In this study, phase equilibria of gas hydrates of CO 2 in the presence of tetra n-butyl phosphonium bromide (TBPB) and tetrahydrofuran (THF) have been investigated. The experiments were performed using the isochoric pressure search method at varying compositions of promoters. The phase equilibrium data have been reported at 0.01, 0.05, and 0.1 mass fractions of TBPB in aqueous solutions at the temperature and pressure ranges of 278−295 K and 1.1−4.5 MPa, respectively. The results showed that adding the aqueous mixtures of TBPB and THF to the system changes the hydrate phase equilibrium conditions as expected. In comparison with the system including only TBPB, the promotion effect of the applied mixture is low at all studied concentrations of TBPB in the presence of 0.01 mass fraction of THF. However, at 0.05 mass fraction of THF, the hydrate equilibrium pressures at constant temperatures decrease dramatically.

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