(191ah) Pressure-Temperature Phase Diagrams for Clathrate Hydrates of Hydrogen + Tetrahydrofuran

Hydrogen is a promising clean fuel of the future and its safe storage at low pressures and ambient temperatures is still a challenge. Gas hydrates, or clathrate hydrates, have recently been proposed as a potential medium for hydrogen storage. Clathrate hydrates are a group of ice-like crystalline compounds formed through a combination of water and suitably sized guest molecule(s), like methane but unlike ice, can form at temperatures well above the ice point. The common gas hydrate crystalline structures are structures I (sI), II (sII) and H (sH), where each structure is composed of a certain number of cavities formed by water molecules. Until recently, hydrogen was considered a non-hydrate former as it was believed that this molecule could not enter gas hydrate lattice because of its small molecular size. However, it was later proven that hydrogen can form sII gas hydrates at low temperatures and extremely high pressures. It has also been shown that the addition of tetrahydrofuran (THF) in its aqueous solution can reduce the pressure required for hydrogen hydrate formation. However, there are some inconsistencies among the literature data, especially at stoichiometric concentration of THF in aqueous solution (i.e. 0.056 mole fraction), which warrant new phase equilibrium measurements for H2 + THF clathrate hydrates. This works aims at providing dissociation conditions for clathrate hydrates of hydrogen + THF at various mole fractions of tetrahydrofuran in aqueous solutions. An isochoric pressure-search method was used to perform the measurements. The experimental data are compared with the literature data and a discussion is made on the reliability of the experimental data reported in the literature.