Estudo comparativo da utilização do pentóxido de Nióbio e das lipases imobilizadas em Nb2O5/PVA como catalisadores na síntese de oleato de etila

Abstract

Since the mid-twentieth century, for economic and environmental reasons, many researchers and some industries invest in the development of synthetic technologies that are environmentally favorable, generating less toxic wastes and economy of energy. The biodiesel has the function of substitute totally or partially the petroleum diesel, because it is a renewable biofuel, biodegradable, less toxic and generates less greenhouse effect gases. One of the process used to obtain the biodiesel consist in the esterification of fat acids with alcohol, and this process can occur by catalysis homogenous, heterogeneous or enzymatic. The biocatalytic process using lipases has arouse interest, because this enzymes have vantages in comparison with the chemical process as the fact of present high selectivity, act in mild conditions and minimize the lateral reactions. In the heterogeneous catalyst class the niobium pentoxide (Nb2O5) stands out, by having surface properties, as Bronsted-Lowry acidity and high surface area, which capacity as an excellent catalyst in chemical reactions and also as support for others catalysts. This paper has the objective test the efficiency of the heterogeneous and enzymatic catalysis in the synthesis of ethyl oleate from oleic acid and ethanol. For the enzymatic catalysis were uses the lipases Aspergillus niger (AS), Candida rugosa, (AY) and Rhizopus oryzae (F-AP) immobilized in niobium pentoxide compounds and PVA. The relation of oleic acid and ethanol in the analyses was 1:1, and the reaction temperature was of 40º C, aliquots was retired after 3, 6, 12 and 24 hours of reaction. For the heterogeneous catalysis was used niobium pentoxide calcined at 500º C in two reaction systems: Autoclaved reactor (relation oleic acid and ethanol 1:1, temperature of 180ºC) and reflux reactor (relation oleic acid and ethanol 1:20, temperature of 72ºC), changing in both systems the catalyst mass (50, 100 and 200 mg). All catalysts were characterized by MEV and DRX. which comfirmed the morfologic characteristics of Nb2O5 and the presence of the lipases in the niobium pentoxide films. With the obtained results the best system for the synthesis of ethyl oleate was evaluate through the methods of Lowry-Tinsley and gas chromatography. The best result was of 97% of conversion to ethyl oleate, obtained by the niobium pentoxide during the heterogeneous catalyst, using the autoclaved reactor at 10 atm and 180ºC, with the mass of 200 mg of Nb2O5.