Chlorine resistance

Considerable research and development effort is being placed on a chlorine-resistant membrane that wiU maintain permeabUity and selectivity over considerable time periods (years). This polymer activity is not limited to hoUow fibers, but the thick assymetric skin of hoUow-fiber constmction might offer an advantage in resolving the end use need as opposed to the ultrathin dat-sheet composite membranes. 

There has been considerable research on chlorine-resistant RO membranes (48—52). A poly(/n j -2,5 dimethyl)pipera2inthiofura2anainide used in the presence of low (3 mg/L) concentrations of chlorine resulted in a membrane life of three years (48). A copolyamide hoUow-fiber membrane for use in desalination has been developed that is resistant to 0.5 mg/L chlorine (49). Millipore Corporation has also developed a sulfonated polysulfone member that has desirable chlorine-resistance properties. 

Reactive green dyes are obtained by combination of a blue chromophore (a bromamine acid derivative) and a yellow chromophore with a tria2inyl group. Green [70210-47-8] (87) (104) is an example. The yellow chromophore of this dye was invented by ICI for diclilorotria2ine dyes and exhibits good lightfastness and chlorine resistance. 

Rejection Rejection is defined in Background and Definitions. The highest-rejection membranes are those designed for single-pass production of potable water from the sea. The generally accepted criterion is 99.4 percent rejection of NaCl. Some membranes, notably cellulose triacetate fibers are rated even higher. A whole range of membranes is available as rejection requirements ease, and membranes with excellent chlorine resistance and hydrolytic stability can be made with salt rejection over 90 percent. 

Anode supports, cable insulators and the coating on the object to be protected can be destroyed by anodic evolution of chlorine (see Section 7.1), Only chorine-resistant materials should be used. Anodes on retaining walls or between pile foundations can be installed in perforated or fabricated plastic tubes (half-shells) (see Fig. 16-8). They must naturally be provided with very many holes to avoid uneven removal of anode material. Filter tubes of a chlorine-resistant special material or... 

Chlorine replacement, via electrochemical synthesis, 12 809-810 Chlorine reservoirs, formation of, 17 788 Chlorine resistance, of reverse osmosis membranes, 15 835-836... 

Furuhata K, Kato Y, Goto K et al (2007) Identification of yellow-pigmented bacteria isolated from hospital tap water in Japan and their chlorine resistance. Biocontrol Sci 12(2) 39-46... 

Toray s data are plotted as the reciprocal of membrane constants against time elasped like Fig. U. The first generation of Toray module tested at the laboratory might have some defect In the membrane backing material. After 6000 hours in operation, they exchanged half of the modules for the second generation chlorine resistant. The second had been improved about twice in its resistance against flux decline. 

Limited testing on chlorine sensitivity of poly(ether/amidel and poly(ether/urea) thin film composite membranes have been reported by Fluid Systems Division of UOP [4]. Poly(ether/amide] membrane (PA-300] exposed to 1 ppm chlorine in feedwater for 24 hours showed a significant decline in salt rejection. Additional experiments at Fluid Systems were directed toward improvement of membrane resistance to chlorine. Different amide polymers and fabrication techniques were attempted but these variations had little effect on chlorine resistance [5]. Chlorine sensitivity of polyamide membranes was also demonstrated by Spatz and Fried-lander [3]. It is generally concluded that polyamide type membranes deteriorate rapidly when exposed to low chlorine concentrations in water solution. 

NS-300 Membrane. The NS-300 membrane evolved from an effort at North Star to form an interfacial poly(piperazine Isophthala-mide) membrane. Credali and coworkers had demonstrated chlorine-resistant poly(piperazineamide) membranes in the asymmetric form (20). The NS-lOO, NS-200, and PA-300 membranes were all readily attacked by low levels of chlorine in reverse osmosis feedwaters. In the pursuit of a chlorine-resistant, nonbiodegra-dable thin-fiim-composite membrane, our efforts to develop interfaclally formed piperazine isophthalamide and terephthalamide membranes were partially successful in that membranes were made with salt rejections as high as 98 percent in seawater tests. 

In summary, the FT-30 membrane is a significant improvement in the art of thin-film-composite membranes, offering major improvements in flux, pH resistance, and chlorine resistance. Salt rejections consistent with single-pass production of potable water from seawater can be obtained and held under a wide variety of operating conditions (ph, temperature, pressure, and brine concentration). This membrane comes close to being the ideal membrane for seawater desalination in terms of productivity, chemical stability, and nonbiodegradability. 

In pursuit of a chlorine-resistant, non-biodegradable thin-film-composite membrane, Cadotte et al. 97 )03,104 fabricated interfacially the poly(piperazineamide) membrane (NS-300). The interfacially formed piperazine isophthalamide and terephthalamide membranes exhibited high salt rejection (98 %) in sea water tests but their flux was low (Table 8). The replacing of the isophthaloyl chloride with its triacyl chloride analog, trimesoyl chloride improved vastly the flux of the membrane but its seawater salt rejection was low — in the range of 60 70 % (55). The trimesoyl... 

Kawaguchi et al.105) in Teijin Ltd. prepared a similar polyamide composite membrane from piperazine, trimesoyl chloride, and isophthaloyl chloride on a polysulfone support. The membrane exhibited high chlorine-resistance and excellent pressure-resistance. When used for reverse osmosis of an aqueous solution of 0.5% NaCl and NaOCl (available Cl 4 5 ppm) at pH 6.5 7.0, 25 °C, and 42,5 kg/cm2, the water permeation was 1400 and 13301/m2 - day and desalination was 93.4% and 95.7% after 2 and 100 hr, respectively. 

Considerable research and development effort is being placed on a chlorine-resistant membrane that will maintain permeability and selectivity over considerable time periods (years). 

Loeb-Sourirajan membranes based on sulfonated polysulfone and substituted poly(vinyl alcohol) produced by Hydranautics (Nitto) have also found a commercial market as high-flux, low-rejection membranes in water softening applications because their divalent ion rejection is high. These membranes are also chlorine-resistant and have been able to withstand up to 40 000 ppm h of chlorine exposure without degradation.1 The structures of the polymers used by Hydranautics are shown in Figure 5.8. 

The key short-term technical issue is the limited chlorine resistance of interfacial composite membranes. A number of incremental steps made over the past 10-15 years have improved resistance, but current chlorine-resistant interfacial composites do not have the rejection and flux of the best conventional membranes. 

J. Glater, S.K. Hong and M. Elimelech, The Search for a Chlorine-Resistant Reverse Osmosis Membrane, Desalination 95, 325 (1994). 

Indanth rones. The blue indanthrone was the first synthetic vat dye of the anthra-quinone series. Because of its excellent fastness and bright colors it has remained the most important vat dye for a long time despite its low resistance to chlorine. Its chlorine resistance can be improved somewhat by post-halogenation. Introduction of hydroxy or amino groups shifts the shade to green. 

Since the late 1970 s, researchers in the US, Japan, Korea, and other locations have been making an effort to develop chlorine-tolerant RO membranes that exhibit high flux and high rejection. Most work, such as that by Riley and Ridgway et.al., focuses on modifications in the preparation of polyamide composite membranes (see Chapter 4.2.2).11 Other work by Freeman (University of Texas at Austin) and others involves the development of chlorine-tolerant membrane materials other than polyamide. To date, no chlorine-resistant polyamide composite membranes are commercially available for large-scale application. 

Membrane pretreatment includes microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF). Microfiltration and UF membrane processes can remove microbes and algae. However, the pores of MF and UF membranes are too large to remove the smaller, low-molecular weight organics that provide nutrients for microbes. As a result, MF and UF can remove microbes in the source water, but any microbes that are introduced downstream of these membranes will have nutrients to metabolize. Therefore, chlorination along with MF and UF is often recommended to minimize the potential for microbial fouling of RO membranes. The MF or UF membranes used should be chlorine resistant to tolerate chlorine treatment. It is suggested that chlorine be fed prior to the MF or UF membrane and then after the membrane (into the clearwell), with dechlorination just prior to the RO membranes. See Chapter 16.1 for additional discussion about MF and UF membranes for RO pretreatment. 

Si Improves oxidation, nitriding, sulfidation and carburizing resistance. Detrimental to nonoxidizing chlorination resistance Synergistically acts with chromium to improve high-temperature degradation... 

Ni Improves carburization, nitriding, and chlorination resistance detrimental to sulfidation resistance ... 

FIBRAMOLL NI is an economical nonionic softener and lubricant for application on synthetics, cotton and cotton/synthetic blends. FIBRAMOLL NI is recommended for resin finishing where excellent whites are needed. Treated fabrics are non-yellowing and chlorine resistant. 

The wash resistance of finishes with KAURIT S, W and KFN can be improved markedly by addition of KAURIT M90. The chlorine resistance can also be Improved to a certain extent by this addition. 

FIXAPRET AC has essentially the same behaviour as FIXAPRET AH, except that it has somewhat lower activity. It produces finishes with moderate chlorine resistance. 

FIXAPRET PH is, therefore, a top-ranking product for the chlorine resistant finishing of white goods, poplin shirting, blouse materials, and collar interlinings. Good fixation of the product on the fibre is, of course, essential. It should be noted, however, that FIXAPRET PH is liable to impair the light fastness of direct and reactive dyed shades to a certain extent. 

Textiles finished with FIXAPRET PCL have very good easy-care properties, very good hydrolysis stability, and good chlorine resistance. This finish generally has no influence on the light fastness of reactive dyed or printed shades, and in the few cases where it does, the influence is only very slight. 

The usefulness of the product in moist crosslinking is based on its good hydrolysis stability, which permits a strongly acid catalysis e.g. with CONDENSOL FN. The chlorine resistance of finishes obtained by moist crosslinking is good, provided crosslinking is complete. 

They are recommended for the easy-care and antishrink finishing of textiles composed of cotton and rayon staple, alone or in blends with synthetics. The products are eminently suitable for coloured goods, because they do not impair the light fastness of reactive and direct dyed shades in many cases they actually improve this property. The products have no influence on the dyed shade itself, provided the correct catalyst has been selected. FIXAPRET CPN and CP Conc. are also suitable for white goods, provided chlorine resistance of the finish is not required. They are very suitable for the production of peramanent calender effects. 

In contrast to FIXAPRET CPN, FIXAPRET COC produces chlorine resistant finishes when applied by the dry curing process. FIXAPRET COC finishes produced by moist and wet crosslinking, however, are not resistant to chlorine. 

The anticrease effect can be improved still further by combining FIXAPRET TN with FIXAPRET AH, for instance. Finishes produced in this manner also have a useful degree of chlorine resistance. 

In order to obtain good dry crease-recovery, it is advisable to combine the product with a KAURIT type. FIXAPRET BU has no influence on the light fastness of reactive and direct dyed shades. On the other hand, the finishes are not chlorine resistant. 

It is a chlorine-resistant finishing agent for full and stiff effects on textiles of all types when dried at a temperature of at least 120C, the finishes are also resistant to washing. PERAPRET WF is used mainly for Interllnings and for tablecloths and bedsheets. 

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