Membranes oxygen permeation rates

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

Figure 11.17 C2 product yield and selectivity of oxidative coupling of methane of a 0.5-m long plug-flow membrane reactor as a function of (ratio of oxygen permeation rate to methane flowrate at the reactor entrance) [Wang and Lin, 1995]...

They have also modeled a perfectly mixed membrane reactor for the same reaction. For this membrane configuration, the C2 selectivity is essentially 1(X)% for a jo value of less than 0.2 and drops off rapidly with increasing The yield becomes greater as the relative oxygen permeation rate increases. The yield reaches a maximum and then decreases with the permeation rate. There is only a limited range of Jo in which the yield can reach beyond 20%. 

Fig. 10.8. Temperature variation of the oxygen permeation rate from the air to the helium (30 cm min ) side of disc membranes Lao.6Ao. oo.8Feo.z03.5 (A = Na, Ba, Ca, Sr), 20 mm in diameter and 1.5 mm thick, after Teraoka et al. [38]. Reproduced (data re-scaled) from Teraoka et al. [38].

Investigations carried out on membrane reactors based on pure oxide ion-conducting membranes have been reviewed [12]. Compared to the M lEC-membrane reactor, SEMRs allow for direct control of the oxygen permeation rate due to the faradaic coupling of oxygen flux and cell current. The SEMR has advantages over conventional catalytic reactors [3, 5], including ... 

The disk type membrane reactor made of BaCoo.4Feo.4Zro.203 j in syngas production experiments at 850°C can be operated steadily for more than 2,200 h with a high catalytic performance of 96-98% CH4 conversion, 98-99% CO selectivity and an oxygen permeation rate of 5.4-5.S ml/cm. min. Moreover, a short induction period of 2 h was also obtained. 

These estimates give only an upper limit of oxygen permeation rate because surface exchange reactions may result in some suppression of the overall transport. For the conditions typical for syngas generation (pO2=0.21 atm, pOj = 10 atm, 950°C), the results for the membranes with L = 0.1cm and different chromium contents are shown in Fig. 3. In the calculations at high pressures the ion conductivity values were assumed to be nearly equal to those at low pressures. Fig. 2. It is seen that the permeation rate in chromium doped samples is smaller than in the parent ferrite. Nonetheless, it may achieve a value of about 4 ml cm min in the sample with y = 1, which corresponds to the syngas production rate of about 20-25 ml-cm -min in the methane partial oxidation process. In combination... 

A material for which the chemical stability in the presence of CO2 and SO2 has been extensively studied is BSCF, as it is one of the membrane materials with the highest flux. The presence of CO2 causes a reversible decline in oxygen flux. Even at concentrations of 500 ppm CO2 (ambient air), a slight decrease in the oxygen permeation rate is observed [34]. This decrease is caused by the formation of carbonates of alkaline earth metals on the exposed surface of the membrane. The carbonate formation of perovskite materials AB03 g in the presence of CO2 can be expressed as follows [72] ... 

Figure 4.8 Effect of CO2 on the oxygen permeation rate of a BSCF membrane at 10 bar feed pressure and temperatures between 800 and 900°C. (Source Reproduced from Ref. [70], with permission from Elsevier)...

As a result, the oxygen permeation flux under POM reaction conditions is much higher than that when helium is used as the sweep gas at the same temperature (Gong and Hong, 2011). Furthermore, the POM catalyst has great influence on the oxygen permeation rate of the membrane, although the mechanism is not very clear (Ishihara et al, 2002). 

To date, a variety of oxygen permeable membranes have been reported. In 1985, Teraoka et al. reported that La-Sr-Co-Fe-based perovskite-type oxides (LSCF), especially with high Sr and Co content, have a high oxygen permeation rate (Teraoka,... 

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