Palladium Membrane Purification -

Palladium and palladium alloy membranes have been known for over 100 years to selectively permeate hydrogen over all other gases. The nearly infinite selectivity of palladium alloy membranes is due to the nature of the permeability process. As it is understood today, the permeation mechanism involves several discrete steps (Hydrogen shown as the small red circles, the larger blue and green circles generically represent other non-hydrogen species):

1. Chemisorption of hydrogen molecules from the gas phase onto the membrane surface

2. Dissociation of the hydrogen molecules into two hydrogen atoms

3. Dissolution of the hydrogen atoms into the metal lattice

4. Diffusion of the hydrogen atoms through the bulk metal

5. Precipitation of the hydrogen atoms onto the opposing membrane surface

6. Re-association of the hydrogen atoms into hydrogen molecules on the surface

7. Desorption of the hydrogen molecules from the surface into the gas phase

To see the equation detailing this process, click here.