Hydrate Phase Equilibrium of CH₄-Rich Binary and Ternary Gas Mixtures in the Presence of Tetra-<i>n</i>-butyl Ammonium Bromide

Abstract

In this work, binary gas mixtures of 92 mol % CH4/CO2 and ternary gas mixtures of 87 mol % CH4/5 mol % C2H6/CO2 were studied as simulate associated petroleum gas. It mainly consists of two parts: one is the hydrate phase equilibrium of the binary and ternary gas mixtures both in water and 0.293 mol % tetra-n-butyl ammonium bromide (TBAB) solution by isochoric pressure-search method, and the other is the enthalpy of hydrate dissociation calculated by the Clausius–Clapeyron equation. The hydrate phase equilibrium measured temperature ranged from 278.61 to 289.46 K and pressure from 2.12 to 10.06 MPa with 24 points in total. The results show that the hydrate phase equilibrium line of 87 mol % CH4/5 mol % C2H6/CO2 + water was shifted about 2.4 K toward the higher temperature compared to that of 92 mol % CH4/CO2 + water. After adding 0.293 mol % TBAB, it could be found that the hydrate phase equilibrium line of binary gas mixtures and ternary gas mixtures in 0.293 mol % TBAB(aq) were shifted about 5.3 and 2.7 K toward the higher temperature compared to that of water. Besides, the enthalpy of the hydrate dissociation in 0.293 mol % TBAB(aq) is much higher than that in water. Average enthalpy of the hydrate dissociation of binary gas mixture hydrate increased from 62.46 kJ/mol in water to 160.21 kJ/mol in 0.0293 mol % TBAB(aq). Meanwhile the average enthalpy of hydrate dissociation of ternary gas mixture hydrate increased from 72.89 kJ/mol in water to 181.61 kJ/mol in 0.0293 mol % TBAB(aq).