Methane hydrate phase stability with lower mole fractions of tetrahydrofuran (THF) and tert-butylamine (t-BuNH2)

A systematic study on methane hydrate formation and dissociation was carried out in presence of liquid hydrocarbon promoters namely tetrahydrofuran (THF) and tert-butylamine (t-BuNH2). Mixed hydrates with THF/t-BuNH2 (mole fraction x = 0.05) were of sII symmetry. The hydrate formation/dissociation of mixed hydrates with x = 0.033 and 0.0056 were complex with co-existence of sII and sI structures. We observed the hydrate formation in two steps, hydrates in the first stage (∼T = 295 K) were mostly with sII and in the second stage (∼T = 275 K) were with sI structure, corroborating the literature. However, dissociation pattern of the hydrates formed in second stage significantly differ from pure methane hydrates and the above two liquid hydrocarbons show considerable promoter effect for sI hydrates.

► Methane hydrate formation with thermodynamic promoters such as THF and tert-butylamine (x = 0.06, 0.033, and 0.0056).
► Two stage MH formation when x = 0.033.
► sI hydrates (second stage) formation dominated when x = 0.0056 and the pattern is different to pure MH.