Conversão catalítica do óleo de soja utilizando catalisadores de ni e ni-sn suportados em γ-al2o3

Abstract

The main objective of this work was to evaluate the performance of catalysts based on nickel and nickel promoted with tin, all supported in γ-Al2O3, in the hydrolysis reaction of soybean oil, and for the subsequent reaction, the hydrogenation of free fatty acids by hydrogen generated in situ through the aqueous phase reforming of glycerol (APR). This is a new process, called simultaneous hydrolysis-hydrogenation. At same time, the catalysts were studied in relation to the effect of the calcination temperature and the addition of tin promoter, as well as its stability for the hydrogen generation by aqueous phase reforming, in a continuous flow reactor. Temperature Programmed Reduction (TPR), X-Ray Diffraction (XRD), UV-Visible Spectroscopy Region (DRS), Temperature Programmed Desorption (TPD-H2) and Spectroscopy Mössbauer, made the characterization of catalysts. For the hydrolysis-hydrogenation reaction, a batch reactor was used. The results of the characterization tests showed that the increase in the calcination temperature promoted an increase in the interaction between NiO and the support. The calcination at 300 °C provided better results in relation to NiO/γ-Al2O3 properties at the temperature of reduction of the catalyst used. After the addition of the tin, a modification in the interaction between NiO and γ-Al2O3 could occur due to a possible interaction between the metals. All the catalysts tested showed activity for the aqueous phase reforming of glycerol, in a continuous flow. The monometallic catalyst (NiO/γ-Al2O3) deactivated after a few hours of reaction. The bimetallic catalysts (Ni-Sn/γ-Al2O3) did not show deactivation during the reaction time studied. The addition of tin inhibited the formation of methane and other alkanes, preventing deactivation of the catalyst. A lower content of Sn favored yield and selectivity in hydrogen. The hydrolysis reaction apparently occurs incompletely, under the reaction conditions studied, without catalyst. Perfoming reaction without catalyst and at a temperature lower than that studied, the conversion decreased, showing that the temperature has a direct influence on the reaction. Using the γ-Al2O3 as catalyst, the complete reaction was facilitated, obtaining a high conversion of the glycerides, with high yield in free fatty acids. No significant change in the performance of the monometallic catalysts for hydrolysis reaction due to the calcination temperature employed in the synthesis of the catalysts was verified. In the reactions using the metallic catalysts, it was verified that the in situ generation of hydrogen occurred, as well as the subsequent reaction, the hydrogenation of the unsaturated free fatty acids, produced from the hydrolysis. Hydrogenation was evidenced by increased selectivity for stearic acid (C18:0), and decreased selectivity for unsaturated acids. The addition of tin, in all molar ratios studied, increased the conversion of glycerides and greatly accelerated the hydrolysis reaction. The tin addition also improved the performance, in relation to the monometallic catalyst, for the in situ generation of hydrogen and for the hydrogenation reaction, which, consequently, increased the yield in stearic acid. The beneficial effect afforded by tin may be due to the presence of tin in nickel deficient sites, or by the formation of a Ni-Sn (Ni3Sn) type alloy.