The conventional flow method of measuring H permeation flux was found to be inaccurate and inadequate to obtain a consistent value of H flux and permeance because of changing H concentration along the Pd membrane tube in a H mixture. A new method was designed in which the H concentration was kept constant in the retentate. This constant concentration method was a more accurate measurement of H permeation flux in all of the possible H mixtures: H2+Y with Y = Ar, N2 and CH4 and various H concentrations under different pressure. Permselectivity of the H mixture was measured under this constant concentration method and was compared with both the conventional flow-through method and separate flow measurement of pure component gases. All 3 methods gave a different value of permselectivity for the same composite mixture. This method permitted the accurate measurement of the H flux and permeance in the corresponding composition. It was found that, even with the same partial H pressure differential for Sieverts’ equation, the H flux and permeance decreased dramatically with the lowering of H concentration in the feed.

Constant Concentration Method of Measuring Hydrogen Permeation from a Hydrogen Mixture with Pd Membrane. C.C.Y.Hung, M.H.Rei: Journal of the Chinese Institute of Chemical Engineers, 2007, 38[3-4], 341-8