US2006710A - Acid inhibitor - Google Patents

Description

ZDL. bulvll'uol l lune,

Patented July 2, 1935 UNITED STATES PATENT OFFICE ACID INHIBITOR D Wilmington, Delaware Del.,

a corporation of No Drawing. Application February 23, 1932, Serial No. 5 9L8 50 Claims.

This invention relates to acid pickling solutions for metals and more particularly to pickling solutions containing substances for inhibiting the solvent action of the acids on metals while permitting the acid to attack and remove corrosion and like products from the surfaces of the metal.

It is well known that iron, steel, nickel and like metals in use and on exposure to the elements and to certain chemicals become coated with scale, basic salts, and corrosion products such as rust and the like. It is common to treat such metals to remove these objectionable matters by immersing the metals in a pickling solution comprising a dilute aqueous solution of a strong non-oxidizing acid. The acid attacks and dissolves the scale, basic salts, and corrosion products but at the same time has a tendency to attack the base metal. It has, therefore, been proposed to incorporate into such pickling solutions a substance or substances which will inhibit the solvent action of the acid on the metal while at the same time permitting the acid to dissolve and remove the objectionable matters. The substances employed for this purpose up to the present time have not been entirely satisfactory for various reasons. For example, the inhibitors are not sufficiently soluble in dilute acid to enable their ready incorporation into the pickling solutions; some of them require complicated processes therefor; others have but very weak inhibiting action requiring the addition of large amounts thereof to the pickling solution; still others are very unstable in the acid used; and some of the inhibitors can not be readily removed from the metal by rinsing with water but require the use of an organic solvent or the like.

The present invention has as an object to provide substances to be added to pickling solutions to inhibit the solvent action of acids on metals while permitting the removal of objectionable matters. Another object is to provide a class of acid inhibitors which are readily soluble in dilute acid. A further object is to provide a class of acid inhibitors which may be readily washed from metal by rinsing with water. Still further objects are to provide a new composition of matter and to advance the art. Other objects will appear hereinafter.

These objects are accomplished by the following invention which comprises the preparation of a pickling solution by adding to a dilute solution of a strong non-oxidizing acid the product or products which may be obtained nation of cert combination takes place under conditions such as do not permit the evolution of hydrogen sulfide. The amine employed in accordance with our invention comprises a class of organic wines in which at leastgig'o'f thfanunq groups is and at least one of the other amino groups 1 s t'eTtiary. The'aldehyde and carbon disulfide may be caused to combine with any single member of the class, a mixture of two or more members of the class, or a mixture of one or more of such polyamines with an aromatic monoamine such as aniline. Such combination produces a compound or compounds which have very effective acid inhibiting properties when dissolved in a pickling bath of dilute acid. These compounds have the additional advantage of being readily soluble in dilute acids and are also readily washed from the surface of the metal by water.

While the acid inhibitors forming the subject matter of this invention may be prepared in a number of different ways we prefer to employ the methods illustrated in the following examples:

Example 1.--Twenty-two grams of alpha amino pyridine and 10.3 grams of acetaldehyde are mixed and heated together at a temperature of about 50 C. for minutes and then cooled. To the resulting liquid mass is then added 30 grams of carbon disulfide and the whole heated at about 90 C. for 13 hours. The resulting oily mass is then dried in a vacuum at 90 C. for 100 hours. If desired the dried product may be recrystallized by dissolving it in a srnallamounteothet-lo% sulfuric acid and allowing the solution to cool. Tfimfistal lized material may then be filtered off and dried as before. The product is a brown amorphous powder, fusing at about 70 C. It is readily soluble in either warm or cold 5% sulfuric W---- Example 2.--The reaction is carried out in accordance with the method described in Example 1, using 22 grams of para amino dimethylaniline, 10 grams of acetaldehyde and 30 grams of carbon disulflde. The resulting product in unrecrystallized state is a black amorphous solid, fusing at about C. and soluble in either warm of cold 5% sulfuric acid.

The condensations take place very slowly at room temperatures. In practical operation the temperatures employed are limited to a large extent by the boiling points of the reactants. For example, the condensation of alpha amino pyridine with acetaldehyde may be carried out at 35 C. but the reaction requires a great deal of time. At '75 C. the aldehyde may be partly LAQHHHUI lost before it can react. Accordingly, it is preferable to carry out the condensation of the polyamines with acetaldehyde at temperatures between 40 and 60 C. Where the polyamine and the aliphatic aldehyde boil at higher temperatures, the temperature of the condensation reaction may be raised proportionately. In the condensation with carbon disulfide temperatures much below 75 C. are substantially ineffective and where temperatures much above C. are employed loss of carbon disulfide is likely to result. Therefore, in practical operation, it is preferable to maintain the temperature of the condensation with carbon disulfide at approximately 75 C. to 100 C.

While in the above examples we have disclosed the use of acetaldehyde it is to be understood that aliphatic aldehydes generally may be employed. Some of the aldehydes which have given particularly satisfactory results are butyraldehyde, heptaldehyde, crotonaldehyde, and furfuraldehyde.

In the above examples we have illustrated the production of acid inhibitors from alpha amino pyridine and para amino dimethyl aniline, however, it is to be understood that any polyamine having at least one primary amino group and one or more tertiary amino groups may be substituted therefor. Some of the polyamines which we have found to produce particularly effective acid inhibitors are gamma-aminopyridine, mixed amin'o-pyridines, a,a'-diaminodipyridyl, a-amino-a-picoline, a-amino-lutedine, a-aminouinoline, p-amino-diethylaniline, pamino-methyl-ethylaniline. The various isomers and homologues of the specifically mentioned polyamines may also be mentioned. Furthermore, mixtures of two or more members of the class may be employed with advantageous results. Also one or more members of the class admixed with aromatic monoamines such as aniline, the toluidines, dibenzylamine, diphenylamine and phenyl-naphthylamine may be employed to advantage with the obtention of a composition which is more soluble in dilute acids than would be the compounds produced by the use of monoamines only.

The compounds produced as above described are very effective acid inhibitors requiring the addition of only very small amounts thereof to a pickling bath in order to effectively inhibit the solvent action of the acid in the bath on the metal, as may be appreciated from the following tests. The efliciency of the products was determined in the following manner.

Small strips of 26 gauge black sheet mild steel, 2 cm. wide and 6 cm. long were superficially oxidized by heating in the flame of a Bunsen burner for a few minutes. These strips were then cooled and weighed and placed in separate 400 cc. beakers each containing 250 cc. of 5% sulfuric acid at 821-? C. For each test, two strips were employed, one being placed in a beaker containing acid to which a small amount of the agent being tested was added, and the other being placed in a beaker containing acid to which no agent had been added. The beakers containing the solutions and the metal strips were then maintained at 82:2" C. for 30 minutes. At the end of this time all of the oxide scale had been dissolved whereupon the strips were removed, rinsed in water and acetone and dried. The strips were reweighed and the loss in weight calculated. These losses were of little significance since they included the loss in weight due to removal of scale as well as loss due to removal of metal. The strips were then returned to the beakers from which they were taken and the solutions maintained at 82:2" C. for another hour, the strips were then removed, rinsed and dried as before. The loss in weight of the strips due to the one hours immersion in the acid solution was of great significance since such loss represented free metal dissolved in the acid.

In calculating the efficiency of the acid inhibitors from the above described tests, the loss in weight of the strip in the acid bath containing no inhibitor was taken as unity or 100%; the difference between such loss and the loss in weight of the strip immersed in acid containing acid inhibitor is a measure of the efliciency of the inhibitor used in the second bath. The quotient of the difference between the loss in weight of the two strips and the loss in weight of the strip which was immersed in acid containing no inhibitor constitutes the efiiciency or per cent inhibition" of the inhibitor tested, at the temperature, acid concentration and inhibitor concentration used when pickling steel of the given composition.

The result of such tests of the compounds whose preparation has been given in Examples 1 and 2, computed as above described, is given in the following table:

Table I Concentra- Loss in wt. Percent Agent tion of or metal inhibingent, gms. tion percent None 1 }l.4l0 96.6 96.8 98.9 96. 2 v 2 97. 5

From the above tests it will be appreciated that the acid inhibitors of our invention are very effective even at extremely low concentrations. They are also readily soluble in either warm or cold dilute acid solutions and can be readily rinsed off of the surface of the metal with water. Their ready solubility makes them very convenient to apply and to handle and greatly decreases the risks attendant upon the use of this type of composition. The ease with which they may be removed from the surface of the metal is of great advantage in cleaning metal for electroplating, galvanizing and the like.

The pickling solutions prepared in accordance with our invention are particularly adapted for use in cleaning metal of scale such as occurs in welding pipe and the like. They may be used in cleaning pipe and chemical equipment of rust without undue corrosion of the metal and also for cleaning metal in preparation for electroplating, galvanizing or lacquering.

While we have disclosed certain specific compounds and a specific method of producing the same, it is to be understood that such disclosure is merely by way of illustration and that many modifications and changes may be made in the compounds, proportions, temperatures, and methods employed without departing from the spirit of our invention. Accordingly the scope of our invention is to be limited solely by the ap- I l 1; mary and at eas Either a ogroupistg':

construed as broadly as is perof the prior art.

amines and aromatic monoamines.

4. A composition of matter useful as an acid inhibitor comprising a product obtainable by the chemical combination of an aliphatic aldehyde matic monoamine.

5. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the combination of an 6. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the combination of an aliphatic aldehyde and carbon disuliide with a diamine in which one amino group is primary and the other is tertiary.

7. A pickling solution for metals comprising a strong non-oxidizing acid and a small propor- Dyridine nucleus.

8. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a composition obtainable bythe combination of an aliphatic aldehyde and carbon disulflde with a mixture of an aromatic monoamine and a diamine in which one amino group is primary and the other amino group is tertiary.

9. The method of cleaning a ferrous metal which comprises treating the metal with a solution containing a strong non-oxidizing acid and a compound obtainable by the combination of an disulfide with a diamine in which one amino group is primary and the other is tertiary.

11. The method of cleaning a ferrous metal Examiner which comprises treating the metal with a solution containing a strong non-oxidizing acid and a composition obtainable by the combination of 13. The method of cleaning a ferrous metal the metal with a solution containing a strong non-oxidizing acid and a compound obtainable by the chemical combination of an aliphatic aldehyde and carbon disulfide with an amino pyridine.

alpha amino pyridine.

16. The method of cleaning a ferrous metal which comprises treating the metal with a solution containing a strong non-oxidizing acid and one other amino group is tertiary.

20. A composition of matter useful of an aliphatic almixture of polyamines and monostrong non-oxidizing acid and a small proportion of a compound obtainable by the combination of carbon disulfide with a condensation product of an aliphatic aldehyde and at least one polyamine having at least one primary amino group and at least one tertiary amino group.

24. A pickling solution for metals comprising a strong nonoxidizing acid and a small proportion of a compound obtainable by the combination of carbon disulfide with a condensation product of an aliphatic aldehyde and a diamine in which one amino group is primary and the other is tertiary.

25. A pickling solution for metals comprising a strong nonoxidizing acid and a small proportion of a compound obtainable by the combination or carbon disulfide with a condensation product of an aliphatic aldehyde and a compound having an amino-pyridine nucleus.

26. A pickling solution for metals comprising a strong nonoxidizing acid and a small proportion of a composition obtainable by the combination of carbon disulfide with a condensation product of an aliphatic aldehyde and a mixture of an aromatic monoamine and a diamine in which one amino group is primary and the other amino group is tertiary.

2'7. A composition of matter useful as an acid inhibitor comprising a product obtainable by the chemical combination of carbon disulfide with a condensation product of acetaldehyde and a mixture of polyamines in which at least one of the amino groups is primary and at least one other amino group is tertiary.

28. A composition of matter useful as an acid inhibitor comprising a product obtainable by the chemical combination of carbon disulfide with a condensation product of acetaldehyde and a mixture of polyamines and monoamines.

29. A composition of matter useful as an acid inhibitor comprising a product obtainable by the chemical combination of carbon disulfide with a condensation product of acetaldehyde and a mixture of polyamines and aromatic monoamines.

30. A composition of matter useful as an acid inhibitor comprising a product obtainable by the chemical combination of carbon disulfide with a condensation product of acetaldehyde and a mixture of a polyamine having at least one primary amino group and at least one tertiary amino group and an aromatic monoamine.

31. A pickling solution for metals comprising a strong nonoxidizing acid and a small proportion of a compound obtainable by the combination of carbon disulfide with a condensation product of acetaldehyde and at least one polyamine having at least one primary amino group and at least one tertiary amino group.

32. A pickling solution for metals comprising a strong nonoxidizing acid and a small proportion of a compound obtainable by the combination of carbon disulfide with a condensation product of acetaldehyde a'nd a diamine in which one amino group is primary and the other is tertiary.

33. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the combination of carbon disulfide with a condensation product of acetaldehyde and a compound having an aminopyridine nucleus.

34. A pickling solution for metals comprising a strong nonoxidizing acid and a small proportion of a composition obtainable by the combination of carbon disulfide with a condensation product of acetaldehyde and a mixture of an aromatic monoamine and a diamine in which one amino group is primary and the other amino group is tertiary.

35. The mehod of cleaning a ferrous metal which comprises treating the metal with a solution containing a strong nonoxidizing acid and a compound obtainable by the chemical combination of carbon disulfide with the condensation product of an aliphatic aldehyde and an amino pyridine.

36. The method of cleaning a ferrous metal which comprises treating the metal with a solution containing a strong nonoxidizing acid and a compound obtainable by the chemical combination of carbon disulfide with the condensation product of an aliphatic aldehyde and an amino dialkylaniline.

37. A'pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of an aliphatic aldehyde and an amino pyridine.

38. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of acetaldehyde and an amino pyridine.

39. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of acetaldehyde and alpha amino pyridine.

40. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of an aliphatic aldehyde and an amino dialkylaniline.

41. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of acetaldehyde and an amino dialkylaniline.

42. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of an aliphatic aldehyde and an amino dimethylaniline.

43. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of acetaldehyde and an amino dimethylaniline.

44. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of an aliphatic aldehyde and para amino dimethylaniline.

45. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with the condensation product of acetaldehyde and para amino dimethylaniline.

46. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of an aliphatic aldehyde and carbon disulfide with a mixture of polyamines in which at least one of the amino groups is primary and at least one other amino group is tertiary.

4'7. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of an aliphatic aldehyde and carbon disulfide with a mixture of polyamines and monoamines.

48. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with a condensation product of an aliphatic aldehyde and a mixture of polyamines in which at least one of the amino groups is primary and at least one other amino group is tertiary.

49. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with a condensation product of an aliphatic aldehyde and a mixture of polyamines and aromatic mono-amines.

50. A pickling solution for metals comprising a strong non-oxidizing acid and a small proportion of a compound obtainable by the chemical combination of carbon disulfide with a condensation product of an aliphatic aldehyde and a mixture of a polyamine having at least one primary amino group and at least one tertiary amino group and an aromatic monoamine.

FREDERICK B. DOWNING. RICHARD G. CLARKSON.