Source: http://www.google.com/patents/US4888116?dq=7751826
Timestamp: 2017-12-16 13:23:38
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Patent US4888116 - Method of improving membrane properties via reaction of diazonium compounds ... - Google Patents
A method of improving the properties of a reverse osmosis membrane having a polyamide discriminating layer containing residual aromatic primary amine groups is described. In this method, the polyamide discriminating layer of the membrane is treated with an aqueous solution of a reagent which reacts with...http://www.google.com/patents/US4888116?utm_source=gb-gplus-sharePatent US4888116 - Method of improving membrane properties via reaction of diazonium compounds or precursors
Publication number US4888116 A
Application number US 07/286,677
Publication number 07286677, 286677, US 4888116 A, US 4888116A, US-A-4888116, US4888116 A, US4888116A
Inventors John E. Cadotte, Donald L. Schmidt
Original Assignee The Dow Chemical Company, Filmtec Corp.
Patent Citations (30), Non-Patent Citations (2), Referenced by (74), Classifications (11), Legal Events (4)
Method of improving membrane properties via reaction of diazonium compounds or precursors
US 4888116 A
9. The method as described in claim 8 wherein the polyamide is treated with nitrous acid at a temperature in the range from about 0° to about 30° C.
11. The method as described in claim 1 wherein the reagent is nitrous acid or a precursor which forms nitrous acid during treatment of the membrane and the water flux of the treated membrane at a pressure of 200 psi and a temperature of 25° C. using a 0.2 weight percent aqueous NaCl solution is at least 10 percent greater than the water flux of the same membrane at these conditions prior to treatment.
The sodium chloride rejection and water flux of the polyamide reverse osmosis membrane prior to treatment can operably vary over a wide range. For convenience in reporting flux and sodium chloride rejection, all of the values reported herein will be made with reference to standard test conditions using an aqueous 0.2 weight percent sodium chloride solution at 200 lbs./in2 gauge (psig) at 25° C. unless otherwise indicated. Desirably, the reverse osmosis membrane after treatment will have a sodium chloride rejection of at least about 90 percent and a water flux of at least about 10 gallons per square foot per day (gfd) when tested at standard conditions. More preferably, the membrane after treatment will have a sodium chloride rejection of at least about 95 percent and a flux of at least about 15 gfd. It has been found by the method of this invention that new polyamide membranes having a water flux of 1 gfd and salt rejection of less than 60 percent at standard conditions can be restored to the desired flux and salt rejection in the preferred range stated hereinbefore. Membranes which have become fouled during operation and after air-drying exhibit essentially zero water flux have also been restored to water fluxes greater than 10 gfd and rejections greater than 95 percent by the method described herein.
TABLE I__________________________________________________________________________       Initial                 Final          Percent               Treatment          PercentComparative       Flux          Salt Acid       Time Flux                                  SaltExampleExperiment       (gfd)          Rejection               (Parts)                     NaNO.sub.2                          (Hours)                               (gfd)                                  Rejection__________________________________________________________________________6    --     12.7          98.1 H.sub.2 SO.sub.4 (2)                     1 part                          1    28.2                                  97.87    --     17.6          93.2 H.sub.2 SO.sub.4 (2)                     1 part                          1    23.6                                  98.18    --     22.0          91.0 H.sub.2 SO.sub.4 (2)                     1 part                          1    18.0                                  97.79    --     17.0          97.0 H.sub.2 SO.sub.4 (2)                     1 part                          1    22.6                                  98.010   --     1.4          85.0 H.sub.2 SO.sub.4 (2)                     1 part                          1    16.0                                  91.011   --     1.0          76.0 H.sub.2 SO.sub.4 (2)                     1 part                          1    21.0                                  96.012   --     6.0          96.5 37% HCl                     1 part                          1    24.0                                  98.2               (2)13   --     6.0          96.5 37% HCl                     12 parts                          1    30.0                                  97.9               (4)14   --     6.0          96.5 37% HCl                     1 part                          72   30.0                                  97.9               (2)E      6.0          96.5 None  1 part                          1    9.8                                  97.815   --     7.0          97.3 37% HCl                     1 part                          1    25.0                                  98.8               (2)16   --     7.0          97.3 37% HCl                     12 parts                          1    33.6                                  98.0               (4)17   --     7.0          97.3 37% HCl                     1 part                          72   32.3                                  98.7               (2)F      7.0          97.3 None  1 part                          1    10.0                                  98.918   --     4.2          86.3 37% HCl                     1 Part                          18   12.1                                  97.8               (2)G      4.2          86.3 None  None 18   10.0                                  97.819   --     5.2          93.1 37% HCl                     1 part                          18   15.4                                  97.6               (2)H      5.2          93.1 None  None 18   11.0                                  98.0__________________________________________________________________________
In general, the monomers were combined in a mixed solution of water and butyl alcohol, the solution purged with nitrogen and warmed to 50° C. To the mixture was added 0.1 gram (g) t-butyl hydroperoxide and 0.075 g Formopon, both in water over a period of one hour. The solution was then concentrated by heating under vacuum and then optionally dialyzed to remove low molecular weight fractions.
The polymers were diluted to a 3 weight percent aqueous solution containing 0.0075 weight percent on a solids basis of a fluorinated anionic surfactant (available from Minnesota Mining and Manufacturing Company as FLUORAD FC-129). One side of a microporous mixed cellulose ester filter (available from Millipore as filter type VSWP-04700) was washed with the solution. The coated filter was dried at 80° C. for 10 minutes. The filter was then immersed in a fresh aqueous solution of 5N NaNO2 and 0.5N HCl at 0° C. for 15 minutes. A second layer of the addition polymer was applied, cured and treated.
Ten g of a 10 weight percent solution of the ammonium salt of a terpolymer containing 80 weight percent 2-hydroxyethyl methacrylate (HEMA), 10 weight percent methacrylic acid (MAA), 10 weight percent 9N10MA was mixed with 0.5 g of ethylenediamine. The solution was dialyzed using a dialysis membrane having a 12,000 to 14,000 molecular weight cut-off. A solution containing 0.5 weight percent polymer and 0.0015 percent of a commercial fluorocarbon surfactant (Fluorad FC 129, available from Minnesota Mining and Manufacturing Company) was wiped onto a microporous filter like the one used in Example 32 and dried at 80° C. for 10 minutes. The coated filter was then immersed for 10 minutes in a 0° C. solution of a 1:1 (by volume) aqueous solution of 0.5N HCl and 5.0N NaNO2. The coated filter was soaked in ice water for two hours, dried and the process repeated three more times. The resulting composite membrane had a sodium chloride rejection of 68 percent and a flux of 2.17 gfd when tested with an aqueous solution of 2500 ppm NaCl at 400 psi.
Ten g of a 10 weight percent solution of the ammonium salt of the terpolymer HEMA/MAA/9N10MA (at a 70:20:10 weight ratio) was mixed with 1 g of m-phenylenediamine. The solution was dialyzed using a dialysis membrane having a 12,000 to 14,000 molecular weight cut-off. A 3 percent solution containing 0.006 percent of a fluorocarbon surfactant was wiped onto a filter like the one used in Example 32 and dried at 80° C. for 10 minutes. The coated filter was then immersed at 0° C. in a 1:1 solution by volume of 0.5N HCl and 5N NaNO2.
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U.S. Classification 210/636, 210/654, 210/500.38, 210/655
International Classification B01D69/12, B01D67/00
Cooperative Classification B01D69/125, B01D2323/30, B01D67/0093
European Classification B01D67/00R18, B01D69/12D