Study Of The Catalysts And Reaction In The Vapor-Phase Aldol Condensation Of Formaldehyde And Acetaldehyde

The reaction mechanism and feasibility of aldol condensation of formaldehyde and acetaldehyde are discussed in this thesis. Vapor-phase aldol condensation of formaldehyde and acetaldehyde was also investigated on the basis of liquid experiments. Inexpensive and facile feedstock formaldehyde, as well as acetaldehyde, were fed into a self-designed tube reactor, catalysts are prepared and the preliminary process optimization is performed. Under the condition of proper catalysts and reaction parameters, acrolein or 3-hydroxypropanal can be prepared, which is important to synthesis monomer of PTT polyester.The feedstock and products are analyzed by GC/MS, and the conversion of acetaldehyde, selectivity and yield of acrolein are analyzed and calculated by GC and internal standard method. A series of catalysts are prepared by impregnating or sol-gel method, characterized by IR, N₂ adsorption (BET) and XRD, and tested by reaction. It is found that the MgO-SiO₂, ZnO-SiO₂ catalysts exhibited good catalytic activity for the aldol condensation of formaldehyde and acetaldehyde. The acetaldehyde conversion and the acrolein formation are governed by the basicity and the number of basic sites. The more the basic sites the catalysts have, the higher the yield of acrolein can be get. The catalysts which prepared by sol-gel method or experienced ultra fining process have better activity. The catalyst regenerating data can be get from TG ananlysis. The reaction parameters are optimized preliminarily in the fixed-bed tube reactor, catalyst volume 40 ml, temperature 310°C , n_HCHO/n_AcH=1.5, feed rate 0.2 ml/min, residence time 10 s. The maximum yield of acrolein is about 85%.According to the results of catalysts preparation and process optimization, further studies are discussed from the catalysts improvement, catalysts refresh, the products collecting and separation.