Preparation Of Industrial Oleic Acid From Soy Acidic Oil

Soy soap stock is a by-product with predominant compostion of neuter oil and soap produced from the soybean oil refineries. The object of this study is to prepare of soy oleic acid from the acidic oil, which was made from soap stock by acidification with sulfur acid, followed by hydrolysis, distillation and emulsification separation.Effect of different catalysts on hydrolysis of soy acidic oil (SAO) under normal pressure was studied. Results showed that sodium dodecylbenzene sulfonate (LAS) was very active to catalyze the hydrolysis of the SAO. After orthogonal experiment, the optimal parameters for hydrolysis of the SAO was: amount of LAS 1.5 % (w/w, oil), hydrolysis time 7 h, concentration of sulfur acid 10 % (w/w, water), weight ratio of oil to water 2:1. The acid value of hydrolyzed SAO reached 185 mg KOH/g that met the need for the distillation by one-step hydrolysis under this optimal condition. Compared with the raw material, soy fatty acid mixture obtained by the distillation under vacuum had lower content of unsaturated fatty acid, but higher content of saturated one.After compared of catalysis activities of metal oxides with alkalis, potassium hydroxide was selected as the catalyst for the medium pressure hydrolysis of the soy acidic oil. Based on one-way factor experiment, hydrolysis temperature, time and amount of potassium hydroxide added were major factors impacting hydrolysis, By using the method of response surface with the index of the acid value of the hydrolysis, The optimal hydrolysis parameters obtained under medium pressure were following: temperature of reaction of 240℃, hydrolysis time of 7 h and amount of potassium hydroxide of 4% (w/w, oil), leading the yield of acid value of 189.5 mg KOH/g(crude fatty acid).Emulsification was introduced to separate the soy oleic acid from the fatty acid mixture. Amount of emulsifier, salt and water were selected to the impact factors. Results showed the optimal data:amount of emulsifier of 2.3% (w/w, fatty acid mixture), salt of 1.2% (w/w, fatty acid mixture) and water of 1.7 times of fatty acid mixture, leading to the yield of soy oleic acid of 55.0% with the iodine number of 130.0 g I₂/100g, qualified water content and color.Hydrolysis under normal pressure, distillation and emulsification separation were...