Soybean and Soybean/Beef-Tallow Biodiesel: A Comparative Study on Oxidative Degradation During Long-Term Storage

Vegetable oils are the primary raw materials used in biodiesel production; however, they usually present oxidative stabilities inferior to the EN 14214 specifications. An alternative to improve the oxidative quality of vegetable oil biodiesel is blending it with animal fat biodiesel. In this paper, we studied the oxidative degradation of soybean/beef-tallow biodiesel (SB) 70/30 and 50/50 (w/w) during long-term storage. Soybean biodiesel (SO) was used as a control sample. The biodiesel samples were stored for 350 days and analyzed periodically via oxidative stability, tocopherol content, peroxide value, polar compounds, and kinematic viscosity. The results showed that SB 70/30 and 50/50 biodiesel samples presented higher oxidative stabilities than SO biodiesel. Additionally, the blends met the limits proposed by EN 14214 for oxidative stability (8 h). During long-term storage, the SB biodiesel showed greater resistance to oxidative degradation, which was indicated by the lower formation of hydroperoxides and polar compounds. Similarly, the decline in the tocopherol content was slower in SB biodiesel. Blends of soybean and beef-tallow biodiesel at levels of 70/30 and 50/50 are, therefore, proper alternatives to improve the oxidative quality of this biofuel.