Research on the phase behavior and thermodynamic analysis of CO₂ hydrate in saline systems

Carbon Capture and Storage (CCS) is a critical technology for addressing climate changes, and CO₂ hydrate storage has gained attention due to its high-density potential and stability. This study investigates the phase behavior of CO₂ hydrates in saline conditions through experiments and thermodynamic analysis, providing a theoretical foundation and data support for optimizing sequestration strategies. The results show that in saline solutions, induction time decreases with increasing salt concentration. The maximum gas storage capacity (79.5 mmol/mol) occurs at 0.3 wt% NaCl, but the decomposition stability is weakest. In different salt solutions, the gas storage capacity in Na⁺ systems is 1.82 times higher than in K⁺ systems, while K⁺ systems have stronger decomposition stability (2.56 times longer decomposition time). SO₄²⁻ systems outperform Cl⁻ systems in formation rate and stability. In addition, the hydrate phase equilibrium conditions are significantly influenced by salt concentration, with a maximum temperature shift of 1.0 K, but differences between salt types at the same concentration are negligible. Finally, an improved model incorporating the mechanisms of each system’s influence on hydrate phase behavior is developed to predict phase equilibrium conditions in submarine sediment environments, which achieves less than 0.25 K deviation with high accuracy. This study provides essential data and theoretical support for the engineering application of CO₂ hydrate sequestration technology. • Studied salt concentration's impact on hydrate phase equilibrium in dilute solutions. • Transitional salt concentrations optimally promote CO 2 hydrate formation. • Salt concentration increase enhances inhibition on phase equilibrium. • Various salts affects hydrate uniquely, linked to ion radius and hydration strength. • Improves Chen-Guo model by mixing capillary, surface & ionic electrostatic effects.