Uso de zeólitas ácidas na conversão de glicóis em produtos de interesse comercial

Abstract

Converting glycerol into value-added products, for example propylene glycols and ethylene glycol, provides an alternative for glycerol disposal and for its surplus problems. One possibility to add value to these glycols is through their transformation into ethers. The etherification of alcohols is an acid catalyzed reaction, widely used in chemical industry. The ethers produced are stable and have many applications, including diesel fuel additives, surfactants, polymer precursors, antiseptic, anti-inflammatory and antibacterial agents. Due to the great potential of direct etherification reaction to add value to the biomass-derived alcohols, in this work a family of USY zeolites and commercial H-Beta and HZSM-5 zeolites were characterized through their physical, chemical, textural and hydrophilic/hydrophobic properties and their catalytic behavior were evaluated in the etherification reactions of glycols (glycerol, propylene glycol and ethylene glycol) with different alcohols (ethanol, tert-butanol, 1-octanol, 1-decanol and 1-dodecanol). Besides the etherification reaction desired, in some cases other reactions, including the self-etherification of the reactants, could also be observed. In all studied reactions, the catalytic activity was influenced by the global Si/Al molar ratio of the samples, and the best results were achieved with zeolites whose global Si/Al molar ratio was between 11.2 and 12.3. It was also noticed that the difference in the chain size and the hydrophilicity/hydrophobicity of the alcohols used influenced their interaction with the surface of the catalysts and, consequently, the selectivity to the products. Although a deep characterization of the studied zeolites was made, it was not possible to establish an unique relationship between the catalytic activity and the structural, textural or acid characteristics of the studied material. However some effects in a limited group of samples were detected. Among the characterizations, the measurement of the hydrophobicity index (Rtoluene/water) was the only property that indicated a correlation with catalytic activity, allowing the discussion of the results. The mechanisms of the reactions for the formation of the desired ethers have been proposed, but there is no evidence that allows the selection of one of them as the main one. An unequivocal identification of all the products formed was established using gas chromatography coupled to mass spectrometry associated with standard libraries and mass spectra data