Palladium alloy membranes preparation

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). 

Tanaka D.A.P., Llosa Tanco M.A., Niwa Si., Wakui Y., Mizukami F., Namba T., Suzuki T.M. Preparation of palladium and silver alloy membrane on a porous a-alumina tube via simultaneous electroless plating. J.Membr.Sci 2005 247 21-27. 

Electroplating. Basically in electroplating, a substrate is coated with a metal or its alloy in a plating bath where the substrate is the cathode and the temperature is maintained constant Membranes from a few microns to a few millimeters thick can be deposited by carefully controlling the plating time, temperature, current density and the bath composition. Dense membranes made of palladium and its various alloys such as Pd-Cu have been prepared. Porous palladium-based membranes have also been made by deposition on porous support materials such as glass, ceramics, etc. 

In the case of catalytic dense membranes such as palladium alloy sheets or tubes, a smooth membrane surface suffers from a small active surface area per unit volume of catalyst. This drawback can be remedied to some extent by adopting some conventional catalyst preparation methods to roughen the membrane suiface(s) to ensure that only the region near the surface is affected unlike the Raney metal catalysts where the entire matrix is leached. For example, Gryaznov [1992] suggested the use of thermal diffusion of a chemically active metal into a Pd alloy sheet followed by acid treatment to remove this metal. 

The alloying of palladium with some other metals permits one to overcome the disadvantages of pure palladium and to prepare the materials with a hydrogen permeability above that of palladium. The insertion of a second and a third component into the palladium membrane may increase its mechanical strength, the hydrogen solubility, and catalytic activity of the membrane toward hydrogen dissociation. This was discussed in many original papers and reviews [26-36]. 

The methods for preparation of nonporous composite membrane catalyst are discussed in Ref. 10. The porous stainless steel sheets were covered with a dense palladium alloy film by magnetron sputtering [113] or by corolling of palladium alloy foil and porous steel sheet. The electroless plating of palladium or palladium alloy on stainless steel [114] or on porous alumina ceramic [115,116] gives the composite membranes with an ultrathin, dense palladium top layer. 

E. Kikuchi and S. Uemiya, Preparation of supported thin palladium-silver alloy membranes and their characteristics for hydrogen separation. Gas Sep. Purif. 5 261 (1991). 

Z.Y. Li, H. Maeda, K. Kusakabe, S. Morooka, H. Anzai and S. Akiyama, Preparation of palladium-silver alloy membranes for hydrogen separation by the spray pyrolysis method. J. Membr. Sci., 78 (1993) 247. 

Palladium and palladium-silver alloy membranes on porous alumina tubes were prepared by means of simultaneous and sequential electroless plating techniques [234], The membrane reactor was used for the direct formation of hydrogen peroxide by catalytic reaction of H2 and 02 at 293 K. The concentration of H202 increased with increases in the transmembrane partial pressure gradient of H2. A high concentration of H202 was obtained with a membrane that consisted of a palladium layer on the outer surface, porous alumina in the middle, and a palladium-silver alloy layer on the inside. 

D.A.PTanaka, M.A.L. Tanco, S. Niwa, Y. Wakui, F. Mizukami, T. Namba and T.M. Suzuki, Preparation of Palladium and Silver Alloy Membrane on a Porous a-Alumina Tube via Simultaneous Electroless Plating, J. Membr. Sci., 247, 21-27 (2005). 

The palladium-silver alloy membrane system was successfully commercialized in the early 1960s [12], but the reduction of palladium content by the addition of silver would still not be a cost-effective alternative for large-scale processes [42] unless micron-scale films could be prepared, a goal currently being addressed by many researchers. In recent years, the Pd-Cu system has been the most heavily investigated alloy for hydrogen membrane applications due to the high permeability of select alloys [67, 90, 91], enhanced mechanical properties [92] and reported chemical resistance. The elevated permeability identifled for select Pd-Cu alloys is attributed to an increase in both the solubility and diffusivity of the B2 crystalline phase [86-88] as compared to the face-centered-cubic (fee) phase that exhibits permeability values proportional to the Pd-content [89, 91, 93]. 

S. E. Nam, K.H. Lee, Preparation and characterization of palladium alloy composite membranes with a diffusion barrier for hydrogen separation, Ind. Eng. Chem. Res. 2005, 44, 100-105. 

A two-step membrane manufacturing process has been reported where a defect free Pd-alloy membrane is first prepared by sputtering deposition onto the perfect surface of a silicon wafer, for example. In a second step the membrane is removed from the wafer and transferred to a porous stainless steel support (see Figure 11.1). This allows the preparation of very thin ( 1-2 pm) defect-free membranes supported on macroporous substrates (pore size equals 2 pm). By this technique, the ratio of the membrane thickness over the pore size of the support may become less than 1, which is two orders of magnitude smaller than obtained by more conventional membrane preparation techniques. Tubular-supported palladium membranes prepared by the two-step method show a H2/N2 permselectivity equal to 2600 at 26 bars and hydrogen flux of 2477 mL(STP) min cm . Since the method enables the combination of macro-porous stainless steel supports and thin membrane layers, the support resistance is negligible. ... 

S. F. Hou, K. Jiang, W. Z. Li, H. Y. Xu and L. X. Yuan, W02005/ 065806, A metal palladium composite membrane or alloy palladium composite membrane and their preparation methods, 2005. 

Nam S-E., Lee S-H., Lee K-H (1999) Preparation of a palladium alloy composite membrane supported in a porous stainless steel by vacuum electrodeposition , J. Membrane ScL, 153(2), 163-173. 

Roa F, Way D, Paglieri SN. Process for preparing palladium alloy composition membranes for use in hydrogen separation, palladium alloy composite membranes and products incorporation or made from the membranes. United States Patent 8119205 2012. 

Due to these problems, research on the development of alternative PEM has been carried out to minimize the shortcomings. Developments in preparing new membranes can be classified into three different branches such as (1) synthesizing new polymers based on nonfluorinated backbones [7,8] (2) incorporating inorganic fillers such as montmorillonite (MMT) [9], palladium alloy [10], silicon [11], titanium oxide [12], and zeolite [13] into parent polymer matrices and (3) sulfonated polymers [14,15]. 

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