Comparative evaluation of conventional and microwave assisted epoxidation of soybean oil with citric acid, acetic acid using homogeneous and heterogeneous catalysis

Abstract

Epoxidized soybean oil was produced in this study by in situ generated peroxycitric with citric acid and hydrogen peroxide. Different production techniques were applied, namely conventional heating epoxidation and microwave-assisted epoxidation, using the Prileschajew method. Three different processes were studied in the conventional heating process: homogeneous catalysis with sulfuric acid, heterogeneous catalysis with Amberlite IR-120, and a process with no catalyst. Compared to acetic acid, citric acid is less toxic, safer for the epoxidation process, and does not require a strong acid catalyst for the reaction to occur, although oxirane oxygen content is higher when acetic acid is used as the oxygen carrier. Thermal runaway risks can be reduced by replacing acetic acid with citric acid since the latter is less volatile and more susceptible to steric hindrance. Citric acid is more acid than acetic acid, evidenced by a lower pKa, and then tends to favor ring-opening reactions once the epoxy group is produced. In the microwave heating process, epoxidation using both acetic acid and citric acid was studied. Microwave-assisted epoxidation allowed a decrease in reaction time from 2 h to 15 min when citric acid epoxidation was performed with similar resulting oxirane oxygen contents. In epoxidation with acetic acid, time was reduced from 2.3 h to 10 min in homogeneous catalysis with sulfuric acid and from 5 h to 25 min in heterogeneous catalysis with Amberlite IR-120.