Oxygen permeation MIEC membranes

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... 

In most MIEC perovskite membranes for oxygen permeation, the electronic conductivity usually overwhelms the ionic conductivity, i.e. CyDy and... 

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 should be noted that mixed rate control is often reported in the literature on MIEC for oxygen separation in three cases when the membrane thickness is very close to its critical value, when the oxygen permeation flux values no longer seem to progress in a linear manner and when the oxygen permeation is co-controlled by both bulk diffusion and surface exchange processes (as shown in the illustration in Figure 4.3) [10]. To better... 

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)...

Oxygen permeation measurements and sealing dense MIEC ceramic membranes... 

Oxy Fuel Combustion Power Production Using High Temperature O2 Membranes 99 Table 4.2 Comparison of oxygen permeation performance of C02 tolerant MIEC materials... 

Engels, S., Markus, T., Modigell, M. and Singheiser, L. (2011) Oxygen permeation and stability investigations on MIEC membrane materials under operating conditions for power plant processes. Journal of Membrane Science, 370,58-769. 

Figure 3.2 Schematic illustration of oxygen permeation through mixed ionic-electronic conducting (MIEC) membranes when air is used as the feedstock stream (Zhu Yang, 2011). Reprinted with permission hy Elsevier.

The influence of carbon dioxide on the oxygen permeation of MIEC membranes has been extensively studied compared with the effect of other gases, such as SO2, which can also be present in the gas streams. Of course, CO2 will be the major component of a hypothetical gas mixture where the MIEC membrane should work (e.g., oxy-fuel process). Nevertheless, the influence of SO2 must be mandatorily evaluated and represents one of the biggest concerns in this area. For example, the SO2 concentration in the flux gas can be around 400 ppm or even higher than 1000 ppm, as reported before the scrubber system in some power plants in China [82]. Up to 2011, few reports can be found dealing with membrane operation in SO2 environments. However, on related topics, for example, catalysis, several studies revealed the formation of sulfetes and sulfldes... 

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