Effect of Physical Nature (Intact and Powder) of Coal on CO2 Adsorption at the Subcritical Pressure Range (up to 6.4 MPa at 298.15 K)

This study examines the influence of subcritical pressure and the physical nature (intact and powder) of coal samples on CO2 adsorption capacity and kinetics in the context of CO2 sequestration in shallow level coal seams. Manometric adsorption experiments were carried out on two anthracite and one bituminous coal samples. Isothermal adsorption experiments were carried out at 298.15 K in two pressure ranges: less than 6.1 MPa and up to 6.4 MPa relevant to gas/ liquid adsorption. The adsorption isotherms of intact anthracite and bituminous samples were compared to that of the powdered samples. The powdered samples of the anthracitic samples had a higher adsorption than that of intact samples due to the exposed adsorption sites. The intact and powdered samples of bituminous coal, on the other hand, exhibited comparable adsorption capacities. The comparable adsorption capacity is attributed to the intact samples' channel-like pores and microfractures, where high density CO2 adsorption occurs. The adsorption-desorption hysteresis patterns and the residual amount of CO2 trapped in the pores reinforce the influence of the physical nature of the sample and pressure range on the CO2 adsorption-desorption behavior. The intact 18 ft AB samples showed significantly different adsorption isotherm pattern to that of powdered samples for experiments conducted up to 6.4 MPa equilibrium pressure due to the high-density CO2 adsorbed phase in the intact samples. The adsorption experimental data fit into the theoretical models showed that the BET model fit better than the Langmuir model. The experimental data fit into the pseudo first order, second order, and Bangham pore diffusion kinetic models showed that the rate-determining steps are bulk pore diffusion and surface interaction. Generally, the results obtained from the study demonstrated the significance of conducting experiments with large, intact core samples pertinent to CO2 sequestration in shallow coal seams.