Glycerol conversion to acrylonitrile by consecutive dehydration over WO3/TiO2 and ammoxidation over Sb-(Fe,V)-O

Abstract

The indirect ammoxidation of glycerol to acrylonitrile via intermediate formation of acrolein was studied using a tandem reactor coupling a dehydration step with an ammoxidation step. For the first step of dehydration of glycerol to acrolein, we used a previously optimized WO3/TiO2 catalyst, while Sb-V-O or Sb-Fe-O catalysts were developed and used for the subsequent ammoxidation step. Especially, the Sb-Fe-O catalysts were found highly selective and thus were more-deeply investigated. The corresponding catalysts were characterized by nitrogen physisorption, X-ray powder diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and temperature-programmed reduction in the presence of H2. We found that the presence of a FeSbO4 mixed phase on the synthesized samples was correlated to a high selectivity to acrylonitrile. Further, we observed an increase in selectivity to acrylonitrile with the reaction time, which was explained by the progressive formation of additional amounts of FeSbO4 on the catalysts during the reaction. Finally, the reaction parameters (temperature, catalyst amount, molar NH3/AC ratio and molar O2/AC ratio) for the catalyst with an Sb/Fe molar ratio of 0.6 were optimized, whereby a maximum yield in acrylonitrile of 40% (based on glycerol) could be achieved.