Membrane palladium

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

Palladium Diffusion. Palladium is very permeable to hydrogen but not permeable to other gases. As a result, it is a useful hydrogen purifier. A palladium membrane, heated to 400 °C, purifies hydrogen to <10 ppb but requires a high pressure differential for net diffusion to take place at reasonable rates of hydrogen supply. 

Fig. 4. Structure of stream reformer equipped with palladium membranes...

The auto-thermal reaction of ethanol occurred in the shell side of a palladium membrane reactor in which a Zn-Cu/AlaOs industrial catalyst (MDC-3) was packed with silica powder. Ethanol-water mixture (nH2o/nEioH=l or 3) and oxygen (noa/nEioH=0.2,0.776 or 1.035) are fed concurrently to the shell side. The reaction temperatures were set at 593-723 K and the pijrasures were 3 10 atm. 

Figure 4. Comparison of Propane Aromatization Performances of a Palladium Membrane Reactor (PMR) and a Conventional Reactor (CR) using a Ga-H-ZSM-5 Catalyst...

Figure 3.2 Flow chart for palladium membrane fabrication process [10].

The cost of Pd-alloy membranes used for hydrogen separation may be reduced by depositing a thin Pd-alloy film on a suitable porous substrate to form a composite membrane. Almost all of the Pd-alloy membrane development efforts are, thus, focused on preparing thin yet defect-free Pd-alloy composite membranes (e.g., Hopkins, 2007 Coulter, 2007 Delft et al., 2005 Damle et al., 2005 Mardilovich et al., 2002). A detailed review of the Pd-alloy membrane research has been prepared by Paglieri and Way (2002) with an extensive bibliography of the palladium membrane research to date. An updated review has been recently prepared by Collot (2003) and Paglieri (2006). 

Pure palladium becomes brittle in the presence of hydrogen during thermal cycling due to dimensional changes caused by a transformation between two phases (a and ft) of palladium hydride around 300°C. To avoid metal embrittlement and resulting membrane cracking or distortion, pure palladium membrane should not be exposed to hydrogen at temperatures below 300°C. To increase resistance to embrittlement, Pd is alloyed with... 

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. 

Gryaznov, V.M., Hydrogen permeable palladium membrane catalysts, an aid to the efficient production of ultra purechemicals and pharmaceuticals, Plat. Met. Rev., 30,68-72,1986. 

Itoh, N. and R. Govind, Combined oxidation and dehydrogenation in a palladium membrane, Ind. 

Lin, Y.M. and M.H. Rei, Separation of hydrogen from the gas mixture out of a catalytic reformer by using supported palladium membrane, Sep. Purif. Technol., 25,87-95,2001a. 

Paglieri, S.N., Palladium membranes, Nonporous Inorganic Membranes, Chapter 3, eds. A.F. Sammells and M.V. Mundschau, Wiley-VCH Verlag GmBH, Weinheim, 2006. 

Palladium catalysts, 10 42 14 49 16 250 Palladium-catalyzed carbonylation, 13 656 Palladium chloride/copper chloride, supported catalyst, 5 329 Palladium compounds, 19 650-654 synthesis of, 19 652 uses for, 19 653-654 Palladium films, 19 654 Palladium membranes, 15 813 Palladium monoxide, 19 651 Palladium oxide, 19 601... 

Membrane processes are based on the selective transmission characteristics of the membrane material for different molecules, whereby the most effective membranes are usually also the most expensive. For example, the purest hydrogen can be captured by palladium membranes with suitable additives, but their low permeability make it necessary to use large membrane surfaces and high pressures, which result in high costs. 

Mikhalenko, N. N., E. V. Khrapova and V. M. Gryaznov. 1986. Influence of hydrogen on the dehydrogenation of isopropyl alcohol in the presence of a palladium membrane catalyst. Kinet. and Catal. 27(1) 125-128. 

Nagamoto, H. and H. Inoue. 1986. The hydrogenation of 1,3-butadiene over a palladium membrane. Bull. Chem. Soc. Japan 59 3935-3939. 

Nazarkina, E. B. and N. A. Kirichenko 1979. Improvement in the steam catalytic conversion of methane by hydrogen liberation via palladium membranes Khim. Tekhnol. Topi. Masel. 3 5-10. 

Lin, Y.-M., Rei, M.-Fl. 2000. Proeess development for generating high purity hydrogen by using supported palladium membrane reaetor as steam reformer. Int J Flydrogen Energy 25 211-219. 

Researchers at Lehigh University are developing a methanol reforming silicon reactor with a palladium membrane for a hydrogen purification system built using semiconductor fabrication techniques. The device is designed to produce hydrogen for fuel cells for portable electronic devices, such as laptop computers and cell phones. 

Figure 16. Microscale palladium membrane. (Reprinted with permission from refs 83 and 84. Copyright 2001 and 2002 Springer.)...

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. 

Low-loaded, organophilic Pd-montmorillonites were shown to exhibit high cis-selectivity in the hydrogenation of 1-phenyl-1-alkynes working with high (=5000) substrate catalyst ratio.402 Studies with respect to the use palladium membrane catalysts403 105 and polymeric hollow fiber reactors406"408 were reported. 

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