Acid activated montmorillonite for gas-phase catalytic dehydration of monoethanolamine

Abstract

The acid activated montmorillonite (Acid-Mt) was investigated for the first time as a catalyst for the gaseous-phase dehydration of monoethanolamine (MEA). A series of Acid-Mt was obtained by treating the Na-type montmorillonite (NaMt) at 104 °C in 3.2 mol L−1 HNO3 aqueous solution for 4–24 h followed by calcining at 450–1150 °C for 4 h, respectively. The Acid-Mts were characterized by X-ray diffraction, temperature programmed desorption of NH3, temperature programmed desorption of CO2, and N2 adsorption-desorption, and were evaluated as catalysts for the gaseous-phase dehydration of MEA. With increasing the activation time or calcination temperature, both the amounts of acidic and basic sites over Acid-Mt were decreased, and more pronounced extent was observed in the case of changing the calcination temperature. By correlating the catalytic results with the characterization results, the acidity of the catalyst was revealed to be the key factor in determining the MEA conversion. In contrast, a complex picture was observed in the case of the product selectivity. Generally, a higher acidity over Acid-Mt favored the intermolecular dehydration and 1,2-elimination reactions of MEA, leading to a higher selectivity of piperazine (PIP) and triethylenediamine (TEDA). When the acidity of Acid-Mt was lower, the intramolecular dehydration and deamination reactions were improved resulting in an increasing selectivity of ethyleneimine (EI). Importantly, the product distribution of the MEA dehydration was greatly regulated by the simply changing the acid activation parameters of Mt. Thus, Acid-Mt is a promising catalyst for selectively synthesizing different N-containing fine chemicals via the MEA dehydration reaction.