Modelagem por DFT e avaliação catalítica da reação de acetalização do glicerol com butiraldeído

Abstract

The catalytic reaction of glycerol acetalization in the presence of aldehydes or ketones has as an objective to produce cyclic acetals of interest to the industry of the cosmetics, food and petrochemical. In this reaction, glycerol interacts with butyraldehyde, employing catalysts containing active acid-base or redox sites. The products formed by this reaction are acetal and cyclic ketals, such as solketal, which are chemical intermediates used in perfumery and as fuel additives. The literature shows the catalysts utilized in the glycerol acetalization reaction are deactivated in the reaction medium, due to the leaching of the active sites. Other challenges to be overcome in this reaction include improvements in the reaction parameters needed to allow the process to be implemented as a useful route for glycerol recovery. In this way, catalysts supported on mixed oxides based on CeO2-MnOx or La2O3-Al2O3 containing NiO and Co3O4, as active sites were used in the acetalization reaction of glycerol with butyraldehyde. The reaction parameters were evaluated in catalytic tests by varying the type of solvent, temperature, and reaction composition. The steps of the reaction were investigated through modeling using the density functional theory (DFT). The catalysts were evaluated using X-ray Diffraction (DRX) techniques, Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS), Raman spectroscopy, Nitrogen physisorption isotherms, Fourier Transforms Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). The results obtained revealed high values of glycerol conversion and selectivity to solketal on the CeO2-MnOx catalysts series at 50 °C, with an equimolar ratio between glycerol and butyraldehyde, in the absence of solvents. The solids based on La2O3-Al2O3 showed low conversions and leaching of the active sites, due to the water generated in the reaction medium. The mechanistic modeling by DFT presents information about the binding energies of the possible chemical intermediates of the reaction, as well as the interatomic distances involved in the reaction centers. Theoretical studies culminated in a mechanistic reaction proposal for the production of solketal, in different routes, and corroborated aspects related to the selectivity of the reaction.