Method for degrading polycarbonate

Abstract

The invention discloses a method for degrading polycarbonate. The method comprises the following steps: providing a depolymerization solvent, wherein the depolymerization solvent is phenol; adding a metal hydroxide into the depolymerization solvent to form a mixed liquid; and adding a polycarbonate material to the mixed liquid, and adding a predetermined amount of water to the mixed liquid, thereby forming a reaction liquid. Wherein the addition concentration of the metal hydroxide is not less than 100 ppm, and the water content in the reaction liquid is regulated to be not more than 10 wt%. According to the present invention, the polycarbonate material is subjected to a depolymerization reaction to form bisphenol A and carbon dioxide, such that the chemical reaction is easily performed toward the depolymerization reaction, such that the polycarbonate depolymerization conversion rate is improved, and the bisphenol A (BPA) product yield is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a chemical method, in particular to a method for degrading polycarbonate. BACKGROUND

[0002] In the prior art, most of the patent contents proposed by companies such as LG (US2023 / 0382837 Al) and Sabic (WO 2020 / 257234 Al) use low-carbon alcohols (methanol or ethanol, etc.) and co-solvents (toluene or dichloromethane, etc.) for depolymerization of polycarbonate, and the use of co-solvents is beneficial to improve the depolymerization efficiency. However, the co-solvents used in the prior art may be left in the product BPA and affect the subsequent reaction, and toxic co-solvents will increase the difficulty of subsequent processing.

[0003] Therefore, the present inventors felt that the above-mentioned defects could be improved, and after diligent research and the use of scientific principles, the present application was finally proposed, which is reasonably designed and effectively improves the above-mentioned defects. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for degrading polycarbonate in view of the deficiencies of the prior art.

[0005] The present application discloses a method for degrading polycarbonate, characterized in that the method for degrading polycarbonate comprises: performing a preparation operation, comprising: providing a depolymerization solvent, wherein the depolymerization solvent is phenol; performing an adding operation, comprising: adding metal hydroxide to the depolymerization solvent to form a mixed liquid; and performing a depolymerization operation, comprising: adding polycarbonate material (PC) to the mixed liquid, and adding a predetermined amount of water to the mixed liquid to form a reaction liquid; wherein the addition concentration of the metal hydroxide is not less than 100 ppm, and the water content in the reaction liquid is regulated to be not more than 10 wt%; wherein the polycarbonate material performs a depolymerization reaction in the depolymerization operation to form a Bisphenol A (BPA) product and carbon dioxide (CO2).

[0006] Preferably, the preparation operation further comprises: heating the depolymerization solvent to a first heating temperature between 60°C and 100°C; wherein the depolymerization operation further comprises heating the reaction liquid to a second heating temperature between 110°C and 150°C.

[0007] Preferably, the preparation operation further comprises: heating the depolymerization solvent to a first heating temperature between 60°C to 100°C; wherein the depolymerization operation further comprises heating the reaction liquid to a second heating temperature between 110°C to 150°C.

[0008] Preferably, the depolymerization operation further comprises: during the depolymerization reaction, regulating the water content in the reaction liquid to be between 0.5wt% to 10wt%.

[0009] Preferably, when the water content in the reaction liquid is consumed to be lower than 0.5wt%, the depolymerization operation further comprises supplementing water into the reaction liquid to regulate the water content in the reaction liquid to be between 0.5wt% to 10wt%.

[0010] Preferably, the initial weight ratio of the depolymerization solvent to the polycarbonate material is between 1 to 14.

[0011] Preferably, the intermediate product formed from the depolymerization of the polycarbonate material is diphenyl carbonate, which is further depolymerized into phenol and carbon dioxide (CO2) in the depolymerization reaction; wherein the weight ratio of the depolymerization solvent to the polycarbonate material is continuously increased during the depolymerization reaction.

[0012] Preferably, the metal hydroxide is at least one selected from the group consisting of: alkali metal (Group 1A metal) hydroxide, alkaline earth metal (Group 2A metal) hydroxide, and transition metal hydroxide.

[0013] Preferably, the metal hydroxide is at least one of sodium hydroxide (NaOH) and potassium hydroxide (KOH).

[0014] Preferably, the addition concentration of the metal hydroxide is between 500ppm to 10,000ppm.

[0015] Preferably, the addition operation is adding an aqueous solution containing the metal hydroxide into the depolymerization solvent to form the mixed liquid.

[0016] Preferably, the weight percentage concentration of the metal hydroxide in the aqueous solution is between 15wt% to 60%.

[0017] To sum up, the method for degrading polycarbonate disclosed by the embodiment of the present application can make the chemical reaction favorably proceed in the direction of depolymerization reaction, thereby improving the conversion rate of polycarbonate depolymerization and improving the yield of bisphenol A (BPA) product, by the technical solutions of "preparation operation, comprising: providing a depolymerization solvent, wherein the depolymerization solvent is phenol; adding operation, comprising: adding metal hydroxide into the depolymerization solvent to form a mixed liquid; and depolymerization operation, comprising: adding polycarbonate (PC) material into the mixed liquid, and adding a predetermined amount of water into the mixed liquid to form a reaction liquid"; and "the adding concentration of the metal hydroxide is not less than 100 ppm, and the water content in the reaction liquid is regulated to be not more than 10 wt%".

[0018] The method for degrading polycarbonate of the present application can effectively avoid the problem that the co-solvent (such as toluene or dichloromethane, etc.) may remain in the product (such as BPA) after using the co-solvent in the prior art.

[0019] For further understanding of the features and technical contents of the present application, please refer to the following detailed description and drawings of the present application, but these descriptions and drawings are only used to illustrate the present application, and do not limit the protection scope of the present application in any way. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The flowchart of the method for degrading polycarbonate of the embodiment of the present application. DETAILED DESCRIPTION

[0021] The following is to illustrate the disclosed embodiments of the present application by specific embodiments, and those skilled in the art can understand the advantages and effects of the present application from the disclosed contents of the present application. The present application can be implemented or applied by other different embodiments, and each detail in the present specification can be modified and changed in various ways based on different viewpoints and applications without departing from the concept of the present application. In addition, the drawings of the present application are only simple schematic illustrations, and are not the depiction of actual size, which is declared in advance. The following embodiments will further illustrate the related technical contents of the present application, but the disclosed contents are not used to limit the protection scope of the present application.

[0022] It should be understood that, although the terms "first", "second", "third", etc. can be used herein to describe various materials or parameters, these materials or parameters should not be limited by these terms. These terms are only used to distinguish one material or parameter from another. In addition, the term "or" used herein can include a combination of any one or more of the associated listed items as the case can be.

[0023] [Method for degrading polycarbonate]

[0024] As shown in Figure 1 , the embodiments of the present application aim to provide a method for degrading polycarbonate (PC), in particular, a method for degrading polycarbonate by using a transesterification technique. The method for degrading polycarbonate according to the embodiments of the present application can effectively avoid the problem that, in the prior art, after using a co-solvent (such as toluene or dichloromethane, etc.), the co-solvent can be left in the product (such as BPA).

[0025] Specifically, the method for degrading polycarbonate (PC) according to the embodiments of the present application comprises: a step S110, a step S120, and a step S130. It should be noted that the order of the steps described in the embodiments and the actual operation mode can be adjusted according to requirements, and are not limited to the embodiments described herein.

[0026] The step S110 is a preparation operation, which comprises: providing a de-polymerizing solvent and adding it into a reaction tank. The de-polymerizing solvent is phenol. More specifically, the preparation operation according to the embodiments of the present application uses phenol as the only de-polymerizing solvent.

[0027] In the embodiments, the preparation operation further comprises: heating the de-polymerizing solvent to a first heating temperature.

[0028] The first heating temperature is between 60°C and 100°C, preferably between 70°C and 90°C, and more preferably between 75°C and 85°C. For example, the first heating temperature can be 80°C, but the present application is not limited thereto.

[0029] The step S120 is an adding operation, which comprises: adding a metal hydroxide into the de-polymerizing solvent in the reaction tank to form a mixed liquid.

[0030] The metal hydroxide is an anion OH - ) and a metal cation Mn +It is composed of metal hydroxides that can dissociate in the presence of water.

[0031] In some embodiments of the present invention, the metal hydroxide may be at least one of the group of materials selected from: hydroxides of alkali metals (Group 1A metals), hydroxides of alkaline earth metals (Group 2A metals), and hydroxides of transition metals.

[0032] For example, the hydroxide of the alkali metal (Group 1A metal) can be, for example, sodium hydroxide (NaOH) or potassium hydroxide (KOH). The hydroxide of the alkaline earth metal (Group 2A metal) can be, for example, magnesium hydroxide (Mg(OH)2) or calcium hydroxide (Ca(OH)2). Additionally, the hydroxide of the transition metal can be, for example, manganese hydroxide (Mn(OH)2), but the invention is not limited thereto. In this embodiment, the metal hydroxide is preferably at least one of sodium hydroxide (NaOH) and potassium hydroxide (KOH).

[0033] Furthermore, in the mixed liquid, the concentration of the added metal hydroxide is not less than 100 ppm (parts per million), preferably between 100 ppm and 200,000 ppm, and particularly preferably between 500 ppm and 10,000 ppm. Specifically, it can be between 829 ppm and 8,719 ppm, but is not limited thereto.

[0034] Furthermore, in this embodiment of the invention, the addition process involves adding an aqueous solution containing the metal hydroxide to the depolymerization solvent to mix with it, thereby forming a mixed liquid comprising the depolymerization solvent, the metal hydroxide, and water. The metal hydroxide is capable of dissociating into hydroxide ions (OH-) in the presence of water. - Anions and metal cations Mn + (eg: Na + or K + This catalyzes the depolymerization of subsequently added polycarbonate (PC).

[0035] In the aqueous solution, the weight percentage concentration of the metal hydroxide is between 15 wt% and 60%, preferably between 20 wt% and 45 wt%, and particularly preferably between 25 wt% and 40 wt%. For example, in an embodiment of the present invention, the metal hydroxide added to the aqueous solution is sodium hydroxide (NaOH), and its weight percentage concentration is 32 wt%, but the present invention is not limited thereto.

[0036] In addition, the water solution (containing metal hydroxide) is added to the depolymerization solvent in an amount of about 1 / 400 to 1 / 20 of the depolymerization solvent, and the concentration of the metal hydroxide in the depolymerization solvent can be adjusted by the amount of the water solution added, which is in the range of the above-mentioned concentration (e.g., not less than 100 ppm, preferably 100 to 200,000 ppm, and more preferably 500 to 100,000 ppm).

[0037] However, the present application is not limited to the above-mentioned embodiments, and the adding operation of the present application can also be, for example, directly adding the powder of the metal hydroxide to the depolymerization solvent, and then adding an appropriate amount of water to form a mixed liquid containing a specific concentration of metal hydroxide.

[0038] The step S130 is to perform a depolymerization operation, which includes adding polycarbonate material to the mixed liquid in the reaction tank, and optionally adding a predetermined amount of water to the mixed liquid to form a reaction liquid.

[0039] Accordingly, the reaction liquid contains water, depolymerization solvent, metal hydroxide, and polycarbonate material. The water content in the reaction liquid is adjusted to not more than 10 wt%.

[0040] In the present embodiment, the polycarbonate material is polycarbonate particles to be depolymerized, which can be crushed from recycled polycarbonate waste, but the present application is not limited thereto.

[0041] The depolymerization operation further includes heating the reaction liquid to a second heating temperature to make the polycarbonate material undergo a depolymerization reaction, and finally produce Bisphenol A (BPA) product and carbon dioxide (CO2) gas.

[0042] More specifically, the depolymerization operation is to heat the reaction liquid from the above-mentioned first temperature (e.g., 60 to 100°C) to a second heating temperature, and the second heating temperature is between 110 to 150°C, preferably between 110 to 140°C, and more preferably between 110 to 135°C. For example, the second heating temperature can be, for example, 120°C, but the present application is not limited thereto.

[0043] Further, the depolymerization operation continues to stir the reaction liquid for 1 to 10 hours, preferably 2 to 8 hours, and more preferably 3 to 6 hours after the reaction liquid is heated to the second heating temperature, so that the depolymerization reaction is sufficiently carried out.

[0044] It is worth mentioning that in the present embodiment, the depolymerization operation further comprises: during the depolymerization reaction, the water content in the reaction liquid is regulated to be between 0.5wt% and 10wt%, preferably between 1wt% and 10wt%, and particularly preferably between 1.4wt% and 9wt%.

[0045] Accordingly, the polycarbonate material can achieve a high depolymerization conversion rate under the conditions of the above-mentioned addition concentration (not less than 100 ppm) and water content (0.5-10wt%) of the metal hydroxide.

[0046] In the embodiment of the present application, the initial weight ratio between the depolymerization solvent in the reaction liquid and the polycarbonate material (the weight ratio of the feed) is between 300-700: 50-300, preferably between 400-600: 100-300, and particularly preferably between 450-550: 150-250.

[0047] In other words, the initial weight ratio between the depolymerization solvent in the reaction liquid and the polycarbonate material (i.e., the ratio of the initial weight of the depolymerization solvent to the initial weight of the polycarbonate material) is between 1-14, preferably between 1.5-5.0, and particularly preferably between 2-3.

[0048] For example, the initial amount of the depolymerization solvent (phenol) is 500 parts by weight, and the initial amount of the polycarbonate material (PC) is 200 parts by weight, so the ratio of the initial weight of the depolymerization solvent to the initial weight of the polycarbonate material is 2.5 (i.e., 500 / 200).

[0049] Further, in the depolymerization operation (step S130), the water content in the reaction liquid is regulated to be between 0.5wt% and 10wt%, for example, by taking out a small amount of reaction liquid (e.g., 1ml-10ml of reaction liquid) from the reaction tank and detecting the water content in the reaction liquid with a water content detector.

[0050] It is worth mentioning that the depolymerization reaction can reduce the water content in the reaction liquid (because the depolymerization reaction consumes water). The embodiment of the present application monitors the water content during the depolymerization reaction. When the water content in the reaction liquid is consumed to be lower than 0.5wt%, the depolymerization operation can further comprise supplementing water to the reaction liquid to regulate the water content in the reaction liquid to be between 0.5wt% and 10wt%. Accordingly, the above-mentioned operation can help the polycarbonate material to further depolymerize without causing the bisphenol A (BPA) product to crack, thereby improving the yield of the bisphenol A product.

[0051] It is also worth mentioning that in the depolymerization reaction, the intermediate product formed from the depolymerization of the polycarbonate material is diphenyl carbonate (DC), which will further depolymerize to phenol (R-OH) and carbon dioxide (CO2) gas in the depolymerization reaction.

[0052] Overall, the depolymerization reaction is carried out in the order of the following chemical reaction mechanism 1 and chemical reaction mechanism 2.

[0053] Chemical reaction mechanism 1: The polycarbonate (PC) material is first depolymerized to form the product of bisphenol A (BPA) and the intermediate product of diphenyl carbonate (DC) in the presence of a depolymerization solvent (i.e., phenol, R-OH, where R is phenyl), a metal hydroxide (catalyst, M-OH, where M is a metal), and water (H2O).

[0054] [Chemical reaction mechanism 1: PC → BPA + DC]

[0055]

[0056] Chemical reaction mechanism 2: The diphenyl carbonate intermediate product (DC) will further depolymerize to form phenol (R-OH) and carbon dioxide (CO2) gas in the depolymerization reaction (in the presence of water).

[0057] [Chemical reaction mechanism 2: DC → R-OH + CO2(g)]

[0058]

[0059] In the chemical reaction mechanism 1, the product of bisphenol A (BPA) produced will not further crack under the above conditions (water content is controlled to 0.5wt% to 10wt%) (only the diphenyl carbonate intermediate product DC will crack), so that the bisphenol A product is retained and the yield is improved.

[0060] Accordingly, the polycarbonate material ultimately forms the bisphenol A (BPA) product and the phenol (R-OH) byproduct under the above water content and metal oxide concentration, and additionally produces carbon dioxide (CO2) gas. The conversion rate of polycarbonate (PC) depolymerization is 90% to 99% (i.e., the conversion rate of PC from a high molecular compound to a small molecule chemical, representing 90% to 99% of PC depolymerization).

[0061] Finally, the bisphenol A (BPA) product can be recovered, for example, by cooling crystallization.

[0062] It is worth mentioning that, since the intermediate product (diphenyl carbonate) generated by polycarbonate (PC) can be further depolymerized into phenol (R-OH) during the reaction process, and the phenol (R-OH) used in the single depolymerization solvent (phenol) employed in the embodiments of the present application is the same compound, therefore, during the depolymerization reaction process, the weight ratio of the depolymerization solvent (phenol) to polycarbonate (PC) (i.e., the weight ratio of phenol / polycarbonate) will continue to increase, thereby facilitating the depolymerization reaction and facilitating the recovery of the depolymerization solvent. In addition, since the depolymerization solvent / polycarbonate weight ratio will continue to increase during the depolymerization reaction process, the initial amount of the depolymerization solvent can be reduced.

[0063] In addition, it is worth mentioning that the present inventors have found through experiments that the metal hydroxide (such as NaOH or KOH) greater than 100 ppm and water content of 0.5-10 wt% is beneficial to the rapid depolymerization of polycarbonate (PC) to form bisphenol A (BPA) and carbon dioxide. Accordingly, the polycarbonate depolymerization reaction can be carried out in a single depolymerization solvent. If the water content is less than 0.5 wt%, the concentration of the metal hydroxide will be too high (since the metal hydroxide is dissociated in water to form hydroxide anion OH - and metal cation Mn+), which can cause the bisphenol A (BPA) product to be degraded in a strong alkali environment, which is an undesirable reaction. Conversely, if the water content is greater than 10 wt%, the concentration of the metal hydroxide will be too low, thereby reducing the overall depolymerization efficiency.

[0064] It is worth mentioning that, in the embodiments, taking 100 g of polycarbonate as an example, it can be depolymerized into 89.7 g of BPA, 17.3 g of CO2(g), and about 7 g of water is consumed, that is, the water content of the reaction liquid will decrease during the depolymerization reaction process. The embodiments of the present application control the water content in the reaction liquid by monitoring and adding water to achieve the technical effects described above.

[0065] To sum up, in order to solve the technical problems existing in the prior art, the present application provides a method for degrading polycarbonate (a method for degrading polycarbonate by transesterification technology), which comprises using phenol as a single depolymerization solvent, and under the condition that the content of metal hydroxide (such as NaOH or KOH) is greater than 100 ppm (preferably 100-200,000 ppm, and more preferably 500-10,000 ppm), and by adjusting the water content of the reaction liquid to be between 0.5wt% and 10wt% during the depolymerization reaction, the intermediate product (diphenyl carbonate) in the reaction is further depolymerized to form phenol (the same as the depolymerization solvent) and carbon dioxide (which can be removed from the system tail gas or removed by carbon dioxide adsorption), thereby making the system reaction beneficial to the direction of the depolymerization reaction, so as to improve the conversion rate of polycarbonate depolymerization to 90%-99%, and the yield of the product bisphenol A (BPA) is not less than 60%.

[0066] Furthermore, the method for degrading polycarbonate according to the embodiments of the present application can effectively avoid the problem that the co-solvent (such as toluene or dichloromethane) may remain in the product (such as BPA) after using the co-solvent in the prior art.

[0067] [Experimental data and test results]

[0068] The following embodiments are used to illustrate the content of the present application. However, the following embodiments are only used to help understand the present application, and the scope of the present application is not limited to these embodiments.

[0069] [Example 1]

[0070] 500 parts by weight of a depolymerization solvent (phenol) was added to the reaction tank, and the temperature of the depolymerization solvent was heated to 80°C (i.e., the first heating temperature). 4 parts by weight of an aqueous metal hydroxide solution (32% NaOH) was added to the reaction tank and mixed with the depolymerization solvent to form a mixed liquid. 200 parts by weight of polycarbonate (PC) particles and 35 parts by weight of water were added to the mixed liquid in the reaction tank to form a reaction liquid. The reaction liquid was heated to 120°C (i.e., the second heating temperature), and the reaction liquid was continuously stirred for 5 hours to make the polycarbonate (PC) undergo a depolymerization reaction to form bisphenol A (BPA), phenol, and carbon dioxide. Among them, the concentration of metal hydroxide (NaOH) in the reaction liquid was 1,732 ppm, and the water content in the reaction liquid was adjusted to 4.7wt%.

[0071] [Example 2]

[0072] 500 parts by weight of a depolymerization solvent (phenol) was added to the reaction tank, and the temperature of the depolymerization solvent was heated to 80°C (i.e., a first heating temperature). 2 parts by weight of an aqueous metal hydroxide solution (32% NaOH) was added to the reaction tank, mixed with the depolymerization solvent to form a mixed liquid. 200 parts by weight of polycarbonate (PC) pellets and 70 parts by weight of water were added to the mixed liquid in the reaction tank to form a reaction liquid. The reaction liquid was heated to 120°C (i.e., a second heating temperature), and the reaction liquid was continuously stirred for 5 hours to allow the polycarbonate (PC) to undergo a depolymerization reaction to form bisphenol A (BPA), phenol, and carbon dioxide. The concentration of the metal hydroxide (NaOH) in the reaction liquid was 829 ppm, and the water content in the reaction liquid was regulated to 9.0 wt%.

[0073] <Example 3>

[0074] 500 parts by weight of a depolymerization solvent (phenol) was added to the reaction tank, and the temperature of the depolymerization solvent was heated to 80°C (i.e., a first heating temperature). 20 parts by weight of an aqueous metal hydroxide solution (32% NaOH) was added to the reaction tank, mixed with the depolymerization solvent to form a mixed liquid. 200 parts by weight of polycarbonate (PC) pellets and 14 parts by weight of water were added to the mixed liquid in the reaction tank to form a reaction liquid. The reaction liquid was heated to 120°C (i.e., a second heating temperature), and the reaction liquid was continuously stirred for 5 hours to allow the polycarbonate (PC) to undergo a depolymerization reaction to form bisphenol A (BPA), phenol, and carbon dioxide. The concentration of the metal hydroxide (NaOH) in the reaction liquid was 8,719 ppm, and the water content in the reaction liquid was regulated to 1.4 wt%.

[0075] <Comparative Example 1>

[0076] 500 parts by weight of a depolymerization solvent (phenol) was added to the reaction tank, and the temperature of the depolymerization solvent was heated to 80°C (i.e., a first heating temperature). 4 parts by weight of an aqueous metal hydroxide solution (32% NaOH) was added to the reaction tank, mixed with the depolymerization solvent to form a mixed liquid. 200 parts by weight of polycarbonate (PC) pellets were added to the mixed liquid in the reaction tank to form a reaction liquid. The reaction liquid was heated to 120°C (i.e., a second heating temperature), and the reaction liquid was continuously stirred for 5 hours to allow the polycarbonate (PC) to undergo a depolymerization reaction. The concentration of the metal hydroxide (NaOH) in the reaction liquid was 1,818 ppm, and the water content in the reaction liquid was 0.18 wt% (not regulated).

[0077] Comparative Example 1 was prepared in substantially the same manner as Example 1 above, except that Comparative Example 1 did not additionally add water in the reaction liquid, and the water content in the reaction liquid was 0.18 wt%, which was lower than 4.7 wt% of Example 1, and also lower than the requirement of 0.5 wt% of the present application.

[0078] Next, Examples 1 to 3 and Comparative Example 1 above were tested to obtain the depolymerization conversion rate of polycarbonate (PC) and the product yield (%) of bisphenol A (BPA).

[0079] It is worth mentioning that in the item of test results in Table 1, the depolymerization conversion rate of polycarbonate (PC) was obtained by the following manner: first, 10 grams of the crude reaction liquid after the depolymerization reaction (i.e. the reaction liquid after the depolymerization reaction) was taken. The 10 grams of the crude reaction liquid was added into 50 grams of methanol, and then filtered. After the filtration, the filter cake was washed with 50 grams of methanol. Then, the filter cake was dried to record the weight (S) of the obtained solid.

[0080] The depolymerization conversion rate (%) = (100 - S / (10*(PC / total weight of reaction liquid))).

[0081] In the formula, S is the weight of the obtained solid after drying, 10 grams is the weight of the initial crude reaction liquid taken, PC is the initial amount of polycarbonate (PC) particles, and the total weight of reaction liquid is the total weight of the reaction liquid.

[0082] In addition, the product yield (%) of bisphenol A (BPA) was tested by the following manner: first, the crude reaction liquid after the depolymerization reaction was taken and analyzed by high performance liquid chromatography (HPLC) to determine the concentration A of BPA. Then, the product yield (%) of bisphenol A (BPA) was calculated by the following formula:

[0083] A / (PC / total weight of reaction liquid)*100.

[0084] In the formula, A is the concentration of BPA, PC is the initial amount of polycarbonate (PC) particles, and the total weight of reaction liquid is the total weight of the reaction liquid.

[0085] [Table 1 Process Conditions and Test Results]

[0086]

[0087] From the experimental results of Table 1 above, it can be seen that the process conditions of Examples 1 to 3 meet the requirements of the present application for the concentration of metal hydroxide and the water content in the reaction liquid, and the depolymerization conversion rate of polycarbonate (PC) is not less than 90%, and the product yield of bisphenol A (BPA) is not less than 60%.

[0088] Comparative Example 1 does not add water additionally in the reaction liquid, and the water content in the reaction liquid is 0.18wt% (not regulated), which is lower than 4.7wt% of Example 1, and also lower than the requirement of 0.5wt%.

[0089] The depolymerization conversion rate of polycarbonate (PC) of Comparative Example 1 is 53%, which is far lower than the test results of Examples 1-3, and the product yield of bisphenol A (BPA) of Comparative Example 1 is 38%, which is also far lower than the test results of Examples 1-3.

[0090] [Advantages of the embodiments]

[0091] The method for degrading polycarbonate provided by the present application can make the chemical reaction favorably proceed in the direction of depolymerization reaction, thereby improving the conversion rate of polycarbonate depolymerization and the yield of bisphenol A (BPA) product, by the technical solutions of "preparation operation, comprising: providing a depolymerization solvent, wherein the depolymerization solvent is phenol; adding operation, comprising: adding metal hydroxide into the depolymerization solvent to form a mixed liquid; and depolymerization operation, comprising: adding polycarbonate material (PC) into the mixed liquid, and adding a predetermined amount of water into the mixed liquid to form a reaction liquid"; and "the addition concentration of the metal hydroxide is not less than 100ppm, and the water content in the reaction liquid is regulated to not more than 10wt%".

[0092] The method for degrading polycarbonate provided by the present application can effectively avoid the problem that the co-solvent (such as toluene or dichloromethane, etc.) may remain in the product (such as BPA) after using the co-solvent in the prior art.

[0093] The above description is only the preferred and feasible embodiments of the present application, and is not intended to limit the protection scope of the present application. Any equivalent changes and modifications made according to the claims of the present application shall be within the protection scope of the claims of the present application.

Claims

1. A method for degrading polycarbonate, characterized in that, The method for degrading polycarbonate includes: performing a preparation operation, comprising: providing a depolymerization solvent, wherein the depolymerization solvent is phenol; The addition process includes: adding a metal hydroxide to the depolymerization solvent to form a mixed liquid; and The depolymerization process includes: adding polycarbonate material to the mixed liquid and adding a predetermined amount of water to the mixed liquid to form a reaction liquid; Wherein, the concentration of the added metal hydroxide is not less than 100 ppm, and the water content in the reaction liquid is controlled to be not more than 10 wt%; The polycarbonate material undergoes a depolymerization reaction during the depolymerization process to form bisphenol A product and carbon dioxide.

2. The method for degrading polycarbonate according to claim 1, characterized in that, The preparation process further includes heating the depolymerization solvent to a first heating temperature between 60°C and 100°C; wherein the depolymerization process further includes heating the reaction liquid to a second heating temperature between 110°C and 150°C.

3. The method for degrading polycarbonate according to claim 2, characterized in that, The preparation process further includes heating the depolymerization solvent to a first heating temperature between 60°C and 100°C; wherein the depolymerization process further includes heating the reaction liquid to a second heating temperature between 110°C and 150°C.

4. The method for degrading polycarbonate according to claim 1, characterized in that, The depolymerization process further includes: adjusting the water content in the reaction liquid to between 0.5 wt% and 10 wt% during the depolymerization reaction.

5. The method for degrading polycarbonate according to claim 4, characterized in that, When the water content in the reaction liquid is consumed to below 0.5 wt%, the depolymerization process further includes adding water to the reaction liquid to adjust the water content in the reaction liquid to between 0.5 wt% and 10 wt%.

6. The method for degrading polycarbonate according to claim 1, characterized in that, The initial weight ratio of the depolymerization solvent to the polycarbonate material is between 1 and 14.

7. The method for degrading polycarbonate according to claim 1, characterized in that, The intermediate product formed by the depolymerization of the polycarbonate material is diphenyl carbonate, which is further depolymerized into phenol and carbon dioxide in the depolymerization reaction; wherein, during the depolymerization reaction, the weight ratio of the depolymerization solvent to the polycarbonate material continuously increases.

8. The method for degrading polycarbonate according to claim 1, characterized in that, The metal hydroxide is selected from at least one of the group of materials consisting of alkali metal hydroxides, alkaline earth metal hydroxides, and transition metal hydroxides.

9. The method for degrading polycarbonate according to claim 8, characterized in that, The metal hydroxide is at least one of sodium hydroxide and potassium hydroxide.

10. The method for degrading polycarbonate according to claim 1, characterized in that, The concentration of the added metal hydroxide is between 500 ppm and 10,000 ppm.

11. The method for degrading polycarbonate according to claim 1, characterized in that, The addition process involves adding an aqueous solution containing the metal hydroxide to the depolymerization solvent to form the mixed liquid.

12. The method for degrading polycarbonate according to claim 11, characterized in that, In the aqueous solution, the weight percentage concentration of the metal hydroxide is between 15 wt% and 60 wt%.

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