Phase Equilibrium of the Methane Hydrate System in the Presence of Mixed Promoters (THF + TBAB) and the Effect of Inhibitors (NaCl, Methanol, and Ethylene Glycol)

Tetra-n-butyl ammonium bromide (TBAB) and tetrahydrofuran (THF) are being widely used in gas hydrate research for their potential to store natural gas. The mixed promoter system of THF and TBAB has not yet been investigated for the phase stability conditions of methane hydrate. In this work, the phase stability of methane hydrate has been investigated in the presence of a mixed promoter (THF + TBAB) in the absence and presence of various inhibitors, viz., sodium chloride (NaCl), methanol (MeOH), and ethylene glycol (EG), at various concentrations. The phase equilibrium data has been reported in the temperature and pressure ranges of (282.25-289.65) K and (2.25-6.43) MPa, respectively. The heat of dissociation has been determined using the Clausius-Clapeyron equation for various methane hydrate systems. MeOH is observed to be an effective inhibitor as compared to EG and NaCl on the methane hydrate system formed from the mixed promoter system of THF + TBAB. With an increase in the concentration of MeOH, the inhibition effect of methane hydrate formed from the mixed promoter system has been increased. At a low concentration of NaCl, the promotion of the mixed hydrate has been observed, and at a higher NaCl concentration, inhibition has been observed. EG is observed to show mixed behavior with respect to the phase stability of the methane hydrate system formed from mixed promoters. The heat of dissociation is found to decrease with increasing concentrations of MeOH, EG, and NaCl for the methane hydrate system formed from mixed promoters.