1. Optimized antioxidants for biodiesel Richard A. Larson and Karen A. Marley Department of Natural Resources and Environmental Sciences

2. Soybeans Rapeseed Oilseeds = high in lipids (triglycerides)

3. Methyl linoleate Methyl stearate Methyl oleate Glycerol Hydrolysis of triglycerides with methanol and base affords fatty acid methyl esters (FAMEs) and the by- product, glycerol. + Unsaturated triglyceride

4. Biodiesel defined B(n) = Fraction of biodiesel in fuel. B100 = Pure biodiesel B20 = 20% biodiesel, 80% petroleum biodiesel.

5. Biodiesel is susceptible to oxidative damage upon storage Unsaturated FAMEs are readily attacked by oxygen (linolenic [3 double bonds]> linoleic [2]> oleic [1]) Oxidized products are deleterious to engine performance

6. (N. Li, Biodiesel Magazine, June 2007)

7. Free radical chain mechanism of lipid peroxidation

8. Free radical kinetics Free radical chain reaction kinetics (Peroxide concentration)

9. Types of antioxidants Peroxyl radical quenchers (chain breakers) Peroxide destroyers (reducing agents) Metal chelating agents Acid neutralizers

10. Chain-breaking antioxidants (radical quenchers) Vitamin E (alpha-tocopherol)

11. Peroxide destroyers (reducing agents) Phosphine Phosphine oxide

12. Peroxide analytical method B. Mihaljevic et al., Free Radical Biol. Med. 21:53 (1996) ROOH + Fe 2+ + H + ROH + Fe 3+ Fe 3+ + 5 SCN - Fe(SCN) 5- = 510 nm

13. Propyl gallate was the most effective chain-breaking antioxidant (as shown by inhibition of peroxide formation) for biodiesel B100 SME = soy methyl ester (B100); Trolox = a Vitamin E analog; AP = ascorbyl palmitate; PG = propyl gallate

14. Tests were run at 60C because propyl gallate rapidly decomposed at higher temperatures Also observed by Dittmar et al., 2004 (Chem.-Ing.Technol. 1167-1170).

15. A peroxide destroyer (triphenylphosphine, TPP) alone was of limited effectiveness. However, note the great improvement when propyl gallate (PG) was added. This is a waste oil-derived B100 with a high initial peroxide value.

16. A different B100 with a very high initial peroxide value was stable for more than 70 days (!) at 60C when treated with stoichiometric TPP and 1 mM PG LT = low [TPP] (0.5 equivalent); HT = high [TPP] (1.0 equivalent)

17. Conclusions Propyl gallate (PG) was the most effective chain-breaking antioxidant tested. This agrees with similar studies reported in the literature (Loh et al., 2006). A peroxide destroyer (triphenylphosphine, TPP) was of limited effectiveness except when added in an equivalent amount to peroxide concentration. Stoichiometric TPP plus a small amount of PG was very effective in preventing B100 oxidation over a long time at 60C. Initial peroxide concentration is an important parameter for assessing biodiesel stability.

18. Acknowledgments Illinois Sustainable Technology Center for financial support and for providing waste-oil derived B100. Columbus Foods for purified B100. The UIUC Intsoy program also provided B100. W. Zhang, N. Holm, K. Rajagopalan and J. Scott for helpful discussions.