Hidrogenólise do glicerol a propilenoglicol sob catalisadores de Ni-Cu/Al2O3 utilizando hidrogênio produzido in situ

Abstract

Catalytic hydrogenolysis of glycerol is one of the possible routes for converting glycerol into high commercial value products. The production of propylene glycol by catalytic hydrogenolysis of glycerol can be carried out in the liquid or gas phase with H2 feed. However, it is possible to perform this process without the addition of external H2 by using a suitable solvent. Thus, the aim of this work is to study the catalytic conversion of glycerol to propylene glycol and other products in the liquid phase by transfer catalytic hydrogenation using ethanol as a donor (CTH). For this purpose, Cu and Ni bimetallic catalysts supported on commercial alumina were synthesized with different metal ratios by wet impregnation method. The materials were characterized by transmission electron microscopy, X-ray fluorescence and diffraction, N2 physisorption, temperature-programmed reduction, thermogravimetric analysis and Fourier-transform infrared spectroscopy. The characterizations of the materials showed that Cu and Ni have a synergistic effect on decreasing reduction reduction. The catalysts also showed low particle size (5-10nm) and good metal dispersion. The tests for catalytic evaluation were performed in a batch reactor and the parameters were 200 °C, 450 rpm, 20 mL of aqueous glycerol or ethanol solution (2.257 mol/L), reaction time of 4 or 24 h, and initial pressure of 20 bar of N2 or H2 with 350 mg of catalyst. The 6Ni4Cu/Al2O3 catalyst showed the best performance for CTH in 24 h of reaction with a conversion of 34.2% and selectivity for propylene glycol of 14.5%, while the reaction with external H2 resulted in a performance of 9.3% with a selectivity of 55.3%. For both hydrogen sources, there was a correlation between glycerol conversion and Cu/Ni ratio, and the process substitution for molecular hydrogen is achievable under the conditions of this work. Ni played a role in the catalyst increased the cleavage of the C-C bond, while Cu was important in increasing the selectivity to the desired product of the reaction. Post-reaction, X-ray fluorescence and diffraction, thermogravimetric analysis and transmission electron microscopy showed that the main causes of catalytic deactivation are sintering, adsorption of products and reactants at the catalytic sites, boehmite formation and, to a minor extent, Cu leaching.