Avaliação do catalisador SO42-/ZrO2/Mo-MCM-41destinado a reação de transesterificação do óleo de soja.

Abstract

Biodiesel is produced from natural and renewable raw materials, such as vegetable or waste oils; its properties are similar to those of fossil diesel, making it a promising source of alternative energy. The biodiesel production process involves the reaction between a vegetable oil and a short-chain alcohol in the presence of a catalyst, known as transesterification. The reaction conditions and subsequent separation steps depend on the nature of the catalyst used. Solid catalysts have been studied by the scientific community due to their potential for reuse and ease of separation. The MCM-41 molecular sieve has a large surface area and adjustable pore size, ensuring that triglyceride molecules diffuse into the mesopores. Additionally, the incorporation of heteroatoms improves acidic properties and textural characteristics, and consequently, its catalytic activity. Among the metals and functional groups with important catalytic properties, molybdenum (Mo), zirconia (ZrO2), and sulfate groups (SO42-) are active phases that enhance biodiesel production. The aim of the study was to develop a solid catalyst modified with Mo, ZrO2, and SO42- for the transesterification of soybean oil via the methylic route. For this purpose, molybdenum was incorporated into the MCM-41 structure during the synthesis process with a Si/Mo molar ratio of 20. Subsequently, 20 % of zirconia was impregnated by pore volume saturation (dry impregnation) onto the catalyst. Finally, the catalyst underwent the sulfation process. An experimental design 2² + 3 PtCt was used as an evaluation tool, where the independent variables were reaction time and oil:alcohol ratio, and the dependent variable was the yield of methyl esters. From the X-ray diffraction analysis and obtained crystallographic parameters, it was observed that the Mo-MCM-41 catalyst exhibited characteristics similar to MCM-41. The impregnation of ZrO2 and sulfation of the catalyst favored the monoclinic phase of zirconia and did not compromise the structure. FTIR spectra showed vibrations associated with molybdenum, zirconia, and sulfate. The adsorption/desorption profiles of the Mo-MCM-41, ZrO2/Mo-MCM-41, and SO42-/ZrO2/Mo- MCM-41 catalysts were similar to type IV isotherms, characteristic of porous solids. The specific surface area decreased with the dispersion of metals and sulfate groups in the structure. The ZSMM catalyst exhibited weak, moderate, and strong acid sites. Statistical analysis of the data showed that the model and experimental levels adopted did not detect the significance of the variables under study within the established limits. The highest biodiesel yield obtained was 75.51 %, under the following reaction conditions: reaction time of 4 hours, oil:alcohol ratio of 1:25, temperature of 150°C, and 3 % catalyst in the reaction medium.