Hydrogen production dense metallic membranes

Sholl DS, Ma YH. Dense metal membranes for production of high purity hydrogen. MRS Bull 2006 31 770-3. 

In cases where high purity hydrogen is valued, dense metal membranes are an attractive option over polymeric membranes and porous membranes that exhibit much lower selectivities. Two examples where this is true are low-temperature fuel cells (e.g., proton exchange membrane fuel cells [PEMFCs] and alkaline fuel cells [AFCs]) and hydrogen-generating sites where the product hydrogen is to be compressed and stored for future use. 

As with any engineering exercise, when the objective is to successfully scale-up and develop a product for commercial and industrial applications, the focus must be on achieving acceptable economics. Of course, economics involves the upfront capital expenditure, as well as any ongoing maintenance costs and fuel or other utiUty costs. One of the potential advantages of dense metal membranes for hydrogen purification is that the membranes are preferably operated at signifi-... 

Figure 7.4 shows the structure of an FBMR with plate-type Pd-Ag dense metal membranes for hydrogen production [8, 9]. Two-sided planar membrane panels are suspended vertically in the reactor. Each side of the panels consists of 25 pm thick Pd-Ag foil mounted on a porous stainless steel base with a barrier layer to prevent interdiffusion... 

Enhancement in conversion by the usage of a membrane reactor has been demonstrated for many dehydrogenation reactions. Product selectivity of some hydrogenation and other reactions arc found to improve with a permselective membrane as part of the reactor. Several dense metal as well as solid elecu olyte membranes and porous metal as well as various oxide membranes have been discovered to be effective for the reaction performance. 

Inorganic membrane reactors for hydrogen production an overview with particular emphasis on dense metallic... 

Although the results of the research on these new materials for hydrogen separation membranes are very promising, no important applications are reported at the present time. The aspects of stability and reliability still have to be addressed. Examples of applications are reported for the refractory metals which exhibit a good resistance to aggressive environments such as hydroiodic acid. A study has also demonstrated that Nb or Ta dense membranes could be applied for hydrogen recovery from the decomposition of HI in the iodine-sulphur process for thermochemical hydrogen production. 

Membrane separators offer the possibility of compact systems that can achieve fuel conversions in excess of equilibrium values by continuously removing the product hydrogen. Many different types of membrane material are available and a choice between them has to be made on the basis of their compatibility with the operational environment, their performance and their cost. Separators may be classified as (i) non-porous membranes, e.g., membranes based on metals, alloys, metal oxides or metal—ceramic composites, and (ii) ordered microporous membranes, e.g., dense silica, zeolites and polymers. For the separation of hot gases, the most promising are ceramic membranes. 

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