Phase Equilibrium Conditions of Tetrabutyl Ammonium Nitrate + CO₂, N₂, or CH₄ Semiclathrate Hydrate Systems

Phase equilibrium conditions for semiclathrate hydrates formed from tetrabutyl ammonium nitrate (TBANO 3 ) + CO 2, N 2, or CH 4 + water system were investigated under high-pressure in a “full view” sapphire cell. An isochoric equilibrium step-heating pressure-search method was used for the determination of the hydrate phase transition points through plotting the points of intersection of hydrate-liquid–vapor (H-L-V) to liquid–vapor (L-V) experimentally. All the experimental equilibrium data were obtained in the presence of TBANO 3 solution at ammonium salt mass fraction of 0.3941 corresponding to a stoichiometric composition for TBANO 3 ·26H 2 O. Measurements were performed for TBANO 3 + CO 2 + water, TBANO 3 + N 2 + water, and TBANO 3 + CH 4 + water system in the temperature range of (281.5 to 290.9) K and in the pressure range of (1.19 to 32.89) MPa. The three-phase equilibrium lines of TBANO 3 + N 2 and TBANO 3 + CO 2 semiclathrate hydrate shifted the hydrate stability region to lower pressure and higher temperature than that of the pure N 2 and CO 2 hydrate, respectively. However, the addition of TBANO 3 made TBANO 3 + CH 4 semiclathrate hydrate phase equilibrium curve at higher pressure than the pure CH 4 hydrate.