Hollow fiber reverse osmosis membranes

Schiffer, D.K. Davis, R.B. Coplan, M.J. "Development of Composite Hollow Fiber Reverse Osmosis Membranes" NTIS Report No, 80-213044, 1979. 

Orofino, T. A. (1977). Technology of hollow fiber reverse osmosis systems. In Reverse Osmosis and Synthetic Membranes (S. Sourirajan, eds.), pp. 313-341 National Research Council, Ottawa, Canada. 

Hollow-Fiber Reverse-Osmosis Composite Membranes Process and Properties... 

In reverse osmosis, the commonly used modules are spiral-wound. Plate-and-frame and tubular modules are limited to a few applications in which membrane fouling is particularly severe, for example, in food applications or processing heavily contaminated industrial wastewater. The hollow fiber reverse osmosis modules used in the past have now been almost completely displaced by spiral-wound modules, which are inherently more fouling resistant, and require less feed pretreatment. 

Fig. 13. A hoUow-fiber reverse osmosis membrane element. Courtesy of DuPont Permasep. In this twin design, the feedwater is fed under pressure into a central distributor tube where half the water is forced out radiaUy through the first, ie, left-hand, fiber bundle and thus desalted. The remaining portion of the feedwater flows through the iaterconnector to an annular feed tube of the second, ie, right-hand, fiber bundle. As in the first bundle, the pressurized feedwater is forced out radially and desalted. The product water flows through the hollow fibers, collects at each end of the element, and exits there. The concentrated brine from both bundles flows through the concentric tube in the center of the second bundle and exits the element on the right.

Davis, R.B. Schiffer, D.K. and Kramer C.E. "Hollow Fiber Reverse Osmosis Composite Membranes Process and Properties", ACS Symposium Series 153, Synthetic Membranes, Vol 1 ACS, Washington D.C. 367, 1981. 

Figure 15. Bottom surfaces (A) phos-phonylated-PPO reverse osmosis membrane (B) interior skin at lumen of the polysulfone hollow fiber shown in Figure 12.

Albany International Research Co. has developed an advanced hollow fiber composite reverse osmosis membrane and module under the name of Quantro II . This composite membrane is comprised of a porous hollow fiber substrate on which has been deposited a rejection barrier capable of fluxes of commercial importance at high rejection of dissolved salts at elevated temperatures. Resistance to active chlorine has been demonstrated. Proprietary processes have been developed for spinning of the fiber, establishment of the rejection barrier and processing of the fiber to prepare modules of commercial size. Prototype modules are currently in field trials against brackish and seawater feed solutions. Applications under consideration for this membrane include brackish and seawater desalination as well as selected industrial concentration processes. 

As Figure 5.12 shows, Toray s PEC-1000 crosslinked furfuryl alcohol membrane has by far the best sodium chloride rejection combined with good fluxes. This explains the sustained interest in this membrane despite its extreme sensitivity to dissolved chlorine and oxygen in the feed water. Hollow fine fiber membranes made from cellulose triacetate by Toyobo or aromatic polyamides by Permasep (Du Pont) are also comfortably in the one-stage seawater desalination performance range, but the water fluxes of these membranes are low. However, because large-surface-area, hollow fine fiber reverse osmosis modules can be... 

Much effort has been expended in attempting to use membranes for separations. Reverse osmosis membranes are used worldwide for water purification. These membranes are based on size selectivity depending on the pores used. They do not have the ability to selectively separate target species other than by size. Incorporation of carrier molecules into liquid membrane systems of various types has resulted in achievement of highly selective separations on a laboratory scale. Reviews of the extensive literature on the use of liquid membrane systems for carrier-mediated ion separations have been published [15-20]. A variety of liquid membranes has been studied including bulk (BLM), emulsion (ELM), thin sheet supported (TSSLM), hollow fiber supported (HFSLM), and two module hollow fiber supported (TMHFSLM) types. Of these liquid membranes, only the ELM and TMHFSLM types are likely to be commercialized. Inadequacies of the remaining... 

All reverse osmosis membranes shown above were with flat sheet porous membranes. However, this was also extended to hollow fiber membranes. The first hollow fibers... 

Membrane technology may become essential if zero-discharge mills become a requirement or legislation on water use becomes very restrictive. The type of membrane fractionation required varies according to the use that is to be made of the treated water. This issue is addressed in Chapter 35, which describes the apphcation of membrane processes in the pulp and paper industry for treatment of the effluent generated. Chapter 36 focuses on the apphcation of membrane bioreactors in wastewater treatment. Chapter 37 describes the apphcations of hollow fiber contactors in membrane-assisted solvent extraction for the recovery of metallic pollutants. The apphcations of membrane contactors in the treatment of gaseous waste streams are presented in Chapter 38. Chapter 39 deals with an important development in the strip dispersion technique for actinide recovery/metal separation. Chapter 40 focuses on electrically enhanced membrane separation and catalysis. Chapter 41 contains important case studies on the treatment of effluent in the leather industry. The case studies cover the work carried out at pilot plant level with membrane bioreactors and reverse osmosis. Development in nanofiltration and a case study on the recovery of impurity-free sodium thiocyanate in the acrylic industry are described in Chapter 42. 

During the 1960 s, the DuPont Company screened numerous polymers to determine the suitability of materials other than cellulose acetate for use in reverse osmosis desalination. The results of this work indicated that aromatic polyamides were the "choice as the best polymer type for use in the DuPont commercial permeators".7 The company was most successful in developing an asymmetric aromatic polyamide reverse osmosis membrane in a hollow fine fiber configuration which successfully competed with cellulose acetate in the market place. 

Reverse osmosis membrane is produced in sheet form-up to 60 inches wide and lengths up to 1,500 feet-and as a hollow fine fiber. The asymmetric cellulose acetate was originally produced as a sheet and later as a hollow fine fiber. The asymmetric aromatic polyamide was originally produced as a hollow fine fiber and later in sheet form. The composite membranes with polyamide or polyurea membrane barrier layers are produced in sheet form as of the end of 1987, but research has been and will continue to be done to produce the composite reverse osmosis membranes as a hollow fine fiber. 

In this context, only two polymers have ever been used on a large scale in asymmetric membranes cellulose acetate and Permasep B-9/B-10 aramids. The former polymer predates the era of reverse osmosis membranes. The latter polymer has been used in hollow fiber membranes for 15 years. Attempts to bring other new polymers into asymmetric membrane production have been few (PBIL, PBI, polypiperazineamides), generally without particular success. 

Meiny different supports have been used to prepare ILMs Including cellulose acetate reverse osmosis membranes (1 6, 25, 29, ), micro-porous polypropylene ultrafiltration membranes (31-3 T7 polyvinyl chloride filters (35), and hollow fiber cellulose acetate reverse osmosis membranes T36). Way et al. ( ) discuss the chemical and physical properties that must be considered when an ILM support Is selected. 

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. As described previously, the breakthrough discovery that made reverse osmosis possible was the development of the Loeb-Sourirajan as5mimetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. Currently, the total worldwide market for reverse osmosis membrane modules is about 300 million/year, split approximately between 15% hollow-fiber and 85% spiral-woimd modules. The general trend of the industry is toward spiral-wound modules for this application, and the market share of the hollow-fiber products is falling (75). 

The polymer ntxlules were observed not only on the surface of reverse osmosis membranes, but also on the surface of asymmetric membranes prepared for the separation of gas mixtures by Kazama et al [86]. While preparing hollow fiber membranes from their Cardo-type polyamide polymer, they investigated the microstructure of the membrane by an electron microscope. Skin layers... 

An example described in detail in this chapter shows that a reverse osmosis membrane can also be used for the separation of the product from the mixture of microorganisms, substrates, and nutrients. Often, microorganisms and enzymes that act as biocatalysts are immobilized to membranes, mostly to hollow fiber membranes. 

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