A selective pump for hydrogen isotopes based on the superpermeation effect in iron

Hydrogen pumping by superpermeation through a pure iron membrane exposed to hydrogen atoms on its upstream side and the compression of the released H2 molecules on the downstream side has been investigated at various driving pressures between 10-6 and 10-3 mbar and in the presence of helium. The compression has been extended to downstream pressures around 10 mbar with corresponding compression factors up to 6x105. They are considerably reduced if the membrane temperature is raised from 520 and 930 K. In the low downstream pressure regime up to 1 mbar the pressure increase depends linearly on both time and atomic flux onto the membrane. Hydrogen pump speeds of about 30 l/s in the 10-6 mbar range are attained with the small oil-free permeation cell. A helium inlet upstream to a partial pressure of 10-3 mbar has no influence on the hydrogen superpermeation. Hydrogen is selectively pumped out. The data are important for the technical utilization of the superpermeation effect, particularly in fusion devices. (orig.)