CA2034655A1

CA2034655A1 - Water treatment with water-soluble copolymers based on ethylenically unsaturated carboxylic acids

Info

Publication number: CA2034655A1
Application number: CA 2034655
Authority: CA
Inventors: Charalampos Gousetis; Ulrich Goeckel; Karl-Heinz Buechner; Walter Denzinger; Heinrich Hartmann
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1990-01-23
Filing date: 1991-01-21
Publication date: 1991-07-24
Also published as: DE4001808A1; AU6949591A; JPH07100492A; EP0438744A1

Abstract

Abstract of the Disclosure: Water-soluble copolymers containing as characteristic monomers (a) from 99 to 50% by weight of monoethylenically unsaturated carboxylic acids of 3 to 8 carbon atoms or salts thereof and (b) from 1 to 50% by weight of monomers of the formula CH2=CH-NR2-CO-R1, where R1 and R2 are each H or C1-C6-alkyl, as copolymerized units and have K values of from 10 to 50, and the copolymers obtainable therefrom by elimina-tion of formyl groups with the formation of vinylamine units are suitable for use as water treatment agents for preventing scale formation and water hardness precipita-tion in water carrying systems.

Description

O.Z. 0050/41361 Water treatment with water-soluble copolymers bas~d on ethvlenicallY unsaturated carboxylic acids It i8 known from US Patent 3,810,334 that hydro-lyzed polymaleic anhydrides which prior to the hydrolysis have a molecular weight of from 300 to 5000 or water-soluble salts thereof can be used as water treatment agents to substantially suppreqs or prevent ~caling. The polymer3 suitable for thi~ purpose are prepared by polymerization of maleic anhydride in toluene using benzoyl peroxide and sub~equent hydroly~is of the result-ing polymaleic anhydride. Since the polymerization of the maleic anhydride is not complete and the removal of unpolymerized maleic anhydride from the polymer is difficult, the polymaleic acids still contain consider-able amount~ of maleic acid.
US Patent 3,755,264 disclo~e~ low molecular weight copolymers containing from 85 to 99 mol ~ of maleic anhydride and, as the difference from 100 mol %, acrylic acid, vinyl acetate, styrene and mixtures thereof as copolymerized units. The copolymers are prepared by copolymerizing maleic anhydride with the monomers mentioned in dry organic solvents at 100 - 145~ in the presence of peroxides. Suitable peroxides are for example di-tert-butyl peroxide, acetyl peroxide, dicumyl perox-ide, diisopropyl percarbonate and in particular benzoyl peroxide. The anhydride groupa of the copolymer can be hydrolyzed into acid groups or converted into salts after the polymerization. The water-soluble copolymer~ are uqed for preventing sc~ling. The products obtainable by thi~
process contain a very high level of unpolymerized maleic anhydride.
The use of low molecular weight polymers of acrylic acid for water treatment, ie. as scale inhibi-tors, is known for example from US Patents 3,904,522 and 3,514,376. From US Patent 3,709,816 it i8 known that copolym6rs which contain acrylamidopropanesulfonic acid a~e ~uitable for use as water treatment agents. Examples ~`; ' :
: ~ . ~ . : . .- . . ........................ .

:

- 2 - ~.Z. 0050/41361 are partially polymerized copolymers of 2-acrylamidoprop-anesulfonic acid and acrylamide. The disadvantage i8 the inevitable presence of residual acrylamide in the poly-mer, which much restrict~ their usefulness. On the other hand, homopolymer~ of acrylic acid perform satisfactorily only again~t relatively easily inhibited types of scale, for example calcium carbonate.
It is an ob~ect of the present invention to provide water treatment polymer~ which achi~ve or even exceed the effectivene~ of prior art polymer~ based on acrylic acid and at the same time are more ~oluble at high calcium ion concentrations than the prior art polyacrylates. In particular, they should effectively anticipate particularly obstinate ~cale problems in water carrying sy~tems, such as the formation of calcium phosphate and the deposition of silicate precipitates.
We have found that this ob~ect is achieved according to the present invention by using water-soluble copolymers which contain as characteristic monomers 0 (a) from 99 to 50% by weight of monoeth~lenically unsaturated carboxylic acids of from 3 to 8 carbon atoms or alkali metal, ammonium or amine salts thereof and (b) from 1 to 50% by weight of monomers of the formula CH 2=CH - N~ ( I) 11_ o where R' and R2 are each hydrogen or C~-C~-alkyl, a~ copolymerized units and have R values of from 8 to 50 (determined by the method of H. FikentschQr in 1%
~trength aqueous solution at pH 7 and 25C) and the vinylamino-containing copolymers obtainable therefrom by partial or complete elimination of the formyl group from the copolymerized monomers of the formula I, as water treatment agents.

:

.
- : - , ~()3~655 - 3 - O.Z. 0050/41361 The copolymers are prepared by copolymerizing the monomer~ in the preQence of polymerization initiators.
The copolymers to be used according to the present invention contain as characteri3tic monomers of group ta) monoethylenically unsaturated carboxylic acids of from 3 to 8 carbon atoms or ~alts thereof as copolymerized units. These monomers include for example 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 acid. Of this group of monomers, preference is given to acrylic acid, methacrylic acid or maleic acid and to mixtures thereof, in particular mixtures of acrylic acid and maleic acid, for preparing the copolymers to be used according to the present invention. These monomer~ can be present in the copolymers either in the form of the free acids or in a partially or completely neutralized form. These monomerQ
may be neutralized with alkali metal bases, ammonia or amines. Of the bases mentioned, sodium hydroxide ~olu-tion, potassium hydroxide solution and ammonia are of particular practical importance. The neutraliz~tion may also be effected with amines, such as ethanolamine, diethanolamine or triethanolamine. The monomers of group (a) are involved in the con~truction of the copolymers to an extent of from 99 to 50, preferably from 95 to 70, %
by weight.
The copolymers contain as characteristic monomers of group (b) compounds of the formula ~R2 CH 2=CH--N ( I ) C--RI

where R1 and RZ may be identical or different and each is hydrogen or C1-C~-alkyl, as copolymerized units. Suitable compound~ of group (b) are for example N-vinylformamide .

:~ ' , ' .

~ 03~65S

- 4 - O.Z. OOSO/41361 tRl=R2=H in the formula I), N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinyl-N-methylpropionamide and N-vinylpropionamide. The monomers mentioned can be polymer-ized alone or mixed with one another. Of this group ofmonomers, N-vinylformamide i8 preferred. The proportion of monomer~ of group (b) in the construction of the copolymers i~ from 1 to 50, preferably from 5 to 30, ~ by weight.
The copolymers may contain by way of modification copolymerized units of a further group of monoethyleni-cally unsaturated monomers (c) which are copolymerizable with the monomers (a) and (b). These monomer~ are copoly-merized into the copolymers of (a) and (b) only in such an amount that the copolymers are still water-soluble.
The amount of monomers (c) can therefore vary within wide limits. If monomers (c) are included in the copolymers by way of modification, their proportion in the construction of the copolymers is up to 20% by weight. To achieve modification it is possible to use for example esters, amides and nitriles of the carboxylic acids ~pecified under (a). Preferred compounds of this type are for example methyl acrylate, ethyl acrylate, methyl meth-acrylate, ethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxy-ethyl methacrylate, hydroxypropyl methacrylate, methyl hydrogen maleate, dimethyl maleate, ethyl hydrogen maleate, diethyl maleate, acrylamide, methacrylamide, N-dimethylacrylamide, N-tert.-butylacrylamide, dimethyl-aminopropylmethacrylamide, acrylamidoglycolic acid,acrylonitrile and methacrylonitrile. Other suitable monomer~ of group (c) are sulfo-containing monomers, eg.
vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate and acrylamidomethylpropane-sulfonic acid, and also phosphono-containing monomers, ~uch a~ vinyl phosphonate, allyl phosphonate and . ~ , . .
,. , - . : :
: . : .. .. .

: .... . . . - . . . .
. - - ,. - . . , - ~ , . . ..

- 5 - o. z . 0050/41361 acrylamidomethylpropanephosphonic acid . Suitable monomers of group (c) also include N-vinylpyrrolidone, N-vinyl-caprolactam, N-vinyl-2-methylimidazoline, diallyldian~nonium chloride, vinyl acetate and vinyl propionate. It i of cour~e al~o possible to use mixtures of ~aid monomers of group (c), for example acrylic e~ter~
and vinyl acetate or acrylamide and hydroxyethyl acry-late . Of the monomers of group ( c ) which can be u~ed for modifying the copolymers of (a) and (b), vinylQulfonic acid, methallylsulfonic acid, acrylamidomethylpropane-sul f onic ac id, N-vinylpyrrol idone, dimethyldiallyl -ammonium chloride and vinyl acetate are pref erred . The monomers of group ( c ) -if pre~ent at all in the copoly-mers of (a) and (b) by way of modification - are prefer-ably pre~ent as copolymerized units in amounts of up to 15% by weight.
Particular preference is given to th0 use of copolymers which contain (a) from 95 to 70% by weight of acrylic acid, meth-acxylic acid, maleic acid or mixtures thereof and (b) from 5 to 30% by weight of N-vinylformamide and also (c) from 0 to 1596 by weight of vinylsulfonic acid, acrylamidomethylpropanesulfonic acid, methallyl-sulfonic acid, N-vinylpyrrolidone, dimethyldiallyl-ammonium chloride or hydroxypropyl acrylate a~ copolymerizad units. The copolymers are preferably used in.a completely or partially neutralized form. The copolymers have g values of from 8 to 50, preferably from 10 to 40 (determined by the method of H. Fikentscher on 1% strength by weight solutions of the sodium salt~ of the copolymers at pH 7 and 2 5 C ) .
The copolymer~ c~n be prepsred by any known continuous or batchwise proce~ of bulk, precipitation, suspension or solution polymerization in the presence of polymerization initistors which form free radical~ under the condition~ of the polymerization, for example in-organic and organic peroxides, persulfates, azo compound~

... .

~ , ~ .

~()3~65S

- 6 - O.Z. 005~/41361 and redox cataly~ts.
The preferred free radical initiator~ have a half~ e of less than 3 hours at the particular chosen polymerization temperature. If the polymerLzation is ~tarted at a low temperature and completed at a hl~her temperature, it is advantageous to use at least 2 initi-ators which decompose at different temperatures, namely at first at the stsrt of the polymerization an initiator which decomposQs at the low temperature and then toward the end of the main polymerization an initiator which decomposes at the higher temperature. It i8 possible to use water-soluble and water-insoluble initiators or mixtures of the two. The water-insoluble initiators are then ~oluble in the organic phase. Examples of which initiator~ can be used within which temperature ranges are as followss 40 - 60C:
acetylcyclohexanesulfonyl peroxide, d$acetyl paroxodi-carbonate, dicyclohexyl peroxodicarbonate, di-2-ethyl-hexyl peroxodicarbonate, tert.-butyl perneodecanoate, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile~, 2,2'-azobi~(2-methyl-N-phenylpropionamidine) dihydrochloride, 2,2'-azobis(2-methylpropionamidine) dihydrochloride 60 - 80C:
tert.-butyl perpivalate, dioctanoyl peroxide, dilauroyl peroxide, 2,2'-azobis(2,4-dimethylvaleronitrile) 80 - 100C:
dibenzoyl peroxide, tert.-butyl per-2-ethylhexanoate, tert.-butyl permaleate, 2~2~-azobis(isobutyronitrile)~
dimethyl 2,2'-azobisisobutyrate, sodium persulfate, potassium persulfate, ammonium persulfate 100 - 120-C:
bis(tert.-butylperoxy)cyclohexane,tert.-butylperoxyiso-propylcarbonate, tert.-butyl peracetate, hydrogen perox-ide120 ~ 140-C:
2,2-bis(tert.-butylperoxy)butane, dicumyl peroxide, ... . .
. . .' .. . ~ :

.

,. , , . ~ , . . . ~.

- 7 - o.Z. 0050/41361 di-tert.-amyl peroxide, di-tert.-butyl peroxide >140C:
p-methane hydroparoxide, pentane hydroperoxide, cumene hydroperoxide, tert.-butyl hydroperoxide If together with at least one of the above-mentioned initiator~ a salt or complex of a heavy metal, for example a copper, cobalt, manganese, iron, nickel or chromium ~alt, or an organic compound such as benzoin, dimethylaniline or a~corbic acid is used, it is possible to reduce the half-lives of the stated free radical initiators. For instance, tert.-butyl hydroperoxide can be activated with 5 ppm of copper(II) acetylacetonate to such an extent that polymerization i8 possible at 100C.
The reducing component of redox cataly~ts may al~o be formed for example by compounds such as qodium ~ulfite, sodium bisulfite, ~odium formaldehyde sulfoxylate or hydrazine. Based on the monomers used in the polymeriza-tion, from 0.01 to 20, preferably from 0.05 to 10, % by weight of polymerization initiator or a mixture of a plurality of polymerization initiators is used~ A redox catalyst includes 0.01 to 5% of a reducing compound.
Heavy metals are used within the range from 0.1 to 100 ppm, preferably from 0.5 to 10 ppm. It is often of advantage to use a combination of peroxide, reducing agent and heavy metal as redox catalyst. The copolymer-ization of the essential monomers (a) and (b) can also be carried out using ultraviolet radiation with or without W initiators. The polymerization with W rays is carried out using the photoinitiators or sensitizers customary for this purpose. They are for example compounds such as benzoin and benzoin ethers, ~-substituted benzoin com-pounds, such as ~-methylolbenzoin and ~-methylolbenzoin ether, ~-methylbenzoin and ~-phenylbenzoin. It is also possible to use triplet 3ensitizers, such as benzil diketals. Suitable W sources are for example not only high-energy W lamp~, such as carbon arc lamps, mercury vapor lamps or xenon lamps, but also low- W light , . .
' . . , - : , `

~03~655 - 8 - O.Z. 0~50/41361 sources, such a~ fluora cent tube~ with a high blue content.
To prepare polymers having a low K value, the polymerization is advantageou~ly carried out in the pre~ence of regulators. Suitable regulators are for example mercapto compounds, such as mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid, mercaptopropionic acid, butylmercaptan or dodecyl-mercaptan. Other ~uitable regulators are allyl compounds, such as allyl alcohol, aldehydes, such as formaldHhyde, acetaldehyde, propionaldehyde, n-butyraldehyde or iso-butyraldehyde, formic acid, propionic acid, hypophos-phorous acid and phosphorous acid. If the polymerization i8 carried ont in the presence of regulator , they are required in an amount of from 0.05 to 20~ by weight, based on the monomers used in the polymerization. To prepare copolymers having R values of from 30 to 50, it may be advantageous to carry out the copolymerization in the additional presence of monomers which have at least two ethylenically unsaturated, non-con~ugated double bonds in the molecule. These monomers are for example crosslinkers, such as methylenebisacrylamide, e~ter~ of acrylic acid and methacrylic acid with polyhydric alco-hols, eg. glycol diacrylate, glycerol triacrylate, glycol dimethacrylate, or glycerol trimethacrylate, and also at least doubly acrylated or methacrylated polyols, such as pentaerythritol or glucose. Suitable crosslinkers also include divinylbenzene, divinyldioxane, pentaerythritol triallyl ether and pentaallylsucrose. If crosslinkers are used in the copolymerization, their amount is up to 5% by weight, based on the total monomers.
In a bulk polymerization, the monomer~ are heated together with the free radical initiators, and it is usually necessary to heat the reaction mixture to tem-peratures above the softening point in order to keep themixture fluent. The preparation is advantageously carried out continuously in order that the high heat of -: ', : . . .
. ' , , .
. .

;~0;~6S5 - 9 - O.Z. 0050/41361 polymeriæation may be Rafely removed. The polymers obtained uqu~lly have R Yalue~ within the range from 10 to about 30. To prep~e copolymer~ having R value~ of from 30 to 50, it i~ possible to reaort to a precipitat-5ion polymerization or to a ~uspen~ion polymerization. In a precipitation polymerization, the monomers are soluble in the diluent while the copolymers formed are insoluble and therefore precipitate. In a ~u~pension polymeriz-ation, both the monomers and polymer~ are in~oluble in 10the diluent. To avoid aggregation of the copolymer particles, it is advantageous to carry out the copoly-merization in the presence of protective colloids. After the copolymerization the copolymers can be i~olated in solid form by filtration and drying. The preferred 15polymerization method i8 solution polymerization, where the monomers and copolymers are dissolved in the solvent.
Particularly suitable solvents for a solution polymeriza-tion are water, secondary alcohols and mixtures of water and secondary alcohols. If water is u~ed a~ solvent, the 20polymerization must be carried out in the presence of regulators since otherwi~e the copolymer~ formed have an excessively high K value. If, on the other hand, the monomers are polymerized in secondary alcohols, it is possible to dispense with regulators since, as will be 25known, secondary alcohols ha~e a regulating effect. In the case of a polymerization in water, it i8 advantageous to carr~ out the polymerization at a pH within the range from 4 to 10, preferably from 5 to 8, in order to avoid an unwanted hydrolysis of the monomers of component (b).
30In the polymerization processes mentioned, the polymerization is conducted in such a way that the polymer concentration of the reaction mixture is from 5 to 80, preferably from 10 to 60, % by weight. Suitable polymerization temperatures range from 20 to 250C, 35preferably from 40 to 180C. In practice, the particu-larly preferred temperatures for the copolymerization range from 60 to 130C. If the polymerization temperature ..

-. : . ................................ ..... .
, :. .
. ., -2()3~65S

- 10 - O.Z. 0050~41361 i~ above the boiling point of the ~olvent or ~olvent mixture, the copolymerization is carried out under ~uperatmospheric pre~sure. If the copolymerization is carried out in an organic olvent, the reaction mixture is afterward~ neutralized if nece~sary and sub~ected to a steam di~tillation to di~til off the organic solvent.
It is of courqe also possible to distil the organic solvent out of the reaction mixture and then to add water to obtain a copolymer ~olution.
The u~e according to the prasent invention is also possible with those copolymers which are obtainable by hydrolysis, ie. partial or complete elimination of the formyl groups, from the above-described copolymers which contain the monomers of groups (a) and (b) with or without (c) as copolymerized unit~. On hydrolysis of these copolymers up to 100%, for example from 1 to 100~, of the copolymerized units of the formula /N\ (II) where R1 and R2 may be identical or different and each is hydrogen or Cl-Ca-alkyl, are converted through el~mination of the formyl group into vinylamine units of the formula -cH2-lCH_ (III) where R2 i~ as defined in the formula II. A partial hydrolysis of a copolymer of monomers (a), (b) and ~ 25 optionslly (c) gives copolymers which in addition to the ; copolymerized monomers (a), (b) and optionally (c) contain units of the formula IIT. Complete hydrolysis of the copolymerized monomers (b), on the other hand, will convert all the units of the formula II into units of the formula III.
The copolymers are hydrolyzed in the presence of - .
.
:.:: . : . . - . . . - -~0;~4~55 - 11 - O.Z. 0050/41361 acid~ or base~ at up to 170C, for example in the range from 20 to 170C, preferably ~rom 50 to 120C. The degree of hydroly~i~ of the copolymerized unitq of the formula II depends on the temperature and on the concentration of the amount~ of acid or base used for thi~ purpose.
Suitable acids for hydrolyzing the copolymer~ are mineral acid~, such as hydrogen halides, sulfuric acid, nitric acid and pho~phoric acid, and also organic acids, for example acetic acid, propionic acid, benzenesulfonic acid and alkylsulfonic acids, such a~ dodecylsulfonic acid. Of the acids mentioned, sulfuric acid and hydrochloric acid are preferred. Each formyl group equivalént present in the copolymer requires in general from 0.05 to 1.5, preferably from 0.4 to 1.2, equivalents of acid.
In the hydrolysi~ of the copolymers of (a), (b) and optionally (c) it is possible to use hydroxides of metal~ of main groups I and II of the Periodic Table, for example lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide and magnesium hydroxide.
Similarly, the base used can be ammonia or a derivative of ammonia, for example triethylamine, monoethanolamine, diethanolamine, triethanolamine and morpholine. If the copolymers are to be hydrolyzed at an alkaline pH it is preferable to use those bases which are cust~marily used in connection with the application of scale inhibitors, for example sodium hydroxide solution, potassium hydrox-ide solution, ammonia or triethanolamine. If the copoly-mers are hydrolyzed with base~, the pH will in general be from 8 to 14. The hydrolysis of the copolymers i8 in general complete after about 1 - 8, preferably 2 - 5, hours. In the casQ of an acid hydrolysis, the reaction mixture is afterwards ad~usted to the pH range from 7 to 10 customary for scale inhibitors. Hydrolyzed copolymers to be used according to the present invention are also obtainable for example by hydrolyzing copolymer3 of Cl-C8-alkyl e~ters of ethylenically unsaturated C3-C8-carbox-ylic acids and a monomer of group (b), such as .

;. ' ' . ' ' :
~- '. . ., ~ ~ ' ' `. ' ''' : . .. .

- 12 - O~Z. 0050/41361 N-vinylformamide, and optionally (c). This is because the copolymerized alkyl esters of the ethylenically unsatura-ted C3-C~-carboxylic acids are converted into the parent acids and the copolymerized units of the formula II are converted into unit~ of the formula III, but units of the formula II may still be pre~ent in the copolymer, a~ well a~ unit~ of the formula III, depending on the degree of hydrolysis.
The thus obtainable aqueous copolymer solutions can be used directly as water treatment agent~ for reducing ~cale and water hardne~s depo~ition in water carrying systems. It is possible to combine the polymers according to the present invention with other disper-sants, such as phosphonates, phosphonoalkanecarboxylic acids, etc.
The copolymers act as scale inhibitors in that they prevent the formation of crystals of the hardness ion salts, such as calcium carbonate, magnesium oxide, magnesium carbonate, calcium sulfate, barium sulfate, strontium sulfate, calcium phosphate (apatite~ and the like, when added in substoichiometric amounts, or influ-ence the formation of the~e precipitates in such a way as to prevent the formation of hard and rocklike deposits and instead favor the formation of r0adily resuspendable, ~ 25 water-disper~ible precipitates. In this way the ~urfaces 'i of for example he~t exchangers, pipes or pump components - are kept.free of deposits and their corrosion is reduced.
Especially, the danger of pitting corrosion under these depo~its is reduced. Furthermore, the growth of micro-organisms on these metal surfaces 18 inhibited. By virtue of scale inhibitors it is pos~ible to lengthen the life of such equipment and to considerably reduce downtime for the cleaning of apparatus. The required amounts of scale ` inhibitor range from 0.1 to 100, preferably from 0.5 to 25, ppm, based on the particular amount of water. The water carrying systems are for example open or closed cooling cycles, for example of power stations or chemical :` `
. f " ~ i ' ` ' . ' , ~ ',', " ., ' '~.''. . ., ' ~
" ~ ' ' , '. ', ' , '~ " , , ' "' ,., " ~ , ' ' ' ' ,',' ' ; ~ ' ' , ~ " ' ~ ' ' '. ' ~3465S

- 13 - O.Z. 0~5Q/41361 plants, such as reactors, distillation apparatu~ and the like, where heat mu~t be removed. These ~cale lnhibitor~
can also be u~ed in boiler waters and steam generator~, preferably at water temperature~ below 150C. A preferred use for the scale inhibitors to be u~ed accordinq to the pre~ent inven~ion, furthermore, iB the de~alination of ~eawater and bracki~h water by di~tillation or membrane proce~ses, for example reverse o~mosis or electrodialy-sis. In desalination by multistage flash evaporation, for example, ~cale inhibitors in the seawater circulating at elevated temperature are effective in suppressing the precipitation of hardness ions, for example brucite, and their buildup on equipment surfaces.
In membrane proce~ses, damage to the membranes due to cry~tallizing hardnQs~ ions can be effectively prevented. These scale inhibitors consequently permit higher thickening factors, improved yields of pure water and longer membrane lifetimes. A further application of scale inhibitors i8 the evaporation of sugar ~uices from sugar cane or beet. In contradistinction to the above-described applications, here the thin sugar ~uice is admixed for example with calcium hydroxide~ carbon dioxide, sulfur dioxide or possibly phosphoric acid for purification. Sparingly soluble calcium salts remaining in the sugar ~uice after filtration, for example calcium carbonate, calcium sulfate or calcium phosphate, then precipitpte during the evaporation process and may form rockhard deposits on heat exchanger surfaces. Thi~ is also true of ~ugar concomitants, such as silica or calcium salts of organic acids, eg. oxalic acid.
The same is true of downstream processes, for example the production of alcohol from sugar production residues.
The copolymers which are usablQ according to the present invention as scale inhibitors substantially suppress the abovementioned scale formation proces~es, 80 that downtimes for cleaning the equipment, for example by ~.~

.- . ' j .
., , . . ~ - .

.' : ~ : ~ . ,:
, 2034~i5~

- 14 - o.Z. 0050/41361 boiling out, can be significantly reduced. A further significant aspect here i~ the conqiderable energy saving through prevention of the heat insulating scale deposits in question.
The amounts of scale inhibitor required in the above-described applications vary, but range from 0.1 to lO0 ppm, based on treated cooling water, boiler water, process water or, for example, sugar ~uice.
The produsts to be used according to the present invention give better dispersing of hardne~s ion salts, such a~ calcium carbonate, calcium sulfate and calcium phosphate, and al~o are more compatible with calcium ions than homopolymers of acrylic acid.
The K values of the copolymers were determined by the method of H. Fikentscher, Cellulosechemie 13 (1932) 48 - 64 and 71 - 74, in aqueous ~olution at pH 7 and 25CC
and at a polymer concentration of the sodium salt of the copolymer of 1% by weight. The percentages are by weight.
EXAMPLES
Preparation of copolymers - Copolymer 1 A stainles~ steel polymerization reactor con-structed for superatmospheric work is charged with 1250 g of isopropanol. The reactor is than pressurized three time~ with nitrogen up to a pressure of 3 bar and depres-surized again. It is then sealed pressure-tight. The contents are heated to 120C with stirring. As soon as that temperature i8 reached, 1081.5 g of a~rylic acid and a ~olution of 118.5 g of N-vinylformamide in 200 g of isopropanol on the one hand and a solution of 36 g of di-tert.-butyl peroxide in 200 g of isopropanol on the other are metered in at a uniform rate over 4 and 5 hour~
respectively. The reaction mixture is then heated at 130C for 2 hours, then depressurized with distillative removal of some of the isopropanol, and diluted with 600 g of water. The remaining isopropanol is then dis-tilled off with steam until a boiling point of 100C is .:

.::
- ~, . . ~
: - . .

- 15 - O.z. 0050/41361 raached. The reaction mixture is then cooled down to 50C
and is admixed with 825 g of 50% ~trength aqueou~ sodium hydroxide solution to pH 7.5. The neutralized aqueous copolymer solution has a solids content of 41.1%. The copolymer has a K value of 25.4.
Copolymer 2 In the aforedescribed polymerization reactor, 1250 g of isopropanol are heated to the boil at about 82C with ~tirring. 602 g of acrylic acid, a ~olution of 148 g of N-vinylformamide in 250 g of isopropanol and a solution of 22.5 g of tert.-butyl perethylhexanoate in 250 g of isopropanol are then added at a uniform rate over 3 hours, and the reaction mixture i9 heated to the boil. On completion of the initiator addition the reac-tion mixture is heated at the boil for a further 2 hours and then diluted with 300 g of water. Steam is then passed to the reaction mixture to distil off the iso-propanol until the boiling point i~ 100C. The aqueous copolymer solution is cooled down and neutralized with 620 g of 50% strength aqueous sodium hydroxide ~olution.
The aqueous copolymer solution thus obtained ha~ a solids ; content of 49.3% and a pH of 7.1. The R value of the copolymer i8 21.4.
Copolymer 3 Example 1 is repeated, except that the copolymer-ization is carried out at 130-C and the steam d$~tilla-tion is.carried out in such a way as to produce an ~queous copolymer solution having a solids content of 52.9% at pH 7.2. The ~ value of the copolymer is 16.3.
Copolymer 4 Example 3 is repeated, except that after the ; steam distillation the reaction mixture is cooled down to 50C, 130 g of concentrated sulfuric acid are added in the course of 10 minutes, and the reaction mixture is hydrolyzed by stirring at 50-C for 2 hours. 1100 g of 50%
strength aqueous sodium hydroxide solution are then metered in to pH 7Ø The N-vinylformamide units of the .

,: ;."
, . ., . .. . ,. .. . . . - . ;

, ~. . ... . . . .
.

;~03~6S5 - 16 - O.Z. 0050/41361 copolymer were completely converted into vinylamine units during the hydroly~is. The aqueous ~olution of the copolymer salt obtained ha~ a Yolid~ content of 51.2~.
The R value of the hydrolyzed copolymer i~ 14.2.
S The abovede~cribed copolymsrs were sub~ected to ~he following tests in re~pect of their suitability for use as water treatment agent~:
CaS0~ test 500 ml of a saturated CaS0~ solution are reduced down to 200 g at 200C in a d~ying cabinet. ~he mixture i~ left to stand overnight and then fil~ered through a membrane filter (O.45 ym).
50 ml of the filtrate are titrated with an aqueous 0.2 M solution of Na2H2 EDTA (EDT~ - ethylenedi-aminetetraacetic acid) to determine the calcium content still in ~olution. The inhibition on addition of 1 ppm of polymer i6 calculated in comparison with a blank te~t without polymer. ~
/ mg of CaS0; on filter (with 1 ppm \
/ of polymer inhibitions 100 1-mg of CaS0~ on filter (blank test \ without polymer) CaC03 te~t An aqueous ~olution is prepared of components A
and B~
As 3.36 g of NaHC03/l Bs 1.58 g of CaCl2 2H20/l 0.88 g of MgS0~1 100 ml each of the above solutions A and B are pipetted into a 250 ml flask together with 5 ppm of dispersant, and the flask is sealed and stored at 86C
for 16 hours. After cooling down to room temperature and filtration, the solution i8 titrated with a 0.2 M ~olu-tion of Na2H2 EDTA.

' : ' 203'~655 - 17 - O.Z. 0050/41361 mg of CaO on filter (with poly mer) % inhibition: 100 . 1~
mg of CaO on filter (blank test \ without polymerl Ca3 ( P~ ) 2 test 100 ml of a ~olution are prepared with the foliowing concentrations:
1. 095 g/l of CaCl2 6H20 0.019 g/l of Na2HPO4 2H20 2 ppm of polymer The pH i8 ad~usted to 8.6 with a borax buffer.
The solution i~ then stirred at 70C for 3 hours and left to stand for 24 hours. Afterwards the light transmittance lS (LT, white light) i8 measured with a photometer. The photometer is set beforehand to 100% LT with distilled water.
100 - LT with 2 ppm of polymer\
% inhibition: 1 - xlOO
100 - LT of a blank sample \ without polymer Calcium ion compatibility 200 ml are prepared of a solution of the follow-ing compositions 1.565 g of CaCl2 6H20/l 3 g of RCl~l 45 ppm of polymer The pH i~ ad~usted to 9 with NaOH and thesolution is then boiled for 30 minutes. After boiling the solution is made up to 200 ml with distilled water and the light tran~mittance (LT) is measured (LT for dis-tilled water = 100%). The higher the LT, the better the compatibility of the product with calcium ions.
The test results are ~hown in the Table.

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Z03~65S

- 18 - O.Z. OOS0/41361 ~ inhibition LT
Example Copolymer K CaSO~ CaC03 Ca3 ( P04 ) z ( Polymer No. value induced clouding) 1 1 25.4 68 47 79 ~9 2 2 21.4 43 49 58 95 3 3 16.3 40 23 54 97 4 4 14.2 41 20 69 90 Comparative Example 1 (homopolymer of 30 29 45 61 <60 acrylic acid) As can be ~een from the Table, copolymer 1 is in all te~ts ~uperior to the homopolymer of acrylic acid. This copolymer is suitable in particular for treating those water carrying systems which have a high calcium ion concentration, for example sugar ~uices.
Copolymers 2 and 4 are better than the homopoly-mer of acrylic acid in 3 of 4 tests.

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Claims

1. A method of scale inhibition in water carrying systems, which comprises adding to the water carrying system a scale inhibitor and water treatment agent comprising a water-soluble copolymer containing as characteristic monomers (a) from 99 to 50% by weight of a monoethylenically unsaturated carboxylic acid of 3 to 8 carbon atoms or an alkali metal, ammonium or amine salt thereof and (b) from 1 to 50% by weight of a monomer of the formula (I) where R1 and R2 are each hydrogen or C1-C6-alkyl, as copolymerized units and has a K value of from 8 to 50 (determined by the method of H. Fikentscher in 1%
strength aqueous solution at pH 7 and 25°C).

2. A method as claimed in claim 1, wherein the water-soluble copolymer contains units of the formula (III) where R2 is as defined in formula I and the units of the formula III are obtainable by partial or complete elimi-nation of the formyl groups from the copolymerized monomers of the formula I.

3. A method as claimed in claim 1, wherein the copolymer contains as a further group of monomers (c) from 0 to 20% by weight of other monoethylenically unsaturated monomers copolymerizable with monomers (a) and (b) as copolymerized units.

4. A method as claimed in claim 1, wherein the copolymer contains (a) from 95 to 70% by weight of acrylic acid, meth-acrylic acid, maleic acid or mixture thereof and (b) from 5 to 30% by weight of N-vinylformamide as copolymerized units.

5. A method as claimed in claim 4, wherein the N-vinylformamide units present in the copolymer have been converted into vinylamine units to an extent of from 1 to 100%.

6. A method as claimed in claim 1, wherein the copolymer is used in an amount of from 0.1 to 100 ppm, based on the aqueous medium to be treated.