Low temperature diffusion bonding of Pd-based composite membranes with metallic module for hydrogen separation

Abstract

A diffusion-bonding procedure at a low temperature, i.e. 500 degrees C, based on the high mobility of silver atoms was developed with a newly designed plate-and-frame type hydrogen purification membrane module consisting of a unit cell and a housing. Two membranes made of palladium and copper sputtered on polished porous nickel supports (PNS) followed by Cu-reflow at 750 degrees C, respectively, were assembled in a unit cell to verify that the low temperature diffusion-bonding method could be applied to gas-tight membranes. Ring-shaped silver foils with a thickness of 50 mu m were placed between the membranes and the unit cell body made of nickel plate. A pair of membranes, a pair of silver foils and the unit cell body were compressed with a pair of covers and eight screws by a 17 cm long torque wrench at 12 N m. The diffusion-bonded unit cell was welded in a module housing comprised of a feed port and a retentate port by a laser-operated welder. After the module was constructed, gas-tightness tests were carried out using helium and the measured helium leakage was 8 x 10(-5) mol m(-2) s(-1) at 0.7 MPa, which is the same as the value detected before diffusion bonding with a Viton O-ring. The hydrogen permeation test and durability test consisting of three cycles of alternately changing the temperature and transmembrane pressure difference were carried out using a single gas, hydrogen, and it was found that the hydrogen permeation flux remained constant during the durability test and that the helium leakage did not increase after the durability test. (C) 2008 Elsevier B.V. All rights reserved.