JPH11140029A - Production of diaryl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a diaryl carbonate containing no polymerization inhibitor and having very high polymerization activity as a raw material for producing an aromatic polycarbonate by the fused ester interchange method. SOLUTION: The carbonate (e.g. diphenyl carbonate) containing only a small amount of hydrolyzable chlorine by reacting phosgene containing tetrachloromethane at 200 ppm or lower with a monohydroxy aromatic compound wherein the reaction is carried out without solvent, the phosgene contains chlorine at 10 ppm or less, and the diaryl carbonate is diphenyl carbonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The diaryl carbonate is
It is useful as a raw material for producing an aromatic polycarbonate by subjecting it and bisphenol A to a transesterification reaction. The present invention relates to a method for producing a diaryl carbonate having an extremely high polymerization activity when producing an aromatic polycarbonate.

[0002]

2. Description of the Related Art Various methods for producing diaryl carbonate are known. For example, a phase interface phosgenation method in which an aromatic monohydroxy compound is reacted with phosgene in a solvent and an aqueous alkali solution (Schottte)
n-Baumann reaction) is known. in this case,
Since the phosgene is partially saponified by the aqueous alkali solution and a large amount of sodium chloride is generated as a by-product, 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 occur. Also,
Increased construction costs due to equipment for solvent reuse and pollution of the air and water environment due to solvent leakage are also significant issues.

Further, US Pat. No. 2,837,555 discloses that a diaryl carbonate is produced by subjecting an aromatic monohydroxy compound and phosgene to solventless condensation in the presence of a tetramethylammonium halide as a catalyst. A method has been proposed. However, this method requires a relatively large amount of catalyst and requires a reaction at a high temperature of 180 to 215 ° C. in order to obtain an economical reaction rate. Tetramethylammonium halide is decomposed,
With the disadvantage that catalyst activity is impaired. In addition, phosgene is consumed at a much higher rate than required stoichiometrically.

[0004] In addition, production by transesterification of an aromatic monohydroxy compound and a dialkyl carbonate has been studied. However, in this method, a reaction is performed against an equilibrium that is remarkably biased in the reaction system, so that an extremely large amount of energy is required. , And the equipment is complicated because there are many by-products. As means for solving such a problem, there has been proposed a method for producing a diaryl carbonate by performing a reaction between an aromatic monohydroxy compound and phosgene in the presence of a catalytic amount of an aromatic heterocyclic basic nitrogen compound or a salt thereof. (See Japanese Patent Publication No. 58-50977). As a method for separating the catalyst contained in the reaction mixture, the publication discloses a method for isolating the catalyst residue as a readily meltable adduct of the bottom material during distillation of the reaction mixture, and a method for 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 type of the catalyst which can be separated in the form of an easily meltable adduct as a distillation still residue is limited in view of the thermal stability and boiling point of the hydrochloric acid adduct. In the latter case of liquid-liquid separation from the reaction melt, a considerable amount of the salt of the catalyst is dissolved in the diaryl carbonate, and the aromatic polycarbonate produced by transesterification of the diaryl carbonate with bisphenol A using this as a raw material is Poor hue or corrodes mold.

Further, an aromatic monohydroxy compound,
When diaryl carbonate is produced by reacting with phosgene or an aryl chloroformate, hydrogen chloride is by-produced in addition to the desired diaryl carbonate.
Except for a reaction example in an alkaline aqueous solution, a part of the hydrogen chloride dissolves in the reaction mixture or reacts with a basic catalyst to form an adduct salt, which remains in the reaction mixture. When a diaryl carbonate containing a compound having hydrolyzable chlorine such as hydrogen chloride and a raw material are used as raw materials for producing an aromatic polycarbonate by a melt transesterification method, the hydrolyzable chlorine poisons the polymerization catalyst. Therefore, from the relationship between the amount of polymerization catalyst added and the amount of hydrolyzed chlorine, in order to obtain sufficient polymerization activity, the content of hydrolyzable chlorine in the diaryl carbonate is desirably 50 ppb or less.

[0007] A small amount of chlorine as a raw material remains in phosgene depending on the conditions at the time of production, and chlorination of an aromatic monohydroxy compound or diaryl carbonate may occur. Even if these chlorine compounds are generated, they are not contained in the main chain of the aromatic polycarbonate after polymerization,
The effects of corrosion of the mold, coloring of the container, and the like when remaining in the aromatic polycarbonate as impurities are not negligible. It is also expected that the same impurities as the below-described organic chlorine compound derived from carbon tetrachloride will be generated, and will be a source of the hydrolyzable chlorine-containing compound. Therefore, it is necessary to keep the chlorine concentration in phosgene low, and it is necessary to keep it at 10 ppm or less.

An industrial method for producing phosgene is generally a method in which activated carbon is used as a catalyst to react carbon monoxide with chlorine. Carbon tetrachloride is produced from impurities such as methane in carbon monoxide as a raw material. That cannot be avoided. According to Japanese Patent Publication No. 55-14044, phosgene usually contains 250 to 2,000 ppm of carbon tetrachloride.

[0009]

The present invention relates to a method for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene, wherein the content of the hydrolyzable chlorine in the product diaryl carbonate is 50 ppb or less.
It is intended to provide a method for reducing the amount to preferably 30 ppb or less.

[0010]

The present invention provides a method for producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene by purifying the phosgene used to a carbon tetrachloride content of 200 ppm or less. It suppresses the production of an organic chlorine compound derived from carbon tetrachloride, prevents the hydrolyzable chlorine-containing compound accompanying the decomposition of the organic chlorine compound from being contained in the diaryl carbonate as a product, and suppresses the hydrolysis in the diaryl carbonate of the product. It is intended to provide a method for reducing the decomposable chlorine content to 50 ppb or less.

In the present invention, in addition to the case where an aromatic monohydroxy compound is directly reacted with phosgene to obtain a diaryl carbonate, an arylchloroformate is produced by reacting an aromatic monohydroxy compound with phosgene, The case where a diaryl carbonate is produced by a reaction between a chloroformate and an aromatic monohydroxy compound is also included.

[0012]

When a diaryl carbonate is produced by reacting an aromatic monohydroxy compound with phosgene in the absence of a solvent, most of the by-produced hydrogen chloride is discharged out of the system as an exhaust gas, and the dissolved hydrogen chloride is also neutralized with alkaline water. By washing with sodium chloride after washing with water, a considerable portion can be removed. Further purification by distillation yields high-purity diaryl carbonate.

However, if the target of the content of hydrolyzed chlorine in the product diaryl carbonate is set to 50 ppb or less, distillation after simple neutralization and washing with water is not sufficient. The cause is that the carbon tetrachloride contained in the used phosgene reacts with the aromatic monohydroxy compound as a raw material to produce an organic chlorine compound, which is not removed in the neutralization and washing steps, and leads to the distillation step. In this case, thermal decomposition occurs under high-temperature distillation conditions (150 to 200 ° C.) to release the hydrolyzable chlorine-containing compound, which is mixed into the diaryl carbonate to be a product.

In order to solve this problem, in the present invention, the content of carbon tetrachloride in phosgene used is set to 200.
By purifying to below ppm, it is possible to suppress the production of organic chlorine compounds and, consequently, to reduce the amount of hydrolyzable chlorine-containing compounds generated by thermal decomposition in the distillation step, and to obtain hydrolyzable chlorine in diaryl carbonate as a product. The content can be reduced to 50 ppb or less.

When an aromatic polycarbonate is produced by polycondensation with bisphenol A by a melt transesterification method using this diaryl carbonate, hydrolyzable chlorine, which has a significant poisoning effect on the polymerization catalyst, is reduced. Therefore, the polymerization activity of the polymerization catalyst is extremely high, and the amount of the polymerization catalyst to be added can be reduced. As a result, an aromatic polycarbonate having a very low content of hydrolyzable chlorine can be obtained.

[0016]

DETAILED DESCRIPTION OF THE INVENTION Phosgene: Phosgene is liquefied and purified by distillation from crude phosgene obtained by reacting 1 mol of carbon monoxide with 0.65 to 1 mol of chlorine at 100 to 400 ° C. using activated carbon as a catalyst. (10-50 ° C, pressure 0.5-4kgf / cm
² ) By removing impurities such as raw material gas, use high-purity phosgene whose carbon tetrachloride content in phosgene is 200 ppm or less, preferably 100 ppm or less, more preferably 50 ppm or less, and most preferably 10 ppm or less. I do. The chlorine content is desirably 10 ppm or less, preferably 5 ppm or less, more preferably 2 ppm or less. The analysis of carbon tetrachloride in phosgene is based on gas chromatography, and the analysis of chlorine in phosgene is based on iodine titration. Phosgene is contained in 1.0 mole of the aromatic monohydroxy compound.
It is used in a proportion of 1.0 mol or less, preferably 0.4 to 0.5 mol.

Aromatic monohydroxy compound: An aromatic monohydroxy compound is a compound in which a hydroxy group is directly bonded to an aromatic ring, and includes alkylphenols such as phenol, cresol and butylphenol, arylphenols, halogenated phenols and the like. Phenols with an alkyl or aryl group attached through a heteroatom can be used.

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

Catalyst: As a catalyst for reacting an aromatic monohydroxy compound with phosgene, an aromatic heterocyclic nitrogen-containing basic compound is preferable. As the aromatic heterocyclic nitrogen-containing basic compound, a nitrogen atom is present in an aromatic 5- or 6-membered ring, and a strong bond is easily formed with phosgene or a carbonate under reaction conditions. This is a basic nitrogen compound having no functional group (for example, amino group or hydroxy group), and the ring may have another hetero atom such as oxygen or sulfur in addition to the nitrogen atom. Specific examples of such a catalyst include pyridine, quinoline, picoline, imidazoles, benzimidazoles, pyrazoles,
Triazoles, benzotriazoles and their salts.

The aromatic heterocyclic nitrogen-containing basic compound of the catalyst is immediately converted into 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 0.02 mol, per 1.0 mol of the aromatic monohydroxy compound.
It is used in an amount of 1 to 0.10 mol.

Alkali: Examples of alkalis for neutralizing a mixed solution containing a diaryl carbonate obtained by the reaction include hydroxides of alkali metals or alkaline earth metals such as sodium, potassium, calcium and barium, carbonates and phosphoric acids. Sodium and ammonium salts of 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.
The reaction is carried out by introducing into the mixture phosgene (3) having a CCl ₄ content of 200 ppm or less, which has been gasified and purified at the same temperature, while sufficiently stirring and melting.

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 aqueous phase separated in the separation tank (11) is reused for preparing the alkaline aqueous solution (8).

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. The temperature of the neutralization step and the water treatment step can be set at a temperature equal to or higher than the melting point of the reaction solution, but in consideration of the promotion of the neutralization reaction and the effect of extracting the generated salt into the aqueous phase, the range of 50 to 100 ° C. It is desirable to perform in.

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 hydrochloric acid adduct of the above 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. It can be recovered quantitatively.

In order to easily and efficiently recover the basic catalyst, the aqueous phase and the separated organic phase are led to a distillation column, where the free basic catalyst (12) and the unreacted aromatic monohydroxyl are separated by distillation. Compound (13) and diaryl carbonate (14) are separated. The separated diaryl carbonate is again distilled in a distillation column and recovered as a distillate in order to separate impurities having a high boiling point.

The conditions for distilling diphenyl carbonate using a continuous vacuum distillation apparatus are as follows. A commercially available structured packing made of a wire mesh or a sheet is used as the packing, and the raw material liquid is continuously supplied between upper and lower distillation columns having an upper stage having 1 to 20 theoretical plates and a lower stage having 1 to 20 theoretical plates. The degree of vacuum is 2
The continuous operation is performed at 40 torr, the reboiler temperature is 130 to 230 ° C, and the reflux ratio is 0.01 to 10.

In the distillation for separating the basic catalyst and unreacted phenol from crude diphenyl carbonate as the raw organic phase, the degree of vacuum is preferably 10 to 20 torr.
Reboiler temperature is 160-190 ° C, reflux ratio is 0.3-
2 to perform continuous operation. In the distillation for separating diphenyl carbonate from the basic catalyst and unreacted phenol from impurities having a high boiling point, the degree of vacuum is preferably 7 to 15
Continuous operation is performed at a torr and reboiler temperature of 170 to 190 ° C. and a reflux ratio of 0.1 to 2. The distillation used in the present invention can be performed either continuously or batchwise (batchwise).

[0030]

The present invention will be described below in more detail with reference to examples. Example 1 A jacketed glass reaction vessel connected to an oil circulation type external heating device (internal volume: 1 liter,
(An overflow tube was installed at a position of 0 ml). 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.

The molten phenol, which was previously added with 5 mol% of pyridine and stirred, was added to about 700 ml / hr.
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.

As phosgene, crude phosgene obtained by reacting carbon monoxide with chlorine using activated carbon as a catalyst is liquefied and purified by distillation to remove impurities such as a raw material gas and the like. The one having a carbon content of 150 ppm was used. 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, and phenyl chloroformate not 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. 372 g of a 5% by weight aqueous sodium hydroxide solution heated to 85 ° C.
Was added, and the mixture was 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.

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. 300 g of demineralized water heated to 85 ° C. was added, stirred for 5 minutes, allowed to stand for 5 minutes, and then the aqueous phase and the organic phase were separately extracted. The separated organic phase was distilled and purified in a vacuum distillation column packed with 15 Sumitomo / Sulzer Lab Packing (manufactured by Sumitomo Heavy Industries). Specifically, after removing the free form of pyridine and phenol at a degree of vacuum of 10 to 20 torr, a reboiler temperature of about 180 ° C. and a reflux ratio of 1, at a degree of vacuum of 10 torr, a reboiler temperature of about 180 ° C. and a reflux ratio of 0.5, Contains no free pyridine and phenyl chloroformate (0 pp
m) 750 g of purified diphenyl carbonate were obtained.

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 placed in a thermostatic chamber at 23 ° C. at 1000 rpm using a magnetic stirrer.
After stirring for 1 minute, chlorine in the aqueous phase was analyzed by ion chromatography to find that it was 10 ppb.

Application Example 1 182.6 g of bisphenol A (manufactured by Nippon Steel Chemical Co., Ltd.)
800 mol), 188.5 g (0.880 mol) of diphenyl carbonate obtained in Example 1, and 50 μl of 0.18% cesium carbonate aqueous solution as a transesterification catalyst
(0.35 μmol / bisphenol A mol)
The mixture was placed in a 00 ml glass flask equipped with a stirrer and a distilling apparatus, and the inside of the reaction vessel was purged with nitrogen gas. After the contents were completely dissolved, this state was maintained at 210 ° C. and normal pressure for 1 hour.

Next, the pressure inside the reactor was gradually increased to 100 t.
The phenol was distilled off by lowering to orr, and this state was maintained for 1 hour. The amount of distillate distilled out during this period is shown as an initial distillate amount in Table 1 as a measure of the initial polymerization rate.
Thereafter, the polymerization temperature was raised to 240 ° C., the pressure in the reactor was gradually reduced to 15 torr, and polymerization was advanced for 1 hour. Then, the temperature was further raised to 270 ° C., and the pressure in the reactor was raised to 0.5 t.
orr and polymerization was continued for 1 hour. Thereafter, the pressure in the reactor was restored with nitrogen, and about 200 g of the produced polymer was obtained.
And the viscosity average molecular weight (Mv) was determined. Table 1 shows the results.

The viscosity average molecular weight (Mv) was determined by the following equation by measuring the intrinsic viscosity (η) in methylene chloride at 20 ° C. using an Ubbelohde viscometer. η = 1.23 × 10 ⁻⁴ × Mv ^{0.83 The} diphenyl carbonate obtained in Example 1 has a high polymerization activity and was able to synthesize an aromatic polycarbonate having a sufficient molecular weight. Also, the solution YI value showing the color tone was excellent at 1.25.

Comparative Example 1 The procedure of Example 1 was repeated, except that crude phosgene having a carbon tetrachloride content of 300 ppm was used as phosgene. 5 g of diphenyl carbonate obtained by this operation was added to 10 ml of toluene, dissolved at 60 ° C., and then 10 ml of ultrapure water (ion-exchanged water containing no Cl).
After stirring at 1000 rpm for 10 minutes using a magnetic stirrer in a constant temperature room at 23 ° C., chlorine in the aqueous phase was analyzed by ion chromatography to find that it was 80 ppb. Using this diphenyl carbonate, a condensation operation was performed with bisphenol A in the same manner as in Application Example 1 to produce an aromatic polycarbonate. Table 1 shows the results. Since the diphenyl carbonate obtained in Comparative Example 1 had low polymerization activity, an aromatic polycarbonate having a sufficient molecular weight could not be obtained.

[0040]

[Table 1] * 5 g of diphenyl carbonate is added to 10 ml of toluene and dissolved at 60 ° C., then 10 ml of ultrapure water (ion-exchanged water containing no chlorine) is added, and the mixture is stirred at 1000 rpm for 10 minutes using a magnetic stirrer in a constant temperature room at 23 ° C. The chlorine in the aqueous phase was analyzed by ion chromatography. ** Not measured due to low molecular weight.

[0041]

The diaryl carbonate obtained by the practice of the present invention has a very high polymerization activity when producing an aromatic polycarbonate by reacting the diaryl carbonate with bisphenol A by a melt transesterification method. Can be reduced.

[Brief description of the drawings]

FIG. 1 shows an apparatus for producing a diaryl carbonate by reacting phosgene with an aromatic monohydroxy compound.

Claims (7)

[Claims] 1. A method for producing a diaryl carbonate, comprising using phosgene having a carbon tetrachloride content of 200 ppm or less when producing a diaryl carbonate by reacting an aromatic monohydroxy compound with phosgene. 2. The method for producing a diaryl carbonate according to claim 1, wherein the reaction between the aromatic monohydroxy compound and phosgene is carried out without a solvent. 3. The method for producing a diaryl carbonate according to claim 1, wherein phosgene having a chlorine content of 10 ppm or less is used. 4. The method for producing diphenyl carbonate according to claim 1, wherein the diaryl carbonate is diphenyl carbonate. 5. After reacting an aromatic monohydroxy compound with phosgene, neutralize the reaction solution with alkaline water to separate an aqueous phase, wash the organic phase with water, and separate the aqueous phase to obtain a hydrolyzate. The method for producing a diaryl carbonate according to claim 1, wherein a diaryl carbonate having a decomposable chlorine content of 30 ppb or less is obtained. 6. The production of diphenyl carbonate according to claim 3, wherein the phosgene is obtained by liquefying phosgene obtained by reacting carbon monoxide and chlorine in the presence of activated carbon and purifying the phosgene by distillation. Method. 7. The process for producing a diaryl carbonate according to claim 2, wherein the reaction is carried out using an aromatic heterocyclic nitrogen-containing basic compound as a catalyst.