Structure identification of binary 1-propanol+methane hydrate using neutron powder diffraction

Alcohols are frequently used in hydrate communities as thermodynamic hydrate inhibitors, but some alcohol molecules are also known to be hydrate formers with a help gas. In this study, the crystal structures of binary 1-propanol+methane hydrates at various temperatures were identified using neutron powder diffraction analysis with Rietveld refinement. Characteristic behaviors of the guest molecules in the hydrate structure were also analyzed to verify possible host-guest interactions from the refinement results. The results showed that the thermal factors of host water and guest methane increased continuously as the temperature increased. However, the isotropic thermal factors (B values) of 1-propanol were abnormally high compared to those of methane in the small cages of structure II (sII) hydrates, which could be because the 1-propanol molecules were off-centered in the large cages of sII hydrates. This implies that hydrogen bonding interactions between host and guest molecules can occur in the large cages of sII hydrates. The present findings may lead to a better understanding of the nature of guest-host interactions that occur in alcohol hydrates.