Hollow fibers, performance

RO membrane performance in the utility industry is a function of two major factors the membrane material and the configuration of the membrane module. Most utility applications use either spiral-wound or hollow-fiber elements. Hollow-fiber elements are particularly prone to fouling and, once fouled, are hard to clean. Thus, applications that employ these fibers require a great deal of pretreatment to remove all suspended and colloidal material in the feed stream. Spiral-wound modules (refer to Figure 50), due to their relative resistance to fouling, have a broader range of applications. A major advantage of the hollow-fiber modules, however, is the fact that they can pack 5000 ft of surface area in a 1 ft volume, while a spiral wound module can only contain 300 ftVff. 

In the present study, we fabricated hollow fiber membrane modules and performed experiments at several conditions. The energy consumption of this process is compared to those of conventional gas absorption processes and membrane gas separation processes. 

The main difference between titania nanotube and the ID nanostructures discussed before is the presence of an hollow structure, but which has significant consequences for their use as catalytic materials (i) in the hollow fiber nanoconfinement effects are possible, which can be relevant for enhancing the catalytic performance (ii) due to the curvature, similarly to multi-wall carbon nanotubes, the inner surface in the nanotube is different from that present on the external surface this effect could be also used to develop new catalysts and (iii) different active components can be localized on the external and internal walls to realize spatially separated (on a nanoscale level) multifunctional catalysts. 

Hydrogel membranes are particularly attractive because of high permeability and separation factor [300], and good stability for CO2/N2 separation [299], PVDF hollow fiber membrane modified by alkali was coated by PYA hydrogel on its surface and PVDF-PVA hydrogel membranes show better hydrophilic performance. For carbonate hydrogel (sodium carbonate concentration of 3.7 %) membrane, C02, concentration from 1.3 % to 0.6 % in feed gas could be decreased to 0.9-0.4 % at the outlet at 25 °C. 

Molecular sieves are porous aluminosilicates (zeolites) or carbon solids that contain pores of molecular dimensions which can exhibit seleaivity according to the size of the gas molecule. The most extensive study on carbon molecular sieve membranes is the one by Koresh and Soffer (1980,1987). Bird and Trimm (1983) also described the performance of carbon molecular sieve membranes, but they were unable to prepare a continuous membrane. Koresh and Soffer (1980) prepared hollow-fiber carbon molecular sieves, with pores dimensions between 0.3 and 2.0 run radius (see Chapter 2). 

Ismail, A.F., Kusworo, T.D., and Mustafa, A. (2008) Enhanced gas permeation performance of polye-thersulfone mixed matrix hollow fiber membranes using novel Dynasylan Ameo silane agent. /. Memhr. Sci.,... 

Jiang, L.Y., Chung, T.S., and Kulprathipanja, S. (2006) An investigation to revitalize the separation performance of hollow fibers with a thin mixed matrix composite skin for gas separation. 

The results obtained were partially reported elsewhere (4) and they are quite similar to those obtained at other experimental sites. Results of long term performance, some of them approaching 10,000 hours are shown in Fig. 3 and Fig. 4. As can be seen in Fig. 3 the initial productivity values for all membranes were better than the specified nominal values and continued to be better than predicted. The results shown in Fig. 4 indicated that the normalized rejection of the membranes tested, except for one of the hollow fiber membranes was better or within the limits specified by the membrane producers. One of the membranes that showed an initially low rejection was successfully restored to the nominal value after treatment as recommended by the manufacturer. 

Measurements of RO Performance. RO performances were measured by the simple apparatus, as shown in Figure 2. The water flux and salt rejection of the hollow fiber membranes under operating pressure in the range of 50 to 120 Kg/cm2c were determined using the feed water of 3.5 NaCl, at 25 C and at product water recovery ratio of less than 1 , after an elapsed time of 2 hrs. 

RO performance of the CTA hollow fiber membrane used in Hollosep was measured under higher pressure and analysed in terms of A and D j j/K value. These values remained almost unchanged under operating pressure of up to 100 Kg/cm G. Moreover, long term performance test of the module at high pressure of 75 Kg/ cm2G was satisfactorily carried out with compaction factor less than 0.03. 

Module performance calculated by the simplified module model based on the permeability of hollow fiber membrane was in fair agreement with actual module over the wide range of operating conditions. 

Yazdi, A. S. and Es haghi, Z., Two-step hollow fiber-based, liquid-phase microextraction combined with high-performance liqnid chromatography A new approach to determination of aromatic amines in water. Journal of Chromatography A 1082(2), 136-142, 2005. 

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. 

Peng, J.-R, Liu, J.-R, Hu, J.-T., and Jiang, G.-B., Direct determination of chlorophenols in environmental water samples by hollow fiber supported ionic liquid membrane extraction coupled with high-performance liquid chromatography, J. Chromatogr. A, 1139,165-170, 2007. 

The greatest use of membranes is for reverse osmosis desalination of seawater and purification of brackish waters. Spiral wound and hollow fiber equipment primarily are applied to this service. Table 19.6 has some operating data, but the literature is very extensive and reference should be made there for details of performance and economics. 

Figure 19.6. Gas permeation equipment and performance, (a) Cutaway of a Monsanto Prism hollow fiber module for gas separation by permeation, (b) Flowsketch of a continuous column membrane gas separator, (c) Composition profiles of a mixture of C02 and Oz in a column 5 m long operated at total reflux [Thorman and Hwang in ( Turbak, Ed.), Synthetic Membranes II, American Chemical Society, Washington DC, 1981, pp. 259-279],...

Hollow fibers - [FRACTIONATION,BLOOD - CELL SEPARATION] (Vol 11) - [HIGH PERFORMANCE FIBERS] (Vol 13)... 

In preparation of permselective hollow-fiber membranes, morphology must be controlled to obtain desired mechanical and transport properties. Fiber lubrication is performed wilhottl a easting surface. Therefore, in the moving unsupported thread line, the nascent hollow -liber membrane musi establish mechanical integrity in a very short time. 

J. Lemanski and G.G. Lipscomb, Effect of Fiber Variation on the Performance of Counter-current Hollow-fiber Gas Separation Modules, 7. Membr. Sci. 167, 241 (2000). 

K. Watanabe and S. Kyo, Pervaporation Performance of Hollow-fiber Chitosan-Polyacrylonitrile Composite Membrane in Dehydration of Ethanol, J. Chem. Eng. Jpn 25, 17 (1992). 

Concurrently with the work on carbon dioxide and hydrogen sulfide at General Electric, Steigelmann and Hughes [27] and others at Standard Oil were developing facilitated transport membranes for olefin separations. The principal target was the separation of ethylene/ethane and propylene/propane mixtures. Both separations are performed on a massive scale by distillation, but the relative volatilities of the olefins and paraffins are so small that large columns with up to 200 trays are required. In the facilitated transport process, concentrated aqueous silver salt solutions, held in microporous cellulose acetate flat sheets or hollow fibers, were used as the carrier. 

Figure 11.26 Performance of a 37 m2 hollow fiber silver-nitrate-impregnated facilitated transport membrane for the separation of propylene/propane mixtures. The feed pressure was 5-13 atm the permeate was a hexane liquid sweep stream. The vertical dotted lines show when the membrane was regenerated with fresh silver nitrate solution [27]. Reprinted with permission from R.D. Hughes, J.A. Mahoney and E.F. Steigelmann, Olefin Separation by Facilitated Transport Membranes, in Recent Developments in Separation Science, N.N. Li and J.M. Calo (eds) (1986). Copyright CRC Press, Boca Raton, FL...

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