JP3288743B2 - Catalyst recovery method - 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 efficiently recovering a heavy metal oxidation catalyst in a process for producing dimethyl naphthalenedicarboxylate (hereinafter sometimes abbreviated as NDM).

NDM and its derivatives are valuable compounds as a dibasic component such as polyester and polyamide. In particular, polyethylene naphthalenedicarboxylate formed from NDM and ethylene glycol is superior in heat resistance and mechanical properties as compared with polyethylene terephthalate, and is useful as a polymer that gives more excellent films and fiber products. Further, a resin produced by using polybutylene naphthalenedicarboxylate formed from NDM and 1,4-butanediol has a higher crystallization rate and higher moist heat resistance than polybutylene terephthalate resin. Therefore, NDM is also useful as a resin raw material.

[0003]

2. Description of the Related Art Naphthalenedicarboxylic acid formed by oxidizing dialkylnaphthalene and / or its oxidized derivative with molecular oxygen in a solvent containing a lower fatty acid in the presence of an oxidation catalyst composed of heavy metal and bromine. When producing an NDM by reacting an acid (hereinafter sometimes abbreviated as NDCA) with methanol, various heavy metal organic acid salts such as cobalt, manganese, and rare earth elements, halides, etc. are used as the heavy metal oxidation catalyst. It is used. By the way, these heavy metal compounds serving as catalysts are relatively expensive, and their concentration conditions are much higher than the terephthalic acid production conditions under which the same reaction is carried out. Therefore, the heavy metal compounds are recovered and recycled to the oxidation step. It is desirable to make it.

Here, NDCA is obtained by extracting a reaction mixture from the oxidation reactor, depositing crystals, separating the crystals by a method such as centrifugation or filtration, and, if necessary, washing with acetic acid. It is obtained by drying. At this time, ND
Since a considerable amount of heavy metal oxidation catalyst remains on the CA side, the prior art has proposed a method of contacting separated NDCA with an aqueous solution of mineral acid to elute the heavy metal catalyst (Japanese Patent Application Laid-Open No. 62-212345). Further, a method of washing or recrystallizing a crude crystal of an aromatic carboxylic acid with water to elute a heavy metal catalyst (Japanese Patent Application Laid-Open No. 1-123737) has also been proposed.

However, as described above, in the method of eluting a heavy metal catalyst using water as a solvent, since the particle size of NDCA is small, a large amount of water is contained in the NDCA cake after solid-liquid separation of the washing liquid. The Rukoto. In the esterification step subsequent to this step, water adversely affects the reaction, so that it is necessary to perform an operation such as drying in advance to remove water, which undesirably increases equipment costs and utility costs. Furthermore, in the above method, it is necessary to use a large amount of washing liquid, and a large amount of waste liquid is generated after separating and recovering the heavy metal oxidation catalyst from the washing liquid by, for example, changing to water-insoluble carbonate. Is required.

[0006]

As described above, the conventional method for recovering a heavy metal oxidation catalyst from crude NDCA cannot be said to be efficient, and has a problem as an industrial production method.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, to reduce the cost of equipment and to produce an efficient NDC without generating a large amount of waste liquid.
A method for recovering a heavy metal oxidation catalyst from A.

That is, the present inventors have conducted intensive studies and as a result,
Instead of an aqueous solution, an alkyl alcohol solution, which had been considered to have no effect at all, was used, and a small amount of an acid component was added thereto, followed by washing to efficiently remove the heavy metal oxidation catalyst contained in NDCA. They found that they could be separated and recovered, and completed the present invention.

[0009]

According to the method of the present invention, NDCA obtained by oxidizing dialkylnaphthalene and / or its oxidized derivative with molecular oxygen (containing a heavy metal oxidation catalyst) is reacted with an alcohol such as methanol to obtain naphthalenedicarboxylic acid. It comprises a step of producing an esterification product such as a dialkyl, and a step of separating and recovering the heavy metal oxidation catalyst contained in the NDCA by washing it with an acid component-containing alcohol solution.

Examples of the dialkylnaphthalene used in the present invention include dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene and the like, and oxidized derivatives thereof include oxidation intermediates of the above-mentioned dialkylnaphthalene such as formylnaphthoic acid and acetylnaphthoic acid, and methylacetyl. Examples include alkylacylnaphthalene such as naphthalene and methylbutyrylnaphthalene, and diacylnaphthalene. It is particularly effective in the oxidation of diisopropylnaphthalene using a heavy metal oxidation catalyst at a high concentration. The oxidation reaction is usually carried out in a lower aliphatic monocarboxylic acid solvent to obtain NDCA. As the solvent, formic acid,
Examples thereof include acetic acid, propionic acid, butyric acid, and mixtures thereof with water.
0% by weight acetic acid is the preferred solvent.

The oxidation catalyst used in the production process of NDCA is a heavy metal compound and a bromine compound. The heavy metal catalyst is preferably cobalt and / or manganese,
If necessary, cerium, nickel, etc. may be added. These are used in the form of organic acid salts, halides, hydroxides, oxides, carbonates and the like, and as the bromide and fatty acid salts, acetates are particularly preferred. On the other hand, the bromine compound may be either an organic compound or an inorganic compound, as long as it can dissolve in the oxidation reaction system and generate bromine ions. Specifically, molecular bromine (Br ₂ ), bromine Hydrogen fluoride,
Examples thereof include inorganic bromides such as ammonium bromide and organic bromides such as alkyl bromide and brominated fatty acid such as bromoacetic acid. Hydrogen bromide, ammonium bromide, cobalt bromide and manganese bromide are particularly preferred examples.

The concentration of the heavy metal oxidation catalyst varies depending on the starting material, but is usually 0.01 to 1 per mol of the starting material.
0 mol is used, and bromine is used usually in an atomic ratio of 0.01 to 2 with respect to the total of heavy metal elements.

The molecular oxygen used in the oxidation reaction of the present invention is
Oxygen gas or a mixture thereof diluted with an inert gas is used. Industrially, air is most easily available and preferred. In the oxidation reactor, the raw material naphthalene compound, a solvent,
After feeding the catalyst and air and reacting for a predetermined time,
The reaction mixture was withdrawn from the reactor to precipitate NDCA crystals, separated by a method such as centrifugation or filtration, and, if necessary, washed with the same solvent as the oxidizing solvent and dried to obtain crude NDCA. can get. Depending on the oxidation reaction conditions, NDCA cleaning conditions, etc., this NDCA contains a considerable amount of heavy metal oxidation catalyst.

The esterification reaction of the present invention can be carried out without a catalyst or in the presence of an esterification catalyst, usually using methanol as an alkyl alcohol, but preferably in the presence of an esterification catalyst. In this case, the esterification catalyst is preferably an acid catalyst soluble in methanol, for example, sulfuric acid, hydrochloric acid, phosphoric acid, organic sulfonic acid and the like.

The esterification reaction temperature may be above or below the critical temperature of methanol (240 ° C.). Of course, it is preferable to maintain the reaction pressure below the critical temperature so that the methanol is in the liquid phase. Methanol is usually preferably used in an amount of 3 to 10 times the weight of crude NDCA. In this case, since the esterification product is taken out as a methanol solution, it can be cooled to a predetermined temperature and then subjected to solid-liquid separation to obtain crude NDM .

The above esterification reaction may be carried out continuously or batchwise. Further, the reaction time is preferably as short as possible within a range in which a desired eslute conversion ratio can be obtained. If the reaction time is too long, dimethyl ether by-product is increased, which is not preferable. Esterification rate is 80
% Or more, preferably 90% or more, more preferably 95%
That is all.

Hereinafter, the method for recovering a heavy metal oxidation catalyst of the present invention will be described.

In the recovery method of the present invention, a crude NDCA containing a heavy metal oxidation catalyst is washed with an alkyl alcohol solution containing an acid component, and a heavy metal oxidation catalyst such as cobalt or manganese is eluted and transferred to a washing solution.

Usually, the heavy metal oxidation catalyst thus obtained is further subjected to solid-liquid separation by adding a compound capable of generating carbonate ions to the washing filtrate in which these are dissolved, replacing the heavy metal oxidation catalyst with insoluble carbonate. And can be easily separated and recovered in high yield.

The heavy metal oxidation catalyst thus separated and recovered can be recycled to the oxidation step as it is, or, if necessary, dissolved in an aliphatic carboxylic acid solution such as acetic acid to form an aliphatic carboxylic acid. Instead of the acid salt, it can be recycled to the oxidation step.

As the alkyl alcohol used for washing the crude NDCA, at least one of methanol, ethanol, propanol, butanol and isomers thereof can be used, but the same alcohol as that used for the esterification can be used. It is particularly preferred to use

The acid component contained in the cleaning alcohol solution is an acid component soluble in the cleaning alcohol, and examples thereof include sulfuric acid, hydrochloric acid, phosphoric acid and organic sulfonic acids such as paratoluenesulfonic acid. Preferably, the same acid component as the acid catalyst used in the esterification reaction is used.

Further, in the alcohol solution for washing, water,
An organic substance such as NDCA or NDM may be contained. Therefore, as the alcohol solution for washing, the esterification reaction is carried out under liquid phase conditions in the presence of an acid catalyst. It is particularly preferable to use a filtrate obtained by solid-liquid separation. As described above, when the filtrate obtained by solid-liquid separation of the esterification product is used as the washing liquid, the liquid contained in the wet cake of NDCA after washing and solid-liquid separation is used for the esterification reaction. Unlike the case where an aqueous solution is used as a washing liquid, the alcohol and the acid catalyst are the same as those used in the present invention, so that pretreatment such as drying or replacement with an alcohol used for the esterification reaction is not required, and the esterification reaction can be directly performed. . Also, in this case, the acid catalyst contained in the filtrate obtained by solid-liquid separation of the esterification product forms a salt with the heavy metal oxidation catalyst, so that the corrosiveness to the equipment when recovering alcohol from this filtrate is small. Thus, the amount of the alkali compound used to neutralize the acid can be reduced. Further, since no water is used for washing, wastewater requiring a large amount of treatment is not generated.

Hereinafter, the method of the present invention will be described in detail with reference to examples.

[0025]

[Comparative Example 1] A gas injection pipe, a gas discharge pipe, and a cooling pipe were provided.
In a titanium autoclave equipped with a stirrer, the solvent was solid-liquid separated from the reaction mixture obtained by air-oxidizing 2,6-dimethylnaphthalene using acetic acid solvent with cobalt acetate, manganese acetate and hydrogen bromide as catalysts. Removed. The reaction was washed with acetic acid, dried and the crude 2,6-NDC
A was obtained. Cobalt 0.1 in this 2,6-NDCA
0 wt% and manganese 0.51 wt% are contained,
The yield of 2,6-NDCA was 93.0 mol%.

Next, 100 parts by weight of the crude 2,6-NDCA and 300 parts of water were placed in a three-necked flask equipped with a condenser and a stirrer.
The mixture was stirred at 90 ° C. for 1 hour, and then filtered while hot with a glass filter. The liquid content of the cake was 38 wt%, and the distribution of cobalt and manganese on the filtrate side (that is, the recovery of cobalt and manganese) was 71%, respectively.
And 70%. Since the cake contained 60 parts by weight of water, it was subjected to an esterification reaction after drying.

Next, 245 parts by weight of the washing filtrate obtained above and 20 watts were placed in a three-necked flask equipped with a condenser and a stirrer.
6% by weight of an aqueous t% sodium carbonate solution is added.
After stirring for an hour, the deposited precipitate was separated by filtration and dried. The recovery rates of cobalt and manganese are 99.3% and 98.5%, respectively.
Met. On the other hand, the amount of waste liquid requiring treatment including sodium trimellitate and the like was 250 parts by weight.

[0028]

Comparative Example 2, Examples 1 and 2 The 2,6-NDCA10 obtained in Comparative Example 1 was placed in a three-necked flask equipped with a cooling tube and a stirrer.
0 parts by weight, and 500 parts by weight of the cleaning liquid shown in Table 1 were charged.
After stirring at 60 ° C. for 1 hour, the mixture was filtered with a glass filter. The distribution ratio of cobalt and manganese to the filtrate side is as shown in Table 1, and the liquid content of the cake was 30 to 33 wt%.

[0029]

[Table 1]

[0030]

Example 3 In a Hastelloy autoclave equipped with a stirrer, 145 parts by weight of the washed wet cake (liquid content 31 wt%) obtained in Example 2 and methanol 555 were added.
Parts by weight and 3 parts by weight of sulfuric acid, and sealed (reaction pressure: 20
〜25 kg / cm ² G) The reaction was carried out at 160 ° C. for 1 hour under stirring. After completion of the reaction, the mixture was cooled to 40 ° C. to precipitate crystals, and then filtered through a glass filter to obtain 525 parts by weight of a filtrate (water content: 5%).

Then, the washing solution alone was changed from 500 parts by weight of methanol to 525 parts by weight of the filtrate from the esterification product, and crude 2,6-NDC was prepared in the same manner as in Comparative Example 2.
A was washed. As a result, 90% and 85% of the cobalt and manganese in the crude 2,6-NDCA were reduced to 48% respectively by the washing filtrate 48.
Collected in 0 parts by weight.

Next, the washing filtrate was concentrated by an evaporator, and 9 parts by weight of a 20 wt% sodium carbonate aqueous solution was added.
After stirring at 70 ° C. for 1 hour, the deposited precipitate was separated by filtration and dried. The recovery rates of cobalt and manganese in the carbonate generation step were 99.5% and 99.2%, respectively. The amount of waste liquid after completely distilling and recovering methanol from the filtrate was 36 parts by weight, which was mainly by-product water of the esterification reaction.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-364152 (JP, A) JP-A-2-250851 (JP, A) JP-A-1-121237 (JP, A) JP-A-62-162 212345 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 C07C 51 / 21,63 / 38 C07C 67 / 56,69 / 76

Claims (7)

(57) [Claims] 1. A process for producing an esterified product by esterifying a naphthalenedicarboxylic acid obtained by oxidizing a dialkylnaphthalene and / or an oxidized derivative thereof with molecular oxygen with an alkyl alcohol, and comprising the step of: Separating and recovering the heavy metal oxidation catalyst contained therein by washing it with an alkyl alcohol solution containing an acid component. 2. The method of claim 1, wherein the heavy metal oxidation catalyst is at least one selected from the group consisting of cobalt, manganese, cerium and nickel.
The method for recovering a catalyst according to claim 1, which is a kind of component. 3. The esterification is carried out using methanol at 240
2. The method for recovering a catalyst according to claim 1, wherein the method is carried out at a reaction pressure of not more than 0 ° C and higher than a saturated vapor pressure of methanol at the reaction temperature. 4. The method for recovering a catalyst according to claim 3, wherein the esterification is performed in the presence of an esterification catalyst. 5. The method according to claim 4, wherein at least one of sulfuric acid, hydrochloric acid, phosphoric acid and organic sulfonic acid is used as the esterification catalyst. 6. The method according to claim 1, wherein the acid component contained in the cleaning alkyl alcohol solution is at least one component selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid and organic sulfonic acid.
The method for recovering a catalyst according to the above. 7. The method for recovering a catalyst according to claim 3, wherein the alkyl alcohol solution for washing is a filtrate obtained by solid-liquid separation of an esterification reaction product.