Five natural derivatives [ferulic acid (FA), lipid-soluble tea polyphenol (LTP), water-soluble tea polyphenol (WTP), sesamol (SE) and caffeic acid (CA)] were evaluated as antioxidative additives for enhancing the oxidation stability of soybean oil based biodiesel (SBO-BD). It was found that WTP, LTP, SE and CA could significantly improve the oxidation stability of SBO-BD. CA displayed the best performance in the concentration range from 500 to 1500 ppm, whereas WTP displayed the highest activeness at a concentration of 2000 ppm. For comparison, the stabilizing effect of three synthetic anti-oxidants [α-tocopherol (α-T), butylhydroxytoluene (BHT) and butylhydroxyanisol (BHA)] was simultaneously evaluated. The results showed that the effect of some natural additives (WTP, LTP, SE and CA) was better than that of synthetic additives (α-T, BHT and BHA) on the oxidation stability of SBO-BD. A possible explanation for the different effects among the tested antioxidants was given based on their molecular structures.
biodiesel; oxidation stability; antioxidant; natural derivatives; Rancimat method
