The effect of pore structure and gas pressure upon the transport properties of coal: a laboratory and modeling study. 1. Isotherms and pore volume distributions

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 thigh inertinite, (high ash content have a,a greater percentage of mesoporosity and less microporosity than bright or banded bright coals thigh 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 similar to 8 MPa) methane isotherms determined on dried and moisture-equilibrated coals, and carbon dioxide isotherms (up to similar 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, (C) 1999 Elsevier Science Ltd. All rights reserved.