Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2000-10-11
2003-12-23
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S025000, C521S027000, C521S031000, C525S378000, C525S379000
Reexamination Certificate
active
06667349
ABSTRACT:
The invention relates to a process for preparing basic anion exchangers with improved mechanical and osmotic stability.
Nowadays there is a wide variety of interesting applications for anion exchangers. For example, they are used in treating drinking water, in preparing ultrahigh-purity water (needed for the computer industry in microchip production), for purifying and decolourizing sugar solutions and for removing heavy metal complexes from solutions.
For all of these applications it is desirable for the anion exchangers, which are in the form of beads, to retain their form and not to fragment or lose their structure, partially or completely, during use. If this happens, these polymer fragments can pass into the actual solutions to be purified and contaminate them during the purification process. The presence of damaged bead polymers is moreover detrimental to the functioning of the very anion exchangers used in column processes. Fragments cause increased pressure loss in the column system, thus reducing the throughput of liquid to be purified through the column.
Various factors affect the physical stability of the anion exchangers. These include the conditions of bead polymer preparation, and also the conditions of amination of the bead polymers prepared, which are aromatic, crosslinked copolymers containing haloalkyl groups.
The object of the invention was therefore to provide a process for preparing anion exchangers with improved stability. Surprisingly, it has now been found that this object is achieved by aminating the gel-like chloromethylate in an aqueous solution comprising small amounts of an inorganic salt.
The invention therefore provides a process for preparing gel-like anion exchangers by aminating crosslinked gel-like styrene divinylbenzene bead polymers which contain halogenoalkyl groups.
The base polymer is a crosslinked polymer of monoethylenically unsaturated monomers composed predominantly of at least one compound from the series styrene, vinyltoluene, ethylstyrene, &agr;-methylstyrene and ring-halogenated derivatives of these, such as chlorostyrene.
In recent times, ion exchangers with a very uniform particle size (termed “mono-disperse” below) have become increasingly important, since the more advantageous hydrodynamic properties of an exchanger bed made of monodisperse ion exchangers can achieve economic advantages in many applications. One of the ways of preparing monodisperse ion exchangers is that known as the seed-feed process, in which a monodisperse nonfunctionalized polymer (“seed”) is steeped in monomer, and this is then polymerized. Examples of patent specifications which describe seed-feed processes are EP-0 098 130, EP-0 101 943, EP-0 418 603, EP-0 448 391, EP-0 062 088, U.S. Pat. No. 4,419,245.
Another way of preparing monodisperse ion exchangers is to prepare the underlying monodisperse bead polymers by a process in which the uniform monomer droplets are formed by subjecting monomers to vibration while in laminar flow, and then carrying out polymerization, U.S. Pat. No. 4,444,961, EP-0 046 535.
A process carried out industrially for preparing anion exchangers starting from bead polymers based on styrene divinylbenzene (DVB) proceeds by first functionalizing (chloromethylating) the aromatic ring systems present in the bead polymers, using chloromethyl groups, and then reacting these with amines.
In the chloromethylation the crosslinked bead polymer based on styrene/divinyl-benzene (DVB) reacts with monochlorodimethyl ether using Fe
2
O
3
, FeCl
3
, zinc chloride, tin(IV) chloride, aluminium chloride or other Friedel-Crafts compounds as catalysts, releasing methanol and other components—see EP-0 327 255.
The preparation of monochlorodimethyl ether is usually accompanied by the production of carcinogenic bischlorodimethyl ether. There are various versions of the process for preparing the monochlorodimethyl ether and for its reaction with bead polymers based on styrene divinylbenzene (DVB)—see EP-0 327 255, U.S. Pat. No. 4,225,677, U.S. Pat. No. 4,207,398, U.S. Pat. No. 5,523,327, DD-250 128, U.S. Pat. No. 4,207,398.
An excess of the chloromethylating agent is usually used, since this acts not only as an agent but also as a medium for steeping the bead polymer—see EP-0 776 911.
After the chloromethylation there are various ways of separating the remaining reaction medium, which in particular comprises monochlorodimethyl ether, from the chloromethylated bead polymer and for working up the chloromethylate.
JP-A-7-188 333 removes the remaining monochlorodimethyl ether by solvent extraction after the chloromethylation.
EP-0-776 911 meters in aqueous hydrochloric acid after the chloromethylation, heats the mixture to 110° C. and distils unreacted monochlorodimethyl ether. The chloro-methylate is centrifuged and precipitates as a moist product.
EP-0-327 255 meters in methanol and formaldehyde, and, if desired, also methylal, after the chloromethylation. The mixture is stirred, and hydrochloric acid is metered in after about 1 hour. The monochlorodimethyl ether, both that already present and that newly formed, is distilled off. The chloromethylate is, if desired, washed with methylal, then with water, and then neutralized with aqueous sodium hydroxide.
EP-0 481 603 adds methanol after the chloromethylation in order to break down remaining monochlorodimethyl ether. The gel-like chloromethylate is then washed with methanol to remove by-products.
DD-250 129 separates off the chloromethylate after the chloromethylation via a frit, and then washes the product with methanol.
There are various ways of reacting the chloromethylate obtained to give anion exchangers, using various amines.
In industry use is often made of anion exchangers having tertiary—or quaternary ammonium groups. For example, use is commonly made of anion exchangers having trimethylamine and/or dimethyl-or hydroxyethylammonium groups.
EP-0 776 911 describes the amination of an aromatic, crosslinked copolymer containing haloalkyl groups. The actual copolymer is a porous bead polymer, prepared by suspension polymerization. Examples 1 to 4 describe the amination of porous chloromethylates in aqueous sodium chloride solutions with addition of toluene. The chloromethylate is reacted with an amine in the presence of at least 100 parts by weight of water per 100 parts by weight of chloromethylate, and at least 5 parts by weight of a water-soluble inorganic salt per 100 parts by weight of water, with addition of toluene. The amine used comprises trimethylamine, and the inorganic salt used comprises sodium chloride in the presence of organic solvents, such as benzene, toluene, xylene or dichloroethane. The temperature for the amination is 50° C. The resistance of the resultant anion exchanger beads to pressure was measured. The presence of at least 5% by weight of sodium chloride in the water during the amination considerably increases the resistance of the anion exchangers to pressure when comparison is made with the product prepared without sodium chloride.
U.S. Pat. No. 5,182,026 describes the amination of an aromatic, crosslinked copolymer containing haloalkyl groups. The actual copolymer is a porous bead polymer prepared by suspension polymerization. Examples 1 to 3 and A to C describe the amination of porous chloromethylates. The amination is carried out in two steps. The first reagents used are primary or secondary amines, resulting in reaction of from 15 to 95% of the haloalkyl groups. The partly aminated resin is then reacted with tertiary amines, such as trimethylamine or triethylamine, to give strongly basic anion exchangers. The first amination is carried out in water with addition of from 100 to 280 g of sodium chloride, and also of a base, such as NaOH, at temperatures from 60 to 100° C. The copolymer used may also comprise a gel-like polymer prepared by the seed process.
EP-0 481 603 describes the amination of gel-like copolymer beads prepared by a seed process. The bead polymers have core-shell morphology. This means that the poly-meric structure of the beads varies with the distance
Holzbrecher Michael
Klipper Reinhold
Lütjens Holger
Martin Georg
Mitschker Alfred
Akorli Godfried R.
Bayer Aktiengesellschaft
Eyl Diderico van
Zitomer Fred
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