Soapstock
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Contents
Description
As mentioned above, crude edible oils contain different types of undesirable substances. The quantity of free fatty acids (ffa) is about 0.5 to 0.7%. The removal of ffa (< 0.1% in refined oil) can be achieved either by caustic neutralisation in a chemical refinery or by distillation in a physical refinery.
The chemical neutralisation consist of an addition of caustic soda (at 75-110ºC) to saponify the ffa in order to precipitate soaps in the heavy aqueous phase and remove the heavy phase, called soapstock, by using gravity or centrifugation.
Block diagram of the physical and chemical refining
Source: Edible Oil Processing,R.S.; The ACVS Lipid Library
Valorisation techniques
Soapstock always requires subsequent treatment. The method of treating soapstock is known as splitting. The soapstock is split into fatty acids (acid oil) and wash water by acidification with sulphuric acid. The soapstock can be sold to a third party and in case of an integrated plant, there is an option to recycle it into the process.
References
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