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

Abstract

• D 2 O was introduced as host molecular to form methane hydrate. • Self-preservation effect was first observed above 273.2 K for methane hydrate. • Self-preservation was improved at least 3.5 K for methane hydrate. • Mixed cages were first found during methane hydrate formation in (D 2 O + H 2 O) system. 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 (D 2 O) 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 D 2 O, while the methane hydrate dissociated percentage decreased to 55.2 % with the addition of 30 wt% D 2 O. The methane hydrate dissociated percentage reduced to 15.7% when methane hydrate formed in D 2 O 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 (CH 4 + D 2 O) hydrate was improved at least 3.5 K higher than that for (CH 4 + H 2 O) hydrate. From the simulation results, some (D 2 O + H 2 O) mixed cages with different D 2 O and H 2 O molecules formed, and CH 4 inserted into the mixed cages to form CH 4 hydrate as sI structure. The (D 2 O + H 2 O) mixed cages may explain the self-preservation effect of (CH 4 + D 2 O + H 2 O) hydrate above 273.2 K to some extent. Finally, it was also found from the simulation results that (CH 4 + D 2 O + H 2 O) hydrate not only formed from hydrate/(D 2 O + H 2 O) contact, but also nucleated independently.