Esterificação e transesterificação em presença de complexos de titânio e zircônio.

Abstract

Alkyl esters, identified as biodiesel, are obtained by transesterification of vegetable oils or by esterifications of fatty acids. The transesterification process, to produce biodiesel, consists of a chemical reaction of vegetable and animal oils or fats with the common alcohol (ethanol) or methanol, in the presence of a catalyst (Brönsted acid or base). By esterification, biodiesel results of the reaction of fatty acids with an alcohol, forming monoesters and water. This reaction can be catalyzed by species as Brösnted acids. Titanium and zirconium compounds, mainly the alcoxides, are known as good catalysts in transesterification and esterification reactions. However, these systems are sensible to the humidity and impurities of the reactional medium. In this context, this work presents results of the synthesis of titanium and zirconium compounds, exhibiting stability and tolerance to impurities present in the reactional medium. Complexes exhibiting the formule M (n-butoxide)x(malthol)4-x, where M=Ti or Zr, had been synthesized by the reaction of M (n-butoxide)4 with the ligand 3- hydroxi-2-methyl-4-pirone, during 48 hours, in THF. They had been washed with THF, dried and characterized. By spectroscopy in medium infra-red region, was determined that the complexation of the ligand occurs by the ά-hydroxyquinone deprotonated fragment. The most remarkable differences between the ligand spectrum and those of the complexes were the disappearance of the OH stretching mode at 3262 cm-1 and the shift of C=O stretching from 1656 cm-1 in the pyrone to ca. 1610 cm-1 in the pyronate complexes. The esterification reactions conduced in the presence of the metallic precursors (M(n-butoxide)4), (M=Ti or Zr), had confirmed the sensitivity of catalysts. In the reactions conduced in the presence of complexes M(nbutoxide) x(maltol)4-x (M=Ti or Zr) yields among 15 and 92 % (% FAMEs) were obtained, according of reactional conditions used.