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 14-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.