Estudo do uso de estanhas sulfatadas como catalisadores ácidos para produção de bioaditivo de diesel

Abstract

Biomass can be processed to obtain numerous inputs of interest, including fuels, which is particularly interesting because it is renewable. Among the most used biomass processing methods is acid hydrolysis, which generates some platform molecules that can be converted into other substances. One of these molecules is levulinic acid, which can be catalytically converted into ethyl levulinate, which is an oxygenated additive that can be mixed with diesel, improving its flash point and reducing sulfur emissions from burning it. The esterification reaction of carboxylic acids usually occurs in the presence of acid catalysts and, as homogeneous mineral acids have been replaced by solids, such as HCl and H2SO4, several acidic materials have been studied in this reaction. Among these heterogeneous catalysts, it is possible to highlight the sulfated oxides, which are classified as superacids, due to their high acidity. Sulphated tin stands out, as in previous studies this type of material showed high activity, but all sulfated by treatment method using excess solution suffered deactivation in the esterification of levulinic acid with ethanol in liquid phase. In this perspective, the objective of this work was to synthesize sulfated tins by wet-spot impregnation under different conditions, to characterize the materials obtained and to evaluate them in the esterification of levulinic acid with ethanol at 70 °C, atmospheric pressure, 2.5% by mass of solid and ethanol: acid molar ratio of 5:1, in a batch reactor. The characterization methods used were textural analysis, X-ray diffraction, FTIR, elemental analysis and NH3 TPD. Four sulfated solids per impregnation were evaluated, in addition to one per treatment used as a reference and another of pure tin. It was found that sulfated tin with nominal contents of 2.5 and 5% of sulfur showed typical cassiterite crystallinity, and specific area and acidity values greater than pure tin. These results explain the higher activities of sulfated materials than the pure oxide. FTIR spectra indicate the presence of different sulfate species in sulfated solids and the most active materials show bands compatible with monodentate species of this group. The three most active catalysts were submitted to reuse, showing deactivation, but the catalyst obtained by impregnation using sulfuric acid with a higher sulfate content was the one that suffered the smallest reduction in activity. The characterization analyzes of the catalysts used indicated a decrease in the sulfur content, indicating leaching of the surface sulfate groups, although the textural properties were preserved.