JPH03287565A - Method for recovering catalyst for producing naphthalenecarboxylic acid - Google Patents

Abstract

PURPOSE:To recover a heavy metal at a high recovery ratio by keeping the pH and temperature within specific ranges in recovering a heavy metal catalyst as a carbonate in oxidizing an alkyl- and/or acyl-substituted naphthalene in the liquid phase and producing the subject compound. CONSTITUTION:A lower alkyl- or acyl-substituted naphthalene or both are oxidized in the presence of a catalyst containing a heavy metal compound and a bromine compound in a solvent containing a lower aliphatic monocarboxylic acid to provide crude naphthalenecarboxylic acid(NCA), which is then esterified by reaction thereof with an alcohol to afford an NCA ester. A filtrate obtained by filtering the NCA crystals or NCA ester crystals and a wash liquid prepared by washing the aforementioned crystals, together with a compound (e.g. an alkali carbonate) capable of producing carbonate ions, are kept at pH>=7.5 and >=50 deg.C temperature to recover a heavy metal carbonate as precipitates. The resultant carbonate is excellent in filterability and the separated carbonate is washed with an alcohol and/or ketone to improve handleability.

Description

Detailed Description of the Invention '(Industrial Application Field) The present invention involves the oxidation of substituted naphthalene with molecular oxygen in a solvent containing a lower aliphatic monocarboxylic acid in the presence of a catalyst containing a heavy metal compound and a bromine compound. The present invention relates to a method for recovering heavy metal catalysts when producing naphthalenecarboxylic acid (hereinafter referred to as NCA) or when further esterifying the obtained NCA.

(Prior Art) Among NCAs having at least one carboxyl group directly bonded to a naphthalene ring, naphthoic acid, which is a monocarboxylic acid, is used as a raw material for photographic agents, dyes, and the like. In addition, naphthalene dicarboxylic acids, especially 2.6 monomer, are used as raw materials for various polyesters and polyamides, including polyethylene naphthalate, because they provide films and textile products with excellent heat resistance, mechanical strength, and dimensional stability. Demand is increasing. Furthermore, naphthalene tricarboxylic acids are seen as promising raw materials for highly functional resins and the like.

Conventionally, many proposals have been made regarding the production method of NCA. A method of oxidizing with a molecular oxygen-containing gas in the presence of a catalyst consisting of
No.-21017, No. 59-13495, JP-A-49-
No. 42654, No. 60-89445, No. 60-894
46 publications), or a method in which the oxidation reaction is carried out using a heavy metal compound consisting of cobalt and cerium and a bromine compound as a catalyst (Japanese Patent Application Laid-Open No. 62-212344).

NCA obtained by the above method is sometimes used as it is for various purposes, but in many cases NCA is subjected to an esterification reaction and the obtained NCA ester is used.

Regarding the esterification of NCA, there is a method in which NCA is esterified under pressure with methanol in the presence of a catalyst selected from sulfuric acid, hydrogen chloride, hydrochloric acid, and sulfonic acid (Japanese Patent Publication No. 49-174); Alternatively, there are many proposals for contacting the NCA esterification intermediate at a predetermined temperature and then supplying it to the esterification reaction vessel (JP-A-50-76).

By the way, in order to produce NCA or NCA ester on an industrial scale at low cost and with high yield, it is very important to recover and recycle the relatively expensive heavy metal catalyst used in NCA production. .

A method for recovering heavy metal catalysts such as cobalt and manganese used in the production of NCA is to recover the solvent from the filtrate from which the terephthalic acid produced is separated during the production of terephthalic acid by liquid phase oxidation of p-xylene, and then recover the residue. Method of recovering carbonate from
9, Japanese Patent Application Laid-Open No. 47-34088), the oxidation reaction by-products that are harmful to the oxidation reaction, which are recovered at the same time as the cobalt and manganese used, are oxidized again with molecular oxygen to remove them. A method for restoring the activity (Japanese Unexamined Patent Publication No. 49-106986), in which 2,6-diituprobylnaphthalene or its oxidized intermediate is oxidized with molecular oxygen in the presence of a catalyst containing cobalt, manganese, and bromine. A method in which the crude 2.6 naphthalenedicarboxylic acid obtained is brought into contact with an aqueous mineral acid solution to elute the catalyst metal, and an alkali carbonate or alkali bicarbonate is added thereto to recover the heavy metal catalyst as a carbonate or bicarbonate. (Unexamined Japanese Patent Publication No. 62-21
2345), or in liquid phase oxidation of aromatic compounds, the obtained crude crystals of aromatic carboxylic acid are purified by washing or recrystallization with water, and a compound that produces carbonate ions is added to the washing solution or recrystallization mother liquor. A method for recovering added and dissolved heavy metal catalysts as water-insoluble carbonates (
Methods such as JP-A-1-121237 have been proposed so far.

The conventional heavy metal catalyst recovery methods described above all use crude N
The carbonate is recovered from the filtrate from which CA is separated, the washing solution obtained by washing or recrystallization of crude NCA, or the mother liquor. Until now, no attempt had been made to recover heavy metals from the filtrate or wash solution generated during the esterification step. Moreover, the recovered heavy metal catalyst carbonate has
Reaction intermediates and polymers produced as by-products during the oxidation reaction are mixed in, and if this recovered catalyst is recycled and used, reaction by-products will accumulate. In addition, when carbonates of heavy metal catalysts are separated by filtration, the particles of the recovered heavy metal catalysts are fine and the recovery rate is very low, and the filtered heavy metal catalysts have a clay-like appearance when the liquid content is over 30%. There are problems in handling, such as adhesion to the filtration device, which requires scraping.

(Issues to be Solved by the Invention) The present invention is capable of recovering heavy metal components at a very high recovery rate when recovering heavy metal catalysts used in the production of NCA as carbonates, and is free from contamination with oxidation reaction intermediates and polymers. An object of the present invention is to provide a method for recovering a catalyst for producing NCA, which can prevent the above-mentioned carbonates from occurring and improve the filterability and handling properties of the carbonate of the obtained heavy metal catalyst.

(Means for Solving the Problems) As a result of research on a method for recovering heavy metal catalysts used in the production of NCA, the present inventors found that, in 1 case, crude NCA obtained by oxidation reaction is directly esterified. Since a significant portion of the metal is carried over to the esterification process, it is necessary to recover heavy metal components from the filtrate and washing liquid in the esterification process.
A compound that generates carbonate ions is added to a solution containing a heavy metal catalyst obtained in the production process of ester A, and a predetermined p
If the heavy metals are precipitated as carbonates by maintaining the temperature at The present inventors have discovered that the ease of handling is dramatically improved by this method, and have arrived at the present invention.

Here, the present invention provides a method for producing crude NCA by oxidizing lower alkyl- and/or acyl-substituted naphthalene with molecular oxygen in a solvent containing a lower aliphatic monocarboxylic acid in the presence of a catalyst containing a heavy metal compound; Alternatively, in a method of producing an NCA ester by esterifying the crude NCA obtained by this method by reaction with alcohol, a solution containing a heavy metal compound of the catalyst obtained in this production process is mixed with a compound that produces carbonate ions at a pH of 7. 5 or higher, the temperature is maintained at 50° C. or higher to generate a precipitate, the precipitate is separated, and the separated precipitate is preferably washed with alcohol and/or ketone.
The gist is the recovery method of the manufactured catalyst.

The present invention will be explained in detail below.

The raw material for the method for producing NCA by liquid phase oxidation, which is the object of the present invention, is any isomer of substituted naphthalene in which at least one lower alkyl and/or acyl group is bonded to the naphthalene ring. Examples of substituents include lower alkyl groups such as methyl, ethyl and isopropyl, and lower acyl groups such as acetyl and formyl.

Specific examples of substituted naphthalene include methylnaphthalene,
Isopropylnaphthalene, dimethylnaphthalene, methylacetylnaphthalene, diethylnaphthalene, and diisopropylnaphthalene are exemplified, and as a reaction solvent for liquid phase oxidation, a solvent containing a lower aliphatic monocarboxylic acid such as acetic acid, propionic acid, and butyric acid is used. Acetic acid is particularly preferred. As a solvent, lower monocarboxylic acids can be used as they are, but water, chlorobenzene,
It can also be used in combination with a hydrocarbon solvent such as bromobenzene.

As molecular oxygen, air, oxygen, or a mixed gas of oxygen and an inert gas can be used, but it is economical to use air as it is.

The oxidation catalyst comprises a compound of at least one heavy metal such as cobalt, manganese, cerium, nickel, copper, iron, zinc, and usually also a bromine compound. As the heavy metal compound, use one that dissolves in the lower monocarboxylic solvent, and lower fatty acid salts such as acetate are particularly preferable.As the bromine compound, potassium bromide, sodium bromide, ammonium bromide, etc. can be used. . Furthermore, ketones such as methyl ethyl ketone and alkali metal compounds such as potassium acetate may be used in combination as co-catalysts.

Liquid phase oxidation can be carried out under the same reaction conditions as conventional ones.
The reaction temperature is 20-250'C1, preferably 100-2
00℃, reaction pressure is 0.2-20kg as oxygen partial pressure
/cd, preferably within the range of 3 to 15 kg/cd.

After the completion of the oxidation reaction, the crude NCA crystals separated from the reaction mixture by filtration, which contain the residue of the heavy metal catalyst, can be dried as is, washed with water, alcohol, or an aqueous acid solution, and then dried, or without drying. , and can be subjected to an esterification reaction step. When esterification is not performed, the filtered and washed crude NCA crystals may be subjected to an appropriate purification step.

A heavy metal catalyst is dissolved in the filtrate obtained by filtering the crude NCA crystals. This filtrate may be directly subjected to the catalyst recovery step according to the present invention, but the solvent is distilled off from the filtrate to recover the solvent, and a solution of the solid matter of the distillation residue dissolved in water or an aqueous mineral acid solution is used as a solution. It is preferable to subject it to the catalyst recovery step according to the invention.

This is because if the filtrate is used as it is, the aliphatic monocarboxylic acid in the solvent cannot be recovered, and a large amount of alkali is required for neutralization in the catalyst recovery step, which results in the production of a large amount of carboxylic acid salt.

The esterification step of NCA can be carried out by reacting NCA with alcohol in the presence of an acid catalyst by a conventional method.

The acid catalyst used in esterification is preferably a strong acid such as sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, or toluenesulfonic acid.

The alcohol used as the esterifying agent is preferably a lower alkyl alcohol such as methanol, ethanol, propatool, isopropanol, or butanol, and one or more types can be used.

Alcohol usually serves as a solvent and is used in excess.

The esterification reaction conditions may be those commonly used, but the reaction temperature is preferably 160° C. or lower.

After the esterification reaction is completed, the crude NCA ester crystals are filtered off from the reaction mixture. The obtained crystals contain residues of the heavy metal catalyst used in the oxidation step, but when washed with at least one of water, acid aqueous solution, and alcohol,
Since heavy metal compounds dissolve and easily migrate into the cleaning solution, heavy metal bones can be recovered into the cleaning solution at a high yield.

Methanol, ethanol, etc. can be used as the alcohol for cleaning the crude NCA crystal or crude NCA ester crystal. As the acid aqueous solution, an aqueous solution of sulfuric acid, hydrochloric acid, nitric acid, acetic acid, etc. can be used.

That is, when the above process for producing NCA or NCA ester is carried out, the product crude NCA crystals or crude N
The filtrate obtained by filtering the CA ester crystals and the washing liquid obtained by washing these crystals contain heavy metal catalyst components.

In the case of a filtrate of crude NCA crystals, it is advantageous to use a solution obtained by recovering the solvent by distillation and dissolving the solid residue of the distillation in water or a dilute aqueous mineral acid solution as described above. .

The filtrate of the crude NCA ester crystals, and optionally the wash liquor, may be treated similarly. Solutions containing heavy metal catalyst components may be concentrated, but usually no concentration is necessary.

In the present invention, heavy metal compounds are recovered from the solution containing such heavy metal catalyst components by the method described below. This treatment is usually carried out by combining the resulting solutions together.

A compound that generates carbonate ions is added to a solution containing a heavy metal catalyst component, and the dissolved heavy metal ions react with the carbonate ions to precipitate as an insoluble carbonate.

As the compound that produces carbonate ions, any compound that produces carbonate ions when dissolved in the solution to be treated can be used. Specifically, carbonates or hydrogen carbonates of alkali metals or ammonium, such as sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate, can be used.

When adding a compound that produces carbonate ions, the solution pH is maintained at 7.5 or higher and the temperature is maintained at 50°C or higher, preferably 60°C or higher. This increases the particle size of the resulting heavy metal/carbonate precipitate, improves the filterability of the precipitate, and improves the recovery rate of heavy metals.

If the pHfl at this time is lower than 7.5, the recovery rate of the heavy metal catalyst will be low. When an alkaline carbonate such as sodium carbonate is added, the pH value can be adjusted by adjusting the amount of the alkaline carbonate added. If necessary, add an alkali such as sodium hydroxide or potassium hydroxide to adjust the pH value to 7.5 or higher.

If the heating temperature is lower than 50°C, the filterability of the precipitate will be poor and the filtration time will be extremely long. The heating holding time varies depending on conditions such as pH1 temperature, but is usually 30 to 60 minutes.

After heating and holding a solution containing a heavy metal catalyst together with a compound that produces carbonate ions, the deposited precipitate is filtered off to recover the heavy metal carbonate. It is preferred that this precipitate is then washed with at least one organic solvent selected from alcohols and ketones.

This not only removes organic substances such as reaction intermediates and polymers produced as by-products during the reaction, but also reduces the liquid content (water content) in the precipitate, resulting in a semi-dry state, which dramatically improves ease of handling. do.

Ketones used for this cleaning include acetone, methyl ethyl ketone, etc. Alcohols include methanol, ethanol, propatool, butanol, etc. The heavy metal carbonates recovered and cleaned in this way are is recycled to the substituted naphthalene oxidation step,
It can be used as is as a catalyst component. When heavy metal carbonates are added into an aliphatic monocarboxylic acid solvent (e.g., acetic acid) using an oxidation reaction, the salts of the monocarboxylic acids (
e.g., acetate) and dissolves in this solvent.
Functions effectively as a catalyst.

According to the present invention, the heavy metal catalyst component used in liquid phase oxidation can be
% or more, NCA production can be continued by simply adding a small amount of heavy metal catalyst along with other catalyst components if necessary.

EXAMPLES Hereinafter, the present invention will be illustrated by examples, but the present invention is not limited thereto. In the examples, parts and % are
Parts and percentages are by weight unless otherwise specified. Also,
The analytical methods used in the examples are plasma emission spectrometry for cobalt, manganese, and cerium, and ion chromatography for bromine.

In a titanium autoclave with a capacity of 51 g, 49.8 g of cobalt acetate tetrahydrate and 48 g of manganese acetate tetrahydrate were added as catalysts.
9g, cerium acetate hydrate 67.1g, potassium bromide 7
1.4 g, 59.1 g of potassium acetate, and 2300 g of acetic acid as a solvent, and while stirring, the reaction pressure was increased to 3.
0 kg/d, reaction temperature 200°C, while blowing excess air, 2,6-diitubrobylnaphthalene 630
．． 0 g was fed over 4 hours, and then only air was blown for 1 hour to complete the oxidation reaction. Insoluble matter was filtered from this reaction product, and the filter cake was dried to obtain 674.2 g of crude NDCA crystals containing a cerium compound. When this was analyzed by gas chromatography, the yield of 2,6-NDCA was 93.2 mol % based on the amount of 2,6-diituprobylnaphthalene charged.

This crude NDCA, 6800 g of methanol and 96 g of catalyst
% sulfuric acid was charged into a 51-capacity Hastelloy autoclave in two batches, and an esterification reaction was carried out at a reaction temperature of 120° C. for 4 hours.

After the reaction is completed, the esterification reaction mixture taken out from the autoclave is filtered to remove the crude ND containing the cerium compound.
CA ester crystals were separated and collected.

This NDCA ester and water 7000 wa with a capacity of 101
After stirring at room temperature for 30 minutes, the solid matter was filtered and dried to obtain 667.5 g of yellow-white NDCA methyl ester.

The Co concentration in this washed NDCA methyl ester crystal was 0.8 ppm, and the Mn concentration was 1.2 pp@%.
The Ce concentration was 162 pp-. On the other hand, in the washing filtrate, Co, Mn, and Ce are each contained, based on the recent amounts of 100 parts, Co 3.1 parts and Mn 5.
2 parts of Ce and 99.6 parts of Ce.

That is, it can be seen that most of the cerium in particular is carried into the esterification process, and other heavy metals also enter the esterification process to some extent.

From 2100 g of the filtrate remaining after filtering the crude NDCA crystals from the oxidation reaction mixture, acetic acid,
Water and the like were distilled off to obtain 192.1 g of solid content. Methanol, water, sulfuric acid, etc. were similarly distilled off from the filtrate obtained by filtering the crude NDCA methyl ester crystals from the esterification reaction mixture to obtain 25.2 g of a solid. These solids were mixed and dissolved in 1000 g of water, and insoluble matter was filtered off, followed by mixing with the NDCA methyl ester wash water.

This mixture was heated to 80"C, 10% aqueous sodium hydrogen carbonate solution was added until the pH was 7.5 or higher, and the mixture was heated to 80"C.
The mixture was heated and stirred at ℃ for 30 minutes. After stirring, the precipitated gray-brown precipitate was filtered and dried to obtain a gray-brown solid 120.2
I got g.

When the filtration specific resistance α was measured during filtration, it was α-3.1x.
1O'' m/kg, which was within a range that allowed the application of a centrifuge.

This filtration specific resistance α (m/kg) is determined by the filtration time θ (sec
): From the filtrate volume v (of), the basic formula for filtration resistance θ/
Using V = V / K + 2 v / K, R
The low-pressure filtration coefficient K (m/s) of uth is determined and calculated as 1 from the relationship of the following equation.

K-2・ΔP・(1-m-s)/1)・#-s・av
(rrr/nf): filtrate volume per unit area that produces a filter slag that provides resistance equal to the filter media resistance, ΔP (
kg/cj): Differential pressure between operating pressure and atmospheric pressure, m(-):
Wet and dry weight ratio of cake, solid mass fraction in 5(-) Nislary, ρ (kg/d)
: Density of filtrate, u (kg/-・5ec) : Viscosity of filtrate.

The solid material after drying was clay-like and difficult to handle, but when it was washed with 50 g of methanol,
It has an easy-to-handle property that can be easily peeled off and powdered.

As a result of quantitative analysis of each metal on the washed solid matter, the recovery rate of each metal was 97% cobalt, 97% cobalt,
2%, manganese 96.7%, and cerium 99.8%.

The solid thus recovered was used as a heavy metal catalyst, the loss of heavy metal was supplemented with new heavy metal catalyst, potassium bromide and potassium acetate were added separately, and 2,6-diitubrobylnaphthalene was prepared under the same conditions as above. When liquid phase oxidation of 2,6-naphthalene dicarboxylic acid was performed, no decrease in the yield of 2,6-naphthalene dicarboxylic acid was observed.

Comparative Example 1 A solution obtained by dissolving the solid matter from the oxidation reaction filtrate and the solid matter from the esterification reaction filtrate obtained in the same manner as in Example 1 in water, and the washing solution of the produced ester crude crystals were combined and mixed together. Add 10% sodium bicarbonate aqueous solution to pH 7.
5 or more and then stirring at 25°C, the filtration specific resistance α of the generated precipitate was α-3,9xlO'
・(m/kg), making it difficult to apply a centrifugal filter. That is, compared to the case of heat treatment in Example 1, about 9
It took 0 times more filtration time.

The obtained solid material was clay-like and difficult to handle.

Comparative Example 2 A solution obtained by dissolving the solid matter from the oxidation reaction filtrate and the solid matter from the esterification reaction filtrate obtained in the same manner as in Example 1 in water, and the washing solution of the produced ester crude crystals were combined and mixed together. Add 10% aqueous sodium hydrogen carbonate solution to pH 7.
The mixture was stirred at 80° C. for 30 minutes, and the resulting precipitate was collected by filtration. The resulting gray-brown solid was about 5 g, and almost no heavy metal catalyst components were recovered.

(Effects of the Invention) According to the method of the present invention, when performing esterification, NCA can be
All heavy metal catalyst components used in the oxidation reaction during production were reduced to 95%.
It can be recovered and recycled with a high yield of more than %. The precipitate has good filterability and can be easily and quickly recovered by centrifugation or the like. Furthermore, since the reaction intermediates and polymers produced as by-products in the oxidation reaction are suppressed from being mixed into the recovered catalyst acid, accumulation of these by-products is prevented when the recovered material is recycled. In addition, when the filtrate is washed with alcohol or ketone, its liquid content is reduced, making it possible to recover heavy metal catalyst components in a semi-dry state that is easy to handle, and operations such as scraping are not necessary. This becomes unnecessary and is extremely advantageous.

Claims (2)

[Claims] (1) A method for producing crude naphthalene carboxylic acid by oxidizing lower alkyl- and/or acyl-substituted naphthalene with molecular oxygen in a solvent containing a lower aliphatic monocarboxylic acid in the presence of a catalyst containing a heavy metal compound; In a method for producing naphthalene carboxylic acid ester by esterifying the crude naphthalene carboxylic acid obtained by the method, a solution containing a heavy metal compound of the catalyst obtained in this production process is combined with a compound that produces carbonate ions. A method for recovering a catalyst for producing naphthalene carboxylic acid, the method comprising: maintaining the pH at 7.5 or higher and the temperature at 50° C. or higher to generate a precipitate, and separating the precipitate. The method according to claim 1, characterized in that (2) the separated precipitate is washed with alcohol and/or ketone.