Walnut oil deacidification by liquid–liquid extraction with ethanol in a single- and multistage crossflow process

Abstract

Liquid–liquid extraction of vegetable oil with ethanol predominantly removes the components having the greatest affinity for ethanol, such as free fatty acids responsible for the acidity of oil, but also some contaminants such as phthalates. The aim of this work is to study the effect of several operating parameters on the deacidification process: the initial free fatty acid content in oil (3.1, 5.8, 7.6 and 11.7% OA eq.), the ethanol-water content in solvent (70.0/30.0, 80.0/20.0, 87.8/12.2 and 95.6/4.4 g/g), and the oil/solvent ratio (0.50, 0.75 and 1.00 g/g). The economic assessment of the deacidification based on the costs of distilling solvent and neutral oil loss showed that the use of solvents containing 82 to 90 wt.% of ethanol enables to achieve a trade-off between efficiency of the extraction of free fatty acid and the neutral oil losses. A three-stage crosscurrent extraction using a solvent at 88.6 wt.% of ethanol (global solvent/oil ratio: 8.0 g/g) reduced the free fatty acid content from 5.8% OA eq. (in crude walnut oil) to 0.3–0.4% OA eq. with a loss of 4.0% of neutral oil mass. Regarding the extraction of phthalates, our results showed that the lower the water content in the hydroethanolic solvent, the more efficient the extraction of butyl benzyl phthalate (BBP). Moreover, extraction with ethanol has successfully reduced the BBP content below the current regulatory limit.