JP7613067B2 - Method for producing bisphenol and method for producing recycled polycarbonate resin - Google Patents

Description

The present invention relates to a method for producing bisphenol. More specifically, the present invention relates to a method for producing bisphenol by utilizing the decomposition of polycarbonate resin. Furthermore, the present invention relates to a method for producing recycled polycarbonate resin using bisphenol obtained by the above-mentioned method for producing bisphenol.

Plastic is produced in large quantities not only in Japan but all over the world because it is easy to use, durable, and inexpensive. As most of this plastic is used as "disposable," some of it is not properly disposed of and ends up in the environment. Specifically, plastic waste flows from rivers into the ocean, where it is degraded by waves and ultraviolet rays and becomes 5 mm or smaller. Such small plastic waste is called microplastics. Animals and fish mistakenly ingest these microplastics. In this way, plastic waste has a huge impact on ecosystems, and in recent years it has become a problem around the world as marine plastics. Polycarbonate resin, which is used in a wide range of fields due to its transparency, mechanical properties, flame retardancy, dimensional stability, and electrical properties, is no exception.

One method for recycling polycarbonate resin is chemical recycling, in which polycarbonate resin is chemically decomposed and returned to bisphenol for reuse. Glycolysis is known as one method for decomposing polycarbonate resin. As a glycolysis method, a method is known in which bisphenol-based polycarbonate (PC) is reacted with an aliphatic diol, polyol, or corresponding epoxide, and alkylene carbonate to produce bisphenol, which is one of the structural units of PC, and/or a hydroxyalkyl ether compound of the bisphenol (Patent Document 1). In addition, a method is also known in which polycarbonate resin is depolymerized by reacting polycarbonate resin with 1,2-propanediol in tetrahydrofuran using zinc oxide nanoparticles, ionic liquid, or the like as a catalyst (Non-Patent Document 1).

JP 2001-192497 A

J. Mol. Catal. A: Chem. 2017, 426, 107-116.

However, the method of Patent Document 1 has the problem that the hydroxyalkyl ether compound of bisphenol is obtained as the main component, and the yield of bisphenol is low. For example, in Example 1 of Patent Document 1, bishydroxyethyl ether (BHE-BPA) is quantitatively produced, and the production of bisphenol A (BPA) is not confirmed.

In addition, the method in Non-Patent Document 1 requires the use of special catalysts such as zinc oxide nanoparticles and ionic liquids, and depending on the catalyst, there are problems such as a low reaction rate and a long reaction time, so further improvement is required.

The present invention has been made in consideration of these circumstances, and aims to provide a method for producing bisphenol by using a mild and efficient decomposition method that can decompose polycarbonate resin. It also aims to provide a method for producing recycled polycarbonate resin using the obtained bisphenol.

The inventors of the present invention conducted intensive research to solve the above problems, and as a result, discovered a method for decomposing polycarbonate resin using a combination of an aromatic monoalcohol and a glycol. They also discovered a method for producing bisphenol using the above-mentioned polycarbonate resin decomposition method. They also discovered a method for producing recycled polycarbonate resin using the obtained bisphenol.

式中、Ｒ^Aは、炭素数１～３のアルキル基を表し、Ｒ^B～Ｒ^Cは、それぞれに独立に水素原子又は炭素数１～３のアルキル基を表す。
＜５＞ 前記アルキルアミンが、第三級アミンである、前記＜２＞又は＜４＞に記載のビスフェノールの製造方法。
＜６＞ 前記酸が、塩酸、硫酸、リン酸及びスルホン酸からなる群から選択されるいずれかである、前記＜２＞に記載のビスフェノールの製造方法。
＜７＞ 前記芳香族モノアルコールが、フェノール、クレゾール及びキシレノールからなる群から選択されるいずれかである、前記＜１＞から＜６＞のいずれかに記載のビスフェノールの製造方法。
＜８＞ 前記グリコールが、エチレングリコール又はプロピレングリコールである、前記＜１＞から＜７＞のいずれかに記載のビスフェノールの製造方法。
＜９＞ 前記ポリカーボネート樹脂の繰り返し単位１モルに対する、前記グリコールのモル比が、１．０以上２．０以下である、前記＜１＞から＜８＞のいずれかに記載のビスフェノールの製造方法。
＜１０＞ 前記ビスフェノールが、２，２－ビス（４－ヒドロキシフェニル）プロパンである、前記＜１＞から＜９＞のいずれかに記載のビスフェノールの製造方法。
＜１１＞ 前記分解反応工程で得られた炭酸アルキレンを回収する炭酸アルキレン回収工程を有する、前記＜１＞から＜１０＞のいずれかに記載のビスフェノールの製造方法。
＜１２＞ 前記＜１＞から＜１１＞のいずれかに記載のビスフェノールの製造方法で得られたビスフェノールを含むビスフェノール原料を用いて、再生ポリカーボネート樹脂を製造する、再生ポリカーボネート樹脂の製造方法。 That is, the present invention relates to the following inventions.
<1> A method for producing bisphenol, comprising: a preparation step of preparing a reaction liquid containing a polycarbonate resin, an aromatic monoalcohol, a glycol, and a catalyst; a decomposition reaction step of decomposing the polycarbonate resin in the reaction liquid prepared in the preparation step into bisphenol and alkylene carbonate; and a bisphenol recovery step of recovering the bisphenol obtained in the decomposition reaction step.
<2> The method for producing bisphenol according to <1>, wherein the catalyst is any one selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkylamines and acids.
<3> The method for producing bisphenol according to <2>, wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.
<4> The method for producing bisphenol according to <2> above, wherein the alkylamine is represented by the following formula (I):

In the formula, R ^A represents an alkyl group having 1 to 3 carbon atoms, and R ^B to R ^C each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
<5> The method for producing bisphenol according to <2> or <4>, wherein the alkylamine is a tertiary amine.
<6> The method for producing bisphenol according to <2>, wherein the acid is any one selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid and sulfonic acid.
<7> The method for producing bisphenol according to any one of <1> to <6>, wherein the aromatic monoalcohol is any one selected from the group consisting of phenol, cresol, and xylenol.
<8> The method for producing bisphenol according to any one of <1> to <7>, wherein the glycol is ethylene glycol or propylene glycol.
<9> The method for producing bisphenol according to any one of <1> to <8>, wherein a molar ratio of the glycol to 1 mole of the repeating unit of the polycarbonate resin is 1.0 or more and 2.0 or less.
<10> The method for producing bisphenol according to any one of <1> to <9>, wherein the bisphenol is 2,2-bis(4-hydroxyphenyl)propane.
<11> The method for producing bisphenol according to any one of <1> to <10>, further comprising an alkylene carbonate recovery step of recovering the alkylene carbonate obtained in the decomposition reaction step.
<12> A method for producing a recycled polycarbonate resin, comprising producing a recycled polycarbonate resin using a bisphenol raw material containing bisphenol obtained by the method for producing bisphenol according to any one of <1> to <11>.

The present invention provides a method for producing bisphenol by using a decomposition method that can efficiently decompose polycarbonate resin under mild conditions. Furthermore, a method for producing recycled polycarbonate resin using the obtained bisphenol is provided.

The following describes in detail the embodiments of the present invention, but the description of the constituent elements described below is one example of the embodiment of the present invention, and the present invention is not limited to the following description as long as it does not deviate from the gist of the invention. Note that when the expression "~" is used in this specification, it is used as an expression including the numerical values or physical property values before and after it.

<Production method of bisphenol>
The present invention relates to a method for producing bisphenol, which includes a preparation step of preparing a reaction liquid containing a polycarbonate resin, an aromatic monoalcohol, a glycol, and a catalyst, a decomposition reaction step of decomposing the polycarbonate resin in the reaction liquid prepared in the preparation step into bisphenol and alkylene carbonate, and a bisphenol recovery step of recovering the bisphenol obtained in the decomposition reaction step (hereinafter, this may be referred to as the "method for producing bisphenol of the present invention").

The method for producing bisphenol of the present invention utilizes a decomposition method in which a polycarbonate resin is decomposed in the presence of an aromatic monoalcohol, a glycol and a catalyst.
The present inventors have found that, in the presence of a catalyst, the polycarbonate resin can be decomposed into bisphenol and alkylene carbonate even under mild conditions by using an aromatic monoalcohol and a glycol in combination. In addition, it has been found that the decomposition reaction of the polycarbonate resin occurs at a high reaction rate by using an aromatic monoalcohol and a glycol in combination, even if the polycarbonate resin is not completely dissolved using a solvent that has a high solubility for the polycarbonate resin, such as a halogen solvent.

By using aromatic monoalcohols and glycols in combination, both solvolysis reactions by the aromatic monoalcohol and solvolysis by the glycol occur in the system, which is thought to make the polycarbonate resin more susceptible to decomposition even under mild conditions.

<Preparation process>
The method for producing bisphenol of the present invention includes a preparation step of preparing a reaction liquid containing a polycarbonate resin, an aromatic monoalcohol, a glycol and a catalyst.

(Polycarbonate resin)
The polycarbonate resin used in the method for producing bisphenol of the present invention contains a polymer composition containing a carbonate bond (-O-C(=O)-O-). Specifically, the polycarbonate resin used in the method for producing bisphenol of the present invention contains a polymer containing a repeating unit derived from bisphenol, which is represented by general formula (1).

The substituents of R ¹ to R ⁴ each independently include a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, etc. Examples of the substituents include a hydrogen atom, a fluoro group, a chloro group, a bromo group, an iodo group, a methyl group, an ethyl group, a n-propyl group, an i-propyl group, a n-butyl group, an i-butyl group, a t-butyl group, a n-pentyl group, an i-pentyl group, a n-hexyl group, a n-heptyl group, a n-octyl group, a n-nonyl group, a n-decyl group, a n-undecyl group, a n-dodecyl group, a methoxy group, an ethoxy group, a n-propoxy group, an i-propoxy group, a n-butoxy group, an i-butoxy group, a t-butoxy group, etc. Examples of such aryloxy groups include an n-pentyloxy group, an i-pentyloxy group, an n-hexyloxy group, an n-heptyloxy group, an n-octyloxy group, an n-nonyloxy group, an n-decyloxy group, an n-undecyloxy group, an n-dodecyloxy group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclododecyl group, a benzyl group, a phenyl group, a tolyl group, and a 2,6-dimethylphenyl group.

Substituents of ^R5 and ^R6 each independently include a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, etc. Examples of such groups include a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, an n-pentyl group, an i-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a 2-ethylhexyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, an n-butoxy group, an i-butoxy group, a t-butoxy group, an n-pentyl group, an i ... Examples of such aryloxy groups include an n-butyloxy group, an i-pentyloxy group, an n-hexyloxy group, an n-heptyloxy group, an n-octyloxy group, an n-nonyloxy group, an n-decyloxy group, an n-undecyloxy group, an n-dodecyloxy group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclododecyl group, a benzyl group, a phenyl group, a tolyl group, and a 2,6-dimethylphenyl group.

^R5 and ^R6 may bond or bridge each other between the two groups to form a cycloalkylidene group, such as cyclopropylidene, cyclobutylidene, cyclopentylidene, cyclohexylidene, 3,3,5-trimethylcyclohexylidene, cycloheptylidene, cyclooctylidene, cyclononylidene, cyclodecylidene, cycloundecylidene, cyclododecylidene, fluorenylidene, xanthonylidene, and thioxanthonylidene.

In addition, the polycarbonate resin may be not only a single polycarbonate resin, which is generally simply called polycarbonate, but also a composition containing a resin other than the polycarbonate resin, such as a copolymer or a polymer alloy. Examples of compositions containing a resin other than the polycarbonate resin include polycarbonate/polyester copolymers, polycarbonate/polyester alloys, polycarbonate/polyarylate copolymers, and polycarbonate/polyarylate alloys. When using a composition containing a resin other than the polycarbonate resin, it is preferable that the composition is mainly composed of polycarbonate resin (containing 50% by mass or more of polycarbonate resin in the composition).
The polycarbonate resin may be a mixture of two or more different polycarbonate resins.

From the viewpoint of chemical recycling, the polycarbonate resin is preferably polycarbonate resin contained in waste plastics. Polycarbonate resin is molded and used into various molded products such as optical components such as headlamps and optical recording media such as optical disks. As waste plastics containing polycarbonate resin, scraps and defective products generated when molding polycarbonate resin into these molded products, used molded products, etc. can be used.

Waste plastics may be washed, crushed, pulverized, etc., as appropriate. Methods for crushing waste plastics include coarse crushing using a jaw crusher or a rotary crusher to crush to 20 cm or less, medium crushing using a rotary crusher, cone crusher, or mill to crush to 1 cm or less, and crushing using a mill to crush to 1 mm or less. Any method can be used to reduce the size of the waste plastics to a size that can be fed to the decomposition tank. In addition, if the waste plastic is a thin plastic such as a CD or DVD, it can be cut using a shredder or the like and fed to the decomposition tank. In addition, parts formed of components other than polycarbonate resin, such as other resins of copolymers and polymer alloys, and the layers on the front and back of optical disks, may be removed in advance before use.

(Aromatic monoalcohol)
One of the features of the method for producing bisphenol of the present invention is the use of an aromatic monoalcohol, which is a compound in which one hydroxyl group is bonded to a carbon atom forming an aromatic ring, and is preferably any one selected from the group consisting of phenol, cresol, and xylenol.
Examples of cresol include ortho-cresol, meta-cresol, para-cresol, and isomeric mixtures containing one or more of these. Since cresol is easily supplied to the decomposition tank if it is liquid at around 30° C., it is preferable to use ortho-cresol, meta-cresol, an isomeric mixture of meta-cresol and para-cresol, or an isomeric mixture of ortho-cresol, meta-cresol and para-cresol.
Examples of xylenol include 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,5-xylenol, 3,4-xylenol, and isomer mixtures containing one or more of these. 2,5-xylenol is preferred because it is industrially available at low cost.

If the amount of aromatic monoalcohol used is small relative to the polycarbonate resin used, the amount of solid (polycarbonate resin) relative to the liquid increases, the slurry concentration increases, and mixing tends to be poor. Therefore, the molar ratio of aromatic monoalcohol to 1 mole of repeating unit of polycarbonate resin (i.e., repeating unit represented by the above general formula (1)) ((mass [g] of aromatic monoalcohol used/molecular weight [g/mol] of aromatic monoalcohol)/(mass [g] of polycarbonate resin used/molecular weight of repeating unit [g/mol])) is preferably 0.005 or more, more preferably 0.01 or more, and even more preferably 0.03 or more. In addition, if the amount of aromatic monoalcohol used is large relative to the polycarbonate resin used, the production efficiency tends to deteriorate. Therefore, the molar ratio of aromatic monoalcohol to 1 mole of repeating unit of polycarbonate resin is preferably 100 or less, more preferably 70 or less, and even more preferably 50 or less.

(Glycol)
One of the features of the method for producing bisphenol of the present invention is the use of glycol. Glycol is a compound in which one hydroxyl group is bonded to each of two carbon atoms of an alkyl group having two or more carbon atoms. The glycol is preferably ethylene glycol or propylene glycol.

If the amount of glycol used is small relative to the amount of polycarbonate resin used, the polycarbonate resin is difficult to decompose or the decomposition rate is reduced, so the decomposition time is prolonged and efficiency tends to deteriorate. Therefore, the molar ratio of glycol to 1 mole of repeating unit of polycarbonate resin ((mass [g] of glycol used/molecular weight [g/mol] of glycol)/(mass [g] of polycarbonate resin used/molecular weight of repeating unit [g/mol])) is preferably 1.0 or more, more preferably 1.1 or more, and even more preferably 1.2 or more. Also, if the amount of glycol used is large relative to the amount of polycarbonate resin used, production efficiency tends to deteriorate. Therefore, the molar ratio of glycol to 1 mole of repeating unit of polycarbonate resin is preferably 2.0 or less, more preferably 1.9 or less, and even more preferably 1.8 or less.

The molar ratio of glycol to aromatic monoalcohol (moles of glycol to be used/moles of aromatic monoalcohol to be used) is preferably 0.01 or more, more preferably 0.05 or more. The molar ratio is preferably 0.5 or less, more preferably 0.3 or less. If the molar ratio of glycol to aromatic monoalcohol is small, the polycarbonate resin is difficult to decompose, or the decomposition rate is reduced, resulting in a long decomposition time. If the molar ratio is large, separation of glycol and alkylene carbonate becomes complicated when recovering alkylene carbonate.

(catalyst)
One of the features of the method for producing bisphenol of the present invention is that a catalyst is further used. The catalyst may be any catalyst capable of promoting the decomposition of polycarbonate resin, and is preferably any one selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkylamines and acids.

[Alkali metal hydroxide]
An alkali metal hydroxide is a salt of an alkali metal ion (M ⁺ ) and a hydroxide ion (OH ⁻ ), and is a compound represented by MOH (M represents an alkali metal atom). As the alkali metal hydroxide, sodium hydroxide or potassium hydroxide is preferred.

If the amount of alkali metal hydroxide used is small relative to the polycarbonate resin used, the decomposition rate will be slow, the decomposition time will be long, and the efficiency will tend to deteriorate. Therefore, the molar ratio of alkali metal hydroxide to 1 mole of repeating unit of polycarbonate resin ((mass [g] of alkali metal hydroxide used / molecular weight [g/mol] of alkali metal hydroxide) / (mass [g] of polycarbonate resin used / molecular weight of repeating unit [g/mol])) is preferably 0.0001 or more, more preferably 0.0005 or more, and even more preferably 0.0007 or more. For example, it can be 0.001 or more, 0.01 or more, 0.1 or more, etc. If the amount of alkali metal hydroxide used is large relative to the polycarbonate resin used, the amount of acid required for neutralization after decomposition will increase, and the production efficiency will tend to decrease. Therefore, the molar ratio of alkali metal hydroxide to 1 mole of repeating units of polycarbonate resin is preferably 1 or less, more preferably 0.9 or less, and even more preferably 0.8 or less.

[Alkali metal carbonate]
An alkali metal carbonate is a salt of an alkali metal ion (M ⁺ ) and a carbonate ion (CO ₃ ²⁻ ), and is a compound represented by M ₂ CO ₃ (M represents an alkali metal atom). As the alkali metal carbonate, sodium carbonate or potassium carbonate is preferred.

If the amount of alkali metal carbonate used is small relative to the polycarbonate resin used, the decomposition rate will be slow, the decomposition time will be long, and the efficiency will tend to deteriorate. Therefore, the molar ratio of alkali metal carbonate to 1 mole of repeating unit of polycarbonate resin ((mass [g] of alkali metal carbonate used / molecular weight [g/mol] of alkali metal carbonate) / (mass [g] of polycarbonate resin used / molecular weight of repeating unit [g/mol])) is preferably 0.0001 moles or more, more preferably 0.0005 or more, and even more preferably 0.0007 or more. For example, it can be 0.001 or more, 0.01 or more, 0.1 or more, etc. If the amount of alkali metal carbonate used is large relative to the polycarbonate resin used, the amount of acid required for neutralization after decomposition will increase, and the production efficiency will tend to decrease. Therefore, the molar ratio of alkali metal carbonate to 1 mole of repeating units of polycarbonate resin is preferably 1 or less, more preferably 0.9 or less, and even more preferably 0.8 or less.

[Alkylamine]
An alkylamine is a compound in which at least one hydrogen atom of ammonia is substituted with an alkyl group. Among alkylamines, monoalkylamines, which are primary amines, react with the carbonate bond of a polycarbonate resin to produce isocyanates, and therefore dialkylamines, which are secondary amines, and trialkylamines, which are tertiary amines, are more preferable.
Since dialkylamines, which are secondary amines, react with the carbonate bond portion of the polycarbonate resin to produce tetraalkylureas, trialkylamines, which are tertiary amines, are more preferred.

The alkylamine preferably has a boiling point of 200°C or less, and more preferably has a boiling point of 160°C or less. If the boiling point is in this range, it can be removed by heating under reduced pressure together with aromatic monoalcohols such as phenol. If the boiling point is too low, the alkylamine may volatilize during the decomposition reaction, slowing down the decomposition rate. Therefore, the alkylamine preferably has a boiling point of 10°C or more, and more preferably has a boiling point of 30°C or more.

The alkylamine is preferably one represented by the general formula (I).

In formula (I), R ^A represents an alkyl group having 1 to 3 carbon atoms, and R ^B to R ^C each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
R ^A is preferably a methyl group, an ethyl group, an n-propyl group, or an isopropyl group, and R ^B to R ^C are each preferably independently a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, or an isopropyl group.

Specific examples of alkylamines represented by general formula (I) include methylamine, ethylamine, propylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, etc.

If the amount of alkylamine used is small relative to the polycarbonate resin used, the decomposition rate will be slow, the decomposition time will be long, and the efficiency will tend to deteriorate. Therefore, the molar ratio of alkylamine to 1 mole of repeating unit of polycarbonate resin ((mass [g] of alkylamine used/molecular weight [g/mol] of alkylamine)/(mass [g] of polycarbonate resin used/molecular weight of repeating unit [g/mol])) is preferably 0.0001 or more, more preferably 0.0005 or more, and even more preferably 0.0007 or more. If the amount of alkylamine used is large relative to the polycarbonate resin used, it becomes easier for an amine odor to be generated and it becomes difficult to generate alkylene carbonate. Therefore, the molar ratio of alkylamine to 1 mole of repeating unit of polycarbonate resin is preferably 1 mole or less, more preferably 0.9 or less, and even more preferably 0.8 or less.

[acid]
The acid may be an inorganic acid such as hydrochloric acid, sulfuric acid, or phosphoric acid, or an organic acid such as carboxylic acid or sulfonic acid. Preferably, the acid is any one selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, and sulfonic acid. The sulfonic acid may be an alkylsulfonic acid such as methanesulfonic acid, or an aromatic sulfonic acid such as toluenesulfonic acid.

If the amount of acid used is small relative to the amount of polycarbonate resin used, the decomposition rate will be slow, the decomposition time will be long, and the efficiency will tend to deteriorate. Therefore, the molar ratio of acid to 1 mole of repeating unit of polycarbonate resin ((mass [g] of acid used/molecular weight [g/mol] of acid)/(mass [g] of polycarbonate resin used/molecular weight of repeating unit [g/mol])) is preferably 0.0001 moles or more, more preferably 0.0005 or more, and even more preferably 0.0007 or more. If the amount of acid used is large relative to the amount of polycarbonate resin used, the amount of base required for neutralization after decomposition will increase, and the production efficiency will tend to decrease. Therefore, the molar ratio of acid to 1 mole of repeating unit of polycarbonate resin is preferably 1 or less, more preferably 0.9 or less, and even more preferably 0.8 or less.

(Preparation of reaction solution)
The reaction liquid prepared in the preparation step contains a polycarbonate resin, an aromatic monoalcohol, a glycol, and a catalyst. Even if the polycarbonate resin is not completely dissolved, the decomposition reaction of the polycarbonate resin proceeds by using an aromatic monoalcohol and a glycol in combination, so that the reaction liquid prepared can be in a slurry state. By preparing a slurry reaction liquid in which the polycarbonate resin is dispersed in a solvent containing an aromatic monoalcohol and a glycol, and decomposing the polycarbonate resin in the slurry reaction liquid, only the polycarbonate resin dissolved to the solubility level is involved in the decomposition reaction, and the decomposition reaction does not proceed rapidly, and the reaction can proceed stably, which makes it easy to control the reaction and is preferable.

The slurry concentration in the reaction liquid (mass of solids in the reaction liquid/mass of the reaction liquid) is preferably 0.01 or more, more preferably 0.05 or more. It is also preferably 0.5 or less, more preferably 0.3 or less. If the slurry concentration (concentration of solids) is too low, the decomposition efficiency decreases, and if the slurry concentration is too high, mixing is poor.

The liquid components in the prepared reaction solution are mainly composed of aromatic monoalcohol and glycol, and the total mass of the aromatic monoalcohol and glycol relative to the mass of the liquid components is 0.8 or more, 0.9 or more, 0.95 or more, etc.

When attempting to obtain alkylene carbonate together with bisphenol, the alkylene carbonate is more likely to decompose if water is present in the reaction solution. Therefore, the water content in the reaction solution (mass of water/mass of reaction solution) is usually 0.5 or less. The water content in the reaction solution is preferably 0.1 or less, more preferably 0.05 or less.

The reaction liquid is preferably prepared at 10°C or higher, and more preferably at 20°C or higher. The reaction liquid is preferably prepared at 40°C or lower, and more preferably at 35°C or lower. If the temperature during preparation of the reaction liquid is too low, some types of aromatic monoalcohols may be prone to solidification, leading to poor mixing or making it difficult to mix uniformly. If the temperature during preparation of the reaction liquid is too high, some types of catalysts may be prone to volatilization, making it difficult to prepare the desired concentration or to control the decomposition reaction.

The order of mixing the polycarbonate resin, aromatic monoalcohol, glycol and catalyst is not particularly limited. For example, the aromatic monoalcohol, glycol and catalyst may be sequentially supplied to the polycarbonate resin, or the polycarbonate resin, glycol and catalyst may be sequentially supplied to the aromatic monoalcohol. Since this allows for more uniform mixing, it is preferable to supply the polycarbonate resin to the reaction tank after the aromatic monoalcohol and/or glycol.

<Decomposition reaction step>
The method for producing bisphenol of the present invention includes a decomposition reaction step in which the polycarbonate resin is decomposed into bisphenol and alkylene carbonate in the reaction liquid prepared in the preparation step. In the decomposition reaction step, the carbonate bond of the polycarbonate resin is cut in the presence of an aromatic monoalcohol, a glycol, and a catalyst, and bisphenol and alkylene carbonate are produced. For example, when ethylene glycol or propylene glycol is used, the reaction shown in the following reaction formula (2) occurs. In reaction formula (2), R ¹ to R ⁶ are the same as those in the above general formula (1), and R ⁷ is a hydrogen atom or a methyl group.

The decomposition reaction may be carried out under normal pressure or under pressure, but since the reaction proceeds sufficiently under normal pressure, it is preferable to carry it out under normal pressure.

(Reaction temperature)
The decomposition reaction may be carried out at the same temperature as the temperature at which the reaction solution is prepared, but it is preferable to carry out the decomposition reaction by raising the temperature to a predetermined reaction temperature after the preparation of the reaction solution. If the temperature at which the reaction solution is prepared is too high, it may be difficult to control the decomposition reaction. It is preferable to carry out the decomposition reaction by raising the temperature after the preparation of the reaction solution, since the decomposition reaction can proceed stably.

The reaction temperature is appropriately selected depending on the type of aromatic monoalcohol and the reaction time, but if the temperature is high, the glycol in the reaction solution will evaporate and glycolysis will stop. If the temperature is low, the aromatic monoalcohol will solidify, or the solvolysis will not proceed easily, slowing down the reaction rate, and the time required for decomposition will increase. For these reasons, the reaction temperature is preferably 60°C or higher, and the higher the numerical value, the more preferable it is in the order of 70°C or higher, 75°C or higher, and 80°C or higher. Also, 150°C or lower is preferable, and the lower the numerical value, the more preferable it is in the order of 130°C or lower, 110°C or lower, 100°C or lower, and 95°C or lower.

When the reaction is carried out at the same temperature as when the reaction liquid was prepared, the reaction temperature is the average temperature from the time when mixing of the polycarbonate resin, aromatic monoalcohol, glycol, and catalyst is completed to the time when neutralization and distillation operations to stop the decomposition reaction begin. When the reaction is carried out by raising the temperature after the reaction liquid is prepared, the reaction temperature is the average temperature from the time when a predetermined temperature is reached to the time when neutralization and distillation operations to stop the decomposition reaction begin.

(Reaction Time)
The reaction time is appropriately selected depending on the slurry concentration, reaction temperature, etc., but since a long reaction time tends to decompose the produced bisphenol, it is preferably 30 hours or less, and more preferably 25 hours or less, 20 hours or less, 15 hours or less, 10 hours or less, and 5 hours or less in that order. Also, since a short reaction time may cause the decomposition reaction to not proceed sufficiently, it is preferably 0.1 hours or more, more preferably 0.5 hours or more, and even more preferably 1 hour or more.

The reaction time is the time from when mixing of the polycarbonate resin, aromatic monoalcohol, glycol, and catalyst is completed to when neutralization and distillation operations to stop the decomposition reaction begin. The end point of the reaction time may be determined by tracking the decomposition reaction using liquid chromatography or the like.

<Bisphenol recovery process>
The method for producing bisphenol of the present invention includes a bisphenol recovery step for recovering the bisphenol obtained in the decomposition reaction step. The recovery of bisphenol from the reaction solution after the decomposition reaction can be carried out by means of crystallization, column chromatography, or the like after the decomposition reaction of the polycarbonate resin is terminated.

(Method of stopping the decomposition reaction of polycarbonate resin)
The method for stopping the decomposition reaction of the polycarbonate resin is appropriately selected depending on the type of catalyst used. When an alkali metal hydroxide, an alkali metal carbonate, or an acid is used as the catalyst, the decomposition reaction can be stopped by neutralization or the like. When an alkylamine is used as the catalyst, the decomposition reaction can be stopped by distilling off or neutralizing the alkylamine. In the method of removing the alkylamine by neutralization with the supply of an acid, an ammonium salt is generated, which also needs to be removed, so that the alkylamine is preferably removed by distillation.

The bisphenol recovery process preferably includes a crystallization process for recovering bisphenol by crystallization. Specifically, after the decomposition reaction of the polycarbonate resin, the catalyst and solvent are removed from the reaction liquid and an organic solvent is mixed, and the resulting organic phase is washed with water or saline, and further neutralized and washed with ammonium chloride water, if necessary. The washed organic phase is then cooled and crystallized.

Organic solvents that can be used during neutralization and crystallization include aromatic hydrocarbons such as toluene, xylene, ethylbenzene, diethylbenzene, isopropylbenzene, and mesitylene; aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane, and dodecane; and aliphatic alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-pentanol, i-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol, ethylene glycol, diethylene glycol, and triethylene glycol.

Incidentally, the crystallization may be carried out after distilling off excess aromatic monoalcohol and organic solvent before the crystallization. When bisphenol A is crystallized in the presence of phenol, it forms a co-crystal with phenol. When a polycarbonate resin containing a repeating unit derived from bisphenol A (a repeating unit in which R ¹ to R ⁶ in the above general formula (1) are hydrogen atoms) is decomposed using phenol, it is necessary to distill off phenol before crystallization in order to avoid forming a co-crystal.

<Alkylene carbonate recovery process>
The method for producing bisphenol of the present invention may include an alkylene carbonate recovery step for recovering the alkylene carbonate obtained in the decomposition reaction step. Recovery (isolation, purification) of the alkylene carbonate can be carried out by a conventional method. For example, a method of distilling the reaction liquid or the organic phase after neutralizing the reaction liquid can be mentioned. The distillation can be carried out under conditions of, for example, 10 to 101 kPa and 100 to 250°C.

The bisphenol production method of the present invention will be described in more detail below with reference to bisphenol production methods (A) to (C) as examples, in which bisphenol A is produced by decomposing a polycarbonate resin containing repeating units derived from 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) into bisphenol A and ethylene carbonate, using phenol as the aromatic monoalcohol and ethylene glycol as the glycol.

<Production method of bisphenol (A)>
The method for producing bisphenol (A) includes a step (A1) of preparing a reaction liquid containing a polycarbonate resin containing a repeating unit derived from bisphenol A, phenol, ethylene glycol, and an alkali metal hydroxide as a catalyst, a step (A2) of decomposing the polycarbonate resin in the reaction liquid, a step (A3) of neutralizing the reaction liquid after the step (A2) to obtain an organic phase in which bisphenol A is dissolved, and a step (A4) of heating the organic phase obtained in the step (A3) under reduced pressure and then recovering bisphenol A by crystallization.

In the bisphenol production method (A) of the present invention, step (A1) is a preparation step, step (A2) is a decomposition reaction step, and steps (A3) and (A4) are bisphenol recovery steps.

In step (A3), the reaction liquid, acid, and water are mixed and neutralized, followed by separation of oil and water, and removal of the separated aqueous phase. Since alkali metal hydroxides, etc. (alkali metal hydroxides, acid added for neutralization, and salts produced by neutralization) are contained in the aqueous phase, removing the aqueous phase allows the alkali metal hydroxides, etc. to be removed. Ethylene glycol is also miscible with water, so it is removed into the aqueous phase. This results in an organic phase in which the produced bisphenol A is dissolved.

Examples of acids used for neutralization include hydrochloric acid, sulfuric acid, and phosphoric acid. Neutralization by mixing an acid may be performed so that the pH of the reaction solution is less than 7 or greater than 7, but if the pH is less than 7, the quality of the isolated bisphenol A may decrease. Therefore, it is preferable to mix the acid so that the reaction solution has an end point where the pH is greater than 7 (for example, pH 7.5 or greater or pH 8.0 or greater). On the other hand, if the pH of the reaction solution is too high, the alkylene carbonate is easily hydrolyzed, and the yield when recovering the dialkyl carbonate decreases, so the acid is mixed so that the pH is 10 or less, and preferably 9.5 or less.

An organic solvent such as an aromatic hydrocarbon may be mixed before or after mixing the acid. After mixing the acid, water, and organic solvent into the reaction liquid and neutralizing it, the oil-water separation is performed and the aqueous phase is removed to obtain an organic phase in which bisphenol A is dissolved. Mixing the organic solvent makes it easier to separate the oil and water, which makes it easier to remove the aqueous phase in which alkali metal hydroxides and the like are dissolved.

In step (A4), the organic phase obtained in step (A3) is heated under reduced pressure, and then bisphenol A is recovered by crystallization. If phenol is present during crystallization, bisphenol A forms co-crystals with phenol and precipitates. Therefore, in order to obtain bisphenol A, phenol is removed before crystallization in step (A4).
Specifically, the organic phase obtained in step (A3) is heated under reduced pressure to distill off liquid components such as phenol and ethylene carbonate to obtain a crude product of bisphenol A. Next, an organic solvent such as an aromatic hydrocarbon is added to the crude product of bisphenol A to prepare a crystallization solution in which bisphenol A is dissolved, and the solution is cooled to precipitate bisphenol A. The precipitated bisphenol A is recovered by solid-liquid separation.

Furthermore, ethylene carbonate can be recovered by heating the organic phase obtained in step (A3) under reduced pressure and controlling the pressure and temperature when distilling off the liquid components. For example, the organic phase obtained in step (A3) is transferred to a distillation apparatus under normal pressure (101 kPa), and then heated to 80 to 250°C (preferably 100 to 250°C) and/or reduced pressure to 10 to 100 kPa, whereby phenol is distilled off, and then ethylene carbonate is distilled off. Ethylene carbonate can be obtained by recovering the ethylene carbonate fraction. The obtained ethylene carbonate may be further distilled.

When an alkali metal carbonate is used as a catalyst, the process can be carried out in the same manner as in the bisphenol production process (A).

<Production method of bisphenol (B)>
The method for producing bisphenol (B) includes a step (B1) of preparing a reaction liquid containing a polycarbonate resin containing a repeating unit derived from bisphenol A, phenol, ethylene glycol, and an alkylamine as a catalyst, a step (B2) of decomposing the polycarbonate resin in the reaction liquid, and a step (B3) of heating the reaction liquid after step (B2) under reduced pressure and recovering bisphenol A by crystallization.

In the bisphenol production method (B) of the present invention, step (B1) is a preparation step, step (B2) is a decomposition reaction step, and step (B3) is a bisphenol recovery step.

Specifically, in step (B3), the reaction liquid after step (B2) is heated under reduced pressure to distill off liquid components such as alkylamines, phenol, ethylene glycol, and ethylene carbonate, thereby obtaining a crude product of bisphenol A. Next, an organic solvent such as an aromatic hydrocarbon is added to the crude product of bisphenol A to prepare a crystallization solution in which bisphenol A is dissolved, and this is then cooled to precipitate bisphenol A. The precipitated bisphenol A is recovered by solid-liquid separation.

Furthermore, ethylene carbonate can be recovered by heating the reaction liquid after step (B2) under reduced pressure and controlling the pressure and temperature when distilling off the liquid components. For example, the reaction liquid after step (B2) is transferred to a distillation apparatus under normal pressure (101 kPa) and then heated to 80 to 250°C (preferably 100 to 250°C) and/or reduced pressure to 10 to 100 kPa, whereby ethylene glycol, ethylene carbonate, alkylamines, and phenols are distilled off in order of lowest boiling point.

When an alkylamine is used as the catalyst, the alkylamine may be removed by a method of neutralizing the reaction by supplying an acid. In this case, as in step (A3) of the bisphenol production method (A), the reaction liquid after the decomposition reaction is mixed with acid and water to neutralize it, and then the oil-water separation is performed and the aqueous phase is removed to obtain an organic phase in which bisphenol A is dissolved. Next, as in step (A4) of the bisphenol production method (A), the obtained organic phase is heated under reduced pressure, and bisphenol A can be recovered by crystallization.

As described above, methods for removing alkylamines from the polycarbonate resin decomposition reaction liquid include distillation and neutralization by supplying acid. However, the method of neutralization by supplying acid generates ammonium salts, which also need to be removed, so distillation is preferred. By using alkylamines as a catalyst, the alkylamines can be removed together with phenol by heating under reduced pressure, and since neutralization is not essential, purification can be simplified.

<Production method of bisphenol (C)>
The method for producing bisphenol (C) includes a step (C1) of preparing a reaction liquid containing a polycarbonate resin containing a repeating unit derived from bisphenol A, phenol, ethylene glycol, and an acid as a catalyst, a step (C2) of decomposing the polycarbonate resin in the reaction liquid, a step (C3) of neutralizing the reaction liquid after the step (C2) to obtain an organic phase in which bisphenol A is dissolved, and a step (C4) of heating the organic phase obtained in the step (C3) under reduced pressure and then recovering bisphenol A by crystallization.

In the bisphenol production method (C) of the present invention, step (C1) is a preparation step, step (C2) is a decomposition reaction step, and steps (C3) and (C4) are bisphenol recovery steps.

In step (C3), the reaction liquid, base, and water are mixed and neutralized, and then the oil-water separation is performed, and the separated aqueous phase is removed to obtain an organic phase in which bisphenol A is dissolved. Alternatively, the organic phase in which bisphenol A is dissolved may be obtained by separating the mixture of the reaction liquid, base, water, and organic solvent into oil and aqueous phase and removing the aqueous phase.

Examples of bases used for neutralization include sodium carbonate and sodium hydroxide. As in step (A3) of the bisphenol production method (A), neutralization is preferably carried out so that the pH of the reaction solution is greater than 7 as the end point. For example, it is preferable to mix a base so that the pH is 7.5 or higher or 8.0 or higher. It is also preferable to mix a base so that the pH is 10 or lower or 9.5 or lower.

In step (C4), bisphenol A is recovered from the organic phase in which bisphenol A is dissolved, obtained in step (C3). As in step (A4) of the bisphenol production method (A), the organic phase obtained in step (C3) is heated under reduced pressure, and then bisphenol A can be recovered by crystallization.

In addition, by controlling the pressure and temperature during the reduced pressure heating in step (C3), ethylene carbonate can be recovered in the same manner as in the bisphenol production method (A).

The bisphenol production methods (A) to (C) are examples in which phenol is used as the aromatic monoalcohol. However, when an aromatic monoalcohol other than phenol, such as cresol or xylenol, is used as the aromatic monoalcohol, bisphenol A does not form a cocrystal, and therefore removal of the aromatic monoalcohol by heating under reduced pressure in steps (A4), (B3), and (C4) is not essential. In this case, bisphenol A can be recovered by precipitating bisphenol A by cooling the reaction liquid after step (B2) or the organic phase obtained in steps (A3) and (C3). The use of cresol or xylenol can simplify the purification of bisphenol A.

Bisphenol A may also be recovered as a co-crystal of bisphenol A and phenol. In this case, without distilling off the phenol, the reaction liquid after step (B2) or the organic phase obtained in step (A3) or step (C3) is cooled to precipitate and recover the co-crystal of bisphenol A and phenol.

As described above, the polycarbonate resin used in the bisphenol production method of the present invention is not limited to polycarbonate resin containing repeating units derived from bisphenol A. The bisphenol production method of the present invention using a polycarbonate resin containing repeating units derived from a bisphenol other than bisphenol A can also be carried out appropriately in the same manner as the above bisphenol production methods (A) to (C).

<Uses of bisphenol>
The bisphenol obtained by the bisphenol production method of the present invention (hereinafter, sometimes referred to as "regenerated bisphenol") can be used as a constituent, curing agent, additive, or precursor thereof for various thermoplastic resins such as polyether resins, polyester resins, polyarylate resins, polycarbonate resins, polyurethane resins, and acrylic resins, and various thermosetting resins such as epoxy resins, unsaturated polyester resins, phenolic resins, polybenzoxazine resins, and cyanate resins, which are used for various applications such as optical materials, recording materials, insulating materials, transparent materials, electronic materials, adhesive materials, and heat-resistant materials. It is also useful as an additive for color developers and anti-fading agents for thermal recording materials, as well as for disinfectants, antibacterial and antifungal agents, etc.

Of these, it is preferable to use it as a raw material (monomer) for thermoplastic resins and thermosetting resins, since it can impart good mechanical properties, and it is more preferable to use it as a raw material for polycarbonate resins and epoxy resins. It is also preferable to use it as a color developer, and it is particularly preferable to use it in combination with a leuco dye and a discoloration temperature regulator.

<Method of producing recycled polycarbonate resin>
The present invention also relates to a method for producing a recycled polycarbonate resin (hereinafter, sometimes referred to as the "method for producing a recycled polycarbonate resin of the present invention"), which produces a recycled polycarbonate resin using a bisphenol raw material containing bisphenol (recycled bisphenol) obtained by the method for producing bisphenol of the present invention. The method for producing a recycled polycarbonate resin of the present invention utilizes a chemical recycling method for producing a polycarbonate resin using recycled bisphenol obtained by decomposing polycarbonate resin contained in waste plastics, etc., down to the monomer bisphenol, as a raw material.

Specifically, the recycled polycarbonate resin can be obtained by polymerizing a bisphenol raw material containing recycled bisphenol (regenerated bisphenol obtained by decomposing a polycarbonate resin by the bisphenol production method of the present invention) and a carbonate diester raw material. The polymerization can be carried out by appropriately selecting a known method.
For example, recycled polycarbonate resin can be produced by a method in which a bisphenol raw material containing recycled bisphenol is subjected to an ester exchange reaction with a diester carbonate raw material such as diphenyl carbonate in the presence of an alkali metal compound and/or an alkaline earth metal compound.

Recycled bisphenol may be used as the entire bisphenol raw material, or may be mixed with non-recycled general bisphenol and used as part of the bisphenol raw material. There is no particular limit to the amount of recycled bisphenol, but the higher the proportion of recycled bisphenol, the more environmentally friendly it is. Therefore, from the viewpoint of environmental consideration, the amount of recycled bisphenol relative to the bisphenol raw material is preferably 50% by mass or more, and more preferably 70% by mass or more, 80% by mass or more, and 90% by mass or more in that order.

The above transesterification reaction can be carried out by appropriately selecting a known method, but an example of a method using diphenyl carbonate as the carbonate diester raw material is described below.

In the above-mentioned method for producing recycled polycarbonate resin, it is preferable to use an excess amount of diphenyl carbonate relative to the bisphenol raw material. The amount of diphenyl carbonate used relative to the bisphenol raw material is preferably large in terms of the number of terminal hydroxyl groups in the produced recycled polycarbonate resin and excellent thermal stability of the polymer, and is preferably small in terms of the fast transesterification reaction rate and ease of producing recycled polycarbonate resin of the desired molecular weight. For these reasons, the amount of diphenyl carbonate used relative to 1 mole of bisphenol raw material is usually 1.001 moles or more, preferably 1.002 moles or more, and usually 1.3 moles or less, preferably 1.2 moles or less.

As for the method of supplying the raw materials, the bisphenol raw material and diphenyl carbonate can be supplied in solid form, but it is preferable to melt one or both and supply them in a liquid state.

When producing recycled polycarbonate resin by the transesterification reaction of diphenyl carbonate with a bisphenol raw material, a transesterification catalyst is usually used. It is preferable to use an alkali metal compound and/or an alkaline earth metal compound as this transesterification catalyst. These may be used alone or in any combination and ratio of two or more types. For practical purposes, it is desirable to use an alkali metal compound.

The amount of catalyst used per mole of bisphenol raw material or diphenyl carbonate is usually 0.05 μmol or more, preferably 0.08 μmol or more, more preferably 0.10 μmol or more, and is usually 100 μmol or less, preferably 50 μmol or less, more preferably 20 μmol or less.

By using the catalyst in an amount within the above range, it is easy to obtain the polymerization activity required to produce a recycled polycarbonate resin having a desired molecular weight, and it is easy to obtain a polycarbonate resin that has excellent polymer color, does not undergo excessive polymer branching, and has excellent fluidity during molding.
In order to produce a recycled polycarbonate resin by the above method, it is preferable to continuously supply both of the above raw materials to a raw material mixing tank, and then continuously supply the resulting mixture and the transesterification catalyst to a polymerization tank.

In the production of recycled polycarbonate resin using the transesterification method, the two raw materials are usually fed into a raw material mixing tank, stirred uniformly, and then fed into a polymerization tank where a catalyst is added to produce the polymer.

The obtained recycled polycarbonate resin may be used as it is, or may be used as a recycled polycarbonate resin composition containing a virgin polycarbonate resin and a recycled polycarbonate resin. The recycled polycarbonate resin composition can be obtained by appropriately selecting a known kneading method or the like to mix a virgin polycarbonate resin and a recycled polycarbonate resin. When a recycled polycarbonate resin composition containing a virgin polycarbonate resin and a recycled polycarbonate resin is used, the amount of the recycled polycarbonate resin is not particularly limited, but the higher the proportion of the recycled polycarbonate resin, the more environmentally friendly it is. Therefore, from the viewpoint of environmental consideration, the amount of the recycled polycarbonate resin relative to the recycled polycarbonate resin composition is preferably 50% by mass or more, and more preferably in the order of 70% by mass or more, 80% by mass or more, and 90% by mass or more.
The obtained recycled polycarbonate resin and composition can be molded into various molded articles such as optical members and optical recording media, in the same manner as virgin polycarbonate resin.

The present invention will be explained in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist of the invention is not exceeded.

[Raw materials and reagents]
The polycarbonate resin used was "NOVAREX (registered trademark) M7027BF" manufactured by Mitsubishi Chemical Engineering Plastics Corporation.
The reagents used were phenol, toluene, sodium hydroxide, paratoluenesulfonic acid, ethylene glycol, propylene glycol, triethylamine, acetonitrile, and cesium carbonate from Fujifilm Wako Pure Chemical Industries, Ltd.
Diphenyl carbonate used was a product of Mitsubishi Chemical Corporation.

[analysis]
The production and purity of bisphenol were confirmed by high performance liquid chromatography according to the following procedure and conditions.
Equipment: Shimadzu LC-2010A, Waters 5 μm 150 mm x 4.6 mm ID
Method: Low pressure gradient method Analysis temperature: 40°C
Eluent composition:
Solution A: acetonitrile Solution B: 85% phosphoric acid:water = 1 mL:999 mL solution At analysis time 0 min, the eluent composition was Solution A: Solution B = 35:65 (volume ratio, same below), and from analysis time 0 to 5 min, the eluent composition was Solution A: Solution B = 35:65, and then gradually changed to Solution A: Solution B = 90:10 from analysis time 5 to 40 min.
Flow rate: 0.85 mL/min Detection wavelength: 280 nm

Ethylene carbonate and propylene carbonate were analyzed by gas chromatography according to the following procedures and conditions.
・Apparatus: Shimadzu Corporation GC-2014
Agilent DB-1 0.530mm x 30m 1.5μm
Detection method: FID
Vaporization chamber temperature: 230°C
Detector temperature: 300°C
From 0 to 5 minutes of analysis time, the column temperature was kept at 50°C, from 5 to 30 minutes of analysis time, the column temperature was gradually increased to 280°C, and from 30 to 40 minutes of analysis time, the column temperature was maintained at 280°C.
Quantitative method: Internal standard method using biphenyl as an internal standard

[Viscosity average molecular weight (Mv)]
The viscosity average molecular weight (Mv) was determined by dissolving the polycarbonate resin in methylene chloride (concentration: 6.0 g/L), measuring the specific viscosity (ηsp) at 20°C using an Ubbelohde viscometer, and calculating the viscosity average molecular weight according to the following formula: (Mv) was calculated.
ηsp/C=[η] (1+0.28ηsp)
[η]=1.23×10 ^-4 Mv ^0.83

[Melted color of bisphenol]
The melt color of bisphenol was measured by placing 20 g of bisphenol in a test tube "P-24" (2 mmφ×200 mm) manufactured by Nippon Denshikaga Glass Co., Ltd., melting it at 174° C. for 30 minutes, and measuring the Hazen color number using "OME7700" manufactured by Nippon Denshoku Industries Co., Ltd.

[pH Measurement]
The pH was measured using a pH meter "pH METER ES-73" manufactured by Horiba, Ltd., with respect to the aqueous phase at 25°C taken out of the flask.

[Example 1]
(Preparation process)
In a jacketed separable flask equipped with a Dimroth condenser, a stirring blade, and a thermometer, 80 g of polycarbonate resin (since the molecular weight of the repeating unit of the polycarbonate resin is 254 g/mol, the number of moles of the repeating unit=80 g÷254 g/mol=0.31 mol), 240 g of phenol, 35 g of ethylene glycol (0.56 mol, molar ratio of ethylene glycol to 1 mole of the repeating unit of the polycarbonate resin=0.56 mol÷0.31 mol=1.8), and 2 g of sodium hydroxide (2 g÷40 g/mol=0.05 mol) were placed at room temperature under a nitrogen atmosphere (amount of liquid: 80 g+240 g+35 g+2 g=357 g).

(Decomposition reaction process)
Thereafter, the internal temperature was raised to 85° C. Undissolved polycarbonate resin was observed in the reaction liquid when it reached 85° C. (It was in a slurry state.) The reaction was continued for 4 hours while maintaining the temperature at 85° C., and a homogeneous reaction liquid was obtained.

The composition of a portion of the resulting reaction solution was confirmed by high performance liquid chromatography, and it was confirmed that 19.4% by mass (19.4 ÷ 100 × 357 g ÷ 228 g/mol ÷ 0.31 mol = 98 mol%) of bisphenol A was produced. The production of ethylene carbonate was also confirmed.

[Example 2]
The same procedure as in Example 1 was repeated, except that 43 g (0.56 mol) of propylene glycol was used instead of 35 g of ethylene glycol.
A portion of the reaction solution was analyzed for composition by high performance liquid chromatography, and it was confirmed that 19.6% by mass (19.6÷100×365 g÷228 g/mol÷0.31 mol=100 mol%) of bisphenol A was produced. In addition, production of propylene carbonate was also confirmed.

[Example 3]
The same procedure as in Example 1 was repeated, except that 20 g (0.12 mol) of paratoluenesulfonic acid was used instead of 2 g of sodium hydroxide.
A portion of the reaction solution was analyzed for composition by high performance liquid chromatography, and it was confirmed that 10.2% by mass (10.2÷100×375 g÷228 g/mol÷0.31 mol=54 mol%) of bisphenol A was produced. In addition, production of ethylene carbonate was also confirmed.

[Example 4]
(Preparation process)
Into a jacketed separable flask equipped with a Dimroth condenser, a stirring blade, and a thermometer, 80 g (0.31 mol) of polycarbonate resin, 240 g of phenol, 35 g of ethylene glycol (0.56 mol, molar ratio of ethylene glycol to 1 mol of repeating unit of polycarbonate resin=1.8), and 8 g of triethylamine (8 g÷101 g/mol=0.08 mol) were placed at room temperature under a nitrogen atmosphere (amount of liquid: 80 g+240 g+35 g+8 g=363 g).

(Decomposition reaction process)
Thereafter, the internal temperature was raised to 85° C. Undissolved polycarbonate resin was observed in the reaction liquid when it reached 85° C. (It was in a slurry state.) The reaction was continued for 4 hours while maintaining the temperature at 85° C., and a homogeneous reaction liquid was obtained.

A portion of the resulting reaction liquid was analyzed for composition by high performance liquid chromatography, and it was found that bisphenol A was produced in an amount of 19.0% by mass (19.0÷100×363 g÷228 g/mol÷0.31 mol=98 mol%).
Furthermore, a portion of the obtained reaction liquid was subjected to gas chromatography to confirm the composition, and it was found that 6.9% by mass (6.9÷100×363 g÷88 g/mol÷0.31 mol=92 mol%) of ethylene carbonate was produced.

(Bisphenol recovery process and alkylene carbonate recovery process)
The obtained reaction liquid was transferred to a distillation apparatus equipped with a thermometer, stirring blades, a distillation tube, and a pressure regulator, and while monitoring the amount of distillation, the internal temperature was gradually increased to 180° C., and the internal pressure was gradually decreased from normal pressure to 100 kPa to distill off triethylamine and phenol. The pressure was further decreased to 10 kPa to distill off ethylene carbonate, obtaining 14 g of ethylene carbonate.

Then, the flask was re-pressurized with nitrogen, the internal temperature was lowered to 80°C, and 200 g of toluene was added to obtain organic phase 1. The obtained organic phase 1 was washed five times with 50 g of desalted water to obtain organic phase 2.

The obtained organic phase 2 was cooled to 20° C. to obtain a slurry. The obtained slurry was filtered to obtain a cake. The obtained cake was dried by a rotary evaporator to obtain 32 g of bisphenol A.
The purity of the obtained bisphenol A was 99.8% by mass and the melt color was APHA181.

[Comparative Example 1]
The same procedure as in Example 4 was repeated, except that 240 g of phenol was not added, and 275 g of ethylene glycol was added instead of 35 g of ethylene glycol. The reaction was carried out for 4 hours while maintaining the temperature at 85° C., but solid polycarbonate resin remained. When the composition of a part of the reaction solution obtained was confirmed by high performance liquid chromatography, a trace amount of bisphenol A was found, and it was confirmed that decomposition had not progressed.

[Comparative Example 2]
The same procedure as in Example 4 was repeated, except that 35 g of ethylene glycol was not used and 15 g of triethylamine was used instead of 8 g of triethylamine.
A portion of the resulting reaction liquid was analyzed for composition by high performance liquid chromatography, and it was found that bisphenol A was produced in an amount of 8.5% by mass (8.5÷100×335 g÷228 g/mol÷0.31 mol=40 mol%).

Table 1 summarizes the types of aromatic monoalcohols, glycols, and catalysts, and the production rate of bisphenol A in Examples 1 to 4 and Comparative Examples 1 and 2. Table 1 shows that the use of phenol and glycol efficiently decomposes polycarbonate resin and produces bisphenol A.

[Example 5]
In a 45 mL glass reaction vessel equipped with a stirrer and a distillation tube, 10.00 g (0.04 mol) of bisphenol A obtained in Example 4, 9.95 g (0.05 mol) of diphenyl carbonate, and 18 μL of a 400 ppm by mass aqueous solution of cesium carbonate were placed. The glass reaction vessel was depressurized to about 100 Pa, and then the operation of returning the pressure to atmospheric pressure with nitrogen was repeated three times to replace the inside of the reaction vessel with nitrogen. Thereafter, the reaction vessel was immersed in an oil bath at 220° C. to dissolve the contents.

The agitator was rotated at 100 revolutions per minute, and the pressure in the reaction vessel was reduced from 101.3 kPa absolute pressure to 13.3 kPa over a period of 40 minutes while distilling off the phenol by-product of the oligomerization reaction of bisphenol A and diphenyl carbonate in the reaction vessel.

The pressure in the reaction vessel was then maintained at 13.3 kPa, and the ester exchange reaction was carried out for 80 minutes while further distilling off the phenol.

Then, the temperature outside the reactor was raised to 290°C, and the pressure inside the reactor was reduced from 13.3 kPa to 399 Pa absolute over a period of 40 minutes, and the distilled phenol was removed from the system.

Then, the absolute pressure in the reaction tank was reduced to 30 Pa, and the polycondensation reaction was carried out. The polycondensation reaction was terminated when the agitator in the reaction tank reached a predetermined stirring power. The time from raising the temperature to 290°C to ending the polymerization was 120 minutes.

The reactor was then pressurized with nitrogen to an absolute pressure of 101.3 kPa, and then the gauge pressure was increased to 0.2 MPa. The polycarbonate resin was extracted from the reactor to obtain a polycarbonate resin. The viscosity average molecular weight (Mv) of the obtained polycarbonate resin was 27,100.

The bisphenol production method of the present invention makes it possible to obtain bisphenol from waste plastics and the like by utilizing chemical recycling. Furthermore, this can be used to produce polycarbonate resin again, making it industrially useful.

Claims (9)

A preparation step of preparing a reaction liquid containing a polycarbonate resin, an aromatic monoalcohol, a glycol, and a catalyst;
a decomposition reaction step of decomposing the polycarbonate resin into bisphenol and alkylene carbonate in the reaction liquid prepared in the preparation step;
and a bisphenol recovery step of recovering the bisphenol obtained in the decomposition reaction step .
the catalyst is any one selected from the group consisting of an alkali metal hydroxide, an alkali metal carbonate, an alkylamine, and an acid;
The aromatic monoalcohol is any one selected from the group consisting of phenol, cresol, and xylenol;
the glycol is ethylene glycol or propylene glycol;
A method for producing bisphenol , wherein a molar ratio of the glycol to 1 mole of the repeating unit of the polycarbonate resin is 1.0 or more and 2.0 or less . 2. The method for producing bisphenol according to claim 1, wherein the decomposition reaction step is a step of decomposing a polycarbonate resin in a slurry-like reaction liquid. The method for producing bisphenol according to claim 1 , wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide. The method for producing bisphenol according to claim 1 , wherein the alkylamine is represented by the following formula (I):
In the formula, R ^A represents an alkyl group having 1 to 3 carbon atoms, and R ^B to R ^C each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. The method for producing bisphenol according to claim 1 or 4, wherein the alkylamine is a tertiary amine. 2. The method for producing bisphenol according to claim 1 , wherein the acid is any one selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid and sulfonic acid. The method for producing bisphenol according to any one of claims 1 to 6 , wherein the bisphenol is 2,2-bis(4-hydroxyphenyl)propane. The method for producing bisphenol according to any one of claims 1 to 7 , further comprising an alkylene carbonate recovery step of recovering the alkylene carbonate obtained in the decomposition reaction step. A method for producing a recycled polycarbonate resin, comprising producing a recycled polycarbonate resin using a bisphenol raw material containing bisphenol obtained by the method for producing bisphenol according to any one of claims 1 to 8 .