Extraction of soybean oil using ethanol and mixtures with alkyl esters (biodiesel) as co-solvent: Kinetics and thermodynamics

- An ethanolic extraction of soybean oil using biodiesel as co-solvent is proposed.
- The extractions were improved at higher temperatures and solvent to soybean ratios.
- Higher extraction rates were achieved for higher biodiesel contents in the solvent.
- Overall extraction curves were better correlated by second-order and mass transfer models.
- This process showed to be endothermic, irreversible and spontaneous.

The kinetics and thermodynamics of soybean extraction using ethanol and ethanol + alkyl esters mixtures (biodiesel) as co-solvent were investigated. The extraction parameters investigated were temperature (25, 40 and 55 °C) and biodiesel to ethanol mass ratio. The extractions were carried out in batch mode at a fixed solvent to soybean mass ratio (4:1). Three different kinetic models were used to correlate the overall extraction curves, namely a first-order, second-order, and a mass transfer model based on Fick's Law. The mass transfer model presented a mean absolute relative deviation of 4.7%, while de first and second-order models showed values around 10.1% and 4.4%, respectively. From the experimental results obtained, it was observed that higher temperatures affected positively the extraction yields. Furthermore, higher mass ratio of biodiesel to anhydrous ethanol provide higher extraction yields, at temperatures of 25 and 40 °C. At 55 °C, the extraction yields were not improved when adding the biodiesel as co-solvent to the anhydrous ethanol. On the other hand, using hydrated ethanol as solvent resulted in lower extraction yields, so higher amounts of biodiesel were necessary to reach the same levels of extractions performed using anhydrous ethanol. The thermodynamic analyses showed that both ΔH° and ΔS° are positive for this process, while negative values of ΔG° were found, that means the process evaluated is characterized as endothermic, irreversible and occurs spontaneously.