Effects of ethanol-mixed supercritical CO 2 fluid on CO 2 adsorption on coals: implications for CO 2 geologic storage in coal seams

The coal matrix swelling induced by CO2 decreases the permeability of the target coal seams, and it will trigger disadvantages to CO2 storage in deep coal reservoirs. In order to mitigate such swelling effect, the addition of ethanol into CO2 is proposed. The effects of ethanol-mixed supercritical CO2 on the adsorption equilibrium and kinetics behaviors of CO2 adsorption on coals are studied in this paper. The results indicate that the ethanol-mixed supercritical CO2 fluid could increase CO2 adsorption capacity of two coals with low metamorphic degree, but decrease that of two coals with high metamorphic degree. The addition of ethanol into CO2 fluid remarkably enhances the diffusion and adsorption rate of CO2 within the micropores and macropores of coals. The alterations of pore system of various rank coals could account for the changing law of CO2 adsorption equilibrium and kinetics behaviors on coals after interacting with ethanol-mixed supercritical CO2.