Thermodynamic Stabilities of Tetra-n-butyl Ammonium Chloride + H₂, N₂, CH₄, CO₂, or C₂H₆ Semiclathrate Hydrate Systems

The thermodynamic stabilities of semiclathrate hydrates were investigated in the tetra- n -butyl ammonium chloride (TBAC) aqueous solution (mole fraction of TBAC is 0.0323) + H 2, + N 2, + CH 4, + CO 2, and + C 2 H 6 systems. The dissociation temperature of each semiclathrate hydrate is higher than that of the simple TBAC semiclathrate hydrate (hydration number is 30) except for the C 2 H 6 -containing system in the whole pressure region under the present experimental conditions. Isobaric dissociation temperatures of the TBAC + H 2, + N 2, + CH 4, and + CO 2 hydrates increase in this order. The temperature−pressure projection indicated that the hydrate structural transition occurs around 3 MPa in the TBAC + CH 4 semiclathrate hydrate system, while the three-phase equilibrium curves of the other TBAC hydrate systems do not show any discontinuity in gradient under the present conditions.