Method for degrading polycarbonate

Abstract

To provide a method for degrading polycarbonate.SOLUTION: A method for degrading polycarbonate includes: providing a depolymerizing solvent, in which the depolymerizing solvent is phenol; adding a metal hydroxide to the depolymerizing 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 to form a reaction liquid. An added concentration of the metal hydroxide is 100 ppm or more, and the water content in the reaction liquid is 10 wt % or less. The polycarbonate material undergoes a depolymerization reaction to form bisphenol A and carbon dioxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a chemical process, in particular to a process for decomposing polycarbonate. [Background technology]

[0002] In existing technologies, most of the patents proposed by companies such as LG (Patent Document 1) and Sabic (Patent Document 2) use low-carbon alcohols (e.g., methanol or ethanol) and co-solvents (e.g., toluene or dichloromethane) to depolymerize polycarbonate, and the use of co-solvents improves depolymerization efficiency. However, the co-solvents used in existing technologies remain in the product, bisphenol A (BPA), which can affect subsequent reactions, and the toxic co-solvents make subsequent processing difficult.

[0003] Therefore, the inventors believed that the above-mentioned defects could be improved, and after diligent research and in line with scientific principles, they discovered an invention that is rationally designed and can effectively improve the above-mentioned drawbacks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Publication No. 2023 / 0382837 [Patent Document 2] International Publication No. 2020 / 257234 Summary of the Invention [Problem to be solved by the invention]

[0005] The technical problem to be solved by the present invention is to provide a method for decomposing polycarbonate in response to the shortcomings of the prior art. [Means for solving the problem]

[0006] To solve the above technical problems, one technical solution adopted by the present invention is a method for decomposing polycarbonate, which includes a preparation step of providing a depolymerization solvent that is phenol, an addition step of adding a metal hydroxide to the depolymerization solvent to prepare a mixed solution, and a depolymerization step of adding a polycarbonate material (PC) to the mixed solution and a predetermined amount of water to prepare a reaction solution, where the concentration of the metal hydroxide added is 100 ppm or more and the water content of the reaction solution is 10 wt% or less. In the depolymerization step, the polycarbonate material is subjected to a depolymerization reaction to form products, bisphenol A (BPA) and carbon dioxide (CO2).

[0007] Preferably, the preparation step further includes heating the depolymerization solvent to a first heating temperature of 60°C to 100°C, and the depolymerization step further includes heating the reaction solution to a second heating temperature of 110°C to 150°C.

[0008] Preferably, the first heating temperature is 70°C to 90°C, and the second heating temperature is 110°C to 140°C.

[0009] Preferably, in the depolymerization step, the water content in the reaction liquid is controlled to 0.5 wt % to 10 wt % during the depolymerization reaction.

[0010] Preferably, when the water content in the reaction solution is consumed to less than 0.5 wt%, the depolymerization step further includes supplementing water to the reaction solution so as to control the water content in the reaction solution to 0.5 wt% to 10 wt%.

[0011] Preferably, the initial weight ratio of the depolymerization solvent to the polycarbonate material is 1-14.

[0012] Preferably, the intermediate produced by depolymerizing the polycarbonate material is diphenyl carbonate, and the diphenyl carbonate is further depolymerized into phenol and carbon dioxide (CO2) in the depolymerization reaction, and the weight ratio of the depolymerization solvent to the polycarbonate material continues to increase during the depolymerization reaction.

[0013] Preferably, the metal hydroxide is at least one selected from the group consisting of alkali metal (Group 1 element) hydroxides, alkaline earth metal (Group 2 element) hydroxides, and transition metal hydroxides.

[0014] Preferably, the metal hydroxide is at least one selected from the group consisting of sodium hydroxide (NaOH) and potassium hydroxide (KOH).

[0015] Preferably, the concentration of the metal hydroxide added is 500 ppm to 10,000 ppm.

[0016] Preferably, in the adding step, the mixed solution is prepared by adding the aqueous solution containing the metal hydroxide to the depolymerization solvent.

[0017] Preferably, the aqueous solution contains the metal hydroxide at a weight percent concentration of 15 wt % to 60 wt %. [Effects of the Invention]

[0018] As an advantageous effect of the present invention, the polycarbonate decomposition method of the present invention includes "a preparation step, which includes providing a depolymerization solvent that is phenol; an addition step, which includes adding a metal hydroxide to the depolymerization solvent to prepare a mixed solution; and a depolymerization step, which includes adding a polycarbonate material (polycarbonate, PC) to the mixed solution and adding a predetermined amount of water to the mixed solution to prepare a reaction solution" and "the concentration of the metal hydroxide added is 100 ppm or more, and the water content in the reaction solution is 10 wt% or less." These technical features allow the chemical reaction to proceed in a manner that is favorable for the depolymerization reaction, improving the conversion rate of polycarbonate depolymerization and increasing the yield of the product bisphenol A (BPA).

[0019] The method for decomposing polycarbonate of the present invention can efficiently avoid the problem of co-solvents (such as toluene and dichloromethane) remaining in the product (e.g., BPA) after using them in existing techniques. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic flowchart of a method for decomposing polycarbonate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] To better understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings, which are provided for reference and explanation only and do not limit the scope of the present invention.

[0022] The following describes the implementation of the present invention through certain specific embodiments, and those skilled in the art can understand the advantages and effects of the present invention based on the content disclosed herein. The present invention can be implemented or applied through other different specific embodiments, and various modifications and changes can be made to the details in this specification based on different perspectives and applications without departing from the concept of the present invention. It should be noted in advance that the accompanying drawings of the present invention are for simple schematic illustrations and are not drawn to actual size. The technical content of the present invention will be described in more detail based on the following implementation, but the disclosed content does not limit the protection scope of the present invention.

[0023] It should be understood that although terms such as "first," "second," and "third" may be used herein to describe various materials or parameters, these materials or parameters are not limited by these terms. These terms are primarily used to distinguish one material from another or one parameter from another. Furthermore, the term "or" used herein may include any one or more combinations of the associated listed items, depending on the actual circumstances.

[0024] [How to disassemble polycarbonate] As shown in Figure 1, an embodiment of the present invention provides a method for decomposing polycarbonate (PC), particularly a method for decomposing polycarbonate using a transesterification reaction technique. The polycarbonate decomposition method according to an embodiment of the present invention can effectively avoid the problem of using a co-solvent (such as toluene or dichloromethane) in existing techniques, where the co-solvent may remain in the product (e.g., BPA).

[0025] Specifically, the method for decomposing polycarbonate (PC) according to an embodiment of the present invention includes steps S110, S120, and S130. It should be noted that the order and operation method of each step in this embodiment can be adjusted as needed and are not limited to this embodiment.

[0026] In step S110, a preparation step is performed. The preparation step includes providing a depolymerizing solvent, which is phenol, and adding it to a reaction tank. More specifically, in the preparation step of this embodiment, phenol is used as the sole depolymerizing solvent.

[0027] In this embodiment, the preparing step further includes heating the depolymerization solvent to a first heating temperature.

[0028] Here, the first heating temperature is 60° C. to 100° C., preferably 70° C. to 90° C., and particularly preferably 75° C. to 85° C. For example, the first heating temperature may be 80° C., but the present invention is not limited thereto.

[0029] In step S120, an adding step is carried out, which includes adding metal hydroxide to the depolymerization solvent in the reaction tank to prepare a mixed solution.

[0030] Here, the metal hydroxide has an anion, hydroxide ion (OH - ), and a metal cation M n+ wherein the metal hydroxide is capable of dissociating in the presence of water.

[0031] In one embodiment of the present invention, the metal hydroxide may be at least one selected from the group consisting of alkali metal (Group 1 element) hydroxides, alkaline earth metal (Group 2 element) hydroxides, and transition metal hydroxides.

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

[0033] The concentration of the metal hydroxide added to the mixed solution is 100 ppm (parts per million) or more, preferably 100 ppm to 200,000 ppm, and particularly preferably 500 ppm to 10,000 ppm. Specifically, it may be 829 ppm to 8,719 ppm, but the present invention is not limited thereto.

[0034] More specifically, in the adding step according to an embodiment of the present invention, the aqueous solution containing the metal hydroxide is added to the depolymerization solvent, thereby mixing with the depolymerization solvent to prepare the mixed solution containing the depolymerization solvent, the metal hydroxide, and water. Here, the metal hydroxide converts into hydroxide ions (OH - ) and metal cation M n+ (Na + YaK + etc.), thereby catalyzing the depolymerization of the subsequently added polycarbonate (PC).

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

[0036] The amount of the aqueous solution (containing a metal hydroxide) added to the depolymerization solvent is approximately 1 / 400 to 1 / 20 of the depolymerization solvent, and the concentration of the metal hydroxide in the depolymerization solvent can be controlled within the range (for example, 100 ppm or more, preferably 100 to 200,000 ppm, and particularly preferably 500 to 100,000 ppm) by adjusting the amount of the aqueous solution added.

[0037] However, the present invention is not limited to the above embodiment, and the adding step of the embodiment of the present invention may be, for example, by directly adding the metal hydroxide powder to the depolymerization solvent and then adding an appropriate amount of water to prepare a metal hydroxide mixed solution having a specific concentration.

[0038] In step S130, a depolymerization step is carried out, which includes adding a polycarbonate material to a mixture in a reaction tank and selectively adding a predetermined amount of water to the mixture to prepare a reaction solution.

[0039] Thus, the reaction solution contains water, a depolymerization solvent, a metal hydroxide, and a polycarbonate material, and the water content in the reaction solution is controlled to 10 wt % or less.

[0040] In this embodiment, the polycarbonate material is polycarbonate particles that have not yet been depolymerized, and the polycarbonate may be crushed recycled polycarbonate waste, but the present invention is not limited thereto.

[0041] The depolymerization step further includes heating the reaction solution to a second heating temperature to cause a depolymerization reaction on the polycarbonate material, ultimately producing products of bisphenol A (BPA) and carbon dioxide (CO2) gas.

[0042] More specifically, in the depolymerization step, the reaction solution is heated from the first heating temperature (for example, 60°C to 100°C) to a second heating temperature, and the second heating temperature is 110°C to 150°C, preferably 110°C to 140°C, and particularly preferably 110°C to 135°C. For example, the second heating temperature may be 120°C, but the present invention is not limited thereto.

[0043] In the depolymerization step, after the reaction solution is heated to the second heating temperature, the reaction solution is continuously stirred for 1 to 10 hours. The stirring time is preferably 2 to 8 hours, and particularly preferably 3 to 6 hours. This allows the depolymerization reaction to proceed sufficiently.

[0044] It is noteworthy that in the depolymerization step of the present embodiment, during the depolymerization reaction, the water content in the reaction liquid is controlled to 0.5 wt % to 10 wt %, preferably 1 wt % to 10 wt %, and particularly preferably 1.4 wt % to 9 wt %.

[0045] Thus, the polycarbonate material can achieve a high depolymerization conversion rate under the conditions of the metal hydroxide addition concentration (100 ppm or more) and water content (0.5 to 10 wt%).

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

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

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

[0049] Furthermore, in the depolymerization step (step S130), the water content in the reaction liquid is controlled to 0.5 wt% to 10 wt%, and as a method for controlling the water content, for example, a small amount of reaction liquid (for example, 1 ml to 10 ml of reaction liquid) is taken out from the reaction tank, and the water content in the reaction liquid is detected with a water detector.

[0050] It is worth noting that the depolymerization reaction may reduce the water content of the reaction solution (because water is consumed during the depolymerization reaction). In an embodiment of the present invention, by monitoring the water content during the depolymerization reaction, when the water content of the reaction solution is consumed to less than 0.5 wt%, the depolymerization step may further include adding water to the reaction solution to control the water content of the reaction solution to 0.5 wt% to 10 wt%. In this way, this operating method helps to further depolymerize the polycarbonate material without decomposing the product bisphenol A (BPA), thereby improving the yield of the product bisphenol A.

[0051] It is further noted that in the depolymerization reaction, the intermediate product obtained by depolymerizing the polycarbonate material is diphenyl carbonate (DC), which is further depolymerized into phenol (R—OH) and carbon dioxide (CO2) in the depolymerization reaction.

[0052] Generally speaking, the depolymerization reaction proceeds in the following order of Chemical Reaction Mechanism 1 and Chemical Reaction Mechanism 2.

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

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

[0055] Chemical Reaction Mechanism 2: The diphenyl carbonate intermediate (DC) is further depolymerized in the depolymerization reaction (in the presence of water) to form phenol (R—OH) and carbon dioxide (CO2) gas.

[0056] [Chemical reaction mechanism 2: DC → R-OH + CO 2(g) ] [ka]

[0057] Here, bisphenol A (BPA), the product produced in chemical reaction mechanism 1, is not further decomposed under the above conditions (water content is controlled to 0.5 wt% to 10 wt%) (only the diphenyl carbonate intermediate DC is decomposed), so the bisphenol A product is retained and the yield is improved.

[0058] Thus, the polycarbonate material ultimately forms the product bisphenol A (BPA) and the by-product phenol (R-OH) at the above water content and metal oxide concentration, and also produces carbon dioxide (CO2) gas. Here, the conversion rate of depolymerization of polycarbonate (PC) is 90% to 99% (i.e., the conversion rate of PC decomposition from a high molecular compound to a small molecular compound, and 90% to 99% of PC is depolymerized).

[0059] Finally, the product bisphenol A (BPA) may be recycled, for example, by cooling crystallization.

[0060] It is noteworthy that the intermediate (diphenyl carbonate) produced from polycarbonate (PC) can be decomposed into phenol (R-OH) during the reaction. Phenol (R-OH) is the same compound as the single depolymerization solvent (phenol) employed in the present invention. Therefore, during the depolymerization reaction, the weight ratio of the depolymerization solvent (phenol) to polycarbonate (PC) (i.e., the weight ratio of phenol / polycarbonate) continues to increase, which is beneficial for the progress of the depolymerization reaction and for recycling the depolymerization solvent. Furthermore, since the weight ratio of the depolymerization solvent / polycarbonate continues to increase during the depolymerization reaction, the initial amount of depolymerization solvent can be reduced.

[0061] It is also worth noting that the inventors of the present application have found through experiments that a combination of 100 ppm or more of the metal hydroxide (NaOH, KOH, etc.) and a water content of 0.5 to 10 wt% is advantageous for the rapid depolymerization of polycarbonate (PC) to form bisphenol A (BPA) and carbon dioxide. In this way, it is possible to achieve the depolymerization reaction of polycarbonate using a single depolymerization solvent. If the water content is less than 0.5 wt%, the concentration of the metal hydroxide will be excessive (this is because the metal hydroxide will not form hydroxide ions (OH), which are anions, in water). - and metal cation M n+ The product, bisphenol A (BPA), may undergo an undesirable reaction of being decomposed in a strongly alkaline environment. On the other hand, if the water content exceeds 10 wt%, the concentration of metal hydroxides becomes too low, resulting in a decrease in the overall depolymerization efficiency.

[0062] It is worth noting that in one embodiment, for example, 100 g of polycarbonate is used to produce 89.7 g of bisphenol A (BPA), 17.3 g of carbon dioxide (CO 2(g)), and about 7 g of water is consumed, i.e., the water content in the reaction solution decreases during the depolymerization reaction. In an embodiment of the present invention, the water content in the reaction solution is controlled by monitoring and replenishing water, thereby achieving the above technical effects of the present invention.

[0063] To solve the technical problems of existing technologies, the present invention provides a method for decomposing polycarbonate (a method for decomposing polycarbonate using transesterification technology). This method uses phenol as the sole depolymerization solvent. The polycarbonate material is decomposed under conditions where a metal hydroxide (e.g., NaOH or KOH) is present at 100 ppm or more (preferably 100 to 200,000 ppm, and particularly preferably 500 to 10,000 ppm). Furthermore, during the depolymerization reaction, the water content of the reaction solution is controlled to 0.5 wt% to 10 wt%. The reaction intermediate (diphenyl carbonate) is further depolymerized to form phenol (the same as the depolymerization solvent) and carbon dioxide (which can be discharged as exhaust gas from the system or removed by carbon dioxide adsorption). This allows the system to proceed in a manner favorable to the depolymerization reaction, improving the polycarbonate depolymerization conversion rate to 90% to 99% and achieving a yield of the product bisphenol A (BPA) of 60% or less.

[0064] Furthermore, the polycarbonate decomposition method according to the embodiment of the present invention can efficiently avoid the problem of the co-solvent (e.g., toluene or dichloromethane) remaining in the product (e.g., BPA) after using the co-solvent in the existing technology.

[0065] [Experimental data and measurement results] The present invention will be explained in detail below with reference to Examples 1 to 3 and Comparative Example 1. However, these Examples are provided to facilitate understanding of the present invention, and the present invention is not limited to these Examples.

[0066] Example 1 500 parts by weight of a depolymerization solvent (phenol) was added to a reaction tank and heated to 80°C (i.e., the first heating temperature). 4 parts by weight of a metal hydroxide aqueous solution (32% NaOH) was added to the reaction tank and mixed with the depolymerization solvent to prepare a mixed solution. 200 parts by weight of polycarbonate (PC) particles and 35 parts by weight of water were added to the mixed solution in the reaction tank to prepare a reaction solution. The reaction solution was heated to 120°C (i.e., the second heating temperature) and stirred continuously for 5 hours to depolymerize the polycarbonate (PC) and produce bisphenol A (BPA), phenol, and carbon dioxide. The concentration of metal hydroxide (NaOH) in the reaction solution was 1,732 ppm, and the water content in the reaction solution was controlled at 4.7 wt%.

[0067] <Example 2> 500 parts by weight of a depolymerization solvent (phenol) was added to a reaction tank and heated to 80°C (i.e., the first heating temperature). 2 parts by weight of a metal hydroxide aqueous solution (32% NaOH) was added to the reaction tank and mixed with the depolymerization solvent to prepare a mixed solution. 200 parts by weight of polycarbonate (PC) particles and 70 parts by weight of water were added to the mixed solution in the reaction tank to prepare a reaction solution. The reaction solution was heated to 120°C (i.e., the second heating temperature) and stirred continuously for 5 hours to depolymerize the polycarbonate (PC) to form bisphenol A (BPA), phenol, and carbon dioxide. The concentration of metal hydroxide (NaOH) in the reaction solution was 829 ppm, and the water content in the reaction solution was controlled at 9.0 wt%.

[0068] Example 3 500 parts by weight of a depolymerization solvent (phenol) was added to a reaction tank and heated to 80°C (i.e., the first heating temperature). 20 parts by weight of a metal hydroxide aqueous solution (32% NaOH) was added to the reaction tank and mixed with the depolymerization solvent to prepare a mixed solution. 200 parts by weight of polycarbonate (PC) particles and 14 parts by weight of water were added to the mixed solution in the reaction tank to prepare a reaction solution. The reaction solution was heated to 120°C (i.e., the second heating temperature) and stirred continuously for 5 hours to depolymerize the polycarbonate (PC) to form bisphenol A (BPA), phenol, and carbon dioxide. The concentration of metal hydroxide (NaOH) in the reaction solution was 8,719 ppm, and the water content in the reaction solution was controlled at 1.4.

[0069] <Comparative Example 1> 500 parts by weight of a depolymerization solvent (phenol) was added to a reaction tank and heated to 80°C (i.e., the first heating temperature). 4 parts by weight of a metal hydroxide aqueous solution (32% NaOH) was added to the reaction tank and mixed with the depolymerization solvent to prepare a mixed solution. 200 parts by weight of polycarbonate (PC) particles were added to the mixed solution in the reaction tank to prepare a reaction solution. The reaction solution was heated to 120°C (i.e., the second heating temperature) and stirred continuously for 5 hours to carry out a depolymerization reaction of polycarbonate (PC). Here, the concentration of metal hydroxide (NaOH) in the reaction solution was 1,818 ppm, and the water content in the reaction solution was 0.18 wt% (uncontrolled).

[0070] The manufacturing method of <Comparative Example 1> is almost the same as that of <Example 1>, but the difference between them is that in <Comparative Example 1>, water was not added separately to the reaction solution, and the water content of the reaction solution was 0.18 wt%, which was lower than 4.7 wt% in <Example 1> and also lower than 0.5 wt% required by the present invention.

[0071] Next, measurements were carried out for Examples 1 to 3 and Comparative Example 1 to obtain the conversion rate of depolymerization of polycarbonate (PC) and the yield (%) of bisphenol A (BPA) product.

[0072] It is worth noting that in the measurement results section of Table 1, the depolymerization conversion rate of polycarbonate (PC) was measured by the method described below. First, 10 g of the crude reaction solution (i.e., the reaction solution after the depolymerization reaction) was taken out. 50 g of methanol was added to this 10 g of crude reaction solution, and the mixture was filtered. After filtration, the filter cake was washed with 50 g of methanol. The filter cake was then dried, and the weight (S) of the resulting solid was recorded.

[0073] Depolymerization conversion rate (%) = (100 - S / (10 * (PC / total weight of reaction solution)).

[0074] In the above formula, S is the weight of the solid obtained after drying, 10 g is the weight of the crude reaction solution initially taken out, PC is the initial amount of polycarbonate (PC) particles, and the total weight of the reaction solution is the total weight of the reaction solution.

[0075] The yield (%) of the bisphenol A (BPA) product was measured as follows: First, the crude reaction solution after the depolymerization reaction was taken out and analyzed by high performance liquid chromatography (HPLC) to determine the concentration A of bisphenol A (BPA). Then, the yield (%) of the product bisphenol A (BPA) was calculated using the following formula:

[0076] A / (PC / total weight of reaction solution)*100.

[0077] In this formula, A is the concentration of bisphenol A (BPA), PC is the initial dosage of polycarbonate (PC) particles, and total reaction weight is the total weight of the reaction solution.

[0078] [Table 1]

[0079] As can be seen from the experimental results in Table 1 above, the production conditions of Examples 1 to 3 met the requirements for the metal hydroxide concentration and water content in the reaction solution of the present invention, and the conversion rates of polycarbonate (PC) depolymerization were all 90% or higher, and the yields of bisphenol A (BPA) products were all 60% or higher.

[0080] In Comparative Example 1, water was not added to the reaction solution, and the water content in the reaction solution was 0.18 wt% (uncontrolled), which was lower than 4.7 wt% in Example 1 and lower than the 0.5 wt% required by the present invention.

[0081] The depolymerization conversion rate of polycarbonate (PC) in Comparative Example 1 was 53%, which was much lower than the measurement results of Examples 1 to 3. The yield of bisphenol A (BPA) product in Comparative Example 1 was 38%, which was also much lower than the measurement results of Examples 1 to 3.

[0082] [Advantageous Effects of the Embodiments] As an advantageous effect of the present invention, the polycarbonate decomposition method of the present invention includes "a preparation step, which includes providing a depolymerization solvent that is phenol; an addition step, which includes adding a metal hydroxide to the depolymerization solvent to prepare a mixed solution; and a depolymerization step, which includes adding a polycarbonate material (polycarbonate, PC) to the mixed solution and adding a predetermined amount of water to the mixed solution to prepare a reaction solution" and "the concentration of the metal hydroxide added is 100 ppm or more, and the water content in the reaction solution is 10 wt% or less." These technical features allow the chemical reaction to proceed in a manner that is favorable for the depolymerization reaction, thereby improving the conversion rate of polycarbonate depolymerization and increasing the yield of bisphenol A (BPA) products.

[0083] The method for decomposing polycarbonate of the present invention can efficiently avoid the problem of using a co-solvent (such as toluene or dichloromethane) in the existing technology, where the co-solvent remains in the product (such as BPA).

[0084] The above disclosure is merely a preferred embodiment of the present invention, and the scope of the claims of the present invention is not limited thereto. Therefore, any equivalent technical modifications made by utilizing the contents of the specification and drawings of the present invention are included in the scope of the claims of the present invention. [Explanation of symbols]

[0085] S110...Process S110 S120...Process S120 S130...Process S130

Claims

1. a preparing step including providing a depolymerization solvent, the depolymerization solvent being phenol; an adding step including adding a metal hydroxide to the depolymerization solvent to prepare a mixed solution; a depolymerization step, which includes preparing a reaction solution by adding a polycarbonate material (polycarbonate, PC) to the mixed solution and adding a predetermined amount of water to the mixed solution; the concentration of the metal hydroxide added is 100 ppm or more, and the water content in the reaction solution is 10 wt % or less; In the depolymerization process, the polycarbonate material is subjected to a depolymerization reaction to produce products, bisphenol A (BPA) and carbon dioxide (CO ２ ) and forming a polycarbonate.

2. the preparing step further includes heating the depolymerization solvent to a first heating temperature of 60°C to 100°C; 2. The method for decomposing polycarbonate according to claim 1, wherein the depolymerization step further comprises heating the reaction solution to a second heating temperature of 110°C to 150°C.

3. 3. The method for decomposing polycarbonate according to claim 2, wherein the first heating temperature is 70°C to 90°C, and the second heating temperature is 110°C to 140°C.

4. 2. The method for decomposing polycarbonate according to claim 1, wherein the depolymerization step controls the water content in the reaction liquid to 0.5 wt % to 10 wt % during the depolymerization reaction.

5. 5. The method for decomposing polycarbonate according to claim 4, wherein, when the water content in the reaction solution is depleted to less than 0.5 wt %, the depolymerization step further comprises replenishing water to the reaction solution so as to control the water content in the reaction solution to 0.5 wt % to 10 wt %.

6. 2. The method for decomposing polycarbonate according to claim 1, wherein the initial weight ratio of the depolymerization solvent to the polycarbonate material is 1 to 14.

7. The intermediate produced by depolymerizing the polycarbonate material is diphenyl carbonate, which is further reacted with phenol and carbon dioxide (CO ) in the depolymerization reaction. ２ 2. The method for decomposing polycarbonate according to claim 1, wherein the weight ratio of the depolymerization solvent to the polycarbonate material continues to increase during the depolymerization reaction.

8. 2. The method for decomposing polycarbonate according to claim 1, wherein the metal hydroxide is at least one selected from the group consisting of alkali metal (Group 1 element) hydroxides, alkaline earth metal (Group 2 element) hydroxides, and transition metal hydroxides.

9. 9. The method for decomposing polycarbonate according to claim 8, wherein the metal hydroxide is at least one selected from the group consisting of sodium hydroxide (NaOH) and potassium hydroxide (KOH).

10. 2. The method for decomposing polycarbonate according to claim 1, wherein the concentration of the metal hydroxide added is 500 ppm to 10,000 ppm.

11. 2. The method for decomposing a polycarbonate according to claim 1, wherein in the adding step, the mixed solution is prepared by adding the aqueous solution containing the metal hydroxide to the depolymerization solvent.

12. 12. The method for decomposing polycarbonate according to claim 11, wherein the aqueous solution contains the metal hydroxide at a weight percent concentration of 15 wt % to 60 wt %.

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