Membrane and additional adsorption processes for quality improvement of used frying oils

The main focus of our study was to improve the quality of used frying oils for recycling as edible oils. Experiments were conducted with hexane-diluted, used frying oils in a batch membrane cell using a nonporous polymeric composite membrane for improving permeate (oil) flux. The oil flux increased by 9- to I 4-fold as compared to the permeate flux obtained with undiluted oil. Furthermore, the quality of processed oils was comparable with membrane-processed, undiluted oil. The maximal oil flux was obtained when the weight ratio of oil to oil-hexane retentate (feed) was 0.47 in the process stream. Examination of successive fractions of permeate revealed that membrane performance was not affected by variation in the feed quality. Although the membrane process improved the overall quality of used frying oil, it was not effective in reducing FFA and oxidation products. By combining membrane and adsorption processes, the quality of the used frying oil could be improved to the level of fresh frying oil. Silica gel along with a small amount of magnesium oxide gave the best results in the adsorption process. Combined membrane and adsorption processes seem to be the appropriate approach for the complete regeneration of used frying oils.