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|Title: ||Partial oxidation of propene using solid electrolyte membrane reactors|
|Authors: ||Al-Musa, Abdullah Abdulaziz|
|Issue Date: ||2002|
|Publisher: ||© Abdullah Abdulaziz Al-Musa|
|Abstract: ||This study investigates the efficiency of a calcia stabilised zirconia (CaSZ) solid
electrolyte as an oxygen ion conductor. The study also examines the behaviour of the
oxygen species conducted by the solid electrolyte compared to species provided in the
gas phase for partial oxidation of hydrocarbons.
In this work, an electrochemical cell of the form Air, AgHCaSZ//Ag, Carrier gas was
used to investigate the electrochemical efficiency and stability of the solid electrolyte
CaSZ conducting of oxygen ions under atmospheric pressure conditions at 500 degrees C by
applying a range of electrical potentials from I to 16 volts across the electrochemical
cell. Due to the applied potential oxygen anions are transferred across the solid
electrolyte from the cathode side of the cell to the anode side. It was found that the
employed electrolyte is approximately a 100% purely ionic conductor of oxygen ions
in the range of electrical voltage applied from I to 10 volts. Above that range the cell
started to degrade and loose its ionic efficiency.
It was possible to generate gas mixtures containing trace quantities of oxygen. The
viscosity of these gas mixtures as a function of oxygen concentration was determined
using an established flow perturbation technique (Flux Response Technology).
Partial oxidation of propene was used to investigate the difference between the
oxygen species produced electrochemically via electrical potential application across
the electrochemical cell Air, AgHCaSZ//Ag, Propene, Ar and oxygen provided in the
gaseous state co-fed with propene over silver electrode under atmospheric pressure
and 450 degrees C and 500 degrees C. It was found that the method of electrochemical provision of
oxygen caused the silver catalyst to be more selective to 1,5-hexadeine, whereas the
gaseous oxygen provision produced acrolein as the major product. Carbon dioxide
formation was not affected by the method of oxygen provision.
The Ag electrode was compared to an Au-rich Ag alloy electrode for propene partial
oxidation using electrochemical provision. It was found that 1,5-hexadiene was the
major product over both electrodes, but the Au-rich alloy was more selective for
acrolein than the Ag electrode. This might be due to the gold serving as a separator
between Ag particles which hinder the back-spill over of oxygen and allow desorption of molecular oxygen in the gas phase, which then re-adsorb molecularly on silver sites
The effect of the sequence of the method of oxygen provision on the partial oxidation
of propene was tested using the electrochemical cell Y-BiMoHAg//CaSZ//Ag at 450 degrees C
and atmospheric pressure. A sharp decrease in acrolein selectivity was found when
oxygen was provided in the gas phase after treatment with electrochemical oxygen,
while no significant effect was noticed when the electrochemical oxygen was used
after treatment with gaseous oxygen. This large decrease in acrolein selectivity might
be attributed to the severe reduction of the catalyst, which is probably caused by high
electrical potential application.
A temperature increase from 450 to 500 degrees C seemed to suppress the formation of acrolein for both methods of oxygen provision and enhance the 1,5-hexadiene formation.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Chemical Engineering)|
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