JPH06293697A - Method for producing naphthalenedicarboxylic acid - Google Patents

Abstract

(57) [Summary] [Objective] When oxidizing a dialkylnaphthalene to obtain a naphthalenedicarboxylic acid, to increase the grain size of fine crystals of the precipitated acid to facilitate separation. [Structure] In the oxidation step in the naphthalene dicarboxylic acid production process, the fine crystals of the acid contained in the reaction mother liquor, the washing filtrate, etc. are supplied to the oxidation reactor again, so that the particle size of the fine crystals becomes a size suitable for solid-liquid separation. What grows up.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a naphthalenedicarboxylic acid (hereinafter sometimes abbreviated as NDCA) by oxidizing a dialkylnaphthalene and / or an oxidized derivative thereof.

[0002]

2. Description of the Related Art NDCA and its ester (hereinafter, ester may be abbreviated as NDCA, etc.) are useful substances as polymer materials, dye intermediates and the like. In particular, polyethylene naphthalate formed from 2,6-NDCA and the like and ethylene glycol is more excellent in heat resistance and breaking strength than polyethylene terephthalate, and is attracting attention as a material for films, food packaging materials and the like.
Further, since polybutylene naphthalate resin has a higher crystallization rate and higher wet heat resistance than polybutylene terephthalate resin, NDCA or the like is useful as a resin raw material.

Conventionally, as a method for producing NDCA, a method of oxidizing dialkylnaphthalene and / or an oxidized derivative thereof with molecular oxygen in a solvent containing a lower aliphatic carboxylic acid using cobalt, manganese, bromine or the like as a catalyst. Have been proposed.

However, in either method,
Since the crystal grain size of the obtained crude NDCA is small and the solubility of NDCA in the reaction solvent is very small, the grain size of NDCA cannot be increased so much even if multi-stage crystallization is performed as in the terephthalic acid production process. There is a problem that solid-liquid separation in the separation step of the reaction mother liquor or the subsequent washing step, particularly solid-liquid separation by an industrially advantageous centrifugal separator, is extremely difficult.

[0005]

DISCLOSURE OF THE INVENTION In view of such circumstances, the present invention has as its object the NDCA obtained by oxidizing dialkylnaphthalene and / or its derivative.
NDCA is used to increase the crystal grain size and facilitate solid-liquid separation.
It is to provide a method for industrially producing the above.

[0006]

Means for Solving the Problems As a result of diligent studies on the relationship between the oxidizing conditions and the particle size of the obtained NDCA crystals, the present inventors have found that dialkylnaphthalene and / or its oxidized derivative is a lower aliphatic monocarboxylic acid. In the presence of a heavy metal oxidation catalyst and a catalyst composed of bromine in a solvent containing, when the molecular oxygen-containing gas is used for oxidation, the reaction product is subjected to solid-liquid separation, and the separated filtrate is circulated to the oxidation reactor. Then, it was possible to grow the particle size of the fine particles of the oxidized derivative contained in this filtrate, and as a result, solid-liquid separation of the reaction product was facilitated, leading to the completion of the present invention. It was

The present invention will be described in detail below.

Examples of the dialkylnaphthalene used as an oxidizing raw material in the present invention include dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene and the like, and its oxidized derivative is an oxidized intermediate of the dialkylnaphthalene such as formylnaphthoic acid and acetylnaphthoic acid. Alternatively, alkylacylnaphthalene such as methylacetylnaphthalene and methylbutyrylnaphthalene, diacylnaphthalene and the like can be mentioned. Of these, the 2,6-body is industrially useful.

In the method of the present invention, an aliphatic monocarboxylic acid having 1 to 5 carbon atoms, that is, formic acid, acetic acid, propionic acid, butyric acid, or a mixture thereof is used as the lower aliphatic carboxylic acid as a solvent. , Acetic acid and propionic acid are preferable, and acetic acid is particularly preferable. The amount of the solvent used is usually 2 to 15 times by weight, preferably 3 to 10 times by weight, the amount of dialkylnaphthalene and / or its oxidized derivative.

The oxidation catalysts used in the process of the present invention are heavy metal compounds and bromine compounds. As the heavy metal oxidation catalyst, cobalt and / or manganese are preferable, and cerium, nickel and the like may be added if necessary. These are used in the form of organic acid salts, halides, hydroxides, oxides, carbonates and the like, and fatty acid salts, particularly acetates and bromides are preferable.

The amount of the heavy metal oxidation catalyst used in the method of the present invention varies depending on the kind of the oxidizing raw material used, but is 0.1% by weight or more, preferably 0.5% by weight or more with respect to the solvent.

On the other hand, the bromine compound may be either an organic compound or an inorganic compound as long as it dissolves in an oxidation reaction system and generates a bromine ion. Specifically, molecular bromine (Br ₂ ), Hydrogen bromide, sodium bromide, potassium bromide, inorganic bromide such as ammonium bromide,
Alternatively, organic bromides such as alkyl bromide and brominated fatty acids such as bromoacetic acid can be used. Hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide, manganese bromide and the like are particularly preferable examples. Bromine is usually used in an atomic ratio of 0.01 to 2 with respect to the total weight of the heavy metal oxidation catalyst.

In the method of the present invention, crude NDCA is obtained by subjecting the reaction product obtained by oxidation to solid-liquid separation with a centrifuge. In this case, the centrifuge has an allowable solid concentration of 3 A decanter type (particularly, conveyor type) centrifugal settler having a high as high as -30% and capable of stable operation without clogging and continuous discharge of cake is preferably used.
When a separation plate type centrifugal settler is adopted, it is suitable for separating fine particles, but since the allowable solid concentration is as low as several% to 10%, it is necessary to use a large amount of solvent during the oxidation reaction. It is not preferable because the volumetric efficiency of the expensive oxidation reactor becomes poor. Further, the solid-liquid separation by the centrifugal dehydrator is not preferable because it has a drawback that the fine particles are likely to be clogged.

Crude NDCA can be further purified by removing the catalyst, reaction intermediates and by-products by washing with acetic acid, water, alcohol and the like, and the decanter type is also used for solid-liquid separation at this time. The centrifugal sedimentation machine of is preferably used.

The separation and collection diameter of the decanter type centrifugal settler is about 1 to 500 μm, and it is said that it is suitable for separating particles of about 2 μm or more, but crude NDCA obtained by oxidation of dialkylnaphthalene is preferable. Because of the small particle size, there have been many operating problems in the past.

The oxidation reaction temperature in the present invention is 180 ° C.
~ 220 ° C, preferably 185 ° C to 215 ° C, and when the oxidation is carried out at the reaction temperature in this range, the average particle size of the crystals of crude NDCA becomes about 2 µm or more, which is stable in a decanter type centrifugal settler. Although solid-liquid separation can be performed by solid-liquid separation, particles having a reaction temperature of less than 2 μm make solid-liquid separation difficult in the reaction mother liquor separation step. In particular, in the solid-liquid separation in the subsequent washing step, the particles that were originally agglomerated are destroyed,
Since it becomes finer, solid-liquid separation becomes more difficult. on the other hand,
If the reaction temperature is higher than this, side reaction products increase,
It is not preferable because the purity of the obtained NDCA is lowered and the combustion loss of the solvent is rapidly increased. On the other hand, if the reaction temperature is lower than this, the particle size of the obtained NDCA crystal becomes small, and solid-liquid separation in the separation step of the reaction mother liquor becomes more difficult.

The reaction pressure for the oxidation reaction may be any pressure as long as the reaction system is kept in the liquid phase at the reaction temperature, but is usually 1
About 0 to 30 kg / cm ² G is suitable.

As the molecular oxygen-containing gas used in the method of the present invention, oxygen gas or a mixed gas obtained by diluting it with an inert gas is used. Industrially, air is the most available and preferred.

[0019]

EXAMPLES The present invention will be specifically described below based on examples. The parts and% in the examples and comparative examples represent parts by weight and% by weight, respectively.

[0020]

Comparative Example 1 A titanium autoclave having a gas discharge pipe with a reflux condenser, a gas wiping pipe, a continuous feed pump for raw materials, and a stirrer was placed in 174 parts of acetic acid, 6.74 parts of cobalt acetate (tetrahydrate), and acetic acid. Manganese (tetrahydrate) 13.26
Parts, 47% hydrogen bromide water 1.40 parts, and water 12 parts. The water concentration in this catalyst liquid was 9%. The catalyst solution was stirred vigorously at a temperature of 200 ° C. and a pressure of 30 kg / cm ² G while adding 2,6-diethylnaphthalene 5
5 parts and compressed air were continuously fed in over 1.3 hours,
The oxidation reaction was carried out. After the reaction was completed, the reaction product was taken out, and the filtrate was used to separate a solid precipitate mainly composed of 2,6-NDCA. The purity of the obtained crude 2,6-NDCA was 95.0%, and the average particle size was as shown in Table 1.

[0021]

[Table 1]

In addition, mainly filtered and leaked 2,6-ND
The particle size distribution of the fine particles of CA is shown in Table 2.

[0023]

[Table 2]

[0024]

Comparative Example 2 Coarse 2,6 obtained by solid-liquid separation in Comparative Example 1
Table 3 shows the particle size distribution when coarse 2,6-NDCA particles leaked by filtration were mixed with -NDCA in an amount corresponding to the filtration leak rate.

[0025]

[Table 3]

[0026]

Example 1 The same experiment as in Comparative Example 1 was conducted, except that the catalyst and the solvent were added to the filtrate obtained in Comparative Example 1. After completion of the reaction, the reaction product was taken out and the particle size distribution of the precipitated crude 2,6-NDCA was measured.
Shown in.

[0027]

[Table 4]

The solid precipitate obtained mainly by solid-liquid separation of this reaction product by filtration was 95.0% in purity, and the filtration leakage rate was 2%.

[0029]

COMPARATIVE EXAMPLE 3 Acetic acid 161 was added to the same reactor as in Comparative Example 1.
Parts, cobalt acetate (tetrahydrate) 1.68 parts, manganese acetate (tetrahydrate) 3.29 parts, and 47% hydrogen bromide water 3.47 parts. This catalyst liquid is used at a temperature of 200 ° C. and a pressure of 30 kg.
/ Cm ² G under vigorous stirring,
48 parts of 6-dimethylnaphthalene and compressed air were continuously fed in over 1.3 hours, and the oxidation reaction was carried out under the same reaction conditions and reaction operation as in Comparative Example 1 except that crude 2,6-ND was used.
A solid precipitate consisting of CA was separated. At this time, coarse 2,6-
The purity of NDCA was 96.9%, and the average particle size was as shown in Table 5.

[0030]

[Table 5]

In addition, mainly filtered and leaked 2,6-ND
The particle size distribution of the fine particles of CA is shown in Table 6.

[0032]

[Table 6]

[0033]

[Comparative Example 4, Example 2] Crude 2,6-ND obtained in Comparative Example 3
Using CA and filtration, the same operations as in Comparative Example 2 and Example 1 were performed. The results are shown in Table 7.

[0034]

[Table 7]

Further, the solid precipitate mainly consisting of 2,6-NDCA obtained by solid-liquid separation of the reaction product in Example 2 by filtration has a purity of 95.0% and a filtration leakage rate of 1.5.
%Met.

[0036]

Comparative Example 5 Acetic acid 177 was added to a reactor similar to Comparative Example 1.
Parts, cobalt acetate (tetrahydrate) 7.63 parts, manganese acetate (tetrahydrate) 7.51 parts, potassium bromide 14.58 parts, and potassium acetate 12.02 parts. This catalyst solution was vigorously stirred under the conditions of a temperature of 200 ° C. and a pressure of 30 kg / cm ² G, to which 65 parts of 2,6-diisopropylnaphthalene and compressed air were continuously fed over 1.3 hours. Then, the oxidation reaction was performed under the same reaction conditions and reaction procedures as in Example 1 except for the above, and a solid precipitate composed of crude 2,6-NDCA was separated. At this time, the purity of the crude 2,6-NDCA is 9
The particle size distribution was 5.0%, as shown in Table 8.

[0037]

[Table 8]

In addition, mainly filtered and leaked 2,6-ND
The particle size distribution of the fine particles of CA is shown in Table 9.

[0039]

[Table 9]

[0040]

[Comparative Example 6, Example 3] Crude 2,6-ND obtained in Comparative Example 5
Using CA and filtration, the same operations as in Comparative Example 2 and Example 1 were performed. The results are shown in Table 10.

[0041]

[Table 10]

Further, the purity of the solid precipitate mainly composed of 2,6-NDCA obtained by solid-liquid separation by filtration of the reaction product in Example 3 was 95.0%, and the filtration leakage rate was 1.5.
%Met.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Sumitani 77, Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Limited Matsuyama Office

Claims (4)

[Claims] 1. 180% of dialkylnaphthalene and / or its oxidized derivative in a solvent containing a lower aliphatic carboxylic acid in the presence of a heavy metal oxidation catalyst and a catalyst consisting of bromine.
After oxidation with molecular oxygen-containing gas at ~ 220 ° C,
A method for producing naphthalenedicarboxylic acid, wherein the fine crystals in the deposited precipitate are supplied to the oxidation reactor again to grow the grain size of the fine crystals. 2. The method according to claim 1, wherein when the obtained naphthalenedicarboxylic acid is washed with a solvent and subjected to solid-liquid separation, fine crystals, which are difficult to collect, are supplied to an oxidation reactor to grow the grain size of the fine crystals. 1. A method for producing naphthalenedicarboxylic acid. 3. The method for producing naphthalenedicarboxylic acid according to claim 1, wherein the centrifuge is a decanter type centrifugal settler. 4. The heavy metal oxidation catalyst is cobalt, manganese,
The method for producing naphthalenedicarboxylic acid according to claim 1, which is at least one component selected from the group consisting of cerium and nickel.