which indicate that the adsorption is physical. No effect of particle size on equilibrium adsorption was observed in the U.S. mesh range 6–325.