JP4080117B2 - Method for producing diaryl carbonate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for reducing drainage load when producing 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]
[Prior art]
As a method for producing diaryl carbonate, various production methods are known. For example, a phase interface phosgenation method (Schotten-Baumann reaction) of an aromatic monohydroxy compound in an alkaline aqueous solution is known. In this case, partial saponification of phosgene occurs due to the aqueous alkali solution, and a large amount of sodium chloride is generated as a by-product, resulting in problems such as a decrease in the effective utilization rate of phosgene, an increase in raw material cost due to the use of alkali, and wastewater treatment .
[0003]
US Pat. No. 2,837,555 proposes solvent-free condensation in the presence of tetramethylammonium halide as a catalyst. However, this method requires a relatively large amount of catalyst and a high temperature of 180 to 215 ° C. in order to obtain an economical reaction rate. With the risk of decomposition of tetramethylammonium bromide. In addition, phosgene is consumed at a much higher rate than is stoichiometrically required.
[0004]
As a means for solving such a problem, the reaction between an aromatic monohydroxy compound and phosgene is carried out in the presence of a catalytic amount of an aromatic heterocyclic basic nitrogen compound (hereinafter sometimes referred to as a basic catalyst) or a salt thereof. A method for producing diaryl carbonate 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 as a readily meltable adduct as a residual material during distillation of the reaction mixture, and a second method that settles at the bottom of the reaction melt. A method for isolating the catalyst from the liquid phase is described.
[0005]
However, the catalyst that can be separated in the form of a readily meltable adduct as the residue of the former still is limited due to the thermal stability and boiling point of the hydrochloric acid adduct. In the case of liquid-liquid separation from the latter reaction melt In this case, a considerable amount of catalyst salt is dissolved in diaryl carbonate, and the aromatic polycarbonate produced by the transesterification method with bisphenol A as a raw material has a poor hue or corrodes the mold.
[0006]
When an aromatic monohydroxy compound is reacted with phosgene or aryl chloroformate in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof, hydrochloric acid is by-produced in addition to diaryl carbonate. Except for reaction examples in an aqueous alkali solution, a part of this hydrochloric acid remains in the reaction mixture by dissolution in the reaction mixture, formation of an adduct with a basic catalyst, or 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 diaryl carbonate by a melt transesterification method, and the content in diaryl carbonate is reduced. It is desirable to set it to several tens of ppb or less.
[0007]
As a method of 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 alkali and remains in a trace amount in the neutralization step. It is conceivable to completely remove the generated hydrochloric acid and the salt produced by neutralization. Therefore, the reaction mixture is brought into contact with an alkaline aqueous solution and neutralized in the range of pH 7.0 to 9.5, preferably pH 8.8 to 9.2, and then separated into an organic phase and an aqueous phase. And a process of separating the aqueous phase and the organic phase again and recovering the diaryl carbonate from the organic phase has been proposed (see JP-A-11-5766).
[0008]
In this method, the aqueous phase separated after neutralization is discharged out of the system as waste water. In these wastewaters, water-soluble aromatic monohydroxy compounds, water-soluble catalysts, etc. are dissolved. When producing at an industrial level, wastewater treatment not only increases raw material costs due to dissolution loss. The increase in costs associated with this is a problem. In particular, aromatic monohydroxy compounds have a large load on activated sludge when activated sludge treatment, which is a normal wastewater treatment method, and it is important to reduce them as much as possible.
Therefore, a method has been proposed in which the aqueous phase separated after contact with the aqueous alkali solution or the aqueous phase separated after contact with the water is distilled and the distilled water is reused as water for preparation of the aqueous alkaline solution or contact with the organic phase. (See JP-A-11-29532).
[0009]
However, in this proposed method, the pH at the time of contact with the alkaline aqueous solution is usually set to the basicity at which the neutralization can be completed, and the pH of the separated aqueous phase is less than 9. No, it is about 9-10. When the next distillation operation is started in this state, since the pH is too high, the aromatic monohydroxy compound becomes a salt form and changes to a high boiling point, and cannot be distilled by a simple distillation operation. At the initial stage of distillation, the basic catalyst is distilled, and the pH of the residual liquid from which the basic catalyst has been distilled becomes slightly higher than the initial pH. In other words, the pH of the system in which the basic catalyst and the aromatic monohydroxy compound coexist is slightly lower than usual due to the action of the basic catalyst. The aromatic monohydroxy compound contained in the residual liquid after distillation is more inclined to salt formation, and is difficult to be distilled.
[0010]
[Problems to be solved by the invention]
The present invention is a by-product of the reaction in the production method of diaryl carbonate in which an aromatic monohydroxy compound and phosgene or aryl chloroformate are reacted in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof. Production of diaryl carbonate that does not contain substances that poison the polymerization catalyst in the production of aromatic polycarbonate by the melt transesterification method, such as hydrochloric acid, arylchloroformate as a reaction intermediate, and hydrochloric acid adduct of basic catalyst It aims at providing the manufacturing method reducing the drainage load discharged | emitted from a process.
[0011]
[Means for Solving the Problems]
The present invention provides a reaction mixture containing a diaryl carbonate obtained by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof, After contacting with an aqueous alkali solution and neutralizing to pH 8.5 to 9.5, the organic phase and the aqueous phase are separated, the separated organic phase is brought into contact with warm water, and again separated into an aqueous phase and an organic phase, In the method for producing diaryl carbonate, wherein diaryl carbonate is recovered from the organic phase, the aqueous phase separated after contact with the alkaline aqueous solution is adjusted to a pH range of 5 to 8.4 and then distilled. Is to provide.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Raw materials and auxiliary materials Aromatic monohydroxy compounds: Aromatic monohydroxy compounds are those in which a hydroxy group is bonded directly to an aromatic ring, such as phenols, alkylphenols such as cresol and butylphenol, and arylphenols. Further, halogenated phenols and phenols having an alkyl or aryl group bonded through a hetero atom can be used.
Aryl chloroformate: As the aryl chloroformate, the chloroformate of the aromatic monohydroxy compound can be used.
[0013]
Phosgene: As the phosgene, pure one containing no impurities such as methylene chloride, carbon tetrachloride and chlorine is preferable. The amount of phosgene introduced is preferably 1.0 mol or less, more preferably 0.4 to 0.5 mol, relative to 1.0 mol of the aromatic monohydroxy compound. Although the stoichiometric amount is 0.5 mol, the unreacted aromatic monohydroxy compound is inevitably left by suppressing the introduction amount of phosgene below the stoichiometric amount, and the reaction intermediate aryl The diaryl carbonate formation reaction of chloroformate and aromatic monohydroxy compound is promoted to obtain an industrial grade uncolored polycarbonate.
[0014]
Aromatic heterocyclic nitrogen-containing basic compound or salt thereof: As an aromatic heterocyclic nitrogen-containing basic compound used as a catalyst, a nitrogen atom is present in an aromatic 5-membered ring or 6-membered ring. And a basic nitrogen compound that does not have a functional group (for example, an amino group or a hydroxy group) that tends to form a strong bond with phosgene or a carbonate ester under reaction conditions. It may have other hetero atoms such as oxygen and sulfur. Specific examples of such basic catalysts are pyridine, quinoline, picoline, imidazoles, benzimidazoles, pyrazoles, triazoles and benzotriazoles.
[0015]
The basic catalyst immediately changes to the corresponding hydrochloride salt in the reaction mixture. Since this hydrochloride is in a dissociation equilibrium 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, formate, etc. And organic acid salts such as acetate can be used. These catalysts are preferably used in an amount of 0.001 to 0.20 mol, more preferably 0.01 to 0.10 mol, relative to 1.0 mol of the aromatic monohydroxy compound.
[0016]
Alkali: As the alkali used as a neutralizing agent for the basic catalyst of the hydrochloride type, hydroxides of sodium, potassium, calcium and barium, sodium and ammonium salts of carbonic acid and phosphoric acid can be used.
[0017]
Flow sheet An example of the method for producing diaryl carbonate of the present invention will be described with reference to the flow sheet of FIG.
In the figure, 1 is a first reactor, 2 is a second reactor, 3 is a third reactor, 4 is a neutralization tank, 5 and 7 are separation tanks, 6 is a hot water treatment tank, 8 and 9 are distillation apparatuses, 11, 12, 13, 14, 15, 16 and 17 are aromatic monohydroxy compounds, basic catalysts or salts thereof, phosgene, inert gas, alkaline aqueous solution, piping for introducing hot water and acidic aqueous solution, 21, 22, 23, 24, 25, 26, 27, 28, and 29 are the first reactor reaction mixture, the second reactor exhaust gas, the second reactor exhaust liquid, the third reactor exhaust gas, the third reactor exhaust liquid, and the neutralization, respectively. Liquid, its separated organic phase, hot water treatment liquid and piping for its separated organic phase discharge, 27 ', 27 "and 29' are for discharge of neutralized liquid separated water phase, for circulation and for hot water treated liquid separated water phase, respectively. The exhaust circulation pipes 31, 32, 33, 34 and 35 are the first reactor, 2 reactor, the third reactor, the agitator installed in the neutralization tank and hot water treatment tank showing.
[0018]
reaction:
An aromatic monohydroxy compound (11) heated and melted, a basic catalyst or a salt thereof (12), and gaseous phosgene (13) are continuously fed to the first reactor (1), and heated at 120 to 190 ° C. The reaction is carried out with stirring (31) at temperature. At that time, phosgene (13) is introduced into the liquid phase part in the reactor as shown in the figure. Moreover, you may introduce a basic catalyst or its salt (12), mixing with a part or all of the aromatic monohydroxy compound (11) heated and melted.
[0019]
The reaction mixture in the first reactor is continuously discharged in a gas-liquid dispersion state, introduced into the second reactor (2) through the pipe (21), and further reacted under stirring (32) to increase the conversion rate of phosgene. Improve. The second reactor exhaust gas mainly consists of hydrogen chloride and unreacted phosgene generated by the reaction, and is discharged from the pipe (22) and purged outside the system through a condenser (not shown). Therefore, it is important to improve the phosgene consumption rate.
[0020]
The second reactor effluent is discharged from the pipe (23) and further introduced into the third reactor (3). Under stirring (33), an inert gas (14) such as nitrogen gas is blown into the liquid. The dissolved hydrogen chloride gas is removed, and the push-off reaction of the chloroformate body (conversion to diaryl carbonate by an equilibrium reaction with an aromatic monohydroxy compound) is promoted. The third reactor exhaust gas is hydrogen chloride accompanying the inert gas, and is discharged from the pipe (24). The hydrogen chloride is purified as necessary and reused as recovered hydrochloric acid. The inert gas can also be recycled to the reactor after hydrochloric acid recovery. In the case of two reactors, the second reactor can be omitted and the first reactor and the third reactor can be operated.
[0021]
Separation / recovery:
In the mixture after completion of the reaction, diaryl carbonate, unreacted aromatic monohydroxy compound, basic catalyst hydrochloride and trace impurities are contained, and the chlorine content is about 300 to 300 depending on the amount of catalyst used. 60,000 ppm. The third reactor effluent is supplied to the neutralization tank (4) through the pipe (25), and is brought into contact with the alkaline aqueous solution (15) with stirring (34) to neutralize the hydrochloride of the basic catalyst. In the neutralization step, the treatment conditions are selected such that the basic catalyst hydrochloride present in the reaction mixture can be completely converted to a free basic catalyst by contact with an aqueous alkaline solution. Specifically, it is important to adjust the pH during neutralization within a predetermined range. That is, a range of pH 8.5 to 9.5, preferably pH 8.8 to 9.2 is selected. If the pH during neutralization exceeds the above range, decomposition of diaryl carbonate increases, and if it is less than the above range, conversion to a free basic catalyst becomes insufficient, such being undesirable.
[0022]
The neutralized liquid is introduced into the separation tank (5) through the pipe (26), and is separated into an organic phase and an aqueous phase.
The aqueous phase separated in the separation tank (5) is supplied to the distillation apparatus (9) via the pipe (27 ′), and a basic catalyst and an aromatic hydroxy compound dissolved in a small amount are recovered as distillate water. Therefore, prior to distillation, an acidic aqueous solution (17) such as an aqueous hydrochloric acid solution is added to and mixed with the separated aqueous phase to adjust the pH to a range of 5 to 8.4, preferably a pH of 6 to 8. It is necessary. That is, when the pH of the aqueous phase supplied to the distillation apparatus (9) is too high, the aromatic monohydroxy compound becomes a salt form and changes to a high boiling point, and cannot be distilled by a simple distillation operation. . On the other hand, if the pH of the aqueous phase is too low, the basic catalyst will be in the form of a salt and will change to a high-boiling product, which will no longer be distilled by a simple distillation operation. However, if the aqueous phase has a pH adjusted within the above range, almost the entire amount of both the basic catalyst and the aromatic hydroxy compound can be easily recovered as distilled water by a normal distillation operation. Therefore, the distillate collected in the distillation apparatus (9) is effectively reused in the system and never discharged directly as waste water. For example, it may be recycled for the preparation of the alkaline aqueous solution (15), or may be recycled as the washing water (16) of the hot water treatment tank (6) via the pipe (27 ″) as shown in the figure. The still liquid in the distillation apparatus (9) mainly contains alkali hydrochloride (hereinafter sometimes referred to as neutralized salt) produced in the neutralization step, but contains almost no basic catalyst and aromatic hydroxy compound. Although it is discharged out of the system as wastewater, the loss of dissolution of raw materials is reduced and the wastewater treatment load is greatly reduced.
[0023]
On the other hand, the organic phase separated in the separation tank (5) is supplied to the hot water treatment tank (6) through the pipe (27), and is brought into contact with the warm water (16) under stirring (35). The hot water treatment liquid is introduced into the separation tank (7) via the pipe (28), and again separated into an organic phase and an aqueous phase. The aqueous phase discharged from the separation tank (7) is usually circulated and used for the preparation of the alkaline aqueous solution (15) via the pipe (29 ′) as shown in the figure.
The temperature of the neutralization step and the hot water treatment step is selected such that the organic phase and the aqueous phase are both liquid and can be contacted with each other. In view of the extraction effect on the aqueous phase, it is desirable to carry out in the range of 50 to 100 ° C, preferably 65 to 100 ° C.
[0024]
In the hot water treatment process, most of the water was transferred into the aqueous phase in the separation tank (5), but a small amount of neutralized salt dissolved in the organic phase was sufficiently extracted with hot water to contain chlorine in the product diaryl carbonate. Processing conditions are selected that can reduce the amount to an amount that does not inhibit polymerization. Specifically, the amount of warm water (16) to be used is usually 0.01 to 20 times, preferably 0.2 to 1 times the weight of the organic phase (27). If the amount of water is too small, the effect of removing chlorine is not sufficient, and if it is too large, it takes a lot of time to recover the phenol contained in the separated aqueous phase by saturation, which is not preferable. If the neutralization process and the warm water treatment process are appropriately stirred and separated, the warm water treatment is sufficient once, but if the stirring and separation are insufficient and the chlorine content does not decrease sufficiently, The same effect can be obtained by performing the operation of contacting and separating the aqueous phase and the organic phase a plurality of times. The organic phase (29) finally subjected to the neutralization / warm water treatment and having been separated has a chlorine content reduced to about 100 ppb or less.
[0025]
The organic phase discharged from the separation tank (7) is supplied to the distillation apparatus (8) via the pipe (29), where free basic catalyst, unreacted aromatic monohydroxy compound and diaryl carbonate are obtained by distillation. Separate and collect. The distillation pressure is preferably 1 to 100 torr and practically 5 to 50 torr in order to suppress decomposition of diallyl carbonate due to heating during distillation. When the free basic catalyst is pyridine, the distillation temperature is 20 to 40 torr at 50 to 80 ° C., and when the unreacted aromatic monohydroxy compound is phenol or the like, 20 to 40 torr at 50 to 100 ° C., diaryl carbonate is In the case of diphenyl carbonate or the like, the temperature is 140 to 160 ° C. at 5 to 10 torr. The distillation apparatus (8) may be composed of a plurality of distillation columns (not shown). For example, in order to easily and efficiently recover the basic catalyst, light boiling matters (unreacted aromatic monohydroxy compound, free basic catalyst and moisture, etc.) are separated in the first distillation column, and the second distillation column May be separated into high boiling impurities and product diaryl carbonate. The product diaryl carbonate thus obtained has a chlorine content of 40 ppb or less and does not inhibit the polymerization.
[0026]
The production of the diaryl carbonate of the present invention may be a continuous type or a batch type (batch type).
[0027]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
In the following Examples and Comparative Examples, analysis of phenol, pyridine and sodium chloride, and measurement and display of the chlorine content in DPC (diphenyl carbonate) are based on the following procedure.
Quantitative analysis was performed with a phenol and pyridine liquid chromatograph.
It was quantitatively analyzed by sodium chloride ion chromatograph.
[0028]
About 5 g of chlorine content DPC is precisely weighed and added to 10 ml of toluene. After dissolution at 60 ° C., 10 ml of ultrapure water (ion exchange water not containing chlorine ions) is added, and a magnetic stirrer is placed in a constant temperature room at 23 ° C. After stirring for 10 minutes at 1000 rpm, the aqueous phase was separated from the DPC. Chlorine ions extracted into the aqueous phase were quantitatively analyzed by ion chromatography. The analysis result was expressed as the amount of chlorine with respect to the weight of DPC.
[0029]
Example 1
Reaction As shown in FIG. 1, a glass-lined reaction vessel with a jacket and a stirrer connected to an oil circulation external heating device (with an internal volume of 60 l and an overflow pipe at the position of 29 l of the actual liquid). 3 sets) were connected in series. A phenol introduction pipe (11), a catalyst introduction pipe (12) and a phosgene introduction pipe (13) are connected to the first reactor (1), and a hydrogen chloride gas discharge pipe is connected to the second reactor (2). An exhaust pipe (22) with a condenser was connected, and a nitrogen gas introduction pipe (14) and an exhaust pipe (24) for discharging hydrogen chloride gas were connected to the third reactor (3). To the first reactor (1), 5 mol% of the catalyst pyridine was added in advance, and the molten phenol that had been stirred was about 29 l / hr (phenol 29.7 kg / hr, corresponding to pyridine 1.24 kg / hr). While continuously supplying, the temperature was raised to 150 ° C. The stirrer (31) was equipped with a disk turbine blade made of Teflon lining and was driven. On the other hand, 0.46 molar ratio of phosgene (14.4 kg / hr) to the fed phenol was continuously fed to the first reactor. The reaction mixture flowing out from the first reactor (1) is supplied to the second reactor (2) through the overflow pipe (21), and the reaction mixture flowing out from the second reactor is transferred to the third reactor (3 ) And mixed contact with 0.5 m ³ / hr of nitrogen gas introduced into the reaction mixture to remove hydrogen chloride gas and phenyl chloroformate gas.
[0030]
Neutralization / warm water treatment The reaction mixture (composition: DPC 89% by weight, phenol 6% by weight, pyridine hydrochloride 5% by weight, phenyl chloroformate not detected) discharged from the third reactor (3) was oil A 25% aqueous sodium hydroxide solution (15) containing circulating water (29 ') from the hot water treatment step, supplied to a Teflon-lined neutralization tank (4) with a jacket and a stirrer, connected to a circulation type external heating device And neutralization by mixing and contacting at a temperature of 85 ° C. At this time, the supply amount of the alkaline aqueous solution (15) was adjusted so that the value of the pH meter installed in the neutralization tank was 9 to 9.5. The liquid residence time in the neutralization tank (4) at this time was 8 minutes. This neutralized liquid was introduced into a separation tank (5) made of Teflon lining, and separated into an organic phase and an aqueous phase. The residence time in the separation tank (5) at this time was 30 minutes.
The organic phase separated in the separation tank (5) is further supplied to the hot water treatment tank (6) and warm water (distillation water (27 ″) of the distillation apparatus (9) (water phase / organic phase ratio = 0). 3) and a temperature of 85 ° C. for 8 minutes while stirring and mixing, the mixture was separated from the aqueous phase again after a standing time of 30 minutes in the separation tank (7). It was recycled to the neutralization tank (4) through the pipe (29 ').
On the other hand, the aqueous phase separated in the separation tank (5) contained 1.0% phenol, 0.3% pyridine and 4.5% sodium chloride, and had a pH of 9.5. 35% hydrochloric acid was added to the aqueous phase discharged through the pipe (27 ′) to adjust the pH to 6.0, and then supplied to the distillation apparatus (9). As a result of continuous distillation using an Oldershaw type 18-stage continuous distillation column under normal pressure, with a reflux ratio of 0.5 and a distillation rate of 70%, 99.2% of phenol in the distilled water was obtained. 99.9% of the pyridine was recovered. This distilled water was circulated and used in the hot water treatment tank (6) via the pipe (27 "). The distillation kettle residue of the distillation apparatus (9) was a liquid containing 15% sodium chloride and 255 ppm phenol. However, pyridine was below the detection limit (5 ppm).
[0031]
Distillation The organic phase separated after the hot water treatment was supplied to the distillation apparatus (8) via the pipe (29). Here, light-boiling products of unreacted phenol, pyridine and water were separated and removed by vacuum distillation in a first distillation column (not shown), and then product DPC was separated and obtained in a second distillation column (not shown). .
[0032]
Example 2
In Example 1, DPC was produced in exactly the same manner as in Example 1 except that the pH adjustment of the separated aqueous phase before distillation was changed to 8.0 instead of 6.0.
As a result, 99.1% of phenol and 99.9% of pyridine were recovered in the distilled water. The residue in the distillation pot was a liquid containing 15% sodium chloride and 300 ppm of phenol, but pyridine was below the detection limit (5 ppm).
[0033]
Comparative Example 1
In Example 1, DPC was produced in exactly the same manner as in Example 1 except that the pH of the separated aqueous phase before distillation was not adjusted (pH = 9.5).
As a result, 92.4% of phenol and 99.9% of pyridine were recovered in the distilled water. The residue in the still was a liquid containing 15% sodium chloride and 2530 ppm of phenol, but pyridine was below the detection limit (5 ppm).
[0034]
Comparative Example 2
In Example 1, DPC was produced in exactly the same manner as in Example 1 except that the pH of the separated aqueous phase before distillation was changed to 4.5 instead of 6.0.
As a result, 99.2% of phenol and 95% of pyridine were recovered in the distilled water. The residue in the still was a liquid containing 15% sodium chloride, 253 ppm of phenol and 50 ppm of pyridine.
[0035]
【The invention's effect】
According to the method of the present invention, an aromatic monohydroxy compound or an organic basic catalyst dissolved in a water phase after neutralization can be recovered in distilled water at a high yield by distillation. As a result, the residual amount in the distillation still residue containing hydrochloride and the like generated by neutralization is remarkably reduced, and the load in waste water treatment can be reduced. Further, there is no problem even if the distilled distilled water containing the recovered aromatic monohydroxy compound and catalyst is reused as the water to be brought into contact with the alkaline aqueous solution and the organic phase. Rather, the wastewater discharged out of the system due to reuse is only the residual liquid from the distillation kettle when the separated aqueous phase is distilled. In addition to reducing the dissolution loss of raw materials, the wastewater treatment load must be greatly reduced. Became possible.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing a method for producing a diaryl carbonate of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st reactor 2 2nd reactor 3 3rd reactor 4 Neutralization tank 5, 7 Separation tank 6 Hot water treatment tank 8, 9 Distillation apparatuses 11-17 Piping 21-29 Piping 31-35 for discharge mixer

Claims (3)

A reaction mixture containing a diaryl carbonate obtained by reacting an aromatic monohydroxy compound with phosgene or an aryl chloroformate in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof is contacted with an aqueous alkali solution. After neutralizing to pH 8.5 to 9.5, the organic phase and the aqueous phase are separated, the separated organic phase is brought into contact with warm water, and again separated into an aqueous phase and an organic phase. In the method for producing diaryl carbonate for recovering diaryl carbonate, the aqueous phase separated after contact with the aqueous alkali solution is adjusted to a pH range of 5 to 8.4 and then distilled. The method for producing a diaryl carbonate according to claim 1, wherein the distilled distillate water is reused as water for contacting with an organic phase or an organic phase. The method for producing a diaryl carbonate according to claim 1, wherein the contact with the aqueous alkali solution and water is performed in the range of 50 to 100 ° C.

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