Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
1999-05-17
2001-06-19
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C562S485000, C562S494000, C562S580000, C562S593000
Reexamination Certificate
active
06248797
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of removing contaminants from ion exchange resins, and more specifically to the use of supercritical carbon dioxide for the removal of leachable organic and inorganic materials from commercial ion exchange resins to thereby produce ion exchange resins acceptable for use in critical applications.
BACKGROUND OF THE INVENTION
Ion exchange resins are widely used in the production of highly pure water in the nuclear, electronics (semi-conductor), pharmaceutical and food industries. In the nuclear industry, for example, ion exchange resins are used for purification of nuclear process water.
The problem exists that commercial grade ion exchange resins contain varying quantities of organic and inorganic impurities which have a tendency to leach out of the resin during use. Many of these impurities arise during manufacture of the resin, and include monomers and oligomers of the polymer from which the resin beads are formed, as well as impurities in the starting materials. These impurities may become functionalized, for example, with sulphate or amino groups during functionalization of the resin.
Due to the presence of leachable impurities, commercial ion exchange resins must be treated prior to use in critical applications where extraneous organic materials are unacceptable. Presently used purification methods include a variety of proprietary techniques, most of which are based on extraction of leachable impurities by organic solvents. In one of these methods, the resin is washed with a series of solvents of decreasing polarity. In addition to being slow, costly and wasteful, this process suffers from a number of other disadvantages. Firstly, it is not very effective. Organic solvent molecules are relatively bulky and cannot effectively penetrate into the interior of the cross-linked resin beads to leach out the impurities contained therein. Secondly, solvent treatments may require high temperatures and pressures, which may damage the integrity of the resin beads, for example by de-crosslinking, or facilitating loss of functional groups. Thirdly, the organic solvents used to wash the resin may be absorbed by the resin beads, resulting in further contamination.
Therefore, there is a need for a more economical and effective method for removing leachable impurities from commercial ion exchange resins.
SUMMARY OF THE INVENTION
The present invention overcomes the above difficulties by providing a method for removing unwanted contaminants from ion exchange resins in which resins are exposed to supercritical carbon dioxide for a period of time sufficient to permit leachable impurities to diffuse out of the resin. The inventors have found that supercritical carbon dioxide is capable of reducing the levels of impurities in commercial ion exchange resins to levels low enough to permit the use of the treated resins in critical applications in the nuclear, semi-conductor, pharmaceutical and food industries.
The high density, high solvent power and low viscosity of supercritical carbon dioxide allow it to quickly diffuse throughout the entire resin bead, and solubilize the leachable impurities contained in the resin structure. The degree to which leachable impurities are removed by the method of the present invention suggests that supercritical carbon dioxide removes impurities trapped deep inside the cross-linked matrix of the resin beads. This is surprising in that many of the impurities contained within the resin beads are relatively bulky organic molecules which became trapped in the cross-linked matrix during its formation. One would expect that such impurities could only be removed slowly, if at all.
The inventors believe that, during treatment with supercritical carbon dioxide, the cross-linked cage structure of the bead is expanded temporarily under pressure. This expansion is believed to result in escape of organic materials from the interior of the resin bead which ordinarily would leach out very gradually over time.
Furthermore, the inventors have surprisingly found that treatment of ion exchange resins by the method of the present invention results in a resin which has a noticeably higher initial effectiveness than untreated or conventionally treated commercial resins. The inventors believe that this is due to removal of organic impurities on the surface of the bead, which have the effect of reducing the initial activity of the resin.
REFERENCES:
patent: 4061566 (1977-12-01), Modell
patent: 4250331 (1981-02-01), Shimshick
patent: 4698153 (1987-10-01), Matsuzaki et al.
patent: 4703105 (1987-10-01), Allada
patent: 4902780 (1990-02-01), Bourrain et al.
patent: 5695973 (1997-12-01), Subbiach
patent: 195 45 100 (1997-06-01), None
patent: WO 84/02291 (1984-06-01), None
J.R. Stahlbush, R,M. Strom, J.B. Henry and N.E. Skelly, “Prediction and Identification of Leachables from Cation Exchange Resins”,Proceedings of the 48thInternational Water Conference, Engineering Society of Western PA, Pittsburgh, 67, (1987).
J.R. Stahlbush and R.M. Strom, “Decomposition Mechanism for Cation Exchange Resins”,Reactive Polymers, 13, pp 233-240, 1990.
S. Fisher and G. Otten, “What Really Happens to Organics in Water Treatment Systems”, Proceedings of the 39thInternational Water Conference, Engineering Society of Western PA, Pittsburgh, pp 420-426, (1978).
S.A. Fisher, “Leachables vs Ionic Leakage in Powdered Resin Systems”, Proceedings of the 49thInternational Water Conference, Engineering Society of Western PA, Pittsburgh, pp 68-79, (1988).
S.A. Fisher and G. Otten, “Extractables in New Resins: A further Look at What They are and What Becomes of Them”, Proceedings of the 47thInternational Water Conference, Engineering Society of Western PA, Pittsburgh, pp 169-176, (1986).
S.J. Poirier, “The New Role of TOC Analysis in Pure Water System Management”, The 49thAnnual Semiconductor Pure Water Conference, Transcripts (1985), p 197.
R.R. Harries and M. Ball, “Equilibrium Versus Kinetics in Water Purification”. In: P.A. Williams and M.J. Hudson, eds. “Recent Developments in Ion Exchange”, Ed Elsevier Applied Science, (ISBN 1-85166-101-8), 1987: 402-418.
F.S. Brooks and M.A. Seguin, “Report on the Use of Ion Exchange in Nuclear Service in Ontario Hydro Nuclear Stations”, Ontario Hydro—Design and Development Division Report No. 80016 (Nuclear Materials Management), Feb. 1980.
Clarence D. Colley, Prepared Discussion of IWC -90-19, “Comparison of Operational Data from Three Type I Gel Anion Resins”, Proceedings of the International Water Conference, Pittsburgh, Penn., Oct. 21-24, 1990.
Wataru Agui, Masahito Takeuchi, Masahiko Abe, and Keizo Ogino, “Fundamental Study on the Production of Ultrapure Water VIII: Removal of Leachables from Mixed-Bed Ion Exchange Resins”, Bulletine of the Chemical Society of Japan, vol. 63, No. 10, pp 2872-2876 (1990).
Ontario Hydro Standard Specification No. M-678-86, Jan. 1986, and Draft No. 1 of Revision to Standard Specification for Resin, Ion Exchange, Nuclear Grade Type: Strong Acid/Strong Base, Material Management Department Document No. M-678-xx (not issued yet), File 178.2-929-7, Job S0193, Dec. 15, 1988.
Wataru Agui, Masahito Takeuchi, Masahiko Abe, and Keizo Ogino, “Removal of Leachables from Strong Acid Cation Exchange Resins”,Journal of Japan, Oil Chemists' Society(Yukagaku), vol. 38, No. 5, p 405-414, 1989.
S.L. Wiser, Y.H. Lee G.R. Stroh, and M. O'Brien, “Removal of Organics from Secondary Make-up Water”, Proceedings of the 46thInternational Water Conference, pp 1-17, 1985.
L.S. Hartjen, “Progress in the Removal of Organics Present in Utility Water Systems”, Proceedings of the 46thInternational Water Conference, Engineering Society of Western PA, Pittsburgh (1985), Paper No. IWC-85-22.
Supercritical Fluid Science and Technology, ed Keith P. Johnston and Johannes M.L. Penninger, ACS Symposium Series 406, American Chemical Society, Washington, DC 1989 (ISBN 0-8412-1678-9).
F.R. Groves, Jr., B. Brady, and F.C. Knopf, “State-of-the-Art on the Supercritical Extraction of Organics from Hazardous Wastes”, CRC Cr
Dias Shelton A.
Shapka Walter
Ridout & Maybee LLP
Wu David W.
Zalukaeva Tanya
LandOfFree
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