Oxygen permeation rate

Gas permeation through Teflon AF thin films is extraordinarily high, with permeation rates increasing as PDD content increases. AF-2400 has an oxygen permeation rate of 99,000 cB (centi-Barrers) and a carbon dioxide permeation rate of 280,000 cB compared to 420 cB and 1200 cB for PTFE respectively. These unusually high permeation rates are thought to be the direct result of the microvoids present in the copolymer. 

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 ... 

Not only is there negligible Retort Shock, but with desiccant containers, a lag time to reestablish oxygen barrier in the EVOH is not detectable. In fact, a very low permeability coefficient of 0.02 is established within seven days of retorting, the minimum time period at which permeability can be measured. The high initial oxygen permeation rate, that is seen immediately after retorting with non-desiccant containers, is never seen with desiccant containers. 

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... 

Molar flow rate of air feed and the sweep gas Oxygen permeation rate Reverse surface exchange reaction rate constant... 

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