Biodiesel Production From High Acidity Raw Materials

B.O. DALLA COSTA; M.L. PISARELLO; C.A. QUERINI

Río de Janeiro - Brasil

Congreso; ENPROMER 2nd Mercosur Congress on Chemical Engineering 4th Mercosur Congress on Process Systems Engineering; 2005

Biodiesel is an alternative fuel produced from renewable resources like vegetable oils or fats, through transesterification reaction with methanol and sodium hydroxide as catalyst. It has advantages with respect to the petroleum-based diesel such as no accumulation of carbon dioxide in the atmosphere and lower sulfur emissions. Furthermore is biodegradable and non toxic. In our laboratory we have studied the process in order to use alternative raw materials with high acidity and low cost, as waste oil, acid greases and brown greases. The high acidity of these materials does not allow the use of the conventional process of alkaline catalysis, because of the formation of soap that cause problems in the steps of washing and purification of biodiesel, and decrease of yield. The process developed consist of a first stage reaction, with sulfuric acid as catalyst, to convert the fatty acids to methyl esters and reduce the acidity, followed by the alkaline catalyst reaction. We have worked on the kinetics and thermodynamics of this reaction with different amounts of methanol and sulfuric acid, following the conversion of the reaction during the acid-catalyzed step by measuring the acidity. We also found that the esterification equilibrium constants values are similar for different raw materials, what makes it possible to design the steps of the reaction for a given initial acidity. The final product obtained by the combination of acid-alkaline catalysis meets international standards, such as ASTM specifications.