Reverse Osmosis and Ultrafiltration - ACS Publications - American

7 γ-Ray Induced Enhancement Effect on Salt Rejection Properties of Irradiated Membranes R. Y. M. HUANG and J. J. KIM

Downloaded by YORK UNIV on July 1, 2012 | http://pubs.acs.org Publication Date: January 1, 1985 | doi: 10.1021/bk-1985-0281.ch007

Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 The effect of gamma-rays on the thin film com posite membranes of sulfonated poly(phenylene oxide) (SPPO) was investigated. Composite thin film mem branes of sulfonated poly(phenylene oxide) on polysulfone (PS) substrate (SPPO-PS) were prepared by coating the hydrogen or sodium form of SPPO onto the porous polysulfone (PS) substrate in various thick nesses. The SPPO-PS membranes were then irradiated in air, oxygen or nitrogen atmospheres to doses of 0.5 megarads from a Cobalt-60 gamma-ray source at a dose rate of 0.11 megarads/hour. The effect of the gammaray irradiation was found to be beneficial in enhan cing the separation characteristics while monitoring constant flux rates. The improvement in salt rejec tions in reverse osmosis of samples of Alberta tar sands waste waters containing Na + , Ca + + , Mg + + , Cl - , SO4-- , HCO 3 - , CO3-- , SiO2-- , and heavy oil residue was found to be quite significant and are presented in detail. The best results were obtained at radia tion doses of 2-5 megarads and resulted in increases of salt rejections from 88% to over 98% of the irra diated SPPO-PS membranes, at flux rates of 10-30 gfd. Although success has been achieved in the past decade in reclaiming non-potable waters by RO through various types of thin cellulosic ester membrane films, there exists the need for more stable longer life materials. One of the most promising noncellulosic membrane systems for reverse osmosis (RO) applications appears to be sulfon ated poly (2,6-dimethyl-l,4-phenylene oxide) (SPPO) (j_). During the past few years considerable progress has been made in the development of thin film composite membranes of various polymers and their development has been described in detail in an article by Cadotte and Petersen (2) in 1981. The synthesis of poly(phenylene oxide) and its sulfonation has been described in a report to the office of Saline Water Research and Development in 1971 by Chludzinski et al (3) of the General Electric Company. Huang et al have recently reported work on ionically crosslinked 0097-6156/85/0281-0083$06.00/0 © 1985 American Chemical Society

In Reverse Osmosis and Ultrafiltration; Sourirajan, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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poly(acrylic acid)composite thin film membrane cast onto a porous polysulfone substrate (4_). The present series of papers (5-7) is concerned with the synthesis and transport properties of sulfonated poly(phenylene oxide) thin film composite membranes for reverse osmosis applications. Part I (5) dealt with the synthesis of sulfonated poly(phenylene oxide) (SPPO) polymer and Part II (6) has described the preparation of thin film composite membranes of sulfonated poly(phenylene oxide) (SPPO)-(PS), (SPPO-PS) membranes and its application for the purification of Alberta tar sands waste waters using reverse osmosis. This study (Part III) will focus on the enhancement effect of gamma-ray irradiation of the SPPO-PS thin film composite membranes on the separation characteristics of the reverse osmosis separation process. Experimental Procedures Synthesis of Poly(phenylene oxide) PPO and its sulfonation to sulfonated poly(phenylene oxide) SPPO. The synthesis of PPO and its subsequent sulfonation to SPPO has been described in detail In Part I of this series. Materials. 2,6-Dimethylphenol (Gold Label, 99.8% purity), Copper(I)chloride (Purified Grade, 99% purity) and O-Dichlorobenzene (99% purity) were obtained from Aldrich Chemicals. Chlorosulfonic acid (Practical Grade), Anhydrous magnesium sulfate (Baker Analytical Reagent Grade, 99.4% purity) and Chloroform (Baker Analytical Reagent Grade, 99.2% purity) were obtained from J.T.Baker Chemicals. Pyridine (Fisher Certified Reagent, 99% purity) was from Fisher Scientific. The oxygen used was high purity, 99.6% supplied by Union Carbide Ltd., while the Polysulfone (MW * 30,000) was obtained from Polyscience Inc. The Alberta tar sands waste water samples were obtained from the Water Sample Bank, Alberta Research Council, Edmonton, Alberta. Preparation of Porous Polysulfone Substrate. A solution containing 12.5 wt. % PS and 12.5 wt. % methyl cellosolve in dimethylformamide was cast onto a clean glass plate using a glass bar in the thickness of 0.3 mm. After the casting, the coated liquid film was immersed into 15 wt. % NaCl quenching bath immediately. The film gelled very quickly, it was then washed with water, and cut into the required size with a membrane die. Finally, it was put into deionized water for at least 24 hours and thoroughly dried before SPPO polymer solution casting. Preparation of Sulfonated Poly(phenylene oxide) Composite Membrane. The SPPO polymer was exhaustively dried for 200 hours under vacuum at room temperature (hydrogen form) or 70°C (sodium form), and the dry SPPO polymer was dissolved in 2:1 chloroform/ methanol or pure methanol solvents, to form a 4 wt. % casting solution and cast onto 1.0 mil microporous polypropylene or polysulfone substrate stuck onto a glass plate to form a coating of SPPO polymer of 0.2 mil dried thickness, and the composite membrane formed was dried for a minimum of 2 hours under cover and overnight without cover at ambient conditions. . The dried membranes were removed


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from the glass plate immersed into 10 wt. % NaCl aqueous solution to convert the hydrogen form into sodium form and stored wet in a 10 wt. % NaCl aqueous solution container. Since polysulfone substrate was soluble in chloroform, the casting solvent was pure methanol (without chloroform). Gamma-ray Irradiation of SPPO-PS Thin Film Composite Membrane.


To effect crosslinking, the SPPO-PS thin film composite membrane was Cobalt-60 gamma-ray irradiated in a Gammacell-220-Co-60 unit, supplied by Atomic Energy of Canada Ltd., to various irradiation doses up to 5 megarads at a dose rate of 0.11 megarad/hour in air, nitrogen or oxygen atmospheres at room temperature. Membrane Durability to Chlorine, Acid and Base (8,9). Immersion tests were performed to evaluate the resistance of membranes to oxidative chlorine, acid and base. All membrane exposures were carried out under equilibrium conditions at fixed concentration and constant pH. Chlorine was added as sodium hypochlorite to buffer solution at pH 7. The selected chlorine level was 30 ppm, representing a tenfold higher level than 3 ppm, the average chlorine residual applied in water disinfection practice. Aqueous sulfuric acid solution (IN, pH=0.3) was used as acid and aqueous sodium hydroxide solution (IN, pH=14) as base. The solutions in one liter poly-ethylene jars were stirred magnetically and the jars tightly stoppered to prevent concentration change by volatility. Chlorine level and pH were checked periodically and adjusted, as needed, by the addition of a small volume of concentrated stock solution or deionized water. Solutions of these chemicals were quite stable when tighly stoppered. After immersion of membranes to various exposure times, these were washed with deionized water and membrane performance characteristics were then measured. Measurement of Tensile Strength. The Universal testing instrument (Instron Model 1122) was used for tensile strength measurements of the membranes. The thin film membrane specimen, saturated with water, was about 8 mm wide and 20 mm long. The crosshead speed was 1 ram/min. Analytical Procedures. Sodium chloride or other inorganic compound concentrations for single component solutions were determined using a Water Associates differetial refractometer Model R403. Quantitative analyses of the mixed component solution in aqueous phases were carried out by standard methods (10). Atomic absorption spectroscopy (Perkin-Elmer Model 303) was used for determination of dissolved sodium, calcium and magnesium. Sulfate was determined by the turbidimetric method with BaCl 2 using a spectrophotometer (Bausch and Lomb Spectronic 20) at 420 nm. Choride was determined by potentiometric titration with AgN0 2 solution using glass and silver-silver chloride electrodes (Potentiograph E576, Metrohm Herisaw Co., Switzerland). Heavy oil was determined by ultraviolet absorbance at 253.7 nm (Varian Techtron UV-VIS Spectrophotometer Model 635) (10). The intrinsic viscosities of SPPO and gamma-ray irradiated SPPO polymers were determined in an Uhbelohde viscosimeter in methanol solutions at 25°C.



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Purification of Waste Water from Heavy Oil Fields* Reverse osmosis tests were carried out on synthetic and natural waste waters from the heavy oil fields. The waste waters were obtained from the Esso facility at Cold Lake, Alberta, the Shell facility at Peace River, Alberta, and the Texaco facility at Athabasca, Alberta. The aqueous phase remaining from the bitumen-water separation contained residual minerals, usually about 5000 to about 15000 ppm total dissolved solids (TDS), and a certain amount of heavy oil (10). These waste waters were prefiltered before reverse osmosis tests to remove suspended solid particles for membrane protection. The reverse osmosis tests were conducted in 6 high pressure cells, which have been described in detail in the previous paper (6) • The effective membrane area was 18.1 cm (4.3 cm in diamter). The experiments were conducted at pressures of 300 to 700 psig, at a room temperature of approximately 20°C, and with feed solution circulated during the experiment. The recovery for each membrane sample was about 0.1%. With this low recovery, concentration polarization effects were minimized and a true measure of the intrinsic performance of the membrane could be approached. Results and Discussion Reverse Osmosis Results of Irradiated Membrane. Tables I, II and III show the results of reverse osmosis for the purification of waste waters from Esso Cold Lake, Alberta, Shell Peace River, Alberta, and Texaco Athabasca, Alberta heavy oil fields respectively, for a SPPO-PS composite membrane. These tables compare the separation characteristics of non-irradiated and gamma-ray irradiated (5M Rads) SPPO-PS composite membranes and show the significant improvement in % rejection of the various salts caused by the gamma-ray irradiation process with very little change in the production rate. These results indicate that the membrane rejection characteristics are excellent and can be considered adequate for application for the purification of waste waters from the heavy oil fields. Both the hydrogen form and sodium form of sulfonated poly(phenylene oxide) in SPPO-PS composite membranes were exposed to irradiation doses ranging from 0 to 5 M Rads, in air, nitrogen and oxygen atmospheres and the results are shown in Figures 1 and 2. As can be seen, their salt rejection characteristics were increased considerably from 88 to 98% without a change in production rates. The best results were obtained at radiation doses ranging from 2-5 M Rads while differences in the irradiation atmospheres were found to be negligible. Figure 3 shows the effects of radiation dose and IEC (ion exchange capacity) of the SPPO-PS membranes on their salt rejection and production rates. The best results were obtained with an IEC of 2.10 at a radiation dose of 5 M Rads. The effect of membrane ion exchange capacity, membrane water content, coated polymer thickness as well as the dependence of feed composition on the production rate and salt rejection for non-irradiated membranes have been discussed in detail in Part II of this series (6). Radiation Chemistry of Sulfonated Poly(phenylene oxide) Polymer The radiation chemistry of sulfonated poly(phenylene oxide) is not clearly understood and is currently still undergoing investigation. Chapiro (11-12) has reviewed the basic mechanisms of radiation-




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Figure 1. Effect of gamma-ray irradiation on sulfonated poly(phenylene oxide) in SPPO-PS composite membrane (SPPO hydrogen form, IEC = 2.83 meq/g).

Figure 2. Effect of gamma-ray irradiation on sulfonated poly(phenylene oxide) in SPPO-PS composite membrane (SPPO sodium form, IEC » 2.10 meq/g).



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Figure 3. Reverse osmosis results of gamma-ray irradiated SPPOPS composite membranes (sodium form SPPO, 600 psig, 1000 ppm NaCl, 25°C).


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induced changes in polymers, most reactions are commonly interpreted on the basis of free radical processes, but other species, ions and other reactive intermediates may also play a significant role. The main end effects of gamma-rays on polymers are crossiinking and degradation of the polymer chains. There is no published literature on the radiation chemistry of sulfonated poly(phenylene oxide) but the main effects can be considered to be crosslinking coupled with some degradations. King (13) has reviewed the radiation chemistry of an analogous polymer poly(ethylene oxide) where the main-effects of gamma radiation have been found to be crosslinking at low doses after which chain degradation predominates. The final result was a combination of cross linking and oxidative degradation. No exact G-values for crosslinking and degradation have yet been reported. However, since the phenylene oxide unit in poly(phenylene oxide) contains a benzene ring structure which is more stable to radiation, it may be surmised that degradation is less prone to occur in favour of more crosslinking. Figure 4 shows the intrinsic viscosity of SPPO and gamma-ray irradiated SPPO (2 M Rads), as can be seen there appears to be some degradation of the y-ray irradiated SPPO. However, an indication of the crosslinking process can be seen in the tensile strength (psi) vs radiation dose plot as shown in Figure 5. The A(SPPO/PS-PS) psi plot shows an increase up to 5 M Rads after which it decreases. This is a strong indication that crosslinking occurs at low radiation doses followed by degradation at higher doses as observed for poly(ethylene oxide). The results of solubility tests for SPPO and gamma-ray irradiated SPPO polymers are shown in Table IV. Durability and Stability of SPPO-PS Thin Film Composite Membranes to Chlorine, Acids and Bases. Figure 6 shows the changes in RO performance and tensile strength of irradiated or non-irradiated SPPO-PS memranes on continuous exposure to 30 ppm chlorine at pH 7.0 As can be seen, there was very little change in the % salt rejection and tensile strength even after exposure to 600 hrs, while there was a slighu increase in the production rate. Figure 7, shows an identical plot on continuous exposure to lN-NaOH (pH 14.0). Similar trends can be noted, except for the significant increase in production rate as exposure time increases. Changes in RO performance and tensile strength on continuous exposure to lN-^SO^ (pH - 0.3) are shown in Figure 8, similar trends as for the case of chlorine exposure are observed. These durability and stability tests indicate the excellent stability of the irradiated and non-irradiated SPPO-PS thin film composite membranes to chlorine, acids and bases which make them very suitable for use in the purification of the Alberta tar sands waste waters. This compares favourably to conventional membranes such as assymetric cellulose acetate membranes which fail rapidly under these conditions. Conclusions The gamma-ray irradiation of SPPO-PS thin film composite membranes in air, oxygen or nitrogen atmospheres at radiation doses ranging from 2-5 M Rads has shown significant improvements in the % salt rejection and constant flux rates in the purification of Alberta Tar sands waste water for recycling use in steam generation. The



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Figure 4. Measurement of intrinsic viscosity of SPPO and gammaray irradiated SPPO in methanol at 25°C. (a) SPPOH; sulfonated poly(phenylene oxide) hydrogen form, IEC = 2 . 0 7 meq/g. SPPONa; sulfonated poly(phenylene oxide) sodium form, IEC = 2.07 meq/g. (b) radiation dose; 2 M Rad

Figure 5. Tensile strength changes of SPPO-PS composite membrane and PS substrate with gamma-ray irradiation (sodium form SPPO, IEO2.10 meq/g, thickness SPPO/PS - 5ym/75ym)


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Figure 6. Changes in RO performance and tensile strength of SPPO-PS composite membranes on continuous exposure to 30 ppm chlorine at pH 7.0


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Figure 7. Changes in R0 performance and tensile strength of SPPO-PS composite membranes on continuous exposure to IN-NaOH (pH = 14.0)



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Figure 8. Changes in RO performance and tensile strength of SPPO-PS composite membranes on continuous exposure to lN-I^SO^ (pH=0.3)

irradiated membranes also showed a considerable degree of stability to the effect of chlorine, acids and bases after long exposure to these media and is considered suitable for this application. The enhancement effect is believed to be caused by a crosslinking of the SPPO polymer in the thin film composite membranes caused by the gamma-ray irradiation. Acknowledgments We would like to thank the National Science and Engineering Research Council of Canada (NSERC) for its support of this research programme. Thanks are also due to Dean Wallace, Alberta Research Council, Edmonton, Alberta for providing the Alberta tar sands waste water samples. Literature Cited 1.

LaConti, A.B. "Advances in Development of Sulfonated PPO and Modified PPO Membrane Systems for Some Unique Reverse Osmosis Applications". In Reverse Osmosis and Synthetic Membranes, Edited by S. Sourirajan, Ottawa, 1977. pp.211-229,


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REVERSE OSMOSIS AND ULTRAFILTRATION Cadotte,J.E.; Petersen,R.J., ACS Symposium Series, No. 153, American Chemical Society, Washington, D.C., In "Synthetic Membranes:, Vol. 1, Desalination, (1981), pp305-325. Chludzinski,P.J.; Austin,J.F.; Enos,J.F. "Development of Polyphenylene Oxide Membranes", Office of Saline Water Research and Development Progress Report No. 697, General Electric Co., Lynn, Mass., 1971. Huang,R.Y.M.; Gao,C.J.; Kim,J.J., J. Appl. Polym. Sci., 28, 3063 (1983). Huang,R.Y.M.; Kim,J.J. "Synthesis and Transport Properties of Thin Film Composite Membranes I. Synthesis of Poly(phenylene oxide) Polymer and its Sulfonation", J.Appl.Poly.Sci., accepted for publication, April 1984. Huang,R.Y.M.; Kim,J.J. "Synthesis and Transport Properties of Thin Film Composite Membranes II. Preparation of Sulfonated Poly(phenylene oxide) Thin Film Composite Membranes for the Purification of Alberta Tar Sands Waste Waters", J. Appl.Poly. Sci., accepted for publication, April 1984. Huang,R.Y.M.; Kim,J.J. "Treatment of Oil Recovery Process Waste Water", Canadian Patent Application filed July 18, 1984, Serial No. 459,169. Slater, J.; Zacharian, M.R.; McCray, S.B.; McCutchon, J.W., Desalination, 48, 1(1983). Kuwahara,H.; Yasuda,T.; Nakamura,M., Proc. of 7th Inter. Symp. on Fresh Water from the Sea, 2, 165 (1980). Asano,B.H. et al., In "Review of Treatment and Recycling of Produced Water from Heavy Oil Fields", CH2M HILL Canada Ltd., Calgary, 1981. Chapiro,A., In "Radiation Chemistry of Polymeric Systems", p.339, Interscience - John Wiley, 1962. Chapiro,A., In "Advances in Chemistry Series", American Chemical Society, No.66, p.22, "Irradiation of Polymers", 1967. King,R.A., In "Advances in Chemistry Series", American Chemical Society, No. 66, 113, "Irradiation of Polymers", 1967.

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Reverse Osmosis and Ultrafiltration - ACS Publications - American

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