The effect of direction of hydrogen permeation on the rate through a composite palladium membrane

This paper reports the effect of direction of hydrogen permeation on the rate through a composite palladium membrane. Palladium film is coated on the outer surface of a tubular ceramic support. Permeation rates of hydrogen through the palladium membrane were measured at 573, 673 and 773 K under two modes. The first one is called 'CP mode' in which hydrogen permeates at first through the ceramic support and then through the palladium film. The other mode is called 'PC mode' in which hydrogen permeates in the opposite manner. It was found from the measurements that the permeation rate of hydrogen increased with the increase of temperature and that the permeation rate under CP mode was higher than that under PC mode. Mathematical models taking into account the combined resistances of both palladium film and ceramic support were developed to describe the hydrogen permeation rate through the composite palladium membrane tube under both modes of permeation. In addition, the mathematical models were used to predict the relative contributions of two resistances for both CP mode and PC mode. (C) 2000 Elsevier Science B.V. All rights reserved.