Method for producing polycarbonate, method for recovering dihydroxy compounds, and apparatus for producing polycarbonate

Abstract

The present invention provides a polycarbonate production method including: a polymerization step for polymerizing a dihydroxy compound and a diaryl carbonate, or prepolymers thereof in a polymerization reactor; a cleaning step in which an exhaust vapor that is discharged from the polymerization reactor used in the polymerization step, and that contains a hydroxyaryl compound, a diaryl carbonate, and a dihydroxy compound is brought into contact with a cleaning liquid in a scrubber; and a condensation step for condensing the exhaust vapor cleaned in the cleaning step, wherein at least a portion of a bottom liquid in the scrubber used in the cleaning step is supplied to the polymerization reactor.

Description

[Technical Field]

[0001] This invention relates to a method for producing polycarbonate, a method for recovering dihydroxy compounds, and an apparatus for producing polycarbonate. [Background technology]

[0002] Polycarbonate, leveraging its advantages such as transparency, heat resistance, and mechanical strength, is widely used as an engineering plastic in fields such as electrical and electronic components, automotive parts, optical recording media, and lenses.

[0003] The typical methods for producing polycarbonates are transesterification or melting. In these methods, a dihydroxy compound, such as bisphenol A (BPA), is transesterified with a diaryl carbonate, such as diphenyl carbonate (DPC), and polymerization proceeds by removing the by-product hydroxyaryl compound from the system.

[0004] In the production of polycarbonate, a method using a polymerization reactor with a condenser has been proposed, for example, as shown in Patent Document 1. In this method, monohydroxy compounds produced as by-products in the condenser are condensed and recovered, thereby reducing production costs and making effective use of resources. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-214801 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the method for producing polycarbonate using a polymerization reactor with a condenser as shown in Patent Document 1, the vapor of hydroxyaryl compounds produced as a by-product is discharged from the polymerization reactor. It was previously thought that the vapor of hydroxyaryl compounds could be discharged from the system without any particular problems due to the large difference in boiling points between dihydroxyaryl compounds and dihydroxy compounds. However, it has become clear that in reality, droplets of dihydroxy compounds, which are reaction raw materials, are introduced into the condenser along with the vapor, resulting in the loss of dihydroxy compounds in the subsequent distillation and purification process, indicating that there is room for improvement.

[0007] Therefore, the object of the present invention is to provide a method for producing polycarbonate, a method for recovering dihydroxy compounds, and an apparatus for producing polycarbonate that can recover dihydroxy compounds from vapor discharged from a polymerization reactor and reduce the amount of loss of said dihydroxy compounds. [Means for solving the problem]

[0008] The present invention encompasses the following embodiments. <1> A polymerization step in which a dihydroxy compound and diaryl carbonate, or a prepolymer thereof, is polymerized in a polymerization reactor, A washing step in which exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from the polymerization reactor in the polymerization step is brought into contact with a washing solution in a scrubber, The process includes a condensation step for condensing the exhaust steam that has been cleaned by the cleaning step, At least a portion of the bottom liquid of the scrubber in the washing step is supplied to the polymerization reactor. A method for manufacturing polycarbonate. <2> At least a portion of the condensate of the exhaust steam from the condensation process is used as the cleaning liquid in the cleaning process. <1> A method for producing polycarbonate as described above. <3> The method for producing a polycarbonate according to <2>, wherein the mass ratio of the condensate from the condensation step to the liquid supplied to the washing step as a washing liquid is 0.1 or more and 1 or less with respect to the amount of the discharged steam at the inlet of the washing step. <4> The method for producing a polycarbonate according to any one of <1> to <3>, wherein the bottom liquid of the scrubber in the washing step is supplied to the washing step as a washing liquid. <5> The method for producing a polycarbonate according to <4>, wherein the mass ratio of the liquid in which the bottom liquid of the scrubber in the washing step is supplied to the washing step as a washing liquid is 0.1 or more and 10 or less with respect to the amount of the discharged steam at the inlet of the washing step. <6> The method for producing a polycarbonate according to any one of <1> to <5>, wherein the content of the diaryl carbonate in the bottom liquid of the scrubber in the washing step is 20% by mass to 90% by mass. <7> The method for producing a polycarbonate according to any one of <1> to <6>, wherein the scrubber in the washing step is provided with irregular packing. <8> The method for producing a polycarbonate according to any one of <1> to <7>, wherein in the washing step, droplets of entrained liquid are separated by a demister. <9> The method for producing a polycarbonate according to <8>, wherein the void fraction of the demister is 95 vol% to 99 vol%. <10> The method for producing a polycarbonate according to any one of <1> to <9>, wherein the dihydroxy compound contains diphenyl carbonate. <11> The method for producing a polycarbonate according to any one of <1> to <10>, wherein the diaryl carbonate contains bisphenol A. <12> A washing step of bringing the discharged steam containing a hydroxyaryl compound, a diaryl carbonate and a dihydroxy compound discharged from a polymerization reactor for polymerizing a dihydroxy compound and a diaryl carbonate, or a prepolymer thereof into contact with a washing liquid in a scrubber; The process includes a condensation step for condensing the exhaust steam that has been cleaned by the cleaning step, A method for recovering dihydroxy compounds. <13> The dihydroxy compound includes diphenyl carbonate. <12> A method for recovering the dihydroxy compound described above. <14> The diaryl carbonate contains bisphenol A. <12> or <13> A method for recovering the dihydroxy compound described above. <15> A polymerization reactor for polymerizing dihydroxy compounds and diaryl carbonates, or prepolymers thereof, A scrubber that brings the exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from the polymerization reactor into contact with a washing liquid, A condenser for condensing the exhaust steam washed by the scrubber, A supply channel for supplying at least a portion of the bottom liquid of the scrubber to the polymerization reactor, A manufacturing apparatus for polycarbonate containing [a specific substance]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for producing polycarbonate, a method for recovering dihydroxy compounds, and an apparatus for producing polycarbonate, which can recover dihydroxy compounds from vapor discharged from a polymerization reactor and reduce the amount of loss. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of a polycarbonate manufacturing apparatus. [Figure 2] Figure 2 is a schematic diagram of a polycarbonate manufacturing apparatus according to another embodiment. [Figure 3] Figure 3 is a schematic diagram of the polycarbonate manufacturing apparatus used in the comparative experiment. [Modes for carrying out the invention]

[0011] The following describes in detail embodiments for carrying out the present invention (hereinafter referred to as "this embodiment"). This embodiment is illustrative for explaining the present invention, and the present invention is not limited to this embodiment. The present invention can be implemented with appropriate modifications within the scope of its gist. In this specification, for example, the notation of a numerical range such as "1 to 100" includes both the lower limit "1" and the upper limit "100". The same applies to other numerical range notations.

[0012] [Method for manufacturing polycarbonate] The method for manufacturing polycarbonate according to this embodiment is as follows: A polymerization step in which a dihydroxy compound and diaryl carbonate, or a prepolymer thereof, is polymerized in a polymerization reactor, A washing step in which exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from the polymerization reactor in the polymerization step is brought into contact with a washing solution in a scrubber, The process includes a condensation step for condensing the exhaust steam that has been cleaned by the cleaning step, At least a portion of the bottom liquid from the scrubber in the washing step is supplied to the polymerization reactor. According to this embodiment, it is possible to provide a method for producing polycarbonate, a method for recovering dihydroxy compounds, and an apparatus for producing polycarbonate, which can recover dihydroxy compounds from the vapor discharged from the polymerization reactor and reduce the amount of loss.

[0013] In this embodiment, during the washing process, dihydroxy compounds in the exhaust vapor discharged from the polymerization reactor can be recovered by contacting the exhaust vapor with a washing solution in a scrubber. The bottom liquid of the scrubber contains relatively high-boiling-point compounds such as diaryl carbonates and dihydroxy compounds contained in the exhaust vapor. Therefore, by supplying at least a portion of the bottom liquid of the scrubber to the polymerization reactor, the recovered diaryl carbonates and dihydroxy compounds can be reused in polymerization, thereby reducing the amount of dihydroxy compound lost.

[0014] <Polycarbonate manufacturing equipment> The apparatus used in the method for manufacturing polycarbonate according to this embodiment will be described. Figure 1 is a schematic diagram of a polycarbonate manufacturing apparatus. The polycarbonate manufacturing apparatus includes a polymerization reactor 1, a scrubber 2, a condenser 3, and a supply line 4.

[0015] Polymerization reactor 1 polymerizes dihydroxy compounds and diaryl carbonates, or prepolymers thereof. Polymerization reactor 1 may be a large-area polymerization reactor for evaporating hydroxyaryl compounds and the like generated as the polymerization reaction progresses. Examples of polymerization reactors include thin-film polymerization reactors, centrifugal thin-film evaporation polymerization reactors, surface-renewal twin-screw kneading polymerization reactors, twin-screw horizontal stirring polymerization reactors, wet-wall polymerization reactors, porous plate polymerization reactors that polymerize while free-falling, polymerization reactors that allow polymer to melt and fall along a support to proceed with polymerization, and porous plate polymerization reactors with wires. These polymerization reactors may be used individually or in combination. The polymerization process using the polymerization reactor may be in a batch or continuous manner.

[0016] The polymerization reactor may be equipped with impellers that directly agitate the liquid surface. An impeller that directly agitates the liquid surface refers to an impeller where the portion of the impeller other than the agitation axis is located at the gas interface of the polymerization reactor. While the impeller may or may not be located within the liquid outside the gas-liquid interface, using an impeller that agitates not only the gas-liquid interface but also the liquid interior is a preferred configuration in this embodiment. There are no particular restrictions on the shape of the impeller; various types can be used, such as Fardler impellers, anchor impellers, turbine impellers, double helical impellers, and Maxblend type impellers. It has been shown that using a polymerization reactor equipped with impellers that directly agitate the liquid surface increases the polymerization rate and suppresses foaming in the polymerization tank. The reason for this is unclear, but it is presumed to be due to its superior foam-breaking effect on bubbles present on the liquid surface. Polymerization can be carried out in a batch manner, where the entire molten mixture is charged into the polymerization reactor before polymerization, or in a continuous manner, where the molten mixture is continuously supplied while polymerization is carried out.

[0017] There are no particular restrictions on the method of heating the polymerization reactor. Methods such as heating by providing a jacket to the polymerization reactor, heating by providing an internal coil to the polymerization reactor, and heating by providing a heat exchanger outside the polymerization reactor and circulating the liquid are used. 3 Heat transfer area (m²) relative to ) 2 From the viewpoint of producing high-quality, uncolored polycarbonate, it is preferable that the ratio of ) be in the range of 1 to 70.

[0018] Polymerization reactor 1 has a supply port 11 for supplying reaction materials into the reactor. When the reaction materials are reacted in polymerization reactor 1, vapor containing the hydroxyaryl compound is discharged from the system of polymerization reactor 1 through a vapor outlet 12. The vapor generated by the reaction is supplied to scrubber 2 from the vapor outlet 12.

[0019] The polymerization reactor 1 has a discharge pump 13 for extracting the polycarbonate produced. The discharge pump 13 may be a gear pump capable of quantitatively discharging high-viscosity substances, and the material of these gears may be stainless steel or other special metals.

[0020] In Scrubber 2, the exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from polymerization reactor 1 is brought into contact with a washing liquid. A "scrubber" is a device that separates components from a gas by bringing a gas and a liquid into contact.

[0021] Scrubber 2 has a spray nozzle 21 for the cleaning liquid near the top of the tower and packing material 22 installed below it. The cleaning liquid introduced from the spray nozzle 21 is sprayed inside the scrubber and supplied to the packing material 22. On the other hand, scrubber 2 has an exhaust steam inlet 23 at the bottom of the tower. The exhaust steam introduced from the inlet 23 comes into contact with the cleaning liquid inside the packing material 22, and diaryl carbonates and dihydroxy compounds are separated from the exhaust steam. By providing this scrubber 2, substances with higher boiling points than aromatic monohydroxy compounds distilled from the polymerization reactor, especially dihydroxy compounds, can be returned to the polymerization reactor, thereby reducing raw material loss. After being cleaned inside scrubber 2, the exhaust steam is discharged from the exhaust steam outlet 24. The exhaust steam treated in scrubber 2 is supplied to the condenser 3 from the exhaust steam outlet 24.

[0022] The packing material used here may be either a regular packing material or an irregular packing material, but an irregular packing material is preferred. Examples of such packing materials include Raschig rings, Lessing rings, Pall rings, Berl saddles, Interox saddles, Dixon packing, McMahon packing, Helipak, Cascade Mini rings, and Raschig Super rings.

[0023] The scrubber 2 may have a demister 25 above the spray nozzle 21. The demister 25 separates the droplets that are carried along with the spray. When the exhaust vapor comes into contact with the cleaning liquid, fine liquid particles are generated, and these fine particles rise on the exhaust vapor. Here, if demisters are installed in the flow path, the flow path of the exhaust vapor becomes complex, so the light exhaust vapor easily passes through the mesh space between the demisters, but in comparison, the heavier liquid droplets cannot change their flow path quickly due to inertia, and deviate from the flow path of the exhaust vapor and collide with the demisters. The liquid droplets that collide with the demisters adhere to the demisters due to surface tension, gradually gather and become coarser, descend along the demisters and rejoin the liquid phase.

[0024] In condenser 3, the exhaust steam washed by scrubber 2 is condensed. A reflux condenser may also be used as condenser 3. Condenser 3 condenses the exhaust steam washed by scrubber 2 and recovers hydroxyaryl compounds. Condenser 3 is connected to a circulation channel 31, and a portion of the condensate is supplied into the condenser. In this way, condenser 3 cleans the inside of condenser 3 by circulating a portion of the condensate.

[0025] The supply channel 4 supplies at least a portion of the scrubber bottom liquid to the polymerization reactor 1. The supply channel 4 has a transfer pump 41. Although not shown, the supply channel 4 may also have a flow control valve. By supplying at least a portion of the scrubber bottom liquid to the polymerization reactor 1, the dihydroxy compounds and diaryl carbonates contained in the bottom liquid are recycled, and the amount of raw material loss can be reduced.

[0026] The polycarbonate production apparatus may have a supply channel 5 for supplying the bottom liquid of the condenser 3 as a washing liquid for the scrubber 2. Having a supply channel 5 allows the hydroxyaryl compound obtained by the coagulator 3 to be reused as a washing liquid.

[0027] Supply channel 6 resupplies the bottom liquid of the scrubber to scrubber 2 as a washing liquid. Although not shown in the diagram, supply channel 6 may have a flow rate control valve. By reusing at least a portion of the bottom liquid of the scrubber as a washing liquid for scrubber 2, dihydroxy compounds and diaryl carbonates are recycled, and the amount of raw material loss can be reduced.

[0028] There are no particular restrictions on the material of piping and other components in polycarbonate manufacturing equipment. Typically, these are selected from metals such as stainless steel, carbon steel, Hastelloy, nickel, titanium, chromium, and other alloys, as well as highly heat-resistant polymer materials. Furthermore, the surfaces of these materials may be subjected to various treatments as needed, such as plating, lining, passivation, acid cleaning, and phenol cleaning. Preferred materials include stainless steel, nickel, and glass lining, with stainless steel being particularly preferred. For molten polycarbonate or polycarbonate discharge pumps, gear pumps capable of quantitatively discharging high-viscosity substances are generally preferred. The material of these gears may be stainless steel or other special metals.

[0029] A single polymerization reactor is sufficient, but it is also possible to use two or more reactors in combination. Figure 2 is a schematic diagram of a polycarbonate manufacturing apparatus according to another embodiment. For the polycarbonate manufacturing apparatus according to the other embodiment, components common to the above-described embodiment are denoted by the same reference numerals and their descriptions are omitted. This polycarbonate manufacturing apparatus has two polymerization reactors. Components related to the second polymerization reactor are denoted by the same reference numerals as components of the first polymerization reactor, and to clearly indicate that they are components of the second apparatus, a "'" is added to the reference numerals and their descriptions are omitted.

[0030] Next, the method for producing polycarbonate according to this embodiment will be explained using the polycarbonate manufacturing apparatus described above as an example.

[0031] <Polymerization process> In the polymerization process, a dihydroxy compound and a diaryl carbonate, or prepolymers thereof, are polymerized in a polymerization reactor.

[0032] (Dihydroxy compound) Examples of the dihydroxy compound include aromatic dihydroxy compounds and aliphatic dihydroxy compounds.

[0033] The aromatic dihydroxy compound is, for example, a compound represented by the following formula. HO-Ar-OH (In the formula, Ar represents a divalent aromatic group.)

[0034] The divalent aromatic group is, for example, a group represented by the following formula. -Ar 1 -Y-Ar 2 - (In the formula, Ar 1 and Ar 2 each independently represent 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.)

[0035] The divalent aromatic group, Ar 1 , Ar 2 may be those in which one or more hydrogen atoms are substituted by other substituents that do not adversely affect the reaction, such as a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a phenyl group, a phenoxy group, a vinyl group, a cyano group, an ester group, an amide group, a nitro group, etc. Preferred specific examples of the heterocyclic aromatic group include aromatic groups having one or more ring-forming nitrogen atoms, oxygen atoms or sulfur atoms. The divalent aromatic group Ar 1 , Ar 2 represents, for example, groups such as substituted or unsubstituted phenylene, substituted or unsubstituted biphenylene, substituted or unsubstituted viridylene, etc. The substituents here are as described above.

[0036] The divalent alkylene group Y is, for example, a group represented by the following formula.

[0037] [ka]

[0038] In the formula, R 1 , R 2 , R 3 , R 4 Each of these independently represents hydrogen, a C1-C10 alkyl group, a C1-C10 alkoxy group, a cycloalkyl group with 5-C10 ring configurations, a carbocyclic aromatic group with 5-C10 ring configurations, and a carbocyclic aralkyl group with 6-C10 ring configurations. k represents an integer from 3 to 11, and R 5 and R 6 Each X is individually selected and independently represents hydrogen or an alkyl group having 1 to 6 carbon atoms, where X represents carbon. 1 , R 2 , R 3 , R 4 , R 5 and R 6 In this case, one or more hydrogen atoms may be substituted with other substituents, such as halogen atoms, C1-C10 alkyl groups, C1-C10 alkoxy groups, phenyl groups, vinyl groups, cyano groups, ester groups, amide groups, nitro groups, etc., as long as they do not adversely affect the reaction.

[0039] Examples of such divalent aromatic groups Ar include the group represented by the following formula.

[0040] [ka]

[0041] In the formula, R 7 , R 8 Each of these independently represents a hydrogen atom, a halogen atom, a C1-C10 alkyl group, a C1-C10 alkoxy group, a cyclic alkyl group with 5-C10 ring structures, or a phenyl group. m and n are integers from 1 to 4, and when m is 2 to 4, each R 7 These may be the same or different, and when n is 2 to 4, each R 8These may be the same or different.

[0042] The divalent aromatic group Ar may be a group represented by the following formula. -Ar 1 -Z-Ar 2 - (In the formula, Ar 1 Ar 2 As mentioned above, Z is a single bond or -O-, -CO-, -S-, -SO2-, -SO-, -COO-, -CON(R 1 )- represents a divalent group such as R. 1 (As mentioned above.)

[0043] Examples of such divalent aromatic groups Ar include the group represented by the following formula.

[0044] [ka]

[0045] In the formula, R 7 , R 8 m and n are as described above.

[0046] Specific examples of divalent aromatic groups Ar include substituted or unsubstituted phenylene, substituted or unsubstituted naphthylene, and substituted or unsubstituted pyridylene.

[0047] The aromatic dihydroxy compound may be a single compound or two or more compounds. Among these aromatic dihydroxy compounds, bisphenol A is preferred. It is preferable to use a high-purity bisphenol A for polycarbonate with a chlorine content of 1 ppb or less. Furthermore, a trivalent aromatic trihydroxy compound may be used in combination to introduce a branched structure.

[0048] (Diaryl carbonate) Diaryl carbonates are preferably compounds represented by the following formula. [ka] (In the above formula, Ar'' represents a monovalent aromatic group having 5 to 20 carbon atoms.)

[0049] Examples of monovalent aromatic groups include phenyl group, methylphenyl group, dimethylphenyl group, trimethylphenyl group, ethylphenyl group, diethylphenyl group, triethylphenyl group, butylphenyl group, dibutylphenyl group, and tributylphenyl group.

[0050] These diaryl carbonates may be used individually or in combination of two or more types.

[0051] Among these diaryl carbonates, symmetrical diaryl carbonates such as unsubstituted diphenyl carbonate, ditolyl carbonate, and lower alkyl-substituted diphenyl carbonate such as di-t-butylphenyl carbonate are preferred, but diphenyl carbonate, which has the simplest structure, is particularly preferred. These diaryl carbonates may be used individually or in combination of two or more. Diphenyl carbonate is preferably used in combination with bisphenol A as a hydroxyl compound, from the viewpoint of recovering dihydroxy compounds from the vapor discharged from the polymerization reactor and reducing losses.

[0052] While diphenyl carbonate is not particularly limited, it is preferable to use distilled dimethyl carbonate produced by reacting methanol with ethylene carbonate, which is produced by reacting ethylene oxide with CO2, and phenol. Furthermore, it is preferable that the diphenyl carbonate is an ultra-high purity product that does not contain alkali metals, alkaline earth metals, or chlorine.

[0053] The ratio of dihydroxy compounds to diaryl carbonates used (compound ratio) varies depending on the type of aromatic dihydroxy compound and diaryl carbonate used, as well as the polymerization temperature and other polymerization conditions. Diaryl carbonates are typically used in a ratio of 0.9 to 2.5 moles, preferably 0.95 to 2.0 moles, and more preferably 0.98 to 1.5 moles per mole of aromatic dihydroxy compound.

[0054] In the polycarbonate production method according to this embodiment, a prepolymer may be used as a raw material. The prepolymer is a condensate of a dihydroxy compound and a diaryl carbonate. The ratio of its use (preparation ratio) is the same as the ratio of the dihydroxy compound and diaryl carbonate used (preparation ratio) described above. The average degree of polymerization of the prepolymer is not particularly limited, but for example, it is 2 to 2,000.

[0055] (catalyst) The polymerization process can be carried out without a catalyst, but it may be carried out in the presence of a catalyst to increase the polymerization rate. The catalyst is not particularly limited, but examples include: alkali metal and alkaline earth metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide; alkali metal salts, alkaline earth metal salts, and quaternary ammonium salts of boron and aluminum hydrides such as lithium aluminum hydride, sodium borohydride, and tetramethylammonium borohydride; alkali metal and alkaline earth metal hydrogen compounds such as lithium hydride, sodium hydride, and calcium hydride; alkali metal and alkaline earth metal alkoxides such as lithium methoxide, sodium ethoxide, and calcium methoxide; lithium phenoxide, sodium phenoxide, magnesium phenoxide, LiO-Ar-OLi, and NaO-Ar-O Examples of catalysts include: allyloxides of alkali metals and alkaline earth metals such as Na (Ar is an aryl group); organic acid salts of alkali metals and alkaline earth metals such as lithium acetate, calcium acetate, and sodium benzoate; zinc compounds such as zinc oxide, zinc acetate, and zinc phenoxide; tin compounds such as boron oxide, boric acid, sodium borate, trimethyl borate, tributyl borate, triphenyl borate, tin oxide, dialkyltin oxide, dialkyltin carboxylate, tin acetate, and ethyltin tributoxide, as well as tin compounds bonded to alkoxy or allyloxy groups, and organotin compounds; lead compounds such as lead oxide, lead acetate, lead carbonate, basic carbonates, lead, and alkoxides or allyloxides of organoleads; and quaternary ammonium salts and quaternary phosphonium salts. These catalysts may be used individually or in combination of two or more.

[0056] The amount of catalyst used is typically 10 times the amount of the dihydroxy compound used as a raw material. -10 ~1% by mass, preferably 10% -9 ~10 -1 Mass%, more preferably 10 -8 ~10 -2 It is within the range of mass percent.

[0057] The raw materials used in the polymerization process are preferably a mixture melted and mixed at a temperature of 100°C to 250°C, preferably 140°C to 200°C. Depending on the melting and mixing conditions, the reaction between the dihydroxy compound and diaryl carbonate may proceed partially. There are no particular restrictions on the reaction rate of the dihydroxy compound in the melted mixture, but it is usually in the range of 0.001 to 95%, preferably 20 to 85%.

[0058] In the polymerization process, it is preferable to polymerize a dihydroxy compound with a diaryl carbonate to produce a polycarbonate with a number average molecular weight of 5000 or less. By keeping the molecular weight within this range, the reaction pressure in the polymerization reactor shown in the polymerization process can be maintained appropriately, and the amount of inert gas shared can be used within an appropriate range without becoming excessively large. The number average molecular weight of the polycarbonate produced is preferably 350 to 4000.

[0059] The temperature of the polymerization reactor is preferably 120 to 320°C, more preferably 160 to 300°C, and even more preferably 180 to 280°C.

[0060] As the reaction progresses, aromatic monohydroxy compounds are generated. These are distilled off as vapor, introduced into a condenser for condensation, and then removed from the reaction system, thereby increasing the reaction rate. The reaction pressure in the polymerization reactor varies depending on the type and molecular weight of the polycarbonate being produced, the polymerization temperature, etc. For example, when producing polycarbonate from a molten mixture of bisphenol A and diphenyl carbonate, the pressure is usually in the range of 670 Pa (5 mmHg) to atmospheric pressure when the number average molecular weight is 1500 or less, and 4000 Pa (30 mmHg) or less when the number average molecular weight is 1500 to 5000. As mentioned above, lowering the reaction pressure intensifies foaming in the polymerization tank, so a pressure of 2670 Pa (20 mmHg) or higher is particularly preferred. A method of carrying out the reaction under reduced pressure and while introducing the aforementioned inert gas is also preferably used.

[0061] The hydroxyaryl compound distilled from the polymerization reactor may contain compounds with higher boiling points than the compound itself, such as dihydroxy compounds, due to droplet entrainment. In this embodiment, in order to reduce the droplet entrainment of dihydroxy compounds in the hydroxyaryl compound, a washing step is provided between the polymerization reaction step and the condensation step in which the vapor is washed with a scrubber.

[0062] <Washing process> In the washing process, exhaust vapors containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from the polymerization reactor in the polymerization process are brought into contact with a washing solution in a scrubber. By bringing the exhaust vapor into contact with the washing solution, diaryl carbonates and dihydroxy compounds can be separated from the exhaust vapor and recovered from the bottom of the scrubber column.

[0063] (Cleaning solution) The cleaning solution is not particularly limited, but it is preferably a liquid composition mainly composed of diaryl carbonate. Here, "main component" refers to a component that makes up more than 50% by mass. The diaryl carbonate is preferably the same compound as the diaryl carbonate used in the polymerization process.

[0064] The washing solution may contain a dihydroxy compound. Preferably, the dihydroxy compound is the same compound used in the polymerization process. The content of the dihydroxy compound is not particularly limited, but may be 1-50% by mass, 3-40% by mass, or 5-30% by mass.

[0065] The washing solution may contain a hydroxyaryl compound. Preferably, the hydroxyaryl compound is a hydroxyaryl compound that is detached by polymerization from the diaryl carbonate used in the polymerization process. The content of the hydroxyaryl compound is not particularly limited, but may be 1 to 40% by mass, 3 to 30% by mass, or 5 to 20% by mass.

[0066] At least a portion of the condensate from the exhaust steam of the condensation process described later may be used as the washing liquid in the washing process. By using the condensate as the washing liquid, the temperature of the washing liquid can be lowered, and diaryl carbonates and dihydroxy compounds can be recovered efficiently.

[0067] The mass ratio of the condensate from the condensation process to the cleaning process as a cleaning liquid is preferably 0.1 to 1, more preferably 0.2 to 0.7, and even more preferably 0.2 to 0.5, relative to the amount of discharged steam at the cleaning process inlet. The amount of discharged steam at the cleaning process inlet refers to the amount of discharged steam introduced into the scrubber.

[0068] It is preferable to supply the bottom liquid of the scrubber in the washing process as the washing liquid and reuse it as the washing liquid. The bottom liquid contains the components of the washing liquid, as well as hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds recovered from the exhaust steam. By reusing the bottom liquid of the scrubber in the washing process as the washing liquid, resources can be effectively utilized and diaryl carbonates and dihydroxy compounds can be recovered efficiently.

[0069] The mass ratio of the scrubber bottom liquid supplied to the cleaning process as the cleaning liquid in the cleaning process is preferably 0.1 to 10, more preferably 0.5 to 7, and even more preferably 1 to 5, relative to the amount of discharged steam at the cleaning process inlet. The amount of discharged steam at the cleaning process inlet refers to the amount of discharged steam introduced into the scrubber.

[0070] (bottom liquid) The bottom liquid of the scrubber in the washing process is a liquid composition that comes into contact with the exhaust vapor and accumulates at the bottom of the scrubber. The diaryl carbonate content in the bottom liquid is preferably 20% to 90% by mass, more preferably 40% to 90% by mass, and even more preferably 60% to 90% by mass.

[0071] The scrubber in the washing process preferably has irregular packing. In the washing process, by passing the exhaust steam through the irregular packing and bringing it into contact with the washing solution, the recovery rate of diaryl carbonates and dihydroxy compounds in the exhaust steam can be increased, and the amount of dihydroxy compound loss can be reduced more significantly.

[0072] In the washing process, it is preferable to separate droplets containing airborne particles using a demister. After contact with the washing solution, the discharged vapor may contain droplets containing airborne particles. These droplets may also contain diaryl carbonates and dihydroxy compounds, and separating these droplets with a demister can increase the recovery rate of these compounds.

[0073] The void ratio of the demister is preferably 95 vol% to 99 vol%, more preferably 97 vol% to 99 vol%, and even more preferably 98 vol% to 99 vol%. The "void ratio of the demister" is the ratio of the volume of space to the total volume of the demister.

[0074] In the condensation step, the exhaust vapor that has been washed in the washing step is condensed. The exhaust vapor that has been washed in the washing step contains hydroxyaryl compounds, which are condensed into a liquid in the condensation step. In the manufacturing method according to this embodiment, because a washing step is included, diaryl carbonates and dihydroxy compounds that can be reused in polymerization reactions are separated from the exhaust vapor, thus reducing the amount of loss of these compounds. In addition, since a highly pure hydroxyaryl compound is obtained in the condensation step, a liquid composition that can be easily reused for the production of diaryl carbonates and the like is obtained.

[0075] In the polycarbonate production method according to this embodiment, at least a portion of the bottom liquid of the scrubber in the washing step is supplied to the polymerization reactor. This allows for the reuse of diaryl carbonate and dihydroxy compounds recovered in the washing step in the polymerization step, thereby increasing the efficiency of raw material utilization.

[0076] The above steps may be performed sequentially, but it is preferable that they be performed continuously and simultaneously.

[0077] Furthermore, the polycarbonate produced by the polycarbonate manufacturing apparatus described above may be sent to the post-polymerization process described later to produce high molecular weight polycarbonate.

[0078] <Post-polymerization process> In the post-polymerization step, the polycarbonate obtained in the above polymerization step is further polymerized to produce polycarbonate with a higher degree of polymerization. The number-average molecular weight of the polycarbonate produced in the post-polymerization step is usually 500 to 100,000, preferably 2,000 to 30,000. There are no particular restrictions on the polymerization reactor used in the post-polymerization step, but a polymerization reactor with a large surface area for evaporating by-products such as hydroxyaryl compounds is preferred. Specifically, thin-film polymerization reactors, centrifugal thin-film evaporation polymerization reactors, surface-renewal twin-screw kneading polymerization reactors, twin-screw horizontal stirring polymerization reactors, wet-wall polymerization reactors, porous plate polymerization reactors that polymerize while the polymer is free-falling, and polymerization reactors that allow polymerization to proceed by melting and dropping the polymer along a support, such as a wire-equipped porous plate polymerization reactor, are used, and polymerization reactors using these individually or in combination are employed. In the post-polymerization step, multiple of the above-mentioned production apparatuses may be combined for polymerization. In the post-polymerization step, it is preferable to allow polymerization to proceed by melting and dropping the polymer along a support.

[0079] 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 high molecular weight polycarbonate, the reaction pressure in the post-polymerization step is preferably 267 Pa (2 mmHg) or less.

[0080] The reaction temperature for the postpolymerization step is usually selected within the range of 50 to 350°C, preferably 100 to 290°C.

[0081] In the polycarbonate manufacturing apparatus of this embodiment, when manufacturing polycarbonate, a known catalyst deactivator described in, for example, International Publication No. 2005 / 121213 may be used. The amount of catalyst deactivator used is preferably 0.5 to 50 moles per mole of transesterification catalyst, more preferably 0.5 to 10 moles, and even more preferably 0.8 to 5 moles. The catalyst deactivator is added, for example, in the extruder.

[0082] (Polycarbonate) The polycarbonate obtained by the method for producing polycarbonate according to this embodiment has, for example, repeating units represented by the following formula. [ka] (Ar is the same as the definition above.)

[0083] The polycarbonate is preferably one in which 85 mol% or more of the repeating units represented by the following formula are present in the total repeating units. [ka]

[0084] The terminal groups of polycarbonate are usually hydroxyl groups, or aryl carbonate groups represented by the following formula. [ka] (In the formula, Ar 5 This is the same definition as Ar'' mentioned above.

[0085] There are no particular restrictions on the ratio of hydroxyl groups to aryl carbonate groups, but it 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. Particularly preferred is a polycarbonate in which the proportion of phenyl carbonate groups in the terminal groups is 85 mol% or more.

[0086] Polycarbonate may consist of multiple polycarbonate main chains, and these multiple polycarbonate main chains as a whole may be partially branched, with each chain being linked to at least one side chain via a type of branching selected from the group consisting of ester bonds and ether bonds.

[0087] [Collection Method] The method for producing polycarbonate according to this embodiment has been described above. From another perspective, the method for producing polycarbonate according to this embodiment is also a method for recovering dihydroxy compounds. The method for recovering dihydroxy compounds according to this embodiment is: A washing step in which exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from a polymerization reactor that polymerizes dihydroxy compounds and diaryl carbonates, or prepolymers thereof, is brought into contact with a washing solution in a scrubber, The process includes a condensation step of condensing the exhaust steam that has been cleaned by the cleaning step. According to the recovery method of this embodiment, dihydroxy compounds can be recovered from the vapor discharged from the polymerization reactor, thereby reducing the amount of loss of said dihydroxy compounds. The washing and condensing processes are as described above, so their explanation will be omitted. [Examples]

[0088] The embodiment will be described in more detail below with reference to examples, but this embodiment is not limited to the following examples.

[0089] [Example 1] The apparatus shown in Figure 2 was used. Bisphenol-A (BPA) was used as the dihydroxy compound, and diphenyl carbonate (DPC) was used as the diaryl carbonate. Polymerization reactor 1 was operated at 220°C / 70 mmHg. Scrubber 2 was made of stainless steel and had one theoretical stage.

[0090] Process steam from the preceding polymerization reactor 1 was introduced into the bottom of scrubber 2 at a flow rate of 8900 kg / hour. Diaryl carbonate was used as the washing liquid in scrubber 2. The process steam from the top of scrubber 2 was 10650 kg / hour and was introduced into condenser 3. The process liquid flow rate at the bottom of scrubber 2 was 16250 kg / hour, and the process liquid composition was 80 wt% by DPC mass. Of this, 250 kg / hour was introduced into polymerization reactor 1, and 16000 kg / hour was introduced again into the top of scrubber 2 as washing liquid. The process liquid flow rate at the bottom of condenser 3 was 10650 kg / hour, of which 8650 kg / hour was withdrawn, and 2000 kg / hour was introduced again into the top of scrubber 2 as washing liquid. In condenser 3, the withdrawn process liquid had a BPA concentration of 20 ppm by mass. From these results, it was found that the amount of dihydroxy compound loss could be reduced.

[0091] The subsequent polymerization reactor 1' was operated at 270°C / 32mmHg. Scrubber 2' was made of stainless steel and had one theoretical stage.

[0092] Process vapor from polymerization reactor 1' was introduced into the bottom of scrubber 2' at a flow rate of 1380 kg / hour. Process vapor from the top of scrubber 2' was introduced into condenser 3' at a flow rate of 1830 kg / hour. The process liquid flow rate at the bottom of scrubber 2' was 4050 kg / hour, and the process liquid composition was 90% DPC by mass ratio. Of this, 50 kg / hour was introduced into polymerization reactor 1', and 4000 kg / hour was reintroduced to the top of scrubber 2' as washing liquid. The process liquid flow rate at the bottom of condenser 3' was 1830 kg / hour, of which 1330 kg / hour was withdrawn, and 500 kg / hour was reintroduced to the top of scrubber 2' as washing liquid. In condenser 3', the withdrawn process liquid had a BPA concentration of 40 ppm by mass. From these results, it was found that the amount of dihydroxy compound loss can be reduced.

[0093] [Example 2] The apparatus shown in Figure 1 was used. Bisphenol-A (BPA) was used as the dihydroxy compound, and diphenyl carbonate (DPC) was used as the diaryl carbonate. Polymerization reactor 1 was operated at 220°C / 70 mmHg. Scrubber 2 was made of stainless steel and had one theoretical stage.

[0094] Process steam from the preceding polymerization reactor 1 was introduced into the bottom of scrubber 2 at a flow rate of 8670 kg / hour. Process steam from the top of scrubber 2 flowed at 9850 kg / hour and was introduced into condenser 3. The process liquid flow rate at the bottom of scrubber 2 was 2820 kg / hour, and the process liquid composition had a DPC content of 30 wt%. Of this, 20 kg / hour was introduced into polymerization reactor 1, and 2800 kg / hour was introduced back into the top of scrubber 2 as a washing liquid. The process liquid flow rate at the bottom of condenser 3 was 9850 kg / hour, of which 8650 kg / hour was withdrawn, and 1200 kg / hour was introduced back into the top of scrubber 2 as a washing liquid. In condenser 3, the withdrawn process liquid had a BPA concentration of 2000 ppm by mass. From these results, it was found that the amount of dihydroxy compound loss could be reduced.

[0095] The subsequent polymerization reactor 1' was operated at 270°C / 32mmHg. Scrubber 2' was made of stainless steel and had one theoretical stage. Process vapor from polymerization reactor 1' was introduced into the bottom of scrubber 2' at a flow rate of 1340 kg / hour. Process vapor from the top of scrubber 2' was introduced into condenser 3' at a flow rate of 1660 kg / hour. The process liquid flow rate at the bottom of scrubber 2' was 710 kg / hour, and the process liquid composition was 20% DPC by mass ratio. Of this, 10 kg / hour was introduced into polymerization reactor 1', and 700 kg / hour was reintroduced to the top of scrubber 2' as washing liquid. The process liquid flow rate at the bottom of condenser 3' was 1660 kg / hour, of which 1330 kg / hour was withdrawn, and 330 kg / hour was reintroduced to the top of scrubber 2' as washing liquid. In condenser 3', the withdrawn process liquid had a BPA concentration of 4000 ppm by mass. From these results, it was found that the amount of dihydroxy compound loss could be reduced.

[0096] [Example 3] The apparatus shown in Figure 1 was used. Bisphenol-A (BPA) was used as the dihydroxy compound, and diphenyl carbonate (DPC) was used as the diaryl carbonate. Polymerization reactor 1 was operated at 220°C / 70 mmHg. Scrubber 2 was made of stainless steel and had one theoretical stage.

[0097] Process steam from polymerization reactor 1 was introduced into the bottom of scrubber 2 at a flow rate of 10,500 kg / hour. Process steam from the top of scrubber 2 flowed at 12,650 kg / hour and was introduced into condenser 3. The process liquid flow rate at the bottom of scrubber 2 was 33,850 kg / hour, and the process liquid composition was 60% DPC by mass ratio. Of this, 1,850 kg / hour was introduced into polymerization reactor 1, and 32,000 kg / hour was introduced back into the top of scrubber 2 as washing liquid. The process liquid flow rate at the bottom of condenser 3 was 12,650 kg / hour, of which 8,650 kg / hour was withdrawn, and 4,000 kg / hour was introduced back into the top of scrubber 2 as washing liquid. In condenser 3, the withdrawn process liquid had a BPA concentration of 1 ppm by mass. From these results, it was found that the amount of dihydroxy compound loss could be reduced.

[0098] Polymerization reactor 1' was operated at 270°C / 32 mmHg. Scrubber 2' was made of stainless steel and had one theoretical stage.

[0099] Process steam from polymerization reactor 1' was introduced into the bottom of scrubber 2' at a flow rate of 1560 kg / hour. Process steam from the top of scrubber 2' was introduced into condenser 3' at a flow rate of 2030 kg / hour. The process liquid flow rate at the bottom of scrubber 2' was 8230 kg / hour, and the process liquid composition was 90% DPC by mass ratio. Of this, 230 kg / hour was introduced into polymerization reactor 1', and 8000 kg / hour was introduced again to the top of scrubber 5 as washing liquid. The process liquid flow rate at the bottom of condenser 3' was 2030 kg / hour, of which 1330 kg / hour was withdrawn, and 700 kg / hour was introduced again to the top of scrubber 2' as washing liquid. In condenser 3', the withdrawn process liquid had a BPA concentration of 5 ppm by mass. From these results, it was found that the amount of dihydroxy compound loss could be reduced.

[0100] [Comparative Example 1] The apparatus shown in Figure 3 was used. The apparatus shown in Figure 3 does not have a scrubber 2, and components common to the polycarbonate manufacturing apparatus according to this embodiment are denoted by the same symbols and their explanations are omitted.

[0101] BPA was used as the dihydroxy compound and DPC as the diaryl carbonate. Polymerization reactor 1 was operated at 220°C / 70 mmHg. Polymerization reactor 2 was operated at 270°C / 32 mmHg.

[0102] Process steam was introduced into condenser 3 at a flow rate of 8650 kg / hour. The process liquid flow rate at the bottom of condenser 3 was 8650 kg / hour, and the extracted process liquid had a BPA concentration of 4000 ppm by mass.

[0103] Process steam was introduced into condenser 3' at a flow rate of 1330 kg / hour. The process liquid flow rate at the bottom of condenser 3' was 1330 kg / hour, and the extracted process liquid had a BPA concentration of 9000 ppm by mass. [Industrial applicability]

[0104] The method for producing polycarbonate according to this embodiment has industrial applicability in the field of polycarbonate production. [Explanation of Symbols]

[0105] 1, 1' polymerization reactor 2, 2' Scrubber 3, 3' condenser 4, 4', 5, 5', 6, 6' supply path 13, 13' Discharge pump 22, 22' filling 25, 25' Demista

Claims

1. A polymerization step in which a dihydroxy compound and diaryl carbonate, or a prepolymer thereof, is polymerized in a polymerization reactor, A washing step in which exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from the polymerization reactor in the polymerization step is brought into contact with a washing solution in a scrubber, The process includes a condensation step for condensing the exhaust steam that has been cleaned by the cleaning step, At least a portion of the bottom liquid of the scrubber in the washing step is supplied to the polymerization reactor. A method for manufacturing polycarbonate.

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

3. The method for producing polycarbonate according to claim 2, wherein the mass ratio of the liquid supplied to the washing process as a washing liquid from the condensate from the condensation process is 0.1 or more and 1 or less with respect to the amount of steam discharged at the inlet of the washing process.

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

5. The method for producing polycarbonate according to claim 4, wherein the mass ratio of the liquid supplied to the washing process as the washing liquid from the bottom liquid of the scrubber in the washing process is 0.1 or more and 10 or less with respect to the amount of steam discharged at the inlet of the washing process.

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

7. A method for producing polycarbonate according to any one of claims 1 to 6, wherein the scrubber in the washing step comprises irregular fillers.

8. A method for producing polycarbonate according to any one of claims 1 to 6, wherein in the washing step, droplets containing airborne particles are separated by a demister.

9. A method for producing polycarbonate according to claim 8, wherein the void ratio of the demister is 95 vol% to 99 vol%.

10. The method for producing polycarbonate according to claim 1, wherein the dihydroxy compound comprises bisphenol A.

11. The method for producing a polycarbonate according to claim 10, wherein the diaryl carbonate includes diphenyl carbonate.

12. A washing step in which exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from a polymerization reactor that polymerizes dihydroxy compounds and diaryl carbonates, or prepolymers thereof, is brought into contact with a washing solution in a scrubber, The process includes a condensation step for condensing the exhaust steam that has been cleaned by the cleaning step, A method for recovering dihydroxy compounds.

13. A polymerization reactor for polymerizing dihydroxy compounds and diaryl carbonates, or prepolymers thereof, A scrubber that brings the exhaust vapor containing hydroxyaryl compounds, diaryl carbonates, and dihydroxy compounds discharged from the polymerization reactor into contact with a washing liquid, A condenser for condensing the exhaust steam washed by the scrubber, A supply channel for supplying at least a portion of the bottom liquid of the scrubber to the polymerization reactor, A manufacturing apparatus for polycarbonate containing [a specific substance].

Images