Epoxidation of waste used-oil biodiesel: Effect of reaction factors and its impact on the oxidative stability

Epoxidation of waste used-oil biodiesel (WUO-B) was performed to test the feasibility of properties improvement. The effects of the reaction temperature (30–50 °C) and time (2–12 h), molar ratio of H2O2: HCOOH (1: 7 to 1: 1) and the stirring rate (100–300 rpm) on the level of unsaturated carbon bond conversion and the epoxy compound selectivity were identified using a 2k (two levels) factorial design. Besides epoxy biodiesel as the main product, only one by-product, hydroxyl-biodiesel, was generated. The conversion of unsaturated carbon bonds was positively affected by the molar ratio of H2O2: HCOOH and the stirring rate, while the reaction temperature and time had no significant affect (in the investigated ranges). In contrast, with respect to the epoxy compound selectivity, the stirring rate had a positive effect, while both the reaction temperature and time each had a negative effect. The oxidative stability (OS) of the epoxy waste used-oil biodiesel (EWUO-B) revealed a linear relationship to the unsaturated carbon bond conversion level, but no significant relationship to the epoxy compound selectivity. EWUO-B prepared from a 1: 1 molar ratio of H2O2: HCOOH at 50 °C with stirring at 300 rpm for 12 h exhibited a higher OS (around 37.85 h) than that of the WUO-B. Except for the cold flow properties and methyl ester content, all other key properties of the EWUOB were within the specifications of the EN14214 standard set by the Department of Energy Business.