JPH04370115A - Recovery of n-methyl-2-pyrrolidone - Google Patents

Abstract

PURPOSE:To efficiently recover N-methyl-2-pyrrolidone as a polymerization solvent in a powdery state in a production process of polycyanoaryl ether and further to make a recovery process continuous. CONSTITUTION:An aqueous solution containing N-methyl-2-pyrrolidone and a formed salt is heated while successively feeding N-methyl-2-pyrrolidone to an evaporator 1, N-methyl-2-pyrrolidone and water are evaporated and then successively introduced to a distillation column to separate N-methyl-2- pyrrolidone from water.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] 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.
The present invention relates to a method for recovering 2-pyrrolidone (hereinafter referred to as NMP).

0002

[Prior art and problems to be solved by the invention] Conventionally,
Polycyanoaryl ether is widely used as a material for electronic equipment, 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 (Japanese Unexamined Patent Publication No. 62-2232
No. 26), and a method of reacting difluorobenzonitrile after the above polymerization reaction (Japanese Patent Application Laid-Open No. 1894-1894)
Publication No. 35), etc. have been proposed.

In these methods, NMP is used as a polymerization solvent.
However, in the manufacturing process, particularly in the separation and washing steps, a large amount of an aqueous solution containing 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 handling wastes, such as combustibility, flammability, and odor, can be improved.

That is, from the polymer reaction produced by the polymerization reaction, salts such as NaCl and organic substances such as oligomers that remain after the reaction are generated, and in order to increase the purity of the polymer, large amounts of water and organic solvents are added Washed. From an economic point of view, it is preferable that the solvent be recovered in its entirety;
The cleaning liquid contains 1 to several tens of percent solids. Among these, organic substances such as oligomers are highly adhesive and the solvent cannot be easily recovered, and it is not economical to recover the solvent to a liquid content that does not exhibit adhesive properties.

[0005] For this reason, several methods have been proposed for recovering NMP from NMP-containing liquids containing organic substances of this type. The method is
It was a batch process and not efficient. In addition, U.S. Patent No. 4,965,370 attempts to achieve continuous operation using a thin film evaporator, but it is difficult to extract the solid content with a liquid content of 10% or less, and the recovery rate is also low. . Furthermore, although JP-A-2-111402 states that continuous processing is possible, the oligomer has strong adhesive properties and solidifies at a liquid content of 20% or less in a thin film evaporator. There was a problem with the discharge.

[0006] The present inventors have developed a method for efficiently discharging NMP as a polymerization solvent in the production process of polycyanoaryl ether, discharging wastes such as salts and oligomers in powder form, and further making the recovery process continuous. We conducted extensive research to develop a method that could be used.

[0007]

[Means for solving the problem] As a result, an aqueous solution containing NMP and a salt produced in the polycyanoaryl ether manufacturing process is first introduced into an evaporator to separate the solvent to some extent, and then the solvent is distilled. By separating water and NMP, NMP is recovered with less decomposition and deterioration.
It was discovered that it can be used again as it is. Furthermore, it has been found that the solid content can be pulverized by introducing the solid content separated in the evaporator into a specific dryer to separate the solvent and the solid content. The present invention was completed based on this knowledge.

That is, the present invention involves reacting a dihalogenobenzonitrile and a dihydric phenol with an alkali metal salt or an alkali metal salt of a dihydric phenol using N-methyl-2-pyrrolidone as a polymerization solvent to form a polycyanoarylether. When producing (1), N-methyl-2-pyrrolidone or N-methyl-2-pyrrolidone is added to the resulting reaction mixture.
An aqueous solution containing N-methyl-2-pyrrolidone and the resulting salt obtained after adding a mixture of pyrrolidone and water and separating and collecting the precipitated polycyanoaryl ether; The resulting aqueous solution containing N-methyl-2-pyrrolidone and the salt produced, ③ the aqueous solution containing N-methyl-2-pyrrolidone and the salt produced in ① and/or ③ above is washed with water to separate and recover the polycyanoarylether oligomer. N-
Aqueous solution containing methyl-2-pyrrolidone and the produced salt, and
At least one type of N-methyl-2-pyrrolidone and generated salt-containing aqueous solution selected from the N-methyl-2-pyrrolidone and generated salt-containing aqueous solution obtained by washing the polycyanoaryl ether oligomer separated and recovered in the above ①. ,
Heating it while continuously introducing it into the evaporator, N-methyl-2
- Provides a method for recovering N-methyl-2-pyrrolidone, which comprises evaporating pyrrolidone and water and then continuously introducing the mixture into a distillation column to separate N-methyl-2-pyrrolidone and water. It is.

First, the stock solution to be subjected to the recovery method of the present invention is subjected to polymerization using dihalogenobenzonitrile and dihydric phenol and an alkali metal salt or an alkali metal salt of dihydric phenol as raw materials and using NMP as a polymerization solvent. liquid or cleaning liquid.

Here, the dihalogenobenzonitrile includes 2,6-dichlorobenzonitrile; 2,4-dichlorobenzonitrile; 2,6-difluorobenzonitrile; 2,4-difluorobenzonitrile; 2-chloro-6
-fluorobenzonitrile; 2-fluoro-6-chlorobenzonitrile; and the like, 2,6-dichlorobenzonitrile; 2,6-difluorobenzonitrile is particularly preferred.

[0011] Also, as dihydric phenol, 1,2-
Dihydroxybenzene; 1,3-dihydroxybenzene; 1,4-dihydroxybenzene; 2-methyl-1,4
-dihydroxybenzene; 2,6-dimethyl-1,4-
Dihydroxybenzene; dihydroxybenzenes such as 2-methoxy-1,4-dihydroxybenzene, 4,4'
-dihydroxybiphenyl; 3,5'-dihydroxybiphenyl;3,5-dihydroxybiphenyl;3-methyl-4,4'-dihydroxybiphenyl; dihydroxybiphenyls such as 2,2'-dimethyl-4,4'-dihydroxybiphenyl , 1,2-dihydroxynaphthalene; 1,3-dihydroxynaphthalene; 1,4-dihydroxynaphthalene; 1,5-dihydroxynaphthalene; 1
, 6-dihydroxynaphthalene; 1,7-dihydroxynaphthalene; 1,8-dihydroxynaphthalene; 2,3
-dihydroxynaphthalene; 2,6-dihydroxynaphthalene; 2,7-dihydroxynaphthalene; dihydroxynaphthalenes such as 4,8-dimethyl-2,6-dihydroxynaphthalene, dihydroxydiphenyl ethers such as 4,4'-dihydroxydiphenyl ether, etc. can be mentioned. Particularly preferred dihydroxyaryl compounds are 1,3 and 1,4-dihydroxybenzenes (resorcinol, hydroquinone).

Further, examples of the alkali metal salts include carbonates and hydrogen carbonates of alkali metals. Specific examples include lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and cesium hydrogen carbonate. 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.

[0013] The amount of such raw materials to be used may be appropriately selected without any particular restriction, but usually 0.95 to 1.03 (mole ratio) of dihalogenobenzonitrile to dihydric phenol;
Preferably 0.98 to 1.01, and in the case of alkali metal salts 1.0 to 0.3 (molar ratio), preferably 1.0
~2.0, 2.0-6.0 for alkali metal hydrogen salts
(molar ratio), preferably 2.0 to 4.0. Also,
When an alkali metal salt of a dihydric phenol is used, the amount of dihalogenobenzonitrile is usually used in approximately an equimolar amount to the alkali metal salt of a 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.
It is preferable to adjust the amount to 5 mol/liter.

[0015] This polymerization reaction is usually carried out at 160 to 300°C.
Preferably at a temperature range of 190 to 210°C, 1 to 10
It may be carried out for a period of time, preferably from 2 to 5 hours. Furthermore, this reaction may be carried out under normal pressure or may be carried out under slightly increased pressure. In particular, it is more effective to carry out the reaction under an inert gas atmosphere such as argon gas or nitrogen gas.

[0016] In addition, during the above polymerization reaction, a molecular weight regulator can be added as necessary. Examples of molecular weight modifiers 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.

[0017] 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. As a terminal capping agent, monovalent phenols such as phenol, cumylphenol, methoxyphenol, and cyanophenol; monovalent halides such as methyl chloride, chlorobenzonitrile, fluorobenzonitrile, chlorobenzophenone, and fluorobenzophenone;
, 4-dichlorobenzonitrile, 2,6-dichlorobenzonitrile, 2,4-difluorobenzonitrile, 2,
Examples include polyhalogenated benzonitriles such as 6-difluorobenzonitrile.

More specific conditions for the above polymerization are as described in JP-A-62-223226, JP-A-63-189435, JP-A-63-370733, and the like.

After completion of this reaction, the reaction product polycyanoaryl ether remains dissolved in NMP. This reaction product is further added with NMP if necessary.
Add and dilute. 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 is NM
The weight ratio of P/water is preferably 100/0 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. As this cleaning solvent, a mixed solution having a weight ratio of NMP/water of 100/0 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.

[0022] Through this washing, the polycyanoaryl ether oligomer is separated. 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 the aqueous solution (2) obtained as described above has an NMP content of less than 65% by weight, a water content of 35% by weight or more, and a polycyanoarylether oligomer content of 0. .05-1% by weight,
The amount of generated salt is approximately 0.1 to 5% by weight. Water is added to this solution and the polycyanoaryl 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 produced salt, and is the above-mentioned aqueous solution (2). By this operation, the content of polycyanoaryl ether oligomer can be reduced to 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.

Furthermore, the stock solution to be used in the recovery method of the present invention includes:
5-1), NMP-containing liquid obtained by cooling the reaction mixture while applying shearing force, and then performing distillation or evaporation operation (5-2), particle formation of polycyanoaryl ether into the obtained reaction mixture NMP-containing liquid (5 -3), to the obtained reaction mixture,
NM to the extent that polycyanoaryl ether does not become particles
NMP-containing liquid (5-4) obtained by adding P to dilute it, then adding a polycyanoaryl ether particle-forming solvent to particleize the polycyanoaryl ether, and then performing a distillation or evaporation operation, The obtained reaction mixture is cooled to precipitate polycyanoaryl ether, and then pulverized as it is or by adding a particulate solvent or NMP, and then distilled or evaporated to obtain NM.
The P-containing liquid (5-5) or the reaction mixture is cooled under shearing conditions to precipitate the polycyanoaryl ether, which is then pulverized as it is or by adding a particulate solvent or NMP, followed by distillation or NMP-containing liquid (5-6) obtained by performing the evaporation operation, ■ oligomer-containing NMP-containing liquid obtained by washing the polycyanoaryl ether separated and recovered in above ■ with NMP, or ■ above ■
An NMP-containing liquid obtained by washing the polycyanoaryl ether oligomer separated and recovered with water can also be included.

[0026] In the above (2), as a device (particulation device) that applies shear force to the reaction mixture (slurry), a stirring blade such as an ordinary anchor blade, swept blade, paddle, leak blade, sigma type, etc. is installed in the tank. It is possible to use a tank-type stirring tank, a single-screw or multi-screw kneader or extruder, a vibrating type, a paddle dryer, etc. This particle generation device may be integrated with the reaction container, for example, by providing a stirring blade in the reaction container.
A granulation tank or granulation device separate from the reaction vessel may be provided.

[0027] The slurry temperature at this time can be from room temperature to the boiling point (according to atmospheric pressure), and the pressure can be at normal pressure using various inert gases, azeotropic solvents, or autogenous pressure as the distillation medium, or under reduced pressure. . In addition, the solvent distillation (distillation operation) time is adjusted so that the NMP distillation rate is distilled off 0.007 to 0.7 times the amount used in the reaction per minute.
It is preferable to adjust so that 0.3 to 0.97 times as much NMP as used in the reaction is distilled off.

Further, as described in (5-2) above, the obtained reaction mixture was cooled while applying a shearing force, and then N
By distilling off the MP it is possible to reduce the cake volume. The cooling temperature at this time is preferably a temperature lower than the polymerization reaction temperature, for example from room temperature to about 195°C, and can be carried out continuously or at appropriate intervals during the whole or part of the solvent distillation time, but usually, 0 (above (5)
-1)) to 480 minutes.

In the above (5-1), a solvent (particulate solvent) that is compatible with the polymerization solvent but does not dissolve the produced polymer is added. When such a solvent is added, the resulting polymer is not dissolved but is subdivided into particles. Also, the above (
As shown in 5-4), the particulate solvent may be added after the diluent is added to the polymerization solution and cooled.

As the diluent, a neutral polar solvent similar to the polymerization solvent can be used. The amount of diluent added is 1 cc or more per 1 g of produced polymer, or 3 cc or more of the polymerization solvent.
As a guideline, the amount may be within twice as much (volume ratio), and the amount may be added all at once or gradually over a period of 30 minutes or less. The temperature of the reaction system during dilution is 150℃~
The polymerization temperature and the temperature of the system after dilution are preferably 50 to 190°C.

On the other hand, methanol,
ethanol, propanol, isopropanol, acetone, methyl ethyl ketone, water, or mixtures thereof;
Alternatively, polymerization solvents and mixtures thereof may be used, and those having a low boiling point are preferred so that they do not remain in the polymer. In addition, the amount of particle-forming solvent added varies depending on various conditions.
Although it cannot be determined uniquely, the amount is usually 0.2 times or more, preferably 0.5 to 5.0 times the amount of the polymer solution. If the amount added is too small, some of the polymers will become particles, while others will become lumps, which may reduce the yield.

When adding the particle-forming solvent, the temperature of the polymer solution may be set within an appropriate range, but generally the temperature is below the boiling point of the mixture of the polymer solution and the particle-forming solvent, preferably 1
00-180°C. If the temperature is too low, the polymer will solidify before the solvent is added, and if the temperature is too high, the amount of the particulate solvent will volatilize, which is not preferable.

The above particle-forming solvent may be added in its entirety to the polymer solution at once, but it is usually added over about 1 to 60 minutes, preferably about 3 to 20 minutes. If it is added too quickly, some of the polymer may not become particles and may form lumps, while if it is added for too long, productivity will decrease.

[0034] Further, as the above-mentioned particle forming solvent, a mixed solvent with a polymerization solvent, for example, a mixed solvent of NMP and water can be used. N in this mixed solvent of NMP and water
There is no particular restriction on the mixing ratio of MP and water, but usually N
MP/water = 95/5 to 30/70 (volume ratio), preferably 90/10 to 50/50 (volume ratio). Further, the amount of the particulate solvent consisting of NMP and water may be approximately 0.5 to 5 times (volume ratio) the amount of the polymerization solvent. After forming the resulting polymer into particles in this manner, the solvent may be distilled off under the same conditions as above.

Next, as described in (5-5) above, it is also possible to cool the polymer as it is after the completion of the reaction, precipitate the polymer, and then perform pulverization. The cooling conditions at this time are 1
It is preferable to bring the temperature from room temperature to 130°C over 480 minutes, and by applying shearing force during cooling, a more preferable precipitation state can be obtained. Further, the pulverization can be carried out using a normal mechanical pulverization means at a temperature ranging from room temperature to the boiling point of the solvent. The polymer can be easily pulverized by adding 1 cc or more of the polymerization solvent or the above-mentioned granulation solvent per 1 g of the produced polymer during the pulverization. The solvent may be distilled off after pulverization in the same manner as described above.

After the polymer particles are obtained in this way, they are filtered and subjected to necessary post-treatments such as washing and drying according to a conventional method. As the washing solvent, a polymerization solvent or a granulation solvent is used. be able to. The appropriate amount of washing solvent to be used is usually 0 (no washing) to 10 times the amount of the polymerization solvent, and when using a mixed solvent with the polymerization solvent, the ratio is 0 (no washing) to 10 times the amount of the polymerization solvent.
The particle forming solvent may be set to 100/0 to 0/100. Further, the temperature of the cleaning solution is from room temperature to the boiling point, the cleaning time is from 1 to 60 minutes, and the number of times of washing is suitably from 0 (no washing) to 10 times. This washing effectively removes residual oligomers and the like in the polymer cake ((2) above).

In the NMP recovery method of the present invention, the above-mentioned aqueous solution (1), aqueous solution (2), aqueous solution (2),
Aqueous solution ■, NMP-containing liquid ■, NMP-containing liquid ■, and NMP
At least one selected from the containing liquids (1) is collected or sent separately to a recovery process to recover NMP and pulverize the waste.

[0038] An outline of all the steps of the recovery method of the present invention is shown in Figure 1.
As shown in This treatment process basically consists of the following three steps. Each step will be explained in order below. First, the above-mentioned stock solution is introduced into the evaporator 1. This evaporator 1
The method separates solid and liquid while converting the solid content in the stock solution into large particles, and various types can be used depending on the processing amount and the like. For example, natural convection by bubbling of evaporated steam, or forced convection by propellers or jets, promotes aggregation and crystallization of salt particles.Generally used types include natural circulation immersion tube type, natural circulation type, etc. Horizontal tube type, natural circulation vertical short tube type, basket type, calandria type, vertical long tube rising membrane type, propeller calandria type, horizontal tube descending membrane type, vertical long tube descending membrane type, forced circulation horizontal tube type , forced circulation vertical tube type, coil type, stirred membrane type, centrifugal type, flash evaporation type, etc. can be used, especially propellers that have a small amount of adhesion to each part of the device and force convection. It is preferable to use a calandria type or a propeller coil type.

[0039] The operating temperature in this evaporator 1 is 60~
A suitable temperature range is 204°C, preferably 80 to 150°C, and the pressure is 50 to 760 mmHg, preferably 50 to 150°C.
It is 200mmHg. That is, the boiling point of NMP is 204° C. at normal pressure, and at higher temperatures or pressures, a large amount of heat must be added, resulting in large operating costs, and furthermore, at high temperatures, the deterioration of NMP is accelerated. Further, at low temperatures, the evaporation operation time becomes long, and a large-capacity vacuum pump is required to achieve low pressure.

The NMP and water separated by evaporation in the evaporator 1 are introduced into the distillation column 2, and water is obtained from the top of the column through a distillation operation, and NMP is obtained from the bottom or side cut of the column. The operating conditions for this distillation column may be appropriately selected as long as they can separate NMP and water. The obtained NMP has a water content of 0.05% by weight or less, contains almost no generated salts or oligomers, and is hardly decomposed or altered. Therefore, it can be used as it is again as a solvent for the above-mentioned polymerization reaction.

On the other hand, the solid content separated in the evaporator 1 is
It is introduced into a dryer 3 equipped with a stirring means having shearing force and crushing force, and is dried until the liquid content becomes about 0.5%. The liquid component evaporated and separated at this time is returned to the original solution before being introduced into the evaporator 1 and processed again. Moreover, the liquid content is about 0.
The solid content reduced to 5% becomes powder and is discharged from the system.

The solid content introduced into the dryer 3 has a dry basis liquid content of 25 to 300%, preferably 50 to 300%.
%, it is desirable to maintain fluidity in a slurry state. If the liquid content is less than 25%, it will be difficult to transfer from the evaporator 1 to the dryer 3, and if the liquid content is high, it will be difficult to dry. This is not desirable as it increases the load on the machine. In addition, the temperature and pressure are
For the same reason as the evaporator 1, the temperature is set to 100 to 220°C.
, preferably 130~200℃, pressure 50~760m
mHg, preferably in the range of 80 to 200 mmHg.

Furthermore, the jacket temperature for heating this dryer 3 should be at least 150°C, preferably 160°C, in order to prevent oligomers in the solid content from adhering to the wall surface and solidifying. .

[0044] Also, the stirring means having shearing force and crushing force means that the raw material is forcibly stirred to constantly renew the raw material near the heat transfer wall surface so as to prevent local heating of the high viscosity raw material, and also to prevent sticking of the raw material. It has the ability to crush and powderize the solid matter when it occurs, and examples of commonly used types include cylindrical and groove type stirring dryers, Nirwa dryers, stirring membrane dryers, A rotary mill or a vibrating mill type dryer can be used, but planetary mills have a particularly good scraping effect on materials near the wall due to the planetary movement of the stirring blades, and have a strong crushing force by evenly mixing the entire raw material. Preferably, a mixer is used.

[0045]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Example 1 (1) 6.61 kg of resorcinol,
Add 10.31 kg of 2,6-dichlorobenzonitrile, 7.00 kg of sodium carbonate, and 60 liters of N-methyl-2-pyrrolidone (NMP), raise the temperature to 195°C while blowing argon gas, and then azeotrope with toluene. The produced water was dehydrated for 1 hour, and then reacted at 200°C for 1 hour. Next, a solution of 0.10 kg of 2,6-difluorobenzonitrile dissolved in 0.8 liters of NMP was added thereto, and polymerization was carried out at 200° C. for 2 hours. Furthermore, N
A solution in which 0.08 kg of 2,6-difluorobenzonitrile was dissolved in 0.8 liters of MP was added and reacted at 200° C. for 30 minutes to perform terminal termination treatment. After the reaction was completed, 56 liters of NMP at room temperature was added to the polymerization solution at a temperature of 200° C. over 5 minutes to dilute it. The internal temperature at this time is 170℃
Met. Next, NMP/water (64
liter/16 liter) of the mixed solvent 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 designated as aqueous solution 1. The resulting cake was mixed with NMP/water (172 liters/44 liters)
The oligomers were removed by washing once with a mixed solution. This filtrate is designated as aqueous solution 2. Thereafter, heat washing was performed for 20 minutes once with an aqueous solution of 180 liters of water/1 kg of oxalic acid dihydrate and 11 times with 180 liters of water for 20 minutes, and then dried in a drier overnight to recover the polymer. Washing with water 1st time, 2nd time
The cleaning solutions for the third and third times were aqueous solutions 3, 4, and 5, respectively. The composition of each aqueous solution is shown in Table 1.

[0046]

[Table 1]

(2) NMP-containing liquids, ie, aqueous solutions 1 and 2 (N
MP266kg, water 36kg, oligomer 1.6kg,
3.8 kg of generated salt) and polymer washing solution, i.e., aqueous solution 3,
4 and 5 (NMP 49 kg, water 492 kg, produced salt 3.
5 kg) was added to prepare NMP-containing aqueous solution A. This aqueous solution A contained 315 kg of NMP, 528 kg of water, 1.6 kg of oligomer, and 7.3 kg of produced salt.

(3) Separation of solid content This aqueous solution A was supplied to an evaporative crystallizer at a flow rate of 125 kg/hour, and was continuously evaporated and crystallized. The vapor evaporated at that time was designated as B. A slurry containing solids was intermittently extracted from the bottom of the can every 8 hours. This slurry was designated as C. Table 2 shows the particle size of the precipitated salt in this chiller. The dry basis liquid content of the slurry was 300% by weight.

(4) Distillation The evaporated vapor B from (3) was supplied to a distillation column for continuous distillation. The distillation column has an inner diameter of 300 mm, 19 theoretical plates/12 supply plates.
stage, side cut 18 stages, reflux ratio 0.3, tower top pressure 10
The temperature was 0 Torr and the bottom temperature was 140°C. Through this distillation, the purity of the water obtained from the top of the column is 99.995% or more,
The purity of NMP recovered from the side cut was 99.98.
%, water content 0.01%, and heavy content 0.01%.

(5) Recovery of NMP from slurry (3
) The slurry C was supplied to a planetary stirring dryer, and the liquid was evaporated to recover NMP. The minimum drying pressure is 5
The drying temperature varied between 0 Torr and a maximum of 150 Torr, and the drying temperature was 125°C to 145°C. The vapor obtained by evaporation was condensed, and this was used as recovered liquid D. Since this liquid contained oligomers entrained by droplets, it was returned to NMP-containing aqueous solution A. Drying was continued for about 6 hours until no more evaporation steam was produced. The pressure was then returned to normal and discharged from the system. The solid thus obtained was designated as E. Table 3 shows the liquid content on a dry basis in this solid and the amount attached to the dryer. Table 4 also shows the relationship between jacket temperature and powdering.

Comparative Example 1 The same procedure as in Example 1 was carried out except that in (3) above, a simple flash drum was used instead of the evaporative crystallizer for heating. The results are shown in Table 2.

Comparative Example 2 The same procedure as in Example 1 was carried out except that in (5) above, a uniaxial anchor blade having the same clearance with the wall was used instead of the planetary motion stirring dryer. The results are shown in Tables 3 and 4.

Comparative Example 3 The same procedure as in Example 1 was carried out except that in (5) above, a vibrating ball mill type dryer was used instead of the planetary stirring type dryer. The results are shown in Tables 3 and 4.

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

Example 2 A polymerization reaction similar to that in Example 1 was carried out, but instead of adding a particulate solvent, the reaction mixture was cooled while applying a shearing force, and
The same procedure as in Example 1 was carried out except that the solvent was then distilled off to obtain a polycyanoaryl ether powder. Table 5 shows the compositions of the distillate and cleaning solution.

[0058]

[Table 5]

Example 3 Stirring device, argon gas blowing tube, thermocouple, Dean
- In a separable flask equipped with a Stark trap, 22.02 kg of resorcinol, 34.35 kg of 2,6-dichlorobenzonitrile, 23.3 kg of sodium carbonate.
2 kg, 0.01% water content NM recovered in Example 1
After adding 200 ml of P and raising the temperature to 195°C while blowing argon gas, the water produced was dehydrated for 1 hour by azeotropy with toluene, and then reacted at 200°C for 1 hour. Next, a solution of 0.35 g of 2,6-difluorobenzonitrile dissolved in 2 ml of NMP was added thereto, and polymerization was carried out at 200°C. During the reaction, a small amount of the polymerization solution was sampled after 2 hours, 3 hours, 4 hours, and 5 hours, and the reduced viscosity was measured. The reduced viscosity was measured after washing the sampled solution with water and drying it in a p-chlorophenol solvent at a concentration of 0.2 g/dl at 60°C. The results are shown in Table 6.

Comparative Example 4 The same operation as in Example 3 was carried out except that the commercially available NMP shown in Table 6 was used as the solvent. The results are shown in Table 6.

Example 4 Polymerization and recovery were carried out in the same manner as in Example 1 using a solvent.
The same operation as in Example 3 was performed except that NMP was used repeatedly. The results are shown in Table 6.

[0062]

[Table 6]

[0063]

As explained above, according to the recovery method of the present invention, NMP with extremely low impurities can be efficiently and continuously recovered. This NMP can be used again as a polymerization solvent without any purification or other treatment, and by recycling it, polycyanoaryl ether can be produced economically and waste can be reduced. Can be done. Also, waste can be pulverized, so
Its handling properties are improved, and the safety environment can be improved. Therefore, the present invention can improve the production efficiency of polycyanoaryl ether suitable for materials for various parts, and is expected to be effectively utilized.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the processing steps of the present invention.

[Explanation of symbols]

Claims (6)

[Claims] Claim 1: A polycyanoarylether is produced by reacting dihalogenobenzonitrile and a dihydric phenol with an alkali metal salt or an alkali metal salt of a dihydric phenol using N-methyl-2-pyrrolidone as a polymerization solvent. In this case, (1) N-methyl- is added to the resulting reaction mixture.
An aqueous solution containing N-methyl-2-pyrrolidone and the resulting salt obtained after adding 2-pyrrolidone or a mixture of N-methyl-2-pyrrolidone and water and separating and recovering the polycyanoaryl ether precipitated, N-methyl-2-pyrrolidone and the resulting salt-containing aqueous solution obtained by washing the separated and recovered polycyanoaryl ether with water; An aqueous solution containing N-methyl-2-pyrrolidone and the produced salt obtained after separating and recovering the polycyanoaryl ether oligomer, and N-methyl-2- obtained by washing with water the polycyanoaryl ether oligomer separated and recovering in (2) above. At least one type of N-methyl- selected from aqueous solution containing pyrrolidone and a generated salt.
The aqueous solution containing 2-pyrrolidone and the produced salt is heated while being continuously introduced into an evaporator to evaporate N-methyl-2-pyrrolidone and water, and then continuously introduced into a distillation column to evaporate N-methyl-2-pyrrolidone and water.
- A method for recovering N-methyl-2-pyrrolidone, which comprises separating methyl-2-pyrrolidone and water. 2. In the evaporator, the produced salt and polycyanoaryl ether oligomer are crystallized into large particles, and the solid content is settled at the bottom of the can, and then the solid content is
While maintaining fluidity in the form of a slurry, it is introduced into a dryer equipped with a stirring means with shearing force and crushing force and heated, and the liquid content is evaporated until the solid content reaches 10%. 2. The method for recovering N-methyl-2-pyrrolidone according to claim 1, characterized in that while recovering methyl-2-pyrrolidone, the solid content is discharged as a powder or as an aqueous solution by adding water. 3. N-methyl-2- according to claim 2, wherein the temperature of the jacket heating medium of the dryer is set to 150° C. or higher to suppress adhesion and solidification of solids to the wall surface.
How to recover pyrrolidone. 4. A polycyanoaryl ether is produced by reacting dihalogenobenzonitrile and a dihydric phenol with an alkali metal salt or an alkali metal salt of a dihydric phenol using N-methyl-2-pyrrolidone as a polymerization solvent. In this case, (1) the N-methyl-2-pyrrolidone-containing liquid obtained by distilling or evaporating the reaction mixture while applying a shearing force, cooling the reaction mixture while applying a shearing force, and then distilling or evaporating the reaction mixture; A polycyanoaryl ether particle forming solvent is added to the N-methyl-2-pyrrolidone-containing liquid obtained by the operation and the obtained reaction mixture to form particles of polycyanoaryl ether, or to the reaction mixture N- The polycyanoaryl ether is made into particles by adding methyl-2-pyrrolidone and cooling, and then the N-methyl-2-pyrrolidone-containing liquid obtained by distillation or evaporation is added to the obtained reaction mixture. The cyanoaryl ether is diluted by adding enough N-methyl-2-pyrrolidone to prevent it from turning into particles, and then the polycyanoaryl ether particle-forming solvent is added to turn the polycyanoaryl ether into particles, followed by a distillation or evaporation operation. The resulting N-methyl-2-pyrrolidone-containing liquid and the resulting reaction mixture were cooled to precipitate the polycyanoaryl ether, and then either directly or with a particulate solvent or N-methyl-2-pyrrolidone. After cooling the N-methyl-2-pyrrolidone-containing liquid obtained by adding and pulverizing, and then performing a distillation or evaporation operation, or the reaction mixture under shear conditions to precipitate polycyanoaryl ether, The N-methyl-2-pyrrolidone-containing liquid obtained as it is or by adding a particle-forming solvent or N-methyl-2-pyrrolidone and then performing a distillation or evaporation operation; Oligomer-containing N-methyl-2 obtained by washing cyanoaryl ether with N-methyl-2-pyrrolidone
- At least one type of N-methyl-2-pyrrolidone-containing liquid selected from a pyrrolidone-containing liquid and an N-methyl-2-pyrrolidone-containing liquid obtained by washing with water the polycyanoarylether oligomer separated and recovered in ② above. The liquid is heated while being continuously introduced into the evaporator, and N-methyl-
A method for recovering N-methyl-2-pyrrolidone, which comprises evaporating 2-pyrrolidone and water and then continuously introducing the mixture into a distillation column to separate N-methyl-2-pyrrolidone and water. 5. In the evaporator, the produced salt and polycyanoarylether oligomer are crystallized into large particles, and the solid content is settled at the bottom of the can, and then the solid content is
While maintaining fluidity in the form of a slurry, it is introduced into a dryer equipped with a stirring means with shearing force and crushing force and heated, and the liquid content is evaporated until the solid content reaches 10%. 5. The method for recovering N-methyl-2-pyrrolidone according to claim 4, characterized in that while recovering methyl-2-pyrrolidone, the solid content is discharged as a powder or as an aqueous solution by adding water. 6. N-methyl-2- according to claim 5, wherein the temperature of the jacket heating medium of the dryer is set to 150° C. or higher to suppress adhesion and solidification of solids to the wall surface.
How to recover pyrrolidone.