Oxygen permeation values

Very recently oxygen permeation values reported by Shen et al. [Ill], Chen et al. [112] and Teraoka et al. [110] show that the obtainable flux values at high... 

Figure 1 shows the effect of relative humidity (RH) upon the oxygen permeation values (OPV) of a few representative polymers. This data is reported in the units of cc-mil/(100 sq.in.-day-atm). For many polymers such as polyethylene, OPV is essentially unaffected by changes in RH. 

A Mocon (Modern Controls, Inc.) instrument modified for accurate humidity control was used to measure the oxygen permeation value (OFV) on film structures. These were generally measured at 30°C and 80% relative humidity and are reported as cm3 O2/100 in2-day-atm. 

Figure 1 shows the oxygen permeation values for a series of blends of aluminum, mica and talc in an EVOH resin containing 44 mole % ethylene. The relative effectiveness of the three fillers are proportional to their aspect ratios as predicted by theory. 

Barrier Layer Resin Barrier Layer Thickness Mil Oxygen Permeation Value, 30°C, 75% RH... 

Oxygen Permeation Values of Pure Matrices and 3vol% Filler—Polypropylene Nanocomposites with and without 2 wt% Compatibilizer... 

Nylon barrier layers are used in packaging films and blow molded bottles. In these applications, their excellent resistance to oxygen permeation are valued when packaging greasy foods, such as potato crisps (chips), that rapidly turn stale when exposed to oxygen. 

Example 9-2. What is the maximum value for oxygen permeation (/) through a 50 pm thick LDPE film at 10°C when the exterior of the film is in contact with air and the maximum estimated value for oxygen permeation at 25 C from example 1 is used ... 

Example 9-3. A 20 cm long HDPE tube with an external diameter of 10 cm and a wall thickness of 1 mm is filled with an oxygen absorbing substance. Both ends of the pipe are sealed with a 100 pm thick LDPE film and the tube is stored in air. What is the total oxygen permeation into this tube using the permeability coefficient values from Table 9-2 for HDPE and LDPE at 25 °C ... 

Therefore, assnming an effective area size as S and a membrane thickness as L, respectively, the total jonle heat value caused by oxygen permeation can be derive as ... 

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%. 

These types of membranes are currently only suitable for oxygen separation — mainly with oxidic layers, or hydrogen separation — mainly with Pd(Ag) alloys. As discussed in Chapter 6, reasonable fluxes (permeation values) can be obtained at high (for oxygen) to intermediate (for hydrogen) temperatures. The production of defect-free thin layers of these materials remains problematic. 

A more direct method to determine the free volume differences in the series is to calculate them using the method of Lee (12), which uses a group contribution approach. Table I contains the values for 1/SFV (specific free volume) which were calculated using the additive molar volumes provided by Van Krevelen (13). Figure 5 shows a plot of the log of the dry OPV for the n-l series against 1/SFV. A linear relationship, which is what would be expected if free volume is a determining factor in oxygen permeation, is obtained in this plot. 

With a proper understanding of the transport properties in such multilayered structures, the containers for use in sterilization processes can be appropriately designed. As an example in designing for such a situation, a mass balance on water permeating into or out of a multilayered structure can be made to estimate the amount of water which can affect the hydrophilic polymer. With this analysis, the time required to dry the water sensitive layer and return the container to ambient oxygen permeability values can be estimated. Assuming the transport of water in the multilayer configuration is limited by the outer layers, the water content (M) of the inner layer in a prescribed container can be described by ... 

Fig. 6.5 Oxygen permeation flux through LSFG/5M membrane versus oxygen partial pressure on air side for different temperatures lep) and corresponding values of the surface exchange coefficient calculated with Eq. 6.3 (right)...

NOTE k values were estimated from oxygen permeation fluxes versus... 

The applicability of oxygen membrane materials depends essentially on their oxygen permeation fluxes. The dependence of the flux density j02 on the oxygen pressure difference across the membrane of thickness L can be calculated by the using of the measured total conductivity o and calculated values Oi for the ion conductivity. 

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... 

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