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In the process of making soap from used frying oil, I need to purify the oil.

I filtered the cooking oil but I also want to remove the polar compounds that are formed during frying : free fatty acids, monoglycerides, diglycerides.

To do so, I've seen that I can separate the polar compounds from the oil using a salt water solution (sources : 1, 2). The process is slightly different in the 2 sources but it always consist of mixing salt water in the oil and letting it rest until water and oil separates, and that impurties will be in the salt water.

I understand we use water so that it can "catch" the polar compounds from the oil, but what could be the role of the salt in this process ?

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    $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Sep 5 '21 at 19:24
  • $\begingroup$ Salt can increase solubility of some proteins: fac.ksu.edu.sa/sites/default/files/bch_332_lectures_3_and_4.pdf $\endgroup$ Sep 5 '21 at 20:25
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    $\begingroup$ Search the concepts of salting-in and salting-out. $\endgroup$
    – M. Farooq
    Sep 5 '21 at 20:25
  • $\begingroup$ So we have here a salting-in process ? In the meantime, I found this article that says that adding salt allows to reduce the interfacial tension beetween water and oil. This also seems good for mixing the 2 more easily.. $\endgroup$
    – Raphael
    Sep 5 '21 at 21:10
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    $\begingroup$ Additionally, the two phases can layer back easily $\endgroup$
    – Alchimista
    Sep 6 '21 at 8:34

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