Hydrogen permeation coefficient

In Eq. (8.43), aj and 2 are transfer coefficients for reactions (8.41) and (8.42), is the cathodic current density and a = F/RT. If ai = 2. the hydrogen permeation current is directly proportional to the cathodic current. This expression is consistent with experiment [16] for atomic hydrogen permeation transients through a HY-130 steel membrane as a function of time for different appHed potentials and other experimental data [20-27]. 

Figure 5.7. Plots of the gas permeation coefficients in 1100 equivalent weight Nafion . (a) Hydrogen and oxygen permeation coefficients at 30°C as a function of water content. The dotted lines signify the transition-region values, (b) Arrhenius plot of the oxygen permeation coefficient as a function of temperature for a liquid-equilibrated membrane, a vapor-equilibrated membrane, and a dry membrane. Also plotted are the oxygen permeation coefficients in water [79] and Teflon [80, 81]. (Figure b is reproduced from Ref. [39] with permission of The Electrochemical Society, Inc.)...

Archimedes number Area of bed cross section Membrane surface area per cell, n Particle diameter Heat capacity Dispersion coefficient Gas diffusivity Bubble phase fraction Emulsion phase fraction Activation energy for hydrogen permeation Gravitational acceleration ( = 9.81) Enthalpy of species j Enthalpy of component i at temperature T at position x... 

All of the considerations made in the previous section lead to the necessity of defining a concentration polarization coefficient that could be directly connected to specific permeation quantities.Here, this approach will be direct to hydrogen permeation through Pd-based membranes. 

The effect of inhibition by CO on hydrogen permeation has recently become the object of several investigations, since CO is typically present in significant amounts in the hydrogen streams to be separated. In particular, a macroscopic model equation was developed to describe the influence of CO on permeation. This equation modifies Sieverts law to take into account the permeance reduction due to CO as reported in eqn (14.15), where the quantities a, and 6co represent a coefficient accounting for other additional effects of CO on adsorbed hydrogen and the membrane surface coverage by CO, respectively ... 

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. 

By varying the electrolyte composition in the left compartment, we can study the effect of adsorbed species on the rate of hydrogen permeation. Figure 11.31 shows the results of experiments carried out with thin iron sheets (0.2 to 2 mm) in different electrolytes saturated or not with H2S [13]. Hydrogen sulfide does not change the diffusion coefficient in the metal but it facilitates the hydrogen dissolution into iron. As a consequence, its presence in the solution increases the observed permeability. In equation (11.24), this translates into an inerease of Chj- The described effect of H2S... 

Figure 8. Hydrocarbon/light gas separation properties of PTMSP. (a) Effect of propane relative pressure on propane and hydrogen permeability coefficients in PTMSP at 25°C. (b) Effect of propane relative pressure on C3H8/H2 mixture selectivity. The feed pressure of the propane/hydrogen binary mixture was 200 psig and the permeate pressure was atmospheric (0 psig) (9). Propane relative pressure is p/psa, where p is the partial pressure of propane in the feed and p, is the saturation vapor pressure of propane.

Hydrogen permeability (or permeation coefficient) of various metals. (Reprinted from Reference 28.)... 

Fig. 20.21 J-l transients for the permeation of hydrogen through ferrous alloys. The normal transient enables the diffusion coefficient ) to be evaluated from the relationship /, = L /6D, where /, is the time at which J attains a value of 0-63 of the steady-state permeation J...

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