Production Process of Epoxidized Soybean Oil via Performic Acid Oxidation
Epoxidized Soybean Oil (ESO) is a pale yellow, viscous oily liquid with a freezing point below 5°C and a water solubility of less than 0.01% (25°C). It is the most widely used non-toxic plasticizer and stabilizer for polyvinyl chloride (PVC). ESO exhibits good compatibility with PVC resin, low volatility, and low migration tendency. It possesses excellent thermal stability, light stability, water resistance, and oil resistance. ESO imparts good mechanical strength, weather resistance, and electrical properties to finished products. Being non-toxic, it is internationally recognized as a chemical additive suitable for food packaging materials.
Current production methods for ESO primarily fall into two categories: solvent-based and solvent-free processes. Specific production techniques include performic acid oxidation, ion-exchange resin catalysis, aluminum sulfate catalysis, percarboxylic acid oxidation, and phase-transfer catalytic oxidation.
Performic Acid Oxidation Process
This process uses benzene as the solvent and sulfuric acid as the catalyst. Formic acid and hydrogen peroxide first react under sulfuric acid catalysis to generate performic acid. Subsequently, the performic acid epoxidizes the soybean oil to produce ESO.
The operational procedure is as follows: Soybean oil, formic acid, sulfuric acid, and benzene are charged into a reactor in predetermined proportions and mixed thoroughly. While stirring, a 40% (mass fraction) hydrogen peroxide solution is added slowly. During the addition, the reaction temperature is maintained near room temperature by circulating cooling water and controlling the addition rate. After the hydrogen peroxide addition is complete, stirring continues until the material temperature stabilizes or even slightly decreases without cooling, at which point stirring is stopped. The mixture is then allowed to settle and separate: the upper layer is the oil phase (containing product and benzene), and the lower layer is waste acid water.
After separating the waste acid water, the oil phase is first neutralized and washed with a 2%~5% dilute sodium carbonate solution, then rinsed with soft water until neutral. Following water separation, the oil phase undergoes distillation. The distilled benzene-water mixture is condensed and separated, allowing recovery of approximately 80% of the benzene for reuse. The residue in the reactor is subjected to vacuum distillation and then filtered under pressure to obtain the final ESO product.
This process offers fast reaction rates and low temperatures. However, it suffers from a long and complex flow path, unstable product quality (epoxy value around 5%), high production costs, significant equipment requirements, and substantial "three wastes" (waste gas, waste water, solid waste) treatment needs. Furthermore, the solvent benzene is toxic. Consequently, this method is gradually being replaced by solvent-free processes.