Desenvolvimento do catalisador yzro2/xmo-kit-6 para avaliação na reação de transesterificação do óleo de soja.

Abstract

Biodiesel is a mixture of fatty acid esters and can be obtained from the transesterification of vegetable oils and animal fats with a short-chain alcohol. It is a biofuel that appears as an alternative to fossil fuels, as it is renewable, biodegradable and non-toxic. Traditionally, transesterification is catalyzed by homogeneous catalysts, but heterogeneous catalysis can facilitate the separation of catalyst products. Mesoporous materials, such as KIT6, have been studied due to their promising characteristics in the area of catalysis, as they have a symmetrical three-dimensional Ia3d cubic structure, with large pore diameter, high hydrothermal stability, high specific area and bicontinuous interpenetrating network of channels. The addition of metallic oxides, such as molybdenum trioxide and zirconium oxide in the structure of the KIT-6 molecular sieve, allows an increase in catalytic activity and selectivity, improving its performance in the transesterification reaction. The present work aimed to develop a catalyst from the modification of the KIT-6 molecular sieve with molybdenum and zirconium, for application in the transesterification reaction of soybean oil, using the Box-Behnken experimental design to define the matrix of experiments. For this purpose, molybdenum trioxide was hydrothermally synthesized via microwave, obtaining its orthorhombic phase from thermal activation. Through the techniques of X-ray diffractometry and Raman spectroscopy, it was found that the synthesis with a time of 5 min and 150 ºC was necessary to obtain the hexagonal phase. Thermogravimetric analysis indicated that 400 °C is the ideal temperature for the transition to the orthorhombic phase. Molybdenum trioxide was incorporated into the cubic structure of KIT-6 by the direct synthesis method, evaluating the different Si/Mo molar ratios (10, 20 and 30). Through the analysis of x-ray diffractometry and physical adsorption of N2, it was concluded that the 20Mo-KIT-6 catalyst presented better crystallographic and textural properties, with greater specific surface area and diffraction reflections characteristic of KIT-6 with greater intensity, being chosen for impregnation with different ZrO2 contents (10, 15 and 20%). ZrO2 was obtained by the precipitation of Zr(OH)4 which was activated at 700 ºC to obtain its monoclinic phase. The XRD technique confirmed the impregnation of the ZrO2 species in the structure of 20Mo-KIT-6, through the analysis of physical adsorption of N2, the catalysts presented isotherms of type IV with "loop" of hysteresis H3, indicating that the catalysts presented structure mesoporous with the formation of pores with different geometries. The operational variables (ZrO2 content, alcohol:oil ratio and catalyst concentration) adopted for the Box-Behnken experimental design did not present a significant influence on the transesterification reaction, the highest yield obtained was 62.13% using the conditions of 10% ZrO2, alcohol:oil molar ratio of 20:1 , 4 wt.% catalyst loading, 150°C and 3h.