Hydrogen permeation mechanism membranes

Figure 8.7 Mechanism of permeation of hydrogen through metal membranes...

The main problem with the integration of inert membranes in fixed bed reactors is the membrane itself. It has to be sufficiently stable against thermal and mechanical stress, inexpensive and of high selectivity and permeability. At present, Pd-based alloys are the only sufficiently temperature stable and permselective membranes for hydrogen permeation. Since permeation through homogeneous membranes is a rather slow process, large membrane areas are required for reasonable production quantities. 

Evaluation of hydrogen absorption and permeation provides valuable information on the hydrogen evolution and hydrogen embrittlement mechanism. Devanathan-Stachurski [5,6] developed a technique to measure hydrogen permeation though metallic membranes. This technique is based on the assumption that the following conditions are established at each surface of the membrane under potentiostatic control ... 

Use the hydrogen atom direct mechanism [18,19] discussed in Ref [16] to explain why the steady state hydrogen permeation current density, Joo. is directly proportional to the cathodic current density, f, and is independent of the membrane thickness when the cathodic current density is small. 

Then Uemiya et al. [2] reported another Pd membrane reactor for WGS reaction using Fe-Cr oxide catalysts. The model of flow in the palladium membrane reactor is illustrated in Figure 6.3. They proposed that hydrogen is permeated through palladium membrane via a solution diffusion transport mechanism, and the rate of hydrogen permeation, /, per unit area of membrane, is written in terms of Fick s first law as follows ... 

---