Note: Descriptions are shown in the official language in which they were submitted.
- Z03465S
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
~`; '
:
: ~ . ~ . : . .- . . ........................ .
:
2034655
- 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 monomers0 (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
R2
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.
:
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- 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
. ~ , . .
,. , - . : :
: . : .. .. .
: .... . . . - . . . .
. - - ,. - . . , - ~ ,
. . ..
X034655
- 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,
... . .
. . .' .. . ~ :
.
,. , , . ~ , . . . ~.
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- 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
, . .
' . . ,
- : ,
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~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
--CH 2--CH--
/N\ (II)
R2 CO-R1
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)
R2 H
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
- .
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:.:: . : . . - . . . - -
~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
.
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X034655
- 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
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~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
~.~
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,
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
.:
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. . ~
: - . .
2034655
- 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.
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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.
., .
.
: . . ~ :. -
: :.-:,. ... :
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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