Significance of wettability of porous media and its implication for hydrate-based pre-combustion CO₂ capture

Gas hydrate-based pre-combustion CO₂ capture is considered a promising technology for CO₂ separation. To further improve hydrate-based CO₂ capture from gaseous mixtures (i.e., CO₂ + H₂) generated from pre-combustion processes, it is necessary to enhance the hydrate thermodynamic stability and formation kinetics. Surfactants and interstitial pore materials have been suggested to enhance formation kinetics, but the optimum confined space and wettability of the porous media, which are the key factors affecting kinetic performance, have not been fully determined when using thermodynamic promoters. In this study, the thermodynamic stability and formation kinetics (e.g., induction time, formation rate, gas composition, and gas uptake) of THF (5.56 mol%) hydrates of CO₂ (40%) + H₂ (60%) mixtures in the presence of SDS (0, 100, or 500 ppm) were evaluated in silica gels of various hydrophobicities. The results revealed that the hydrophobicity of the porous media significantly affects both the thermodynamic phase equilibria and kinetic properties. Interestingly, the weak hydrophobic silica gel enhanced the thermodynamic stability, induction time, formation rate, and gas uptake with 96% CO₂ composition. The SDS (particularly 500 ppm) also improved the kinetic properties of the hydrate. The present findings provide a new guideline for designing the optimum hydrophobicity of porous media to enhance the thermodynamic stability and formation kinetics for hydrate-based pre-combustion CO₂ capture.