WO1997003167A1

WO1997003167A1 - Inhibited pickling acids containing chloride and zinc ions

Info

Publication number: WO1997003167A1
Application number: PCT/US1996/011425
Authority: WO
Inventors: Gerald A. Black
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1995-07-13
Filing date: 1996-07-12
Publication date: 1997-01-30
Anticipated expiration: 1998-01-13
Also published as: MX9800363A; ZA965687B; AU6543396A; AR002819A1; BR9609785A; CA2226887A1

Abstract

Triazine ring containing inhibitors, which have been widely taught in the prior art as excellent inhibitors for hydrochloric acid based pickling compositions, have been found not to be effective for prolonged use when the pickling compositions can dissolve significant amounts of zinc ions, because the inhibitor precipitates as a solid in the presence of both zinc and chloride ions. Other nitrogen containing pickling inhibitors are free from this difficulty and function effectively even in the presence of zinc. Combinations of alkyl aryl polyalkyleneamine and hexamethylene tetramine inhibitors are particularly effective.

Description

Description INHIBITED PICKLING ACIDS CONTAINING CHLORIDE AND ZINC IONS

BACKGROUND OF THE INVENTION Field ofthe Invention

This invention relates to the treatment of metal surfaces with aqueous acids to re¬ move scale and like materials from the surface, a process commonly known in the art as "pickling", and to aqueous liquid pickling compositions used in such processes, that con¬ tain both chloride and zinc ions and an inhibitor. Statement of Related Art

Strong mineral acids such as hydrochloric and sulfuric acids, together with an in¬ hibitor component that substantially reduces the rate of dissolution of clean metal surface from the rate that would prevail in the same type of acid solution without the inhibitor, are normally used as pickling compositions

Advantageous inhibitors reduce the rate of dissolution of clean metal as much as possible while reducing the rate of dissolution of surface scale and like contaminating materials as little as possible. One common quantitative method of rating inhibitors used in the art, and in this description below, involves measuring the corrosion rate ofthe met¬ al to be pickled in a solution containing the type and concentration of acid to be used for pickling, measuring the corrosion rate in a solution otherwise the same except for adding the inhibitor to be used, and then reporting the results as the percent "protection" ofthe inhibitor. The percent protection is defined by the following equation: P = 100[1-(R. /RJ] where P = percent protection, R, = corrosion rate ofthe metal in the inhibited solution, and R_u = the corrosion rate ofthe metal in the uninhibited solution, expressed in the same units as Rj.

Avery wide variety of inhibitors for pickling compositions are known in the art. A useful review is given by G. Trabanelli and V. Carassiti, "Mechanism and Phenome¬ nology of Organic Inhibitors", in Advances in Corrosion Science and Technology, Vol¬ ume 1 (Plenum Press, New York, 1970). Triazine inhibitors are among those most high¬ ly recommended in the prior art for aqueous solutions of hydrochloric and/or sulfuric ac¬ ids, the basic pickling compositions most often used. DESCRIPTION OF THE INVENTION General Principles of Description

Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, unless expressly stated to the contrary: per¬ cent, "parts of. and ratio values are by weight; the term "polymer" includes "oligomer", "copolymer", "terpolymer", and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more ofthe members ofthe group or class are equally suitable or preferred; description of electrically neutral constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; specification of materials in ionic form means that a soluble salt or acid con¬ taining the ions is actually supplied in an amount sufficient to provide the stated amount ofthe stated ionic material and further implies the presence, in the composition contain¬ ing a constituent specified in ionic form, of sufficient counterions to produce electrical neutrality for the composition as a whole; any counterions thus implicitly specified pref- erably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoid¬ ing counterions that act adversely to the objects of the invention; and the terms "solu¬ tion", "soluble", and the like are to be understood as including not only true equilibrium solutions but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 1000 hours.

Summary and Object ofthe Invention

It has been found that zinc ions, triazine inhibitors, and chloride ions are mutually incompatible constituents in aqueous solutions, resulting in a precipitate. The same is not true for any two of these three components in the absence ofthe third one, and it is also not true for the combination of zinc, triazine inhibitors, and sulfate ions. This unex¬ pected discovery is of practical importance, because, although zinciferous surfaces are not usually pickled with hydrochloric acid based pickling compositions, steel surfaces prior to galvanizing often are pickled with such pickling compositions. In many cases, the conveying equipment for the steel objects to be galvanized includes chains or other elements that have the form of a continuous band, and therefore are exposed to both the pickling composition used and to the galvanizing stage, and subsequently return to the pickling zone with zinc on their surfaces. Any such zinc present that contacts the liquid pickling composition usually rapidly dissolves, because the pickling inhibitors that are most effective for inhibiting the dissolution of steel often do not inhibit the dissolution of zinc very effectively.

When triazine inhibited hydrochloric acid pickling solutions, or other triazine in- hibited pickling solutions containing substantial amounts of chloride ions, are used in contact with zinciferous surfaces, the inhibiting effect has been noted to diminish, or ev¬ en disappear entirely, with prolonged use. This is very undesirable, because excessive dissolution ofthe ferrous metal surfaces exposed to the pickling composition then rapidly occurs. Investigation of such operations led to the observation of a precipitate in the pickling compositions, something not observed under the same conditions when pickling only ferrous surfaces that do not contain zinc. A major object of this invention is to pro¬ vide a well inhibited, chloride containing pickling composition that can be used on mixed ferrous and zinciferous surfaces without losing its inhibiting character as rapidly as tria¬ zine inhibited hydrochloric acid solutions do when so used. It has been found that nitro- gen containing inhibitors, exclusive of those containing a triazine ring in their molecules, are satisfactory for this purpose

A pickling composition according to the invention accordingly comprises, prefer¬ ably consists essentially of, or more preferably consists of water and (A) chloride anions; (B) zinc cations;

(C) an inhibitor selected from the group consisting of nitrogen containing organic compounds that do not include a triazine ring; and

(D) acid; and, optionally,

(E) iron cations. A process according to the invention comprises contacting a metal workpiece to be pickled with a working pickling solution according to the invention as described above. Detailed Description ofthe Invention. Including Preferred Embodiments

Pickling compositions according to the invention preferably contain chloride ions in a concentration that is at least, with increasing preference in the order given, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, or 20.0 % and independently, primarily for reasons of economy and worker safety and comfort, preferably is not more than, with increasing preference in the order given, 50. 40, 35, 30, or 25 %. The preferred source ofthe chlor¬ ide ions is hydrochloric acid, because this supplies both chloride and acid, both of which are needed. Thus the stoichiometric equivalents as hydrochlori . cid ofthe above stated amounts of chloride ions¹ are preferred. However, other acids .-* h as sulfuric could also be used, together with another source of chloride. The concentr n of acid present pref¬ erably is high enough to produce a practically useful rate of pickling; such concentrations may be readily determined by those skilled in the art.

Independently, pickling compositions according to the invention preferably con- tain zinc ions in a concentration that is at least, with increasing preference in the order given, 0.0001, 0.0002, 0.0005, 0.001 , 0.002. 0.005, 0.008, 0.010, 0.020, 0.030, 0.035, 0.040, 0.045, or 0.048 %

Also independently, pickling compositions according to the invention preferably contain nitrogen-containing inhibitor molecules, exclusive of those that have molecular structures including a triazine ring, in a concentration that is at least, with increasing preference in the order given, 0.0001, 0.0002, 0.0005, 0.001, 0.002, 0.005, 0.008, 0.010, 0.020, 0.030, or 0.035 % and independently, primarily for reasons of economy, preferab¬ ly is not more than, with increasing preference in the order given, 5, 3, 2, 1, 0.5, 0.2, 0.1, 0.08, 0.060, 0.055, 0.050, 0.045, or 0.040 %. Independently, the nitrogenous inhibitor molecules are preferably selected from the group consisting of alkyl pyridines; hexa¬ methylene tetramine; abietyl, hydroabietyl, and dihydroabietyl amines and keto substitut¬ ed derivatives thereof, most preferably ketonylated rosin amines as described in U. S. Patent 2,975,125 of Mar. 14, 1961 to Saukaitis et al., the entire disclosure of which, to the extent that it describes ketonylated abietyl, hydroabietyl, and dihydroabietyl amines

^■"Not much more than 35 % chloride can be achieved from aqueous hydrochloric acid, except under more than normal atmospheric pressure, because of equilibrium with gaseous hydrogen chloride. and is not inconsistent with any explicit statement herein is hereby incorporated herein by reference; and all other amines including both at least one alkyl group and at least one aryl group attached to a single nitrogen atom. Most preferably, the inhibitors contain both alkyl aryl polyalkyleneamines and hexamethylene tetramine in a ratio that preferably is at least, with increasing preference in the order given, 0.10: 1.0, 0.15: 1.0,

0.20: 1.0, 0.25: 1.0, 0.30: 1.0, 0.33 : 1.0, 0.35 : 1.0, or 0.37: 1.0 and independently preferably is not more than, with increasing preference in the order given, 1.5: 1.0, 1.0: 1.0, 0.9: 1.0,

0.8: 1.0, 0.7: 1.0, 0.6: 1.0, 0.55 : 1.0, 0.50: 1.0, 0.45 : 1.0, 0.42: 1.0, 0.40: 1.0, or 0.39: 1.0.

A process according to the invention comprises contacting a metal workpiece to be pickled with a working pickling solution according to the invention as described above, preferably at a temperature that is, with increasing preference in the order given, at least 16, 30, or 38 °C and, ifthe scale to be removed is relatively thick, fast pickling is desired, and adequate protection of workers against the fuming tendency ofthe pick¬ ling solution at higher temperatures is provided, more preferably is at least, with increas- ing preference in the order given, 52, 60, 66, 70, 74, 78, or 81 °C and independently pref¬ erably is, with increasing preference in the order given, not more than 93, 88, or 83, °C, for a time sufficient to remove scale and other bulk oxide coatings from the workpiece surface. Independently, the time of contact for most pickling applications preferably is at least, with increasing preference in the order given, 1, 5, 10, 15, 20, or 25 minutes and independently preferably is not more than, with increasing preference in the order given,

60, 55, 50, 45, 40, or 35 minutes, although the time naturally will vary considerably as a function ofthe amount and type of surface contamination to be removed. Contact be¬ tween the workpiece and the working pickling solution is generally by immersion, but any process of establishing the requisite contact, many of which are known per se in the art, may be used.

The practice and benefits ofthe invention may be further appreciated by consider¬ ation ofthe following non-limiting examples and comparison examples. Laboratory Demonstration ofthe Incompatibility of Zinc. Chloride, and Triazines

Attempts were made to prepare solutions with the constituents shown in Table 1, with the results also shown there. RODINE® 51 inhibitor shown in Table 1 contains substantial amounts of triazines, while RODINE® 1 150 inhibitor also shown in Table 1 contains no known triazines but does contain alkyl aryl polyalkyleneamines and hexa- methylene tetramine in a ratio of about 0.38:1.0.

TABLE 1

Ingredient Amount of Ingredient in Attempted Composition Number:

1 2 3 4

Tap water 100 mL 100 mL 100 mL 100 mL

32 % HCl in water 100 mL 100 mL 100 mL 100 mL

Fe⁺² ions 0.05 % none 0.05 % 0.05 %

Zn⁺² ions none 0.05 % 0.05 % 0.05 %

RODINE® 51 0.2 v% 0.2 v% 0.2 v% none

RODINE® 1150 none none none 0.2 v%

Result: Solution Precipitate Precipitate Solution

Abbreviations for Table 1 "mL" = "milliliters"; v%" = "percent by volume".

Attempts were made to complete Attempted Compositions 2 and 3 as shown in Table 1 without precipitation by adding RODINE® 51 inhibitor only to the HCl solution initially, then mixing this solution with another made by adding zinc and iron, or zinc alone, to water. Precipitation occurred immediately upon mixing the two solutions. In another attempt, the inhibitor was mixed with water, zinc, and iron and formed a clear solution, but precipitation occurred as soon as the hydrochloric acid was added to this mixture. Results from Large Scale Operations

A sample of rinse water from a commercial galvanizing plant was obtained. This rinse water is used in the plant to make pickling compositions that contain about 10 % of HCl. Tbis rinse water contains iron and zinc cations at levels of at least about 0.03 % each. Furthermore, pickling compositions inhibited with RODINE® 51 inhibitor at this operation, used to pickle steel to prepare it for galvanizing, initially give satisfactory per¬ formance when made with fresh tap water, but soon cease to be satisfactory as continued additions of rinse water containing zinc are added, along with additional concentrated hy¬ drochloric acid, to make up for operating losses ofthe pickling compositions. The compositions shown in Table 2 below, some using the above noted practical rinse water containing small amounts of iron and zinc, were attempted, to determine whether obvious precipitation would occur.

TABLE 2

Ingredient Amount of Ingredient in Attempted Composition Number:

5 6 7 8

Rinse water 100 mL 100 mL 100 mL none

Tap water none none none 100 mL

32 % HCl in water 100 mL 100 mL none none

98 - 100 % H₂SO₄ none none 100 mL 100 mL

Fe⁺² ions none none none 0.05 %

Zn⁺² ions none none none 0.05 %

RODINE® 51 0.2 v% none 0.2 v% 0.2 v%

RODINE® 1150 none 0.2 v% none none

Result: Precipitate Solution Precipitate Solution

Abbreviations for Table 2 "mL" = "milliliters"; v%" = "percent by volume"

Even the relatively small amount of hydrochloric acid in the rinse water caused a precipitate in Attempted Composition 7; the zinc and iron contents alone did not result in any precipitation in otherwise similar Attempted Composition 8 Characteristically, although the rinse water contained all of hydrochloric acid, zinc, and iron and was clear with no evidence of precipitate, as soon as the triazine containing inhibitor was added in Attempted Composition 5, precipitation occurred. This did not happen when the other, triazine-free inhibitor was used in Composition 6.

Claims

The invention claimed is:

1. An inhibited pickling composition comprising water and:

(A) chloride anions;

(B) zinc cations; (C) an inhibitor selected from the group consisting of nitrogen containing organic compounds that do not include a triazine ring; and (D) sufficient acid to produce a practically useful pickling rate on steel.

2. An inhibited pickling composition according to claim 1, comprising from about 1.0 to about 50 % of chloride ions, at least about 0.0002 % of zinc ions, and from about 0.001 to about 5 % of inhibitors selected from the group consisting of (i) alkyl pyridines,

(ii) hexamethylene tetramine, (iii) abietyl, hydroabietyl, and dihydroabietyl amines and keto substituted derivatives thereof, and (iv) all other amines including both at least one alkyl group and at least one aryl group attached to a single nitrogen atom, but not includ¬ ing any triazine ring. 3. An inhibited pickling composition according to claim 2, comprising from about 2.0 to about 40 % of chloride ions, at least about 0.0005 % of zinc ions, and from about 0.002 to about 3 % of inhibitor component (C) .

4. An inhibited pickling composition according to claim 3, comprising from about 4.0 to about 40 % of chloride ions, at least about 0.001 % of zinc ions, and from about 0.005 to about 2 % of inhibitor component (C) .

5. An inhibited pickling composition according to claim 4, comprising from about 6.0 to about 35 % of chloride ions derived from hydrochloric acid, at least about 0.002 % of zinc ions, and from about 0.008 to about 1 % of inhibitor component (C) .

6. An inhibited pickling composition according to claim 5, comprising from about 8.0 to about 35 % of chloride ions derived from hydrochloric acid, at least about 0.005

% of zinc ions, and from about 0.010 to about 0.5 % of inhibitor component (C) .

7. An inhibited pickling composition according to claim 6, comprising from about 10.0 to about 30 % of chloride ions derived from hydrochloric acid, at least about 0.010 % of zinc ions, and from about 0.010 to about 0.2 % of inhibitors selected from the group consisting of (i) alkyl pyridines, (ii) hexamethylene tetramine, (iii) ketonylated rosin amines, and (iv) all other amines including both at least one alkyl group and at least one aryl group attached to a single nitrogen atom, but not including any triazine ring

8 An inhibited pickling composition according to claim 7, wherein component (A) is present in a concentration from about 16 0 to about 30 % derived from hydrochloric acid, component (B) is present in a concentration of at least about 0 030 %, component (C) is present in a total concentration from about 0 020 to about 0 01 % and consists essentially of (C 1) alkyl aryl polyalkylene amines and (C 2) hexamethylene tetramine in a ratio of (C 1) (C 2) that is from about 0 15 1 0 to about 0 9 1 0

9 An inhibited pickling composition according to claim 8, wherein component (A) is present in a concentration from about 16 0 to about 30 % derived from hydrochloric acid, component (B) is present in a concentration of at least about 0 040 %, component (C) is present in a total concentration from about 0 030 to about 0 060 % and consists essential¬ ly of (C 1) alkyl aryl polyalkylene amines and (C 2) hexamethylene tetramine in a ratio of (C 1) (C 2) that is from about 0 30 1 0 to about 0 50 1 0

10 An inhibited pickling composition according to claim 9, wherein component (A) is present in a concentration from about 20 to about 25 % derived from hydrochloric acid, component (B) is present in a concentration of at least about 0 048 %, component (C) is present in a total concentration from about 0 035 to about 0 040 % and consists es¬ sentially of (C 1) alkyl aryl polyalkylene amines and (C 2) hexamethylene tetramine in a ratio of (C 1) (C 2) that is from about 0 35 1 0 to about 0 40 1 0 1 1 A process comprising contacting a metal workpiece to be pickled with an inhibit¬ ed pickling composition according to any one of claims 1 - 10 for a time sufficient to re¬ move scale and other bulk oxides from the workpiece surface

12 A process according to claim 1 1 , wherein the inhibited pickling composition during its contact with the workpiece has a temperature from about 30 to about 93 °C and is maintained in contact with the workpiece for a time from about 1 to about 60 minutes

13 A process according to claim 12, wherein the inhibited pickling composition during its contact with the workpiece has a tempe^rature from about 38 to about 83 °C and is maintained in contact with the workpiece for a time from about 5 to about 55 minutes

14 A process according to claim 13, wherein the inhibited pickling composition during its contact with the workpiece has a temperature from about 52 to about 83 °C and is maintained in contact with the workpiece for a time from about 10 to about 40 minutes.

15. A process according to claim 12, wherein the inhibited pickling composition during its contact with the workpiece has a temperature from about 60 to about 83 °C and is maintained in contact with the workpiece for a time from about 15 to about 35 minutes.