Spectroscopic identifications and phase equilibria of THF + 3-OH THF + CH₄ clathrate hydrates

In this study, the inclusion phenomena of tetrahydrofuran + 3-hydroxytetrahydrofuran + CH₄ clathrate hydrates were explored via thermodynamic and spectroscopic approaches. The phase equilibria of the double hydrates - THF + CH₄ and 3-OH THF + CH₄ clathrate hydrates - were determined by pressure-temperature trace during hydrate formation and dissociation, and the result revealed that the equilibrium pressures were shifted to lower pressure region compared to pure CH₄ hydrate. The powder X-ray diffraction patterns revealed that the double hydrates of THF + 3-OH THF formed structure II type clathrate hydrates with CH₄. The dispersive Raman spectra of the double clathrate hydrates also exhibited that CH₄ can be trapped in both 5¹²6⁴ and 5¹² cages whereas THF and 3-OH THF were encaged in 5¹²6⁴ cage.