Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
S P E C I F I C A T I O N
TITLE OF THE INVENTION
CORROSION INHIBITOR
BACK&ROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a composition
and a method for using the same for the prevention of
ferrous metals in machines and equipment for using water
in the petroleum industry, chemical industry, paper making
industry, iron industry, and other industries.
2~ Description of the Prior Art
In view of the worsening supply condi-tion of
industrial water, efforts are being made to save water by
recycling. For instance, efforts are being made to reduce
water to be discharged from the water cooling system and
to run the boiler without blowing water. Recycling of
water, however, involves problems. The recycled water
increases in concentration of salts, which leads to the
formation of scale and to cause corrosion of metals in
contact with it. Thus, the measure for these problems,or
the treatment of recycled water, is a matter of great im-
portance.
In order to solve the problems, we have proposed
~L~ 7~
a corrosion inhibitor composed of gluconic acid or a salt
thereof, a molybdate, and a specific acrylic acid polymer,
for high concentrated recycli.ng water (Japanese Patent
Publication No. 43376/1978); a corrosion inhibiting compo-
sition of an aliphatic dicarboxylic acid, molybdate and
nitrite (Japanese Unexamined Patent Publication No.62181/
1978) and a corrosion inhibitor of an aliphatic dicarboxy-
lic acid and nitrite (Japanese Unexamined Patent Publica-
tion No. 62182/1978). A further corrosion inhibiting com-
position of polymaleic acid, an aliphatic hydroxycarboxylic
acid, zinc ion and a triazole was proposed in JapaneseUnexamined Patent Publication No. 149836/1978.
SUMMARY OF THE INVENTION
The present invention provides a corrosion inhibi-
tor for ferrous metals such as iron, mild steel, and cast
iron in water systems, which can exhibit an excellent
effect when added to water, especially high concentrated
recycling water in an apparatus such as heat exchanger,
- cooler, radiator, boiler and so forth.
More particularly, this invention provides a
corrosion inhibitor which contains as the active ingredients:
(a) one or more inorganic acid components of molybdic acid
or its alkali salt, tungstic acid or its alkali sal-t, or
alkali salt of nitrous acid;
(b) an aliphatic hydroxycarboxylic acid or aliphatic di-
carbo~ylic acid having up to seven carbon atoms or salt
thereof;
(c) an inorganic heavy metal com~ound which may readily
release a heavy metal ion in water; and
(d) a water-saluble polymer component having a molecular
weight in the range of 500 to 100,000, of a homo- or co-
polymer of acryl~c acid, methacrylic acid or maleic acid;
a copolymer of any of said three monomers with other co-
polymerizable compound having an ethylenic double bond;
or a mixture of said homopolymer and copolymer.
`:
-` - The inhibitor of this invention is non-phosphorous
~ composition and is highly effective for preventing ferrous
-- - metal corrosion in high concentrated water recycling system~
or a ~oiler operating at a high temperature of 100 - 200C,
-`~ ; coinciden-tly preventing scale formation in such a system.
PREFERRED E~IBODIMENTS OF THE INVENTION
The alkali salts of molybdic acid, tungstic acid,
-` and nitrous acid which are used in this invention include,
for example, alkali metal salts such as lithium sal-t, so-
dium salt, and potassium salt, and arnmonium salt Econo-
: mically preferable among therr; are sodium molybdate, ammo-
nium molybdate, sodium tungstate, sodium nitrite, and
ammonium nitrite. They may be used in combination.
The aliphatic hydroxycarboxylic acid having
the carbon number of 7 or less that is used in this inven-
tion includes, for example, glycolic acid, citric acid,
malic acid, tartaric acid, lactic acid, gluconic acid,
and tartronic acid. The aliphatic dicarboxylic acid
having the carbon number of 7 or less includes, for example,
glutaric acid, adipic acid succinic acid.
The salts of the above-mentioned carboxylic acids
include, for example, alkali metal salts such as lithium,
sodium or potassium salt and ammonium salt; and salts with
aliphatic amines having 6 or less carbon atoms such as mono,
di or tri-alkylamine (e.g., methylamine, ethylamine, propyl-
amine, butylamine, pentylamine, hexylamine, or dimethylamine,
diethylamine or dipropylamine, or trimethylamine or tri-
ethylamine), cyclic alkylamine (e.g., cyclohexylamine or
morpholine), or mono, di or tri-hydroxyalkylamine (e.g~,
ethanolamine, propanolamine, 3-hydroxy-2-methyl-propylamine,
diethanolamine or dipropanolamine).
If the hydroxycarboxylic acids or dicarboxylic
acids having a carbon number greater than 7 are used, the
resulting corrosion inhibitor decreases in corrosion in-
hibiting effect and in solubility in wa-ter. In addition,
if they are used in the form of salt, the resulting cor-
rosion inhibitor causes foaming due to increased surface
activity and combines with the compounds that make water
hard to form insoluble salts which pass into sludge and
scale.
If a salt of the hydroxycarboxylic acid or di-
carboxylic acid with an aliphatic amine having 7 or more
~7~
is used, the resulting corrosion inhibitor will increase
in surface activity.
Preferable among the above-mentioned components
(b) are gluconic acid, succinic acid, citric acid, malic
acid, glutaric acid, and adipic acid, and sodium salts,
cyclohexvlamine salts, and morpholine salts thereof.
Citric acid, malic acia, and gluconic acid, and
sodium salt, ammoniul~ salt, cyclohexylamine salt, and
morpholine salt thereof are preferable in the case where
an aliphatic hydroxycarboxylic acid is used. Glutaric acid,
succinic acid, and adipic acid, and sodium salt, ammonium
salt, cyclohexylamine salt, and morpholine salt thereof
are preferable in the case where an aliphatic dicarboxylic
acid is used.
In the meantime, if an aliphatic monocarboxylic
acid or salt thereof (e.g., acetic acid, propionic acid,
and salt thereof), which is a homologue of the aliphatic
hydroxylcarboxylic acid and dicarboxylic acid, is used, the
outstanding corrosion inhibiting effect of this inven-tion
cannot be obtained. This suggests that the action on metals
differs even among homologous compounds, depending on the
functional group contained -therein.
The compound that readily may release a heavy
metal ion in water includes, for example, sulfates, chlo-
rides, nitrates, and sulfamates of zinc,manganese, tin,
cobalt, nickel, titanium, copper, and lead, and mi.YtureS
- 5 -
~7~
thereof. Preferable among them are salts of manganese,
tin, zinc and nickel~ The first two are particularly
preferable when the cor.-osion inhibitor is added to boiler
water.
The polymer or copolymer of acrylic acid, metha-
crylic acid, or maleic acid which is used in this invention
is a water-soluble polymer which has a molecular weight of
500 to 100,000, preferably 500 to 20,000. Examples of
such polymer or copolymer include homopolymers of acrylic
acid, methacrylic acid, or maleic acid or mixtures thereof;
and copolymers or terpolymers thereof; copolymers of one
of said three monomers and a copolymerizable compound hav-
ing a ethylenic double bond such as methyl acrylate, ethyl
acrylate, methyl methacrylate, ethyl methacrylate, acryl-
amide, methacrylamide, acrylamide-N-propanesulfonic acid,
fumaric acid, itaconic acid, and vinyl alcohol, whose co-
polymers are composed of at least 20 mol% of any of said
three monomers, preferably 50 mol% or more. Preferable
among them are acrylic acid homopolymer, methacrylic acid
homopolymer, maleic acid homopolymer, acylic acid-methacylic
acid copolymer, acrylic acid-maleic acid copolymer, meth-
acrylic acid-maleic acid copolymer, acrylic acid-acrylamide
copolymer, acrylic acid~acrylamide-N-propanesulfonic acid
copolymer, and acrylic acid-methacrylic acid-methyl acrylate
terpolymer.
The above-mentioned homopolymers or copolymers
~7~
should be soluble in water and have a molecular weight
of about 500 to 100,000. Those which have a molecular
weight greater than about 100,000 is not preferable,
because it tends to show a flocculation even though it is
soluble in water. From the standpoint of ease of synthe-
sis, an acrylic acid polymer or methacrylic acid polymer
having a molecular weight of about 1,000 to 20,000 is
preferred and a maleic acid homopolymer having a molecular
weight of about 500 to 2,000 is preferred. If the polymer
is not readily soluble in water even though it has a mole-
cular weight in the specified range, it may be made solu-
ble by converting the free acid or ester thereof in the
polymer molecule into a soluble salt (alkali metal salt,
ammonium salt, or amine salt).
The above-mentioned four components are formu-
lated into a liquid formulation or mixed directly into a
powdery formulation. The aqueous solution should be
neutral to alkaline. If it is acidic, molybdic acid or
tungstic acid liberates and condenses, or the nitrous acid
deco~oses, ort'nealiphatic hydroxycarboxylic acid oxidizes
slowly. Thus, it is desirable to add an alkali such as
sodium hydroxide and lower amine to adjust the pH.
The preferred weight ratio that permits the four
components to exhibit their synergistic effect is
1 : 0.2 - 30 : 0.1 - 5 : 0.1 - 5, preferably 1 : 0.5 -
10 : 0.1 - 1.5 : 0.2 - 1.6, for (a) : (b) : (c) : (d)
by weight. In the case of liquid formulation, the total
concentration of the four components is dependent on the
solubility and pH of each component. A concentration of
5 to 60 wt% is suitable from the standpoint of stability -
of the formulation. In addition, the liquid formulation
may contain a small quantity of stabilizer and other ad-
ditives.
The formulation composed of the above-mentioned four
components should be added to water in an amount of 1 to
200 ppm, preferably 15 to 100 ppm, in terms of the total
quantity of the four components, depending on the water
quality and the area that requires corrosion inh;.bition.
Thus, the present invention also provides the method
for the co-rrosion inhibition of metals by adding the
above-mentioned four compounds (a), (b), (c), and (d).
Each the active ingredients may be added to water indi-
vidually in the form of single formulation.
The corrosion inhibitor of this invention is effective
6~
for pr-~venting heat e~ch~ngers, coolers, radiators, boilers,-and
the like ~rom water corrosion. It is particularly effec-
tive when added to recvcled water which contains salts
at high concentrations. It protects ferrous metals from
corrosion and pitting corrosion and prevents the forma-
tion of scale.
It is nct elucidated yet how the four components
of this invention act on t~e metal surface, but it is
believed that they form a strong protective coating due
to the combined effect of their passivating action,
dispersing action, and film forming action, in view of
the fact that the effect o the four components is much
better than that of any three components of them.
The invention is now described in detail with ref-
erence to the following non-limitative examples.
TEST 1
Corrosion inhibition tests were conducted as fol-
lows using corrosion inhibitors composed of the above-
mentioned four ccimponents in varied quantiti.es.
A mild steel test piece (tradç name: SPCC) ~.easuring
30 x 50 x 1 mm, suspended by a stainless steel sti~ring
rod, was immersed in one liter of test liquid containing
chemicals at pLedetermined concentrations, contained in
a flat bottcim beaker enclosed in a circular ~antle heater
in which water temperature is kept constant by a ther~o-
~'7~ 3
stat. The stirring rod was turned by a motor at a rate
of 100 rpm. The tests were carried out for five days
with agitation while keeping the water temperature at
50C. The test water was prepared by concentrating
city water (Osaka City) five times. The quality of
the tes~ water is shown in Table 1.
Table 1
Item Value
_
pH 8.3
Electric conductivity (~s/cm) 910.2
P alkalinity (ppm) 0
M alkalinity (ppm) 71.0
Total hardness (ppm)238.8
Chloride ion (ppm) 94.5
Sulfate ion (ppm) 172.0
Silica (SiO2) (ppm) 28.5
Total iron (ppm) 0.50
Calcium hardness (ppm)190.0
A-fter the prescribed period of test, the test
piece was removed and dried. The weight Ml (mg) was
measured. The test piece was then treated according
to JIS K-0101. After drying, the weight M2 (mg) was
- 10 -
~ ~ 76~
measured. The m.d.d. (mg/day.dm2) was calcurated
according to the following formula.
m.d.d. = (A - M2)~(B x C) = D/0.3142 x 5
where:
A : ~eight (mg) of test piece before testing,
B : Area (dm2) of test piece,
C : Number of days of test, and
D : Corrosion weight loss.
After completion of test, 500 ml of the test liquid
was filtered using Toyo Filter Paper No. 6 and the weight
of the solids was measured after drying at 110C for one
day. The weight of the substance formed on the test piece
was calculated by subtracting M2 from Ml. The quantity of
scale formed from 1 liter of test liquid is defined by the
following formula.
Scale (mg/liter) = P x 2 + (Ml - M2)
where P : dry weight of precipitates.
The results obtained in Examples and Comparative
Examples are shown in Table 2.
r~49
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It is to be noted from Table 2 that the corrosion
inhibitors composed of the four components according
to this invention are superior to the conventional
corrosion inhibitors composed of three components of
sodium m~lybdate, sodium gluconate, and polyacrylate.
It is also to be noted that the corrosion inhab-
itors of this invention decreases the quantity of
scale to a great extent.
TEST 2
Several formulations composed of the four com-
ponents of this invention were prepared as shown in
Table 3. Using these formulations, the same tests
as in TEST 1 were carried out. The results are
shown in Table 3.
:~ 7~
Table 3
Concentration Quantity
I of corrosion of scale
No. Formulation (wtg6) ~ inhibitor (ppm) (mg/l) m.d.d.
1 Sodium molybdate 10% ~
Sodium gluconate 15g6 ¦
Zinc chloride 2% 1
Sodium hydroxide 1% ¦ 100 5.7 3.3
Acrylic acid-metha-
crylic acid copolymer
(1:1) (MW: 4000) 3%
Water 69% 1
. __
2 Sodium tungstate 3%
Sodium gluconate 20%
Stannous chloride 3%
Sodium hydroxide 0.5% ~ 100 5.8 4.0
Acrylie acid-metha-
crylic acid-methyl
acrylate terpolymer
(2:2:1) (MW: 4500) 3%
Water 70.5%
_ ! _ _
3 Sodium molybdate lOgo
Sodium gluconate 10%
Sodium citrate 5g6
Sodium hydroxide 1%
Zinc chloride 1% 100 5.7 3.5
Polyacrylic acid 4gO ¦
(MW: 8000)
Water 69% ;
Table 3 (cont'd)
4 Sodium molybdate 5% ¦
Dimorpholine salt
of adipic acid 5%
Morpholine salt
of gluconic acid 15~ 100 6.3 3.5
Stannous chloride 3~
Acrylic acid- 3%
maleic acid co-
polymer
Water 69%
~.~ 7~!~D49
TEST 3
The following tests were conducted for medium- and
low-pressure boilers. The SPCC test piece as used in
TEST 1 was attached to an apparatus which rotates
the test piece at 100 rpm in an autoclave containing
800 ml of test water. The test piece was subjected to
corrosion at 200C under a prssure of 16 kg/cm2 for 2
days. For accelerated corrosion, the test water was
prepared by concentrating city water (Osaka City) 20
times and adjusting to pH 9. A prescribed quantity
of the corrosion inhibitor was added to the test water
and the test piece suspended by the stirring rod was
immersed in the test water.
The corrosion weight loss of the test pieces was
measured, and the number of pittings was counted. The
quality of the test water is shown in Table 4 and the
results are shown in Table 5.
- 18 -
Table 4
I _ Value
pH 9.0
Electric conduc~i.vity (~s/cm) 3750
P alkalinity (ppm) 35
M alkalinity (ppm) 470
Total hardness (ppm) 0
Chloride ion (ppm) 530
Sulfate ion (ppm) 520
Silica (ppm) 144.0
Total iron (ppm) 0.1
-- 19 --
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- 21 -
~'7~
It is ~:o be noted from the above results that the
corrosion inhibitor of this invention is also effective
to prevent pitting. Especially the corrosion inhibitor
containing tin or manganse ions of this invention is
effective for corrosion prevention of boilers.
- 22 -
