US3029127A

US3029127A - Corrosion inhibitors

Info

Publication number: US3029127A
Application number: US698917A
Authority: US
Inventors: Ernest L Pollitzer
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1957-11-26
Filing date: 1957-11-26
Publication date: 1962-04-10
Anticipated expiration: 1979-04-10

Description

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Unitd raes Free 3,029,127 CORROSION INHIBITORS Ernest L. Pollitzer, Hinsdale, IlL, assiguor, by mesne assignments, to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware No Drawing. Filed Nov. 26, 1957, Ser. No. 698,917 12 Claims. (Cl. 21--2.7)

This invention relates to a novel method of inhibiting corrosion and more particularly to the use of a substantially water soluble inhibitor to prevent corrosion of metallic surfaces upon contact with water.

Corrosion of metallic surfaces, particularly iron and steel, in contact with fresh or salt water or various aqueous solutions, results in a serious economical loss. There is an urgent need for, and the present invention provides, improved water soluble corrosion inhibitors which will retard and/or prevent such corrosion.

While the novel inhibitors of the present invention may be used in any system wherein water or aqueous solutions contact metallic surfaces, the following specific examples are set forth as illustrative, but not limiting, instances in which the inhibitors of the present invention are useful. Storage tanks, pipe lines and the like containing petroleum oils or other organic compounds generally contain water which causes corrosion of the metallic surfaces. For example, in storage tanks the water settles to the bottom and causes corrosion of the internal surfaces of the storage tank. The water soluble corrosion inhibitor of the present invention will dissolve in the water phases and will serve to retard and/ or prevent such corrosion. Another example is in the stamping, rolling or other working of metal in which a water stream is sprayed or otherwise used as a coolant. Because these operations are effected at high temperature, the cooling water often causes extensive corrosion. Such corrosion is avoided by incorporating the corrosion inhibitor of the present invention in the water spray. Still another application is in the salt-ice water solutions used as refrigerants, for example, in railroad cars, trucks, etc. When used in railroad cars, the salt solution not only effects corrosion of the railroad cars but also drips onto the rails and causes corrosion thereof. It is readily seen that such corrosion is a serious economical problem because it requires frequent replacement of rails, which is expensive both in manpower and in material cost. Still other applications include boiler Water, acid solutions such as pickling solutions, etc.

In one embodiment the present invention relates to a method of retarding corrosion of a metal upon contact with water which comprises effecting said contact in the presence of a corrosion inhibitor comprising a monoalkali metal salt of an alkyl acid orthophosphate, the alkyl group containing from 9 to about 18 carbon atoms.

In a specific embodiment the present invention relates to the method of retarding corrosion of a metal upon contact with water which comprises effecting said contact in the presence of the monosodium salt of decyl acid orthophosphate.

In another embodiment the present invention relates to water containing as a corrosion inhibitor a mono-alkali metal salt of an alkyl acid orthophosphate, in which the alkyl group contains from 9 to about 18 carbon atoms.

It will be noted that the novel corrosion inhibitors of the present invention are mono-alkali metal salts of specific alkyl orthophosphates. As will be shown in the examples appended to the present specifications, it is essential that, when using alkyl acid orthophosphate, the alkyl group contains from 9 to about 13 carbon atoms and preferably from about to about 14 carbon atoms. When a dialkyl orthophosphate is employed, at least one of the alkyl groups must contain from 9 to about 18 carbon atoms and preferably from about 10 to about 14 carbon atoms in order to achieve the improved results.

As will be shown in the following examples, the limitations hereinbefore set forth are critical in order to obtain the improved results of the present invention. :Sur-

prisingly, it has been found that the mono-alkali metal salt of octyl acid orthophosphate (alkyl group containing 8 carbon atoms) did not produce the improved results obtained by corresponding compounds having 10 or 13 carbon atoms in the alkyl group. Also it has been found that the mono-alkali metal salt appears unique for this purpose because the di-alkali metal salts did not produce these improved results.

While it is preferred to utilize the mono-alkali metal salt of the mono alkyl acid orthophosphate, further limited in the manner herein described, in another embodiment of the invention the mono-alkali metal salts of the dialkyl orthophosphates maybe employed, provided at least one of the alkyl groups contains from 9 to about 18 carbon atoms. In some cases the dialkyl orthophosphate salts or even the mono alkyl acid orthophosphate salts containing 16 to 18 carbon atoms may not be as water soluble as the corresponding salts containing a fewer number of carbon atoms in the alkyl group or groups as, for example, from about 9 to about 16. However, in some cases, the requirement for complete water solubility is not necessary because the partly soluble or readily dispersible salt will serve the intended purpose to prevent corrosion of the metallic surfaces and, accordingly, such salts may be satisfactorily employed. Y

From the above discussion, it is seen that the particular alkyl orthophosphates used in preparing the salt must be selected with reference to the very strict requirements heretofore set forth. These strict requirements .will be further elaborated upon in the examples appended to the present specification.

Any suitable alkali metal salt of the alkyl or dialkyl orthophosphates may be utilized in the present invention. A preferred alkali metal comprises sodium and thus a preferred salt comprises a monosodium salt of the specified alkyl acid orthophosphate. Other alkali metals which may be used in preparing the salt include potassium, lithium, rubidium and cesium. Of these, potassium and lithium generally are preferred because of their ready avail ability and lower cost.

In most cases it is preferred that the alkyl group of 9 to about 18 carbon atoms contains some branching in the chain. This appears to improve the corrosion inhibiting properties of the salt. As will be shown in the following examples, a monodecyl acid orthophosphate derived from C Oxo alcohols-Le. alcohols containing highly branched alkyl chainsgave a monosodium salt which was a very effective corrosion inhibitor.

Illustrative preferred salts for use in the present invention include monosodium salt of monyl acid orthophosphate, monosodium salt of decyl acid orthophosphate, monosodium salt of undecyl acid orthophosphate, monosodium salt of dodecyl acid orthophosphate, monosodium salt of tridecyl acid orthophosphate, monosodium salt of tetradecyl acid orthophosphate, monosodium salt of pentadecyl acid orthophosphate, monosodium salt of hexadecyl acid orthophosphate, monosodium salt of heptadecyl acid orthophosphate, monosodium salt of octadecyl acid orthophosphate, monosodium salt of mixed monoand didecyl orthophosphate, monosodium salt of mixed monoand diundecyl orthophosphate, monosodium salt of mixed monoand didodecyl orthophosphate, monosodium salt of mixed monoand ditridecyl orthophosphate, monosodium salt of mixed monoand tetradecyl orthophosphate, etc. It is understood that these different salts are not necessarily equivalent. The monopotassium salts and monolithium salts corresponding to the monosodium salts recited above likewise are particularly suitable for use in the present invention, but not necessarily equivalent.

The salts may be prepared in any suitable manner. In many cases the desired mono alkyl acid orthophosphate or dialkyl orthophosphate is available commercially and may be purchased in the open market. When not so available, the specific alkyl acid orthophosphate ay be synthetically prepared by reacting the desired alcohol with the desired stoichiometric amount of phosphorus oxychloride or phosphours pentachloride. The mixed monoand dialkyl acid orthophosphates may be cheaply and conveniently prepared by reaction of the desired alcohol with phosphorus pentoxide.

The salt is prepared readily by reacting the alkyl acid orthosphosphate with the alkali metal hydroxide, alkali metal carbonate or other suitable alkali metal salt, preferably in the presence of a suitable solvent as, for example, an alcohol such as ethanol, 1 or Z-propanol, a butanol, etc., ethers, aromatic or aliphatic hydrocarbons, etc. In general, the reaction is effected by mixing equal molar proportions of the alkali metal hydroxide and alkyl orthophosphate, and reacting the same at a temperature of from about 20 to about 80 C. and more preferably of from about 40 to about 60 C. In some cases higher temperatures may be employed but, in any event, the temperature should not exceed that at which decomposition of the salt occurs. In some cases the salt precipitates and thus is readily collected and separated from the solvent. In other cases the solvent may be separated by heating to evaporate the same. In still another embodiment, the salt may be used as a solution in the sol vent and, in cases where the salt does not precipitate out of solution, it may be recovered and used in the same solvent employed in the preparation of the salt.

As hereinbefore set forth, the salts prepared in the above manner'are utilized as water soluble or substantially water soluble corrosion inhibitors. The salt is incorporated in water, aqueous solutions or substrates containing water or contacting water, in a sufficient concentration to effectively retard corrosion of metallic surfaces. Generally the salt is used in a concentration of below about 1% by weight of the water, aqueous solution or substrate containing water, and usually in a concentration within the range of from about 0.001% to about 1% and more particularly from about 0.01% to about 0.5% by weight thereof, although higher concentrations may be employed when excessive corrosion is encountered. It is understood that the corrosion inhibitor may be used in conjunction with other additives which are incorporated in the substrate for various reasons.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not With the intention of unduly limiting the same.

Example I The corrosion inhibior of this example is the monosodium salt of decyl acid orthophosphate and was prepared by reacting equal molar proportions of sodium hydroxide with decyl acid orthophosphate purchased in the open market and prepared from Oxo alcohols. The salt was prepared by mixing sodium hydroxide with the decyl acid orthophosphate at room temperature, utilizing Z-propanol as the solvent. The salt was recovered by evaporating the solvent under vacuum.

The salt prepared in the above manner was evaluated as a corrosion inhibitor by the following method. A 600 cc. beaker was used as the reaction vessel and 300 cc. of a 5% sodium chloride solution containing the inhibitor was introduced into the beaker. A 0.5" x 3 x A mild steel strip was inserted in the beaker and held in a horizontal position with one end resting on a glass rod. The sodium chloride solution was stirred by a single blade stirrer revolving at 250 rpm. Air was continuously bubbled in at the rate of 5.6 liters per hour.

When evaluated in the above manner, a steel strip, after six hours exposure in a brine not containing in hibitor, showed a weight loss of 22-24 mg.

0.05% of the salt prepared in the above manner was. incorporated in another sample of the brine and, when evaluated in the above manner, the loss of weight was only 2.6 mg. after six hours exposure. It will be noted that this inhibitor considerably retarded corrosion of the steel strip.

Example II In a run similar to that described in Example I the monosodium salt of decyl acid orthophosphate was incorporated in another sample of the brine in a concentration of 0.03% by weight and, when evaluated in the manner described in Example I, the loss of weight was only 2.9 mg. Here again it will be noted that the corrosion inhibitor was effective in retarding corrosion of the steel strip.

Example III The corrosion inhibitor of this example is the monosodium salt of tridecyl acid orthophosphate and, when evaluated in another sample of the brine and in the manner described in Example I, utilizing 0.05% by weight of the inhibitor, the loss in weight was only 2.1 mg. In another run, using 0.03% by weight of this inhibitor, the loss in weight also was only 2.1 mg. Thus it will be noted that this inhibitor is equally effective even at the low concentration of 0.03% by weight.

Example IV The corrosion inhibitor of this example was the monosodium salt of mixed monoand ditridecyl orthophosphate, the latter being commercially available and purchased on the open market. This inhibitor was evaluated in another sample of the brine and substantially in the same manner as described in Example III, utilizing 0.05% by weight of the inhibitor. After six hours exposure the loss in weight was 3.2 mg. It will be seen that the mixed monoand ditridecyl orthophosphate salt is an effective inhibitor but is not as good as the corresponding salt of the monotridecyl alkyl acid orthophosphate. However, the mixed monoand ditridecyl orthophosphates may be purchased at a lower price than the monotridecyl acid orthophosphate and, therefore, the slightly poorer results may be justified economically by the lower cost.

Example V As hereinbefore set forth, it is essential that the alkyl group of the alkyl acid orthophosphate contains at least 9 carbon atoms. In an evaluation of the monosodium salt prepared from octyl acid orthophosphate (containing 8 carbon atoms in the alkyl group) in another sample of the brine and in the same manner as described in Example I, utilizing 0.05% by weight of inhibitor, the loss in weight was 10.0 mg. after six hours exposure. It will be noted that this is from 4 to 5 times greater than the reduction in weight obtained by the salts prepared from decyl (containing 10 carbon atoms in the alkyl group) and tridecyl (containing 13 carbon atoms in the alkyl group) orthophosphates.

Example VI As hereinbefore set forth, the mono-alkali metal salt must he used for the improved results. This is illustrated in the present example in which the disodium salt of the mixed monoand ditridecyl orthophosphate was evaluated in another sample of the brine and in the same manner as described in Example I, utilizing 0.05 by weight of additive. The loss in weight after six hours exposure was 14.3 mg. by weight. This is to be compared with the results reported in Example IV (3.2 mg. weight loss) using the monosodium salt of the mixed monoand ditridecyl orthophosphate.

Example VII The disodium salt of octyl acid orthophosphate also was evaluated in the same manner described in Example I in another sample of the brine. The loss in weight, when using 0.05% by Weight of the salt was 13.7 mg. It will be noted that the disodium salt of the octyl acid orthophosphate Was even of lower potency than the monosodium salt of the same orthophosphate.

Example VIII As also hereinbefore set forth, when the dialkyl orthophosphate is utilized in preparing the salt, it is essential that at least one of the allzyl groups contains from 9 to about 18 carbon atoms. This is illustrated in the present example in which 0.02% by weight of the monopotassium salt of mixed amyl octyl orthophosphate was evaluated in the same manner heretofore described. The loss in weight was 9.8 mg, which is considerably higher {4 to 5 times) than obtained with the corrosion inhibitors of the present invention.

I claim as my invention:

1. The method of retarding corrosion of a ferrous metal upon contact with water which comprises effecting said contact in the presence of a Water-soluble corrosion inhibitor consisting essentially of a mono-alkali metal salt of an alkyl orthophosphate, wherein the alkyl group contains from 9 to about 18 carbon atoms.

2. The method, of retarding corrosion of a ferrous metal upon contact with water which comprises effecting said contact in the presence of a water-soluble corrosion inhibitor. consisting essentially of the monosodium salt of decyl acid orthophosphate.

3. The method of retarding corrosion of a ferrous metal upon contact with water which comprises effecting said contact in the presence of a water-soluble corrosion inhibitor consisting essentially of the monosodium salt of undecyl acid orthophosphate.

4. The method of retarding corrosion of a ferrous metal upon contact with water Which'comprises elfecting said contact in the presence of a water-soluble corrosion inhibitor consisting essentially of the monosodium salt of dodecyl acid orthophosphate.

5. The method of retarding corrosion of a ferrous metal upon contact with water which comprises effecting said contact in the presence of a Water-soluble corrosion inhibitor consisting essentially of the monosodium salt of tridecyl acid orthophosphate.

6. Water containing a water-soluble corrosion inhibitor consisting essentially of a mono-alkali metal salt of an alkyl orthophosphate wherein the alkyl group contains from 9 to 18 carbon atoms.

7. Water containing a water-soluble corrosion inhibitor consisting essentially of the monosodium salt of decyl acid orthophosphate. v

8. Water containing a Water-soluble corrosion inhibitor consisting essentially of the monosodiurn salt of undecyl acid orthophosphate.

9. Water containing a water-soluble corrosion inhibitor consisting essentially of the monosodium salt of dodecyl acid orthophosphate.

10. Water containing a water-soluble corrosion inhibitor consisting essentially of the rnonosodium salt of tridecyl acid orthophosphate.

11. Water containing a Water-soluble corrosion inhibitor consisting essentially of a mono-alkali metal salt of a mixed monoand dialkyl o-rthophosphate, wherein the alkyl group of said mono alkyl orthophosphate and at least one of the alkyl groups of the dialkyl orthophosphate contains from 9 to about 18 carbon atoms.

12. Water containing a water-soluble corrosion inhibitor consisting essentially of the monosodium salt of a mixed monoand ditridecyl orthophosphate.

References Qited in the file of this patent UNITED STATES PATENTS Hughes June 23, 1959

Claims

1. THE METHOD OF RETARDING CORROSION OF A FERROUS METAL UPON CONTACT WITH WATER WHICH COMPRISES EFFECTING SAID CONTACT IN THE PRESENCE OF A WATER-SOLUBLE CORROSION INHIBITOR CONSISTING ESSENTIALLY OF A MONO-ALKLI METAL SALT OF AN ALKYL ORTHOPHOSPHATE, WHEREIN THE ALKYL GROUP CONTAINS FROM 9 TO ABOUT 18 CARBON ATOMS.