JPH10316615A - Production of 2,6-naphthalenedicarboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing 2,6-naphthalenedicarboxylic acid by which a substance inhibiting an oxidizing reaction can be prevented from accumulating and a high yield can be maintained when circulating an oxidizing reaction mother liquor for use in the liquid-phase oxidizing reaction of 2,6- dimethylnaphthalene. SOLUTION: The total amount of cobalt and manganese which are catalyst components is 50-300 mg atoms based on 1 g atom 2,6-dimethylnaphthalene at an atomic ratio of the manganese to the cobalt of (1:20) to (1:4) and an oxidizing reaction is carried out at 200-250 deg.C temperature in a method for oxidizing the 2,6-dimthylnaphthalene with an oxygen-containing gas in the presence of a catalyst containing the cobalt, manganese and bromine in a solvent containing a lower aliphatic carboxylic acid and producing 2,6- naphthalenedicarboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing 2,6-naphthalenedicarboxylic acid by liquid phase oxidation of 2,6-dimethylnaphthalene, and more particularly to a method for producing 2,6-naphthalenedicarboxylic acid by liquid phase oxidation in order to reuse an oxidation catalyst. Mother liquor from which 2,6-naphthalenedicarboxylic acid crystals separated (hereinafter referred to as oxidation reaction mother liquor)
To a reaction system efficiently.

[0002]

2. Description of the Related Art 2,6-Naphthalenedicarboxylic acid and its esters are useful substances as raw materials for high-performance polyesters. 2,6-Naphthalenedicarboxylic acid is produced by oxidizing 2,6-dialkylnaphthalene in a solvent containing a lower aliphatic carboxylic acid using a catalyst containing cobalt, manganese and bromine (JP-B-48-43893). No., JP 62
-212345, JP-A-3-220157, JP-A-4-266846, etc.).

[0003] In this oxidation reaction, the naphthalene ring itself is also easily oxidized, and trimellitic acid is produced. Trimellitic acid tends to form a strong complex with the metal catalyst for oxidation. Such complexed metals are difficult to remove from 2,6-naphthalenedicarboxylic acid. The mother liquor from which crystals of 2,6-naphthalenedicarboxylic acid have been separated contains trimellitic acid together with a useful metal catalyst for oxidation, but when returned to the oxidation reaction system, forms a complex with the metal catalyst for oxidation to form a metal with oxidation. Deactivate the catalyst.

To deal with such deactivation of the oxidation metal catalyst by trimellitic acid, Japanese Patent Application Laid-Open No. 6-509823 discloses that the oxidation reaction mother liquor is subjected to high-temperature heat treatment to reduce trimellitic acid and return to the reaction system. Have been described. According to Japanese Patent Publication No. 6-503586, the ratio of gram moles of trimellitic acid to the total gram atoms of cobalt and manganese in the oxidation reaction product should be less than about 1.0 when the oxidation reaction mother liquor is recycled to the oxidation reaction. Has been described.

JP-A-4-266846 discloses that a 2,6-dialkylnaphthalene is oxidized by a molecular oxygen-containing gas in a solution containing a catalyst containing cobalt, manganese and bromine in a solvent containing a lower aliphatic carboxylic acid. In the process for producing 2,6-naphthalenedicarboxylic acid, it is described that the mother liquor of the oxidation reaction is reused in the oxidation reaction. JP 7-4831
No. 4 circulates and reuses 2,6-dimethylnaphthalene in a method in which a catalyst containing heavy metals and bromine is dissolved in a solvent containing a lower aliphatic carboxylic acid in a solvent containing a lower aliphatic carboxylic acid with a molecular oxygen-containing gas. In this case, it is described that the catalyst is replenished so that the concentration of the heavy metal catalyst excluding the heavy metal ortho-benzenedicarboxylic acid complex contained in the solvent becomes 0.2% by weight or more.

[0006]

[Problems to be Solved by the Invention]
In order to heat-treat the oxidation reaction mother liquor at a high temperature, new equipment is required. Since the heat treatment is performed at a high temperature in the presence of a bromine compound, the apparatus is made of a high quality material. The preferred ratio of the mother liquor of the oxidation reaction which is circulated to the direct oxidation reactor in Japanese Patent Publication No. 6-503586 is about 10 to about 30%, and the rest requires oxalic acid treatment. Japanese Patent Application Laid-Open No. 4-266846 discloses that the yield is improved by reusing the mother liquor of the oxidation reaction for the oxidation reaction, and an example using 2,6-diisopropylnaphthalene and diethylnaphthalene as raw materials is disclosed. As a result of an experiment conducted by the present inventors using dimethylnaphthalene, no improvement in yield was obtained. In addition, the present inventors disclosed in JP-A-7-48
According to No. 314, improvement in the yield was not obtained even if the catalyst was replenished so that the concentration of the heavy metal catalyst excluding the ortho-benzenedicarboxylic acid complex of the heavy metal contained in the solvent was 0.2% by weight or more.

[0007] By circulating the oxidation reaction mother liquor, the catalyst component and the solvent component in the oxidation reaction mother liquor are effectively used,
Since the raw material components and intermediates contained in the mother liquor of the oxidation reaction and the fine particles of 2,6-naphthalenedicarboxylic acid are collected, it is desirable to increase the circulation rate as much as possible. However, the oxidation reaction mother liquor contains low levels of impurities and by-products together with the useful components as described above,
Substances that inhibit the oxidation reaction will accumulate, resulting in a decrease in yield. An object of the present invention is to provide a 2,6-naphthalenedicarboxylic acid capable of preventing the accumulation of substances that inhibit the oxidation reaction and maintaining a high yield when using the oxidation reaction mother liquor in the liquid phase oxidation reaction of dimethylnaphthalene. It is to provide a manufacturing method of.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for producing 2,6-naphthalenedicarboxylic acid having the above-mentioned problems, and as a result, increased the manganese concentration under specific catalyst conditions, By combining the conditions, accumulation of substances that inhibit the oxidation reaction is avoided, and it has been found that the oxidation reaction mother liquor can be recycled to the oxidation reactor at a high ratio without lowering the yield of 2,6-naphthalenedicarboxylic acid, The present invention has been reached.

That is, according to the present invention, 2,6-dimethylnaphthalene is oxidized with an oxygen-containing gas in a solvent containing a lower aliphatic carboxylic acid in the presence of a catalyst containing cobalt, manganese and bromine to form 2,6-naphthalenedicarboxylic acid. In producing the acid, the total amount of cobalt and manganese in the catalyst component is 50-300 milligram atoms per gram mole of 2,6-dimethylnaphthalene and the atomic ratio of manganese to cobalt is
1:20 to 1: 4, wherein the oxidation reaction is carried out at a temperature of 200 to 250 ° C., which is a process for producing 2,6-naphthalenedicarboxylic acid.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The purity of 2,6-dimethylnaphthalene used as a raw material for an oxidation reaction in the present invention is preferably 98%.
% By weight or more, more preferably 99% by weight or more. In order to recycle the oxidation reaction mother liquor at a high ratio without reducing the yield in the oxidation reactor, it is preferable to increase the purity of 2,6-dimethylnaphthalene used as a raw material for the oxidation reaction in the present invention. As the solvent for the oxidation reaction, lower aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid and butyric acid are used, and acetic acid is most preferred. Water may be contained in the solvent, but the content is 1 to 20% by weight, preferably 1 to 15% by weight, based on the total amount of lower aliphatic carboxylic acid and water added to the oxidation reaction zone. And more preferably 1 to 10% by weight. The ratio of the lower aliphatic carboxylic acid to 2,6-dimethylnaphthalene added to the oxidation reaction zone is in the range of 2: 1 to 12: 1, preferably in the range of 2: 1 to 6: 1.

As the oxidation catalyst, a cobalt compound, a manganese compound and a bromine compound are used. If necessary, heavy metal compounds such as iron, cerium, nickel and palladium may be added. As these cobalt, manganese and other heavy metal compounds, organic acid salts, hydroxides, halides, carbonates and the like can be exemplified, but acetates and bromides are particularly preferred. The bromine compound may be any compound as long as it dissolves in the reaction system to generate bromine ions, but hydrogen bromide, cobalt bromide and manganese bromide are particularly preferable.

In the present invention, in order to avoid accumulation of a reaction inhibitor such as trimellitic acid due to recycling of the oxidation reaction mother liquor, an appropriate amount of the catalyst component is particularly important.
The amount of the metal catalyst used is 50 to 50 as the total amount of cobalt and manganese per gram mole of 2,6-dimethylnaphthalene.
300 milligram atoms, preferably 100-250 milligram atoms. The amount of the metal catalyst used was increased by about 20 to 40% as compared with the case where the conventional oxidation reaction mother liquor was not recycled. It has the effect of reducing the adverse effects caused by the accumulation of reaction inhibiting substances such as trimellitic acid when recycled.

The atomic ratio of manganese to cobalt in the oxidation catalyst is between 20: 1 and 4: 1, preferably between 12: 1 and 5: 1. Conventional 2,
The atomic ratio of manganese to cobalt in the liquid phase oxidation of 6-dimethylnaphthalene is about 3: 1. On the other hand, by increasing the ratio of manganese according to the present invention, the amount of trimellitic acid produced decreases. Manganese is also more likely to form a complex with trimellitic acid than cobalt, and such a complex with trimellitic acid is separated from the mother liquor of the oxidation reaction together with the crystals of 2,6-naphthalenedicarboxylic acid. By increasing the value, the accumulation of trimellitic acid in the oxidation reaction when the oxidation reaction mother liquor is recycled is reduced.

2,6-Naphthalenedicarboxylic acid containing a metal salt of trimellitic acid is easy to be dissolved in an organic solvent by esterifying 2,6-naphthalenedicarboxylic acid with an alcohol.
The removal of the metal salt can be easily separated by a method such as separation from the insoluble metal salt as a naphthalenedicarboxylic acid ester. Therefore, by increasing the ratio of manganese, the amount of metal salt accompanying the crystal of 2,6-naphthalenedicarboxylic acid increases, but since the metal salt can be easily separated, the purification step of 2,6-naphthalenedicarboxylic acid is performed. The effect on the oxidation reaction mother liquor can be advantageously reduced.

The bromine component in the oxidation catalyst is 1-500 milligram atoms per gram mole of 2,6-dimethylnaphthalene,
Preferably it is 10 to 300 milligram atoms. When the bromine component is too small, the yield of 2,6-naphthalenedicarboxylic acid when the recycling rate of the oxidation reaction mother liquor is increased is lowered. On the other hand, if the bromine component is too large, a by-product of a bromine compound such as bromonaphthalenedicarboxylic acid increases.

The oxygen-containing gas used in the present invention includes oxygen gas or a gas obtained by mixing oxygen with an inert gas such as nitrogen or argon, and air is the most common. As the oxidation reactor, a stirring tank or a bubble column is used, but a stirring tank is preferably used to sufficiently stir the inside of the reactor. As a reaction system, a semi-batch system or a continuous system is suitably used. In the semi-batch mode, it is desirable to stop supplying the raw material and continue supplying the oxygen-containing gas for 5 to 60 minutes in order to complete the oxidation reaction. In the continuous system, it is desirable to provide a plurality of reactors in series to perform a sequential reaction in order to increase the reaction yield.

The temperature of the oxidation reaction is from 200 to 250 ° C., preferably from 200 to 240 ° C. If the reaction temperature is too low, the accumulation of the reaction inhibitor occurs when the recycling of the mother liquor of the oxidation reaction is repeated, and the yield of 2,6-naphthalenedicarboxylic acid decreases. If the reaction temperature is too high, the combustion loss of the lower aliphatic carboxylic acid in the solvent will increase. Therefore, the temperature of the oxidation reaction is
While the combustion of the reaction inhibitor occurs, the yield of 2,6-naphthalenedicarboxylic acid must not be reduced, and the combustion loss of the lower aliphatic carboxylic acid in the solvent must be within an acceptable range,
The above temperature range is extremely important when the oxidation reaction mother liquor is recycled by the method of the present invention, and an appropriate temperature is selected.

In the oxidation reaction, an oxygen-containing gas is continuously supplied to the reactor, and the gas after the reaction has a pressure of 5 to 40 kg / cm ² G,
It is preferably continuously withdrawn from the reactor to a pressure of 10 to 30 kg / cm ² G. The reactor is provided with a reflux condenser,
A large amount of solvent entrained in the exhaust gas and water generated by the oxidation reaction are condensed. The condensed solvent and water are usually refluxed to the reactor, but in order to adjust the water concentration in the reactor,
Part of the reaction is also taken out of the reaction system. The oxygen concentration in the exhaust gas from the reactor is 0.1 to 8% by volume (dry gas basis), preferably 1 to 5% by volume (dry gas basis).

The throughput of the starting material 2,6-dimethylnaphthalene in the oxidation reactor (the amount added to the unit liquid amount in the reactor per unit time) is 50 to 500 kg / m ³ hr. This throughput is a measure of the productivity of the reactor. The 2,6-naphthalenedicarboxylic acid produced by the oxidation reaction is in the form of a slurry, and is usually cooled under reduced pressure, passed through a crystallization tank, and subjected to 2,6-naphthalenedicarboxylic acid by a solid-liquid separator such as centrifugal sedimentation, centrifugal filtration, and vacuum filtration. The acid and the oxidation reaction mother liquor are separated.

The mother liquor of the oxidation reaction contains a lower aliphatic carboxylic acid as a solvent and water, a metal catalyst and a bromine compound for the oxidation reaction, and many active ingredients such as unreacted 2,6-dimethylnaphthalene and an oxidation reaction intermediate. And a reaction inhibitor such as trimellitic acid. The water contained in the oxidation reaction mother liquor includes water generated by the oxidation reaction in addition to water added to the reaction system. Therefore, when returning the oxidation reaction mother liquor directly to the reactor, it is necessary to remove water from the oxidation reaction mixture.
When a large amount of the mother liquor of the oxidation reaction is returned to the reactor according to the method of the present invention, a vapor mixture containing lower aliphatic carboxylic acid and water generated by heat generation during the oxidation reaction is extracted, and water generated by the oxidation reaction by distillation is removed. After the removal operation, it is desirable to return to the oxidation reactor.

According to the present invention, in the liquid phase oxidation of 2,6-dimethylnaphthalene, by combining specific catalyst conditions and oxidation conditions, 40% of the oxidation reaction mother liquor generated when separating the crystals of 2,6-naphthalenedicarboxylic acid is obtained. As described above, if necessary, almost 100% of the mother liquor of the oxidation reaction can be directly recycled to the oxidation reactor. The metal complex salt of trimellitic acid that accompanies the crystal of 2,6-naphthalenedicarboxylic acid is esterified with 2,6-naphthalenedicarboxylic acid with an alcohol to form 2,6-naphthalenedicarboxylic acid ester that is easily dissolved in an organic solvent. Thereby, the metal complex salt is easily separated as an insoluble substance. That is, during the esterification reaction of 2,6-naphthalenedicarboxylic acid, a metal salt such as trimellitic acid changes to a metal salt of 2,6-naphthalenedicarboxylic acid,
Even if the insoluble metal salt is returned to the oxidation reaction as it is, there is no accumulation of trimellitic acid, and manganese and cobalt can be advantageously recovered.

[0022]

Next, the present invention will be described in detail with reference to examples. Note that the present invention is not limited by these examples. In the following Examples and Comparative Examples, the entire amount of the mother liquor obtained in the recycling test was reused, and the metal salts attached to the crystals were supplemented with cobalt acetate tetrahydrate and manganese acetate tetrahydrate. The bromine was replenished with hydrobromic acid so as to be constant with bromine ions. The following abbreviations were used. NDCA: 2,6-Naphthalenedicarboxylic acid TMA: Trimellitic acid ALAC: Formylnaphthoic acid

Example 1 A 2000 ml titanium autoclave having a raw material supply port, a solvent supply port, a gas supply port, a gas discharge port, a reaction product outlet, a reflux condenser, an electromagnetic stirrer, a heating device and a liquid level detection device. Acetic acid, cobalt acetate tetrahydrate, manganese acetate tetrahydrate, a 47% by weight aqueous solution of hydrogen bromide and water are mixed and dissolved to obtain a cobalt concentration of 0.1% by weight, a manganese concentration of 0.6% by weight, and a bromine concentration of 0%. 650 g of a catalyst liquid having a concentration of 0.5% by weight and a water concentration of 3% by weight were charged, nitrogen gas was injected into the gas supply port to adjust the pressure to 20 kg / cm ² G, and the mixture was heated to 220 ° C. by a heating device. After the temperature and pressure are stabilized, the purity is 99.4% by weight.
The autoclave was supplied with 2,6-dimethylnaphthalene at 120 g / h and a catalyst solution having the same composition as above at 720 g / h, and air was introduced to adjust the oxygen concentration in the exhaust gas to 3%. Withdrawal of the reaction mixture was started 15 minutes after the start of the supply, and the supply of the raw material liquid and the catalyst liquid was continued for 8 hours while keeping the liquid level constant. The extracted reaction mixture is 70
Crystal filtration was performed at 80 ° C. to separate the crystal from the mother liquor of the oxidation reaction. The obtained crystals were dried and subjected to analysis. The oxidation reaction mother liquor is analyzed and adjusted by evaporating the generated water, replenishing the loss of cobalt, manganese, and bromine adhered to the crystals. The recycling test was repeated. Table 1 shows the results.

[0024]

[Table 1] Number of recycles 0 1 2 3 4 NDCA (mol%) 93.9 93.1 93.5 92.8 92.8 TMA (mol%) 1.98 2.49 2.36 2.56 2.50 ALAC (mol%) 0.20 0.24 0.19 0.20 0.20 2,6-dimethyl in Example 1 The total amount of cobalt and manganese per gram mole of naphthalene is 118 milligram atoms, and the atomic ratio of manganese to cobalt is
1: 6.43. According to Table 1, even if the oxidation reaction mother liquor is used repeatedly four times, the NDCA yield hardly decreases and the TMA
The by-product also shows a substantially constant value.

Comparative Example 1 A recycle test was conducted in the same manner as in Example 1 except that the catalyst solution was changed to a cobalt concentration of 0.24% by weight, a manganese concentration of 0.47% by weight, a bromine concentration of 0.5% by weight, and a water concentration of 3% by weight. Was repeated. Table 2 shows the results.

[Table 2] Recycled number 0 1 2 3 NDCA (mol%) 93.21 92.19 91.50 90.31 TMA (mol%) 2.23 3.18 3.70 4.36 ALAC (mol%) 0.51 0.58 0.81 0.78 1 gram mole of 2,6-dimethylnaphthalene in Comparative Example 1 The total amount of cobalt and manganese per unit is 118 milligram atoms, and the atomic ratio of manganese to cobalt is
1: 2.12. As shown in Table 2, by repeatedly using the mother liquor of the oxidation reaction, the proportion of ALAC was increased, the amount of TMA by-product was increased, and the NDCA yield was reduced.

Example 2 Except that the catalyst solution was made 0.12% by weight of cobalt, 0.9% by weight of manganese, 0.5% by weight of bromine and 3% by weight of water, and the catalyst solution was supplied at 480 kg / h. The recycle test was repeated as in Example 1. Table 3 shows the results.

[Table 3] Number of recycles 0 1 2 3 4 NDCA (mol%) 93.7 93.3 93.0 92.5 92.5 TMA (mol%) 2.23 2.76 2.91 3.13 3.00 ALAC (mol%) 0.19 0.24 0.48 0.17 0.20 2,6-dimethyl in Example 2 The total amount of cobalt and manganese per gram mole of naphthalene is 115 milligram atoms, and the atomic ratio of manganese to cobalt is
1: 8.04. According to Table 3, the NDCA yield was hardly reduced even if the oxidation reaction mother liquor was repeatedly used four times.
The by-product also shows a substantially constant value.

Comparative Example 2 In Example 2, the reaction temperature was 195 ° C. and the pressure was 18 kg / cm.
² G. Table 4 shows the results.

[Table 4] Number of recycles 0 1 2 3 4 NDCA (mol%) 92.5 91.6 90.9 89.8 89.8 TMA (mol%) 3.22 3.67 4.23 4.76 5.03 ALAC (mol%) 0.66 0.24 0.48 0.17 0.40 In Comparative Example 2, the reaction temperature was 195 ° C. In this case, by repeatedly using the mother liquor of the oxidation reaction, the amount of TMA by-product increased and the yield of NDCA decreased.

[0028]

As is clear from the examples, in the liquid phase oxidation reaction of dimethylnaphthalene, the specific catalytic conditions, especially the manganese concentration, are increased by the method of the present invention, and the oxidation reaction is carried out by combining this with the oxidation conditions. Accumulation of substances that inhibit the reaction can be avoided, and the mother liquor of the oxidation reaction can be recycled at an extremely high ratio without lowering the reaction yield. By circulating the oxidation reaction mother liquor, the catalyst component and the solvent component in the oxidation reaction mother liquor are effectively used, and the raw material components and intermediates and the 2,6-naphthalenedicarboxylic acid fine particles contained in the oxidation reaction mother liquor are used. Will be collected.
Therefore, according to the present invention, dimethyl 2,6-naphthalenedicarboxylate can be produced industrially very advantageously, and the present invention has great industrial significance.

Claims (2)

[Claims] 1. Production of 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-dimethylnaphthalene with an oxygen-containing gas in a solvent containing a lower aliphatic carboxylic acid in the presence of a catalyst containing cobalt, manganese and bromine The total amount of cobalt and manganese of the catalyst component is 50 to 300 milligram atoms per gram mole of 2,6-dimethylnaphthalene, and the atomic ratio of manganese to cobalt is 1:20 to 1: 4, A process for producing 2,6-naphthalenedicarboxylic acid, wherein the reaction is carried out at a temperature of from 200 to 250 ° C. 2. The process for producing 2,6-naphthalenedicarboxylic acid according to claim 1, wherein at least 40% of the mother liquor obtained by separating the crystals of 2,6-naphthalenedicarboxylic acid from the oxidation reaction product is recycled to the oxidation reactor. .