JP3187212B2 - Continuous production method of naphthalenedicarboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously producing naphthalenedicarboxylic acid (hereinafter sometimes abbreviated to NDCA) by oxidizing dimethylnaphthalene and / or its oxidized derivative. More specifically, the present invention relates to an oxidation method in which an oxidation reaction catalyst is recycled and reused.

[0002]

2. Description of the Related Art NDCA and its esters (hereinafter referred to as NDCA)
Is sometimes useful as a polymer material, a dye intermediate or the like. Especially 2,6-NDCA
Polyethylene naphthalate formed from E. coli 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. Furthermore, since polybutylene naphthalate resin has a higher crystallization rate and higher moist heat resistance than polybutylene terephthalate resin, NDCA or the like is useful as a resin raw material.

Heretofore, as a method for producing NDCA, a method has been proposed in which dialkylnaphthalene and / or its oxidized derivative is oxidized with molecular oxygen in a lower aliphatic carboxylic acid solvent using cobalt, manganese, bromine or the like as a catalyst. Have been.

[0004] This method is classified into a batch type, a semi-continuous type and a continuous type according to the reaction mode, and is classified into a case where the catalyst is recovered and reused and a case where it is not used.

In order to produce NDCA at low cost on an industrial scale, the efficiency of the apparatus is low in a batch or semi-continuous reaction mode. In general, in the production of carboxylic acid by liquid phase oxidation of aromatic hydrocarbon, a relatively expensive catalyst is used. Therefore, the catalyst is recycled and used, that is, the remaining reaction mother liquor obtained by recovering the crude NDCA produced from the reaction mixture Recycling the washed filtrate of the crude NDCA and / or produced is advantageous in increasing the economics of the process.

[0006] As one of the methods of recovering the oxidation reaction catalyst from the oxidation reaction mixture and reusing the same, it has been proposed to recover only the catalyst from the reaction mixture. For example, 2,6
In the oxidation reaction of diisopropylnaphthalene, when using cobalt, manganese, cerium and bromine as catalysts, a method using an alkali to recover the catalyst from the reaction mother liquor (JP-A-2-250850), using sulfuric acid (JP-A-2-250851), a method using sulfuric acid and an alkali (JP-A-2-25261).
No. 3) has been proposed. However, none of these methods is sufficiently realistic and economical to manufacture NDCA at low cost on an industrial scale in terms of corrosiveness to the material of the apparatus or operability.

On the other hand, as another method of recovering the oxidation reaction catalyst from the oxidation reaction mixture and recycling and using the same, a method of recycling the reaction filtrate has been proposed. For example, 2,6
-In the oxidation reaction of diisopropylnaphthalene, a method has been proposed in which, when performing a reaction using cobalt, manganese, cerium and bromine as catalysts, a two-step reaction is carried out and a reaction filtrate is recycled (JP-A-4-330039). However, this method has a post-oxidation step,
The initial investment in the process increases, which is not economically advantageous.

Further, as a method for oxidizing 2,6-diisopropylnaphthalene or 2,6-diethylnaphthalene, a method of reusing a reaction mother liquor has been proposed (Japanese Patent Application Laid-Open No. Hei 4-1992).
266846). Although the cyclic oxidation reaction by this method is basically possible, in the case of the oxidation reaction of 2,6-diisopropylnaphthalene or 2,6-diethylnaphthalene, a large amount of cobalt is still contained in the crude NDCA after the reaction mother liquor separation. Considering that manganese is entrained, it is necessary to wash the crude NDCA with acetic acid, water or the like to recover these catalysts, thereby reducing the catalyst cost. by the way,
No mention is made of dimethylnaphthalene regarding the oxidation reaction in this mode. In addition, according to the study of the present inventors, in the case of dimethylnaphthalene, a serious problem has occurred that if the oxidation reaction is performed in this manner, the reaction is stopped at the first circulation.

The inventors of the present invention have conducted intensive studies on the cause. Unlike the case of 2,6-diisopropylnaphthalene and 2,6-diethylnaphthalene, the reaction was stopped at the first circulation in the case of dimethylnaphthalene. The cause of this is that naphthalene nucleus cleavage by-products such as trimellitic acid, phthalic acid, and methyl-substituted phthalic acids, such as ortho-benzenedicarboxylic acids (hereinafter abbreviated as ODCA), are stable chelates with heavy metal oxidation catalysts. It has been clarified that the formation of a type complex inactivates the catalyst, and thus merely supplementing the catalyst entrained in the crude NDCA results in a shortage of the effective catalyst amount.

As a measure to avoid these problems, it is conceivable to use a large amount of a heavy metal catalyst. However, in the case of dimethylnaphthalene (as opposed to the case of 2,6-diisopropylnaphthalene or 2,6-diethylnaphthalene), ), The yield of the catalyst is relatively low, and if too much catalyst is used, the yield of NDCA will be reduced. In addition to alteration during the added heavy metal oxidation reaction over-over -, oxides generated ends up colored dark gray by the action of the altered catalyst, the purification is very difficult,
Furthermore, a very disadvantageous result is caused in that the combustion loss of the lower aliphatic carboxylic acid used as a solvent increases.

[0011]

SUMMARY OF THE INVENTION In order to solve such a situation, the present invention provides a method for producing NDCA from dimethylnaphthalene and / or its oxidized derivative, which forms a complex with cobalt or manganese to reduce its oxidizing activity. O to deactivate
An object of the present invention is to provide a continuous production process by oxidation by selectively removing DCA.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to establish the above-mentioned method. In the liquid-phase oxidation reaction of dimethylnaphthalene and / or its oxidized derivative using heavy metals and bromine as catalysts, If cerium is added to cobalt and manganese as a heavy metal oxidation catalyst, cerium selectively forms a chelate-type complex with ODCA present in the reaction system, preventing the inactivation of the oxidation activity of cobalt and manganese, In addition, the inventors have found that ODCA can be removed from the reaction mother liquor by being precipitated as a solid and accompanying the crude NDCA, thereby completing the present invention.

That is, the present invention provides a method for oxidizing dimethylnaphthalene and / or its oxidized derivative using a molecular oxygen-containing gas in the presence of a heavy metal oxidation catalyst and a catalyst comprising bromine in a lower aliphatic carboxylic acid solvent. In the method, when the catalyst is recycled, by adding cobalt, manganese and cerium as a heavy metal oxidation catalyst,
This is a continuous method for producing NDCA by maintaining the activity of cobalt and manganese, selectively removing ODCA out of the reaction system, and circulating and recycling all of the reaction mother liquor and / or the washing filtrate of the resulting cake.

Hereinafter, the present invention will be described in detail.

[0015] Dimethylnaphthalene and / or its oxidized derivative used as an oxidation raw material in the present invention may be obtained by any method. Further, a mixture thereof may be used. Examples of the oxidized derivative include formylnaphthoic acid and methylnaphthoic acid, but are not limited thereto. Of these, the 2,6-form is particularly industrially useful. The oxidizing raw material is preferably of high purity, having a purity of 95% or more, preferably 98% or more. If present, components other than the 2,6-form, for example, isomers such as 2,7-dimethylnaphthalene may be contained.

In the method of the present invention, an aliphatic monocarboxylic acid having 1 to 5 carbon atoms, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, bromoacetic acid, or a mixture thereof is used as a lower aliphatic solvent. Among them, acetic acid and propionic acid are preferable, and acetic acid is particularly preferable.

The solvent used in the method of the present invention contains 5-45% by weight, preferably 7-35% by weight, more preferably 10-30% by weight of water in the above aliphatic monocarboxylic acid. . If the water content in the solvent is less than this, the combustion loss of the aliphatic monocarboxylic acid is large, while if it is more than this, the yield of NDCA and the purity are undesirably reduced.

The amount of the solvent used for the starting material dimethylnaphthalene and / or its oxidized derivative is usually 2 to
It is 15 times by weight, preferably 3 to 10 times by weight.

The oxidation catalyst used in the present invention is cobalt,
It is a heavy metal compound consisting of manganese and cerium and a bromine compound. The heavy metal oxidation catalyst is used in the form of organic acid salts such as formate, acetate and propionate, halides, hydroxides, oxides, carbonates and the like, and fatty acid salts, particularly acetates and bromides, are preferred.

The total amount of the heavy metal oxidation catalyst used in the method of the present invention is from 0.2 to 4% by weight, preferably from 0.4 to 2% by weight, based on the solvent.
0% by weight or less. If the amount of the heavy metal oxidation catalyst used is smaller or larger than this, the yield of NDCA and the purity are undesirably reduced. The ratio of manganese to cobalt (gram atomic ratio) is not particularly limited, but in consideration of the yield of ODCA and the like, this ratio is preferably 1.0 or less. The amount of cerium added is desirably equal to or greater than the molar number of ODCA by-produced or more.

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

The oxidation reaction temperature in the method of the present invention is 180
To 230 ° C, preferably 190 to 220 ° C. When the reaction temperature is low, the reaction rate decreases, while when it is high, the side reaction products increase and the purity of NDCA decreases. The reaction pressure is usually 10 to 30 kg under the condition that the reaction system is maintained at a liquid phase at the above-mentioned reaction temperature.
/ Cm ² is appropriate.

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 such as nitrogen is used. Industrially, air is most easily available and preferred.

The method of the present invention is effective when applied to any of the batch oxidation method, the semi-continuous oxidation method and the continuous oxidation method, but is particularly effective in the case of the continuous oxidation method.

The crude NDCA produced by the oxidation reaction can be obtained on the solid phase side by subjecting the reaction product to solid-liquid separation. The crude DNCA obtained by the solid-liquid separation can remove the attached catalyst solution, the oxidation reaction intermediate and the ODCA catalyst metal complex by washing with acetic acid or the like and washing with water, and can be highly purified. If necessary, NDCA of extremely high purity can be obtained by using a normal NDCA purification method known as a known method.

[0026]

According to the method of the present invention, NDCA can be produced efficiently and continuously on an industrial scale.

[0027]

The present invention will be specifically described below with reference to examples. Parts and% in Examples and Comparative Examples indicate parts by weight and% by weight, respectively. The decomposition rate of the lower aliphatic carboxylic acid was determined by gas chromatographic analysis of the product composition.

[0028]

Example 1 A titanium autoclave having a gas discharge pipe, a gas injection pipe, a continuous feed pump for raw materials, a continuous feed pump for catalyst liquid, a product discharge pipe and a stirrer equipped with a reflux condenser, 160 parts of acetic acid and cobalt acetate tetrahydrate _{[Co (OOCCH 3) 2 ·} 4H 2 O] 2.36 parts of manganese acetate tetrahydrate _{[Mn (OOCCH 3) 2 ·} 4H 2 O] 1.26 parts cerium acetate monohydrate [Ce _{(OOCCH 3) 3 · 1H 2} O] 0.93 parts water 17 parts 3.50 parts of 47% aqueous hydrogen bromide was charged. The water concentration in this catalyst solution was 10%. This catalyst solution was heated at a temperature of 200 ° C. and a pressure of 20 kg / cm.
Under vigorous stirring under the conditions of ² , 42 parts of 2,6-dimethylnaphthalene were continuously fed into the mixture over 1 hour, and an oxidation reaction was carried out by flowing excess compressed air. One hour after the start of the feeding of 2,6-dimethylnaphthalene, the feeding of the catalyst liquid having the above composition was started while the feeding of 2,6-dimethylnaphthalene was continued. Thereafter, in order to keep the amount of the reaction mixture in the autoclave constant, the reaction was continued while extracting a part of the reaction mixture, and the reaction was performed for a total of 15 hours.

From the withdrawn reaction mixture, mainly NDCA
The resulting solid precipitate was separated to obtain a reaction mother liquor. The solid precipitate was washed with acetic acid and then solid-liquid separated to obtain a washed filtrate. The separability of the solid precipitate was good. At this time, the yield of NDCA was 9
3.9 mol%, the yield of ODCA was 3.7 mol%, and the decomposition rate of acetic acid was 5.0%. Further, ODCA contained in the reaction mother liquor and the washing filtrate all formed a complex with cerium.

After the reaction mother liquor and the washing filtrate were all combined, they were concentrated to remove excess water. At this time, of the cobalt, manganese, and cerium used in the reaction, each was 98.5.
%, 97.5%, and 6.0% were contained in the liquid after concentration. Further, 3.7% of the generated ODCA was contained in the liquid after concentration.

[0031]

Example 2 The concentrated solution obtained in Example 1 was added with the same amount of cobalt, manganese, cerium as that entrained in the washing cake.
Bromine was added, and acetic acid and water were added so that the catalyst concentration used in Example 1 was equal to the catalyst solution to prepare a catalyst solution. The same operation as in Example 1 was performed except that this catalyst liquid was used. The separability of the solid precipitate of the reaction solution was good. At this time, the yield of NDCA was 93.7 mol%, the yield of ODCA was 3.6 mol%, and the decomposition rate of acetic acid was 5.2%.
Further, ODCA contained in the reaction mother liquor and the washing filtrate all formed a complex with cerium. After the reaction mother liquor and the washing filtrate were all combined, they were concentrated to remove excess water. At this time, of the cobalt, manganese, and cerium used, 97.5%, 96.0%, and 7.0% were contained in the liquid after concentration, respectively. In addition, the OD contained in the reaction mixture
Among the CAs, those contained in the liquid after concentration were 3.5.
%Met.

[0032]

Examples 3 to 11 The same operation as in Example 2 was performed using the concentrated solution obtained in Example 2. Hereinafter, the same operation was repeated, and the reaction was performed ten times in total. The separability of the solid precipitate in each reaction was good. No accumulation of by-products was observed. Table 1 shows the reaction results.

[0033]

[Table 1]

As shown in Table 1, cobalt and manganese are:
Most of the ODCA was recovered on the liquid side, and most of the ODCA could be removed from the reaction system. Also, the cobalt entrained in the produced crude ND CA, supplemented manganese, cerium, bromine, the reaction mother liquor, by the washing filtrate circulating reuse, generates a reactive intermediate dissolved in these solutions NDCA From the results, it was found that the NDCA yield was improved in Examples 2 and 3 as compared with Example 1 and maintained at a favorable level thereafter.

[0035]

Comparative Example 1 The same operation as in Example 2 was performed except that cerium was not added to the concentrate obtained in Example 1. At this time, the yield of NDCA was 92.0 mol%, the yield of ODCA was 4.9 mol%, and the decomposition rate of acetic acid was 5.4%. At this time, 80.0% and 65.0% of cobalt and manganese used for the reaction were contained in the reaction mother liquor and the washing filtrate, respectively. Moreover, 72.0% of ODCA was contained in the liquid after concentration.

[0036]

Comparative Example 2 Using the concentrated solution obtained in Comparative Example 1, Comparative Example 1
The same operation as described above was performed. At this time, oxygen absorption was stopped 40 minutes after the start of 2,6-dimethylnaphthalene feeding, and it was impossible to recover the reaction. The conversion of 2,6-dimethylnaphthalene was 65%.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-250851 (JP, A) JP-A-7-48314 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 51/487 C07C 51/265 C07C 63/38 C07B 61/00 300 B01J 31/04

Claims (5)

(57) [Claims] 1. Using dimethylnaphthalene and / or an oxidized derivative thereof as a raw material, and using a lower aliphatic carboxylic acid solvent at least twice as much as the raw material in the presence of a catalyst composed of cobalt, manganese and bromine, In the method of oxidizing using an oxygen-containing gas, (i) cerium is added to selectively form a chelate complex with ortho-benzenedicarboxylic acids by-produced, and (ii ) the resulting reaction mixture is formed into a cake and a filtrate. To the solid
And liquid separation, the chelate complex is brought removed as product cake out reaction system, (iii) cobalt, to maintain the catalytic activity of manganese, at (iv) generating cake or which lower aliphatic carboxylic acid
Cobalt and mask entrained in the washed cake obtained by washing
Replenish with gangue, cerium and bromine and add the reaction mother liquor and / or
Or continuous preparation of naphthalenedicarboxylic acid, wherein the allowed to total amount recycling reuse washing filtrate product cake. 2. The continuous production method of naphthalenedicarboxylic acid according to claim 1, wherein the concentration of the catalyst in the solvent is 0.2% by weight or more. 3. The method for continuous production of naphthalenedicarboxylic acid according to claim 1, wherein the lower aliphatic carboxylic acid is acetic acid. 4. The continuous production method of naphthalenedicarboxylic acid according to claim 1, wherein the oxidation is performed at a reaction temperature of 180 to 230 ° C. 5. The method for continuously producing naphthalenedicarboxylic acid according to claim 1, wherein the solvent has a water concentration of 5 to 45% by weight.