Investigating the Effect of NaCl Concentration on CO ₂ Hydrate Formation Kinetics: Experimental and Modeling Insights for CO ₂ Sequestration

Gas hydrate-based CO₂ sequestration stands out as a potential approach for the permanent storage of CO₂ in marine sediments, leveraging its exceptional capacity for CO₂ storage along with long-term stability and safety. This study presents a systematic investigation of the kinetics of CO₂ hydrate formation in a silica sand matrix over a wide range of NaCl concentrations (0-5.0 wt %). While gas hydrates are typically stable in freshwater-saturated silica sediments, the presence of NaCl (in seawater) poses significant challenges by inhibiting hydrate growth, reducing thermodynamic stability, and lowering storage capacity. Previous studies often considered a single salt concentration, limiting our understanding of the salinity effect. This work provides a comprehensive kinetic analysis, supported by a chemical potential-driven model, to elucidate the impact of varying salt content on CO₂ hydrate formation. The findings indicate that higher NaCl concentrations (≥3 wt %) markedly hinder hydrate formation rates, reaffirming the suppressive effect of salt. To address this challenge, biodegradable amino acid l-leucine (LL) was employed as a kinetic hydrate promoter. In the presence of 5.0 wt % NaCl, incorporating 2.0 wt % LL boosted gas uptake by nearly 2.6 times, highlighting its strong promotional impact. The proposed model, first of its kind, accurately represents the kinetics across diverse salinity levels and additive scenarios, providing actionable insights for advancing CO₂ hydrate-based sequestration.