Investigation of hydrogen-propane hydrate formation mechanism and optimal pressure range via hydrate-based hydrogen storage

Hydrogen-propane hydrate is a promising practical hydrogen storage medium. However, the optimal conditions for the hydrogen-propane hydrate remain unclear. In this study, the thermodynamic and kinetic characteristics of hydrogen-propane gas (molar ratio 0.67/0.33) hydrate formation were investigated using experiments and molecular dynamics simulation. Moreover, the effect of liquid propane on hydrogen-propane hydrate formation in the pressure range of 0.5-2.8 MPa was investigated. The characteristic peaks of the heat flow curve during the experiment showed that under the pressure range of 2.0-2.8 MPa, propane hydrate and the ice-liquid propane mixture formed but not hydrogen-propane hydrate. Raman spectroscopy verified that when the initial pressure was higher than 2.0 MPa, only propane hydrate formed. Molecular dynamics simulation results showed that if liquefied propane exists, propane molecules will aggregate, preventing water molecules from contacting crystal nuclei and inhibiting hydrogen bonding, further hindering the growth of hydrogen-propane hydrate. Based on the experimental and theoretical analysis, the pressure range of 0.8-1.8 MPa is optimal for hydrogen-propane hydrate formation, specifically corresponding to the initial molar ratio of hydrogen to propane at 0.67/0.33. This study aids in determining the optimal operating conditions for hydrate-based hydrogen storage.