Seawater-based methane storage via mixed CH4/1,3-dioxane hydrates: Insights from experimental and molecular dynamic simulations

Natural gas is essential in the global energy landscape due to its clean-burning properties and widespread availability. While Solidified Natural Gas (SNG) offers a promising solution for non-explosive and long-term gas storage, it confronts issues tied to toxic additives and substantial water-related expenses. This work addressed these challenges by employing the environmentally benign promoter 1,3-dioxane to synthesize sII methane hydrate in artificial seawater. The concentration of 1,3-dioxane employed in this study spans 2.5 mol%, 4 mol%, the stoichiometric concentration of 5.56 mol%, and 7 mol%. The phase equilibrium points slightly downwards shift as the concentration of 1,3-dioxane increases. Under initial conditions of 10 MPa/283.2 K, the CH4/dioxane (4.00 mol%)/seawater system exhibited a methane storage capacity of 80.66 (±0.74) v/v, which closely approached the highest level of 83.54 (±1.48) v/v achieved in the stoichiometric 1,3-dioxane (5.56 mol%) system. The excess 1,3-dioxane (7.00 mol%) system exhibited the highest methane uptake rate of 2.11 (±0.06) v/v/min in the initial 10 min. In situ Raman spectroscopic analyses confirmed the early emergence of encaged guest molecules with increasing 1,3-dioxane concentration. Molecular dynamic simulations revealed that the aggregation of additional guest molecules impeded the formation of well-defined hydrate structures. These findings contribute to the advancement of methane storage in seawater-based hydrates.