The feasibility of CO emission reduction by adsorptive storage on Polish hard coals in the Upper Silesia Coal Basin: An experimental and modeling study of equilibrium, kinetics and thermodynamics.

Carbon dioxide storage in unmineable coal seams is advantageous in the highly industrialized areas, such as the Upper Silesia Coal Basin (USCB), Poland, where heavy industry constitutes the source of huge CO emissions and coal mines will be closed in the future, due to unprofitability. The paper presents the results of experimental and theoretical research of CO capture on medium rank C and B bituminous coals coming from three mines located in the USCB. The porous texture of the investigated adsorbents was analyzed using SEM images and the N and CO isotherms at -196 °C and 0 °C, respectively. Qualitative studies using DRIFT spectroscopy showed that band intensity attributed to the functional groups of coals changed after CO adsorption. The analyses encompassed the equilibrium, kinetics and thermodynamics of CO adsorption on coals at 25, 50 and 75 °C (up to 2000 kPa). The adsorption isotherms were obtained by the static gravimetric method and described by means of the Langmuir, Freundlich, Dubinin-Radushkevich and Dubinin-Astakhov models. The highest CO uptakes were obtained for medium rank C bituminous coals at 25 °C; the values were 1.600 mol/kg and 1.274 mol/kg. The adsorption kinetics was better characterized by the Avrami fractional-order model rather than by the pseudo-first and pseudo-second order models. The results reveal that the adsorption process is the fastest for medium rank C bituminous coals. The isosteric heats of adsorption were calculated in the following two ways: based on the multi-temperature Toth isotherm and the Clausius-Clapeyron equations. Depending on degree of coal metamorphism, the heat of adsorption ranged from 18 to 26 kJ/mol. The estimated maximum temperature increase due to heat accumulation in the insulated coalbed during CO adsorption was 6 °C and did not reach the self-ignition temperature in any of the tested adsorption systems.