Study of light wavelength on the oxidative stability of Jatropha biodiesel

The oxidative stability of Jatropha biodiesel after exposure to different wavelengths of visible light was studied and kinetic analysis of the oxidation process was carried out. The results showed that the induction period of Jatropha biodiesel was 5.12 h and visible light at different wavelengths affected the oxidation of biodiesel differently. Effect of oxidation was the strongest in the purple, where the induction period was reduced to 2.65 h. The red had the weakest effect on biodiesel oxidation, and the induction period was reduced to 4.61 h. Acid value detection, component analysis and UV characterization of biodiesel oxidized by visible light at different wavelengths. The results showed that with the decrease of light wavelength, the acid value of the biodiesel increased from 0.2577 mg KOH/g to 0.3438 mg KOH/g and the content of methyl linoleate containing two carbon–carbon double bonds decreases. UV characterization results showed that the absorption peak absorbance of conjugated double bond of Jatropha biodiesel oxidized by purple light was 5.282, while the absorption peak absorbance of conjugated double bond of Jatropha biodiesel oxidized by red light was only 2.877, and purple light was helpful to stimulate the generation of conjugate double bond. The kinetic analysis results showed that the different wavelengths had different rates of biodiesel degradation. Purple light has the fastest oxidation rate. The oxidation rate constant k1 was 0.06011, the reaction order was n = 1, and the minimum activation energy of the oxidation reaction process was 19.79 kJ·mol−1.