SYNTHESIS OF ACROLEIN BY VAPOR-PHASE CONDENSATION OF FORMALDEHYDE AND ACETALDEHYDE OVER OXIDES LOADED ZEOLITES

The synthesis of acrolein by means of the catalytic vapor phase condensation of formaldehyde and acetaldehyde was studied. Oxides such as ZnO, MgO, MoO3, B2O3 and P2O5 deposited over ZSM-5, Y-faujasite, Al2O3 and SiO2 were tested as catalysts. The effect of the nature and the content of the oxides and the nature of the support as well as the influence of the reaction parameters (temperature, mole ratio of reagents, number of pulses etc.) on the conversion of acetaldehyde were investigated. Oxides deposition over the HZSM-5 support improved the catalytic activity and the highest performances were obtained using a 4 wt. % MgO/ZSM-5 catalyst. An excess of magnesia could hinder pore accessibility to the reagents. The activity of such a catalyst was explained assuming the possible cooperation between the basic MgO centers and the zeolite acidic sites. It was also observed that the aldol condensation occurs mainly on medium strength sites, the strong acidic centers being mainly involved in the coking process.