Fundamental Study of Gas Hydrate Formation: Correlation between Structure of Aqueous Solution and Stability of Hydrate Crystal

Stability of gas hydrate in pure H₂O, THF/H₂O and CH₃OH/H₂O solutions were measured by high pressure optical vessel. From the measurement of stability conditions for the gas hydrate against temperature and pressure, the order of hydrate crystal stability is as follows; THF solution>pure H₂O>CH₃OH solution. The resulting solvent effect on the stability of the gas hydrate is closely related with the microscopic molecular clustering structure in solutions observed through the liquid cluster beam mass spectrometer. The stable clusters with dodecahedral structure (H₂O)₂₁H⁺ (THF)_n were observed in high probability in the THF solution. On the other hand, water structure is strongly influenced by methanol and hydrogen-bonding networks of water molecules were broken in the high concentration region of methanol solution. The difference of the stability of hydrate crystal in these solutions seems to be caused by clustering structure difference of these aqueous solutions.