Note: Descriptions are shown in the official language in which they were submitted.
~323824
Field of the Invention
The present invention pertains to a method of utilizing
novel polymers to inhibit corros~on and control the formation and
deposition of scale imparting compounds in steam generating systems
such as boiler water systems.
Background of the Invention
The problems of corrosion and scale formation and
attendant effects have troubled water systems for years. For
instance, scale tends to accumulate on internal walls of various
water systems, such as boiler and cooling systems, thereby
materially lessens the operational efficiency of the system.
,
1 3 2 3 8 2 4
neposits ~n lines, heat exchange equ~pment, etc., may
originate from several causes. For example, precip~tat~on of
calcium carbonate, calcium sulfate and calcium phosphate in the
water system leads to an accumulation of these scale impart~ng
compounds along or around the metal surfaces wh1ch contact the
flowing water circulating through the system. In this manner, heat
transfer funct~ons of the particular system are severely impeded.
Corrosion, on the other hand, is a degradative electro-
chemical reaction of a metal with its environment. Simply stated,
it is the reversion of refined metals to their natural state. For
example, iron ore is iron oxide. Iron oxide is refined into steel.
When the steel corrodes, it forms iron oxide which, if unattended,
may result in failure or destruction of the metal, causing the
particular water system to be shut down until the necessary repairs
can be made.
As detailed in the Betz Handbook of Industrial Water
Conditioning, 8th Edition, 1980, Betz Laboratories, Inc., Trevose,
PA Pages 85-96, the formation of scale and sludge deposits on boiler
heating surfaces is a serious problem encountered in steam
generation. Although current industrial steam producing systems
make use ~f sophisticated external treatments of the boiler
feedwater, e.g., coagulation, filtration, softening of water prior
to its feed into the boiler system, these operations are only
moderately effective. In all cases, external treatment does not in
itself provide adequate treatment since muds, sludge, silts and
hardness-imparting ions escape the treatment, and eventually are
introduced into the steam generating system.
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In addition to the problems caused by mud, sludge or
silts, the industry has also had to contend with boiler scale.
Although external treatment ~s ut~lized specifically ~n an attempt
to remove calcium and magnesium from the feedwater, scale formation
due to residual hardness, i.e., calcium and magnesium salts, is
always experienced. Accordingly, internal treatment, i.e.,
treatment of the water fed to the system, is necessary to prevent,
reduce and/or retard formation of the scale imparting compounds and
their resultant deposition. The carbonates of magnesium and calcium
are not the only problem compounds as regards scale, but also water
having high contents of phosphate, sulfate and silicate ions either
occurring naturally or added for other purposes cause problems since
calcium and magnesium, and any iron or copper present, react with
each and deposit as boiler scale. As is obvious, the deposition of
scale on the structural parts of a steam generatlng system causes
poorer circulation and lower heat transfer capacity, resulting
accordingly in an overall loss in efficiency.
Summary of the Invent~on
It has been discovered that water soluble copolymers, as
shown in Formula I hereinafter, are effective in controlling the
formation of mineral deposits and in inhibiting corrosion in steam
generating systems such as boiler water systems.
The water soluble copolymers of the invention have the
structure:
i32382~
-- 4 -
R
I
- [E]- _[CH2 - CH] -
c I d
S CH2
o
I
R2
I
(XZ)
a
wherein E is the repeat unit remaining after polymerization of an
ethylenically unsaturated compound, Rl is H or lower (Cl -C3) alkyl,
R2 is a hydroxy substituted alkyl or alkylene having from 1 to about
6 carbon atoms or a non-substituted alkyl or alkylene having from 1
to about 6 carbon atoms; a is 0 or 1, X is an anionic radical
selected from the group consisting of S03, P03, P04, and C00, Z is H
or a water soluble cation or cations, Z being chosen to counter-
balance the valence of X, XZ combined may also denote an amino
functionality of the formula
Fl~
~ N
F2
wherein Fl and F2 are independently selected from H, and Cl -Cs
alkyl, the molar ratio of repeat units c:d being from about 30:1 to
about 1:20.
In accordance with the method, from 0.1 to 500 parts of the
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allyl ether containing copolymer are admitted to the desired aqueous
system, based upon one million parts of the aqueous system,
Prior Art
Some of the water soluble or water d~spersible copolymers
used in accordance with the invention are not new. For instance,
U.S. Patent 4,500,693 (Takehara et al) discloses water soluble
copolymers having an acrylic acid or methacrylic acid repeat unit
which is co-polymerized with certain allyl ether monomers. The
polymers disclosed in accordance with Takehara et al are useful
calcium carbonate inhibitors in cooling water systems and may also
be used as a pigment dispersant. Use of those polymers for the
boiler water treatment is not suggested in the '693 patent.
U.S. Patent 4,469,615 tTsuruoka et al) discloses water
treatment compositions comprising a water soluble copolymer having,
as the components, one repeat it formed from an addition reaction
product of a glycidyl ether or glycidyl ester and an ocJ ~3
ethylenically unsaturated carboxylic acid. The co-monomer may
comprise any vinyl monomer. The copolymers are reported as being
useful as corrosion inhibition agents in water systems.
Offenlegungsschrift 25 22 637 discloses varied acrylic
acid/allyl alcohol type copolymers which may be utilized to
stabilize hardness in water systems.
European Publication 0142929 (Chen) discloses water
treatment polymers which are in many cases coextensive with those
herein disclosed. The polymers are utilized to inhibit calcium
phosphate and calcium phosphonate in aqueous systems. They also
function to provide a passivated oxide film along treated metal
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surfaces when they are used con~ointly with a water soluble
orthophosphate source.
U.S. Patents 4,659,481 (Chen) and 4,732,698 (Chen)
disclose the utllization of certa~n (meth)acrylic acid/allyl ether
copolymers that may be util~zed to provide the elus~ve passiYe oxide
film along water system metallurgy when used con~ointly with an
orthophosphate ~on source. Most spec~fically preferred is
utilization of an acrylic acid/2-hydroxypropylsulfonate ether
copolymer.
U.S. Patents 4,659,482 (Chen) and 4,717,499 (Chen)
disclose use of (meth)acrylic acid/allyl ether copolymers to
simultaneously inhibit corrosion and calcium carbonate deposition in
cooling water systems under elevated pH (i.e., 7.5-9.0) and calcium
carbonate supersaturation conditions.
U.S. Patent 4,701,262 (Chen) discloses the utilization of
acrylic acid/allylhydroxyalkyl ether copolymers In combination with
2-phosphonobutane 1,2,4-tricarboxylic acid to Inhibit calcium
sulfate and calcium carbonate scale.
U.S. patent 4,759,851 (Chen) discloses utilization of
acrylic acid/allylhydroxyalkyl ether copolymers to control calcium
phosphonate scale in water systems.
U.S. patents 4,659,480 (Chen et al~ and 4,708,815 (Chen et
al) disclose utilization of certain acrylic acid/allylalkylene
phosphite ether copolymers in water treatment systems.
Japanese Patent Publication SH056-155692, "Method of
Collecting Dust" discloses use of acrylic acid/polyethylene glycol
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monoallylether copolymers which are utilized to treat the
recirculating water in an aqueous dust collecting system. In thls
disclosure, the number of moles of ethoxylation is taught as belng
from 5 to 100. If the number is less than 5, the scale control and
dispersant efficacies are insufficient.
U.S. patent Bl 4,288,327 teaches using of sulfona~ed
styrene/maleic anhydride copolymer for controlling the formation and
deposition ln an aqueous medium. U.S. patent Bl 4,457,847 cites the
use of certain carboxylic acid polymers to treat hardness ~n boiler
water. The preferred polymers taught to prevent scale in the '847
patent are usually acrylic acid or methacrylic homopolymers or
water-soluble copolymers of these acrylates. However, as pointed
out by U.S. patent 4,680,124, such treatment is prone to form
calcium-polyacrylate scale on heat transfer surfaces. Phosphorous
compounds may be added to prevent the formation of calcium
polyacrylate scale.
Detailed Description of the Preferred Embodiment
In accordance with the invention, it has been discovered
that certain water soluble copolymers, as shown in Formula I
hereinafter, are effective in controlling the formation of deposits
and in inhibiting corrosion in steam generating systems such as
boiler water systems.
The polymers comprise repeat units composed of an oC, ~
ethylenically unsaturated compound and an allylalkylene ether based
compound. The (meth)acrylic acid/allyl ether polymers useful in
accordance with the invention have the structure:
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-~E]- -~CH2 - CH]-
c I d
CH2
I
o
I FORMULA I
R2
(XZ)a
wherein E in the above formula is the repeat unit remaining after
polymerization of an o~, ~ ethylenically unsaturated compound, Rl is
H or lower (Cl -C3) alkyl, R2 is a hydroxy substituted alkyl or
alkylene having from 1 to about 6 carbon atoms or a non-substituted
alkyl or alkylene having from 1 to 6 carbon atoms, a is O or 1, X is
an anionic radical selected from the group consisting of S03, P03,
P04, and COO, Z is H or a water soluble cation or cations, Z being
chosen to counterbalance the valence of X, XZ combined may also
denote an amino functionality of the formula
wherein Fl and F2 are independently selected from H and Cl -Cs
alkyl, linear or branched, the molar ratio of repeat unit c:d being
from about 30:1 to about 1:20, more desirably within 15:1 to 1:10.
E in the above formula may, for instance, comprise the
repeat unit remaining after polymerization of an oc, ~ ethylenically
1323824
unsaturated monomer, preferably a carboxylic acid, amide form
thereof, or lower alkyl (Cl - C6) ester or hydroxylated lower alkyl
(Cl -C6) ester of such carboxylic acid. Exemplary compounds
encompassed by E include, but are not restricted to the repeat unit
formed by polymerization of acrylic acid, methacrylic acid,
acrylamide, maleic acid or anhydride, fumaric acid, itaconic acid,
2-hydroxypropyl acrylate, styrene sulfonic acid, and 2-acrylamido-
2-methylpropanesulfonic acid and the like. Water soluble salt forms
`of these acids are also within the purview of the invention. These
monomers are commercially available.
The second repeat unit in Formula I may include, as
exemplary, repeat units formed from monomers such as l-allyloxy-2-
propanol, l-allyloxypropane 2,3-diol (glyceryl allyl ether),
l-allyloxy-2-hydroxypropylsulfonic acid, 1-allyloxy-2-hydroxy-
propyl phosphite, 1-allyloxy-2-hydroxypropyl phosphonic acid,
l-allyloxy-2-hydroxybutanoic acid and water soluble salt forms of
these acids.
The allyl containing monomers, monomer d, in the FORMULA I
- above, these may be produced by reacting~allyl alcohol with an
20 non-tertiary alcohol in the temperature range of about 25-150C as
is detailed in U.S. Patent 2,847,477 followed by, if desired,
sulfonation, phosphorylation, phosphonation or carboxylation of the
monomer via well-known techniques. They may conveniently be
prepared via a ring opening reaction of the epoxy group of an allyl
glycidyl ether precursor. Synthesis of these monomers are disclosed
in U.S. patent 4,659,481 (Chen) and 4,708,815 (Chen et al), both
being of common assignment herewith~
It is noted that in the case m which X2 in
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- 10 -
repeat unit (d) is an amino functlonality, the monomer can be
prepared in accordance with the following mechanism:
H Fl
CH2 = CH - CH2 - O - CH2 - C - CH2 + N - H
\l /
O F2
CH2 = CH - CH2 - O - CH2 - CHOH - CH2 - N
It should be mentioned that water soluble terpolymers
comprising monomers E and allyl ether of Formula I may also be used
in this invention. It is also to be understood that minor amount of
additional monomers such as ethylene, styrene, alkylvinyl phosphonic
ac1d, etc. may be added to the polymers.
The number average molecular weight of the water soluble
copolymers of Formula I is not critical and may fall within the Mn
range of from about l,OOO to l,OOO,OOO, desirably, l,OOO to 300,000,
and most desirably 1,500 to 25,000. The key criterion is that the
copolymer be water soluble.
After the desired monomers have been obtained, free
radical polymerization may proceed in accordance with conventional
solution, precipitation or emulsion polymerization techniques.
Conventional polymerization initiators such as azo compounds,
_
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persulfates, peroxides, UV light, etc. may be used. Chain transfer
agents such as a1cohols (preferably isopropanol), amine or mercapto
compounds may be used to regulate the molecular weight of the
polymer. The resulting polymer may be isolated by well known
techniques including precipitat1On, etc. If polymerized in water,
the polymer may simply be used in its aqueous solution.
The polymers should be added to the aqueous system, for
which corrosion inhibiting, and/or deposit control activity is
desired, in an amount effective for the purpose. This amount will
vary depending upon the particular system for which treatment is
desired and will be influenced by factors such as, the area subject
to corrosion, pH, temperature, water quantity and the respective
concentratlons in the water of the potential scale and deposit
forming species. For the most part, the polymers will be effective
when used at levels of about 0.1-500 parts per million parts of
water. The polymers may be added directly into the desired water
system in a fixed quantity and in the state of an aqueous solution,
continuously or intermittently.
The water soluble polymers of the present invention can
also be used with topping agent components in order to enhance the
corrosion inhibition and scale controlling properties thereof. For
instance the polymers may be used in combination with one or more
kinds of compounds selected from the group consisting of inorganic
phosphoric acids, phosphonic acid salts, and polyvalent metal
salts. Such topping agents may be added to the system in an amount
of from about 1 to 500 ppm.
Examples of such inorganic phosphoric acids include
condensed phosphoric acids and water soluble salts thereof. The
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- 12 -
phosphoric acids include an orthophosphoric acid, a primary
phosphoric acid and a secondary phosphoric acid. Inorganic
condensed phosphoric acids ~nclude polyphosphoric acids such as
pyrophosphoric acid, tripolyphosphoric acid and the like,
methaphosphoric acids such as trimetaphosphoric acid, and
tetrametaphosphoric acid.
As to the other phosphonic acid derivatives which are to
be added in addition to the polymers of the present invention, there
may be mentioned aminopolyphosphonic acids such as aminotrimethylene
phosphonic acid, ethylenediaminetetramethylene phosphonic acid and
the like, methylene diphosphonic acid, hydroxyethylidene diphosphonic
acid, 2-phosphonobutane 1,2,4 tricarboxylic acid, etc.
The polymers may be used in combination with yet other
topping agents including corrosion inhibitors for iron, steel,
copper, copper alloys or other metals, conventional scale and
contamination inhibitors, metal ion chelating agents, and other
conventional water treatment agents. Other corrosion inhibitors
comprise tungstate, nitrites, borages, silicates, oxycarboxylic
acids, amino acids, catechols, and aliphatic amino surface active
agents. Other scale and contamination inhibitors include lignin
derivatives, tannic acids, starch, polyacrylic soda, polyacrylic
amide, etc. Metal ion chelating agents include polyamines, such as
ethylenediamine, diethylenetriamine and the like and polyamino
carboxylic acids, such as nitrilo triacetic (NTA) acid, ethylene
diaminetetraacetic acid (EDTA), diethylenetriamine pentaacetic acid,
hydroxyethylethylenediaminetriacetic acid (HEDTA), and salt forms of
the acids mentioned. Synergistic effect may be obtained by
combining the polymers of the invention with surfactants.
_ ....
~32382~
- 13 -
The present polymers can also be used along with chemicals
that are capable to reduce dissolved oxygen in boiler water
systems. These chemicals referred as oxygen scavenger, comprise:
hydrazine, sulfite, bisulfite, hydroquinone, carbohydrazide,
alkylhydroxyamines, and alkylamines, citric acid, ascorbic acid and
its analogs or salt forms, etc. Amines such as morpholine,
cyclohexylamine, ammonia, various alkylhydroxyamines such as
diethylaminoethanol, and dimethyllsopropanolamine may be used with
the polymers of the invention in steam generating systems.
The water soluble polymers may be added separately to the
aqueous system or may be blended with the above topping agent
compounds and then added in the state of aqueous solution into the
water system either continuously or intermittently.
Examples
The invention will now be further described with reference
to a number of specific examples with are to be regarded solely as
illustrative, and not as restricting the scope of the invention.
The polymers of the invention were prepared in accordance
with the method described above. The fact that polymer were formed
was substantiated by viscosity increase, gel permeation chroma-
tography, IR, 13C and/or 31P NMR spectroscopy. Table I hereinbelow
presents a summary of the physical properties of the copolymers.
~3%382~
- 14 -
TABLE I
Polymer Properties
Brookfield Vis.
Mole cps, 25 C
S ~opolymer CompositionRatio pH (X solids) Mn*
Example 1 MAA/AHPS 3/1 6.7 28.2 (25X) 3,400
Example 2 MAA/AHPS 6/1 7.0 58.3 (25%) 5,800
Example 3 MM/AHPS 6/1 6.2 35.4 (25X) 3.550
Example 4 MAA/AHPS 6/1 6.5 106.4 (30.8X) 13,000
Example 5 MAA/AOP 6.1/1 6.5 113.0 (30g)
Example 6 MAA/AHPP 4/1 5.2 84.4 (25.2X) 8,500
Example 7 MAA/AHPDEA 6/1 9.6 38.4 (25.7X) - -
Example 8 MAA/AHPDEA 6/1 6.4 81.9 (28.7X)
MAA = methacrylic acid [79-41-4]
AHPS = l-allyloxy-2-hydroxypropyl sulfonate [52556-42-0]
AOP = l-allyloxy-2-propanol ~21460-36-6]
AHPP = l-allyloxy-2-hydroxypropyl phosphite [11608-49-6]
AHPDEA = l-allyloxy-2-hydroxypropyl diethylamino [14112-80-2]
* Mn, number average molecular weight, was measured by gel
permeation chromatography (GPC) method using Toyo Soda G-2000 SW
or G-4000 SW column calibrated with polystyrene sulfonate
standards in sodium nitrate solution. Molecular weight results
from GPC depend on the type of column, condition and standards
used.
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Boiler Studies
In order to assess the efficacy of the polymers of the
present invention in inhibiting scale formation in steam generating
systems, research boilers were fitted with two 4,000 watt electrical
heater probes, giYing 185,000 BTU/ft2/hr and about 8 Kg/hr steam.
The boiler feedwater contained the contaminants and treatment agents
g~ven hereinbelow. The boilers were operated for 44 hours per run at
an average of 15 cycles of concentration. At the conclusion of each
run, the deposits were cleaned from the probes with an acid solution
and the deposit densities were then calculated based on the known
probe surface areas. The estimated uncertainties are about 0.2 g/ft2.
TABLE II
Phosphate Precipitation/Polymer Program
Condition: sodium sulfite oxygen scavenger, 900 psig, 4 ppm Ca and
1 ppm Mg (as CaC03) in feed water.
Phosphate added to produce about 30 ppm P04.
Treatment Dosage Average D posit
Polymer(ppm active) (g/ft~)
Control 0 8.1
Example 12.5 0.59
Example 15.0 0.28
Example 17.5 0.20*
Example 110.0 0.18
Example 22.5 0.40*
Example 25.0 0.27
Example 27.5 0.45*
Example 210.0 0.36
*Average of two runs.
... :
.
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- 16 -
TABLE I~ (Continued)
Phosphate Precip~tation/Polymer Program
Condition: sodium sulf~te oxygen scavenger, 900 psig, 4 ppm Ca, and
1 ppm Mg (as CaC03) in feed water.
Phosphate added to produce about 30 ppm P04.
Treatment Dosage Average De2posit
Polymer (ppm active) (g/ft )
Example 3 2.5 0.38*
Example 3 5 0 0 27
Example 3 10 0 0 35
Example 5 2.5 0 25
Example 5 5.0 0 24
Example 5 10.0 0.24
Example 6 5.0 0 26
Example 6 10.0 0 20
Example 6 20.0 0.56
Example 7 2.5 0 99
Example 7 5.0 0 22
Example 8 5.0 2.19
Example 8 10.0 0 21
Example 8 20.0 0 41
*Average of two runs.
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TABLE III
Chelant/Polymer Program
Cond~tion: sod~um sulfite oxygen scavenger, 900 psig, 4 ppm Ca,
1 ppm Mg, and 1 ppm Fe in feedwater, stolchiometr~c
amount of EDTA added.
Treatment Dosage Average D2eposit
Polymer(ppm active) (g/ft )
Control 0 2.0-3.0
Example 12.5 0.79
Example 15.0 0-49
Example 15.0 0.19
Example 22.5 2.5
Example 25.0 0.65
Example 25.0 0 25
Example 32.5 0.24
Example 35.0 1.05
TABLE IV
Coord~nated Phosphate/pH~Polymer Program
Condition: Hydrazine oxygen scavenger, 1450 psig, 5 ppm Fe in
20feedwater, phosphate added to produce 7 ppm P04 as Ca
.
Treatment Dosage Average Deposit
Polymer(ppm active) (9/ft2)
Example 15.0 2.55
Example 25.0 2.2
PMA 5.0 0.93
PMA = polymethacrylic acid
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- 18 -
TABLE V
All Polymer Program
Condition: sodium sulf~te oxygen scavenger, 600 psig, 4 ppm Ca,
1 ppm Mg, and 1 ppm Fe in feedwater
Treatment Dosage Average Deposit
Polymer (ppm active) (g/ft2)
Example 4 0 4.08
Example 4 38 0.64
Example 4 76 0.39
Example 4 126 0.22
Example 4 151 0.17
Example 4 504 0.15
It is to be understood that the above boller studies in no
way limit the utility of the present invention for other boiler
treatment programs.
While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous other
forms and modifications of this invention will be obvious to those
skilled in the art. The appended claims and this invention generally
should be construed to cover all such obvious forms and modifications
which are within the true spirit and scope of the present invention.
