Tubular inorganic membranes

A few other players in the nuclear membranes activity also developed inorganic membranes for the filtration of liquids. This was the case with Norton-USA who with the know-how of Euroceral developed MF membranes made of an 0-AI2O3 tubular support with an a-Al203 layer. The inner tube diameter was 3 mm and the outer diameter 5 mm. In 1988-1989, Norton also produced the multichannel membrane elements. These membranes produced by Norton are now sold by Millipore under the trademark Ceraflo . 

Another participant in the French nuclear program, Le Carbone-Lorraine, developed inorganic membranes by combining their know-how in the field of membranes with their expertise in carbon. They developed tubular UF and MF membranes using a tubular carbon support (inner diameter 6 mm, outer diameter 10 mm). The carbon support is made of carbon fibers coated with and bonded by CVD carbon, the separating layers also being made of carbon. These membranes have been marketed since 1988. 

Inorganic membranes employed in reaction/transport studies were either in tubular form (a single membrane tube incorporating an inner tube side and an outer shell side in double pipe configuration or as multichannel monolith) or plate-shaped disks as shown in Figure 7.1 (Shinji et al. 1982, Zaspalis et al. 1990, Cussler 1988). For increased mechanical resistance the thin porous (usually mesoporous) membrane layers are usually supported on top of macroporous supports (pores 1-lS /im), very often via an intermediate porous layer, with pore size 100-1500 nm, (Keizer and Burggraaf 1988). 

For convenience of discussion, modeling studies of packed-bed inert membrane tubular reactors will be divided into two categories depending on the type of inorganic membranes dense or porous. 

Inorganic membranes are very resistant and quite stable at hard-operating conditions. Several materials are available. Different membranes have been successfully tested for separations involving supercritical fluids such as tubular carbon membranes [ 1 ], mbular silica membranes [2-5], silica hollow fibber membranes [6], zeolite membranes [7-10], titane-nafion membranes [11], polycarbonate membrane [12], nanofilter having a thin layer of Zr02-Ti02 [12], and silicalite membranes [4]. 

Crossflow filtration membranes can be produced in flat sheet, hollow fiber, tubular formats when using polymeric materials, and in monolith and tubular configurations when using inorganic membrane materials. Table 14.2 summarizes the various module configurations. 

Membrane processes are classified according to the nature of the membrane and the driving force employed. A number of different types of polymeric/inorganic membranes have been developed in recent times in basically four types of modular assemblies, namely, plate and frame, spiral, tubular, and hollow fine fiber. Table 29.4 gives the application of various membrane processes for the separation of different types of contaminants encountered in effluents. 

Figure 8.7. Shell-and-tube membrane module containing either hollow-fiber polymeric membranes or tubular inorganic membranes.

W. Wang and Y. S. Lin, A theoretical analysis of oxidative coupling of CH4 in a tubular dense membrane reactor. Paper presented at the 3rd International Congress on Inorganic Membranes, July 10-14,1994, Worcester, MA, USA. 

This is a combined organic-inorganic membrane that comprises a macropor-ous a-alumina substrate (tubular or multichannel), an intermediate mesopor-ous inorganic titanium oxide layer (thickness 1 pm) and a microporous Nafion polymer top-layer (thickness less than 0.1 pm). The overall performance and... 

Catalytically active supported ionic liquid membranes were used for propylene/propane vapor mixture separation. In this case, the ionic Hquid was immobilized in the pores of an asymmetric ceramic support, displaying sufficient permeability, good selectivity, and long-term stabUity [51]. Porous inorganic membranes were also used as a support for chiral-selective liquid membranes. For this purpose, porous tubular ceramic membranes were impregnated with 3-cyclodextrin polymer. Such SLMs were used for separation of enantiomers of racemic pharmaceutical chlorthahdone [52]. 

Most inorganic membrane supports exhibit a tubular shape. This is a well-adapted geometry for cross-flow filtration in which the feed stream is circulated across the surface of the membrane and the permeated flux passes through the membrane in a perpendicular direction. Stainless steel, carbon, and ceramic are the most frequently used materials in the preparation of supports. As shown in Fig. 2, tubes or multichannel substrates can act as membrane supports. A well-designed support must be mechanically strong, and its resistance to fluid flow must be very low. Aiming at enhancing flux performances, multilayered substrates have been prepared that exhibit an asymmetric structure... 

UltrafUtration membranes are commonly asymmetric (skinned) polymeric membranes prepared by the phase inversion process. Materials commercially made into membranes include cellulose nitrate, cellulose acetate, polysulfone, aramids, polyvinylidene fluoride, and acrylonitrile polymers and copolymers. Inorganic membranes of hydrous zirconium oxide dqrosited on a tubular carbon liking are alM commercially available. 

Torres et al. (1994) studied nitrobenzene hydrogenation on an asymmetric catalytic porous tubular membrane where a thin catalytic layer (ca. 3 pm) is supported by a thick (ca 1.1 mm) macroporous inert tube and they developed a model using experimental kinetics. They showed that by using an inorganic membrane the most beneficial configuration to the overall reaction kinetics is when the gas phase flows directly on the catalytic layer while the liquid phase flows along the inert support. It should be noted that the support was impregnated by the liquid phase. 

Figure 1.6 Tubular (a), monolithic (b), and hollow fiber (c) inorganic membranes.

In addition to the planar geometry, inorganic membranes can also be produced in flat disk, tubular (dead-end or not), monolithic multi-channel, or hollow fiber configurations as shown in Figure 1.6. Disk membranes are often used in the laboratory because they can easily be fabricated by the conventional pressing method. In the case of tubes, they can be assembled in a module containing a number of tubes connected to a single manifold system. 

A Monolith The monolith configuration is a type of tubular configuration used in inorganic membrane systems (Fig. 6.8) and comprises a ceramic support (or hexagonal log)... 

The book then continues with a review of the current methods and development of fabrication processes for inorganic membrane, and Section II starts with a review of ceramic hollow-fiber membrane fabrication and application. Ceramic hollow-fiber membranes, sometimes called capillary or microtubular membranes, are relatively new types of ceramic membranes compared with planar and tubular counterparts. They have a high surface-area-to-volume ratio, with unique microchannels that have led to innovative applications in separation and catalytic reaction technologies. Chapter 10 introduces the fundamental principles of fabricating microstructured ceramic hollow-fiber membranes and discusses the processing parameters and their influence on the microstructures of the fabricated membranes. Chapter 11 deals with the fabrication of ceramic hollow fibers used as a support for energy conversion... 

The proximal tubular cell plays a major role in the elimination of both inorganic and organic substrates. The ceUs have two distinct membrane domains. The basolateral membrane is in contact with the blood, and the apical brush-border membrane lines the tubular lumen. 

Inorganic Hg+ (less toxic) Hg2+ (more toxic) Gastrointestinal, skin (minor) Soft tissues, especially kidney Acute tubular necrosis gastroenteritis CNS effects (rare) Inhibits enzymes alters membranes Urine... 

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