JP4306430B2 - Method for producing adipic acid - Google Patents

Description

  The present invention relates to a method for producing adipic acid.

  It is known that a mixture of cyclohexanol and cyclohexanone is obtained by liquid-phase oxidation of cyclohexane with molecular oxygen, and the mixture is used as a raw material for producing adipic acid (see, for example, Non-Patent Document 1). .

  When cyclohexane is oxidized in a liquid phase, various oxidation by-products are produced in addition to the desired cyclohexanol and cyclohexanone. Therefore, the conversion rate of cyclohexane is not increased industrially, and the target cyclohexanol and cyclohexanone are not improved. Although it is generally carried out to increase the selectivity, still a considerable amount of oxidation by-products is generated, so that the oxidation reaction solution is washed with water or alkaline water, for example, cyclohexanol, cyclohexanone and cyclohexane. Separation into a mixture containing sewage and waste water containing oxidation by-products.

  Most of the oxidation by-products contained in the wastewater discharged by such washing treatment are adipic acid and hydroxycaproic acid. Among these, adipic acid is used to crystallize the wastewater, for example, under acidic conditions. However, hydroxycaproic acid may be less demanded as it is, and is generally disposed of by incineration without recovery. Met.

  However, it is very important from an industrial point of view to effectively use carbon resources and reduce wastes to reduce environmental burdens, and effectively use wastewater containing such hydroxycaproic acid. Development of a method was desired. As such a method, a method of oxidizing the waste water with oxygen in the presence of a platinum group metal catalyst such as palladium and converting hydroxycaproic acid contained in the waste water into adipic acid has been proposed (for example, Patent Document 1). However, the catalyst used is relatively expensive and further improvements have been desired.

JP 2000-103760 A Translated by Mitsuaki Mukayama, "Industrial Organic Chemistry-Main Raw Materials and Intermediates", 1st Edition, Tokyo Chemical Co., Ltd., December 1978, p. 229-230

  Under such circumstances, the present inventors diligently studied a method for more effectively using wastewater containing hydroxycaproic acid discharged from the liquid phase oxidation of cyclohexane with molecular oxygen. The present inventors have found that adipic acid can be produced by reacting tungsten with hydrogen peroxide in the presence of tungsten oxide or tungsten oxide obtained by reacting tungsten with hydrogen peroxide.

  That is, the present invention provides an adipic acid characterized by reacting a wastewater containing hydroxycaproic acid discharged from a liquid phase oxidation process of cyclohexane with molecular oxygen and hydrogen peroxide in the presence of a tungsten catalyst. A manufacturing method is provided.

  According to the present invention, wastewater containing hydroxycaproic acid discharged from the step of liquid-phase oxidation of cyclohexane is easily obtained by reacting tungsten such as tungsten metal, sodium tungstate or the like with tungsten or hydrogen peroxide. Adipic acid can be obtained by reacting with hydrogen peroxide in the presence of a tungsten catalyst such as tungsten oxide, so that carbon resources can be used effectively, waste is reduced, and environmental treatment is reduced. Since the load can be reduced, it is industrially advantageous.

  First, wastewater containing hydroxycaproic acid discharged from the step of liquid-phase oxidation of cyclohexane with molecular oxygen (hereinafter abbreviated as wastewater) will be described. Such waste water is waste water discharged after subjecting cyclohexane to liquid phase oxidation with molecular oxygen and then washing the resulting reaction solution with water or alkaline water.

  The liquid phase oxidation of cyclohexane is carried out according to a known method such as Japanese Patent No. 2841696, and is generally carried out by blowing molecular oxygen into liquid cyclohexane. The molecular oxygen may be oxygen gas or air. A mixed gas of oxygen and inert gas may be used. The amount of molecular oxygen used is not particularly limited, but in order to suppress the formation of oxidation by-products as much as possible and improve the selectivity of the target product, molecular oxygen should be used so as not to increase the conversion rate of cyclohexane so much. The amount is set.

  The oxidation temperature is usually in the range of 80 to 200 ° C., and the reaction pressure may be any pressure that keeps the reaction mixture in the liquid phase, and is usually in the range of about 100 to 3000 kPa.

  The liquid phase oxidation of cyclohexane may be performed without a catalyst or in the presence of a catalyst. Examples of the catalyst include cobalt salts such as cobalt naphthenate and cobalt octoate, manganese salts such as manganese naphthenate and manganese octoate, and boric acid compounds such as boric acid. The amount of the catalyst used is usually in the range of 0.001 to 1% by weight with respect to cyclohexane.

  The reaction liquid obtained by liquid-phase oxidation of cyclohexane with molecular oxygen usually contains cyclohexanol and cyclohexanone, which are the target products, as well as unreacted cyclohexane, various oxidation by-products and catalysts. Contains catalysts and catalyst degradation products. Examples of the oxidation by-products include carboxylic acids such as formic acid, acetic acid, caproic acid, hexanoic acid, oxalic acid, glutaric acid, adipic acid, and hydroxycaproic acid, and lactones such as ε-caprolactone, such as the above carboxylic acids and hydroxycaprone. Esters in which acids are condensed, for example, esters in which the carboxylic acids and cyclohexanol are condensed, esters in which two molecules of hydroxycaproic acid are self-condensed, and the type and by-product amount depend on the reaction conditions. However, adipic acid and hydroxycaproic acid are often produced as by-products.

  Since these oxidation by-products represented by hydroxycaproic acid are relatively soluble in water and alkaline water, the oxidation reaction solution is usually washed with water or alkaline water, and wastewater containing the oxidation by-product and the desired cyclohexanol. , Cyclohexanone, and a mixture containing unreacted cyclohexane. In the present invention, wastewater containing hydroxycaproic acid discharged by the washing treatment is used.

  Such waste water is usually used in this reaction as it is. However, since the waste water often contains adipic acid, in that case, a part or all of the adipic acid contained in the waste water is taken out. After that, the waste water may be used in the present invention. Examples of a method for removing a part or all of adipic acid from the waste water include a method of crystallizing adipic acid from the waste water and separating the crystallized adipic acid. Examples of the method for crystallizing adipic acid from the waste water include a method for cooling the waste water and a method for partially concentrating the waste water.

  Next, a method for producing adipic acid by reacting such waste water with hydrogen peroxide in the presence of a tungsten catalyst will be described.

  Examples of the tungsten catalyst include tungsten metal, tungsten boride, tungsten carbide, tungsten sulfide, tungsten oxide, tungstic acid, tungstate, tungsten oxide, tungsten oxide formed by reacting these tungsten with hydrogen peroxide, etc. These may be used singly or in combination of two or more. Examples of tungstates include alkali metal tungstates such as sodium tungstate and potassium tungstate, alkaline earth metal tungstates such as calcium tungstate and magnesium tungstate, and ammonium tungstate. As tungsten, what is marketed normally is used. When tungstic acid is used as the tungsten catalyst, for example, tungstic acid prepared by neutralizing a tungstate such as sodium tungstate with an acid such as sulfuric acid may be used. When tungstate is used as the tungsten catalyst, for example, tungstate prepared by reacting tungstic acid with a corresponding base may be used. Among such tungsten catalysts, tungstic acid, tungstate, and tungstic acid prepared by neutralizing tungstate with an acid are preferable.

  An aqueous solution is usually used as the hydrogen peroxide used when preparing tungsten oxide obtained by reacting tungsten with hydrogen peroxide. Of course, an organic solvent solution of hydrogen peroxide may be used, but it is preferable to use hydrogen peroxide water in terms of easy handling. The hydrogen peroxide concentration in the hydrogen peroxide solution or the organic solvent solution of hydrogen peroxide is not particularly limited, but is practically in the range of about 1 to 60% by weight in consideration of volume efficiency, safety and the like. As the hydrogen peroxide solution, a commercially available one may be used as it is or after adjusting the concentration by dilution, concentration or the like, if necessary. As the organic solvent solution of hydrogen peroxide, for example, a solution prepared by a means such as extraction treatment of aqueous hydrogen peroxide with an organic solvent or distillation treatment in the presence of an organic solvent may be used. In addition, it is preferable to use tungsten having a small particle diameter in terms of facilitating preparation of tungsten oxide.

  The amount of hydrogen peroxide to be reacted with tungsten is usually 3 mol times or more, preferably 5 mol times or more with respect to tungsten, and there is no particular upper limit.

  Tungsten oxide is prepared by reacting such tungsten with hydrogen peroxide. This reaction is usually carried out in an aqueous solution. Of course, for example, in an organic solvent such as an ether solvent such as diethyl ether, methyl tert-butyl ether and tetrahydrofuran, an ester solvent such as ethyl acetate, a tertiary alcohol solvent such as tert-butanol, a nitrile solvent such as acetonitrile and propionitrile, or the like You may implement in the mixed solvent of an organic solvent and water.

  The reaction between tungsten and hydrogen peroxide is usually carried out by mixing the two, so that the tungsten is sufficiently dispersed in the tungsten oxide preparation solution in order to improve the contact efficiency between tungsten and hydrogen peroxide. It is preferable to carry out the reaction while stirring. In addition, it is preferable to use tungsten having a small particle diameter such as a powder from the viewpoint of increasing the contact efficiency between tungsten and hydrogen peroxide and facilitating control during preparation of tungsten oxide. The preparation temperature at the time of preparation of tungsten oxide is usually about −10 to 100 ° C.

  A uniform solution or suspension containing tungsten oxide can be prepared by reacting tungsten with hydrogen peroxide in water or an organic solvent. The tungsten oxide can be prepared by, for example, concentration treatment. It may be taken out from the solution and used for the reaction between waste water and hydrogen peroxide, or the prepared solution may be used as it is.

  Adipic acid can be produced by reacting waste water with hydrogen peroxide in the presence of such a tungsten catalyst. As hydrogen peroxide, an aqueous solution is usually used. Of course, an organic solvent solution of hydrogen peroxide may be used. The hydrogen peroxide concentration in the aqueous hydrogen peroxide solution or the hydrogen peroxide / organic solvent solution is not particularly limited, but is practically in the range of about 1 to 60% by weight in consideration of volume efficiency, safety and the like.

  Since hydrogen peroxide may be consumed and decomposed by oxidation by-products other than hydroxycaproic acid contained in the wastewater and the catalyst used for liquid phase oxidation of cyclohexane, the amount of hydrogen peroxide used in the wastewater In consideration of the amount of oxidation products and catalysts other than hydroxycaproic acid contained in the water, it may be determined as appropriate. Two moles or more of hydrogen peroxide is used. There is no particular upper limit on the amount of hydrogen peroxide used, but if it is too much, it tends to be economically disadvantageous, so it is practically 10 mole times or less, preferably about 5 mole times or less.

  The usage-amount of a tungsten catalyst is 0.005-50 mol% normally with respect to the hydroxycaproic acid contained in wastewater as tungsten metal, Preferably it is about 0.01-20 mol%.

  This reaction is usually performed by contacting and mixing a tungsten catalyst, waste water and hydrogen peroxide. The mixing order of the tungsten catalyst, waste water and hydrogen peroxide is not particularly limited, but it is preferable to add hydrogen peroxide to the mixture of waste water and tungsten catalyst from the viewpoint of producing adipic acid with higher yield. In this case, hydrogen peroxide is preferably added dropwise. When tungsten oxide obtained by reacting tungsten with hydrogen peroxide is used as the tungsten catalyst, the tungsten oxide, hydrogen peroxide, and waste water are contacted and mixed to prepare tungsten oxide as a catalyst. The operation and the reaction between the waste water and hydrogen peroxide may be performed simultaneously.

  The reaction temperature is usually about 20 to 130 ° C., preferably about 70 to 110 ° C., and is usually performed under normal pressure conditions, but may be performed under pressure or reduced pressure conditions.

  The reaction between the waste water and hydrogen peroxide may be performed in the presence of an organic solvent. Examples of the organic solvent include ether solvents such as diethyl ether, methyl tert-butyl ether and diglyme, ester solvents such as ethyl acetate, tertiary alcohol solvents such as tert-butanol, and nitrile solvents such as acetonitrile and propionitrile. The amount of use is not particularly limited.

  This reaction is preferably performed in the range of pH 0 to 6, more preferably in the range of pH 0 to 4, and still more preferably in the range of pH 0 to 2, from the viewpoint of reaction rate and the like. Therefore, when the pH of the reaction solution is not within the above range, it is preferable to carry out the reaction by adjusting the pH of the reaction solution with an acid such as sulfuric acid, hydrochloric acid or nitric acid or an alkali such as sodium hydroxide. .

  After completion of the reaction, the adipic acid can be taken out by subjecting the reaction solution as it is or if necessary to decompose the remaining hydrogen peroxide with a reducing agent such as sodium sulfite, followed by concentration treatment, crystallization treatment, etc. . Moreover, adipic acid can also be taken out by adding an organic solvent insoluble in water to the reaction solution, performing extraction treatment, and subjecting the resulting organic layer to concentration treatment, crystallization treatment, and the like.

  Depending on the tungsten catalyst used, the tungsten catalyst may be present as an insoluble substance in the reaction solution. In that case, for example, filtration is performed while adipic acid is dissolved in the reaction solution. Thus, the used tungsten catalyst and the filtrate containing adipic acid can be easily separated, and the tungsten catalyst can be recovered as a solid. The obtained adipic acid-containing filtrate is taken as it is or if necessary, after remaining hydrogen peroxide is decomposed with a reducing agent such as sodium sulfite, followed by concentration treatment, crystallization treatment, etc., to take out adipic acid be able to. Moreover, adipic acid can also be taken out by adding an organic solvent insoluble in water to the filtrate, performing an extraction treatment, and subjecting the resulting organic layer to a concentration treatment, a crystallization treatment, or the like.

  The taken out adipic acid may be further purified by a usual purification method such as recrystallization. In addition, the filtrate and reaction solution after extraction of adipic acid by crystallization treatment is extracted, and the aqueous layer after removal of the organic layer contains the tungsten catalyst of this reaction and can be concentrated as it is or as necessary. After carrying out the treatment, it can be used again for this reaction. Further, when the tungsten catalyst is taken out as a solid, the taken-out tungsten catalyst solid can be used again in this reaction after being washed as it is or with water or an organic solvent as necessary.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all. A high performance liquid chromatograph was used for the analysis. In addition, the adipic acid yield in the following examples was generated in this reaction by subtracting the amount of adipic acid contained in the wastewater used as a raw material from the amount of adipic acid contained in the reaction solution. The amount of adipic acid is calculated based on the amount of hydroxycaproic acid in the wastewater.

Example 1
Cyclohexane was subjected to liquid phase oxidation and washed with water to obtain a mixture of cyclohexanone and cyclohexanol, and waste water containing hydroxycaproic acid was obtained. The wastewater was cooled and crystallized adipic acid was collected by filtration to obtain wastewater having a hydroxycaproic acid content of 18.5% by weight. In addition to hydroxycaproic acid, the wastewater contained adipic acid, glutaric acid, ε-caprolactone, an ester of adipic acid, an ester of hydroxycaproic acid, and the like.

  A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.07 g of sodium tungstate, 9.61 g of 30% by weight hydrogen peroxide and 80 mg of sulfuric acid at room temperature, and stirred at room temperature for 1 minute to obtain a tungsten catalyst suspension. Prepared. To this, 14.3 g of the waste water containing hydroxycaproic acid obtained above (hydroxycaproic acid content: 18.5% by weight) was charged, and stirred and reacted at an internal temperature of 90 ° C. for 4 hours to prepare a reaction solution containing adipic acid. Obtained. Adipic acid yield: 26%.

Example 2
A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.07 g of sodium tungstate, 1 g of water and 80 mg of sulfuric acid at room temperature, and stirred at room temperature for 1 minute to prepare a tungsten catalyst suspension. 14.1 g of waste water containing the same hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight) was charged into the preparation solution, and the internal temperature was adjusted to 90 ° C. Hydrogen oxide water 9.61g was dripped over 7 hours. Thereafter, the mixture was stirred and reacted at the same temperature for 2 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 52%.

Example 3
A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.04 g of sodium tungstate and 1.1 g of 30 wt% hydrogen peroxide at room temperature, and stirred at an internal temperature of 50 ° C. for 15 minutes to prepare tungsten oxide. . The prepared solution was charged with 8.5 g of 30% by weight hydrogen peroxide water and 14.3 g of waste water containing the same hydroxycaproic acid as used in Example 1 above (hydroxycaproic acid content: 18.5% by weight). The mixture was stirred and reacted at 90 ° C. for 4 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 26%.

Example 4
A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.33 g of sodium tungstate, 1 g of water and 0.3 g of sulfuric acid to prepare a tungstic acid aqueous solution. To this was added 14.3 g of the waste water containing hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight), and the internal temperature was adjusted to 90 ° C. At the same temperature, 9.6 g of 30% by weight hydrogen peroxide water was added dropwise over 10 hours, followed by stirring and reaction for 2 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 80%.

Example 5
A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.66 g of sodium tungstate, 1 g of water, and 0.6 g of sulfuric acid to prepare a tungsten catalyst suspension. To this, 14.3 g of waste water containing hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight) was charged, and the internal temperature was adjusted to 90 ° C. 9.6 g of 30% by weight hydrogen peroxide solution was added dropwise over 7 hours, followed by stirring and reaction for 2 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 86%.

Example 6
A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.04 g of tungsten metal and 1.1 g of 30 wt% hydrogen peroxide solution and stirred at an internal temperature of 50 ° C. for 15 minutes to prepare tungsten oxide. To this, 14.3 g of waste water containing hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight) was charged, and the internal temperature was adjusted to 90 ° C. At the same temperature, 8.5 g of 30 wt% aqueous hydrogen peroxide was added dropwise over 7 hours, followed by stirring and reaction for 2 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 35%.

Example 7
A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.23 g of tungsten oxide, 1 g of water and 0.6 g of sulfuric acid and stirred at room temperature for 1 minute. To this, 14.3 g of waste water containing hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight) was charged, and the internal temperature was adjusted to 90 ° C. At the same temperature, 9.61 g of 30 wt% hydrogen peroxide water was added dropwise over 4 hours, followed by stirring and reaction for 3 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 60%.

Example 8
A 100 mL Schlenk tube equipped with a reflux condenser was charged with 0.25 g of tungstic acid, 1 g of water and 0.6 g of sulfuric acid, and stirred at room temperature for 1 minute. To this, 14.3 g of waste water containing hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight) was charged, and the internal temperature was adjusted to 90 ° C. At the same temperature, 9.61 g of 30 wt% hydrogen peroxide water was added dropwise over 4 hours, followed by stirring and reaction for 3 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 62%.

Example 9
A 500 mL four-necked flask equipped with a reflux condenser was charged with 4.95 g of sodium tungstate, 15 g of water and 9 g of sulfuric acid to prepare a tungsten catalyst suspension. This was charged with 214.3 g of waste water containing hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight) and adjusted to an internal temperature of 100 ° C. At the same temperature, 123.6 g of 30 wt% aqueous hydrogen peroxide was added dropwise over 4 hours, followed by stirring and reaction for 3 hours to obtain a reaction solution containing adipic acid. The reaction solution was filtered at an internal temperature of 70 ° C., and a yellow solid was separated by filtration. The obtained filtrate was cooled to an internal temperature of 10 ° C. over 12 hours, and the precipitated crystals of adipic acid were collected by filtration. Acquisition rate of adipic acid crystals: 59%, adipic acid yield combining the crystals and adipic acid contained in the filtrate: 81%. The yellow solid was washed with water and then with acetone, dried and then analyzed, and confirmed to be tungstic acid. Tungstic acid content: 95% by weight.

Example 10
To a 500 mL four-necked flask equipped with a reflux condenser, 4.4 g of the tungstic acid yellow solid obtained in Example 9 above, 0.5 g of sodium tungstate, 15 g of water and 9 g of sulfuric acid were added, and the tungsten catalyst suspension was added. Prepared. This was charged with 214.3 g of waste water containing hydroxycaproic acid as used in Example 1 (hydroxycaproic acid content: 18.5% by weight) and adjusted to an internal temperature of 100 ° C. At the same temperature, 123.6 g of 30 wt% aqueous hydrogen peroxide was added dropwise over 4 hours, followed by stirring and reaction for 3 hours to obtain a reaction solution containing adipic acid. The reaction solution was filtered at an internal temperature of 70 ° C., and a yellow solid was separated by filtration. The obtained filtrate was cooled to an internal temperature of 10 ° C. over 12 hours, and the precipitated crystals of adipic acid were collected by filtration. The adipic acid yield which combined the crystal and the adipic acid in a filtrate: 68%.

Example 11
Cyclohexane was subjected to liquid phase oxidation and washed with water to obtain a mixture of cyclohexanone and cyclohexanol, and wastewater containing hydroxycaproic acid (hydroxycaproic acid content: 8.8% by weight) was obtained. In addition to hydroxycaproic acid, the wastewater contained adipic acid, glutaric acid, ε-caprolactone, an ester of adipic acid, an ester of hydroxycaproic acid, and the like.

  A 500 mL four-necked flask equipped with a reflux condenser was charged with 2.47 g of sodium tungstate, 7.5 g of water and 9.0 g of sulfuric acid at room temperature to prepare a tungsten catalyst suspension. To this was added 226.6 g of waste water containing hydroxycaproic acid (hydroxycaproic acid content: 8.8 wt%), and the internal temperature was adjusted to 100 ° C. At the same temperature, 72.1 g of 30% by weight hydrogen peroxide solution was added dropwise over 8 hours, followed by stirring and reaction for 3 hours to obtain a reaction solution containing adipic acid. The reaction solution was filtered at an internal temperature of 70 ° C., and a yellow solid was separated by filtration. The obtained filtrate was cooled to an internal temperature of 10 ° C. over 12 hours, and the precipitated crystals of adipic acid were collected by filtration. Adipic acid yield of crystals and adipic acid in filtrate: 89%.

Example 12
A 500 mL four-necked flask equipped with a reflux condenser was charged with 2.47 g of sodium tungstate, 7.5 g of water and 9.0 g of sulfuric acid at room temperature to prepare a tungsten catalyst suspension. To this was added 233.2 g of waste water containing hydroxycaproic acid as used in Example 11 (hydroxycaproic acid content: 8.8 wt%), and the internal temperature was adjusted to 100 ° C. At the same temperature, 432.4 g of 5 wt% aqueous hydrogen peroxide was added dropwise over 10 hours, followed by stirring and reaction for 3 hours to obtain a reaction solution containing adipic acid. The reaction solution was filtered at an internal temperature of 70 ° C., and a yellow solid was separated by filtration. The obtained filtrate was cooled to an internal temperature of 10 ° C. over 12 hours, and the precipitated crystals of adipic acid were collected by filtration. The adipic acid yield which combined the crystal and the adipic acid in a filtrate: 95%.

Example 13
Cyclohexane was subjected to liquid phase oxidation and washed with water to obtain a mixture of cyclohexanone and cyclohexanol, and wastewater containing hydroxycaproic acid (hydroxycaproic acid content: 7.5% by weight) was obtained. In addition to hydroxycaproic acid, the wastewater contained adipic acid, glutaric acid, ε-caprolactone, an ester of adipic acid, an ester of hydroxycaproic acid, and the like.

  A 300 mL four-necked flask equipped with a reflux condenser was charged with 1.29 g of sodium tungstate, 3.9 g of water and 6.8 g of 60% nitric acid at room temperature to prepare a tungsten catalyst suspension. To this was added 120 g of waste water containing hydroxycaproic acid (hydroxycaproic acid content: 7.5% by weight), and the internal temperature was adjusted to 100 ° C. At the same temperature, 37.6 g of 30 wt% aqueous hydrogen peroxide was added dropwise over 6 hours, and then stirred and reacted for 4 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 73%.

Example 14
A 300 mL four-necked flask equipped with a reflux condenser was charged with 2.6 g of sodium tungstate, 30 g of water, and 6.8 g of 60% nitric acid at room temperature to prepare a tungsten catalyst suspension. To this, 120 g of waste water containing hydroxycaproic acid (hydroxycaproic acid content: 7.5% by weight) as used in Example 13 was added, and the internal temperature was adjusted to 80 ° C. At the same temperature, 32.9 g of 30 wt% aqueous hydrogen peroxide was added dropwise over 6 hours, followed by stirring and reaction for 4 hours to obtain a reaction solution containing adipic acid. Adipic acid yield: 84%.

Claims (7)

A method for producing adipic acid, comprising reacting wastewater containing hydroxycaproic acid discharged from a step of liquid-phase oxidation of cyclohexane with molecular oxygen and hydrogen peroxide in the presence of a tungsten catalyst. A tungsten catalyst reacts at least one tungsten selected from the group consisting of tungsten metal, tungsten boride, tungsten carbide, tungsten sulfide, tungsten oxide, tungstic acid and tungstate, or the tungsten and hydrogen peroxide. The method for producing adipic acid according to claim 1, which is a tungsten oxide. The method for producing adipic acid according to claim 1, wherein hydrogen peroxide is added to a mixture of wastewater containing a tungsten catalyst and hydroxycaproic acid. The method for producing adipic acid according to claim 3, wherein hydrogen peroxide is dropped. The method for producing adipic acid according to claim 1, wherein the reaction is carried out in the range of pH 0-6. The method for producing adipic acid according to claim 1, wherein the wastewater containing hydroxycaproic acid is wastewater further containing adipic acid. 2. The adipic acid according to claim 1, wherein the wastewater containing hydroxycaproic acid further contains wastewater containing adipic acid, and a part or all of the adipic acid contained in the wastewater is taken out and then reacted with hydrogen peroxide. Manufacturing method.