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.
In the first part of this work, the electrical conductivity of vanadium phosphorous oxide (VPO) catalyst was investigated by means of the 2-probe EIS method. The VPO showed an extremely low conductivity at low oxygen partial pressure, which is the prevailing condition in the anodic compartment in an electrochemical membrane reactor (EMR). In the second part of this study, fresh as well as VPO catalyst already used in an EMR were characterised with XRD, XPS and temperature programmed oxidation (TPO). The XRD measurements revealed an unchanged bulk phase structure after operation in the EMR. Significant differences in the average oxidation states of vanadium in the catalyst layer in the EMR were determined via XPS, where the catalyst surface facing the electrolyte membrane was more oxidised than the surface facing the anodic gas compartment. The lowered uptake and release of oxygen was observed in TPO experiments for the catalyst used in the EMR.
IntroductionThe present chapter introduces a specifi c type of membrane reactor only briefl y mentioned in Chapter 1 . The solid electrolyte membrane reactor s ( SEMR ) -or electrochemical membrane reactors as they also are called -are equipped with ion -conducting membranes, which ideally are impermeable for non -charged reaction species. These reactors operate as electrochemical cells, in which the oxidation and reduction reactions are carried out separately on catalyst/electrodes layers located on the opposite sides of the electrolyte. The development of solid electrolyte membrane reactors has reached a semi -commercial stage in fuel cells, in which the maximal generation of electric energy by the total oxidation of hydrogen or hydrocarbon feeds is the primary goal of operation. Research on chemical reactor applications is strongly concentrated in the high -temperature range using either oxygen ion -or proton -conducting inorganic membranes. Some interesting examples were published recently, investigating proton -conducting polymeric membranes for the production of chemicals.This chapter gives a brief overview on the current status and future trends in the development and application of solid electrolyte reactors equipped with solid electrolyte ( SE ) materials used as membranes in these reactors. Initially the working principle of a solid electrolyte membrane reactor and material aspects are discussed. The second part of the chapter gives a detailed description of the special aspects concerning the modeling of solid electrolyte membrane reactors, as well as the application examples of maleic anhydride ( MA ) synthesis and oxidative dehydrogenation of ethane. Finally the chapter reviews recent papers concerning solid electrolyte membrane reactors applying:• high -temperature oxygen ion conductors, • high -temperature proton conductors, • low -temperature proton conductors.There are some recent review papers, especially written for high -temperature applications, which we would like to recommend to readers interested in more
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