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Oxidation and Polymerization of Biodiesel from Vegetables Oils under Accelerated Oxidation

When used as a fuel, the oxidized products of biodiesel (BD) from the degradation of organic matter may cause some problems in the engine and injection parts. The heating of vegetable oils can cause complementary decomposition reactions, which can lead to the formation of polymeric compounds. The oxidation stability of biodiesel also depends on the fatty acid composition. In this study, biodiesels were examined to determine the oxidation characteristics rapidly at 95 ℃ under accelerated oxidation conditions using the ASTM method D 2274 as a demonstration of long-term storage for 16 weeks. An analysis of biodiesel and after accelerated oxidation revealed an increase in the density, kinematic viscosity, and total acid number (TAN) with increasing oxidation time. The reduction changes in the unsaturated fatty acid methyl ester (FAME) content in biodiesel showed a similar trend for C18:2 ME and C18:3 ME. Higher molecular polymer materials produced after accelerated oxidation can affect the vehicle. To identify these polymers materials, the reaction was carried out at 180 °C with accelerated oxidized biodiesel. A model reaction was performed with a C18:2 ME, which can be polymerized at high temperatures. The biodiesels were polymerized after accelerated oxidation at 180 °C for 72 hr. followed by purified flash chromatography to give the FAME polymer product. The product was identified by 1H-nuclear magnetic resonance spectroscopy, normal phase high performance liquid chromatography (HPLC) with atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) for structural analysis. At 180 ℃, thermal dimerization of the FAME occurred due to the Diels-Alder reaction. The dimer and epoxy-dimer of C18:2 ME via the Diels-Alder reaction were identified by HPLC-APCI MS.