Knoevenagel condensation reaction between benzaldehyde and ethyl acetoacetate in microreactor and membrane microreactor

Abstract

The Knoevenagel condensation reaction between benzaldehyde and ethyl acetoacetate was performed in microreactor using Cs-exchanged NaX catalyst and NaA membrane. The laminar flow and slow diffusion of the bulky product molecules in the microchannel resulted in the further reactions of the main Knoevenagel condensation product, 2-acetyl-3-phenylacrylic acid ethyl ester that led to byproduct formation and poorer reaction selectivity. Replacing the powder catalyst in the microchannels with a thin CsNaX film improved the selectivity (78% vs. 55%), while increasing the microchannel height-to-width aspect ratio from 2 to 5 doubled the conversion from 25% to 60%. The selective removal of water byproduct in the membrane microreactors benefited the Knoevenagel condensation reactions. Higher conversions were observed for the reactions between benzaldehyde and (1) ethyl cyanoacetate (ECA), (2) ethyl acetoacetate (EAA) and (3) diethyl malonate (DEM), but the improvement diminished with increasing difficulty of the reaction. Higher selectivity and product yield for 2-acetyl-3-phenylacrylic acid ethyl ester were obtained for the membrane microreactor with a hybrid NaA membrane-CsNaX catalyst film deposited in the microchannels.