Hollow fiber membranes, commercially

See also Gas separation adsorption adsorbents for, 1 612 coal gasification, 6 824 commercial separations, l 618t hollow-fiber membrane modules for, 15 823... 

Many nitrogen generator devices are commercially available to produce high purity gas in small amounts. In these, nitrogen is obtained from compressed air. It is separated from other air components by selective permeation through polymeric hollow fiber membranes after prefiltration. 

The process design principles of SLM, non-dispersive extraction, and hybrid hquid membrane systems need to be understood through bench scale experiments using feed solution of practical relevance. While the economic analysis of an ELM process can be performed from small scale experiments, such an analysis is difficult for other LM systems. In particular, availability and cost of hollow fiber membranes for commercial application are not known apriori. A simple rule of thumb for cost scale-up may not be apphcable in the case of an HE membrane. Yet we feel that the pilot plant tests would be adequate to make realistic cost benefit analysis of a liquid membrane process, since the volume of production in )8-lactam antibiotic industries is usually low. 

Polymer precipitahon by cooling to produce microporous membranes was hrst developed and commercialized by Akzo [33,37], which continues to market microhltration polypropylene and poly(vinylidene fluoride) membranes produced by this technique under the trade name Accurel . Flat sheet and hollow fiber membranes are made. Polypropylene membranes are prepared from a solution of polypropylene in N, A-bis(2-liydroxyethyl)tal lowamine. The amine... 

A commercial nitrogen enrichment system is illustrated in Fig. 17. Hollow-fiber membrane modules are connected to a compressed air feed at 70-150 psi. The feed in usually to the bore side of the hollow fibers. Oxygen (and water vapor that may be present) permeate out of the fiber into the shell and exit at low pressure. Dry, nitrogen-enriched air... 

On the commercial front, an artificial liver system has reached advanced clinical trial stage. Based on pig hep-atocytes immobilized in a hollow-fiber membrane module, this system provides temporary life support until a liver from a human donor is available for transplantation (Fig. 50). Also under development is an artificial pancreas intended as a permanent replacement of the native organ (Fig. 51). 

With respect to carbon membranes, the molecular sieving carbon membranes, produced as unsupported flat, capillary tubes, or hollow fibers membranes, and supported membranes on a macropo-rous material are good in terms of separation properties as well as reasonable flux and stabilities, but are not yet commercially available at a sufficiently large scale, because of brittleness and cost among other drawbacks [3,6],... 

So, Sulfolane and Carom, ca 1997, are two current rival processes. Sulfolane has a slight advantage over Carom in energy consumption, while Carom has 6—8% less capital for the same capacity Sulfolane unit. In 1995, Exxon (37) commercialized the most recent technology for aromatics recovery when it used copolymer hollow-fiber membrane in concentration-driven processes, pervaporation and perstraction, for aromatic—paraffin separation. Once the nonaromatic paraffins and cycloparaffins are removed, fractionation to separate the C6 to C9 aromatics is relatively simple. 

First commercial hollow-fiber membrane module developed by DuPont. This module configuration further increased the packing density of membrane modules. 

There have been numerous studies exploring the concept of membrane reactors. Many of them, however, are related to biotechnological applications where enzymes are used as catalysts in such reactions as saccharification of celluloses and hydrolysis of proteins at relatively low temperatures. Some applications such as production of monoclonal antibodies in a hollow fiber membrane bioreactor have just begun to be commercialized. 

Extraction of phenol from aqueous solution using hollow fiber membrane contactor was first investigated in Ref. [100]. However, the membrane used was not completely microporous. Instead, it was a dialysis-type membrane. A commercial plant to separate phenol from hydrocarbon fraction using microporous membrane contactors was reported in Ref. [101]. Soda lye was used to react with the phenol transferred from the feed phase to create and maintain the driving force for separation. This industrial-scale application enabled the processing of hydrocarbon fraction to a full-value raw material for phenol and acetone synthesis. 

Table 1 Commercially available hollow fiber membranes Company... 

Fig. 15. A commercial cartridge containing hollow fiber membranes. This is a Permasep cartridge made by DuPont.

Du Pont does not currently market Permasep permeators for gas separations. They did, however, in the B-1 Permasep permeator, introduce the first commercial, hollow fiber permeator for gas separations. This permeator employed hollow fibers of polyethylene terephthalate as the membrane. Later, permeators having aramid hollow fiber membranes were field tested for hydrogen separations. Du Pont is presently actively engaged in research for the development of membrane technology for a wide variety of applications. 

Compared to batch processes, continuous processes often show a higher space-time yield. Reaction conditions may be kept within certain limits more easily. For easier scale-up of some enzyme-catalyzed reactions, the Enzyme Membrane Reactor (EMR) has been developed. The principle is shown in Fig. 7-26 A. The difference in size between a biocatalyst and the reactants enables continuous homogeneous catalysis to be achieved while retaining the catalyst in the vessel. For this purpose, commercially available ultrafiltration membranes are used. When continuously operated, the EMR behaves as a continuous stirred tank reactor (CSTR) with complete backmixing. For large-scale membrane reactors, hollow-fiber membranes or stacked flat membranes are used 129. To prevent concentration polarization on the membrane, the reaction mixture is circulated along the membrane surface by a low-shear recirculation pump (Fig. 7-26 B). 

FLOW PATTERNS IN MEMBRANE SEPARATORS. There are several ways of arranging the surface area in a gas separator, and some of these are illustrated in Fig. 26.5 for hollow-fiber membranes with an external skin. Only a few fibers are shown, and their si2S is greatly exaggerated for clarity. A commercial separator has up to a million fibers in a shell several inches in diameter. The fibers are sealed... 

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