CH638468A5 - Process for reducing the colouring of aqueous waste solutions containing arylazo, arylnitro or metallised arylazo compounds - Google Patents

Description

The invention relates to a method for reducing the color of aqueous waste solutions containing chromophoric arylazo and / or arylnitro compounds or for reducing the color and the metal content of aqueous waste solutions containing chromophore metallized arylazo compounds to predetermined ecologically acceptable values.

In view of recent considerations about the color value of solutions that are discharged into rivers and streams, as well as a tightening of the relevant official regulations, there is an urgent need to decolorize such solutions effectively, but relatively cheaply, but without causing further ecological disturbances. Industrial plants in which waste liquids occur which contain ecologically significant amounts of chromophoric compounds such as arylazo or arylnitro compounds are particularly affected. Such solutions are strongly colored and will therefore usually not meet the official guidelines for limiting the color value of industrial waste water. Solutions containing aryl nitro compounds are also problematic because such compounds are bactericidal and harmful to anaerobic wastewater treatment systems.

In the production of water-soluble dyes, after the "salting out" for the isolation of the dyes by filtration, significant amounts of dye always remain in the solution. In addition, numerous undesirable materials such as unreacted starting materials, by-products and decomposition products are not isolated with the reaction products. Many of these materials are strongly colored and also contribute to the coloring of the solution.

Common methods for decolorizing such solutions include oxidation with chlorine, hypochlorites, ozone and the like. However, these procedures are not very desirable from a commercial point of view, since they are usually quite expensive, because the decolorization is too slow and large storage containers and / or longer treatment times are necessary, or the treatment reagents themselves are expensive. Anaerobic systems will destroy some of the color due to azo color chromophores, but they are not economically attractive.

In Japanese Patent Publication No. 76 853/1973 dated 3/7/1976 a process for decolorizing waste liquid is described, the azo, phthalocyanine, xanthene or. Contains azine dyes. According to this method, the waste liquid is decolorized by adding both (A) sulfite and / or bisulfite and (B) a catalytic amount of iron powder and / or ferrosilicon powder. According to this, (A) and (B) should be necessary to achieve decolorization. According to Comparative Example 2 of this publication, iron powder alone is not sufficient for decolorization of liquid which contains a diazo dye (C.I. Direct Blue I) and has an APHA value of approximately 500,000.

However, the use of sulfite or bisulfite as specified in the above publication is not desirable from a commercial point of view, since sulfite or bisulfite, which may be discharged into the sewer, incur additional process costs and become one during treatment lead to unpleasant sulfur dioxide release.

The object of the invention is therefore to provide a method for decolorizing solutions with significant amounts of dye with respect to the environment - in particular in the form of arylazo and aryl nitro compounds. Such decolorization is said to be economically attractive in particular and to avoid the problems of the usual decolorization processes for solutions containing such compounds. The object of the invention is also to provide a method for reducing the metal content and the color of solutions with metallized or metal-containing compounds.

The invention relates to a process for reducing the color of chromophore arylazo and / or aryl nitro compounds containing aqueous waste solutions to predetermined ecologically acceptable values, which is characterized in that the solution with a reducing substance consisting of Fe2 + in the presence of metallic iron in a pH in the range of 3 to 9 and at a temperature of 40 to 80 ° C for a sufficient period of time to bring about a chemical reduction of the arylazo or arylnitro compounds while reducing the color of the solution to the predetermined ecologically acceptable values.

The invention further relates to a process for reducing the color and the metal content of aqueous waste solutions containing chromophore metallized aryalcohol compounds to predetermined ecologically acceptable values, which is characterized in that the solution is reduced with a reducing agent consisting of Fe2 +

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Contact substance in the presence of metallic iron at a pH of 3 to 9 and at a temperature of 40 to 80 ° C for a sufficiently long time for chemical reduction of the metallized compounds and then adjust the pH of the solution to 9 to 12 Precipitation of the metal of the metallized compounds and iron in insoluble form and that the precipitate is separated from the treated solution.

The invention is described in more detail below on the basis of exemplary embodiments.

The method developed to solve the problems outlined above to decolorize or reduce the color of solutions which contain arylazo or aryl nitro compounds consists essentially in that the effluent is treated with Fe2 + in the presence of iron at a pH of about 3 to about 9 in contact at a sufficient temperature and for a sufficient period of time to bring about a desired reduction in the arylazo or arylnitro groups of the compounds and thus to weaken the color.

According to a further embodiment, the metallized compound, such as metallized azo dyes and by-products of the preparation thereof, alone or in combination with the solution containing the arylazo or arylnitro compounds, after the treatment with Fe2 *, by means of which the structure of the metallized compounds is chemically changed and the metal is reduced, subjected to an “alkaline neutralization” to cause the metal portion of the metallized dyes to precipitate out of the solution.

The term "decolorization" as used here is not intended to mean complete removal of the color, but instead a desired reduction in the color of a solution. In general, of course, a considerable reduction in color at level heights will be desired, which will allow the solution to be dispensed with an ecologically acceptable color, which can be achieved according to the invention. For example, the color of a solution that is produced in the manufacture of water-soluble dyes can range from about a few thousand to 106 APHA or above (APHA refers to the platinum-cobalt scale of the American Public Health Association for designation the color values of water; further information can be found in “Standard Methods for the Examina- tion of Water and Sewage”, 8th edition, American Public Health Association, NYC, 1936, page 12). On the other hand, the allowable limits for release into a river are sometimes as low as 100 APHA. Although a reduction in the APHA value of solutions to such a low value may not be necessary industrially because of a possible combination with other colorless solutions, a considerable reduction in the color value is nevertheless necessary.

Although the method of the present invention can be effectively used to treat solutions containing any chromophores that are reducible with Fe2 + (hereinafter simply referred to as Fe (II)), one preferred application from the standpoint of ecological necessity is the decolorization of a solution whose color is mainly caused by arylazo or aryl nitro compounds dissolved in the solution. The method is particularly useful in the treatment of solutions whose arylazo or aryl nitro compounds result from the preparation of water-soluble dyes.

The arylazo compounds under consideration here are those in which at least one of the nitrogen atoms of the azo group is bonded to an aromatic ring derived from benzene or naphthalene; these include mono-, bis-, tris- and tetrakisazo compounds as well as azo-like compounds. The aryl nitro compounds are those in which the nitrogen sits on an aromatic ring derived from benzene, naphthalene or anthracene. The designation arylazo or aryl nitro compounds is intended to encompass all compounds which the dye specialist would generally consider to be aryl or aromatic, azo or nitro dyes.

io The solution can also be obtained from the use of water-soluble azo or nitro dyes such as for dyeing paper.

Furthermore, the method according to the invention is considered useful for the treatment of solutions containing xanthene or azine dyes.

As indicated above, the method according to the invention also serves to treat a solution containing metallized compounds. Such metallized or metal-containing compounds include e.g. azo compounds metallized with copper, 20 cobalt or chromium and soluble inorganic salts. In addition to reducing the color of the solution, the process also provides a separable, insoluble form of the metal by alkaline neutralization of the solution and filtration. It is found that the Fe (II) destroys the chromophores of the metallized compound and reduces the metal associated therewith, thereby reducing or weakening the color of the solution and removing the metal as an insoluble metal or an insoluble metal compound after alkaline neutralization-30 sation of the solution is made possible.

The solution may and will typically contain mixtures of the above chromophoric compounds.

It is assumed that there are no material restrictions with regard to the amounts of arylazo or aryl nitro compounds and metallized compounds which can be contained in the solution decolorized according to the invention. However, the solution will generally contain concentrations of arylazo, arylnitro and / or metallized Verbin-40 fertilizers that are environmentally significant. The process can thus be used to decolorize solutions which are released or discarded in commercial processes for producing water-soluble azo, nitro and metallized colors. It is generally not possible to specify the amounts of these compounds contained in such solutions, since such solutions contain not only the water-soluble dyes not removed by salting-out techniques, but also incompletely formed dyes, by-products and unreacted starting materials.

Second, the nature of the solution will vary significantly depending on the level of development and customer needs for specific products. Such solutions are typically characterized by their APHA values, amounts of suspended and dissolved solids, amounts of metals and the like. One such method for labeling dye solutions is given in U.S. Patent No. 4,005,011, which describes the properties of raw sewage from the manufacture of a synthetic dye 60. As mentioned above, the solution in which the method according to the invention can be used will typically have APHA values ranging from a few thousand to 106 and above. There is no definable lower APHA range for ss solutions to which the method can be used. However, it can be seen that a certain proportion of the color of the solution obtained in the preparation of water-soluble dyes may not be removable, since a certain coloration of the

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Solution due to dirt, rust or the like in the solution.

According to the invention, the color of the solution is reduced by its contact with Fe (II), which acts as a reducing agent. As already mentioned, Fe (II) here refers to the Fe2 + ion, which is sometimes called "soluble iron". The Fe (II) can be produced in the solution by dissolving iron present therein or by adding ferrous salts to the solution. For example, the pH of the solution can be adjusted to acidic values before or after contacting it with the iron by adding a suitable acid. Any mineral or organic acid can be used as the acid, including, for example, sulfuric acid, acetic acid, nitric acid and hydrochloric acid. The iron is "etched" at the acidic pH to remove fat or the like and expose the iron and facilitate the formation of Fe (II). The amount of acid required will vary depending on the initial pH, buffering capacity of the solution and the like and can be readily determined. Amounts corresponding to a few percent by weight or less (based on the amount of the solution) are typical.

The Fe (II) can also be produced in the solution by adding ferrous salts. However, it is used up in the reduction and it is desirable to carry out the treatment in the presence of iron as a source of Fe (II).

The Fe (II) content required at any given time in the solution is given by the amount necessary to form a reducing solution. This Fe (II) content may not be detectable by conventional means. In addition, enough Fe (II) must be generated in the system to reduce the color of the solution to a predetermined ecologically acceptable range.

The required amount of Fe (II) is produced in the solution treated according to the invention by using amounts of iron which are excess in relation to the theoretically for chemical reduction of the azo or nitrochromophores or the metallized compounds in the solution. A large excess of iron can be provided since or insofar as the iron is not otherwise harmful to the procedure and the excess is not released or discarded with the treated solution, but is instead recovered for reuse. On the other hand, the amount of iron used should not be so great as to hinder its removal from the treated solution. In theory, 6 moles of iron are required for the reduction of 1 mole of nitro groups to amines and 4 moles of iron for the reduction of 1 mole of azo groups to amines. In practice, however, the amount of iron actually consumed is less than the theoretical amount, since a complete reduction to the primary amine is not necessary in order to achieve an acceptable color. For example, some azo groups in the treated solution are likely to be reduced only to the hydrazoform. The amount of iron actually required, as will be apparent to those skilled in the art, will depend on the concentrations of colored components in the solution and will typically be less than a few percent by weight (based on the weight of the treated solution).

The iron can be in the form of metallic iron or iron alloys, as long as the Fe (II) required for a reducing solution can be produced therefrom under the treatment conditions. Although the iron can theoretically be in any physical form, the best results (because of the larger specific surface area available) are achieved with finely divided iron.

About 80 mesh (177 (im) finely divided iron has been found to be particularly useful because it provides effective treatment speeds and is suitable for handling properties. 20 mesh (841 pm) finely divided iron and turnings have also been used, although their efficiency or The choice of the shape of the metal is mainly determined by the convenience of its use and the speed with which the Fe (II) is produced.

The pH of the solution is maintained within a range of about 3 to about 9 during treatment. The process is preferably carried out at a pH within a range from about 5 to about 7.5 and in particular at a pH from about 5 to about 6.5. At a pH below about 3, the iron is used up too quickly, while at a pH above about 9 oxides and hydroxides of the iron can be eliminated more quickly than practicable. At a pH above about 7.5, the rate of production of Fe (II) becomes impractical, although decolorization itself can be carried out if the amount of Fe (II) already in solution is used to reduce the arylazo or. Aryl nitro compounds and metallized compounds in the solution to the desired range is sufficient. At a pH within the range of about 5 to about 6.5, the iron is continuously dissolved at an acceptable rate, but not used up excessively quickly.

The decolorization of solutions containing arylazo or aryl nitro compounds or metallized compounds depends on the temperature of the solution. At a temperature in the range of about 25 ° C, the decolorization rate is so slow that it is not practical or operationally attractive. A practical and preferred lower temperature range is 40 to 50 ° C. The decolorization rate increases significantly with an increase in temperature from about 50 ° C to about 80 ° C. A particularly effective decolorization is achieved at around 60 to 75 ° C. However, the most effective temperature does not always have to be the most economical. For example, a temperature in the range of about 40 ° C to 70 ° C will be sufficient to treat solutions that are produced in the manufacture of most water-soluble dyes and in the dyeing of paper, since these solutions are typically released at these temperatures. As noted above, higher temperatures can be provided to take advantage of particularly effective temperatures, but they are not generally used for reasons of economy and energy conservation. For example, the APHA value of solutions containing arylazo and aryl nitro compounds at 50 to 60 ° C and a pH value of about 5 to 6.5 is slightly reduced from 500,000 to about 10,000 (with rapid decolorization reaction within a magnitude minutes). The solution is almost colorless within 0.5 to about 1 hour. Increasing the temperature of the solution above 80 ° C is generally not so effective that it would justify the increased energy requirement and it can impair the filterability of the solution.

The length of time that the solution is contacted with Fe (II) in the presence of iron depends on the initial APHA value of the solution and the degree of decolorization desired. At the above temperatures and pH values, the decolorization to predetermined ecologically acceptable values will typically be achieved in a few minutes to a few hours. Aryl nitro compounds are also reduced to biodegradable forms within this time.

The decolorization can be carried out batchwise or continuously. In the case of batch decolorization, the

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The solution is preferably stirred or moved at such a speed that an intensive contact between Fe (II) and the arylazo or arylnitro compounds or metallized compounds is ensured and an adequate Fe (II) generation rate is ensured. For a continuous implementation, the solution with a previously adjusted pH value can be passed over an iron column. The speed at which the solution is passed through the column depends, of course, on the concentration of the colored components, the pH and the temperature of the solution, the desired degree of decolorization and the available specific surface or total surface area of the iron.

In the treatment of solutions, the Fe (II) is converted into Fe (III), which can be eliminated from the solution by alkaline neutralization if its separation is required. In addition, when treating solutions with metallized compounds such as e.g. metallized azo dyes - as indicated above - the insoluble metal or a form which can be precipitated by increasing the pH, which can likewise be removed from the treated solution by alkaline neutralization. The alkaline neutralization can be carried out in any conventional manner, e.g. by adding a suitable hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide (to the decolorized solution). The use of powdered limestone (CaO, Ca (OH) a) for alkaline neutralization has proven to be economically practical. The amount of neutralizing agent used is the amount required to raise the pH of the treated solution to about 9 to 12, in which pH range an insoluble substance formed is precipitated. Amounts of a few percent by weight based on the weight of the treated solution (not including the weight of iron) are generally sufficient. The Fe (III) in the treated solution precipitates out as ferric hydroxide and can be removed by conventional procedures. Copper, cobalt and chromium from metallized compounds in the solution are generally either elemental as metal or as oxides or hydroxides.

The following examples will help to better understand the invention.

example 1

A solution with a metallized water-soluble azo dye formed by coupling l-phenyl-3-methyl-5-pyrazoIon with diazotized 2-amino-l-phenol-4-sulfonamide and chromating was decolorized according to the invention. The solution had an initial APHA of 350,000; pH 5.5 to 6.0; a temperature of 55 to 60 ° C and a Cr content of 600 ppm. Finely divided iron of about 177 µm was used in an amount of about 2% by weight based on the weight of the solution. The APHA was reduced to 80,000 and the Cr content to 20 ppm by keeping the solution in contact with the iron for one hour and 45 minutes, then alkaline neutralizing and filtering to remove the metal portion.

Example 2

A solution containing a water-soluble metallized dye prepared by diazotizing anthranilic acid and coupling with l- (p-sulfophenyl) -3-methyl-5-pyrazolone and chromating was treated as in Example 1. The following results have been achieved;

Decrease in APHA from 1,000,000 (initial) to 50,000;

io decrease in Cr content from 500 ppm to 15 ppm;

Duration: 45 minutes.

Example 3

One in the manufacture of C.I. Direct Black 190 (Tri-15 sazo dye; made by diazotizing dianisidine and coupling one end with R salt and the other end with H acid; diazotizing the resulting dye and coupling with l-phenyl-3-methyl-5-pyrazo! on and subsequent metallization of the resulting dye 20 with copper) resulting solution was treated as in Example 1. The following results were achieved:

APHA: from 105-106 (initially) to 4000 Cu: from 3200 ppm to 0.4 ppm 25 Duration: 1 hour

Example 4

One in the manufacture of C.I. Direct red 80 (tetrakisa-zofarbstoff; formed by diazotization of 2 mol of amino-30-azobenzenedisulfonic acid and coupling with J-urea) was treated as in Example 1. The following results were achieved:

APHA: from 106 (initially) to 6000 35 Duration: 2 hours and 42 minutes

Example 5

A solution obtained in the preparation of a dye formed by diazotization of 2,5-dichlorosulfanilic acid and coupling with N-ethyl-N-40 benzylaniline with an initial APHA value of 500,000 and a pH value of 5.0 to 6. 5 was treated according to the invention. The solution was brought into contact with approximately 2% by weight (based on the weight of the solution) of iron turning chips at approximately 40 to 50 ° C. After approximately 0.5 to 0.75 hours, the APHA had decreased to approximately 10,000. During this period the pH rose to 8.5.

Example 6

So A solution of a typical daily production of a plant for the production of water-soluble azo dyes, which contained both metallized and non-metallized direct colors and acid azo dyes, was treated according to the invention. The solution had an APHA 55 of about 70,000; a temperature of about 60 to 70 ° C and a pH of about 9. The pH was adjusted to 5.0 and the solution was treated under conditions similar to Example 5 for one hour. The APHA value was reduced to 5000.

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Claims (8)

638468 PATENT CLAIMS 1. A method for reducing the color of chromophore arylazo and / or aryl nitro compounds containing aqueous waste solutions to predetermined ecologically acceptable values, characterized in that the solution with a reducing substance consisting of Fe2 + in the presence of metallic iron at a pH in the range of 3 to 9 and at a temperature of 40 to 80 ° C for a sufficient period of time to bring about a chemical reduction of the arylazo or arylnitro compounds while reducing the color of the solution to the predetermined ecologically acceptable values. 2. The method according to claim 1, characterized in that the temperature is selected in the range from 60 ° C to 75 ° C. 3. The method according to claim 2, characterized in that the pH is selected in the range from 5.0 to 6.5. 4. The method according to claim 3, characterized in that finely divided iron with an average particle size of 177 to 841 µm is used as the iron. 5. Process for reducing the color and the metal content of aqueous waste solutions containing chromophore metallized arylazo compounds to predetermined ecologically acceptable values, characterized in that the solution is mixed with a reducing substance consisting of Fe2 + in the presence of metallic iron at a pH of 3 to 9 and at a temperature of 40 to 80 ° C for a sufficiently long time for chemical reduction of the metallized compounds in contact and then adjusts the pH of the solution to 9 to 12 to precipitate the metal of the metallized compounds and the iron in insoluble form and separating the precipitate from the solution. 6. The method according to claim 5, characterized in that the temperature is selected in the range from 60 ° C to 75 ° C. 7. The method according to claim 6, characterized in that the pH for contact with iron is selected in the range from 5.0 to about 6.5. 8. The method according to claim 7, characterized in that the iron used is finely divided iron with an average particle size of 177 to 841 mm.