Ultrafiltration of vegetable oils - Degumming by polymeric membranes

In this work, four different membranes synthesized in our laboratories have been tested for their permeation flux, phospholipid retention and stabilit y in hexane during membrane degumming of crude soybean oil. Membranes were made of three different polymeric materials, i.e. Polyvinylidenfluroide (PV DF), Polyethersulfone (PES) and Polysulfone (PSf), and prepared by the phas e inversion process. Raw membranes were characterized by the molecular weig ht cut-off (MWCO) and the water permeability, L-h,L-w. Ultrafiltration (UF) of an oil-hexane miscella was performed in a stirred dead-end UF cell, pre ssurized with N-2. All membranes were soaked in solvent of decreasing polar ities to minimize the action of solvent on pore size. Each membrane was tes ted with pure solvent first and the membrane permeability to pure hexane, L -h,L-h, was determined. The degumming experiments were carried out with a 2 5% crude soybean oil-hexane mixture right after the pure solvent test. The ratio (L-h,L-h/L-h,L-w) is used to indicate the degree of change in membran e structure due to the organic solvent. Results show that PVDF is more stab le with hexane than PES and PSf In addition to membrane material, pore size influences membrane stability also. Small pore sizes give more stable memb ranes. During degumming, a sharp decrease in the permeate flux with lime oc curs at the beginning of the permeation process. This behaviour is explaine d in terms of concentration polarization effects and internal fouling. PES and PSF membranes have a larger initial decrease than PVDF ones. (C) 2001 E lsevier Science B.V. All rights reserved.