US2726215A - Rust inhibitors for aqueous systems - Google Patents

Description

United States, Patent ce a 2,726,215 RUST INHIBITORS non AQUEOUS sYsrEMs Donald T. Jones, Springfield, Pa., assignor to The Atlantic Refining Company,'Philadelphia, Pa., a corporation of Pennsylvania N Drawing. Application April 19, 1952, Serial No. 283,267

' This invention is directed to a method for suppressing the corrosion of metal surfaces in the presence of aqueous solutions. More particularly, this invention is directed to the suppression of corrosion which occurs when ferrous metals are contacted with water, or aqueous solutions containing dissolved salts or acids, or aqueous solutions which are admixed with non-aqueous solutions.

The hazards of corrosion which are involved when aqueous solutions contact metal surfaces are well-known in every industry. Corrosion not only causes replacement of metals, but also often results ,in'darnage to products by contamination, shutdown of production, loss of ethciency, and mechanical failure by weakening of theequipment. In addition, corrosion often loosens finely divided metal oxides which may act as oxidation catalysts increasing the rate of deterioration of various organic compounds with which they come in contact, or may enter between moving parts of machinery where they act as abrasives. Even when corrosion proceeds at a rather slow rate, continued corrosion over an extended period of time can be extremely serious and involve a considerable expense in both repair and replacement.

The increased cost of nearly all metals'during the last decade as well as the difficulty of obtaining replacement equipment at any cost during periods of national emergency have stimulated efforts to minimize corrosion problems. The serious nature of the problem is reflected by the ever increasing amount of literature on both the broad and specific aspects of the subject.

One approach to the problem is to introduce a chemical into the fluid solution which is to contact the metal surface in an effort to minimize corrosion. Thousands of chemical compounds, both organic and inorganic, have been disclosed for this purpose, but the fact that none of these compounds has achieved universal acceptance in industry indicates that each chemical compound has only a limited field of application.

t is therefore the main object of the present invention to provide a process whereby the corrosion of metallic surfaces in the presence of aqueous solutions is materially inhibited. Another object of the invention is to provide a method whereby the corrosion and rusting of ferrous metals in the presence of aqueous solutions is materially inhibited. It is a further object of this invention to introduce specific organic salts into an aqueous solution to materially inhibit corrosion of metallic surfaces by said solution.

In its broadest conception the invention is regarded as embracing the inhibition of the corrosion of metal surfaces in aqueous systems by introducing particular salts of certain dicarboxylic acids in said aqueous solutions.

More particularly, it has been found that the alkali and alkali earth metal salts of certain dicarboxylic acids, namely, sebacic acid and azelaic acid, exhibit exceptional anti-corrosion powers when incorporated in an aqueous solution which is to contact a metal surface. The unexpectedness of this invention resides in the fact that,

2,726,215 Patented nee. ,1955

although various dicarboxylic acids have been alluded for use in the practice of the present invention are the alkalimetal salts, such as, lithium, sodium, or potassium, and the alkaline earth metal salts, such as,.barium, .calcium, or magnesium.

The sebacic and azelaic acids which are employed to produce the salts used in the present invention maybe obtained inany manner well-known to the art. The

production of these acids has been fully discussed in both the chemical and patent literature. For instance, a conventional method of preparing azelaic acid is by the oxidation of oleic acid, and sebacic acid can be prepared by heating a castor oil soap with NaOI-I, followed by hydrolysis.

Having described in detail the characteristics of the preferred anti-corrosion agent, the following examples Will illustrate certain of the numerous possible specific embodiments of the invention. The examples are intended to illustrate the invention and not to limit the same as it is defined more broadly in the appended claims.

The eifectiveness of my composition in inhibitingthe corrosivity of aqueous solutions may-be better and more fully understood by reference .to certain tests which have been conducted, using both water and aqueous solutions containing substances known to promote corrosion of metal, such as, inorganic chlorides, or sulfates, and acetic or sulfuric acids. The test procedure involved a measurement of the corrosive action of these aqueous solutions, as inhibited with the novel compositions of this invention, upon thoroughly cleaned and sanded steel panels and steel buttons, and a comparison thereof with the results obtained by subjecting identical test strips and buttons to the corrosive action of aqueous solutions not containing the anti-corrosion agent of the instant invention. The steel buttons and panels were immersed in the above mentioned solutions at a temperature of about F. and observed daily for any evidence of rust.

It was not possible to dissolved more than .05% of sebacic acid or more than .1% of azelaic in the distilled water. It will be observed from the data in the foregoing table that when sebacic acid'or azelaic acid were added to the distilled water, there was practically no corrosion inhibition. However, when the alkali or alkali earth metal salts of sebacic or azelaic acid were incorporated into the distilled water, corrosion inhibition was as much as 2000% greater. it is thusseen that when the quantity of the alkali or alkali earth metal salts of sebacic or azelaic acid become greater than the corresponding molar quantity of sebacic acid which can be dissolved, the rust inhibiting properties increased tremendously.

Another series of runs, similar to those shown in Table 1,, were conducted with aqueous solutions containing various substances known to promote rusting of iron and steel, such as, inorganic chlorides or sulfates and acetic or sulfuric acids. The results obtained in these runs are set forth in Table II below:

Table II Composition of Test Solutions Number of Days t 7 Prior to Rust Inhibiting Agent Rust Promoting Agent Busting 3% Lithium Azelate Synthetic Sea Water 20+ 3% Sodium A'mlntp (in 7 None do 1 3% Lithium Azelete '0.1H%IzSO4 in Distilled 20+ 7 2 0.8% Barium azelate.- do 7+ 3.0% Sodium Azelate. do. 20+ None .do 1 3% Lithium Azclate 0.1% Acetic Acid in Dis- 20% tilled H20. 0.8% Barium Azelate (1 7+ 3% Sodium Azelate 10 None 1 Synthetic sea water: 11.0 g. MgClzfiHzO, 1.2 g. CaOlz, 4.0 g. NaaSOa, 25.0 g. NaCl per liter of distilled water.

It will be observed from the data presented in the foregoing table that the salts of this invention are capable of inhibiting corrosion of metal surfaces in aqueous solutions which are normally considered to be extremely corrosive-the lithium salt of azelaic acid being particularly effective.

Additional corrosion inhibitors or anti-rusting compounds may also be present in some instances, as long as there is no chemical interaction between the two additives which would tend to diminish the efiectiveness of the salts of the present invention. Thus, in instances where a metal surface is to contact a fluid medium which contains both water and oil, corrosion protective compositions which are particularly valuable in an oil medium may be used in conjunction with the additive of this invention, subject to the aforementioned limitations.

I claim:' 1. A method for reducing the corrosion of metals in contact with aqueous solutions which comprises introducing into said aqueous solution a minor but corrosioninhibiting amount of a salt selected from the group consisting of an alkalimet'al salt and an alkaline earth metal salt of an acid selected from the group consisting of sebacic acid and azelaic acid.

2. The method according to claim 1, wherein the salt is an alkali metal salt of azelaic acid.

3. The method according to claim 2, wherein the salt is lithium azelate.

4. The method according to claim 1, wherein the salt is sodium azelate.

5. The method according to claim 1, wherein the salt is an alkali earth metal salt of azelaic acid.

6. The method according to claim 5, wherein the salt is barium azelate.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A METHOD FOR REDUCING THE CORROSION OF METALS IN CONTACT WITH AQUEOUS SOLUTIONS WHICH COMPRISES INTRODUCING INTO SAID AQUEOUS SOLUTION A MINOR BUT CORROSIONINHIBITING AMOUNT OF A SALT SELECTED FROM THE GROUP CONSISTING OF AN ALKALI METAL SALT AND AN ALKALINE EARTH METAL SALT OF AN ACID SELECTED FROM THE GROUP CONSISTING OF SEBACIC ACID AZELAIC ACID.