Processing vegetable oils using nonporous denser polymeric composite membranes

Membrane processing offers several advantages over conventional processes for edible oil refining. In recent years, processing solvent-extracted, screw-pressed, and used frying oils using nonporous denser polymeric composite membranes without pretreatment and addition of chemicals has been extensively investigated. In the present review, results obtained with real and model systems have been summarized and a comprehensive explanation is provided on the mechanism of rejection and differential permeation of oil constituents. Phospholipid-TG and pigment-TG systems are construed as conventional solute-solvent systems, and tocopherol-TG and FFA-TG systems are treated as liquid mixtures exhibiting differential permeability. Dense membrane theory appears more applicable than the reverse osmosis theory in qualitatively explaining the differential permeability of liquid constituents of the oil. Membrane processing of oils appears to have the potential to be a one-step process, especially for screw-pressed oils, in producing a premium-quality product. However, the development of suitable membranes that enable higher fluxes is necessary for industrial adoption of this technology.