Steady-state reaction studies of acetic acid and ethanol were used to identify co-adsorbed acetic acid/ethanol dimers as surface intermediates within specific elementary steps involved in the esterification of acetic acid with ethanol on zeolites. A reaction mechanism involving two dominating surface species, an inactive ethanol dimeric species adsorbed on Bronsted sites inhibiting ester formation and a co-adsorbed complex of acetic acid and ethanol on the active site reacting to produce ethyl acetate, is shown to describe the reaction rate as a function of temperature (323-383 K), acetic acid (0.5-6.0 kPa), and ethanol (5.0-13.0 kPa) partial pressure on proton-form BEA, FER, MFI, and MOR zeolites. Measured differences in rates as a function of zeolite structure and the rigorous interpretation of these differences in terms of esterification rate and equilibrium constants is presented to show that the intrinsic rate constant for the activation of the co-adsorbed complex increases in the order FER < MOR < MFI < BEA.
Bibliographical noteFunding Information:
The authors acknowledge financial support from the National Science Foundation Emerging Frontiers in Research and Innovation – Hydrocarbons from Biomass Grant (NSF-EFRI 0937706). Hsu Chiang was partially supported by ADMIRE (Abu Dhabi Minnesota Institute for Research Excellence). We thank Srinivas Rangarajan for assistance with Athena Visual Studio.
- Acetic acid
- Ethyl acetate
- Reaction kinetics