Liquid purification or separation – Processes – Preventing – decreasing – or delaying precipitation,...
Patent
1991-11-01
1993-08-03
Hruskoci, Peter
Liquid purification or separation
Processes
Preventing, decreasing, or delaying precipitation,...
210701, 252180, C02F 512
Patent
active
052326039
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the use of water-soluble copolymers of monoethylenically unsaturated carboxylic acids and vinylimidazoles for water treatment and scale inhibition.
US-B 3,810,834 discloses the use of hydrolyzed polymaleic anhydrides which have a molecular weight of from 300 to 5,000 before the hydrolysis, or the water-soluble salts thereof, for treating water in order substantially to reduce or prevent scale formation. The polymers suitable for this purpose are prepared by polymerization of maleic anhydride in toluene, using benzoyl peroxide, and subsequent hydrolysis of the resulting polymaleic anhydride. Since maleic anhydride does not polymerize completely and it is difficult to remove unpolymerized maleic anhydride from the polymer, the polymaleic acids contain considerable amounts of maleic acid.
US-B 3,755,264 discloses low molecular weight copolymers which contain 85 to 99 mol % maleic anhydride and, polymerized in to make up to 100 mol %, acrylic acid, vinyl acetate, styrene or mixtures thereof. The copolymers are prepared by copolymerization of maleic anhydride with the said monomers in dry organic solvents at from 100.degree. to 145.degree. C. in the presence of peroxides. Examples of suitable peroxides are di-tert-butyl peroxide, acetyl peroxide, dicumyl peroxide, diisopropyl percarbonate and, in particular, benzoyl peroxide. The anhydride copolymer can subsequently be hydrolyzed to the acid or converted into the salts. The water-soluble copolymers are used to prevent deposition of scale. The products obtainable by this process contain a very large amount of unpolymerized maleic anhydride.
The use of low molecular weight polymers of acrylic acid for water treatment or scale inhibition is disclosed, for example, in US-B 3,904,522 and US-B 3,514,376. US-B 3,709,816 discloses that copolymers containing acrylamidopropanesulfonic acid are suitable for water treatment. Suitable examples are copolymers with 2-acrylamidopropanesulfonic acid and acrylamide which is partially hydrolyzed. The disadvantage of these is that residues of acrylamide monomer are unavoidable in the polymers, which means that they can be recommended for use only with great restrictions. On the other hand, acrylic acid homopolymers have a satisfactory effect only on types of deposits which are relatively easy to reduce, such as calcium carbonate.
The object of the present invention is to provide polymers for water treatment which equal or even exceed the effectiveness of the polymers based on acrylic acid which have been used hitherto, and which are also more soluble at high calcium ion concentrations than the polyacrylates hitherto used. In particular, the intention is effectively to reduce especially difficult problems of deposits in water-conveying systems, such as the formation of calcium phosphate and of silicate deposits.
We have achieved this object according to the invention by using water-soluble copolymers which contain, polymerized in, as characteristic monomers with 3 to 8 carbon atoms or their salts and ##STR1## where R.sup.1, R.sup.2 and R.sup.3 are H, C.sub.1 --C.sub.4 --alkyl, phenyl or benzyl, their salts or products of quaternization and which have K values of from 10 to 50 (determined in 1% strength aqueous solution at pH 7 and 25.degree. C. by the method of H. Fikentscher) for water treatment.
Copolymers of the type described above are known in principle. Thus, for example, US-B 3,634,366 describes a copolymer of acrylic acid and 1-vinyl-2-methylimidazole. The copolymers are prepared by copolymerization of the monomers in the presence of polymerization initiators. The copolymers to be used according to the invention contain as characteristic monomers of group (a) monoethylenically unsaturated carboxylic acids with 3 to 8 carbon atoms or their salts. Examples of these monomers are acrylic acid, methacrylic acid, dimethylacrylic acid, ethacrylic acid, maleic acid, citraconic acid, methylenemalonic acid, allylacetic acid, vinylacetic acid, crotonic acid, fumaric acid, mesaconic acid and itaconic ac
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Denzinger Walter
Goeckel Ulrich
Gousetis Charalampos
Hartmann Heinrich
Ruland Alfred
BASF - Aktiengesellschaft
Hruskoci Peter
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