Membrane reactor application to hydrogen production

Selective removal of hydrogen in a membrane reactor enables the hydrogen pr oduction by steam reforming at lower reaction temperatures than conventiona l processes. We invented a composite membrane consisting of thin palladium layer deposited on the outer surface of porous ceramics by electroless-plat ing. The palladium layer could completely cover the surface, so that only h ydrogen could permeate through the membrane with a 100% selectivity. By use of this kind of membrane, Tokyo Gas and Mitsubishi Heavy Industries have d eveloped a membrane reformer applicable to the polymer electrolyte fuel cel l system. Our current approach is the application of a CVD technique to dep osit non-Pd metals, such as Pt, to overcome the limitations caused by Pd me mbranes, such as hydrogen embrittlement. The permeability and permeation se lectivity of these metal-ceramic composite CVD membranes were investigated in a comparison with electroless-plating palladium membranes, as well as th e performance in membrane reactors applied to steam reforming of methane. T he permeation of hydrogen through the CVD membranes is not based on the sol ution-diffusion transport mechanism but on the surface diffusion mechanism. Although the CVD membranes gave higher conversion of methane than thermody namic equilibrium, their performance became similar to electroless-plating membranes, only when the membranes showed high H-2/N-2 separation factors. (C) 2000 Elsevier Science B.V. All rights reserved.