Phase Equilibrium of Methane Hydrate in the Presence of Aqueous Solutions of Quaternary Ammonium Salts

Abstract

Families of various quaternary ammonium salts (QAS) have been of great interest to gas hydrate based investigations. In this work, an attempt has been made to understand the effect of QAS of the bromide family with increasing alkyl chain length, such as tetra-methyl, tetra-ethyl, and tetra-butyl ammonium bromide (TMAB, TEAB, and TBAB) at two different concentrations (0.05 and 0.1 mass fraction) in an aqueous solution on the hydrate–liquid–vapor (H-L-V) phase equilibrium of the methane hydrate system. Various experiments were performed to capture phase equilibrium data in the equilibrium pressure range of 7.6–4.2 MPa and temperature range of 282.4–276.8 K. It has been observed that the addition of TMAB and TEAB shifts the phase equilibrium curve of methane hydrate to higher pressure and lower temperature conditions. TMAB and TEAB have shown thermodynamic inhibition unlike TBAB which has shown a promotion effect. The Clausius–Clapeyron equation is used to calculate the enthalpy of dissociation of methane hy...