Oxidative degradation and corrosiveness of biodiesel

Biodiesel fuels are attracting increasing attention worldwide as an environmentally friendly fuel. Despite the numerous advantages of biodiesel compared with diesel, some studies indicate that biodiesel is more susceptible to oxidation and therefore more corrosive to metals. The research indicates that stainless steel, cast iron, galvanized steel, carbon steel, and aluminum materials are relatively compatible with pure biodiesel, whereas copper, bronze, brass, lead, tin, zinc, and iron are incompatible, decreasing the stability of biodiesel and increasing its corrosiveness. The use of synthetic antioxidant additives for biodiesel is a necessity to minimize its susceptibility to oxidation. The efficiency of a given antioxidant depends on the feedstock used for biodiesel production. In general, the effectiveness of order of antioxidants was pyrogallol > propyl gallate > Ethanox4760E > N,N'-di-secbutyl-p-phenylenediamine > 2,2'-methylene-bis-(4-methyl-6-ter-butylphenol) > 2-tert-butyl-4-hydroxyanisole and 3-tert-butyl-4-hydroxyanisole > 2-(1,1-dimethylethyl)-1,4-benzenediol [tert-butylhydroquinone (TBHQ)]similar to 2,6-bis(1,1-dimethylethyl)-4-methylphenol > 2,5-di-tert-butylhydroquinone > alpha-tocopherol. There are few studies showing the effect of inhibitors on the corrosion of metals in biodiesel. Antioxidant compounds may also act as a corrosion inhibitor, but the mechanism of action of these corrosion inhibitors is the formation of a persistent adsorbed monolayer film at the metal/solution interface. For example, the antioxidant TBHQ used in biodiesel retarded the corrosion process in copper, carbon steel, and galvanized steel, acting as a corrosion inhibitor through the formation of a protective film layer.