Palladium-silver thin wall tubes are produced by an innovative procedure based on the diffusion welding: these permeators are proposed for separating and producing high-pure hydrogen in both separators and membrane reactors. The reliability of these dense metallic permeators is strongly related to the design configuration of the membrane modules. in fact, as a consequence of hydrogenation and thermal cycles, the dense metallic tubes vary significantly in their length: in case of constraints between the membrane and the module, cyclic axial stresses are applied to the thin wall tube involving the rupture of the permeator. in our applications, a finger-like assembly of the permeator tube has been designed: it permits the free elongation and contraction of the palladium alloy tube avoiding any mechanical stress. In this work, different configurations of palladium membrane reactors used for separating ultra pure hydrogen are described and a study of a membrane process for producing ultra pure hydrogen from ethanol reforming is also presented. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.