Laboratory Studies on Permeability of Coals Using Briquettes: Understanding Underground Storage of CO2

The work presents the laboratory studies on permeability of two bituminous coal briquettes under confining pressure conditions. The research was carried out in order to assess the possibility of using bituminous coal as a sorbent for CO2 storage in underground seams. Coal permeability tests were carried out on an original apparatus for testing seepage processes under isobaric conditions on samples subjected to confining pressure. In order to determine the impact of the load on the coal briquettes’ permeability, the tests were carried out at four confining pressures: 1.5, 10, 20 and 30 MPa. The obtained results showed that the coal permeability decreases with an increase in confining pressure. At depths below 250 m, the coal can be a rock poorly permeable to CO2, and under such conditions, the applicability of technologies related to the underground storage of CO2 to coal seams is limited or even impossible.

An experimental and molecular simulation study of the adsorption of carbon dioxide and methane in nanoporous carbons in the presence of water

The adsorption of carbon dioxide and methane in nanoporous carbons in the presence of water is studied using experiments and molecular simulations. For all amounts of adsorbed water molecules, the adsorption isotherms for carbon dioxide and methane resemble those obtained for pure fluids. The pore filling mechanism does not seem to be affected by the presence of the water molecules. Moreover, the pressure at which the maximum adsorbed amount of methane or carbon dioxide is reached is nearly insensitive to the loading of preadsorbed water molecules. In contrast, the adsorbed amount of methane or carbon dioxide decreases linearly with the number of guest water molecules. Typical molecular configurations obtained using molecular simulation indicate that the water molecules form isolated clusters within the host porous carbon due to the nonfavorable interaction between carbon dioxide or methane and water.

CO2 adsorption on carbon models of organic constituents of gas shale and coal

Imperfections of the organic matrix in coal and gas shales are modeled using defective and defect-free graphene surfaces to represent the structural heterogeneity and related chemical nature of these complex systems. Based upon previous experimental investigations that have validated the stability and existence of defect sites in graphene, plane-wave electronic density functional theory (DFT) calculations have been performed to investigate the mechanisms of CO(2) adsorption. The interactions of CO(2) with different surfaces have been compared, and the physisorption energy of CO(2) on the defective graphene adsorption site with one carbon atom missing (monovacancy) is approximately 4 times as strong as that on a perfect defect-free graphene surface, specifically, with a physisorption energy of ∼210 meV on the monovacancy site compared to ∼50 meV on a perfect graphene surface. The energy associated with the chemisorption of CO(2) on the monovacancy site is substantially stronger at ∼1.72 eV. Bader charge, density of states, and vibrational frequency estimations were also carried out and the results indicate that the CO(2) molecule binds to the surface becoming more stable upon physisorption onto the monovacancy site followed by the original C═O bonds weakening upon CO(2) chemisorption onto the vacancy site.