Catalytic epoxidation and subsequent conversion of waste cooking oil to dihydroxystearic acid (DHSA) using a synergistic acid system of citric acid and sulfuric acid

Abstract

The catalytic epoxidation and subsequent conversion of waste cooking oil (WCO) to dihydroxystearic acid (DHSA) were investigated using a synergistic acid system consisting of citric acid and sulfuric acid via an in situ peracid mechanism. The study aims to valorize WCO as a sustainable feedstock for bio-based chemical production while addressing limitations in selectivity and process efficiency. A synergistic acid system consisting of 5 g citric acid and 1.2 g sulfuric acid was employed as the catalytic medium for the epoxidation of waste cooking oil. The effects of reaction temperature (60–80 °C) and acetic acid molar ratio (0.5–1.5 mol) on relative oxirane content (RCO) were evaluated. The optimum epoxidation condition was achieved at 70 °C, while a molar ratio of 0.5 provided the highest RCO, indicating favorable epoxide formation prior to ring-opening. FTIR analysis confirmed the formation of oxirane rings and their subsequent conversion into vicinal diols, validating DHSA production. The simulated results showed good agreement with the experimental data, with a low sum of error value of 0.2083, indicating satisfactory predictive accuracy of the developed model.