A refined equation for predicting the solubility of vegetable oils in high-pressure CO2

Abstract

The solubility of vegetable oils in high-pressure CO2 can be best modeled as a direct function of solvent density (ρ) and absolute temperature (T) having as model parameters an association number, k (number of solvent molecules forming a complex with a single solute molecule), and the total heat requirement for synthesizing the complex, ΔH (sum of heats of solution in CO2 and vaporization of the solute). A General Model was developed in this work that considered the solubility of the vegetable oil in CO2 under a reference condition (8.07gkg−1oil/CO2 at 40°C and 30MPa), a density-correction depending on k, and an absolute-temperature-correction depending on ΔH, and best-fit values were estimated using 235 data points from fifteen studies in literature involving eleven different vegetable substrates. The model was validated with many additional data points from seventeen additional vegetable substrates from twenty-one extra studies. The General Model is capable of predicting the solubility of vegetable oils in high-pressure CO2 to within ±40% of the experimental values. It is valid from 7.7MPa at 20°C to 21MPa at 68≤T≤100°C in the low-pressure range, and from 80MPa at 20≤T≤94°C to 77.5MPa at 100°C in the high-pressure range. The model can be used only for triacylglycerols of fatty acids containing mostly 18 carbon atoms, including triolein. Statistical analysis suggested that k depends on ρ and that ΔH depends on T.