GB1602518A - Method of lowering the colour of effluent which contains aryl azo-and/or aryl nitro-containing compounds - Google Patents

Abstract

Aqueous waste solutions containing arylazo, arylnitro or metallised arylazo compounds are, for colour attenuation or decolorisation treated or contacted with Fe<2+> in the presence of iron at a temperature from 40 to 80 DEG C for a sufficiently long time in order to induce a reduction of the colour-bound constituents of the solutions. Waste solutions containing metallised arylazo compounds are treated in the same way and then rendered alkaline (pH 9 to 12), in order to precipitate the dissolved metals and to separate them off.

Description

(54) A METHOD OF LOWERING THE COLOR OF EFFLUENT WHICH CONTAINS ARYL AZO- AND/OR ARYL NITRO-CONTAINING COMPOUNDS (71) We, AMERICAN COLOR & CHEMICAL CORPORATION, a corporation organised under the laws of the State of Delaware, United States of America, of 6525 Morrison Boulevard, Suite 310, Charlotte, North Carolina, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the treatment of effluent, which contains chromophoric compounds and, particularly, aryl azo- and aryl nitro-containing compounds and, optionally, metallized compounds to reduce the color and the heavy metal content thereof.

Recent concern over the color value of effluents discharged into rivers and streams and enforcement of governmental regulations relating thereto have emphasized the need for effective, yet relatively inexpensive, means for decolorizing such effluent without, in turn, creating other ecological disturbances. One area in which such need exists is in those industries which discharge waste liquor containing environmentally unacceptable amounts of chromophoric compounds such as aryl azo- or aryl nitro-containing compounds. Such effluent is highly colored and may not conform to governmental standards restricting the color value of industrial discharge. Effluent which contains aryl nitro-containing compounds is also objectionable in that these compounds are bactericides and are inimical to anaerobic sewage treatment systems.

In the manufacture of water-soluble dyes, there is always a substantial amount of dye left in solution following "salting" techniques employed for isolating the dyes by filtration.

Additionally, there are also many undesired materials such as unreacted starting materials, by-products and decomposition products which are not isolated with the reaction products.

Many of these materials are highly colored and also contribute to the color of the effluent.

Usual methods for decolorizing this effluent include oxidation by chlorine, hypochlorites and ozone. These methods are not preferred from an industrial standpoint, however, because they tend to be too costly either because the decolorization is too slow and requires large holding tanks and/or times or because the reactants, themselves, are expensive.

Anaerobic systems will destroy a certain amount of color caused by azo dye chromophores but the economics are not attractive.

In Japanese Laid-Open Publication No. 76853/1973 published July 3, 1976, a method is disclosed for decolorizing waste liquor containing azo, phthalocyanine, xanthene and azine dyes. According to the process the liquor is decolorized by adding both (A) a sulfite and/or a bisulfite and (B) a catalytic amount of iron powder and/or ferrosilicon powder to the colored waste liquor. The publication teaches that both (A) and (B) must be present to achieve decolorization. In Reference Example 2 of the publication it is shown that decolorization of a liquor containing a disazo dye (C.I. Direct Blue I) and having an APHA of about 500,000 does not occur with the use of iron powder alone.

The use of sulfite or bisulfite, however, as disclosed in the Japanese Laid-Open Publication is not desired from an industrial standpoint because the sulfite or- bisulfite, which is eventually discharged to a sewer, is an extra manufacturing expense and because obnoxious sulfur dioxide is discharged during the treatment.

It is an object of the present invention, therefore, to provide a method for decolorizing effluent containing environmentally unacceptable amounts of color, particularly in the form of aryl azo- and aryl nitro-containing compounds.

It is also an object of the present invention to provide a method for decolorizing effluent containing aryl azo- and aryl nitro-containing compounds which is economically attractive and which avoids the problems of the usual methods employed for decolorization of effluent containing these compounds.

It is a further object of the invention to provide a method for lowering the metal content and the color of effluent containing metallized compounds.

According to one aspect of the present invention, there is provided a method of treating effluent which contains chromophoric aryl azo- and/or aryl nitro-containing compounds to lower the color thereof, which comprises contacting the effluent with a reducing agent consisting of Fe (II) in the presence of metallic iron at a pH in the range of from 3 to 9 at a temperature of from 40"C. to 80"C. and for a time sufficient to cause chemical reduction of said aryl azo- and/or aryl nitro-containing compounds thereby reducing their color.

In another embodiment, effluent containing metallized compounds such as metallized azo dyes and by-products of the production thereof, alone or in combination with the aryl azo- or aryl nitro-containing compounds, following treatment with the Fe(II), which alters the structure of the metallized compounds and chemically reduces the metal, is subjected to alkaline neutralization to cause the metal of the metallized dyes to precipitate out of the effluent. More particularly, the invention provides, in a second aspect, a method of treating effluent which contains chromophoric aryl azo-containing compounds and metal-containing compounds to lower the color and metal content of the effluent, which method comprises contacting said effluent with a reducing agent consisting of Fe(II) in the presence of metallic iron at a pH of from 3 to 9 and at a temperature of from 40"C. to 80"C. for a time sufficient to reduce chemically said metallized compounds; thereafter adjusting the pH of said effluent to a value of from 9 to 12 to cause precipitation of insoluble forms of the metal of the metallized compounds and of the iron, and separating the precipitates from the treated effluent.

The term, decolorization, as employed herein is not intended to mean a complete removal of color but, instead is intended to mean a desired lowering in the color of an effluent. Generally, of course, a significant reduction in color to levels that permit the discharge of effluent of environmentally acceptable color will be desired and this can be accomplished according to the method of the invention. Thus, for example, the color of effluent produced in the production of water-soluble dyes may range anywhere from several thousand up to 1,000,000 APHA (APHA refers to the American Public Health Association's Platinum-Cobalt Scale for designating the colors of waters and is described in "Standard Methods for the Examination of Water and Sewage", 8th Ed. American Public Health Association, NYC, 1936, p. 12) or more. Governmental limits, on the other hand, for discharge to a river are sometimes as low as 100 APHA. Although reduction of the APHA of effluent to this lower limit may not be required industrially because of possible dilution with other colorless effluent, a significant reduction is still required.

Although the method according to the present invention can effectively be applied to the treatment of effluent containing any chromophore that is reducible by Fe(II), a preferred application, from a standpoint of ecological necessity, is in the decolorization of effluent wherein the color is caused primarily by aryl azo- and aryl nitro-containing compounds in solution in the effluent. The method is particularly useful in the treatment of effluent wherein the aryl azo- and aryl nitro-containing compounds result from the manufacture of water-soluble dyes.

The aryl azo-containing compounds referred to herein include those wherein at least one of the nitrogen atoms of the azo group is attached to an aromatic ring derived from benzene or naphthalene and include mono-, dis-, tris- and tetrakisazo compounds and azoic compounds. The aryl nitro-containing compounds include those wherein the nitrogen is attached to an aromatic ring derived from benzene, a naphthalene and anthracene. The terminology aryl azo- and aryl nitro-containing compounds is intended to include all compounds which would generally be considered by one skilled in the dye art to be aryl, or aromatic azo or nitro dyes.

The effluent can also be that resulting from the use of water-soluble azo and nitro dyes such as, for example, in the dyeing of paper.

The method according to the present invention is also believed to be useful in the treatment of effluent containing xanthene and azine dyes.

As mentioned above, the method according to the present invention may also be employed to treat effluent containing metallized compounds. Such metallized compounds include, for example, azo compounds metallized with copper, cobalt, or chromium, and soluble inorganic salts. In addition to lowering the color of the effluent, the method produces an insoluble form of the metal which can be removed by alkaline neutralization of the effluent and filtering thereof. It appears that the Fe(II) reacts with the chromophore of the metallized compound and chemically reduces the metal associated therewith thereby lowering the color of the effluent and enabling the metal to be removed as the insoluble metal or an insoluble compound of the metal following alkaline neutralization of the effluent.

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

There are not believed to be any material limitations regarding the amounts of aryl azoand aryl nitro-containing compounds and metallized compounds that can be contained in effluent decolorized according to the present invention. The effluent, however, will generally contain levels of aryl azo-containing, aryl nitro-containing and/or metallized compounds which may be environmentally unacceptable. Thus the method can be applied to the decolorization of effluent discharged from commercial processes for producing water-soluble azo, nitro and metallized dyes. It is generally not possible to specify the amounts of these compounds contained in such effluent because, firstly, such effluent contains not only the water-soluble dyes not removed by "salting" techniques, but also incompletely formed dyes, by-products and unreacted starting materials. Secondly, the nature of the effluent will vary considerably depending upon inventory levels and customer demands for specific products. Such effluent is typically characterized according to the APHA units thereof, amounts of suspended and dissolved solids, amounts of metals and the like. One such method for characterizing dye effluent is illustrated in United States Patent No. 4,005,011 wherein characteristics of raw waste resulting from the manufacture of a synthetic dyestuff are described. As stated above, effluent to which the method according to the present invention can be applied will typically have APHAs ranging from several thousand up to 1,000,000 and above. There is no definable lower range of APHA for effluent to which the method can be applied. It is to be understood, however, that a certain amount of the color of the effluent produced in the manufacture of water-soluble dyes may not be removable by the process according to the present invention because some of the color of the effluent may be due to dirt or rust present in the effluent.

According to the present invention, the color of the effluent is lowered by contacting the effluent with Fe(II) which acts as a reducing substance. Fe(II) designates Fe++ ion, sometimes referred to as soluble iron. The Fe(II) may be generated in the effluent by solubilizing iron present therein or by the addition of ferrous salts to the effluent. Thus, for example, the pH of the effluent may be adjusted to an acid pH, prior or subsequent to bringing the effluent into contact with the iron, by the addition of a suitable acid to the effluent. The acid can be any mineral or organic acid including, for example, sulfuric acid, acetic, nitric and hydrochloric acid. The iron is "etched" at the acid pH to remove grease or the like to expose the iron and facilitate formation of the Fe(II). The amount of the acid required will vary depending on the initial pH, buffering capacity of the effluent and the like and can be readily determined. Amounts of several percent or less by weight based on the amount of effluent are typical.

The Fe(II) may also be generated in the effluent by the addition of ferrous salts thereto.

The Fe(II), however, is used up in the reduction reaction and it is desirable to conduct the treatment in the presence of iron as a source of the Fe(II).

The amount of Fe(II) required in the effluent at any given time is that amount required to form a reducing solution. It is possible that this amount of Fe(II) may not be detectable by conventional means. Additionally, there should be enough Fe(II) generated in the system to reduce the color of the effluent to a predetermined ecologically acceptable level.

The required amount of Fe(II) is generated in the effluent treated according to the method of the present invention by employing the iron in amounts in excess of that theoretically required to chemically reduce the azo or nitro chromophores or the metallized compounds in the effluent. A large excess of the iron can be used since the iron is not otherwise deleterious to the method and the excess is not discharged with the treated effluent but is recovered for reuse. On the other hand, the amount of iron employed should not be so great as to hinder its removal from the treated effluent. Theoretically, 6 moles of iron are required for the reduction of 1 mole of nitro groups to amines and 4 moles are required 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 because it is not necessary to reduce completely to the primary amine to reach an acceptable color. For example, it is likely that some azo groups in effluent treated according to the present method are reduced only to the hydrazo form. The actual amount of iron required will vary depending on amounts of colored components in the effluent as will be understood by one skilled in the art and will typically be less than several percent by weight based on the weight of the effluent treated.

The iron may be in the form of metallic iron or alloys as long as the Fe(II) required for the reducing solution can be generated therefrom under the conditions of the treatment.

Although, in theory, the iron can have any physical form, best results are obtained employing a finely divided iron because of the greater available surface area. Finely divided iron of about 80 mesh (Tyler sieve-nominal aperture 177 microns) has been found to be particularly useful because it gives efficient rates and its handling characteristics are suitable. Finely divided iron of 20 mesh (Tyler sieve-nominal aperture 841 microns) and iron turnings have also been used although efficiency is somewhat decreased. Finely divided iron of between 20 and 80 mesh (Tyler sieve) is suitable. The choice of the form of the metal is determined primarily by the convenience in its use and the rate at which the Fe(II) is generated.

The pH of the effluent is maintained during the treatment to be within the range of from about 3 to about 9. Preferably, the method is carried out at a pH within the range of from about 5 to about 7.5 and most preferably at a pH of within the range of from about 5 to about 6.5. At a pH less than about 3 the iron will be used up at an excessive rate whereas above a pH of about 9, oxides and hydroxides of the iron may precipitate at a faster rate than is practical. At a pH above about 7.5 the rate of generation of Fe(II) becomes impractical although decolorization itself can be carried out if the amount of Fe(II) already in solution is sufficient to reduce the ryl azo- and aryl nitro-containing compounds and metallized compounds in the effluent to the desired level. At a pH within the range of about 5 to about 6.5 the iron continues to dissolve at an acceptable rate but is not used at an excessive rate.

The decolorization of effluent containing aryl azo- or aryl nitro-containing compounds or metallized compounds is sensitive to the temperature of the effluent. At a temperature of about 25"C the rate of decolorization is so slow as not to be practical or operably attractive.

A practical and preferred lower range of temperature is 40 - 50"C. The rate of decolorization increases significantly with temperature from about 5QCC to about 80"C.

Most efficient decolorization is obtained at about 60 - 750C. The most efficient temperature, however, will not alwavs be the most economical. Thus, a temperature of within the range of about 400C to 70"C will be sufficient in the treatment of effluent discharged in the processes for manufacturing most water-soluble dyes and in the dyeing of paper since the effluent is typically discharged at these temperatures. As noted above. higher temperatures can be employed for efficient temperature utilization but are not generally used for reasons of economy and energy conservation. Thus, for example the APHA of effluent containing aryl azo- and aryl nitro-containing compounds is easily reduced from 500.00Q to about 10,000 at 50 to 60"C and at a pH of frorn about 5 to 6.5 (decolorization is rapid, within several minutes). The effluent is almost colorless within 1/2 to about 1 hour. The effect of raising the temperature of the effluent above 800C is generally not sufficient to warrant the increased energy requirements and may adversely affect the filter-abilitv of the effluent.

The time during which the effluent is contacted with Fe(II) in the presence of iron will depend upon the initial APHA of the effluent and the desired degree of decolorization. For the temperatures and pH specified above, decolorization to predetermined ecologically acceptable levels will typically be complete within from several minutes to several hours.

Aryl nitro-containing compounds will also be reduced to biodegradable forms within this time.

The decolorization may be carried out batchwise or continuously. If the decolorization is carried out batchwise, the effluent is preferably agitated at a rate such that intimate contact between Fe(lI) and the aryl azo- or aryl nitro-containing compounds or metallized compounds is ensured and to ensure a sufficient rate of generation of the Fe(II). The method according to the invention may be carried out in a continuous fashion by passing effluent having a previously adjusted pH through a column containing metallic iron. The rate at which the effluent is passed through the column will depend, of course. on the concentration of the colored components, the pH and temperature of the effluent, the desired degree of decolorization and the available surface area of the iron.

In the treatment of effluent according to the present invention the Fe(II) is converted to Fe(III) which can be precipitated from the effluent by alkaline neutralization if removal thereof is required. Additionally. as stated above, during the treatment of effluent containing metallized compounds such as. for example, metallized azo dyes, the insoluble metal or a form which will become insoluble upon raising the pH is formed which can also be removed from the treated effluent bv alkaline neutralization. The alkaline neutralization may be carried out by any conventional means such as, for example, by the addition of a suitable hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide to the decolorized effluent. It has been found to be economically practical to employ powdered calcined limestone (CaO, Ca(OH).) for the alkaline neutralization. The amounts of the neutralization agent employed is that amount required to raise the pH of the treated effluent to about 9 to 12 at which pH range precipitation of formed insoluble substances occurs. Amounts of several percent by weight based on the weight of treated effluent (not including the weight of the iron) are generally sufficient. The Fe(III) in the treated effluent precipitates out as ferric hydroxide and can be removed by established procedures. Copper, cobalt and chromium of metallized compounds contained in the effluent will generally precipitate out either as the elemental metal or as oxides or hydroxides thereof.

The invention may be better understood, however, by referring to the following examples.

Example I An effluent containing a metallized water-soluble azo dye prepared by coupling 1-phenyl-3-methyl-5-pyrazolone with diazotized 2-amino-1-phenol-4-sulfonamide and metallizing with chromium was decolorized according to the method of the present invention. The effluent had an initial APHA of 350,000; a pH of 5.5 - 6.0; a temperature of 55 - 60"C and a Cr content of 600 ppm. Finely divided iron of about 80 mesh was employed 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 maintaining the solution in contact with the iron for one hour and 45 minutes followed by alkaline neutralization and filtering to remove the metals.

Example II An effluent containing a water-soluble metallized dye prepared by diazotizing anthranilic acid and coupling with 1-(p-sulfophenyl)-3-methyl-5-pyrazolone and metallizing with chromium was treated under conditions identical to those of Example I. The following results were obtained: APHA : 1,000,000 (initial) to 50,000 Cr : 500 ppm to 15 ppm Time 45 minutes.

Example 111 An effluent obtained in the preparation of C.I. Direct Black 190 (a trisazo dye prepared by tetrazotizing dianisidine and coupling one diazonium group with R salt and the other with H acid; diazotizing the resultant dye and coupling with 1-phenyl-3-methyl-5pyrazolone and thereafter coppering the resultant dye) was treated in a manner identical to that of Example I. The following results were obtained: APHA i0 - 106 (initial) to 4,000 Cu : 3.200 ppm to 0.4 ppm Time 1 hour Example IV An effluent obtained in the preparation of C.I. Direct Red 80 (a tetrakisazo dye formed by diazotizing two moles of aminoazobenzenedisulfonic acid and coupling with J acid urea) was treated in a manner identical to that of Example I. The following results were obtained: APHA : 106 (initial) to 6.000 Time 2 hours and 42 minutes Example V A solution obtained in the preparation of a dye formed by diazotizing 2,4dichlorosulfanilic acid and coupling with N-ethyl-N-benzylaniline having an initial APHA of 500,000 and a pH of 5.0 - 6.5 was treated according to the method of the present invention. The solution was contacted with about 2% by weight based on the weight of the effluent of iron turnings at about 40 to 50"C. After about 1/2 - 3/4 hour the APHA was reduced to about 10,000. During this period the pH increased to 8.5.

Example VI An effluent obtained in a typical day's production of a plant manufacturing water-soluble azo dyes and containing both metallized and unmetallized direct azo and acid azo dyes was treated according to the method of the present invention. The effluent had an APHA of about 70,000; a temperature of about 60"C to 700C and a pH of about 9. The pH was adjusted to 5.0 and the effluent was treated under similar conditions to those of Example V for one hour. The APHA was reduced to 5,000.

WHAT WE CLAIM IS: 1. A method of treating effluent which contains chromophoric aryl azo- and/or aryl

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. precipitates out as ferric hydroxide and can be removed by established procedures. Copper, cobalt and chromium of metallized compounds contained in the effluent will generally precipitate out either as the elemental metal or as oxides or hydroxides thereof. The invention may be better understood, however, by referring to the following examples. Example I An effluent containing a metallized water-soluble azo dye prepared by coupling 1-phenyl-3-methyl-5-pyrazolone with diazotized 2-amino-1-phenol-4-sulfonamide and metallizing with chromium was decolorized according to the method of the present invention. The effluent had an initial APHA of 350,000; a pH of 5.5 - 6.0; a temperature of 55 - 60"C and a Cr content of 600 ppm. Finely divided iron of about 80 mesh was employed 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 maintaining the solution in contact with the iron for one hour and 45 minutes followed by alkaline neutralization and filtering to remove the metals. Example II An effluent containing a water-soluble metallized dye prepared by diazotizing anthranilic acid and coupling with 1-(p-sulfophenyl)-3-methyl-5-pyrazolone and metallizing with chromium was treated under conditions identical to those of Example I. The following results were obtained: APHA : 1,000,000 (initial) to 50,000 Cr : 500 ppm to 15 ppm Time 45 minutes. Example 111 An effluent obtained in the preparation of C.I. Direct Black 190 (a trisazo dye prepared by tetrazotizing dianisidine and coupling one diazonium group with R salt and the other with H acid; diazotizing the resultant dye and coupling with 1-phenyl-3-methyl-5pyrazolone and thereafter coppering the resultant dye) was treated in a manner identical to that of Example I. The following results were obtained: APHA i0 - 106 (initial) to 4,000 Cu : 3.200 ppm to 0.4 ppm Time 1 hour Example IV An effluent obtained in the preparation of C.I. Direct Red 80 (a tetrakisazo dye formed by diazotizing two moles of aminoazobenzenedisulfonic acid and coupling with J acid urea) was treated in a manner identical to that of Example I. The following results were obtained: APHA : 106 (initial) to 6.000 Time 2 hours and 42 minutes Example V A solution obtained in the preparation of a dye formed by diazotizing 2,4dichlorosulfanilic acid and coupling with N-ethyl-N-benzylaniline having an initial APHA of 500,000 and a pH of 5.0 - 6.5 was treated according to the method of the present invention. The solution was contacted with about 2% by weight based on the weight of the effluent of iron turnings at about 40 to 50"C. After about 1/2 - 3/4 hour the APHA was reduced to about 10,000. During this period the pH increased to 8.5. Example VI An effluent obtained in a typical day's production of a plant manufacturing water-soluble azo dyes and containing both metallized and unmetallized direct azo and acid azo dyes was treated according to the method of the present invention. The effluent had an APHA of about 70,000; a temperature of about 60"C to 700C and a pH of about 9. The pH was adjusted to 5.0 and the effluent was treated under similar conditions to those of Example V for one hour. The APHA was reduced to 5,000. WHAT WE CLAIM IS:

1. A method of treating effluent which contains chromophoric aryl azo- and/or aryl

nitro-containing compounds to lower the color thereof, which comprises contacting the effluent with a reducing agent consisting of Fe(II) in the presence of metallic iron at a pH in the range of from 3 to 9 and at a temperature of from 40"C. to 80"C. and for a time sufficient to cause chemical reduction of said aryl azo- and/or aryl nitro-containing compounds thereby reducing their color.

2. A method of treating effluent which contains chromophoric aryl azo-containing compounds and metal-containing compounds to lower the color and metal content of the effluent, which method comprises contacting said effluent with a reducing agent consisting of Fe(II) in the presence of metallic iron at a pH of from 3 to 9 and at a temperature of from 40"C. to 80"C. for a time sufficient to reduce chemically said metallized compounds; thereafter adjusting the pH of said effluent to a value of from 9 to 12 to cause precipitation of insoluble forms of the metal of the metallized compounds and of the iron, and separating the precipitates from the treated effluent.

3. A method according to claim 2, wherein the pH is adjusted by addition of powdered calcined limestone to the effluent.

4. A method according to claim 1, 2 or 3, wherein the said temperature is in the range of 60"C. to 75"C.

5. A method according to claim 1, 2, 3 or 4, wherein the effluent is contacted with the said reducing agent at a pH in the range of from 5.0 to 6.5.

6. A method acording to any preceding claim, wherein the metallic iron is finely divided iron.

7. A method according to claim 6, wherein the finely divided iron has a particle size of 80 mesh (Tyler sieve).

8. A method according to claim 6, wherein the finely divided iron has a particle size of from 20 to 80 mesh (Tyler sieve).

9. A method according to any preceding claim, wherein the Fe(II) is generated in situ.

10. A method according to any preceding claim, wherein the metallic iron is present in excess.

11. A method according to any preceding claim, wherein the method is carried out by passing the effluent through a column containing metallic iron particles.

12. A method according to claim 1 or 2, and substantially as hereinbefore described in any one of the foregoing Examples.