Alcoholysis catalyst and method for recovering BPA through alcoholysis of waste PC

Abstract

The invention discloses a phenol sodium salt organic base catalyst and a method for recovering bisphenol A from waste polycarbonate through catalytic alcoholysis by using the phenol sodium salt organic base catalyst. According to the method, phenol sodium salt is used as a catalyst, a carbonic ester substance is used as a solvent for alcoholysis of PC, and an alcoholysis solution is dried and recrystallized to obtain a reusable solvent and a high-purity BPA product. The method provided by the invention can avoid the influence of the sodium residue of the composite metal or organic catalyst on the downstream BPA product quality, the catalyst is simple in preparation method, small in dosage and free of recovery, the solvent can be recycled, the reaction is rapid, the condition is mild, and the method is suitable for practical industrial production and use.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of recycling and reusing waste PC materials, and particularly relates to a phenol sodium salt organic base catalyst and a method for catalyzing alcoholysis of waste polycarbonate to recover BPA by using the catalyst. BACKGROUND

[0002] Polycarbonate (PC) is a high-performance organic material containing bisphenol A carbonate structure, which is widely used in computer, household appliance and automobile parts fields, and accordingly brings about a large amount of waste plastic pollution problem. Developing a recycling method of waste PC has been an important problem of environmental protection.

[0003] The recycling method of waste PC is generally divided into physical recycling method and chemical recycling method. The physical recycling method is to recycle the PC material on the waste product by means of melt granulation, but the recycled material can only be used for preparing low-value-added products with low performance requirements after re-plasticizing, and the recycling times are also limited due to the accumulation of additives.

[0004] The chemical recycling method is to degrade the waste PC into bisphenol A (BPA) by chemical degradation, including hydrolysis method, pyrolysis method and alcoholysis method. Among them, the alcoholysis method as an efficient chemical recycling method, the development of its catalyst has been a hot issue in this field. For example, Zou Changwu et al. (Plastics, 2014, 43, 3, 75-77) used toluene as solvent, NaOH as catalyst, Na2S as product protective agent, and carried out PC methanol alcoholysis at room temperature and normal pressure, which catalytically alcoholized PC into bisphenol A, but there was a problem of low PC conversion rate. Jeung Gon Kim et al. (Polymer, 2018, 143, 106-114) used TBD as catalyst to carry out methanol and PC alcoholysis reaction, but the organic catalyst was difficult to recover. Chinese patent CN201611093341.3 reported that the solid catalyst CaO-SBA-15 molecular sieve was used for methanol alcoholysis of PC, which could also efficiently recover BPA, and the catalyst separation was easy, but the catalyst preparation process was complicated and the cost was high.

[0005] Therefore, it is of great significance to seek an efficient and easy-to-separate, or non-separated catalyst and a mild process for waste PC alcoholysis and BPA recovery. SUMMARY

[0006] In order to solve the above technical problems, the present application provides a phenol sodium salt organic base catalyst, and a method for catalyzing alcoholysis of waste PC to recover BPA by using the catalyst. The method has the advantages of mild reaction conditions, simple catalyst preparation method, small amount of catalyst and no need to recover, less introduction of metal and non-metal impurities into the product BPA, and recyclable solvent.

[0007] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0008] In the first aspect of the present application, a phenol sodium salt organic base catalyst is provided, and the preparation method thereof is as follows:

[0009] The phenolic compound is added into 5-20wt% sodium hydroxide aqueous solution in a molar ratio of phenolic compound:sodium hydroxide of 1:(1-2.5), and after heating and stirring, the phenol sodium salt catalyst is obtained by vacuum distillation and drying.

[0010] Further, in the preparation method of the catalyst, the phenolic compound is one or more of phenol, p-tert-butylphenol, and BPA.

[0011] Further, in the preparation method of the catalyst, the heating temperature is 60-80℃, and the heating time is 1-3h.

[0012] Further, in the preparation method of the catalyst, the pressure of the vacuum distillation is (-0.09MPa)~(-0.1MPa), and the temperature is 50-70℃.

[0013] Further, in the preparation method of the catalyst, the drying temperature is 105-110℃, and the drying time is 0.5-1h.

[0014] In the second aspect of the present application, the phenol sodium salt organic base catalyst is applied in the process of recycling BPA from waste PC by alcoholysis, i.e., a method for recycling BPA from waste PC by alcoholysis is provided, which comprises the following steps:

[0015] (1) a mixed solution is prepared by mixing the phenol sodium salt organic base catalyst, alcohol, waste PC, and solvent in a mass ratio of (0.01-0.05):(1-2):1:(3-6);

[0016] (2) after heating at 40-80℃ for 3-6h, the alcoholysis solution is obtained by filtration;

[0017] (3) after post-treatment of the alcoholysis solution, BPA is obtained, and the solvent is recovered.

[0018] Further, in the step (1), the alcohol can be selected from one or more of methanol, ethanol, and isopropanol.

[0019] Further, in the step (1), the waste PC is selected from bisphenol A polycarbonate, and the shape of the waste PC can be granular, or can be broken and sliced, and the volume is preferably less than 1 cubic centimeter.

[0020] Further, the solvent in step (1) can be one or more of dimethyl carbonate, diethyl carbonate, diisopropyl carbonate, preferably dimethyl carbonate.

[0021] Further, the post-treatment method in step (3) is to reduce and distill the alcoholysis solution obtained in step (2), the light component is alcohol, which is collected and used as the supplement of the alcohol in step (1) and can be recycled to participate in the alcoholysis reaction; and the heavy component is recrystallized to obtain the pure BPA product.

[0022] Preferably, the conditions for the reduced pressure distillation in step (3) are as follows: using a rotary evaporator to reduce and distill at a vacuum degree of (-0.09 MPa) to (-0.1 MPa) and an oil bath temperature of 40-60°C, and collecting the distillated light component (solvent) and the heavy component (crude BPA) respectively. Preferably, the recrystallization of the heavy component can be achieved by conventional means, i.e. heating and refluxing in an ether (such as isopropyl ether) and then cooling to make the BPA recrystallize.

[0023] The heavy component is collected in a three-necked flask, isopropyl ether is added in an amount of half the mass of the heavy component, and then the isopropyl ether is continuously added in small batches until the total mass of the isopropyl ether is close to that of the heavy component, at which point the heavy component is completely dissolved. At this time, the heating and stirring are stopped, and the system is allowed to cool to room temperature, so that the BPA recrystallizes. Then the three-necked flask is immersed in an ice water bath for 0.5 h, and the funnel is used to filter the pure BPA.

[0024] Compared with the prior art, the present application has the following main advantages:

[0025] (1) The catalyst preparation method is simple, the catalyst dosage is small, and the catalyst does not need to be recovered, and the catalytic effect is excellent, and the metal impurities introduced into the product BPA are few;

[0026] (2) The sodium phenolate organic base catalyst used in the present application is a raw material or a blocking agent for the synthesis of PC, and does not introduce additional organic substances, thereby reducing the difficulty of refining the product BPA;

[0027] (3) In the waste PC alcoholysis and BPA recovery process, the excess alcohol and solvent can be recycled, which has significant economic benefits and environmental friendliness. DETAILED DESCRIPTION

[0028] The present application will be further described below by means of specific examples, which are only used to illustrate the present application and do not limit the scope of the present application.

[0029] The waste PC used in the present application is from recycled waste PC material water bucket, which is crushed to a volume of less than 1 cubic centimeter before use. In addition, all instruments, methods and materials used in all examples of the present application are conventional instruments, methods and materials in the art, which can be obtained by commercial channels by those skilled in the art.

[0030] The PC degradation rate described in the present application = (the mass of the remaining waste PC / the total mass of the added waste PC) * 100%; the BPA yield described in the present application = (the mass of the obtained product BPA / the maximum mass of BPA that can be obtained theoretically after the degradation of all PC added) * 100%.

[0031] The Na residue described in the present application is tested by ICP after wet digestion, and the BPA yield is tested by liquid chromatography.

[0032] The liquid chromatography analysis method used in the present application is as follows:

[0033]

[0034]

[0035] The ICP analysis method used in the present application is as follows:

[0036]

[0037] The gas chromatography analysis method used in the present application is as follows:

[0038]

[0039] The proportion of alcohol and solvent is determined by gas chromatography after solvent recovery in the present application, and is supplemented to the original proportion for reuse.

[0040] Example 1

[0041] Take 15 g of BPA into a 100 mL single-necked flask, add 50 g of 11% by mass sodium hydroxide aqueous solution, and heat and stir at 70°C for 3 h with the mouth open. After the reaction is completed, remove water by distillation under reduced pressure using a rotary evaporator at -0.09 MPa vacuum and with an oil bath at 60°C to obtain a crystalline salt of bisphenol A sodium, which is dried in an oven at 105°C for 1 h and then used as a catalyst. Subsequently, add the crystalline salt of bisphenol A sodium 0.4 g, waste PC 15 g, methanol 20 g, and dimethyl carbonate 90 g into a 250 mL three-necked flask, and stir at 60°C for 4 h to obtain an alcoholysis solution. After the alcoholysis solution is filtered, separate light and heavy components by distillation under reduced pressure using a rotary evaporator at -0.09 MPa vacuum and with an oil bath at 40°C. The light component is analyzed for the ratio of methanol / dimethyl carbonate by gas chromatography, and methanol is added and used again. The heavy component is dried at -0.1 MPa vacuum and with an oil bath at 40°C to obtain crude BPA, which is recrystallized in isopropyl ether to obtain pure BPA. The PC degradation rate, BPA yield, and Na residue in BPA are analyzed using the pure BPA. The PC degradation rate is calculated to be 100%, the BPA yield is calculated to be 93.4%, and the Na residue in BPA is calculated to be 630 ppm.

[0042] Example 2

[0043] Take 15 g of phenol into a 100 mL single-necked flask, add 50 g of 13% by mass sodium hydroxide aqueous solution, and heat and stir at 60°C for 3 h with the mouth open. After the reaction is completed, remove water by distillation under reduced pressure using a rotary evaporator at -0.1 MPa vacuum and with an oil bath at 50°C to obtain a crystalline salt of phenol sodium, which is dried in an oven at 110°C for 0.5 h and then used as a catalyst. Subsequently, add the crystalline salt of phenol sodium 0.4 g, waste PC 15 g, methanol 20 g, and dimethyl carbonate 90 g into a 250 mL three-necked flask, and stir at 70°C for 6 h to obtain an alcoholysis solution. After the alcoholysis solution is filtered, separate light and heavy components by distillation under reduced pressure using a rotary evaporator at -0.09 MPa vacuum and with an oil bath at 40°C. The light component is analyzed for the ratio of methanol / dimethyl carbonate by gas chromatography, and methanol is added and used again. The heavy component is dried at -0.1 MPa vacuum and with an oil bath at 60°C to obtain crude BPA, which is recrystallized in isopropyl ether to obtain pure BPA. The PC degradation rate, BPA yield, and Na residue in BPA are analyzed using the pure BPA. The PC degradation rate is calculated to be 96%, the BPA yield is calculated to be 87.7%, and the Na residue in BPA is calculated to be 543 ppm.

[0044] Example 3

[0045] Take 15 g of p-tert-butyl phenol into a 100 mL single-necked flask, add 50 g of 8.5% by mass sodium hydroxide aqueous solution, and heat and stir at 70°C for 2 h with the mouth open. After the reaction is completed, remove water by vacuum distillation at -0.1 MPa under an oil bath at 50°C using a rotary evaporator, and obtain p-tert-butyl phenol sodium crystalline salt. Dry this in an oven at 105°C for 1 h, and use as a catalyst. Subsequently, add p-tert-butyl phenol sodium salt 0.5 g, waste PC 15 g, methanol 20 g, and dimethyl carbonate 90 g into a 250 mL three-necked flask, and stir at 60°C for 6 h. After filtering the reaction liquid, separate light and heavy components by vacuum distillation at -0.09 MPa under an oil bath at 40°C using a rotary evaporator. Analyze the ratio of methanol / dimethyl carbonate in the light component by gas chromatography, and continue to use after supplementing methanol. Dry the heavy component at -0.1 MPa and 40°C, and obtain crude BPA. Recrystallize this in isopropyl ether, and obtain pure BPA. Analyze the PC degradation rate, BPA yield, and Na residue in the pure BPA. The PC degradation rate is calculated to be 99%, the BPA yield is calculated to be 91.5%, and the Na residue in the BPA is calculated to be 658 ppm.

[0046] Example 4

[0047] Take 15 g of BPA into a 100 mL single-necked flask, add 50 g of 11% by mass sodium hydroxide aqueous solution, and heat and stir at 70°C for 3 h with the mouth open. After the reaction is completed, remove water by vacuum distillation at -0.09 MPa under an oil bath at 60°C using a rotary evaporator, and obtain bisphenol A sodium crystalline salt. Dry this in an oven at 105°C for 1 h, and use as a catalyst. Subsequently, add bisphenol A sodium salt 0.4 g, waste PC 15 g, ethanol 20 g, and diethyl carbonate 80 g into a 250 mL three-necked flask, and stir at 70°C for 6 h to obtain an alcoholysis liquid. After filtering the alcoholysis liquid, separate light and heavy components by vacuum distillation at -0.1 MPa under an oil bath at 50°C using a rotary evaporator. Analyze the ratio of ethanol / diethyl carbonate in the light component by gas chromatography, and continue to use after supplementing ethanol. Dry the heavy component at -0.1 MPa and 40°C, and obtain crude BPA. Recrystallize this in isopropyl ether, and obtain pure BPA. Analyze the PC degradation rate, BPA yield, and Na residue in the pure BPA. The PC degradation rate is calculated to be 95%, the BPA yield is calculated to be 88.3%, and the Na residue in the BPA is calculated to be 605 ppm.

[0048] Comparative Example 1

[0049] In a 250 mL three-necked flask, sodium hydroxide 0.4 g, waste PC 15 g, methanol 20 g, dimethyl carbonate 90 g were added respectively, and stirred at 60 °C for 4 h. The reaction liquid was filtered, and then separated into light and heavy components by distillation under reduced pressure using a rotary evaporator at -0.09 MPa vacuum degree with a 40 °C oil bath. The light component was analyzed for the ratio of methanol / dimethyl carbonate by gas chromatography, and methanol was added and used continuously. The heavy component was dried at -0.1 MPa vacuum and 40 °C to obtain crude BPA, which was recrystallized in isopropyl ether to obtain pure BPA. The degradation rate of PC, the yield of BPA, and the residual amount of Na were analyzed by pure BPA. It was calculated that the degradation rate of PC was 100%, the yield of BPA was 96.2%, and the residual amount of Na in BPA was 1571 ppm.

[0050] Comparative Example 2

[0051] In a 250 mL three-necked flask, sodium hydroxide 0.4 g, waste PC 15 g, methanol 20 g, dimethyl carbonate 90 g were added respectively, and stirred at 60 °C for 4 h. The reaction liquid was filtered, and then separated into light and heavy components by distillation under reduced pressure using a rotary evaporator at -0.09 MPa vacuum degree with a 40 °C oil bath. The light component was analyzed for the ratio of methanol / dimethyl carbonate by gas chromatography, and methanol was added and used continuously. The heavy component was dried at -0.1 MPa vacuum and 40 °C to obtain crude BPA, which was recrystallized in isopropyl ether to obtain pure BPA. The degradation rate of PC, the yield of BPA, and the residual amount of Na were analyzed by pure BPA. It was calculated that the degradation rate of PC was 100%, the yield of BPA was 96.2%, and the residual amount of Na in BPA was 1571 ppm.

[0052] From the above examples and comparative examples, it can be clearly found that the sodium phenoxide organic base catalyst can obtain product BPA at a basically flat reaction rate compared with the traditional inorganic strong base (sodium hydroxide) catalysis in the catalysis of waste PC alcoholysis recovery, and due to its good solubility, the added molar amount is also smaller compared with the traditional inorganic strong base, and the introduced metal elements in the product BPA are also less.

[0053] From the results of Example 1 and Comparative Example 1, it can be known that the sodium phenoxide organic base catalyst described in the present application is replaced by the traditional alcoholysis catalyst sodium hydroxide, although the alcoholysis efficiency is very high, but as described in the background art, it will bring serious sodium residue problem, and in order to achieve the same less sodium residue effect as the present application, the amount of sodium hydroxide needs to be reduced, as shown in Comparative Example 2, but it will greatly sacrifice the reaction rate and yield.

[0054] The contents not described in detail in the specification of the present application belong to the prior art known to those skilled in the art, and some improvements and modifications made on the basis of the present application should also be considered within the scope of protection of the present application.

Claims

1. A process for the preparation of a phenolate sodium salt organic base catalyst, characterized in that, The phenolic compound is added into the sodium hydroxide solution in a molar ratio of 1:(1-2.5), and after heating and stirring, a phenolate catalyst is obtained by distillation under reduced pressure and drying.

2. The production method according to claim 1, characterized by, The phenolic compound is one or more of phenol, p-tert-butylphenol, and BPA.

3. The preparation method according to claim 1, characterized in that, The mass fraction of the sodium hydroxide solution is 5-20%.

4. The production method according to claim 1, characterized by, The heating temperature is 60-80°C, and the heating time is 1-3h; and / or: the pressure for distillation under reduced pressure is (-0.09MPa) to (-0.1MPa), and the temperature is 50-70°C.

5. A method for recycling BPA from waste PC through alcoholysis, characterized in that, (1) a mixed solution of the phenolate organic base catalyst, alcohol, waste PC, and solvent is prepared according to any one of claims 1-4; (2) the alcoholysis solution is obtained by filtering after heating; (3) BPA is obtained by post-treatment of the alcoholysis solution, and the solvent is recovered.

6. The method of claim 5, wherein, The alcohol is one or more of methanol, ethanol, and isopropanol, and is preferably methanol; and / or: the solvent is one or more of dimethyl carbonate, diethyl carbonate, and diisopropyl carbonate, and is preferably dimethyl carbonate; and the waste PC is preferably polycarbonate of bisphenol A.

7. The method of claim 5, wherein, The mixed mass ratio of the phenolate organic base catalyst, alcohol, waste PC, and solvent is (0.01-0.05):(1-2):1:(3-6).

8. The method of claim 5, wherein, The heating temperature in step (2) is 40-80°C, and the reaction time is 3-6h.

9. The method of claim 5, wherein, In step (3), the post-treatment method is: the alcoholysis solution obtained in step (2) is distilled under reduced pressure, the light component is alcohol, and is collected as a supplement of the alcohol in step (1); and the heavy component is recrystallized to obtain pure BPA product.

10. The method of claim 9, wherein, The distillation under reduced pressure is performed using a rotary evaporator at a vacuum degree of (-0.09MPa) to (-0.1MPa) and a temperature of 40-60°C, to obtain light and heavy components.

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