Spectroscopic Observation of the Hydroxy Position in Butanol Hydrates and Its Effect on Hydrate Stability

In this study, we investigate the crystal structures and phase equilibria of butanols+CH4+H2O systems to reveal the hydroxy group positioning and its effects on hydrate stability. Four clathrate hydrates formed by structural butanol isomers are identified with powder X-ray diffraction (PXRD). In addition, Raman spectroscopy is used to analyze the guest distributions and inclusion behaviors of large alcohol molecules in these hydrate systems. The existence of a free OH indicates that guest molecules can be captured in the large cages of structure II hydrates without any hydrogen-bonding interactions between the hydroxy group of the guests and the water-host framework. However, Raman spectra of the binary (1-butanol+CH4) hydrate do not show the free OH signal, indicating that there could be possible hydrogen-bonding interactions between the guests and hosts. We also measure the four-phase equilibrium conditions of the butanols+CH4+H2O systems.