US2996350A - Controlling manganese ion impurities in permonosulfate bleaching - Google Patents

Description

United States Patent O No Drawing. Filed July 28, 1959, Ser. No. 830,198 2 Claims. (Cl. 84111) This invention relates to a method of effectively bleaching with a permonosulfate composition in the presence of manganese ions and, more particularly, to a bleaching method wherein any discolorationinduced by manganese ions oxidized to a high valence state by permonosulfate compositions is avoided or removed.

Alkali metal permonosulfates are known as bleaching agents, being stronger oxidizing agents than hydrogen peroxide and many other commonly used per compounds. The use of permonosulfates in tap water presents a problem because some tap water supplies contain manganese in amounts of 0.1 p.p.m. or more and these strong oxidizing agents promote the formation of manganese ions in their higher oxidized states (+3 and .+4) and these manganese ions impart a yellow color to the material being treated. Discoloration by manganese oxidized to the +3 and +4 state is apparent in some tap water which has been found to contain about 0.1 p.p.m. or more manganese. Analysis has shown that ordinary tap water rarely contains more than 0.2 p.p.m. manganese. Discoloration is noticeable when white cloth is laundered or white porcelain is cleansed.

It has been found that yellow-colored manganese ions h can be reduced to the colorless state (+2) even inthe presence of alkali metal permonosulfates through the use of perhydrates as reducing agents. Additionally, it has been found that permonosulfates and perhydrates are mutually tolerant and that solutions containing these compounds in certain ratios will bleach materialsdiscolored by yellow-colored manganese ions. Further, it has been determined that solid mixtures of alkali metal permonosulfates and perhydrates may be used alone or included in various conventional detergent and cleansing formulations and that these formulations ni-ay .be used in virtually any water supply, being unafiected by either the presence of manganese ions or the hardness of the water.

It is an object of the present invention to provide an effective method for bleaching solutions containing an alkali metal permonosulfate and manganese ions.

It is another object of the present invention to'provide' a method of bleaching in solutions containing an alkali metal permonosulfate and manganese ions without discolorin-g the material being treated.

It is still another object of the present invention to provide a method for removing the discoloration caused by manganese ions oxidized to a high valence state.

Some water supplies contain 0.1 p.p.m. or more manganese, usually in the colorless state as Mn++. Manganous ions are colorless and are usually not detrimental in bleaching or laundering solutions because hydrogen peroxide and other conventional bleaching agents will not oxidize manganese to the yellow'colored state of +3 and +4.

In the below table, the various concentrations of Mn were obtained by adding increasing amounts of manganous sulfate to distilled water and the below bleaching composition was added to each solution.

The term Oxone refers to a mixture of KHSO KHSO and K 80 in mole proportions of 221:1, and KHSO constitutes about 50% by weight of the mixture.

I Ce,

Percent Oxone 35 Sodium sulfate 20 Sodium metasilicate 5 Sodium carbonate. 20 Tetrasodium pyrophosphate 20 Each solution contained about 0.2% of the above formulation and standardized washing machine conditions were employed, permonosulfate supplying 25 p.p.m. active oxygen. White cotton cloth swatches at a cloth zwater ratio of 1:20 were used in the bath at 140 F. and the time of wash cycle was 10 minutes.

, TABLE I Manganese Con- Brightness Units as a Function of Wash ce(ntratio;1s

The cloth swatches were given a thorough rinse after washing and dried. After the wash and dry cycle, the re flectances of the swatches were determined in a Hunter Multipurpose Refiectometer using a blue filter, the fall in reflectance representing a measure of the yellowingfof the fabric. The results show that even small concentrations (about 0.1 p.p.m.) of manganese are oxidized and cause yellowing. a;

One method of avoiding discoloration is to eliminate yellow-colored manganese ions by reducing the ions to a colorless state. However, it is necessary to provide a reducing agent that will not .afiect the bleaching action of a'permonosul fateions, i.e., the rate of reductionmu'st be controlled. Furthermore, it is also necessarythatthe agents be "mutually tolerant for at least the jtime required for bleaching and that the reducing agent be c-apableof bleaching, cleansing and laundering. iThese' same sol-u;

tions can be employed to remove the discoloration from materials previously yellowed by'highlyoxidized manga neseions H Perhydrates have all of the above desirablecharactei istics. They may be formulated with alkali metalpefi monosulfiates and simultaneously added to Water; thus used the agents are mutually tolerant for the time period normally used in all bleaching processes. The agents are sufficiently stable to be included in conventional detergent and cleansing formulations and are completely safe for home use. Furthermore, the reducing agents are unaffected by the hardness of the water.

Perhydrates are easily prepared by adding H 0 to aqueous salt solutions and thereafter removing water by drying, leaving crystalline perhydrates. When added to water, perhydrates liberate H 0 and the term perhydrate as used herein refers to compounds so characterized. All of these perhydrates are further characterized by functioning as reducing agents in aqueous solutions containing permonosulfate and highly oxidized manganese (+3 and +4 state of oxidation).

Some well-known compounds that will form perhydrates with H 0 are sodium borate, aluminum sulfate, urea, sodium acetate, sodium silicate, ammonium carbonate, pyrophosphates and the like. Formulas of persodium perborate tetrahydrate is NaBO -H -3H O (contains about active "oxygen). The preferred perhydrate is sodiumperborate monohydrate, known as sodium borate perhydrate, NalBo -H o (contains about 16% active oxygen content). The alkali metal perborates are disclosed in US. 2,491,789.

The amounts of alkali metal permonosulfate and perhydrate necessary to be efiective in solution can be conveniently expressed in terms of active oxygen ratio. The active oxygen ratio of the permonosulfate to that of the perhydrate can vary between 3:1 to 30:1 and this ratio is correct regardless of the specific permonosulfate 'or perhydrate used. Solutions containing these compounds in amounts based on the above ratio of active 'oxygen are stable and eflective bleaching compositions that can be used either to eliminate yellow-colored manganese ions or to avoid yellow discoloration.

EXAMPLE 1 Formulation No. 1 was used in tap water containing about 0.2 p.p.m. manganese. An amount of this formulation equal to about 0.2% solution weight was added so that the active oxygen content supplied to the solution by potassium permonosulfate was about 25 p.p.m. The same standardized conditions noted above were used. The formulation in the first solution included 12% sodium borate perhydrate based on the weight of potassium permonosulfate present.

Residual Brightness UnltsasaFunctlon otWash' Formulation Active No.1 Oxygen,

p.p.m. 0 1 2 a 4 5 6 won Sodium Borete Pertime-.- 85.4 85.5 86.3 85.5 86.1 86.6 86.8- Wg No Reairman... '18 85.9 85.5 85.5 85.5 88.7 82.2 86.2

The next example shows the efiectiveness of sodium perborate in whitening cloth already yellowed by yellowcolored manganese ions.

EXAMPLE 2 Brightness Units as a Function of Wash Formulation N o. 1

Preferred bleaching conditions are obtained whenpotassium permonosul-fate and sodium borate perhydrate are used in combination. It is obvious, however, that any alkali metal permonosulfate and perhydrate are suitable providing that the active oxygen ratio of the two compounds are 3:1 to 30: 1, respectively.

As noted'above, some tap water supplies contain 0.1 p.p.m. manganese or more. The manganese content of tap water is normally not in excess of 0.3 p.p.m. and the above formulations will eliminate discoloration in solutions containing these amounts of manganese.

The effect of combining a reducing agent and a strong oxidizing agent to remove discoloration caused by man- ,ganese does not adversely affect the bleaching efiectiveness of the permonosulfate. Other reducing agents were inefiective.

Throughout the specification, percentages and parts are calculated on a weight basis unless othenvise designated. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows; 1. In the method of bleaching with an alkali me permonosulfate in solution in water containing manganese ions as an impurity, the improvement consisting essentially of incorporating into said solution a suflicient amount of a crystalline salt perhydrate compound which liberates hydrogen peroxide in water to reduce said manganese ions to a colorless state, the ratio of active oxygen content of said permonosulfateto said perhydrate being about 3:1 to 30:1. 7

2. 1n the method of bleaching with potassium permonosulfate in solution in water containing manganese .ions as an impurity, the improvement consisting essentially of incorporating into said solution a suflicient amount of sodium borate perhydrate to reduce said manganese ions to a colorless state, the ratio of active oxygen content of said permonosulfate to said perhydrate being about 3:1 to 30:1.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS 451,025 Great Britain July 27, 1935 451,115 Great Britain July 29, 1935

Claims (1)

1. IN THE METHOD OF BLEACHING WITH AN ALKALI METAL PERMONOSULFATE IN SOLUTION IN WATER CONTAINING MANGANESE IONS AS AN IMPURITY, THE IMPROVEMENT CONSISTING ESSENTIALLY OF INCORPORATING INTO SAID SOLUTION A SUFFICIENT AMOUNT OF A CRYSTALLINE SALT PERHYDRATE COMPOUND WHICH LIBERATES HYDROGEN PEROXIDE IN WATER TO REDUCE SAID MANGANESE IONS TO A COLORLESS STATE, THE RATIO OF ACTIVE OXYGEN CONTENT OF SAID PERMONOSULFATE TO SAID PERHYDRATE BEING ABOUT 3:1 TO 30:1.