Quest for optimal nanoconfinement for hydrate-based CO2 capture

CO₂ capture is a viable solution for mitigating the global CO₂ emission in the atmosphere. Hydrate-based CO₂ capture is a promising technology. In this study, the CO₂ hydrate formation thermodynamics and kinetics, along with the factors that influence CO₂ capture in nanoporous silica gels (named S9, S26, and S77 with an average pore size of 9, 26 and 77 nm, respectively), with different degrees of nanoconfinement were investigated. The CO₂ hydrate phase equilibrium and dissociation heat were determined by heat flow analysis. The heat flow curves revealed the formation of both confined- and bulk-phase hydrates in S9 and only bulk-phase hydrate in S26 and S77. The phase equilibrium temperature of the confined-phase hydrate was about 10 K lower than that of the bulk-phase hydrate and the dissociation heat of confined phase hydrate is 285.81 J/g in S9. According to the pressure curves, the CO₂ hydrate formation time in S9 was 2–3.5 times longer than that in S26 and S77. Compared with dry silica gel, the supersaturated one was more conducive to CO₂ capture. Under the same water saturation condition, the CO₂ capture ability of S26 and S77 was stronger than that of S9, and the effect of water saturation was dominant over that of pressure. Thus, nanoconfinement in S9 has an adverse effect on hydrate-based CO₂ capture whereas that in S26 and S77 is advantageous to it. This study provides an important fundamental basis for enhancing the hydrate-based CO₂ capture ability via nanoconfinement in silica gel.