JPH1129532A - Purification of diaryl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for reducing the waste load in the purification step, in the production of diaryl carbonate free from hydrolyzable chlorine which is a catalyst-poisoning substance in the production of aromatic polycarbonate through the molten ester-interchange reaction. SOLUTION: An aromatic monohydroxy compound is allowed to react with phosgene or an aryl chloroformate to form a diaryl carbonate and the reaction mixture containing the diaryl carbonate is neutralized with an aqueous alkali, separated into the organic phase and water phase, then the organic phase is brought into contact with water, then they are separated into the water phase and the organic phase, and the objective diaryl carbonate is recovered from the organic phase. At this time, the separated water phases after contact with the alkali aqueous solution and/or those after contact with hot water are distilled and the distilled water is used again for preparation of the alkali aqueous solution or the water for bringing into contact with the organic phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing a drainage load in producing a highly purified diaryl carbonate. The diaryl carbonate obtained in the present invention is useful as a raw material for producing an aromatic polycarbonate by a melt transesterification method.

[0002]

2. Description of the Related Art As a method for producing diaryl carbonate, various production methods are known. For example, a phase interface phosgenation method of an aromatic monohydroxy compound in an aqueous alkaline solution (Schotten-Baumann reaction) is known. In this case, partial saponification of phosgene is caused by the aqueous alkali solution, and a large amount of sodium chloride is generated as a by-product, which causes problems such as a decrease in the effective utilization rate of phosgene, an increase in raw material costs due to the use of alkali, and wastewater treatment. .

Further, US Pat. No. 2,837,555 proposes performing solventless condensation in the presence of a tetramethylammonium halide as a catalyst. However, this method requires a relatively large amount of catalyst in order to obtain an economical reaction rate, and 180
It is necessary to use temperatures as high as ２215 ° C.
Therefore, there is a risk of decomposition of thermally unstable tetramethylammonium halide. In addition, phosgene is consumed at a much higher rate than required stoichiometrically.

As a means for solving such a problem, there is a method for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene in the presence of a catalytic amount of an aromatic heterocyclic basic nitrogen compound or a salt thereof. It has been proposed (see Japanese Patent Publication No. 58-50977). As a method for separating the catalyst contained in the reaction mixture, the publication discloses a method of isolating the catalyst as an easily meltable adduct as a bottom material during distillation of the reaction mixture, and a method of separating a second substance precipitated at the bottom of the reaction melt. A method for isolating a catalyst from a liquid phase is described.

However, the catalyst which can be separated in the form of an easily meltable adduct as a distillation still residue is limited due to the thermal stability and boiling point of the hydrochloric acid adduct, and the liquid catalyst from the reaction melt of the latter is limited. In the case of separation, a considerable amount of the salt of the catalyst is dissolved in the diaryl carbonate, and the aromatic polycarbonate produced by transesterification with bisphenol A as a raw material has a bad hue or corrodes the mold.

When an aromatic monohydroxy compound is reacted with phosgene or an aryl chloroformate, hydrochloric acid is by-produced in addition to diaryl carbonate. Except for a reaction example in an alkaline aqueous solution, a part of the hydrochloric acid remains in the reaction mixture due to dissolution in the reaction mixture, formation of an adduct with a basic catalyst, and the like. A compound having hydrolyzable chlorine such as hydrochloric acid is known as a substance having a poisoning effect on a polymerization catalyst when an aromatic polycarbonate is produced from a diaryl carbonate by a melt transesterification method, and the content in the diaryl carbonate is reduced. Tens of pp
It is desirably not more than b.

As a method for removing hydrochloric acid remaining in the reaction mixture as hydrochloric acid or a hydrochloric acid adduct of a basic catalyst to a level that does not affect the polymerization catalyst, the reaction mixture is neutralized with an alkali, and the reaction mixture is extremely neutralized. It is conceivable to completely remove trace amounts of hydrochloric acid and salts generated by neutralization. Thus, the reaction mixture is neutralized by contact with an aqueous alkali solution, then separated into an organic phase and an aqueous phase, the organic phase is contacted with warm water, separated into an aqueous phase and an organic phase again, and the diaryl carbonate is separated from the organic phase. We considered the recovery process.

In this method, the aqueous phase separated after neutralization and the aqueous phase separated after contact with hot water are discharged out of the system as waste water. In these wastewaters, water-soluble aromatic monohydroxy compounds, water-soluble catalysts, and the like are dissolved. When production is performed at an industrial level, not only increases in raw material costs due to dissolution loss, but also in wastewater treatment. However, there is a problem that the cost is increased. In particular, when the aromatic monohydroxy compound is subjected to activated sludge treatment, which is a usual wastewater treatment method, the load on the activated sludge is large, and it is important to reduce it as much as possible.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a process for purifying a diaryl carbonate obtained by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate. In the production of aromatic polycarbonates by the melt transesterification method, such as arylchloroformate, basic catalyst hydrochloride adducts, etc. It is an object of the present invention to provide a method of manufacturing while reducing.

[0010]

According to the present invention, a reaction mixture containing a diaryl carbonate obtained by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate is brought into contact with an aqueous alkali solution to neutralize the reaction mixture. After that, the organic phase and the aqueous phase are separated, the separated organic phase is brought into contact with water, the aqueous phase and the organic phase are again separated, and the diaryl carbonate is recovered from the organic phase. Distilling the aqueous phase separated after contacting with water or the aqueous phase separated after contacting with water, and distilling the distillate water as an aqueous alkali solution or reusing it as water for contacting with an organic phase. It provides a method.

[0011]

Many of the water-soluble aromatic monohydroxy compounds and organic basic catalysts form an azeotrope with water, and can be recovered in distillation water at a high yield by distillation. For this reason, the residual amount in the distillation still residue containing the inorganic salts and the like generated by the neutralization was significantly reduced, and it became possible to reduce the load in the wastewater treatment. Even if the water to be brought into contact with the aqueous alkali solution and the organic phase is prepared from the distilled distillate containing the aromatic monohydroxy compound and the catalyst originally contained in the reaction mixture, there is no problem.
According to the method of the present invention, the wastewater discharged out of the system is only the distillation bottom residue when the separated aqueous phase is distilled, and in addition to reducing the dissolution loss of the raw material, the wastewater treatment load can be significantly reduced. It has become possible.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Aromatic monohydroxy compound: An aromatic monohydroxy compound is a compound in which a hydroxy group is directly bonded to an aromatic ring, such as phenol, alkylphenols such as cresol and butylphenol, arylphenols, and halogen. Phenols having an alkyl or aryl group bonded through a heteroatom can be used.

Aryl chloroformate: As the aryl chloroformate, the above-mentioned aromatic monohydroxy compound chloroformate can be used.

Phosgene: The phosgene is preferably a pure one containing no impurities such as methylene chloride and carbon tetrachloride. Phosgene is at most 1.0 mol, preferably at least 0.4 mol, based on 1.0 mol of the aromatic monohydroxy compound.
It is used in a proportion of 0.5 mol.

An aromatic heterocyclic nitrogen-containing basic compound or
Salt: When an aromatic heterocyclic nitrogen-containing basic compound is used as a catalyst, the aromatic heterocyclic nitrogen-containing basic compound has a nitrogen atom present in an aromatic 5- or 6-membered ring. A basic nitrogen compound that does not have a functional group (for example, an amino group or a hydroxy group) that easily forms a strong bond with phosgene or a carbonate under the reaction conditions. It may have another hetero atom such as oxygen and sulfur.

Specific examples of such a catalyst include pyridine,
Quinoline, picoline, imidazoles, benzimidazoles, pyrazoles, triazoles and benzotriazoles. The aromatic heterocyclic nitrogen-containing basic compound catalyst is immediately converted to the corresponding hydrochloride in the reaction mixture. Since this hydrochloride is in a dissociation equilibrium state with the free basic catalyst, instead of the free basic catalyst, a salt of the basic catalyst, for example, an inorganic acid salt such as hydrochloride or sulfate, or a formate is used. Organic salts such as acetic acid and salts can be used. These catalysts are used in an amount of 0.001 to 0.20 mol, preferably 0.1 to 1.0 mol, per 1.0 mol of the aromatic monohydroxy compound.
It is used in an amount of from 0.1 to 0.10 mol.

Alkali: As the alkali, hydroxides of sodium, potassium, calcium and barium, and sodium and ammonium salts of carbonic acid and phosphoric acid can be used.

Reaction: An example of obtaining a high-purity diaryl carbonate of the present invention will be described with reference to FIG. 1 using an aromatic heterocyclic nitrogen-containing basic compound as a catalyst as an example. A mixture of an aromatic monohydroxy compound (1) and an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof (2) is charged into a reactor (4), and the mixture is charged at 120 to 190 ° C.
Then, the mixture is melted, and the reaction is carried out by introducing gaseous phosgene (3) into the mixture at the same temperature with sufficient stirring.

The amount of phosgene introduced is 1.0 mol or less, preferably 0.4 to 0.5 mol, per 1.0 mol of the aromatic monohydroxy compound. The stoichiometric amount is 0.5 mol, but by controlling the introduced amount of phosgene to a stoichiometric amount or less, an unreacted aromatic monohydroxy compound inevitably remains, and the reaction intermediate aryl The reaction for forming a diaryl carbonate between the chloroformate and the aromatic monohydroxy compound is accelerated, and a reaction mixture containing almost no aryl chloroformate which has a bad influence on the production of an industrial grade colorless polycarbonate can be obtained. At this time, if necessary, nitrogen gas (5) is blown into the reaction mixture after the introduction of phosgene, and hydrochloric acid (6) generated by the reaction is removed to the outside of the system, whereby the arylchloroformate and the aromatic monohydroxy compound can be removed. The equilibrium reaction can be further promoted.

The mixture after completion of the reaction contains diaryl carbonate, unreacted aromatic monohydroxy compound, trace impurities, and a hydrochloride of an aromatic heterocyclic nitrogen-containing basic compound as a catalyst. The content will be about 300 to 60,000 ppm depending on the amount of catalyst used. To remove chlorine, the reaction mixture (7) taken out of the reactor (4) is contacted with an aqueous alkali solution (8) at a temperature equal to or higher than the melting point of the reaction mixture to neutralize the mixture, and the neutralized solution is separated into a separation tank (9). ), The organic phase is separated into an organic phase and an aqueous phase. The organic phase is extracted and brought into contact with water (10) at a temperature not lower than the melting point of the organic phase. This is done by separating.

The amount of water used, preferably hot water, is usually 0.01 to 20 times, preferably 0.2 to 1 times, the weight of the organic phase. If the amount of water is too small, the effect is not sufficient, and if it is too large, it takes time to recover. If the stirring and separation in the neutralization step and the water treatment step are appropriately performed, one water treatment is sufficient, but the stirring and separation are insufficient, and the concentration of hydrolyzable chlorine in the diaryl carbonate is high. In such a case, the same effect can be obtained by performing the steps of contacting with water and separating the aqueous and organic phases a plurality of times. At that time, the aqueous phase separated after the second or subsequent contact with water can be reused as an aqueous alkali solution or water used in the previous step.

Specifically, when the water treatment step is performed twice,
In the second water treatment, water consisting of distillate obtained by distilling the water phase separated after neutralization is supplied, and the water phase separated after the water comes into contact with the organic phase is used for the first time. To hot water treatment. Next, the counter flow method is optimal, in which the aqueous phase separated from the water after contact with the organic phase is reused for the preparation of an aqueous alkaline solution at the time of neutralization.

The temperatures of the neutralization step and the water treatment step are as follows:
The reaction can be carried out at a temperature equal to or higher than the melting point of the reaction solution.
It is desirable to carry out in the range of 00 ° C. Further, when a basic catalyst is used as a catalyst for the reaction with phosgene, the catalyst forms a thermally unstable hydrochloric acid adduct, which makes it difficult to recover and reuse the catalyst. The reaction mixture of the diaryl carbonate containing the product is neutralized with an aqueous alkali solution, then separated into an organic phase and an aqueous phase, and the organic phase is distilled to obtain a stable free basic catalyst almost quantitatively. Can be recovered.

The aqueous phase separated in the separation tank (9) and / or the separation tank (11) is recovered as distillate by distillation, and the alkaline aqueous solution (8) is prepared and / or the water (10) is brought into contact with the organic phase. Will be reused as This distillation can be easily performed by a normal distillation operation, and the still liquid (15) containing the salt generated by the neutralization is discharged as waste water. The aqueous phase separated in the separation tank (11) may be directly reused for preparing the aqueous alkali solution (8).

In order to easily and efficiently recover the basic catalyst, the organic phase separated from the aqueous phase is led to a distillation column, where the free basic catalyst (12) and the unreacted aromatic monohydroxy compound are removed by distillation. (13) and diaryl carbonate (14). The distillation temperature is 50 to 8 at 20 to 40 torr when the free basic catalyst is pyridine.
0 ° C., 50 to 100 ° C. at 20 to 40 torr when the unreacted aromatic monohydroxy compound is phenol or the like, and 140 to 160 ° C. at 5 to 10 torr when the diaryl carbonate is diphenyl carbonate or the like. The production of the diaryl carbonate of the present invention may be of a continuous type or a batch type (batch type).

[0026]

The present invention will be described below in more detail with reference to examples. Example Separated aqueous phase 720 after neutralization collected in the previous experiment
g (including 3.6 g of phenol, 3.0 g of pyridine, and 50 g of sodium chloride) were passed through an Oldershaw type 20-stage batch distillation tower under normal pressure at a reflux ratio of 2, a heating oil bath temperature of 130 to 170 ° C, and a distillation tower. Pot temperature 95-10
As a result of distillation under the condition of 5 ° C., 480 g of distillate water was obtained.
(Containing 3.1 g of phenol and 2.9 g of pyridine). The recovery of phenol was 86% and the recovery of pyridine was 97%. The remaining amount in the distillation still was 240 g (including 0.5 g of phenol, 0.1 g of pyridine and 50 g of sodium chloride).

A glass-made reaction vessel with a jacket connected to an oil circulation type external heating device (an overflow tube is installed at a position of 1 liter in internal volume and 700 ml of actual liquid).
Were connected three in a row. An exhaust pipe with a condenser for removing generated hydrochloric acid gas to the outside of the system was connected to the second and third reaction vessels. About 700 ml / hr of molten phenol, which was previously added with 5 mol% of pyridine and stirred, was added.
The temperature was raised to 150 ° C. while continuously supplying the mixture (corresponding to 716 g / hr of phenol and 30 g / hr of pyridine) to the first reaction vessel. With sufficient stirring, phosgene (361 g / hr) was supplied continuously to the first reaction vessel at a 0.48 molar ratio of the supplied phenol.

The reaction mixture flowing out of the first reaction vessel is
The reaction mixture was supplied to the second reactor via an overflow pipe, and the reaction mixture flowing out of the second reactor was similarly supplied to the third reactor. The reaction mixture flowing out of the third reactor was withdrawn into a polypropylene receiver. A nitrogen gas blowing tube was installed in the third reactor, and 70 Nl / hr of nitrogen gas was continuously supplied into the reaction mixture.

After the composition was sufficiently stabilized, 1 kg of the reaction mixture (composition: 89% by weight of diphenyl carbonate, 6% by weight of phenol, 5% by weight of pyridine hydrochloride, no phenyl chloroformate detected) was taken out of the oil circulation system. It was placed in a jacketed glass reaction vessel connected to a heating device and heated to 85 ° C. Prepared in advance from 74 g of an aqueous sodium hydroxide solution having a concentration of 25% by weight and 300 g of an aqueous phase (containing 1.2 g of phenol and 0.9 g of pyridine) collected from the previous experiment and subjected to hot water treatment,
374 g of a 5% by weight aqueous solution of sodium hydroxide, which had been heated to 5 ° C., was added, stirred for 5 minutes, allowed to stand for 30 minutes, and then the aqueous phase and the organic phase were separately extracted. The pH after the addition of the aqueous sodium hydroxide solution was 9.0.

The extracted organic phase was put again in a jacketed glass reaction vessel connected to an oil circulation type external heating device, and the temperature was raised to 85 ° C. Distilled water 30 obtained by distillation of the separated aqueous phase after neutralization, which has been heated to 85 ° C.
4g (including 1.9g phenol and 1.8g pyridine)
After stirring for 5 minutes, the mixture was allowed to stand for 5 minutes, and then the aqueous phase and the organic phase were separately extracted. The aqueous phase contains phenol 1.2
g and pyridine 0.9 g.

5 g of this diphenyl carbonate is added to 10 ml of toluene, dissolved at 60 ° C., 10 ml of ultrapure water (ion-exchanged water containing no Cl) is added, and the mixture is heated at 1000 rpm in a constant temperature room at 23 ° C. using a magnetic stirrer.
After stirring for minutes, the chlorine in the aqueous phase was analyzed by ion chromatography to find that it was 26 ppb. Next, the separated organic phase was distilled and purified in a vacuum distillation column packed with 10 Sulzer packings (manufactured by Sumitomo Heavy Industries). Specifically, the degree of vacuum is 20 to 40 torr and the oil bath temperature is about 22
After free pyridine and phenol are distilled off at 0 ° C. and a top temperature of 50 to 80 ° C., free pyridine and arylchloroformate are removed at a vacuum of 10 torr, an oil bath temperature of about 230 ° C. and a top temperature of 150 ° C. 750 g of purified diphenyl carbonate containing no (0 ppm) was obtained.

[0032]

According to the method for purifying diaryl carbonate of the present invention, diaryl carbonate having a small amount of residual polymerization catalyst can be produced, and the load of wastewater treatment during purification can be reduced.

[Brief description of the drawings]

FIG. 1 is a flow sheet diagram showing a method for producing a diaryl carbonate of the present invention.

Continued on the front page (72) Inventor Narutoshi Hyoto 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu-shi, Fukuoka Mitsubishi Chemical Corporation Kurosaki Office Development Laboratory

Claims (4)

[Claims] 1. A reaction mixture containing a diaryl carbonate obtained by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate is contacted with an aqueous alkali solution to neutralize the mixture, and then an organic phase and an aqueous phase are mixed. In the purification method of diaryl carbonate, the separated organic phase is brought into contact with water, separated again into an aqueous phase and an organic phase, and the diaryl carbonate is recovered from the organic phase.
Diaryl carbonate, characterized in that an aqueous phase separated after contact with an alkaline aqueous solution or an aqueous phase separated after contact with water is distilled, and distillate is reused as water for preparing an alkaline aqueous solution or for contacting with an organic phase. Purification method. 2. The method for purifying a diaryl carbonate according to claim 1, wherein a step comprising contacting with water and separating an aqueous phase and an organic phase is performed a plurality of times. 3. The contact with an aqueous alkali solution and water is carried out for 50
The method for purifying a diaryl carbonate according to claim 1, wherein the method is carried out at a temperature in the range of -100 ° C. 4. The method according to claim 1, wherein the reaction between the aromatic monohydroxy compound and phosgene or aryl chloroformate is carried out in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof. A method for purifying a diaryl carbonate according to the above.