Sulfonated Polysulfone Membranes Research Articles

Sulfonated polysulfone as promising membranes for polymer electrolyte fuel cells

A new, milder sulfonation process was used to produce ion-exchange polymers from a commercial polysulfone (PSU). Membranes obtained from the sulfonated polysulfone are potential substitutes for perfluorosulfonic acid membranes used now in polymer electrolyte fuel cells. Sulfonation levels from 20 to 50% were easily achieved by varying the content of the sulfonating agent and the reaction time. Ion-exchange capacities from 0.5 to 1.2 mmol SO3H/g polymer were found via elemental analysis and titration. Proton conductivities between 10−6 and 10−2 S cm−1 were measured at room temperature. An increase in intrinsic viscosity with increasing sulfonation degree confirms that the sulfonation process helps to preserve the polymer chain from degradation. Thermal analysis of the sulfonated polysulfone (SPSU) samples reveals higher glass transition temperatures and lower decomposition temperatures with respect to the unsulfonated sample (PSU). Amorphous structures for both PSU and SPSU membranes were detected by X-ray diffraction analysis and differential scanning calorimetry. Preliminary tests in fuel cells have shown encouraging results in terms of cell performance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1250–1257, 2000

Surface energy of experimental and commercial nanofiltration membranes: effects of wetting and natural organic matter fouling

Contact angle measurements (captive bubble technique) were used to determine the surface energy of three experimental thin-film composite nanofiltration membranes and a commercial nanofiltration membrane (Hydranautics NTR 7450). The two experimental membranes of practical interest were thin film composites (diblock copolymer on a polysulfone support layer). The two blocks were poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(1,1-dihydroperfluorooctyl methacrylate) (PFOMA). The concept was to devise a membrane material that takes advantage of the low adhesion of PFOMA to prevent fouling and the hydrophilic nature of PDMAEMA to produce high water permeation rates. Hydranautics NTR 7450 is a sulfonated polysulfone membrane that purportedly lessens fouling because the surface is more hydrophilic. The change in surface energy upon wetting, permeation of water containing natural organic matter (NOM) and chemical cleaning was of interest. Wetting caused reorganization of the experimental block copolymer surface to move more of PDMAEMA block to the membrane–water interface. After permeation of ultrapure water, however, the surface became more hydrophilic. After permeation of NOM containing water, the surface of both experimental and commercial membranes reached about the same surface energy, indicative of adsorption of NOM. The contact angle measurements were used to calculate a negative change in surface free energy for all but the PFOMA membrane; hence, with this exception, the deposition of NOM into a layer adjacent to the membrane surface was spontaneous. Scanning electron micrographs and atomic force micrographs showed that rigorous chemical cleaning failed to remove the NOM. Although the new polymeric materials were not more resistant to NOM fouling than commercial membranes, the surface energy calculations may help in the search for more successful polymers. Systematic study of charge, molecular size and specific functional groups of NOM on membrane fouling warrants further research to understand why similar fouling occurred on very different polymeric materials.

Characteristics of Sulfonated Poly(arylene ether sulfones) Cation-Exchange Membrane by Variation of Sulforic Acid Group Concentration

Sulfonated Polysulfone (SPSF) cation-exchange membranes were synthesized by introducing various ratio of chlorosulfuric acid (CSA) onto the main chain of polysulfone (PSF). Properties such as ion exchange capacity, water content, liked ion concentration, and partition coefficient were measured, respectively. Through the analysis of DSC and TGA, it has been shown that glass transition temperature increased and weight loss decreased as sulfuric acid group concentration increased. Structure of membrane measured by AFM and SEM was seen to be asymmetric. Apparent diffusion coefficient of sodium ions through SPSF membrane by AC impedance was increased as sulfuric acid group concentration increased.

Sulfonated polysulfone as promising membranes for polymer electrolyte fuel cells

A new, milder sulfonation process was used to produce ion-exchange polymers from a commercial polysulfone (PSU). Membranes obtained from the sulfonated polysulfone are potential substitutes for perfluorosulfonic acid membranes used now in polymer electrolyte fuel cells. Sulfonation levels from 20 to 50% were easily achieved by varying the content of the sulfonating agent and the reaction time. Ion-exchange capacities from 0.5 to 1.2 mmol SO3H/g polymer were found via elemental analysis and titration. Proton conductivities between 10−6 and 10−2 S cm−1 were measured at room temperature. An increase in intrinsic viscosity with increasing sulfonation degree confirms that the sulfonation process helps to preserve the polymer chain from degradation. Thermal analysis of the sulfonated polysulfone (SPSU) samples reveals higher glass transition temperatures and lower decomposition temperatures with respect to the unsulfonated sample (PSU). Amorphous structures for both PSU and SPSU membranes were detected by X-ray diffraction analysis and differential scanning calorimetry. Preliminary tests in fuel cells have shown encouraging results in terms of cell performance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1250–1257, 2000

Impedance characteristics of a rotating disc electrode coated with a sulfonated polysulfone cation-exchange membrane

The transport of sodium ions through a sulfonated polysulfone (SPSF) cation-exchange membrane coated on a rotating disc electrode is investigated by means of cyclic voltammetry (CV) and a.c. impedance spectroscopy. Impedance plots are analyzed by a non-linear least-squares fitting method. The transport (diffusion coefficient), interfacial parameters (double layer capacitance), and total resistance of the SPSF membrane coated electrodes are investigated as the function of sulfonic acid group concentration in the SPSF membrane, membrane thickness, electrolyte concentration, and reduction potential. The diffusion coefficients are found to vary between 1.082×10 −12 and 1.136×10 −11 cm 2 s −1 as the sulfonic acid group concentration is increased from 0.672 to 1.18 mmol/g membrane at open circuit voltage. The double-layer capacitance depends on electrolyte concentration and reduction potential, and sulfonic acid group concentration, but not on the membrane thickness. The total resistance depends on sulfonic acid group concentration, electrolyte concentration, membrane thickness, and reduction potential.

Separation Properties of Negatively Charged Membranes for Pervaporation in Water-Ethanol Mixture.

Different kinds of negatively charged membranes, namely poly (acrylonitrile-co-acrylic acid) (AN-AAc), sulfonated polysulfone (SPSF) and sulfonated polyethersulfone (SPES) membranes, were prepared by changing the contents of carboxyl and sulfonate groups in the membrane polymers. Using the prepared membranes, sorption and pervaporation experiments were conducted at 333 K in the mixtures of water and ethanol. In evaluating the sorption and pervaporation properties of these membranes, the values of ΔHWM and ΔHEM, which are the difference in solubility parameter between water and membrane polymer and that between ethanol and membrane polymer, respectively, are defined. Irrespective of the kind of membrane examined, a linear relation is observed between logarithmic values of selective sorption factor of water to ethanol, βW/E, and (ΔHEM/ΔHWM), as well as between those of separation factor, αW/E, and (ΔHEM/ΔHWM). It is found that the values of βW/E for cellulose acetate and polyion complex membranes can be evaluated from the relationships obtained in the AN-AAc, SPSF and SPES membranes.

Sulfonated polysulfone membranes with antifouling activity

AbstractThe protein fouling phenomenon was investigated on modified polysulfone ultrafiltration membranes. The sulfonation degree was correlated to the extent of deposition of bovine serum albumin. It was shown that membranes prepared from modified polysulfone were less fouled than their off‐charge analogues. The fouling phenomenon was also investigated for membranes prepared from co‐cast blends. It was demonstrated that blends containing more than 50 wt.‐% of sulfonated derivative behaved like a membrane from pure sulfonated polysulfone. The effect was attributed to surface separation of polymers and formation of surfaces enriched with sulfonic groups.

Separation of Humic Substances by Porous Ion-Exchange Membranes from Sulfonated Polysulfone

Abstract Ultrafiltration involving sulfonated polysulfone membranes provides high efficiency for humic matter removal from water. The increase in ion-exchange capacity of the polymer matrix from 0.24 to 0.96 mmol SO3H groups per 1 g of dry membrane increases the membrane pore diameter and its hydrophilicity, and thus the permeate flux from 0.05 to 3.69 m3/m2·d. In order to decrease the manufacturing cost, membranes from polysulfone and sulfonated polysulfone blends were investigated. It was shown that a one-to-one blend resulted in a membrane having similar antifouling properties to pure sulfonated polysulfone. Both membranes reject humic matter in the 91–98% range and show a flux decline of 5–30% as a result of surface fouling.

Ultrafiltration of lysozyme and bovine serum albumin with polysulfone membranes modified with quaternized polyvinylimidazole

In order to investigate the influence of ionic interactions on protein ultrafiltration, sulfonated polysulfone and polyethersulfone membranes were coated with polyvinylimidazole (PVI) and quarternized by a cross-linking agent bearing Bisphenol A. The apparent PVI thickness, from ATR-FTIR, was in the range from 10 to 40 nm for the polyethersulfone and sulfonated polysulfone membranes. Significant difference in protein retention (positive lysozyme and negative bovine serum albumin) was observed at low ionic strength for oppositely charged protein and (modified) membrane. At high ionic strength, protein retention and membrane flux with modified and unmodified membranes were similar due to protein adsoption on the membrane and interactions of adsorbed protein to free protein. Hydrophobic interactions between Bisphenol A and protein were demonstrated with similarly modified HPLC silica. Hence, the hydrophobic interactions could partly explain the unexpected high protein retention observed both with the unmodified and modified membrane at high ionic strength.

Optimal removal of chlorolignin by ultrafiltration achieved by pH control

The ultrafiltration of chlorolignin fractionated from pine kraft pulp bleach effluent originating from the first caustic stage of the bleachery was studied at different chlorolignin concentrations and pH using polysulfone and sulfonated polysulfone membranes. Retention of chlorolignin increased along with pH and increasing degree of dissociation of chlorolignin, which is a low molecular weight anionic polyelectrolyte. Retention stayed very high, about 99 %, at high pH values. This is remarkable as the chlorolignin molecule is considered to be much smaller than the pore size of the membranes used. The high electrostatic repulsion between the chlorolignin molecules and the membrane surface is obviously the reason for that. Flux reduction decreased remarkably along with pH increase as well. The results confirm that sufficient chlorolignin removal can be achieved if its ultrafiltration is carried out at pH ∼ 10, which is approximately the pH of the first caustic stage in the bleach process.

Development of sulfonated polysulfone membranes for redox flow batteries

Sulfonated polysulfone (SPS) membranes were developed which satisfied the stability, resistivity, selectivity and low cost requirements of a flow battery. The chemical stability of SPS membranes was markedly superior to that of commercially available membranes made by grafting of hydrocarbon substrates. SPS membranes were unaffected by exposure to alkaline-ferricyanide, the electrolyte used in a zinc/redox battery. In contrast, grafted membranes suffered weight losses of up to 30 percent when exposed to this solution under similar conditions. The area resistivities of SPS membranes in 5 N NaOH decreased dramatically from 760 Ω-cm 2 to less than 1 Ω-cm 2 as the ion exchange capacity (IEC) increased from 0.84 to 1.91 milliequivalents per dry gram (meq/dg). Ferricyanide permeation rates, which are an inverse measure of the membranes' selectivity, were less than 1 x 10 −5 mmol Fe/cm 2-hr for membranes with an IEC of 1.21 meq/dg, but increased to 13 x 10 −5 mmol Fe/cm 2-hr for membranes with an IEC of 1.91 meq/dg. The best balance of these electrochemical properties was realized at an IEC of 1.61 meq/dg. A cell using an SPS membrane operated at greater than 80 percent energy efficiency in short-term cycling tests (< 100 charge-discharge cycles). In long-term cycling tests (>500 cycles), energy efficiencies were comparable with those obtained with expensive perfluorosulfonate membranes.

Role of the membrane surface in concentration polarization at ion-exchange membrane

A thin convection-free cell was constructed for the characterization of cation-exchange membranes, with CuSO 4 solutions confined between thick copper electrodes. Current—voltage curves were recorded for several homogeneous membranes. The limiting current, i.e. the flat portion of the curve, was 1.5–4 times lower than the theoretical prediction. At high voltage the current increases approximately linearly above its limiting value. Onset of noise and noise frequency were determined. It was suggested that the ion conductance of the membrane surface is not uniform. This inhomogeneity decreases the available area and, at high voltage, gives rise to local mixing of the unstirred layer by electroconvection. High limiting current was observed with a composite membrane comprising a porous heterogeneous layer and a highly permselective dense homogeneous layer (sulfonated polysulfone). This may be due to electroconvection in the porous part of the layered structure. The drastic difference of polarization at homogeneous sulfonated polysulfone membranes and at the composite membrane was confirmed in a laboratory electrodialysis stack.

発酵生産プロセスの膜利用技術

Recent research progresses on membrane technologies to fermentation production processes are reviewed. First, a cross flow filtration of suspended yeast cells by a hollow fiber module was carried out to enhance the ethanol productivity in repeated fedbatch culture. The ethanol productivity obtained in this system was 11.3g ethanol/litre/h compared to 3 in a conventional Melle-Boinnot method. Second, in ethanol fermentation, an immobilized yeast cells system capable of forced permeation of the medium was developed in contrast to conventional immobilized yeast cell system where the mass transfer depends on “diffusion”. In this new system, the cell density on the surface of gel (1 mm thickness) became 1.7×1010 cells/ml gel compared to 4×109 in the conventional system. Hence, the ethanol productivity in this system could increase 60g ethanol/ litre gel/h compared to 20 to 30 in conventional packed bed systems. Third, acetic acid fermentaion from ethanol was conducted in a hollow fiber module bioreactor where the bacterial cells absorbed on the fiber surface could consume oxygen running through the inside of hollow fiber and ethanol running through the outside the fiber. Thus, a mimic vineger production of conventional surface cluture could be established with a remarkable increase of the surface area per reactor volume. Finally, a sulfonated polysulfone membrane was used for in situ regeneration and retention of coenzymes NADP (H) using xylose reductase coupled with oxidoreductase system in the reduction of xylose to xylitol with hydrogen gas. The membrane could almost completely reject the permeation of NADP (H) and F420 and the required enzymes, but not reject for permeation of xylitol.

Regeneration and retention of NADP (H) for xylitol production in an ionized membrane reactor

A sulfonated polysulfone membrane reactor was used forin situ regeneration and retention of coenzymes NADP (H) using the xylose reductase ofCandida pelliculosa coupled with oxidoreductase system ofMethanobacterium sp. in the reduction of xylose to xylitol with hydrogen gas. The membrane could almost completely reject the permeation of NADP (H) (92 and 97%), F420 (97%) and the required enzymes (100%), but not reject for the permeation of xylitol (product). After 4-h reaction for the production of xylitol from xylose (93% yield), although 25% NADP (H) initially added was lost its activity due to unavoidable degradation, the membrane could reject the permeation of the remaining NADP (H) and F420 at the level of 90 and 95%, respectively.

Asymmetric reverse osmosis and ultrafiltration membranes prepared from sulfonated polysulfone

The concept of solubility parameter, developed by Hansen, has been applied to the determination of solubility diagram of polysulfone and sulfonated polysulfone. Data showing the effect of various parameters such as thermodynamic quality of the solvent, casting solution composition and viscosity, solvent evaporation period and precipitation bath composition, on membrane structure and performance have been presented. By adjusting these parameters a wide variety of sulfonated polysulfone membranes useful for both ultrafiltration and reverse osmosis applications could be obtained.