Synergistic Role of Tetrahydrofuran and Cyclopentane in Hydrogen Hydrate Formation: A Dual-Promoter Strategy for Hydrogen Storage

Hydrogen is considered a clean energy source and an alternative to fossil fuels due to its high energy density and zero carbon emissions. Hydrate-based hydrogen storage offers a promising solution for storing hydrogen under moderate temperature and pressure conditions, but its sluggish kinetics and low storage capacity deter its application. Though individual thermodynamic promoters have been examined for their potential in promoting hydrogen hydrate formation, in this work, for the first time, a combination of THF and CP as thermodynamic promoters (sII structure) was used to study the kinetics of hydrogen hydrates. Kinetic and morphological effects of hydrogen hydrate formation at varying concentrations of THF and CP were studied at 278.2 K–280.2 K and in the range of 3–11 MPa. Presaturation of hydrogen gas before cooling significantly improved the induction time. It was found that a 2.8 mol % THF/2.8 mol % CP combination was the optimal concentration that showed the highest gas uptake of 18.8 mmol/mol H2O with a t90 of 222 ± 33.2 min and a very short induction time of 1.8 ± 0.3 min. To improve the formation kinetics, l-valine, sodium dodecyl sulfate (SDS), and Tween 80 kinetic promoters were studied at a concentration of 0.3 wt %. It was observed that 0.3 wt % Tween 80 reduced the t90 from 222 ± 33.2 min to 126.8 ± 0.2 min, corresponding to a 42.86% reduction, with the shortest induction time of 1 ± 0.7 min. Mixed hydrogen hydrate formation under much more moderate conditions (3 MPa and 278.2 K) was also demonstrated, with an observed hydrogen uptake of 6.08 mmol/mol H2O. The effect of driving force in terms of pressure and temperature on the mixed hydrogen hydrate was carried out to understand the behavior of the equimolar concentration of the promoter (2.8 mol % THF/2.8 mol % CP) system. By increasing the driving force by 3 MPa and decreasing ΔT by 2 K, an increase in gas consumption up to 22.39 mmol/mol H2O was observed.