Solketal synthesis from ketalization of glycerol with acetone: A kinetic study over a sulfated zirconia catalyst

摘要

In this work, a series of acid catalysts were synthetized from a commercial zirconium oxide sulfated with a 0.5 M H2SO4 solution by wet impregnation. The characterization results show a correlation between the calcination temperature and the acid sites generated on the materials. Among the catalysts prepared, the sulfated zirconia calcined in air at 400 degrees C (Zr-S-400), with a molar ratio S/Zr = 0.23 was the most active one due to its larger acid density and greater acid strength caused by the generation of new Bronsted sites. The Zr-S-400 catalyst exhibited an initial reaction rate of 0.0497 mol.min(-1).g(-1), and achieved a glycerol conversion of 80 % in 1 h of reaction at 40 degrees C (glycerol:acetone molar ratio = 1:6). The Zr-S-400 material remained stable after four catalytic cycles, demonstrating the stability of the superficial sulfate species (S/Zr similar to 0.2). In addition, the thermodynamics and kinetics of the reaction were evaluated, as well as the influence of some operating conditions such as the molar ratio of reactants and the water content in the reaction mixture. The following standard molar reaction properties were obtained: Delta H degrees = -11.6 +/- 1.1 kJ.mol(-1) and Delta G degrees = 4.0 +/- 0.1 kJ.mol(-1). Taking into account that the adsorption of water on this catalyst did not affect the number of acid sites available, a simple pseudohomogeneous kinetic expression was developed and successfully adjusted to the experimental data in the range under study. Based on this model, the estimated activation energy of the reaction was 88.1 +/- 8.9 kJ.mol(-1).