Effect of NaCl, methanol and ethylene glycol on the phase equilibrium of methane hydrate in aqueous solutions of tetrahydrofuran (THF) and tetra-n-butyl ammonium bromide (TBAB)

Abstract

Hydrate or semiclathrate hydrate systems formed using tetrahydrofuran (THF) and tetra-n-butyl ammonium bromide (TBAB) show potential use for natural gas storage and transportation. Information on the effect of various inhibitors on their phase stability is necessary to effectively dissociate these hydrate systems for the end use application. In this work, the experimental data for the phase equilibrium of methane (CH4) hydrate system have been obtained in the presence of THF (0.005 and 0.01 mass fraction) and TBAB (0.1 and 0.2 mass fraction) with various inhibitors. Various inhibitors used in the study include sodium chloride (NaCl), methanol (MeOH) and ethylene glycol (EG) with mass fraction (0.03 and 0.1) of each inhibitors in aqueous solutions of THF and TBAB. The reported data lie in the temperature and pressure range of (277.56–290.43)K and (2.20–6.16)MPa, respectively. Comparative effects of NaCl, MeOH and EG on hydrate/semiclathrate hydrates of CH4+H2O+THF/TBAB have been studied. The inhibition effect of NaCl on hydrate of CH4+H2O+THF is observed to be higher as compared to MeOH and EG, whereas for semiclathrate hydrate of CH4+H2O+TBAB, MeOH is observed to be an effective inhibitor than NaCl and EG. In addition, as the concentration of promoters (THF and TBAB) increases, the effect of inhibitors is found to decrease. This indicates that lower concentrations of promoters along with inhibitors may be suitable for efficient formation and dissociation of natural gas storage and transportation. The heat of dissociation (Hdiss) determined using Clausius–Clapeyron equation is reported for various hydrate/semiclathrate hydrate system. The values of heat of dissociation are observed to be in good agreement with literature trend. Hdiss is observed to decrease with increase in concentration of NaCl, MeOH and EG for hydrate/semiclathrate hydrate of CH4+H2O+THF/TBAB.