JPH0665143A - Production of naphthalendicarboxylic acid - Google Patents

Abstract

PURPOSE:To provide the grain diameter of a produced naphthalendicarboxylic acid (NDCA) crystal to a size suitable for the solid-liquid separation by carrying out the oxidation at a specific reactional temperature in an oxidizing step for obtaining the NDCA. CONSTITUTION:The objective method for producing NDCA is to oxidize a dialkylnaphthalene and/or its oxidation derivative with a molecular oxygen- containing gas in the presence of a catalyst composed of a heavy metallic oxidation catalyst (e.g. cobalt, manganese, cerium or nickel) in a solvent containing a lower aliphatic carboxylic acid such as acetic acid at 180-220 deg.C and then subjecting the resultant product to the solid-liquid separation with a centrifugal separator.

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 referred to as ND
(Sometimes abbreviated as CA, etc.) is a substance useful as a polymer material, a dye intermediate, and the like. Especially 2,6-NDC
Polyethylene naphthalate formed from A and the like and ethylene glycol is superior to polyethylene terephthalate in heat resistance, breaking strength and the like, 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 intensive 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 a solvent containing, in the presence of a catalyst composed of a heavy metal oxidation catalyst and bromine, using a molecular oxygen-containing gas, if oxidized at a specific reaction temperature,
The inventors have found that the particle size of NDCA crystals is large and solid-liquid separation is easy, and have completed the present invention.

In the present invention, a dialkylnaphthalene and / or an oxidized derivative thereof is treated with a molecular oxygen-containing gas at 180 to 220 ° C. in a solvent containing a lower aliphatic carboxylic acid in the presence of a heavy metal oxidation catalyst and a catalyst consisting of bromine. Is a method for producing naphthalenedicarboxylic acid, in which the reaction product is subjected to solid-liquid separation with a centrifuge after being oxidized with.

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, etc., or a mixture thereof is used as a 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 method 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, based on 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 to generate 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 feed concentration. A decanter-type (particularly, conveyor-type) centrifugal settler having a high 30-50% and capable of stable operation without clogging and continuous discharge of cake is preferably used.
When a separation plate type centrifugal settler is used, it is suitable for separating fine particles, but since the allowable feed liquid concentration is as low as several% to 10%, it is necessary to use a large amount of solvent during the oxidation reaction. However, the volumetric efficiency of the expensive oxidation reactor is deteriorated, which is not preferable. Further, handling of fine particles by a centrifugal dehydrator is not preferable because it has a drawback that clogging is likely to occur.

The 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.

It is said that the decanter type centrifugal settler has a separation and collection diameter of about 1 to 10 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. 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 crystal size of the crude NDCA becomes about 2 µm or more, and the solid-liquid state is stable in a decanter type centrifugal settler. Separation is possible, but if the reaction temperature is lower than this, the particle size of the obtained NDCA crystals becomes small, and solid-liquid separation in the separation step of the reaction mother liquor becomes difficult. Especially in the solid-liquid separation in the subsequent washing step,
The initially aggregated particles are destroyed and become finer, which makes solid-liquid separation more difficult. In addition, the production of reaction intermediates increases and the purity of the obtained NDCA decreases, so that it is necessary to carry out post-oxidation, which is not preferable because the equipment cost becomes high. On the other hand, if the reaction temperature is higher than this range, the side reaction products increase, the purity of the obtained NDCA decreases, and the combustion loss of the solvent rapidly increases, which is not preferable.

The reaction pressure at that time 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.

[0020]

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.

[0021]

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 feeding of the raw material 2,6-diethylnaphthalene is completed, it is further maintained at 200 ° C. and 30 kg / cm.
^It was kept at ² G and compressed air was supplied for 14 minutes. After completion of the reaction, the reaction product was taken out and mainly 2,6-NDC
The solid precipitate consisting of A was separated and dried. The crude 2,6-NDCA obtained has a purity of 95.0% and an average particle size of 10
was μm.

[0022]

Example 2 The same reaction as in Example 1 was carried out to give crude 2,6-
After separating a solid precipitate consisting of NDCA, the solid precipitate was washed with 3 times the amount of acetic acid and separated and dried. Obtained 2,6-
The purity of NDCA was 96.5%, and the average particle size was 3.5 μm.

[0023]

Example 3 The 2,6-NDCA obtained in Example 2 was
It was further washed with 6 times the amount of water and separated and dried. The obtained 2,6-NDCA had a purity of 96.7% and an average particle size of 3.
It was 4 μm.

[0024]

Comparative Examples 1 to 3 The same reaction and separation operations as in Examples 1 to 3 were performed except that the reaction temperature was 170 ° C. The purity and average particle size of the obtained 2,6-NDCA are shown in Table 1.

[0025]

[Table 1]

[0026]

Examples 4 to 5 and Comparative Examples 4 to 5 The same reaction and separation operation as in Example 2 were carried out except that the reaction temperature was changed, and the results shown in Table 2 were obtained.

[0027]

[Table 2]

[0028]

Example 6 Acetic acid 161 was placed in the same reactor as in 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 Example 1 except that crude 2,6-ND was used.
After the solid precipitate of CA was separated, it was further washed with 3 times the amount of acetic acid and separated and dried. At this time, 2,6-ND
The purity of CA was 96.9%, and the average particle size was 5.0 μm.

[0029]

Example 7 Acetic acid 177 was added to a reactor similar to that of 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 is performed under the same reaction conditions and reaction procedures as in Example 1 except that the solid precipitate consisting of crude 2,6-NDCA is separated, washed with 3 times the amount of acetic acid and separated and dried. It was At this time, the purity of 2,6-NDCA is 96.9.
%, And the average particle size was 6.0 μm.

[0030]

Comparative Examples 6 and 7 The same reaction and separation operations as in Examples 6 and 7 were performed except that the reaction temperature was 170 ° C. The purity and average particle size of the obtained 2,6-NDCA are shown in Table 3.

[0031]

[Table 3]

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, in which a reaction product is subjected to solid-liquid separation by a centrifuge. 2. The method for producing naphthalenedicarboxylic acid according to claim 1, wherein the obtained naphthalenedicarboxylic acid is washed with a solvent and solid-liquid separated by a centrifugal separator for purification. 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.