Metallic membranes manufacturing

Three forms of caustic soda are produced to meet customer needs purified diaphragm caustic (50% Rayon grade), 73% caustic, and anhydrous caustic. Regular 50% caustic from the diaphragm cell process is suitable for most appHcations and accounts for about 85% of the NaOH consumed in the United States. However, it caimot be used in operations such as the manufacture of rayon, the synthesis of alkyl aryl sulfonates, or the production of anhydrous caustic because of the presence of salt, sodium chlorate, and heavy metals. Membrane and mercury cell caustic, on the other hand, is of superior quaUty and... 

Micropore diffusion, 1 596, 597-599 Microporous catalysts, in bisphenol A manufacture, 14 420 Microporous metal membranes, 15 813t Microporous particles, apparent effective diffusivity and, 15 729-730 Microporous range, pore diameters within, 16 812... 

The manufacture of dense metal membranes or thin films can be effected by a number of processes casting/rolling, vapor deposition by physical and chemical means, electroplating (or electroforming) and electroless plating. By far, casting in combination with rolling is the predominant preparation and fabrication technique. It is noted that many of these processes have been demonstrated with palladium and its alloys because of their low oxidation propensity. Preparation of dense metal membranes is summarized in some detail as follows. 

The MF membranes are usually made from natural or synthetic polymers such as cellulose acetate (CA), polyvinylidene difiuoride, polyamides, polysulfone, polycarbonate, polypropylene, and polytetrafiuoroethylene (FIFE) (13). Some of the newer MF membranes are ceramic membranes based on alumina, membranes formed during the anodizing of aluminium, and carbon membrane. Glass is being used as a membrane material. Zirconium oxide can also be deposited onto a porous carbon tube. Sintered metal membranes are fabricated from stainless steel, silver, gold, platinum, and nickel, in disks and tubes. The properties of membrane materials are directly reflected in their end applications. Some criteria for their selection are mechanical strength, temperature resistance, chemical compatibility, hydrophobility, hydrophilicity, permeability, permselectivity and the cost of membrane material as well as manufacturing process. 

Other key issues confronting the development of metal membranes include maintenance of a defect-free structure during manufacture, degradation in membrane strength from hydrogen embrittlement and decreased performance over time due to hydrogen entrapment within the structure. 

The most common methods for manufacturing thin metal membranes include rolled foil, drawn tubes, and films deposited onto porous substrates (ceramic or sintered metal). Usually, electroless plating or electrolytic plating are the methods used to deposit the permselective metal onto the porous substrates although vapor deposition methods have been the subject of much research effort However, to date, vapor deposition methods have not proven to be a superior membrane fabrication method. There are pros and cons to each of these methods, but commercial membrane modules have only succeeded using rolled foil and drawn tubular membranes. 

Although metallic and ceramic materials are used as membranes, polymeric materials account for the vast majority of commercial products. Polymer selection depends on a number of factors including intrinsic transport properties, mechanical properties, thermal stability, chemical stability (e.g., chemical resistance and biocompatibility), membrane manufacturability, cost, and patentability. The two most common types of polymers are glassy engineering thermoplastics and rubbery polysiloxanes. 

Tecnimont-KT SpA, has focused on a traditional manufacturing path, realizing an innovative substrate for metallic membranes. 

A high temperature Pd/Stainless Steel H2 separation membrane manufactured by CRI-Criterion by deposition of Pd on sintered porous metal support with permeable dimensions of 1 inch OD and 6 inches length is shown in Figure 11.7. An SEM cross section of the top layers of the membranes showing the porous stainless support, the inter-metal diffusion barrier, and the selective Pd layer. Note that the picture lack pinholes in Figure 11.8. 

High temperature Pd/stainless steel H2 separation membrane manufactured by CRI-Criterion by deposition of Pd on sintered porous metal support with permeable dimensions of 1 inch OD and 6 inch length. 

R. Bredesen and H. Klette, Method of manufacturing thin metal membranes U.S. Patent 6 086 729, 2000. 

Various methods can be applied to produce Pd-based membranes, depending on some factors such as the nature of the selective layer metal, the manufacturing facilities, the required thickness, surface area, shape, purity, etc. Nevertheless, no one method can produce a membrane, which combines advantageously all these factors. Therefore, the choice of the production method is a compromise among these factors. 

Abstract The purpose of this chapter is to provide an overview of palladium-alloy metallic membranes (which are also used in the industry sector for the purification of hydrogen) for applications in the transport industry. Concepts are discussed in the first section. Main membrane materials and manufacturing processes are described in Section 18.2. 

Bredesen R. and Klette H., Methods of manufacturing thin metals membranes, (2000), US Patent 6,086,729. 

Maleic Anhydride. The ACGIH threshold limit value in air for maleic anhydride is 0.25 ppm and the OSHA permissible exposure level (PEL) is also 0.25 ppm (181). Maleic anhydride is a corrosive irritant to eyes, skin, and mucous membranes. Pulmonary edema (collection of fluid in the lungs) can result from airborne exposure. Skin contact should be avoided by the use of mbber gloves. Dust respirators should be used when maleic anhydride dust is present. Maleic anhydride is combustible when exposed to heat or flame and can react vigorously on contact with oxidizers. The material reacts exothermically with water or steam. Violent decompositions of maleic anhydride can be catalyzed at high temperature by strong bases (sodium hydroxide, potassium hydroxide, calcium hydroxide, alkaU metals, and amines). Precaution should be taken during the manufacture and use of maleic anhydride to minimize the presence of basic materials. 

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