Permeate reduction

Permeation reduction factors of up to 10,000, or 10 , have been realized with the best coatings based on aluminized steels. Ferritic-martensitic steels that were aluminized had the Fe2Al5 phase predominant in the layer sequence, while a 316L steel had FeAlj and FeAl2 as the main aluminide phases. The best permeation barrier resulted from an external alumina film of about 1 micron in thickness grown on the aluminide layers. ... 

There are four specific tasks (1) HDPE treatment and development of alternative tank liner materials for hydrogen gas permeation reduction (2) enhancing epoxy resin toughness to improve the tank carbon liber overwrap performance (3) materials and process evaluation for manufacturing the ISS protective shell and (4) engineering an optimized unitary gas control module. An additional task (5) is the formulation of a roadmap for protot5q)ing and... 

However, Sieverts law is very simple and, therefore, it would be very useful to be able to continue using it even when it is not strictly valid. In this sense, the aim of this chapter is to show a systematic method to take into account the presence of both inhibition and polarization by keeping the form of Sieverts law, but modifying its original structure by means of an appropriate overall permeation reduction coeflicient , PRC (eqn (14.2)) ... 

For this aim, an overall permeance reduction coelScient , PRCP was introduced, to take into account the permeation reduction owing to both concentration polarization and inhibition at the same time. Its definition, reported in eqn (14.19), arises from the simple consideration that the lowest permeance is evaluated at bulk conditions when both polarization and inhibition affect the membrane system, whereas, on the other hand, the ideal membrane behavior and the maximum permeance can be found under pure hydrogen conditions ... 

Similarly to what was done for the coefficients CPC and IC, also for PRC some permeation reduction maps were calculated and developed. These maps are reported and discussed in Section 14.6.4.2. 

In this section, the reduction coefficients introduced before CPC, IC and PRC) are presented in the form of the so-called permeation reduction maps , which... 

Permeation reduction coefficient Equivalent coefficient Considered phenomena... 

Finally, in order to observe quantitatively both the influence of concentration polarization and inhibition by CO, the behavior of the overall permeation reduction coeificient is shown in Figure 14.7, which represents a map analogous to the ones presented for CPC and IC. 

As seen before, PRC has a nonlinear dependence on CPC and IC, which, therefore, cannot simply be added to each other to measure the overall permeation reduction. It has also been shown that PRC assumes the characteristic... 

In this chapter, an innovative approach dealing with the combined effect of concentration polarization and inhibition by CO in Pd-based membranes is discussed and analyzed by means of appropriate coefficients measuring the permeation reduction due to these phenomena. 

All reduction coefficients dealt with in this chapter were calculated from the numerical solution of a complex hydrogen permeation model, opportunely validated by a number of experimental data, and reported in form of permeation reduction maps for several operating conditions. From these maps, the values of CPC, IC and PRC can be read directly and used simply in the modified forms of Sieverts law shown above to evaluate the hydrogen permeating flux, providing in this way a possible novel strategy of membrane module design. 

The approach to the permeation reduction by polarization and inhibition introduced in this chapter for Pd-based membranes is a general concept that, in principle, can be applied to all the other types of membranes considering several reduction factors in different situations. This step can be helpful in developing a standard procedure of membrane module design. 

Comparison between oxygen permeation reduction observed in EPM- -DEM composites (dark square), as predicted by the Gusev and Lusti model for disk-like particles with aspect ratio 60 and 100 (square) and as predicted by assuming that the polymer phase adsorbed on particle surface has a negligible permeability to oxygen a schematic representation of excluded volume is reported. 

Caravella, A., Scura, F., Barbieri, G., Drioh, E. (2010). Inhibition by CO and polarization in Pd-based membranes a novel permeation reduction coefficient. Journal of Physical Chemistry B, 774(38), 12264-12276. 

Figure 5.31 Permeation reduction of a 25-)xm thick palladium membrane containing 40wt.% copper at 8-bar feed pressure versus operating temperature (top) and at a 300°C operating temperature versus carbon monoxide partial pressure (bottom) the permeate pressure was 0.95 bar [403].

Fig. 19.3-1. Diffusion across films of aligned, impermeable flakes. The flakes increase the lag before permeation and reduce permeation once it occurs. The permeation reductions shown vary with the amount and shape of the flakes. (Data from De Rocher et al., 2004.)...

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