| Abstract: | The importance of using synthetic antioxidants to improve oxidation stability and shelf life of biodiesel is today generally accepted. In our investigations which started early with the development of biodiesel we have looked at the course of stability, ageing of biodiesel, and the use of synthetic antioxidants. We have shown for the first time that oxidative stability of biodiesel is lower than that of the rape seed oil from which it was produced. The natural stability of biodiesel relates mainly to the content of tocopherols which survive the transesterification process. Biodiesel freed from tocopherols has no stability and will be destroyed immediately in air. Synthetic antioxidants like BHT and the newly developed stronger “Bis‐BHT” dramatically improve oxidative stability and prolong shelf life. Biodiesel rich in polyunsaturated fatty acid methyl ester needs strong antioxidants to be sufficiently protected. The class of hindered phenolic antioxidants from which the BHT and “Bis‐BHT” derive are well suited as industrial biodiesel stabilizer because of their ready availability, sufficient effectiveness and proven safety in diesel fuel. Surprisingly, none of the approved international biodiesel and biodiesel blend specifications refer to shelf life as a quality parameter. There is no definition of shelf life available, although it is well understood that biodiesel ages and loses its oxidative stability over time. We propose to consider the time span from production until the biodiesel reaches zero oxidative stability and becomes rancid and detrimental for the engine as the “shelf life” of biodiesel. From the perspective of a customer running their car on biodiesel blends, shelf life should become a more important issue. |
