Method for depolymerizing polyurethane based on diester carbonate under catalysis of halogen salt substances
By using halogen salt catalysts in carbonate diesters, mild depolymerization of polyurethane was achieved, solving the problems of harsh reaction conditions and environmental pollution in existing technologies. The products are easy to separate and the catalysts are recyclable, which is in line with the development direction of green chemistry and circular economy.
Patent Information
- Application Number
- CN202511472825.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-15
- Publication Date
- 2026-01-27
AI Technical Summary
Existing polyurethane depolymerization methods suffer from problems such as harsh reaction conditions, equipment corrosion, complex and difficult-to-separate products, and environmental pollution. There is a lack of mild and environmentally friendly depolymerization technologies.
Using catalyst-free or halogenated salt substances as catalysts in diesters, polyurethane is converted into urethane derivatives and polyols through chemical depolymerization under mild conditions.
It achieves polyurethane depolymerization under mild conditions, the products are easy to separate, it is environmentally friendly, the catalyst can be recycled and reused, and it provides a way to utilize polyurethane waste resources.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of chemical recycling technology of waste polymer materials, specifically relating to a method for catalytic depolymerization of polyurethane into its monomers or high-value chemicals, and more specifically relating to a method for catalytic depolymerization of polyurethane in diester without a catalyst or using halogen salts. Background Technology
[0002] Polyurethane (PU) is an important polymer material prepared by reacting isocyanates with polyols. Due to its excellent mechanical properties, abrasion resistance, and processability, it is widely used in foams, elastomers, coatings, adhesives, synthetic leather, and other fields. With the continuous growth in consumption, the environmental pollution and resource waste caused by waste polyurethane are becoming increasingly prominent.
[0003] Chemical recycling is an ideal method for converting waste polymers into virgin monomers or other useful chemicals, contributing to a circular economy. Currently, chemical depolymerization methods for polyurethane mainly include hydrolysis, alcoholysis, aminolysis, and acidolysis. However, these methods typically suffer from problems such as harsh reaction conditions (high temperature and pressure), equipment corrosion due to the use of strong acids and alkalis, complex and difficult-to-separate products, and environmental pollution. For example, alcoholysis usually requires a high alcohol ratio and a long reaction time, and the products are often mixtures. Therefore, developing a new chemical depolymerization method for polyurethane with mild reaction conditions, environmental friendliness, high efficiency, and easily separable products has significant scientific and practical value.
[0004] Dicarbonates, particularly dimethyl carbonate (DMC), are considered green solvents and reagents. To the best of our knowledge, there are currently no publicly available technical reports on the use of diesters as reaction media and reagents for the catalytic depolymerization of polyurethanes. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a polyurethane depolymerization method that features mild reaction conditions, high efficiency, and environmental friendliness.
[0006] The polyurethane depolymerization method provided by the present invention includes the following steps: chemically depolymerizing polyurethane or polyurethane-containing composite materials in diester under conditions without a catalyst or with a halogen salt as a catalyst.
[0007] The above method can be used to depolymerize polyurethane under mild conditions, converting it into valuable chemicals such as urethane derivatives and polyols.
[0008] In the above method, the reaction conditions for chemical depolymerization are: a reaction time of 0.5 to 36 hours at a temperature of room temperature to 280°C. The room temperature range is 15 to 30°C.
[0009] In the above method, the halide salt catalyst includes at least one of halide anionic metal salt, halide anionic ionic liquid, and a composite system formed by halide anionic metal salt and halide anionic ionic liquid.
[0010] Furthermore, the halide anionic metal salt has anions including chloride ions, bromide ions, and iodide ions; and metal cations including, but not limited to, lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, magnesium ions, calcium ions, strontium ions, barium ions, zinc ions, iron ions, copper ions, tin ions, zirconium ions, chromium ions, manganese ions, and cobalt ions.
[0011] Specifically, the halide anionic metal salts include, but are not limited to, LiCl, NaCl, KCl, RbCl, CsCl, MgCl2, CaCl2, SrCl2, BaCl2, ZnCl2, FeCl3, CuCl2, SnCl4, ZrCl4, CrCl3, MnCl2, CoCl2, LiBr, NaBr, KBr, CsBr, MgBr2, CaBr2, BaBr2, ZnBr2, FeBr3, CuBr2, SnBr4, ZrBr4, CrBr3, MnBr2, CoBr2, NaI, KI, MgI2, CaI2, BaI2, ZnI2, FeI3, CuI2, ZrI4, CrI3, MnI2, CoI2, etc.
[0012] Furthermore, the halogen anionic liquid contains chloride ions, bromide ions, and iodide ions as anions; Its cations include, but are not limited to, imidazole cations, pyridinyl cations, piperidinyl cations, tetraalkylammonium cations, tetraalkylphosphine cations, guanidinyl cations, alkylpyridinium cations, alkylpiperidine cations, and alkylpyrrole cations; the alkyl groups in the tetraalkylammonium cation, tetraalkylphosphine cation, alkylpyridinium cation, alkylpiperidine cation, and alkylpyrrole cation can all be independently selected from C1-C8 straight-chain or branched alkyl groups.
[0013] Specifically, the halide anionic ionic liquids include, but are not limited to, [BMIm]Cl (1-butyl-3-methylimidazolium chloride), [P 4444 Cl (tetrabutylphosphine chloride), [Py 14 Cl (N-butyl-N-methylpyrrole chloride), [PP 14 ]Cl (N-butyl-N-methylpiperidine chloride), [N 4444 Cl (tetrabutylammonium chloride).
[0014] In the above method, the diester carbonate may be selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, dibenzyl carbonate, etc.; preferably dimethyl carbonate (DMC) or diethyl carbonate (DEC).
[0015] In the above method, the polyurethane includes various types of polyurethane materials and their waste, including but not limited to: The polyurethanes described in this invention include, but are not limited to: thermoplastic polyurethane (TPU), polyether-type polyurethane, polyester-type polyurethane, MDI (4,4'-diphenylmethane diisocyanate) type polyurethane, HDI (1,6-hexamethylene diisocyanate) type polyurethane, TDI (2,4-toluene diisocyanate / 2,6-toluene diisocyanate) type polyurethane, and IPDI (3-isocyanatomethylene-3,5,5-trimethylcyclohexyl diisocyanate) type polyurethane. Polyurethane foams, polyurethane elastomers, polyurethane coatings, polyurethane adhesives, etc., and the polyurethane-containing composite materials include, but are not limited to, at least one of all samples, physical samples, or mixtures thereof containing polyurethane components.
[0016] Furthermore, the polyurethane is an MDI-type polyurethane, and even more specifically, it can be a polyether-type MDI-type polyurethane or a polyester-type MDI-type polyurethane.
[0017] In the above method, additives may be added to the chemical depolymerization reaction system. These additives may be selected from at least one of the following: sulfates, carbonates, phosphates, hydrogen phosphates, nitrates, and perchlorates. Specifically, the additives include, but are not limited to, ZnSO4, ZnCO3, Zn3(PO4)2, [P...]. 4444 H2PO4, [P 4444 NO3, [P] 4444 ClO4 The addition of additives here helps to improve reaction efficiency.
[0018] Furthermore, the molar ratio of the additive to the polyurethane structural unit can be 0.01:1 to 0.5:1, specifically 0.02:1, 0.05:1, etc.
[0019] In the above method, other solvents may be added to the chemical depolymerization reaction system. The other solvents may be selected from at least one of the following: toluene-n-hexane, tetrahydrofuran, alcohol solvents (such as methanol, ethanol, isopropanol), and N,N-dimethylformamide.
[0020] Furthermore, the ratio of the other solvents to the diester is 1 ml / 5 mmol to 20 mL / 1 mmol.
[0021] In the above method, the molar ratio of the carbonate diester to the polyurethane structural unit can be 1:1 to 50:1, specifically 1:1, 10:1, 20:1, 30:1, 40:1 or 50:1, etc. In the above method, the molar ratio of the halogen salt to the polyurethane structural unit can be 1% to 20%, specifically 1%, 5%, 10%, 15% or 20%, etc.
[0022] In the above method, under the condition of no catalyst, the reaction conditions for chemical depolymerization are: reaction at a temperature of 180-280℃ (specifically 180℃, 200℃, 240℃ or 280℃, etc.) for 24-36h (specifically 24h, 30h or 36h, etc.).
[0023] In the above method, under the condition that the halogen salt is the catalyst, the reaction conditions for the chemical depolymerization are: reacting at a temperature of room temperature to 180°C (specifically, 100°C, 120°C, 140°C, 160°C or 180°C, etc.) for 0.5 to 24 hours (specifically, 12 hours or 24 hours, etc.).
[0024] Furthermore, when a halide anionic metal salt is added as a catalyst, the reaction temperature can be 100–180°C (specifically, 100°C, 120°C, 140°C, or 160°C, etc.); the time can be 4–24 h (specifically, 6 h, 8 h, or 12 h, etc.).
[0025] Furthermore, in the above method, when a halide anionic liquid is added as a catalyst, the reaction temperature can be 80–160°C (specifically, 80°C, 100°C, 120°C, or 160°C, etc.); the time can be 0.5–12 h (specifically, 1–8 h, 1 h, 2 h, 3 h, or 4 h, etc.).
[0026] Furthermore, in the above method, when a composite system formed by a halide anion metal salt and a halide anion ionic liquid is added, the reaction temperature can be 80–140°C (specifically, 100°C, 120°C, etc.); the time can be 0.5–12 h (specifically, 0.5 h, 1 h, 2 h, etc.).
[0027] The polyurethane described in this invention is a type of polymer with urethane groups (-NHCOO-) on its main chain. Its structural units mainly include soft segment structural units, hard segment structural units, and end-capping groups. Soft segment structural units are typically composed of low-molecular-weight polyether polyols or polyester polyols. Examples of polyether polyols include polyethylene glycol (PEG), polypropylene glycol (PPG), and polytetramethylene glycol (PTMG), while polyester polyols are obtained by polycondensation of diacids and diols. Hard segment structural units are formed by the reaction of isocyanates and small-molecule chain extenders. Common isocyanates include aromatic isocyanates such as 4,4'-diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI), and aliphatic isocyanates such as isophorone diisocyanate (IPDI) and 1,6-hexamethylene diisocyanate (HDI). Small molecule chain extenders are generally small molecular weight compounds capped with amino or hydroxyl groups, such as ethylene glycol (EG), 1,4-butanediol (BDO), and ethylenediamine. The polyurethane structural unit described in this invention is a block structure segment composed of alternating flexible soft segment units and rigid hard segment units, with urethane groups (-NHCOO-) as the connecting core.
[0028] Further, the specific operating steps of the above method are as follows: placing polyurethane or a polyurethane-containing composite material in a diester, heating it for a certain time at a set reaction temperature without the need for a catalyst or with the addition of a halogen salt as a catalyst; then cooling, separating the undissolved solid, and obtaining a mixture of depolymerization products containing urethane derivatives and polyols or esters.
[0029] The method further includes the following steps: filtering and separating unreacted solids; then, separating and recovering excess diester, generated carbamate derivatives, polyols or esters, and catalyst by conventional vacuum distillation, extraction, or crystallization methods. The recovered catalyst can be reused.
[0030] Regarding the separation of products after the reaction, it also includes adopting appropriate separation methods according to the different catalysts used.
[0031] Examples of products obtained through the above methods are described below: For polyester-type polyurethanes, such as PBA-type and MDI-type polyurethanes (PBA represents polybutylene adipate, and MDI represents 4,4'-diphenylmethane diisocyanate), depolymerization with DMC yields methyl methylene bis(4,1-phenylene)dicarbamate (MDC), dimethyl adipate (DMA), and dimethyl 1,4-butanediol carbonate (BDD); depolymerization with DMC yields ethyl methylene bis(4,1-phenylene)dicarbamate, diethyl adipate, and diethyl 1,4-butanediol carbonate; and for PEA-type and MDI-type polyurethanes (PEA represents polyethylene adipate, and MDI represents 4,4'-diphenylmethane diisocyanate), depolymerization with DMC yields MDC, DMA, BDD, ethylene carbonate (EC), and dimethyl 2,5-dioxadipic acid (DD).
[0032] For polyether-type polyurethanes, such as polytetrahydrofuran-type MDI-type polyurethanes, depolymerization with DMC yields MDC, BDD, tetrahydrofuran (THF), etc.
[0033] Compared with the prior art, the present invention has the following beneficial effects: 1. The reaction conditions are relatively mild, and it can be carried out at a lower temperature in the presence of a catalyst.
[0034] 2. The diester used is a green solvent and is environmentally friendly.
[0035] 3. Catalysts are mostly inexpensive and readily available halogen salts, which have low costs and can be recycled and reused.
[0036] 4. The depolymerization products are urethane derivatives and polyols, which have high economic value.
[0037] 5. This method provides a new approach for the resource utilization of polyurethane waste, which is in line with the development direction of green chemistry and circular economy. Attached Figure Description
[0038] Figure 1 This is a product obtained by depolymerizing polyurethane in dimethyl carbonate. Detailed Implementation
[0039] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.
[0040] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.
[0041] Examples 1-13: Catalytic depolymerization of PBA-type MDI-type polyurethane by metal salts without catalysts or halide anions The experimental procedure involved adding 240 mg (approximately 1 mmol of polyurethane structural units) of PBA-type MDI-type polyurethane, 0.01 mmol of a metal salt containing halide anions, and 900 mg (approximately 10 mmol) of dimethyl carbonate to a 20 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at a set temperature and allowed to react for a certain time. After cooling in an ice-water bath, pyrazine was added as an internal standard, and deuterated dimethyl sulfoxide (DMSO-d6) was added. The product yield was analyzed by NMR, yielding the following results.
[0042] Table 1. Reaction conditions and results of Examples 1-13
[0043] Examples 14-25: Halogen anionic liquid-catalyzed depolymerization of dimethyl carbonate (PBA-type MDI-type polyurethane) Experimental procedure: 240 mg (containing approximately 1 mmol of polyurethane structural units) of PBA-type MDI-type polyurethane, 0.01 mmol of halide anionic ionic liquid, and 900 mg (approximately 10 mmol) of dimethyl carbonate were added to a 20 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at a set temperature and reacted for a certain time. After cooling in an ice-water bath, pyrazine was added as an internal standard and deuterated dimethyl sulfoxide as a deuteration reagent. The product yield was analyzed by NMR, and the following results were obtained.
[0044] Table 2 Reaction conditions and results of Examples 14-25
[0045] Examples 26-31: Catalytic depolymerization of PBA-type MDI-type polyurethane using an additive-containing catalytic system. Experimental procedure: 240 mg (containing approximately 1 mmol of polyurethane structural units) of PBA-type MDI-type polyurethane, 0.01 mmol of catalyst, 0.01 mmol of additive, and 900 mg (approximately 10 mmol) of dimethyl carbonate were added to a 20 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at a set temperature and reacted for a certain time. After cooling to room temperature, pyrazine was added as an internal standard and deuterated dimethyl sulfoxide as a deuteration reagent. The product yield was analyzed by NMR, and the following results were obtained.
[0046] Table 3 Reaction conditions and results of Examples 26-31
[0047] Examples 32-38: Catalytic systems formed by composite systems of halide anionic metal salts and halide anionic ionic liquids for the depolymerization of PBA-type MDI-type polyurethane in DMC. Experimental procedure: 240 mg (approximately 1 mmol of polyurethane structural unit) of PBA-type MDI-type polyurethane, 0.01 mmol of metal salt, 0.01 mmol of ionic liquid chloride, and 900 mg (approximately 10 mmol) of dimethyl carbonate were added to a 20 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at a set temperature and reacted for a certain time. After cooling to room temperature, pyrazine was added as an internal standard and deuterated dimethyl sulfoxide as a deuteration reagent. The product yield was analyzed by NMR, and the following results were obtained.
[0048] Table 4 Reaction conditions and results of Examples 32-38
[0049] Examples 39-46: Depolymerization of PBA-type and MDI-type polyurethanes with DMC in other solvent systems Experimental procedure: 240 mg (approximately 1 mmol of polyurethane structural unit) of PBA-type MDI-type polyurethane, 0.01 mmol of metal salt (zinc chloride), 270 mg (approximately 3 mmol) of dimethyl carbonate, and 1 mL of other solvent were added to a 20 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at a set temperature and reacted for a certain time. After cooling to room temperature, pyrazine was added as an internal standard and deuterated dimethyl sulfoxide as a deuteration reagent. The product yield was analyzed by NMR, and the following results were obtained.
[0050] Table 5. Reaction conditions and results of Examples 39-46
[0051] Example 47: Depolymerization of PBA-type MDI-type polyurethane in diethyl carbonate (DEC) catalyzed by ZnCl2 Experimental procedure: 240 mg (approximately 1 mmol of polyurethane structural unit) of PBA-type MDI-type polyurethane, 0.01 mmol of metal salt (zinc chloride), and 1200 mg of diethyl carbonate (approximately 10 mmol) were added to a 50 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at 120 °C and reacted for 12 hours. After cooling to room temperature, pyrazine was added as an internal standard and deuterated dimethyl sulfoxide as a deuteration reagent. The product yields were analyzed by NMR, yielding ethyl methylenebis(4,1-phenylene)dicarbamate (80.4%), diethyl adipate (80.0%), and diethyl 1,4-butanediol carbonate (80.0%).
[0052] Examples 48-49: Depolymerization of other types of polyurethane in DMC catalyzed by ZnCl2 Experimental procedure: Approximately 1 mmol of polyurethane containing polyurethane structural units, 0.01 mmol of zinc chloride, and 900 mg of DMC (approximately 10 mmol) were added to a 15 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at 120 °C and reacted for 12 hours. After cooling in an ice-water bath, pyrazine was added as an internal standard and deuterated dimethyl sulfoxide as a deuteration reagent. The yield was then determined by NMR analysis using the internal standard method.
[0053] Example 48: Depolymerization of PEA-type MDI-type polyurethane yielded methyl methylene bis(4,1-phenylene)dicarbamate (MDC) with a yield of 90.4%, dimethyl adipate (DMA) with a yield of 90.3%, diethyl 1,4-butanediol carbonate (BDD) with a yield of 89.3%, ethylene carbonate (EC) with a yield of 80.1%, and dimethyl 2,5-dioxa-adipate (DD) with a yield of 8.5%.
[0054] Example 49: Depolymerization of polytetrahydrofuran-type MDI polyurethane yielded methyl methylene bis(4,1-phenylene)dicarbamate (MDC) with a yield of 92.1%, 1,4-butanediol diethyl carbonate (BDD) with a yield of 90.2%, and tetrahydrofuran (THF) with a yield of 89.3%.
[0055] Example 50: Depolymerization of polytetrahydrofuran-type MDI-type spandex yarn in DMC catalyzed by ZnCl2 Experimental procedure: 113 mg (containing approximately 1 mmol of polyurethane structural units) of polytetrahydrofuran-type MDI-type spandex thread, 0.01 mmol of zinc chloride, and 900 mg (approximately 10 mmol) of dimethyl carbonate were added to a 15 mL pressure-resistant reaction tube. The reaction tube was then placed in a heating device at 120 °C and reacted for 12 hours. After cooling in an ice-water bath, pyrazine was added as an internal standard and deuterated dimethyl sulfoxide as a deuteration reagent. The product yields were analyzed by NMR, yielding methyl methylene bis(4,1-phenylene)dicarbamate (MDC) with a yield of 89.4%, 1,4-butanediol diethyl carbonate (BDD) with a yield of 88.3%, and tetrahydrofuran (THF) with a yield of 80.2%.
[0056] The present invention has been described in detail above. For those skilled in the art, the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. Although specific embodiments have been given, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some of the essential features can be applied within the scope of the following appended claims.
Claims
1. A method for catalytic depolymerization of polyurethane, comprising the following steps: chemically depolymerizing polyurethane or a polyurethane-containing composite material in a diester under conditions without a catalyst or with a halogen salt as a catalyst.
2. The method according to claim 1, characterized in that: The reaction conditions for the chemical depolymerization are: a reaction time of 0.5 to 36 hours at a temperature of room temperature to 280°C.
3. The method according to claim 1 or 2, characterized in that: The halogen salts are selected from at least one of the following: halogen anionic metal salts, halogen anionic ionic liquids, and composite systems formed by halogen anionic metal salts and halogen anionic ionic liquids. And / or, the carbonate diester is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, and dibenzyl carbonate; And / or, the polyurethane includes various types of polyurethane materials and their waste.
4. The method according to claim 3, characterized in that: The halide anionic metal salt has an anion selected from at least one of the following: chloride ion, bromide ion, iodide ion; Its metal cation is selected from at least one of the following: lithium ion, sodium ion, potassium ion, rubidium ion, cesium ion, magnesium ion, calcium ion, strontium ion, barium ion, zinc ion, iron ion, copper ion, tin ion, zirconium ion, chromium ion, manganese ion, cobalt ion; Specifically, the halide anion metal salt is selected from at least one of the following: LiCl, NaCl, KCl, RbCl, CsCl, MgCl2, CaCl2, SrCl2, BaCl2, ZnCl2, FeCl3, CuCl2, SnCl4, ZrCl4, CrCl3, MnCl2, CoCl2, LiBr, NaBr, KBr, CsBr, MgBr2, CaBr2, BaBr2, ZnBr2, FeBr3, CuBr2, SnBr4, ZrBr4, CrBr3, MnBr2, CoBr2, NaI, KI, MgI2, CaI2, BaI2, ZnI2, FeI3, CuI2, ZrI4, CrI3, MnI2, CoI2; And / or, the halogen anionic liquid has an anion selected from at least one of the following: chloride ion, bromide ion, iodide ion; and a cation selected from at least one of the following: imidazole cation, pyridinyl cation, piperidinyl cation, tetraalkylammonium cation, tetraalkylphosphine cation, guanidinyl cation, alkylpyridinium cation, alkylpiperidine cation, alkylpyrrole cation, etc.; wherein the alkyl groups in the tetraalkylammonium cation, tetraalkylphosphine cation, alkylpyridinium cation, alkylpiperidine cation, and alkylpyrrole cation are all independently selected from C1-C8 straight-chain or branched alkyl groups; Specifically, the halide anionic ionic liquid is selected from at least one of the following: [BMIm]Cl, [P 4444 Cl、[Py 14 Cl、[PP 14 Cl、[N 4444 ] Cl.
5. The method according to claim 3, characterized in that: The polyurethane is selected from at least one of the following: polyether polyurethane, polyester polyurethane, MDI (4,4'-diphenylmethane diisocyanate) polyurethane, HDI (1,6-hexamethylene diisocyanate) polyurethane, TDI (2,4-toluene diisocyanate / 2,6-toluene diisocyanate) polyurethane, IPDI (3-isocyanatomethylene-3,5,5-trimethylcyclohexyl diisocyanate) polyurethane, and the polyurethane-containing composite material includes, but is not limited to, at least one of all samples, physical objects or mixtures thereof containing polyurethane components; Furthermore, the polyurethane is an MDI-type polyurethane, and even more specifically, a polyether-type MDI-type polyurethane or a polyester-type MDI-type polyurethane.
6. The method according to any one of claims 1-5, characterized in that: Under catalyst-free conditions, the chemical depolymerization reaction is carried out at a temperature of 180–280°C for 24–36 hours. Alternatively, under the condition that a halogen salt is used as a catalyst, the reaction conditions for the chemical depolymerization are: reaction at room temperature to 180°C for 0.5 to 24 hours; Preferably, under the condition that the halide anion metal salt is used as a catalyst, the reaction conditions for the chemical depolymerization are: reaction at a temperature of 100-180°C for 4-24 hours. Preferably, under the condition that the halide anionic liquid is used as a catalyst, the reaction conditions for the chemical depolymerization are: reaction at a temperature of 80-160°C for 0.5-12 hours. Preferably, under the condition that the composite system formed by the halide anion metal salt and the halide anion ionic liquid is used as the catalyst, the reaction conditions for the chemical depolymerization are: reaction at a temperature of 80-140°C for 0.5-12 hours.
7. The method according to any one of claims 1-6, characterized in that: The molar ratio of the diester to the polyurethane structural unit is 1:1 to 50:
1. And / or, the molar ratio of the halogen salt to the polyurethane structural unit is 1% to 20%.
8. The method according to any one of claims 1-7, characterized in that: The chemical depolymerization reaction system also includes an additive, which is selected from at least one of the following: sulfate, carbonate, phosphate, hydrogen phosphate, nitrate, and perchlorate. Further, the additive is selected from at least one of the following: ZnSO4, ZnCO3, Zn3(PO4)2, [P 4444 H2PO4, [P 4444 NO3, [P] 4444 ClO4; Furthermore, the molar ratio of the additive to the polyurethane structural unit is 0.01:1 to 0.5:1; And / or, other solvents are added to the chemical depolymerization reaction system, wherein the other solvents are selected from at least one of: toluene-n-hexane, tetrahydrofuran, alcohol solvents, and N,N-dimethylformamide; Furthermore, the ratio of the other solvents to the diester is 1 ml / 5 mmol to 20 mL / 1 mmol.
9. The method according to any one of claims 1-8, characterized in that: The specific steps of the method are as follows: placing polyurethane or a polyurethane-containing composite material in diester, heating it for a certain time at a set reaction temperature without the need for a catalyst or with the addition of halogen salts as a catalyst; and then cooling it. Furthermore, the method further includes the following operations: filtering and separating unreacted solids; and then separating and recovering excess diester, generated carbamate derivatives, polyols or esters, and catalysts by conventional vacuum distillation, extraction, or crystallization methods.
10. The method according to any one of claims 1-9, characterized in that: The polyurethane is a PBA-type MDI-type polyurethane, which is chemically depolymerized in dimethyl carbonate to obtain methyl methylene bis(4,1-phenylene))dicarbamate (MDC), dimethyl adipate (DMA), and dimethyl 1,4-butanediol carbonate (BDD). And / or, the polyurethane is a PBA-type or MDI-type polyurethane, which is chemically depolymerized in diethyl carbonate to obtain ethyl methylenebis(4,1-phenylene))dicarbamate, diethyl adipate, and diethyl 1,4-butanediol carbonate. And / or, the polyurethane is a PEA-type or MDI-type polyurethane, which is chemically depolymerized in dimethyl carbonate to obtain methyl methylene bis(4,1-phenylene))dicarbamate (MDC), dimethyl adipate (DMA), dimethyl 1,4-butanediol carbonate (BDD), ethylene carbonate (EC), and dimethyl 2,5-dioxa-adipate (DD). And / or, the polyurethane is a polytetrahydrofuran-type MDI polyurethane, which is chemically depolymerized in dimethyl carbonate to obtain methyl methylene bis(4,1-phenylene))dicarbamate (MDC), 1,4-butanediol dimethyl carbonate (BDD), and tetrahydrofuran (THF).