Thermal stability enhancement of biodiesel induced by a synergistic effect between conventional antioxidants and an alternative additive

The thermodegradation of soybean biodiesel stabilised with conventional antioxidants BHT (butylated hydroxytoluene) and PG (propyl gallate) in combination with an alternative additive based on the anthraquinone compound DHQ (1,4-dihydroxyanthraquinone) was investigated by simulating an accelerated storage process at temperatures from 85 to 110 °C. The effectiveness of different combinations of PG and BHT with DHQ were also evaluated by using the Rancimat® method. The results revealed that combinations of the conventional antioxidants and anthraquinone were more effective at imparting biodiesel stability than the individual compounds. By considering the optimum combination containing PG and BHT with DHQ, it was also determined that the final cost of biodiesel may be markedly reduced since the amount of additives used to stabilise the biodiesel can be decreased by 70-88%, requiring a lower content of conventional antioxidant in the mixture to meet the EN-14112 specification.