JP2004339389A - Method for depolymerizing aromatic polycarbonate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for depolymerizing aromatic polycarbonate. <P>SOLUTION: The method for depolymerizing the aromatic polycarbonate comprises subjecting a disc-shaped medium for optical recording, comprising a main component consisting of the aromatic polycarbonate to depolymerization with a 1-6C aliphatic alcohol in a subcritical or supercritical state, converting the 1-6C aliphatic alcohol to a noncritical state by reducing the pressure in the reaction system, and removing an insoluble matter by filtering the reaction product with a filter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for depolymerizing an aromatic polycarbonate. More specifically, a disc-shaped optical recording medium whose main component is made of an aromatic polycarbonate is subjected to a depolymerization reaction with an aliphatic alcohol having 1 to 6 carbon atoms in a subcritical or supercritical state, and after removing insolubles, the monomer component is removed. And a method for recovering an active ingredient such as aromatic bisphenol.
[0002]
[Prior art]
Aromatic polycarbonate resins have excellent transparency, optical properties and tough physical properties, and are used in various applications such as lenses, compact discs, building materials, automotive parts, OA equipment chassis, and camera bodies. It is a high value-added material, and its demand is increasing. When these products are no longer in use, they are often disposed of as waste by incineration or landfill.
[0003]
Above all, the disk-shaped optical recording medium is provided with a thin film layer formed by appropriately combining and stacking a Si-based derivative film, a recording film made of an alloy containing Tb, and an Al-based metal reflection film on an aromatic polycarbonate substrate, Further, it is manufactured by applying a protective paint thereon and performing necessary printing.
[0004]
If a disc-shaped optical recording medium becomes defective or is disposed of in stock during the manufacturing process, it will be taken off by the disc-shaped optical recording medium manufacturer or polycarbonate resin manufacturer, destroyed, landfilled, or incinerated. The disposal has been done in the manner described above. However, disposing of disc-shaped optical recording medium waste, which is expected to increase in the future, in this way not only causes significant waste of resources but also causes global pollution such as environmental pollution and carbon dioxide emissions. Is also a social problem.
[0005]
Attempts have been made to reuse the polycarbonate resin of the disk-shaped optical recording medium substrate, but there are problems with the quality of the recovered resin, recovery efficiency, and the like, and it is difficult to reuse the resin in large quantities.
[0006]
A disc-shaped optical recording medium waste having a recording film or the like provided on a polycarbonate resin substrate is immersed in a basic aqueous solution having a concentration of 1 to 9% by weight. It is disclosed that a polycarbonate resin is recovered by processing in a temperature range and the material is recycled. However, this method is limited to material recycling, and since it is treated in a basic aqueous solution, it is necessary to consider the wastewater treatment of the treatment liquid, which has a large environmental burden and a large equipment cost. Become.
[0007]
Regarding the depolymerization reaction of the aromatic polycarbonate, a method of hydrolyzing the aromatic polycarbonate in the presence of a nitrogen-containing compound such as ammonia water to obtain bisphenol A (for example, see Patent Document 2), the presence of a transesterification catalyst for the aromatic polycarbonate A method of obtaining a diester carbonate corresponding to the alcohol used with bisphenol A by reacting with lower alcohols (for example, see Patent Document 3), a method of obtaining bisphenol A by hydrolyzing an aromatic polycarbonate with an aqueous alkali solution (for example, Patent Document 4), a method of depolymerizing an aromatic polycarbonate using a hydroxy compound and a polar neutral solvent such as dimethyl sulfoxide (for example, see Patent Document 5), bisphenol by subjecting an aromatic polycarbonate to a transesterification reaction with phenols And diaryl mosquitoes Method of generating a Boneto such (for example, see Patent Document 6) have been proposed.
[0008]
However, in most cases, these methods require relatively large amounts of transesterification catalysts such as alkalis due to the slow depolymerization rate, so that the recovery circulation and neutralization of those catalysts are complicated, and economical. There are disadvantages such as significant damage. In addition, in the case of depolymerization with phenols, not only the rate of depolymerization is slow, but also it is difficult to separate bisphenol and diaryl carbonate. There are difficult factors such as happening. Therefore, as a method of separating while leaving an excessive amount of phenol, the amount of residual phenol is adjusted, and then crystallization-separated in the form of a 1: 1 adduct of bisphenol and phenol, and then diaryl carbonate is flashed from the mother liquor. A distillation method (for example, see Patent Document 7) has also been proposed. However, in this method, the diaryl carbonate itself has a tendency to form an adduct of 1: 1 with phenol, so that the separation property is not sufficient, and crystallization separation from phenol must be repeated to obtain bisphenol with high purity. . In addition, it is necessary to finally separate and recover phenol as an adduct and to purify bisphenol by distillation or the like, which is extremely complicated and impairs economic efficiency.
[0009]
In addition, aromatic polycarbonate is hardly subjected to hydrolysis, and hardly undergoes hydrolysis at 230 ° C. or lower without a catalyst. (For example, see Non-Patent Document 1)
[0010]
On the other hand, it is known that hydrolysis to bisphenol A occurs without a catalyst under high temperature and high pressure near the supercritical point of water, but in addition to high temperature exceeding 300 ° C. and high pressure exceeding 200 atm. However, it is considered that it is extremely difficult to carry out the system economically due to the large size of the equipment due to the super-strong acidity of the water itself under supercritical water conditions. Hydrolysis with water also has the disadvantage that the carbonyl component, one of the monomer components of the polycarbonate, is lost as carbon dioxide.
[0011]
For this reason, an attempt has been made to recover the carbonyl component as a carbonate of a monohydric alcohol by depolymerization using a monohydric alcohol, and an aromatic polycarbonate is reacted with an alkoxide or hydroxide catalyst in a polar neutral solvent. A method for depolymerization (for example, see Patent Document 7) and a method for reacting an aromatic polycarbonate with an alcohol in a distillation column using a tin compound as an o-dichlorobenzene solvent and a catalyst (for example, see Patent Document 8) are disclosed. ing. In all of these, depolymerization is proceeding at a relatively low temperature without using a pressure reactor, and the carbonyl component is obtained as a carbonate ester such as dimethyl carbonate simultaneously with the bisphenol compound.
[0012]
A method of depolymerizing a polycarbonate resin by a non-catalytic reaction of subcritical or supercritical methanol (for example, see Patent Document 9) is disclosed. However, this method has a long reaction time of 30 minutes or more, and if the reaction temperature is increased, the amount of by-products increases, and the target bisphenol A recovery rate decreases. The amount of methanol used is as large as 60 times or more the molar ratio of the polycarbonate resin to the amount of polycarbonate resin, so not only the reaction vessel but also the peripheral equipment must be large, and the cost of the entire plant must be increased. Is a factor that leads to an increase in operating costs.
[0013]
Therefore, there is a strong demand for a so-called chemical recycling method for depolymerizing and decomposing aromatic polycarbonate as waste and reusing it as a monomer. However, the aromatic polycarbonate is depolymerized and decomposed without removing the derivative film, recording film, metal reflective film, etc. adhered to the polycarbonate substrate of the disc-shaped optical recording medium, and the active component as a monomer component is recovered. No effective method has been found yet.
[0014]
[Patent Document 1]
JP-A-7-256639 (pages 2-4)
[0015]
[Patent Document 2]
JP-B-39-19159 (page 1-2)
[0016]
[Patent Document 3]
JP-B-39-28648 (page 1-2)
[0017]
[Patent Document 4]
Japanese Patent Publication No. 40-16536 (page 1-2)
[0018]
[Patent Document 5]
JP-T-4-505930 (pages 3-5)
[0019]
[Patent Document 6]
JP-A-6-56985 (pages 2-5)
[0020]
[Patent Document 7]
Japanese Patent Publication No. 6-4549 (pages 3-6)
[0021]
[Patent Document 8]
JP-A-5-255153 (page 2-3)
[0022]
[Patent Document 9]
JP-A-2003-41049 (pages 2-4)
[0023]
[Non-patent document 1]
"Chemical Engineering" September 1999 (pp. 689-690)
[0024]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problem in the conventional method for treating disc-shaped optical recording medium waste whose main component is made of aromatic polycarbonate, and has a derivative film adhered to the polycarbonate substrate of the disc-shaped optical recording medium. In the state where the recording film, the metal reflection film and the like are adhered, a supercritical state or a subcritical state is reacted with an aliphatic alcohol having 1 to 6 carbon atoms so that another monomer component is simultaneously formed with the aromatic bisphenol as a raw material monomer. It is intended to efficiently obtain a certain carbonyl moiety as a carbonate of an aliphatic alcohol having 1 to 6 carbon atoms.
[0025]
According to the present invention, it is possible to depolymerize the disc-shaped optical recording medium waste mainly composed of aromatic polycarbonate without peeling off the laminated thin film on the polycarbonate substrate, and the laminated thin film is insoluble in the reaction solution. Since it can be removed by filtration, it does not require a series of peeling steps such as a laminated thin film. Further, the purity of the recovered aromatic bisphenol obtained is equal to or higher than the purity of the route product on the market.
[0026]
[Means for Solving the Problems]
According to the present invention, a disc-shaped optical recording medium mainly composed of an aromatic polycarbonate is subjected to a depolymerization reaction with an aliphatic alcohol having 1 to 6 carbon atoms in a subcritical or supercritical state to reduce the pressure in the reaction system. After the aliphatic alcohol having 1 to 6 carbon atoms in the reaction system is brought into a non-critical state, the reaction product is filtered through a filter to remove insolubles. After reducing the pressure in the reaction system to bring the aliphatic alcohol having 1 to 6 carbon atoms in the reaction system into a non-critical state, the reaction product is subjected to distillation under normal pressure, under pressure, or under any state. And distilling off the di (1-6alkyl) carbonate while distilling off the fatty alcohol having 1-6 carbons as an azeotrope with the di (1-6alkyl) carbonate. The distillation residue And acquired, further, the solubility parameter (.delta.s) is achieved by isolating the aromatic bisphenol is subjected to crystallization at 10.5 following organic solvents.
[0027]
The aromatic polycarbonate to be depolymerized in the present invention has an aromatic bisphenol carbonate as a repeating unit. Examples of the aromatic bisphenol include dihydroxybenzenes, dihydroxybiphenyl, dihydroxydiphenyl ether, dihydroxydiphenylsulfide, dihydroxydiphenylsulfone, bis (4-hydroxyphenyl) methane (bisphenol F), and 1,1-bis (4-hydroxyphenyl) ethane (Bisphenol E), 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), 2,2-bis (4-hydroxy-3-methylphenyl) propane (bisphenol C), 1,1-bis (4 -Hydroxyphenyl) cyclohexane (bisphenol Z) 3,3,5-trimethyl-1,1-bis (4-hydroxyphenyl) cyclohexane, α, α'-bis (4-hydroxyphenyl) diisopropylbenzene (Bisphenol M), 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis {(4-hydroxy-3-methyl) phenyl} fluorene, 1,3-bis (4-hydroxyphenyl) -5 , 7-dimethyladamantane, 2,2-bis (4-hydroxyphenyl) adamantane, 1,3-bis (4-hydroxyphenyl) -p-menthane (YP-90), 2,8-bis (4-hydroxyphenyl) ) -P-menthane, 1,8-bis (4-hydroxyphenyl) -p-menthane, or a mixture of these bisphenols. Of these, bisphenol A, bisphenol Z, bisphenol M, 3,3,5-trimethyl-1,1-bis (4-hydroxyphenyl) cyclohexane, 9,9-bis {(4-hydroxy-3-methyl) phenyl @Fluorene and YP-90 are preferred, especially bisphenol A.
[0028]
The aromatic polycarbonate to be depolymerized according to the present invention is obtained by polymerizing or copolymerizing the above-mentioned bisphenol compound, and the polymerization method may be any. Usually, an interfacial polymerization method using phosgene and a melt polymerization method using diphenyl carbonate are used, but either method may be used and the production method does not depend on the method.
[0029]
The degree of polymerization varies depending on the application and the like, but is usually in the range of 5,000 to 200,000. However, the degree of polymerization does not depend on the degree of thermoplasticity. For example, an aromatic polycarbonate having a viscosity-average molecular weight in the range of 14,000 to 16,000 is formed on a substrate of an aromatic polycarbonate used for a disk-shaped optical recording medium by using a catalyst or a molecular weight modifier. Used for materials.
[0030]
It is intended for aromatic polycarbonates which have been discarded and discarded, and may contain various contaminants depending on the application. For example, in the case of disc-shaped optical recording medium waste, the laminated thin film provided on the polycarbonate resin substrate differs depending on the form of the information recording medium, for example, a substrate provided with a reflective film and a protective layer on the substrate, A structure in which a dye layer, a reflective film, and a protective layer are laminated on a substrate is used. The magneto-optical recording disk is formed by laminating a dielectric film, a recording film of a metal alloy, and a thin film of a reflective film on a substrate. Any disc-shaped optical recording medium waste provided with the laminated thin film of any of these forms can be a target of the depolymerization method of the present invention.
[0031]
In depolymerizing the aromatic polycarbonate which is a main component of the disc-shaped optical recording medium, it is possible to pulverize these disc-shaped optical recording media in advance and use them. The size at the time of pulverization may be in the range of 0.5 to 10 mm in average size, and is preferably pulverized to a pulverized product of 1 to 5 mm from the viewpoint of ease of continuous introduction into the melting apparatus and ease of melting.
[0032]
The pulverization here is not particularly limited, but may be dry pulverization or wet pulverization. As the crusher, general equipment such as a hammer crusher, a jaw crusher, a hammer mill, a cutter mill, a feather mill, and a turbo mill may be used. The pulverization is preferably carried out at a temperature from room temperature to 50 ° C. The pulverization time varies depending on the type of the pulverizer, but is usually about 10 seconds to 10 minutes, preferably about 1 minute to 7 minutes.
[0033]
The disk-shaped optical recording medium whose main component is an aromatic polycarbonate is usually supplied to the reactor in a pulverized state, but it can be supplied by heating and melting when it is performed continuously.
[0034]
The reaction is carried out in a flow, semi-batch or batch reaction pressure vessel. In a flow-type or semi-batch type apparatus, the reaction solvent and the reaction raw material can be heated in advance by a heat exchanger or the like and supplied to a reaction pressure vessel. It is also possible to form the reaction product by introducing an aliphatic alcohol having 1 to 6 carbon atoms and an aromatic polycarbonate into a pressure-resistant container and heating the mixture.
[0035]
The reactant aliphatic alcohol having 1 to 6 carbon atoms can be introduced into the reactor together with the aromatic polycarbonate in advance. However, when the reaction is continuously performed, the aromatic polycarbonate as the raw material is melted and introduced. The continuous pressurization can be easily performed in the same manner as described above. That is, the depolymerization reaction of the present invention can be continuously performed by continuously supplying the raw material polymer and the aliphatic alcohol having 1 to 6 carbon atoms to the reaction pressure vessel under the reaction conditions.
[0036]
Further, by maintaining a constant pressure at a constant temperature using a pressure regulating valve at the outlet of the reaction pressure vessel, the density of the supercritical fluid of the aliphatic alcohol having 1 to 6 carbon atoms is kept constant, and the depolymerization reaction is continued. The product soluble in the supercritical fluid produced by the above method can be continuously taken out from the outlet of the pressure regulating valve.
[0037]
Examples of the aliphatic alcohol having 1 to 6 carbon atoms used in the present invention include methanol, ethanol, propanol, butanol, hexanol and the like. Of these, methanol and ethanol are preferred, with methanol being most preferred.
[0038]
The amount of the aliphatic alcohol having 1 to 6 carbon atoms is preferably in the range of usually 1 to 100 mol, more preferably less than 40 mol per 1 mol of the repeating unit of the aromatic polycarbonate. The relationship between the amount of the aromatic polycarbonate used in the reaction and the amount of the aliphatic alcohol having 1 to 6 carbon atoms is very important because it relates to the specification of the reaction vessel. When the molar ratio of the aliphatic alcohol having 1 to 6 carbon atoms to the aromatic polycarbonate increases, a large amount of alcohol needs to be added to the reaction vessel. Therefore, the reaction vessel becomes large, and an apparatus for introducing alcohol and an apparatus for separating alcohol remaining after the reaction become large. Therefore, not only the reaction vessel, but also the peripheral equipment must be large, which causes an increase in the cost of the entire plant and further increases the operating cost. Further, since the reaction vessel used for the reaction is designed to withstand high-temperature and high-pressure reactions, a large-sized reactor operating in a general commercial plant becomes very difficult in terms of design and economy. .
[0039]
The depolymerization reaction of the aromatic carbonate in the present invention is carried out, for example, by reacting with an aliphatic alcohol having 1 to 6 carbon atoms at a temperature of 200 ° C. or more under pressure. The reaction is usually carried out in a closed container under a pressure near the vapor pressure of alcohol at the same temperature, but preferably at a reaction temperature of 220 ° C to 360 ° C, more preferably at 230 ° C to 290 ° C. If the reaction temperature is lower than 200 ° C., the reaction is slow, and it takes a long time until the reaction is completed. If the temperature is higher than 350 ° C., side reactions such as alkylation may occur, which is not preferable. A particularly preferred temperature range is from 230 ° C. to 290 ° C., including the supercritical temperature of alcohol.
[0040]
The reaction is carried out under pressure in a closed vessel because the reaction temperature is usually higher than the boiling point of the aliphatic alcohol having 1 to 6 carbon atoms. This reaction is carried out at a pressure of 3.5 MPa or more, preferably a reaction pressure of 4.0 to 30 MPa, particularly preferably a reaction pressure of 6 to 20 MPa, and a pressure range including the supercritical pressure of alcohol. . At temperatures near or above the supercritical temperature of aliphatic alcohols having 1 to 6 carbon atoms, phase separation does not occur due to reaction pressure, but the density of the fluid changes. It is known that the density of a supercritical fluid generally increases as the pressure increases, and the reactivity increases. On the other hand, if the density of the fluid is too high, the viscosity of the fluid may be increased, the diffusivity may be impaired, and the efficiency may deteriorate, and the reaction pressure is usually set to 35 MPa or less. Higher pressures are not preferred not only in terms of economical and safety aspects, such as requiring a large amount of energy but also requiring high strength of the reactor.
[0041]
For example, the critical densities of methanol and ethanol are 0.272 g / cc and 0.276 g / cc, respectively, which are about 1/3 of the density in the liquid state, but exhibit high solubility and high diffusivity, Even without a catalyst, the solvolysis reaction of the aromatic polycarbonate proceeds at an extremely high reaction rate. Reaction conditions near this supercritical point are advantageous. Under the same conditions, the reaction was completed in a very short time, and the product aromatic bisphenol and di (1-6 alkyl) carbonate were dissolved in a supercritical fluid of an aliphatic alcohol having 1-6 carbon atoms. Is obtained.
[0042]
The critical point of an aliphatic alcohol having 1 to 6 carbon atoms is as follows. Hereinafter, the critical temperature (Tc, ° K) and the critical pressure (Pc, MPa) are described in order of the compound name.
Methanol 512.6, 8.09; ethanol 516.2, 6.38;
n-propanol 536.7, 5.17; isopropanol 508.3, 4.76
n-butanol 562.9, 4.42; sec-butanol 536.0, 4.19
iso-butanol 547.7, 4.30; tert-butanol 506.2, 3.97
n-pentanol 586.0, 3.85;
2-methyl-1-butanol 571.0, 3.85;
3-methyl-1-butanol 579.5, 3.85;
2-methyl-2-butanol 545.0, 3.95;
2,2-dimethyl-1-propanol 549.0, 3.95;
n-hexanol 610.0, 4.05; cyclohexanol 625.0, 3.75.
[0043]
Assuming that the critical temperature at which the aliphatic alcohol becomes a supercritical fluid is Tc (° C.) and the critical pressure is Pc (MPa), this reaction is carried out under at least one of Tc ± 30 ° C. and Pc ± 2 MPa. You.
[0044]
The reaction time is adjusted by the reaction temperature and the reaction pressure, but if the reaction time becomes longer, the aromatic bisphenol produced by the reaction will stay for a long time under high temperature and pressure, and side reactions such as decomposition will occur, This leads to lower recovery. Furthermore, the reaction time also depends on the size of the reaction vessel. A longer reaction time leads to a reduction in the processing capacity per unit time, and an attempt to increase the processing capacity leads to an increase in the size of the reaction vessel. For this reason, the reaction time is preferably in the range of 0.1 to 60 minutes, particularly preferably 0.5 to 30 minutes.
[0045]
This reaction can be carried out without adding a catalyst, but can also be carried out in the presence of a catalyst for the purpose of increasing the reaction rate and increasing the selectivity. Examples of such a catalyst include catalysts used for ordinary ester hydrolysis and transesterification. Examples include hydroxides and salts of alkali metals and alkaline earth metals, oxides and salts of zinc, germanium, tin, lead, titanium, zirconium, antimony and rare earth metals.
[0046]
After completion of the reaction, the pressure in the reaction system is reduced to bring the aliphatic alcohol having 1 to 6 carbon atoms in the reaction system into a non-critical state, and then the reaction product is filtered through a filter to remove insolubles. Then, di (C 1 -C 6 alkyl) carbonate and aromatic bisphenol are separated and obtained from the filtrate.
[0047]
The main insolubles are, for example, in the case of a disc-shaped optical recording medium, depending on the form of the information recording medium, but generally, a reflective film, a protective layer film, a dye layer film, which constitute a laminated thin film on a polycarbonate resin substrate, It comprises at least a part of a group consisting of a derivative film, a recording film of a metal alloy, and the like.
[0048]
The filtering device includes a leaf disk type, a candle type, a plate type and the like, but is not particularly limited.
[0049]
The type of the filter is not particularly limited as long as it can filter a high-temperature fluid, but a ceramic filter made of alumina or the like, a laminated metal mesh filter, a metal nonwoven fabric filter, a sintered metal filter made of stainless steel or the like may be used.
[0050]
The size of the mesh of the filter needs to be adjusted according to the average size at the time of pulverization, the flow rate at the time of filtration, and the pressure loss, but may be in the range of 1 μm to 20 mm.
[0051]
The material of the filter is not particularly limited as long as it is inert to the reaction solution and there is no eluting component to the reaction solution, but generally a metal, particularly stainless steel, for example, SUS304, SUS316, etc. It is preferably used.
[0052]
During the continuous filtration process, the filter body is clogged by the captured insoluble matter, the differential pressure of the filter body increases, and continuous processing becomes difficult.
[0053]
Therefore, when the filter body is clogged and the pressure difference between the inlet and the outlet becomes equal to or higher than a certain pressure, the problem can be solved by performing a backwashing treatment on the filter body. The differential pressure at which backwashing is performed varies depending on the type of filter, the type of insoluble impurities to be removed, the particle size, and the like, but is usually preferably in the range of 0.1 to 1.0 MPa. As a medium for the backwashing treatment, an aliphatic alcohol having 1 to 6 carbon atoms at room temperature to 300 ° C. or an aliphatic alcohol having 1 to 6 carbon atoms in a supercritical or subcritical state is used.
[0054]
It is also possible to provide two or more filters in parallel so that backwashing and filtration can be performed simultaneously.
[0055]
In order to separate the aromatic bisphenol and di (C1-6alkyl) carbonate from the filtrate, the filtrate containing the aromatic bisphenol and di (C1-6alkyl) carbonate is subjected to distillation. The aromatic bisphenol and di (1-6 alkyl) carbonate can be isolated by removing the alcohol having 1 to 6 carbon atoms and then subjecting the distillation residue to further distillation or extraction with an organic solvent, respectively. it can.
[0056]
Examples of the resulting di (C1-6 alkyl) carbonate include dimethyl carbonate, diethyl carbonate and the like.
[0057]
In the case of distillation, any apparatus can be used as the distillation apparatus. However, in order to reduce costs and prevent quality deterioration, a small amount of stay and a short stay time are used. For example, a falling liquid film evaporator, a thin film evaporator, a spiral tube evaporator, or a circulating or rising film evaporator is suitable. The residue after distillation can be used as it is for the depolymerization reaction of the aromatic polycarbonate.
[0058]
The reaction product containing the aromatic bisphenol and di (C.sub.1-6 alkyl) carbonate is subjected to distillation to remove the C.sub.1-6 alcohol, and then the distillation residue is further subjected to distillation or an organic solvent. By performing the extraction, the aromatic bisphenol and di (C1-6 alkyl) carbonate can be respectively isolated. However, it is generally known that alcohols having 1 to 6 carbon atoms and di (1 to 6 carbon atoms) carbonate are distilled off as an azeotrope when subjected to distillation. Therefore, after completion of the reaction, the pressure in the reaction system is reduced to bring the aliphatic alcohol having 1 to 6 carbon atoms in the reaction system into a non-critical state, and then the reaction product is subjected to distillation to obtain 1 to 6 carbon atoms. Method of distilling di (1-6alkyl) carbonate and obtaining aromatic bisphenol as a distillation residue while distilling off fatty alcohol No.6 as an azeotrope with di (1-6alkyl) carbonate Is preferably carried out.
[0059]
In order to obtain as many dialkyl carbonates as can be obtained separately from the azeotrope, it is desirable that the proportion of the dialkyl carbonate as the azeotrope be small.
[0060]
The azeotrope preferably has a weight ratio of aliphatic alcohol having 1 to 6 carbon atoms to di (1-6 alkyl) carbonate in the range of 70:30 to 99: 1.
[0061]
When distillation is performed under pressure, the azeotropic composition changes, and the higher the pressure, the greater the proportion of low boiling components in the azeotropic composition.
[0062]
For this reason, when the aliphatic alcohol is, for example, methanol, at 1.5 MPa, the methanol becomes about 93 to dimethyl carbonate 7 (weight ratio). Therefore, by distilling and separating at a higher pressure, a methanol fraction having a smaller dimethyl carbonate composition can be obtained from the top of the column, and dimethyl carbonate can be distilled from the lower portion. Further, if necessary, it can be subjected to purification by distillation or crystallization. The methanol fraction obtained from the top of the column can be returned to the depolymerization reactor while containing a small amount of dimethyl carbonate as an azeotropic composition and recycled.
[0063]
Accordingly, the higher the operating pressure of the distillation column, the lower the dialkyl carbonate composition in the alcohol distilled from the top of the distillation column. Therefore, it is desirable to operate the distillation column at a higher pressure. For example, when methanol is used as the alcohol, the methanol / dimethyl carbonate ratio is about 93/7 at 1.5 MPa, but is about 96/4 at 2.0 MPa and about 98.5 / 1.5 at 3.0 MPa. The amount circulated and recovered together with methanol is small, and the yield of dimethyl carbonate from the lower part of the distillation column is improved.
[0064]
Since the depolymerization reaction is performed under high-temperature pressurization as described above, the operation pressure of the distillation column must be lower than the reaction pressure of the depolymerization reaction but as high as possible in order to perform energy-efficient operation as a whole. It is preferable to carry out. Furthermore, the distillation temperature of di (1-6 alkyl) carbonate distilled from the lower part of the column is determined by the operating pressure of the distillation column. It is more preferable to select the operation pressure of considering the overall energy efficiency. For example, the vapor pressure of dimethyl carbonate at 200 ° C. is about 1.4 MPa, and the vapor pressure at 250 ° C. is about 3.1 MPa. Therefore, the operating pressure of the distillation column is preferably set at a pressure not higher than the vapor pressure of di (1-6 alkyl) carbonate at the reaction temperature of the depolymerization reaction, and is usually not higher than 4.0 MPa.
[0065]
At the same time, a distillation residue containing aromatic bisphenol such as high boiling bisphenol A is obtained from the bottom of the column.
[0066]
The above product is preferably extracted with an organic solvent using an organic solvent having a solubility parameter (δ _s ) of 10.5 or less, and the aromatic bisphenol is preferably isolated from the extracted solution by crystallization.
[0067]
Here, the solubility parameter (δ _s ) is calculated according to K. L. This is a value derived from Hoy's concept of molar traction (J. Paint Technology, 42, 76, 1970).
[0068]
The [delta] _s is 10.5 less organic solvents, such as benzene (δ _s; 9.1), toluene (δ _s; 8.8), xylenes (δ _s; 8.5~8.8), such as aromatic hydrocarbon solvents, methylene chloride, chloroform ([delta] _s; 9.2), carbon tetrachloride ([delta] _s; 8.6), chlorobenzene ([delta] _s; 9.3) halogenated such as hydrocarbons, hexane ( Saturated aliphatic hydrocarbon compounds such as δ _s ; 7.32), cyclohexane (δ _s ; 8.6), heptane (δ _s ; 7.44), pentane (δ _s ; 7.37). . Among these, those having δ of 8.0 to 10.0 are preferable. Solvents in this range dissolve the aromatic bisphenol and have particularly excellent crystallization selectivity.
[0069]
Among these solvents having a solubility parameter δ _s of 10.5 or less, a solvent having a relatively low boiling point that is chemically stable and easy to recover and circulate, does not contaminate the final target substance, and can remove expected impurities is used. Most preferred are, inter alia, benzene, toluene, methylene chloride and chloroform. The amounts of these solvents used are determined by the solubility of each solvent in aromatic bisphenol and the amount of undecomposed aromatic polycarbonate (oligomer). The solvent solubility parameter [delta] _s is 10.5 used herein, a low solubility in ordinary aromatic bisphenols (e.g. solubility at room temperature to solvent 100g is 1 or less) one is chosen. Therefore, the amount of the solvent actually used varies depending on the solubility (difference in solubility) of the solvent, the processing temperature (difference), the amount of contaminants, and the like. For example, when toluene is used, 100 parts by weight of the reaction product is used. Used in the range of 50 to 200 parts by weight. This crystallization method can be carried out using ordinary means, and by repeating this crystallization method, aromatic bisphenol can be separated and recovered with higher purity.
[0070]
After separating and recovering the aromatic bisphenol as a monomer component in this way, the mother liquor is subjected to distillation to separate and recover the crystallization solvent, which can be recycled and used, and the distillation residue can be recycled and used again in the depolymerization step. it can.
[0071]
【The invention's effect】
According to this depolymerization method, in addition to being able to recover the generated active ingredient at a high recovery rate, it is possible to depolymerize without peeling off the laminated thin film and the like on the polycarbonate substrate. Therefore, there is no need for a series of peeling processing steps such as a laminated thin film. Further, the purity of the recovered aromatic bisphenol obtained is equal to or higher than the purity of the route product on the market.
[0072]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[0073]
[Example 1]
0.39 g of a compact disc and 1.21 g of methanol were charged into a batch type reaction tube (SUS316) having a total internal volume of 6 ml, and a sand bath (sand: Showa Denko Brown Alumina Random A-) was maintained at 270 ° C. 40) and reacted for 10 minutes. The pressure at this time was 9.3 MPa. After the reaction, the mixture was quenched and reached room temperature, the contents were taken out, and the insolubles were filtered off with filter paper (4 types of JISP 3801 [filter paper (for chemical analysis)]) having a retained particle diameter of 1 μm. The collected insoluble matter was 4.3 mg. Analysis of 1.20 g of the filtrate by gas chromatography and NMR revealed that 0.31 g (91% yield) of bisphenol A and 0.13 g (93% yield) of dimethyl carbonate had been formed. Was. The remaining filtrate was distilled to remove methanol and dimethyl carbonate, 15 g of toluene was added, and the mixture was heated and dissolved. When the solution was left at room temperature overnight, needle crystals were obtained. After filtration, analysis by liquid chromatography revealed that bisphenol A having a purity of 99% was obtained.

Claims (7)

The main component is subjected to a depolymerization reaction of a disc-shaped optical recording medium made of an aromatic polycarbonate with an aliphatic alcohol having 1 to 6 carbon atoms in a subcritical or supercritical state, reducing the pressure in the reaction system, and reducing the pressure in the reaction system. A method for depolymerizing an aromatic polycarbonate, which comprises removing an insoluble substance by making an aliphatic alcohol having 1 to 6 carbon atoms into a noncritical state and then filtering the reaction product through a filter. The filtrate is subjected to distillation to distill an aliphatic alcohol having 1 to 6 carbon atoms as an azeotrope with di (1 to 6 alkyl) carbonate while di (1 to 6 alkyl) is removed. The method according to claim 1, wherein the carbonate is distilled and the aromatic bisphenol is obtained as a distillation residue. The method according to claim 1, wherein the aliphatic alcohol having 1 to 6 carbon atoms is methanol. The aromatic bisphenol obtained from the bottom of the column is further subjected to crystallization with an organic solvent having a solubility parameter (δs) of 10.5 or less to obtain an aromatic bisphenol having a purity of 95% or more. The method described in. The method of claim 1 wherein the azeotrope has a weight ratio of aliphatic alcohol having 1 to 6 carbon atoms to di (1-6 alkyl) carbonate in the range of 70:30 to 99: 1. The method of claim 1, wherein the non-critical state maintains the reaction system under pressure. A method for producing an aromatic polycarbonate, characterized in that an aromatic bisphenol obtained by the method according to any one of claims 1 to 6 is used in an amount of 0.1% to 100% of the aromatic bisphenol used as a raw material.