(644d) Phase-Transfer Catalysed Epoxidation of Soybean Oil Using Hydrogen Peroxide and Supercritical Carbon Dioxide

Epoxidized vegetable oils are the product of vegetable oil epoxidation reactions. Since the epoxidized vegetable oil is a nonpoisonous plasticizer, it has been wildly used in the plastic packaging of food and medicine. Among the various epoxidized vegetable oils, the application of epoxidized soybean oil is broader than others. Nowadays, it's the third largest category of plasticizers. However, there are serious pollution problems in most of the conventional processes of soybean oil epoxidation.

In this paper, supercritical carbon dioxide and hydrogen peroxide was used in the epoxidation for exploring a clean and efficient process. Supercritical carbon dioxide would be both a solvent and reactant in combination with aqueous hydrogen peroxide, which made the epoxidation be possible through the formation of peroxycarbonic acid as the intermediate oxidizer.

Soybean oil epoxidation was performed in a biphasic system composed of a supercritical CO2/oil phase and an aqueous H2O2 phase. The epoxidation occurred in the aqueous phase. Therefore, the transfer of soybean oil into the aqueous phase is the rate-control step. In order to increase the solubility of soybean oil in the aqueous phase, several phase transfer catalysts was used in this reaction. Adding of NaHCO3 as the stabilizer of H2O2 and the phase transfer catalyst, the conversion of soybean oil increased from 1.88 % (without additives) to 12.08 % (with NaHCO3 and SDBS).

The experimental results provided the evidence of the existence of peroxycarbonic acid, and confirmed that peroxycarbonic acid could make soybean oil be epoxidized. The suitable reaction conditions were determined as 20h in CO2 at 40ºC and 15MPa. The reactant molar ratio (soybean oil:H2O2) was 1:2. The mass ratio of NaHCO3 and H2O2 aqueous solution was 0.05:1. The mass ratio of phase transfer catalyst and soybean oil was 0.01:1.