JPH06200006A - Polycarbonate manufacturing method - Google Patents

Abstract

(57) [Summary] [Structure] When polycarbonate is produced by the interfacial polymerization method, dichloromethane in the waste water produced is replaced with air and / or
Alternatively, it is removed by bubbling with an inert gas, and the removed dichloromethane is further supplied to the production step for reuse. [Effect] The waste water contains almost no dichloromethane,
Moreover, the consumption of dichloromethane can be reduced at low cost.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing polycarbonate. Specifically, by removing the dichloromethane dissolved in the waste water generated in the polycarbonate production process, the danger of environmental pollution due to the dichloromethane contained in the waste water is eliminated, and the removed dichloromethane is supplied to the production process. , A method for producing polycarbonate that reduces the consumption of dichloromethane.

[0002]

2. Description of the Related Art Polycarbonate moldings have transparency comparable to glass and have outstanding impact resistance and excellent heat resistance, flame retardancy, electrical characteristics, dimensional stability, weather resistance and other characteristics. It is an engineering plastic and is used in large quantities in many fields. As a method for producing a polycarbonate, an interfacial polymerization method in which an alkali aqueous solution of a dihydric phenol and a carbonyl halide compound are reacted in the presence of dichloromethane to form a low molecular weight polycarbonate oligomer having a haloformate group, and then the oligomer is polymerized [Interscience
Publishing, "Encyclopedia
of Polymer Science and Te
chnology "10, 710 (1969)," Ch
emissary and Physics of Pol
ycarbononate "33 (1964)] is widely adopted. Here, since polymerization of a polycarbonate oligomer requires a considerably long polymerization time when it is carried out without a catalyst, the polymerization is usually carried out by adding a polymerization catalyst. .
Further, in order to prevent the color tone of the polycarbonate from being deteriorated, an inert gas is purged in some or all of the steps.

Since the polycarbonate solution of polycarbonate synthesized by this method contains a polymerization catalyst and a basic substance, it is neutralized with an acid to form an organic or inorganic salt, and the salt. A water washing step in which a dichloromethane solution of the polycarbonate is mixed with water to remove the above is widely performed. Since the presence of the inorganic salt in the polymer deteriorates its various properties such as thermal stability, moldability and color tone, the washing step is repeated until the electrolyte is exhausted.
As described above, a large amount of water is used in the polycarbonate manufacturing process, but a maximum of 1.96 wt% dichloromethane is dissolved in the large amount of waste water thus generated.

The amount of waste water generated in the process for producing a polycarbonate by the interfacial polymerization method is at least twice the weight of the polycarbonate normally produced, and at least 30 times the amount without recycling. For example, a plant with an annual production capacity of 10,000 tons of polycarbonate produces at least 20,000 tons of wastewater, in which at least 100 tons of dichloromethane are dissolved. Currently, there is no particular restriction on the concentration of dichloromethane in wastewater, and the wastewater is discharged after being treated in the same manner as other industrial wastewater, so the dichloromethane dissolved in the wastewater is released into the atmosphere or industrial wastewater. ing. Dichloromethane is used in a large amount in addition to the manufacturing process, as a cleaning agent, a solvent stripping agent, a refrigerant, etc.
The environmental impact of dichloromethane released in the process is a problem. Part of the dichloromethane released into the atmosphere decomposes and becomes hydrogen chloride, which pollutes the environment. Furthermore, there are many reports on the biotoxicity of dichloromethane in water. To deal with this problem, much effort is currently being put into countermeasures for dichloromethane in groundwater used for drinking water, industrial water and the like.

As a method for removing dichloromethane from waste water, activated carbon treatment has been widely known. When the concentration of dichloromethane in waste water is relatively low, dichloromethane is removed by passing the waste water directly through the activated carbon layer.
When the concentration of dichloromethane in the waste water is high, the waste water is blown with air to explode, and the air used is passed through an activated carbon layer to remove dichloromethane and then exhausted. However, activated carbon also adsorbs substances other than dichloromethane, and since steam is applied to the activated carbon during recovery, the hydrolysis of dichloromethane occurs. Therefore, when the recovered liquid is reused, further purification is required. From the above, the activated carbon treatment of wastewater with a high concentration of dichloromethane has a large amount of wastewater relative to the production volume, such as in the polycarbonate manufacturing process.
It is industrially disadvantageous because the cost required for using a large amount of activated carbon and refining the recovered liquid is very high.

Other methods for removing dichloromethane in waste water have been reported, such as ozone or hydrogen peroxide treatment and oxidation by ultraviolet irradiation (JP-A-2-184393), biological decomposition, decomposition by radiation, etc. Is all
This is a treatment for decomposing dichloromethane to lower COD (chemical oxygen demand) and the like, and it is impossible to recover and reuse dichloromethane by these methods. To reduce the concentration of dichloromethane in wastewater during the polycarbonate manufacturing process, the
A method of adding -40% of an aliphatic or aromatic hydrocarbon (Japanese Patent Laid-Open No. 4-126715) has been reported, but 0.7-0.9 wt% of dichloromethane remains in the treated wastewater. It cannot be said that this method is sufficient as a method for reducing the concentration of dichloromethane in wastewater. Dichloromethane in wastewater is digested by natural microorganisms and decomposed into hydrochloric acid, carbon dioxide, and water to reduce the concentration of dichloromethane in wastewater to 1%.
There is also known a method of reducing it to 1/00 or less. However, this method cannot recover or reuse dichloromethane. Therefore, there has been a demand for a simple and industrially advantageous method for producing a polycarbonate that hardly contains dichloromethane in waste water and reduces the consumption of dichloromethane at a low cost.

[0007]

The problem to be solved by the present invention is to produce an environment from a large amount of waste water generated in any process such as a polymerization process, a neutralization process, a water washing process and an isolation process in the production of a polycarbonate by an interfacial polymerization method. It is an object of the present invention to provide an industrially advantageous method for producing a polycarbonate capable of reducing the amount of dichloromethane used by removing dichloromethane which may become a contaminant and supplying the dichloromethane to the production step.

[0008]

Means for Solving the Problems As a result of intensive studies on the above problems, the inventors of the present invention conducted aeration of dichloromethane dissolved in waste water with air and / or an inert gas to dichlo- romethane in the waste water. Can be easily removed to an arbitrary concentration, and the dichloromethane recovered by an operation such as cooling the air and / or an inert gas after the removal treatment does not require a special purification operation, etc. The present invention has been completed by finding that it can be directly used in. That is, the present invention uses dichloromethane as an organic solvent, and when producing a polycarbonate by an interfacial polymerization method, removes dichloromethane in the produced waste water by aeration with air and / or an inert gas, and removes the removed dichloromethane. Further, it is a method for producing a polycarbonate which is characterized in that it is supplied and reused in the production process.

The present invention will be described in detail below. The interfacial polymerization method in the present invention is not particularly limited, and any method conventionally used in the production of polycarbonate using dichloromethane as an organic solvent can be applied. Examples of these include Japanese Patent Publication No. 41-43.
52, Japanese Patent Publication No. 46-21460, Japanese Patent Publication No. 56-4409
1, JP-B-57-22933, JP-B-59-3072
6, JP-B-61-46486, JP-A-63-13991
4, JP-A-1-278528, Japanese Patent Application No. 4-19955
3, the method described in JP-A-4-259642 and the like. As an example of the interfacial polymerization method, first, the raw material 1
Carbonyl chloride is added to an aqueous solution of an alkali metal salt of one or more dihydric phenols, and the mixture is stirred in the presence of a solvent to produce a polycarbonate oligomer. Then
A reaction mixture is prepared by adding an aqueous alkaline solution of a dihydric phenol, which is a raw material for a polymerization reaction, an end terminating agent, and a polymerization catalyst to the organic layer containing the polycarbonate oligomer in which the aqueous layer is separated. The interfacial polymerization reaction is carried out while stirring the above reaction mixture, and the obtained reaction liquid is allowed to stand to separate the aqueous layer.
Then, the organic layer containing the polycarbonate is washed with alkaline water to remove the unreacted dihydric phenols remaining, and the residual alkali and the polymerization catalyst are neutralized with hydrochloric acid, an acidic aqueous solution of phosphoric acid, etc., Further, to remove inorganic and organic salts, washing with water is repeated until the electrolyte is exhausted. The organic solvent is removed from the washed organic layer by a conventional method to obtain a solid polycarbonate.

In the present invention, the waste water generated in the above polycarbonate manufacturing process is aerated with air and / or an inert gas. In the present invention, ventilation means
This is to forcibly blow a gas into the liquid and positively contact it. As the aeration method, there are an air diffusion method in which compressed air is dispersed in the liquid as fine bubbles, a turbine method in which stirring is also performed, and the like, but the present invention is not particularly limited.

In the present invention, the composition of the recovered liquid or the inert gas after aeration (hereinafter abbreviated as purge gas) that is directly purged by operating the treatment temperature during aeration according to the composition of the wastewater. Can be controlled. The treatment temperature during aeration is 0 to 100 ° C, preferably 10 to 38
℃. If the treatment temperature is lower than this range, the waste water may be frozen, and even if it is not frozen, the time required for removing dichloromethane becomes very long. When the treatment temperature is lower than 38 ° C, which is the azeotropic point of water and dichloromethane, the recovery liquid or the purge gas contains a polymerization catalyst, hydrogen chloride used in the neutralization step, and a dichloromethane hydrolyzate regardless of the composition of waste water. Since almost no hydrogen chloride, water, etc. are mixed in, it can be used in all steps of the polycarbonate production process, such as for polycarbonate polymerization, for diluting a polycarbonate dichloromethane solution after polymerization, and for diluting at the time of isolation. When the treatment temperature is 38 ° C. or higher, the time required for removing dichloromethane in the waste water is shortened, but the process in which the recovered liquid or the purging gas can be used is limited by the composition of the treated waste water. That is, when the wastewater is basic and contains a tertiary amine that is a polymerization catalyst, the recovery liquid or the purge gas contains a tertiary amine, and when the wastewater is acidic, the recovery liquid or the purge gas contains a tertiary amine. Since hydrogen chloride is contained, the place of use is limited to the processes that are not affected by the contamination.

In the present invention, the gas used for ventilation is air and / or an inert gas, and examples of the inert gas include nitrogen, helium, argon and the like, with nitrogen being preferred. The amount of gas depends on the treatment temperature of wastewater, but it is 1
It is at least twice the volume of waste water per hour, preferably at least 15 times. If the amount of gas is small, the processing time becomes very long. In the present invention, the aeration time depends on the concentration of dichloromethane in the waste water before aeration, the degree of removal of dichloromethane in the waste water after aeration, the treatment temperature, the amount of gas, the aeration method, etc., and is therefore arbitrarily determined. For example, the time required to remove dichloromethane in the wastewater from 1.96 wt% to 50 ppm or less with a wastewater temperature of 33 ° C. and a gas amount 15 times the wastewater volume is about 2 hours, or 1.96 wt%.
To about 1 ppm or less is about 3 hours. The aeration time can be shortened by increasing the treatment temperature and the amount of gas used.

In the present invention, the recovery of dichloromethane from the air and / or the inert gas after aeration can be carried out by cooling the gas after aeration, and at the time of cooling, a cooling pipe and a gas liquefier Etc., various cooling devices can be used. Although the cooling temperature is arbitrarily determined by the shape of the cooler, the gas flow rate, etc., it is the boiling point of dichloromethane, 39.8 ° C.
The following, preferably 5 ℃ or less, more preferably -20 ℃
It is the following. If the cooling temperature is high, the recovery rate decreases, and it becomes necessary to upsize the cooling device for sufficient recovery.
In the present invention, the recovered liquid recovered here can be directly supplied to the polycarbonate production process without further purification.

Further, usually, an inert gas is purged in a part or the whole of the polycarbonate production process in order to prevent deterioration of color tone due to oxidation of the raw material and the polycarbonate, but in the present invention, dichloromethane used for aeration is included. An inert gas can also be used directly as the purging gas. A cooling device for the liquefaction of vaporized dichloromethane is installed in the polycarbonate manufacturing process using dichloromethane.By directly purging the inert gas used for aeration in the polycarbonate manufacturing process, a cooling device for liquefying dichloromethane is recovered. It is possible to supply dichloromethane without newly installing.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The concentrations of dichloromethane, hydrogen chloride and triethylamine in water were determined by gas chromatography. The water content in dichloromethane was determined by a Karl Fischer water content meter. The number average molecular weight and the weight average molecular weight of the synthesized polymer were calculated by GPC (gel permeation chromatography) in terms of polystyrene.

Synthetic Example 1 280 g of bisphenol A, 6.34 g of p-tert-butylphenol, 0.56 g of sodium hydrosulfite and 143 g of sodium hydroxide were dissolved in 1600 g of water, and phosgene was stirred and mixed with the aqueous solution and 1330 g of dichloromethane. 145.6 g was fed over 1 hour. Then, 0.5 g of triethylamine, which is a polymerization catalyst, was added to the mixed solution, and the mixture was aged for 2 hours, the reaction solution was allowed to stand still, and a polycarbonate solution in dichloromethane was separated. A dichloromethane solution of this polycarbonate was mixed with 1 liter of 0.1N hydrochloric acid, and the mixture was stirred until a sufficient emulsified state was reached to carry out neutralization treatment. Then, the organic phase was separated again by static separation, mixed with 1 liter of pure water, and similarly stirred to wash with water. This washing treatment was repeated until the electric conductivity of the washing wastewater became 1 μS / cm or less. Finally, the dichloromethane solution of the polycarbonate after the purification treatment was filtered, and then the organic solvent was distilled off to obtain a polycarbonate powder. The obtained polycarbonate has a number average molecular weight (Mn) of 23,000 and a weight average molecular weight (Mw) of 53.
000, polydispersity index (Mw / Mn) 2.30
Met.

Synthesis Example 2 1330 g of dichloromethane in which 1.26 g of triethylamine was dissolved in a 3 liter separable flask equipped with a phosgene blowing tube, a raw material supply tube, a thermometer, an electrode for pH measurement, and a stirrer, and 1% as a base water. Charge 100 g of aqueous NaOH solution. Then, in a separately prepared 2 liter separable flask, 280.0 g of bisphenol A,
6.34 g of p-tert-butylphenol, 0.56 g of sodium hydrosulfite and 100 g of sodium hydroxide are dissolved in 1600 g of water. This bisphenol A alkaline aqueous solution is charged into the reaction tank at a supply rate of 33.1 g / min through a raw material supply pipe using a metering pump. At the same time, 121.8 g of phosgene is 2.0
It is supplied to the reaction tank at a rate of 3 g / min to carry out stirring polymerization. The raw material supply was completed in 60 minutes, and then the reaction was completed by stirring for 90 minutes, and then the reaction solution was allowed to stand and separate to separate a polycarbonate solution in dichloromethane. A solution of this polycarbonate in dichloromethane was added to 0.1N hydrochloric acid 1
The mixture was mixed with liter and stirred until a sufficient emulsified state was reached to carry out neutralization treatment. Then, the organic phase was separated again by static separation, mixed with 1 liter of pure water, and similarly stirred to wash with water. This washing process has a conductivity of 1 μS
It repeated until it became / cm or less. Finally, the dichloromethane solution of the polycarbonate after the purification treatment was filtered, and then the organic solvent was distilled off to obtain a polycarbonate powder. The obtained polycarbonate has a number average molecular weight (Mn)
It was 20800, the weight average molecular weight (Mw) was 52000, and the polydispersity index (Mw / Mn) was 2.50.

Example 1 3000 ml of acidic wastewater (1.27 wt% of dichloromethane, 0.85 wt% of HCl, 140 ppm of triethylamine hydrochloride) produced in the neutralization step in the same polycarbonate synthesis reaction as in Synthesis Example 1 was placed in a separable flask and kept in a constant temperature bath. Kept at 33 ° C with nitrogen (50 l / h)
Was stirred with a stirrer while being blown into the waste water through a glass tube. The evaporate was recovered by a gas liquefier cooled with dry ice-methanol at -72 ° C. After treatment time 3 hours, the concentration of dichloromethane in the waste water was 1 ppm or less, the amount of recovered liquid was 33.2 g, the concentration of dichloromethane was 99.9% (recovery ratio of dichloromethane 87.1%), and the water content was 860 pp.
m, the amount of hydrogen chloride used for neutralization, and the amount of triethylamine as a polymerization catalyst mixed were all 1 ppm or less. Synthesis example 1
The use amount of dichloromethane was reduced by 2.25% by using 1300 g of dichloromethane instead of 1330 g of dichloromethane and 33.2 g of the above recovery solution.
Polycarbonate was manufactured by the same operation. The obtained polycarbonate has a number average molecular weight (Mn) of 2280.
0, weight average molecular weight (Mw) 53000, polydispersity index (Mw / Mn) 2.32 (Synthesis example 1)
Equivalent to the polycarbonate polymerized by.

Example 2 3000 ml of basic waste water (1.34 wt% of dichloromethane, 15 ppm of triethylamine) generated from the polymerization step in the same polycarbonate synthesis reaction as in Synthesis Example 1 was placed in a separable flask and kept at 33 ° C. in a constant temperature bath, Nitrogen (50 l / h) was stirred with a stirrer while being blown into the waste water through a glass tube. The evaporate was recovered by a gas liquefier cooled with dry ice-methanol at -72 ° C. The amount of recovered liquid after 3 hours of treatment is 32.6 g.
Thus, the content of dichloromethane was 99.9% (dichloromethane recovery rate: 81.1%), the water content was 915 ppm, and the mixing amounts of hydrogen chloride as a hydrolysis product of dichloromethane and triethylamine as a polymerization catalyst were both 1 ppm or less. By using 1300 g of dichloromethane instead of 1330 g of dichloromethane in Synthesis Example 1 and 32.6 g of the above recovery solution, the amount of dichloromethane used was reduced by 2.25%, and a polycarbonate was produced by the same operation. The obtained polycarbonate has a number average molecular weight (Mn) of 230.
00, weight average molecular weight (Mw) 53000, and polydispersity index (Mw / Mn) 2.30, which was equivalent to the polycarbonate polymerized by (Synthesis Example 1).

Example 3 3000 ml of basic waste water (1.34 wt% of dichloromethane, 15 ppm of triethylamine) generated from the polymerization step in the same polycarbonate synthesis reaction as in Synthesis Example 1 was placed in a separable flask and kept at 72 ° C. in a thermostat. Nitrogen (50 l / h) was stirred with a stirrer while being blown into the waste water through a glass tube. The evaporate was recovered by a gas liquefier cooled with dry ice-methanol at -72 ° C. The recovered liquid after the treatment time of 30 minutes was divided into two layers, and as a result of the separation, 169.4 g of water containing 1.9 wt% of dichloromethane and 29.9 g of dichloromethane containing 580 ppm of water (dichloromethane recovery rate 82.4%). Met. In the recovered dichloromethane, 425 ppm of triethylamine as a polymerization catalyst was mixed. By using 1300 g of dichloromethane instead of 1330 g of dichloromethane in Synthesis Example 1 and 29.9 g of the above recovery liquid, the amount of dichloromethane used was reduced by 2.25%, and a polycarbonate was produced by the same operation. The obtained polycarbonate has a number average molecular weight (Mn) of 20800,
It had a weight average molecular weight (Mw) of 49400 and a polydispersity index (Mw / Mn) of 2.38, and had a slightly lower degree of polymerization and a wider molecular weight distribution than the polycarbonate polymerized by (Synthesis Example 1).

Example 4 3000 ml of basic waste water (1.34 wt% of dichloromethane, 15 ppm of triethylamine) generated from the polymerization step in the same polycarbonate synthesis reaction as in Synthesis Example 1 was placed in a separable flask and kept at 33 ° C. in a thermostatic chamber. Nitrogen (50 l / h) was stirred with a stirrer while being blown into the waste water through a glass tube. At the same time, while purging the nitrogen gas containing vaporized dichloromethane, the use amount of dichloromethane was reduced by 2.25% by using 1300 g of dichloromethane instead of 1330 g of dichloromethane in Synthesis Example 1, and a polycarbonate was synthesized by the same operation. . The obtained polycarbonate has a number average molecular weight (Mn) of 23000, a weight average molecular weight (Mw) of 53100, and a polydispersity index (Mw / M).
n) was 2.31, which was equivalent to the polycarbonate polymerized in (Synthesis example 1).

Example 5 3000 ml of basic waste water (1.62 wt% of dichloromethane, 19 ppm of triethylamine) generated from the polymerization step in the same polycarbonate synthesis reaction as in Synthesis Example 2 was placed in a separable flask and kept at 33 ° C. in a constant temperature bath, Nitrogen (50 l / h) was stirred with a stirrer while being blown into the waste water through a glass tube. The evaporate was recovered by a gas liquefier cooled with dry ice-methanol at -72 ° C. The amount of recovered liquid after 3 hours of treatment is 39.3 g.
Thus, the content of dichloromethane was 99.9% (dichloromethane recovery rate: 80.9%), the water content was 1020 ppm, and the mixing amounts of hydrogen chloride, which is a hydrolysis product of dichloromethane, and triethylamine, which is a polymerization catalyst, were all 1 ppm or less. By using 1290.7 g of dichloromethane instead of 1330 g of dichloromethane in Synthesis Example 2 and 39.3 g of the above recovery solution, the amount of dichloromethane used was reduced by 2.95%, and a polycarbonate was produced by the same operation. The obtained polycarbonate has a number average molecular weight (Mn)
It was 21000, the weight average molecular weight (Mw) was 52500, and the polydispersity index (Mw / Mn) was 2.50, which was equivalent to the polycarbonate polymerized by (Synthesis example 2).

[0023]

According to the method of the present invention, dichloromethane, which is a solvent, can be efficiently removed from the waste water produced during the production of polycarbonate, so that environmental pollution due to the waste water can be prevented. Further, since the removed dichloromethane can be directly supplied to the polycarbonate production process without requiring a special purification operation, the dichloromethane can be reused inexpensively and efficiently.

Claims (3)

[Claims] 1. Dichloromethane is used as an organic solvent,
When a polycarbonate is produced by an interfacial polymerization method, dichloromethane in the produced waste water is removed by aeration with air and / or an inert gas, and the removed dichloromethane is further supplied to the production step for reuse. Method for producing polycarbonate. 2. The removed dichloromethane is recovered by cooling the air and / or the inert gas after aeration,
2. The supply and reuse in the manufacturing process.
The method described. 3. The method according to claim 1, wherein the removed dichloromethane is supplied again by directly purging the inert gas after aeration to the production step.