Solubilities of Carbon Dioxide in Ethyl Benzoate and Triethyl Citrate at High Temperatures and Pressures

The solubility of carbon dioxide in organic solvents at high temperatures and pressures is required for certain enhanced oil recovery processes. In this study, the solubilities of CO₂ in two different solvents, ethyl benzoate and triethyl citrate, were measured at saturation conditions at temperatures ranging between 298.15 and 373.15 K. The solubility was determined by measuring the saturation pressure of CO₂-solvent using the constant-mass expansion method. For each solvent, six mixtures were tested with CO₂ mole fractions varying between 0.65 and 0.90 with 0.05 increments. The results show each mixture's saturation pressure increasing virtually linearly with temperature. For ethyl benzoate, the saturation pressure varied between 5.38 MPa at 298.15 K for the 0.65 xCO₂ solution to 19.7 MPa at 373.15 K for the 0.90 xCO₂ solution. For triethyl citrate, the saturation pressure varied between 4.00 MPa at 298.15 K for the 0.65 xCO₂ solution to 22.4 MPa at 373.15 K for the 0.90 xCO₂ solution. The saturated solutions' xCO₂ values follow a simple exponential model in pressure and temperature. For both solvents, the saturation conditions predicted by the Peng-Robinson equation of state with adjusted parameters showed deviations, especially at higher temperatures and at larger CO₂ concentrations.