(556b) Intensified Liquid Phase Ethylene Epoxidation: Thermodynamics, Mass Transfer and Kinetic Studies

Recently, we reported a novel liquid phase ethylene oxide (EO) technology.1 In this concept, ethylene is transported from the gas phase to the aqueous phase where it reacts with the oxidant hydrogen peroxide (H2O2) in presence of dissolved methyl trioxorhenium (MTO) catalyst to form EO. Methanol was employed as a co-solvent to increase the ethylene solubility in the liquid phase. The process is highly selective towards EO with no detectable CO2 formed as byproduct. However, the reported EO yields were low and mass transfer limitations were suspected. In this talk, we present detailed mass transfer studies aimed at a better understanding the thermodynamics and mass transfer effects underlying ethylene dissolution into the liquid phase. Volumetric expansion of the liquid phase reaction mixture by ethylene dissolution at various pressures is measured and modeled. With such knowledge, ethylene dissolution rates into the liquid phase at various pressures were experimentally measured at constant pressure in a stirred vessel. Mass transfer coefficients, estimated by regressing the experimental data with a suitable mathematical model, increased with stirrer speed becoming asymptotically constant. These experiments confirmed that the previously reported conversions were subject to mass transfer limitations. Conversion studies repeated at higher stirring speeds showed a sixfold enhancement in the ethylene conversion rates. The ethylene oxide productivity [g EO/(g Re)/hr] is comparable to that observed in of the conventional EO process [g EO/(g Ag)/hr]. These results along with kinetic studies and other process development issues, such as catalyst stability and recycle, will be presented and discussed.

References:

1. Lee, H-J., et. al., Towards a CO2 -free ethylene oxide process: Homogeneous ethylene oxide in gas-expanded liquids. 2010. 65, 128-134.