Thin wall Pd-Ag permeator tubes have been produced by a diffusion welding procedure: these low-cost membranes are proposed for separating and producing high-pure hydrogen in 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 hydrogen and thermal cycling. the dense metallic tubes vary their length: in case of constrains between the membrane and the module, cyclic axial stresses on the tube can rise leading to the rupture of the permeator. In our application, a finger type assembly of the membrane tubes has been designed: it permits the free elongation and contraction of the palladium alloy tube avoiding any mechanical cycling stress. A process in which a membrane reactor produces ultrapure hydrogen needed to a polymeric fuel cell of power 500 W has been designed: the process foresees the use of both traditional and membrane reactors. The membrane reactor consists of a bundle of Pd-Ag thin wall tubes operating in parallel where the water gas shift reaction takes place. The membrane reactor consisting of Pd-Ag tubes operating at 350°C and 200 kPa while the hydrogen stream of about 6 liter/min is recovered in the shell side by means of nitrogen sweep gas at 100 kPa.
