JPH05155807A - Production of naphthalene dicarboxylic acid - Google Patents

Abstract

PURPOSE:To obtain the subject high-purity compound having good hue in high recovery ratio by dissolving a crude naphthalene dicarboxylic acid obtained as the oxidation product of a di-substituted naphthalene containing impurities and coloring components in a mixed solvent of an amine and an alcohol and crystallizing naphthalene dicarboxylic acid. CONSTITUTION:Di-substituted naphthalene such as dialkylnaphthalene is oxidized with O2 in a solvent such as an aliphatic lower monocarboxylic acid or water in the presence of a catalyst such as a heavy metal or bromine to afford a crude naphthalene dicarboxylic acid. Then the crude naphthalene dicarboxylic acid is dissolved in a mixed solvent of an amine (e.g. triethanolamine) and an alcohol (e.g. methanol) and crystallized to provide the objective high-purity naphthalene dicarboxylic acid having good hue. The mixed weight ratio of the amine and alcohol is in the range of approximately (5:95) to (95:5). By using this mixed solvent, solubility of the naphthalene dicarboxylic acid is remarkably improved and temperature dependency of the solubility becomes extremely large and purification by crystallization is facilitated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing naphthalenedicarboxylic acid. Naphthalenedicarboxylic acid is a compound useful as a raw material for highly functional resins such as polyethylene naphthalate (PEN resin).

[0002]

BACKGROUND OF THE INVENTION Naphthalenedicarboxylic acid is generally produced, for example, by oxidizing dialkyl-substituted naphthalene such as dimethylnaphthalene and diisopropylnaphthalene with molecular oxygen in the presence of cobalt, manganese and bromine. .. The crude naphthalenedicarboxylic acid obtained by this method contains impurities such as trimellitic acid and a coloring substance, and therefore requires a purification step.

Conventionally, as a method for purifying naphthalenedicarboxylic acid, crude naphthalenedicarboxylic acid is dissolved in an alkaline aqueous solution, subjected to treatments such as oxidation, hydrogenation and decolorization by adsorption, and then acidified to obtain a high purity. A method for obtaining naphthalenedicarboxylic acid is known (Japanese Patent Application Laid-open No. 48-4848).
-68554, JP-B-52-20993, JP-A-50-
105639, 160248, etc.). However, all of these methods use a large amount of alkali and acid, and thus have a problem that a large amount of inorganic salt and waste water are generated.

Further, the crude naphthalene dicarboxylic acid is mixed with N,
A method has been disclosed in which an organic solvent selected from N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc) and dimethylsulfoxide (DMSO) is used, followed by recrystallization after treatment with activated carbon (Japanese Patent Application Laid-Open No. S60-12069). 62
-230747). However, when the present inventors performed purification by the above method, when the recovery of naphthalenedicarboxylic acid was increased, the hue was hardly improved (see Comparative Examples 6 and 7). Furthermore, those organic solvents have high boiling points and it is difficult to recover the solvent.
There were problems such as high toxicity.

On the other hand, after dissolving crude 2,6-naphthalenedicarboxylic acid in an aqueous solution of a specific alkylamine such as dimethylamine, the amine is distilled off from the aqueous solution to obtain 2,6-
A method of purifying by precipitating naphthalenedicarboxylic acid has been disclosed (JP-A-50-142542). However, according to this method, (1) the amines are precipitated by recovering by distillation, so that only specific amines that can be distilled off can be used. (2) Since these amines azeotrope with water, a large amount of There are drawbacks such as water being distilled out together, and (3) the recovery rate is low because the amine cannot be completely removed from the aqueous solution.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing naphthalene dicarboxylic acid having a high purity and a good hue with a high recovery rate.

[0007]

The present invention is characterized in that crude naphthalene dicarboxylic acid obtained by oxidizing disubstituted naphthalene is dissolved in a mixed solvent of amines and alcohols for crystallization. Is a method for producing naphthalenedicarboxylic acid.

(Di-substituted naphthalene) The di-substituted naphthalene used in the method of the present invention can be converted into a carboxyl group by an oxidation reaction of an alkyl group, an acyl group, a formyl group, a hydroxyalkyl group, a hydroperoxyalkyl group and the like. Disubstituted naphthalene having two different substituents. The positions of the two substituents may be positions other than positions on the adjacent two carbons, specifically, positions other than the 1,2-position and the 2,3-position, and particularly preferably 2,6 positions. -Position 2,
7th place.

(Crude naphthalene dicarboxylic acid) The above di-substituted naphthalene compounds are oxidized with molecular oxygen such as air in the presence of a catalyst such as heavy metal or bromine in a solvent such as aliphatic lower monocarboxylic acid or water. Thus, crude naphthalenedicarboxylic acid is obtained.

As the aliphatic lower monocarboxylic acid solvent,
For example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, bromoacetic acid and the like can be mentioned. Among them, acetic acid is most preferable, and it may be diluted with other solvent such as water or aromatic hydrocarbon. The amount of the solvent used is not particularly limited, but is preferably 0.5 to 10 times by weight, and particularly preferably 1 to 6 times by weight, based on the starting dialkylnaphthalene.

Examples of the cobalt compound and the manganese compound used as the catalyst include, for example, aliphatic carboxylates of cobalt and manganese such as formic acid, acetic acid, propionic acid, oxalic acid and maleic acid, and alicyclic carboxylates such as naphthenic acid. In addition to aromatic carboxylic acid salts such as benzoic acid, terephthalic acid, naphthoic acid and naphthalenedicarboxylic acid, inorganic compounds such as hydroxides, oxides, carbonates and halides can be mentioned. Of these, acetate and bromide are preferable.

The cobalt compound and the manganese compound are used as a mixture, and the mixing ratio thereof is cobalt: manganese (atomic ratio) of 99: 1 to 1:99, preferably 9.
The range is from 7: 3 to 3:97. The amount of cobalt and manganese used is 0.2 to 10% by weight as the total amount of cobalt and manganese atoms with respect to the aliphatic carboxylic acid solvent.
It is preferably in the range of 0.4 to 5% by weight.

Examples of the bromine compound contained in the catalyst component include inorganic bromine compounds such as molecular bromine, hydrogen bromide and hydrobromide, and methyl bromide, ethyl bromide, bromoform, ethylene bromide and bromo. An organic bromine compound such as acetic acid can be exemplified. The amount of the bromine compound used is such that the amount of bromine atoms is 0.1 to the total number of moles of cobalt and manganese atoms contained in the aliphatic carboxylic acid solvent.
The amount is 10 times by mole, preferably 0.2 to 5 times by mole.

The reaction temperature is usually 100 to 300 ° C., and the pressure is 0.2 to 10 kg / c in terms of absolute oxygen partial pressure in the gas phase.
Pressures such as m ² are preferred. After completion of the reaction, the reaction solution is cooled to about room temperature and the precipitated solid is recovered to obtain crude naphthalenedicarboxylic acid. The crude naphthalenedicarboxylic acid thus obtained has a purity of 90% or more, generally 95 to 99%, and usually exhibits a light brown to brown color, but is used as it is in the next crystallization step. Alternatively, the crystallization may be performed after washing with a reaction solvent or the like. In some cases, the purity is 99% or more, such as activated carbon or DM
It is also possible to improve the hue by crystallizing naphthalenedicarboxylic acid after treatment with SO or the like.

(Amines) Examples of amines used as a crystallization solvent in the method of the present invention include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, di-n-propyl. Amine, tri-n-propylamine, isopropylamine, diisopropylamine,
Triisopropylamine, n-butylamine, di-n-
Butylamine, tri-n-butylamine cypyridine, n
-Hexylamine, di-n-hexylamine, tri-n
-Hexylamine, cyclohexylamine, dicyclohexylamine, tricyclohexylamine, n-octylamine, di-n-octylamine, tri-n-octylamine, ethylenediamine, N-methylethylenediamine, N, N-dimethylethylenediamine, N, N '-
Dimethylethylenediamine, N, N, N'-trimethylethylenediamine, N, N, N ', N'-tetramethylethylenediamine, 1,2-diaminopropane, 1,3
-Diaminopropane, N-methyl-1,2-diaminopropane, N-methyl-1,3-diaminopropane, N,
N-dimethyl-1,2-diaminopropane, N, N-dimethyl-1,3-diaminopropane, N, N, N'-trimethyl-1,2-diaminopropane, N, N, N'-
Trimethyl-1,3-diaminopropane, N, N,
Fats such as N ', N'-tetramethyl-1,2-diaminopropane, N, N, N', N'-tetramethyl-1,3-diaminopropane, monoethanolamine, diethanolamine, triethanolamine, glycine Group amines and their derivatives; piperidine, N-methylpiperidine,
Alicyclic amines such as hexamethyleneimine and N-methylhexamethyleneimine; aniline, o-, m- and p-toluidine, N, N-dimethyl-o-, m- and p-toluidine, benzylamine, N- Methylbenzylamine,
Aromatic amines such as N, N-dimethylbenzialamine; and the like. These amines alone,
A mixture of two or more kinds at an arbitrary ratio can be used.

(Alcohols) Examples of alcohols used as a crystallization solvent in the method of the present invention include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isoptyl alcohol, sec. -Butyl alcohol, t-butyl alcohol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, t-
Aliphatic chain monoalcohols such as amyl alcohol, neopentyl alcohol, hexyl alcohol, pentyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol; alicyclic monoalcohols such as cyclopentyl alcohol, cyclohexyl alcohol; ethylene glycol, 1,2- Propylene glycol, 1,3
-Aliphatic chain diols such as propylene glycol;
1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,2-cyclohexanediol, 1,
Alicyclic diols such as 3-cyclohexanediol and 1,4-cyclohexanediol; aliphatic polyols such as glycerin and pentaerythritol; and the like. These alcohols can be used either individually or as a mixture of two or more kinds at an arbitrary ratio.

(Mixed solvent) In the method of the present invention, crude naphthalene dicarboxylic acid is dissolved in the mixed solvent of the above amines and alcohols for crystallization. The mixing ratio of amines and alcohols is 1:99 to 99: 1 by weight, preferably 5:95 to 95: 5.

The amount of the mixed solvent of amines and alcohols used may be an amount sufficient to dissolve the crude naphthalene dicarboxylic acid at the temperature at which the dissolution operation is performed, and the mixing ratio of amines and alcohols and Since it varies depending on the temperature at which it is dissolved, it cannot be specified unconditionally, but it is usually in the range of 0.5 to 100 times by weight, preferably 1 to 50 times by weight, with respect to the crude naphthalenedicarboxylic acid. If the amount of the mixed solvent is less than the above range, a sufficient crystallization effect cannot be obtained, and even if it is used in excess of the above range, the crystallization effect does not change and the amount of solvent used increases, which is rather uneconomical. Is. The higher the melting temperature, the better, but usually room temperature to
It is carried out at 350 ° C, preferably 60 to 250 ° C. The pressure at this time is not particularly limited.

(Crystallization Operation) The crystallization operation of the present invention is performed in the following procedure. That is, the crude naphthalene dicarboxylic acid dissolved in a predetermined amount of mixed solvent is dissolved in a predetermined amount of mixed solvent, and if there is insoluble matter, the insoluble matter is removed by filtration. At this time, it may be treated with activated carbon or the like. When treating with activated carbon, a predetermined amount of activated carbon is added to a mixed solvent in which crude naphthalene dicarboxylic acid is dissolved, and the mixture is heated and stirred, and then the crude naphthalene dicarboxylic acid is dissolved in a column filled with activated carbon even in a batch treatment of filtering. Either the method of passing the mixed solvent may be used.

Then, if necessary, a predetermined amount of the mixed solvent may be recovered by an operation such as distillation and the solution may be concentrated. Then, the mixed solvent in which the crude naphthalenedicarboxylic acid is dissolved is cooled, and the precipitated naphthalenedicarboxylic acid is filtered and recovered. The cooling temperature is lower than the melting temperature by 40 ° C. or more, and is −30 to 100 ° C., preferably −20 to 60 ° C.
The range is.

Alternatively, instead of cooling or after cooling, an acid may be added to precipitate crystals. Examples of the acid used for precipitating naphthalenedicarboxylic acid include aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, monochloroacetic acid, monobromoacetic acid, trifluoroacetic acid, trichloroacetic acid; hydrochloric acid and hydrogen bromide. , Inorganic acids such as sulfuric acid, nitric acid, phosphoric acid and perchloric acid. The acid may be added as it is or in the form of an aqueous solution, but it is preferable to add an aliphatic carboxylic acid such as acetic acid as it is from the viewpoint of easy post-treatment.

The amount of the acid used is 0.1 to 10 relative to the amines in the solution in which the crude naphthalene dicarboxylic acid is dissolved.
Equivalent amount, preferably 0.3 to 6 equivalent amount. By the above operation, the precipitated naphthalenedicarboxylic acid crystals are filtered and dried to obtain a purified naphthalenedicarboxylic acid. The mother liquor of the mixed solvent after filtering the precipitated naphthalenedicarboxylic acid contains impurities and coloring substances, but usually without any special treatment, or if necessary, purified and repeatedly used for crystallization. be able to.

When no acid is added during crystallization, the amines used for crystallization are attached to the crystals of naphthalenedicarboxylic acid obtained by crystallization and filtration. Preferably. As the acid used for washing, for example, formic acid, acetic acid, propionic acid, butyric acid, monochloroacetic acid, monocarboxylic acetic acid, trifluoroacetic acid, aliphatic carboxylic acids such as trichloroacetic acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,
There are inorganic acids such as perchloric acid. Of these, acetic acid is particularly preferable. These acids, as they are, or
Any of those diluted with a solvent such as water, alcohols and ketones to an arbitrary concentration can be used.

The amount of acid used for washing is 0.5 to 20 relative to the naphthalenedicarboxylic acid obtained by crystallization and filtration.
It is in the range of weight times, preferably 1 to 10 times.

[0025]

The naphthalene dicarboxylic acids are N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO).
It dissolves to some extent in pyridine, but hardly dissolves in other organic solvents and water. Therefore, it hardly dissolves in amines and alcohols alone (Comparative Example). However, when a mixed solvent of amines and alcohols is used, surprisingly, the solubility of naphthalenedicarboxylic acids is dramatically improved, and the temperature dependence of the solubility becomes extremely large, Crystallization purification of the crude naphthalene dicarboxylic acid is very easy.

Further, by adding an acid such as an aliphatic carboxylic acid to the mixed solvent of the present invention, the solubility of naphthalenedicarboxylic acid is significantly reduced, so that naphthalenedicarboxylic acid of high purity and good hue can be obtained. it can.

[0027]

INDUSTRIAL APPLICABILITY By using the method of the present invention, naphthalenedicarboxylic acid of high purity and good hue can be recovered with good recovery rate from crude naphthalenedicarboxylic acid containing impurities and coloring components obtained by the oxidation reaction of dialkylnaphthalene. It can be manufactured effectively.

[0028]

EXAMPLES The present invention will be described in detail below with reference to Examples and Comparative Examples. The purity of naphthalenedicarboxylic acid was measured by high performance liquid chromatography. In addition, as for the hue, 10 g of a 25% methylamine aqueous solution was added to 1 g of the sample.
It was dissolved in ml, and the absorbance at a wavelength of 500 nm (hereinafter abbreviated as OD) was measured using a 10 mm quartz cell and evaluated by the value.

(Reference Example) 500 having a reflux condenser, a gas introduction pipe, a raw material feed pump, a back pressure regulator and an induction stirrer
In a titanium autoclave made of titanium, 200 g of acetic acid, 9.4 g (37.5 mmol) of cobalt acetate / tetrahydrate, 9.2 g (37.5 mmol) of manganese acetate / tetrahydrate, and 7.4 g (75. 0 mmol) and 5.9 g (75.0 mmol) of pyridine were charged, the inside of the reaction system was replaced with nitrogen, and the system pressure was adjusted to 30 kg / cm ² with a back pressure regulator.
It became GP. The internal temperature was heated to 200 ° C., and air was supplied at 4 Nl / min so that the internal pressure was maintained at 30 kg / cm ² GP. When the system is stable 2,
79.6 g (375 mmol) of 6-diisopropylnaphthalene was continuously fed over 4 hours. After the supply of 2,6-diisopropylnaphthalene was completed, the inside of the system was kept at 200 ° C. for 30
The air supply was continued for 1 hour while maintaining the kg / cm ² GP.
After completion of the reaction, the autoclave was cooled to room temperature, the precipitated solid was collected by filtration, and washed with 40 g of acetic acid. The solid was dried to obtain 67.2 g of a light brown solid. The yield of this crude 2,6-naphthalenedicarboxylic acid was 80.6.
%, And the purity was 97.2%. The OD was 3.44.

(Example 1) The crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was added to a 200 ml flask.
5 g, 46.5 g of methanol, and 31.0 g of triethanolamine were charged, and the mixture was heated and dissolved at 80 ° C. next,
6 columns with a jacket pre-filled with 4 g of activated carbon
Keep the temperature at 8 ° C and add the above mixed solution to LHSV = 1.0hr.
^-1 was passed. 88.4 g of the collected mixed solution was cooled to room temperature, and the precipitated crystals were filtered. At this time, the recovered filtrate was 60 g. 27 g of separated crystals and 4 g of acetic acid
0 g was placed in a flask, washed at room temperature, and the crystals were separated by filtration.
Rinse with 10 g of acetic acid. When the obtained crystals were dried under reduced pressure, 10.2 g of purified 2,6-naphthalenedicarboxylic acid was obtained. The recovery rate is 75.6% and the purity is 9
The OD was 9.1% and the OD was 0.044.

(Example 2) The crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was added to a 200 ml flask.
0 g, 60.0 g of methanol, and 15.0 g of triethanolamine were charged, and the mixture was heated and dissolved at 80 ° C. next,
6 columns with a jacket pre-filled with 4 g of activated carbon
Keep the temperature at 8 ° C and add the above mixed solution to LHSV = 1.0hr.
^-1 was passed. 85.0 g of the collected mixed solution was cooled to room temperature, and the precipitated crystals were filtered. At this time, the recovered filtrate was 60 g. 12 g of separated crystals and acetic acid 2
0 g was placed in a flask, washed at room temperature, and the crystals were separated by filtration.
Rinse with 5 g of acetic acid. When the obtained crystals were dried under reduced pressure, 6.1 g of purified 2,6-naphthalenedicarboxylic acid was obtained. The recovery rate is 50.8% and the purity is 99.3.
%, OD was 0.039.

Example 3 In a 200 ml flask, the crude 2,6-naphthalenedicarboxylic acid 10.
0 g, methanol 15.0 g, and triethylamine 1
5.0 g was charged and dissolved by heating at 65 ° C. Next, a column with a jacket pre-filled with 4 g of activated carbon was placed at 67 ° C.
The mixture was kept warm and the above mixed solution was passed through at LHSV = 0.5 hr ⁻¹ . 43.9 g of the collected mixed solution was cooled to room temperature, and the precipitated crystals were filtered. At this time, the collected filtrate was 26 g. 17 g of separated crystals and 30 g of acetic acid
Was placed in a flask and washed at room temperature, crystals were filtered off, and rinsed with 10 g of acetic acid. When the obtained crystals were dried under reduced pressure, 5.6 g of purified 2,6-naphthalenedicarboxylic acid was obtained. The recovery rate is 56.3% and the purity is 99.6.
%, OD was 0.022.

(Comparative Example 1) 1.0 ml of crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was placed in a 200 ml flask.
g and 60.0 g of methanol were charged and the mixture was heated under reflux at 80 ° C. for 4 hours, but the crude 2,6-naphthalenedicarboxylic acid was hardly dissolved and the crystallization operation could not be performed.

Comparative Example 2 A 200 ml flask was charged with 1.0 of the crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example.
g and triethylamine (60.0 g) were charged and the mixture was heated under reflux at 80 ° C. for 4 hours, but the crude 2,6-naphthalenedicarboxylic acid was hardly dissolved, and the crystallization operation could not be performed.

(Comparative Example 3) The crude 2,6-naphthalenedicarboxylic acid 6.0 obtained in Reference Example was placed in a 200 ml flask.
10g and triethanolamine 60.0g were charged.
It melt | dissolved by heating at 0 degreeC for 30 minutes. The solution was cooled to room temperature, but no crystals were precipitated. Therefore, when the solution was concentrated by vacuum distillation, the solution gelled and the crystallization operation could not be performed.

Comparative Example 4 A 200 ml flask was charged with 1.0 of the crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example.
g, acetone 15.0 g, and triethanolamine 1
Although 0.0g was charged and the mixture was heated under reflux at 80 ° C for 4 hours, the crude 2,6-naphthalenedicarboxylic acid was hardly dissolved and the crystallization operation could not be performed.

(Comparative Example 5) The crude 2,6-naphthalenedicarboxylic acid 6.0 obtained in Reference Example was placed in a 200 ml flask.
g and 60.0 g of a 20% triethylamine aqueous solution were charged and dissolved by heating at 100 ° C. for 30 minutes. The mixed solution was cooled to room temperature, but no crystals were precipitated and the crystallization operation could not be performed.

(Comparative Example 6) 5.0 ml of the crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was placed in a 200 ml flask.
g, DMSO 27.1 g and activated carbon 0.4 g,
Dissolve by heating at 120 ℃ for 30 minutes, filter the activated carbon,
Rinse with 9 g O. Then, 28.8 g of DMSO was recovered by vacuum distillation. DMSO remaining in the flask
Is 7.0 g, which corresponds to 1.4 times the weight of the crude 2,6-naphthalenedicarboxylic acid. The contents of the flask were cooled to room temperature, and the precipitated 2,6-naphthalenedicarboxylic acid was filtered, rinsed with 5 g of DMSO and then dried to obtain 3.8 g of purified 2,6-naphthalenedicarboxylic acid. The recovery rate is 75.2% and the purity is 99.8.
%, OD was 2.87.

(Comparative Example 7) 3.0 ml of the crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was placed in a 200 ml flask.
g, DMF 74.8 g and activated carbon 0.5 g were charged, and 1
Dissolve by heating at 20 ° C for 30 minutes, filter the activated carbon, and add DMF1.
Rinse with 3 g. Then, 81.6 g of DMF was recovered by vacuum distillation. The DMF remaining in the flask was 6.
At 0 g, this corresponds to 2.0 times the weight of the crude 2,6-naphthalenedicarboxylic acid. When the content in the flask was cooled to room temperature, the precipitated 2,6-naphthalenedicarboxylic acid was filtered, rinsed with 5 g of DMF and then dried.
5 g of purified 2,6-naphthalenedicarboxylic acid was obtained. Recovery rate is 85.0%, purity is 98.5%, OD
Was 1.62.

Example 4 In a 100 ml flask, 3.0 of crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was used.
g, methanol 21.0 g, and triethanolamine 10.0 g were charged and dissolved at room temperature. Next, a column with a jacket pre-filled with 2.5 g of activated carbon was placed at 68 ° C.
The mixture was kept warm and the above mixed solution was passed at LHSV = 1.0 hr ⁻¹ . After passing the whole amount, a mixed solution of 15 g of methanol and 5 g of triethanolamine was further passed. 30 g of acetic acid was added to 53.0 g of the collected mixed solution to precipitate crystals, and the precipitated crystals were filtered. When the separated crystals were washed with methanol and dried, 2.8 g of purified 2,6-
Naphthalenedicarboxylic acid was obtained. The recovery rate is 92.
At 3%, the purity was 99.8% and the OD was 0.017.

Example 5 In a 100 ml flask, 3.0 of crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was added.
g, methanol 20.0 g, and triethylamine 6.
0 g was charged and dissolved at room temperature. Next, activated carbon 2.
The jacketed column filled with 5 g was kept warm at 68 ° C., and the above-mentioned mixed solution was passed through at LHSV = 0.5 hr ⁻¹ . After passing the whole amount, a mixed solution of 10 g of methanol and 3 g of triethylamine was further passed. Collected mixed solution 4
1. 30 g of acetic acid was added to g to precipitate crystals, and the precipitated crystals were filtered. The separated crystals were washed with methanol and dried to obtain 2.5 g of purified 2,6-naphthalenedicarboxylic acid. The recovery rate is 84.0%,
The purity was 99.5% and the OD was 0.015.

Comparative Example 8 In a 100 ml flask, 3.0 of crude 2,6-naphthalenedicarboxylic acid obtained in Reference Example was used.
g, methanol 25.0 g, triethanolamine 1
0.0 g and activated carbon 0.5 g were charged and stirred at 80 ° C. for 1 hour. The mixture was cooled to room temperature and the activated carbon was filtered. 63.0 g of acetone was added, and the precipitated crystals were collected by filtration. To the obtained crystals, 46.0 g of acetone was added, which was heated and washed, cooled, filtered, and dried to obtain 4.8 g of pale yellow crystals. The purity of this crystal is 44.6%
Thus, a large amount of triethanolamine remained.

(Comparative Example 9) A crystallization operation was performed in the same manner as in Comparative Example 8 except that 60.0 g of toluene was used instead of acetone. Toluene was uniformly mixed with a methanol / triethanolamine mixed solvent. They did not mix with each other, and crystals did not precipitate.

(Comparative Example 10) A crystallization operation was performed in the same manner as in Comparative Example 8 except that 60.0 g of hexane was used instead of acetone, but toluene was uniformly mixed with the methanol / triethanolamine mixed solvent. They did not mix with each other, and crystals did not precipitate.

(Comparative Example 11) A crystallization operation was performed in the same manner as in Comparative Example 8 except that 150 g of distilled water was used instead of acetone, but no crystals were deposited at all.

(Comparative Example 12) A crystallization operation was performed in the same manner as in Comparative Example 8 except that 150 g of methanol was used instead of acetone, but no crystals were deposited.

Claims (1)

[Claims] 1. A process for producing naphthalenedicarboxylic acid, which comprises dissolving a crude naphthalenedicarboxylic acid obtained by oxidizing di-substituted naphthalene compounds in a mixed solvent of amines and alcohols and crystallizing the solution.