Tunable Strategies for Controlled CO ₂ Hydrate Formation: Integrating Promoter-Driven Regulation and Cage Occupancy Analysis

Hydrate-based carbon sequestration offers a promising pathway for offshore CCS by exploiting the complementary properties of structure I (sI) and structure II (sII) hydrates in different sedimentary domains. Here, we employed Diffuse Reflectance Infrared Fourier Transformations Spectroscopy (DRIFTS) and chemical potential calculations to quantify cage occupancies in binary 1,3-dioxane/CO2 hydrates. At 8.5 °C and 3.6 MPa with 5.56 mol % dioxane, the large (51264) and small (512) cage occupancies by CO2 were determined to be 0.0810 and 0.7696, respectively. A numerical program was developed to calculate gas uptake, hydration number, density, and hydrate molar mass by incorporating cage occupancies and CO2 solubility in saltwater. Stirring speed and gas–water ratio were optimized for hydrate formation in seamud, yielding an optimal stirring rate of 800 rpm and a gas–liquid ratio of 5. Kinetic experiments across 1,3-dioxane concentrations (5.56 and 2.86 mol %) and diverse kinetic promoters (SL-Na, l-Trp, l-Lys; 300–2000 ppm) reveal that 5.56 mol % 1,3-dioxane/CO2 hydrate achieves a t90 of 2.44 min and a gas uptake of 73.526 mmol/mol (millimoles of gas/mol of saltwater), while the optimal sI hydrate pathway was identified as 800 ppm of SL-Na, with a corresponding t90 and uptake of 18.78 min and 53.719 mmol/mol, respectively. These findings highlight the potential of integrating cage occupancy insights with promoter optimization to design stratified sealing strategies, advancing safe and efficient offshore CO2 sequestration.