Palladium alloy membranes membrane reactors

Damle, A.S., J. Schwartz, and P. Apte, Palladium-alloy based Membrane Reactor Process for Hydrogen Generation, Proceedings of2005 Fuel Cell Seminar, Palm Springs, CA, November 2005. 

The next step in the processor development will be to integrate the palladium alloy membrane with the methanol steam reformer reactor. The researchers anticipate that the addition of the palladium membrane will improve the reactor performance due to in-situ hydrogen removal. 

The key problem of the cross-flow reactor is not how to construct an effective separation of the two flowing phases. It is instead connected with how to design the porosity and location of the catalytic active zones of the separating walls so that the transport resistance across the wall does not limit the conversion and the selectivity of the chemical reactions. Palladium-alloy membranes, or thin films of these alloys on porous ceramic tubs, seem to have the potential to be good solutions of the separating-wall problem for cross-flow reactors used for hydrogenation reactions. 

Gryaznov ct al. [30-32] have done pioneering work in the study of differently designed palladium-alloy membrane reactors for reactions in both gas phase and liquid phase. Most interest was directed to the composition and properties of the membranes, which were decisive questions at this stage of the development, and still are. Selectivity problems in various organic chemical reactions were also of importance to study. 

Yoshida, H. et al., Preliminary design of fusion reactor fuel clean-up system hy the palladium alloy membrane method, Nucl. Technol./ Fusion, 3, 471, 1983. 

Conventional production of vitamin K consists of four steps hydrogenation of 2-methylnaphthoquinone-l,4 to 2-methylnaphthohydroquinone-l,4 in a solvent in the presence of Raney nickel separation of the product from the catalyst by filtration evaporation of the solvent and boiling with acetic anhydride. Because the anhydride is highly corrosive, it tends to attack the nickel, and hence complete separation of the catalyst is necessary. On the other hand, use of a palladium alloy membrane reactor eliminates corrosion and makes it possible to complete the whole process in a single step (Gryaznov et al., 1986). The overall reaction is... 

W. H. Lin, Y. C. Liu and H. F. Chang, Elydrogen production from oxidative steam reforming of ethanol in a palladium-silver alloy composite membrane reactor, J. Chin. Inst. Chem. Eng., 2008, 39, 435-440. 

In parallel with the development of the membrane reformer system, a new concept membrane module, which has a palladium alloy membrane coated on the porous support tube with catalytic activity has been developed (Nishii, 2009). This membrane module is expected to provide a more compact reactor because the reactor does not require a separate catalyst. It is also expected that this module can be manufactured at low cost by applying the industrially-established mass production process used to make oxygen sensors for combustion control in vehicles with internal combustion engines. 

Pex P, van Delft Y, Correia L, 2004, Palladium alloy membranes for energy efficient membrane reactors. Proceedings of the 8th international conference on Inorganic membranes. Cincinnati, July 18-22 s.n., Vols. pp. 524-527. 

Abstract In this chapter, recent progress on palladium (Pd)-based membrane reactors (MRs) is outUned concentrating, in particular, on the production of pure hydrogen. Aspects of many reactions, as well as analysis of both the Pd-based and the amorphous membranes under study, and the governing equations are presented. Some critical aspects of non-Pd-based membranes are also discussed. All the preparation techniques for pure, alloyed, amorphous, non-Pd-based membranes used in MRs are briefly summarized and compared. Moreover, some problems related to the effect of contamination of the Pd-based membranes on the H2 flux are discussed. 

Pinacci P, Broglia M., RadaeUi M., Bottino A., Capannelli G. and Comite A., Development of Palladium Alloy Membranes for Hydrogen Separation from Synthesis Gas in Membrane Reactors, Proc. of 3 Int. Conf on Clean Cod Technologies for our Future, Caghari (I), May 15-17,2007. 

An integrated proof-of-concept (POC) size fluidized-bed methane reformer with embedded palladium membrane modules for simultaneous hydrogen separation is being developed for demonstration (Tamhankar et al., 2007). The membrane modules will use two 6 in. X 11 in. Pd-alloy membrane foils, 25-pm thick, supported on a porous support. The developmental fluidized-bed reactor will house a total of five (5) membrane modules with a total membrane area of about 0.43 m2 and is scheduled for demonstration by September 2007. 

The feasibility of the palladium membrane system with an oxidation reaction on the permeation side and 1-butene dehydrogenation reaction on the reaction side in a membrane reactor has been successfully demonstrated. The palladium and its alloy membrane not only can withstand high temperature but also are selectively permeable to hydrogen... 

V. M. Gryaznov and his co-workers (e.g. IGryaznov, 1986]) have extensively explored the permselective properties of palladium and its alloys as dense membranes and membrane reactors. While their studies will be discussed in later chapters, it suffices to say that the palladium-based membranes have reached the verge of a commercialization potential for the process industry. 

Palladium and selective alloys with other metals can be fabricated into dense membrane reactors in foil or tubular form, mostly in thin layers to reduce permeation resistance. In... 

Shown in Table 8.6 arc some literature data on the use of dense membrane reactors for liquid- or multi-phase catalytic reactions. Compared to gas/vapor phase application studies, these investigations are relatively few in number. Most of them involve hydrogenation reactions of various chemicals such as acetylenic or ethylenic alcohols, acetone, butynediol, cyclohexane, dehydrolinalool, phenylacetylene and quinone. As expected, the majority of the materials adopted as membrane reactors are palladium alloy membranes. High selectivities or yields are observed in many cases. A higher conversion than that in a conventional reactor is found in a few cases. 

Corrosive reaction streams. In some application environments, the reactive or corrosive nature of one or more of the reaction components in a membrane reactor can pose a great technical challenge to the selection as well as the design of the membrane element Feed streams often contain some Impurities that may significantly affect the performance of the membrane. Therefore, attention should also be paid to the response of the selected membrane material to certain impurities in the reactant or product streams. Care should be taken to pretreat the feed streams to remove the key contaminants as far as the membrane is concerned in these cases. For example, palladium alloy membranes can not withstand sulfur- or carbon-containing compounds at a temperature higher than, say, 500 C [Kamcyama et al., 1981]. Even at lOO C, the rate of hydrogen absorption (and, therefore, permeation) in a pure palladium disk is... 

Dense palladium-based membranes. Shown in Table 10.1 are modeling studies of packed-bed dense membrane shell-and-tube reactors. All utilized Pd or Pd-alloy membranes except one [Itoh et al., 19931 which used yttria-stabilized zirconia membranes. As mentioned earlier, the permeation term used in Ihe governing equations for the tube and shell sides of the membrane is expressed by Equation (10-51b) with n equal to 0.5 [c.g., Itoh, 1987] or 0.76 [e.g., Uemiya et al., 1991]. 

The data of Tables 2 and 3 show that palladium-ruthenium alloys with mass % of ruthenium from 4 to 7 have high hydrogen permeability, catalytic activity toward many reactions with hydrogen evolution or consumption, and good mechanical strength [35]. Seamless tubes with a wall thickness of 100 and 60 p.m, as well as foils of 50-tim thickness made of the mentioned alloy, are commercially available in Russia. The tube of outer diameter of 1 mm and wall thickness of 0.1 mm is stable at a pressure drop of up to 100 atm and a temperature up to 900 K. The application of such tubes for membrane reactor will be discussed in next part of this section. 

The increase in membrane catalyst surface per unit volume of the reactor shell was achieved [111] by means of thin-walled palladium alloy tubes in the form of plane double-... 

The main advantages of reactors with composite membrane catalysts arc the higher hydrogen permeability and smaller amount of precious metals in comparison with those presented in Section II. All constructions of the reactors with plane membrane catalyst may be used for composites of thin palladium alloy film and porous metal sheet The design of reactors with composite membranes on polymeric support may be the same as for diffusion apparatus with polymeric membranes (see, for example. Ref. 138). A very promising support for the composite membrane catalysts is hollow carbon fiber [139], once properly thermostable adhesives are found. 

Metal- and alloy-containing membranes are currently applied mainly in ultrapure hydrogen production. Pilot plants with palladium alloy tubular membrane catalyst were used in Moscow for hydrogenation of acetylenic alcohols into ethylenic ones. In the Topchiev Institute of Petrochemical Synthesis, a laboratory-scale reactor of the same type was tested... 

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