Supercritical decoloration and degradation coupling system and method for waste dyed PET (Polyethylene Terephthalate) foam material

Abstract

The invention discloses a supercritical decoloration and degradation coupling system and method for a waste dyed PET (Polyethylene Terephthalate) foam material. Aiming at the problem that two functions of decoloration and degradation cannot be realized in the same set of system at one time in the past, firstly, carbon dioxide and a cosolvent are introduced into a reactor filled with a PET (Polyethylene Terephthalate) foam material in a supercritical state for decoloration, and complete decoloration of the PET foam material can be realized under proper conditions. After the decoloration is finished, methanol is introduced into the reactor to circularly flow, the decolorized PET foam material is subjected to an alcoholysis reaction in a subcritical / supercritical state, and a high-purity degradation product can be obtained through post-treatment. According to the system and the method, two-step reaction of decoloration and alcoholysis is completed in one set of system at one time, the system and the method have the advantages of simple process, small equipment investment, high reaction efficiency, high product quality, low operation cost, continuous production and the like, a new way is provided for purification, recovery and high-quality utilization of the waste dyed PET foam material, and the concept of sustainable development is met.

Description

Technical Field

[0001] The invention relates to the technical field of waste plastic resource utilization and recycling, and in particular to a supercritical decolorization and degradation coupling system and method for waste dyed PET foam. Background Art

[0002] Polyethylene terephthalate (PET) is a semi-crystalline, thermoplastic polymer that occupies an important position in thermoplastic polyesters. It is widely used in the field of plastics because of its stable chemical structure, good flexibility and processability, and low cost. At present, the research on the recycling of waste PET at home and abroad is mostly focused on PET bottles, with the focus on improving the recycling process, increasing the recovery rate, and expanding its application areas. Dyed PET is widely used as an important component of waste polyester, but due to its high separation and purification costs, it is usually treated by landfill or incineration, which limits the scope of use and service life of the degradation products. Therefore, decolorization is the key to realizing its resource recovery and upgrading and reuse.

[0003] Chemical recycling can use chemical means to depolymerize and restore waste polyester to monomers, and then polymerize it into original materials, but still retain the properties of the material or the economic value of the polymer, which can achieve the upgrading and recycling of waste PET polyester. Hydrolysis, alcoholysis and aminolysis are currently the main methods of chemical recycling. Among them, alcoholysis is the most widely used method in industry. It mainly uses methanol, ethylene glycol and polyols to obtain ethylene glycol (EG), dimethyl terephthalate (DMT), ethylene glycol terephthalate (BHET), dioctyl terephthalate (DOTP), etc. Some studies have successfully applied alcoholysis to the degradation of polyester and obtained monomers with a higher yield.

[0004] Decolorization of dyed waste PET can reduce the adverse effects of impurities such as dyes and ensure product quality. At present, direct decolorization of dyed polyester is mostly done by sodium hypochlorite oxidation or using Na2S2O4 / caustic soda as a reducing agent, but its decolorization performance is poor, especially when there is a large demand for dyed polyester, the decolorization efficiency is difficult to meet market demand. Dimethyl sulfoxide (DMSO) has a small molecular weight and is easier to enter the amorphous region of polyester, so it has good swelling properties. N,N-dimethylformamide (DMF) and acetone have strong solubility in organic compounds, good chemical stability and are recyclable, and are suitable as decolorizers for foam materials. However, these are all chemical decolorizations, which inevitably produce a large amount of organic waste liquid, which brings difficulties to subsequent treatment and increases recycling costs. Supercritical CO2 is widely used in extraction, foaming, polymerization reactions and cleaning because it is easy to reach critical conditions, non-toxic, high solubility and excellent diffusion capacity. Supercritical CO2 has the ability to swell polymers, and it can easily enter the interior of polyester. In addition, it has the ability to dissolve dyes, so the dyes can be extracted from polyester. Its decolorization effect is greatly improved compared with traditional decolorization methods. The CO2 used in the decolorization process is non-toxic and cheap, and can be recycled, meeting the requirements of the dual carbon goals. Supercritical fluids have also attracted attention for their relatively mild reaction conditions, strong diffusivity and solubility. Super / subcritical methanol has physical and chemical properties that other organic solvents do not have. It can be used as a reaction medium or a reactant, and has excellent transfer characteristics, solubility characteristics and reaction characteristics. It is applied to the field of plastic degradation, and has the advantages of fast reaction speed, mildness, no gas and by-products, and can be used as a recycled solvent. Chinese patent CN115198509A discloses a supercritical carbon dioxide decolorization system and method, which realizes a process route for multiple recycling of carbon dioxide and decolorizers, and the decolorization rate of textiles can reach more than 90%. However, the system is complicated to operate and can only achieve a single decolorization operation. Chinese patent CN118185123A invented a method for the alcoholysis of waste PET polyester with methanol catalyzed by a non-metallic low eutectic solvent, which successfully degraded PET and obtained a certain yield of DMT monomer, but the method used a catalyst and had a high cost.

[0005] From the existing technology, there are many reports on the simple decolorization and degradation processes of polyester, and even methods for industrialization. However, the significant problems are large equipment investment, long production cycle, high operating costs, high plant and floor space requirements, and cumbersome connection between upstream and downstream processes, which greatly increases the cost of polyester recycling and utilization, and seriously hinders the large-scale industrialization of the technology. To this end, the innovative invention of an integrated decolorization-degradation integrated system and method is the key to solving the above problems.

[0006] At present, the decolorization and degradation problems of dyed PET have always been an obstacle to the industrial recycling of waste PET polyester. There is an urgent need for an efficient, environmentally friendly, low-cost and high-yield PET decolorization and degradation coupling solution to achieve the integration of decolorization and degradation processes, shorten the recycling process of waste polyester, improve economic benefits, and alleviate the environmental pollution and energy consumption problems caused by waste polyester. Summary of the invention

[0007] In view of the technical problems existing in the integration of decolorization and degradation of dyed PET foam, the present invention proposes a supercritical decolorization and degradation coupling system and method for waste dyed PET foam.

[0008] The technical solution of the present invention:

[0009] A supercritical decolorization and degradation coupling system for waste dyed PET foam comprises a first filter, a second filter, a carbon dioxide storage tank, a co-solvent storage tank, a methanol storage tank, a condenser, a first plunger pump, a second plunger pump, a constant flow pump, a heater, a circulation pump, a dye collection tank, a degradation product storage tank, a plurality of reactors and separators.

[0010] The outlet of the carbon dioxide storage tank is connected to the first filter, condenser, regulating valve, and first plunger pump in sequence through a pipeline for conveying liquid carbon dioxide, and the co-solvent storage tank is connected to a constant flow pump through a pipeline for conveying a co-solvent flow, and the mixed fluid after the carbon dioxide flow and the pipeline for conveying the co-solvent flow merge is connected to the inlet of the heater through a pipeline, and the outlet pipeline of the heater is connected to multiple reactors in parallel. Multiple reactors can be interconnected, and the mixed fluid flowing out of the reactor after decolorization is completed is connected to the inlet of the separator; the separator is used to separate gas and liquid, and the gas outlet of the separator is connected to the inlet of the carbon dioxide storage tank through a pipeline and a second filter, and the liquid outlet of the separator is connected to the dye collection tank.

[0011] The methanol storage tank is connected to the second plunger pump through a pipeline, and then the methanol inlets of multiple reactors are connected in parallel. The outlets of multiple reactors are connected to the methanol inlets of respective reactors through pipelines and circulation pumps to form a circulation loop. The product outlets of multiple reactors are all connected to the degradation product storage tank.

[0012] The reactor and separator are used for continuous decolorization and degradation reactions. The outside of the reactor and separator are equipped with heating jackets to achieve temperature control. A pressure reducing valve needs to be installed on the carbon dioxide storage tank. A vent valve needs to be installed on the entire system to facilitate shutdown and maintenance. Valves need to be installed at both ends of the reactor and separator to ensure stable operation of the system.

[0013] A supercritical decolorization and degradation coupling method for waste dyed PET foam comprises the following steps:

[0014] (1) crushing the PET foam material by a crusher;

[0015] (2) The crushed PET foam material is sieved and filled into a reactor to form a packing bed, and the reactor temperature is set at 60° C. to 80° C.;

[0016] (3) The carbon dioxide is mixed with the co-solvent and preheated in a heater before being introduced into a reactor for decolorization, the pressure of the carbon dioxide is maintained at 15-18 MPa, the flow rate of the carbon dioxide is 2 cm / s-10 cm / s, and the flow rate of the co-solvent is set to 0.02 cm / s-0.1 cm / s;

[0017] (4) Carbon dioxide carrying the co-solvent flows through the first reactor and fully contacts the PET foam in the packing bed and decolorizes the PET foam. The decolorization time is 2 to 4 hours.

[0018] (5) After the decolorization is completed, stop passing carbon dioxide and co-solvent into the first reactor, open the valve for conveying the medium from the first reactor to the second reactor, discharge the carbon dioxide medium with co-solvent remaining in the first reactor to the second reactor so that it can be fully utilized, and after the pressure of the two reactors is balanced, close the valve for conveying the medium from the first reactor to the second reactor, input the remaining carbon dioxide in the first reactor into the separator until the pressure of the first reactor is 1MPa~2MPa, and start passing carbon dioxide and co-solvent into the second reactor to complete the switching of the first and second reactors. At this time, the second reactor performs the decolorization operation under the same conditions as the first reactor. The residual carbon dioxide in the first reactor can be used as an enhanced medium for alcoholysis reaction; after the carbon dioxide and co-solvent fluid extracted with the dye are conveyed to the separator, gas-liquid separation is carried out, and the gasified carbon dioxide is filtered by the second filter and returned to the carbon dioxide storage tank, and the co-solvent and dye are stored in the dye collection tank in a liquid state for post-processing;

[0019] (6) Changing the temperature of the first reactor to 200-240° C., introducing methanol into the reactor at a mass ratio of 6-8:1 to the PET foam, the initial pressure of the reactor is 1MPa-2MPa, the residual carbon dioxide pressure during pressure relief, and the final reaction pressure after heating is 8-15MPa. After the temperature and pressure are stable, the methanol feed pump is turned off, and the methanol circulation pump is turned on to circulate methanol, so that it undergoes alcoholysis reaction with the decolorized PET foam, the initial reaction pressure is 1MPa-2MPa, the reaction temperature is 220° C.-240° C., and the reaction time is 1h-2h;

[0020] (7) After the alcoholysis reaction is completed, the product in the first reactor is introduced into the degradation product storage tank, the first reactor is cleaned and refilled with the dyed PET foam, and the decolorization step is repeated. In this way, the decolorization-alcoholysis coupling reaction is carried out in sequence, thereby achieving the purpose of recovering the dye and PET degradation products of the dyed PET foam in one system.

[0021] The solid phase product of the alcoholysis reaction is mainly dimethyl terephthalate (DMT), and the liquid phase product is mainly ethylene glycol (EG). The product is subjected to solid-liquid separation to obtain a solid phase product and a liquid phase. The solid phase product is dried, and the liquid phase is separated from the liquid phase by rotary evaporation. The co-solvent and methanol can be recycled after separation and purification.

[0022] HPLC (high performance liquid chromatography) analysis of the main product DMT shows that the depolymerization rate of PET foam is 100%, the DMT yield is 64% to 80%, the reaction purity is high, and there is no obvious side reaction. Figure 3 It is the product form after decolorization and alcoholysis.

[0023] Furthermore, the co-solvent is dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), ethylene glycol (EG) or acetone.

[0024] Furthermore, the mass ratio of the crushed PET foam material to the co-solvent is 1:8-10.

[0025] The invention has the advantages of completing the two-step reaction of decolorization and alcoholysis at one time in a set of system, realizing the coupled decolorization and alcoholysis, having the advantages of simple process, small equipment investment, high reaction efficiency, green environmental protection, good reaction selectivity, high product quality, low operating cost, continuous production, etc., providing a new way to realize the purification, recovery and high-quality utilization of waste dyed PET foam materials, and conforming to the concept of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A supercritical decolorization and degradation coupling system for waste dyed PET foam material proposed by the present invention;

[0027] Figure 2 The morphology of PET foam material before and after crushing in the specific implementation process of the present invention; the left picture is before crushing; the right picture is after crushing;

[0028] Figure 3 The morphology of the product after decolorization and degradation in the specific implementation process of the present invention; the left picture is after decolorization; the right picture is after degradation;

[0029] Figure 4 It is a liquid chromatogram of DMT after decolorization and degradation in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The process flow in the embodiment of the present invention will be described in detail below in combination with the accompanying drawings and specific implementation methods of the present invention, but this specific implementation method is not intended to limit the present invention.

[0031] The system structure diagram of the embodiment of the present invention is as follows Figure 1As shown, three parallel reactors and one separator are provided. The preheated carbon dioxide carries the co-solvent and enters the decolorization from the lower end of the first reactor, and then flows into the separator from the upper end of the reactor along the pipeline. The carbon dioxide is separated in the separator and then continuously recycled to the carbon dioxide storage tank through the second filter, while the co-solvent and dye are collected in the dye collection tank. The co-solvent can be recycled to the co-solvent storage tank for reuse after separation.

[0032] When the first reactor is finished with continuous decolorization, the introduction of co-solvent and carbon dioxide into it is stopped, and methanol is introduced by the second plunger pump for degradation reaction. The circulating pump can circulate methanol in the first reactor to improve the reaction efficiency.

[0033] While the first reactor is undergoing degradation reaction, co-solvent and carbon dioxide are continuously introduced into the second reactor to decolorize the foam material, and then the foam material in the second reactor is degraded according to the previous steps. When the foam material in the second reactor is undergoing degradation reaction, the foam material in the third reactor can be decolorized. At the same time, the product of the first reactor that has completed the degradation reaction can also be collected, and the reactor can be reloaded to continue the previous decolorization and degradation operations. By scheduling the valves provided in the system, continuous operation of decolorization and degradation can be achieved.

[0034] Example 1

[0035] The PET foam is crushed by a crusher, and then the crushed PET foam is sieved and filled into the reactor to form a packed bed. The reactor temperature is set at 60°C. Carbon dioxide is entrained with DMSO and mixed and preheated by a heater and then introduced into the reactor for decolorization. The pressure of carbon dioxide is maintained at 15MPa, the flow rate of carbon dioxide is 2cm / s, the flow rate of the co-solvent is set to 0.02cm / s, and the mass ratio of the co-solvent DMSO to the crushed PET foam is controlled to be 10:1. Carbon dioxide entrained with the co-solvent flows through the first reactor and fully contacts the PET foam in the packed bed and decolorizes it. The decolorization time is 2h. After the decolorization is completed, stop passing carbon dioxide and co-solvent into the first reactor, open the valve for conveying the medium from the first reactor to the second reactor, discharge the carbon dioxide medium entrained with the co-solvent in the first reactor to the second reactor so that it can be fully utilized, and after the pressure of the two reactors is balanced, close the valve for conveying the medium from the first reactor to the second reactor, and input the remaining carbon dioxide in the first reactor into the separator until the pressure of the first reactor is 1MPa, and start passing carbon dioxide and co-solvent into the second reactor to complete the switching of the first and second reactors. At this time, the second reactor performs the decolorization operation under the same conditions as the first reactor. The residual carbon dioxide in the first reactor can be used as an enhanced medium for alcoholysis reaction; the carbon dioxide and co-solvent fluid extracted from the dye are transported to the separator for gas-liquid separation, and the gasified carbon dioxide is filtered by the second filter and returned to the carbon dioxide storage tank. The co-solvent and the dye are stored in the dye collection tank in a liquid state for post-processing. Change the temperature of the first reactor to 220 ° C, and pass methanol into the reactor at a mass ratio of 6:1 to the foam material. The initial pressure of the reactor is 1MPa, the residual carbon dioxide pressure during pressure relief. After the temperature and pressure are stable, turn off the methanol feed pump, turn on the methanol circulation pump for methanol circulation, and make it react with the decolorized PET foam material for alcoholysis, and the reaction time is 2h. After the alcoholysis reaction is completed, collect the product, and analyze the main product DMT by HPLC (high performance liquid chromatography) to obtain a depolymerization rate of 100% for the PET foam material and a DMT yield of 64%.

[0036] Example 2

[0037] The PET foam is crushed by a crusher, and then the crushed PET foam is sieved and filled into the reactor to form a packed bed. The reactor temperature is set at 70°C. Carbon dioxide is entrained with DMF and mixed and preheated by the heater and then introduced into the reactor for decolorization. The pressure of carbon dioxide is maintained at 16MPa, the flow rate of carbon dioxide is 6cm / s, the flow rate of the co-solvent is set to 0.06cm / s, and the mass ratio of the co-solvent DMF to the crushed PET foam is controlled to be 9:1. Carbon dioxide entrained with the co-solvent flows through the first reactor and fully contacts the PET foam in the packed bed and decolorizes it. The decolorization time is 3h. After the decolorization is completed, stop passing carbon dioxide and co-solvent into the first reactor, open the valve for conveying the medium from the first reactor to the second reactor, discharge the carbon dioxide medium entrained with the co-solvent in the first reactor to the second reactor so that it can be fully utilized, and after the pressure of the two reactors is balanced, close the valve for conveying the medium from the first reactor to the second reactor, and input the remaining carbon dioxide in the first reactor into the separator until the pressure of the first reactor is 1.5MPa, and start passing carbon dioxide and co-solvent into the second reactor to complete the switching of the first and second reactors. At this time, the second reactor performs the decolorization operation under the same conditions as the first reactor. The carbon dioxide remaining in the first reactor can be used as an enhanced medium for alcoholysis reaction; the carbon dioxide and co-solvent fluid extracted from the dye are transported to the separator for gas-liquid separation, and the gasified carbon dioxide is filtered by the second filter and returned to the carbon dioxide storage tank. The co-solvent and the dye are stored in the dye collection tank in a liquid state for post-processing. Change the temperature of the first reactor to 230 ° C, and pass methanol into the reactor at a mass ratio of 7:1 to the foam material. The initial pressure of the reactor is 1.5 MPa, the residual carbon dioxide pressure during pressure relief. After the temperature and pressure are stable, turn off the methanol feed pump, turn on the methanol circulation pump for methanol circulation, and make it react with the decolorized PET foam material for alcoholysis, and the reaction time is 1.5 hours. After the alcoholysis reaction is completed, collect the product, and analyze the main product DMT by HPLC (high performance liquid chromatography) to obtain a depolymerization rate of 100% for the PET foam material and a DMT yield of 71%.

[0038] Example 3

[0039] The PET foam is crushed by a crusher, and then the crushed PET foam is sieved and filled into the reactor to form a packed bed. The reactor temperature is set at 80°C. The carbon dioxide is mixed with acetone and preheated by the heater and then introduced into the reactor for decolorization. The pressure of carbon dioxide is maintained at 18MPa, the flow rate of carbon dioxide is 10cm / s, the flow rate of the co-solvent is set to 0.1cm / s, and the mass ratio of the co-solvent acetone to the crushed PET foam is controlled to be 8:1. The carbon dioxide entrained co-solvent flows through the first reactor and fully contacts the PET foam in the packed bed and decolorizes it. The decolorization time is 4h. After the decolorization is completed, stop passing carbon dioxide and co-solvent into the first reactor, open the valve for conveying the medium from the first reactor to the second reactor, discharge the carbon dioxide medium entrained with co-solvent in the first reactor to the second reactor so that it can be fully utilized, and after the pressure of the two reactors is balanced, close the valve for conveying the medium from the first reactor to the second reactor, and input the remaining carbon dioxide in the first reactor into the separator until the pressure of the first reactor is 2MPa, and start passing carbon dioxide and co-solvent into the second reactor to complete the switching of the first and second reactors. At this time, the second reactor performs the decolorization operation under the same conditions as the first reactor. The residual carbon dioxide in the first reactor can be used as an enhanced medium for alcoholysis reaction; the carbon dioxide and co-solvent fluid extracted from the dye are transported to the separator for gas-liquid separation, and the gasified carbon dioxide is filtered by the second filter and returned to the carbon dioxide storage tank. The co-solvent and the dye are stored in the dye collection tank in a liquid state for post-processing. Change the temperature of the first reactor to 240 ° C, and pass methanol into the reactor at a mass ratio of 8:1 to the foam material. The initial pressure of the reactor is the residual carbon dioxide pressure of 2MPa during pressure relief. After the temperature and pressure are stable, turn off the methanol feed pump, turn on the methanol circulation pump for methanol circulation, and make it react with the decolorized PET foam material for alcoholysis, and the reaction time is 1h. After the alcoholysis reaction is completed, collect the product, and analyze the main product DMT by HPLC (high performance liquid chromatography) to obtain a depolymerization rate of 100% for the PET foam material and a DMT yield of 80%.

Claims

1. A supercritical decolorization and degradation coupling system for waste dyed PET foam, characterized in that: It includes a first filter, a second filter, a carbon dioxide storage tank, a co-solvent storage tank, a methanol storage tank, a condenser, a first plunger pump, a second plunger pump, a constant flow pump, a heater, a circulation pump, a dye collection tank, a degradation product storage tank, a plurality of reactors and a separator; The outlet of the carbon dioxide storage tank is connected to the first filter, the condenser, the regulating valve, and the first plunger pump in sequence through a pipeline for conveying liquid carbon dioxide. The co-solvent storage tank is connected to the constant flow pump through a pipeline for conveying the co-solvent. The mixed fluid after the pipeline for conveying carbon dioxide and the pipeline for conveying the co-solvent are combined is connected to the inlet of the heater through a pipeline. The outlet pipeline of the heater is connected to multiple reactors in parallel; the multiple reactors can be interconnected, and the mixed fluid flowing out of the reactor after decolorization is completed is connected to the inlet of the separator; the separator is used to separate gas and liquid, the gas outlet of the separator is connected to the inlet of the carbon dioxide storage tank through a pipeline and a second filter, and the liquid outlet of the separator is connected to the dye collection tank; The methanol storage tank is connected to the second plunger pump through a pipeline, and then connected to the methanol inlets of multiple reactors in parallel; the outlets of multiple reactors are connected to the methanol inlets of respective reactors through pipelines and circulation pumps to form a circulation loop; the product outlets of multiple reactors are all connected to the degradation product storage tank; The reactor and separator are used for continuous decolorization and degradation reactions. The outside of the reactor and separator are equipped with heating jackets to achieve temperature control. A pressure reducing valve needs to be installed on the carbon dioxide storage tank. A vent valve needs to be installed on the entire system to facilitate shutdown and maintenance. Valves need to be installed at both the inlet and outlet of the reactor and separator to ensure stable operation of the system.

2. A supercritical decolorization and degradation coupling method for waste dyed PET foam is carried out by using the supercritical decolorization and degradation coupling system for waste dyed PET foam according to claim 1, characterized in that: The steps include: (1) crushing the PET foam material by a crusher; (2) The crushed PET foam material is sieved and filled into a reactor to form a packing bed, and the reactor temperature is set at 60° C. to 80° C.; (3) The carbon dioxide is mixed with the co-solvent and preheated in a heater before being introduced into a reactor for decolorization, the pressure of the carbon dioxide is maintained at 15-18 MPa, the flow rate of the carbon dioxide is 2 cm / s-10 cm / s, and the flow rate of the co-solvent is set to 0.02 cm / s-0.1 cm / s; (4) Carbon dioxide carrying the co-solvent flows through the first reactor and fully contacts the PET foam in the packing bed and decolorizes the PET foam. The decolorization time is 2 to 4 hours. (5) After the decolorization is completed, stop passing carbon dioxide and co-solvent into the first reactor, open the valve for conveying the medium from the first reactor to the second reactor, discharge the carbon dioxide medium with co-solvent remaining in the first reactor to the second reactor so that it can be fully utilized, and after the pressure of the two reactors is balanced, close the valve for conveying the medium from the first reactor to the second reactor, input the remaining carbon dioxide in the first reactor into the separator until the pressure of the first reactor is 1MPa~2MPa, and start to pass carbon dioxide and co-solvent into the second reactor to complete the switching of the first and second reactors; at this time, the second reactor performs the decolorization operation under the same conditions as the first reactor; the residual carbon dioxide in the first reactor can be used as an enhanced medium for alcoholysis reaction; after the carbon dioxide and co-solvent fluid extracted with the dye are conveyed to the separator, gas-liquid separation is carried out, and the gasified carbon dioxide is filtered by the second filter and returned to the carbon dioxide storage tank, and the co-solvent and dye are stored in the dye collection tank in a liquid state for post-processing; (6) Changing the temperature of the first reactor to 200-240° C., introducing methanol into the reactor at a mass ratio of 6-8:1 to the PET foam material, the initial pressure of the reactor is 1 MPa-2 MPa of the residual carbon dioxide pressure during pressure relief, and the final reaction pressure after heating is 8-15 MPa. After the temperature and pressure are stabilized, the methanol feed pump is turned off, and the methanol circulation pump is turned on to circulate methanol, so that it undergoes alcoholysis reaction with the decolorized PET foam material, and the reaction lasts for 1 h-2 h; (7) After the alcoholysis reaction is completed, the product in the first reactor is introduced into the degradation product storage tank, the first reactor is cleaned and refilled with the dyed PET foam, and the decolorization step is repeated. In this way, the decolorization-alcoholysis coupling reaction is carried out in sequence, thereby achieving the purpose of recovering the dye and PET degradation products of the dyed PET foam in one system.

3. The supercritical decolorization and degradation coupling method of waste dyed PET foam according to claim 2, characterized in that: The co-solvent is dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), ethylene glycol (EG) or acetone.

4. The supercritical decolorization and degradation coupling method of waste dyed PET foam according to claim 2, characterized in that: The mass ratio of the crushed PET foam material to the co-solvent is 1:8-10.

5. The supercritical decolorization and degradation coupling method of waste dyed PET foam according to claim 2, characterized in that: The decolorization-alcoholysis coupling reaction was completed in sequence within a system.

Images