High-capacity natural gas storage in a water-framework via compositionally tuned ternary emulsions

Storage methods for conventional natural gas (NG), which is primarily composed of methane (CH₄), are complex and energy-intensive. In contrast, CH₄ hydrates offer a simpler and cleaner alternative. The use of thermodynamic promoters enables hydrate formation under milder conditions and makes the hydrates more economically attractive. However, the incorporation of these promoters into the hydrate lattice diminishes cage availability for CH₄ and fundamentally limits the storage capacity. The tuning phenomenon, where CH₄ occupies the large cages of structure II hydrates, has been proposed to address this limitation. Its practical impact, however, has been constrained because it requires low promoter concentrations and thus is applicable to only a fraction of the water. Here we introduce a mechanistic strategy that employs compositionally optimized water-tetrahydrofuran (THF)-isooctane emulsions to extend the tuning phenomenon across the entire water phase. Quantitative NMR established the partitioning behavior of THF between the aqueous and oil phases. Subsequent modeling demonstrated that continuous THF redistribution maintains the aqueous THF concentrations within the range required for the tuning effect throughout the entire growth of the hydrates. Hydrate formation experiments confirmed that ternary emulsions more than double the CH₄ uptake relative to bulk systems. The optimal emulsion formulation (5.56 mol% THF, 15 vol% water) achieved 90.48 mmol CH₄/mol H₂O, surpassing previously reported values, and Raman spectroscopy confirmed that this enhancement arises from the tuning phenomenon. These findings show that the compositionally tuned ternary emulsions overcome the fundamental limitations of hydrate processes using thermodynamic promoters and provide a practical pathway toward scalable hydrate-based NG storage.