A Study of the Catalytic System H3PW12O40/Quaternary Phosphonium Salts for the Epoxidation of Fatty Acid Methyl Esters—The Effect of the Molar Ratio of Hydrogen Peroxide to the Double Bond

In the present work, the epoxidation of fatty acid methyl esters (biodiesel or FAMEs) with an iodine number of 96.4 g/100 g and containing approximately 11% palmitic acid, 4% stearic acid, 51% oleic acid, 25% linoleic acid, and 5% linolenic acid was studied with an aqueous H₂O₂ solution and different quaternary phosphonium salts (QPSs) combined with the phosphotungstic heteropolyacid (HPA) H₃PW₁₂O₄₀ in a biphasic system. The effect of the molar ratio of H₂O₂:C=C on the epoxidation of FAMEs was investigated. The effect of the molar ratio of H₂O₂:C=C on the epoxy number (EN) and iodine number (IN) was measured. Multiple regression analysis methods were used to determine the regression model describing the influence of the various independent variables. In the results obtained, it was found that the highest yields were obtained for [P6][Phosf]. The optimum conditions for the epoxidation process with the systems used were a time range of 30 ± 4 min and a H₂O₂/double bond molar ratio in the range of 1.8 ± 0.2. The formation of epoxidised fatty acid methyl esters (E-FAMEs) was confirmed by FT-IR, ¹H NMR and ¹³C NMR analyses. In the FT-IR spectrum of the E-FAMEs, epoxy ring vibration signals were identified at 826 cm^-1. In the ¹H NMR spectrum, signals appeared in the range of 3.25-3.00 ppm, corresponding to epoxy ring formation in biodiesel, and in the range of 60-55 ppm in the ¹³C NMR spectrum.