substantial benefits and economies are realized in a process for obtaining free fatty acids from soap stock by first acidulating the soap stock to liberate fatty acids from the soap present , separating the resulting first acid oil and aqueous saline phases , recovering free fatty acids by vacuum distillation from this first acid oil phase , saponifyng the glyceride - rich still residue to generate additional soap , acidulating the saponified product to liberate additional fatty acids therefrom and separating the resulting second acid oil and aqueous saline phases . these additional fatty acids can be recovered as free acids by vacuum distillation from the separated second acid oil phase . it is sometimes advantageous to neutralize residual mineral acid in the first acid oil phase before distillation .