Síntese de catalisadores à base de ferritas Ni-Zn dopada com cobre e avaliação do seu desempenho na reação de transesterificação de óleo vegetal em biodiesel.

Abstract

Brazil, especially the Northeast, has a great potential for the production of biofuels, such as biodiesel. In the production of biodiesel makes use of homogeneous catalysts and/or heterogeneous. However, the operating procedures are more easily performed with the use of heterogeneous catalysts, besides significantly reducing the environmental pollution as compared to the use of homogeneous catalysts. Among the materials used as heterogeneous catalysts, the metal oxides are ferrous an important class of compounds and, among them the ferrite materials are more prominent due to their inverted spinel structure, which results in excellent properties, such as high thermodynamic stability, electrical conductivity, catalytic activity and corrosion resistance. Against this background, this study aimed at obtaining the heterogeneous catalysts based on Ni-Zn ferrite pure and doped with copper concentration ranging between 0 < x < 0.4 mol, via the chemical method of combustion reaction, for their use in transesterification process of vegetable soybean oil for biodiesel production. The samples were characterized by X-ray diffraction (XRD), fluorescence spectroscopy, Xray energy dispersive (EDX) spectroscopy, infrared Fourier transform (FTIR), textural analysis by nitrogen adsorption (BET) , scanning electron microscopy (SEM/EDS), thermogravimetric analysis (TG), carbon and magnetic measurements. During the syntheses were measured combustion temperature and flame length of the reactions. The catalytic tests were conducted with a bench 1:20 molar ratio oil/methanol, using 4% by weight of catalyst, reaction products were characterized by gas chromatography. Analysis of the results shows that all samples showed a single phase of Ni-Zn ferrite, with crystallite size between 30 and 43 nm with chemical composition of the oxides present according to the stoichiometry expected, characteristic bands of the inverse spinel type and morphology consisting of large clusters, in the form of irregular blocks, non-porous and fragile-looking, with the exception of the sample doped with 0.3 mol of Cu2 + , which showed clusters of porous aspect. The samples showed values of surface area between 18 and 62 m2.g4 , with classification of pores in mesoporous range. Both had good thermal stability and generally, the increased doping with Cu2 + in Ni-Zn ferrite favors a reduction in surface area, a decrease in carbon content and the values of saturation magnetization. The catalytic tests revealed an excellent and promising catalytic potential for all compositions, with conversion values between 47 and 85%, except for the composition doped with 0.4 mol of Cu2 + , which received only 4.2% conversion. In particular, the sample doped with 0.3 mol of Cu2 + had the highest percentage of conversion of 85% in methyl esters (biodiesel), and this finding could possibly be attributed, among other factors, by doping with Cu2 + , which allowed a decrease of saturation magnetization, also by porous morphology shown by this said sample, so that induce a more effective catalyst during the reaction.