Molecular analysis of hydrogen-propane hydrate formation mechanism and its influencing factors for hydrogen storage

Abstract

Combining hydrogen and propane, which acts as a thermodynamic additive, to form hydrates is a promising hydrogen storage method. However, the mechanism of hydrate formation, which is the core of hydrate-based hydrogen storage, remains obscure. In this study, the effects of gas composition, pressure, and temperature on hydrogen–propane hydrate formation kinetics were investigated through molecular dynamics simulations. A hydrogen fraction (Xh) in the range of 0.47–0.67 was optimal for forming hydrate cages, whereas for Xh ≤ 0.37 and Xh ≥ 0.77, propane or hydrogen bubbles formed, which inhibited hydrate formation. Within the simulated pressure range, the number of hydrate cages increased with the increasing pressure. However, the analyzed self-diffusion coefficients suggested that the effect of pressure on the hydrate formation kinetics gradually weakened as the pressure increased up to a certain value. Within the simulated temperature range, the number of hydrate cages increased with temperature up to a point below the hydrogen–propane hydrate phase-equilibrium temperature. This result can be attributed to the increase in the self-diffusion coefficients of hydrogen and propane with the increasing temperature. These results provide valuable microscopic insights into the hydrogen–propane hydrate formation mechanism for hydrate-based hydrogen storage and will be useful in experimental research.