Enhancing gas storage capacity by controlling the cage occupancy of natural gas hydrate

Abstract

Growing global energy demand has highlighted natural gas as a cleaner alternative to traditional fossil fuels, driving the development for energy-efficient natural storage systems. Gas hydrate offers an alternative approach, providing relatively high storage capacity under moderate formation conditions, yet enhancing gas storage capacity remains a crucial challenge. Gas storage capacity is related to cage occupancy, and since the small cages in hydrates still have partially unoccupied sites, this study focused on increasing small cage occupancy as a strategy to enhance gas storage by slightly controlling the promising thermodynamic promoter’s concentration, tetrahydrofuran (THF) and 1,3-dioxane (Dioxane). Thus, THF and Dioxane hydrates formed with CH4 or CH4 (90%) + C2H6 (7%) + C3H8 (3%) were investigated with varying promoter concentrations (4.0–6.0 mol%). Thermodynamic stability and synchrotron XRD results revealed that there was negligible thermodynamic promotion difference and sII hydrates formation for THF and Dioxane hydrates. Dioxane (5.3 mol%) with natural gas hydrate showed the highest gas uptake below the stoichiometric 5.6 mol%. Furthermore, 13C solid-state NMR revealed increased CH4 cage occupancy at 5.3 mol% compared to 5.6 mol% of THF and Dioxane with natural gas hydrates, demonstrating that improved cage occupancy directly contributed to enhanced storage capacity. Compared to other studies, THF (5.6 mol%) and Dioxane (5.3 mol%) with natural gas hydrates achieved relatively superior storage capacity and formation rates under milder formation conditions. These results provide better understanding into controlling cage occupancy for improving gas storage capacity.