Method for producing polycarbonate, method for recovering dihydroxy compound, and device for producing polycarbonate

Abstract

A method for producing a polycarbonate, said method comprising: a polymerization step in which a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, are polymerized in a polymerization reactor; a cleaning step in which a purge vapor containing a hydroxyaryl compound, a diaryl carbonate, and a dihydroxy compound discharged from the polymerization reactor in the polymerization step is brought into contact with a cleaning liquid in a scrubber; and a condensation step for condensing the exhaust vapor after cleaning in the cleaning step. At least a portion of the bottom liquid of the scrubber in the cleaning step is supplied to the polymerization reactor.

Description

Technical Field

[0001] The present invention relates to a method for producing polycarbonate, a method for recovering a dihydroxy compound, and an apparatus for producing polycarbonate. Background Art

[0002] Polycarbonate is widely used as so-called engineering plastics in the optical fields such as electrical and electronic parts, automobile parts, optical recording media and lenses, etc., taking advantage of its transparency, heat resistance, mechanical strength, etc.

[0003] Typical methods for producing polycarbonate are the transesterification method or the melt method. In this method, a dihydroxy compound represented by bisphenol A (BPA) is transesterified with a diaryl carbonate represented by diphenyl carbonate (DPC), and the hydroxyaryl compound generated as a by-product is removed from the system to perform polymerization.

[0004] In the production of polycarbonate, a method using a polymerization reactor having a condenser has been proposed, for example, as shown in Patent Document 1. In this method, a monohydroxy compound produced as a by-product is condensed and recovered by a condenser, thereby reducing production costs and effectively utilizing resources.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2012-214801 Summary of the invention

[0008] Problems to be solved by the invention

[0009] In the method for producing polycarbonate using a polymerization reactor with a condenser shown in Patent Document 1, the vapor of the hydroxyaryl compound generated as a by-product is discharged from the polymerization reactor to the outside of the system. Since the boiling point difference between the dihydroxyaryl compound and the dihydroxy compound is large, it is generally believed that the vapor of the hydroxyaryl compound can be discharged to the outside of the system without any problem. However, in fact, the mist of the dihydroxy compound as a reaction raw material is introduced into the condenser along with the vapor, resulting in the loss of the dihydroxy compound in the subsequent distillation purification step. Therefore, there is obviously room for improvement.

[0010] Therefore, an object of the present invention is to provide a method for producing polycarbonate, a method for recovering a dihydroxy compound, and an apparatus for producing polycarbonate, which can recover a dihydroxy compound from vapor exhausted from a polymerization reactor and reduce the loss of the dihydroxy compound.

[0011] Means used to solve problems

[0012] The present invention includes the following embodiments.

[0013] <1> A method for producing polycarbonate, wherein the method for producing polycarbonate comprises the following steps:

[0014] A polymerization step of polymerizing a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, in a polymerization reactor;

[0015] a cleaning step of contacting exhaust steam containing a hydroxyaryl compound, a diaryl carbonate and a dihydroxy compound exhausted from a polymerization reactor in the polymerization step with a cleaning liquid in a scrubber; and

[0016] A condensation step of condensing the exhaust steam cleaned in the cleaning step,

[0017] At least a portion of the bottom liquid of the scrubber in the cleaning step is supplied to the polymerization reactor.

[0018] <2> like <1> In the method for producing polycarbonate, at least a part of the condensate of the exhaust steam in the condensation step is used as the cleaning liquid in the cleaning step.

[0019] <3> like <2> In the method for producing polycarbonate, the mass ratio of the condensate from the condensation step to the liquid supplied as the cleaning liquid to the cleaning step is 0.1 to 1 with respect to the amount of exhaust steam at the inlet of the cleaning step.

[0020] <4> like <1> ~ <3> The method for producing a polycarbonate according to any one of the preceding claims, wherein a bottom liquid of the scrubber in the cleaning step is supplied to the cleaning step as a cleaning liquid.

[0021] <5> like <4> The method for producing polycarbonate is characterized in that the mass ratio of the liquid supplied as the cleaning liquid to the cleaning step from the bottom liquid of the scrubber in the cleaning step is 0.1 to 10 with respect to the amount of discharged steam at the inlet of the cleaning step.

[0022] <6> like <1> ~ <5> The method for producing a polycarbonate according to any one of the preceding claims, wherein the content of the diaryl carbonate in the bottom liquid of the scrubber in the cleaning step is 20% by mass to 90% by mass.

[0023] <7> like <1> ~ <6> The method for producing a polycarbonate according to any one of the preceding claims, wherein the scrubber in the cleaning step comprises a random filler.

[0024] <8> like <1> ~ <7> The method for producing a polycarbonate according to any one of the preceding claims, wherein in the cleaning step, droplets of the mist-entrained portion are separated by a demister.

[0025] <9> like <8> In the method for producing polycarbonate, the space ratio of the demister is 95 volume % to 99 volume %.

[0026] <10> like <1> ~ <9> The method for producing a polycarbonate according to any one of the above aspects, wherein the dihydroxy compound comprises diphenyl carbonate.

[0027] <11> like <1> ~ <10> The method for producing a polycarbonate according to any one of the preceding claims, wherein the diaryl carbonate comprises bisphenol A.

[0028] <12> A method for recovering a dihydroxy compound, wherein the method for recovering a dihydroxy compound comprises the following steps:

[0029] a cleaning step, wherein exhaust steam discharged from a polymerization reactor that polymerizes a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, is contacted with a cleaning liquid in a scrubber; and

[0030] A condensation step is performed to condense the exhaust steam cleaned in the cleaning step.

[0031] <13> like <12> The dihydroxy compound recovery method, wherein the dihydroxy compound comprises diphenyl carbonate.

[0032] <14> like <12> or <13> The method for recovering dihydroxy compounds, wherein the diaryl carbonate contains bisphenol A.

[0033] <15> A polycarbonate manufacturing device, wherein the polycarbonate manufacturing device comprises:

[0034] A polymerization reactor for polymerizing a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof;

[0035] a scrubber for contacting exhaust vapors from the polymerization reactor comprising hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds with a cleaning liquid;

[0036] a condenser for condensing the exhaust steam cleaned by the scrubber; and

[0037] A supply path for supplying at least a portion of the bottom liquid of the scrubber to the polymerization reactor.

[0038] Effects of the Invention

[0039] According to the present invention, there can be provided a method for producing polycarbonate, a method for recovering a dihydroxy compound, and a polycarbonate producing apparatus capable of recovering a dihydroxy compound from vapor exhausted from a polymerization reactor and reducing the amount of loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of a polycarbonate production apparatus.

[0041] Figure 2 This is a schematic diagram of a polycarbonate production apparatus according to another embodiment.

[0042] Figure 3 This is a schematic diagram of the polycarbonate production apparatus used in the comparative experiment. DETAILED DESCRIPTION

[0043] Hereinafter, a method for implementing the present invention (hereinafter referred to as "this embodiment") is described in detail. It should be noted that the following embodiment is an example for illustrating the present invention, and the present invention is not limited to the following embodiment. The present invention can be implemented with appropriate changes within the scope of its main purpose. It should be noted that in this specification, for example, the expression of a numerical range of "1 to 100" includes both its lower limit "1" and upper limit "100". In addition, the expression of other numerical ranges is the same.

[0044] [Production method of polycarbonate]

[0045] The method for producing the polycarbonate of the present embodiment includes the following steps:

[0046] A polymerization step of polymerizing a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, in a polymerization reactor;

[0047] a cleaning step of contacting exhaust steam containing a hydroxyaryl compound, a diaryl carbonate and a dihydroxy compound exhausted from a polymerization reactor in the polymerization step with a cleaning liquid in a scrubber; and

[0048] A condensation step of condensing the exhaust steam cleaned in the cleaning step,

[0049] At least a portion of the bottom liquid of the scrubber in the cleaning step is supplied to the polymerization reactor.

[0050] According to the present embodiment, a method for producing polycarbonate, a method for recovering a dihydroxy compound, and a polycarbonate producing apparatus capable of recovering a dihydroxy compound from vapor exhausted from a polymerization reactor and reducing the amount of loss can be provided.

[0051] In this embodiment, in the cleaning step, the exhaust steam discharged from the polymerization reactor is brought into contact with the cleaning liquid in the scrubber, thereby recovering the dihydroxy compounds in the exhaust steam. The bottom liquid of the scrubber contains compounds with higher boiling points such as diaryl carbonate and dihydroxy compounds contained in the exhaust steam. Therefore, by supplying at least a portion of the bottom liquid of the scrubber to the polymerization reactor, the recovered diaryl carbonate and dihydroxy compounds can be used again for polymerization, and the loss of dihydroxy compounds can be reduced.

[0052] <Polycarbonate Production Apparatus>

[0053] An apparatus used in the method for producing polycarbonate according to the present embodiment will be described.

[0054] Figure 1 1 is a schematic diagram of a polycarbonate production apparatus. The polycarbonate production apparatus includes a polymerization reactor 1 , a scrubber 2 , a condenser 3 , and a supply path 4 .

[0055] The polymerization reactor 1 polymerizes the dihydroxy compound and the diaryl carbonate, or their prepolymers. The polymerization reactor 1 can be a polymerization reactor with a large area for evaporating the hydroxyaryl compound and the like generated by the polymerization reaction. As the polymerization reactor, there can be cited: a thin film polymerization reactor, a centrifugal thin film evaporation polymerization reactor, a surface renewal type twin-screw mixing polymerization reactor, a twin-screw horizontal stirring polymerization reactor, a wetted wall polymerization reactor, a porous plate type polymerization reactor that polymerizes while falling freely, a polymerization reactor that causes the polymer to melt and fall along a support body to carry out polymerization, and a porous plate type polymerization reactor with a metal wire. In addition, these polymerization reactors can be used alone or in combination. It should be noted that the polymerization process using the polymerization reactor can be any one of an intermittent type and a continuous type.

[0056] The polymerization reactor can use a polymerization reactor equipped with a stirring blade for directly stirring the liquid surface. The stirring blade for directly stirring the liquid surface refers to a stirring blade in which the portion of the stirring blade other than the stirring shaft is present at the gas interface of the polymerization reactor. Whether there is a stirring blade inside the liquid other than the gas-liquid interface is possible, but the use of a stirring blade that stirs not only the gas-liquid interface but also the liquid interior is a preferred mode of this embodiment. There is no particular restriction on the shape of the stirring blade, and various types of stirring blades can be used, such as three-blade swept (Pfaudler) blades, anchor blades, turbine blades, double helical blades, Maxblend type stirring blades, etc. It can be seen that by using a polymerization reactor equipped with a stirring blade for directly stirring the liquid surface, the polymerization speed becomes faster and the foaming phenomenon in the polymerization tank can be suppressed. Although the reason is unclear, it is speculated that it is due to the excellent bubble breaking effect on the bubbles present on the surface of the liquid. The polymerization can be a batch type in which the entire molten mixture is put into the polymerization reactor for polymerization, or a continuous type in which the molten mixture is continuously supplied while the polymerization is carried out.

[0057] The method for heating the polymerization reactor is not particularly limited, and the following methods can be used: a method of heating by arranging a jacket on the polymerization reactor, a method of heating by arranging an internal coil in the polymerization reactor, a method of heating by arranging a heat exchanger outside the polymerization reactor and circulating the liquid, etc. From the viewpoint of producing high-quality polycarbonate without coloration, it is preferred to heat the heat transfer area (m 2 ) relative to the liquid volume of the polymerization reactor (m 3 ) is in the range of 1 to 70.

[0058] The polymerization reactor 1 has a supply port 11 for supplying a reaction raw material into the reactor. When the reaction raw material is reacted in the polymerization reactor 1, the steam containing the hydroxyaryl compound is discharged from the steam discharge port 12 to the outside of the polymerization reactor 1. The steam generated by the reaction is supplied from the steam discharge port 12 to the scrubber 2.

[0059] The polymerization reactor 1 has a discharge pump 13 for extracting the produced polycarbonate. The discharge pump 13 may be a gear pump capable of quantitatively discharging a high-viscosity substance, and the material of the gears may be stainless steel or other special metals.

[0060] The exhaust vapor containing the hydroxyaryl compound, diaryl carbonate and dihydroxy compound discharged from the polymerization reactor 1 is brought into contact with the cleaning liquid in the scrubber 2. The "scrubber" refers to a device that brings gas and liquid into contact to separate components in the gas.

[0061] The scrubber 2 has a spray port 21 for a cleaning liquid near the top of the tower and a packing 22 arranged at the bottom thereof. The cleaning liquid introduced from the spray port 21 is sprayed in the scrubber and supplied to the packing 22. On the other hand, the scrubber 2 has an inlet 23 for exhaust steam at the bottom of the tower. The exhaust steam introduced from the inlet 23 contacts the cleaning liquid in the packing 22, and diaryl carbonate and dihydroxy compounds are separated from the exhaust steam. By providing the scrubber 2, substances with a higher boiling point than aromatic monohydroxy compounds, especially dihydroxy compounds, which are distilled from the polymerization reactor, can be returned to the polymerization reactor, and the loss of raw materials can be reduced. After the exhaust steam is cleaned in the scrubber 2, it is discharged from the exhaust steam port 24. The exhaust steam treated by the scrubber 2 is supplied to the condenser 3 from the exhaust steam port 24.

[0062] The filler used here may be a regular filler or an irregular filler, but an irregular filler is preferred. Such fillers include, for example, Raschig rings, Lessing rings, Ball rings, Bell saddle rings, rectangular saddle rings, Dixon fillers, McMahon fillers, Helipak fillers, step ring fillers, Raschig super rings, and the like.

[0063] The scrubber 2 may have a demister 25 on the upper side of the spray port 21. The demister 25 is provided to separate the droplets entrained in the mist. When the exhaust steam contacts the cleaning liquid, liquid particles are generated, and the particles rise with the exhaust steam. Here, when a demister is provided in the flow path, the flow path of the exhaust steam becomes complicated, so the light exhaust steam passes between the demisters and easily passes through the mesh space, but the heavy droplets cannot change the flow path quickly due to inertia, and detach from the flow path of the exhaust steam and collide with the demister. Then, the droplets that collide with the demister adhere to the demister due to surface tension, gradually gather and coarsen, descend along the demister, and merge with the liquid phase again.

[0064] In the condenser 3, the exhaust steam after washing by the scrubber 2 is condensed. As the condenser 3, a reflux cooler can be used. The exhaust steam after washing by the scrubber 2 is condensed by the condenser 3 to recover the hydroxyaryl compound. The condenser 3 is connected to the circulation flow path 31, and a part of the condensate is supplied to the condenser. Thus, the inside of the condenser 3 is cleaned by circulating a part of the condensate in the condenser 3.

[0065] The supply path 4 supplies at least a portion of the bottom liquid of the scrubber to the polymerization reactor 1. The supply path 4 has a transfer pump 41. Although not shown, the supply path 4 may have a flow rate regulating valve. By supplying at least a portion of the bottom liquid of the scrubber to the polymerization reactor 1, the dihydroxy compound and diaryl carbonate contained in the bottom liquid are recycled, and the loss of raw materials can be reduced.

[0066] The polycarbonate production apparatus may include a supply path 5 for supplying the bottom liquid of the condenser 3 as a cleaning liquid for the scrubber 2. By including the supply path 5, the hydroxyaryl compound obtained by the condenser 3 can be reused as a cleaning liquid.

[0067] The supply path 6 supplies the bottom liquid of the scrubber as a cleaning liquid to the scrubber 2. Although not shown, the supply path 6 may have a flow rate regulating valve. By reusing at least a portion of the bottom liquid of the scrubber as a cleaning liquid for the scrubber 2, the dihydroxy compound and the diaryl carbonate are recycled, and the loss of the raw materials can be reduced.

[0068] The material of the pipes of the polycarbonate manufacturing device is not particularly limited, and is usually selected from metals such as stainless steel, carbon steel, Hastelloy, nickel, titanium, chromium and other alloys, and polymer materials with high heat resistance. In addition, the surfaces of these materials can be plated, lined, passivated, acid-cleaned, phenol-cleaned, etc. as needed. Stainless steel, nickel, glass lining, etc. are preferred, and stainless steel is particularly preferred. It should be noted that the discharge pump of molten polycarbonate or polycarbonate is usually preferably a gear pump that can quantitatively discharge high-viscosity substances, and the material of these gears can be stainless steel or other special metals.

[0069] The polymerization reactor may be a single unit or a combination of two or more units.

[0070] Figure 2 This is a schematic diagram of a polycarbonate production apparatus according to another embodiment. Regarding the polycarbonate production apparatus according to another embodiment, the same symbols are used for the same structures as those in the above embodiment, and the description thereof is omitted. The polycarbonate production apparatus has two polymerization reactors. Regarding the structure of the second polymerization reactor, the same number is used for the same structure as that of the first polymerization reactor, and in order to make it clear that it is the device structure of the second polymerization reactor, the symbol is marked with "'" and the description thereof is omitted.

[0071] Next, the method for producing polycarbonate according to the present embodiment will be described by taking the case where the above-mentioned polycarbonate production apparatus is used as an example.

[0072] <Polymerization process>

[0073] In the polymerization step, a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, are polymerized in a polymerization reactor.

[0074] (Dihydroxy compounds)

[0075] As a dihydroxy compound, an aromatic dihydroxy compound and an aliphatic dihydroxy compound are mentioned, for example.

[0076] The aromatic dihydroxy compound is, for example, a compound represented by the following formula.

[0077] HO-Ar-OH

[0078] (In the formula, Ar represents a divalent aromatic group.)

[0079] The divalent aromatic group is, for example, a group represented by the following formula.

[0080] -Ar 1 -Y-Ar 2 -

[0081] (Where Ar 1 and Ar 2 Each independently represents a divalent carbocyclic or heterocyclic aromatic group having 5 to 70 carbon atoms, and Y represents a divalent alkylene group having 1 to 30 carbon atoms.

[0082] Divalent aromatic group, Ar 1 ,Ar 2 One or more hydrogen atoms in the divalent aromatic group may be replaced by other substituents that do not adversely affect the reaction, such as halogen atoms, alkyl groups having 1 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, phenyl groups, phenoxy groups, vinyl groups, cyano groups, ester groups, amide groups, nitro groups, etc. As heterocyclic aromatic groups, aromatic groups having one or more ring nitrogen atoms, oxygen atoms or sulfur atoms can be cited as preferred specific examples. The divalent aromatic group Ar 1 ,Ar 2 For example, it represents a substituted or unsubstituted phenylene group, a substituted or unsubstituted biphenylene group, a substituted or unsubstituted pyridylene group, etc. The substituents here are as described above.

[0083] The divalent alkylene group Y is, for example, a group represented by the following formula.

[0084]

[0085] In the formula, R 1 , R 2 , R 3 , R 4 Each independently represents hydrogen, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 ring carbon atoms, a carbocyclic aromatic group having 5 to 10 ring carbon atoms, or a carbocyclic aralkyl group having 6 to 10 carbon atoms. k represents an integer of 3 to 11, and R 5 and R 6 Each X is selected to independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms, and X represents carbon. 1 , R 2 , R3 , R 4 , R 5 and R 6 In the above, one or more hydrogen atoms may be replaced by other substituents such as halogen atoms, alkyl groups having 1 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, phenyl groups, vinyl groups, cyano groups, ester groups, amide groups, nitro groups, etc., within the range that does not adversely affect the reaction.

[0086] Examples of such a divalent aromatic group Ar include groups represented by the following formula.

[0087]

[0088] In the formula, R 7 , R 8 Each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 ring carbon atoms, or a phenyl group. m and n are integers of 1 to 4. When m is 2 to 4, each R 7 Each may be the same or different. When n is 2 to 4, each R 8 Each may be the same or different.

[0089] The divalent aromatic group Ar may be a group represented by the following formula.

[0090] -Ar 1 -Z-Ar 2 -

[0091] (Where Ar 1 ,Ar 2 As mentioned above, Z represents a single bond or -O-, -CO-, -S-, -SO2-, -SO-, -COO-, -CON (R 1 )-and other divalent groups. It should be noted that R 1 As mentioned above.)

[0092] Examples of such a divalent aromatic group Ar include groups represented by the following formula.

[0093]

[0094] In the formula, R 7 , R 8 , m and n are as described above.

[0095] Specific examples of the divalent aromatic group Ar include a substituted or unsubstituted phenylene group, a substituted or unsubstituted naphthylene group, a substituted or unsubstituted pyridylene group, and the like.

[0096] The aromatic dihydroxy compound may be used alone or in combination of two or more.

[0097] Among these aromatic dihydroxy compounds, bisphenol A is preferred. As bisphenol A, a high-purity product for polycarbonate having a chlorine content of 1 ppb or less is preferably used.

[0098] In addition, a trivalent aromatic trihydroxy compound may be used in combination for introducing a branched structure.

[0099] (Diaryl carbonate)

[0100] The diaryl carbonate is preferably a compound represented by the following formula.

[0101]

[0102] (In the above formula, each Ar" represents a monovalent aromatic group having 5 to 20 carbon atoms.)

[0103] Examples of the monovalent aromatic group include a phenyl group, a methylphenyl group, a dimethylphenyl group, a trimethylphenyl group, an ethylphenyl group, a diethylphenyl group, a triethylphenyl group, a butylphenyl group, a dibutylphenyl group, and a tributylphenyl group.

[0104] These diaryl carbonates may be used alone or in combination of two or more.

[0105] Among the diaryl carbonates, unsubstituted diphenyl carbonate is preferred; symmetrical diaryl carbonates such as di(tolyl) carbonate, di(tert-butylphenyl) carbonate and other lower alkyl-substituted diphenyl carbonates are preferred, and diphenyl carbonate, which is the simplest diaryl carbonate in structure, is particularly preferred. These diaryl carbonates can be used alone or in combination of two or more. From the perspective of recovering dihydroxy compounds from the vapor discharged from the polymerization reactor and reducing the amount of loss, diphenyl carbonate is preferably used in combination with bisphenol A as a hydroxy compound.

[0106] The diphenyl carbonate is not particularly limited, but diphenyl carbonate produced by reacting dimethyl carbonate produced by reacting ethylene carbonate produced by reacting ethylene oxide and CO 2 with phenol by a reactive distillation method is preferably used.

[0107] Furthermore, diphenyl carbonate is preferably an ultra-high purity product that does not contain alkali metals, alkaline earth metals, and chlorine.

[0108] The ratio of the dihydroxy compound to the diaryl carbonate used (charging ratio) varies depending on the types of the aromatic dihydroxy compound and the diaryl carbonate used, the polymerization temperature and other polymerization conditions. The diaryl carbonate is usually used in a ratio of 0.9 mol to 2.5 mol, preferably 0.95 mol to 2.0 mol, and more preferably 0.98 mol to 1.5 mol, relative to 1 mol of the aromatic dihydroxy compound.

[0109] In the method for producing polycarbonate of the present embodiment, a prepolymer can be used as a raw material. The prepolymer is a condensate of a dihydroxy compound and a diaryl carbonate. The use ratio (feed ratio) of the prepolymer is the same as the use ratio (feed ratio) of the dihydroxy compound and the diaryl carbonate described above. The average degree of polymerization of the prepolymer is not particularly limited, and is, for example, 2 to 2000.

[0110] (catalyst)

[0111] The polymerization process can be carried out without adding a catalyst, but in order to increase the polymerization rate, it can also be carried out in the presence of a catalyst. There are no particular restrictions on the catalyst, and examples thereof include: hydroxides of alkali metals and alkaline earth metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide; alkali metal salts, alkaline earth metal salts, and quaternary ammonium salts of boron or aluminum hydrides such as lithium aluminum hydride, sodium borohydride, and tetramethylammonium borohydride; hydrides of alkali metals and alkaline earth metals such as lithium hydride, sodium hydride, and calcium hydride; alkoxides of alkali metals and alkaline earth metals such as methoxylithium, sodium ethoxide, and calcium methoxide; phenoxylithium, sodium phenoxide, phenoxymagnesium, LiO-Ar-OLi, NaO-Ar-ONa (Ar is an arylene group) ) and other alkali metal and alkaline earth metal aromatic oxides; lithium acetate, calcium acetate, sodium benzoate and other alkali metal and alkaline earth metal organic acid salts; zinc oxide, zinc acetate, zinc benzoate and other zinc compounds; boron oxide, boric acid, sodium borate, trimethyl borate, tributyl borate, triphenyl borate; tin oxide, dialkyl tin oxide, dialkyl tin carboxylate, tin acetate, ethyltributoxytin and other tin compounds bonded with alkoxy or aryloxy groups, organic tin compounds and other tin compounds; lead oxide, lead acetate, lead carbonate, basic carbonate, lead and organic lead alkoxides or aromatic oxides; quaternary ammonium salts, quaternary These catalysts may be used alone or in combination of two or more.

[0112] The amount of catalyst used is usually 10 -10 The content of the compound is in the range of % to 1% by mass, preferably 10% by mass. -9 Mass%~10 -1 The mass % range is preferably 10 -8 Mass%~10 -2 mass %.

[0113] The raw material used in the polymerization step is preferably a mixture obtained by melt mixing at usually 100° C. to 250° C., preferably 140° C. to 200° C. Depending on the conditions of the melt mixing, the reaction of the dihydroxy compound and the diaryl carbonate is partially carried out. The reaction rate of the dihydroxy compound in the molten mixture is not particularly limited, but is usually in the range of 0.001% to 95%, preferably in the range of 20% to 85%.

[0114] In the polymerization step, it is preferred to polymerize the dihydroxy compound and the diaryl carbonate to produce a polycarbonate having a number average molecular weight of 5000 or less. By setting it within this range, the reaction pressure in the polymerization reactor shown in the polymerization step can be appropriately maintained, and the supply amount of the inert gas will not be extremely increased, and it can be used within an appropriate range. The number average molecular weight of the produced polycarbonate is preferably 350 to 4000.

[0115] The temperature of the polymerization reactor is preferably 120°C to 320°C, more preferably 160°C to 300°C, and further preferably 180°C to 280°C.

[0116] As the reaction proceeds, an aromatic monohydroxy compound is gradually generated, which is distilled out in the form of steam, introduced into a condenser and condensed, and then removed from the reaction system, thereby increasing the reaction rate. The reaction pressure of the polymerization reactor varies according to the type, molecular weight, polymerization temperature, etc. of the polycarbonate to be manufactured. For example, in the case of manufacturing polycarbonate from a molten mixture of bisphenol A and diphenyl carbonate, when the number average molecular weight is less than 1500, the reaction pressure is usually in the range of 670Pa (5mmHg) to normal pressure, and when the number average molecular weight is 1500 to 5000, the reaction pressure is 4000Pa (30mmHg) or less. As mentioned above, reducing the reaction pressure will make the foaming in the polymerization tank violent, so a pressure of more than 2670Pa (20mmHg) is particularly preferred. It is also preferred to use a method of reacting under reduced pressure while introducing the aforementioned inert gas.

[0117] The hydroxyaryl compound distilled from the polymerization reactor may contain compounds with higher boiling points than the compound, such as dihydroxy compounds, due to entrainment of mist. In this embodiment, in order to reduce the entrainment of dihydroxy compounds in the hydroxyaryl compound, a cleaning step using a scrubber to clean steam is provided between the polymerization reaction step and the condensation step.

[0118] <Cleaning process>

[0119] In the cleaning step, the exhaust steam containing the hydroxyaryl compound, the diaryl carbonate and the dihydroxy compound discharged from the polymerization reactor in the polymerization step is contacted with the cleaning liquid in the scrubber. By contacting the exhaust steam, the diaryl carbonate and the dihydroxy compound can be separated from the exhaust steam and recovered from the bottom of the scrubber.

[0120] (Cleaning fluid)

[0121] The cleaning liquid is not particularly limited, but is preferably a liquid composition with diaryl carbonate as the main component. Here, "main component" refers to a component exceeding 50% by mass. The diaryl carbonate is preferably the same compound as the diaryl carbonate used in the polymerization process.

[0122] The cleaning solution may contain a dihydroxy compound. The dihydroxy compound is preferably the same compound as the dihydroxy compound used in the polymerization step. The content of the dihydroxy compound is not particularly limited and may be 1% to 50% by mass, 3% to 40% by mass, or 5% to 30% by mass.

[0123] The cleaning liquid may contain a hydroxyaryl compound. The hydroxyaryl compound is preferably a hydroxyaryl compound removed by polymerization from the diaryl carbonate used in the polymerization step. The content of the hydroxyaryl compound is not particularly limited and may be 1% to 40% by mass, 3% to 30% by mass, or 5% to 20% by mass.

[0124] At least a portion of the condensate of the exhaust steam in the condensation step described below can be used as the cleaning liquid in the cleaning step. By using the condensate as the cleaning liquid, the temperature of the cleaning liquid can be lowered, and the diaryl carbonate and the dihydroxy compound can be efficiently recovered.

[0125] The mass ratio of the liquid supplied as the cleaning liquid from the condensation step to the cleaning step relative to the exhaust steam at the inlet of the cleaning step is preferably 0.1 to 1, more preferably 0.2 to 0.7, and even more preferably 0.2 to 0.5. The exhaust steam at the inlet of the cleaning step refers to the exhaust steam introduced into the scrubber.

[0126] The bottom liquid of the scrubber in the cleaning process is preferably supplied to the cleaning process as a cleaning liquid and used again as a cleaning liquid. The bottom liquid contains the components of the cleaning liquid and the hydroxyaryl compound, diaryl carbonate and dihydroxy compound recovered from the exhaust steam. By reusing the bottom liquid of the scrubber in the cleaning process as a cleaning liquid, resources can be effectively utilized and diaryl carbonate and dihydroxy compound can be effectively recovered.

[0127] The mass ratio of the liquid supplied as the cleaning liquid from the bottom liquid of the scrubber in the cleaning step to the cleaning step relative to the exhaust steam amount at the cleaning step inlet is preferably 0.1 to 10, more preferably 0.5 to 7, and even more preferably 1 to 5. The exhaust steam amount at the cleaning step inlet refers to the exhaust steam amount introduced into the scrubber.

[0128] (Bottom liquid)

[0129] The bottom liquid of the scrubber in the cleaning step is a liquid composition accumulated at the bottom of the scrubber after the cleaning liquid contacts the exhaust steam. The content of the diaryl carbonate in the bottom liquid is preferably 20% to 90% by mass, more preferably 40% to 90% by mass, and further preferably 60% to 90% by mass.

[0130] The scrubber in the cleaning step preferably has a random packing. In the cleaning step, by allowing the exhaust steam to contact the cleaning liquid while passing through the random packing, the recovery rate of the diaryl carbonate and dihydroxy compound in the exhaust steam can be increased, and the loss of the dihydroxy compound can be more significantly reduced.

[0131] In the cleaning process, it is preferred to separate the droplets of the entrained part of the mist using a demister. After the exhaust steam contacts the cleaning liquid, the droplets of the entrained part of the mist may be contained in the exhaust steam. The droplets of the entrained part of the mist also contain diaryl carbonate and dihydroxy compounds. By separating the droplets using a demister, the recovery rate of these compounds can be improved.

[0132] The space ratio of the demister is preferably 95 to 99 volume %, more preferably 97 to 99 volume %, and further preferably 98 to 99 volume %. The “space ratio of the demister” refers to the ratio of the volume of the space to the total volume of the demister.

[0133] In the condensation step, the exhaust steam cleaned in the cleaning step is condensed. The exhaust steam cleaned in the cleaning step contains a hydroxyaryl compound, which is condensed into a liquid in the condensation step. In the production method of this embodiment, since the cleaning step is included, the diaryl carbonate and the dihydroxy compound that can be reused in the polymerization reaction are separated from the exhaust steam, so the loss of these compounds can be reduced. In addition, the hydroxyaryl compound with high purity is obtained by the condensation step, so a liquid composition that is easily reused in the manufacture of diaryl carbonate, etc. is obtained.

[0134] In the method for producing polycarbonate of the present embodiment, at least a portion of the bottom liquid of the scrubber in the cleaning step is supplied to the polymerization reactor, thereby recycling the diaryl carbonate and dihydroxy compound recovered in the cleaning step in the polymerization step, thereby improving the utilization efficiency of the raw materials.

[0135] The above-mentioned steps may be performed sequentially, but are preferably performed continuously and simultaneously.

[0136] The polycarbonate produced by the above-mentioned polycarbonate production apparatus can be subjected to a post-polymerization step described later to produce a high molecular weight polycarbonate.

[0137] <Post-polymerization step>

[0138] In the post-polymerization step, the polycarbonate obtained in the above-mentioned polymerization step is further polymerized to produce a polycarbonate having a higher degree of polymerization.

[0139] The number average molecular weight of the polycarbonate produced in the post-polymerization step is generally 500 to 100,000, preferably 2,000 to 30,000. The polymerization reactor used in the post-polymerization step is not particularly limited, and a polymerization reactor with a large area for evaporating the hydroxyaryl compound generated as a by-product is preferred. Specifically, a thin film polymerization reactor, a centrifugal thin film evaporation polymerization reactor, a surface renewal type twin-screw kneading polymerization reactor, a twin-screw horizontal stirring polymerization reactor, a wetted wall polymerization reactor, a porous plate type polymerization reactor that polymerizes while freely falling, a polymerization reactor that allows the polymer to melt and fall along a support body to carry out polymerization, such as a porous plate type polymerization reactor with a metal wire, etc., can be used alone or in combination. In the post-polymerization step, a plurality of the above-mentioned manufacturing devices can be combined to carry out polymerization. In the post-polymerization step, it is preferred to allow the polymer to melt and fall along a support body to carry out polymerization.

[0140] The reaction pressure in the post-polymerization step is usually 2670 Pa (20 mmHg) or less, preferably 1330 Pa (10 mmHg) or less, and more preferably 670 Pa (5 mmHg) or less. When producing a high molecular weight polycarbonate, the reaction pressure in the post-polymerization step is preferably 267 Pa (2 mmHg) or less.

[0141] The reaction temperature of the post-polymerization step is usually selected within the temperature range of 50°C to 350°C, and preferably within the temperature range of 100°C to 290°C.

[0142] In the polycarbonate production apparatus of the present embodiment, when producing polycarbonate, for example, a known catalyst deactivator described in International Publication No. 2005 / 121213 can be used. The amount of the catalyst deactivator used is preferably 0.5 mol to 50 mol, more preferably 0.5 mol to 10 mol, and even more preferably 0.8 mol to 5 mol relative to 1 mol of the transesterification catalyst. The catalyst deactivator is added, for example, in an extruder.

[0143] (Polycarbonate)

[0144] The polycarbonate obtained by the method for producing a polycarbonate according to the present embodiment has, for example, a repeating unit represented by the following formula.

[0145]

[0146] (Ar has the same definition as above.)

[0147] The polycarbonate is preferably a polycarbonate containing 85 mol % or more of a repeating unit represented by the following formula in all repeating units.

[0148]

[0149] The terminal group of the polycarbonate may generally be a hydroxyl group or an aryl carbonate group represented by the following formula.

[0150]

[0151] (Where Ar 5 Same as the definition of "Ar" above.)

[0152] The ratio of the hydroxyl group to the aryl carbonate group is not particularly limited, but is usually in the range of 95:5 to 5:95, preferably in the range of 90:10 to 10:90, and more preferably in the range of 80:20 to 20:80. In particular, polycarbonates in which the ratio of phenyl carbonate groups in the terminal groups is 85 mol % or more are preferred.

[0153] The polycarbonate may also be a polycarbonate comprising a plurality of polycarbonate main chains which are partially branched as a whole by being bonded to at least one side chain through a branch selected from the group consisting of an ester bond and an ether bond.

[0154] [Recycling method]

[0155] The method for producing polycarbonate according to the present embodiment has been described above. From another perspective, the method for producing polycarbonate according to the present embodiment is also a method for recovering a dihydroxy compound.

[0156] The recovery method of the dihydroxy compound of the present embodiment comprises the following steps:

[0157] a cleaning step, wherein exhaust steam discharged from a polymerization reactor that polymerizes a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, is contacted with a cleaning liquid in a scrubber; and

[0158] A condensation step is performed to condense the exhaust steam cleaned in the cleaning step.

[0159] According to the recovery method of the present embodiment, the dihydroxy compound can be recovered from the vapor exhausted from the polymerization reactor, and the loss amount of the dihydroxy compound can be reduced.

[0160] It should be noted that the washing step and the condensing step are as described above, and therefore their description is omitted.

[0161] Example

[0162] Hereinafter, the present embodiment will be described in more detail by way of examples, but the present embodiment is not limited to the following examples.

[0163] [Example 1]

[0164] use Figure 2 The device shown.

[0165] Bisphenol A (BPA) was used as the dihydroxy compound, and diphenyl carbonate (DPC) was used as the diaryl carbonate. The polymerization reactor 1 was operated at 220°C / 70 mmHg. Stainless steel was used as the material of the scrubber 2, and the theoretical plate number was set to one plate.

[0166] The process vapor from the polymerization reactor 1 in the front section is introduced into the bottom of the tower of the scrubber 2 at a flow rate of 8900 kg / hour. In the scrubber 2, diaryl carbonate is used as a cleaning liquid. The process vapor from the top of the scrubber 2 is 10650 kg / hour, which is introduced into the condenser 3. The process liquid flow rate at the bottom of the tower of the scrubber 2 is 16250 kg / hour, and the process liquid composition is 80% by weight in terms of DPC mass ratio. 250 kg / hour of the process liquid flow rate is introduced into the polymerization reactor 1, and 16000 kg / hour of it is reintroduced into the top of the scrubber 2 as a cleaning liquid. The process liquid flow rate at the bottom of the tower of the condenser 3 is 10650 kg / hour, of which 8650 kg / hour is extracted, and 2000 kg / hour of it is reintroduced into the top of the scrubber 2 as a cleaning liquid. In the condenser 3, the BPA concentration of the extracted process liquid is 20 mass ppm. According to the above results, it can be seen that the loss of dihydroxy compounds can be reduced.

[0167] The polymerization reactor 1' in the latter stage was operated under the conditions of 270°C / 32 mmHg. The scrubber 2' was made of stainless steel and the theoretical plate number was set to one plate.

[0168] The process vapor from the polymerization reactor 1' is introduced into the bottom of the scrubber 2' at a flow rate of 1380 kg / hour. The process vapor from the top of the scrubber 2' is 1830 kg / hour, which is introduced into the condenser 3'. The process liquid flow rate at the bottom of the scrubber 2' is 4050 kg / hour, and the process liquid composition is 90% in terms of DPC mass ratio. 50 kg / hour of the process liquid flow rate is introduced into the polymerization reactor 1', and 4000 kg / hour of it is reintroduced into the top of the scrubber 2' as a cleaning liquid. The process liquid flow rate at the bottom of the condenser 3' is 1830 kg / hour, of which 1330 kg / hour is extracted, and 500 kg / hour of it is reintroduced into the top of the scrubber 2' as a cleaning liquid. In the condenser 3', the BPA concentration of the extracted process liquid is 40 mass ppm. According to the above results, it can be seen that the loss of dihydroxy compounds can be reduced.

[0169] [Example 2]

[0170] use Figure 1 The device shown.

[0171] Bisphenol A (BPA) was used as the dihydroxy compound, and diphenyl carbonate (DPC) was used as the diaryl carbonate. The polymerization reactor 1 was operated at 220°C / 70 mmHg. Stainless steel was used as the material of the scrubber 2, and the theoretical plate number was set to one plate.

[0172] The process vapor from the polymerization reactor 1 in the front stage was introduced into the bottom of the scrubber 2 at a flow rate of 8670 kg / hour. The process vapor from the top of the scrubber 2 was 9850 kg / hour, which was introduced into the condenser 3. The process liquid flow rate at the bottom of the scrubber 2 was 2820 kg / hour, and the content of DPC in the process liquid composition was 30% by weight. 20 kg / hour of the process liquid flow rate was introduced into the polymerization reactor 1, and 2800 kg / hour of it was reintroduced into the top of the scrubber 2 as a cleaning liquid. The process liquid flow rate at the bottom of the condenser 3 was 9850 kg / hour, of which 8650 kg / hour was extracted, and 1200 kg / hour of it was reintroduced into the top of the scrubber 2 as a cleaning liquid. In the condenser 3, the BPA concentration of the extracted process liquid was 2000 mass ppm. According to the above results, it can be seen that the loss of dihydroxy compounds can be reduced.

[0173] The polymerization reactor 1' in the latter stage was operated under the conditions of 270°C / 32 mmHg. The scrubber 2' was made of stainless steel and the theoretical plate number was set to one plate.

[0174] The process vapor from the polymerization reactor 1' is introduced into the bottom of the tower of the scrubber 2' at a flow rate of 1340 kg / hour. The process vapor from the top of the scrubber 2' is 1660 kg / hour, which is introduced into the condenser 3'. The process liquid flow rate at the bottom of the tower of the scrubber 2' is 710 kg / hour, and the process liquid composition is 20% in terms of DPC mass ratio. 10 kg / hour of the process liquid flow rate is introduced into the polymerization reactor 1', and 700 kg / hour of it is reintroduced into the top of the scrubber 2' as a cleaning liquid. The process liquid flow rate at the bottom of the tower of the condenser 3' is 1660 kg / hour, of which 1330 kg / hour is extracted, and 330 kg / hour of it is reintroduced into the top of the scrubber 2' as a cleaning liquid. In the condenser 3', the BPA concentration of the extracted process liquid is 4000 mass ppm. According to the above results, it can be seen that the loss of dihydroxy compounds can be reduced.

[0175] [Example 3]

[0176] use Figure 1 The device shown.

[0177] Bisphenol A (BPA) was used as the dihydroxy compound, and diphenyl carbonate (DPC) was used as the diaryl carbonate. The polymerization reactor 1 was operated at 220°C / 70 mmHg. Stainless steel was used as the material of the scrubber 2, and the theoretical plate number was set to one plate.

[0178] The process vapor from the polymerization reactor 1 is introduced into the bottom of the tower of the scrubber 2 at a flow rate of 10500 kg / hour. The process vapor from the top of the scrubber 2 is 12650 kg / hour, which is introduced into the condenser 3. The process liquid flow rate at the bottom of the tower of the scrubber 2 is 33850 kg / hour, and the process liquid composition is 60% in terms of DPC mass ratio. 1850 kg / hour of the process liquid flow rate is introduced into the polymerization reactor 1, and 32000 kg / hour of it is reintroduced into the top of the scrubber 2 as a cleaning liquid. The process liquid flow rate at the bottom of the tower of the condenser 3 is 12650 kg / hour, of which 8650 kg / hour is extracted, and 4000 kg / hour of it is reintroduced into the top of the scrubber 2 as a cleaning liquid. In the condenser 3, the BPA concentration of the extracted process liquid is 1 mass ppm. According to the above results, it can be seen that the loss of dihydroxy compounds can be reduced.

[0179] The polymerization reactor 1' was operated under the conditions of 270°C / 32 mmHg. The scrubber 2' was made of stainless steel and the number of theoretical plates was set to one plate.

[0180] The process vapor from the polymerization reactor 1' is introduced into the bottom of the tower of the scrubber 2' at a flow rate of 1560 kg / hour. The process vapor from the top of the scrubber 2' is 2030 kg / hour, which is introduced into the condenser 3'. The process liquid flow rate at the bottom of the tower of the scrubber 2' is 8230 kg / hour, and the process liquid composition is 90% in terms of DPC mass ratio. 230 kg / hour of the process liquid flow rate is introduced into the polymerization reactor 1', of which 8000 kg / hour is reintroduced into the top of the scrubber 5 as a cleaning liquid. The process liquid flow rate at the bottom of the tower of the condenser 3' is 2030 kg / hour, of which 1330 kg / hour is extracted, of which 700 kg / hour is reintroduced into the top of the scrubber 2' as a cleaning liquid. In the condenser 3', the BPA concentration of the extracted process liquid is 5 mass ppm. According to the above results, it can be seen that the loss of dihydroxy compounds can be reduced.

[0181] [Comparative Example 1]

[0182] use Figure 3 The device shown. Figure 3 The apparatus shown does not include the scrubber 2 , and the same components as those of the polycarbonate production apparatus of the present embodiment are denoted by the same reference numerals and description thereof will be omitted.

[0183] BPA was used as the dihydroxy compound, and DPC was used as the diaryl carbonate. The polymerization reactor 1 was operated at 220° C. / 70 mmHg. The polymerization reactor 1 was operated at 270° C. / 32 mmHg.

[0184] The process vapor was introduced into the condenser 3 at a flow rate of 8650 kg / hour. The flow rate of the process liquid at the bottom of the condenser 3 was 8650 kg / hour, and the BPA concentration of the extracted process liquid was 4000 mass ppm.

[0185] The process vapor was introduced into the condenser 3' at a flow rate of 1330 kg / hour. The flow rate of the process liquid at the bottom of the condenser 3' was 1330 kg / hour, and the BPA concentration of the extracted process liquid was 9000 mass ppm.

[0186] Industrial Applicability

[0187] The method for producing polycarbonate according to the present embodiment has industrial applicability in the field of production of polycarbonate.

[0188] Description of symbols

[0189] 1. 1' Polymerization reactor

[0190] 2. 2' Scrubber

[0191] 3. 3' condenser

[0192] 4, 4', 5, 5', 6, 6' supply path

[0193] 13, 13' discharge pump

[0194] 22, 22' Filling

[0195] 25, 25' demister

Claims

1. A method for producing a polycarbonate, wherein: The method for producing the polycarbonate comprises the following steps: A polymerization step of polymerizing a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, in a polymerization reactor; a cleaning step of contacting exhaust steam containing a hydroxyaryl compound, a diaryl carbonate and a dihydroxy compound discharged from a polymerization reactor in the polymerization step with a cleaning liquid in a scrubber; and A condensation step of condensing the exhaust steam cleaned in the cleaning step, At least a portion of the bottom liquid of the scrubber in the cleaning step is supplied to the polymerization reactor.

2. The method for producing a polycarbonate according to claim 1, wherein: At least a portion of the condensate of the exhaust steam in the condensation step is used as the cleaning liquid in the cleaning step.

3. The method for producing a polycarbonate according to claim 2, wherein: The mass ratio of the condensate from the condensation step to the liquid supplied as the cleaning liquid to the cleaning step is 0.1 or more and 1 or less relative to the amount of exhaust steam at the inlet of the cleaning step.

4. The method for producing a polycarbonate according to claim 1, wherein: The bottom liquid of the scrubber in the cleaning step is supplied to the cleaning step as a cleaning liquid.

5. The method for producing a polycarbonate according to claim 4, wherein: The mass ratio of the liquid supplied as the cleaning liquid to the cleaning step from the bottom liquid of the scrubber in the cleaning step to the cleaning step is 0.1 or more and 10 or less.

6. The method for producing a polycarbonate according to claim 1, wherein: The content of the diaryl carbonate in the bottom liquid of the scrubber in the cleaning step is 20% by mass to 90% by mass.

7. The method for producing a polycarbonate according to any one of claims 1 to 6, wherein The scrubber in the cleaning step has irregular filling.

8. The method for producing a polycarbonate according to any one of claims 1 to 6, wherein In the cleaning process, a demister is used to separate the liquid droplets entrained by the mist.

9. The method for producing a polycarbonate according to claim 8, wherein: The space ratio of the demister is 95 volume % to 99 volume %.

10. The method for producing a polycarbonate according to claim 1, wherein: The dihydroxy compound includes diphenyl carbonate.

11. The method for producing a polycarbonate according to claim 10, wherein: The diaryl carbonate comprises bisphenol-A.

12. A method for recovering a dihydroxy compound, wherein: The recovery method of the dihydroxy compound comprises the following steps: a cleaning step, wherein exhaust steam discharged from a polymerization reactor that polymerizes a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof, is contacted with a cleaning liquid in a scrubber; and A condensation step is performed to condense the exhaust steam cleaned in the cleaning step.

13. A polycarbonate production device, wherein: The polycarbonate production device comprises: A polymerization reactor for polymerizing a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof; a scrubber for contacting exhaust vapors from the polymerization reactor comprising hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds with a cleaning liquid; a condenser for condensing the exhaust steam cleaned by the scrubber; and A supply path for supplying at least a portion of the bottom liquid of the scrubber to the polymerization reactor.

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