Structure H (sH) Clathrate Hydrate with New Large Molecule Guest Substances
2013-11-14T00:00:00Z (GMT) by
This study characterized new structure H (sH) clathrate hydrates with bromide large-molecule guest substances (LMGSs) bromocyclopentane (BrCP) and bromocyclohexane (BrCH), using powder X-ray diffraction (PXRD) and Raman spectroscopy. The lattice parameters of sH hydrates with (CH<sub>4</sub> + BrCP) and (CH<sub>4</sub> + BrCH) were determined from their PXRD profiles. On the basis of their Raman spectra, the M-cage to S-cage occupancy ratio (4<sup>3</sup>5<sup>6</sup>6<sup>3</sup> and 5<sup>12</sup> cages, respectively), θ<sub>M</sub>/θ<sub>S</sub>, was estimated to be approximately 1.3, and the Raman shift of the symmetric C–H vibrational modes of CH<sub>4</sub> in S- and M-cages was 2911.1 and 2909.1 cm<sup>–1</sup>, respectively. The phase-equilibrium conditions of sH hydrates with (CH<sub>4</sub> + BrCP) and (CH<sub>4</sub> + BrCH) were determined by an isochoric method. A comparison between the equilibria of sH hydrates with BrCP and BrCH and those with other typical nonpolar and polar LMGSs (methylcyclopentane, MCP; methylcyclohexane, MCH; neohexane, NH; and <i>tert</i>-butyl methyl ether, TBME) at the same temperature revealed that the equilibrium pressure increased in the order NH < MCH < BrCH < TBME ∼ MCP < BrCP. The phase stabilities of sH hydrates can be determined by not only molecular geometry but also their polar properties, which affect guest–host interactions.