JPH03281531A - Recovery of n-methyl-2-pyrrolidone - Google Patents

Abstract

PURPOSE:To recover the title pyrrolidone useful as a polymerization catalyst having extremely low impurities by a simple process by distilling an aqueous solution containing pyrrolidone prepared in production process of polycyanoaryl ether and resultantly formed salt followed by filtering. CONSTITUTION:In producing a polycyanoaryl ether by reacting a dihalogenobenzonitrile with a dihydric phenol with an alkali metal salt or an alkali metal salt of dihydric phenol by using N-methyl-2-pyrrolidone as a polymerization solvent, the obtained reaction mixture is blended with the pyrrolidone or a mixture of the pyrrolidone and water, precipitated polycyanoaryl ether is separated and recovered. The prepared aqueous solution containing the pyrrolidone and formed salt is distilled to remove water, and further distillation residue is filtered or centrifuged to recover the objective pyrrolidone.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for recovering N-methyl-2-pyrrolidone, and more specifically, to a method for recovering N-methyl-2-pyrrolidone, which is a polymerization solvent used in the production of polycyanoaryl ether. Pyrrolidone (hereinafter referred to as
The present invention relates to a method for recovering NMP) and an industrially advantageous method for producing polycyanoaryl ether using the recovered NMP.

[Problems to be solved by conventional techniques and inventions] Conventionally,
Polycyanoaryl ether is an electronic device.

It is widely used as a material for electrical equipment, mechanical parts, etc. The method for producing it is a method of polymerizing dihalogenobenzonitrile and dihydric phenol with an alkali metal salt or an alkali metal salt of dihydric phenol.
2-223226), and a method of reacting difluorobenzonitrile after the above polymerization reaction (Japanese Patent Laid-open No. 6
3189435) and the like have been proposed.

In these methods, NMP is very preferably used as a polymerization solvent, but in the manufacturing process, particularly in the separation and washing steps, a large amount of an aqueous solution of NMP mixed with water is produced. Disposing of this as it is poses safety and environmental problems, and also leads to increased costs. If this NMP can be efficiently recovered, economic efficiency will be improved, and the safety environment for waste handling, such as combustibility, flammability, and odor, can be improved.

Therefore, the present inventors have developed a method to efficiently recover NMP, which is a polymerization solvent, in the production process of polycyanoaryl ether, and to enable reuse of the NMP.
I have done extensive research.

(Means for solving the problem) As a result, NMP can be efficiently recovered by performing distillation, filtration, etc. on the aqueous solution containing NMP and the salt produced in the polycyanoaryl ether production process, In addition, this method causes less decomposition and deterioration, and the recovered NM
It was discovered that P can be used again as it is. The present invention was completed based on this knowledge.

That is, in the present invention, dihalogenobenzonitrile and a dihydric phenol are reacted with an alkali metal salt or an alkali metal salt of a dihydric phenol using 7NMP as a polymerization solvent to produce polycyanoa+7-lether. An aqueous solution containing NMP and the resulting salt (hereinafter referred to as aqueous solution) obtained after adding NMP or a mixture of NMP and water to the reaction mixture and separating and recovering the precipitated polycyanoaryl ether. An aqueous solution containing NMP and the produced salt obtained by washing the polycyanoaryl ether with water (hereinafter referred to as
(hereinafter referred to as aqueous solution ■), (hereinafter referred to as aqueous solution ■), (hereinafter referred to as aqueous solution ), and ■ an aqueous solution containing NMP and the generated salt obtained by washing the polycyanoarylether oligomer separated and recovered in the above (■) (hereinafter referred to as aqueous solution ■).
NM characterized in that the aqueous solution containing NMP and the produced salt is distilled to remove water, and the distillation residue is further filtered or centrifuged to separate the produced salt and NMP.
The present invention provides a method for recovering P (hereinafter referred to as the first invention).

Furthermore, the present invention provides a polypropylene polymer characterized in that a dihalogenobenzonitrile, a dihydric phenol, and an alkali metal salt or an alkali metal salt of a dihydric phenol are polymerized using the NMP recovered in the first invention as a polymerization solvent. Provided is a method for producing cyanoaryl ether (hereinafter referred to as the second invention), and also provides a method for reacting dihalogenobenzonitrile and a dihydric phenol with an alkali metal salt or an alkali metal salt of a dihydric phenol using recovered NMP as a polymerization solvent. and then reacting the obtained reaction product with difluorobenzonitrile (hereinafter referred to as the third invention)
It provides:

In the method of the first invention, dihalogenobenzonitrile and a dihydric phenol and an alkali metal salt or an alkali metal salt of a dihydric phenol are used as raw materials, and NMP is used as a polymerization solvent. Here, as the dihalogenobenzonitrile, 2,6-cyclobenzonitrile; 2,4-
Dichlorobenzonitrile; 2,6-cyfluoropenzonitrile; 2,4-difluorobenzonitrile; 2-chloro-6-fluorohendinitrile; 2-fluoro-6-
Examples thereof include chlorobenzonitrile, and 2.6-cyclobenzonitrile and 2.6-difluorobenzonitrile are particularly preferred.

In addition, examples of the dihydric phenol include catechol, resorcinol, quinol, etc., and resorcinol is particularly preferred. Furthermore, examples of the alkali metal salts include alkali metal carbonates, hydrogen carbonates, and the like. in particular,
Examples include lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, cesium hydrogen carbonate, and the like. The dihydric phenol and the alkali metal salt form an alkali metal salt of the dihydric phenol in the reaction system to advance the polymerization reaction. Therefore, instead of the dihydric phenol and alkali metal salt described above as reaction raw materials, a corresponding alkali metal salt of a dihydric phenol may be used.

The amount of such raw materials to be used may be appropriately selected without any particular restriction, but it is usually 0.95 to 1.03 (molar ratio) of dihalogenobenzonitrile to dihydric phenol, preferably 0.
．． 98 to 1.01, and 1.0 in the case of alkali metal salts.
0 to 0.3 (molar ratio), preferably 1.0 to 2.0, 2.0 to 6.0 (molar ratio) in the case of alkali metal hydrogen salts,
Preferably it is 2.0 to 4.0.

In addition, when using an alkali metal salt of dihydric phenol, usually about the same mole of dihalogenobenzonitrile is used relative to the alkali metal salt of dihydric phenol.

In the present invention, NMP is used as a polymerization solvent for such raw materials. The amount used is not particularly limited, but the polymerization concentration of the product polymer in the solvent is 0.5 to 2.5 mol/i!
, preferably.

This polymerization reaction may be carried out at a temperature range of usually 160 to 300°C, preferably 190 to 210°C, for 1 to 10 hours, preferably 2 to 5 hours. Furthermore, this reaction may be carried out under normal pressure or may be carried out under slightly increased pressure. Especially argon gas.

It is more effective to carry out the reaction under an inert gas atmosphere such as nitrogen gas.

In addition, during the above polymerization reaction, a molecular regulator can be added as necessary. Examples of molecular regulators that can be used include monohalogenobenzonitrile, monophenol, and the like. Moreover, the amount to be used may be appropriately determined in relation to the molecular weight of the target polymer.

Further, in the above reaction, after the temperature is raised, dehydration may be performed using a solvent that is azeotropic with the produced water or dehydration using an inert gas. Examples of azeotropic solvents include toluene, chlorobenzene, and anisole.

Furthermore, a terminal capping agent may be added to terminate the reaction. Examples of terminal capping agents include monovalent phenols such as phenol, cumylphenol, methoxyphenol, and cyanophenol; monovalent halides such as methyl chloride, chlorobenzonitrile, fluorobenzonitrile, chlorohensiphenone, and fluorohensephenol; 2,4-dichlorohenzonitocle, 2,6-cyclohenzonitrile, 2
Examples include polyhalogenated pennztriles such as 4-difluorobenzonitrile and 22.6-difluorobenzonitrile.

More specific conditions for the above polymerization are disclosed in JP-A-62-223
No. 226, No. 63-189435, No. 63-
This is as described in Publication No. 370733 and the like.

After completion of this reaction, the reaction product polycyanoaryl ether remains dissolved in NMP. This reaction product is further diluted by adding NMP if necessary. This is to reduce the viscosity of the polymerization solution, and the amount of NMP added is usually not more than three times the amount of the polymerization solvent.

Furthermore, NMP or a mixture of NMP and water is added to this diluted solution. As a result, the polycyanoaryl ether product is precipitated as particles. Such a particulate solvent has a weight ratio of NMP/water of 1001.
The ratio is preferably 0 to 30/70, and the amount used is 0.5 to 3 times the amount of the polymerization solvent. The polycyanoaryl ether thus precipitated and the solution are separated by filtration or centrifugation. This filtrate is an aqueous solution that contains a large amount of NMP and further contains formed salts.

Here, the produced salt is an alkali metal halide produced by the reaction. This aqueous solution containing NMP and the produced salt is the above-mentioned aqueous solution (2).

The polycyanoaryl ether separated as described above is washed with a mixed solution of NMP and water, and then with water.

For this cleaning solvent, the weight ratio of NMP/water is 1 OO1
A mixed solution having a ratio of 0 to 30/70 is suitable. The amount used is about 0.5 to 5 times the amount of the polymerization solvent. Further, washing is performed with water, but this water washing may also be performed with neutralization treatment using an inorganic acid such as hydrochloric acid or an organic acid such as oxalic acid.

This washing separates the polycyanoaryl ether oligomer. As described above, the cleaning liquid obtained by cleaning with a mixed solution of NMP and water and cleaning with water is an aqueous solution containing NMP and the generated salt, and constitutes the above-mentioned aqueous solution (2).

In the present invention, the aqueous solution (1) and/or
Alternatively, the aqueous solution (■) has an NMP content of less than 65% by weight, a water content of 35% by weight or more, and a polycyanoaryl ether oligomer content of 0.05 to 1% by weight, 0.1% by weight.
It is about 5% by weight.

Water is added to this solution and the lipolycyanoaryl ether oligomer is separated by filtration or centrifugation. The polycyanoaryl ether oligomer begins to precipitate when the NMP concentration becomes 65% by weight or less, and precipitates when it becomes 40% by weight or less. This cleaning solution is an aqueous solution containing NMP and the generated salt, and is the above-mentioned aqueous solution (2). With this operation,
The content of polycyanoaryl ether oligomer can be approximately 0%. This aqueous solution (1) can be used again for recovering oligomers.

The oligomer thus separated may be further washed with water in the same manner as above. The aqueous solution containing NMP and the produced salt obtained here is the aqueous solution (2) described above.

In the NMP recovery method of the present invention, the above-mentioned aqueous solution
At least one aqueous solution selected from , aqueous solution (1), aqueous solution (2), and aqueous solution (2) is distilled together or separately. This distillation may be carried out batchwise or continuously, but it is usually preferable to carry it out continuously for efficiency. Distillation conditions may be appropriately selected as long as water can be removed from the aqueous solution.

The distillation residue obtained by removing water by such distillation is a mixture of the reaction product salt and NMP. Next, the generated salt and NMP
Separate. This generated salt is precipitated in NMP,
Since it is a smooth crystalline salt, it is easily separated by filtration or centrifugation.

In this recovery method, when distillation is carried out continuously, an aqueous solution for recovering NMP is continuously supplied to the distillation column, water is taken out from the top of the distillation column, and a mixture of produced salt and NMP is taken out from the bottom of the column. If carried out, it is efficient and a normal distillation column can be used.

The NMP recovered in this way has a water content of 5% by weight.
The content of the produced salt is less than 0.1% by weight, almost no oligomer is contained, and there is almost no decomposition or deterioration. Therefore, it can be used as is as a solvent for polymerization reactions.

On the other hand, in the second invention, the NMP recovered in this way
The present invention provides a method for producing polycyanoaryl ether by reacting dihalogenobenzonitrile and a dihydric phenol with an alkali metal salt or an alkali metal salt of a dihydric phenol using the above-described method as a solvent. In this method, the recovered NMP is used as a solvent in the polymerization reaction. Furthermore, in this method as well, recovered NMP can be used repeatedly by performing the above NMP recovery method.

Further, in the third invention, recovered NMP is used as a solvent, and a dihalogenobenzonitrile such as dichlorobenzonitrile and a dihydric phenol are reacted with an alkali metal salt or an alkali metal salt of a dihydric phenol, and then the obtained The present invention provides a method for producing polycyanoaryl ether by reacting a reaction product with difluorobenzonitrile. This method is the same as the second invention up to the step of reacting dihalogenobenzonitrile and dihydric phenol with an alkali metal salt or an alkali metal salt of dihydric phenol using recovered NMP as a solvent. The reaction product thus obtained is further reacted with difluorobenzonitrile. Examples of difluorobenzonitrile include 2,6-difluorobenzonitrile; 24-difluorobenzonitrile.

This difluorobenzonitrile acts as a main chain extender in the polymerization reaction and can increase the molecular weight of the polycyanoaryl ether produced.

The amount of difluorobenzonitrile added is not particularly limited and may be selected as appropriate, but it is 0.005 to 0.05 (molar ratio), preferably 0.01 to the dihydric phenol as the raw material.
~0.05 (molar ratio). Moreover, the reaction conditions are the same as above.

The reaction product thus obtained is treated in the same manner as in the second invention to obtain polycyanoaryl ether. Furthermore, in this manufacturing method as well, recovered NMP can be used repeatedly by performing the above NMP recovery method.

[Example] Next, the present invention will be explained in detail with reference to Examples and Comparative Examples.

Example 1 (1) 6.61 kg of resorcinol, 2
．． 10.31 kg of 6-dichlorobenzonitrile, 7.00 kg of sodium carbonate, N-methyl-2-pyrrolidone (
NMP) 60j2 was introduced, and the temperature was raised to 195" (j) while blowing argon gas, and then the produced water was dehydrated for 1 hour by azeotropy with toluene, and then reacted at 200°C for 1 hour.

Next, 0.1 of 2,6-dichlorobenzonitrile was added to this.
Adding a solution of 0 kg dissolved in NMPo, 842,
Polymerization was carried out at 200°C for 2 hours. Furthermore, NMPo,8
0.08 kg of 2,6-dichlorobenzonitrile to 42
A solution in which was dissolved was added and reacted at 200°C for 30 minutes to perform terminal termination treatment.

After the reaction is completed, add room temperature NMP to the polymerization solution at a temperature of 200°C.
56f was added for 5 minutes to dilute. The internal temperature at this time is 1
The temperature was 70°C. Next, NMP/
A mixed solvent of water (64f/16f) was added over 10 minutes to obtain a slurry of polycyanoaryl ether. The slurry temperature at this time was 130°C. The resulting slurry was filtered.

This filtrate is referred to as aqueous solution 1.

The resulting cake was washed once with a mixed solution of NMP/water (1721/44 l) to remove oligomers.

This filtrate is designated as aqueous solution 2.

Thereafter, heat washing was performed for 20 minutes once with an aqueous solution of 180 f water/1 kg oxalic acid dihydrate and 11 times with 1802 water for 20 minutes, and then dried in a drier overnight to recover the polymer. The cleaning solutions for the first, second, and third washings were designated as aqueous solutions 3, 4, and 5, respectively.

The composition of each aqueous solution is shown in Table 1.

(Margins below) Table 1 (2) Precipitation and removal of oligomers NMP-containing liquids from which the polymer was collected and removed, i.e. aqueous solutions 1 and 2 (NMP 266 kg, water 36 kg, oligomer 1
．． 6 kg, 3.84 cg of produced salt), polymer washing solution,
That is, aqueous solutions 3, 4 and 5 (NMP 49kg, water 492k
g, 3.54 cg of produced salt) were added to prepare NMP-containing aqueous solution A. This aqueous solution A has NMP of 315 dazzles and water of 528 k.
g, 1.6 kg of oligomer, and 7.3 ml of produced salt. Next, the oligomer and the liquid were separated by filtration. N
The weight percentages of the MP-containing aqueous solution and filtrate are shown in Table 2.

Table (3) Recovery of NMP from oligomers The oligomers separated in (2) above were suspended in 100 kg of water and then filtered. This operation was repeated twice. The amount of residual NMP in the oligomer was determined by gas chromatography.
It was confirmed that 999% or more was recovered. In addition, -
degree, it was 99.8%.

(4) Distill the NMP-containing aqueous solution of (2) to 30! ! ,/h to the distillation column for continuous distillation. The distillation column has an inner diameter of 100 mm.
14 theoretical stages/11 supply stages, reflux ratio 0.1.

The bottom temperature of the column was 202°C.

Through this distillation, the purity of the water obtained from the top of the column was 99.9.
% or more, and the purity of NMP from the bottom of the column was 9.9% or more.

(5) Removal of salt The mixture of salt and NMP from the bottom of the column in (4) was filtered under reduced pressure. The remaining NMP was recovered from the separated salt by further heating and drying. The recovered NMP has a purity of 9
9.9%, water 0.1%.

Examples 2 to 4 In (4) of Example 1, the distillation conditions were changed to ? 17
NMP was recovered as 1.0%, 3.0%, and 5.0%. The results are shown in Table 3.

Example 5 Stirring device, argon gas blowing tube, thermocouple Dean-
In a monochrome flask equipped with a 5tark trap, 22.02 kg of resorcinol, 34.35 kg of 2,6-cyclopendunitrile, and 23 kg of sodium carbonate were added.
．． 32 kg, 10% water NMP recovered in Example 1
200d, and while blowing argon gas, reduce the temperature to 1.
After raising the temperature to 95°C, the produced water was dehydrated for 1 hour by azeotropy with toluene, and then reacted at 200°C for 1 hour.

Next, 0.3 of 2,6-difluorohenzonitrile was added to this.
A solution of 5 g of NMP 2 mfl was added and polymerized at 200°C. During the reaction, 2 hours later, 3
After 4 hours and 5 hours, a small amount of the polymerization solution was sampled and the reduced viscosity was measured. The reduced viscosity was determined by washing the sampled solution with water, drying it, and then setting it in a P-chlorophenol solvent at a concentration of 0.
Measured at 2g/d1.60'C. The results are shown in Table 4.

Examples 6 to 8 In Example 6, the solvent NMP recovered in Example 2 was used, in Example 7 the one recovered in Example 3, and in Example 8 the one recovered in Example 4 was used. Except for this, the same procedure as in Example 5 was carried out. The results are shown in Table 4.

Comparative Examples 1 and 2 The same operation as in Example 5 was performed, except that NMP, a commercially available product shown in Table 4, was used as the solvent.

The results are shown in Table 4.

Table 4 *1...Analysis by Karl Fischer method*2...
After 2 hours, the value immediately before addition of 2.6-cyfluorobenzonitrile *3... Commercial product with water content of 206 ppm *4... Commercial product with water content of 200 ppm (same as *3 above: [Effects of the invention] As described above, according to the recovery method of the present invention, NMP with extremely low impurities can be recovered in a simple process using a conventional distillation column. This NMP can be used again as a polymerization solvent without undergoing any treatment such as purification, and by recycling it, polycyanoaryl ether can be produced economically and waste can be reduced. can be measured.

Therefore, the present invention is expected to be effectively utilized as a method for efficiently producing polycyanoaryl ether suitable for materials for various parts.

Claims (3)

[Claims] (1) When producing polycyanoarylether by reacting dihalogenobenzonitrile and dihydric phenol with an alkali metal salt or an alkali metal salt of dihydric phenol using N-methyl-2-pyrrolidone as a polymerization solvent. , [1] N-methyl-2-pyrrolidone or a mixture of N-methyl-2-pyrrolidone and water is added to the resulting reaction mixture and the precipitated polycyanoarylether is separated and recovered. 2-pyrrolidone and generated salt-containing aqueous solution, [2] N-methyl- obtained by washing the polycyanoaryl ether separated and recovered in [1] above with water
2-pyrrolidone and produced salt-containing aqueous solution, [3] N-methyl-2 of [1] and/or [2] above
- An aqueous solution containing N-methyl-2-pyrrolidone and the produced salt obtained after washing the aqueous solution containing the pyrrolidone and the produced salt with water to separate and recover the polycyanoarylether oligomer, and [4] the polycyano separated and recovered in [3] above. N-methyl-2- obtained by washing aryl ether oligomer with water
At least one type of N-methyl-2-pyrrolidone and product salt-containing aqueous solution selected from pyrrolidone and product salt-containing aqueous solutions is distilled to remove water;
A method for recovering N-methyl-2-pyrrolidone, which further comprises separating the produced salt and N-methyl-2-pyrrolidone by filtering or centrifuging the distillation residue. (2) Using dihalogenobenzonitrile and a dihydric phenol and an alkali metal salt or an alkali metal salt of a dihydric phenol as a polymerization solvent and N-methyl-2-pyrrolidone recovered by the recovery method according to claim 1. A method for producing polycyanoaryl ether, which comprises reacting. (3) Using dihalogenobenzonitrile and a dihydric phenol and an alkali metal salt or an alkali metal salt of a dihydric phenol as a polymerization solvent and N-methyl-2-pyrrolidone recovered by the recovery method according to claim 1. react,
A method for producing polycyanoaryl ether, which comprises then reacting the obtained reaction product with difluorobenzonitrile.