NO855199L - PROCEDURE FOR MANUFACTURING IONE EXCHANGE RESINS USING CULTIVATION POLYERIZATION TECHNOLOGY. - Google Patents

Description

The present invention relates to ion exchange resin particles and in particular such particles which are produced using seed polymerization technology.

Ion exchange resins are typically prepared by providing functional groups capable of ion exchange for crosslinked copolymer particles or beads. The copolymer beads provide a strong, insoluble and rigid substrate for carrying the ion exchange functional groups. Thus, the durability and hydraulic characteristics of the ion exchange resin are generally limited by the characteristics of the copolymer from which it is derived.

Typically, ion exchange copolymers are prepared using a batch process whereby monomer droplets are formed and suspended in an aqueous phase and polymerized. Unfortunately, such a process can provide a wide distribution of bead particle sizes. It therefore becomes necessary to sieve the beads and/or the ion exchange resin particles mechanically in order to obtain a desirable product which has a relatively uniform or narrow distribution of the bead size.

In a batch-seeded process, e.g. a lightly cross-linked copolymer seed is swollen in the presence of a monomer mixture containing an initiator and a cross-linker. The absorbed monomer mixture is polymerized in situ by a standard suspension polymerization process. Such particles have very high physical strength values. The copolymer particles are then functionalized by chemically treating the insoluble, crosslinked bead to attach an ion exchange group to it.

Although the batch-seeded process provides the expert in the field with an aid for the production of particles with a relatively strong uniform size, the particles produced in this way can exhibit several disadvantages. E.g. it may be that an ion-exchange resin produced using the batch-seeded process does not provide sufficient ion-exchange properties, or the bed operation time before breakthrough may be very short. Also, if such ion exchange resins are stirred in relatively pure water, a cloudy water suspension can be observed to form. It is believed that insoluble organic materials leaching from the resin particle provide this unwanted contamination of the water. Therefore, those resin particles having highly desirable physical characteristics are not acceptable for use for such purposes as water treatment.

Based on the shortcomings of what is known from the state of the art, it would be highly desirable to provide ion exchange resin particles that have relatively uniform particle sizes, good physical characteristics, good ion exchange properties and a minimal amount of leachable organic substances.

The present invention is a seed process for the production of improved cross-linked copolymer particles capable of being functionalized to provide ion exchange copolymer particles with a high ability to withstand osmotic shock during use, namely a method comprising: (a) forming an agitated aqueous suspension of polymerized, light

cross-linked seed particles and

(b) contacting said suspended seed particles with a monomer or monomer mixture comprising a small amount of the total cross-linking monomer used in order to ultimately produce a seed which is swollen by absorption of said monomer or monomer mixture and

the polyvinyl crosslinking monomer, and

(c) contacting the suspended swollen seeds with suspending agent in an amount sufficient to provide suspension of said swollen seeds, prevent substantial agglomeration of said swollen seeds and also

allow further absorption of monomer, and

(d) subjecting the suspended swollen seeds to polymerization conditions to the extent that at least

substantial polymerization of absorbed monomers, and

(e) substantially stopping the polymerization reaction and contacting the partially polymerized particles with another monomer or monomer mixture comprising a major amount of

the total cross-linking monomer used, and

(f) subjecting the further absorbed swollen seed to polymerization conditions to provide a copolymer bead.

In another aspect, the present invention is a seed process for the production of improved cross-linked copolymer particles capable of being functionalized to provide ion exchange copolymer particles with a high ability to withstand osmotic shock during use, namely a method comprising: (a) forming a agitated aqueous suspension of polymerized, light

cross-linked seed particles, and

(b) contacting the suspended seed particles with a monomer or monomer mixture comprising a small amount of the total polyvinyl cross-linking monomer used in order to ultimately produce a seed which is swollen by absorption of said monomer or monomer mixture and

crosslinking monomer, and

(c) contacting the suspended swollen seeds with a suspending agent in an amount sufficient to provide suspension of said swollen seeds, prevent substantial agglomeration of said swollen seeds and also to

allow further absorption of monomer, and

(d) subjecting the suspended swollen seeds to polymerization conditions to the extent that at least substantial polymerization of absorbed monomers occurs, and (e) contacting the partially polymerized particles with another monomer or monomer mixture comprising a major amount of the total crosslinking monomer used, while the rate of addition of the monomer mixture and the polymerization conditions are controlled so that the monomer mixture can be absorbed into the swollen seed under polymerization conditions and the polymerization is continued to provide a copolymer bead.

The copolymer particles produced by the method according to the invention can be functionalized to provide ion exchange resin beads, and these resin beads have good osmotic shock and mechanical resistance to breakage. This will e.g. say that functionalized copolymer particles produced by the method according to the invention possess crushing strength values (i.e. mechanical load required to break up single resin beads) of at least 500 g/bead crushing strength and a resistance to osmotic shock such that if the said particles are brought into contact with 10 cycles of alternating treatments with 8 molar sodium hydroxide and 8 molar hydrochloric acid, separated by backwashing with deionized water, fewer than approx. 15% of the number of particles up. A full cycle of said treatment comprises (a) immersing a quantity of beads into 8 M HC1 for 1 minute, (b) washing with deionized water until the wash water becomes neutral, (c) immersing the beads in 8 M NaoH for 1 minute and (d) washing the beads with deionized water until the wash water becomes neutral. All references to alternating treatments with 8 M HCl and 8 M NaOH contained herein refer to repeated cycles of this test. The resistance to osmotic shock of the beads is measured by the number of beads that remain unbroken after 10 cycles of the test. Typically, at least 85% of the functionalized beads according to the invention will remain unbroken after 10 cycles of the osmotic shock test. Ion exchange resins can be either anionic or cationic in nature. Such ion exchange resins are useful for a wide variety of applications known in the art. Of particular interest is the treatment of aqueous fluids with the aim of obtaining high-purity water.

The monoethylenically unsaturated monomers which are useful here are those which are usually used in the production of ion exchange resins. Examples of suitable monomers are given in US patent 4,419,245. Reference is made to Polymer Processes, edited by Calvin E. Schildknecht, published in 1956 by Interscience Publishers, Inc., New York, Chapter II, "Polymerization in Suspension" by E. Trommsdoff and C. E. Schildknecht, pp. 69-109 for illustrative purposes. In Table II on pp. 78-81 in Schildknecht, different types of monomers are indicated which can be used in carrying out the present invention. Styrene is the most preferred monomer.

Suitable cross-linking monomers are preferably those polyethylenically unsaturated monomers which include those disclosed in US Patent 4,419,245. The preferred polyethylene unsaturated monomer is divinylbenzene.

The cross-linked seed particles useful in the present invention are those which are lightly cross-linked to achieve the degree of swelling required to produce the final copolymer products of the desired size. Preferably, the seed particles are spheroidal beads derived from one or more polymerized monoethylenically unsaturated monomers and a cross-linking agent for such. The crosslinking agent is preferably a polyethylene unsaturated monomer. In general, the amount of cross-linking agent in the germ can vary from approx. 0.1 to approx. 3% by weight, based on the weight of total monomer used in the production of the seed.

Typically, the amounts of each of the mono- and polyethylenically unsaturated monomers that are most advantageously used in the preparation of the seed and nucleated bead depend on a number of factors including the type of each monomer used and the desired size of the seed, nucleated bead and the resulting ion exchange bead. In addition, the amount and type of the mono- and polyethylenically unsaturated monomers used in the production of nucleated pearl from the pearl (ie such monomers which are absorbed by the pearl) most advantageously used here will also vary, depending on the size (ie the diameter) and the composition (ie the amount and type of monomers) of the kimperl. In general, the seed and the seeded beads are advantageously produced using amounts of the mono- and polyethylenic monomers which are such that the seeded beads can be converted into ion exchange resin beads by such techniques as sulphonation, chloromethylation, amination and the like. The resulting functionalized beads, when fully saturated with water, preferably have a particle size of 0.3-1.0 mm and exhibit improved integrity (ie, spheroidal character) and increased resistance to osmotic shock compared to a conventionally prepared copolymer bead functionalized applying similar conditions.

The size of the germ can vary. Typically, the size varies from 100 pm to 600 pm, preferably from approx. 200 pm to approx.

400 p.m. The germ generally swells from approx. 1.5 to approx. 2.2 times its original size. It is absorbed with monomer to approx. 3 to approx. 10 times its original weight.

Polymerization initiators useful herein include those initiators useful in the manufacture of kimperl. Preferably, the aqueous suspension of seed particles is contacted with the initiator together with the first monomer mixture comprising the small amount of polyvinyl crosslinking monomer. Preferably, the initiator is a conventional chemical initiator useful as a free radical generator in the polymerization of ethylenically unsaturated monomers. Representatives of such initiators are UV irradiation and chemical initiators including azo compounds such as e.g. azobisisobutyronitrile; peroxygen compounds such as benzoyl peroxide, t-butyl peroctoate, t-butyl perbenzoate and isopropyl percarbonate and the like. Several catalysts are described in US Patent Nos. 4,192,921, 4,246,386 and 4,283,499. The initiator is used in an amount that is sufficient to cause copolymerization of the monomeric components in the monomer mixture. Such an amount will generally vary depending on a number of factors including the type of initiator used, the reaction temperature, the composition of the pearl and the type and proportion of monomers in the monomer mixture which are thereby absorbed. In general, the initiator is used in amounts from 0.02 to 1, preferably from 0.05 to 0.5, weight% based on the total weight of the monomer mixture.

The pearls are advantageously suspended, using relatively high agitation rates, in a suitable suspending medium such as e.g. water or another aqueous liquid. Suspending agents are preferably added after the first monomer mixture has been allowed to absorb into the germ. Suspending agents useful herein are those materials which assist in maintaining a more uniform dispersion of the swollen pearls in the aqueous liquid. Although the suspending agents most advantageously used here are dependent on the type and amount of monomers used in the production of the swollen kimberle, suspending agents that are conventionally used for this in the suspension polymerization of mono- and polyethylenically unsaturated monomers are generally advantageously used. Representative of such suspending agents are gelatin, polyvinyl alcohol, sodium dodecyl sulfonate, sodium methacrylate, magnesium silicate, sodium cellulose glycolate, hydroxyethyl cellulose, methyl celluloses and the like. Suitable suspending agents are disclosed in US Patent 4,419,245. The amount of suspending agent used depends on a number of factors and is advantageously the amount which prevents agglomeration of the swollen pearls, but does not prevent further absorption of monomers. Typically, from 0.05 to 1.0% by weight of the suspending agent is advantageously used based on the weight of the aqueous phase.

Although the amount of the suspending agent advantageously used herein will vary depending on the type and amount of the suspending agent and the swollen bead, in general the suspending agent is used in amounts of from 30 to 70, preferably from 40 to 60, weight percent based on the weight of the swollen kimpernel, i.e. the weight of the kimpernel and the monomer mixture.

The method according to the invention involves two critical stages in the production of the copolymer bead. The first stage involves suspending the seed under such conditions that absorption of monomers brought into contact with the seed can occur. This means that after the kimmerle has been brought into contact with the monomer mixture, the kimmerle swells, and this swelling is believed to be generally due to the absorption of the monomer mixture by means of the kimmerle. The monomer can be added continuously or in batches. The initiator can be added to the medium or added together with the monomer. The pearl can be suspended during absorption using suitable agitation conditions.

It is preferable in the first stage of manufacture that the monomer mixture, for reasons of mechanical strength of the final resin bead, includes a small amount of the cross-linking agent used. This means that a 1 to 15, preferably 1 to 10, preferably 1 to 5, weight% of the total amount of cross-linking agent used is added in the first stage.

The temperature used to polymerize the absorbed monomers in the first stage can vary depending on the choice of initiator. Polymerization is generally carried out at temperatures between 50 and 100°C, preferably between 60 and 90°C, preferably 80°C.

In one aspect of the invention, before the second stage of the process begins, it is necessary to remove the reaction mixture from a state of polymerization conditions. In addition, it is highly desirable that polymerization conditions cease before total polymerization has occurred. If desired, polymerization of absorbed monomer may be substantially complete. This typically occurs when the nucleated, swollen pearl reaches its gel point. Advantageously, the polymerization in the first stage should continue until 40-80% monomer conversion to polymer. This typically means lowering the temperature of the reaction mixture so that the second mixture of monomers can be contacted and absorbed into the swollen germs without significant latex formation. If desired, the monomer mixture from the second stage can include a suitable amount of initiator.

The second stage of the polymerization process begins after the second monomer mixture is brought into contact with the partially polymerized bead. This is believed to be necessary for the other monomer mixture to be absorbed into the bead. The monomer mixture in the second stage includes a major amount of the cross-linking agent used. This means that 85-99, preferably 90-99, preferably 95-99, weight*, of the total amount of cross-linking agent used, is added in the second stage. The reaction mixture is subjected to polymerization conditions until substantially total polymerization of the monomer is achieved. The polymerization is then terminated, e.g. by raising the reactor temperature.

In another aspect of the invention, the second stage of the process involves a continuous feeding of the second monomer mixture to the suspended swollen, partially polymerized seeds. It is not necessary to remove the reaction mixture from a state of polymerization conditions. This means that by regulating the feed rate for the addition of the second monomer mixture, the suspension conditions, the reaction rate and the like, it is possible to continuously absorb the monomer mixture from the second stage into the swollen bead, which is exposed to polymerization conditions where the absorbed monomers continue to undergo polymerization.

The amount of various monomeric components in the monomer mix from the first stage can vary from 0.5 to 5% by weight of the crosslinking agent and from 95 to 99.5% by weight of monoethylenically unsaturated monomer(s). The amount of various monomeric components in the monomer mixture from the second stage can vary from 5 to 20% by weight of cross-linking agent and from 80 to 95% by weight of monoethylenically unsaturated monomer(s). The amount of monomer mixture from the second stage relative to the monomer mixture from the first stage can vary from 50 to 80% by weight based on the total weight of the monomer mixtures, subject to the limitation that the amount of crosslinking agent used in the mixture from the second stage is a major amount based on the total amount of cross-linking agent used. This means that the amount of cross-linking monomer used before the production of the final resin is 2-18, preferably 5-15, % based on the total amount of organic material (ie seed + polymerisable monomer).

The time periods during which each of the two (ie first or second) polymerization stages occurs can vary when only the desired substances are obtained in each case. For example, the monomer mixture from the first stage can be added to the seed suspension either batchwise or continuously and exposed to polymerization conditions over a period of time varying from 2 to 8 hours. The monomer mixture from the second stage is added either batchwise or continuously, preferably over a period of time varying from 3 to 5 hours. If batch addition is used, the absorption is preferably carried out at 20°C to 50°C and allowed to proceed, preferably with suitable mixing, for a period of 1 to 3 hours. The polymerization conditions are maintained in the second stage of the polymerization step for 8-14 hours. Termination of the reaction is carried out for 1-3 hours, preferably at temperatures of 90-120°C.

After the polymerization, the resulting seeded beads are recovered from the reaction media using conventional techniques, e.g. filtration, and the extracted beads are washed and dried. Functional groups are provided to the beads using known techniques. This means that copolymer beads are converted into anion and cation exchange beads. Pearls can be fractionated into various size ranges using techniques such as e.g. sifting.

The following examples are presented to further illustrate, but not limit, the scope of the invention.

Example 1

-3 3

Into a 1-gallon (3.79 x 10 m ) stainless steel reactor equipped with an agitator was charged 875 grams (g) of deionized water, 130 g of 0.3% crosslinked styrene/divinylbenzene copolymer seed particle size -50+70 meshes (from 210 µm to 297 µm) under agitation, and 300 g of monomer I, comprising styrene and 1.3% active divinylbenzenel, 0.05% active t-butyl peroctoate (TBPO) and 0.16% active t-butyl perbenzoate (TBPB) based on monomer I. After 30-60 minutes of swelling time, 325 g of an aqueous solution of 6 g of gelatin and 0.3 g of sodium lauryl sulfate stabilizers and 3.8 g of sodium dichromate latex inhibitor were added. The reactor temperature was raised to and held at 80°C for 4-6 hours. The reactor mass was cooled to 40°C, and 860 g of monomer II containing styrene and 14.5% active divinylbenzene was added to the reactor, and after 60-120 minutes of swelling time, the reactor mass was heated to 85°C, 95°C and 110° C for 12, 1.5 and 1.5 hours each, successively.

The copolymer thus made after appropriate sieving was examined for cross-link density and then converted into a strong acid-cation exchange resin. 50 grams of the copolymer thus obtained was sulfonated to a cation exchange resin. After suitable washing, the resin was tested with regard to capacity, crushing strength, osmotic shock resistance and water quality. A mixture of 50 ml each of resin and water was stirred vigorously magnetically for 30 minutes, and the aqueous layer was examined for clarity.

Example 2

Into a reactor as described in example 1, 850 g of deionized water, 215 g of 0.3% cross-linked styrene/divinylbenzene copolymer seed with a particle size of -50+60 mesh (from 210 µm to 297 µm) were placed under agitation , and 215 of monomer I which contained styrene and 1.7% active divinylbenzene, 0.036% active TBPO and 0.05% active TBPB. After a swelling time of 30 to 60 minutes, 325 g of an aqueous solution of the previously described stabilizers and the latex inhibitor were added. The reactor was sealed, purged with nitrogen and the temperature of the mixture raised to 80°C, 95°C and 110°C for 8, 1.5 and 1.5 hours respectively. The reaction mixture was cooled to 40°C and 995 g of monomer II containing styrene and 13.9% divinylbenzene, 0.015% TBPO and 0.05% TBPB was added to the reactor. The mixture was allowed 60-120 minutes swelling time. The reaction mixture was heated at 85°C, 95°C and 110°C for 10, 1.5 and 1.5 hours, respectively. The copolymer beads were isolated and converted to strong acid cation exchange resins.

Example 3

-3 3

Into a 20 gallon (75.7 x 10 m ) stainless steel reactor equipped with an agitator was charged 70 Ibs. (31.75 kg) of deionized water and while stirring 13.3 Ibs. (6.03 kg) of 0.3% divinylbenzene crosslinked polystyrene core with particle size -50+60 mesh (from 210 µm to 297 µm). 20 Ibs was also staked. (9.07 kg) of monomer I which contained styrene, 1.44% active divinylbenzene, 0.26% active TBPO and 0.22% TBPB. After 30-60 minutes absorption time, 20 Ibs. (9.07 kg) of an aqueous solution of 228 g gelatin and 20 g sodium lauryl sulfate suspending agent and 11.5 g sodium dichromate latex inhibitor added to the mixture. The reactor was purged with nitrogen and the reaction mixture was heated to 80°C. After 90-120 minutes at 80°C, 66.7 Ibs. (30.25 kg) of monomer II containing styrene and 15% active divinylbenzene was added to the reaction mixture. during 5 hours, while the polymerization conditions were continued. The reactor was held at 80°C for another 5-7 hours. At that time, the temperature of the reactor mixture was raised to 95°C and 110°C for 1.5 and 1.5 hours, respectively .The copolymer beads were isolated and converted to strong acid cation exchange resins.

Example 4

Copolymer particles were produced using the methods generally described in examples 1-3. These samples were compared with beads that had been produced using a conventional manufacturing method as follows: -3 3

Into a 1-gallon (3.79 x 10 m ) stainless steel reactor equipped with an agitator was charged 875 g of water and 375 g of 0.3% crosslinked styrene/divinylbenzene copolymer seed with particle size -40+45 mesh (from 354 pm to 420 pm) under agitation. 875 g of monomer mix containing 15.6% active divinylbenzene, 0.036% active TBPO and 0.05% active TBPB were added to the suspended seed particles. The monomer was allowed to absorb for 30-60 minutes and then 375 g of an aqueous solution containing a suspending agent and an aqueous phase inhibitor was added. The reaction mixture was then heated to and held at 80°C for 8 hours, and the temperature was raised to 95°C and 110°C for 90 minutes each. The copolymer beads were isolated and converted to strong acid cation exchange resins.

Properties of the various sulfonated samples according to the invention show excellent properties regarding osmotic shock (ie more than 95 unbroken beads after 10 cycles of alternating treatments with 8 M HCl and 8 M NaOH, separated by backwashes with deionized water). In addition, when 50 ml of beads are placed in 50 ml of deionized water and agitated for 30 minutes, beads according to the invention give clear solutions, while such a test carried out with beads prepared using the previously described conventional method gives cloudy solutions.

Example 5

-3 3

Into a 1 gallon (3.79 x 10 m ) stainless steel reactor, equipped with an agitator, was charged 1750 g of deionized water, 215 g of 0.3% crosslinked styrene/divinylbenzene copolymer seed with a particle size of -50+ 60 meshes (from 210 µm to 297 µm) under agitation, as well as 215 g of monomer I, containing styrene and 1.7% active divinylbenzene, 0.075% active TBPO and 0.25% active TBPB. After a swelling time of 30-60 minutes, 325 g of an aqueous solution of stabilizer and latex inhibitor was added. The reactor temperature was raised to and held at 80°C for 6 hours. The reactor mass was cooled to 40°C, and 640 g of monomer II containing styrene and 8.8% active divinylbenzene was added to the reactor. After a swelling time of 60-90 minutes, the reactor mass was heated to 85°, 95° and 110°C for 10, 1.5 and 1.5 hours respectively each time. The copolymers thus prepared were, after suitable washing and drying, examined for toluene-swell cross-linking density and converted into both anion and cation resins, respectively.

Claims (9)

1. Seed process for the production of improved cross-linked copolymer particles capable of being functionalized to provide ion exchange copolymer particles having a high ability to withstand osmotic shock during use, namely a method characterized by: (a) forming an agitated aqueous suspension of polymerized, lightly cross-linked seed particles; (b) contacting said suspended seed particles with a monomer or monomer mixture comprising a minor amount of the total crosslinking monomer used, to ultimately produce a seed swollen by absorption of said monomer or monomer mixture and the polyvinyl crosslinking monomer; (c) contacting the suspended swollen seeds with a suspending agent in an amount sufficient to provide suspension of said swollen seeds, to prevent substantial agglomeration of said swollen seeds, and also to allow further absorption of monomer; (d) subjecting the suspended swollen seeds to polymerization conditions to the extent that at least substantial polymerization of absorbed monomers occurs; (e) substantially stopping the polymerization reaction and contacting the partially polymerized particles with another monomer or monomer mixture comprising a major amount of the total crosslinking monomer used, and (f) subjecting the further absorbed swollen seed to polymerization conditions to provide a copolymer bead. 2. Seed process for the production of improved cross-linked copolymer particles capable of being functionalized to provide ion-exchange copolymer particles having a high ability to withstand osmotic shock during use, namely a method characterized by: (a) forming an agitated aqueous suspension of polymerized, lightly cross-linked seed particles; (b) contacting said suspended seed particles with a monomer or monomer mixture comprising a minor amount of the total cross-linking monomer used, with the aim of ultimately producing a seed swollen by absorption of said monomer or monomer mixture and the polyvinyl cross-linking monomer , (c) contacting the suspended swollen seeds with a suspending agent in an amount sufficient to provide suspension of said swollen seeds, to prevent substantial agglomeration of said swollen seeds, and also to allow further absorption of monomer; (d) subjecting the suspended swollen seeds to polymerization conditions to the extent that at least substantial polymerization of absorbed monomers occurs, and (e) contacting the partially polymerized particles with another monomer or monomer mixture comprising a major amount of the total cross-linking monomer used, while the rate of addition of the monomer mixture and the polymerization conditions are controlled so that the monomer mixture can be absorbed into the swollen seed which is under polymerization conditions, and the polymerization proceeds to provide a copolymer bead. 3. Method as stated in claim 1 or 2, characterized in that an initiator is included in step (b). 4. Method as stated in claim 1, characterized in that an initiator is included in steps (b) and (e). 5. Method as stated in claim 1 or 2, characterized in that the copolymer beads are functionalized to provide ion exchange resin beads. 6. Copolymer bead produced by the method according to claim 1 or 2. 7. Functionalized copolymer bead produced using the method according to claim 5. 8. Method as stated in 1 or 2, characterized in that 1-15% by weight of the total amount of cross-linking monomer used is used in step (b), and 85-99% by weight of the total amount of cross-linking monomer used is used in step (e). 9. Method as stated in claim 1 or 2, characterized in that the cross-linking monomer is a polyvinyl monomer.