US3258424A - Method of inhibiting corrosion of ferrous metals - Google Patents

Description

United States Patent 3,258,424 METHOD OF INHKBITING CORRUSION 0F FERROUS METALS Edwin E. Claytor, Jr., Tulsa, Okla, assignor to Pan American Petroleum Corporation, Tulsa, ()klzn, a corporation of Delaware No Drawing. Filed Aug. 2, 1963, Ser. No. 299,454

12 Claims. (Cl. 252-855) This invention relates to inhibiting corrosion. More particularly, it relates to inhibiting the corrosion of ferrous metal surfaces by the oil-field corrosive materials hydrogen sulfide, low molecular weight organic acids such as acetic and propionic acids, carbon dioxide, oxygen, and combinations of these corrosive materials.

In US. Patent 2,756,211, Jones, the use of salts of high molecular weight primary amines, and high molecular weight carboxylic acids to inhibit oil-field corrosion is disclosed and claimed. Certain embodiments of these salts have now been in successful widespread use for many years. The most common treating procedure has been to contact the metal surfaces first with a high concentration of the amine salt to form a protective adsorbed film, and then make periodic low-concentration treatments to keep the film in repair.

As more field operations have been made automatic, the frequency of a pumper visiting a well has decreased. The frequency of intermittent treatment with corrosion inhibitors has correspondingly decreased. This has placed a greater emphasis on the need for inhibitors with long film lives. The problem is, of course, particularly severe where high flow rates or similar conditions exist for agitating the corrosive liquids and thus removing the film more quickly. High temperatures have also tended to remove the films rapidly, thus requiring frequent intermittent treatments to keep the fihns in repair. An extreme case, for example, is in deep, high-temperature wells along the Gulf of Mexico coast where both flow velocities and temperatures are'frequently high at the bottom of a well. Most of these Wells are flowing wells which require little attention except for the introduction of corrosion inhibitors.

An object of this invetnion is to provide a method for inhibiting corrosion which produces longer lasting protective films and thus requires less frequent treatment with film-forming inhibitors. Still other objects will be apparent from the following description and claims.

In general, I accomplish the objects of my invention by the use, as inhibitors, of amine salts and amides of a particular acid and derivatives of the acid. The acid is 4,4-bis(4 hydroxyphenyl) pentanoic acid. A more common name is Diphenolic Acid. Although this term and the abbreviation DPA are both trademarks, they are used hereinafter for convenience and mean herein only the compound the structure of which is as follows COOH This can be simplified to H0((J H1 )0H COOH 3,258,424 Patented June 28, 1966 The amides are, in general,

stnaight chain fatty acids. better than the amine salts.

The explanation of the superior action'of the amides and amine salts of Diphenolic Acid and its derivatives is not completely certain, but appears to lie in the peculiar nonemulsifying structure of the acid molecule. It has been known for some time that an amine salt, or amide, which has emulsion-forming tendencies, is not as good an inhibitor as an apparently equivalent salt or amide without emulsion-forming tendencies. The Diphenolic Acid, both because of its nonlinear structure and polar groups in addition to the acid radical, has less emulsifying characteristics than the straight chain soapm aking acids.

The amine can be any of the many high molecular weight amines having more than about 10 carbon atoms per molecule listed in such references as US. Patents 2,756,211, Jones, 2,736,658, Pfohl et -a1., 2,914,557, Oxford, 2,598,213 Blair and the like. The amines which now seem to 'be preferred in the industry are those having the formulas R NH(CH2)2NH(CHz)2NH2 where R is an aliphatic hydrocarbon radical having about 16 to 18 carbon atoms.

These polyamines are particularly useful with some of the preferred Diphenolic Acid derivatives. The preferred acid derivatives are those in which at least two carboxylic acid groups occur in the same molecule. The polyam-ine and the polyacid can react to form a high molecular weight cross-linked salt or amide. The linkages are not, in general, as strong as those in cross-linked plastics, for example, but are strong enough to add to the apparent molecular weight and film stability of the salts and amides.

Some examples of polybasic Diphenolic Acid derivatives which have been found satisfactory, together with shortened names, are as follows:

For convenience, these derivatives will be referred to hereinafter by their simplified names. In these names DPA, of course, stands for Diphenolic Acid, which is, itself, a simplified name.

The dimer diester DPA was formed by reacting 2 mols of DPA with 1 mol of a mixture of dimer acids having the average formula C H (COOH) The dimer acid linked 2 DPA molecules together through phenolic linkages so the resulting molecule had two carboxylic acid groups.

To demonstrate the film stability of the amine salts and amides of Diphenolic Acid and its derivatives, two

principal types of tests were made. One was a flow test while the other was the so-called wheel test.

In the flow test, thin strips of mild steel were exposed to the corrosive liquids, the rate of corrosion being measured by recording the change of electrical resistance of the strips. After an initial rate of corrosion was established, the strips were immersed in a solution of the corrosion-inhibiting composition. The corrosion-inhibiting solution was then allowed to drain off the strips. The strips with their films of inhibitor were then again exposed to the flowing stream of corrosive liquids. A decreased rate of corrosion was noted until the film was lost. When the film was lost, the corrosion rate returned to the original value. The time required for the corrosion rate to return to the original value was, therefore, a measure of the film life of the corrosion inhibitor. The testing apparatus and method are described in more detail in an article entitled, Laboratory Flow Test for Evaluation of Oil Well Corrosion Inhibitors, in the periodical, Corrosion, for August 1962, page 227t.

Results of flow tests at a room temperature of about 75 to 80 F. are reported in Table I. In these tests the concentration of inhibitor in the inhibiting solution was 25,000 parts per million (2.5 percent). The corrosive liquids were a 50-50 mixture of oil and water. The oil consisted of hydrocarbons containing from about 10 to 12 carbon atoms per molecule. The water was a percent sodium chloride brine containing about 700 parts per million of hydrogen sulfide. The flow rate of corrosive liquids was about 1 foot per second. The pH of the brine phase was about 5.7.

The amine portion of both the amides and salts was the same in all cases in Table I to permit better comparison of the various acids. The amine was a mixture of polyamines having the formula RNH(CH NH R beingan aliphatic hydrocarbon radical having usually 16 to 18 carbon atoms. Even though the amine was a polyamine in every case, enough amine was used to provide one amine molecule for each carboxylic acid radical. Thus, in tribasic DPA three moles of amine per mole of the acid derivative were used since each acid molecule contained three carboxylic acid groups.

The DPA soya .monoester salt result is included since it illustrates two points. First, it shows that a long aliphatic hydrocarbon radical attached through an ester linkage to the Diphenolic Acid gives that acid enough emulsifying characteristics to produce a short film life. Second, the test shows, in a rather extreme form, the short film life typical of the soap-forming acids. Many of the soapforming acids provide a somewhat better film life than in Test 7 of Table I, but the results are sometimes erratic. Test 4, using the dimer diester, shows that, if both ends of the long hydrocarbon radical can be attached to Diphenolic Acid molecules, the results are quite good. In order for the emulsifying tendency to be serious, it will be apparent that the Diphenolic Acid derivative must have a free-end aliphatic hydrocarbon radical long enough to cause emulsifying tendencies. Ordinarily, the hydrocarbon radical must contain at least about 12 carbon atoms to provide emulsifying properties. Stated in another way, this means that in order for the Diphenolic Acid derivatives to be suitable for my purpose, they must have no free-end aliphatic hydrocarbon radical containing more than about 12 carbon atoms.

The test of polyglycidyl DPA and amine is included in Table I since the epoxy resin formed in this Way has been found to be an excellent inhibitor for high-temperature acid corrosion. This use is described in more detail, and is claimed, in my co-pending patent application S.N. 299,464, filed August 2, 1963. The inhibitor in this case was formed by reacting one mole of Diphenolic Acid with three moles of epichlorohydrin and then attempting to cross-link the resin by adding the same polyamine used to form the salts and amides. Test 9, using this resin film, shows that simply increasing the molecular weight of the acid by polymerization with epichlorohydrin or the addition of a polyamine at low temperature does not provide the degree of corrosion inhibition nor the film life provided by the Diphenolic Acid derivatives which can form amine salts or amides. The principal reason is probably failure of the amine to react at the low temperature. Tests 1 to 6, and 8, show the very good results provided by the amine salts and amides. It should be mentioned that the flow test is severe. Therefore, the film life of only 50 or 60 hours in the test indicates a better film life than can be expected from many inhibitors now used commercially.

The second type of test, the wheel test, has been in use in many testing laboratories for several years. There have been a number of variations of this test. The one most widely used seems to be a version in which coupons of mild steel are weighed and then soaked in a concentrated corrosion inhibitor solution to form a film of the inhibitor. The coupon is then placed in a bottle containing corrosive liquids. This bottle is placed at or near the outer edge of a wheel on a horizontal axle. The Wheel is turned several times a minute. This turns the bottle over several times a minute to provide agitation of the corrosive liquids in contact with the treated surfaces of the metal coupons. After the desired period of treatment, the coupons are cleaned and again weighed. Percent inhibition is calculated by comparison to the weight lost from a coupon treated with oil containing no inhibitor.

Table II presents the results of wheel tests in which two different strengths of inhibitor were used. The corrosive liquids were actual field-produced fluids from a well. The fluids contained no hydrogen sulfide, but did contain carbon dioxide and low molecular weight organic acids. The fluids were 36 percent oil and 64 percent water.

TABLE II Percent Inhibition Test Inhibitor At 2,500 At 15,000 ppm. p.p.m.

DPA monoamide 79 DPA salt 69 71 Tribasic DPA salt 62 71 'Ietrabasic DPA salt 82 81 Dimer diester DPA salt 81 81 Dimer diester DPA amide 78 77 The amine used, and the ratio of amine to acid, in every case was the same as described in connection with Table I. The Diphenolic Acid salt employed twice as much amine as acid on a molecular basis. This ratio was used in an effort to cause the amine to associate with the phenolic groups as well as reacting with the carboxylic acid group of the Diphenolic Acid. It will be apparent from the results reported in the table that all the materials tested were good inhibitors for this type of corrosion. The Diphenolic Acid salt and the tribasic DPA salt seemed a little less desirable than the other materials, but films of even these salts in a concentration above about 2,000 parts per million provided considerable inhibition in the presence of agitated corrosive liquids.

- One of the most widely used of the amine salt inhibitors at the present time is the salt of naphthenic acid with the amine used in forming the salts and amides listed in the tables. The naphthenic acid salt was not tested with the particular corrosive well fluids used in the tests reported in Table II. With similar fluids, however, the naphthenates have provided, on the average, about 20 to 30 percent protection in wheel tests. Wheel tests of naphthenates in some well fluids show about the same degree. of protection. The naphthenates provide excellent inhibition in the field where frequent treatment is possible. It will be apparent that the Diphenolic Acid derivatives provide better films than the naphthenates and are, therefore, to be considered superior, particularly where treatments are less frequent.

7 To check the ability of the inhibitor films to inhibit oxygen corrosion, mild steel coupons were dipped in inhibitor solution, drained, baked at 160 to 180 F. for two hours to insure completion of any reactions, and then exposed for 24 hours to a salt water spray in the presence of atmospheric oxygen and a temperature of 95 to 100 F. Results of the tests are reported in Table III.

TABLE III Inhibitor Inhibition,

percent DPA monoamide Tribasie DPA amide Tetrabasic DPA amide Dimer diester DPA amide Tetrabasie DPA salt DPA soya monoester salt Dimer diester DPA salt Polyglycidyl DPA amine All the materials listed in Table III have been previously identified in connection with Table I. The inhibitor solution in which the coupons were dipped contained 25 percent of the inhibiting compounds. It will be apparent from the data in Table III that the amides and salts of Diphenolic Acid and its derivatives are effective to inhibit oxygen corrosion. Some are better than others. In Test 6 it will be noted that the emulsion-forming tendency of the soya monoester was not a disadvantage in the spray test, possibly because of the absence of oil in the test. The epoxy resin salt formed in Test 8 was obviously highly effective against oxygen corrosion even though it was not effective in the presence of hydrogen sulfide as shown in Table I. The high temperatures used in the baking step of the procedure of the tests reported in Table III were apparently able to cause the amine to react with the polyglycidyl DPA and form an effective epoxy resin coating on the metal surface. In the tests of Table I the temperatures seem to have been too low to permit the polymerization reactions to occur. The baking step had little effect on the amides, of course, but tended to convert the amine salts to the amides.

It will be apparent from the data in the tables that amides and amine salts of Diphenolic Acid and may of its derivatives are highly effective in forming long-lasting films which inhibit corrosion by hydrogen sulfide, oxygen, carbon dioxide, low molecular weight organic acids, and mixtures of these agents. The derivatives should be limited to those having no free-end hydrocarbon radicals containing more than about 10 carbon atoms. The group should include, in addition to the compounds named in the tables, others such as the polyether acids identified above. No film life tests are available for these derivatives, but static bottle tests show the polymers to be good inhibitors and their similarity to the derivatives reported in the tables would certainly indicate that films of the polyether acid derivatives are also long-lasting.

The Diphenolic Acid inhibitors are principally appli cable to those methods of corrosion inhibiting in which the metal surface to be protected is exposed to a solution containing a high concentration of the inhibiting compound in order to form a good film and is then exposed to the corrosive fluids. Thus, use in so-called squeeze treatments or slug treatments in wells is advantageous since in both cases a rather large volume of high-concentration inhibitor solution is introduced into the well to coat exposed metal surfaces, no further treatment then being provided for a long period of time. It will be apparent, however, that the salts and amides are also useful in methods in which smaller amounts of inhibitor in lower-concentration solutions are introduced more frequently into a well, for example. The inhibitors are not limited in usefulness to oil wells, but may also be used in flow lines, tanks and the like, in oil fields. In addition, the inhibitors may be used in refineries or chemical manufacturing plants where corrosion from the various types of corrosive agents named above may be a problem.

I claim:

1. A method for depositing a long-lasting film for inhibiting corrosion of a ferrous metal surface by an aqueous solution of a corrosive agent selected from the group consisting of hydrogen sulfide, carbon dioxide, low molecular weight caboxylic acids and combinations of these agents, said method comprising contacting said surfaces with a salt of an amine having an aliphatic hydrocarbon radical containing at least about 10 carbon atoms and an acid selected from the group consisting of 4,4-bis (4-hydroxy phenyl) pentanoic acid; 4,4-b'is (4-carboxyrnethyl phenyl) pentanoic acid and di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acid having the approximate formula C H (COOH) and then exposing said surface to said solution of corrosive agent.

2. The method of claim 1 in which said surface is contacted with a solution of said salt containing at least about 2,000 parts per million by weight of said salt.

3. The method of claim 1 in which said reaction product is the salt of 4,4-bis(4-hyd.roxy phenyl) pentanoic acid.

4. The method of claim 3 in which the amine portion of said salt has the formula RNH(CH NH where R is a hydrocarbon radical containing from about 16 to about 18 carbon atoms.

5. A method for depositing a long-lasting film for inhibiting corrosion of a ferrous metal surface by an aqueous solution of a corrosive agent selected from the group consisting of hydrogen sulfide, carbon dioxide, low 'molecular weight carboxylic acids and combinations of these agents, said method comprising introducing into said solution a salt of an amine having an aliphatic hydrocarbon radical containing at least about 10 carbon atoms and an acid selected from the group consisting of 4,4-bis (4-hyd-roxy phenyl) pentanoic acid; 4,4-bis (4-carboxymethyl phenyl) pentanoic acid and di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acid having the approximate formula C H (COOH) 6. A method for depositing a long-lasting film for inhibiting corrosion of a ferrous metal surface by an aqueous solution of a corrosive agent selected from the group consisting of hydrogen sulfide, carbon dioxide, low molecular weight carboxylic acids and combination-s of these agents, said method comprising contacting said surface with a salt of a polyamine having an aliphatic hydrocarbon radical containing at least about 10 carbon atoms and a polybasic acid derivative of 4,4-bis (4-hydroxy phenyl) pentanoic acid, said derivative being selected from the group consisting of 4,4-bis (4-carboxymethyl phenyl) pentanoic acid, and di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acid having the approximate formula C H (COOH) and then exposing said surface to said solution of corrosive agent.

7. The method of claim 6 in which said derivative is 4,4-bis (4-carboxymethyl phenyl) pentanoic acid.

8. The method of claim 6 in which said derivative is di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acid having the approximate formula 9. The method of claim 6 in which said polyamine has the formula RNH(CH NH where R is a hydrocarbon radical containing from about 16 to about 18 carbon atoms.

10. The method of claim 9 in which said derivative is 4,4-bis (4-carboxymethyl phenyl) pentanoic acid.

11. The method of claim 9 in which said derivative is di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acid having the approximate formula 12. A method for depositing a long-lasting film for inhibiting corrosion of a ferrous metal surface by an aqueous solution of a corrosive agent selected. from the group consisting of hydrogen sulfide, carbon dioxide, low molecular weight carboxylic acids and combinations of these agents, said method comprising introducing into said solution a salt of a polyamine having an aliphatic hydrocarbon radical containing at least about 10 carbon atoms and a polybasic acid deravative of 4,4-'bis (4-hydroxy 20 phenyl) pentanoic acid, said derivative being selected 8 from the group consisting of 4,4-bis (4-carboxymethyl phenyl) pentanoic acid, and di 4-(4(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acid having the approximate formula C H (COOH) References ited by the Examiner UNITED STATES PATENTS 2,598,213 5/1952 Blair.

2,756,211 7/1956 Jones.

2,893,968 7/ 1959 Greenlee 260559 X 2,920,040 1/1960 Jolly.

2,933,520 4/1960 Bader.

3,031,402 4/1962 Nelson 25251.5 3,061,553 10/1962 Riggs 252392 3,190,734 6/1965 Nelson 252392 X ALBERT T. MEYERS, Primary Examiner.

JULIUS GREENWALD, Examiner.

H. B. GUYNN, Assistant Examiner.

Claims (1)

1. A METHOD FOR DEPOSITING A LONG-LASTING FILM FOR INHIBITING CORROSION OF A FERROUS METAL SURFACE BY AN AQUEOUS SOLUTION OF A CORROSIVE AGENT SELECTED FROM THE GROUP CONSISTING OF HYDROGEN SULFIDE, CARBON DIOXIDE, LOW MOLECULAR WEIGHT CARBOXYLIC ACIDS AND COMBINATIONS OF THESE AGENTS, SAID METHOD COMPRISING CONTACING SAID SURFACES WITH A SALT OF AN AMINE HAVING AN ALIPHATIC HYDROCARBON RADICAL CONTAINING AT LEAST ABOUT 10 CARBON ATOMS AND AN ACID SELECTED FROM THE GROUP CONSISTING OF 4,4-BIS (4-HYDROXY PHENYL) PENTANOIC ACID; 4,4-BIS (4-CARBOXYMETHYL PHENYL) PENTANOIC ACID AND DI4-(4-(4-(4-HYDROXY) PHENYL) PENTANOIC ACID) PHENYL ESTER OF A DIMER ACID HAVING THE APPROXIMATE FORMULA C32H62(COOH)2, AND THEN EXPOSING SAID SURFACE TO SAID SOLUTION OF CORROSIVE AGENT.