US 3156654 A
Description (OCR text may contain errors)
United States Patent "ice 3,156,654 BLEACHING Jan 0. Konecny and Robert E. Meeker, both of Berkeley, Calif., assignors to Shell Gil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed June 19, 1961, Ser. No. 117,791 5 Claims. (Cl. 25295) This invention relates to the improvement of peroxide bleaching, particularly to a method for increasing the bleaching activity of peroxides and to novel compositions which are advantageous for all kinds of bleaching.
A variety of peroxides, including hydrogen peroxide, inorganic persalts such as the water soluble perborates, percarbonates, perphosphate etc., percarboxylic acids and the like have been used for bleaching, especially, textiles. Persalts in particular have been widely used, particularly in Europe, in detergent compositions to provide bleaching simultaneously with laundering. These compositions have had to be used at boiling temperatures in order to achieve a satisfactory bleach. This has precluded their use in home washing machines since temperatures above about 50 to 60 C. are generally not feasible therewith.
A number of proposals have been made for improving the effectiveness of peroxide bleaching agents. U.S. Patent 2,898,181 recommends the addition of certain amides to washing compositions containing perborate bleaching agents so they can be used at temperatures of about 60-70 C. Special carboxylic acid esters are described in British Patent 836,988 as useful for improving textile bleaching with either aqueous hydrogen peroxide or inorganic persalts while British Patent 847,702 shows the use of urea for making percarboxylic acids more useful bleaching agents. German Patents 1,010,048 and 1,018,181 disclose the use of formamide and organic nitriles, respectively, as accelerators of bleaching with peroxides. These additives are not as effective as would be desirable and must be used in relatively large amounts, to 100 mole percent of the peroxy-bleaching compounds, in order to match the bleaching which can be obtained at boiling temperatures with sodium perborate, for example. As a result, the cost of the product is greatly increased and the usefulness of the final composition for some purposes may be interfered with by the large amount of additive.
An important object of the present invention is the provision of bleaching compositions which avoid the foregoing disadvantages of prior peroxy bleaching agents. A particular object is the provision of novel bleaching compositions which contain a new type of accelerator of peroxide bleaching which has such a high activity that only a relatively small amount is suficient to insure the desired effective bleaching. Another object is to provide a new method of textile bleaching with peroxidic com pounds in which improved bleaching can be obtained without excessive peroxide loss through decomposition. A special object is the provision of detergent compositions which are capable of providing desirable bleaching action during laundering in home Washing machines. Still other objects and advantages of the invention will be apparent from the following description of suitable modes of carrying out the invention which, however, is not limited to the advantageous modifications thus given by way of illustration.
It has been discovered that the bleaching activity of peroxy compounds can be materially improved by using therewith heavy metal ions which catalyze peroxide decomposition together with a special type of chelating agent for said heavy metal. The chelating agent must be one which is not only itself stable and without undesirable catalytic effect on peroxide decomposition in the bleaching composition and/or bath in which it is to be used,
3,l56,54 Patented Nov. 10, 19 64 but also should be one which forms a complex with the said heavy metal ions which complex is soluble and similarly stable in the bleaching bath. The chelating agent used must furthermore be one which is not a stronger complexing agent for the heavy metal ions present than is the material to be bleached. When the heavy metal ion peroxide decomposition catalyst and chelating agent therefor are selected so they have this unique relationship to the material which is to be bleached, they cooperate to accelerate and enhance the bleaching by peroxide bleaching agents making them effective at lower temperatures so that their use in home laundry equipment becomes practical. This is quite unexpected since heavy metal ions would have been predicted to be undesirable in bleaching with peroxides. They would have been expected only to promote loss of peroxide through decomposition without providing any advantage. There was no reason to predict any acceleration or improvement in bleaching effect from the addition of a chelating agent. Indeed many combinations of heavy metal ions with chelating agents therefor do not show the advantages of the invention. Only by proper choice of the heavy metal catalyst of peroxide decomposition and of chelating agent not only with respect to each other, but also in regard to the adsorptive power of the material to be bleached relative to complexing strength of the chelating agent can the new results of the invention be obtained.
With the heavy metal and chelating agent chosen in the above-indicated special relationship to each other and to the material to be bleached, it has been found that there will be a substantial adsorption of heavy metal ions on the material to be bleached but at the same time the heavy metal ions not so adsorbed will be maintained in solution in an inert complexed form so they will not catalyze undesirable decomposition of peroxide. Representing the complexing agent by Q and the material to be bleached as R, one can write equations representing the equilibria which control the proportion of the heavy metal ions which will be available for promoting the desired bleaching and which will be held in inert complexed form in the solution so that loss of peroxide through undesirable decomposition away from contact with the material being bleached can be minimized. These are,
using cobalt ions as an example of suitable heavy metal ions:
Thus besides its desirable synergistic effect in promoting the bleaching, the chelating agent should also preferably form sufficient of the chelate (CoQ) to maintain essentially all the heavy metal ions not adsorbed on R in inert soluble complexed form so that undesirable peroxide decomposition is minimized without interfering with the required amount of adsorption of cobalt ions indicated in the second of these equations.
Thus an important feature of the invention is that it provides a simple, one step method of operation whereby bleaching is improved by heavy metal ions adsorbed on the material to be bleached so as to catalyze the deco1nposition of the peroxide at the precise location where bleaching is desired. The metal ions are believed to decompose hydrogen peroxide by a catalytic cycle illustrated, in the case of copper ions, by the equations:
This localized production of OH radicals from the peroxide'initially present as the peroxide bleaching agent, either by direct catalytic decomposition as when using hydrogen peroxide or by catalytic decomposition of such peroxide formed from the starting peroxide bleaching agent, for instance by hydrolysis of a .peracid or persalt such as a perborate or the like. These OH radicals are among the strongest oxidizing agents known and probably contribute to the observed improvement in the bleaching. However, that may be, the improvement in bleaching obtained by using the indicated combination of chelating agent and heavy metal ions depends on the amount of heavy metal ion adsorbed on the fabric or other material being bleached, e.g., Co++ adsorbed on R. It has been found that with a constant amount of chelating agent such as pyridine-Z-carboxylic acid for example, the bleach increases with increasing amounts of cobalt sulfate or the like. With a constant amount of the latter and increasing amounts of the chelating agent, sufficient in all cases to provide an appreciable excess and thus prevent precipitation of heavy metal hydroxide which would promote undesirable peroxide decomposition, the bleaching decreases, the decrease being coincident with decreased adsorption of heavy metal ions by the fabric. The total concentration of heavy metal in the bleach bath can be varied widely Without detrimentally aifecting'the bleach provided the heavy metal to chelating agent ration is maintained at a proper constant ratio.
It is not desirable to use peroxide decomposition catalysts such as heavy metal ions alone. A small improvement in bleaching can indeed be obtained by adding copper or cobalt sulfate to a sodium perborate bleaching bath, for example. But the increase in bleaching effect is small and accompanied by extensive peroxide loss through decomposition both by the metal ions and precipitated hydroxides. For example, when bleaching of a standard cotton test cloth for 15 minutes with sodium perborate grams per liter of bleach solution) at 60 C., the addition of 0.015 millimole of copper sulfate per liter, results in an increase of reflectance (AR) of the cotton cloth of 9.4 units compared with 6.1 units under the same conditions without added copper sulfate, but the loss of peroxide through decomposition is increased from 10% to 32%. However, when the catalysis of peroxide decomposition by copper is localized at the surface of the cloth, the increase in reflectance (AR) is 17.4 units and the loss of peroxide in the solution not in contact with the cloth is no greater than when no copper is used.
Any of the heavy metals of the transition series which catalyze the desired decomposition of peroxide at the surface to be bleached can be used provided the proper chelating agent is employed therewith. In making up liquid or powdered bleaching composition-s it is advantageous to add the heavy metal and chelating agent therefor to the peroxide bleaching agent as a preformed complex of heavy metal with the chelating agent. Such preformed complexes can also be added to the solution used for bleaching separately or together with the peroxide bleaching agent. The preformed complex can be made readily by mixing together in aqueous solution the chosen chelating agent with a suitable source of the required metal ions. Alternatively one can add to the peroxide-contain: ing bleaching solution the source of heavy metal ions and chelating agent separately. In this case it is desirable to introduce the chelating agent first and to then add the heavy metal so that localized high concentrations which can catalyze loss of peroxide by decomposition are avoided. Soluble salts are one of the more convenient sources of the required heavy metal ions. Inorganic soluble salts are generally more economical but other sources of heavy metal ions can also be used successfully. Copper and cobalt chlorides, sulfates, nitrates, perchlorates and the like are typical of the salts which are useful. Other metals whose salts can be used in the same Way include chromium, manganese, iron, nickel, zinc, molybdenum, ruthenium, silver, cadmium, tungsten, osmium, gold and ther- -cury. Thebest results are. usually obtained, however,
with copper. and cobalt salts. Cobalt salts have. special advantages because of their outstanding effectiveness in improving peroxide bleaching when used with a chelating agent in accordance with the invention.
The chelating agent chosen should preferably be one which forms a chelate complex with the heavy metal or mixture of heavy metal ions which chelate is soluble in the bleaching solution to the extent of at least 5 l0 moles per liter of solution. While there are differences in the effectiveness of various chelating agents with different heavy metal catalysts in bleaching different materials, all those which will give up heavy metal to the material being bleached can be successfully used.
There are special advantages in using as the chelating agent a particular subgroup of amino carboxylic acids having not more than 2 carbon atoms separating the 'carboxyl group frorrithe amino nitrogen ato'rnj These are the pyridine-2-carboxylic acids such as pyridine-2- carboxylic acid itself and pyridine-2,6-dicarboxylic acid and the like, which meet the foregoing requirements as to complexing power. These are not only outstanding in their effectiveness as bleach promoters but also are especially advantageous in minimizing loss of peroxide by undesirable decomposition during bleaching by the new method. Other useful pyridine carboxylic acids are described in US. Patent 2,624,655 as useful hydrogen peroxide stabilizer. An es ecially preferred subgroup of these chelating agents are those having a pyridine ring which is substituted by a single carboxy group attached to the 2-position of the ring, as for example, picolinic acid, 4-methyl-picolinic acid, and the like. The amino carboxylic acids can be used in the free acid form or as their water soluble salts, particularly the alkali metal salts or the like.
Another type of aminocarboxylic acid chelating agents which can be used in bleaching materials which have a stronger adsorption power for heavy metal ions than does cellulose are the compounds which contain at least one N,N-dicarboxyalkylarnino group, N-(R-COOX) wherein R is an alkylene radical of up to two carbon atoms and X is hydrogen or a salt-forming cation such, for instance, as an alkali metal or alkaline earth metal or ammonium ion, the two indicated Xs being the same or different. US. Patent 2,371,623 describes a number of polycarboxy amines of this kind such as nitrilotriacetic acid, aminoethyl-N,N-diacetic acid, ethylenediamine-N,N,
N',N-tetraacetic acid, etc., which can be successfully used in the stock solutions of the invention. Especially advantageous are those polycarboxy amines which contain a plurality of N,N-discarboxyalkylamino groups in the molecule, especially those having at least two adjacent carbon atoms to each of which is directly attached at least one of said N,N-dicarboxyalkylamino group. A particularly suitable sub-group of polycarboxyamines of this preferred type are the water-soluble N,N-(dicarboxyalkyl)amino-substituted carbocyclic compounds having a saturated carboeyclic ring with at least two adjacent ring carbon atoms each directly linked to the nitrogen atom V of an N,N-di(carboxyalkyl) amino group containing up to two carbon atoms in each of said alkyl radicals. Examples of water-soluble chelating agents of this type are the 1,2-diaminocycloalkane-N,N,N',N-tetraacetic acids and their salts having 5 to 18 carbon atoms in the cycloalkane radical, such as 1,Z-diaminocyclopentane-N,N,N', N-tetraacetic acid, disodium 1,Z-diaminocyclohexane-N, N,N,N'-tetraacetic acid, tetra-potassium 1,2-diaminoperhydronaphthalene-N,N,N,N'-tetraacetic acid, tri-arnmonium 4,7-diisobutyl-1,Z-diaminoperhydronaphthalene-N, N,N,N-tetraaceticacid and the like. i e
At least a sufiicientamount of chelating agent for chelating with the heavy metal ion or ions used shouldzbe employed in the bleaching bath to complex essentially all heavy metal ionperoxide decomposition catalyst not adsorbed by the material being bleached. More advantageously an excess of organic-chelating'agent over such amount is used. As a general rule amounts between.
about 0.01 to about. 20 millimolesof chelating agent per liter of bleaching solution are employed and most desirably amounts between about 0.05 to about 1 millimole per liter. The amounts of heavy metal ion and chelating agent used can be relatively small compared with the amount of peroxide bleaching agent employed since the action of the complex is catalytic in the bleaching. Suitable amounts of heavy metal are about 0.001 to about 1, more advantageously between about 0.01 and about 0.3 millimole per liter of the bleaching solution used. Bleaching solutions containing peroxide bleaching agent in concentrations of at least about 0.2 millimole per liter and more preferably about 3 to about 140 millimoles per liter, are used. In choosing the proportions of the different components to use within these ranges, the relationship previously noted in connection with the discussion of the equilibrium involved should be kept in mind.
As previously indicated, the invention is applicable with any of the peroxide bleaching agents, such as hydrogen peroxide and per compounds which give rise to hydrogen peroxide in aqueous solution. Suitable compounds include alkali metal persulfates, perborates, percarbonates, perpyrophosphates and persilicates. These are not true persalts in the strict chemical sense but are believed to contain hydrogen peroxide of crystallization, which is liberated in aqueous solution.
The invention can be applied to bleaching baths such as are used for treating textiles, wood pulp and the like, to wash liquors, such as are used in commercial laundering and to solid bleaching compositions. Solid bleaching compositions prepared according to the invention, preferably contain the peroxy bleaching agent, source of heavy metal ions and organic chelating agent therefor in the ratios previously indicated as desirable in the bleaching bath. In addition, inert salts and any of the conventional adjuncts used in bleaching with or without detergents or other auxiliary agents.
18 carbon atoms per molecule. Examples of non-ionic surface active agents which can be used in making new bleaching compositions according to the invention are the saponines, ethylene oxide condensation products with fatty acids, alcohols, alkyl phenols, esters, and the like, especially those with alkyl chains of 7 to 14 carbon atoms and 10 to 20 glycol units per molecule.
The portions in which the detergents can be used with the new bleaching agents can vary widely. Usually amounts in the range of about 1 to 10 parts by weight of detergent or detergent mixture can be used with an amount of peroxide bleaching compound sufiicient to provide about 0.1 to 5 parts by weight of active oxygen.
Any of the builders or other additives useful in deter- 15 gents can be used in the new washing compositions of the invention. These include alkaline materials such as alkali metal phosphates, particularly the orthophosphates, tripolyphosphates and pyrophosphates, and silicates, or inert compounds such as alkali metal sulfates or chlorides, or organic additives of which carboxymethylcellulose and fluorescent agents are representative examples.
The advantages of the invention are shown in the following illustrative examples of certain of the Ways in which it can be applied.
Example I A series of bleaching tests were made using a stirred bath containing an aqueous solution containing 10 grams per liter of sodium perborate (NaBO -H O -3H O) as the feet was determined by measuring the reflectance of the sample. The following results were obtained:
Increase in Milllmoles Millimoles Reflectance Peroxide of Heavy Complexing of Cloth* Decom- Heavy Metal Salt Metal M++) Complexiug Agent Agent per (Standard position,
per Liter Liter Units- Percent Maximum: About 20) None None None None 6. 1 10 Cobalt sulfate 0. 010 None 7. 6 30 Do 0.020 .do None 8.1 54 Do 0.015 Pyridine-2,6-dicarboxylie 0. 25 11. 1 17 act Do 0. 005 Pyridine-learboxylic acid 0.25 12.1 17 Do 0.025 o 0.25 15. 7 19 *Limiting increase in reflectance under repeated bleaching was 20 units.
When washing and bleaching compositions are prepared by combining an organic surface active agent with a peroxy bleaching agent, heavy metal salt and organic chelating agent or a preformed complex of the heavy metal and chelating agent. It is usually desirable to use a larger amount of heavy metal salt because of the tendency of detergents to decrease adsorption of heavy metals by the cloth or other material being bleached. The organic surface-active agents used can be any of the soaps or synthetic detergents. Alkali metal salts of fatty acids such as stearic and/or palmitic acids, or of rosin acids are examples of commonly used soaps which can be employed. Synthetic detergents which can be used with or without such soaps include the anionic, cationic and nonionic organic surface-active agents. Typical anionic detergents which can be successfuily used in making washing compositions having improved bleaching action in accordance with the invention include sulfonates such as alkyl benzene sulfonates, alkyl sulfonates, sulfonates of fatty acid-monoglycerides, fatty acid oxyethylamide sulfonates, oleylrnethyltauride, sodium alkylphenol polyether sulfonates, and the like having aliphatic hydrocarbon chains of about 10 to about 20 carbon atoms, and alkyl sulfate salts such as sodium lauryl sulfate, and mixed secondary alkyl sulfate alkali metal salts of 8 to Example II The effect of adding cobalt sulfate with an excess of pyridine-Z-carboxylic acid, 3.10 M cobalt with 2.5.l0- chelating agent, to a bleaching bath containing various concentrations sodium perborate was determined in the same way as in Example I in comparison with bleaching in the same way without added catalyst. The following are the results obtained together with the loss of perborate by decomposition in the 1% solution at 15 minutes bleaching time.
Example IV Tests to show the amount of heavy metal adsorbed by the cotton cloth in the bleaching were carried out as in Example I using 15 minutes bleaching time at 60 C. with a bath containing 10 grams of sodium perborate per liter to which was added different amounts of cobalt sulfate and pyridine-Z-carboxylic acid. After bleaching and rinsing the samples of cloth, reflectance measurements were made in the usual way and the amount of cobalt adsorbed was determined by neutron activation. The following results were obtained:
Cobalt Sulfate Pyridine-2- Cobalt Ad- Bleach (increase added (millicarboxylic acid sorbed on Cloth in reflectance moles per liter) added (millimoles (millimoles per AR units) per liter) 1,000 grams) Example V Cotton cloth was bleached using a stirred vbath containing 10 grams per liter of sodium perborate to which had been added 1.1 millimoles per liter of sodium pyrophosphate as chelating agent and 0.015 millimole per liter of cobalt sulfate. In a 15 minute bleach at 60 C., an increase in reflectance of the cloth of 14.7 units was obtained.
xample VI The effectiveness of the new bleaching mixture in combination with a commercial, heavily built, alkylbenzene sodium sulfonate detergent was determined by tests carried out with a mixture of the detergent Tide with sodium perborate in a Weight ratioof 0.17:1 together with cobalt sulfate and pyridine-Z-carboxylic acid in small amounts sufiicient to make their concentrations in the bleaching bath 0.05 and 0.25 millimole per liter, respectively. The bleaching was carried out as in Example I using 10 grams of sodium perborate per liter and a bleaching time of 15 minutes at 60 C. The bleached cotton cloth showed an increase in reflectance AR of 13.3 units.
While perborate bleaching of cellulose fibers has been emphasized in the foregoing examples, this has been for purposes of simplification of the description only and it is to be understood that the invention is not limited thereto butis broadly applicable to the bleaching of any bleachable material which adsorbs heavy metal ions from aqueous media using any peroxide bleaching agent. Among other textile fibers which can be bleached using .the same operations as with cotton, are the synthetic fibers including polyamide fibers such as Orlon, nylon, Dacron, etc., polyester fibers of which polyacrylate fibers are an example, etc. Hair, furs, and the like are other types of bleachable materials with which the invention can be used.. The bleaching process is also applicable with cellulose in other forms than fabrics or threads, being useful in paper pulpbleaching and the like, for instance. ,Witlrthese and similanmaterials improved bleaching can be similarly obtained using other peroxide bleaching agents such as sodium perphosphate or hydrogen peroxide itself for instance.
Still other variations can be made in the invention which will be recognized as not limited to the examples given by way of illustration nor by any theory proposed in explanation of the improved results which are obtained.
We claim as our invention:
1. A composition adapted for bleaching cellulosic textiles consisting essentially of granules of sodium perborate uniformly admixed with a water soluble inorganic salt of cobalt, each molecule of said cobalt salt being in 10 the form of a chelate compound thereof with pyridine- Z-carboxylic acid, there being about 0.2 to about 140 millimoles of perborate to from about 0.001 to about 1 millimole of Water-soluble cobalt salt and 0.01 to 20 millimoles of pyridine-Z-carboxylic acid providing a molar excess of said acid to water-soluble cobalt salt present so that in aqueous solution the chelate gives up cobalt to cellulosic material but preserves the perborate from decomposition by cobalt not absorbed by the cellulosic material.
2. A composition in accordance with claim 1 wherein sodium perborate is present in uniform admixture with a chelate of cobalt sulfate and pyridine-Z-carboxylic acid. 3. In a process for bleaching cellulosic textile material by contact with an aqueous solution of a peroxide bleaching agent which gives rise to hydrogen peroxide in aqueous solution, which bleaching agent is present in a concentration of about 0.2 to about 140 millimoles per liter of solution, the improvement of maintaining in the solution a concentration of cobalt ion between about 0.001 and about 1 millimole per liter of solution, also maintaining in the solution about 0.01 toabout 20 millimoles of pyridine-Z-carboxylic acid, said pyridine-Z-carboxylic acid being maintained in me- 5 lar excess over the cobalt ions present so that while the cobalt ion is adsorbed on the textile material and catalyzes its bleaching, the remaining cobalt maintaining in the solution a concentration of cobalt ions between about 0.001 and about 1 millimole per liter of-solution, also maintaining in the solution about 0.01 to about 20 millimoles of pyridine-Z-carboxylic acid,
said acid being maintained in molar excess over the amount of cobalt ions present so that while cobalt ions are adsorbed from the solution on to the cellulose fibers and catalyze its bleaching, the remaining unadsorbed cobalt ions are maintained in soluble complexed form in the solution and do not catalyze decomposition of hydrogen peroxide out of cont-act with the textile material. 5. In a process for bleaching cotton cloth by contact 6 with an aqueous solution of sodium perborate containing about 0.2 to about 14.0 millimoles of sodium perborate perliter, the improvement of maintaining in the bleaching solution a concentration of cobalt ions between about. 0.001 and about 1 millimole per liter of solution, also maintaining in the solution about 0.01 to about Y 20 millimoles of pyridine-2-carboxylic acid, the pyridine- Z-carboxylic acid being in molar excess over the cobalt-ionspresent so that While cobalt ions are adsorbed on the cotton cloth and catalyze its bleaching, the unadsorbed cobalt ions are maintained in soluble complexed form which does not catalyze decomposition of the sodium perborate out of contact with the cloth. 1
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