U.S. patent application number 14/513237 was filed with the patent office on 2015-01-29 for low molecular weight phosphorus-containing polyacrylic acids and use thereof as scale inhibitors in water-carrying systems.
This patent application is currently assigned to BASF SE. The applicant listed for this patent is BASF SE. Invention is credited to Juergen DETERING, Ewald HEINTZ, Stephan NIED, Bolette URTEL.
Application Number | 20150027956 14/513237 |
Document ID | / |
Family ID | 46600039 |
Filed Date | 2015-01-29 |
United States Patent
Application |
20150027956 |
Kind Code |
A1 |
DETERING; Juergen ; et
al. |
January 29, 2015 |
LOW MOLECULAR WEIGHT PHOSPHORUS-CONTAINING POLYACRYLIC ACIDS AND
USE THEREOF AS SCALE INHIBITORS IN WATER-CARRYING SYSTEMS
Abstract
The invention relates to an aqueous solution of acrylic acid
polymers, obtainable by polymerization of acrylic acid in feed mode
with peroxodisulfate as initiator in the presence of hypophosphite
in water as solvent, wherein (i) water and optionally one or more
ethylenically unsaturated comonomers are initially charged, and
(ii) acrylic acid in acidic, unneutralized form, optionally one or
more ethylenically unsaturated comonomers, aqueous peroxodisulfate
solution and aqueous hypophosphite solution are added continuously,
and (iii) a base is added on completion of the acrylic acid feed to
the aqueous solution, wherein the comonomer content does not exceed
30% by weight, based on total monomer content.
Inventors: |
DETERING; Juergen;
(Limburgerhof, DE) ; URTEL; Bolette;
(Bobenheim-Roxheim, DE) ; NIED; Stephan;
(Neustadt/Wstr., DE) ; HEINTZ; Ewald;
(Schweigen-Rechtenbach, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
|
DE |
|
|
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
46600039 |
Appl. No.: |
14/513237 |
Filed: |
October 14, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13363576 |
Feb 1, 2012 |
8889033 |
|
|
14513237 |
|
|
|
|
61439380 |
Feb 4, 2011 |
|
|
|
Current U.S.
Class: |
210/699 ;
252/180 |
Current CPC
Class: |
C02F 5/10 20130101; C02F
5/145 20130101; C02F 2103/023 20130101; C02F 2103/08 20130101; C02F
2303/22 20130101 |
Class at
Publication: |
210/699 ;
252/180 |
International
Class: |
C02F 5/14 20060101
C02F005/14 |
Claims
1. A process for producing an aqueous solution of an acrylic acid
polymer by polymerization of acrylic acid in feed mode with
peroxodisulfate as initiator in the presence of hypophosphite in
water as solvent, wherein: (i) water and optionally one or more
ethylenically unsaturated comonomers are initially charged, and
(ii) acrylic acid in acidic, unneutralized form, optionally one or
more ethylenically unsaturated comonomers, aqueous peroxodisulfate
solution and aqueous hypophosphite solution are added continuously,
and (iii) a base is added on completion of the acrylic acid feed to
the aqueous solution, wherein the comonomer content does not exceed
30% by weight, based on total monomer content.
2-10. (canceled)
11. The process according to claim 1, wherein the polymerization is
carried out under an inert gas atmosphere.
12. A method, comprising adding an aqueous solution of an acrylic
acid polymer to a water carrying system, wherein the aqueous
solution of the acrylic acid polymer is obtained by polymerization
of acrylic acid in feed mode with peroxodisulfate as initiator in
the presence of hypophosphite in water as solvent, wherein: (i)
water and optionally one or more ethylenically unsaturated
comonomers are initially charged, and (ii) acrylic acid in acidic,
unneutralized form, optionally one or more ethylenically
unsaturated comonomers, aqueous peroxodisulfate solution and
aqueous hypophosphite solution are added continuously, and (iii) a
base is added on completion of the acrylic acid feed to the aqueous
solution, and wherein the comonomer content does not exceed 30% by
weight, based on total monomer content.
13. The method according to claim 12, wherein said method is a
method for inhibiting calcium sulfate scale deposits.
14. The method according to claim 12, wherein said method is a
method for inhibiting scale deposits in seawater desalination
plants, cooling water systems and boiler feed water systems.
15. A method, comprising adding an acrylic acid polymer to a water
carrying system, wherein the acrylic acid polymer is obtained by
polymerization of acrylic acid in feed mode with peroxodisulfate as
initiator in the presence of hypophosphite in water as solvent,
wherein: (i) water and optionally one or more ethylenically
unsaturated comonomers are initially charged, and (ii) acrylic acid
in acidic, unneutralized form, optionally one or more ethylenically
unsaturated comonomers, aqueous peroxodisulfate solution and
aqueous hypophosphite solution are added continuously, and (iii) a
base is added on completion of the acrylic acid feed to the aqueous
solution, and wherein the comonomer content does not exceed 30% by
weight, based on total monomer content.
16. The method according to claim 15, wherein said method is a
method for inhibiting calcium sulfate scale deposits.
17. The method according to claim 15, wherein said method is a
method for inhibiting scale deposits in seawater desalination
plants, cooling water systems and boiler feed water systems.
18. The process according to claim 1, wherein the acrylic acid
polymer has a weight average molecular weight ranging from 1000 to
2500 g/mol and wherein at most 8% of phosphorous contained in said
acrylic acid polymer is present in the form of phosphinate and/or
phosphonate groups bound at a polymer chain end.
19. The process according to claim 1, wherein the weight average
molecular weight of the acrylic acid polymer ranges from 1200 to
2500 g/mol.
20. The process according to claim 1, wherein the M.sub.w/M.sub.n
polydispersity index of the acrylic polymer is .ltoreq.2.5.
21. The process according to claim 1, wherein the acrylic acid
polymer is an acrylic acid homopolymer.
22. The process according to claim 1, wherein the acrylic acid
polymer is an acrylic acid copolymer comprising up to 30% by
weight, based on all ethylenically unsaturated monomers, of one or
more ethylenically unsaturated comonomers selected from the group
consisting of methacrylic acid, maleic acid, maleic anhydride,
vinylsulfonic acid, allylsulfonic acid and
2-acrylamido-2-methylpropanesulfonic acid, as polymerized units.
Description
[0001] This invention relates to low molecular weight
phosphorus-containing polyacrylic acids, aqueous solutions
comprising same, processes for production thereof and also use
thereof as scale inhibitors in water-carrying systems.
[0002] The solubility of most substances in water is limited. The
prevention of mineral deposits in water-carrying systems is
important in industrial water treatment in particular. Inorganic
substances and salts such as, for example, calcium carbonate,
magnesium carbonate, magnesium hydroxide, calcium sulfate, barium
sulfate and calcium phosphate have low solubility in water. When
these dissolved ingredients become concentrated in aqueous systems,
their solubility product is exceeded, which causes these substances
to precipitate and form deposits. The solubility of substances is
dependent on the temperature and the pH. Temperature and/or pH
increases can likewise be the cause of undesirable precipitations
and scale formations in cooling and boiler feed water systems, on
heat transfer surfaces or in pipework.
[0003] Precipitations and deposits of calcium sulfate in
water-carrying systems are worth avoiding in particular, since they
are very difficult to remove again. The cost- and time-intensive
use of potent complexing agents such as EDTA is generally
indispensible, since standard methods such as mechanical cleaning
or the use of an acid are not satisfactory in removing the
deposits.
[0004] It is not just in cooling and boiler feed water systems
where it is attempted to avoid the formation of calcium sulfate
scale deposits and of other salt scale deposits. Seawater
desalination by distillation and by membrane processes such as
reverse osmosis or electrodialysis is another water-carrying system
where it is desired to prevent the formation of these firm scale
deposits.
[0005] It is known that low molecular weight polyacrylic acids
produced by free-radical polymerization and their salts are used as
scale inhibitors in industrial water treatment and in seawater
desalination because of their dispersing and crystal growth
inhibiting properties. The weight average molecular weight
(M.sub.w) of these polymers should be <50 000 for good
performance. Polyacrylic acids with M.sub.w<10 000 are often
particularly effective. To produce low molecular weight polyacrylic
acids, chain transfer agents are added as molecular weight
regulators during the free-radical polymerization of acrylic acid.
These regulators have to be adapted to the polymerization initiator
and also to the polymerization process. Examples of initiators are
organic and inorganic percompounds, such as peroxodisulfates
(persulfates), peroxides, hydroperoxides and peresters, azo
compounds such as 2,2'-azobisisobutyronitrile and redox systems
with organic and inorganic components. The regulators used are
frequently inorganic sulfur compounds such as hydrogensulfites,
disulfites and dithionites, organic sulfides, sulfoxides, sulfones
and mercapto compounds such as mercaptoethanol, mercaptoacetic acid
and also inorganic phosphorus compounds such as hypophosphorous
acid (phosphinic acid) and its salts (e.g., sodium
hypophosphite).
[0006] EP-A 405 818 discloses a process for forming polymers from
monoethylenically unsaturated monocarboxylic acids and optionally
further monomers using sodium persulfate as initiator in the
presence of hypophosphite as chain transfer agent, wherein an
alkaline neutralizer is present during the polymerization in an
amount sufficient to neutralize at least 20% of the acidic groups.
The low molecular weight polymers obtained comprise at least 80% of
the phosphorus from the hypophosphite. At least 70% of the
phosphorus is said to end up within the polymer chain, as dialkyl
phosphinate. The polymers thus obtained are used inter alia as
laundry detergent additives, dispersants for clay slurries or scale
inhibitors for water treatment.
[0007] In the exemplary embodiments, acrylic acid is polymerized in
water in the presence of hypophosphite as chain transfer agent and
sodium persulfate as initiator using the feed method wherein
aqueous sodium hydroxide solution is added during the
polymerization as a further continuous feed. This gives an aqueous
polyacrylic acid having a weight average molecular weight M.sub.w
of 2700 g/mol, which comprises 72% of the phosphorus in sodium
hypophosphite as dialkyl phosphinate, 18% as monoalkyl phosphinate
and 10% as inorganic salts. A comparative example dispenses with
the aqueous sodium hydroxide feed and neutralizes with sodium
hydroxide solution only after the polymerization has ended. The
product obtained here is an aqueous polyacrylic acid having a
weight average molecular weight M.sub.w of 4320 g/mol, which
comprises just 45% of the phosphorus in sodium hypophosphite as
dialkyl phosphinate, 25% as monoalkyl phosphinate and 30% as
inorganic salts.
[0008] EP-A 0 510 831 discloses a process for forming polymers from
monoethylenically unsaturated monocarboxylic acids,
monoethylenically unsaturated dicarboxylic acids and optionally
further monomers, comprising no carboxyl group, in the presence of
hypophosphorous acid as chain transfer agent. At least 40% of the
phosphorus incorporated in the polymer is present as monoalkyl
phosphinate and monoalkyl phosphonate at the end of the polymer
chain. The copolymers are used inter alia as dispersants, scale
inhibitors and laundry detergent additives.
[0009] EP-A 0 618 240 discloses a process for polymerization of
monomers in water in the presence of a water-soluble initiator and
hypophosphorous acid or a salt thereof. The process is carried out
such that the polymer content at the end of the polymerization is
at least 50% by weight. This method provides an increased
incorporation of the phosphorus in the polymer. The hypophosphite
phosphorus is present in the polymer in the form of dialkyl
phosphinate, monoalkyl phosphinate and also monoalkyl phosphonate.
No information is provided as to the distribution of the
phosphorus. The copolymers are used inter alia as dispersants,
scale inhibitors and laundry detergent additives.
[0010] EP-A 1 074 293 discloses phosphonate-terminated polyacrylic
acid having a molecular weight M.sub.w of 2000 to 5800 g/mol as a
dispersant for producing aqueous slurries of calcium carbonate,
kaolin, clay, talc and metal oxides having a solids content of at
least 60% by weight.
[0011] The problem addressed by the present invention is that of
providing low molecular weight polyacrylic acids having improved
scale-inhibiting performance, which are effective in inhibiting
precipitates and deposits of calcium sulfate in water-carrying
systems in particular, and also a process for production
thereof.
[0012] The problem is solved by aqueous solutions of acrylic acid
polymers, obtainable by polymerization of acrylic acid in feed mode
with peroxodisulfate as initiator in the presence of hypophosphite
as chain transfer agent in water as solvent, wherein
(i) water and optionally one or more ethylenically unsaturated
comonomers are initially charged, and (ii) acrylic acid in acidic,
unneutralized form, optionally one or more ethylenically
unsaturated comonomers, an aqueous peroxodisulfate solution and an
aqueous hypophosphite solution are added continuously, and (iii) a
base is added on completion of the acrylic acid feed to the
obtained solution, wherein the comonomer content does not exceed
30% by weight, based on the total monomer content.
[0013] The invention also provides a process for producing aqueous
solutions by polymerization of acrylic acid in feed mode with
peroxodisulfate as initiator in the presence of hypophosphite as
chain transfer agent in water as solvent, wherein water and
optionally one or more ethylenically unsaturated comonomers are
initially charged, and acrylic acid in acidic, unneutralized form,
optionally one or more ethylenically unsaturated comonomers, an
aqueous peroxodisulfate solution and an aqueous hypophosphite
solution are added continuously, and on completion of the acrylic
acid feed, the solution obtained is at least partially neutralized
by adding base, wherein the comonomer content does not exceed 30%
by weight, based on the total monomer content.
[0014] In general, water is initially charged and heated to the
reaction temperature of at least 75.degree. C. and preferably in
the range from 95 to 105.degree. C. At temperatures below
75.degree. C., the rate of decomposition of peroxodisulfate is
generally no longer sufficient.
[0015] In addition, an aqueous solution of phosphorous acid can be
included in the initial charge as a corrosion inhibitor.
[0016] This is followed by the commencement of the continuous feeds
of acrylic acid, optionally of further monomer, initiator and chain
transfer agent. Acrylic acid is added in unneutralized, acidic
form. In general, the feeds are commenced simultaneously. Both
peroxodisulfate as initiator and hypophosphite as chain transfer
agent are added in the form of their aqueous solutions.
Peroxodisulfate is generally used in the form of the sodium salt or
ammonium salt. Hypophosphite can be used in the form of
hypophosphorous acid (phosphinic acid) or in the form of salts of
hypophosphorous acid. It is particularly preferable to use
hypophosphite as hypophosphorous acid or as sodium salt.
[0017] The peroxodisulfate content of the aqueous peroxodisulfate
solution is preferably in the range from 5% to 10% by weight. The
hypophosphite content of the aqueous hypophosphite solution is
preferably in the range from 35% to 70% by weight.
[0018] Preferably, peroxodisulfate is used in amounts of 0.5% to
10% by weight and preferably 0.8% to 5% by weight, based on the
total amount of monomers (acrylic acid plus any comonomers).
[0019] Preferably, hypophosphite is used in amounts of 8% to 25% by
weight and more preferably 8% to 15% by weight, based on the total
amount of monomers.
[0020] The individual feeds are preferably added linearly, i.e.,
the feed quantity per unit time .DELTA.m/.DELTA.t (=feed rate) is
constant throughout the entire duration of the feed.
[0021] The duration of the initiator feed can be up to 50% longer
than the duration of the acrylic acid feed. Preferably, the
duration of the initiator feed is about 3 to 25% longer than the
duration of the acrylic acid feed. The duration of the chain
transfer agent feed may be up to 30% shorter than the duration of
the acrylic acid feed. Preferably, the duration of the chain
transfer agent feed is about 3 to 20% shorter than the duration of
the acrylic acid feed.
[0022] The duration of the acrylic acid feed is in the range from 3
to 6 h for example. When all the feeds are commenced
simultaneously, for example, the chain transfer agent feed will end
from 10 to 20 min before the end of the acrylic acid feed and the
initiator feed will end from 10 to 20 min after the end of the
acrylic acid feed.
[0023] In general, on completion of the acrylic acid feed, the
aqueous solution is at least partially neutralized by adding a
base. Aqueous sodium hydroxide solution is preferably used as base.
The neutralization is generally carried out over a comparatively
long period ranging for example from 1/2 hour to 3 hours in order
that the heat of neutralization may be efficiently removed. In
general, sufficient base is added for the pH to be subsequently in
the range from 3 to 9 and preferably in the range from 3.5 to
8.5.
[0024] In one version, the polymerization is carried out under an
inert gas atmosphere. This provides acrylic acid polymers where the
terminally bound phosphorus thereof is substantially (generally at
least 90%) present in the form of phosphinate groups.
[0025] This provides aqueous solutions of acrylic acid polymers
having a solids content of generally at least 30% by weight,
preferably at least 35% by weight, more preferably in the range
from 40% to 70% by weight and more particularly in the range from
40% to 55% by weight of polymer.
[0026] The acrylic acid polymers can also be converted into powder
or granule form using suitable methods of drying such as spray
drying, spray granulation, roll drying or paddle drying.
[0027] The aqueous solution of acrylic acid polymers which is thus
obtainable generally has a total phosphorus content of organically
and possibly inorganically bound phosphorus, wherein [0028] (a) a
first portion of the phosphorus is present in the form of
phosphinate groups bound within the polymer chain, [0029] (b) a
second portion of the phosphorus is present in the form of
phosphinate and/or phosphonate groups bound at the polymer chain
end, [0030] (c) possibly a third portion of the phosphorus is
present in the form of dissolved inorganic salts of phosphorus.
[0031] Generally at least 70% and preferably at least 76% of the
total phosphorus content is present in the form of phosphinate
groups bound within the polymer chain.
[0032] In many cases, even at least 78% of the total phosphorus
content is present in the form of phosphinate groups bound within
the polymer chain.
[0033] Generally at most 20% and preferably at most 16% of the
phosphorus is present in the form of phosphinate and/or phosphonate
groups bound at the polymer chain end. It is more preferable for 8
to 6% of the phosphorus to be present in the form of phosphinate
and/or phosphonate groups bound at the polymer chain end.
[0034] Up to 20% of the phosphorus present in the aqueous solution
of the acrylic acid polymers can be present in the form of
inorganic phosphorus, more particularly in the form of
hypophosphite and phosphite. Preferably from 2 to 15% and more
preferably from 4 to 11% of total phosphorus is present in the form
of inorganically bound phosphorus.
[0035] The ratio of phosphorus bound within the polymer chain to
phosphorus bound at the chain end is at least 4:1. This ratio is
preferably at least 4.5:1 to 10:1 and more particularly 5:1 to
8:1.
[0036] The weight average molecular weight of the acrylic acid
polymer is generally in the range from 1000 to 5000 g/mol,
preferably in the range from 1000 to 4000 g/mol, more preferably in
the range from 1000 to 3000 g/mol and more particularly in the
range from 1200 to 2500 g/mol.
[0037] The molecular weight of the acrylic acid polymer can be set
in a specific manner via the amount of chain transfer agent
used.
[0038] The molecular weight is determined via gel permeation
chromatography on neutral aqueous solutions of the acrylic acid
polymers using hydroxyethyl methacrylate copolymer network (HEMA)
as stationary phase and polyacrylate standards.
[0039] The M.sub.w/M.sub.n polydispersity index of the acrylic acid
polymer is generally .ltoreq.2.5 and preferably .ltoreq.2.
[0040] The K-values of the polymers are between 10 and 25,
preferably between 10 and 20 and more preferably between 12 and 18,
as measured at pH 7 in 1% by weight aqueous solution at 25.degree.
C. after H. Fikentscher, Cellulose-Chemie volume 13, pages 58-64
and 71-74 (1932).
[0041] The acrylic acid polymer may comprise up to 30% by weight,
preferably up to 20% by weight and more preferably up to 10% by
weight, based on all ethylenically unsaturated monomers, of
ethylenically unsaturated comonomers as polymerized units. Examples
of suitable ethylenically unsaturated comonomers are methacrylic
acid, maleic acid, maleic anhydride, vinylsulfonic acid,
allylsulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid
and also salts thereof. Mixtures of these comonomers may also be
present.
[0042] The comonomers can be wholly included in the initial
reaction charge; partly initially charged and partly added as feed;
or exclusively added as feed. When they are partly or wholly added
as feed, they are generally added simultaneously with the acrylic
acid.
[0043] Particular preference is given to acrylic acid homopolymers
without comonomer content.
[0044] The invention also provides for the use of the aqueous
solutions of the acrylic acid polymers as scale inhibitors in
water-carrying systems.
[0045] The acrylic acid polymers of the invention serve to inhibit
the formation of calcium sulfate scale deposits in particular.
[0046] Water-carrying systems in which the acrylic acid polymers
can be used are more particularly seawater desalination plants,
cooling water systems and boiler feed water systems.
[0047] The polymers of the present invention are generally added to
the water-carrying systems in amounts from 0.1 mg/l to 100 mg/l,
Optimum dosage depends on the requirement of the particular use
and/or the operating conditions of the particular process. Thermal
seawater desalination preferably utilizes the polymers in
concentrations of 0.5 mg/l to 10 mg/l. Industrial cooling circuits
or boiler feed water systems utilize polymer concentrations of up
to 100 mg/l. Water analyses are frequently carried out to determine
the proportion of scale-forming salts and hence optimum dosage.
[0048] The polymers of the present invention can also be added to
the water-carrying systems in formulations which, in addition to
the polymers of the present invention, may inter alia comprise,
depending on the requirements, phosphonates, polyphosphates, zinc
salts, molybdenum salts, organic corrosion inhibitors such as
benzotriazole, tolyltriazole, benzimidazole or ethynylcarbinol
alkoxylates, biocides, complexing agents and/or surfactants.
Examples of phosphonates are 1-hydroxyethane-1,1-diphosphonic acid
(HEDP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC),
aminotrimethylene-phosphoric acid (ATMP)
diethylenetriaminepenta(methylenephosphonic acid) (DTPMP) and
ethylenediaminetetra(methylenephosphonic acid) (EDTMP), which are
each used in the form of their sodium salts.
[0049] The examples which follow illustrate the invention.
EXAMPLES
[0050] All molecular weights are determined using gel permeation
chromatography (GPC). The GPC conditions used are as follows: 2
columns (Suprema Linear M) and a precolumn (Suprema Vorsaule), all
of the brand Suprema-Gel (HEMA) from Polymer Standard Services
(Mainz, Germany), were operated at 35.degree. C. at a flow rate of
0.8 ml/min. The eluent used was an aqueous solution admixed with
0.15 M NaCl and 0.01 M NaN.sub.3 and buffered with IRIS at pH 7.
Calibration was done with an Na--PAA standard, the cumulative
molecular weight distribution curve of which had been determined by
SEC laser light dispersion coupling, using the calibration method
of M. J. R. Cantow et al. (J. Polym. Sci., A-1, 5(1967) 1391-1394),
albeit without the concentration correction proposed therein. The
samples were all adjusted to pH 7, a portion of the solution was
diluted with completely ion-free water to a solids content of 1.5
mg/mL and stirred for 12 hours. The samples were then filtered, and
100 .mu.L was injected through a Sartorius Minisart RC 25 (0.2
.mu.m) in each case.
Inventive Examples
Example A
[0051] A reactor was initially charged with 425.0 g of completely
ion-free water followed by heating under nitrogen to 102.degree. C.
internal temperature. At this temperature, 481.0 g of a distilled
acrylic acid, 206.0 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 246.0 g of a 59% by weight aqueous
sodium hypophosphite solution were simultaneously added separately
and concurrently under agitation. Acrylic acid was added within 4
hours, sodium peroxodisulfate within 4.25 hours and sodium
hypophosphite within 3.75 hours. On completion of the acrylic acid
feed the line was flushed with 30.0 g of completely ion-free water
and 536.0 g of a 50% by weight aqueous sodium hydroxide solution
were added at 100.degree. C. internal temperature within one hour.
Thereafter, polymer solution was cooled down to room temperature.
The pH, the molecular weights M.sub.n and M.sub.w, the solids
content and the residual acrylic acid content were determined and
the solution was visually assessed.
Example B
[0052] A reactor was initially charged with 425.0 g of completely
ion-free water followed by heating under nitrogen to 102.degree. C.
internal temperature. At this temperature, 481.0 g of a distilled
acrylic acid, 138.0 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 164.0 g of a 59% by weight aqueous
sodium hypophosphite solution were simultaneously added separately
and concurrently under agitation. Acrylic acid was added within 4
hours, sodium peroxodisulfate within 4.25 hours and sodium
hypophosphite within 3.75 hours. On completion of the acrylic acid
feed the line was flushed with 30.0 g of completely ion-free water
and 525.0 g of a 50% by weight aqueous sodium hydroxide solution
were added at 102.degree. C. internal temperature within one hour.
Thereafter, the polymer solution was cooled down to room
temperature. The pH, the molecular weights M.sub.n and M.sub.w and
the solids content were determined and the solution was visually
assessed.
Example C
[0053] A closed reactor was initially charged with 425 g of
completely ion-free water. The water was then heated under nitrogen
to 98.degree. C. internal temperature. At this temperature, 481 g
of a distilled acrylic acid, 69 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 82 g of a 59% by weight aqueous sodium
hypophosphite solution were simultaneously added separately and
concurrently under agitation. Acrylic acid was added within 4
hours, sodium peroxodisulfate within 4.25 hours and sodium
hypophosphite within 3.75 hours. On completion of the acrylic acid
feed, the acrylic acid line was flushed with 30 g of completely
ion-free water and then 55 g of a 50% by weight aqueous sodium
hydroxide solution were added at 98.degree. C. internal temperature
within 1 hour. This was followed by the addition of a further 225 g
of completely ion-free water and the polymer solution was cooled
down to room temperature. The pH, the molecular weights M.sub.n and
M.sub.w and the solids content were determined and the solution was
visually assessed.
Example D
[0054] A reactor was initially charged with 50 g of polymer from
example 9. At room temperature, 17.5 g of 50% by weight aqueous
sodium hydroxide solution were added at 98.degree. C. internal
temperature within 1 hour. The pH, the molecular weights M.sub.n
and M.sub.w and the solids content were determined and the solution
was visually assessed.
Example E
[0055] A reactor was initially charged with 230.0 g of completely
ion-free water followed by heating under nitrogen to 102.degree. C.
internal temperature. At this temperature, 480.8 g of a distilled
acrylic acid, 69.0 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 57.0 g of a 59% by weight aqueous
sodium hypophosphite solution were simultaneously added separately
and concurrently under agitation. Acrylic acid was added within 5
hours, sodium peroxodisulfate with 5.25 hours and sodium
hypophosphite within 4.75 hours. On completion of the acrylic acid
feed the line was flushed with 30.0 g of completely ion-free water
and the batch was stirred at 95.degree. C. internal temperature for
2 hours. Then, 175.0 g of completely ion-free water were added and
in the process the polymer solution cooled down to room
temperature. The polymer solution was then adjusted with 50% by
weight aqueous sodium hydroxide solution to pH 7. The pH, the
molecular weights M.sub.n and M.sub.w and the solids content were
determined and the solution was visually assessed.
Example F
[0056] A reactor was initially charged with 425.0 g of completely
ion-free water followed by heating under nitrogen to 100.degree. C.
internal temperature. At this temperature, 481.0 g of a distilled
acrylic acid, 69.0 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 41.0 g of a 59% by weight aqueous
sodium hypophosphite solution were simultaneously added separately
and concurrently under agitation. Acrylic acid was added within 4
hours, sodium peroxodisulfate with 4.25 hours and sodium
hypophosphite within 3.75 hours. On completion of the acrylic acid
feed the line was flushed with 30.0 g of completely ion-free water
and 527.0 g of a 50% by weight aqueous sodium hydroxide solution
were added at 100.degree. C. internal temperature within 1 hour.
Thereafter, the polymer solution was cooled down to room
temperature. The pH, the molecular weights M.sub.n and M.sub.w the
solids content and the residual acrylic acid content were
determined and the solution was visually assessed.
Example G
[0057] A reactor was initially charged with 325.0 g of completely
ion-free water followed by heating under nitrogen to 95.degree. C.
internal temperature. At this temperature, 562.5 g of a distilled
acrylic acid, 542.4 of a 49% by weight aqueous
2-acrylamido-2-methylpropanesulfonic acid sodium salt (Na-AMPS)
solution stabilized with 250 ppm of MEHQ, 533.0 g of a 7% by weight
aqueous sodium peroxodisulfate solution and 127.1 g of a 59% by
weight aqueous sodium hypophosphite solution were simultaneously
added separately and concurrently under agitation. Acrylic acid and
Na-AMPS were added within 3 hours, sodium peroxodisulfate with 4.5
hours and sodium hypophosphite within 2.75 hours. On completion of
the acrylic acid feed 175.0 g of a 50% by weight aqueous sodium
hydroxide solution were added at 95.degree. C. internal temperature
within 2 hours. Thereafter, the polymer solution was cooled down to
room temperature. The pH, the molecular weights M.sub.n and
M.sub.w, the solids content and the residual acrylic acid content
were determined and the solution was visually assessed.
Comparative Examples
Example H
[0058] A reactor was initially charged with 200.0 g of completely
ion-free water together with 2.7 g of a 50% by weight aqueous
solution of phosphorous acid followed by heating under nitrogen to
101.degree. C. internal temperature. At this temperature, 428.0 g
of a distilled acrylic acid, 123.0 g of a 7% by weight aqueous
sodium peroxodisulfate solution and 108.0 g of 2-mercaptoethanol
were simultaneously added separately and concurrently under
agitation. Acrylic acid was added within 5 hours, sodium
peroxodisulfate within 5.25 hours and 2-mercaptoethanol within 4.75
hours. On completion of the sodium peroxodisulfate feed stirring
was continued at 101.degree. C. internal temperature for a further
15 minutes followed by cooling to 80.degree. C. internal
temperature. At 80.degree. C. internal temperature, 16.2 g of a
5.38% by weight aqueous solution of an azo initiator (Wako V50)
were added within 30 minutes followed by stirring for 1 hour. Then,
475.0 g of 50% by weight aqueous sodium hydroxide solution were
added at 80-95.degree. C. internal temperature in 1 hour followed
by stirring for 10 min. Then, 14.0 g of a 50% by weight aqueous
hydrogen peroxide solution were added in 30 minutes followed by
polymerization at 80.degree. C. for 4 hours. Thereafter, the
polymer solution was cooled down to room temperature. The pH, the
molecular weights M.sub.n and M.sub.w and the solids content were
determined and the solution was visually assessed.
Example I
[0059] A reactor was initially charged with 230.0 g of completely
ion-free water together with 3.05 g of a 50% by weight aqueous
solution of phosphorous acid solution followed by heating under
nitrogen to 99.degree. C. internal temperature. At this
temperature, 479.35 g of a distilled acrylic acid, 68.65 g of a 7%
by weight aqueous sodium peroxodisulfate solution and 59.9 g of
2-mercaptoethanol were simultaneously added separately and
concurrently under agitation. Acrylic acid was added within 5
hours, sodium peroxodisulfate within 5.25 hours and
2-mercaptoethanol within 4.75 hours. On completion of the acrylic
acid feed the line was flushed with 12.5 g of completely ion-free
water and on completion of the sodium peroxodisulfate feed stirring
was continued at 105.degree. C. internal temperature for a further
15 minutes followed by cooling to 80.degree. C. internal
temperature. At 80.degree. C. internal temperature, 5.0 g of a 5%
by weight aqueous Wako V50 solution were added within 1 hour. On
completion of the addition the line was flushed with 5.0 g of
completely ion-free water followed by stirring at 80.degree. C. for
1 hour. Then, 521.5 g of 50% by weight aqueous sodium hydroxide
solution were added at most 105.degree. C. internal temperature in
1 hour. This was followed by stirring for 10 minutes, then, 26.25 g
of a 50% by weight aqueous hydrogen peroxide solution were added
within 1.3 hours followed by polymerization at 80.degree. C. for 15
minutes. Thereafter, 140.0 g of completely ion-free water were
added and in the process the polymer solution was cooled down to
room temperature. The pH, the molecular weights M.sub.n and M.sub.w
and the solids content were determined and the solution was
visually assessed.
Example J
[0060] A reactor was initially charged with 230.0 g of completely
ion-free water together with 3 kg of a 50% by weight aqueous
solution of phosphorous acid followed by heating under nitrogen to
99.degree. C. internal temperature. At this temperature, 516.9 g of
a distilled acrylic acid, 67.4 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 44 g of 2-mercaptoethanol were
simultaneously added separately and concurrently under agitation.
Acrylic acid was added within 4 hours, sodium peroxodisulfate
within 4 hours and 2-mercaptoethanol within 3.75 hours. On
completion of the acrylic acid feed the acrylic acid line was
flushed with 12.5 g of completely ion-free water and a further 20 g
of a 7% by weight aqueous sodium peroxodisulfate solution were
added within 30 minutes. This was followed by stirring at
99.degree. C. internal temperature for 30 minutes and cooling down
to 80.degree. C. internal temperature. At 80.degree. C. internal
temperature, 10 g of a 6% by weight aqueous Wako V50 solution were
added within 1 hour, the line was flushed with 5 g of completely
ion-free water and stirring was continued for 1 hour. Then, 560 g
of a 50% by weight aqueous sodium hydroxide solution were added at
95.degree. C. internal temperature in 1 hour followed by stirring
for 10 minutes. Then, 20 g of a 50% by weight aqueous hydrogen
peroxide solution were added within 1 hour followed by
polymerization at 80.degree. C. for 15 minutes. Thereafter, 100 g
of completely ion-free water were added and the polymer solution
was cooled down to room temperature. The pH, the molecular weights
M.sub.n and M.sub.w the solids content and the residual acrylic
acid content were determined and the solution was visually
assessed.
Example K
[0061] Example 1 was repeated except that 50 g of a 56% by weight
solution of 2-mercaptoethanol and only 62 g of a 7% by weight
aqueous solution of sodium peroxodisulfate were added.
Example L
[0062] A 2 L reactor was initially charged with 230 g of completely
ion-free water together with 3.1 g of a 50% by weight aqueous
solution of phosphorous acid. This was followed by heating under
nitrogen to 99.degree. C. internal temperature. At this
temperature, 520 g of a distilled acrylic acid, 74 g of a 7% by
weight aqueous sodium peroxodisulfate solution and 23.4 g of
2-mercaptoethanol were simultaneously added separately and
concurrently under agitation. Acrylic acid was added within 4
hours, sodium peroxodisulfate within 4 hours and 2-mercaptoethanol
within 3.75 hours. On completion of the acrylic acid feed 500 g of
a 50% by weight aqueous sodium hydroxide solution were added within
15 minutes. This was followed by stirring at 99.degree. C. for 15
minutes and then cooling down to 80.degree. C. internal
temperature. At 80.degree. C. internal temperature, 10.1 g of a 6%
by weight aqueous Wako V50 solution were added within 1 hour
followed by 1 hour of stirring. Then, 525 g of a 50% by weight
aqueous sodium hydroxide solution were added within 2.8 hours at
95.degree. C. internal temperature followed by stirring for 1 hour.
Then 10.75 g of a 50% by weight aqueous hydrogen peroxide solution
were added in 0.5 hours followed by polymerization at 80.degree. C.
for 15 minutes. Thereafter, 125 g of completely ion-free water were
added and in the process the polymer solution was cooled down to
room temperature. The pH, the molecular weights M.sub.n and
M.sub.w, the solids content and the residual acrylic acid content
were determined and the solution was visually assessed.
Example M
[0063] A closed reactor was initially charged with 4525 kg of
completely ion-free water. This was followed by heating under
nitrogen to 95.degree. C. internal temperature. At this
temperature, 11 096 kg of a distilled acrylic acid, 4756 kg of a 7%
by weight aqueous sodium peroxodisulfate solution and 4993 kg of a
40% by weight aqueous sodium bisulfite solution were simultaneously
added separately and concurrently under agitation. Acrylic acid was
added within 5.5 hours, sodium peroxodisulfate within 5.75 hours
and sodium bisulfite within 5.5 hours. On completion of the acrylic
acid feed the line was flushed with 50 kg of completely ion-free
water. This was followed by stirring at 95.degree. C. for 15
minutes and then cooling down to 80.degree. C. internal
temperature. At this temperature, 189 kg of a 6% by weight aqueous
Wako V50 solution were added within 1 hour. Thereafter, 12 505 kg
of a 50% by weight aqueous sodium hydroxide solution were added
while the internal temperature did not exceed 85.degree. C.
Thereafter, the polymer solution was cooled down to room
temperature. The pH, the molecular weights M.sub.n and M.sub.w and
the solids content were determined and the solution was visually
assessed.
Example N
[0064] A reactor was initially charged with 304.0 g of completely
ion-free water together with 1.84 g of a 50% by weight aqueous
solution of phosphorous acid followed by heating under nitrogen to
98.degree. C. internal temperature. At this temperature, 461.0 g of
a distilled acrylic acid, 132.0 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 196.0 g of a 40% by weight aqueous
sodium bisulfite solution were simultaneously added separately and
concurrently under agitation. Acrylic acid was added within 4
hours, sodium peroxodisulfate within 4.25 hours and sodium
bisulfite within 3.75 hours.
[0065] On completion of the acrylic acid feed 496.0 g of a 50% by
weight aqueous sodium hydroxide solution were added within 1 hour
at 98.degree. C. internal temperature followed by polymerization at
98.degree. C. for 1 hour. Thereafter, the polymer solution was
cooled down to room temperature. The pH, the molecular weights
M.sub.n and M.sub.w, the solids content and the residual acrylic
acid content were determined and the solution was visually
assessed.
Example O
[0066] A reactor was initially charged with 184.0 g of completely
ion-free water. This was followed by heating under nitrogen to
95.degree. C. internal temperature. At this temperature, 647.7 g of
a distilled acrylic acid, 277.6 g of a 7% by weight aqueous sodium
peroxodisulfate solution and 105.3 g of a 40% by weight aqueous
sodium bisulfite solution were simultaneously added separately and
concurrently under agitation. The acrylic acid was added within 5
hours, sodium peroxodisulfate within 5.25 hours and sodium
bisulfite within 5 hours. On completion of the acrylic acid feed
the line was flushed with 10.0 g of completely ion-free water for 6
minutes followed by stirring at 95.degree. C. internal temperature
for a further 35 minutes. Thereafter, 728.0 g of a 50% by weight
aqueous sodium hydroxide solution were added, while the internal
temperature did not exceed 95.degree. C., followed by
polymerization at 95.degree. C. for 30 minutes. Then, 136.0 g of
completely ion-free water were added and in the process the polymer
solution cooled down to room temperature. After the internal
temperature had dropped to <75.degree. C., 5.8 g of a 49% by
weight aqueous hydrogen peroxide solution were added. The pH, the
molecular weights M.sub.n and M.sub.w and the solids content were
determined and the solution was visually assessed.
[0067] The analytical data of the polymers are summarized in table
1.
TABLE-US-00001 TABLE 1 Solids %-P %-P Exam- content K pH inter-
exter- %-P ple [%].sup.a value.sup.b (tq) Mw.sup.c PDI.sup.c
nal.sup.d nal.sup.d inorg.sup.d A 40.2 12.6 6.9 1270 1.2 81.2 13.5
5.3 B 42.2 14.6 7.0 2000 1.4 76.3 15.0 8.7 C 36.4 20.1 4.5 3620 1.7
81.4 11.4 7.2 D 39.0 20.1 7.0 3620 1.7 81.4 11.4 7.2 E 45.2 25.0
7.0 5560 2.1 84.7 12.1 2.6 F 42.3 29.1 7.0 7180 2.4 72.1 16.1 5.6 G
42.3 17.9 4.3 2870 2.0 89.5 8.2 2.2 H 49.7 12.6 7.6 1070 1.3 -- --
-- I 44.9 18.4 7.0 1860 1.8 -- -- -- J 46.7 22.0 7.2 3580 2.1 -- --
-- K 49.0 24.1 7.0 5020 1.7 -- -- -- L 45.2 29.5 7.2 7220 2.8 -- --
-- M 40.6 14.5 6.9 2470 1.5 -- -- -- N 43.5 20.3 6.9 4450 1.8 -- --
-- O 44.7 30.6 6.9 9560 3.1 -- -- -- .sup.aISO 3251, (0.25 g,
150.degree. C., 2 h) .sup.bdetermined by Fikentscher method with 1%
solution in completely ion-free water .sup.cdetermined by gel
permeation chromatography .sup.ddetermined with .sup.31P{.sup.1H}
and .sup.31P NMR
Use as Scale Inhibitor
Calcium Sulfate Inhibition Test
[0068] A solution of NaCl, Na.sub.2SO.sub.4, CaCl.sub.2 and polymer
was shaken for 24 h at 70.degree. C. in a water bath. After the
still warm solution has been filtered through a 0.45 .mu.m Milex
filter, the Ca content of the filtrate is determined
complexometrically or by means of a Ca.sup.2+-selective electrode
and the CaSO.sub.4 inhibition determined in % by before/after
comparison (see formula I).
Conditions
TABLE-US-00002 [0069] Ca.sup.2+ 2940 mg/l SO.sub.4.sup.2- 7200 mg/l
Na.sup.+ 6400 mg/l Cl.sup.- 9700 mg/l Polymer 5 mg/l (100%)
Temperature 70.degree. C. Time 24 hours pH 8.0-8.5
CaSO.sub.4 inhibition(%)=mg(Ca.sup.2+) after 24 h-mg(Ca.sup.2+)
blank value after 24 h/mg(Ca.sup.2+) null value-mg(Ca.sup.2+) blank
value 24 h.times.100 Formula I:
TABLE-US-00003 TABLE 2 Initiator/ K value Mw Inhibition (Example)
regulator (1% in water) (GPC) [%] A NPS/NHP 12.6 1270 79.2 B
NPS/NHP 14.6 2000 84.4 D NPS/NHP 20.1 3620 43.6 E NPS/NHP 25.0 5560
14.5 F NPS/NHP 29.1 7180 12.1 G NPS/NHP 17.9 2870 66.9 H
NPS/MCE/Azo 12.6 1070 22.6 I NPS/MCE/Azo 18.4 1860 32.6 J
NPS/MCE/Azo 22.0 3580 19.3 K NPS/MCE/Azo 24.1 5020 15.3 L
NPS/MCE/Azo 29.5 7220 12.6 M NPS/NBS 14.5 2470 25.5 N NPS/NBS 20.3
4450 19.9 O NPS/NBS 30.6 9560 9.1 NPS = sodium peroxodisulfate NHP
= sodium hypophosphite MCE = mercaptoethanol NBS = sodium bisulfite
Azo = 2,2'-azobis(2-amidinopropane) dihydrochloride for secondary
polymerization
[0070] The results are an unequivocal demonstration of the
superiority of the inventive polymers as per examples A, B and D
over the comparative polymers as per examples H, I, J, M, N.
According to examples A, B and D, the preferred molecular weights
Mw are <4000 and more particularly <2500.
* * * * *