Note: Descriptions are shown in the official language in which they were submitted.
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WO 97/39078 PCT/EP97/01690
The Use of Polymers Containing Aspartic Acid in Biocide-containing
Cooling Circuits
The present invention relates generally to the conditioning of cooling
waters for water-based cooling systems. Conditioning in the context of the
invention means above all reducing the corrosive effect of the water phase
and stabilizing it against the formation of deposits, the deposition of hardnesssalts and the formation of biological coatings. The invention is suitable both
for open and for closed cooling systems and relates equally to throughflow
cooling systems and to circulation-type cooling systems. It is designed in
particular for open circulation cooling systems. Since the cooling effect of
open circulation cooling systems is based on the evaporation of water, the
resulting concentration of water ingredients and the free access of air makes
them particularly susceptible to the formation of inorganic and organic
coatings or deposits.
Key components in the conditioning of cooling water include hardness
stabilizers, dispersants, corrosion inhibitors and biocides. Examples of
hardness stabilizers are inorganic polyphosphates, phosphonic acids,
aminomethylene phosphonic acids, phosphoric acid esters, phosphono-
carboxylic acids and polycarboxylic acids, for example of the partly saponified
polyacrylamide type or the acrylic acid and/or methacrylic acid polymer or
copolymer type. The polycarboxylic acids mentioned can also act as
dispersants, in other words they stabilize microdispersed solid particles
against ~edimentation and sludge formation. Apart from the partly hydrolyzed
polyacrylamides and the acrylic acid and/or methacrylic acid polymers or
copolymers mentioned, other suitable dispersants include polystyrene
sulfonates, polyvinyl sulfonates, quaternary ammonium compounds,
unsaponified polyacrylamides and polyalkylene glycols. Besides substances
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which have a toxic effect on microorganisms, the microbicides used also
include substances whose microbicidal effect is based on their oxidation
potential. Oxidative microbicides have the disadvantage that they lose their
effectiveness when they have oxidized other substances and have thus been
exhausted. However, this disadvantage, which can be offset by continuous
or periodic replenishment, is an advantage when the cooling water is
completely or partly drained from the cooling system. Since oxidative
microbicides are rapidly exhausted, they have generally become inactive by
the time the cooling containing them enters the environment. Examples of
oxidative microbicides are ozone, chlorine, bromine, chlorine dioxide,
hypochlorites, hypobromites or hydrogen peroxide.
The organophosphorus compounds or organic polymers used as
hardness stabilizers and/or as dispersants generally have the disadvantage
that they are not biologically degradable. This lack of degradability is an
advantage as long as these conditioning agents remain in the cooling circuit.
However, it becomes a disadvantage when the cooling medium is completely
or partly drained off and enters the environment with or without any waste-
water treatment. Accordingly, there is a need for hardness stabilizers and/or
dispersants which show adequate biological degradability so that they can be
rapidly biologically degraded at the latest when the cooling water to which
they are added is drained from the cooling system.
Biologically degradable polymers suitable for use in the conditioning
of water have recently been described. For example, WO 94/01476 relates
to graft copolymers of unsaturated monomers and sugars, to processes for
their production and to their use. The polymers described in this document
consist of graft copolymers of monosaccharides, disaccharides and
oligosaccharides, reaction products and derivatives thereof and a monomer
mixture obtainable by radical graft copolymerization of a monomer mixture of
1 ) 45 to 96% by weight of at least one monoethylenically unsaturated C3 10
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WO 97/39078 3 PCT/EP97/01690
monocarboxylic acid, 2) 4 to 55% by weight of at least one monoethylenically
unsaturated monomer containing sulfonic acid groups, a monoethylenically
unsaturated sulfuric acid ester and/or vinyl phosphonic acid, 3) 0 to 30% by
weight of at least one water-soluble monoethylenically unsaturated compound
modified with 2 to 50 moles of alkylene oxide per mole, 4) 0 to 45% by weight
of at least one other water-soluble, radical-polymerizable monomer, 5) 0 to
30% by weight of other water-insoluble or substantially water-insoluble
radical-polymerizable monomers, the sum of 1 ) to 5) being 100% by weight
and the acids being replaceable by their salts with monovalent cations, in the
presence of mono-, di- and oligosaccharides, reaction products and
derivatives thereof or mixtures thereof, the content of the saccharide
components in the mixture as a whole being from 5 to 60% by weight.
DE-A 43 00 772 also describes biologically degradable copolymers, a
process for their production and their use. These biologically degradable
copolymers are polymers of 1) 10 to 70% by weight of monoethylenically
unsaturated C48 dicarboxylic acids, 2) 20 to 85% by weight of monoethy-
lenically unsaturated C3 ,0 monocarboxylic acids, 3) 1 to 50% by weight of
monounsaturated monomers which, after hydrolysis or saponification, can be
converted into monomer units with one or more hydroxyl groups covalently
bonded to the C-C chain and 4) 0 to 10% by weight of other radical-copoly-
merizable monomers, the sum of 1 ) to 4) being 100% by weight and the acids
being replaceable by their salts with monovalent cations.
Biologically degradable polymers suitable for use in the conditioning
of water can also be found among naturally occurring polymers and
derivatives thereof selected from polysaccharides, polyglycosides, poly-
glucosides, oxidized cellulose, oxidized starch, oxidized dextrin, proteins.
In addition, polyaspartic acids and polymers containing aspartic acid
have been proposed as biologically degradable polymers which may be used
as dispersants or as scale inhibitors in the treatment of water. For example,
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WO 97/39078 4 PCT/EP97/01690
WO 94/19409 describes the production and use as dispersants of water-
soluble salts of beta-polyaspartic acid, i.e. a polyaspartic acid in which most
of the monomers are linked by beta-bonds. The average molecular weight is
in the range from about 1,000 to about 5,000. In addition, it is apparent from
WO 92/16462 that a polyaspartic acid obtained by hydrolysis of anhydro-
aspartic acid is eminently suitable for preventing calcium carbonate and
calcium phosphate scale. Other particulars of the synthesis of alpha- and
beta-polyaspartic acid can be found in US-A-5,057,597. According to this
document, the particulate monomeric amino acid is heated in a fluidized bed
to a temperature of at least 180~C and is kept at a temperature of 180 to
250~C until the required degree of polymerization to anhydroaspartic acid is
achieved with elimination of water. The anhydropolyaspartic acid is then
hydrolyzed, preferably under alkaline conditions. An alternative method of
production is described in WO 93/23452, according to which maleic acid is
reacted with excess ammonia at temperatures of 200 to 300~C to form
polyaspartic acid. The acid can be converted into its salts by reaction with a
base.
WO 94/01486 describes modified polyaspartic acids, which may be
used for example as water treatment agents, and processes for their
production. These modified polyaspartic acids are obtained by polycon-
densation of 1 to 99.9 mole-% of aspartic acid with 99 to 0.1 mole-% of fatty
acids, polybasic carboxylic acids, monobasic polyhydroxycarboxylic acids,
alcohols, amines, alkoxylated alcohols and amines, amino sugars, carbo-
hydrates, sugar carboxylic acids and/or non-proteinogenic aminocarboxylic
acids. The modified polyaspartic acids may also be prepared by radical-
initiated graft copolymerization of monoethylenically unsaturated monomers
in the presence of polyaspartic acids. In addition, WO 94/20563 describes a
process for the production of reaction products of polyaspartic acid imides
and amino acids and reaction products of polyaspartic acid imides with
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WO 97/39078 5 PCT/EP97/01690
alkanolamines or aminated fatty alcohol ethoxylates. Reaction products such
as these are also suitable as scale inhibitors and as dispersants.
Other polymers and copolymers of aspartic acid, optionally in
conjunction with other amino acids, are described for example in WO
92/17194, WO 94/03527, WO 94/21710 and DE-A-43 08 426. WO 94/19288
describes the use of polyaspartic acid and a large number of other products
for preventing deposits in a building drainage system, for example in tunnels,
galleries, concrete dams, dikes and the like. According to the teaching of EP-
A-672 625, improved formulations for treating water are obtained by using
polyaspartic acid or a derivative thereof in conjunction with a phosphonic acid.The ratio by weight of polyaspartic acid or derivative to phosphonic acid is
preferably in the range from 90:10 to 10:90. The preferred polyaspartic acid
is beta-polyaspartic acid with a molecular weight of 1,000 to 10,000.
Although the use of biologically degradable polymers, such as for
example polyaspartic acid or other polymers containing polyaspartic acid, for
the treatment of water is generally known from the literature cited above, the
use of these biodegradable polymers at least in open cooling systems is
problematical. The polymers can be expected to undergo rapid degradation
in the cooling circuit itself, so that their effect is soon lost and their use is
uneconomical. The problem addressed by the present invention was to
stabilize these polymers against biological degradation in the cooling system
without in any way impeding their degradation after leaving the cooling
system. The prior-art literature does not contain any reference to the fact thatproducts of the type in question can be used together with biocidal oxidizing
agents in cooling circuits. A potential application such as this appears
doubfful because the oxidizing agents can be expected to react with and
deactivate the polymers. By contrast, the present invention addressed the
further problem of providing a combination of biodegradable polymers and
biocidal oxidizing agents which could be used for conditioning water in cooling
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WO 97/39078 6 PCT/EP97/01690
circuits and which would remain active for a suffficiently long period under in-use conditions.
The problems stated above have been solved by the use of biologically
degradable organic polymers with an average molecular weight above 500 in
water-based cooling systems, characterized in that the water phase of the
cooling systems additionally contains 0.05 to 5 mg/l of an oxidizing agent with
a more positive standard redox potential than oxygen.
Standard redox potentials, also known as normal potentials, are
generally known thermodynamic terms which are described in manuals of
general or physical chemistry, cf. for example Chapter 11 of the manual: H.R.
Christen "Grundlagen der allgemeinen und anorganischen Chemie",
Verlag Sauerlader-Salle, 1973. On pages 692 to 697, this manual contains
a list of different normal potentials which can also be found in many other
manuals and tabular works. The value of the standard redox potential is
normally expressed in volts.
Oxidizing agents which a standard redox potential of > 0.4 volt are
preferably used for the purposes of the present invention. This oxidizing
agent is preferably selected from hydrogen peroxide, chlorine, bromine,
chlorine dioxide, hypochlorites, hypobromites and ozone. Since these
chemicals are capable of entering into acid-base and/or disproportionation
reactions with water, the oxidizing agents mentioned above also include their
reaction products with water.
Biological degradability can be measured by various methods. For
example, it can be evaluated by the modified STURM Test (OECD Guideline
No. 301 B) in which the quantity of carbon dioxide formed during degradation
is measured. Alternatively, a modified MITI Test (OECD Guideline 301 for
testing chemicals), in which the amount of oxygen consumed during
degradation is measured, can be used. In the context of the present
invention, polymers are regarded as biologically degradable if more than 50%
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WO 97/39078 7 PCT/EP97/01690
degradation is observed after a test period of 28 days.
The biologically degradable polymers suitable for the purposes of the
invention may be selected, for example, from
a) graft copolymers of monosaccharides, disaccharides and oligosaccha-
rides, reaction products and derivatives thereof and a monomer mixture
obtainable by radical graft copolymerization of a monomer mixture of 1 ) 45 to
96% by weight of at least one monoethylenically unsaturated C3 ,0 monocar-
boxylic acid, 2) 4 to 55% by weight of at least one monoethylenically
unsaturated monomer containing sulfonic acid groups, a monoethylenically
unsaturated sulfuric acid ester and/or vinyl phosphonic acid, 3) 0 to 30% by
weight of at least one water-soluble, monoethylenically unsaturated
compound modified with 2 to 50 moles of alkylene oxide per mole, 4) 0 to
45% by weight of at least one other water-soluble, radical-polymerizable
monomer, 5) 0 to 30% by weight of other water-soluble or substantially water-
insoluble radical-polymerizable monomers, the sum of 1 ) to 5) being 100% by
weight and the acids being replaceable by their salts with monovalent cations,
in the presence of mono-, di- and oligosaccharides, reaction products and
derivatives or mixtures thereof, the content of the saccharide components in
the mixture as a whole being 5 to 60% by weight,
b) polymers of 1 ) 10 to 70% by weight of monoethylenically unsaturated C4 8
dicarboxylic acids, 2) 20 to 85% by weight of monoethylenically unsaturated
C310 monocarboxylic acids, 3) 1 to 50% by weight of monounsaturated
monomers which, after hydrolysis or saponification, can be converted into
monomer units with one or more hydroxyl groups covalently bonded to the C-
C chain and 4) 0 to 10% by weight of other radical-copolymerizable
monomers, the sum of 1 ) to 4) being 100% by weight and the acids being
replaceable by their salts with monovalent cations,
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WO 97/39078 8 PCT/EP97/01690
c) naturally occurring polymers and derivatives thereof selected from
polysaccharides, polyglycosides, polyglucosides, oxidized cellulose, oxidized
starch, oxidized dextrin, proteins,
d) organic polymers of which at least 80 mole-% consist of aspartic acid.
The graft copolymers of group a) are described in more detail in WO
94/01476 which is hereby specifically made part of the present disclosure.
According to this document, the following are preferably used: as monomers
1), acrylic acid and/or methacrylic acid, alkali metal, ammonium and/or amine
salts thereof; as group 2) monomers, allyl sulfonic acid, methallyl sulfonic
acid, acrylamidomethyl propane sulfonic acid, vinyl sulfonic acid, sulfatoethyl
(meth)acrylate, vinyl phosphonic acid and/or salts of these acids with
monomeric cations; as components 3), allyl alcohol or the esters of unsatu-
rated carboxylic acids, such as acrylic acid or methacrylic acid, of which the
alcohol component is modified with alkylene oxide; as component 4),
molecular weight-increasing monomers and monomers containing mono-
ethylenically polyunsaturated double bonds or an ethylenically unsaturated
double bond and another functional crosslinking group. The polymerization
is carried out as described in detail in the above-cited reference WO
94/01 476.
The group b) polymers suitable for use for the purposes of the
invention are described in detail in DE-A 43 00 772 which is hereby
specifically made part of the present disclosure. The components of these
polymers are preferably selected from 1) maleic acid, itaconic acid and
fumaric acid or salts thereof, 2) acrylic or methacrylic acid or salts thereof and
3) vinyl acetate, vinyl propionate and/or methyl vinyl ether.
Pure polyaspartic acids or copolymers containing aspartic acid, as
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described for example in the literature cited at the beginning, are preferably
used as organic polymers. In a preferred embodiment, at least 95 mole-%,
preferably at least 98 mole-% and more preferably 100 mole-% of the organic
polymers consist of aspartic acid. The average molecular weight, which may
be determined for example by gel permeation chromatography in accordance
with the above-cited WO 94/19409, is preferably in the range from about
1,000 to about 5,000. Preferably at least 50% and, more particularly, at least
70% of the polyaspartic acid or the polyaspartic acid component of the
organic polymer is present in the so-called beta-form. The difference between
the alpha-linkage and the beta-linkage is illustrated by formulae in the above-
cited US-A-5,057,597. The distinction is based on whether the chemical bond
to the adjacent monomer is in the alpha-position or the beta-position to the
amide functions formed by the polycodensation.
The concentration of the organic polymers in the water phase of the
water-based cooling systems is preferably adjusted to be in the range from
about 1 to about 50 mg/l and more particularly in the range from about 5 to
about 20 mg/l. The optimal concentration depends on the purity of the cooling
water used. Accordingly, the expert will adapt the quantity used to the
particular water quality by experimentation.
It is normal and preferred for the purposes of the invention for the
water phase of the water-based cooling systems to contain other components
which may have a corrosion-inhibiting or scale-inhibiting or dispersing effect.
Examples of such other components are zinc ions (1 to 10 mg/l), monomeric
or oligomeric molybdate ions (1 to 200 mg/l), organic phosphates in such a
concentration that the phosphorus content, expressed as phosphate, is
between 1 and 20 mg/l phosphate, monomeric, oligomeric or polymeric
inorganic phosphates in such a concentration that the phosphorus content,
expressed as phosphate, is between 1 and 20 mg/l phosphate and non-
ferrous metal inhibitors, for example triazoles. The water phase may contain
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known substances as further corrosion inhibitors, for example alkanolamines,
more particularly triethanolamine, borates, sulfites, sorbitol, ascorbic acid,
hydroquinone, hydroxyl amines, such as in particular N,N-diethyl hydroxyl-
amine, nitrites, nitrates and silicates. Other corrosion-inhibiting and/or
dispersing additives which may be used include phosphate esters, poly-
phosphoric acid esters, aminophosphates, aminomethylene phosphoric acids,
N-containing phosphates, more particularly aminoalkylene phosphonic acids,
phosphonocarboxylic acids, succinic acid amide, gluconates, polyoxycarboxy-
lic acids and copolymers thereof, tannin derivatives, lignin sulfonates,
sulfonated condensation products of naphthalene with formaldehyde,
polyacrylates, polymethacrylates, polyacrylamides, copolymers of acrylic or
methacrylic acid and acrylamide, phosphinic acid-containing homopolymers
and copolymers of acrylic acid and acrylamide, oligomeric phosphinosuccinic
acid compounds, sulfomethylated or sulfoethylated polyacrylamides and
copolymers or terpolymers with acrylic acid and maleic acid ester, N-butyl
acrylamide and copolymers thereof, acrylamidopropionosulfonic acid and
copolymers thereof, maleic anhydride polymers and copolymers, phosphino-
alkylated acrylamide polymers and copolymers with acrylic acid, citric acid,
ether carboxylates or oxidized carbohydrates.
In order to obtain optimal protection against corrosion, the water phase
of the water-based cooling systems is preferably adjusted to a pH value in the
range from about 7 to about 9. The biocidal oxidizing agent may be added
to the cooling system either continuously or, preferably, discontinuously by
batch treatment.
As mentioned at the beginning, the water-based cooling systems may
be throughflow systems or open or closed circulation systems. The invention
is designed in particular for use in open circulation systems because it is
particularly suitable for counteracting the problems of scaling, deposit
formation and/or biological contamination occurring in such systems.
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WO 97/39078 11 PCT/EP97/01690
To determine the stability of polyaspartic acid in the presence of
various known biocidal oxidizing agents, the scale-inhibiting effect of
polyaspartic acid was tested as a function of time in the presence of the
oxidizing agent. The polyaspartic acid selected was the product Donlar GS
12-30 available from Donlar Corporation, 6502 S. Archer Ave., Bedford Park,
IL 60501-9998, USA. The polymer has a molecular weight, as determined by
gel permeation chromatography, of about 3,000 and a ratio of alpha- to beta-
linkages of about 30:70. The polymer was used in a quantity of 10 mg/l in
water adjusted to pH 8.5 with dilute sodium hydroxide or dilute sulfuric acid.
To this end, the oxidizing agent was added in a quantity of 0.4 mg/l, the
oxidizing agents used in separate tests being a) sodium hypochlorite, b)
chlorine dioxide, c) hydrogen peroxide, d) a mixture of sodium hypochlorite
and sodium hypobromite in a ratio by weight of 1 :1.
The scale-inhibiting effect of the polyaspartic acid/oxidizing agent
mixture was assessed immediately after addition of the oxidizing agent and
then every 30 minutes up to a total test duration of 4 hours. The effectiveness
test was carried out as follows. A test water containing 5.4 mmole/l calcium
ions and 1.8 mmole/l magnesium ions was prepared. First the polyaspartic
acid/oxidizing agent mixture and then 20 mmole/l sodium hydrogen carbonate
were added to the test water. Using a flow inducer, the test solution was
pumped at a rate of 0.5 I/h through the glass coil of a glass condenser in the
outer space of which circulated water heated to a temperature of 80~C. After
a test period of 2 hours, the glass condenser was emptied and the hardness
deposit formed was removed with hydrochloric acid. The content of hardness
ions in the hydrochloric acid solution was determined by titrimetry. The scale-
inhibiting effect of the test mixture is better, the smaller the number of
hardness ions present in the hydrochloric acid solution. The beginning of the
two-hour test was taken as the test time.
The tests showed that, where sodium hypochlorite, chlorine dioxide or
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hydrogen peroxide was used, there was no measurable deterioration in the
scale-inhibiting effect over the four hour test period. Where mixture d) was
used, around 95% of the initial effectiveness was still present after four hours.
The chlorine stability of another two biodegradable polymers was
similarly tested: an anionically modified graft copolymer (product W 70280
according to DE-A 42 21 381, supplier: Stockhausen, Germany) and an
acrylic acid/maleic acid/vinyl alcohol terpolymer (product W 71409 according
to DE-A-43 00 772, supplier: Stockhausen, Germany). The first polymer was
dissolved in water in a concentration of 5 ppm and the second in a concen-
tration of 15 ppm and the pH was adjusted to a value of 8.5. The solutions
were then divided. Chlorine was added to half of each divided solution in a
quantity of 0.4 mg/l. After four hours, the scale-inhibiting effect of these
solutions was tested by the method described above. No difference was
found between the scale-inhibiting effects of the chlorine-containing solution
and the chlorine-free solution. Accordingly, the polymers are stable to
chlorine.
The degradation behavior of polyaspartic acid with and without an
added oxidizing agent (sodium hypochlorite) was studied for one month in a
cooling tower. Between 20 and 50 mg/l of polyaspartic acid were added daily
and the actual polyaspartic acid content of the cooling circuit was determined
before each addition. This was done by precipitating the polyaspartic acid
from a sodium citrate-buffered solution with a cationic surfactant (Hyamin
1622, Rohm & Hass). This resulted in clouding which was photometrically
determined and compared with a calibration curve.
During the first two test weeks, the quantities of polyaspartic acid
actually found decreased continuously despite replenishment and were in the
range from about 11 to about 2 mg/l. After two weeks with daily additions of
30 to 40 mg/l polyaspartic acid, 0.2 mg/l chlorine in the form of sodium
hypochlorite was additionally introduced. The content of measurable
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polyaspartic acid in the cooling circuit increased in two days to around 20 mg/land remained at that level for the remainder of the test. Accordingly, the
degradation of the polyaspartic acid in the cooling circuit was distinctly
reduced by the additional introduction of sodium hypochlorite.
