The increase in biodiesel production is a worldwide tendency due to petroleum scarcity and for its less pollutant usage. Due to this fuel being biodegradable, non-toxic and practically free of sulfur and aromatics, emits a small amount of harmful chemical compounds in its combustion process when compared to fossil fuels. Biodiesel is a biofuel which can be produced from vegetal oils and animal fats. Moreover, residual oils have become a sustainable alternative to biodiesel production once the incorrect disposal of these substances have caused concerning environmental problems in the whole world. Nonetheless, the problematic involved in the usage of this raw material is its high acidity index, which comes from the exposure to high temperatures. This produces a highly acidic fuel, reducing the work life of combustion engines. Therefore, this work aims to optimize the biodiesel production process from residual oil with the goal of obtaining an adequate acidity according to the Brazilian National Petroleum Agency standards. With this objective in mind, distinct tests were performed. The temperature of the transesterification reaction was varied and its effects on the acidity and heat value of the fuel were evaluated. After the analysis of experimental data, a proportional relation between transesterification temperature and acidity of the resulting fuel was obtained. The acidity was minimized when the process was carried out at 30°C without compromising the yield of the process or the heat value of the fuel.
KEYWORDS: Biodiesel, Residual cooking oil, acidity, temperature.