MIEC membranes

In the previous sections, it has been demonstrated that, in order to improve the properties of known MIEC membrane materials and to develop new materials, a fundamental understanding of their defect chemistry and the transport of defects is crucial. This is achieved through interpretation of experimental thermochemical and transport data by means of defect models. 

Oxygen partial pressure between the two sides of the membrane is the driving force of oxygen permeation. Figure 3.1c shows a dual-phase MIEC membrane, which can be visualized as a dispersion of a continuous electronic conducting phase into an SE matrix. The electronic conducting phase is usually made from precious metal or metal oxides. 

Table 3.1 Oxygen permeation fluxes of some MIEC membrane materials...

Figure 18.1 Schematic of oxygen permeation across the MIEC membranes ( oxygen vacancy o-lattice oxygen h-electron hole).

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... 

Combining eqns (18.9) and (18.10) gives the specific permeation rate through the MIEC membranes in terms of the oxygen partial pressures and membrane dimensions as ... 

It is known that the MIEC membranes inevitably undergo a kinetic demixing/ decomposition process under oxygen separation conditions. When an oxygen ion conductive membrane is exposed to an oxygen chemical potential... 

The calculation also indicates that the oxygen recovery should be limited within 20 — 40% so as to reduce the overall oxygen production cost of the MIEC membrane systems. 

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)...

Several groups have tried to extend the chemical stability of MIEC membrane materials against CO2 by using different approaches, some of which are discussed in the following sections. 

MIEC membrane material Membrane type Flux (ml/cmVmin) Temperature t C) Reference... 

Figure 4.15 (a) 3D CAD model and (b) a photo of a demonstration unit equipped with MIEC membranes for oxygen separation. fSource Reproduced with permission from Ref [92], Copyright 2012, Ralf Kriegel and Ingolf Voigt)... 

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