Sulfonated polysulfone

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. 

Typically RO systems are preceded by pretreatment units to remove suspended solids/colloidal matter and add chemicals that control biological growth and reduce scaling. Membranes are typically made of synthetic polymers coated on a backing (skin). Examples of membrane materials include polyamides, cellulose acetate and sulfonated polysulfone. 

The addition of an ester sulfonate of an unsaturated fatty acid improves the rinsing properties in washing tests. A mixture of 50% sodium methyl a-sulfostearate and 50% sodium salt of sulfonated methyl oleate (30 70 mono-sulfonate/polysulfonate ratio) was used [83]. 

To date, much effort has been undertaken to develop new alternatives. For example, sulfonated aromatic polymers, i.e., polymers with the sulfonic acid groups directly attached to the main chain or carrying short pendant side chains with terminal sulfonic acid units, attract increasing interest because of their chemical and thermal stability, and the ease of the sulfonation procedure. Some of the proposed polymers are sulfonated polysulfone (SPSU) [134] sulfonated poly(phenylene oxide) (SPPO) [135] sulfonated poly-(ether ether ketone) (SPEEK) [136] poly(phenylquinoxaline) (PPQ) [137] and poly(benzeneimidazole) (PBI) [138],... 

In addition to Nafion-based catalyst layers, additional types have been developed, including CLs with different ion exchange capacities (lECs) [57,58] or with other hydrocarbon-type ionomers such as sulfonated poly(ether ether ketone) [58-60], sulfonated polysulfone [61,62], sulfonated polyether ionomers [63], and borosiloxane electrolytes [64], as well as sulfonated polyimide [65]. These nonfluorinated polymer materials have been targeted to reduce cost and/or increase operating temperature. Unfortunately, such CLs still encounter problems with low Pt utilization, flooding, and inferior performance compared wifh convenfional Nafion-based CLs. 

Kraemer, S. V., Lindbergh, G., Lafitte, B., Puchner, M., andJannasch, P. Substitution of Nafion with sulfonated polysulfone in membrane-electrode assembly components for 60-120°C PEMFC operation. Journal of the Electrochemical Society 2008 155 B1001-B1007. 

Manea, C. and Mulder, M. 2002. Characterization of polymer blends of poly-ethersulfone/sulfonated polysulfone and polyethersulfone/sulfonated poly-etheretherketone for direct methanol fuel cell applications. Journal of Membrane Science 206 443-453. 

A prominent class of poly(aryl ethers) is the sulfone-containing poly(aryl ethers) that is, poly(arylene ether sulfones), or polysulfones (PSF), and their sulfonated derivatives. The structure of a typical sulfonated polysulfone (SPSF) repeat unit is... 

The ability of a liquid to "wet" the membrane material is an indication of that liquids ability to establish and maintain such an interfacial layer. Liquids of surface tension values less than the critical surface tension iy ) of the membrane material are capable of completely "wetting" the polymer. It may be possible therefore, to select membrane materials capable of accomplishing specific separations by their ability to be wet by one solution component but not by the other. For this reason Yc membrane materials is important. By employing the standard techniques of Zisman (43), the critical surface tension for PSF and CA were determined to be 43.0 and 36.5 dynes/cm, respectively. This data indicates that PSF is more readily wet by a larger number of liquids than is CA. Similar measurements for the various sulfonated polysulfones are underway. 

Transport of Ions and Water in Sulfonated Polysulfone Membranes... 

Poly N-amideimide (UOP) Polybenzooxadinon (Bayer) Polyhidantoin (Bayer) Sulfonated polysulfone Sulfonated PPO (GE) NS-100 (North Star) ... 

Chloride, sulfate, and other anions may affect the removal of arsenic by nanofiltration. The effects often depend on the composition of the nanofilter. Specifically, increasing NaCl concentrations actually improves arsenic removals with polyamide thin-film composite filters. On the other hand, NaCl solutions may interfere with the removal of arsenic with sulfonated polysulfone thin-film composite nanofilters (Shih,... 

Figure 5.8 Membranes based on sulfonated polysulfone and substituted poly(vinyl alcohol) are produced by Hydranautics (Nitto) for nanofiltration applications...

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. 

More recently cation-exchange membranes with good mechanical and chemical stability and well-controlled ion-exchange capacity are prepared by dissolving and casting a functionalized polymer such as sulfonated polysulfone, or sulfonated polyetheretherketone in an appropriate solvent, followed by casting the mixture into a film and then evaporation of the solvent [12]. 

The sulfonated polysulfone as well as polyetheretherketone can be cast as a film on a screen. After the evaporation of the solvent a reinforced membrane with excellent chemical and mechanical stabilities and good electrochemical properties is obtained. 

Hasiotis, C. et al.. Development and characterization of acid-doped polybenzimid-azole/sulfonated polysulfone blend polymer electrolytes for fuel cells, J. Electrochem. Soc., 148, A513, 2001. 

Most MF, UF, RO, and NF membranes are synthetic organic polymers. NF membranes are made from cellulose acetate blends, cellulose triacetate (CTA), or polyamide composites such as the RO membranes, or they could be modified forms of UF membranes such as sulfonated polysulfone [27]. On the other hand, poly(vinyl alcohol) (PVA) is a significant polymer for nonaqueous applications. Chemical stmctures of a few of the prominent polymers are shown in Figure 42.4. 

Fig. 7 Chemical structures of some sulfonated polymers and a polyimide (A) sulfonated polyetheretherketone, PEEK, PSE (B) sulfonated polyphenylenesulfide, PPS (C) sulfonated polysulfone (D) poly(4,4 -biphenol) (4,4 -dichlorodiphenyl sulfone), BPSH-XX (XX is mol% of disulfdonated units) (E) sulfonated polybenzimidazole, PBI (F) polyimide.

Another method of preparing NF membranes is to dip-coat a thin layer of sulfonated polyphenylene oxide (SPPO), sulfonated polysulfone (SPS), or carboxylated polysulfone on a porous substrate membrane. 

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