Spectroscopic observations of host–guest interactions occurring in (cyclobutanemethanol + methane) hydrate and their potential application to gas storage

Abstract

We discovered a new structure II (sII) hydrate former, cyclobutanemethanol (CBM), for potential use in gas storage applications. The crystal structure and guest behaviors of the binary (CBM + CH4) hydrate were investigated through spectroscopic observations, using 13C solid-state NMR and PXRD. Binary (CBM + CH4) hydrate NMR spectra confirmed formation of sII hydrates, indicating that CBM could be enclathrated in the large cages of sII hydrates. CH4 molecules were captured in the large and small cages of sII hydrates; thus, the binary (CBM + CH4) hydrate system could be open to tuning behaviors. The crystal structure of the binary (CBM + CH4) hydrate was confirmed to be a cubic Fd3m hydrate by the Rietveld analysis, with a lattice parameter of 17.23630 Å. CBM inclusion behaviors were elucidated from the shortest distance of the oxygen–oxygen atoms between the host–water and CBM (2.34 Å), and the results indicated that there were possible hydrogen bonding interactions between host and guest. The thermodynamic stability of the binary (CBM + CH4) hydrate was examined, to check the possibility for potential applications in gas storage using gas hydrates. Compared to the equilibrium conditions of pure CH4 hydrates, the equilibrium temperature and pressure of the binary (CBM + CH4) hydrate were more stable. Finally, the CH4 storage capacity of binary (CBM + CH4) hydrate is examined and the results indicate that the CH4 storage capacity of binary (CBM + CH4) hydrate is superior to that of binary (tetrahydrofuran + CH4) and (cyclopentane + CH4) hydrates. These findings may provide fundamental knowledge on the complex nature of host–guest inclusion chemistry, and lend useful insights for its potential application in gas storage using hydrates.