CA1159246A

CA1159246A - Corrosion inhibitors

Info

Publication number: CA1159246A
Application number: CA000381755A
Authority: CA
Inventors: Edwin J. Latos; John C. Payne
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 1980-07-21
Filing date: 1981-07-15
Publication date: 1983-12-27
Also published as: AU7344981A; JPS5741381A; PH18729A

Abstract

"CORROSION INHIBITORS"

ABSTRACT

Corrosion and scale inhibiting compositions which are useful in recirculating aqueous systems comprise a mixture of a phosphate com-pound, a phosphonate compound, an aryl triazole, and a salt of a metal selected from the group consisting of molybdenum, tungsten and chromium.
The components of the mixture are present in an amount of at least 0.5 and not greater than 50% of the total composition. An example of an effective anticorrosion composition comprises a mixture of sodium tri-polyphosphate, 1-hydroxyethyledene-1, 1-triphosphonic acid, benzotriazole, and sodium molybdate, said composition being present in an amount of from about 5 to about 5000 ppm.

Description

~ 15924~

"CORROSION INHIBITORS"

BACKGROUND OF THE INVENTION

In many industrial applications it is necessary to use aqueous solutions or water for a variety of purposes such as heat transfer sys-tems in which the water ~s used in heat exchangers, cooling towers, chillers, etc. The water will come in contact with metal surfaces of the system and, when being used in a recirculating system after being exposed to or saturated with air will have a tendency to sorrode the metal surfaces with which it comes in contact with. In addition, when utilizing water in a recirculating system, the metal salts which are inherently present in certain types of water such as calcium, magnesium~
etc., will tend to depos1t out on the surface of the meta'l to cause a scale. The presence of this scale on the surface of the metal will ; inhibit the heat transfer capability of the meta'l and thus reduce the efficiency of the system.
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It is there~ore imperative that the deposition of scale and ; ~ 15 the corrosion of the metal surfaces of the heat transfer equipment be ~' minimi~ed. The minimization of these problems can be accomplished by the addition of corrosion inhibitors to the water. In many instances different types of metals are used in the apparatus including iron, in the form of steel9 aluminum~ coppery etc. Copper is known as an accelerator for the corrosion of iron and therefore any corrosion inhibitor must include a copper chelating component in order to again minimize the corrosion of the metal.
The prior art has disclosed many compositions which are used to inhibit the corrosion of metal in heat transfer systems. For example, ~mongothers, U. S. Patent 3,985,671 discloses a scale control agent ,~

1 1592~S

comprising a mixture of a polyaminoalkylenephosphonate and poly[oxy-ethylene(dimethyliminio)ethylene(dimethyliminio)ethylenedichloride] and U.S. Patent 4,176,059 which discloses a corrosion inhibiting compound comprising a mixture of a soluble molybdate ion, a water soluble or dis-S persible organic non-ionic or cationic surfactant, a water soluble poly-phosphate and an azole. The surfactants which are employed in this patent comprise substituted polyethylene oxide compounds which in one variety include polyamine substituents.
As will hereinafter be shown in greater detail, the use of a composition containing a phosphate compound9 a phosphonate compound, an aryl triazole and a metal salt in wh;ch the metal is either molybdenum9 tungsten or chromium will exhibit greater corrosion inhibiting properties than other compositions which may be similar in nature but do not contain the aforementioned four components.

~` 15DESCRIPTION OF THE INVENTION

This invention relates to novel compositions wh;ch may be used as corrosion inhibitors. More specifically, the invention is concerned ; with novel compositions comprising an admixture of a phosphate compound, a phosphonate compound, an aryl triazole and a metal salt, said composi-tion exhibiting superior properties in the abil;ty to retard corrosion of metal surfaces which are used in heat transfer equipment.
~; As hereinbefore set forth, various compositions of matter have been utilized to prevent the corrosion of metal surfaces, as well as the build-up of scale on said surfaces. It has now been discovered that certain compositions of matter of a type hereinafter set forth in greater detail wil~ exhibit superior characteristics when compared to those which have been known in the prior art. These compositions will Qnable a heat transfer apparatus to be utilized for a longer period of time without 1 1592~

havin~ to shut down and replace any metal parts which have become cor-roded due to the pres-ence of certain metal ions in water.
It is therefore an object of this invention to provide an improved corrosion inhibitor composition.
In one aspect an embodiment of this invention is found in a composition for the prevention of corrosion comprising a mixture of a phosphate compound, a phosphonate compound, an aryl triazole and a salt of a metal selected from the group consisting of molybdenum, tungsten and chromium.
A specific embodiment of this invention comprises a composition comprising a mixture of sodium tripolyphosphate~ l-hydroxyethylidene-l,l-diphosphonic acid, ben~otriazole and sodium molybdate.
Other objects and embodiments will be found in the following further detailed description of the present invention.
As hereinbefore set forth, the present invention is concerned with an improvement in the corrosion inhibition activity of compositions of matter which can be obtained by utilizing a novel blend of various components. One component of the composition of matter of the present ; invention comprises a phosphate compound, specific examples of these com-pounds, including sodium tripolyphosphate, potassium tripolyphosphate, lithium tripolyphosphate, tetrasodium pyrophosphate, tetrapotassium pyro-phosphate, tetralithium pyrophosphate, rubidium tripolyphosphate, cesium tripolyphosphate, tetrarubidium pyrophosphate, tetracesium pyrophosphate, ~ disodium orthophosphate, trisodium orthophosphate, dipotassium ortho-phosphate, tripotassium orthophosphate, dilithium orthophosphate, tri-lithium orthophosphate, etc.
The second component of the 4 component composition will com-prise a phosphonate compound, specific examples of this phosphonate ~ ~5~24~

component ;ncluding l-hydroxyethylidene-l,l-diphosphonic acid, nitri-lotris (methylene) triphosphonic acid, amino tri(methylidene)phosphonic acid, amino tri~propylidene) phosphonic acid, etc.
The third component of the composition of the present invention . .
comprises an aryl triazole sù~ as 1,2,3-benzotriazole, 1,2,4-benzotri-azole, l,3,5-benzotriazole9 2,3,4-tolyltriazole, 2,3,5-tolyltriazole, etc.
The fourth component of this composition comprises a salt of a metal selected from the group consisting of molybdenum, tungsten and chromium. In particular, the salt of the metal is water-soluble in nature, specific examples of these salts including sodium molybdate, patassium molybdate, lithium molybdate, rubidium molybdate, cesium molyb-date, sodium tungstate, potassium tungstate, lithium tungstate, rubidium tungstate, cesium tungstate, sodium chromate, potassium chromate, lithium chromate, rubidium chromate, cesium chromate, ammonium molybdate, ammonium tungstate, ammonium chromate, etc. It is i31so contemplated that molybdenum may be introduced into the mixture by utilizing molybdic aci as the source. Inasmuch as the ~inal corrosion inhibitor composition will con-; tain a sufficient amount of a caustic or basic compound to insure a p~
of about 10 for said composition it is poss;ble to use the acid which will form a molybdate salt. It is to be understood that the after-mentioned phosphate compounds, phosphonate compounds, aryl triazoles and metal salts are only representative of the class of compounds ~hich may be improved, and that the present invention is not necessarily limited thereto.
~ The four components of the mixture ~ill be present therein in an amount of at least 0.5%, and not greater than about 50% of the composi-tion. Preferred ranges will comprise from about 0.5% to about 7% of the phosphonate compoundi from about 0.5% to about 5% of the aryl triazole and from about 0.5% to about 7% by ~eight of the metal salt, the remainder of ~ 1S9246 the final composi~ion ~ei~g wat~r p7us a caustic. The desired composi-tion may be prepared by admixing all of the components and thereafter dissolving the components in water, plus the addition of a caustic substance. The latter is present in the event that the starting material comprises a metal acid, which, when reacted with the caustic substance, will provide the desired metal salt. It is contemplated within the scope of this invention that the corrosion inhibitor composition may ~ also be utilized in solid form. When this form is desired, the 4 com-; ponents are admixed in the proper proportions and thereafter added in this form to the heat transfer fluid, which usually comprises water.
The corrosion inhibitor composition in either solid or liquid form is added to ~he water system, so that the concentration of the com-position in the water will be in a range of from about 5 to about 5000 ppm. By utilizing the composition in this concentration, it is possible to inhibit the formation of scale on the surface of the equipment, as well as preventing the corrosion3 by pitting or over-rusting the equip-ment. In the referenced embodiment of the invention the various components will be present in the system in various r~nges. For example, the phos-phate compound wi11 be present in such an amount so as to provide a con-centration in the water system in the range of from about 2.9 to about2900 ppm. Likewise, the phosphonate compound will be present to provide a concentration in the water system of from about 1.44 to 1440 ppm; the aryl triazole in a concentration of from about 0.72 to about 720 ppm and ~ the salt of a metal of the type hereinbefore set forth in a concentration

2~ of from about 1.0 to about 1000 ppm of the water system.
It is also contemplated within the scope of this invention that the final inhibitor composition may also contain, if so desired, a com-pound which will act as an anti-foulant or silt dispersant, a1though the 1 1592~L6 presence of such a compound is not necessarily required for the ability of the rem~ining components of the composition to function as corrosion inhibitors. The anti-foulant or silt dispersants may comprise polyacryl-ate or polymethacrylate compounds such as sodium polyacrylate, potassium polyacrylate, sodium polymethacrylate, potassium polymethacrylateg poly-acrylic acids having a molecular weight varying from about 800 to about 10,000; maleic acids such as polyethylene maleic acid, polystyrene maleic acid, etc. The aforementioned anti-foulants or silt dispersants will preferably be present in the final corrosion inhibitor composition in a range of from about 1 to about 5% by weight of the composition.
The following examples are given for purposes of il'lustrating the compositions of the present invention and to the increased efficiency by the use thereof. However, it is to be understood that the examples are illustrative in nature only, and that the present invention is not ; 15 necessarily limited thereto.
EXAMPLE I
The equipment which was used to perform the ~'ollowing experi-ments comprised a circulating loop having a 22 liter reservoir. In 2 ~ legs of the loop metal coupons mounted on a Rulo ~holder comprising copper ; ~Q and steel were inserted. In addition, at various other points in theloop the apparatus was provided with a pH electrode connected to a pH
meter, a dissolved oXygen electrode, a Corrosometer, thermocouples placed to monitor the temperature, a paddle whee'l flowmeter and a pump for cir-~ culation of the test solution. The apparatus was washed ~wice at room temperature with a synthetic cooling tower water blend and once while maintaining the apparatus at a temperature of 140~F.
The particular corrosion inhibitor compositions were prepared by adding the particular compositions to the synthetic cooling tower water ~ 1592~6 in a 5 gallon glass bottle. After thorough mixing, the solution was withdrawn from the bottle through a vacuum aspirator and passed into the circulatin~ 1QP~ After the blend was filled, the loop was brought to operating temDerature, ~hich in the experiments was 140F., and the copper and steel coupons were inserted.
In the first test a solution of sodium molybdate in a concen-tration of 100 ppm was tested for a total of 40 hours. In the second ; testing solution containing 100 ppm of sodium molybdate and 14.4 ppm oF
a phosphonate compound comprising l-hydroxyethylidene-l,l-diphosphonic acid was treated for a period of 48 hours. In the third experiment a solution containing 100 ppm o~ sodium molybdate, 14.4 ppm of the afore-said phosphonate compound and 23 ppm of sodium tripolyphosphate was treated for a period of 40 hours, and in the fourtil test a composition of the pre-sent invention, namely, a solution containing 10 ppm of sodium molybdate, 14.4 ppm of the phosphonate and 29.9 ppm oF the tripolyphosphate salt, along with 7.2 ppm of benzotriazole, was tested For a period of ~28 hours.
The results of these tests are set forth in Table I below:

TABLE I

Corrosion ~ate MPY
pH 2 ppm Steel Copper 17.4 - 7.8 5.4 - 5.5 74 2 2 8 6.8 - 7.8 41 1.5 37.9 - 8.1 6.5 - 6.6 11.5 1.2 ~8.0 - 8.2 0.81 0.21 It is evident from a comparison of the above data that the cor-rosion inhibitor composition oF the present invention exhibits markedly superior characteristics in that the corrosion rate as measured in mils 1 ~59246 per year (M~Y) is significantly lower when compared to other corrosion inhibitors which do not-contain all four components.
EXA~PLE II
To ~ stra~e the efficie~cy of the corrosion inhibitor of the present invention a c~mparison test was run in which a synthetic cooling tower water was subjected to a corrosion test. In test A no inhibitor was usedi in test B a corrosion inhibitor prepared according to the method set forth in U. S. Patent 4,176,059 was usedi and in test C the corrosion inhibitor of the present invention was present. The synthetic cooling tower water which was used in the test was similar to that employed in Example I and contained 224 ppm of magnesium chloride, 252 ppm of sodium bicarbonate, 503 ppm of sodium chloride, 740 ppm of sodium sulfate, and 183 ppm of calcium chloride. The ionic concentrations included 66 ppm of Ca~2, 27 ppm of Mg~2, 507 ppm of Na+l, 183 ppm of HC03 19 500 ppm of S04-2, and 500 ppm of Cl-l. The operation parameters of the water included a total hardness of 275 ppm, a oa1cium hardness of 165 ppm, a magnesium hardness of 110 ppm and a M-alkalinity of 150 ppm.
~he total dissolved solids in the water was 1776 ppm, said water having a pH at 130F. in a range of from 7.0 to 7.6 and a pH at 72 of 7.6. The apparatus which was used was similar to that described in Example I above while the temperature of the test was 130F. The test coupons which were used measured 1/2"- x 3" x 1/16" and the mils per year corrosion rate was calculated from weight loss measurements. The results of these tests c are set forth in Table II below:

1 ~5~246 T~BLE I I

Steel Corrosion Copper Corrosion Test Rate MPY _ Rate MPY
A 132 1.7 B 112 1.33 C 1.12 0.3 lt is readily ascertainable from the above table that the form~
ulation set forth in U. S. Patent 4,176,059 possessed little or no activity in inhibiting the corrosion of steel and a limited activity in inhibiting the corrosion of copper. In contraction to this, the corrosion inhibitor of the present invention showed a significant improvement in corrosion inhibiting activity with regards to both the steel and the copper coupons.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition for the prevention of corrosion comprising a mixture of a phosphate compound, a phosphonate compound, an aryl triazole, and a salt of a metal selected from the group consisting of molybdenum, tungsten and chromium, wherein the components of the mixture are present in an amount of at least .5% and not greater than 50% of the composition.

2. The composition as set forth in claim 1 in which said phosphate compound is sodium tripolyphosphate.

3. The composition as set forth in claim 1 in which said phosphate compound is tetrasodium pyrophosphate.

4. The composition as set forth in claim 1 in which the aryl triazole is benzotriazole.

5. The composition as set forth in claim 1 in which the aryl triazole is tolyltriazole.

6. The composition as set forth in claim 1 in which the phosphonate compound is 1-hydroxyethylidene-1,1-diphosphonic acid.

7. The composition as set forth in claim 1 in which the phosphonate compound is nitrilotris(methylene)triphos-phonic acid.

8, The composition as set forth in claim 1 in which the salt of a metal is sodium molybdate.

9. The composition as set forth in claim 1 in which the salt of a metal is potassium molybdate.

10. The composition as set forth in claim 1 in which each of said phosphate compound, phosphonate compound, aryl triazole and metal salt is present in an amount of at least 0.5% and not greater than about 50% of the composition.

11. The composition as set forth in claim 1 being a mixture of sodium tripolyphosphate, l-hydroxyethylidene-l,l-diphosphonic acid, benzotriazole and sodium molybdate.