Bifunkcyjny przepływowy mikroreaktor do procesu tandemowego deacetalizacji-kondensacji knoevenagela: wpływ stężenia wody

Przeprowadzono badania reakcji tandemowej deacetalizacji-kondensacji Knoevenagela w bifunkcyjnym przepływowym monolitycznym mikroreaktorze z cyrkonowymi centrami kwasowymi i zasadowymi grupami aminoetyloaminopropylowymi osadzonymi na powierzchni krzemionkowego monolitu o hierarchicznej porowatości. Zbadano wpływ stosunku molowego wody do acetalu oraz stabilność właściwości katalitycznych. Stwierdzono istotną zależność wydajności produktu reakcji tandemowej od ilości wody w układzie reakcyjnym. Nie obserwowano natomiast zmiany selektywności jego tworzenia. Potwierdzono stabilność właściwości katalitycznych centrów kwasowych oraz zmniejszenie aktywności centrów zasadowych w trakcie trzech kolejnych cykli pracy mikroreaktora.

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A study of the tandem deacetalization-Knoevenagel condensation reaction was carried out in a bifunctional continuous-flow microreactor. A core of this reactor was made of a silica monolith with hierarchical porosity, which was functionalised with zirconium acid centres and basic aminoethylaminopropyl groups. The structural properties of the materials were investigated using low temperature nitrogen adsorption and scanning electron microscopy. The concentration of active sites was determined. The studied tandem process involved the deactalization of benzaldehyde dimethyl acetal on the acid centres, and the product of this reaction (benzaldehyde) reacted with ethyl cyanoacetate in the Knoevenagel condensation on basic centres to obtain D-ethyl cyanocinnamate (ECC). There was also an additional reaction in the system and a by-product D-methyl cyanocinnamate was formed. The main objective of the presented work was to study the impact of the molar ratio of water to acetal on the performance of the microreactor and to check the stability of the catalytic properties in the long term process. It was found that for a molar ratio of acetal to water equal to 1 the conversion of acetal was 95%, and that of ethyl cyanoacetate was 83%. The final product yield of ECC reached a value of 67.5%, and the selectivity was equal to 81%. The presence of unreacted benzaldehyde (BA) in the post-reaction solution was found to be about 4%. Reducing the amount of water input below the stoichiometric molar ratio value resulted in a decrease in acetal conversion, and consequently a lower yield of ECC was observed. The selectivity of the reaction toward the formation of the desired product did not depend on the amount of water introduced and was ca. 80%. The catalytic stability of the microreactor was checked in three cycles. No changes in acetal conversion were observed, which indicated the stability of the acid centres. However, a decrease in the activity of the amine centres was detected.