Adsorption Characteristics of CO2, CH4, H2S in Kaolinite Nanopores with the Implications for Carbon Sequestration

Abstract

Abstract The sequestration of carbon dioxide (CO2) in shale formation has dual benefits of reducing carbon emissions and enhanced oil recovery (EOR). CO2 purified from industrial waste gas is the main gas source for CO2 injection into oil reservoirs, but industrial waste gas may contain impurities such as hydrogen sulfide (H2S). Impurity gases may impair carbon storage and EOR via competitive adsorption. Consequently, it is worthwhile to evaluate the adsorption characteristics of CO2, CH4, and H2S within kaolinite nanopores and their implications on carbon sequestration and CH4 recovery. Drawing upon the kaolinite nanopores model, the impact of various surfaces on the adsorption characteristics of CO2, CH4, H2S, and their mixes was examined using the Grand Canonical Monte Carlo (GCMC) methods. Various factors, including temperature (293.15-383.15 K), pressure (0-20 MPa), pore width, and gas mole fraction, are investigated in the adsorption behaviors of the mixtures in the nano-confined space. The quantity of three molecules adsorbed enhances as pressure grows and falls with rising temperature. The rank of absolute adsorbed amount is H2S > CO2 >CH4. The interaction energies of kaolinite with CO2, CH4, and H2S at 20 MPa, 293.15 K are −1421.1138, −479.0825, −2528.245 kcal/mol, respectively, and Van der Waals energy is the main component of interaction energy. Compared to 1 nm hydrophobic pores, the loading of H2S, CO2, and CH4 in hydrophilic pores under 323.15 K and 20 MPa is 22.76%, 13.17%, and 11.57% greater, respectively. The adsorption of CO2 and CH4 are negatively impacted by H2S, and the adsorbed CO2 and CH4 are reduced by roughly 59.66% and 87.11%, respectively, at 25% (molar fraction) H2S. The nanoscale mechanism of gas adsorption in the clay mineral was disclosed from a molecular perspective, which theoretically supports the application of CO2 storage and EOR projects in shale reservoirs.