Method for depolymerizing copolyester, depolymerized product and application of depolymerized product in preparation of copolyester
By using a titanium-containing catalyst to depolymerize PETG or PCTG copolyesters, combined with purification treatment, the problems of yellowing and low depolymerization efficiency in the recycling and reuse of waste copolyesters are solved, achieving efficient and low-cost production of recycled copolyesters.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2024-11-12
- Publication Date
- 2026-05-12
AI Technical Summary
In the existing technology, it is difficult to recycle and reuse waste PETG or PCTG copolyesters. Physical recycling cannot obtain recycled products with stable performance, while chemical recycling process can easily cause the product to turn yellow, with low depolymerization efficiency and high cost.
A titanium-containing catalyst was used to carry out the depolymerization reaction in the presence of a depolymerizing agent. The particle size and water content of the copolyester were controlled, and combined with purification treatment, high-purity depolymerization products were obtained, avoiding yellowing of CHDM and improving the depolymerization rate.
It achieves a high depolymerization rate of ≥99.9%, obtains high-purity monomers that can be recycled, simplifies the recycling process, reduces production costs, and yields high-performance recycled PETG or PCTG copolyesters.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of waste polyester recycling technology, specifically to a method for depolymerizing copolyester, the depolymerization product, and the application of the depolymerization product in the preparation of copolyester. Background Technology
[0002] PETG or PCTG polyester is a copolyester copolymerized from terephthalic acid (PTA), ethylene glycol (EG), and 1,4-cyclohexanediethanol (CHDM) monomers. Its full name is ethylene terephthalate-1,4-cyclohexanediethanol ester. Copolyesters with a CHDM content greater than 50% are called PCTG, and those with a CHDM content less than 50% are called PETG. Compared to ethylene terephthalate (PET), the random insertion of 1,4-cyclohexanediethanol (CHDM) into the polymer chains hinders the regular arrangement of the molecular chains, significantly reducing crystallinity. This results in PETG copolyester exhibiting excellent light transmittance, high impact resistance, toughness, gloss, and weather resistance, and it has been commercially applied in high-transparency beverage bottles, sheets, label films, photochemical and medical devices.
[0003] PETG or PCTG exhibits excellent processing and molding properties. Due to its slow crystallization rate and the rigid chain of CHDM, it possesses excellent impact resistance. It can be processed using various molding methods such as injection molding, extrusion, compression molding, blow molding, and vacuum forming, according to the designer's specifications, to produce thick-walled transparent products, sheets, tubes, profiles, and special-shaped profiles, with a wide range of applications. The main producers of PETG or PCTG copolyesters are Eastman Chemical Company (USA) and SK Group (South Korea), with a total production of approximately 400,000 tons in 2022. Domestic sales in China were approximately 120,000 tons. Domestic demand for PETG is increasing, but used PETG or PCTG copolyesters cannot degrade themselves and can only be disposed of through physical recycling. However, the processing of PETG or PCTG often involves blending with other raw materials, making recycling even more difficult.
[0004] The increasing domestic demand for PETG or PCTG copolyester products, coupled with the low domestic production of the monomer CHDM and reliance on imports, makes PETG or PCTG copolyesters extremely expensive. Failure to recycle and reuse them would result in significant waste. Physical recycling methods can only downgrade the polymer, offering simple operation but failing to yield stable recycled polyester products. Repeated recycling leads to a decline in polymer properties, making them unsuitable for performance requirements. Therefore, a chemical method is used to depolymerize waste PETG or PCTG polyester products down to the monomer level. The resulting high-purity monomers are then reused and polymerized into high-quality recycled products, achieving true closed-loop recycling. Summary of the Invention
[0005] The purpose of this invention is to overcome the problem of recycling and reusing waste PETG or PCTG polyester products in the prior art, and to provide a method for depolymerizing copolyesters, the depolymerization products, and the application of the depolymerization products in the preparation of copolyesters.
[0006] To achieve the above objectives, a first aspect of the present invention provides a method for depolymerizing a copolyester, the method comprising: in the presence of a catalyst and a depolymerizing agent, subjecting a copolyester with an average particle size of 0.1-5 cm to a depolymerization reaction to obtain a depolymerization solution containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer, and cyclohexanediethanol terephthalate; wherein the copolyester is polyethylene terephthalate-1,4-cyclohexanediethanol terephthalate, the water content in the copolyester is ≤2% by weight, and the catalyst is a titanium-containing catalyst.
[0007] A second aspect of the present invention provides a depolymerization product prepared by the method described above.
[0008] A third aspect of the present invention provides the use of the above-described depolymerization product in the preparation of polyethylene terephthalate-1,4-cyclohexanediethanol ester.
[0009] Through the above technical solution, the present invention achieves the following beneficial effects:
[0010] (1) This invention utilizes a titanium-containing catalyst for the chemical depolymerization and recovery of PETG (or PCTG) copolyesters, while simultaneously controlling the average particle size and water content of the copolyesters. This improves the depolymerization rate of the copolyesters and yields recyclable monomers. CHDM has a high boiling point (283°C), making it difficult to remove during the synthesis of PETG or PCTG. The high reaction temperature and long reaction time easily cause yellowing of the product, resulting in a high yellow index. The method of this invention can depolymerize the 1,4-cyclohexanedimethyl structural units in PETG (or PCTG) copolyesters into cyclohexanedimethyl terephthalate (BHCT), effectively avoiding the problem of yellowing and a high yellow index caused by CHDM. Preferably, the method of this invention can achieve a depolymerization rate of ≥99.9% for the copolyesters.
[0011] (2) In a preferred embodiment, the method of the present invention further includes a purification process. After purification, the content of impurities in the depolymerization product can be further reduced, and the content of the target product (bis(2-hydroxyethyl) terephthalate (BHET), BHET dimer and cyclohexanediethanol terephthalate (BHCT)) can be increased. At the same time, the L value of the depolymerization product can be increased and the b value of the depolymerization product can be reduced, so that the depolymerization product has a good color and can be directly used to prepare PETG (or PCTG) copolyester products, realizing the chemical recycling and reuse of PETG or PCTG copolyester, which has good economic benefits.
[0012] (3) In a preferred embodiment, the method of the present invention can keep the amount of catalyst residue in the depolymerization product within a certain range, so that the purified depolymerization product can be directly regenerated to prepare PETG (or PCTG) copolyester without adding catalyst, thereby simplifying the process and reducing the production cost of copolyester. Detailed Implementation
[0013] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0014] The first aspect of the present invention provides a method for depolymerizing a copolyester, the method comprising: in the presence of a catalyst and a depolymerizing agent, subjecting a copolyester with an average particle size of 0.1-5 cm to a depolymerization reaction to obtain a depolymerization solution containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer and cyclohexanediethanol terephthalate; wherein the copolyester is polyethylene terephthalate-1,4-cyclohexanediethanol terephthalate, the water content in the copolyester is ≤2% by weight, and the catalyst is a titanium-containing catalyst.
[0015] According to the present invention, preferably, the catalyst is a titanium-containing compound and / or a titanium-containing composition, more preferably at least one of an organotitanium catalyst, a titanium-silicon composite catalyst, and a titanium-rare earth composite catalyst. The organotitanium catalyst may have 1-5 carbon atoms and may include at least one of titanium glycolate, tetrabutyl titanate, and tetraisopropyl titanate. The titanium-rare earth composite catalyst includes a titanium component and a rare earth component. The titanium component may be at least one of titanium glycolate, tetrabutyl titanate, and tetraisopropyl titanate. The rare earth component may contain at least one of lanthanum, yttrium, neodymium, dysprosium, and terbium; the rare earth component may also contain at least one of lanthanum acetylacetonate and yttrium acetylacetonate. The titanium component content in the titanium-rare earth composite catalyst may be 50-90% by weight, and the rare earth component content may be 10-50% by weight. Using a titanium-rare earth composite catalyst can further improve the product depolymerization rate and yield.
[0016] According to the present invention, preferably, the amount of catalyst used is 0.1-0.5g, more preferably 0.1-0.3g, relative to 100g of copolyester. When the amount of catalyst is limited to the above range, the depolymerization rate of the copolyester can be further improved.
[0017] According to the present invention, preferably, the depolymerizing agent is ethylene glycol. More preferably, the weight ratio of the depolymerizing agent to the copolyester is 2-6:1, and even more preferably 2.5-5:1.
[0018] According to the present invention, in order to further improve the depolymerization rate and reduce the energy consumption of depolymerization, preferably, the temperature of the depolymerization reaction is 190-240°C, more preferably 200-230°C. Preferably, the pressure of the depolymerization reaction is 0.2-0.6 MPa, more preferably 0.35-0.5 MPa. Preferably, the time of the depolymerization reaction is 1-10 h, more preferably 2.5-5 h.
[0019] According to the present invention, preferably, the oxygen content in the reaction system during the depolymerization reaction is less than 3.5% by weight; more preferably, the depolymerization reaction is carried out under an inert atmosphere; even more preferably, the inert atmosphere includes nitrogen and / or an inert gas. In the present invention, the inert atmosphere may be provided by at least one of argon, helium, and neon.
[0020] According to the present invention, preferably, the average particle size of the copolyester is 0.1-3 cm, more preferably 0.1-2 cm. When the average particle size of the copolyester is within the above-mentioned preferred range, it can not only further improve the depolymerization rate of the copolyester, increase the content of the target product, and reduce the content of the polymer, but also further improve the depolymerization rate.
[0021] According to the present invention, preferably, the water content in the copolyester is ≤1% by weight. When the water content in the copolyester is within the above-mentioned preferred range, the depolymerization rate of the copolyester can be further improved, thereby increasing the content of the target product.
[0022] According to the present invention, in order to further improve the purity of the product obtained from the depolymerization reaction, preferably, the method further includes purifying the product obtained from the depolymerization reaction, the purification process including the following steps:
[0023] (a) The depolymerization solution is subjected to a first solid-liquid separation to obtain a first filtrate;
[0024] (b) The first filtrate is mixed with a diluent, and then a second solid-liquid separation is performed to obtain the second filtrate;
[0025] (c) The second filtrate is mixed with activated carbon, and then a third solid-liquid separation is performed to obtain the third filtrate;
[0026] (d) The third filtrate is crystallized and dried to obtain a mixture containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer and cyclohexanediethanol terephthalate.
[0027] In this invention, the first solid-liquid separation, the second solid-liquid separation, and the third solid-liquid separation can be separation methods commonly used in the art, such as filtration, centrifugal separation, etc.
[0028] According to the present invention, preferably, the first solid-liquid separation is carried out at 80-105°C. The first solid-liquid separation mainly removes non-depolymerizable components and impurities from PETG (or PCTG), such as blends, fillers, or dust introduced during the PETG (or PCTG) processing.
[0029] According to the present invention, washing the first filtrate with a diluent can increase the content of BHET, BHET dimer, and BHCT in the product obtained from the depolymerization reaction, while reducing the content of other impurities (e.g., BHET oligomers with a degree of polymerization greater than 3, polyurethane, titanium dioxide, etc.). Preferably, the diluent is water, more preferably deionized water. Preferably, the mass ratio of the depolymerization solution to the diluent is 1:1-10, more preferably 1:2-5. When the mass ratio of the depolymerization solution to the diluent is limited to the above range, the content of BHET, BHET dimer, and BHCT in the product obtained from the depolymerization reaction can be further increased, and the content of impurities can be reduced, thereby obtaining a depolymerized product with high purity and low degree of polymerization (BHET degree of polymerization is only 1 and 2). Preferably, the mixing conditions of the first filtrate and the diluent include: a temperature of 70-90°C and a time of 1-3 hours. The second method of solid-liquid separation is filtration, in which the filter paper used has a pore size of 0.5-20μm, preferably 2-15μm.
[0030] According to the present invention, when activated carbon is used to adsorb the second filtrate, not only can the purity of the depolymerization product be further improved, but also the L value and b value of the depolymerization product can be further increased, while the residual amount of catalyst in the depolymerization product can be effectively controlled. Preferably, the amount of activated carbon used is 1-10g relative to 100g of copolyester. Preferably, the mixing conditions of the second filtrate and activated carbon include: a temperature of 70-90℃ and a time of 0.1-2h.
[0031] According to the present invention, preferably, the crystallization conditions include a temperature of 2-10°C and a time of 4-12 hours. Preferably, the drying conditions include a temperature of 50-90°C and a time of 1-3 hours.
[0032] This invention does not impose particular limitations on the content of ethylene glycol terephthalate structural units and 1,4-cyclohexane terephthalic acid structural units in PETG or PCTG polyester raw materials. The method of this invention can be applied to the depolymerization of PETG or PCTG polyesters with different structural contents. For example, the content of 1,4-cyclohexane terephthalic acid structural units in PETG polyester is 0.01-50 mol%; the content of 1,4-cyclohexane terephthalic acid structural units in PCTG polyester is 50-100 mol%. The embodiments of this invention use waste PETG copolyester raw materials as examples, but the invention is not limited thereto.
[0033] A second aspect of the present invention provides a depolymerization product prepared by the method described above.
[0034] In preferred embodiments, the depolymerization products of the present invention have high purity, good color, L value ≥ 90, b value ≤ 2, and the esterification time for directly using them as esterification raw materials to prepare recycled PETG (or PCTG) is short and the b value is low.
[0035] In this invention, L value represents whiteness; the larger the L value, the higher the brightness; the smaller the L value, the lower the brightness. b value represents yellow-blue tint; a positive b value indicates a higher yellow tint, a negative b value indicates a lower bluish tint, and b = 0 indicates neither yellow nor blue tint. The larger the L value, the closer the b value is to 0, indicating a good hue for the object.
[0036] A third aspect of the present invention provides the use of the above-described depolymerization product in the preparation of polyethylene terephthalate-1,4-cyclohexanediethanol ester.
[0037] According to a particularly preferred embodiment of the present invention, the method for depolymerizing the copolyester includes the following steps:
[0038] (1) The depolymerization process of waste PETG copolyester is as follows:
[0039] Waste PETG copolyester is crushed into particles with an average particle size of 0.5-0.8 cm and dried until the water content in the copolyester is 0.4-0.5% by weight. The crushed PETG copolyester and depolymerizing agent (ethylene glycol) are added to the depolymerization reactor at a weight ratio of 1:4-5. A catalyst is added, and the air in the reactor is replaced with nitrogen to ensure that the oxygen weight fraction in the reactor is less than 3.5%. After checking the airtightness, a certain amount of nitrogen is introduced to make the pressure in the reactor reach 0.4-0.45 MPa. Stirring is started, and the temperature in the reactor is set to 205-210℃. Once the reactor temperature reaches the set temperature, the reaction time is started and the reaction time is 3-3.5 hours to obtain the depolymerization liquid, which contains bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer, and cyclohexanediol terephthalate. The catalyst is titanium glycolate and / or tetraisopropyl titanate, wherein the amount of the catalyst is 0.1-0.35g (e.g., 0.1-0.15g or 0.3-0.35g) relative to 100g of copolyester.
[0040] (2) The purification process of the depolymerization solution is as follows:
[0041] (a) The depolymerization solution is filtered while hot at 100-105°C to obtain the first filtrate.
[0042] (b) Then add the diluent at a weight ratio of 1:2-2.2 for the first filtrate: diluent (deionized water), stir in a water bath at 70-75°C for 1.5-1.8 hours, and filter with filter paper with a pore size of 10-15 μm to obtain a clear second filtrate.
[0043] (c) The activated carbon added to the second filtrate is stirred at 70-80℃ for 20-60 minutes, filtered, and the third filtrate is obtained; wherein, the amount of activated carbon used is 8-10g relative to 100g of copolyester.
[0044] (d) Cool the third filtrate at 4-5℃ for 10-11 h to crystallize, filter to obtain a solid, and dry in an oven at 60-65℃ for 2-3 h to obtain a mixture of bis(2-hydroxyethyl) terephthalate (BHET), BHET dimer and cyclohexanediethanol terephthalate (BHCT).
[0045] The present invention will be described in detail below through embodiments. In the following embodiments,
[0046] The waste PETG copolyester raw material contains 70 mol% ethylene glycol terephthalate structural units and 30 mol% 1,4-cyclohexane terephthalic acid structural units.
[0047] The formula for calculating the depolymerization rate of PETG copolyester is:
[0048]
[0049] The purity and composition of the depolymerized and purified products were determined by high-purity liquid chromatography (HPLC). The elution times of BHET, BHET dimer, and BHCT were determined by HPLC, and the content of each component was calculated by peak area.
[0050] The color values L and b of the purified product were determined by a spectrophotometer.
[0051] The residual amount of titanium (or Zn) in the mixture was determined using an Agilent inductively coupled plasma optical emission spectrometer (ICP-OES).
[0052] Example 1
[0053] (1) The depolymerization process of waste PETG copolyester is as follows:
[0054] Waste PETG copolyester was crushed into particles with an average particle size of 0.5 cm and dried until the water content in the copolyester was 0.5% by weight. The crushed PETG copolyester and depolymerizing agent (ethylene glycol) were added to a depolymerization reactor at a weight ratio of 1:5, along with a catalyst (ethylene glycol titanium, wherein the amount of catalyst was 0.1 g relative to 100 g of copolyester). The air in the reactor was replaced with nitrogen to ensure the oxygen weight fraction was less than 3.5%. After checking the airtightness, a certain amount of nitrogen was introduced to bring the pressure inside the reactor to 0.4 MPa. Stirring was started, and the reactor temperature was set to 210℃. The reaction time was 3 hours after the reactor temperature reached the set temperature, yielding a depolymerization solution containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer, and cyclohexanediol terephthalate. The depolymerization rate of the waste PETG copolyester is shown in Table 1.
[0055] (2) The purification process of the depolymerization solution is as follows:
[0056] (a) The depolymerization solution is filtered while hot at 100°C to obtain the first filtrate.
[0057] (b) Then add the diluent at a weight ratio of 1:2 for the first filtrate: diluent (deionized water), stir in a 70°C water bath for 1.5 h, and filter with filter paper with a pore size of 10-15 μm to obtain a clear second filtrate.
[0058] (c) The activated carbon added to the second filtrate is stirred at 70°C for 20 min and filtered to obtain the third filtrate; wherein, the amount of activated carbon used is 8 g relative to 100 g of copolyester.
[0059] (d) The third filtrate was cooled and crystallized at 4°C for 10 h, filtered to obtain a solid, and dried in an oven at 60°C for 2 h to obtain a mixture of bis(2-hydroxyethyl) terephthalate (BHET), BHET dimer, and cyclohexanediol terephthalate (BHCT). The total weight percentage of BHET, BHET dimer, and BHCT in the mixture (i.e., the purity of the mixture), the weight percentage of BHCT in the mixture, the L value and b value of the mixture, and the Ti content of the mixture are shown in Table 1.
[0060] Example 2
[0061] (1) The depolymerization process of waste PETG copolyester is as follows:
[0062] Waste PETG copolyester was crushed into particles with an average particle size of 1 cm and dried until the water content in the copolyester was 0.8% by weight. The crushed PETG copolyester and depolymerizing agent (ethylene glycol) were added to a depolymerization reactor at a weight ratio of 1:5, along with a catalyst (tetrabutyl titanate, wherein the amount of catalyst was 0.3 g relative to 100 g of copolyester). The air in the reactor was replaced with nitrogen to ensure the oxygen weight fraction was less than 3.5%. After checking the airtightness, a certain amount of nitrogen was introduced to bring the pressure inside the reactor to 0.4 MPa. Stirring was started, and the reactor temperature was set to 210℃. The reaction time was 3 hours after the reactor temperature reached the set temperature, yielding a depolymerization solution containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer, and cyclohexanediol terephthalate. The depolymerization rate of the waste PETG copolyester is shown in Table 1.
[0063] (2) The purification process of the depolymerization solution is as follows:
[0064] (a) The depolymerization solution is filtered while hot at 100°C to obtain the first filtrate.
[0065] (b) Then add the diluent at a weight ratio of 1:3 for the first filtrate: diluent (deionized water), stir in an 80°C water bath for 1.5 h, and filter with filter paper with a pore size of 10-15 μm to obtain a clear second filtrate.
[0066] (c) The activated carbon added to the second filtrate is stirred at 75°C for 40 min and filtered to obtain the third filtrate; wherein, the amount of activated carbon used is 2 g relative to 100 g of copolyester.
[0067] (d) The third filtrate was cooled and crystallized at 10°C for 12 h, filtered to obtain a solid, and dried in an oven at 70°C for 2 h to obtain a mixture of bis(2-hydroxyethyl) terephthalate (BHET), BHET dimer, and cyclohexanediethanol terephthalate (BHCT). The total weight percentage of BHET, BHET dimer, and BHCT in the mixture, the weight percentage of BHCT in the mixture, the L value and b value of the mixture, and the Ti content of the mixture are shown in Table 1.
[0068] Example 3
[0069] (1) The depolymerization process of waste PETG copolyester is as follows:
[0070] Waste PETG copolyester was crushed into particles with an average particle size of 3 cm and dried until the water content in the copolyester was 0.8% by weight. The pulverized PETG copolyester and depolymerizing agent (ethylene glycol) were added to the depolymerization reactor at a weight ratio of 1:5. A titanium-rare earth composite catalyst (ethylene glycol titanium-lanthanum acetylacetone composite catalyst, wherein the titanium-rare earth composite catalyst contains 50% by weight of titanium glycol and 50% by weight of lanthanum acetylacetone; the amount of catalyst used is 0.2g per 100g of copolyester) was added. The air inside the reactor was replaced with nitrogen to ensure the oxygen weight fraction was less than 3.5%. After checking the airtightness, a certain amount of nitrogen was introduced to bring the pressure inside the reactor to 0.4MPa. Stirring was started, and the reactor temperature was set to 210℃. The reaction time was 3 hours after the reactor temperature reached the set temperature, yielding a depolymerization solution containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer, and cyclohexanediol terephthalate. The depolymerization rate of the waste PETG copolyester is shown in Table 1.
[0071] (2) The purification process of the depolymerization solution is as follows:
[0072] (a) The depolymerization solution is filtered while hot at 90°C to obtain the first filtrate.
[0073] (b) Then add the diluent at a weight ratio of 1:4 for the first filtrate: diluent (deionized water), stir in an 85°C water bath for 3 hours, and filter with filter paper with a pore size of 10-15 μm to obtain a clear second filtrate.
[0074] (c) The activated carbon added to the second filtrate is stirred at 80°C for 60 min and filtered to obtain the third filtrate; wherein, the amount of activated carbon used is 5 g relative to 100 g of copolyester.
[0075] (d) The third filtrate was cooled and crystallized at 2°C for 24 h, filtered to obtain a solid, and dried in an oven at 70°C for 2 h to obtain a mixture of bis(2-hydroxyethyl) terephthalate (BHET), BHET dimer, and cyclohexanediol terephthalate (BHCT). The total weight percentage of BHET, BHET dimer, and BHCT in the mixture, the weight percentage of BHCT in the mixture, the L value and b value of the mixture, and the Ti content of the mixture are shown in Table 1.
[0076] Example 4
[0077] The waste PETG copolyester was depolymerized and purified according to the method in Example 1, except that...
[0078] In step (1), the catalyst added is tetraisopropyl titanate, wherein the amount of the catalyst used is 0.3g relative to 100g of copolyester.
[0079] In step (2), (c) the activated carbon added to the second filtrate is stirred at 80°C for 60 min and filtered to obtain the third filtrate; wherein, the amount of activated carbon used is 10 g relative to 100 g of copolyester.
[0080] Example 5
[0081] (1) The depolymerization process of waste PETG copolyester is as follows:
[0082] Waste PETG copolyester was crushed into particles with an average particle size of 1.5 cm and dried until the water content in the copolyester was 1% by weight. The pulverized PETG copolyester and depolymerizing agent (ethylene glycol) were added to the depolymerization reactor at a weight ratio of 1:5. A titanium-rare earth composite catalyst (ethylene glycol titanium-yttrium acetylacetone composite catalyst, wherein the titanium-rare earth composite catalyst contains 80% titanium glycol by weight and 20% yttrium acetylacetone by weight; the amount of the catalyst is 0.2g per 100g of copolyester) was added. The air in the reactor was replaced with nitrogen to ensure that the oxygen weight fraction in the reactor was less than 3.5%. After checking the airtightness, a certain amount of nitrogen was introduced to make the pressure in the reactor reach 0.4MPa. Stirring was started, and the temperature in the reactor was set to 210℃. The reaction time was 3h after the reactor temperature reached the set temperature to obtain a depolymerization liquid containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer and cyclohexanediol terephthalate. The depolymerization rate of waste PETG copolyester is shown in Table 1.
[0083] (2) The purification process of the depolymerization solution is as follows:
[0084] (a) The depolymerization solution was filtered while hot at 80°C to obtain the first filtrate.
[0085] (b) Then add the diluent at a weight ratio of 1:2.5 for the first filtrate: diluent (deionized water), stir in an 80°C water bath for 2 hours, and filter with filter paper with a pore size of 10-15 μm to obtain a clear second filtrate.
[0086] (c) The activated carbon added to the second filtrate is stirred at 80°C for 80 min and filtered to obtain the third filtrate; wherein, the amount of activated carbon used is 7 g relative to 100 g of the second filtrate.
[0087] (d) The third filtrate was cooled and crystallized at 4°C for 16 h, filtered to obtain a solid, and dried in an oven at 70°C for 2 h to obtain a mixture of bis(2-hydroxyethyl) terephthalate (BHET), BHET dimer, and cyclohexanediethanol terephthalate (BHCT). The total weight percentage of BHET, BHET dimer, and BHCT in the mixture, the weight percentage of BHCT in the mixture, the L value and b value of the mixture, and the Ti content of the mixture are shown in Table 1.
[0088] Example 6
[0089] The waste PETG copolyester was depolymerized and purified according to the method of Example 1, except that step (2) does not include step (c), that is, the second filtrate is directly subjected to the operation of step (d).
[0090] Example 7
[0091] The waste PETG copolyester was depolymerized and purified according to the method of Example 1, except that in step (1), the waste PETG copolyester was crushed into particles with an average particle size of 4 cm.
[0092] Example 8
[0093] The waste PETG copolyester was depolymerized and purified according to the method of Example 1, except that in step (1), it was dried until the water content in the copolyester was 2% by weight.
[0094] Example 9
[0095] The waste PETG copolyester was depolymerized and purified according to the method of Example 1, except that a diluent was added at a weight ratio of 1:10 for the first filtrate to diluent (deionized water).
[0096] Comparative Example 1
[0097] The waste PETG copolyester was depolymerized and purified according to the method of Example 1, except that the catalyst was replaced with an equal weight amount of zinc acetate catalyst.
[0098] Comparative Example 2
[0099] The waste PETG copolyester was depolymerized and purified according to the method in Example 3, except that the catalyst was replaced with an equal weight amount of lanthanum acetylacetone. The copolyester did not depolymerize.
[0100] Comparative Example 3
[0101] The waste PETG copolyester was depolymerized and purified according to the method of Example 1, except that in step (1), the waste PETG copolyester was crushed into particles with an average particle size of 10 cm.
[0102] Comparative Example 4
[0103] The waste PETG copolyester was depolymerized and purified according to the method of Example 1, except that in step (1), it was dried until the water content in the copolyester was 5% by weight.
[0104] Table 1
[0105]
[0106]
[0107] As can be seen from the results in Table 1, compared with the comparative example, the method of the present invention can improve the depolymerization rate of the copolyester.
[0108] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A method for depolymerizing copolyesters, characterized in that, The method includes: in the presence of a catalyst and a depolymerizing agent, subjecting a copolyester with an average particle size of 0.1-5 cm to a depolymerization reaction to obtain a depolymerization solution containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer, and cyclohexanediethanol terephthalate; wherein the copolyester is polyethylene terephthalate-1,4-cyclohexanediethanol ester, the water content in the copolyester is ≤2% by weight, and the catalyst is a titanium-containing catalyst.
2. The method according to claim 1, wherein, The catalyst is at least one of organotitanium catalyst, titanium-silicon composite catalyst, and titanium-rare earth composite catalyst. And / or, relative to 100g of copolyester, the amount of catalyst used is 0.1-0.5g, preferably 0.1-0.3g.
3. The method according to claim 1 or 2, wherein, The depolymerizing agent is ethylene glycol; And / or, the weight ratio of the depolymerizing agent to the copolyester is 2-6:1, preferably 2.5-5:
1.
4. The method according to any one of claims 1-3, wherein, The conditions for the depolymerization reaction include: a temperature of 190-240℃, preferably 200-230℃; a pressure of 0.2-0.6MPa, preferably 0.35-0.5MPa; and a time of 1-10h, preferably 2.5-5h.
5. The method according to any one of claims 1-4, wherein, The oxygen content in the reaction system during the depolymerization reaction is less than 3.5% by weight; preferably, the depolymerization reaction is carried out in an inactive atmosphere, more preferably, the inactive atmosphere includes nitrogen and / or an inert gas.
6. The method according to any one of claims 1-5, wherein, The average particle size of the copolyester is 0.1-3 cm; And / or, the water content in the copolyester is ≤1% by weight.
7. The method according to any one of claims 1-6, wherein, The method further includes purifying the product obtained from the depolymerization reaction, and the purification process includes the following steps: (a) The depolymerization solution is subjected to a first solid-liquid separation to obtain a first filtrate; (b) The first filtrate is mixed with a diluent, and then a second solid-liquid separation is performed to obtain the second filtrate; (c) The second filtrate is mixed with activated carbon, and then a third solid-liquid separation is performed to obtain the third filtrate; (d) The third filtrate is crystallized and dried to obtain a mixture containing bis(2-hydroxyethyl) terephthalate, bis(2-hydroxyethyl) terephthalate dimer and cyclohexanediethanol terephthalate.
8. The method according to claim 7, wherein, The first solid-liquid separation was carried out at 80-105℃; And / or, the diluent is water, preferably deionized water; the weight ratio of the depolymerization solution to the diluent is 1:1-10, more preferably 1:2-5; the conditions for mixing the first filtrate with the diluent include: a temperature of 70-90°C and a time of 1-3 hours.
9. The method according to claim 7 or 8, wherein, The amount of activated carbon used is 1-10g relative to 100g of copolyester; The conditions for mixing the second filtrate with activated carbon include: a temperature of 70-90℃ and a time of 0.1-2h; And / or, the crystallization conditions include: a temperature of 2-10°C and a time of 4-12 hours; And / or, the drying conditions include: a temperature of 50-90°C and a time of 1-3 hours.
10. The depolymerization product prepared by the method according to any one of claims 1-9.
11. The use of the depolymerization product of claim 10 in the preparation of polyethylene terephthalate-1,4-cyclohexanediethanol ester.