Extraction of borage seed oil by compressed CO2: Effect of extraction parameters and modelling

The extraction of borage seed oil using compressed CO2 was studied on a pilot plant apparatus with the aim of optimise plant performance and collect data for scale-up purposes. The seeds were pre-treated by flaking them into 0.3 mm flake prior to the extraction tests for achieving quantitative recovery of the oil. Effects of extraction pressure (200–300 bar) and temperature (10–55 °C), solvent flow rate (7.5–12 kg/h) and bed length (0.25–0.50 m) were examined. As a major factor, oil solubility in CO2 controlled the extraction rate until 70% of the oil had been extracted, and then intraparticle resistances appear to have dictated the rate of extracting the remaining fraction of the oil. A mathematical model, based on the evidence that the oil is partially exposed to solvent after the pre-treatment of the seed, was used to correlate the experimental data. Average deviation between measured and calculated oil yields was 8%. The best-fitting values of the model parameters, namely fraction of readily accessible oil (fk), solid phase mass transfer coefficient (ks) and specific interfacial area (a) were 0.7, 2.8 × 10−7 m/s and 350 m−1, respectively.