Permeation perovskite membrane

Xu, S.J. and Thomson, W.J. (1999) Oxygen permeation rates through ion-conducting perovskite membranes. Chemical Engineering Science, 54, 3839-3850. 

Dixon et al. simulated the partial oxidation of o-xylene to phthalic anhydride over a vanadium pentoxide catalyst supported on alumina, in a dense perovskite membrane tube. A non-isothermal model was used, which included the effect of temperature on the permeation rate. The competing reaction, complete oxidation to combustion products, is favored at higher temperatures. Comparisons were made to fixed bed reactors operated under the same conditions. For the fixed bed with inlet temperature 630 K, the usual hotspot near the front of the bed was seen, as shown in Figure 11. 

The motivation for both was the report of high rates of O2 permeation through perovskite membranes of the formula Lai tSr Coi >,Fe j,03 5 by Teraoka et al. which have been discussed above. 

Because the physical parameters such as the diffusivities and the equilibrium constants for the BCN membranes are not readily available in the literature, modeling analysis of hydrogen permeation through the MPEC membrane was carried out for the SrCe0.95Y0.05O3 X (SCY) perovskite membrane. The required physical parameters are taken from the literature [15-19] and are listed in Table 7.1. 

Air separation membranes are typically dense ceramic (typically perovskite) membranes, which selectively permeate oxygen in ionic form. Over the past two decades. Air Products (ITMs) and Praxair (oxygen transport membranes [OTMs]) have worked towards the commercial scale-up of these membranes for applications in power generation, gasification, and gas to liquid conversion [94]. Air Products has focused on a planar configuration, whereas Praxair on tubular membranes. 

Fig. 7.7 Temperature dependence of the rate of oxygen permeation through perovskite membranes.

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

As described above, the resistances to oxygen permeation in perovskite membranes may be from the bulk diffusion and the surface exchange reactions. 

In the oxidation section, CH4 is partially oxidized in order to achieve the high temperatures required for O2 permeation through the perovskite membranes and to simultaneously preheat part of the CH4/steam feed. 

Table 4.1 Comparison of oxygen permeation performance of BSCF5582 membranes in different geometries with other most studied A Sr, ByCo 0 i based perovskite membranes. All flux values and sweep gas flow rates are quoted at standard temperature and pressure (STP) s C) ... 

Zeng Y, Lin Y S and Swartz S L (1998), Perovskite-type ceramic membrane synthesis, oxygen permeation and membrane reactor performance for oxidative coupling of methane , Membrane Sci, 150,87-98. 

Concerning non-porous membranes, these are categorized as dense ceramic electrolytes such as yttria-stabilized zirconia (YSZ) and perovskite membranes [16], which allow only the permeation of ionic oxygen. Permeation through metal membranes such as palladium and a palladium alloy is based on the selective dissolution of hydrogen and diffusion through the metal membrane. 

CO2 Capture Using Dense Perovskite Membranes Permeation Models... 

Figure 14.1 (a) O2 and (b) H2 semipermeation within single-phase perovskite membranes, and (c) chemical activity profile in the presence of a pressure gradient. In this representation, and fifp indicate the chemical potential of the permeating gas (/ = 02, H2) at... 

In Section 14.3 we concentrate our attention on the formulation of equations for modeling gas semipermeation within perovskite membranes for high-tem-perature CO2 capture applications. In such derivations, we assume that external diffusion at both the feed/membrane and permeate/membrane sides of the membrane (steps 1 and 2, respectively) can be neglected. In such a situation, bulk diffusion (step 3) and surface exchange kinetics (steps 2 and 4) are expected to contribute only to the permeation process. 

Equations (14.14) and (14.18) can be used as starting point for generating equations describing O2 and H2 permeation within single-phase perovskite membranes. Key to these equations is the nature of the boundary conditions at the feed/membrane and permeate/membrane surfaces. To this aim, one needs to address appropriate defect point thermodynamics to establish equilibrium and surface exchange relations for all potential species that can play a role during permeation. As a general rule, the law of mass action can be used to predict the concentration of ionic vacancies, protons, electrons, and electron holes in the membrane. Below we describe a series of models that can be deduced for ID steady-state permeation within perovskite and extensively other MIEC membranes. 

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