[en] Highlights: • The traditional PC washing approach was improved by adding mIm to PC with the presence of EG as cosolvent. • CO₂ solubility increases rapidly while those of CH₄, N₂ and H₂ decrease drastically in the presence of mIm. • Viscosity and absorption heat could remain on low level for EG-mIm-PC complex solvents. • The selectivity of CO₂ over CH₄, N₂ and H₂ could be increased significantly using EG-mIm-PC complex solvents. -- Abstract: Although a series of advanced technologies and materials, like ionic liquids and metal organic frameworks, is being developed for carbon capture, traditional techniques, like propylene carbonate (PC) washing, are still widely applied in industry because of their low material costs and ease of operation. Considering the low CO₂ solubility and selectivity in PC, we have tried to improve the PC washing process by adding 2-methylimidazole (mIm) to PC in the presence of ethylene glycol (EG) as cosolvent. A series of EG-mIm-PC complex solvents was prepared and their viscosities measured at different temperatures. The absorption isotherms of CO₂ in these complex absorbents, as well as in pure PC, were measured at 293.15, 303.15, and 313.15 K at 0.1–0.8 MPa. The heats of CO₂ absorption in these solvent mixtures were calculated using the Clausius-Clapeyron equation. For evaluating the effect of mIm on the selectivity of CO₂ over other gas species, the absorption isotherms of CH₄, N₂, and H₂ in pure PC and in 24%-mIm complex solvent with highest CO₂ solubility were also measured. The results showed that the viscosities of these complex absorbents, as well as the solubility and heats of absorption of CO₂ in all of them, moderately or slowly increased with an increase in mIm mass fraction, when the mIm content was lower than 20 wt%, and rapidly increased when it surpassed 20 wt%. The CO₂ solubility could be more than doubled when the mIm content reached 24 wt% while viscosity and absorption heat still remains at low levels, that is, lower than 14 mPa·s and 26 kJ/mol, respectively. More importantly, the solubilities of CH₄, N₂, and H₂ drastically decreased in the presence of mIm; using the 24 wt%-mIm complex absorbent instead of pure PC, the selectivity of CO₂ over those other gas species increased by: 0.7–2.8 times for CH₄, 3.9–6.3 times for N₂, and 3.5–7.7 times for H₂, with more significant improvements at lower pressure ranges. This work presents a very promising approach to PC washing technology upgrading.

[en] Highlights: • Realistic kerogen models are utilized to quantify CO₂/CH₄ competitive adsorption. • Effect mechanisms of organic type and moisture on gas adsorption are elaborated. • Dynamic distribution characteristic of moisture in kerogen models is revealed. • Kerogen IIIA is the optimized organic type for CS-EGR. • Moisture can potentially boost the displacement of CH₄ by CO₂. - Abstract: Although research attentions for CO₂ injection in gas-bearing reservoirs have been drawn to CO₂ sequestration with enhanced gas recovery (CS-EGR), the microscopic competitive adsorption mechanism of methane (CH₄) and carbon dioxide (CO₂) considering the effect of organic type and moisture remains to be determined. In this work, we focus on the competitive adsorption behaviors of CH₄ and CO₂ on dry and moist realistic kerogen models of different organic types by performing combined molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The effects of organic type and moisture content on kerogen pore structures, moisture distribution and interaction between CH₄/CO₂ and kerogen surfaces are discussed in details. Simulation results show that CO₂/CH₄ adsorption capacity and adsorption selectivity are in the order of kerogen IA 2O molecules are preferentially adsorbed on the sulfur- and oxygen-containing groups at low moisture, and then migrate and aggregate into clusters in the middle of enterable pores at high moisture. The CO₂/CH₄ adsorption capacity decreases with increasing moisture content, while the CO₂/CH₄ adsorption selectivity, specific adsorption energy and CO₂ isosteric heat decrease at the beginning, and then increase with the moisture content. Moisture has a bigger effect on the adsorption of CO₂ than that of CH₄. This study indicates that kerogen IIIA is the optimized organic type for CS-EGS due to its large and stable CO₂ storage capacity. Despite its negative effect on gas adsorption capacity, moisture can potentially boost the displacement of CH₄ by CO₂ at certain moisture conditions. Results of this study lay the foundation for future optimization design of CS-EGR projects with application to coal and shale systems.