(153b) Phase Equilibria in the Ternary System of Carbon Dioxide–Tetrahydrofuran-Water at Gas Hydrate Forming Conditions

With growing interest in gas hydrate technology as a possible method for carbon dioxide separation and sequestration, there have been necessities for more experimental data of carbon dioxide hydrate-containing systems. In the present work, the three- and four-phase hydrate equilibria of the ternary system of carbon dioxide (CO2) + tetrahydrofuran (THF) + water are measured by using a Cailletet equipment. The experimental temperature ranged from 275 to 295K and pressure up 1 to 7.5 MPa has been applied. Measurements show that the addition of tetrahydrofuran cause the hydrate equilibrium pressure to be drastically lowered by 60-80% at a specified temperature and equivalently the hydrate equilibrium temperature to be raised with about 6-8K at a specified pressure depending on the concentration of tetrahydrofuran in water. Moreover, depending on the overall composition of the systems, a liquid-liquid phase split is observed creating a four-phase equilibrium in the system and it is bounded by the bubble (Lw-Lv-V → Lw-Lv) and dew (Lw-Lv-V → Lw + V) points lines of the ternary system. At higher overall concentration of carbon dioxide, experimental measurements show that a pseudo-retrograde phenomenon exists at pressure between 2.5 to 5 MPa at a temperature of 291K.