JP2730390B2 - Method for producing naphthalenedicarboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid phase oxidation of diisopropylnaphthalene (hereinafter sometimes referred to as "DIPN") with molecular oxygen to obtain naphthalenedicarboxylic acid (hereinafter referred to as "NDCA"). There is a manufacturing method. NDCA is a raw material for producing polyesters and polyamides, such as polyethylene naphthalate (PEN), which have high heat resistance, high strength, and excellent characteristics as an engineering plastic, such as low oxygen passage, and the like.

[0002]

2. Description of the Related Art A method for producing NDCA by subjecting DIPN to liquid phase oxidation with molecular oxygen in the presence of a catalyst comprising a heavy metal such as cobalt or manganese and a bromine compound is known.

[0003] The oxidation reaction of DIPN is not as easy as the oxidation of 2,6-dimethylnaphthalene, and known oxidation conditions for 2,6-dimethylnaphthalene, for example, JP-B-56-3337.
The method described in No. 2 is applied to the liquid phase oxidation of 2,6-DIPN.
The yield of NDCA is below 50%, producing a large amount of by-products and tar-like substances and products of naphthalene ring cleavage such as trimellitic acid. Thus, in the case of oxidizing the isopropyl group, the inability to smoothly oxidize the oxidized intermediate to the carboxylic acid is a cause of the difficulty in selective liquid phase oxidation.

Various solutions have been proposed (JP-A-1-121240, JP-B-63-250344, JP-A-1-160943, JP-A-60-89445, JP-A-60-89445). 89446
Issue). Of these, the method described in Japanese Patent Application Laid-Open No. 60-89445 discloses a method in which 2,6-DIPN is dissolved in a solvent containing at least 50% by weight of an aliphatic monocarboxylic acid having 3 or less carbon atoms.
Or, in the presence of a catalyst comprising a heavy metal comprising manganese and bromine, the heavy metal is present in at least 0.
It is a liquid phase air oxidation method using 2 moles and is disclosed in Japanese Patent Application Laid-Open No. 60-89446.
The method described in the publication is a liquid phase air oxidation method in which the heavy metal is present in an amount of at least 1% by weight based on the solvent. JP-A-60-
In the examples disclosed in JP 89445 and JP-A-60-89446, by using a heavy metal in an acetic acid solvent in a large amount of 0.28 to 3.9 mol per 1 mol of 2,6-DIPN, 2,6- NDCA
Has been obtained with a high yield of 70-90%. Although the effect of using a large amount of catalyst is not clear, the catalyst is deactivated by the oxidation intermediate generated in large amounts at the beginning of the reaction, and activation and regeneration in the reaction system are slow. The necessity is described in JP-A-60-89445 and JP-A-60-89446.

Regarding the reaction conditions, in the examples described in JP-A-60-89445 and JP-A-60-89446, the reaction temperature is 160 to 200 ° C., and the reaction pressure is 20 to 30 kg / cm ² G (gauge). Pressure), and in the embodiment described in JP-A-1-121240.
180-200 ° C, reaction pressure 15-30 kg / cm ² G,
In the examples described in JP-A-63-250344, the reaction pressure is 180 to 200 ° C. and the reaction pressure is 15 kg / cm ² G. In the examples described in JP-A-1-160943, the temperature is 200 ° C. and 30 kg / cm ² G. .

The above prior arts have in common that acetic acid and / or propionic acid are used as solvents, and D and D are used in the presence of a heavy metal catalyst such as cobalt or manganese and a bromine compound catalyst.
When producing NDCA by subjecting IPN to liquid phase air oxidation, D
Using a large amount of heavy metal and bromine catalyst for IPN,
NDCA is obtained under high-temperature and high-pressure conditions of 160 to 200 ° C. and 15 to 30 kg / cm ² G.

[0007]

In any of the above-mentioned conventional methods for producing NDCA by oxidizing DIPN, the catalyst is deactivated during the reaction. In addition, a large amount of heavy metal catalyst and bromine compound must be used, and the reaction temperature and the reaction pressure are high.

[0008] The present invention is intended to provide a high-quality NDCA which has a very small reduction in the activity of the cobalt and manganese catalysts, is stable over a long period of time even when the catalyst is recycled, and has a high yield.
It is an object of the present invention to provide a method capable of producing a compound and reducing the reaction temperature and the reaction pressure.

[0009]

Means for Solving the Problems The present inventors have solved the above-mentioned problems, and have conducted liquid phase oxidation of DIPN with a molecular oxygen-containing gas in the presence of heavy metals such as cobalt and manganese and a bromine compound to convert NDCA to NDCA. Various methods for obtaining the same were examined. As a result, a large amount of heavy metal and bromine compound catalyst is used for DIPN, and 160 to 200 ° C., 15 to 30 kg / cm ²
Liquid phase oxidation of DIPN under high temperature and high pressure
Under the conditions for producing A, it was found that the NDCA yield in the initial stage certainly obtained a high value, but on the other hand, the activity of the cobalt and manganese catalysts was significantly reduced (deteriorated). When the catalyst was recycled, it was difficult to maintain the initial activity, and the NDCA yield decreased with time, and the amount of impurity by-products increased at the same time. By these,
It has been found that not only the yield of the product NDCA is reduced but also the purity is lowered and the hue is deteriorated, which is undesirable for industrial production. If recycling is difficult, a large amount of fresh catalyst must be re-input in order to maintain the production rate of NDCA, and the recovery cost is increased due to an increase in the amount of waste catalyst.
The disadvantage of increased manufacturing costs has been found.

The present inventors have conducted intensive studies on a method for obtaining NDCA by subjecting DIPN to liquid phase oxidation with a molecular oxygen-containing gas in the presence of a heavy metal such as cobalt or manganese and a bromine compound. By adding at least one organic acid selected from the group consisting of trichloroacetic acid and tribromoacetic acid, it is possible to surprisingly suppress catalyst deterioration that could not be solved by conventional oxidation techniques, and to recycle the catalyst. Even when used, the initial activity can be maintained for a long time,
A decrease in the CA yield and an increase in the amount of impurity by-products can be suppressed, and as a result, high-quality N
They found a method for producing DCA, and completed the present invention.

That is, the present invention provides a method for producing naphthalenedicarboxylic acid by oxidizing diisopropylnaphthalene with molecular oxygen in acetic acid or propionic acid containing cobalt, manganese and bromine compounds or a mixed solution thereof, comprising the steps of: Provided is a method for producing naphthalenedicarboxylic acid, characterized by containing at least one organic acid selected from the group consisting of trichloroacetic acid and tribromoacetic acid.

The production method of the present invention is characterized in that at least one organic acid selected from the group consisting of trifluoroacetic acid, trichloroacetic acid and tribromoacetic acid is used. The composition of the organic acid is not limited, but among them, trichloroacetic acid is preferred.

The addition amount is 0.1 to 1 mol, preferably 0.1 to 0.5 mol, per 1 mol of the total amount of heavy metals of cobalt and manganese described below. If the amount of the organic acid is out of the above range, the deterioration of the cobalt / manganese catalyst over time (decrease in activity) cannot be suppressed. Even if an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, or hydrobromic acid is added in place of the organic acid, the same effect cannot be expected, and the catalyst is deactivated in return, or a phenolic oxidation inhibitor is used. A phenomenon in which the oxidation reaction was stopped by a small amount of by-product was observed. In particular, in the case of nitric acid, corrosive gas is generated by decomposing itself, or because of its low boiling point, it flows out of the system along with off-gas and is concentrated in a cooled place. Hydrobromic acid is
It is used as a bromine source, which is an auxiliary catalyst for the cobalt / manganese catalyst. However, if it is added in a large amount as in the above range, a suitable Br / (Co + Mn) ratio which will be described later is deviated. Adversely affect

The method of adding the organic acid includes cobalt,
It is preferable to add in advance to an acetic acid and / or propionic acid solution containing manganese and a bromine compound.

As the diisopropylnaphthalene (DIPN) as a raw material in the present invention, all isomers and mixtures thereof can be used in addition to 2,6- and 2,7-isomers. The DIPN supply amount is based on the solvent used.
It may be 4 to 40% by weight.

As the solvent used in the present invention, acetic acid and / or propionic acid or a mixture of acetic acid and / or propionic acid with another solvent may be used. When a mixture of acetic acid and / or propionic acid and another solvent is used as the oxidizing solvent, the proportion of acetic acid and / or propionic acid in the solvent is at least
It is preferred to keep it at 50% by weight or more. If it is less than 50% by weight, the oxidation rate is suppressed, and the yield of NDCA is undesirably reduced. As the other solvent, a solvent stable to oxidation, such as benzene, monochlorobenzene, and monobromobenzene, is used.

Although the presence of water is tolerated to some extent, the presence of a large amount is not preferred because it inhibits oxidation. The water content is preferably 10 mol or less based on the total molar amount of cobalt and manganese metal. If it exceeds 10 moles, the catalytic activity decreases and the NDCA yield decreases.

As the oxidation catalyst, a heavy metal comprising cobalt and manganese and a bromine compound are used in combination. Examples of cobalt and manganese include oxides, hydroxides, carbonates, organic acid salts, and halides. Of these, organic acid salts, particularly acetate salts, are preferred. Examples of the bromine compound include inorganic bromine compounds such as bromine (Br ₂ ), hydrogen bromide and hydrogen bromide, and alkyl bromides such as methyl bromide, ethyl bromide, propyl bromide and ethylene bromide. Among them, hydrogen bromide, sodium bromide, potassium bromide, ammonium bromide, cobalt bromide and manganese bromide are particularly preferred.

By using cobalt and manganese in combination, a higher catalytic action is observed as compared with the case where cobalt or manganese is used alone. The ratio of each heavy metal used as a catalyst is 0.1 ≦ Co / (Co + Mn) ≦ 0.
9, particularly preferably 0.2 ≦ Co / (Co + Mn) ≦ 0.7. Outside this range, the NDCA yield decreases.

[0020] The D of heavy metal, which is the sum of cobalt and manganese,
The amount used relative to IPN is expressed as a molar ratio, 0.1 ≦
(Co + Mn) / DIPN ≦ 10, especially 0.5 ≦ (Co + Mn) / DIP
N ≦ 4 is preferred. Below this range, the yield of NDCA decreases and the amount of trimellitic acid by-product increases significantly. Above this range, a large amount of catalyst will be used,
The generated and precipitated NDCA is accompanied by heavy metals, which not only lowers the purity of NDCA but also leads to catalyst loss.
In addition, the catalyst is deposited on the blowing tube of the molecular oxygen-containing gas, which increases the reactor size and lowers NDCA productivity,
Industrially undesirable situations such as blockage occur.

The amount of the bromine compound used as the oxidation reaction accelerator relative to the total amount of the cobalt and manganese metals is expressed in a molar ratio of 0.1 ≦ Br / (Co + Mn) ≦ 1, particularly 0.2 ≦
It is preferred that Br / (Co + Mn) ≦ 0.5. Below this range, the oxidation reaction does not proceed smoothly and the NDCA yield decreases. Above this range, an addition reaction of bromine to the naphthalene ring occurs, resulting in a decrease in NDCA yield, a decrease in NDCA purity and quality deterioration, and an increase in the amount of methyl bromide entrained in the exhaust gas. It is not preferable because a problem of contamination occurs.

As the molecular oxygen-containing gas, air can be used as it is. Further, oxygen or air diluted with an inert gas can be used. The oxygen partial pressure is preferably 0.2 to ² kg / cm ² .

The reaction is preferably carried out at a temperature in the range of 150 to 180 ° C. Below this range, oxidation of DIPN to the oxidized intermediate proceeds rapidly, but ND
The oxidation to CA does not proceed smoothly, and the NDCA yield decreases. If it exceeds this range, the burning loss of acetic acid or propionic acid as a solvent increases, which is not economically preferable. The reaction time may be from 0.5 to 5 hours.

The pressure to be used may be any pressure at which the liquid phase can be maintained in the reactor. If it exceeds 10 kg / cm ² G, the burning loss of acetic acid and / or propionic acid constituting the solvent increases. Is not preferred. The reaction pressure in the case of using air of 10 kg / cm ² G or less is sufficient. Usually, the reaction pressure may be between 5 and 10, especially between 6 and 8 kg / cm ² G.

In carrying out the oxidation reaction of the method of the present invention, diisopropylnaphthalene and a molecular oxygen-containing gas are simultaneously supplied to a heated gas-liquid mixing tank, brought into contact in advance, and gas-liquid mixed. It is desirable to feed the gas-liquid mixture into an acetic acid and / or propiolenic acid solution containing cobalt, manganese, organic acids and bromine compounds pre-oxidized with a molecular oxygen-containing gas. The gas-liquid mixing tank only needs to have a structure in which the oxygen-containing gas and the raw material DIPN, which is a liquid, can be mixed efficiently and efficiently, and the structure is not limited. The melting point of raw material DIPN, for example, 2,6-DIPN is 70
℃ and easy to solidify. The gas-liquid mixing tank is set at 100 to 300 ° C., particularly 200 to 250 ° C. in order to prevent blockage of the line due to solidification and to increase the efficiency of diffusion of the raw material into the acetic acid and / or propionic acid solution containing the catalyst and the organic acid. It is preferable to heat in the range described above. To prevent solidification of 2,6-DIPN in the gas-liquid mixing tank, benzene, monochlorobenzene,
It may be diluted with an oxidation-stable solvent such as monobromobenzene. The supply rate of the molecular oxygen-containing gas is calculated as DI
It may be from 1000 l to 5000 l per mole of PN. The gas-liquid mixing time is not particularly limited as long as gas-liquid contact can be sufficiently performed.

Cobalt, manganese, organic acids and bromine compounds are dissolved in acetic acid and / or propionic acid, or a mixture of acetic acid and / or propionic acid and another solvent, and subjected to an oxidation reaction. In order to produce NDCA, it is preferable to perform a pre-oxidation treatment with an oxygen-containing gas in advance. The treatment temperature is preferably in the range of room temperature to 180 ° C. If it exceeds this range, the loss of combustion of the solvent cannot be ignored. The pressure is preferably 1 to 10 kg / cm ² G. Processing time may be 0.5-2 hours. The method of pre-oxidation is carried out by stirring or supplying an oxygen-containing gas to the catalyst solution through a nozzle, a ring sparger, a sintered metal, a fine bubble diffuser made of porous porcelain, or the like.

The method of the present invention can be carried out batchwise or continuously, but a continuous or semi-batch system in which the raw material DIPN and the oxygen-containing gas are continuously supplied into the catalyst solution to carry out the oxidation reaction is preferred.

After the completion of the above oxidation reaction, if necessary, so-called post-oxidation (post-oxidation) may be performed to further complete the oxidation. Such post-oxidation is carried out as it is in the oxidation reaction vessel following the main oxidation reaction, or after the main oxidation reaction, once transferred to another vessel and brought into contact with molecular oxygen for a required time.

At this time, the reaction pressure and temperature of the post-oxidation do not need to be the same as those of the main reaction, and may be higher or lower.

Thereafter, the catalyst is separated from the catalyst by a usual post-treatment, for example, filtration, and subsequently washed with hot acetic acid or water to obtain a naphthalenedicarboxylic acid containing no catalyst. Crude naphthalenedicarboxylic acid can be further purified by crystallization. Alternatively, it can be purified by crystallization or precision distillation after conversion to dimethyl ester with methanol.

The spent catalyst is hardly modified,
Of course, the catalyst activity has not decreased. Therefore, the catalyst used once can be reused for the oxidation reaction any number of times without essentially replenishing any fresh catalyst.

[0032]

In the present invention, an organic acid is added, thereby preventing catalyst deterioration. Although the reason for the effect of the addition of the organic acid is not clear, it seems that the deactivation of the heavy metal catalyst by the trimellitic acid is effectively suppressed by the addition of the organic acid. That is, since trimellitic acid has two carboxyl groups at positions adjacent to the benzene ring (ortho positions), it is strongly coordinated with heavy metals such as cobalt and manganese to form poorly soluble salts and loses catalytic activity. The organic acid has a function of effectively suppressing the formation of this hardly soluble salt.

[0033]

Example 1 In a titanium autoclave having a capacity of 500 ml, as a catalyst, 0.1 mol of cobalt acetate tetrahydrate, 0.1 mol of manganese acetate tetrahydrate, 0.05 mol of sodium bromide, 0.15 mol of trimellitic acid,
0.05 mol of trichloroacetic acid and 250 ml of glacial acetic acid were charged and compressed air was supplied at 500 ml / min in terms of standard condition while maintaining the pressure at 8 kg / cm ² G. The temperature was gradually increased from room temperature to 170 ° C. over 1 hour to perform a pre-oxidation treatment of the catalyst. After reaching 170 ° C, increase the air supply to 2000ml / min,
A raw material solution in which 50 g of 2,6-DIPN was dissolved in 100 g of chlorobenzene was heated for 2 hours using a metering pump at a supply speed of 15.9 g / hr to 220 ° C. with compressed air using an external heater. The mixture was supplied into a SUS tube having an inner diameter of 21.4 mm and a length of 250 mm (filled with a helipack), mixed with gas and liquid, and then dispersed in the above catalyst solution. The air supply speed was maintained at 2000 ml / min in terms of standard conditions. After supplying the raw materials for 2 hours, only the compressed air was supplied and post-oxidation was performed for 2 hours. After completion of the reaction, the product was filtered, separated into a pale yellow solid and a filtrate containing a catalyst, and 2,6-NDCA contained in each was quantified by liquid chromatography. The conversion of DIPN is 100%, and the yield of 2,6-NDCA (based on 2,6-DIPN)
Was 86%. Further, the amount of acetic acid accompanying the off-gas, the amount of acetic acid contained in the filtrate (catalyst liquid) and the amount of acetic acid remaining in the crude NDCA were measured by gas chromatography to determine the amount of combustion loss with respect to the charged acetic acid. Was 0.4 mol% per hour.

Comparative Example 1 The same oxidation reaction as in Example 1 was carried out except that no trichloroacetic acid was added. As a result, the catalyst was partially deactivated by the added trimellitic acid, and the yield of 2,6-NDCA (2,6-NDCA)
DIPN standard) had dropped to 62%.

As is clear from the comparison between Example 1 and Comparative Example 1, the addition of trichloroacetic acid (Example 1) enables the oxidation reaction to be performed in high yield even in the presence of trimellitic acid.

Example 2 A 500 ml titanium autoclave was charged with 0.05 mol of cobalt acetate tetrahydrate, 0.05 mol of manganese acetate tetrahydrate, 0.025 mol of sodium bromide, 0.1 mol of trichloroacetic acid and 142 ml of glacial acetic acid as a catalyst. , While maintaining the pressure at 8 kg / cm ² G, the compressed air was converted to a standard state of 500 ml / min.
Supplied with The temperature was gradually increased from room temperature to 170 ° C. over 1 hour to perform a pre-oxidation treatment of the catalyst. After reaching 170 ° C, the air supply rate was increased to 1000 ml / min, and a raw material solution in which 50 g of 2,6-DIPN was dissolved in 100 g of chlorobenzene was used for 20 hours using a metering pump, and compressed air was supplied at a supply speed of 7.95 g / hr. With 220 ℃
The mixture was supplied into a SUS tube having an outer diameter of 1 inch, an inner diameter of 21.4 mm, and a length of 250 mm (filled with a Helipack), mixed with gas and liquid, and dispersed in the above catalyst solution. The air supply speed was maintained at 1000 ml / min in terms of standard conditions. 20
After completion of the time supply, the reactor was cooled to return the pressure to normal pressure, and then the product was filtered to separate into a pale yellow solid and a filtrate containing a catalyst. The solid was rinsed with hot acetic acid, and the contained catalyst component was recovered, mixed with the first filtrate, and acetic acid was distilled off under reduced pressure using a rotary evaporator to recover the used catalyst and trichloroacetic acid. 0.025 mol of sodium bromide and 142 ml of glacial acetic acid were newly added to the recovered catalyst to dissolve the catalyst, and reused in the next oxidation reaction as a circulating catalyst.

Under stirring again, while maintaining the pressure at 8 kg / cm ² G, compressed air was supplied at 500 ml / min in terms of standard condition, and the temperature was gradually raised from room temperature to 170 ° C. over 1 hour. Was pre-oxidized. After reaching 170 ° C, the air supply rate was increased to 1000 ml / min, and 50 g of 2,6-DIPN was added to 10 parts of chlorobenzene.
The raw material liquid dissolved in 0g was heated to 220 ° C with compressed air at a feed rate of 7.95g / hr for 20 hours using a metering pump at 220 ° C with an outer diameter of 1 inch, an inner diameter of 21.4mm, and a length of 250mm. Was supplied to a sus tube and mixed with gas and liquid, and then dispersed in the above catalyst solution. The air supply speed was maintained at 1000 ml / min in terms of standard conditions. After the supply was completed for 20 hours, the reactor was cooled and the pressure was returned to normal pressure. Then, the product was filtered to separate a pale yellow solid and a filtrate containing a catalyst. The solid is rinsed with hot acetic acid, and after recovering the contained catalyst component, mixing with the first filtrate, distilling off acetic acid under reduced pressure using a rotary evaporator, recovering the catalyst and trichloroacetic acid, and recovering trichloroacetic acid. As a result of measuring the residual amount, 0.01
Molar disappearance was noted. 0.025 mol of sodium bromide, 142 ml of glacial acetic acid, and 0.1 ml of trichloroacetic acid were used as the total recovery catalyst.
01 mol was newly added and dissolved and reused as a circulating catalyst.

The same operation was repeated two more times. Meanwhile, sodium bromide was added as described above, but no cobalt and manganese catalyst, and no trichloroacetic acid was added. The total amount of the pale yellow solid (crude NDCA) collected by filtration over a total of four times and 2,6-NDCA contained in the fourth filtrate
Was determined by liquid chromatography, and the reaction result was calculated. As a result, the yield of 2,6-NDCA (based on 2,6-DIPN) based on the total number of moles of DIPN supplied over 80 hours was 85%.

Comparative Example 2 Example 2 was repeated except that no trichloroacetic acid was added.
The same oxidation reaction was carried out. As a result, the 2,6-NDCA yield up to the 40th hour was based on the total molar amount of the supplied DIPN.
The results were as high as 85%, but decreased as the number of circulations of the catalyst increased, and decreased to 82% after 60 hours and 76% after 80 hours.

Example 3 An oxidation reaction was carried out in exactly the same manner as in Example 1 except that 0.15 mol of trifluoroacetic acid was added instead of trichloroacetic acid. As a result, the yield of 2,6-NDCA (based on 2,6-DIPN)
Was 84%.

Example 4 The same oxidation reaction as in Example 1 was carried out except that an equimolar mixture of trichloroacetic acid and tribromoacetic acid (0.05 mol in total) was added instead of trichloroacetic acid. As a result, the yield of 2,6-NDCA (based on 2,6-DIPN) was 87%.

Reference Example 1 An oxidation reaction was carried out in exactly the same manner as in Example 1 except that the amount of trichloroacetic acid was 0.5 mol. As a result, the conversion of DIPN was reduced to 56%, and the yield of 2,6-NDCA (2,
6-DIPN standard) was 0%.

Reference Example 2 An oxidation reaction was carried out in exactly the same manner as in Example 1 except that the addition amount of trichloroacetic acid was 0.01 mol. As a result, the 2,6-NDCA yield (based on 2,6-DIPN) was reduced to 65%.
This is probably because the catalyst deactivation effect due to the added trimellitic acid could not be suppressed.

[0044]

As described above, according to the present invention, it is possible to suppress the deterioration of the catalyst which cannot be solved by the conventional oxidation technology, and even if the catalyst is recycled, the initial activity is maintained for a long period of time. Can be maintained, and a decrease in NDCA yield and an increase in the amount of impurity by-products over time can be suppressed.
It is possible to produce high-quality NDCA with a stable yield over a long period of time. Also, only a small amount of catalyst is used, which is economical.

Claims (4)

(57) [Claims] 1. Diisopropyl naphthalene is cobalt,
A method for producing naphthalenedicarboxylic acid by oxidizing with molecular oxygen in acetic acid or propionic acid containing manganese and bromine compounds or a mixed solution thereof, wherein at least one selected from the group consisting of trifluoroacetic acid, trichloroacetic acid and tribromoacetic acid. For producing naphthalenedicarboxylic acid, characterized by containing at least one organic acid 2. The method for producing naphthalenedicarboxylic acid according to claim 1, wherein the content of the organic acid is 0.1 to 1 mol per 1 mol of the total amount of heavy metals of cobalt and manganese. 3. The method according to claim 1, wherein the diisopropylnaphthalene is 2,6-diisopropylnaphthalene, 2,7-diisopropylnaphthalene or a mixture thereof.
For producing naphthalenedicarboxylic acid as described 4. The oxidation is carried out at 150 to 180 ° C. under a reaction pressure of 10 kg / cm ^2.
4. The process for producing naphthalenedicarboxylic acid according to claim 1, wherein the process is performed at a pressure of G (gauge pressure) or less.