JPWO2001034543A1 - Method for producing a diol mixture - Google Patents

Abstract

(57) [Abstract] A method for producing a diol mixture containing 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol is disclosed, comprising: (A) providing a dicarboxylic acid mixture containing succinic acid, glutaric acid, and adipic acid, the dicarboxylic acid mixture being prepared by denitrating an aqueous by-product obtained in an adipic acid production process, the dicarboxylic acid mixture having a nitric acid content of 3% by weight or less, based on the total weight of the succinic acid, glutaric acid, and adipic acid; and (B) subjecting the dicarboxylic acid mixture to a hydrogenation reaction in the presence of water, hydrogen gas, and a hydrogenation catalyst containing active metal species consisting of ruthenium and tin, to obtain a hydrogenation reaction liquid containing a diol mixture containing 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

Description

TECHNICAL FIELD The present invention relates to a method for producing a diol mixture, more particularly to a method for producing a 1,4-diol mixture.
The method for producing a diol mixture containing butanediol, 1,5-pentanediol, and 1,6-hexanediol includes the steps of: (A) providing a dicarboxylic acid mixture containing succinic acid, glutaric acid, and adipic acid, the dicarboxylic acid mixture being prepared by denitrating an aqueous by-product obtained in a process for producing adipic acid, and having a nitric acid content of not more than a specific amount; and (B) subjecting the dicarboxylic acid mixture to a hydrogenation reaction in the presence of water, hydrogen gas, and a hydrogenation catalyst containing active metal species consisting of ruthenium and tin, to produce 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.
The method for producing a diol mixture of the present invention includes obtaining a hydrogenation reaction solution containing a diol mixture including 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. The method uses an aqueous by-product solution containing a dicarboxylic acid mixture including succinic acid, glutaric acid, and adipic acid, which is obtained from a process for producing adipic acid, as a raw material, and hydrogenates the dicarboxylic acids directly without converting them to esters, thereby enabling the stable production of a diol mixture including 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol over a long period of time.

Diols are extremely important compounds widely used in industrial fields as raw materials for polyester resins, urethane foams, urethane paints, adhesives, etc., and are mass-produced industrially. The main method used to produce diols is the hydrogenation of dicarboxylic acid diesters. This method will be explained using the production of 1,4-butanediol as an example.

One method for producing 1,4-butanediol is to introduce two hydroxyl groups into n-butane to produce 1,4-butanediol, but this method is economically very disadvantageous and is therefore virtually impossible to carry out on an industrial scale at present. In practice, a method is used in which n-butane is oxidized with air to produce succinic acid, maleic acid, or anhydrides thereof, particularly maleic acid or maleic anhydride, and then 1,4-butanediol is produced using these as a raw material.

Dicarboxylic acids such as maleic acid can be easily converted to diols by reduction. This reduction is carried out using a suitable reducing agent, but typically requires a highly reactive, powerful reducing agent (e.g., lithium aluminum hydride). Such reducing agents require special care in handling and storage, making them unsuitable for industrial use.

On the other hand, a reduction method using hydrogen gas as a reducing agent in the presence of a suitable catalyst (so-called hydrogenation reaction) is suitable for industrial scale implementation.
Hydrogenation reactions are generally not applicable to the reduction of dicarboxylic acids because the catalysts conventionally used in hydrogenation reactions are soluble in dicarboxylic acids and therefore do not maintain activity in the presence of acid.

For this reason, in the production of 1,4-butanediol, n-
A method is used in which maleic acid or maleic anhydride obtained by air oxidation of butane is further converted into a diester by reacting it with a suitable alcohol, and the resulting maleic acid diester is then hydrogenated in the presence of a copper catalyst at high temperature and high pressure to convert it into 1,4-butanediol.
No. 00-510837 (corresponding to U.S. Pat. No. 6,100,410),
Japanese Patent Publication No. 2000-510475 (corresponding to the specification of U.S. Patent No. 6,077,964), Japanese Patent Publication No. 2000-506134 (corresponding to U.S. Patent No. 5,
No. 981,769), Japanese Patent Laid-Open No. 7-196558 (corresponding to U.S. Pat. No. 5,414,159), U.S. Pat. No. 5,334,779, and the like.

However, all of these methods require three steps: the production of dicarboxylic acid, the esterification of the dicarboxylic acid, and the hydrogenation of the ester, which inevitably lengthens the production process. Furthermore, these methods require a large amount of equipment. For example, equipment is required for esterifying the dicarboxylic acid, and when hydrogenating the diester, the alcohol used in the esterification is by-produced, which results in a long production time.
Equipment is also required to separate and recover this by-produced alcohol from the reaction mixture and reuse it.

Because of these problems, the production of diols by hydrogenating diesters is clearly disadvantageous in terms of production costs, etc. Therefore, various means for shortening the industrial production process of diols have been investigated.

One example of such a method is to use a catalyst that maintains its activity even in the presence of an acid,
One approach being considered is to produce diols by hydrogenating the dicarboxylic acids themselves without esterification.

This method involves two steps: the production of dicarboxylic acids and the hydrogenation of dicarboxylic acids.
In this case, the step of esterifying dicarboxylic acid, which was necessary in the conventional method, is not necessary, and therefore no equipment for esterification is required. Furthermore, since esterification of dicarboxylic acid is not performed,
The alcohol used in esterification is not produced as a by-product during hydrogenation, and no equipment is required to recover and reuse the by-product alcohol. As a result, the diol production process is shortened and the amount of equipment required is significantly reduced.

Many catalysts for producing diols by hydrogenating dicarboxylic acids and methods for producing diols using the catalysts have been proposed, including several methods for producing 1,4-butanediol by hydrogenating succinic acid or maleic acid itself. In these methods, the hydrogenation is usually carried out in the presence of water. Only the catalyst systems used in these methods are listed below.

Ruthenium-iron oxide catalysts (U.S. Pat. No. 4,827,001); Ruthenium-tin catalysts based on the BET specific surface area (Brunauer-Emmett-Teller
Catalysts supported on porous carbon with a specific surface area of 2,000 m ² /g or more (as determined by applying the Nauer-Emmett-Teller adsorption isotherm) (Japanese Patent Application Laid-Open No. 5-2002)
46915); a catalyst in which ruthenium and tin are supported on silica modified with titanium and/or alumina (Japanese Patent Laid-Open No. 6-116182); a catalyst in which ruthenium and tin, and an alkali metal compound or an alkaline earth metal compound, are supported on a support (Japanese Patent Laid-Open No. 6-239778); a catalyst in which at least one metal selected from ruthenium, platinum, and rhodium, and tin, are supported on a porous support (Japanese Patent Laid-Open No. 7-165644); a catalyst in which ruthenium and tin are supported on a support (Japanese Patent Laid-Open No. 9-12492).
(In the method using this catalyst, excess hydrogen is circulated through the reaction system, and the reaction is carried out while removing the products that come with the hydrogen from the system.) A catalyst in which ruthenium-tin-platinum is supported on a porous carrier (Japanese Patent Application Laid-Open No. 9-591
a ruthenium-tin-platinum catalyst supported on a carbonaceous support, prepared by impregnating the carbonaceous support with a solution containing a carbonyl compound having 5 or less carbon atoms and the metal component to be supported (Japanese Patent Laid-Open No. 10-15388); and a ruthenium-tin-platinum catalyst supported on a carbonaceous support that has been previously contacted with nitric acid (Japanese Patent Laid-Open No. 10-71332).

In addition, Japanese Patent Application Laid-Open No. 7-82190 proposes a method of hydrogenating dicarboxylic acids using a tertiary alcohol as a solvent in the presence of a catalyst consisting of palladium and a rhenium compound. Also, U.S. Patent No. 5,698,749 describes that 1,4-butanediol can be obtained in a relatively high yield from maleic acid using a catalyst in which palladium-silver-rhenium is supported on activated carbon that has been previously oxidized with nitric acid. Furthermore, with regard to the direct hydrogenation of adipic acid, it has been reported that 1,6-hexanediol can be obtained in a high yield using a catalyst in which ruthenium-tin-platinum is supported on activated carbon that has been previously treated with acid (Japanese Patent Application Laid-Open No. 11-62190).
No. 0523 (corresponding to the specification of U.S. Pat. No. 5,969,194) and the like are disclosed.

As described above, various techniques for hydrogenating individual dicarboxylic acids such as succinic acid, maleic acid, and adipic acid have been disclosed, but no method for directly hydrogenating a mixture of such dicarboxylic acids to produce a mixture containing multiple diols has been described. If a hydrogenation reaction could be carried out using as a raw material a substance that has not previously been used much, such as an aqueous solution containing a dicarboxylic acid mixture produced as a by-product during the production of adipic acid, it would be extremely advantageous, as it would enable the production of diols useful as raw materials for polyurethanes and polyesters. Specifically, when adipic acid is produced by oxidizing a cyclic aliphatic compound such as cyclohexanone or cyclohexanol with nitric acid, a by-product aqueous solution is obtained after crystallization and separation of the adipic acid. This by-product aqueous solution is an aqueous solution containing a dicarboxylic acid mixture containing succinic acid, glutaric acid, and adipic acid, and is esterified and used as a solvent. However, the demand for such solvents is not necessarily large, and currently, a portion of the by-product aqueous solution is discarded without being used. Therefore, if a hydrogenation reaction could be carried out using as a raw material an aqueous solution containing a dicarboxylic acid mixture produced as a by-product during the production of adipic acid, it would be possible to obtain 1,4-diols.
Diols useful as raw materials for polyurethanes and polyesters, such as 1,5-butanediol, 1,5-pentanediol, and 1,6-hexanediol, can be advantageously obtained.

However, the inventors' research has revealed that when the above-mentioned direct hydrogenation reaction is carried out using an aqueous by-product containing a dicarboxylic acid mixture obtained during the production of adipic acid as a raw material, the activity of the catalyst decreases significantly with the lapse of reaction time.
There has been no industrially implemented method for producing a diol using an aqueous by-product containing a dicarboxylic acid mixture obtained during the production of adipic acid.

In view of the above circumstances, the present inventors have conducted extensive research to develop a method for stably and efficiently producing diols over a long period of time by hydrogenating an aqueous by-product solution containing a dicarboxylic acid mixture obtained during the production of adipic acid. As a result, they have surprisingly found that the nitric acid content of the aqueous by-product solution containing a dicarboxylic acid mixture obtained during the production of adipic acid is reduced to a specific concentration or less to form a dicarboxylic acid mixture,
It has been found that by subjecting a hydrogenation reaction to a catalyst containing ruthenium and tin as active metal species, diols can be produced efficiently and stably over a long period of time without a decrease in catalytic activity over a long period of time. It has also been found that in the above-mentioned method, diols can be produced efficiently and stably over a long period of time by reducing the amounts of metals such as copper and vanadium and other impurities such as sulfur contained in the raw material by-product aqueous solution to below a specific concentration. The present invention has been completed based on these new findings.

Therefore, a main object of the present invention is to provide a method for efficiently producing diols stably over a long period of time by hydrogenating an aqueous by-product solution containing a dicarboxylic acid mixture obtained when adipic acid is produced by oxidizing a cyclic aliphatic compound having 6 carbon atoms with nitric acid, as a raw material.

These and other objects, features, and advantages of the present invention will become apparent from the following detailed description and claims.

Detailed Description of the Invention According to one embodiment of the present invention, there is provided a method for producing a diol mixture containing 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol, comprising: (A) providing a dicarboxylic acid mixture containing succinic acid, glutaric acid, and adipic acid, and having a nitric acid content of 3% by weight or less based on the total weight of the succinic acid, glutaric acid, and adipic acid; the dicarboxylic acid mixture is prepared by denitrating an aqueous by-product solution obtained in a process for producing adipic acid, the process comprising: subjecting at least one cyclic aliphatic compound having 6 carbon atoms to oxidation with nitric acid in an aqueous medium in the presence of an oxidation catalyst to obtain an aqueous reaction solution containing succinic acid, glutaric acid, and adipic acid; precipitating crystals of the adipic acid; isolating the precipitated crystals from the reaction solution; and obtaining an aqueous by-product solution; (B) subjecting the dicarboxylic acid mixture to a hydrogenation reaction in the presence of water, hydrogen gas, and a hydrogenation catalyst containing active metal species consisting of ruthenium and tin,
obtaining a hydrogenation reaction liquid containing a diol mixture including 4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

Next, in order to facilitate understanding of the present invention, the basic features and preferred embodiments of the present invention will be listed.

1. A method for producing a diol mixture containing 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol, comprising: (A) providing a dicarboxylic acid mixture containing succinic acid, glutaric acid, and adipic acid, and having a nitric acid content of 3% by weight or less based on the total weight of the succinic acid, glutaric acid, and adipic acid; the dicarboxylic acid mixture is prepared by denitrating an aqueous by-product solution obtained in a process for producing adipic acid, the process comprising: subjecting at least one cyclic aliphatic compound having 6 carbon atoms to oxidation with nitric acid in an aqueous medium in the presence of an oxidation catalyst to obtain an aqueous reaction solution containing succinic acid, glutaric acid, and adipic acid; precipitating crystals of the adipic acid; isolating the precipitated crystals from the reaction solution; and obtaining an aqueous by-product solution; and (B) subjecting the dicarboxylic acid mixture to a hydrogenation reaction in the presence of water, hydrogen gas, and a hydrogenation catalyst containing active metal species consisting of ruthenium and tin,
obtaining a hydrogenation reaction liquid containing a diol mixture including 4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

2. The method according to item 1 above, wherein the dicarboxylic acid mixture is prepared before step (B) so as to satisfy at least one condition selected from the group consisting of the following conditions (1) to (3):

(1) the mixture has a nitric acid content of 0.2% by weight or less, based on the total weight of succinic acid, glutaric acid, and adipic acid; (2) the mixture has a copper content and a vanadium content of 10 ppm or less, based on the total weight of succinic acid, glutaric acid, and adipic acid; and (3) the mixture has a sulfur content of 200 ppm or less, based on the total weight of succinic acid, glutaric acid, and adipic acid.

3. The method according to item 2 above, wherein the mixture under condition (3) has a sulfur content of 40 ppm or less based on the total weight of succinic acid, glutaric acid, and adipic acid.

4. The method according to any one of items 1 to 3 above, wherein an aqueous solution of the dicarboxylic acid mixture in distilled water has an absorption coefficient at 355 nm calculated by the following formula of 0.3 or less.

E = A / (c × b) (wherein E is the absorption coefficient at 355 nm, A is the absorbance at room temperature of an aqueous solution obtained by dissolving the dicarboxylic acid mixture in distilled water, c is the weight (g) of the dicarboxylic acid mixture dissolved in 100 g of distilled water, and b is the length (cm) of the cell used to measure the absorbance.) 5. The production method according to item 4 above, wherein an aqueous solution obtained by dissolving the dicarboxylic acid mixture in distilled water exhibits an absorption coefficient of 0.1 or less.

6. The dicarboxylic acid mixture contains a compound having an oxygen-nitrogen bond in an amount, converted into the weight of nitric acid, of 2,000 times the total weight of succinic acid, glutaric acid, and adipic acid.
6. The method according to any one of items 1 to 5 above, wherein the content is less than ppm.
7. The production method according to any one of items 1 to 6 above, wherein the active metal species contained in the hydrogenation catalyst further contains at least one metal selected from the metals of Group 7 of the periodic table.

8. The method according to item 7 above, wherein the at least one metal selected from the metals of Group 7 of the periodic table is rhenium.

9. The production method according to any one of items 1 to 8 above, wherein the active metal species contained in the hydrogenation catalyst further contains at least one metal selected from the group consisting of metals in Group 8 of the periodic table other than ruthenium and metals in Groups 9 and 10 of the periodic table.

10. The method according to item 9 above, wherein the at least one metal selected from the group consisting of metals in Group 8 of the periodic table other than ruthenium and metals in Groups 9 and 10 of the periodic table is platinum.

11. The production method according to any one of items 1 to 10 above, wherein the hydrogenation catalyst further comprises activated carbon supporting the active metal species.

12. The production method according to any one of items 1 to 11 above, wherein the hydrogenation reaction is carried out under conditions of a temperature of 100 to 300°C and a hydrogen pressure of 1 to 25 MPa.

13. The production method according to any one of items 1 to 12 above, wherein the dicarboxylic acid mixture is prepared as an aqueous solution by a first purification process including the following steps (a) to (c):

(a) the by-product aqueous solution is heated at a temperature of 80 to 200°C and at a pressure equal to or lower than atmospheric pressure to perform dehydration and denitration to obtain a dehydrated and denitrated dicarboxylic acid mixture; (b) water is added to the obtained dehydrated and denitrated dicarboxylic acid mixture to obtain a denitrated dicarboxylic acid mixture aqueous solution; and (c) copper and vanadium are removed by contacting the denitrated dicarboxylic acid mixture aqueous solution with a cation exchange resin.

14. The method according to claim 1, wherein the first purification process further comprises a step (d) of contacting the denitrated aqueous dicarboxylic acid mixture with an anion-adsorbing material.
3. The manufacturing method according to claim 3.

15. The method according to item 13 or 14 above, wherein the first purification process further comprises a step of contacting the denitrated aqueous dicarboxylic acid mixture solution with activated carbon.

16. The production method according to any one of items 1 to 12 above, wherein the dicarboxylic acid mixture is prepared by a second purification process comprising the following steps (a) to (f):

(a) heating the by-product aqueous solution at a temperature of 80 to 130°C and a pressure equal to or lower than atmospheric pressure;
(b) further heating the dehydrated and denitrated dicarboxylic acid mixture at a temperature of 130 to 180°C and atmospheric pressure to obtain a denitrated dicarboxylic acid mixture; (b) adding water to the obtained dehydrated and denitrated dicarboxylic acid mixture to obtain an aqueous denitrated dicarboxylic acid mixture; (c) contacting the denitrated dicarboxylic acid aqueous mixture with a cation exchange resin to remove copper and vanadium; (d) heating the obtained denitrated dicarboxylic acid aqueous mixture at a pressure equal to or lower than atmospheric pressure at a temperature sufficient to distill off water from the denitrated dicarboxylic acid aqueous mixture; (e) adding an aromatic hydrocarbon having 6 to 14 carbon atoms and having a boiling point of 200°C or lower at atmospheric pressure to the denitrated dicarboxylic acid mixture obtained in step (d), heating the resulting mixture at a temperature equal to or lower than the boiling point of the aromatic hydrocarbon, and then cooling; and (f) recovering the denitrated dicarboxylic acid mixture from the mixture by filtration to prepare the dicarboxylic acid mixture.

17. The production method according to item 16 above, wherein the second purification process further comprises, after step (a), a step of contacting the denitrated dicarboxylic acid mixture in the form of an aqueous solution or an aqueous solution obtained by dissolving the denitrated dicarboxylic acid mixture in water with an anion-adsorbing material.

18. The process according to any one of items 1 to 12 above, wherein the dicarboxylic acid mixture is prepared by a third purification process including contacting the by-product aqueous solution with hydrogen gas in the presence of a reduction catalyst containing an active metal species including at least one metal selected from the group consisting of metals of Groups 7 to 10 of the Periodic Table, thereby reducing nitric acid and compounds having an oxygen-nitrogen bond contained in the by-product aqueous solution, thereby obtaining the dicarboxylic acid mixture in the form of an aqueous solution.
1. The manufacturing method according to any one of the preceding claims.

19. The production method according to item 18 above, wherein the reduction reaction of the nitric acid and the compound having an oxygen-nitrogen bond in the third purification step is carried out under conditions of a temperature of 50 to 200°C and a hydrogen pressure of 0.2 to 5 MPa.

20. The process according to claim 1, wherein the active metal species contained in the reduction catalyst used in the third purification process is at least one metal selected from the group consisting of platinum, rhenium, palladium, rhodium, nickel, iridium, and ruthenium.
8 or 19. The method for producing the same according to claim 19.

21. The method according to any one of items 18 to 20 above, wherein in the third purification process, the by-product aqueous solution is subjected to the following step before being brought into contact with hydrogen gas:

The by-product aqueous solution is heated at a temperature of 80 to 130°C under a pressure equal to or lower than atmospheric pressure, and then further heated at a temperature of 130 to 180°C under atmospheric pressure, and water is added thereto.

22. A method for recovering 1,4-butanediol and a mixture of 1,5-pentanediol and 1,6-hexanediol from a diol mixture obtained by the production method according to any one of items 1 to 21 above, comprising: (i) adjusting the temperature of a hydrogenation reaction liquid containing the diol mixture to a temperature between room temperature and less than 100°C, and performing gas-liquid separation at atmospheric pressure or less to remove hydrogen gas from the hydrogenation reaction liquid; (ii) heating the hydrogenation reaction liquid from which hydrogen gas has been removed under atmospheric pressure to distill off a mixture of water and cyclic ethers and monohydric alcohols by-produced in the hydrogenation reaction; (iii) subjecting the resulting mixture to multi-stage distillation to distill off water and γ-butyrolactone by-produced in the hydrogenation reaction to obtain a purified diol mixture; (iv) subjecting the purified diol mixture to multi-stage distillation to obtain 1,4-butanediol as a low-boiling component; and (v) further subjecting the remaining high-boiling mixture obtained in step (iv) to multi-stage distillation,
obtaining a mixture of 1,5-pentanediol and 1,6-hexanediol as a distillate.

The present invention will be described in detail below.

Adipic acid is produced by oxidizing at least one cyclic aliphatic compound having 6 carbon atoms, such as cyclohexanone or cyclohexanol, with nitric acid in the presence of an oxidation catalyst containing copper and vanadium. In this reaction, in addition to the main reaction product adipic acid, by-products such as glutaric acid, succinic acid, malonic acid, and oxalic acid are produced, along with trace amounts of coloring substances. Because these by-products have higher solubility in water than adipic acid, adipic acid can be separated by crystallization by cooling the reaction solution below room temperature. The crystallized adipic acid is recovered by filtration, and the remaining by-product aqueous solution contains the by-products, nitric acid, and catalyst. This by-product aqueous solution is generally concentrated, and an appropriate amount of nitric acid is added for reuse in the production of adipic acid. However, as this process is repeated, the concentration of by-products in the reaction product increases, and
This results in a decrease in the purity of the product adipic acid.

In order to prevent a decrease in the purity of adipic acid, a portion of the by-product aqueous solution is usually discharged outside the system. After useful components are recovered from the discharged by-product aqueous solution by distillation to recover nitric acid and further by recovering the catalyst by ion exchange, the other by-products are recovered as a by-product aqueous solution containing a dicarboxylic acid mixture. The main components of the by-product aqueous solution containing a dicarboxylic acid mixture are glutaric acid, succinic acid, and the unrecovered adipic acid, and these dicarboxylic acids are esterified and used as solvents, etc.

In the present invention, a by-product aqueous solution obtained after producing adipic acid from at least one cyclic aliphatic compound having 6 carbon atoms and precipitating and isolating the resulting adipic acid crystals is used. This by-product aqueous solution may be the aqueous solution obtained by isolating the product adipic acid from the reaction solution, or it may be the aqueous solution obtained after further recovery of useful components such as nitric acid and catalyst. The concentration of the dicarboxylic acid mixture in this by-product aqueous solution is 5 to 40 wt%, and the dicarboxylic acids contained therein are mainly by-produced succinic acid and glutaric acid, and unrecovered adipic acid. The concentrations of succinic acid, glutaric acid, and adipic acid relative to the total weight of succinic acid, glutaric acid, and adipic acid in the aqueous solution are typically about 15 to 35 wt%, about 45 to 75 wt%, and about 3 to 40 wt%, respectively. Other impurities contained in the aqueous solution include unremoved nitric acid, copper and vanadium derived from the catalyst used in the oxidation with nitric acid, and other trace impurities. The nitric acid content of the by-product aqueous solution depends on the conditions of the nitric acid recovery step, but is usually at least about 6% by weight based on the total weight of succinic acid, glutaric acid, and adipic acid. The by-product aqueous solution is colored yellow, which is thought to be due to impurities contained therein.

In the present invention, the aqueous by-product solution obtained during the above-mentioned production of adipic acid is used, and the nitric acid content thereof is adjusted to 3% by weight or less based on the total weight of succinic acid, glutaric acid, and adipic acid to obtain a dicarboxylic acid mixture, and the obtained dicarboxylic acid mixture is subjected to a hydrogenation reaction to produce a diol mixture.

The nitric acid content of the dicarboxylic acid mixture used in the present invention is 3% by weight or less, preferably 0.2% by weight or less, based on the total weight of succinic acid, glutaric acid, and adipic acid.
It is most preferable that the nitric acid in the dicarboxylic acid mixture is completely removed, but this is not practical because it requires repeated heat treatment or treatment with an ion exchange resin, which makes the operation complicated.
In the treatments usually used, the nitric acid content can be reduced to about 0.01 ppm at most. If the nitric acid content of the dicarboxylic acid mixture is more than 3% by weight, the activity of the hydrogenation catalyst used to produce the diol mixture decreases over time, and the diol mixture cannot be obtained stably for a long period of time. It is not entirely clear how nitric acid affects the hydrogenation reaction, but it is thought that the presence of nitric acid causes some of the catalytic metal to be eluted, resulting in a decrease in catalytic activity. Whether or not metals are eluted by nitric acid can be determined by the following:
It depends on the atmosphere. For example, it is known that stainless steel forms a passive film on its surface and does not corrode even in the presence of nitric acid. However, under the hydrogenation reaction conditions used in the present invention, a reducing atmosphere is present in the presence of hydrogen, which makes the passive film on the metal surface unstable, and it is thought that this causes the metal to be eluted by nitric acid.

As a method for removing nitric acid from the aqueous by-product obtained in the process for producing adipic acid, a known method can be used, for example, a method for removing nitric acid from the aqueous by-product obtained in the process for producing adipic acid under a reduced pressure of from normal pressure to about 80 kPa at 80 to 200°C.
Specifically, the method is to heat the mixture at a reduced pressure of about normal pressure to about 80 kPa.
One method is to remove the nitric acid by azeotropic distillation with water at 0 to 130°C. In this case, if the amount of water is less than that of nitric acid, the nitric acid concentration in the still will be high after the water is distilled off by azeotropy. Although the high nitric acid concentration is not necessarily a problem, in order to continue the azeotropic distillation, it is preferable to distill off the nitric acid by azeotropy while adding new water to the still. Another method is to remove the nitric acid by heating to 100 to 200°C, preferably 130 to 180°C, under approximately atmospheric pressure (in this case, nitric acid is removed by azeotropy with water at the beginning of the distillation). Another method is to remove the nitric acid by using an anion exchange resin. These methods can be used alone or in combination. Among these, the method is to heat at 100 to 130°C under atmospheric pressure for 10 minutes to 3 hours to distill off the water and most of the nitric acid, and then to heat at 130 to 200°C, preferably 160°C.
A simple and preferred method is to heat the solution at 160 to 180°C for 1 minute to 1 hour. This method, particularly heating to 160 to 180°C, decomposes and removes not only nitric acid but also some of the compounds having oxygen-nitrogen bonds, as described below. The temperature range is divided into two stages because the preferred time for maintaining the solution at 100 to 130°C is different from the preferred time for maintaining the solution at 130 to 200°C. Removal using an anion exchange resin is also effective, but if a large amount of nitric acid needs to be removed, a large amount of ion exchange resin is required, and the regeneration process requires a great deal of effort. However, this method is effective for removing extremely small amounts of nitric acid. Furthermore, when the nitric acid content is several weight percent to approximately 10 weight percent, the nitric acid can be neutralized and removed using hydroxides, carbonates, bicarbonates, etc. of alkali metals and alkaline earth metals, such as caustic soda.

Nitric acid can also be removed together with compounds having oxygen-nitrogen bonds by reduction treatment. Specifically, a reduction catalyst containing an active metal species including at least one metal selected from the group consisting of metals in Groups 7 to 10 of the periodic table is used, and the by-product aqueous solution is brought into contact with hydrogen to reduce and/or decompose the nitric acid and compounds having oxygen-nitrogen bonds contained in the by-product aqueous solution. The conditions for the reduction treatment are not particularly limited as long as nitric acid is removed and reduction or decomposition of dicarboxylic acids does not occur. A preferred treatment temperature is 50 to 200°C, more preferably 100 to 180°C. If the treatment temperature is below 50°C, the reaction rate is slow, and the treatment time required to achieve a sufficient effect becomes extremely long. Furthermore, if the treatment temperature exceeds 200°C, even dicarboxylic acids may be reduced or decomposed depending on the treatment time. The hydrogen pressure used for the reduction treatment is preferably 0.2 to 5 MPa.
The hydrogen pressure is more preferably 1 to 4 MPa. If the hydrogen pressure is lower than 0.2 MPa, it is difficult to obtain a sufficient treatment effect, and if the hydrogen pressure is higher than 5 MPa, the cost of the reduction treatment equipment will increase and even the dicarboxylic acid may be reduced or decomposed. The reduction treatment usually takes several minutes to several tens of hours, preferably 10 minutes to 5 hours. There are no particular limitations on the reaction method used when contacting hydrogen with the by-product aqueous solution, and batch treatment can be performed using a stirred tank or continuous treatment can be performed using a fixed-bed reaction tower.

The reduction catalyst for removing nitric acid is a catalyst generally used in hydrogenation reactions, containing an active metal species including at least one metal selected from the group consisting of metals in Groups 7 to 10 of the periodic table, and more preferably a catalyst in which the active metal species includes at least one metal selected from the group consisting of platinum, rhenium, palladium, rhodium, nickel, iridium, and ruthenium. From the viewpoint of catalytic activity, more preferred is a catalyst in which the active metal species includes at least one metal selected from the group consisting of platinum, rhenium, palladium, rhodium, and ruthenium, and from the viewpoint of durability, a catalyst in which the active metal species includes platinum is most preferred.

In the present invention, the term "periodic table" refers to the periodic table proposed by the Division of Inorganic Chemistry of the American Chemical Society in 1985.

The reduction catalyst can also be used by being supported on a carrier. As the carrier, porous carriers such as activated carbon, diatomaceous earth, silica, alumina, titania, and zirconia can be used alone or in combination. As a method for supporting the metal on the carrier, methods commonly used in the preparation of supported catalysts, such as impregnation and ion exchange, can be used. The raw materials of the metal components used in the preparation of the reduction catalyst vary depending on the catalyst preparation method, but are usually mineral salts such as nitrates, sulfates, and hydrochlorides, organic salts such as acetates,
The metal component may be a hydroxide, an oxide, or an organic metal compound. The amount of the metal component supported is usually 0.5 to 50% by weight based on the weight of the carrier.

Furthermore, as a reduction catalyst for removing nitric acid, a hydrogenation catalyst containing active metal species containing ruthenium and tin, which is used to produce a diol mixture, as will be described in detail later, can also be used. In this case, the catalyst used in the reduction treatment can also be used for hydrogenation. However, since the activity of the catalyst can decrease when used for a long period of time, different catalysts are usually used for the reduction treatment and the hydrogenation reaction.

When nitric acid is removed by a batchwise reduction treatment using a stirring tank, the amount of the reduction catalyst is preferably 0.01 to 50 parts by weight per 100 parts by weight of the by-product aqueous solution to be treated. This amount can be selected as desired depending on conditions such as the treatment temperature and treatment pressure.

The dicarboxylic acid mixture used in the present invention preferably has a copper and vanadium content of no more than 10 ppm, and more preferably no more than 5 ppm, based on the total weight of succinic acid, glutaric acid, and adipic acid. While the form of the copper and vanadium compounds contained in the dicarboxylic acid mixture is not necessarily clear, the copper and vanadium content in the present invention refers to the elemental copper and vanadium content. The copper and vanadium are derived from the oxidation catalyst used to produce adipic acid. When a diol mixture is produced using a dicarboxylic acid mixture containing a high copper and vanadium content as a raw material, the copper and vanadium accumulate on the active metal species of the hydrogenation catalyst, reducing the surface area of the active metal species and thereby reducing the catalytic activity. While it is most desirable to completely remove the copper and vanadium from the dicarboxylic acid mixture, this requires repeated treatment with a cation exchange resin, which makes the process complicated and impractical. Conventional treatments can only reduce the copper and vanadium content to approximately 0.05 ppm each.

There are no particular limitations on the method for removing copper and vanadium contained in the by-product aqueous solution obtained during the production of adipic acid, and known methods can be used. However, a method using a cation exchange resin is preferred because it is simple and produces a small amount of by-product waste. Specifically, copper and vanadium can be removed by obtaining the by-product aqueous solution (or adding ion-exchanged water to a solid dicarboxylic acid mixture obtained during purification to obtain an aqueous solution) and contacting it with a cation exchange resin at a temperature of room temperature to 100°C or lower. The cation exchange resin can be one having a sulfonic acid group or a carboxyl group as a functional group and a styrene-based or methacrylic base structure. 1 to 100 parts by weight of the cation exchange resin can be mixed with 100 parts by weight of the dicarboxylic acid by stirring or by using a packed tower system.

The dicarboxylic acid mixture used in the present invention preferably has a sulfur content of 200 ppm or less, more preferably 40 ppm or less, and particularly preferably 20 ppm or less, based on the total weight of succinic acid, glutaric acid, and adipic acid.
When a diol mixture is produced using a dicarboxylic acid mixture with a high sulfur content as a raw material, sulfur accumulates on the active metal species of the hydrogenation catalyst, reducing the surface area of the active metal species and thereby reducing the activity of the catalyst. Complete removal of sulfur is most desirable, but this is not practical because repeated treatment with an anion exchange resin or the like is required, making the operation complicated. A commonly used treatment reduces the sulfur content to 0.2
The limit is to reduce it to about ppm.

The sulfur in the dicarboxylic acid mixture is thought to exist as a compound containing sulfate radicals, but the exact origin of the sulfur is unclear. The origin of the sulfur is also unclear, but it is thought that when a sulfonic acid cation exchange resin is used to remove copper and vanadium, sulfur-containing impurities are eluted into the aqueous solution of the dicarboxylic acid mixture due to the elimination of sulfonic acid groups or the decomposition of the polymer chains of the ion exchange resin. This idea is supported by the fact that sulfur can be removed using an anion exchange resin.

There is no particular limitation on the method for removing sulfur compounds from the by-product aqueous solution obtained in the adipic acid production process, but a method of contacting the by-product aqueous solution with an anion exchange resin is effective. Furthermore, when the dicarboxylic acid mixture being purified to be treated is in a solid state, ion-exchanged water is added to the dicarboxylic acid mixture to form a 5 to 50 wt % aqueous dicarboxylic acid solution, which is then contacted with the anion exchange resin. As the anion exchange resin, a styrene-based or acrylic resin having a quaternary ammonium salt as a functional group is preferred. Furthermore, a styrene-based or acrylic weakly basic ion exchange resin having a tertiary amine as a functional group can also be used if desired. The anion exchange resin can be used in the following manner:
The method of contacting 100 parts by weight of dicarboxylic acid with 1 to 100 parts by weight of anion exchange resin can be used by mixing with stirring or by using a packed column.

Furthermore, in the present invention, the absorption coefficient at 355 nm of an aqueous solution of the dicarboxylic acid mixture dissolved in distilled water is preferably 0.3 or less, more preferably 0.1 or less, and particularly preferably 0.03 or less. In the present invention, the absorption coefficient is a value expressed by the following formula.

E = A / (c x b) (wherein E is the absorption coefficient at 355 nm, A is the absorbance at room temperature of an aqueous solution of the dicarboxylic acid mixture dissolved in distilled water, c is the weight (g) of the dicarboxylic acid mixture dissolved in 100 g of distilled water, and b is the length (cm) of the cell used to measure the absorbance.) The absorption at 355 nm is not due to succinic acid, glutaric acid, or adipic acid. Therefore, this absorption is due to impurities contained in the dicarboxylic acid mixture. The present inventors have not yet identified the molecular structure of this impurity, but according to the literature (Zh. Prikl. Khim. Leningrad, Vol. 47, No. 4, pp. 862-868),
865, 1974, etc., it is believed that the compounds are either dinitrophenols such as 2,5-dinitrophenol, 2,4-dinitrophenol, and 2,6-dinitrophenol, trinitrophenols, 1-nitrocyclohexene, and 2-nitrocyclohexenol, or a mixture thereof, and are by-produced in the oxidation reaction with nitric acid during the production of adipic acid. As mentioned above, since there is no absorption by the dicarboxylic acid mixture that is the raw material for the diol mixture, it is most desirable for the absorption coefficient to be zero. However, this is not realistic because repeated treatment with activated carbon or anion exchange resin is required, which makes the operation complicated. With commonly used treatments, the absorption coefficient can only be reduced to about 0.0001.

The method for removing impurities with absorption at 355 nm is not particularly limited, and known decolorization methods can be used. For example, a method in which the by-product aqueous solution is treated with an anion-adsorbing substance and then heated at 120 to 200°C (see Japanese Patent Publication No. 53-41652) can be used. Examples of anion-adsorbing substances include activated carbon, anion exchange resins, and liquid anion exchangers. The liquid anion exchangers are one or more amines selected from water-insoluble primary, secondary, and tertiary amines having a molecular weight of 200 to 500.

As a method for removing impurities using activated carbon, for example, a method is mentioned in which an aqueous by-product solution is obtained, and 1 to 20 parts by weight of powdered activated carbon or granular activated carbon is mixed with the aqueous by-product solution relative to 100 parts by weight of dicarboxylic acid, and the mixture is stirred for 5 minutes to 2 hours, and then the activated carbon is filtered off. As a method for removing impurities using an anion exchange resin, the above-mentioned method for removing sulfur compounds can be used. Furthermore, when a liquid anion exchanger is used, a liquid anion exchanger, typified by tri-n-octylamine, is mixed with a water-insoluble organic solvent at a concentration of about 0.1 to 10% by weight to prepare an adsorption solution, and this adsorption solution is mixed with the liquid anion exchanger at a concentration of about 1 to 10% by weight relative to the weight of dicarboxylic acid.
The by-product aqueous solution is contacted with the by-product aqueous solution so that the concentration becomes 30% by weight. Specific examples of the water-insoluble organic solvent include carbon tetrachloride, perchlorate, trichlene, and liquid paraffin. The apparatus used for the contact treatment can be a conventional liquid-liquid contact apparatus such as an extraction tower or a mixer-settler type.

Furthermore, the inventors have found that the extinction coefficient can also be reduced by adding an aromatic hydrocarbon having 6 to 14 carbon atoms and a boiling point of 200°C or less at atmospheric pressure to the dehydrated dicarboxylic acid mixture, heating the mixture to a temperature below the boiling point of the aromatic hydrocarbon, cooling to below room temperature, and then filtering the mixture to recover the dicarboxylic acid mixture. Treatment with an aromatic hydrocarbon also has a sulfur removal effect, so it can be used instead of the sulfur removal treatment using an anion exchange resin. Examples of aromatic hydrocarbons having 6 to 14 carbon atoms and a boiling point of 200°C or less that can be used in this treatment include benzene, toluene, xylene, ethylbenzene, isopropylbenzene, propylbenzene, trimethylbenzene, and butylbenzene. Among these, benzene, toluene, and xylene have low boiling points, and even if they remain in the dicarboxylic acid mixture recovered by filtration, they are easily removed by methods such as heating under reduced pressure. The weight of the aromatic hydrocarbon used is preferably 0.5 to 20 times the combined weight of succinic acid, glutaric acid, and adipic acid. If the weight of the aromatic hydrocarbon is less than 0.5 times the combined weight, the decolorizing effect is significantly reduced. There is a tendency that the decolorizing effect increases as the amount used increases, but if the amount used exceeds 20 times the total weight of succinic acid, glutaric acid and adipic acid, the decolorizing effect almost levels off, and this is not preferred because it simply increases the amount of aromatic hydrocarbons that must be treated for recovery and reuse.

In addition, the colored substance (
In other words, by contacting the by-product aqueous solution with hydrogen gas in the presence of a reduction catalyst containing at least one metal selected from the group consisting of metals in Groups 7 to 10 of the periodic table as an active metal species, the colored substances can be reduced and/or decomposed to remove them.

Furthermore, in the present invention, the content of the compound having an oxygen-nitrogen bond in the dicarboxylic acid mixture is preferably 2,000 ppm or less, and more preferably 1,200 ppm or less, based on the total weight of succinic acid, glutaric acid, and adipic acid, calculated as the weight of nitric acid.
In the present invention, the term "compound having an oxygen-nitrogen bond" refers to an organic compound having a functional group such as _-NO2 , -NH- _NO2 , or =N-OH, and an inorganic nitrogen oxide compound such as nitric acid or nitrous acid.

Specifically, the content of compounds having oxygen-nitrogen bonds is determined by adding NaOH to an aqueous solution of dicarboxylic acid, heating the solution, removing volatile components such as ammonia, adding DeValta's alloy, performing a reduction treatment, quantifying the amount of ammonia produced, and converting this to the amount of nitric acid. Therefore, compounds having oxygen-nitrogen bonds also include nitric acid. Some compounds having oxygen-nitrogen bonds other than nitric acid have absorption at 355 nm, and these impurities are thought to be by-products of the oxidation reaction with nitric acid during the production of adipic acid. Complete removal of compounds having oxygen-nitrogen bonds is most desirable, but this is not practical because repeated treatment with activated carbon is required, making the process complicated. Conventional treatments can only reduce the content of compounds having oxygen-nitrogen bonds to about 50 ppm.

The compound having an oxygen-nitrogen bond can be removed by the method for removing nitric acid described above.
The method of heating the by-product aqueous solution at 200°C or the method of reducing the by-product aqueous solution in the presence of a reducing catalyst containing an active metal species containing at least one metal selected from the group consisting of metals in Groups 7 to 10 of the periodic table can be used. Furthermore, research by the present inventors has revealed that a method of contacting activated carbon with the by-product aqueous solution is effective for removing organic compounds other than nitric acid, particularly those having functional groups containing oxygen-nitrogen bonds. As a removal method using activated carbon, the method described above for removing impurities having absorption at 355 nm can be used.

The dicarboxylic acid mixture used as the raw material for the diol mixture in the present invention has a nitric acid content of 3% by weight or less based on the total weight of the dicarboxylic acids.
It is preferable that the solution does not contain impurities that hinder the hydrogenation reaction, such as coloring substances containing vanadium, sulfur, or compounds having an oxygen-nitrogen bond. To obtain a dicarboxylic acid mixture that does not contain these components, the above-mentioned methods for removing the impurities can be appropriately combined. Next, we will explain preferred combinations of steps for removing impurities contained in the by-product aqueous solution to obtain a dicarboxylic acid mixture. First, we will list preferred purification processes for obtaining a diol mixture from the by-product aqueous solution.

First purification process: (a) dehydrating and denitrating the by-product aqueous solution by heating it at a temperature of 80 to 200°C and at a pressure equal to or less than atmospheric pressure to obtain a dehydrated and denitrated dicarboxylic acid mixture; (b) adding water to the obtained dehydrated and denitrated dicarboxylic acid mixture to obtain a denitrated dicarboxylic acid mixture aqueous solution; and (c) contacting the denitrated dicarboxylic acid mixture aqueous solution with a cation exchange resin to remove copper and vanadium.

Second purification process: (a) heating the by-product aqueous solution at a temperature of 80 to 130°C and a pressure equal to or less than atmospheric pressure, and then further heating at a temperature of 130 to 180°C and a pressure equal to or less than atmospheric pressure to obtain a dehydrated and denitrated dicarboxylic acid mixture; (b) adding water to the obtained dehydrated and denitrated dicarboxylic acid mixture to obtain a denitrated dicarboxylic acid mixture aqueous solution; (c) contacting the denitrated dicarboxylic acid mixture aqueous solution with a cation exchange resin to remove copper and vanadium; (d) heating the obtained denitrated dicarboxylic acid mixture aqueous solution at a pressure equal to or less than atmospheric pressure at a temperature sufficient to distill off water from the denitrated dicarboxylic acid mixture aqueous solution; (e) adding an aromatic hydrocarbon having 6 to 14 carbon atoms and having a boiling point of 200°C or less at atmospheric pressure to the denitrated dicarboxylic acid mixture obtained in step (d), heating the obtained mixture at a temperature equal to or less than the boiling point of the aromatic hydrocarbon, and then cooling; and (f) recovering the denitrated dicarboxylic acid mixture from the mixture by filtration to prepare a dicarboxylic acid mixture.

Third purification process: The by-product aqueous solution is contacted with hydrogen gas in the presence of a reduction catalyst containing an active metal species including at least one metal selected from the group consisting of metals of Groups 7 to 10 of the periodic table, thereby reducing nitric acid and compounds having an oxygen-nitrogen bond contained in the by-product aqueous solution to obtain a dicarboxylic acid mixture in the form of an aqueous solution.

In the present invention, it is preferred to remove nitric acid at the beginning of the purification process when preparing the dicarboxylic acid mixture. A preferred method for removing nitric acid is as follows:
Examples of suitable reduction methods include heating the by-product aqueous solution at a temperature of 80 to 200°C and at a pressure equal to or lower than atmospheric pressure. Specifically, the by-product aqueous solution is heated at a temperature of 80 to 130°C and at a pressure equal to or lower than atmospheric pressure for 10 minutes to 3 hours, and then further heated at a temperature of 130 to 180°C and at atmospheric pressure for 1 minute to 1 hour. Furthermore, since colored substances containing compounds having oxygen-nitrogen bonds can also be removed simultaneously, a preferred method is to contact the by-product aqueous solution with hydrogen gas in the presence of a reduction catalyst containing an active metal species containing at least one metal selected from the group consisting of metals in Groups 7 to 10 of the Periodic Table, thereby reducing the nitric acid and compounds having oxygen-nitrogen bonds contained in the by-product aqueous solution. When performing reduction treatment using a catalyst, it is more preferable to heat the by-product aqueous solution at a pressure equal to or lower than atmospheric pressure, and then further heat it at a temperature of 130 to 180°C and at atmospheric pressure to partially denitrate the dicarboxylic acid mixture, add water to the partially denitrated dicarboxylic acid mixture to obtain a partially denitrated dicarboxylic acid mixture aqueous solution, and then perform the reduction treatment.

In addition, since the presence of nitric acid reduces the efficiency of copper and vanadium removal by the cation exchange resin, it is preferable to remove nitric acid at the beginning of the production process.

In the present invention, it is preferable to remove copper and vanadium using a cation exchange resin after the nitric acid removal step. Specifically, an aqueous solution of the denitrated dicarboxylic acid mixture is brought into contact with a cation exchange resin. If nitric acid is removed by heating in the nitric acid removal step, the denitrated dicarboxylic acid mixture is obtained in a solid form. In this case, ion-exchanged water is added to the denitrated dicarboxylic acid mixture and the mixture is heated for 5 to 10 minutes.
The 50% by weight aqueous solution of the denitrated dicarboxylic acid mixture is then contacted with a cation exchange resin. After the treatment with the cation exchange resin, a dehydration and denitration step may be carried out again, if necessary.

Contacting an anion-adsorbing substance with an aqueous solution of dicarboxylic acid can remove sulfur compounds and decolorize (i.e., remove coloring substances including compounds with oxygen-nitrogen bonds). This step can be omitted if the dicarboxylic acid mixture during purification has a low sulfur content and/or is not colored. Treatment with an anion-adsorbing substance is preferably performed after treatment with a cation exchange resin. Although the reason is not clear, treatment with a cation exchange resin first is more effective in decolorizing the anion-adsorbing substance. Furthermore, treating the dicarboxylic acid mixture during purification in this order also makes it possible to remove sulfur compounds derived from sulfonic acid-based cation exchange resins.

Furthermore, to obtain a dicarboxylic acid mixture, a purification step using activated carbon can be carried out in any desired order after the nitric acid removal step. The treatment with activated carbon not only decolorizes the dicarboxylic acid mixture but also simultaneously removes compounds having oxygen-nitrogen bonds.

Alternatively, the dicarboxylic acid mixture can be recovered by adding an aromatic hydrocarbon to the denitrated dicarboxylic acid mixture, heating, cooling, and filtering. This process is effective for removing sulfur and decolorizing, and by performing this process, a dicarboxylic acid mixture containing fewer impurities that would interfere with the hydrogenation reaction can be obtained. Treatment with an aromatic hydrocarbon can be performed after denitration and removal of copper and vanadium, and by performing treatment with an anion-adsorbing substance in combination, a dicarboxylic acid mixture with even fewer impurities can be obtained.

In addition to the above-mentioned methods for removing impurities, methods such as distillation under reduced pressure and heating and steam distillation under reduced pressure are also effective and can be used in combination with the methods already mentioned.

As already mentioned above, in the present invention, the methods for removing the impurities may be appropriately combined. However, in order to almost completely remove the impurities contained in the by-product aqueous solution obtained in the process for producing adipic acid, it is desirable to carry out a purification process comprising the following steps (1) to (5):

Dehydration and denitration by heating (heating the by-product aqueous solution at a temperature of 100 to 130°C and a pressure below atmospheric pressure for 10 minutes to 3 hours, and then heating at a temperature of 130 to 180°C and atmospheric pressure for an additional 1 minute to 1 hour); removal of copper and vanadium using a cation exchange resin; removal of impurities using a liquid anion exchanger; removal of impurities using activated carbon; and removal of sulfur and decolorization using an anion exchange resin.

If desired, the step using the liquid anion exchanger can be omitted and the amount of activated carbon used in the step can be increased.

In the present invention, the dicarboxylic acid mixture obtained by purifying the by-product aqueous solution as described above is subjected to a hydrogenation reaction in the presence of water, hydrogen gas, and a hydrogenation catalyst containing active metal species consisting of ruthenium and tin to produce 1,4-butanediol, 1,5
The present invention is characterized by comprising obtaining a hydrogenation reaction solution containing a diol mixture including 1,6-pentanediol and 1,6-hexanediol. The hydrogenation catalyst used in the present invention contains ruthenium and tin as active metal species. A hydrogenation catalyst containing, in addition to ruthenium and tin, at least one metal selected from Group 7 metals of the periodic table and/or at least one metal selected from the group consisting of metals in Group 8 of the periodic table other than ruthenium, and metals in Groups 9 and 10 of the periodic table is preferred because of its high activity. Furthermore, rhenium is particularly preferred as the Group 7 metal because of its high activity, and platinum is particularly preferred as the at least one metal selected from the group consisting of metals in Group 8 of the periodic table other than ruthenium, and metals in Groups 9 and 10 of the periodic table because of its high activity.

The hydrogenation catalyst used in the present invention may be either an unsupported catalyst, which does not use a carrier, or a supported catalyst, which uses a carrier. As the carrier for supporting the catalyst, commonly used porous carriers such as activated carbon, alumina, and silica can be used. Among these carriers, activated carbon, titania, and zirconia are preferred from the viewpoint of acid resistance.
Activated carbon is more preferred. Either steam-activated carbon or chemically activated carbon can be used as the activated carbon. Depending on the reaction type, granular activated carbon or powdered activated carbon can be used. There are no particular limitations on the method for supporting the metal species on the support, and methods commonly used for preparing supported catalysts, such as the impregnation method and ion exchange method, can be applied. When the impregnation method is used, the raw material compound of the metal species to be supported is dissolved in a solvent,
For example, the metal species are dissolved in water to prepare an aqueous solution of the metal compound, and a separately prepared porous support is immersed in this solution to support the metal species on the support. There are no particular restrictions on the order in which the metals are supported on the support, and all metal species may be supported simultaneously, or each metal species may be supported individually. Furthermore, each metal species may be supported in multiple batches as desired.

The raw materials for the metal species used in preparing the catalyst vary depending on the catalyst preparation method, but typically include mineral acid salts such as nitrates, sulfates, and hydrochlorides, organic acid salts such as acetates, hydroxides, oxides, and organometallic compounds such as amine complexes and carbonyl complexes. Preferred raw materials for ruthenium include ruthenium chloride, ruthenium bromide, ruthenium nitrate, ruthenium acetylacetonate, ruthenium carbonyl, ruthenium black, ruthenium powder, ruthenium oxide, nitrosylruthenium nitrate, and ammonium oxydecachlorodiruthenate.
Examples of tin raw materials include tin(II) chloride, sodium stannate, tin(II) acetate, etc. Examples of rhenium raw materials include dirhenium decacarbonyl (rhenium carbonyl), rhenium oxide, perrhenic acid, ammonium perrhenate, rhenium chloride, cyclopentadienylrhenium tricarbonyl, etc. Examples of platinum raw materials include chloroplatinic acid, platinum nitrate, platinum acetylacetonate, platinum chloride, platinum bromide, platinum cyanide, etc.

The amount of ruthenium and tin supported on the carrier is 0.5 to 50% by weight, preferably 1 to 10% by weight. The atomic ratio of ruthenium to tin is 1:0.
The ratio is preferably in the range of 1:1 to 1:2, more preferably 1:0.2 to 1:1.3. The amount of at least one metal selected from the group consisting of metals of Group 7 of the periodic table and/or metals of Groups 8, 9, and 10 of the periodic table other than ruthenium (the total amount of metals when multiple metals are used) supported is preferably in the range of 0.01 to 5, more preferably 0.1 to 2, in atomic ratio to ruthenium.

The carrier carrying the metal species is dried, and then calcined and reduced as desired to obtain a hydrogenation catalyst. Drying is usually carried out by holding the carrier under reduced pressure at a temperature of from room temperature to less than 200°C, or by passing a dry gas such as nitrogen or air through the carrier. Calcination is usually carried out at a temperature of from 200°C to less than 200°C.
The reduction is carried out at a temperature of 600°C for 1 to 24 hours while flowing nitrogen, air, or the like. The reduction may be carried out in either a liquid phase or a gas phase. Usually, hydrogen is used as the reducing gas.
The gas phase reduction is carried out at a temperature of 200 to 500°C for 30 minutes to 24 hours.

In addition, non-supported hydrogenation catalysts that do not use a carrier can also be prepared by reducing an aqueous solution of a metal compound with a reducing agent, or by reducing a solid containing active metal species obtained by coprecipitation in the liquid or gas phase. Non-supported catalysts can also be produced using the metal raw materials listed above. The atomic ratio of ruthenium to tin is preferably in the range of 1:0.1 to 1:2, more preferably 1:0.
The amount of at least one metal selected from the group consisting of metals of Group 7 of the periodic table and/or metals of Group 8 of the periodic table other than ruthenium, and metals of Groups 9 and 10 of the periodic table (if there are multiple metals, the total amount of these) is preferably in an atomic ratio to ruthenium of 0.01 to 5, more preferably 0.1 to 2.

In the present invention, a hydrogenation catalyst containing the above-mentioned ruthenium and tin, and at least one metal selected from the group consisting of metals of Group 7 of the periodic table, such as rhenium, and/or metals of Group 8 of the periodic table other than ruthenium, and metals of Groups 9 and 10 of the periodic table, is used to carry out a hydrogenation reaction of a dicarboxylic acid mixture containing succinic acid, glutaric acid, and adipic acid, and having a nitric acid content of 3% by weight or less based on the total weight of succinic acid, glutaric acid, and adipic acid, in the presence of water and hydrogen gas. In addition to water, solvents such as alcohols and ethers may be added to the reaction system where hydrogenation is carried out, if desired. The amount of water present in the reaction system where hydrogenation is carried out is
The amount of water is preferably such that the entire amount of the dicarboxylic acid mixture is dissolved at the temperature at which hydrogenation is carried out, specifically, 0.3 to 100 parts by weight per part by weight of the dicarboxylic acid mixture.
The amount is preferably 1 to 20 parts by weight, and more preferably 2 to 10 parts by weight.

The temperature of the hydrogenation reaction is preferably 100 to 300°C, more preferably 130
The hydrogen pressure is 1 to 25 MPa, more preferably 5 to 20 MPa.
The amount of the hydrogenation catalyst used is preferably 0.001 to 10 parts by weight, more preferably 0.01 to 1 part by weight, per part by weight of the dicarboxylic acid mixture.

The hydrogenation reaction may be carried out either continuously or batchwise, and the reaction format may be either a liquid phase suspension reaction or a fixed bed flow reaction.

As described above, 1,4-butanediol, 1,5-pentanediol and 1
A reaction solution containing a diol mixture including 1,6-hexanediol is obtained. The diols obtained by the production method of the present invention are useful materials as raw materials for polyester resins, urethane foams, urethane paints, adhesives, etc. For example, as a raw material for polyurethane, they can be used as chain extenders as they are, or they can be made into polycarbonate diols or polyester polyols and used as soft segments.

In the present invention, 1,4-butanediol,
1,5-pentanediol and 1,6-hexanediol can be recovered. The recovery method is not particularly limited, but for example, 1,4-butanediol and a mixture of 1,5-pentanediol and 1,6-hexanediol can be recovered according to the following method.

(i) adjusting the temperature of the hydrogenation reaction liquid containing the diol mixture to a temperature between room temperature and less than 100°C, and performing gas-liquid separation at atmospheric pressure or less to remove hydrogen gas from the hydrogenation reaction liquid; (ii) heating the hydrogenation reaction liquid from which hydrogen gas has been removed under atmospheric pressure to distill off a mixture of water and cyclic ethers and monohydric alcohols by-produced in the hydrogenation reaction; (iii) subjecting the resulting mixture to multi-stage distillation to distill off water and γ-butyrolactone by-produced in the hydrogenation reaction to obtain a purified diol mixture; (iv) subjecting the purified diol mixture to multi-stage distillation to obtain 1,4-butanediol as a low-boiling component; and (v) further subjecting the remaining high-boiling mixture obtained in step (iv) to multi-stage distillation.
A mixture of 1,5-pentanediol and 1,6-hexanediol is obtained as the distillate.

After the hydrogenation reaction, the hydrogen gas is removed by gas-liquid separation of the hydrogenation reaction solution containing the diol mixture from hydrogen gas. The gas-liquid separation conditions are as follows: the hydrogenation reaction solution containing the diol mixture is cooled to a temperature of room temperature to less than 100°C, and then the pressure is reduced to a pressure at which water does not boil at normal pressure or the cooled temperature, and the excess hydrogen used in the hydrogenation reaction is separated from the reaction solution containing the diol mixture. The hydrogen separated from the gas-liquid can be reused in the hydrogenation reaction after trace amounts of carbon monoxide and carbon dioxide are removed using a removal device.

Next, the hydrogenation reaction liquid from which hydrogen gas has been removed is heated to 100 to 120°C under normal pressure to distill off most of the water and a mixture of cyclic ethers by-produced in the hydrogenation reaction, specifically tetrahydrofuran, tetrahydropyran, hexamethylene oxide, etc., and monohydric alcohols, specifically propanol, butanol, pentanol, hexanol, etc.

The mixture obtained by distilling off most of the low boiling organic compounds and water is subjected to a column bottom temperature of 130 to 190°C, a column bottom pressure of 5.5 to 7.0 kPa, a column top temperature of 10 to 60°C, and
The distillation column is then set at 0°C and 3.5 to 5.5 kPa at the top of which the remaining water and γ-butyrolactone produced as a by-product in the hydrogenation reaction are distilled off to obtain a purified diol mixture. Trace amounts of pentanol, hexanol, and the like are also distilled off along with γ-butyrolactone.

The resulting purified diol mixture is subjected to multistage distillation to obtain 1,4-butanediol as a low boiling point component. The conditions for distillation separation of 1,4-butanediol include, for example, using a multistage distillation column with 20 to 40 plates and maintaining the column bottom temperature at 140 to 180°C.
0°C, column bottom pressure 4.0 to 7 kPa, column top temperature 30 to 60°C, column top pressure 0.
The purified diol mixture can be separated by distillation by adjusting the pressure to 3 to 1.0 kPa and feeding it to an intermediate stage approximately 15 stages from the bottom of the column.

Next, the remaining high-boiling mixture obtained above is further subjected to multi-stage distillation to obtain a mixture of 1,5-pentanediol and 1,6-hexanediol as a distillate. Specifically, for example, a distillation column having 3 to 15 stages is used, and the column bottom temperature is set to 180 to 220°C.
The column is set at a temperature of 140 to 180°C, a column bottom pressure of 5.5 to 9.0 kPa, a column top temperature of 140 to 180°C, and a column top pressure of 4.0 to 7.0 kPa, and the liquid after separation of 1,4-butanediol is supplied to the intermediate stage, whereby a mixture of 1,5-pentanediol and 1,6-hexanediol is separated by distillation.

The above-described distillation separation method may be carried out continuously or batchwise.

The purity of 1,4-butanediol obtained by the above separation and recovery process is 98%.
Preferably, the total content of lactones, hydroxycarboxylic acids, monohydric alcohols, and diol compounds having a secondary OH group and a primary OH group is less than 0.5% by weight. The lactones are γ-butyrolactone, δ-valerolactone, and ε-caprolactone, and the hydroxycarboxylic acids are
Examples of the monohydric alcohols include propanol, butanol, pentanol, and hexanol, and examples of the diol compounds having a secondary OH group and a primary OH group include 1,3-butanediol, 1,4-pentanediol, and 1,5-hexanediol.

Since the boiling points of the impurities δ-valerolactone and ε-caprolactone are close to that of 1,4-butanediol, separating them from 1,4-butanediol by distillation requires a distillation column with many plates, which undesirably increases the size of the equipment.
Therefore, it is desirable that δ-valerolactone and ε-caprolactone are not contained in the diol produced. Specifically, since these lactones are hydrogenation intermediates of dicarboxylic acids in the hydrogenation reaction, the combined weight of δ-valerolactone and ε-caprolactone should be 0.01 times the weight of 1,4-butanediol produced.
It is desirable to select hydrogenation reaction conditions such that the total amount of δ-valerolactone and ε-caprolactone is less than 5% by weight. However, if a large amount of δ-valerolactone and ε-caprolactone (i.e., 0.5% by weight or more based on the weight of 1,4-butanediol) is by-produced in the hydrogenation reaction due to equipment limitations, the lactones can be removed by the following method. After gas-liquid separation after the hydrogenation reaction or distillation treatment immediately thereafter, at least one compound selected from hydroxides, carbonates, and hydrogencarbonates of alkali metals and/or alkaline earth metals is added to the liquid containing the diols in an amount of 0.01 to 10% by weight of the liquid, thereby converting the lactones and hydroxycarboxylic acids contained therein into alkali metal and/or alkaline earth metal salts, which are compounds with a boiling point higher than that of the diols. Such metal salts with a boiling point higher than that of the diols can be easily removed.

When the 1,4-butanediol obtained by the production method of the present invention is used as a raw material for polyurethane, it is preferable that the total content of lactones, hydroxycarboxylic acids, monohydric alcohols, and diol compounds having a secondary OH group and a primary OH group is 0.5% by weight or less.
If the amount exceeds this limit, the polymerization reactivity of 1,4-butanediol deteriorates, making it difficult to obtain a high molecular weight polyurethane. Furthermore, lactones and hydroxycarboxylic acids adversely affect the physical properties of the polyurethane, such as its hydrolysis resistance.

The 1,5-pentanediol and 1,6-pentanediol obtained by the above separation and recovery process
The mixture with hexanediol is mainly composed of 1,5-pentanediol, and as a result of investigations by the present inventors into its impurities, it has been found that it does not substantially contain 1,5-hexanediol or 1,4-dihydroxycyclohexane, which are contained in conventional 1,5-pentanediol. Specifically, conventional 1,5-pentanediol contains 0.2% by weight or more of 1,5-hexanediol and 1,4-dihydroxycyclohexane, respectively, but the 1,5-pentanediol of the present invention contains 0.2% by weight or more of 1,5-hexanediol and 1,4-dihydroxycyclohexane, which are contained in conventional 1,5-pentanediol.
The amount of these impurities contained in a mixture of 5-pentanediol and 1,6-hexanediol is no more than 0.1% by weight.

Conventionally, 1,5-pentanediol has been produced from a carboxylic acid mixture containing glutaric acid, adipic acid, and 6-hydroxycaproic acid, which is a by-product of the production of cyclohexanone and/or cyclohexanol by air oxidation of cyclohexane. Specifically, the carboxylic acid mixture containing glutaric acid, adipic acid, and 6-hydroxycaproic acid is esterified, followed by hydrogenation using a copper catalyst to obtain 1,5-pentanediol and 1,6-hexanediol, which are then separated by distillation (see U.S. Pat. No. 3,268,588). However, the 1,5-pentanediol obtained by this conventional method contains 0.2 to 1 wt.% of 1,5-hexanediol and 1,4-dihydroxycyclohexane, respectively. 1,5-Hexanediol is a diol having a secondary OH group and a primary OH group, and when polycarbonate diol or polyester polyol is produced from 1,5-pentanediol containing this as a raw material, the dihydroxycyclohexane of 1,5-hexanediol is decomposed.
The secondary OH groups have low reactivity and therefore become the terminal groups of polyols. When such polyols are used in a urethane reaction, problems arise, such as a slow polymerization rate and insufficient molecular weight. Similar problems also arise when 1,5-pentanediol containing 1,5-hexanediol is directly used as a chain extender in the production of polyurethane. Furthermore, 1,4-dihydroxycyclohexane is not preferred because both of its two OH groups are secondary OH groups, which means it has low reactivity and remains unreacted in the polycarbonate diol.

In contrast, the mixture of 1,5-pentanediol and 1,6-hexanediol obtained by the production method of the present invention contains 1,5-hexanediol and 1,4-
Since it does not substantially contain dihydroxycyclohexane, it is suitable as a raw material for polycarbonate diols and polyester polyols that become chain extenders and soft segments of polyurethanes. In particular, copolymerized polycarbonate diols obtained from 1,5-pentanediol and 1,6-hexanediol (see Japanese Patent Publication No. 5-2001-14444) are suitable.
JP-B-029648) has reported that thermoplastic polyurethanes made from it (JP-B-7-684) are more resistant to hydrolysis than thermoplastic polyurethanes obtained using polycarbonate diols obtained only from 1,6-hexanediol.
In addition to its excellent heat resistance, it has recently attracted attention for its greatly improved low-temperature flexibility. Therefore, the mixture of 1,5-pentanediol and 1,6-hexanediol obtained by the production method of the present invention is suitable as a raw material for copolymeric polycarbonate diol.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be explained in more detail with reference to the following Reference Examples, Examples and Comparative Examples, but the present invention is not limited to these in any way.

In the following examples and comparative examples, various properties of the by-product aqueous solution, dicarboxylic acid mixture and diol mixture were measured as follows.

(1) Concentrations of succinic acid, glutaric acid, and adipic acid 10 parts by weight of pimelic acid was precisely weighed and added as an internal standard to 100 parts by weight of an aqueous solution of the dicarboxylic acid mixture or a by-product aqueous solution to prepare a sample solution. This sample solution was subjected to high performance liquid chromatography (HPLC) under the following conditions to determine the concentrations of succinic acid, glutaric acid, and adipic acid.

Based on the obtained data, the total weight of succinic acid, glutaric acid and adipic acid was calculated, and the amounts of nitric acid, copper, vanadium, sulfur, and
and the content of compounds having oxygen-nitrogen bonds was calculated.

HPLC Conditions Apparatus: LC-6A High Performance Liquid Chromatograph (Shimadzu Corporation, Japan) Column: SCR-101H (Shimadzu Corporation, Japan) Column Temperature: 40°C Mobile Phase: Perchloric Acid Aqueous Solution (pH 2.3) Flow Rate: 0.8 ml/min Sample Injection Amount: 5 μl Detector: Differential Refractive Index Detector (2) Nitric Acid Content A sample solution with a dicarboxylic acid concentration of 2 wt% was prepared using ion-exchanged water (in the case of a by-product aqueous solution, a sample solution with a dicarboxylic acid concentration of 2 wt% was also prepared), and subjected to high performance liquid chromatography (HPLC) under the following conditions. From the obtained analytical values, the nitric acid content relative to the total weight of succinic acid, glutaric acid, and adipic acid was calculated.

HPLC Conditions Apparatus: LC-6A High Performance Liquid Chromatograph (Shimadzu Corporation, Japan) Column: TSK-GEL GL-DEAE-2SW (Tosoh Corporation, Japan) Column temperature: 40°C Mobile phase: A solution prepared by adding 85% phosphoric acid to a solution of acetonitrile/water in a volume ratio of 30/70 so that the phosphoric acid concentration was 0.085 mol/L, and adjusting the pH to 3.4 with aqueous ammonia Flow rate: 0.8 ml/min Sample injection amount: 50 μl Detector: UV detector (210 nm) (3) Copper Content, Vanadium Content, and Sulfur Content A sample solution with a dicarboxylic acid concentration of 10 wt% was prepared using ion-exchanged water.
The sample solution was analyzed by an inductively coupled plasma emission spectrometer (ICP) (JOBIN YV, USA).
The resulting solution was analyzed using an analyzer (manufactured by ON EMISSION Instrument S.A.) to determine the copper content, vanadium content, and sulfur content relative to the total weight of succinic acid, glutaric acid, and adipic acid.

(4) Absorption coefficient at 355 nm 0.1 g of a solid dicarboxylic acid mixture was dissolved in 10 g of distilled water to prepare a sample solution. Using a spectrophotometer (Shimadzu Corporation, Japan), the absorbance of the sample solution at 355 nm was measured at room temperature using a 1 cm long cell. When the absorbance of the sample solution was 0.
When the dicarboxylic acid concentration was 10 times lower than the reference value, a sample solution containing 100% dicarboxylic acid mixture (i.e., 1 g of the dicarboxylic acid mixture dissolved in 10 g of distilled water) was prepared, and the absorbance was measured again. The extinction coefficient at 355 nm was calculated from the absorbance according to the following formula.

E = A / (c × b) (wherein E is the absorption coefficient at 355 nm, A is the absorbance at room temperature of an aqueous solution of a dicarboxylic acid mixture dissolved in distilled water, c is the weight (g) of the dicarboxylic acid mixture dissolved in 100 g of distilled water, and b is the length (cm) of the cell used to measure the absorbance.) (5) Content of Compound Having Oxygen-Nitrogen Bond An aqueous solution of a dicarboxylic acid mixture of any concentration was prepared, and about 50% NaO was added to it.
A 1/3 to 1/2 volumetric volume of aqueous NaOH solution was added to the aqueous dicarboxylic acid mixture, and then methanol was added in an amount approximately equal to the NaOH aqueous solution. The resulting mixture was heated for approximately 1 hour to reflux the methanol. The methanol was then distilled off, and the basic substance was also distilled off along with the methanol. An appropriate amount of DeValta's alloy was added to the remaining aqueous dicarboxylic acid solution, and methanol was added in an amount 1/3 to 1/2 volumetric times the dicarboxylic acid mixture aqueous solution. The mixture was again heated and refluxed for 1 hour.
Ammonia was then distilled off together with methanol, and the ammonia in the distilled methanol was neutralized with dilute hydrochloric acid to quantify the amount of ammonia generated. From the amount of ammonia thus determined, the amount of the compound having an oxygen-nitrogen bond was converted into the weight of nitric acid, and the content of the compound having an oxygen-nitrogen bond relative to the total weight of succinic acid, glutaric acid, and adipic acid was calculated.

(6) Analysis of Diol Mixture The diol mixture was diluted with dioxane to a concentration of approximately 1 wt %. Diethylene glycol diethyl ether was added to the diluted solution as an internal standard to a concentration of approximately 1 wt % to prepare a sample solution.
This sample solution was subjected to gas chromatography (GC) under the following conditions to detect 1,4-butanediol, 1,5-pentanediol, 1,6-
Hexanediol and by-products were analyzed.

Furthermore, based on the obtained data, the yield of the diol mixture relative to the dicarboxylic acid mixture used as the raw material was calculated.

GC conditions Apparatus: GC-14B gas chromatograph (Shimadzu Corporation, Japan) Column: DB-WAX (column length: 30 m, inner diameter: 0.25 mm, film thickness: 0.25 μm) manufactured by J & W Scientific, USA Carrier gas: Helium Detector: Flame ionization detector (FID) The hydrogenation catalysts used in the examples and comparative examples were prepared in the following Reference Examples 1 and 2.

Reference Example 1 <Preparation of hydrogenation catalyst (Ru-Sn-Re catalyst)> 7.0 g of ion-exchanged water and 1.29 g of ruthenium chloride trihydrate were dissolved in a 100 ml recovery flask. 0.5 g of tin(II) chloride dihydrate was added to the solution.
1.7 g of rhenium heptoxide was added and dissolved, and then 1.30 g of rhenium heptoxide was added and dissolved. To this solution was added granular activated carbon (particle size: 10-20 mesh, nitrogen adsorption-BET specific surface area: 1,
10.0 g of a sintered body (100 m ² /g) was added and the mixture was left to stand at room temperature for 15 hours. After removing water using an evaporator, the mixture was dried under a nitrogen gas flow at 150°C for 2 hours and then reduced under a hydrogen atmosphere at 450°C for 2 hours. The mixture was again placed in a nitrogen gas atmosphere, cooled to room temperature, and then placed in an oxygen/nitrogen atmosphere (oxygen concentration: 0.1% by volume).
The mixture was allowed to stand at rt for 2 hours to obtain a hydrogenation catalyst comprising 5.0 wt % ruthenium, 3.0 wt % tin and 5.0 wt % rhenium supported on activated carbon.

Reference Example 2 <Preparation of hydrogenation catalyst (Ru-Sn-Pt catalyst)> 0.93 g of chloroplatinic acid hexahydrate was placed in a 100 ml recovery flask, and 7.0 ml of 5N hydrochloric acid was added to dissolve it. 0.
95 g of ruthenium trichloride trihydrate was added and dissolved, and then 1.55 g of ruthenium trichloride trihydrate was added and dissolved. 10.0 g of the same activated carbon used in Reference Example 1 was added to this solution, and the mixture was shaken at room temperature for 15 hours. After water was distilled off using an evaporator, the mixture was dried at 150°C for 2 hours under a nitrogen gas flow, and then reduced at 450°C for 2 hours under a hydrogen atmosphere. The mixture was again placed in a nitrogen gas atmosphere, cooled to room temperature, and then allowed to stand for 2 hours in an oxygen/nitrogen atmosphere (oxygen concentration: 0.1% by volume) to obtain a hydrogenation catalyst comprising 6.0 wt% ruthenium, 5.0 wt% tin, and 3.5 wt% platinum supported on activated carbon.

Example 1 <Preparation of By-Product Aqueous Solution> Cyclohexanol was oxidized with nitric acid according to the method described in "Experimental Chemistry Lectures," 1st Edition, Vol. 17, p. 182, except that commercially available reagent cyclohexanol was distilled and purified, nitric acid (special grade reagent) was used, and 2 g of copper powder was used together with ammonium vanadate as an oxidation catalyst. An aqueous reaction solution containing succinic acid, glutaric acid, and adipic acid was obtained. Crystals of adipic acid contained in the resulting aqueous reaction solution were precipitated, and the precipitated crystals were isolated to obtain an aqueous by-product solution. The above procedure was repeated three times.
5,000 g of the resulting by-product aqueous solution was heated at about 120°C under normal pressure for 1 hour to recover most of the water and nitric acid. Ion-exchanged water was added to the remaining dicarboxylic acid to reduce the water content to 60%.
A 7% by weight aqueous solution was obtained. 100 g of a sulfonic acid cation exchange resin (trade name: Amberlite IR120B) (manufactured by Organo Corporation, Japan) having a styrene base structure was added to this aqueous solution, and the mixture was gently stirred at room temperature for 2 hours to recover the oxidation catalysts, copper and vanadium. The mixture was then filtered to remove the ion exchange resin, and a by-product aqueous solution was obtained after recovering the nitric acid and oxidation catalyst. The by-product aqueous solution thus obtained contained 67% by weight of water, and HPLC analysis revealed that it contained 7% by weight of succinic acid, 18% by weight of glutaric acid, and 100 g of acetic acid.
It was confirmed that the adipic acid was 5% by weight and the nitric acid was 3% by weight (however, the nitric acid content relative to the total weight of succinic acid, glutaric acid, and adipic acid was 10% by weight). Furthermore, analysis by ICP revealed that the copper content, vanadium content, and sulfur content of the by-product aqueous solution were 6 ppm, 2 ppm, and 5 ppm, respectively.
The extinction coefficient at m was 0.051, and the content of compounds having oxygen-nitrogen bonds was 1,147 ppm.

<Preparation of dicarboxylic acid mixture> 500 g of the above by-product aqueous solution was placed in a 1-liter flask and stirred for about 1
The mixture was heated at 20° C. for 1 hour, and then heated at 170° C. for 15 minutes with stirring to dehydrate and denitrate the dicarboxylic acid mixture. The resulting reaction mixture was cooled to obtain a dicarboxylic acid mixture.

The dicarboxylic acid mixture obtained was analyzed by HPLC, and the composition of the dicarboxylic acid mixture was found to be 23% by weight of succinic acid, 60% by weight of glutaric acid, and 17% by weight of adipic acid. The nitric acid content was 0.1% by weight, and the copper content, vanadium content, and sulfur content were 6 ppm, 2 ppm, and 5 ppm, respectively.
The absorption coefficient at 55 nm was 0.085, and the content of compounds having oxygen-nitrogen bonds was 1,136 ppm.

<Production of a diol mixture by hydrogenation reaction> Next, a diol mixture was produced using the dicarboxylic acid mixture.

In a 100 ml Hastelloy autoclave equipped with an electromagnetic induction stirrer, 10 g of water, 5.0 g of the dicarboxylic acid mixture, and the Ru-
0.3 g of a Sn-Re catalyst was charged. After the atmosphere in the autoclave was replaced with nitrogen at room temperature, hydrogen was introduced under pressure to 2 MPa, and the temperature was raised to 180°C.
When the temperature reached 80°C, hydrogen was further pressurized to 15 MPa, and the hydrogenation reaction was carried out at this pressure for 18 hours. After the reaction was completed, the hydrogenation reaction solution containing the diol mixture was extracted while leaving the catalyst in the autoclave. Analysis of the diol mixture contained in the hydrogenation reaction solution by gas chromatography revealed that the yields of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol were 75%, 98%, and 96%, respectively.

The autoclave containing the catalyst was charged with 5.0 g of a dicarboxylic acid mixture and 10 g of water, and hydrogenation was carried out under the same conditions as above to produce a diol mixture. This operation was repeated seven times to produce a diol mixture. The total amount of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol obtained in the seventh run was calculated by multiplying the total amount of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol produced in the first run by the same amount as above.
The activity retention rate (%) was calculated by dividing the total amount of pentanediol and 1,6-hexanediol by 100. An activity retention rate of less than 100% indicates a decrease in catalytic activity. The results are shown in Table 1.

Example 2 <Production of diol mixture by hydrogenation reaction> A 100 ml autoclave made of Hastelloy and equipped with an electromagnetic induction stirrer was charged with 10 g of water, 5.0 g of the dicarboxylic acid mixture prepared in Example 1, and 0.3 g of the Ru-Sn-Pt catalyst prepared in Reference Example 2. After the atmosphere in the autoclave was replaced with nitrogen at room temperature, hydrogen was injected to a pressure of 2 MPa.
When the temperature reached 180°C, hydrogen was further injected to make the pressure 15 MPa.
The hydrogenation reaction was carried out at this pressure for 18 hours. After the reaction was completed, the hydrogenation reaction solution containing the diol mixture was extracted while leaving the catalyst in the autoclave, and the diol mixture contained in the hydrogenation reaction solution was analyzed by gas chromatography.

The autoclave containing the remaining catalyst was charged with 5.0 g of a dicarboxylic acid mixture and 10 g of water, and a hydrogenation reaction was carried out under the same conditions as above to produce a diol mixture. This procedure was repeated seven times to produce a diol mixture, and the activity retention rate was determined. The results are shown in Table 1.

Example 3 <Preparation of aqueous by-product solution> An aqueous reaction solution containing succinic acid, glutaric acid, and adipic acid was obtained by oxidizing cyclohexanol with nitric acid in the same manner as in Example 1. The adipic acid contained in the obtained reaction solution was precipitated, and the precipitated crystals were isolated to obtain an aqueous by-product solution.

<Preparation of dicarboxylic acid mixture (preparation by first purification process)> 5,000 g of the above by-product aqueous solution was heated at about 120°C under normal pressure for 1 hour, and then further
The dicarboxylic acid mixture was heated at 70 to 175°C for 30 minutes with stirring to dehydrate and denitrate the dicarboxylic acid mixture. After cooling, ion-exchanged water was added to the dehydrated and denitrated dicarboxylic acid mixture to obtain an aqueous solution with a water content of 70% by weight. A sulfonic acid cation exchange resin (trade name: Amberlite I) having a styrene base structure was added to this aqueous solution.
10 g of R120B (manufactured by Organo Corporation, Japan) was added, and the mixture was gently stirred at room temperature for 2 hours to remove copper and vanadium. Thereafter, the mixture was filtered to remove the ion exchange resin.
An aqueous solution of the dicarboxylic acid mixture was obtained.

The resulting aqueous solution of the dicarboxylic acid mixture contained 70% water, 7% by weight succinic acid, 18% by weight glutaric acid, and 5% by weight adipic acid. The nitric acid content was 0.1
7% by weight, and the copper content, vanadium content and sulfur content were 31.
The extinction coefficient at 355 nm was 0.114, and the content of compounds having oxygen-nitrogen bonds was 1,143 ppm.
It was m.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that the aqueous solution of the dicarboxylic acid mixture described above was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was carried out a total of seven times, and the activity retention rate was determined. The results are shown in Table 1.

Comparative Example 1 A diol mixture was produced using the by-product aqueous solution used in the preparation of the dicarboxylic acid mixture in Example 1 as a raw material for the diol mixture. The composition of the by-product aqueous solution used as a raw material was 67% by weight of water, 7% by weight of succinic acid, 18% by weight of glutaric acid, 5% by weight of adipic acid, and 3% by weight of nitric acid (10% by weight relative to the total weight of the dicarboxylic acids). The copper content, vanadium content, and sulfur content were 6 ppm and 2 ppm, respectively.
The extinction coefficient at 355 nm was 0.051.
and the content of compounds having oxygen-nitrogen bonds was 1,147 ppm.

<Production of diol mixture by hydrogenation reaction> A hydrogenation reaction was carried out in the same manner as in Example 1, except that 15.0 g of the by-product aqueous solution was used instead of the dicarboxylic acid mixture and water used in Example 1. After completion of the reaction, the hydrogenation reaction solution containing the diol mixture was extracted alone, leaving the catalyst in the autoclave. Analysis of the diol mixture contained in the hydrogenation reaction solution by gas chromatography revealed that the yields of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol were 45%, 73%, and 72%, respectively.

The same procedure as above was repeated to produce a diol mixture seven times in total, and the activity retention rate was determined. The results are shown in Table 1 together with the results of Examples 1, 2 and 3.

As is clear from Table 1, when a diol mixture is produced using a dicarboxylic acid mixture having a nitric acid content of more than 3% by weight, the activity retention rate of the hydrogenation catalyst decreases.

Example 4 <Preparation of dicarboxylic acid mixture (preparation by first purification process)> A dicarboxylic acid mixture was prepared using an aqueous by-product solution obtained after isolating adipic acid in an adipic acid production process. The composition of the aqueous by-product solution used was 55% water,
The saturation concentration was 1.0% by weight, 19% by weight of glutaric acid, 7% by weight of succinic acid, 11% by weight of adipic acid, and 6% by weight of nitric acid. The copper content, vanadium content, and sulfur content were 0.6% by weight, 0.4% by weight, and 340 ppm, respectively. The extinction coefficient at 355 nm was 1.460, and the content of compounds having oxygen-nitrogen bonds was 7.30.
It was 0 ppm.

1,000 g of the by-product aqueous solution was stirred in a beaker at atmospheric pressure and approximately 120°C for 1 hour.
The mixture was heated for 1 hour, and then further heated at 170-175°C for 30 minutes with stirring to dehydrate and denitrate the dicarboxylic acid mixture. After cooling, the weight of the dehydrated and denitrated dicarboxylic acid obtained was 380 g. This was made into a 38 wt% aqueous solution with ion-exchanged water, and insoluble materials were filtered off. 300 g of a sulfonic acid-based cation exchange resin (trade name: Amberlite IR120B) (manufactured by Organo Corporation, Japan) with a styrene base structure was added to the resulting filtrate, and the mixture was gently stirred at room temperature for 3 hours to remove copper and vanadium. The ion exchange resin was then removed by filtration, and 300 g of a quaternary ammonium salt-type anion exchange resin (trade name: Amberlite IRA900) (manufactured by Organo Corporation, Japan) with a styrene base structure was added to the resulting filtrate, and the mixture was gently stirred at room temperature for 3 hours to remove sulfur. The ion exchange resin was then removed by filtration, and an aqueous solution of the dicarboxylic acid mixture was obtained.

The resulting aqueous solution of the dicarboxylic acid mixture was analyzed by HPLC, and it was found that the dicarboxylic acid mixture accounted for 35% by weight of the aqueous solution, and that the composition of the dicarboxylic acid mixture was 2% by weight of succinic acid.
The nitric acid content was 0.03% by weight, and the copper, vanadium, and sulfur contents were 4 ppm, 4 ppm, and 1 ppm, respectively. Furthermore, the absorption coefficient at 355 nm was 0.014, and the content of compounds having oxygen-nitrogen bonds was 1,083.
It was ppm.

<Production of a diol mixture by hydrogenation reaction> Next, a diol mixture was produced using the dicarboxylic acid mixture prepared above.

In a 100 ml Hastelloy autoclave equipped with an electromagnetic induction stirrer, 16.1 g of an aqueous solution of a dicarboxylic acid mixture and the Ru-S prepared in Reference Example 1 were added.
0.3 g of n-Re catalyst was charged. After the atmosphere in the autoclave was replaced with nitrogen at room temperature, hydrogen was introduced under pressure to 2 MPa, and the temperature was raised to 180°C.
When the temperature reached 0°C, hydrogen was further pressurized to 15 MPa, and the hydrogenation reaction was carried out at this pressure for 18 hours. After the reaction was completed, the hydrogenation reaction solution containing the diol mixture was extracted alone while leaving the catalyst in the autoclave, and the diol mixture contained in the hydrogenation reaction solution was analyzed by gas chromatography.

15. Add a new aqueous solution of the dicarboxylic acid mixture to the autoclave containing the remaining catalyst.
1 g of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol were added to the reactor and subjected to a hydrogenation reaction under the same conditions as above to produce a diol mixture. This operation was repeated 10 times to produce a diol mixture. The total amount of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol obtained in the 10th run was calculated based on the total amount of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol produced in the first run.
The activity retention rate (%) was determined by dividing the result by the total amount of pentanediol and 1,6-hexanediol and multiplying the result by 100. The results are shown in Table 2.

Example 5 <Production of diol mixture by hydrogenation reaction> 16.1 g of the aqueous solution of the dicarboxylic acid mixture prepared in Example 4 and Reference Example 2 were placed in a 100 ml Hastelloy autoclave equipped with an electromagnetic induction stirrer.
The atmosphere in the autoclave was replaced with nitrogen at room temperature, and then hydrogen was introduced under pressure to 2 MPa.
The temperature was raised to 180°C. When the temperature reached 180°C, hydrogen was further pressurized to 15 MPa, and the hydrogenation reaction was carried out at this pressure for 18 hours. After completion of the reaction, the hydrogenation reaction solution containing the diol mixture was extracted alone while leaving the catalyst in the autoclave, and the diol mixture contained in the hydrogenation reaction solution was analyzed by gas chromatography.

15. Add a new aqueous solution of the dicarboxylic acid mixture to the autoclave containing the remaining catalyst.
1 g of the diol mixture was charged and subjected to a hydrogenation reaction under the same conditions as above to produce a diol mixture. The diol mixture was produced 10 times in total, and the activity retention rate was calculated. The results are shown in Table 2.
Shown below.

Example 6 <Preparation of Dicarboxylic Acid Mixture (Preparation by First Purification Process)> A dicarboxylic acid mixture was prepared using the same aqueous by-product solution as in Example 4.

1,000 g of the by-product aqueous solution was stirred in a beaker at atmospheric pressure and approximately 120°C for 1 hour.
The mixture was heated for 1 hour, and then heated at 170-175°C for 30 minutes with stirring to dehydrate and denitrate the dicarboxylic acid mixture. After cooling, the weight of the dehydrated and denitrated dicarboxylic acid mixture obtained was 380g. This was diluted with ion-exchanged water to a concentration of 38% by weight.
The resulting solution was dissolved in water, and insoluble materials were filtered off. 300 g of a sulfonic acid-based cation exchange resin (trade name: Amberlite IR120B) (manufactured by Organo Corporation, Japan) having a styrene base structure was added to the resulting filtrate, and the mixture was gently stirred at room temperature for 3 hours to remove copper and vanadium. The ion exchange resin was then removed by filtration, and 100 g of powdered activated carbon was added to the resulting filtrate, and the mixture was stirred at room temperature for 3 hours. The activated carbon was then removed by filtration, and the resulting filtrate was diluted with a quaternary ammonium salt-type anion exchange resin (trade name: Amberlite IRA900) having a styrene base structure (manufactured by Organo Corporation, Japan).
To the mixture was added 300 g of ethanol (manufactured by HOSO.RTM.) and the mixture was gently stirred at room temperature for 3 hours to remove sulfur. The ion exchange resin was then removed by filtration to obtain an aqueous solution of a dicarboxylic acid mixture.

The resulting aqueous solution of the dicarboxylic acid mixture was analyzed by HPLC, and it was found that the dicarboxylic acid mixture accounted for 35% by weight of the aqueous solution, and that the composition of the dicarboxylic acid mixture was 2% by weight of succinic acid.
The nitric acid content was 0.03 wt%, and the copper, vanadium, and sulfur contents were 4 ppm, 4 ppm, and 1 ppm, respectively. Furthermore, the absorption coefficient at 355 nm was 0.010, and the content of compounds having oxygen-nitrogen bonds was 653 ppm.
It was m.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that 16.1 g of the prepared aqueous solution of the dicarboxylic acid mixture was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was repeated 10 times, and the activity retention rate was determined. The results are shown in Table 2.

Example 7 <Preparation of Dicarboxylic Acid Mixture (Preparation by Second Purification Process)> A dicarboxylic acid mixture was prepared using the same aqueous by-product solution as in Example 4.

1,000 g of the by-product aqueous solution was stirred in a beaker at atmospheric pressure and approximately 120°C for 1 hour.
The mixture was heated for 1 hour, and then heated at 170-175°C for 30 minutes with stirring to dehydrate and denitrate the dicarboxylic acid mixture. After cooling, the weight of the dehydrated and denitrated dicarboxylic acid mixture obtained was 380g. This was made into a 38% by weight aqueous solution with ion-exchanged water, and insoluble materials were filtered off. The obtained filtrate was added to a sulfonic acid cation exchange resin (trade name: Amberlite IR120B) having a styrene base structure (Japan,
300 g of Organo Co., Ltd. (manufactured by Organo Corporation) was added and gently stirred at room temperature for 3 hours to remove copper and vanadium. The ion exchange resin was then removed by filtration, yielding a filtrate containing dicarboxylic acids. The resulting filtrate was heated in a beaker at approximately 120°C for 1 hour while stirring to distill off water, and after cooling, 3,000 g of xylene was added thereto to obtain a suspension containing dicarboxylic acids. The resulting suspension was heated to 80°C for 20 minutes while vigorously stirring. After cooling with stirring, the denitrified dicarboxylic acid mixture was filtered off.
The resulting dicarboxylic acid mixture was kept at 60°C under vacuum to remove xylene, and 3
61 g of a dicarboxylic acid mixture was obtained.

The dicarboxylic acid mixture obtained was analyzed by HPLC, and the composition of the dicarboxylic acid mixture was found to be 20% by weight of succinic acid, 50% by weight of glutaric acid, and 30% by weight of adipic acid. The nitric acid content was 0.02% by weight, and the copper content, vanadium content, and sulfur content were 4 ppm, 4 ppm, and 10 ppm, respectively.
The absorption coefficient at 55 nm was 0.040, and the content of compounds having oxygen-nitrogen bonds was 848 ppm.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that 5.85 g of the above dicarboxylic acid mixture and 10.86 g of ion-exchanged water were used. The production of the diol mixture was repeated 10 times, and the activity retention rate was determined. The results are shown in Table 2.

Example 8 <Preparation of Dicarboxylic Acid Mixture (Preparation by First Purification Process)> A dicarboxylic acid mixture was prepared using the same aqueous by-product solution as in Example 4.

1,000 g of the by-product aqueous solution was stirred in a beaker at atmospheric pressure and approximately 120°C for 1 hour.
The mixture was heated for 1 hour, and then heated at 170-175°C for 30 minutes with stirring to dehydrate and denitrate the dicarboxylic acid mixture. After cooling, the weight of the dehydrated and denitrated dicarboxylic acid mixture obtained was 380g. This was diluted with ion-exchanged water to a concentration of 38% by weight.
The resulting solution was filtered to remove insoluble materials. 500 g of a sulfonic acid cation exchange resin (trade name: Amberlite IR120B) (manufactured by Organo Corporation, Japan) having a styrene base structure was added to the resulting filtrate, and the mixture was gently stirred at 80°C for 3 hours to remove copper and vanadium. The ion exchange resin was then removed by filtration to obtain an aqueous solution of a dicarboxylic acid mixture.

The resulting aqueous solution of the dicarboxylic acid mixture was analyzed by HPLC, and it was found that the dicarboxylic acid mixture accounted for 35% by weight of the aqueous solution, and that the composition of the dicarboxylic acid mixture was 2% by weight of succinic acid.
The nitric acid content was 0.03% by weight, and the copper, vanadium, and sulfur contents were 3 ppm, 1 ppm, and 182 ppm, respectively. Furthermore, the absorption coefficient at 355 nm was 1.437, and the content of compounds having oxygen-nitrogen bonds was 5.6.
00 ppm.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that 16.1 g of the aqueous solution of the dicarboxylic acid mixture described above was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was repeated 10 times, and the activity retention rate was determined. The results are shown in Table 2.

Example 9 <Production of a diol mixture by hydrogenation reaction> Using the dicarboxylic acid mixture prepared in Example 1, a diol mixture was produced.

In a 1000 ml Hastelloy autoclave equipped with an electromagnetic induction stirrer, 175 g of the dicarboxylic acid mixture prepared in Example 1 and 325 g of ion-exchanged water were added.
The autoclave was charged with 10 g of ZnO and 10 g of the Ru—Sn—Re catalyst prepared in Reference Example 1. After the atmosphere in the autoclave was replaced with nitrogen at room temperature, hydrogen was injected to 2 MPa and the temperature was raised to 180° C. When the temperature reached 180° C., hydrogen was further injected to raise the temperature to 15 MPa.
The autoclave was heated to 100 Pa and the hydrogenation reaction was carried out at this pressure for 30 hours. After the reaction was completed, the catalyst was left in the autoclave, and only the hydrogenation reaction solution containing the diol mixture was extracted. The diol mixture contained in the hydrogenation reaction solution was analyzed by gas chromatography, and it was found that 1,4-butanediol, 1,5-pentanediol, and 1,4-butanediol were present.
The yields of 1,6-hexanediol were 89%, 97% and 87%, respectively.

Add 175 g of the dicarboxylic acid mixture and 3 g of water to the autoclave containing the catalyst.
25 g of the diol mixture was charged and subjected to a hydrogenation reaction under the same conditions as above to produce a diol mixture. This operation was repeated to perform a total of 10 hydrogenation reactions.
The yields of the first run were almost the same as those of the first run. Furthermore, as a result of HPLC analysis, the amounts of δ-valerolactone and ε-caprolactone contained in the hydrogenation reaction solution were both 0.01% or less.

<Recovery of a Mixture of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol> After the hydrogenation reaction was completed, the autoclave was cooled to room temperature and returned to atmospheric pressure to remove hydrogen gas from the hydrogenation reaction solution. Approximately 5 kg of the hydrogenation reaction solution from which hydrogen gas had been removed was heated to 109°C under atmospheric pressure to distill off approximately 85% of the water and a mixture of tetrahydrofuran, tetrahydropyran, butanol, and pentanol produced as by-products in the hydrogenation reaction, thereby obtaining a mixture. The resulting mixture was subjected to multi-stage distillation. The multi-stage distillation was carried out using a 12-stage multi-stage distillation column under conditions of a column bottom temperature of 160°C, a column bottom pressure of 6 kPa, a column top temperature of 25°C, and a column top pressure of 3.5 kPa. Water and a mixture of γ-butyrolactone, pentanol, and hexanol produced as by-products in the hydrogenation reaction were distilled off to obtain a purified diol mixture.

The resulting purified diol mixture was subjected to the following multi-stage distillation. A 35-stage multi-stage distillation column was used for the multi-stage distillation, and the column bottom temperature was 180°C, the column bottom pressure was 12 kPa, the column top temperature was 95°C, and
Multistage distillation was carried out under the condition of a column top pressure of 3 kPa, and 1,4-butanediol was recovered as a low boiling point component. The recovered amount of 1,4-butanediol was 238 g, and analysis by gas chromatography revealed that the purity was 98.5% and the amount of impurities was 1,5
The product was confirmed to be pentanediol, and no lactones were found to be present.

The high-boiling mixture remaining after recovering 1,4-butanediol was subjected to multi-stage distillation. A seven-stage multi-stage distillation column was used for the multi-stage distillation, and the column bottom temperature was 200°C and the column bottom pressure was 7 kPa.
The distillation was carried out under the conditions of a column top temperature of 163°C and a column top pressure of 6 kPa, and a mixture of 1,5-pentanediol and 1,6-hexanediol was recovered as a distillate. The recovered mixture of 1,5-pentanediol and 1,6-hexanediol weighed 866 g, and analysis by gas chromatography confirmed that the purity was 99.8% and that the impurity was 1,4-butanediol. Furthermore, neither 1,5-hexanediol nor 1,4-dihydroxycyclohexane was contained.

Example 10 <Preparation of dicarboxylic acid mixture (preparation by the third purification process)> Adipic acid obtained in an adipic acid production process was isolated, and a dicarboxylic acid mixture was prepared using the by-product aqueous solution obtained after recovering nitric acid and catalyst. The by-product aqueous solution used had a composition of 19 wt% glutaric acid, 6 wt% succinic acid, 5 wt% adipic acid, and 4.1 wt% nitric acid. The copper content, vanadium content, and sulfur content were 7 ppm, 5 ppm, and 230 ppm, respectively. Furthermore, the content of compounds having oxygen-nitrogen bonds was 6,640 ppm, and the remainder was water. The absorption coefficient at 355 nm was 0.79.

In a 100 ml Hastelloy autoclave equipped with an electromagnetic induction stirrer, 15.0 g of the by-product aqueous solution and a platinum catalyst (a catalyst in which 3% by weight of platinum is supported on activated carbon) were added.
The autoclave was charged with 0.15 g of ethylene glycol stearate (manufactured by N.E. Chemcat Corporation, Japan). The atmosphere inside the autoclave was replaced with nitrogen, and then further replaced with hydrogen. Hydrogen was then injected into the autoclave to a pressure of 1 MPa at room temperature. The temperature was raised to 140°C, and the hydrogen pressure in the autoclave reached 1.5 MPa.
The pressure was adjusted to Pa. The reduction treatment of nitric acid and the compound having an oxygen-nitrogen bond was carried out at this pressure for 4 hours. After the reduction treatment was completed, the catalyst was separated to obtain an aqueous solution of a dicarboxylic acid mixture.

The resulting dicarboxylic acid mixture had a composition of 19% by weight of glutaric acid, 6% by weight of succinic acid, and 5% by weight of adipic acid. The nitric acid content was 0.036% by weight, and the copper, vanadium, and sulfur contents were 7 ppm, 5 ppm, and 170 ppm, respectively. Furthermore, the extinction coefficient at 355 nm was 0.043.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that 15.0 g of the prepared aqueous solution of the dicarboxylic acid mixture was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was carried out a total of 10 times, and the activity retention rate was determined. The results are shown in Table 3.

Example 11 <Preparation of dicarboxylic acid mixture (preparation by the third purification process)> Using the same aqueous by-product solution as used in Example 10, a dicarboxylic acid mixture was prepared.

500 g of the by-product aqueous solution was mixed with 12 g of a sulfonic acid cation exchange resin (trade name: Amberlite IR120B) (manufactured by Organo Corporation, Japan) having a styrene base structure.
The mixture was stirred gently at room temperature for 3 hours to remove copper and vanadium. The ion exchange resin was then removed by filtration, and the resulting aqueous by-product solution was subjected to a reduction treatment similar to that in Example 10. After completion of the reduction treatment, the catalyst was separated to obtain an aqueous solution of a dicarboxylic acid mixture.

The resulting dicarboxylic acid mixture had a composition of 19% by weight of glutaric acid, 6% by weight of succinic acid, and 5% by weight of adipic acid. The nitric acid content was 0.031% by weight, and the copper, vanadium, and sulfur contents were 3 ppm, 3 ppm, and 180 ppm, respectively. Furthermore, the extinction coefficient at 355 nm was 0.040.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that 15.0 g of the prepared aqueous solution of the dicarboxylic acid mixture was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was carried out a total of 10 times, and the activity retention rate was determined. The results are shown in Table 3.

Example 12 <Preparation of dicarboxylic acid mixture (preparation by the third purification process)> Using the same aqueous by-product solution as used in Example 10, a dicarboxylic acid mixture was prepared as follows.

The reduction treatment was carried out in the same manner as in Example 10, except that the temperature for the reduction treatment was 60°C, the hydrogen pressure was 2.0 MPa, and the treatment time was 6 hours. After completion of the reduction treatment, the catalyst was separated to obtain an aqueous solution of a dicarboxylic acid mixture.

The resulting dicarboxylic acid mixture had a composition of 19% by weight of glutaric acid, 6% by weight of succinic acid, and 5% by weight of adipic acid. The nitric acid content was 0.18% by weight, and the copper content, vanadium content, and sulfur content were 7 ppm, 5 ppm, and 1 ppm, respectively.
The extinction coefficient at 355 nm was 0.061.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that 15.0 g of the prepared aqueous solution of the dicarboxylic acid mixture was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was repeated 10 times, and the activity retention rate was determined. The results are shown in Table 3.

Example 13 Preparation of Dicarboxylic Acid Mixture (Preparation by Third Purification Process) Using the same aqueous by-product solution as used in Example 10, a dicarboxylic acid mixture was prepared as follows.

500 g of the by-product aqueous solution was mixed with 12 g of a sulfonic acid cation exchange resin (trade name: Amberlite IR120B) (manufactured by Organo Corporation, Japan) having a styrene base structure.
To the mixture was added 0 g of ruthenium, and the mixture was gently stirred at room temperature for 3 hours to remove copper and vanadium. The ion exchange resin was then removed by filtration, and the resulting aqueous by-product solution was subjected to the same reduction treatment as in Example 10, except that a ruthenium catalyst (5 wt % supported on activated carbon) (manufactured by N.E. Chemcat Corporation, Japan) was used as the catalyst. After completion of the reduction treatment, the catalyst was separated to obtain an aqueous solution of a dicarboxylic acid mixture.

The resulting dicarboxylic acid mixture had a composition of 19% by weight of glutaric acid, 6% by weight of succinic acid, and 5% by weight of adipic acid. The nitric acid content was 0.073% by weight, and the copper, vanadium, and sulfur contents were 5 ppm, 5 ppm, and 190 ppm, respectively. Furthermore, the extinction coefficient at 355 nm was 0.038.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by carrying out a hydrogenation reaction in the same manner as in Example 1, except that 15.0 g of the prepared aqueous solution of the dicarboxylic acid mixture was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was carried out a total of 10 times, and the activity retention rate was determined. The results are shown in Table 3.

Example 14 <Preparation of dicarboxylic acid mixture (preparation by the third purification process)> A dicarboxylic acid mixture was prepared using the same aqueous by-product solution as used in Example 10. The composition of the aqueous by-product solution used was 19% by weight of glutaric acid, 6% by weight of succinic acid, 5% by weight of adipic acid, and 4.1% by weight of nitric acid. Furthermore, the absorption coefficient at 355 nm was 0.79, and the content of compounds having oxygen-nitrogen bonds was 6.
It was 640 ppm.

1,000 g of the by-product aqueous solution was stirred in a beaker at atmospheric pressure and approximately 120°C for 1 hour.
The mixture was heated for 1 hour, and then heated at 170-175°C for 30 minutes with stirring to dehydrate and denitrate the dicarboxylic acid mixture. After cooling, the weight of the dehydrated and denitrated dicarboxylic acid mixture obtained was 300g, and this was made into a 30% by weight aqueous solution with ion-exchanged water. 15.0g of the resulting aqueous solution was charged into a 100ml Hastelloy autoclave equipped with an electromagnetic induction stirrer, together with 0.15g of the ruthenium catalyst used in Example 13. The atmosphere inside the autoclave was replaced with nitrogen, and then further replaced with hydrogen, and hydrogen was pressurized to 1 MPa at room temperature. The temperature was raised to 140°C,
The hydrogen pressure in the autoclave was adjusted to 1.5 MPa. The reduction treatment of the remaining nitric acid and the compound having an oxygen-nitrogen bond was carried out at this pressure for 4 hours. After the reduction treatment was completed, the catalyst was separated to obtain an aqueous solution of a dicarboxylic acid mixture.

The resulting dicarboxylic acid mixture had a composition of 19% by weight of glutaric acid, 6% by weight of succinic acid, and 5% by weight of adipic acid. The nitric acid content was 0.005% by weight, and the copper, vanadium, and sulfur contents were 7 ppm, 5 ppm, and 160 ppm, respectively. Furthermore, the extinction coefficient at 355 nm was 0.021.

<Production of diol mixture by hydrogenation reaction> A diol mixture was produced by hydrogenation reaction in the same manner as in Example 1, except that 15.0 g of the prepared aqueous solution of the dicarboxylic acid mixture was used instead of the dicarboxylic acid mixture and water used in Example 1. The production of the diol mixture was repeated 10 times in total, and the activity retention rate was determined. The results are shown in Table 3.

INDUSTRIAL APPLICABILITY By using the method for producing a diol mixture of the present invention, a by-product aqueous solution containing a dicarboxylic acid mixture including succinic acid, glutaric acid, and adipic acid, which is obtained from the process for producing adipic acid and which has not previously been used for any purpose other than as a solvent, can be used to produce 1,4-butanediol, 1,5-pentanediol, and 1,6-pentanediol by hydrogenating the dicarboxylic acids directly without converting them into esters.
The diols obtained by the method of the present invention are useful as raw materials for polyurethanes and polyesters.

──────────────────────────────────────────────────Continuation of front page (51) Int.Cl. ⁷ Identification code FI C07C 51/42 C07C 51/42 (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE, TR), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), UA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, B Z, CA, CH, CN, CR, CU, CZ, DE, DK , DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, J P, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, R O, RU, SD, SE, SG, SI, SK, SL, TJ , TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW (Note) This publication is based on the gazette published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act), and is unrelated to this publication.

Claims (22)

[Claims] Claim 1: 1,4-butanediol, 1,5-pentanediol and 1,6-
A method for producing a diol mixture including hexanediol, comprising: (A) providing a dicarboxylic acid mixture including succinic acid, glutaric acid, and adipic acid, and having a nitric acid content of 3% by weight or less based on the total weight of the succinic acid, glutaric acid, and adipic acid, the dicarboxylic acid mixture being prepared by denitrating an aqueous by-product solution obtained in a process for producing adipic acid, the process for producing adipic acid comprising: subjecting at least one cyclic aliphatic compound having 6 carbon atoms to oxidation with nitric acid in an aqueous medium in the presence of an oxidation catalyst to obtain an aqueous reaction solution including succinic acid, glutaric acid, and adipic acid, precipitating crystals of the adipic acid, isolating the precipitated crystals from the reaction solution, and obtaining an aqueous by-product solution; and (B) subjecting the dicarboxylic acid mixture to a hydrogenation reaction in the presence of water, hydrogen gas, and a hydrogenation catalyst containing active metal species consisting of ruthenium and tin, to obtain 1,
obtaining a hydrogenation reaction liquid containing a diol mixture including 4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. 2. The method of claim 1, wherein the dicarboxylic acid mixture is subjected to the following conditions (1) to (3) before step (B):
The method of claim 1, wherein the mixture is prepared to satisfy at least one of the following conditions: (1) the mixture has a nitric acid content of 0.2% by weight or less, based on the total weight of succinic acid, glutaric acid, and adipic acid; (2) the mixture has a copper content and a vanadium content of 10 ppm or less, based on the total weight of succinic acid, glutaric acid, and adipic acid; and (3) the mixture has a sulfur content of 200 ppm or less, based on the total weight of succinic acid, glutaric acid, and adipic acid. 3. The method according to claim 2, wherein the mixture under condition (3) has a sulfur content of 40 ppm or less based on the total weight of succinic acid, glutaric acid, and adipic acid. 4. The method according to any one of claims 1 to 3, wherein an aqueous solution of the dicarboxylic acid mixture dissolved in distilled water exhibits an absorption coefficient at 355 nm calculated by the following formula: E = A/(c x b) (where E is the absorption coefficient at 355 nm, A is the absorbance at room temperature of the aqueous solution of the dicarboxylic acid mixture dissolved in distilled water, c is the weight (g) of the dicarboxylic acid mixture dissolved in 100 g of distilled water, and b is the length (cm) of the cell used to measure the absorbance.) 5. The method according to claim 4, wherein an aqueous solution of the dicarboxylic acid mixture dissolved in distilled water has an absorption coefficient of 0.1 or less. 6. The dicarboxylic acid mixture contains a compound having an oxygen-nitrogen bond in an amount of 2% by weight of nitric acid relative to the total weight of succinic acid, glutaric acid and adipic acid.
The manufacturing method according to any one of claims 1 to 5, characterized in that the content is 0,000 ppm or less. 7. The method according to claim 1, wherein the active metal species contained in the hydrogenation catalyst further contains at least one metal selected from the metals of Group 7 of the periodic table.
7. The manufacturing method according to any one of claims 1 to 6. 8. The method according to claim 7, wherein the at least one metal selected from the metals of Group 7 of the periodic table is rhenium. [Claim 9] A production method described in any one of claims 1 to 8, characterized in that the active metal species contained in the hydrogenation catalyst further contains at least one metal selected from the group consisting of metals in Group 8 of the periodic table other than ruthenium, and metals in Groups 9 and 10 of the periodic table. 10. The method according to claim 9, wherein the at least one metal selected from the group consisting of metals in Group 8 of the periodic table other than ruthenium and metals in Groups 9 and 10 of the periodic table is platinum. 11. The method according to claim 1, wherein the hydrogenation catalyst further comprises activated carbon supporting the active metal species. 12. The hydrogenation reaction is carried out at a temperature of 100 to 300°C and a hydrogen pressure of 1 to 25 M.
The method according to any one of claims 1 to 11, characterized in that the method is carried out under conditions of Pa. 13. The method of claim 1, wherein the dicarboxylic acid mixture is prepared as an aqueous solution by a first purification process comprising the following steps (a) to (c):
2. The method for producing a dicarboxylic acid mixture according to any one of claims 1 to 11, further comprising the steps of: (a) heating the by-product aqueous solution at a temperature of 80 to 200°C and at a pressure equal to or less than atmospheric pressure to perform dehydration and denitration to obtain a dehydrated and denitrated dicarboxylic acid mixture; (b) adding water to the obtained dehydrated and denitrated dicarboxylic acid mixture to obtain a denitrated aqueous dicarboxylic acid mixture; and (c) contacting the denitrated aqueous dicarboxylic acid mixture with a cation exchange resin to remove copper and vanadium. 14. The method of claim 13, wherein the first purification process further comprises a step (d) of contacting the denitrated aqueous dicarboxylic acid mixture with an anion-adsorbing material. 15. The method of claim 13, wherein the first purification process further comprises contacting the denitrated aqueous dicarboxylic acid mixture with activated carbon.
4. The manufacturing method according to claim 4. 16. The method according to any one of claims 1 to 12, wherein the dicarboxylic acid mixture is prepared by a second purification process comprising the following steps (a) to (f): (a) heating the by-product aqueous solution at a temperature of 80 to 130°C and at a pressure equal to or lower than atmospheric pressure;
(b) further heating the dehydrated and denitrated dicarboxylic acid mixture at a temperature of 130 to 180°C and atmospheric pressure to obtain a denitrated dicarboxylic acid mixture; (b) adding water to the obtained dehydrated and denitrated dicarboxylic acid mixture to obtain an aqueous denitrated dicarboxylic acid mixture; (c) contacting the denitrated dicarboxylic acid aqueous mixture with a cation exchange resin to remove copper and vanadium; (d) heating the obtained denitrated dicarboxylic acid aqueous mixture at a pressure equal to or lower than atmospheric pressure at a temperature sufficient to distill off water from the denitrated dicarboxylic acid aqueous mixture; (e) adding an aromatic hydrocarbon having 6 to 14 carbon atoms and having a boiling point of 200°C or lower at atmospheric pressure to the denitrated dicarboxylic acid mixture obtained in step (d), heating the resulting mixture at a temperature equal to or lower than the boiling point of the aromatic hydrocarbon, and then cooling; and (f) recovering the denitrated dicarboxylic acid mixture from the mixture by filtration to prepare the dicarboxylic acid mixture. 17. The method of claim 16, wherein the second purification process further comprises, after step (a), a step of contacting the denitrated dicarboxylic acid mixture in the form of an aqueous solution or an aqueous solution obtained by dissolving the denitrated dicarboxylic acid mixture in water with an anion-adsorbing material. [Claim 18] A production method described in any one of claims 1 to 12, characterized in that the dicarboxylic acid mixture is prepared by a third purification process comprising contacting the by-product aqueous solution with hydrogen gas in the presence of a reduction catalyst containing an active metal species including at least one metal selected from the group consisting of metals of Groups 7 to 10 of the periodic table, thereby reducing nitric acid and compounds having an oxygen-nitrogen bond contained in the by-product aqueous solution to obtain the dicarboxylic acid mixture in the form of an aqueous solution. 19. The method for producing a nitric acid according to claim 18, wherein the reduction reaction of the nitric acid and the compound having an oxygen-nitrogen bond in the third purification process is carried out under conditions of a temperature of 50 to 200°C and a hydrogen pressure of 0.2 to 5 MPa. 20. The method for producing a sulphur dioxide gas according to claim 18 or 19, wherein the active metal species contained in the reduction catalyst used in the third purification process is at least one metal selected from the group consisting of platinum, rhenium, palladium, rhodium, nickel, iridium and ruthenium. 21. The method according to any one of claims 18 to 20, wherein in the third purification process, the by-product aqueous solution is subjected to the following steps before contacting the by-product aqueous solution with hydrogen gas:
The by-product aqueous solution is heated at a temperature of 80 to 130°C and at a pressure equal to or lower than atmospheric pressure, and then further heated at a temperature of 130 to 180°C and at atmospheric pressure, and water is added thereto. 22. A method for producing a 1,4-butanediol copolymer comprising the steps of: 1,4-butanediol; 1,5-pentanediol; and 1,5-pentanediol.
22. A method for recovering a mixture of 1,4-hexanediol and 1,4-hexanediol from a diol mixture obtained by the production method according to any one of claims 1 to 21, comprising the steps of: (i) adjusting the temperature of a hydrogenation reaction solution containing the diol mixture to a temperature from room temperature to less than 100°C, and performing gas-liquid separation at atmospheric pressure or less to remove hydrogen gas from the hydrogenation reaction solution; (ii) heating the hydrogenation reaction solution from which hydrogen gas has been removed under atmospheric pressure to distill off a mixture of water and a mixture of cyclic ethers and monohydric alcohols by-produced in the hydrogenation reaction; (iii) subjecting the resulting mixture to multi-stage distillation to distill off water and γ-butyrolactone by-produced in the hydrogenation reaction to obtain a purified diol mixture; (iv) subjecting the purified diol mixture to multi-stage distillation to obtain 1,4-butanediol as a low-boiling component; and (v) further subjecting the remaining high-boiling mixture obtained in step (iv) to multi-stage distillation to obtain a purified diol mixture.
obtaining a mixture of 1,5-pentanediol and 1,6-hexanediol as a distillate.