CA1046388A - Prevention of discoloration in nickel-contaminated caustic solutions containing chlorine - Google Patents

Abstract

ABSTRACT
The discoloration in aqueous slurries or solutions of alkaline products containing nickel-contaminated caustic and available chlorine is prevented by adding to the granular or powdered alkaline composition prior to the addition of water an organic chelating agent which is sodium gluconate, sodium glucoheptonate, sodium ethylene diamine tetraacetate or a mixture thereof. Other readily available chelating agents and sequestrants have been found ineffective for this application.

Description

~046388 BACKGROUND
1. Field of the Invention This invention relates to a method for preventing the discoloration in alkaline solutions of nickel-contaminated caustic and available chlorine which are typically used in applications such as dishwashing and the like.

2. Description of the Prior Art A review of the prior art sh~ws lt is ve~y common to use in clear.ing compositions so~.e for~ulation employing a builder which is often an alkali metal composition and/or an organlc chelating agent. Among the prior art references is the W. R. Meyer U. S. Patent 2,915,444 wherein Meyer discloses cleaning and plating ferrous metais with an ; el~ctrolytic cleaning solution cc,ntaining sodium gluconate as the iron complexing agent and sodium hydroxide. Hydroxy-ethyl ethylene diamine triacetic acid can be used in place of the gluconate. A later U. S. Patent (2,992,187) to H. Gershon discloses the removing of rust by the use of an aqueous solution of sodium hydroxide and sodium gluco-heptonate along with sorbitol or other polyhydroxy compounds.
Another U. S. Patent (2,992,997) to B. Arden et al discloses the removing of corrosion coatings from ferrous bodies with aqueous alkali metal hydroxide solutions containing an alkali metal complexing salt of a hydroxy aliphatic acid and trialkanolamine. Among the hydroxy aliphatic acid salts ' disclosed are sodium gluconate and mixtures of triethanol-amine and a salt of ethylene diamine tetraacetic acid.
Other washing and cleaning compositions are disclosed in patent such as U. S. Patent 2,615,846 to ~ ., -1046388B. Dvorkovitz et al, who disclose a washing composition for rubber, metal and glassware which comprises caustic alkali metal hydroxide, water and alkali metal gluconate such as potassium or sodium gluconate. Another patent is U. S. Patent 2,975,140 to W. L. Yaroch which discloses the use of sodium gluconate in an organic finish remover which is composed of alkali metal hydroxide and watPr. Finally, still another patent is U. S. Patent 3,28l~,36~ to G. P.
Bourean et al which discloses a paint stripping composition containing sodium hydroxide and a halogenated organic acid compound. The patent furtker teach s the use of sodium gluconate snd other se~uester-ng Pgen~s were already kno~.m in the prior art previous to Bourean et al substituting the halogenated organic acid ccmpound for ~Jario7ls p~enols.
, SUMMARY OF THE INVENTION
In accordance with this invention there is provided a method for inhibiting the discoloration of alkaline aqueous slurries or solutions of compositions containing nickel-contaminated caustic and available chlorine comprising adding to said composition while in a dry state prior to the addition of water a chelating agent `- selected from the group of sodium gluconate, sodium gluco-heptonate, sodium ethylene diamine tetraacetate and mixtures thereof in an amount f~om 0.5 to 10 weight percent of the amount of said composition, said caustic being caustic soda or caustic potash or mixtures thereof.

` DESCRIPTION OF THE PREFERRED EMBODIMENT
When aqueous slurries or solutions of products containing nickel-contaminated caustic alkali metal and , .

1046388 ~
available chlorine-releasing compounds are prepared, purple discoloration or a black precipitate occurs. This dis-coloration or precipitate is particularly objectionable when the slurry or solution is to be used in the food service industry such as for dishwashing applications.
~leaning compositions for machine dishwashing are largely inorganic since low foam rather than high foam is desirable along with cl~rity of glassware. The dishwashing problem in restaurants is complicated by the requirement for sterilization also.
It has been the practice of formulating machine dishwashing composiL-ons or detergents to use in the m~in various combinations of inorganic sodium and potassium ~alts such as polyphosphates, silicates, carbonates and basic materials such as sodium and potassium hydroxides.
It has not been possible to use effective amounts of well-known organic detergents such as the alkyl aryl sulfonates, alkyl sulfonates, alkyl aryl polyethers or alkanol amides because of the foam these detergents develop during the washing operation. However, certain low-foaming, organic, nonionic detergents have been made available commercially which can be incorporated in small amounts with inorganic materials in mechanical dishwashing formulations without seriously increasing their foaming tendency. Surfactants of the low-foaming type are well known in the art, for example, see U. S. Patent 3,308,607 to Diehl et al. Avail-able chlorine-releasing compounds have also been added.
Finally, but not necessarily in the least amount, certain other salts have been added such as sodium chloride or -~
sodium carbonate partly as a bulking and filling agent although in the case of sodium or potassium carbonate, .

10~6388 there is some water softening effect. The particular builder, water softener, bulking agent and corrosion resisting material selected for the dishwashing composition depends upon the type of soil expected to be encountered, the type of equipment used and the water co~ditions encountered in the use of the composition.
It w~s discovered that when d~hwashing compo-sitions and other cleaning solutions were prepared for us~
as aqueous solutions, that an obJectionable purple dis-coloration and/or a black precipitate would occur if an alkali metal hydroxide (caustic alkali) contaminated by nickel and an availabl~ chlorine-releesi~g c~pound were both present in the granular or powdored cleaning compo-sition. It was found that ~n such circu~st2nces the addition of a small amount of an organic chelating agent selected from the group consisting of sodium gluconate, sodium glucoheptonate, sodium ethylene diamine tetraacetate and mixtures thereof when used in an amount from about 0.5 to 10 and preferably from 0.5 to 5 weight percent of the amount of the dry ingredients of the cleaning composition would avoid the condition.
The caustic alkali or alkali metal hydroxide useful in the cleaning compositions within the ambient of tbis invention are sodium hydroxide and potassium hydroxide or mixtures of the two. While for reasons of convenience, .
` of availability, and cost, sodium hydroxide is typically used, there are instances when the greater efficiency of A~.
potassium hydroxide makes it a more desirable caustic even though it is economically less attractive. In the manu~
facture of the foregoing caustic alkali materials, ~ -unavoidably though unintentionally, sometimes nickel is introduced in a contaminating amount into the caustic.

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The term 'available chlorine-xeleasing compounds" is fairly well understood in the detergent and laundry arts to embrace a particular class of chlorine compounds. Not all chlorine compounds will release chlorine and, therefore, be suitable as a cleaning composi`ti`on. The American Society for testing Materials in Standard Test Method B2022-64, reapproved in l970, defines available chlorine as the measure of the oxidizing power of the chlorine present as hypochlorite. It further provides in Sections 42-45 a standardized test method for determining available chlorine by the thiosulfate method.
This method is also reported in classical chemical textbooks.
A wide variety of available chlorine-containing compounds, including both inorganic and organic available chlorine-containing compounds, may be present as the chlorine-containing species of solid particles employed in the composition of this invention. Inorganic available chlorine-containing compounds include, for example, the so-called chlorinated trisodium phosphates, a class of compounds which consists of physico-chemical combinations in unitary crystalline form ; 20 of trisodium phosphate and sodium hypochlorite. Such compounds are known and are described, along with their method of preparation, in U.S. Patents 1,555,474 or 1,965,304. Other inorganic chlorine-releasing compounds include calcium hypo-chlorite, sodium hypochlorite and lithium hypochlorite.
Organic available chlorine-containing compounds include N-chlorinated heterocyclic compounds such as the N-chlorinated triazines, for example, melamine, ammelide, ammeline and cyanuric acids; other N-chlorinated organic compounds include N-chlorinated alkyl, aryl, and alkaryl sulfonamides, such as N-chlorobenzene sulfonamide, N-chloro-nitrobenzene sulfonamide, N-chloromethyl and ethyl benzene sulfonamides. Of these available chlor~r.e-containing co~pounds, the N-chlorinated organic comp~unds, particu-larly the chlorinated triazine compounds are advantageous.
Examples of such N-chlorinated cyaruric ~cids,often referred to as chlorocyanurate compounds, include chloro-cyanuric acid such as dichlorc_yanuric 2C ids ~nd trichloro-cyanuric acids; the metal salts of ',:he dichlorocyanuric acld and part cularly the alkali meta! s~lts thereof. -Anhydrous potassium dichlorocyan1tric acid is one of the more stable compounds and is, therefore, particularly preferred. An interesting related compound having a polymeric nature is mono(trichloro)-tetra-(monopotassium dichloro)-penta-s-triazine trione which up till recently was more commonly known as ~(monotrichloro)-tetra-(mono-potassium dichloro)] penta isocyanurate.
As previously pointed out, the amount of the available chlorine-releasing compound in the granular or ; powdered cleaning composition will vary according to many extraneous factors but, typically, the amount of chlorine-releasing compounds in the composition will range from about 1 to about 50 percent, with from about 1 to about 10 percent being more typical when an organic compound is employed and the higher amounts being more typical when an ~0 inorganic chlorinated compound such as chlorinated phosphates are used. The caustic soda or caustic potash employed in the cleaning composition will also be somewhat varied with a figure from about 10 to about 50 percent being typical, again depending upon what other alkalinity builders, such as soda ash or sodium metasilicate, may be present.
The composi~ions are prepared by dry-blending n random order all of the solid ingredients employed in the invention. T~ereafter, the granular composition is added to water when ready to be used by the ultimate consumer.
In the case where minor amounts of the synthetic nonior,ic l~w foaming deterg~nt is employed in such a cleaning appli-cation, the detergent is added after some, if not all, of the dry ingredients have been blended together. The blending is carried ou~ by a dry-blendlng method such as a ribbon blender until the complete formulation is prepared.
The subsequent slurrying or dissolving of the surfactant containing composition by the ultimate customer is carried out in the same manner as noted for the dry composition without any surfactant being added.
It was surprising to discover in the course of developing this invention that other well-known sequestering agents utilized in the detergent and cleaning industry such as sodium nitrilotriacetate, sodium tripolyphosphate, sodium citrate, citric acid and the like were completely ineffective for the purposes of this invention.
The following examples are included to illustrate the method of this invention and the preparation of compositions utilized in the present invention but they are not to be considered limiting. Unless otherwise - .

, 104~3~8 specified, all parts are by weight and all temperatures are expressed as degrees centigrade.
A typical commercial granular machine dishwashing detergent composition was prepared by dry-blending together 44 parts of sodium carbonate (commonly called soda ash),

3 parts of rmono(trichloro)-tetra-(monopotassium dichloron -penta-s-triazine trione (available under t'~e trademark ACL-66), 2~ parts of sodium tripolyphosphate, i2 parts of sodium metasilicate and 20 parts of granular sodium hydroxide (better known as caustic soda). After dry-blending the foregoing composition was used as a master batch for the examples below. The effectiveness of the sequestering agent was determined by taking 50 gr~ms of the dishwashing composition prepared in that example And. c~nverting it into a liquid concentrate by the addition of 25 ml. of water.
This concentrate approximates the use conditions encountered in feeding dishwashing detergent concentrate to commercial dishwashers by automatic means. The color of the concen-; trate solution at room temperature was then observed.

EXAMPLE I
In this example no additional sequestrant was added to a portion of the master batch. It should be noted that sodium tripolyphosphate present in the master batch is considered in addition to having cleanlng ability to act as a sequestrant. The liquid concentrate prepared as specified above had very much purple discoloration.

EXAMPLE II
To a portion of the master batch was added 5 percent sodium citrate. The liquid concentrate prepared _9_ .! :

, from this composition had a discoloration similar to that in Example I.

EXAMPLE III
To a portion of the master batch above was added 5 percent by weight of citric acid. The concentrated detergent so'ution from this composition had a reduced but still very pronounced discoloration.

EXAMPLE IV
~o a portion of the above master batch was added 1 percent by weight of sodium nitrilotriacet~te. The concentrate solution prepared from this compasltion had ; very much purple discoloration equivalent to E~ample 1.

EXAMPLE V
To a portion of the above master batch was added 1 percent by weight of sodium ethylenediamine tetraacetate.
The concentrated composition when tested as indicated above had no discoloration.

EXAMPLE VI
To a portion of the above master batch was added 1 percent by weight of sodium gluconate. When tested as indicated above the detergent concentrate had no dis-coloration.
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EXAMPLE VII
To a portion of the above master batch was added ~ percent by weight of sodium gluconate. The concentrate i when prepared and tested as above had no discoloration.

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EXAMPLE VIII
To a portion of the above master batch was added 5 percent by weight of sodium gluconate. The liquid detergent concentrate prepared from this composition had no discoloration when tested as above.

EXAMPLE IX
To a portion of the above master batch was added 1 percent by weight of sodium glucoheptonate. The detergent concentrate of this composition when tested as above had no discoloration.
Examples I through IV are comparative examples which show the state of the cleaning compositions with organic sequestrant~ and inorganic sequestrants (sodium tripolyphosphate) which are outside the scope of this invention. The sequestrants whi~e well known and of use in the detergent art have no real efficacy in avoiding the discoloration problems introduced when nickel-contaminated cau8tic such as sodium hydroxide is used in the formulation with an available chlorine-releasing composition.
~ 20 Examples V through IX are illustrative of the ; invention and show that small amounts ofsodium gluconate?
sodium glucoheptonate and/or sodium salt of ethylene-diamine tetraacetic acid are effective in inhibiting the otherwise resultant discoloration. Applicants are unable to explain this phenomena or advance any theories as to the pos8ible reaction or reactions involved.
While the invention has been illustrated in the foregoing examples by the use of sodium hydroxide contaminated with nickel since it is the more common caustic eF~loyed, equally advantage~us results are obtainab~ when the nickel-contaminated caustic is potassium hydroxide.
In the same manner mixtures of the foregoing chelating agents found useful in this invention can be employed in obtaining the benefits of this invention.
The foregoing examples and methods have been described in the foregoing specification for the purpose of illustra_ion and not limitation. Many other ~odifi cations and ramifications will naturally suggest themselves to those skilled in the art based on this disclosure.
These are intended to be oomprehended as ~ithin the scope oi this invention.

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Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for inhibiting the discoloration in alkaline aqueous slurries or solutions of compositions containing nickel-contaminated caustic and available chlorine-releasing compounds comprising adding to said composition while in a dried state prior to the addition of water, a chelating agent selected from the group consisting of sodium gluconate, sodium glucoheptonate, sodium salt of ethylene diamine tetraacetic acid and mixtures thereof in an amount from about 0.5 to 10 weight percent of the amount of said dry composition, said caustic being sodium hydroxide or potassium hydroxide or mixtures thereof.

2. The method of claim 1 wherein the amount of chelating agent is from about 0.5 percent to about 5 percent by weight.

3. The method of claim 1 wherein the caustic is sodium hydroxide.

4. The method of claim 3 wherein the chelating agent is sodium gluconate.

5. The method of claim 3 wherein the chelating agent is sodium glucoheptonate.

6. The method of claim 3 wherein the chelating agent is the sodium salt of ethylene diamine tetraacetic acid.

7. The method of claim 1 wherein the caustic is potassium hydroxide.

8. The method of claim 1 wherein the caustic is a mixture of sodium hydroxide and potassium hydroxide.