Semiclathrate Hydrate Phase Equilibria for CO₂ in the Presence of Tetra-<i>n</i>-butyl Ammonium Halide (Bromide, Chloride, or Fluoride)

Abstract

Phase equilibrium data for the semiclathrate hydrates formed in three three-component systems, the CO2 + tetra-n-butyl ammonium bromide (TBAB) + water system, the CO2 + tetra-n-butyl ammonium chloride (TBAC) + water system, and the CO2 + tetra-n-butyl ammonium fluoride (TBAF) + water system, were measured in the pressure range of (0.40 to 3.77 MPa) and temperature range of (280.2 to 293.5 K) at (2.93·10−3 and 6.17·10−3) mole fraction of tetra-n-butyl ammonium halide. The experimental data were generated using an isochoric pressure-search method. The equilibrium data for the CO2 + TBAB + water system were compared with some experimental data from the literature. The effects of tetra-n-butyl ammonium halide concentration on the stability zone of the semiclathrate hydrates were studied. It was shown that TBAB, TBAC, and TBAF all can enlarge the hydrate stability zone, and as the tetra-n-butyl ammonium halide concentration increases, so does the hydrate stability zone. The three-phase equilibrium pressure of the CO2 + TBAF + water system is lower than others at the same temperature.