Iodine value of tung biodiesel fuel using Wijs method is significantly lower than calculated value

Abstract

AbstractThe tung tree (Vernicia fordii) is a non-edible oil plant native to southern China and was introduced in Japan in the nineteenth century. The tree produces tung oil, which is composed of approximately 80% α-eleostearic acid (9c, 11t, 13t-octadecatrienoic acid), 7% linoleic acid, and 6% oleic acid. Tung oil may be a non-edible source of biodiesel fuel (BDF) production. The iodine value (IV) is one of parameters to guarantee BDF quality, and the most common method for the determination of IV is the Wijs method. The IV can be calculated from the average molecular weight and the number of double bonds from the GC–MS data. In this study, the IVs of olive, castor, soybean, linseed, and perilla BDF using the Wijs method were found to be almost the same as the calculated IV. On the other hand, the IV of tung BDF by the Wijs method indicated a significantly lower value than that of the calculated value. To determine the cause of this discrepancy, the samples before and after halogenation using the Wijs method, were analyzed by 1H NMR. The conjugated double bond signals did not disappear, and a broad double bond signal remained in the tung BDF spectrum after halogenation. These results demonstrated that iodine, with a large atomic radius, could not react completely with the three conjugated double bonds in α-eleostearic acid. Therefore, the IV of tung BDF was significantly lower than the calculated value.