| Transition metals have the ability to catalyze free radical autoxidation of unsaturated fatty acid methyl esters (i.e., biodiesel). The catalytic effects of the eight period IV transition metals: V, Cr, Mn, Fe, Co Ni, Cu and Zn in soybean oil and cottonseed oil-based biodiesel are investigated. All metals produced a reduction of the induction period of biodiesel, although there are considerable differences in their catalytic capacity. The amount of reduction is a function of metal selected, the concentration of the metal and the feedstock of the biodiesel. A linear model describing the algebraic relationship between metal concentration and induction period was devised. A least squares fit was used to fit a curve to the induction period data. Good results were only achieved after eliminating one of the free radical termination reactions in the equation of the linear model. This implies that the high temperature of Rancimat run under DIN EN 14112 suppresses one free radical termination reaction and calls into question whether or not this test represent "real world" biodiesel oxidation. |
