There are a variety of needs for essentially pure hydrogen. Included among these are fuel cells, membrane reactors and fuel reforming operations. As a result there is a strong interest in economical methods for hydrogen separation.
Composite multilayer metal membranes are known for the separation of hydrogen from gaseous mixtures. For example, U.S. Pat. No. 3,350,846 (Makrides et al.) describes separation of hydrogen by permeation through multilayer metal membranes including a Group VB metal sandwiched between two layers of palladium. In U.S. Pat. No. 5,149,420, Buxbaum et al. describe a method for plating palladium onto Group IVB or VB metals to form articles useful for hydrogen separation. U.S. Pat. No. 5,393,325 (Edlund) describes a composite hydrogen separation multilayer metal membrane, as does U.S. Pat. No. 5,738,708 (Peachey et al.).
In some applications of such composite multilayer metal membranes, improved operation at higher temperatures is desirable. Additionally, the catalytic metal layer can often be susceptible to poisoning from species in the feed stream such as, e.g., sulfur and chlorine. Accordingly, despite all of the previous work in the development of composite multilayer metal membranes for hydrogen separation, improvements have been continually sought to improve high temperature efficiency and to reduce susceptibility to poisoning.
It is an object of this invention to provide a composite multilayer metal membrane capable of separating hydrogen or its isotopes by selective diffusion through the membrane and more preferably essentially pure hydrogen or its isotopes, the composite multilayer metal membrane having improved high temperature efficiency.
It is another object of this invention to provide a composite multilayer metal membrane capable of separating hydrogen or its isotopes by selective diffusion through the membrane and more preferably essentially pure hydrogen or its isotopes, the composite multilayer metal membrane having reduced susceptibility to poisoning.
Still another object of the present invention is a process of forming a composite multilayer metal membrane for subsequent separation of essentially pure hydrogen by selective diffusion through the membrane.