A method for hydrolytic recovery of bisphenol a from polycarbonate

Abstract

The present application provides a method for recycling bisphenol A from polycarbonate. The method comprises the following steps: (1) dissolving polycarbonate material in an organic solvent to obtain solution X; (2) mixing bisphenol A monomer, alkali and water to obtain solution Y; (3) mixing solution X and solution Y, shearing to obtain a uniform emulsion, and transferring into a reactor for hydrolysis reaction; (4) demulsifying and separating the reaction liquid to obtain water phase and oil phase, wherein the water phase is an aqueous solution containing bisphenol A. The aqueous solution containing bisphenol A obtained by the method can be directly used for the synthesis of polycarbonate by interfacial phosgene method, and the remaining oil phase is concentrated by distillation and returned to solution X, mixed with solution Y to prepare an emulsion. Under the condition that the reaction system is recycled less than 5 times, the hydrolysis rate of solid polycarbonate waste can reach more than 50%. The whole reaction process is carried out in a non-catalyst and non-high-temperature environment. The bisphenol A solution produced by hydrolysis can be directly applied to the synthesis of polycarbonate, which reduces the production cost of the material and has considerable economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the technical field of extracting bisphenol A from waste polycarbonate, specifically relating to a method for completing the alkaline hydrolysis of polycarbonate materials under mild conditions without adding a catalyst. Background Technology

[0002] Polycarbonate (PC) materials possess excellent impact resistance and good optical properties, which makes them widely used in the construction, automotive, and electronics industries. As one of the three major engineering plastics, it has gradually become one of the top-consumed engineering plastic products globally in recent years. However, the large-scale use of this material has also brought about the problem of waste polycarbonate disposal. Currently, the best solution for this type of material is the alcoholysis method to recover bisphenol A monomers from waste PC.

[0003] For example, Liu Yaoyuan et al. (Plastics Technology, 2014, 42(3):74-77) reported a method for recovering bisphenol A (BPA) from optical disc-grade PC by methanol alcoholysis. Although this process can effectively degrade PC, it requires a large amount of strong alkali as a catalyst, which corrodes the equipment, generates a large amount of wastewater, and the catalyst cannot be recycled. In addition, the alcoholysis process often occurs at high temperatures, and the increased temperature inevitably affects the stability of bisphenol A. Furthermore, the residue of small molecule alcohols will also have a certain impact on the application of bisphenol A-synthesized polycarbonate materials in the optical field.

[0004] Ionic liquids can also be used as catalysts and reaction media to catalyze the methanolysis of waste PC. This method overcomes the technical problems of consuming large amounts of high-concentration inorganic strong acids / bases that cannot be reused. However, the synthesis of ionic liquids is complicated, costly, and requires large quantities. Although ionic liquids are novel green solvents, their greenness lies in their lack of significant vapor pressure, good thermal stability, and safe operation. However, the synthesis, purification, and recovery processes of ionic liquids all use large amounts of volatile organic solvents. As catalysts or solvents, some ionic liquids will eventually be lost into the environment, causing varying degrees of environmental impact.

[0005] Therefore, it is of great significance to find a polycarbonate decomposition method with mild reaction conditions and minimal impurity introduction to improve the shortcomings of existing processes and realize the chemical recycling of waste polycarbonate materials. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, the present invention aims to provide a method for recovering bisphenol A from polycarbonate (PC) by hydrolysis. The method involves hydrolyzing the PC polymer under mild conditions of room temperature and atmospheric pressure / without a catalyst to obtain an aqueous solution containing bisphenol A. This aqueous solution does not contain impurities such as inorganic salts and can be directly applied to the interfacial polycondensation method for the synthesis of polycarbonate.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for recovering bisphenol A by hydrolysis of polycarbonate, the method comprising the following steps:

[0009] (1) Dissolve the polycarbonate material in an organic solvent to obtain solution X;

[0010] (2) Mix bisphenol A monomer, alkali and water to obtain solution Y;

[0011] (3) Mix solution X and solution Y, and after shearing, obtain a homogeneous emulsion, which is then transferred to a reactor for hydrolysis reaction;

[0012] (4) The reaction solution is demulsified and separated to obtain an aqueous phase and an oil phase, wherein the aqueous phase is an aqueous solution containing bisphenol A.

[0013] In one embodiment, the polycarbonate material in step (1) is selected from polymers whose molecular chains contain bisphenol A type carbonate structural units, preferably polymers whose molecular chains contain only bisphenol A type carbonate structural units; more preferably, the molecular chain refers to the main chain.

[0014] In a preferred embodiment, the average molecular weight of the polycarbonate material is 2000-40000 g / mol, including but not limited to 2000 g / mol, 5000 g / mol, 10000 g / mol, 15000 g / mol, 20000 g / mol, 25000 g / mol, 30000 g / mol, 35000 g / mol, 40000 g / mol, or any combination thereof;

[0015] Specifically, the polycarbonate material can be a homopolymer having repeating bisphenol A type carbonate structural units, or a copolymer containing repeating bisphenol A type carbonate structural units, such as copolymers derived from bisphenol A and optionally one or more other bisphenol / dihydroxy aromatic compounds (such as resorcinol), and further comprising one or more non-carbonate structural units such as aromatic ester units (such as terephthalic acid, isophthalic acid), aromatic-aliphatic ester units based on C6-20 aliphatic diacids, and polysiloxane units (such as polydimethylsiloxane units);

[0016] The polycarbonate material can be a linear polymer or a branched polymer, and can be a single-structure polycarbonate or a composition of multiple-structure polycarbonates.

[0017] The specific source of the polycarbonate material applicable to this method is not limited; it can be virgin polycarbonate or recycled polycarbonate. Specifically, the polycarbonate material can include, but is not limited to, virgin polycarbonate, recycled polycarbonate from consumer products, and recycled polycarbonate from industrial production. There are no particular requirements for the preparation method of the polycarbonate material; it can be obtained from multiple sources and can include combinations of polycarbonates with slight structural differences. These differences can be due to variations in comonomers or end groups, for example, polycarbonates prepared by introducing various end-capping agents / chain terminators during polymerization.

[0018] It should be noted that when the raw material is recycled polycarbonate, it may also contain one or more blended modified polymers, such as thermoplastic polymers other than polycarbonate.

[0019] In one embodiment, step (1) dissolves the polycarbonate material in an organic solvent to obtain solution X, wherein the mass percentage of the polycarbonate material in solution X is 10-30%, including but not limited to 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any combination thereof.

[0020] In one embodiment, the organic solvent selected for dissolving in step (1) is a polar solvent, preferably a chlorinated organic solvent such as halogenated hydrocarbons, and more preferably one or more of dichloromethane, chlorobenzene, etc.

[0021] In one embodiment, the dissolution process in step (1) may be appropriately heated. Specifically, the temperature of the dissolution process is controlled between 24-38°C, including but not limited to 24°C, 26°C, 28°C, 30°C, 32°C, 34°C, 36°C, 38°C, or any combination thereof; the temperature of the resulting dissolved solution X is controlled between 25-35°C, including but not limited to 25°C, 26°C, 28°C, 30°C, 32°C, 34°C, 35°C, or any combination thereof.

[0022] In one embodiment, step (1) involves dissolving the polycarbonate material in an organic solvent. The polycarbonate material can be waste powder / granules from the production process or commercially available used polycarbonate molding materials. When using powder / granules, especially pre-molded polycarbonate material, as raw material, the material needs to be pulverized first. Suitable pulverizing equipment includes grinders and crushers. To accelerate dissolution, the diameter of the pulverized particles should be as small as possible. Preferably, the diameter of the pulverized polycarbonate material should not exceed 1 mm, and more preferably 0.05-0.5 mm. Specifically, the diameter of the pulverized particles includes, but is not limited to, 1 mm, 0.8 mm, 0.6 mm, 0.5 mm, 0.3 mm, 0.2 mm, 0.1 mm, 0.05 mm, 0.01 mm, or any combination thereof.

[0023] In one embodiment, the solution X obtained after dissolving the polycarbonate material in step (1) needs to be filtered, that is, the solution X passes through a filtration device before being conveyed to the next stage; the filter material selected for filtration should have a pore size range of less than 10 μm, preferably 0.5-7 μm. Specifically, the pore size of the filter material includes, but is not limited to, 10 μm, 9 μm, 8 μm, 6 μm, 4 μm, 2 μm, 1 μm, 0.5 μm, 0.1 μm or any combination thereof; the material of the filter material is not limited and can be an oleophilic material such as PTFE (polytetrafluoroethylene).

[0024] In one embodiment, step (2) involves mixing bisphenol A monomer, alkali, and water to obtain solution Y, wherein solution Y is an alkaline aqueous solution containing bisphenol A monomer, wherein the mass percentage of bisphenol A monomer is 0.05-1.5%, and the mass percentage of alkali is 2-8%; specifically, the mass percentage of bisphenol A monomer includes, but is not limited to, 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any combination thereof, and the mass percentage of alkali includes, but is not limited to, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any combination thereof;

[0025] In a preferred example, the solution Y is strongly alkaline, with a pH of 12-14, including but not limited to 12, 12.2, 12.5, 12.8, 13, 13.2, 13.5, 13.8, 14, or any combination thereof;

[0026] In a preferred example, the mixing in step (2) is carried out at room temperature, and the temperature of the solution Y obtained by mixing the raw materials is controlled at 25-35°C, including but not limited to 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C or any combination thereof.

[0027] In one embodiment, the solution Y in step (2) contains an alkali to make it strongly alkaline, wherein the added alkali is an inorganic alkali, preferably a hydroxide; specifically, the hydroxide includes, but is not limited to, alkali metal hydroxides, alkaline earth metal hydroxides, tetraalkylammonium hydroxides, ammonium hydroxides, etc.

[0028] In a preferred embodiment, the base is selected from one or more alkali metal hydroxides, such as NaOH, KOH, etc.

[0029] In practical applications, the alkali can also be an aqueous solution, such as an aqueous solution with a concentration of 1-40 wt%, but the amount used is calculated based on the alkali contained therein. Specifically, the concentration of the aqueous solution includes, but is not limited to, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, or any combination thereof.

[0030] In one embodiment, the solution Y in step (2) further includes a certain amount of reducing agent, wherein the content of the reducing agent in the system is 50-500 ppm, including but not limited to 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm or any combination thereof.

[0031] Specifically, the reducing agent is selected from sodium or potassium sulfides, sulfites, etc., and is preferably sodium thiosulfate.

[0032] In one embodiment, when the solution X and solution Y are mixed in step (3) for shearing, they need to be carried out in a certain proportion. Specifically, the mass ratio of the solution X to the solution Y is 0.5-5.0, preferably 0.5-2.0, including but not limited to 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5.0 or any combination thereof.

[0033] In one embodiment, after mixing solution X and solution Y in step (3), the bisphenol A monomer contained in solution Y can promote the formation of a uniform emulsion. High-speed shearing can completely mix solution X and solution Y to form a uniform and stable emulsion. Specifically, the linear velocity range used for shearing is 2-20 m / s, including but not limited to 2 m / s, 5 m / s, 8 m / s, 10 m / s, 12 m / s, 14 m / s, 16 m / s, 18 m / s, 20 m / s or any combination thereof.

[0034] Preferably, the total shear power of the system during the shearing process is controlled to be 0.5-3.0*10. 6 J / m 3 Including but not limited to 0.5*10 6 J / m 3 0.8*10 6 J / m 3 1*10 6 J / m 3 1.2*10 6 J / m 3 1.5*10 6 J / m 3 1.8*10 6 J / m 3 2*10 6 J / m 3 2.2*10 6 J / m 3 2.5*10 6 J / m 3 2.8*10 6 J / m 3 3.0*10 6 J / m 3 Or a range consisting of any two of them; the total shear power of the shearing process is time-dependent. By controlling the linear velocity and duration of shearing to keep the total shear power within a certain range, the desired emulsification effect can be achieved, forming a uniform emulsion.

[0035] In one embodiment, the emulsion formed after shearing in step (3) has a viscosity of 500-150000 mPa·s, including but not limited to 500 mPa·s, 5000 mPa·s, 10000 mPa·s, 30000 mPa·s, 50000 mPa·s, 70000 mPa·s, 90000 mPa·s, 100000 mPa·s, 110000 mPa·s, 130000 mPa·s, 150000 mPa·s, or any combination thereof.

[0036] In one embodiment, the emulsion formed by mixing solution X and solution Y in step (3) can be continuously generated by the polycarbonate material through hydrolysis and migrated into the aqueous phase. Since the emulsion can remain stable under the action of sufficient bisphenol A monomer, the hydrolysis process of polycarbonate can continue to proceed when the interfacial area is sufficient.

[0037] Specifically, the hydrolysis reaction is carried out at a temperature of 30-70℃ for a time of 24-48h. Specifically, the temperature includes, but is not limited to, a range of 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃ or any two of these ranges, and the time includes, but is not limited to, a range of 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h, 48h or any two of these ranges.

[0038] Specifically, the hydrolysis reaction maintains the pH of the reaction system at 12-14, including but not limited to a range of 12, 12.2, 12.5, 12.8, 13, 13.2, 13.5, 13.8, 14, or any two of these ranges;

[0039] Preferably, the pH of the system is maintained by adding an alkaline solution during the hydrolysis reaction of the polycarbonate material. The alkaline solution can be selected from the range of alkaline added to solution Y in step (2). The specific selection of the two can be the same or different. Specifically, the alkaline solution is preferably an aqueous solution of NaOH, for example, with a mass concentration of 2-35%, preferably 15-20% NaOH aqueous solution.

[0040] In one embodiment, the emulsion formed by shearing in step (3) needs to be transferred into a reactor to complete the hydrolysis reaction. Preferably, a batch reactor or tubular reactor is used for the hydrolysis reaction.

[0041] In one specific example, the hydrolysis reaction can be carried out in a batch reactor, wherein the linear velocity of the mixing impeller is preferably 0.5-5.0 m / s; and the single-pass residence time in the reactor is preferably 24-48 h; specifically, the linear velocity includes, but is not limited to, 0.5 m / s, 1 m / s, 1.5 m / s, 2 m / s, 2.5 m / s, 3 m / s, 3.5 m / s, 4 m / s, 4.5 m / s, 5.0 m / s or any combination thereof, and the single-pass residence time includes, but is not limited to, 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, 40 h, 42 h, 44 h, 46 h, 48 h or any combination thereof.

[0042] In one embodiment, the reaction solution after the single-pass hydrolysis reaction in step (4) needs to be demulsified and separated to obtain an aqueous solution containing bisphenol A, wherein bisphenol A exists in the form of a salt (e.g., sodium BPA salt), and the composition is relatively clean and does not contain impurities such as inorganic salts, and can be directly applied to the interfacial phosgene method for the synthesis of polycarbonate.

[0043] The aqueous solution containing bisphenol A, wherein the content of bisphenol A can be determined by liquid phase method, preferably 5-20 wt%, with the remainder being 70-90 wt% water and about 3-7 wt% alkali.

[0044] In the method described above in this invention, after demulsification and separation in step (4), the oil phase is also obtained, which mainly contains organic solvents, components of polycarbonate material that do not participate in the hydrolysis reaction, and unhydrolyzed polycarbonate material. The hydrolysis rate of polycarbonate material that only undergoes a single-pass hydrolysis reaction is low, usually less than 50%. Therefore, the oil phase can be concentrated to remove organic solvents and control the solvent removal rate to obtain a concentrated solution with a polymer content of 10-30 wt%, which is then returned to step (1) to continue participating in the preparation of solution X. This cycle is repeated to improve the hydrolysis rate of polycarbonate material. It should be noted that the concentrated solution with a polymer content of 10-30 wt% includes components of polycarbonate material that do not participate in the hydrolysis reaction and unhydrolyzed polycarbonate material. Therefore, polycarbonate and its possible blended modified polymers are all included. In one embodiment, the demulsification and separation in step (4) can be carried out using conventional operating methods in the field; preferably, demulsification is carried out using hydrophilic filter paper, such as fiber filter paper with a pore size of 1-20 μm, specifically, the pore size includes but is not limited to 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or any combination thereof; preferably, separation is carried out using centrifugation or a coalescing device.

[0045] In this invention, the aqueous solution containing bisphenol A obtained after hydrolysis / demulsification / separation has a BPA mass fraction of 5-20% and an aqueous solution pH of 12-14, and can be applied to the process of preparing polycarbonate by interfacial polycondensation.

[0046] Currently, interfacial polycondensation is a commonly used industrial process for preparing polycarbonate. Its direct raw materials include a solution of approximately 15 wt% sodium BPA, organic solvents such as dichloromethane, phosgene, triethylamine catalyst, and end-capping agents. After mixing, rapid stirring enhances interfacial renewal and mass transfer, achieving a fast polycondensation reaction to prepare high-molecular-weight polycarbonate materials. Therefore, the bisphenol A-containing aqueous solution obtained in this invention can be used directly or, with appropriate concentration control, directly as a raw material for the preparation of PC via interfacial polycondensation. This eliminates the need to repurchase corresponding powder raw materials for solution preparation, effectively reducing raw material costs and equipment dust risks.

[0047] In one embodiment, the aqueous phase in step (3) is a solution containing bisphenol A. When applying it, the concentration and pH of bisphenol A in the solution are first analyzed, and then bisphenol A monomer and alkali solution are added to the required amount. Then, the interfacial phosgene method is used to synthesize polycarbonate.

[0048] In this invention, the bisphenol A solution obtained from the aqueous phase in step (3) can be further purified to obtain bisphenol A monomer. The purification process can be conventional methods such as crystallization and distillation. The specific operations, process conditions, and equipment used can all be chosen from conventional methods in the field, and there are no particular restrictions. Those skilled in the art can optimize the process based on existing technology and known processes according to actual needs; this invention will not elaborate further.

[0049] Compared with the prior art, the positive effects of the present invention are as follows:

[0050] This invention provides a chemical method for recycling waste polycarbonate materials. This method is implemented in an emulsion system of organic solvent and water. In the emulsion state provided by this invention, no additional catalysts or substances such as methanol are required, and the decomposition of polycarbonate chains can be completed under mild conditions. Furthermore, the resulting BPA salt aqueous solution is relatively pure and can be directly used in the interfacial polycondensation synthesis of polycarbonate, saving costs and improving the economic efficiency of the equipment. Detailed Implementation

[0051] The following detailed embodiments describe the process of promoting the hydrolysis of polycarbonate chains through shear emulsification under water-oil interface conditions. It should be noted that this invention is not limited to the following embodiments.

[0052] The main raw materials used in the various embodiments and comparative examples of this invention are sourced as follows. Unless otherwise specified, other raw materials and reagents were obtained through commercially available channels:

[0053] Polycarbonate material A: Wanhua 2600, Mw = 17456 g / mol, PD = 2.4, λ = 0.0067;

[0054] Polycarbonate material B: derived from recycled CDs, Mw = 16735 g / mol, monomer composition includes approximately 94 wt% bisphenol A and approximately 6 wt% vinyl monomers;

[0055] Polycarbonate material C: derived from recycled PC transparent protective screen, Mw = 24566 g / mol, monomer composition includes bisphenol A of about 96 wt%, styrene and other vinyl monomers of about 4 wt%;

[0056] Bisphenol A: Analytical grade, Anexic;

[0057] Dichloromethane: Analytical grade / chromatographic grade, Energi;

[0058] NaOH: Analytical grade, Anergy;

[0059] Deionized water: pH = 7.2, conductivity < 5.0.

[0060] The main analytical methods used in the embodiments and comparative examples of this invention are as follows:

[0061] The molecular weight of polycarbonate was obtained by Agilent Technologies 1260infinity testing using an RI detector, a UV detector, dichloromethane as the mobile phase, a flow rate of 1 mL / min, and column and chamber temperatures of 30 °C.

[0062] The monomer content in the aqueous solution was determined by liquid chromatography using methanol as the eluent.

[0063] The monomer composition of polycarbonate materials B and C adopts H 1 -NMR nuclear magnetic resonance, obtained by scanning a solution prepared with deuterated dichloromethane as a solvent at a concentration of 4.0 mg / ml.

[0064] The emulsion viscosity was tested using a Borelfeld DV2T viscometer with a 63# rotor at 35°C and a rotation speed of 1-20 rpm. Viscosity data were read under stable fluctuations in torque range of 40-60%.

[0065] The polymer content in the oil phase is determined by an evaporation test. A certain mass of organic solution m is taken and evaporated on an analytical balance. After evaporation until the mass stabilizes, the balance reading is n. Then the polymer content in the solution is n / m*100%.

[0066] The particle size of the pulverized particles was characterized using a Helos-Rodos dry particle size analyzer from Synpatek, Germany. The test temperature was 25°C, and the humidity was not higher than 80%. The particle diameter was expressed as D. 3，2 Description, i.e., area average particle size.

[0067] The test method for sodium carbonate and NaOH in the aqueous phase shall be performed in accordance with the standard GB / T4348.1-2013.

[0068] Example 1

[0069] (1) Prepare a 1L flask and crush polycarbonate material A into particles with a diameter of approximately D. 3，2 Take 100g of 0.08mm particles and add them to the solution. Then add 450g of dichloromethane solution and maintain a 30℃ water bath. After the polycarbonate material A is completely dissolved, the solution X is obtained. After filtering through PTFE filter material with a pore size of 0.2μm, the solution is sealed and stored for later use.

[0070] (2) Prepare a 1L flask, add 500g of deionized water, 0.1g of sodium thiosulfate, 5g of bisphenol A monomer, and then add 80g of 32wt% sodium hydroxide aqueous solution. Maintain a 30℃ water bath until the bisphenol A monomer is completely dissolved to obtain solution Y with a pH of 13.5.

[0071] (3) Prepare a 1L beaker, add 241g of solution X and 337g of solution Y, insert the dynamic shear head below the liquid surface, control the rotation speed at 10000rpm and the linear velocity at 7m / s to start emulsification, and input the total shear power to reach 0.6*10 after 60s. 6 J / m 3 A homogeneous and stable emulsion with a viscosity of 900 cp was formed and then transferred to a 1 L three-necked flask. The hydrolysis reaction was carried out at 35 °C with the stirring speed controlled at 0.5 m / s. At the same time, 10 wt% sodium hydroxide aqueous solution was added dropwise to the reaction system to maintain the pH of the reaction system at 12-14. After the reaction was carried out for 24 hours, stirring was stopped.

[0072] (4) The reaction solution was demulsified by pressure filtration using a fiber filter paper with a pore size of 1.0 μm, and the aqueous phase (i.e., an aqueous solution containing bisphenol A) was separated with a pH of 12.5.

[0073] At the same time, an oil phase is obtained, which mainly contains dichloromethane and polymers (including monomer components in polycarbonate materials that do not participate in the hydrolysis reaction and unhydrolyzed polycarbonate material A).

[0074] Using the oil phase as raw material, the polymer concentration was concentrated by rotary evaporation until it matched the initial concentration of polycarbonate material A in solution X of step (1). The raw material ratio and operating parameters of steps (1)-(4) were then repeated to carry out the hydrolysis reaction in cycles. The mass of the remaining polymer in the oil phase separated after each reaction was tested. At the same time, the aqueous phase obtained after the cyclic hydrolysis reaction was combined with the previous one, and the total mass of BPA contained in the combined solution was tested one by one.

[0075] After five cycles of hydrolysis, the total mass of the final aqueous phase combined solution of the above-mentioned 100g polycarbonate material A initial raw material is 676.2g. It contains approximately 13.00wt% BPA monomer, 3.26wt% sodium hydroxide, 5.73wt% sodium carbonate, and the remainder is water. This combined solution can be directly used for the interfacial phosgene method to synthesize polycarbonate by adding bisphenol A monomer and alkali solution to the required amount.

[0076] The results of polymer content tests in the aqueous and oil phases after each separation are shown in Table 1 below.

[0077] Table 1

[0078] Number of hydrolysis reactions 0 1 2 3 4 5 Total BPA content in aqueous phase (g) 5.0 29.9 54.1 67.4 81.1 87.9 Total mass of polymer in the oil phase (g) 100.0 71.8 44.6 29.7 14.7 6.9

[0079] Example 2

[0080] (1) Prepare a 1L flask and crush polycarbonate material B into particles with a diameter of approximately D. 3，2 Take 150g of 0.21mm particles and add them to the solution. Then add 450g of dichloromethane solution and maintain a 35℃ water bath. After the polycarbonate material B is completely dissolved, the solution X is obtained. After filtering through PTFE filter material with a pore size of 4.0μm, the solution is sealed and stored for later use.

[0081] (2) Prepare a 1L flask, add 500g of deionized water, 0.1g of sodium thiosulfate, 2g of bisphenol A monomer, and then add 40g of 32wt% sodium hydroxide aqueous solution. Maintain a 30℃ water bath until the bisphenol A monomer is completely dissolved to obtain solution Y with a pH of 13.0.

[0082] (3) Prepare a 1L beaker, add 241g of solution X and 127g of solution Y, insert the dynamic shear head below the liquid surface, control the rotation speed at 10000rpm and the linear velocity at 13m / s to start emulsification, and after 60s, input the total shear power to reach 1.4*10 6 J / m 3 A homogeneous and stable emulsion with a viscosity of 7000 cp was formed. This emulsion was then transferred to a 1L three-necked flask and subjected to hydrolysis at 45°C. The stirring speed was controlled at 2.4 m / s, and a 10wt% sodium hydroxide aqueous solution was added dropwise to maintain the pH of the reaction system at 12-14. Stirring was stopped after 48 hours of reaction.

[0083] (4) The reaction solution was demulsified by pressure filtration using a fiber filter paper with a pore size of 10 μm, and the aqueous phase (i.e., an aqueous solution containing bisphenol A) was separated with a pH of 13.7.

[0084] At the same time, an oil phase is obtained, which mainly contains dichloromethane and polymers (including monomer components in polycarbonate materials that do not participate in the hydrolysis reaction and unhydrolyzed polycarbonate material B).

[0085] Using the oil phase as raw material, the polymer concentration was concentrated by rotary evaporation until it matched the initial concentration of polycarbonate material B in solution X of step (1). The raw material ratio and operating parameters of steps (1)-(4) were then repeated to carry out the hydrolysis reaction in cycles. The mass of the remaining polymer in the oil phase separated after each reaction was tested. At the same time, the aqueous phase obtained after the cyclic hydrolysis reaction was combined with the previous one, and the total mass of BPA contained in the combined solution was tested one by one.

[0086] After five cycles of hydrolysis, the total mass of the final aqueous phase combined solution of the above-mentioned 150g polycarbonate material B initial raw material is 707.4g. It contains approximately 17.90wt% BPA monomer, 5.35wt% sodium hydroxide, 8.00wt% sodium carbonate, and the remainder is water. This combined solution can be directly used for the interfacial phosgene method to synthesize polycarbonate by adding bisphenol A monomer and alkali solution to the required amount.

[0087] The results of polymer content tests in the aqueous and oil phases after each separation are shown in Table 2 below.

[0088] Table 2

[0089] Number of hydrolysis reactions 0 1 2 3 4 5 Total BPA content in aqueous phase (g) 2.0 32.3 60.74 90.11 108.80 126.60 Total mass of polymer in the oil phase (g) 150.0 115.6 83.7 50.8 29.8 9.2

[0090] Example 3

[0091] (1) Prepare a 1L flask and crush the polycarbonate material C into particles with a diameter of approximately D. 3，2 Take 60g of particles with a diameter of 0.48mm and add them to the solution. Then add 450g of dichloromethane solution and maintain a water bath at 35℃. After the polycarbonate material C is completely dissolved, the solution X is obtained. After filtering through PTFE filter material with a pore size of 9.0μm, the solution is sealed and stored for later use.

[0092] (2) Prepare a 1L flask, add 500g of deionized water, 0.1g of sodium thiosulfate, 0.5g of bisphenol A monomer, and then add 100g of 32wt% sodium hydroxide aqueous solution. Maintain a 30℃ water bath until the bisphenol A monomer is completely dissolved to obtain solution Y with a pH of 13.8. Set aside for later use.

[0093] (3) Prepare a 1L beaker, add 180g of solution X and 180g of solution Y, insert the dynamic shear head below the liquid surface, control the rotation speed at 10000rpm and the linear velocity at 20m / s to start emulsification, and input the total shear power to reach 2.9*10 after 120s. 6 J / m 3A homogeneous and stable emulsion with a viscosity of 14000 cp was formed. It was then transferred to a 1L three-necked flask and hydrolyzed at 55°C. The stirring speed was controlled at 4.8 m / s, and 10 wt% sodium hydroxide aqueous solution was added dropwise to the reaction system to maintain the pH of the reaction system at 12-14. After 48 hours of reaction, stirring was stopped.

[0094] (4) The reaction solution was demulsified by pressure filtration using a fiber filter paper with a pore size of 15 μm, and the aqueous phase (i.e., an aqueous solution containing bisphenol A) was separated with a pH of 13.4.

[0095] At the same time, an oil phase is obtained, which mainly contains dichloromethane and polymers (including monomer components in polycarbonate materials that do not participate in the hydrolysis reaction and unhydrolyzed polycarbonate material C).

[0096] Using the oil phase as raw material, the polymer concentration was concentrated by rotary evaporation until it matched the initial concentration of polycarbonate material C in solution X of step (1). The raw material ratio and operating parameters of steps (1)-(4) were then repeated to carry out the hydrolysis reaction in cycles. The mass of the remaining polymer in the organic oil phase separated after each reaction was tested. At the same time, the aqueous phase obtained after the cyclic hydrolysis reaction was combined with the previous one, and the total mass of BPA contained in the combined solution was tested one by one.

[0097] After five cycles of hydrolysis, the total mass of the final aqueous phase combined solution of the above-mentioned 60g polycarbonate material C initial raw material is 656.6g. It contains approximately 7.80wt% BPA monomer, 2.26wt% sodium hydroxide, 3.59wt% sodium carbonate, and the remainder is water. This combined solution can be directly used for the interfacial phosgene method to synthesize polycarbonate by adding bisphenol A monomer and alkali solution to the required amount.

[0098] The test results of the monomers and polymers in the organic phase after each separation are shown in Table 3 below.

[0099] Table 3

[0100] Number of hydrolysis reactions 0 1 2 3 4 5 Total BPA content in aqueous phase (g) 0.5 13.85 36.1 51.23 51.24 51.23 Total mass (g) of polymer in the organic phase 60 44.8 18.9 2.8 2.9 2.8

[0101] Comparative Example 1

[0102] Referring to the method of Example 1, the only difference is that bisphenol A monomer is not added to solution Y in step 2), and other operations and conditions remain unchanged. After 5 cycles of hydrolysis, the total mass of the final aqueous phase combined liquid is 604.6 g, which contains about 3.68 wt% BPA monomer, 1.25 wt% sodium hydroxide, 1.71 wt% sodium carbonate, and the remainder is water.

[0103] The results of polymer content tests in the aqueous and oil phases after each separation are shown in Table 4 below.

[0104] Table 4

[0105] Number of hydrolysis reactions 0 1 2 3 4 5 Total BPA content in aqueous phase (g) 0 4.45 7.12 14.24 21.36 22.25 Total mass of polymer in the oil phase (g) 100.0 94.8 91.7 83.6 75.6 75.3

[0106] Comparative Example 2

[0107] Referring to the method of Example 1, the only difference is that: bisphenol A monomer is not added to solution Y in step 2), and the shear emulsification process is omitted in step 3). After mixing solution X and solution Y, the mixture is directly transferred to the reactor for hydrolysis. Other operations and conditions remain unchanged. After 5 cycles of hydrolysis, the total mass of the final aqueous phase combined liquid is 587.9g, which contains about 1.30wt% BPA monomer, 1.34wt% sodium hydroxide, 0.56wt% sodium carbonate, and the remainder is water.

[0108] The results of polymer content tests in the aqueous and oil phases after each separation are shown in Table 4 below.

[0109] Table 4

[0110] Number of hydrolysis reactions 0 1 2 3 4 5 Total BPA content in aqueous phase (g) 0 2.28 3.56 4.45 5.84 7.63 Total mass of polymer in the oil phase (g) 100.0 97.2 96.2 95.5 93.5 91.3

Claims

1. A method for hydrolytic recycling of polycarbonate to bisphenol A, characterized in that, The method comprises the following steps: (1) dissolving polycarbonate material in an organic solvent to obtain solution X; (2) mixing bisphenol A monomer, alkali and water to obtain solution Y; (3) mixing solution X and solution Y, shearing to obtain a uniform emulsion, and transferring into a reactor to perform hydrolysis reaction; (4) breaking emulsion and separating the reaction liquid to obtain water phase and oil phase, wherein the water phase is a bisphenol A-containing aqueous solution.

2. The method of claim 1, wherein, The polycarbonate material in step (1) is selected from polymers containing bisphenol A carbonate structural units in the molecular chain; and / or The average molecular weight of the polycarbonate material in step (1) is 2000-40000 g / mol.

3. The method of claim 2, wherein, The polycarbonate material is selected from polymers containing only bisphenol A carbonate structural units in the molecular chain.

4. The method of claim 2, wherein, The molecular chain refers to the main chain.

5. The method of claim 1, wherein, The mass percentage of polycarbonate material in solution X in step (1) is 10-30%; and / or The organic solvent in step (1) is a polar solvent; and / or The temperature of the dissolving in step (1) is 24-38℃; and / or The polycarbonate material in step (1) is crushed to a diameter of not more than 1 mm; and / or Solution X in step (1) is subjected to filtration treatment, and the pore size of the filter selected for filtration is 10 μm or less.

6. The method of claim 5, wherein, The organic solvent is a chlorine-containing organic solvent.

7. The method of claim 6, wherein, The organic solvent is one or more of dichloromethane and chlorobenzene.

8. The method of claim 5, wherein, The polycarbonate material is crushed into particles with a diameter of 0.05-0.5 mm.

9. The method of claim 5, wherein, The pore size of the filter selected for filtration is 0.5-7 μm.

10. The method of claim 1, wherein, The mass percentage of bisphenol A monomer in solution Y in step (2) is 0.05-1.5%, and the mass percentage of alkali is 2-8%; and / or The temperature of the mixing in step (2) is 25-35℃.

11. The method of claim 1, wherein, Solution Y in step (2) is strongly alkaline, with a pH of 12-14.

12. The method of claim 1, wherein, The alkali in step (2) is one or more of inorganic alkalis.

13. The method of claim 12, wherein, The alkali is one or more of hydroxides.

14. The method of claim 13, wherein, The alkali is one or more of alkali metal hydroxides, alkaline earth metal hydroxides, tetraalkylammonium hydroxides and ammonium hydroxides.

15. The method of claim 13, wherein, The alkali is selected from one or more of alkali metal hydroxides.

16. The method of claim 15, wherein, The alkali is selected from one or more of NaOH and KOH.

17. The method of claim 1, wherein, In solution Y in step (2), a reducing agent is added, and the content of the reducing agent in the system is 50-500 ppm.

18. The method of claim 17, wherein, The reducing agent is selected from one or more of sodium or potassium sulfides and sulfites.

19. The method of claim 18, wherein, The reducing agent is sodium thiosulfate.

20. The method of claim 1, wherein, The mass ratio of solution X to solution Y in step (3) is 0.5-5.0; and / or The linear velocity used for shearing in step (3) is 2-20 m / s; and / or The viscosity of the emulsion in step (3) is 500-150000 mPa·s.

21. The method of claim 20, wherein, The mass ratio of solution X to solution Y is 0.5-2.

0.

22. The method of claim 1, wherein, Step (3) controls the total shear power of the shear process system to be 0.5-3.0*10 6 J / m 3 .

23. The method of claim 1, wherein, The temperature of the hydrolysis reaction in step (3) is 30-70℃, and the time is 24-48 h.

24. The method of claim 1, wherein, The pH of the reaction system is maintained at 12-14 during the hydrolysis reaction in step (3).

25. The method of claim 1, wherein, The hydrolysis reaction in step (3) is performed in a kettle-type reaction kettle or a tubular reactor.

26. The method of claim 25, wherein, The hydrolysis reaction is carried out in a tank reactor, wherein the linear speed of the mixing stirrer is 0.5-5.0 m / s.

27. The method of claim 25, wherein, The hydrolysis reaction has a single-pass residence time in the reactor of 24-48 h.

28. The method of claim 1, wherein, The oil phase in step (4) is concentrated to remove the organic solvent, to obtain a concentrated solution with a polymer content of 10-30 wt%, which is returned to step (1) to continue participating in the preparation of solution X.

29. The method of claim 1, wherein, The aqueous solution containing bisphenol A is used for interfacial polycondensation to prepare polycarbonate.