Research of Acidulation Parameters Affecting the Extraction of Acid Oil from Rapeseed Soapstock

The problems of climate change, especially the greenhouse effect caused by transport exhaust gas emissions, make the issue of finding alternatives to fossil fuels increasingly urgent. One such alternative is biodiesel. The valorisation of industrial biomass based by-products such as soapstock, generated during vegetable oil refining, supports both waste reduction and sustainable biodiesel production. This study investigates the acidulation of rapeseed soapstock to obtain acid oil – a mixture of free fatty acids and glycerides suitable for advanced biodiesel synthesis. The effects of acid type (concentrated sulphuric acid, 50 % sulphuric acid, 25 % citric acid), pH (2–7), and temperature (20, 45, 70 °C) on purified acid oil yield and phospholipid removal were examined under controlled laboratory conditions. Rapeseed soapstock was acidified till defined pH using chosen acid at set temperature. Then extraction with cyclohexane followed by purification with cold acetone yielded acid oil. The optimal acidulation parameters were achieved with concentrated sulphuric acid at pH 5 and initial soapstock temperature around 20 °C, producing 34.7 % of purified acid oil. These results demonstrate that optimized acidulation of rapeseed soapstock provides a cost-effective route for converting industrial waste into a viable feedstock for biodiesel synthesis, contributing to circular bioeconomy principles and the reduction of fossil fuel dependence.