Feasibility Study of the Oxidative Dehydrogenation of Ethane in an Electrochemical Packed-Bed Membrane Reactor

Abstract

The feasibility of the oxidative dehydrogenation of ethane to ethylene with alumina-supported vanadium oxide catalyst (VO x /γ-Al2O3) in an electrochemical packed-bed membrane reactor was investigated at temperatures between 500 and 620 °C with molar ratios of oxygen to ethane of 0.06−3.10. An oxygen-ion-conducting yttria-stabilized zirconia (YSZ) membrane was employed in a reactor of Au|YSZ|Pt, and the oxygen flux transferred across the membrane was controlled over the faradic coupling of oxygen-ion conduction and the external current between the electrodes. The oxidative dehydrogenation of ethane with electrochemically supplied oxygen in the membrane reactor was compared to that obtained with gaseous dioxygen in a conventional packed-bed reactor. The selectivity to ethylene was found to decrease as a function of supplied oxygen in both investigated operating modes. For all investigated oxygen/ethane molar ratios, the selectivity ratio, S CO 2 /S CO, was found to be clearly higher in the electrochemical than in the packed-bed reactor mode. The electrochemical oxygen supply significantly promoted CO2 formation, whereas the ethane conversion and ethylene selectivity were almost equal in the two investigated reactors. The experimental results indicate that, in the electrochemical operation, additional oxygen species exist in the system and are especially reactive in the total oxidation reactions.

Solid Electrolyte Membrane Reactors

“…The model, including the equations for charge transfer reactions of oxygen on the cathode and the anode ( 7.12 -7.14 ), was not able to predict the experimental results of the EMR operation conditions with electrochemically supplied oxygen. One reason for the discrepancies between the experimental data and the simulated was concuded to be the additional electrochemically induced side reactions, as suggested already by Chalakov et al ( 2007 ), Ye et al ( 2004 ) and Ye et al ( 2005 ). In contrary to the co -feed mode, where the oxygen on the anode exists only in form of gaseous O 2 , additional oxygen species, e.g.,…”

“…In the experimental investigation of ODHE was found that the ethylene selectivity was not positively infl uenced in the solid electrolyte membrane reactor operation compared to the packed -bed membrane reactor operation (Chalakov et al , 2007 ). The selectivity ratio S S CO CO 2 was found to depend on the type of oxygen supply, so that with a gaseous oxygen supply the ratio was always lower than that with an electrochemically supplied oxygen.…”

“…Ye et al . ( 2006 ) and Chalakov et al . ( 2007 ) observed high reactivities for the desired intermediate, which was likely due to the additional electrochemical reactions between oxygen ions on the anode and the intermediate, as discussed later in detail.…”

“…In the present Chapter 7 we discuss the characteristics of carrying out the reaction in a solid electrolyte packed -bed membrane reactor. In the analysis, the basic reactor model including the electron transfer reactions and the ion transfer in the electrolyte as presented above for the electrochemical synthesis of MA was applied also here for the oxidative dehydrogenation of ethane ( ODHE ) with a VO x / γ -Al 2 O 3 catalyst (Chalakov et al , 2007 ). However, in the present ODHE studies the catalyst particles were placed in a packed -bed solid electrolyte membrane reactor and not fi xed with the electrode, as in the example of MA synthesis.…”

“…Therefore the model was completed fi nally by implementing two electrochemical side reactions into the reaction network. The charged oxygen species are likely highly active in oxidation reactions, as concluded by Chalakov et al ( 2007 ) and therefore two further reactions were added to the model describing the ethylene reaction with O 2 − either to CO ( 7.26 ) The backward reactions were assumed to be unlikely and therefore the kinetics of the reactions in Equations 7.26 and 7.27 were described by the simple Tafel equation.…”