Utilização de um rejeito de minério de ferro no desenvolvimento de um catalisador heterogêneo ácido para a síntese de biodiesel

Abstract

In this work, a heterogeneous acid catalyst based on sulfated iron oxide was produced for the esterification of oleic acid with methanol. An iron mining waste was used as an iron oxide source. The catalysts were prepared by three different processes: dry synthesis with ammonium sulfate, wet synthesis with ammonium sulfate solution and acidic synthesis with sulfuric acid solution. Thereafter, the materials were calcined at temperatures of 300, 400, 500 and 600°C. The produced catalysts were characterized by Mössbauer spectroscopy, X-Raydiffraction (XDR), infrared spectroscopy (IR), Raman spectroscopy, scanning electron microscopy (SEM), pyridine adsorption infrared spectroscopy and potentiometric titration. The results obtained in the characterization techniques and in the catalytic tests indicated that the materials calcined at 500°C showed higher activity, and the acidic synthesis with sulfuric acid solution was the most efficient process due to the formation of a greater amount of dispersed acidic sites. In the esterification reactions, the best reaction conditions were 10% ofcatalyst, oleic acid:methanol molar fraction 1:60, temperature of 120°C and reaction time of 8 hours for the materials produced by the dry synthesis and the wet synthesis and calcined at 500°C, yielding conversion values of 98 and 93%, respectively. For the material produced by acid synthesis and calcined at 500°C, the best conditions were 5% of catalyst, 1:15 oleic acid:methanol molar fraction, temperature of 120°C and reaction time of 4 hours, yielding the conversion valueof 100%. The obtained results indicate that the heterogeneous acid catalysts produced are efficient and promising in the esterification reactions of oleic acid for the production of biodiesel.