Sorption rate of CH₄ and CO₂ in coal at different pressure ranges

The aim of this study was to verify the dynamic factor, that is the diffusion rate, which can directly affect the efficiency of CO₂ injection and as a consequence - storage. A manometric setup was used for experiments on two hard coals from Upper Silesian Coal Basin in Poland. A model combining two firs-order rate functions with different rate constants was used to plot normalized equilibration curves. Diffusion curves were plotted at three pressure ranges 5-6 MPa, 3.5-4 MPa and 1.5-2 MPa. Result show that fast adsorption rate is higher at 5.5-6 MPa than at lower pressure range with highest fast adsorption rate fraction both for CH₄ and CO₂. Lower (1.5-2 MPa) pressure range allows achieving sorption equilibrium in less time for both gases. Diffusion rates are lower for CO₂ than for methane the CH₄ desorption rate has a slight impact on the CO₂ adsorption and as a consequence CO₂ storage capacity.