Note: Descriptions are shown in the official language in which they were submitted.
FIELD OF THE INVENTION
The present invention relates to the inhibition and
prevention of corrosion of ferrous-based metals which are
in contact with an aqueous system. More particularly,
this invention relates to a method wherein an ortho-
hydroxybenzenephosphonic acid is added to the aqueous
system in an amount effective to inhibit corrosion of the
ferrous based metal.
BACKGROUND OF THE INVENTION
Iron and iron-based metal-containing alloys, such as
mild steel, are well-known materials used in constructing
the apparatus of aqueous systems. In these systems water
circulates, contacts the ferrous-based metal surface, and
may be concentrated, such as by evaporation of a portion
of the water from the system. Even though such metals
are readily subject to corrosion in such environments,
they are used over other metals due to their strength and
availability.
It is known that various materials which are
naturally or synthetically occurring in the aqueous
systems, especially systems using water derived from
natural resources such as seawater, rivers, lakes and the
like, attack ferrous-based metals. The term "ferrous-
based metals", as used herein, shall mean iron metal and
metal alloys containing iron therein, i.e., ferrous
metals. Typical devices in which the ferrous-metal parts
are subject to corrosion include evaporators, single and
multi-pass ~eat exchangers, cooling towers, and
associated equipment and the like. As the system water
passes thro~lgh or over the device, a portion of the
system water evaporates causing a concentration of the
dissolved malterials contained in the system. These
materials reach a concentration at which they may cause
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severe pitting and corrosion which eventually requires
replacement of the metal parts. Various corrosion
inhibitors have been previously used.
For example, chromates and inorganic phosphates or
polyphosphates have successfully been used to inhibit the
corrosion of metals in aqueous systems. The chromates,
though effective, are highly toxic and, consequently,
present handling and disposal problems. While inorganic
phosphates are nontoxic, due to the limited solubility of
calcium phosphate, it is often difficult to maintain
adequate concentrations of phosphates in aqueous systems
containing hard water. The polyphosphates are also
relatively non-toxic, but tend to hydrolyze to form
orthophosph~te, which like phosphate, can create scale
and sludge problems in aqueous systems (e.g. by combining
with calcium in the system to form calcium phosphate)~
Moreover, where there is concern over eutrophication of
receiving waters, excess phosphate compounds can serve as
a nutrient source which results in disposal problems.
Borates, nitrates, and nitrites have also been used for
corrosion inhibition. These too can serve as nutrients
in low concentrations, and/or represent potential health
concerns at high concentrations.
In addition, environmental considerations have also
recently increased concerns over the discharge of other
metals such as zinc, which previously were considered
acceptable for water treatment.
Much recent research has been concerned with the
development of organic corrosion inhibitors which can
reduce reliance on the traditional inorganic inhibitors.
Among the organic inhibitors successfully employed are
numerous organic phosphonates. These compounds may
generally be used without detrimentally interfering with
other conventional water treatment additives. There is a
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continuing need, however, for safe and effective water
treatment agents which can be used to control corrosion.
U.S. Patent No. 3,630,790 discloses a method for
protecting thin metal films, particularly aluminum films,
by contacting the metal film with a solution in a polar
organic solvent of one of a number of organophosphonic
acids, including benzenephosphonic acid. The combination
of benzenephosphonic acid and a water-soluble
orthophosphate was reported in U.S. Patent No. 3,837,803,
to inhibit the corrosion of metallic parts, particularly
those made of high carbon steel, that are in contact with
aqueous systems. The presence of the ortho-phosphate
compound was considered essential for this treatment
program to operate. The use of combinations of
benzenephosphonic and a water soluble organic or
inorganic polyphosphate to inhibit the corrosion of metal
parts in contact with an aqueous system containing
solubilized calcium salts is disclosed in G.B. Patent No.
1,386,718. It is noted that the presence of the
polyphosphate compound is essential for this treatment
program to operate.
SUMMARY ~F THE INVENTION
It is an object of this invention to provide a
method of ir~hi~iting the corrosion of ferrous-based
metals in contact with an aqueous system.
In accordance with the present invention there has
been provided a method of inhibiting corrosion of
ferrous-based metals in contact with an aqueous system,
wherein an ortho-hydroxybenzenephosphonic acid is added
to the aqueous system in an amount effective to inhibit
corroslon .
DETAILED DESCRIPTION
This invention is directed to the use of certain
ortho-hydroxybenzenephosphonic acid compounds as
corrosion control agents for treating aqueous systems.
The ortho-hydroxybenzenephosphonic acid compounds of this
invention have the general ~ormula:
R3 - ~ PO
R2 OH
Rl
wherein R1, R2, R3 and R4 independently are hydrogen,
alkyl, alkoxy, halogen, carboxy or -SO3H; preferably
hydrogen or alkoxy; most preferably hydrogen or methoxy
and water soluble salts thereof.
The ortho-hydroxybenzenephosphonic acid of this
invention can be prepared according to the teaching of B.
Dhawan and D. Redmore, J. Org. Chem. 49, 4018-4021
(1984), which is incorporated herein by reerence in its
entirety. Treatment of a hydroxybenzene compound with a
dialkyl phosphate in the presence of carbontetrachloride
and a trialkylamine produces a dialkyl aryl phosphate
ester. Treatment of this aryl phosphate ester with an
organolithium reagent produces a dialkyl ortho-
hydroxybenzenephosphonic acid ester. Hydrolysis of the
phosphonic acid ester by sequential treatment with
trimethylsilyl iodide and water produces the
corresponding ortho-hydroxybenzenephosphonic acid
compound.
These ortho-hydroxybenzenephosphonic acid compounds
have been found to be effective for inhibiting corrosion
in aqueous systems. Thus, in accordance with this
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invention, corrosion of metals which are in contact with
an aqueous system may be prevented or inhibited by adding
to the system a corrosion inhibiting amount of the ortho-
hydroxybenzenephosphonic acid compounds of this
invention, or their water soluble salts.
The precise dosage of the corrosion inhibiting
agents of this invention depends, to some extent, on the
nature of the aqueous system in which it is to be
incorporated and the degree of protection desired. In
general, however, the concentration of the ortho-
hydroxybenzenephosphonic acid compound maintained in the
system can be from about 0.1 to about 1,000 ppm. Within
this range, generally low dosages of about 200 ppm or
less are preferred, with a dosage of about 100 ppm or
less being most preferred for many aqueous systems, such
as for example, many open recirculating cooling water
systems. Typically, dosages of about 0.5 ppm or more are
preferred, with a dosage of about 2 ppm or more being
most preferred. The exact amount required with respect
to a particular aqueous system can be readily determined
by one of ordinary skill in the art in conventional
manners. As is typical of most aqueous systems, the pH
is preferably maintained at 7 or above, and is most
preferably maintained at 8 or above.
The corrosion inhibiting compositions of this
invention may be added to the system water by any
convenient mode, such as by first forming a concentrated
solution of the treating agent with water, preferably
containing between 1 and 50 total weight percent of the
ortho-hydroxybenzenephosphonic acid compound, and then
feeding the concentrated solution to the system water at
some convenient point in the system. In many instances,
the treatment compositions may be added to the make up
water or feed water lines through which water enters the
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system. For ~xample, an injection calibrated to deliver
a predetermined amount periodically or continuously to
the make-up water may be employed.
The present invention is particularly useful in the
treatment of cooling water systems which operate at
temperatures between 60 and 200F, particularly open
recirculating cooling water systems which operate at
temperatures of from about 80F to 150F
It will be appreciated that while the chemical
corrosion inhibiting compositions of this invention may
be used as the sole corrosion inhibitor for the aqueous
system, other conventional water treatment compositions
customarily employed in aqueous systems may
advantageously be used in combination with th~ claimed
treatment agents. Thus, other water treatmen~ additives
which may be used include, but are not limited to,
biocides, scale inhibitors, chelants, sequestering
agents, dispersing agents, other corrosion inhibitors,
polymeric agents (e.g. copolymers of 2-acrylamido-2-
methyl propane sulfonic acid and methacrylic acid orpolymers of acrylic acid and methacrylic acid), and the
like.
Without further elaboration, it is believed that one
of skill in the art, using the preceding detailed
description, can utilize the present invention to its
fullest extent.
The following example is provided to illustrate the
invention in accordance with the principles of this
invention, but is not to be construed as limiting the
invention in any way except as indicated in the appended
claims.
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Example 1
The corrosion inhibitor activity of several
representative compounds of this invention is
demonstrated by an Aerated Bottle Test as described in
the following procedure which used two standard corrosive
waters with the following compositions:
Water A
30 ppm CaCl2
37 ppm MgS04
100 ppm Na2S04
50 ppm NaCl
100 ppm Na2C03
Water B
166.5 ppm CaCl2
60 ppm MgS04
150 ppm Na2S04
212 ppm Na2C03
Mild steel coupons (4.5 in x 0.5 in) were immersed
in 15% hydrochloric acid for 15 minutes, then rinsed
se~uentially in saturated sodium bicarbonate solution,
distilled water and isopropanol, dried and stored in a
desiccator. They were weighed prior to being used in the
corrosion test.
The desired amount of corrosion inhibitor was
dissolved in 850 ml of one of the standard corrosive
waters listed above. The solution was heated in a
thermostatted bath at 55C. After the temperature had
equilibrated, the pH of the solution was adjusted to 8.5.
Two coupons were suspended in the solution and air was
passed into the solution at 250 ml/min. After 48 hours,
the coupons were removed and cleaned with steel wool,
rinsed, dried, and weighed again. The rate of corrosion
_g_ ~ ~ ?~
was calculated from the weight loss and was expressed in
mils per year (mpy). Corrosion inhibition was expressed
as the reduction in the rate of corrosion relative to an
untreated blank calculated according to the formula:
% Corrosion Inhibition =
(Corrosion Rate of Untreated Blank-Corrosion Rate with Treatment) x 100
Corrosion Rate of Untreated Blank
An effective corrosion inhibitor will reduce the
corrosion rate by at least 80% compared to the blank.
The results shown in Table 1 demonstrate that the
ortho-hydroxybenzenephosphonic acids of this invention
were effective corrosion inhibitors. This was surprising
and unexpected particularly since those benzene-
phosphonic acids lacking the ortho-hydroxy substituent
were ineffective corrosion inhibitors, even when present
at a high concentration.
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Table 1
~osage% Corrosion Inhibition
Inhibitor fPPm) .Water AWater B
2-hydroxybenzenephos- 150 92 92
phonic acial 100 52 62
2-hydroxy-3-methoxy- 150 86 93
benzenephosphonic 125 82
acid 100 66 91
- 63
2-hydroxy-5-methoxy- 150 95
benzenephosphonic 125 - 79
acid 100 89
42
Comparison Compound 1 200 25
(benzenephosphonic 150 26 39
acid)
Comparison Compound 2 200 40
(2,3-Dimethoxybenzene- 150 - 39
phosphonic acid)
