Double occupancy of large cavity of diethylamin+methane sH hydrate at low pressures

New data on the composition of hexagonal structure III (sH) diethylamine+methane double hydrate are presented. The hydrate was synthesized from methane and aqueous solutions of diethylamine with the molar ratio of diethylamine to water 1:17, 1:20, 1:30, 1:40, and 1:50. In the first case, pure sH hydrate was obtained; in other cases, the mixtures of sH hydrates and methane hydrate were formed. The content of each of the hydrates in mixture as well as the total content of methane in these samples were determined experimentally. The compositions of the formed sH hydrates in all samples were calculated on the basis of these data. It turned out that in all samples, substantial part of large cavities of sH hydrate framework was filled with two diethylamine molecules. To the best of our knowledge, this is the first example of double occupancy of hydrate cavities for gas hydrate synthesized at comparatively low (100 bar) pressure. Multiple filling of the hydrate cavities by guest molecules was previously observed only at pressures above 1000 bar.