Adsorption of gases on coals and heattreated coals at elevated temperature and pressure. 1. Adsorption from hydrogen and methane as single gases

Adsorption isotherms of CH₄ and H₂ are reported for the temperature range 22-300 °C and pressure range 0-6.9 MPa. The adsorbents were Pittsburgh bituminous coal, Pittsburgh coke, Montana lignite, Montana lignite char and PCB activated carbon. Carbonization of coals increased the equilibrium adsorption several-fold. However, the increase was not entirely associated with the increase in surface area, because changes in energetics of adsorption were involved. Montana lignite char, on a bulk volume basis, adsorbed approximately the same amount of CH₄ as did activated carbon. Pretreatment of the coal surface e.g. by oxidation or reduction, had no or negligible effects on CH₄ adsorption. Surface areas for coals calculated on the basis of CH₄ adsorption, using the Langmuir equation under supercritical conditions, were similar to those from CO₂ adsorption. Data on the isosteric heats of adsorption of CH₄ indicated that the coal surface became more heterogeneous on carbonization.