Influence of Liquid CO₂ Extraction and Dissolution on Coal Adsorption Characteristics

Liquid CO2 is a non-polar fluid, and the injection of CO2 fluid into a coal seam causes a strong water-rock interaction between the inorganic minerals and organic matter in the coal and acidic fluid. The minerals in the coal are thereby corroded and precipitated to different degrees, and the organic matter is dissolved and extracted, which further changes the physical and chemical properties of the coal and rock. Three kinds of coal samples with different metamorphic degrees were selected as the research objects, and the research methods of theoretical analysis and experimental testing were used to carry out the related research on the modification of coal by liquid CO2 extraction and dissolution. After the three kinds of coal samples were extracted by liquid CO2, the pore specific surface area decreased and the CO2 adsorption decreased with the increase in extraction pressure. The reduction in anthracite adsorption was greater than that of bituminous coal and lignite; after being corroded by different CO2 pressures, the adsorption capacity of bituminous coal gradually increased with the increase in corrosion pressure, and the increase in adsorption capacity of bituminous coal was larger than that of anthracite and lignite. After corrosion, bituminous coal was suitable for CO2 geological storage.