Regulation of acidity and basicity of oxide/montmorillonite catalysts for selective dehydration of monoethanolamine to ethylenimine

Abstract

The heterogeneous dehydration of monoethanolamine (MEA) to ethylenimine (EI) over solid acids/bases has garnered significant attention in industry because of the importance of EI in fine chemical engineering and the advantage in product separation. Unfortunately, lacking insight into the impacts of acidity/basicity on product selectivity in the reaction hinders the development of high-performance solid acids/bases. To investigate the effect of acidity/basicity, this work employs acid-activated montmorillonite (Acid-MMT) as catalyst and the acidity/basicity is adjusted by adding different acidic/basic oxides and changing preparation conditions. Under the conditions of reaction temperature = 420 °C, GHSV = 5000 h−1, N2/MEA = 19, the optimized Acid-MMT based catalyst modified by Cs2O and P2O5 exhibits a MEA conversion of 86.4% and an EI selectivity of 80.3%. By correlating the catalyst performance with the acidity/basicity, lower amount of acidic/basic sites leads to a higher selectivity of EI via intramolecular dehydration of MEA, while intermolecular dehydration of MEA is inhibited. This is because the intermolecular dehydration reaction is kinetically obstructed by the low acidic/basic amounts, and the parallel intramolecular dehydration reaction becomes kinetically dominated. Furthermore, the catalytic results and the statistical study demonstrate that more balanced amounts between acidic and basic sites favor the intramolecular dehydration reaction. Therefore, we can obtain an effective Cs-P/Acid-MMT catalyst for the selective dehydration of MEA to EI, and propose some solid evidences about the effect of acidity/basicity on product distribution in MEA dehydration over the solid acids/bases.