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-sec-butyl-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)]∼2,6-bis(1,1-dimethylethyl)-4-methylphenol>2,5-di-tert-butyl-hydroquinone>α-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.

RESUMOO Brasil é o segundo país produtor de biodiesel e a demanda por este biocombustível deve aumentar nos próximos anos. Considerando a importância do biodiesel para a matriz energética do Brasil e do mundo, este trabalho teve como objetivo fazer um levantamento do estado da técnica de produção do biodiesel levando-se em conta os depósitos de patentes. A China é o país com maior número de depósitos de patentes seguida pelos Estados Unidos e Alemanha. A reação de transesterificação através da catálise alcalina homogênea é a tecnologia mais comum de produção de biodiesel. No entanto, em função de suas desvantagens como a difícil purificação do biodiesel e a geração de efluentes, outras rotas vem sendo propostas, como a catálise heterogênea e o uso do álcool supercrítico.Palavras chave: Produção de Biodiesel. Processos. Patentes. ABSTRACTBrazil is the second producer of biodiesel and the use of this biofuel should increase in coming years. Considering the relevance of biodiesel for the energy matrix of Brazil and of the world, this study aimed to survey the state of the art of biodiesel production taking into account the patent applications. China is the country with the highest number of patent applications followed by the United States and Germany. The transesterification reaction by homogeneous alkaline catalysis is the most common technology for producing biodiesel. However, due to its disadvantages like difficult purification of biodiesel and effluent generation, other routes have been proposed, such as heterogeneous catalysis and the use of supercritical alcohol.