Deacidification of model vegetable oils using polymeric membranes

Selectivity of polymeric hydrophobic nonporous and hydrophilic nanofiltration (NF) membranes was assessed for the deacidification of model vegetable oils with and without addition of organic solvents. In the model undiluted system, oleic acid permeated preferentially over triacylglycerols in the nonporous membrane, over a wide range of concentrations (˜5–70%). The effect of oleic acid concentration on selectivity indicated that the solubility of triacylglycerols in oleic acid played a role in determining the selectivity, besides the solubility and diffusivity of the permeating components. Dilution with hexane improved oil flux by 14-fold; however, membrane selectivity was completely lost as both triacylglycerols and oleic acid permeated along with the solvent, which clearly showed that the solvent played a greater role than the membrane. Processing of the model oil after diluting with acetone showed that oleic acid was retained less than triacylglycerols by the NF membrane, resulting in higher selectivity (7), indicating its potential. However, the selectivity decreased during successive runs, owing to the gradual loss of hydrophilicity due to polarity conditioning of the membrane. The differences in molecular size, solubility, diffusivity and polarity between triacylglycerols and oleic acid appear insufficient for achieving direct deacidification in terms of reasonable selectivity and throughput with these two membranes. Direct deacidification using membranes still remains as a challenge.