Clathrate hydrate dissociation conditions and structure of the methane + cyclopentane + trimethylene sulfide hydrate in NaCl aqueous solution

Abstract

In present work, the phase equilibrium of methane + cyclopentane (CP) + timethylene sulfide (TMS) hydrate were measured in NaCl solution at the temperature range from 286.42 to 303.77 K and the pressure varying from 1.16 to 12.49 MPa. The experimental data were measured with an isochoric T-cycle method. The phase equilibrium pressure of organic compounds (VCP:V TMS = 4:1) + CH4 hydrate increases with the temperature and the NaCl concentration. When the temperature was higher, the effect of temperature and NaCl concentration on the phase equilibrium pressure was more remarkable. The dissociation enthalpies of organic compounds (VCP:VTMS = 4:1) + CH4 hydrate in 3.5, 5.0, 7.0, 10% (mass fraction) NaCl solution were calculated through the Clausius−Clapeyron equation based on the phase equilibrium data. The dissociation enthalpy decreases with the increase of either the temperature or the NaCl concentration. The crystal structure of organic compounds (VCP:VTMS = 4:1) + CH4 hydrate was determined by using Raman spectroscopy. Methane was present only in the small sII cavity, cyclopentane and timethylene sulfide were all in the large sII cavities.