Heterogeneous acid catalyst based on sulfated iron ore tailings for oleic acid esterification

Abstract

In this work, heterogeneous acid catalysts based on sulfated iron oxide produced from mining tailings were prepared by different processes, i.e. ammonium sulfate by simple grinding, (NH4)2SO4 aqueous impregnation and sulfuric acid impregnation, all treated at 500 °C. The materials were characterized by Mössbauer and Raman spectroscopies, FTIR, XRD, SEM, pyridine adsorption FTIR and potentiometric titration. The main mineral phases found were hematite and quartz and it was observed a great increase in the acidity of the materials produced due to the presence of sulfate groups. The synthesis with sulfuric acid was the most efficient process due to the formation of a greater amount of dispersed acid sites (density 0.1211 mmol g−1). The materials were used in esterification reactions. Ester production using 5 wt% of catalyst based on acid synthesis, 1:15 oleic acid:methanol molar ratio, 120 °C and 4 h led to conversions of 100%.