The effect of coal composition upon pore structure and adsorption characteristics of four bituminous coals of the Cretaceous Gates Formation coal is investigated. All the coals have multi-modal pore volume distributions as determined from low-pressure (<127 kPa) nitrogen adsorption at 77 K, carbon dioxide adsorption at 273 K, and high-pressure (up to 200 MPa) mercury porosimetry. The individual lithotypes, however, differ in their pore volume distributions and adsorption characteristics. The dull coals (high inertinite, high ash content) have a greater percentage of mesoporosity and less microporosity than bright or banded bright coals (high vitrinite, low ash content) of the same rank. In addition, one banded bright coal has a greater amount of macroporosity than the other coals.
High-pressure (up to ∼8 MPa) methane isotherms determined on dried and moisture-equilibrated coals, and carbon dioxide isotherms (up to ∼ 5 MPa) determined on dried coal at 303 K, show that bright coals tend to adsorb more gas than dull coals. The Dubinin–Astakhov equation provides a better fit to coal gas isotherm data, particularly for carbon dioxide, than the conventionally used Langmuir equation. There is a linear correlation between high-pressure methane and carbon dioxide Langmuir volumes and Dubinin–Radushkevich micropore volumes, indicating that micropore volume is a primary control upon high-pressure gas adsorption for the Gates coals.
Coal; Isotherms; Pore volume distributions