Separation of oil constituents in organic solvents using polymeric membranes

Different types of commercial nonporous (reverse osmosis and gas separation) polymeric membranes were screened for their abilities to separate FFA, MG, DG, and TG from a lipase hydrolysate of high-oleic sunflower oil after diluting it with organic solvents (ethanol and hexane). Cellulose acetate (CA) (NTR-1698) membrane gave the largest difference in rejection between FFA and glycerides and high flux in oil/ethanol mixtures. In the hexane system, the values of permeate flux and rejection were generally lower than those in the ethanol system. The silicone-polyimide composite membrane (NTGS-2100) gave the highest flux and rejections of solutes (70.2% for FFA, 94.4% for TG) in oil/hexane mixtures. In the ethanol system with the CA membrane, TG had the highest rejection (98%) followed by DG (90%) and MG and FFA (50-70%) when the oil concentration was varied from 6.3 to 45.8%. A discontinuous diafiltration process (16 batches) using the CA membrane with ethanol changed the composition of the oil from 31:28:9:32 TG/DG/MG/FFA to 65:30:1:4. The results of this study showed that oil constituents can be separated in suitable solvents using appropriate nonporous membranes.