Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2002-05-30
2004-08-31
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C525S333500, C525S344000
Reexamination Certificate
active
06784213
ABSTRACT:
BACKGROUND
This invention relates to an improved process for the preparation of strong acid cation exchange resins using wet copolymer and non-solvent sulfonation conditions.
Sulfonation of crosslinked vinylaromatic polymers with different types of sulfonating agents is well known. J. A. Patterson, in
Biochemical Aspects of Reactions on Solid Supports
, pp 201-202, Academic Press, Inc. N.Y., N.Y., 1971, discloses the use of three general methods for sulfonating styrene-divinylbenzene (St-DVB) copolymers using H
2
SO
4
alone, H
2
SO
4
plus perchloroethylene, and chlorosulfonic acid plus methylene chloride. In the case of sulfonation with H
2
SO
4
alone, a grade of H
2
SO
4
between 96 and 105% (based on equivalent H
2
SO
4
) is typical, with a recommended temperature range between 110° C. and 145° C., 110° C. being 5° C. above the permeation temperature of the copolymer and 145° C. being a temperature at which chain rupture by oxidation and color throw will begin to occur. U.S. Pat. Nos. 2,500,149 and 4,256,840 disclose examples of solvent-assisted and non-solvent sulfonations, respectively. These references all teach that sulfonation is carried out with copolymers that are dried and free of moisture.
U.S. Pat. No. 3,158,583 discloses that additional sulfonation, that is, polysulfonation, can be obtained using oleum (sulfuric acid containing between 10 and 70% by weight of free SO
3
). EP 868,444-A discloses a process for the sulfonation of St-DVB copolymers with 80-96% sulfuric acid at 125° C. to 180° C. without the addition of inert chlorine-containing swelling agents.
The problem addressed by the present invention is to overcome the deficiencies of prior methods of sulfonation that required the use of dry copolymer or relied on the use of organic swelling solvents to aid the sulfonation process. The present invention overcomes these deficiencies by the use of wet copolymer in conjunction with a non-solvent sulfonation while providing strong acid cation exchange resins having enhanced physical stability.
STATEMENT OF INVENTION
The present invention provides a method for preparing sulfonated crosslinked poly(vinylaromatic) copolymers comprising (a) dewatering a crosslinked poly(vinylaromatic) copolymer prepared by aqueous suspension polymerization to provide a dewatered copolymer having a residual moisture content of 3 to 35 percent, based on weight of the dewatered copolymer; and (b) sulfonating the dewatered copolymer in the presence of 95 to 105 percent sulfuric acid, substantially in the absence of organic swelling solvent, at a temperature of 105° C. to 140° C. for a period of 20 minutes to 20 hours.
In another embodiment the present invention provides the aforementioned method wherein the crosslinked poly(vinylaromatic) copolymer is dewatered by a dewatering device selected from one or more of pressurized wet screener, centrifugal screener, belt filter press, screw press, filter press, centrifuge, gravity separator, density separator, rotary drum separator, airknife dewatering system, pan filter, leaf pressure filter and disk filter.
In a preferred embodiment the present invention provides a method for preparing sulfonated crosslinked poly(vinylaromatic) copolymers comprising (a) dewatering a crosslinked poly(vinylaromatic) copolymer prepared by aqueous suspension polymerization with a centrifugal screener to provide a dewatered copolymer having a residual moisture content of 4 to 7 percent, based on weight of the dewatered copolymer; and (b) sulfonating the dewatered copolymer in the presence of greater than 96 and up to 99 percent sulfuric acid, substantially in the absence of organic swelling solvent, at a temperature of 125° C. to 135° C. for 2 to 6 hours.
DETAILED DESCRIPTION
We have discovered an improved process for preparing strong acid cation exchange resins in the absence of organic swelling solvents based on the use of wet copolymer. The sulfonation process of the present invention involves use of dewatered copolymer having selected residual moisture levels, preferably provided by the use of dewatering devices that do not damage the surfaces of the copolymer beads. Surprisingly, we have found that combining the use of wet copolymer under non-solvent sulfonation conditions provides strong acid cation exchange resins having enhanced physical stability compared to solvent-sulfonated copolymers, while having the added advantage of being free of chlorinated-solvent contaminants.
As used herein, the following terms have the designated definitions, unless the context clearly indicates otherwise. The term “wet” copolymer refers to crosslinked poly(vinylaromatic) copolymers containing from 3 to 35% residual water, either adventitious from processing after suspension polymerization or imbibed within the polymer matrix of the copolymer. The term “dry” copolymer refers to crosslinked poly(vinylaromatic) copolymers containing less than 3% residual water. The term “copolymer” refers to polymer compositions containing units of two or more different monomers, including positional isomers. The term “strong acid cation ion exchange resin” (SAC) is used conventionally herein and refers to strong acid cation exchange resins of either the gelular or macroporous type containing sulfonic acid groups in the free acid (H-form) or neutralized (salt-form, for example, sodium and potassium salts) state.
The following abbreviations are used herein: SAC=strong acid cation exchange resin, g=grams, ml=milliliters, cm=centimeter, mm=millimeter, pressure is in kilopascals (kPa). Unless otherwise specified, ranges listed are to be read as inclusive and combinable, temperatures are in degrees Celsius (° C.) and references to percentages (%) are by weight.
The sulfonation process of the present invention involves dewatering a crosslinked poly(vinylaromatic) copolymer to a level of residual moisture of from 3 to 35%, preferably from 4 to 20%, more preferably from 5 to 10% and most preferably from 4 to 7%, based on weight of the dewatered copolymer, followed by sulfonation in the presence of sulfuric acid and substantially in the absence of organic swelling solvent.
Typically, the dewatered copolymer is provided by subjecting the crosslinked poly(vinylaromatic) copolymer to a dewatering step directly after being prepared by conventional suspension polymerization methods, such as batch-kettle polymerizations, continuous-semicontinuous jetting column polymerizations and combinations thereof. Aqueous suspensions of crosslinked poly(vinylaromatic) copolymer from the polymerization step typically contain about 20 to about 60% crosslinked poly(vinylaromatic) copolymer, based weight of the aqueous suspension. The crosslinked poly(vinylaromatic) copolymer may then be dewatered by one or more dewatering processes sufficient to achieve a final residual moisture level of 3 to 35% without causing damage to the surface of the copolymer. Suitable dewatering devices include, for example, one or more of pressurized wet screener, centrifugal screener, belt filter press, screw press, filter press, centrifuge, gravity separator, density separator, rotary drum separator, airknife dewatering system, pan filter, leaf pressure filter and disk filter. Preferably, the dewatering device is selected from one or more of centrifugal screener and gravity separator.
Pressurized wet screeners include, for example, those disclosed in U.S. Pat. No. 4,284,500, which may be consulted for further general and specific details on the use of these devices. Centrifugal screeners include, for example, those disclosed in U.S. Pat. No. 4,904,377, which may be consulted for further general and specific details on the use of these devices. Centrifugal screeners operate by feeding slurries of crosslinked poly(vinylaromatic) copolymer by gravity or pneumatic means into a centrifugal screener having a cylindrical sifting chamber where rotating helical paddles continuously direct the crosslinked poly(vinylaromatic) copolymer against and through a screen by centrifugal force; oversize material retained by the
Rohrbach William Douglas
Rosenbaum Bruce Maurice
Howell Thomas J.
Lipman Bernard
Rohm and Haas Company
Witold Andrew Ziarno
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