JP3807817B2 - Method for purifying diphenyl carbonate - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for purifying purified diphenyl carbonate. More specifically, the present invention relates to a method for obtaining diphenyl carbonate having a low chlorine (Cl) content by distillation purification.
The diphenyl carbonate purified by the present invention is useful as a raw material for aromatic polycarbonate by the melt transesterification method. The aromatic polycarbonate is useful as an optical disk substrate, a resin for transport containers for precision electronic members of ICs and LEDs, and a housing material for electronic devices.
[0002]
[Prior art]
Various manufacturing methods are known for diphenyl carbonate. For example, there are a method of phosgenating phenol in the presence of a quaternary ammonium salt catalyst, a method of reacting an aqueous solution of metal phenoxide and phosgene in the presence of an organic solvent.
Commercially produced diphenyl carbonate contains various pollutants regardless of the production method and requires a purification process. Contaminants include inorganic and organic chlorides, metal ions, iron compounds, reaction intermediates such as phenyl chloroformate, organic solvents used in the production, and the like. Among these pollutants, the presence of inorganic and organic chlorides is particularly important because they have a great influence on the polymerization rate and hue when producing aromatic polycarbonates (Japanese Patent Publication No. 38-1373, Japanese Patent Publication). 7-96613, JP-B-6-18868, JP-A 63-97627, JP-A 64-24829).
[0003]
In JP-A-4-100824, in producing an aromatic polycarbonate by reacting an aromatic dihydroxy compound and diaryl carbonate, (1) a polymerization catalyst is not used, and (2) the chlorine content is 0.05 ppm. The following describes a process for producing an aromatic polycarbonate, characterized in that a diaryl carbonate having a xanthone content of 10 ppm or less is used. In this, chlorine means chlorine present in acids or salts such as hydrochloric acid, sodium chloride, potassium chloride, or chlorine in organic compounds such as phenyl chloroformate, and potentiometric titration using a silver nitrate solution. It can be quantified by measuring chlorine ions with
[0004]
Various methods have been proposed as purification methods for obtaining such a low chlorine content diphenyl carbonate. For example, a method of adding urea to diphenyl carbonate and melting it by heating (Japanese Patent Publication No. 42-9820), a method of washing molten diphenyl carbonate with water and then distilling (Japanese Patent Laid-Open No. 7-138208), from a crude diphenyl carbonate melt A method of fractionating and crystallizing (JP-A-8-3119), a method of distilling crude diphenyl carbonate in the presence of a basic substance (JP-A-8-198816), and the like are disclosed.
[0005]
As described above, various methods have been devised for reducing the amount of chlorine contained in trace amounts, but several hundred to several hundreds are required when producing diphenyl carbonate as a raw material for polycarbonate which does not have a problem of coloration commercially. It is not satisfactory as a method to obtain diaryl carbonate with low chlorine content from a reaction liquid containing chlorine at a concentration as high as 10,000 ppm, and by purifying it in the presence of water and basic substances during purification. In addition, since there is a concern that hydrolysis occurs and the yield of diphenyl carbonate decreases, a purification method for obtaining diphenyl carbonate having a low chlorine content by suppressing the decomposition of diphenyl carbonate has been required. .
In particular, it is desired to supply diphenyl carbonate having a reduced chlorine content due to the development of information equipment.
[0006]
[Problems to be solved by the invention]
In the present invention, impurities derived from chlorine in diphenyl carbonate, which causes coloring and polymerization inhibition of aromatic polycarbonate by the melt transesterification method using diaryl carbonate, can be applied to industrial processes while suppressing decomposition of diphenyl carbonate. The object is to provide a process for the purification of diphenyl carbonate which is carried out in a continuous manner.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the problems as described above, the present inventors have determined that phenol and phosgene or phenyl chloroformate are used as catalysts in the presence of an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof. After the reaction mixture is brought into contact with an aqueous alkali solution, the organic phase and the aqueous phase are separated, and the organic phase is washed with water and separated from the separated organic phase such as water, catalyst, unreacted phenol, etc. Impurities having a lower boiling point than diphenyl carbonate are removed by distillation, and diphenyl carbonate substantially free of water is passed through a fixed bed made of a basic substance to suppress hydrolysis of diphenyl carbonate and by-produce in the reaction. Chlorine-derived acidic polymerization inhibitor such as hydrogen chloride or hydrochloride of aromatic heterocyclic nitrogen-containing basic compound as catalyst By further distillation was reduced to 1, it found that useful diphenyl carbonate is obtained as a raw material for less colored polycarbonate, and have completed the present invention.
[0008]
That is, the present invention relates to a method for purifying crude diphenyl carbonate containing moisture and impurities by a distillation method, wherein the distillation step comprises a pre-stage for removing low-boiling impurities from diphenyl carbonate and a post-stage for collecting diphenyl carbonate. Moisture in the carbonate and other low-boiling impurities are removed by distillation in the first stage to obtain diphenyl carbonate substantially free of water, and then this is passed through a fixed bed made of a basic substance, and then the second stage diphenyl carbonate. It is intended to provide a method for purifying diphenyl carbonate, characterized in that it is recovered by distillation.
[0009]
[Action]
After removing low-boiling impurities such as water, catalyst, unreacted phenol, etc. in the crude diphenyl carbonate by distillation in the former stage, it is circulated through a fixed bed made of a basic substance. Hydrolysis of diphenyl carbonate is suppressed and impurities derived from chlorine are continuously removed, so that diphenyl carbonate having a low chlorine content can be efficiently recovered.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Crude diphenyl carbonate:
Examples of the method for producing crude diphenyl carbonate include the above-mentioned conventionally known methods (Japanese Patent Publication No. 38-1373, Japanese Patent Publication No. 58-50977, Japanese Patent Publication No. 7-53473, Japanese Patent Publication No. 7-53474) and the like. In particular, phenol and phosgene or phenyl chloroformate are reacted in the presence of a quaternary ammonium salt, an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof as a catalyst, and the resulting reaction mixture is contacted with an aqueous alkali solution. The organic phase and the aqueous phase are separated, the separated organic phase is washed with water, and the aqueous phase is separated to effectively remove the used catalyst residue from diphenyl carbonate. It is.
[0011]
Examples of the quaternary ammonium salt as the catalyst include tetramethylammonium halide and tetraethylammonium halide. Examples of the aromatic heterocyclic nitrogen-containing basic compound include pyridine, quinoline, picoline, imidazoles, benzine. Examples include imidazole, pyrazoles, triazoles, benzotriazoles, etc. These catalysts have a boiling point lower than that of diphenyl carbonate.
[0012]
The reaction is performed, for example, by heating a mixture of phenol and an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof to 120 to 190 ° C. and introducing gaseous phosgene into the mixture with sufficient stirring. Do. 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 phenol.
The mixture after completion of the reaction contains diphenyl carbonate, unreacted phenol, trace impurities and hydrochloride of the aromatic heterocyclic nitrogen-containing basic compound as a catalyst. Depending on the amount, it is about 300-60,000 ppm.
The reaction mixture is then neutralized by contacting with an aqueous alkaline solution at 80 to 95 ° C., separating the organic phase and the aqueous phase in the range of ph 7 to 13, and contacting the organic phase with warm water at 80 to 95 ° C. Separate the organic and aqueous phases.
The organic phase contains several tens to several hundreds ppb of chlorine and about 10,000 ppm of water.
[0013]
First-stage distillation:
Water, free basic catalyst, and unreacted phenol, which are lower boiling components than the crude diphenyl carbonate in the organic phase, are removed by distillation in the previous stage.
In the present invention, there is no particular limitation on the distillation method, and both simple distillation and multistage distillation are possible, and both batch and continuous forms can be adopted.
Due to the previous distillation, virtually no water is detected in the organic phase.
[0014]
Second-stage distillation:
The organic phase substantially free of water (100 ppm or less) thus obtained is circulated in a fixed bed made of a basic substance in a molten state.
Examples of the basic substance include alkali metals, alkaline earth metals and oxides, hydroxides and carbonates thereof. More specific examples of alkali and alkaline earth metals include sodium, potassium, lithium, magnesium and barium. Examples of alkali and alkaline earth metal oxides, hydroxides and carbonates include magnesium oxide, Examples include calcium oxide, lithium carbonate, magnesium carbonate, calcium carbonate, barium carbonate and the like.
Even if the basic substance used is dissolved in molten diphenyl carbonate, it can be separated by distillation in the next step, but the one with low solubility in diphenyl carbonate to suppress the accumulation of high-boiling impurities. Is more preferable. Further, for the separation by distillation at the latter stage, those having a higher boiling point than diphenyl carbonate are preferred. From the above points, barium carbonate, lithium carbonate, calcium carbonate and the like are particularly preferable as the basic substance.
[0015]
As the fixed bed of the basic substance, either a method consisting of only a basic substance or a method supported on a carrier inert to diphenyl carbonate may be used, but considering the dissolution of the carrier in diphenyl carbonate, etc. Those consisting only of a substance are preferred.
The number of fixed beds can be set arbitrarily from a single unit to multiple units, but by setting multiple units, fixing and regeneration or replacement can be performed continuously without stopping production of diphenyl carbonate. Industrially effective.
The amount of basic substance to be used is arbitrarily set in consideration of the production amount of diphenyl carbonate, the frequency of switching the fixed bed, the chlorine concentration in the inflowing diphenyl carbonate, etc., as long as it is equal to or more than the impurity chlorine in diphenyl carbonate. can do.
[0016]
The temperature of the fixed bed is preferably 100 ° C. to 300 ° C., particularly preferably 100 ° C. to 200 ° C., in order to maintain the molten state of diphenyl carbonate.
The chlorine content in the diphenyl carbonate flowing out from the fixed bed is reduced to 0 to 20 ppb.
Diphenyl carbonate flowing out from the fixed bed separates impurities having a higher boiling point than diphenyl carbonate by distillation again, and diphenyl carbonate having a low chlorine content is obtained.
In addition, the amount of chlorine described in this specification is measured by the following method.
Diphenyl carbonate (5 g) is heated and dissolved in purified toluene (10 ml), ultrapure water (10 ml) is added, and the mixture is stirred at room temperature for 10 minutes (magnetic stirrer 1000 rpm), and then chlorine in the aqueous phase is ion chromatographed. Analyze with.
The moisture is measured using a Karl Fischer moisture analyzer.
[0017]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example.
[0018]
Example of production of crude diphenyl carbonate Three consecutive glass reaction vessels with a jacket connected to an oil circulation external heating device (with an internal volume of 1 liter and an overflow pipe installed at a position of 700 ml of actual liquid) Connected. An exhaust pipe with a condenser for removing the generated hydrochloric acid gas out of the system was connected to the second and third reaction vessels.
The molten phenol to which 5 mol% of pyridine had been added in advance was heated to 150 ° C. while being continuously fed to the first reactor at about 700 ml / hr (phenol 716 g / hr, corresponding to 30 g / hr of pyridine). While sufficiently stirring, 0.48 molar ratio of phosgene (361 g / hr) of the supplied phenol was continuously supplied to the first reaction vessel.
[0019]
The reaction mixture flowing out from the first reaction vessel was supplied to the second reactor via the overflow pipe, and the reaction mixture flowing out from the second reactor was similarly supplied to the third reactor. The reaction mixture flowing out of the third reactor was extracted into a polypropylene receiver.
Nitrogen gas was continuously supplied to the third reactor. 1 kg of the reaction mixture (89% by weight of diphenyl carbonate, 6% by weight of phenol, 5% by weight of pyridine hydrochloride, and phenyl chloroformate not detected) extracted after the composition was sufficiently stabilized was connected to an oil circulation external heating device. In a jacketed glass reaction vessel and heated to 85 ° C. After adding 372 g of 5 wt% sodium hydroxide aqueous solution heated to 85 ° C. and stirring for 5 minutes, the mixture was allowed to stand for 30 minutes, and then the aqueous phase and the organic phase were extracted separately. The pH after addition of the aqueous sodium hydroxide solution was 9.
[0020]
The extracted organic phase was again put into a jacketed glass reaction vessel connected to an oil circulation external heating device, and the temperature was raised to 85 ° C. After adding 300 g of demineralized water heated to 85 ° C. and stirring for 5 minutes, the mixture was allowed to stand for 5 minutes, and then the aqueous phase and the organic phase were extracted separately, and the aqueous phase was separated to obtain crude diphenyl carbonate (water content 1 1,000 ppm, 2.4% by weight of pyridine hydrochloride, 6.5% by weight of phenol).
[0021]
Example 1
The above crude diphenyl carbonate is introduced into a vacuum distillation column packed with 10 Sulzer Lab Packing (manufactured by Sumitomo Heavy Industries), and distilled under the conditions of a vacuum degree of 20 to 40 torr, an oil bath temperature of about 220 ° C., and a top temperature of 50 to 80 ° C. Water, free pyridine, and unreacted phenol, which are substances having lower boiling points than diphenyl carbonate, were removed by distillation.
Water was not detected in diphenyl carbonate obtained from the bottom of the column.
The diphenyl carbonate (chlorine amount: 73 ppb) obtained by the above light boiling distillation was kept in a molten state (liquid temperature 150 ° C.), and a packed tower having an inner diameter of 4.6 mm and a length of 150 mm was charged with 2.8 g of barium carbonate powder. It flowed for 83 minutes at a flow rate of 3 g / min through an immobilization column heated to 0 ° C. (the amount of diphenyl carbonate passed was about 120 g).
The chlorine concentration in diphenyl carbonate flowing out from the column was measured and found to be 4.9 ppb. Next, when this diphenyl carbonate was subjected to distillation purification (high boiling distillation) under the conditions of a vacuum degree of 10 torr, an oil bath temperature of about 230 ° C., and a top temperature of 150 ° C., the chlorine concentration in the diphenyl carbonate was 1.0 ppb. .
[0022]
Example 2
Continuous treatment was carried out in the same manner as in Example 1 except that the flow rate of diphenyl carbonate was changed to 5 g / min. The chlorine concentration in diphenyl carbonate flowing out from the column was measured and found to be 3.9 ppb. The diphenyl carbonate was subjected to distillation purification (high boiling distillation) in the same manner as in Example 1. As a result, the chlorine concentration in the diphenyl carbonate was 0.7 ppb.
[0023]
Example 3
Continuous treatment was performed in the same manner as in Example 1 except that lithium carbonate was used as the basic substance instead of barium carbonate. The chlorine concentration in diphenyl carbonate flowing out from the column was measured and found to be 17 ppb. The diphenyl carbonate was subjected to distillation purification (high boiling distillation) in the same manner as in Example 1. As a result, the chlorine concentration in the diphenyl carbonate was 5.0 ppb.
[0024]
Comparative Example 1
As in Example 1, the crude diphenyl carbonate was introduced into a vacuum distillation column filled with 10 Sulzer Lab Packing (manufactured by Sumitomo Heavy Industries), and the degree of vacuum was 20 to 40 torr, the oil bath temperature was about 220 ° C., and the top temperature was 50 to 80 ° C. Distilled under the above conditions, water, free pyridine and unreacted phenol, which are lower boiling substances than diphenyl carbonate, were distilled off.
Next, the diphenyl carbonate (chlorine amount: 73 ppb) obtained by the above light boiling distillation is led to the distillation column without passing through the fixed column, and the conditions are such that the degree of vacuum is 10 torr, the oil bath temperature is about 230 ° C., and the top temperature is 150 ° C. As a result of distillation purification (high boiling distillation), the chlorine concentration in diphenyl carbonate was 30 ppb.
[0025]
【The invention's effect】
According to the present invention, it is possible to continuously remove chlorine-derived impurities in diphenyl carbonate by suppressing decomposition of diphenyl carbonate, and it is effective for industrial production of diphenyl carbonate as a raw material for polycarbonate with little coloration. .

Claims (7)

In the method of purifying crude diphenyl carbonate containing moisture and impurities by distillation method, the distillation step consists of a pre-stage for removing low-boiling impurities from diphenyl carbonate and a post-stage for collecting diphenyl carbonate. After removing low-boiling impurities in the first stage by distillation to make diphenyl carbonate substantially free of water, this is passed through a fixed bed made of a basic substance, and then the second stage diphenyl carbonate is recovered by distillation. A method for purifying diphenyl carbonate, comprising: Crude diphenyl carbonate is reacted with phenol and phosgene or phenyl chloroformate in the presence of a quaternary ammonium salt, an aromatic heterocyclic nitrogen-containing basic compound or a salt thereof as a catalyst. The purification method according to claim 1, wherein the organic phase and the aqueous phase are separated after contacting with the alkaline aqueous solution, the separated organic phase is washed with water, and the aqueous phase is separated. The purification method according to claim 1 or 2, wherein the temperature of the fixed bed is 100 to 300 ° C. The purification method according to any one of claims 1 to 3, wherein the basic substance is one selected from alkali metals, alkaline earth metals and oxides, hydroxides and carbonates thereof. The purification method according to any one of claims 1 to 4, wherein the basic substance is barium carbonate. The purification method according to claim 2, wherein the aromatic heterocyclic nitrogen-containing basic compound is pyridine. The purification method according to claim 1, wherein the chlorine content of the purified diphenyl carbonate is 20 ppb or less.