Oxygen permeation mechanism

Engineering Aspects of MIEC Hollow Fiber Membranes for Oxygen Production 255 

The transfer flux of charged species in a mixed conductor can be described by the Nernst-Planck equation  

Galvanic (internal) potential, the gas constant and temperature, respectively. For the ideal state, the activity of defect can be replaced by its concentration (activity coefficient is unit). 

The conductivity of defect can be correlated to its concentration and diffusivity, which is a measure of the random motion of the species i in the lattice, by the Nernst-Einstein equation  

For the oxygen permeation in MIEC membranes, (i) the overall charge balance is applied or = 0 and (ii) the local velocity of inert marker is 

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Schematics of an oxygen membrane reactor for catalytic POx of methane. A blown up section on the left-hand side shows the details of the ceramic membrane wall explaining the mechanism of oxygen permeation across the membrane. /- is the chemical potential of oxygen and ai and

In the final section water and oxygen permeation experiments were done on thin coextruded films to aid in understanding possible transport mechanisms in multilayer structures. An important conclusion is that water transport is important and must be understood before quantitative calculation of oxygen permeation will be possible. 

OCM catalytic properties of R-based mixed oxide ceramic membranes appeared to be determined by the synthesis method, oxygen permeation from one side to the other, surface composition, and the electronic conduction mechanism. 

High-temperature applications of perovskite-type membrane reactors require improved material performances and operational stability. The reactor microstruc-ture and architecture controls were found to be crucial for thermo-mechanical integrity and oxygen permeation kinetics. A multilayer reactor was developed, using second-phase particles to control its microstructure and a co-sintering process to control its architecture. 

Figure 4.3 Schematic of the counter-current oxygen transport mechanism of a symmetric (dense) MIEC membrane exploited for oxygen separation applications (a) and the change in oxygen permeation flux with the membrane thickness (b). fSource Reproduced from Ref [ 10], with permission from Elsevier)...

Wu, Z Thursfield, A., Metcalfe, I. and Li, K. (2012) Effects of separation layer thickness on oxygen permeation and mechanical strength of DL-HFMR-ScSZ. Journal of Membrane Science, 415-416,229-236. 

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