Process for the preparation of low-bleeding cation exchangers

Details Process for the preparation of low-bleeding cation exchangers Process for the preparation of low-bleeding cation exchangers

1997-10-21

2003-11-11

Cintins, Ivars (Department: 1724)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Ion-exchange polymer or process of preparing

Reexamination Certificate

active

06646017

ABSTRACT:

PROCESS FOR THE PREPARATION OF LOW-BLEEDING CATION EXCHANGERS
The invention relates to a process for the preparation of strongly acid cation exchangers which have a reduced tendency to release impurities into their environment.
There is currently a large number of interesting uses for cation exchangers. They are thus employed, for example, for treatment of drinking water, for the preparation of extra-pure water (necessary in microchip production for the computer industry), for chromatographic separation of glucose and fructose and as catalysts for the most diverse chemical reactions (such as, for example, in the preparation of bisphenyol A from phenol and acetone). For most of these uses, it is desirable that the cation exchangers indeed fulfil their intended task, but do not release to their environment at all, or release in the smallest possible amounts, impurities which can originate from their preparation or are formed by polymer degradation during use.
In the past, attempts have been made to solve the problem by treating the ion exchangers with antioxidants (EP-A-366 258) or modifying them chemically (United States Patent Specification 3 342 755 and EP-A-502 619). Although these measures can reduce polymer degradation, they have no influence on the constituents which are formed during preparation of the ion exchangers—whether these are unreacted starting materials or low molecular weight non-crosslinked polymers. Attempts are made to remove these impurities by repeated washing out with water, which is expensive and brings only partial success.
The object of the invention was thus to provide a method for the preparation of ion exchangers which, from the beginning, comprise a greatly reduced level of impurities which bleed out. Surprisingly, it has been found that this object is achieved by sulphonation of the non-functionalized polymer at a high temperature and/or by sulphonation with exclusion of oxygen.
The invention thus relates to a process for the preparation of strongly acid cation exchangers by sulphonation of crosslinked styrene polymers at elevated temperature, characterized in that the sulphonation is carried out at temperatures from 125 to 150, preferably 130 to 145° C. and/or in the absence of oxygen. The terms “ion exchanger” and “cation exchanger” in the context of this invention also include sulphonated resins which are employed not for the purpose of the ion exchanger but as acid catalysts.
The base polymer used is a crosslinked polymer of ethylenically monounsaturated monomers, which chiefly comprise at least one compound from the series consisting of styrene, vinyltoluene, ethylstyrene, &agr;-methylstyrene and derivatives thereof which are halogenated on the nucleus, such as chlorostyrene; in addition, they can also comprise one or more compounds from the series consisting of vinylbenzyl chloride, acrylic acid, its salts and its esters, in particular its methyl ester, and furthermore vinylnaphthalenes, vinylxylenes and the nitriles and amides of acrylic and methacrylic acids.
The polymers are crosslinked—preferably by copolymerization with crosslinking monomers having more than one, preferably having two or three, copolymerizable C=C double bond(s) per molecule. Such crosslinking monomers include, for example, polyfunctional vinyl aromatics, such as di- and trivinylbenzenes, divinylethylbenzene, divinyltoluene, divinylxylene, divinylethylbenzene, and divinylnaphthalene, polyfunctional allyl aromatics, such as di—and triallylbenzenes, polyfunctional vinyl—and allylheterocyclic compounds, such as trivinyl and triallylcyanurate and isocyanurate, N,N′-C-C
6
-alkylenediacrylamides and-dimethacrylamides, such as N,N′-methylenediacrylamide and -dimethacrylamide and N,N′-ethylenediacrylamide and -dimethacrylamide, polyvinyl and polyallyl ethers of saturated C
2
-C
20
-polyols having 2 to 4 OH groups per molecule, such as, for example, ethylene glycol divinyl and diallyl ether and diethylene glycol divinyl and diallyl ether, esters of unsaturated C
3
-C
12
-alcohols or saturated C
2
-C
20
-polyols having 2 to 4 OH groups per molecule, such as allyl methacrylate, ethylene glycol di(meth)acrylate, glycerol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate, divinyletheyleneurea, divinylpropyleneurea, divinyl adipate and aliphatic and cycloaliphatic olefins having 2 or 3 isolated C=C double bonds, such as hexa-1,5-diene, 2,5-dimethylhexa-1,5-diene, octa-1,7-diene and 1,2,4-trivinylcyclohexane. Crosslinking monomers which have proved to be particularly appropriate are divinylbenzene (as an isomer mixture) and mixtures of divinylbenzene and aliphatic C
6
-C
12
-hydrocarbons having 2 or 3 C=C double bonds. The crosslinking monomers are in general employed in amounts of 1 to 80% by weight, preferably 2 to 25% by weight, based on the total amount of the polymerizable monomers employed.
The crosslinking monomers do not have to be employed in a pure form, but can also be employed in the form of their industrially handled mixtures of lesser purity (such as, for example, divinylbenzene mixed with ethylstyrene).
The copolymerization of monomer and crosslinking agent is usually initiated by agents which form free radicals and are soluble in the monomer. Preferred catalysts which form free radicals include, for example, diacyl peroxides, such as diacetyl peroxide, dibenzoyl peroxide, di-p-chlorobenzoyl peroxide and lauroyl peroxide, peroxy esters, such as tert-butyl peroxyacetate, tert-butyl peroctoate, tert-butyl peroxypivalate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxybenzoate and dicyclohexyl peroxydicarbonate, alkyl peroxides, such as bis-(tert-butyl peroxybutane), dicumyl peroxide and tert-butylcumyl peroxide, hydroperoxides such as cumene hydroperoxide and tert-butyl hydroperoxide, ketone peroxides, such as cyclohexanone hydroperoxide, methyl ethyl ketone hydroperoxide and acetylacetone peroxide, or—preferably—azoisobutyrodinitrile.
The agents which form free radicals can be employed in catalytic amounts, i.e. preferably amounts of 0.01 to 2.5, in particular 0.12 to 1.5% by weight, based on the sum of monomer and crosslinking agent.
The crosslinked base polymers can be prepared by known methods of suspension polymerization; cf. Ullmann's
Encyclopedia of Industrial Chemistry
, 5th Edition, Volume A21, 363-373, VCH Verlagsgesellschaft mbH, Weinheim 1992. The water-insoluble monomer/crosslinking agent mixture is added to an aqueous phase, which preferably comprises at least one protective colloid for stabilization of the monomer/crosslinking agent droplets of the disperse phase and of the bead polymers formed therefrom. Preferred protective colloids are naturally occurring and synthetic water-soluble polymers, such as, for example, gelatin, starch, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, polymethacrylic acid and copolymers of (meth)acrylic acid and (meth)acrylic acid esters. Cellulose derivatives, in particular cellulose ethers and cellulose esters, such as methyl-hydroxyethyl cellulose, methylhydroxypropyl cellulose, hydroxyethyl cellulose or carboxymethyl cellulose, are also particularly suitable. The amount of protective colloids employed is in general 0.02 to 1, preferably 0.05 to 0.3% by weight, based on the aqueous phase.
The weight ratio of aqueous phase/organic phase is in the range of preferably 0.5 to 20, in particular 0.75 to 5.
According to a particular embodiment of the present invention, the polymerization is carried out in the presence of a buffer system. Buffer systems which adjust the pH of the aqueous phase to a value between 14 and 6, preferably between 12 and 8, at the start of the polymerization are preferred. Under these conditions, protective colloids with carboxylic acid groups are present entirely or partly in the form of salts. The action of the protective colloids is influenced favourably in this manner. The concentration of buffer in the aqueous phase is preferably 0.5 to 500, in particular 2.5 to 100 mmol per litre of aqueous phase.
The organic phase can be distr

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