Some problems involved in the water wash of neutralized vegetable oils

Summary An investigation of the removal of soap from neutralized vegetable oils by washing with water has shown that some oils are obtained practically soap‐free after only one water wash whereas the soap in other oils cannot be removed even by repeated washing. Coconut, palm, and olive oils are easily washed whereas linseed and rapeseed oils are not. Peanut, sunflowerseed, soybean, and cottonseed oils are sometimes washable and sometimes not. With unwashable oils different methods for soap determination give inconsistent results because calcium and magnesium soaps, or other naturally‐occurring compounds of these metals, are not determined to the same extent by these methods. Calcium and magnesium in the crude oils are probably combined with phosphatides or other lipids and remain to some extent in this state after neutralization. Calcium and magnesium present as soaps or as any other compound may be detected easily in crude, neutralized, and washed oils by the titration method of Wolff. Washability of neutralized oils may be improved in a number of ways; the most efficient is pre‐treatment with concentrated phosphoric acid or re‐refining with a mixture of sodium hydroxide and sodium carbonate. Either of these treatments can be applied in batch or continuous refining processes. To prevent contamination of washable oils with calcium and magnesium, soft water should be used for washing and in preparation of refining solutions.