Kinetics Study of Ethylbenzene Alkylation with Ethanol over Medium and Large Pore Zeolites

Abstract

The alkylation of ethylbenzene (EB) with ethanol has been studied over medium and large pore zeolite based catalysts in a fluidized-bed reactor. Focus is made on the effects of pore structure of zeolites on activity, selectivity, and reaction kinetics of EB ethylation. In this regard ZSM-5 and mordenite are selected as a medium and large pore zeolite, respectively. The catalysts considered have similar acidity. The EB ethylation experiments are conducted using 1:1 EB to ethanol molar ratio and at various temperature levels and different contact times. The product analysis shows that diethylbenzene (DEB) is the main product. However, the large pore size mordenite catalyst also produces a small amount of triethylbenzene. Phenomenological based kinetics models are developed based on the experimental conversion and selectivity data. The Langmuir–Hinshelwood mechanism with surface reaction control is considered for both the medium and large pore zeolites. The analysis of the developed model suggests that a Langmuir–Hinshelwood mechanism with weakly adsorbed EB and strongly adsorbed ethanol and product DEB fits the experimental data adequately. The kinetic analysis also shows that the modenite requires significantly low activation energy (45.2 kJ/mol) as compared to the ZSM-5 zeolite (112 kJ/mol). On the contrary, the estimated enthalpy of adsorption of product DEB on mordenite (85.3 kJ/mol) is significantly higher than the value on the ZSM-5 sample (67.7 kJ/mol). The enthalpy of adsorption of ethanol is found to be 32.4 and 52.4 kJ/mol on mordenite and ZSM-5 samples, respectively.