Membrane hydrogen diffusion through

FIGt 22-48 Transport mechanisms for separation membranes a) Viscous flow, used in UF and MF. No separation achieved in RO, NF, ED, GAS, or PY (h) Knudsen flow used in some gas membranes. Pore diameter < mean free path, (c) Ultramicroporoiis membrane—precise pore diameter used in gas separation, (d) Solution-diffusion used in gas, RO, PY Molecule dissolves in the membrane and diffuses through. Not shown Electro-dialysis membranes and metallic membranes for hydrogen. 

In permeation measurements the first signs of hydrogen diffusing through 1 mm steel membranes can be observed in a few minutes. The practical measurement of diffusion parameters tends to be rather unreproducibie. 

The sheet of porous stainless steel with Re-carbon deposited film divided membrane reactor onto two equal parts. Cyclohexane vapors were fed to the surface of membrane with Re-carbon film (reaction part of membrane reactor) in argon flow from the thermostated bubler. The second part of reactor was flowed by argon and used for the removal of hydrogen, diffused through a membrane catalyst from the reaction zone. The products of reaction were benzene and hydrogen. 

Permselective Reactor Model. This model was developed to size an experimental reactor system. Even though, some of our initial assun tions are being refined in our continuing efforts, some in ortant conclusions can be drawn from our early work. The first approach used was to idealize the permselectivity, and assume that only hydrogen diffuses through the membrane. This assun tion cannot be justified for the characteristics of the membranes studied experimentally. It does, however, permit one to place an upper limit on the expected performance of the system. 

While H,S removal at the cathode, with sulfur production at the anode, was shown, the process was not yet completely selective as was shown by the removal of CO,. This was due to hydrogen diffusion through the membrane which would cause reactions (7) and (8) to simply become the reverse of reactions (5) and (6). In this situation, there is no net cell reaction for species transport and H,S, CO, and H,0 would simply be concentrated on the anode side of the cell as a function of applied current. 

The dissociated atomic hydrogen diffuses through the membranes and is recombined into molecular hydrogen that desorbs on the other side of the membrane. 

Dissolved platinum can also enter the polymer electrolyte membrane and diffuse through the electrolyte in direction of the anode. Once more reducing potential regions are reached inside the membrane, platinum recrystallizes and forms a band of platinum particles inside the membrane [58]. Direct reduction of Pt -ions via molecular hydrogen dissolved in the electrolyte membrane is also possible. 

This result may be due to the protons inside the connected 3D channels of analcime, obtained after H-form transformation. Therefore, these protons act as bridges for the proton transport, thus increasing the proton conductivity. Furthermore, the incorporation of solid particles in the hybrid membrane increases the resistance to hydrogen diffusion through the membrane, lowering its fuel crossover in PEMFC applications. Nevertheless, at 7 >90°C, the sPEEK/Analcime membrane loses water fast with a consequent depletion of proton conductivity [151]. 

The hydrogen peroxide then diffuses through the innermost membrane of cellulose acetate, where it is oxidized at a Pt anode. 

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