| United States Patent | 3,864,271 |
| Stalter | February 4, 1975 |
Stabilized acidic hydrogen peroxide solutions
Abstract
Stabilizers are provided which control copper ion-catalyzed degradation of hydrogen peroxide. In pickling baths the H.sub.2 O.sub.2 concentration may be up to about 50% by weight, in the presence of strong inorganic nonoxidizing acids at up to about 50% by weight, and at temperatures of up to about 90.degree.C. Such stabilizers are included in concentrations of up to about 1.5% by weight. The stabilizers, at concentrations of up to about 5% by weight, may also be formulated into H.sub.2 O.sub.2 of up to 80% concentration by weight. The stabilizers are selected from the group consisting of adipic acid, glutaric acid, succinic acid, their methyl derivatives, salts, and mixtures of them.
| Inventors: | Stalter; Neil J. (Wilmington, DE) |
| Assignee: |
E. I. du Pont de Nemours and Company
(Wilmington,
DE)
|
| Appl. No.: | 05/311,976 |
| Filed: | December 4, 1972 |
| Current U.S. Class: | 510/254 ; 252/186.29; 423/272; 423/273; 423/584; 510/255; 510/372 |
| Current International Class: | C23G 1/10 (20060101); C23G 1/02 (20060101); C11d 007/08 (); C11d 007/18 (); C11d 007/56 () |
| Field of Search: | 252/186,95,97,99,100,135,157,142 423/272,273,584 |
| 3373113 | March 1968 | Achenbach |
| 3556846 | January 1971 | Hnizda |
| 3563687 | February 1971 | Moyer |
| 3640885 | February 1972 | Rhees |
| 1,041,586 | Sep., 1966 | GB | |||
Assistant Examiner: Gluck; Irwin
I claim:
1. An aqueous, acidic, oxidizing solution stabilized against copper ion-catalyzed degradation at temperatures of up to about 90.degree.C. containing about 0.01 to 50 percent hydrogen peroxide by weight, a strong inorganic acid at a concentration of about 0.01 to 50 percent by weight, and a stabilizing amount of a stabilizer selected from the group consisting of adipic acid, glutaric acid, succinic acid, and mixtures thereof.
2. The solution of claim 1 wherein the stabilizer concentration is about 0.003 to 1.5 percent by weight.
3. The solution of claim 2 wherein the stabilizer concentration is about 0.015 to 1.5 percent by weight.
4. The solution of claim 3 wherein the stabilizer concentration is about 0.03 to 0.1 percent by weight.
5. The solution of claim 1 wherein the acid concentration is about 2 to 25 percent by weight.
6. The solution of claim 1 wherein the H.sub.2 O.sub.2 concentration is about 0.05 to 15 percent by weight.
7. The solution of claim 6 wherein the H.sub.2 O.sub.2 concentration is about 0.5 to 3.0 percent by weight.
8. The solution of claim 1 wherein the stabilizer is adipic acid.
9. The solution of claim 1 wherein the stabilizer is glutaric acid.
10. The solution of claim 1 wherein the stabilizer is succinic acid.
11. The solution of claim 1 wherein the stabilizer is a mixture of the stabilizers.
12. The solution of claim 11 wherein the mixture comprises succinic and adipic acids.
13. The solution of claim 12 wherein the ratio of succinic acid to adipic acid is approximately 2:1 by weight.
14. A concentrated, aqueous, acidic solution of hydrogen peroxide stabilized against copper ion-catalyzed degradation by a stabilizing amount of a stabilizer selected from the group consisting of adipic acid, glutaric acid, succinic acid, and mixtures thereof.
15. The solution of claim 14 wherein the hydrogen peroxide concentration is about 30 to 70 percent by weight.
16. The solution of claim 15 wherein the hydrogen peroxide concentration is about 35 to 50 percent by weight.
17. The solution of claim 14 wherein the stabilizer is adipic acid.
18. The solution of claim 14 wherein the stabilizer is glutaric acid.
19. The solution of claim 14 wherein the stabilizer is succinic acid.
20. The solution of claim 14 wherein the stabilizer is a mixture of the stabilizers.
21. The solution of claim 20 wherein the mixture comprises succinic and adipic acids.
22. The solution of claim 21 wherein the ratio of succinic acid to adipic acid is approximately 2:1 by weight.
23. The solution of claim 14 which contains in addition one or more stabilizing chemicals selected from the group consisting of stannates, sulfates, pyrophosphates, fluosilicates, nitrates, and alkylidene diphosphonic acid.
BACKGROUND OF THE INVENTION
Articles of copper or copper alloys are generally cleaned in an operation known as pickling by treatment with a mineral acid solution containing an oxidizing agent. The function of the oxidizing agent is to oxidize cuprous oxide scale and smut to the cupric form, in which valence state it is soluble in the pickling acid, usually sulfuric acid. The oxidizing agent commonly used has been sodium dichromate. However, because of the unacceptability of that chemical from the pollution standpoint, hydrogen peroxide is finding acceptance as the oxidizer.
It is well known, however, that copper ions catalyze the decomposition of hydrogen peroxide in acid medium, particularly at the elevated temperatures used for pickling baths. Thus, there has been a continuing search for materials which will stabilize H.sub.2 O.sub.2 under pickling conditions. Among the materials suggested have been urea (German Pat. No. 1,255,443), fatty acids (British Pat. No. 1,119,969, French Pat. No. 1,468,442, and U.S. Pat. No. 3,537,895), saturated aliphatic alcohols (French Pat. No. 1,539,960), glycerin (U.S. Pat. No. 3,345,225), certain phenols and unsaturated alcohols (U.S. Pat. No. 3,649,194), and phosphoric acid (U.S. Pat. No. 3,373,113).
SUMMARY OF THE INVENTION
According to the present invention there are provided stabilizers selected from the group consisting of succinic, glutaric, and adipic acids, salts, methyl derivatives, and mixtures thereof, which stabilize against copper ion-induced degradation of H.sub.2 O.sub.2 in acidic oxidizing solutions at temperatures up to about 90.degree.C. The copper ions (primarily in the cupric form) may be present in concentrations of up to about 5% by weight. The stabilizers will function in any nonoxidizing mineral acid, sulfuric acid being the most commonly employed. The acid concentration may range from about 0.01 to 50% by weight, preferably about 2 to 25% by weight. The H.sub.2 O.sub.2 may be present in concentrations from about 0.01 to 80% by weight. These stabilizers may be formulated with H.sub.2 O.sub.2 and acid to form an aqueous, acidic oxidizing solution, or may preferably be included in the concentrated aqueous H.sub.2 O.sub.2 solution, as commercially prepared and sold, prior to adding the H.sub.2 O.sub.2 to the pickling bath.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that copper ion-induced or catalyzed decomposition of H.sub.2 O.sub.2 in aqueous acidic medium at elevated temperatures can be controlled by the addition of stabilizing amounts of succinic, glutaric, or adipic acids, their mono-, di-, or trimethyl derivatives, their salts, or mixtures of them. The effectiveness of the stabilizer is greater the longer the chain length, i.e., adipic acid is the most effective and succinic acid is least effective. The stabilizers may be used in any appropriate concentration; however, if the stabilizer is to be formulated into concentrated H.sub.2 O.sub.2 prior to addition to the pickling bath, the solubility of the stabilizer in concentrated H.sub.2 O.sub.2 may be the controlling factor. For example, the solubility of adipic acid in 35% H.sub.2 O.sub.2 is only about 1% by weight. In pickling baths some stabilizing effect will be seen with as little as 0.003% stabilizer concentration. The usual concentration range in pickling baths will be about 0.015 to 1.5%, preferably about 0.03 to 0.1%. Mixtures of the stabilizers may also be used. Since adipic acid is the most effective, a mixture would preferably include it, attention being paid to the solubility considerations already noted. A particularly preferred mixture is the ratio of about 2 parts of succinic acid to 1 part of adipic acid.
In commercial operations it will be found particularly convenient if the stabilizer is incorporated into the concentrated aqueous H.sub.2 O.sub.2 as available commercially. Such a solution can be readily formulated by the H.sub.2 O.sub.2 manufacturer to contain at least 0.05% and as much as 5% by weight stabilizer, depending on the solubility of the stabilizer and the concentration of the H.sub.2 O.sub.2.
While the stabilizers of this invention will be effective in any strong, nonoxidizing mineral acid solution, sulfuric acid is of most commercial significance. It may also be noted that Caro's acid, an equilibration product of H.sub.2 SO.sub.4 and H.sub.2 O.sub.2, may be present in the stabilized solution without detracting from the usefulness of the stabilizers. The H.sub.2 SO.sub.4 concentration of a pickling bath usually is in the range of about 2 to 25% by weight, preferably 4 to 6%. Other nonoxidizing mineral acids may also be used in these concentration ranges. Such other mineral acids would include hydrochloric, hydrofluoric and phosphoric, such acids being used in the pickling of such metals as iron and aluminum and their alloys.
Hydrogen peroxide concentration in a pickling bath typically ranges from about 0.05 to 15% by weight, preferably 0.5 to 3%, although concentrations as low as 0.01% and as high as 50% may be used. If the stabilizer is formulated into concentrated aqueous H.sub.2 O.sub.2, the H.sub.2 O.sub.2 concentration may range from about 20 to 80% by weight, preferably about 30 to 70%, more preferably about 35 to 50%. While the stabilizers of this invention may be added directly to H.sub.2 O.sub.2 of 70% or greater concentration, this is not recommended since solubility is lessened and there is the possibility of forming peroxyacids. If it is desired to start with, say, 70% H.sub.2 O.sub.2, the preferred procedure would be to dissolve the stabilizer in sufficient water that when added to the 70% H.sub.2 O.sub.2 the overall H.sub.2 O.sub.2 concentration would be reduced to a more easily handled concentration, say, 50%. Even when the stabilizer is to be added to 50% or less H.sub.2 O.sub.2, it is still preferred to dissolve the stabilizer in water before addition to the H.sub.2 O.sub.2. Any commercially available grade of H.sub.2 O.sub.2 may be used in this invention. The H.sub.2 O.sub.2 may be unstabilized or preferably may contain any of the usual stabilizing chemicals, e.g., sodium stannate, sodium pyrophosphate, fluosilicates, magnesium sulfate coupled with an alkylidene diphosphonic acid (as taught by U.S. Pat. No. 3,687,627), as well as sodium nitrate and other additives. When present in concentrated commercial H.sub.2 O.sub.2 solutions, the concentrations in percent by weight of the more common stabilizers are as follows: stannates, 0.001-1.0%, preferably 0.015-0.07%; pyrophosphates, 0.01-5.0%, preferably 0.05-4.0%; nitrates, 0.001-0.05%, preferably 0.0015-0.04%. An alkylidene diphosphonic acid will preferably be present in a concentration of at least 0.1% by weight.
The stabilizers of this invention will effectively control copper catalyzed decomposition of H.sub.2 O.sub.2 at temperatures up to about 90.degree.C. However, in most uses the typical temperature range would be about 15.degree. to 40.degree.C.
The invention is illustrated by the following examples, in which percentages are by weight.
EXAMPLE 1
This example illustrates the stabilizing effect of the acids of this invention.
A solution having the following composition was prepared:
15.0% H.sub.2 SO.sub.4 2.0 CuSO.sub.4.5H.sub.2 O 2.9 H.sub.2 O.sub.2
This solution was then divided and formulated with stabilizer additive and stability of the H.sub.2 O.sub.2 at 120.degree.F. was determined, with the following results. Decomposition of H.sub.2 O.sub.2 was measured by the standard potassium permanganate titration test.
Table I __________________________________________________________________________ Additive Residual H.sub.2 O.sub.2, % __________________________________________________________________________ 2.5 hrs. 5 hrs. 24 hrs. 70 hrs. __________________________________________________________________________ None (control) 85 66 -- 6 0.5% adipic acid 100 96 -- 71 0.2% succinic acid 98 97 81 49 0.5% succinic acid 99 98 90 49 0.17% adipic acid + 0.33% succinic acid 100 99 95 68 __________________________________________________________________________
EXAMPLE 2
Table II illustrates the effect of pH when a stabilizer of the invention is added to standard commercial concentrated H.sub.2 O.sub.2. The H.sub.2 O.sub.2 grades used were:
Sample A -- Du Pont's Albone (regular), 35% concentration
Sample B -- Du Pont's Albone (cosmetic grade), 35% concentration
In Samples A and B the pH of 3.5 was obtained by addition of a sodium hydroxide solution. Samples C and D are the same as A and B, respectively, except that no pH adjustment was made. Sample E was the same as C except that the pH was adjusted by addition of H.sub.3 PO.sub.4.
A pH of about 1.5 is that obtained naturally by addition to 35% H.sub.2 O.sub.2 of about 3% of the acids of this invention. Whereas commercial concentrated H.sub.2 O.sub.2 is typically sold at a pH of about 3.5, Table II shows that it is not desirable to adjust pH to this value after addition of the acid stabilizers. Stability will be optimized by allowing the pH to remain at its natural level.
Table II ______________________________________ 3% Succinic Acid in 35% H.sub.2 O.sub.2 ______________________________________ Sample pH % Loss (20 hrs. at 150.degree.F.) ______________________________________ A 3.5 5.0 B 3.5 3.2 C 1.5 2.0 D 1.5 0.6 E 1.0 >2.0 ______________________________________
A peroxide loss of about 2% or less is considered commercially satisfactory .
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