Soap stock is obtained as a by-product of the chemical neutralization of oils and fats. This stock could be split into fatty acids and water through acidification with strong acids like sulphuric or hydrochloric acid. During the separation phase the phosphatide has a significant effect on the splitting process, specifically during the formation of stable emulsions. This could be prevented in a large extent with secondary saponification.
For this specific reason, the soap stock is exposed to higher than normal temperatures and pressures. During the reaction time under these types of conditions, a portion of the phosphatide are produced as by-products of the neutral oil in the soap stock saponify. After saponification, dilution water may be added in the intermediate tank before the soap stock is actually conveyed to the splitting process. Inside the splitting tank, the pH value is reduced with the addition of a tough acid. The soap stock breaks down into fatty acid and water, which are then distributed into a static decanting vessel. The split fatty acid might be directly processed. The acid water is then conveyed to a fat separator with an upstream flotation chamber. The de-fatted water is finally neutralized along with caustic soda.