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The sulfonated-carbon based catalyst obtained from crambe meal was successfully applied in the esterification reaction of oleic acid. The chemometric tools allowed to evaluate the significance of the parameters: time, catalyst dosage and ethanol-to-oleic acid molar ratio, as well as their interactions towards the conversion yield of oleic acid via esterification reaction. The results showed that the molar ratio had the highest influence in the conversion yield. The analysis of Responses Surfaces and desirability function indicated that is possible undergoes around 75% of oleic acid into esters from the following experimental conditions: time of 2 h, catalyst dosage of 11 wt.% and ethanol-to-oleic acid molar ratio of 18:1 (v:wt.). From the optimization of the factors, it was possible obtain a good conversion yield of oleic acid applying conditions similar or inferior to those reported in the literature. After four cycles of use, the catalyst still gave a conversion yield of 29%. The decrease of esterification yield was evaluated throughout FTIR spectra, which corroborate the losing of sulfonic groups after each reuse cycle concomitantly with the yield decreasing.
Fonseca et al. (Tue,) studied this question.