Aplicação de óxidos mistos derivados de HDL Mg/Al sintetizados a partir de resíduo de alumínio na reação de transesterificação

Abstract

The search for alternative fuels has intensified as a viable solution to replace petrodiesel, promoting both environmental and economic benefits. In this scenario, biodiesel emerges as a sustainable alternative, being a renewable and biodegradable fuel produced through the transesterification reaction of fatty acid esters present in vegetable oils and fats. For this reaction to occur with high efficiency, the use of catalysts, which can be classified as homogeneous or heterogeneous, is essential. In this work, layered double hydroxides (LDHs) were synthesized by two methods: co-precipitation (LDH-CP) and co-precipitation followed by hydrothermal treatment (LDH-H). From these materials, mixed oxides (Al₂O₃/MgO) were obtained by calcination at 550°C and applied as heterogeneous catalysts in the production of alkyl esters. The study of the structural properties of the synthesized oxides was carried out through energy dispersive X-ray spectroscopy (EDX), infrared absorption spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetry (TGA), specific surface area (SSA), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and temperature programmed desorption (TPD). The analysis of the X-ray diffraction profile of the catalysts confirmed the formation of mixed oxides due to calcination. For the model transesterification reactions, ethyl acetate and methanol were used in a molar ratio of 1:5, at 120ºC, with reaction times ranging from 15 to 360 minutes, and 5% by mass of catalyst. The conversion of ethyl acetate was quantified by gas chromatography with flame ionization detector (GC-FID). The HDL-CP catalyst showed 63% conversion, showing promise for transesterification reactions. The results indicate that mixed oxides derived from HDLs may be a viable option as heterogeneous catalysts in transesterification processes.