Title:
Cleaning and pickling of metals
United States Patent 2425320


Abstract:
This invention relates to improvements in pickling and cleaning of metals and in inhibiting or retarding the action of acids on metals. More particularly the invention relates to improvements in inhibitors for acids, solutions containing these inhibitors for cleaning or pickling metals, and...



Inventors:
Hill, William H.
Application Number:
US46313342A
Publication Date:
08/12/1947
Filing Date:
10/23/1942
Assignee:
KOPPERS CO INC
Primary Class:
Other Classes:
510/492, 528/254, 528/255, 528/265, 528/266, 528/268, 528/269, 544/159, 544/162, 558/14
International Classes:
C23G1/06
View Patent Images:



Foreign References:
GB347228A1931-04-24
Description:

This invention relates to improvements in pickling and cleaning of metals and in inhibiting or retarding the action of acids on metals. More particularly the invention relates to improvements in inhibitors for acids, solutions containing these inhibitors for cleaning or pickling metals, and methods of cleaning or pickling metals and removing oxides or scale therefrom.

Such metallic substances as ferruginous metals, aluminum, zinc, nickel and others are, as is well known, subject to surface corrosion when exposed to the atmosphere and certain chemicals.

Metal surfaces that are thus affected and that have become coated with scale, particularly mill scale formed in sheet rolling or other operations, rust and the like are generally treated with a pickling solution to remove the objectionable material. The pickling solution generally contains an acid, and a so-called inhibitor that is added for the purpose of preventing dissolution of the metal without interfering with the dissolution action of the acid on the objectionable material.

It is of considerable advantage to employ as inhibitors, substances that have a high solubility in pickling acid solutions, that are readily wetted by acids, and that, by rinsing with water, are easily and completely washable from metal along with carbon smut and other debris. It is also an advantage to employ compounds that do not have a disagreeable odor and that are not Irritating to the skin and mucous membranes of workmen.

The above and other advantages are gained by the following invention in which a pickling solution is provided by adding to an acid solution a prouct obtained by chemical reaction between an aldehyde, certain nitrogen compounds and a thiocyanic acid compound. -The condensation products formed include in their molecular structure both sulfur and nitrogen thereby rendering them particularly effective as inhibitors.

The nitrogen compounds from which the thiocyanates are prepared are basic amino compounds of either the aliphatic- or tfght chain, carbocyclic, or heterocyclic types They contain one or more amine or imine groups, or tertiary nitrogen atoms, or combinations thereof. It is to be understood in the present instance that the term "amino compound" as herein employed, applies to compounds containing primary, secondary and tertiary amine structures in their configuration and wherein one, two or three atoms of ammoniacal hydrogen have been replaced by other linkages.

Decided benefits are obtained from increasing the number of amine or imine groups in a compound as a starting material. Amidines and polyamines, for instance, are generally found to be particularly satisfactory. Furthermore, by using as starting materials basic organic compounds which will in themselves resinify with aldehydes, as for example, amidines or compounds capable of forming Schiff's bases on condensation with aldehydes, a firmer anchoring of the nitrogen and sulfur atoms in the molecule is obtained.

Under steel plant working conditions it is desirable to use compounds that are thermostable.

It is noted that in general the presence of alkyl, alkoxy, aralkyl, and especially aryl groups in the amiho starting compounds provides increased stability in the inhibitor. For instance, the diphenl guanidine iocyanate aldehyde condensation product is more thermostable than the corresponding condensation product made from guanidine thiocyanate.

The stronger the basic characteristics of the amino compound used as a starting material the better the compound is for purposes of the present invention. It is preferred that the amino compound be basic enough to form with thiocyanic acid true thiocyanates of sufficient stability to avoid continuous splitting off of free thiocyanic acid in too great proportions during condensation. The bases employed should preferably have a basicity greater than that expressed by the dissociation constant 10-14. The presence of water solubilizing groups, such as NH2, NH, OH and others, in the amino compound or in the inhibitor product confers upon the inhibitor increased solubility in the acid baths in which it is used.

The following are some of the amino compounds which have been found to be useful in providing the acid Inhibitors of the present invention.

Guanidine and its derivatives and substitution products such as methyl and dimethyl guanidine, ethyl and diethyl guanidine, butyl and dibutyl guanidine, octyl and dioctyl guanidine, diethanol guanidine, dicyclohexyl guanidine, dibenzyl guanidine, diphenyl guanidine, ditolyl guanidine, dixylyl guanidine, dinaphthyl guanidine; biguanid and its derivatives and substitution products such as ethyl and diethyl biguanid, propyl and dipropyl biguanid, octyl and dioctyl biguanid, mono-, di-, and triethanol biguanid, dimethylclohexyl biguanid, dibenzyl biguanid, phenyl and diphenyl biguanid, tolyl biguanid, morpholino biguanid; guanyl urea and its derivatives and substitution products such as dimethylguanyl urea, diethanol guanyl urea, diphenylguanyl urea; cyclic amidines such as melamine, formoguanamine, acetoguanamine, melam, melem, 2,4,6-trihydrazino-1,3,5-triazine; mono- and polyamines such as dimethylamine, monoethylamine, monon-propylamine, "diT-sopropylamine, tri-n-butyl00 amine, mono-n-butyl diamylamine, dioctylamine, mono-n-dodeeylamibe, mono-n-octadecylamine, benzyl diethylamine, nilin, -tertiary-atylaniline, di-tertiary anyiiline, N-monoamylaniline, N,-diamyl aniline, N-mono-n-butyl aniline, N,N-di-n-butyJaniline, a-naphthylamine, e-naphthylamine, N-n-butyl-a-naphthylamine, o-amino diphenyl, diphenylamine, piperidine, morpholine, phenylmorpholine, phenylmethyl pyrazolone, monoethanolamine, diethanolamine, ethyldiethanolamine, n-butyl monoethanolamine, 2-amino-l-butanol, 2 - amino-2-ethyl - 1,3 - propanediol, tris (hydroxymethyl) aminomethane, phenylethanolamine, p-tertiary-amyl phenyl diethanolamine, ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, 2,3-diamino-2,3-dimethylbutane, pentamethylene diamine, hexamethylene tetramine, pphenylene diamine, benzidine.

The above amino compounds, either singly or mixtures of two or more thereof, are readily converted to thiocyanates or perthiocyanates by reaction with thiocyanic acid or a perthiocyanic acid, or by the double decomposition of an amine salt and a metal or ammonium thiocyanate.

For the aldehyde component of the new com- 2V pounds there may be used for example formaldehyde, acetaldehyde, butyraldehyde, crotonaldehyde, acrolein, benzaldehyde, salicylaldehyde, cinnamic aldehyde, furfural, glyoxal, and others and mixtures thereof. Formaldehyde is in general to 3( be preferred on account of its availability, cheapness, and effectiveness.

As to the relative proportion of amino compound and aldehyde to be used, no general rule can be laid down. The ratio depends on the 3 number of active groups in the amino compound molecule, such as NH2 and thiocyanate groups.

One mol of aldehyde is usually employed for each reactive group, and therefore in most cases two mols of aldehyde are sufficient for a particular 4 thiocyanate. However, an excess of for example formaldehyde does no harm, since it is in itself a pickling inhibitor of some limited value and may therefore be left with the reaction product in many cases. A deficiency of aldehyde also is of 4 no grave consequence since practically all amines and all thiocyanates in a sense have some inhibiting value of their own. Where desired, an excess of aldehyde may be removed by means known to the art, such as evaporation in vacuo or otherwise.

When using the pickling inhibitors of the present invention, it is often advantageous to add wetting agents to the pickling baths or to -incorporate such agents with the inhibitors themselves. Such commercial wetting agents as a naphthalene sulphonic acid type of wetting Igenit, known as Aerosol .OS, render good service.

They should te employed in quantities of about Y2% of the acid weight of the bath. The addition of wetting agents facilitate the removal of carbon smut from pickled steel or other metal goods.

At the same time, though only very small amounts of the inhibitors are needed in a pickling bath in order to inhibit effectively the solvent action of the acid in the bath on the metal as seen in the following examples, the addition of the wetting agent increases the effectiveness of the inhibitors to such an extent that substantially smaller percentages of the inhibitors give satisfactory results.

Examples 1. Approximately 118 parts by weight of guanidine thiocyanate are mixed with about 75 parts by weight of 40% formaldehyde, and the mixture is left stahding at room temperature for three hours. Then it is simmered for about thirty minutes under reflux and allowed to stand. The product is a yellow liquid. This was tested as a pickling inhibitor by adding a drop of it to a solution of 25 cc. concentrated hydrochloric acid in 50 c. c. water, and dropping into the solution 2 lath nails. The compound dissolved in the acid easily and without residue. Parallel tests were run on the same acid concentration and the same kind of nails, but without the addition of the inhibitor product in one case and with a drop of formalin solution in the other case. The inhibition effect brought about by the addition of the guanidine thiocyanate-formaldehyde condensation product was strikingly seen from the lessened attack of the acid on the nails; even after a week the nail surfaces were very little affected.

The product described in Example 1 was evaluated quantitatively in comparison with a commercial inhibitor under conditions simulating steel plant practice. The weight loss of steel plate of known area was determined after pickling Speriods of 10, 20, and 30 minutes. The acid bath used contained 5% by volume of sulfuric acid and was kept at 1800 F. Bessemer steel plate was used for the tests, and the weight losses given in columns (1), (2) and (3) for the inhibitor of SExample 1, and in column (4) for the known commercial inhibitor, were determined in ounces per square foot of surface. The following table includes the results obtained in these tests: 5 Guanidine Length of Immersion thiocyanateformaldehyde cond. product concen- 10 min. 20 min. 30 m tration (per cent of acid 0 weight) (1) (2) (3) .10 .-..... .-- 120 464 1.20 - --- -20 ----------.076 .265 .576 .20 1.85 .30 ..--031 .1 . .382---------- -----.40-----------0.34 .116 .328 .4: .2 S.0...... .013 .029 .053 .50 .138 .5 .50_ -----------__ ___ 2. About 118 parts by weight of guanidine thiocyanate are added to about 150 parts by weight of 40% formaldehyde solution, and the resulting 50 mixture is allowed to stand at room temperature for about three hours. In that time most of the thiocyanate dissolves. The mixture is simmered for abt out hour under reflux and permitted to stand. The resultant yellow liquid was tested as 55 in Example 1 and found to be substantially as effective as the product used in Example 1.

3. Biguanid thiocyanate having the empirical formula C2N5HI.HSCN is prepared from biguanid neutral sulfate and barium thiocyanate. About 60 80 parts of the resulting crystalline compound are dissolved in about 80 parts of formaldehyde solution of 40%. The mixture is gently boiled in an open vessel until a frothy mass is obtained, which is waterwhite and free of odor. The resulting 65 mass, which is a thick liquid, was tested out for its pickling inhibition value as in Example 1 and found to be superior to the compound described therein.

4. Biguanid thiocyanate, having the empirical 70 formula C2N5H7.2HSCN, is prepared by double decomposition of biguanid acid sulfate and barium thiocyanate. To the yellowish concentrate, an amount of formaldehyde is added corresponding to a ratio of 2 mols of formaldehyde to 75 1 mol of biguanid acid thiocyanate. The mixture is gently boiled in an open vessel. As soon as excess formaldehyde disappears heating is discontinued. The product is a clear, thick, oily liquid of little odor, and dissolves in acid speedily.

It was tested as a pickling inhibitor as in Example 1 and found to be very effective.

5. Dicyandiamidine thiocyanate formaldehyde condensation product is prepared as follows: about 320 parts by weight of dicyandiamidine thiocyanate are refluxed for about 1/ hour with about 300 parts by weight of 40% aqueous formaldehyde. A clear, waterwhite solution results which gradually thickens and becomes a little yellowish. On cooling, the product sets to a somewhat translucent gel containing some thick liquid which curdles on addition of water. The gel melts at 240 to 2500 C. with rapid decomposition to a brown froth. The gel on testing according to Example 1 was found to be a very excellent pickling inhibitor. 2 6. 270 parts by weight of diphenylguanidine thiocyanate are mixed with 225 parts by weight of 40% aqueous formaldehyde and gently heated in an open vessel. A slightly pinkish solution results which quickly turns colorless, then yellow. 2 The heating is discontinued as soon as the formaldehyde odor disappears. On cooling, the new product solidifies to a light-yellow, clear, transparent resin. When at room temperature, the resin is hard and tough. When tested out 3 for its pickling inhibition value as in Example 1 it was found to be extremely good.

7. 210 parts by weight of diphenylguanidine thiocyanate and 150 parts by weight of 40% aqueous formaldehyde are heated under reflux for two 3 hours. The product is then heated in an open vessel on a steam bath for six hours, and thereafter on a low hot plate (asbestos pad) for one hour more. The final material is a clear, faintly yellow, somewhat brittle resin having a melting 4 point of 80' to 900 C. It was found to be a good pickling inhibitor when tested according to the procedure outlined in Example 1.

Comparative tests under steel mill conditions with two of the best known marketed commercial 4 inhibitors proved the product of Example 7 to be superior to either of the commercial inhibitors as seen from the following tabulation of results obtained in tests in which open hearth and Bessemer steel plate respectively were immersed for periods of 10, 20, and 30 minutes in acid baths containing 5% by volume of sulfuric acid and kept at 1800 F. The weight losses were determined in ounces per square foot of surface. Weight losses were also established for identical acid baths which contained commercial inhibitors A and R.

Diphenylguanidine Weight Losses, Length of Immersion Thiocyanate Formaldehyde Cond. Product (per cent of acid 10 min. 20 min. 30 min. weight) OPEN HEARTH PLATE .10 -.......- ...... .00.6 .010 .013 .M20 .----..... .... - .004 006 .008 .30 --------------------- .003 .005 .007 40 ...o---------------- .002 .004 .005 .............----------- - .002 .004 .005 BESSEMER PLATE .10 ------------------- .012 .022 .039 20..---------------------- 007 012 .017 .30--------". -----...... ..05 .010 .014 40 ---------------------- .005 .008 .011 .5---------------------- .005 .008 .011 minutes Commercial 30minutes Commercial Inhibitor 30 minutes Inhiitor 30 A (per cent of acid Immersion, (per cent of Immersion, weight) wt. losses acid weight) wt losses OPEN HEARTH PLATE .20----------------------- .130----------- -1--------. .......----------------- --- .9 60 - -- 009 .50 .004 l _ _::::::::::::::::: ._oo9 .0 .o04 BESSEMER PLATE .20..---------5 ........ --- ----------.40 ---------------------- .2150 .. .......50----------------------- 1.38 042 8. 250 parts by weight of o-tolyl biguanid thiocyanate and 300 parts by weight of 40% aqueous formaldehyde are refluxed for 3 hours.--The resultant product is poured out in a thin layer and 0 on cooling turns to a white, opaque resin. After exposure to the room atmosphere for a week, it loses the water derived from the aqueous formaldehyde, and which causes the opaqueness. It is then transparent, water-white, and brittle enough to be coarsely ground. The melting point is about 700 to 80° C. Its pickling inhibiting effect was tested out as in Example 1 and found to be excellent, probably aided by the ease with which 0 it dissolves in the acid.

9. 185 parts by weight of mixed triazine thiocyanates containing the thiocyanates of melamine, melam, melem, and melon and obtained by thermal decomposition of ammonium thiocyanate, are reacted with 225 parts of 40% aqueous formaldehyde by heating the mixture to just under the boiling point. On cooling, the turbid, light tan solution sets to a solid, which is soluble in acid and does not melt at temperatures up to io 3000 C. but commences to turn brown at about 2600 C. It proved to be a good pickling inhibitor when tested according to the scheme used in Example 1.

10. 1940 c. c. of an aqueous solution of aniline 5 thiocyanate containing 3.3 mols of the compound, are slowly added to 495 grams (6.6 mols) of a 40% aqueous formaldehyde solution. The mixture is constantly stirred and kept at about 120 C. Slowly a milkiness begins to appear and 50 the color gradually changes to a light yellow due to finely dispersed solid. The color of the solid deepens while the amount increases, until a large quantity of a scarlet colored, finely divided product is produced at the end of the addition of the 65 aniline thiocyanate solution. Filtration and washing with water yields an almost theoretical quantity of the desired aniline thiocyanate formaldehyde condensation product. The new material is a thermosetting resin which does not melt 60 at temperatures up to 3000 C. and on heating gradually turns brown and then black. Tested by the procedure of Example 1, it was found to be a good pickling inhibitor.

11. 106 parts by weight of diphenylguanidine 65 thiocyanate are refluxed with 44 parts by weight of acetaldehyde. A liquid is formed which gradually turns dark brown. After two hours' refluxing, the product amounts to 116 parts by weight.

Thus, a considerable part of the aldehyde evap70 orates due to its low boiling point. The product is a very dark brown solid with an odor of heterocyclic nitrogenous bases. It is easily soluble in acids and has a melting point of 75* to 85* C. It proved to be a good inhibitor when tested ac<5 cording to the method described in Example 1.

2,425,820 7 12. 270 parts by weight of diphenylguai mne thiocyanate are refluxed with 70 parts by weight mre of croton aldehyde for one hour. The reaction re product is poured out and solidified to clear fro reddish resin which after a few days exposure is pri point of 850 to 90° C. When tested for its in- t hibiting effect according to the procedure in Ex- mtI ample 1, it was found to be a very good inhibitor ti 13. 250 parts by weight of diphe guanidine 10 thiocyanate are refluxed with 120 parts b weight o 40% y.. ......ed Ted- ro uclar lis- 0 of butaldehye or one hour. The product is a gldenew oil which lowly crystallizes to a al solid of crresponding color having a melting point of 1000 to 1050 C. Tested by the procedure 1 al of Examle , proved to be an excellent pickling pickling i nhibitor. n14. 230 parts of 2-amino-2-methYl- propanol i thiocyanate are refluxed with 380 parts of 40% t aqueous formaldehyde for six hours. The result- 20 t ant product is an amber, clear liquid, a little hydrophobic but substantially water soluble. It is entirel soluble in a mixture of one part concen- s trated hydrochloric acid and two parts water.

Tests prove it to be an excellent pickling in- 25 hibitor.

diol thiocyanate are refiuxed with 380 parts of 40% aqueous formaldehyde for six hours. The resultant product is a dark, red-brown, clear liq- 30 uid rather hydrophobic. Tests prove it to be entrated hydrochloric acid and two parts water. It is a most excellent inhibitor.

16. 230 parts of 2haminoh-1butanol thiocyanate are refluxed with 380 parts of 40% aqueous formaldehyde for six hours. The resultant product is a very deep red-brown, thick liquid, quite hydrophobic but completely soluble in a mixture of 1 part concentrated hydrochloric acid and 2 parts water. Tests prove it to be a most excellent pickling inhibitor.

What is claimed is: 1. A cleaning and pickling composition for metal subject to atmospheric corrosion and for removing oxides and other corrosion products from surfaces of said metal, said composition comprising a pickling acid solution having dissolved therein a relatively small proportion of a reaction product of an aldehyde and a preformed .5( thiocyanate of a basic, nitrogenous organic compound having at least one nitrogen-containing radical selected from the group consisting of NH2 and NH, said reaction product being soluble in said pickling acid solution in a proportion which 5 inhibits dissolution of said metal by said acid.

2. A cleaning and pickling composition for metal subject to atmospheric corrosion and for removing oxides and other corrosion products from surfaces of said metal, said composition comprising a pickling acid solution having dissolved therein a relatively small proportion of a reaction product of an aldehyde and a preformed thiocyanate of a basic amino compound, said reaction product being soluble in said pickling acid solution in a proportion which inhibits dissolution of said metal by said acid.

3. The composition of claim 2 in which the aldehyde Is formaldehyde.

4. The composition of claim 2 in which the basic amino compound is an amidine.

5. The composition of claim 2 in which the thiocyanate is normal thiocyanate.

6. The composition of claim 5 in which the basic amino compound is a guanidine.

h. A cleaning and pickling composition for tal subject to atmospheric corrosion and for moving oxides and other corrosion products m surfaces of said metal said composition comising a pickling acid solution having dissolved erein a relatively small proportion of a reacon product of an aldehyde and preformed noral thiocyanate of diphenyl guanidine, said reacon product being soluble in said pickling acid dlution in a proportion which Inhibits dissolution said metal by said acid.

8. The composition of claim 7 in which the idehyde is formaldehyde.

9. A cleaning and pickling composition for metsubject to atmospheric corrosion and for renoving oxides and other corrosion products from urfaces of said metal, said composition comprisg a pickling acid solution having dissolved herein a relatively small proportion of a reacion product of an aldehyde and preformed nornal thiocyanate of dixylyl guanidine, said reacion product being soluble in said pickling acid solution in a proportion (which inhibits dissolution of said metal by said acid.

10. The composition of claim 9 in which the aldehyde is formaldehyde.

11. A cleaning and pickling composition for metal subject to atmospheric corrosion and for removing oxides and other corrosion products from surfaces of said metal, said composition comprising a pickling acid solution having dissolved therein a relatively small proportion of a reaction product of an aldehyde and preformed normal thiocyanate of normal guanidine, said reaction product being soluble in said pickling acid solution in a proportion which inhibits dissolution of said metal by said acid.

12. The composition of claim 11 in which the aldehyde is formaldehyde.

13. In a method of cleaning and pickling a metal, the step comprising treating the metal with an aqueous pickling acid solution having dissolved therein a relatively small proportion of a product of reaction between an aldehyde and a preformed thiocyanate of a basic, nitrogenous, organic compound having at least one nitrogen-containing radical selected from the group consisting of NH2 and NH to inhibit dissolution of said metal by said pickling acid.

S14. In a method of cleaning and pickling a metal, the step comprising treating the metal with an aqueous pickling acid solution in which is dissolved in acid-inhibiting proportions a product of reaction between an aldehyde and a preformed thiocyanate of a basic amino compound to inhibit dissolution of said metal by said pickling acid.

15. The method of claim 14 in which the basic amino compound is an amidine.

60 16. The method of claim 15 in which the thiocyanate is normal thiocyanate.

17. The method of claim 16 in which the basic amino compound is a guanidine.

18. In a method of cleaning and pickling a 65 metal, the step comprising treating the metal with an aqueous pickling acid solution in which is dissolved in acid-inhibiting proportions a product of reaction between an aldehyde and preformed normal thiocyanate of diphenyl guani70 dine, to inhibit dissolution of said metal by said pickling acid.

19. The method of claim 18 in whch the aldehyde is formaldehyde.

20. In a method of cleaning and pickling a 75 metal, the step comprising treating the metal Pk . - 4 2,425,8 9 with an aqueous pickling acid solution in which is dissolved in acid-inhibiting proportions a product of reaction between an aldehyde and preformed normal thiocyanate of dixylyl guanidine, to inhibit dissolution of said metal by said pickling acid.

21. The method of claim 20 in which the aldehyde is formaldehyde.

22. In a method of cleaning and pickling a metal, the step comprising treating the metal with an aqueous pickling acid solution in which is dissolved in acid-inhibiting proportions a product of reaction between an aldehyde and preformed normal thiocyanate of normal guanidine, to inhibit dissolution of said metal by said pickling acid.

23. The method of claim 22 in which the aldehyde is formaldehyde.

WILIAM H. HIIL.

10 REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number 1,780,636 2,203,649 2,072,003 2,335,452 2,050,204 Number 347,228 Name Date Stine --------------- Nov. 4, 1930 Felkers ------------- June 4, 1940 Lutz -------------- Feb. 23, 1937 Schelling ----------- Nov. 30, 1943 Ter Horst ----------- Aug. 4, 1936 FOREIGN PATENTS Country Date Great Britain ------- Apr. 24, 1931 * 4