Desenvolvimento de catalisadores WO3/MMT para a hidrogenólise do glicerol a propanodiol

Abstract

The increase in glycerol production, which is obtained during transesterification to produce biodiesel, has led to a devaluation of this by-product due to the supply on the global market. However, the use of glycerol as a feedstock to produce higher value-added products can improve the economic viability of the biofuels industry. Catalytic hydrogenolysis has emerged as a promising alternative for the synthesis of 1,3-propanediol, an alcohol commonly used in polymerization reactions, especially in the production of polytrimethylene terephthalate and polyurethane, and 1,2-propanediol, a molecule widely used in resins production. The aim of this work is therefore to convert glycerol into its derivatives, especially 1,3-propanediol, in order to increase the value of the biodiesel chain. A montmorillonite clay (pillared with Zr and unpillared) was impregnated with Pt (2% m/m) and WO3 (0, 5, 10 and 15% m/m) and evaluated in the glycerol conversion reaction. The aim of the test was to evaluate the influence of the modification of the catalyst structure, the amount and the strength of the acidic sites on the catalytic activity and the selectivity for propanediols. The samples were characterized by thermogravimetric analysis (TGA), X-ray fluorescence (XRF), N2-physisorption, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy with pyridine (FTIR-Py). The catalytic evaluation was carried out in a stirred batch Parr reactor under a hydrogen pressure of 5 MPa at a temperature of 200°C for 6 h. The synthesized materials showed a micro- and mesoporous structure of plate-like aggregates and slit-like pores characteristic of clays with disaggregated layers. The addition of platinum and tungsten did not alter this structure, forming only platinum sites and a mixture of crystalline WO3 and amorphous mono- and polytungstate species. Although the structure remained unchanged, the acidity of the materials was modified, with a reduction in total acidic sites after impregnation, along with the alteration of the Brønsted/Lewis (B/L) ratio in all samples. Prior to treatment, they had more Brønsted sites, whereas after treatment, they showed more Lewis sites. Clay pillaring was not efficient, as the support used was already quite disorganized, hindering the entry of the pillaring agent into the interlayer spaces. Among the catalysts analyzed, Pt-10WO3/MMT exhibited 17% selectivity for 1,2-PDO and 17% for 1,3-PDO, the best result among the evaluated materials. Pt-MMT catalyst showed the highest selectivity for 1,2-PDO formation (53.5%). Considering the results of catalytic tests, the catalyst with 10% tungsten showed the most promising performance for glycerol hydrogenolysis reaction with a focus on 1,3-PDO formation, while the catalyst with platinum alone was efficient for 1,2-PDO formation.