Self-preservation effect exceeding 273.2 K by introducing deuterium oxide to form methane hydrate

Self-preservation effect of hydrate is an advantage for gas storage by using hydrate-based technology. Unlike focusing on guest molecules in previous publications, deuterium oxides (D2O) were introduced as one of host molecules to form methane hydrate. Methane hydrate dissociated percentage was 92.2% after 12 h of dissociation at 273.7 K without the addition of D2O, while the methane hydrate dissociated percentage decreased to 55.2 % with the addition of 30 wt% D2O. The methane hydrate dissociated percentage reduced to 15.7% when methane hydrate formed in D2O system. The results suggested that the self-preservation effect of methane hydrate was improved to above 273.2 K for the first time since this abnormal phenomenon was found in 1986. The temperature of self-preservation effect for (CH4 + D2O) hydrate was improved at least 3.5 K higher than that for (CH4 + H2O) hydrate. From the simulation results, some (D2O + H2O) mixed cages with different D2O and H2O molecules formed, and CH4 inserted into the mixed cages to form CH4 hydrate as sI structure. The (D2O + H2O) mixed cages may explain the self-preservation effect of (CH4 + D2O + H2O) hydrate above 273.2 K to some extent. Finally, it was also found from the simulation results that (CH4 + D2O + H2O) hydrate not only formed from hydrate/(D2O + H2O) contact, but also nucleated independently.