Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Polymer mixtures as deposit inhibitors in water-bearing systems
Description
The invention relates to polymer mixtures as deposit inhibitors for inhibiting
the
precipitation and sedimentation of calcium salts and magnesium salts in water-
bearing
systems.
The solubility of most substances in water is restricted. In particular, in
industrial water
treatment, the prevention of mineral sediments in water-bearing systems is an
essential
task. Inorganic substances and salts such as calcium carbonate, magnesium
carbonate,
magnesium hydroxide, calcium sulfate and barium sulfate, and calcium phosphate
have a
low solubility in water. If these dissolved components are concentrated in
aqueous
systems (thickening), the solubility product is exceeded with the consequence
that these
substances precipitate out and cause sediments. The solubility of the
substances is, in
addition, dependent on the temperature and the pH. In particular, many
substances such
as calcium carbonate, calcium sulfate or magnesium hydroxide exhibit an
inverse
solubility, i.e. their solubility decreases with increasing temperature. This
leads to high
process temperatures frequently being the cause of unwanted precipitates and
formation
of deposits in cooling and boiler feed water systems on heat-exchange surfaces
or in
pipelines.
Precipitates and sediments of inorganic substances and salts in water-bearing
systems
may only be removed again with great effort. Each mechanical and chemical
cleaning is
costly and time-consuming and inescapably leads to production failures.
Not only in cooling and boiler feed water systems are attempts made to prevent
the
formation of calcium carbonate deposits, calcium sulfate deposits, magnesium
hydroxide
deposits and other salt deposits. Also in seawater desalination by
distillation and by
membrane methods such as reverse osmosis or electrodialysis, efforts are made
to
prevent formation of these solid deposits. In particular in thermal seawater
desalination
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plants, both effects, namely firstly concentration by evaporation of water,
and, secondly,
high processing temperatures, play an important role.
The productivity of desalination plants is limited in this case by the upper
processing
temperature. It is desirable to operate seawater desalination plants at an
evaporation
temperature as high as possible in order to achieve a process efficiency as
high as
possible and to minimize the energy required for producing fresh water. For
characterization of the process efficiency, the characteristic kWh/m3 of water
is used. This
characteristic can be minimized by process temperatures as high as possible
for the
multistage expansion evaporation process and the multiple effect evaporation
process.
The maximum process temperature in these processes is limited, primarily, by
the deposit
formation which increases continuously with increasing temperature. It is
known that, in
particular, the sedimentation of basic magnesium salts such as magnesium
hydroxide
(brucite) and magnesium carbonate hydroxide (hydromagnesite), and also calcium
carbonate and calcium sulfate play a critical role in thermal desalination
plants.
It is known that low-molecular-weight polyacrylic acids and salts thereof
produced by
means of free-radical polymerization are employed as deposit inhibitors in
industrial water
treatment and in seawater desalination owing to the dispersant properties, and
properties
inhibiting crystal growth, thereof. For a good activity, the mean molecular
weight (Mw) of
these polymers should be <50 000 g/mol. Frequently, polyacrylic acids having
Mw
<10 000 g/mol are described as particularly effective. A disadvantage of these
polymers is
their sensitivity to hardness rising with increasing temperature, i.e. the
risk that the
polymers precipitate as Ca or Mg polyacrylates increases. In addition, the
polyacrylic acids
have only a very low inhibitory activity against sediments of brucite or
hydromagnesite.
In addition, it is known that copolymers comprising sulfonic acid groups act
as deposit
inhibitors, in particular for avoiding deposits of calcium phosphates and
calcium
phosphonates. A disadvantage of these polymers is their limited activity for
avoiding
CaCO3 precipitates.
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In order to compensate for the disadvantages of certain polymers, frequently
mixtures of a
plurality of different polymers or copolymers are used. In the case of polymer
mixtures, a
synergistic activity is observed from time to time.
EP 388 836 discloses a mixture of a hydrolyzed polymaleic anhydride and a
hydrolyzed
copolymer of maleic anhydride and ethylenically unsaturated copolymers having
a
molecular weight from 400 to 800 g/mol for inhibiting scale sediments in
aqueous systems.
.Ethylenically unsaturated comonomers mentioned are acrylic acid, methacrylic
acid,
crotonic acid, itaconic acid, aconitic acid, itaconic anhydride, ethyl
acrylate, methyl
methacrylate, acrylonitrile, acrylamide, vinyl acetate, styrene, alpha-
methylstyrene,
vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methyl vinyl
ketone,
acrolein, ethylene and propylene.
US 2009/0101587 Al discloses a deposit-inhibiting composition comprising a
copolymer of
acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid and an oligomeric
phosphinosuccinic acid.
US 5263541 discloses a mixture of polyvinyl sulfonate and polyacrylic acid as
calcium
sulfate deposit inhibitor.
DE 41 07 322 describes a composition of a hydrolyzed homopolymer of maleic
anhydride
having a weight-average molecular weight of 400 to 800 and a carboxyl-
comprising acrylic
polymer having a molecular weight of 800 to 9500 as deposit inhibitor. Acrylic
polymers
mentioned are polyacrylic acid and polymethacrylic acid, and also copolymers
of acrylic
acid or methacrylic acid with a vinyl carboxylate or styrene.
US 4,936,987 describes a mixture of a copolymer of acrylic acid or methacrylic
acid and
2-acrylamido-2-methylpropylsulfonic acid or 2-methacrylamido-2-
methylpropylsulfonic acid
and at least one further component. Further components mentioned are, inter
alia,
homopolymers of maleic acid or acrylic acid, and also copolymers of acrylamide
and
acrylate, copolymers of acrylic acid and 2-hydroxypropyl acrylate, or
copolymers of maleic
acid and sulfonated styrene.
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JP 06154789 describes a composition of hydrolyzed copolymer of maleic
anhydride and
isobutene and hydrolyzed copolymer of maleic anhydride and aliphatic diene as
deposit
inhibitor. The inhibitor acts primarily against silicate and calcium carbonate
deposits.
It is an object of the invention to provide compositions having an improved
deposit-
inhibiting activity which effectively prevent, in particular, precipitation
and deposition of
calcium carbonate, calcium sulfate and basic magnesium salts in the water-
bearing
systems.
The object is achieved by a polymer mixture in solid or aqueous form
comprising, based
on the polymer fraction,
(A) 5 to 95% by weight of a water-soluble or water-dispersible polymer
having a
weight-average molecular weight of 1000 to 20 000 g/mol of
(al) 20 to 80% by weight of at least one monomer selected from the group
consisting of C2 to 08 olefins, ally' alcohol, isoprenol, C1 to C4 alkyl vinyl
ethers and
vinyl esters of Ci to 04 monocarboxylic acids,
(a2) 20 to 80%
by weight of at least one monoethylenically unsaturated 03 to
08 carboxylic acid, an anhydride or salt of same,
(a3)
0 to 50% by weight of one or more monomers comprising sulfonic acid
groups,
(B) 5 to 95% by weight of a water-soluble or water-dispersible polymer
having a
weight-average molecular weight of 1000 to 50 000 g/mol of
(bl)
30 to 100% by weight of at least one monoethylenically unsaturated 03 to
C8 carboxylic acid, an anhydride or salt of same,
(b2) 0 to 70% by weight of one or more monomers comprising sulfonic acid
groups,
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(b3) 0 to 70% by weight of one or more nonionic monomers of the
formula (I)
H2C=C(R1)(CH2),(0[R2-0}0-R3 (I),
5
where R1 is hydrogen or methyl, R2 is identical or different, linear or
branched, Cr
C8 alkylene radicals, which can be arranged in blocks or randomly, and R3 is
hydrogen or a straight-chain or branched C1-C4 alkyl radical, x is 0, 1 or 2,
and o is
a number from 3 to 50.
It has been found that mixtures of the polymers (A) and (B) have a higher
activity in the
inhibition of sediments of calcium carbonate, calcium sulfate and basic
magnesium salts
than the same amount of only one of the polymers (A) or (B) alone. One or more
different
polymers (A) can be mixed with one or more different polymers (B).
The polymer mixture according to the invention comprises 5 to 95% by weight of
a water-
soluble or water-dispersible polymer (A) of 20 to 80% by weight of at least
one monomer
(al) selected from the group consisting of C2 to C8 olefins, allyl alcohol,
isoprenol, C1 to C4
alkyl vinyl ethers and vinyl esters of C1 to C4 monocarboxylic acids, and 20
to 80% by
weight of at least one monomer (a2) selected from unsaturated C3 to C8
carboxylic acids,
anhydrides or salts of same, and also, optionally, 0 to 50% by weight of one
or more
monomers (a3) comprising sulfonic acid groups.
The polymer mixture comprises 5 to 95% by weight of a water-soluble or water-
dispersible
polymer (B) of 30 to 100% by weight of at least one monomer (bl) selected from
monoethylenically unsaturated C3 to C8 carboxylic acids, anhydrides or salts
of same, and
also, optionally, 0 to 70% by weight of one or more monomers (b2) comprising
sulfonic
acid groups.
Suitable C2 to C8 olefins which can be used as monomer (al) are, for example,
ethylene,
propylene, n-butene, isobutene, 1-pentene, 1-hexene, 1-heptene and
diisobutene,
preferably isobutene and diisobutene.
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Suitable alkyl vinyl ethers which can be used as monomer (al) comprise 1 to 4
carbon
atoms in the alkyl chain. Examples are vinyl methyl ether, vinyl ethyl ether,
vinyl n-propyl
ether, vinyl isopropyl ether, vinyl n-butyl ether and vinyl isobutyl ether.
Vinyl esters of C1 to C4 monocarboxylic acids which can be used as monomer
(al) are, for
example, vinyl formate, vinyl acetate, vinyl propionate and vinyl butyrate.
Preferred monomers (al) are isobutene, diisobutene, vinyl acetate, vinyl
methyl ether allyl
alcohol and isoprenol. Particular preference is given to isobutene,
diisobutene and
isoprenol.
Suitable monoethylenically unsaturated C3-C8 carboxylic acids which can be
used as
monomer (a2) and (bl) are, for example, acrylic acid, methacrylic acid,
ethacrylic acid,
vinyl acetic acid, allyl acetic acid, crotonic acid, maleic acid, fumaric
acid, mesaconic acid
and itaconic acid and also water-soluble salts thereof. If said unsaturated C3-
C8 carboxylic
acids can form anhydrides, these anhydrides are also suitable as monomer (al),
for
example maleic anhydride, itaconic anhydride and methacrylic anhydride.
Preferred monoethylenically unsaturated C3-C8 carboxylic acids are acrylic
acid,
methacrylic acid, maleic acid and fumaric acid and also anhydrides and water-
soluble salts
thereof. These are preferred both as monomer (a2) and monomer (bl). Water-
soluble
salts are, in particular, the sodium and potassium salts of the acids.
Monomers comprising sulfonic acid groups (a3) and (b2) are preferably those of
the
formulae (11a) and (11b)
H2C=CH-X-S03H (11a),
H2C=C(CH3)-X-S03H (11b),
where X is an optionally present spacer group which can be selected from -
(CH2),- where
n =0 to 4, -C8I-14-, -CH2-0-C6H4-, -C(0)-NH-C(CH3)2-, -C(0)-NH-CH(CH2CH3)-, -
C(0)NH-
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CH(CH3)CH2-, -C(0)NH-C(CH3)2CH2-, -C(0)NH-CH2CH(OH)CH2-, -C(0)NH-CH2-, -
C(0)NH-CH2CH2- and -C(0)NH-CH2CH2CF12-=
Particularly preferred monomers comprising sulfonic acid groups are in this
case
1-acrylamido-1-propanesulfonic acid (X = -C(0)NH-CH(CH2CH3)- in formula 11a),
2-acrylamido-2-propanesulfonic acid (X = -C(0)NH-CH(CH3)CH2- in formula 11a),
2-acrylamido-2-methylpropanesulfonic acid (AMPS, X = -C(0)NH-C(CH3)2CH2- in
formula
11a), 2-methacrylamido-2-methylpropanesulfonic acid (X = -C(0)NH-C(CH3)2CH2-
in
formula 11b), 3-methacrylamido-2-hydroxypropanesulfonic acid (X = -C(0)NH-
CH2CH(OH)CH2- in formula 11b), allylsulfonic acid (X = CH2 in formula Ha),
methallylsulfonic acid (X = CH2 in formula 11b), allyloxybenzenesulfonic acid
(X = -CH2-0-
C6H4- in formula 11a), methallyloxybenzenesulfonic acid (X = -CH2-0-C6H4- in
formula 11b),
2-hydroxy-3-(2-propenyloxy)propanesulfonic acid, 2-methy1-2-propene-1-sulfonic
acid (X =
CH2 in formula 11b), styrenesulfonic acid (X = C6H4 in formula 11a),
vinylsulfonic acid (X not
present in formula 11a), 3-sulfopropyl acrylate (X = -C(0)0-CH2CH2CH2- in
formula Ha), 2-
sulfoethyl methacrylate (X = -C(0)0-CH2CH2- in formula 11b), 3-sulfopropyl
methacrylate
(X = -C(0)0-CH2CH2CH2- in formula 11b), sulfomethacrylamide (X = -C(0)NH- in
formula
11b), sulfomethylmethacrylamide (X = -C(0)NH-CH2- in formula 11b), and also
salts of said
acids. Suitable salts are generally water-soluble salts, preferably the
sodium, potassium
and ammonium salts of said acids.
Particular preference is given to 1-acrylamidopropanesulfonic acid, 2-
acrylamido-
2-propanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic
acid (AMPS),
2-methacrylamido-2-methylpropanesulfonic acid, 3-methacrylamido-2-
hydroxypropane-
sulfonic acid, 2-hydroxy-3-(2-propenyloxy)propanesulfonic acid, 2-sulfoethyl
methacrylate,
styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid (ALS) and
methallylsulfonic acid,
and also salts of said acids. These are preferred both as monomer (a3) and
also (b2).
Very particularly preferred monomers comprising sulfonic acid groups are 2-
acrylamido-2-
methylpropanesulfonic acid (AMPS) and allylsulfonic acid, and also water-
soluble salts
thereof, in particular sodium, potassium and ammonium salts thereof. These are
preferred
both as monomer (a3) and (b2).
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As component (b3), the copolymer comprises 0 to 70% by weight of at least one
nonionic
monomer of the formula (I)
H2C=C(R1)(CH2),(0[R2-0]0-R3 (I).
where R' is hydrogen or methyl, R2 is identical or different C2-C6 alkylene
radicals, which
can be linear or branched and arranged in blocks and/or randomly, and R3 is
hydrogen or
a straight-chain or branched C1-C4 alkyl radical, x is 0, 1 or 2, and o is a
natural number
from 3 to 50.
The alkylene radicals can also be arranged in blocks and randomly, that is to
say in one or
more blocks of identical alkylene oxide radicals in blocks and, in addition,
randomly in one
or more blocks of two or more different alkylene oxide radicals. This is also
included by the
wording "arranged in blocks or randomly".
Preferred nonionic monomers (b3) are those based on ally' alcohol (R1 = H; x =
1) and
isoprenol (R1 = methyl; x = 2).
The nonionic monomer (b3) preferably comprises on average 8 to 40,
particularly
preferably 10 to 30, especially 10 to 25, alkylene oxide units. The index o in
the formula (I)
relates to the median number of alkylene oxide units.
Preferred alkylene oxide units R2-0 are ethylene oxide, 1,2-propylene oxide
and
1,2-butylene oxide, particular preference is given to ethylene oxide and 1,2-
propylene
oxide.
In a special embodiment, the nonionic monomers (b3) only comprise ethylene
oxide units.
In a further special embodiment, the nonionic monomers (b3) comprise ethylene
oxide and
1,2-propylene oxide units which can be arranged in blocks or randomly.
Preferably, R3 is hydrogen or methyl.
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Generally, the weight-average molecular weight of the copolymers (A) is 1000
to
20 000 g/mol, preferably 1500 to 15 000 g/mol, and particularly preferably
2000 to
000 g/mol, and in particular 2000 to 8000 g/mol.
5 The molecular weight is determined by means of gel-permeation chromatography
in
comparison with polyacrylic acid standards.
Generally, the polydispersity index of the polymers (A) Mw/Mr, is 5 3.0,
preferably 5 2.5.
10 The polymers (A) are preferably binary copolymers or terpolymers. If
they are binary
copolymers, they preferably comprise 20 to 60% by weight of monomer (al) and
40 to
80% by weight of monomer (a2), particularly preferably 25 to 50% by weight of
monomer
(al) and 50 to 75% by weight of monomer (a2).
If they are terpolymers, they preferably comprise 25 to 50% by weight of
monomer (al), 30
to 60% by weight of monomer (a2) and 10 to 30% by weight of monomer (a3).
A plurality of different monomers (al) and/or a plurality of different
monomers (a2) can
also be present in the polymers A. For example, terpolymers and quaterpolymers
can
comprise only monomers (al) and (a2), preferably in the amounts stated above
for binary
copolymers.
In a preferred embodiment of the invention, polymer (A) is a copolymer of
isobutene and
maleic acid, preferably in the quantitative ratios stated above for binary
copolymers.
In a further preferred embodiment of the invention, polymer (A) is a copolymer
of isoprenol
and maleic acid, preferably in the quantitative ratios cited above for binary
copolymers.
In a further embodiment of the invention, polymer (A) is a terpolymer of
isoprenol, maleic
acid and 2-acrylamido-2-methylpropanesulfonic acid, preferably in the
quantitative ratios
cited above for terpolymers. In a further preferred embodiment, allylsulfonic
acid is used
instead of 2-acrylamido-2-methylpropanesulfonic acid.
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In a further embodiment of the invention, polymer (A) is a terpolymer of
isoprenol, maleic
acid and acrylic acid, preferably in the quantitative ratios cited above.
The polymers (B) are homopolymers or copolymers. Copolymers can comprise
monomers
5 (b1), monomers (b1) and (b2), monomers (b1) and (b3), and monomers (b1),
(b2) and
(b3). If copolymers of the monomers (b1) and (b2) are concerned, they
preferably
comprise 50 to 90% by weight of monomers (b1) and 10 to 50% by weight of
monomers
(b2), particularly preferably 60 to 85% by weight of monomers (b1) and 15 to
40% by
weight of monomers (b2).
If copolymers of the monomers (b1) and (b3) are concerned, they preferably
comprise 50
to 95% by weight of monomers (b1) and 5 to 50% by weight of monomers (b3),
particularly
preferably 60 to 90% by weight of monomers (b1) and 10 to 40% by weight of
monomers
(b3).
If copolymers of the monomers (b1), (b2) and (b3) are concerned, they
preferably
comprise 30 to 80% by weight of monomers (b1), 10 to 50% by weight of monomers
(b2)
and 5 to 50% by weight of monomers (b3), particularly preferably 40 to 75% by
weight of
monomers (b1), 15 to 40% by weight of monomers (b2) and 5 to 40% by weight of
monomers (b3). Preference is given to binary copolymers, but they can also be
terpolymers.
In a preferred embodiment of the invention, the polymer (B) is an acrylic acid
homopolymer.
In a further preferred embodiment of the invention, polymer (B) is a copolymer
of acrylic
acid and 2-acrylamido-2-methylpropanesulfonic acid, preferably in the
quantitative ratios
cited above.
In a further preferred embodiment of the invention, polymer (B) is a copolymer
of acrylic
acid and allylsulfonic acid, preferably in the quantitative ratios cited
above.
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Generally, the weight-average molecular weight of the polymers (B) is 1000 to
50 000 g/mol, preferably 1000 to 30 000 g/mol and particularly preferably 1500
to 20 000
g/mol, and in particular 1500 to 10 000 g/mol.
The molecular weight is determined by means of gel-permeation chromatography
in
comparison with polyacrylic acid standards.
Generally, the polydispersity index of the polymers (B) Mw/Mn is 5 2.5,
preferably 5 2Ø
The present invention also relates to compositions comprising
(A) 3 to 95% by weight of the water-soluble or water-dispersible
polymers having a
weight-average molecular weight of 1000 to 20 000 g/mol of
(al) 20 to 80% by weight of at least one monomer selected from the group
consisting of 02 to 08 olefins, allyl alcohol, isoprenol, C1 to C4 alkyl vinyl
ethers and
vinyl esters of C1 to C4 monocarboxylic acids,
(a2) 20 to 80% by weight of at least one monoethylenically unsaturated C3 to
C8
carboxylic acid, an anhydride or salt of same,
(a3) 0 to 50% by weight of one or more monomers comprising sulfonic acid
groups,
(B) 3 to 95% by weight of the water-soluble or water-dispersible
polymer having a
weight-average molecular weight of 1000 g/mol to 50 000 g/mol of
(bl) 30 to 100% by weight of at least one monoethylenically
unsaturated C3 to
08 carboxylic acid, an anhydride or salt of same,
(b2) 0 to 70% by weight of one or more monomers comprising sulfonic acid
groups,
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(b3) 0 to 70% by weight of one or more nonionic monomers of the
formula (I)
H2C=C(R1)(CH2),(0[R2-0]0-R3 (I),
where R1 is hydrogen or methyl, R2 is identical or different, linear or
branched, Cr
06 alkylene radicals, which can be arranged in blocks or randomly, and R3 is
hydrogen or a straight-chain or branched C1-C4 alkyl radical, x is 0, 1 or 2,
and o is
a number from 3 to 50,
(C) 0 to 80% by weight of phosphonates,
(D) 0 to 90% by weight of water;
(E) 0 to 50% by weight of additives such as polyphosphates, zinc salts,
molybdate
salts, organic corrosion inhibitors, biocides, complexing agents, surfactants
or
antifoams.
The weight ratio of polymers (A):(B) is generally from 1:20 to 20:1.
The compositions according to the invention can optionally comprise up to 80%
by weight
phosphonates (C). Phosphonates can additionally support the deposit-inhibiting
activity of
the polymers. In addition, they act as corrosion inhibitors.
Examples of phosphonates are 1-hydroxyethane-1,1-diphosphonic acid (HEDP), 2-
phos-
phonobutane-1,2,4-tricarboxylic acid (PBTC), aminotrimethylenephosphonic acid
(ATMP),
diethylenetriaminepenta(methylenephosphonic acid) (DTPMP) and ethylenediamine-
tetra(methylenephosphonic acid) (EDTMP), and also the water-soluble salts
thereof, in
particular the sodium, potassium and ammonium salts thereof.
In addition, the compositions according to the invention can comprise up to
90% by weight
of water.
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In addition, the formulations can, in addition to the polymer mixtures
according to the
invention, optionally the phosphonates, and optionally water, according to
requirements,
also comprise up to 50% by weight of further additives (E) such as
polyphosphates, zinc
salts, molybdate salts, organic corrosion inhibitors such as benzotriazole,
tolyltriazole,
benzimidazole or ethynyl carbinol alkoxylates, biocides, complexing agents
and/or
surfactants.
The polymer mixtures of polymers (A) and (B) are generally produced by mixing
the
respective polymer solutions in stirred systems such as, e.g., in stirred
tanks, by
pneumatic circulation in containers, by circulation using pumps or by forced
flow in pipes.
Internals in the stirred systems, termed flow baffles, can accelerate the
mixing operation.
By installing fixed mixing elements in pipelines such as metal sheet lamellae,
spirals or
rigids, or mixing nozzles, the mixing operation can likewise be accelerated.
The choice of
the mixer or the mixing process depends on the respective requirements, in
particular the
viscosities and shear strengths of the polymer solutions that are to be mixed.
Solid
polymer mixtures can be produced by spray drying and spray granulation of the
aqueous
polymer mixtures or by mixing the solid polymers by means of rotating mixing
drums,
blade mixers, screw mixers, fluidized-bed mixers or air-shock mixers. The
invention relates
to both solid polymer mixtures, for example obtained by spray drying or spray
granulation,
and aqueous polymer mixtures. The water content of aqueous polymer mixtures is
generally up to 90% by weight, preferably up to 70% by weight, particularly
preferably up
to 50% by weight.
The invention also relates to the use of the polymer mixtures and compositions
as deposit
inhibitors for inhibiting the precipitation and sedimentation of calcium salts
and magnesium
salts in water-bearing systems. Calcium salts the precipitation of which is
inhibited are
generally calcium carbonate, calcium sulfate, calcium phosphonates and calcium
phosphates, in particular calcium carbonate and calcium sulfate. Magnesium
salts the
precipitation of which is inhibited are generally basic magnesium salts such
as
hydromagnesite and brucite.
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Water-bearing systems in which the polymer mixtures are preferably employed
are
seawater desalination plants, brackish water desalination plants, cooling
water systems
and boiler feed water systems.
Surprisingly, it has also been found that the polymer mixtures according to
the invention,
owing to their dispersive properties and properties stabilizing Fe(III) ions,
are outstandingly
suitable for preventing iron-comprising sediments in water-bearing systems.
The invention therefore further relates to the employment of the polymer
mixtures and
compositions as deposit inhibitors for inhibiting the precipitation and
sedimentation of iron-
comprising salts and compounds. In particular, sedimentation of iron oxides
and iron oxide
hydrates (iron hydroxides) are prevented.
Generally, the mixtures according to the invention are added to the water-
bearing systems
in amounts from 0.1 mg/I to 100 mg/I. The optimum dosage depends on the
requirements
of the respective application or the operating conditions of the respective
process. For
instance, in the thermal desalination of seawater, the mixtures are preferably
used in
concentrations from 0.5 mg/I to 10 mg/I. In industrial cooling circuits or
boiler feed water
systems, dosages up to 100 mg/I are employed. Frequently, water analyses are
carried
out in order to determine the proportion of deposit-forming salts and thereby
the optimum
dosage.
The invention will be described in more detail by the examples hereinafter.
Examples
The median molecular weights were determined by means of GPC.
Instrument:
Waters Alliance 2690 with UV-detector (Waters 2487) and RI detector
(Waters 2410)
Columns: Shodex 0Hpak SB 804HQ and 802.5HQ
(PHM gel, 8 x 300 mm, pH 4.0 to 7.5)
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Eluent: 0.05 M aqueous ammonium formate/methanol mixture = 80:20
(parts by
volume)
Flow rate: 0.5 ml/min
Temperature: 50 C
5 Injection: 50 to 100 pl
Detection: RI and UV
Molecular weights of the polymers were determined relative to polyacrylic acid
standards
from Varian Inc. The molecular weight distribution curves of the polyacrylic
acid standards
10 were determined by light scattering. The masses of the polyacrylic acid
standards were
115 000, 47 500, 28 000, 16 000, 7500, 4500, 4100, 2925 and 1250 g/mol.
Polymers 2, 3, 6, 7, 12 and 14 are produced by free-radical polymerization of
the
monomers in water using sodium peroxodisulfate as initiator and sodium
hypophosphite
15 (polymers 2 and 7) and sodium bisulfite (polymers 3, 6, 12 and 14) as
molecular weight
modifier.
Polymers 4, 5, 8, 9 and 13 are produced by free-radical polymerization of the
monomers
using a redox system of hydrogen peroxide, iron(II) sulfate and sodium
hydroxymethanesulfinate as initiator and mercaptoethanol as chain-transfer
agent.
Polymers 1, 10 and 11 are produced by free-radical polymerization of maleic
anhydride
with the respective comonomers in o-xylene or toluene using t-butyl
perpivalate as initiator.
Following the polymerization, a solvent exchange and hydrolysis of the
anhydride ring are
performed.
The aqueous polymer solutions are adjusted in each case to pH 7.5 (using
sodium
hydroxide solution) and a solids content of 40.0% by weight.
Polymers 1,4, 5, 8, 9, 10 and 11 are polymers (A) in accordance with the
abovementioned
definition.
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Polymers 2, 3, 6, 7, 12, 13 and 14 are polymers (B) in accordance with the
abovementioned definition.
Polymer 1: Copolymer of maleic acid and isobutene (weight ratio 70:30), Na
salt, Mw
4000 g/mol, aqueous solution, pH 7.5, solids content: 40.0% by weight
Polymer 2: Copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic
acid
(weight ratio 75:25), Na salt, Mw 7000 g/mol, aqueous solution, pH 7.5, solids
content:
40.0% by weight
Polymer 3: Copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic
acid
(weight ratio 75:25), Na salt, M, 8000 g/mol, aqueous solution, pH 7.5, solids
content:
40.0% by weight
Polymer 4: Copolymer of maleic acid and isoprenol (weight ratio 65:35), Na
salt, Mw 4000
g/mol, aqueous solution, pH 7.5, solids content: 40.0% by weight
Polymer 5: Copolymer of maleic acid and isoprenol (weight ratio 60:40), Na
salt, Mw 7500
g/mol, aqueous solution, pH 7.5, solids content: 40.0% by weight
Polymer 6: Polyacrylic acid, Na salt, Mw 1200 g/mol, aqueous solution, pH 7.5,
solids
content 40.0% by weight
Polymer 7: Polyacrylic acid, Na salt, Mw 3500 g/mol, aqueous solution, pH 7.5,
solids
content 40.0% by weight
Polymer 8: Copolymer of maleic acid, isoprenol and 2-acrylamido-2-
methylpropane-
sulfonic acid (weight ratio 40:40:20), Na salt, Mw 7000 g/mol, aqueous
solution, pH 7.5,
solids content: 40.0% by weight
Polymer 9: Copolymer of maleic acid, isoprenol and acrylic acid (weight ratio
35:40:25), Na
salt, Mw 3800 g/mol, aqueous solution, pH 7.5, solids content: 40.0% by weight
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Polymer 10: Copolymer of maleic acid and methyl vinyl ether (weight ratio
70:30), Na salt,
Mw 9500 g/mol, aqueous solution, pH 7.5, solids content 40.0% by weight
Polymer 11: Copolymer of maleic acid and vinyl acetate (weight ratio 60:40),
Na salt, Mw
6500 g/mol, aqueous solution, pH 7.5, solids content 40.0% by weight
Polymer 12: Copolymer of acrylic acid and allylsulfonic acid (weight ratio
80:20), Na salt,
Mw 5100, aqueous solution, solids content 40.0% by weight
Polymer 13: Copolymer of acrylic acid and isoprenol polyethylene glycol of the
formula
CH2=C(CH3)CH2CH2-(E0)113-H (weight ratio 90:10), Na salt, Mw 6200 g/mol,
aqueous
solution, solids content 40.0% by weight
Polymer 14: Terpolymer of acrylic acid, 2-acrylamido-2-methylpropanesulfonic
acid and
allyl alcohol alkoxylate of the formula CH2=CHCH20-(E0)16-H (weight ratio
55:30:15), Na
salt, Mw 8500 g/mol, aqueous solution, solids content 40.0% by weight
The polymer mixtures are produced by mixing the 40% strength by weight polymer
solutions. The amounts of solution are chosen in such a manner that a mixture
of the
desired polymer composition results. A mixture having a 50:50 composition has
identical
quantitative fractions (in % by weight) of the polymers used.
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Use as deposit inhibitor
Examples 1 to 3
Calcium carbonate inhibition test
A solution of NaHCO3, Mg2SO4, CaCl2 and polymer is shaken for 2 h at 70 C in
the water
bath. After filtering the still-warm solution through a 0.45 pm Milex filter,
the Ca content of
the filtrate is determined complexometrically or by means of a Ca2+-selective
electrode and
the CaCO3 inhibition is determined by comparison of before/after in % in
accordance with
formula I hereinafter:
Ca2+ 215 mg/I
mg2+ 43 mg/I
HCO3- 1220 mg/I
Na + 460 mg/I
ci 380 mg/I
S042- 170 mg/I
Polymer mixture (100% strength) 3 mg/I
Temperature 70 C
Time 2 hours
pH 8.0-8.5
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Formula I:
CaCO3 inhibition (%) = mg (Ca2+) after 24 h ¨ mg (Ca2+) blank value
after 24 h/mg
(Ca2+) zero value ¨ mg (Ca 2+) blank value after 24 h
x100
Table 1
Mixture Inhibition
composition in '% [ok]
by weight
Example 1
Polymer 4 58.4
Polymer 7 80.7
Mixture 4/7 50:50 83.4
Mixture 4/7 35:65 86.8
Example 2
Polymer 1 46.0
Polymer 3 64.8
Polymer 6 68.5
Mixture 1/3/6 30:30:40 72.0
Example 3
Polymer 1 46.0
Polymer 13 66.7
Mixture 1/13 25:75 73.2
Examples 4 to 7
Calcium sulfate inhibition test
A solution of NaCl, Na2SO4, CaCl2 and polymer was shaken for 24 h at 70 C in
the water
bath. After filtration of the still-warm solution through a 0.45 pm Milex
filter, the Ca content
CA 02844585 2014-02-07
of the filtrate is determined complexometrically or by means of a Ca2+-
selective electrode
and the CaS0.4 inhibition in % determined by before/after comparison in
accordance with
formula ll hereinafter:
5 Ca 2+ 2940 mg/I
S042- 7200 mg/I
Na + 6400 mg/I
Cl- 9700 mg/I
Polymer mixture (100% strength) 10 mg/I
10 Temperature 70 C
Time 24 hours
pH 8.0-8.5
Formula II:
CaSO4 inhibition (%) = mg (Ca2+) after 24 h ¨ mg (Ca2+) blank value after
24 h/mg
(Ca2+) zero value ¨ mg (Ca 2+) blank value after 24 h
x 100
Table 2
Mixture Inhibition
composition in % [A]
by weight
Example 4
Polymer 5 51.9
Polymer 6 91.0
Mixture 5/6 50:50 93.7
Example 5
Polymer 7 68.9
Polymer 11 47.7
Mixture 7/11 70:30 72.3
Example 6
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Polymer 4 58.4
Polymer 12 78.9
Mixture 4/12 25:75 81.3
Example 7
Polymer 4 58.4
Polymer 14 57.8
Mixture 4/14 50:50 66.0
Examples 8 to 10
Experiments on inhibiting basic Mg salt sediments (DSL method)
The deposit-inhibiting activity of the polymers according to the invention is
carried out
using a modified version of the "Differential Scale Loop (DSL)" instrument
from PSL
Systemtechnik. This is a "tube blocking system" as a fully automated
laboratory system for
studying precipitates and deposits of salts in pipelines and water pipes. In
this instrument,
in a modified mode of operation, a magnesium chloride solution A is mixed
together with a
sodium hydrogencarbonate solution B which comprises the polymer under test at
a
temperature of 120 C and a specific pressure of 2 bar at a mixing point in the
volumetric
ratio 1:1 and pumped at a constant flow rate through a test capillary of
stainless steel at
constant temperature. In this case, the differential pressure between mixing
point (starter
capillary) and capillary end is determined. A rise of the differential
pressure indicates
deposit formation within the capillary due to basic magnesium salts
(hydromagnesite,
brucite). The time measured up to a pressure rise of a defined height (0.1
bar) is a
measure of the deposit-inhibiting activity of the polymer used.
The specific experimental conditions are:
Solution A: 100 mM MgCl2
Solution B: 200 mM NaHCO3
Concentration of the polymer after mixing A and B: 10 mg/I
Capillary length: 2.5 m
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Capillary diameter: 0.88 mm
Capillary material: stainless steel
Temperature: 120 C
Total flow rate: 5m1/min
System pressure: 2 bar
Pressure rise threshold: 0.1 bar
Table 3: Time taken to pressurize by 0.1 bar (mean value from four
measurements)
Mixture composition Inhibition
in % by weight [min]
Example 8
Polymer 1 18.5
Polymer 3 23.9
Mixture 1/3 50:50 28.0
Example 9
Polymer 2 23.5
Polymer 8 24.9
Mixture 2/8 40:60 30.3
Example 10
Polymer 6 8.2
Polymer 9 20.0
Polymer 10 17.7
Mixture 6/9/10 20:50:30 22.5
