A method of depolymerization of plastics

Abstract

This invention relates to a method for depolymerizing plastics, wherein the plastic undergoes a depolymerization reaction in the presence of a depolymerizing agent and a catalyst. The plastic is selected from one or more of polyesters, polycarbonates, polyamides, and polyurethanes, and the catalyst is selected from one or more of specific mononuclear metal Salen complexes and specific mononuclear metal phthalocyanine complexes. The depolymerization method of this invention can efficiently perform catalytic depolymerization of plastics, produces high-purity monomer products, is applicable to the processing of various plastics, and uses readily available catalysts with good catalytic effect and strong stability.

Description

Technical Field

[0001] This invention relates to a method for depolymerizing plastics, belonging to the field of plastic recycling. Background Technology

[0002] Since the 1950s, plastic production has grown exponentially, and a large number of plastic products have brought great convenience to our lives. However, most plastic products are discarded after a single use, and this linear life cycle model has led to serious plastic pollution problems and the waste of petrochemical resources. Currently, plastic waste scattered around the world has a significant impact on the ecological environment and human health. The increasing plastic pollution has prompted people to seek more effective waste plastic recycling strategies. As the most common polyester plastic, polyethylene terephthalate (PET) accounts for 12% of solid waste. Mechanical recycling of PET often leads to a decline in its mechanical properties and can only process relatively pure waste streams. Chemical recycling, on the other hand, can depolymerize PET waste into PET monomers to achieve recycling. Existing chemical recycling technologies usually require harsh conditions, such as high temperatures (>180°C) and / or high pressures (20–40 atmospheres), and use corrosive concentrated strong alkalis (such as 1–10M NaOH solution) or concentrated strong acids, resulting in high costs and safety issues, making large-scale application difficult.

[0003] Catalysts hold great potential in accelerating reaction rates during the chemical recycling of plastics. Various catalysts for PET degradation have been developed, including Zn(OAc)₂, ZnO nanoparticles, tetrabutylammonium iodide (TBAI), and ionic liquids. In contrast, metal complexes offer advantages due to their structural tunability. Patent Documents 1 and 2 disclose various binuclear metal complex catalysts and their application in the hydrolysis of plastics. Furthermore, Patent Documents 1 and 2 disclose, for example, binuclear metal complexes with Zn(II) and Mg(II) metals that promote the ethylene glycololysis of PET through different ligand structures, while binuclear metal complexes with Ru(II) metals exhibit high tolerance to impurities in catalyzing the hydrogenolysis of PET.

[0004] In addition, many relatively simple transition metal complexes are now commercially available, with typical examples including transition metal Salen complexes and transition metal phthalocyanine complexes. Transition metal Salen complexes have been extensively studied in reactions such as catalytic oxidation, epoxidation, carbonate esterification, and CH bond activation, while transition metal phthalocyanine complexes have demonstrated excellent catalytic performance in redox reactions such as oxygen reduction, photocatalysis, and carbon dioxide reduction. Furthermore, transition metal phthalocyanine complexes exhibit high structural stability, heat resistance, and chemical resistance under common reaction conditions for plastic depolymerization, and transition metal Salen complex catalysts also show good thermal stability and solvent adaptability. However, the catalytic performance of these two types of transition metal complexes in plastic depolymerization reactions has not been fully studied. Exploring their application potential in the chemical recycling of plastics will hopefully improve the economics and practicality of the recycling process.

[0005] References

[0006] Patent Document 1: CN 114377726A

[0007] Patent Document 2: CN 114395233A Summary of the Invention

[0008] The problem the invention aims to solve

[0009] The metal complexes disclosed in Patent Documents 1 and 2 are often complex to synthesize, difficult to obtain, and exhibit poor thermal and air stability, thus limiting their applications. Developing readily available, highly catalytically effective, and stable metal complexes is of great significance for the chemical recycling of plastics.

[0010] In view of the above-mentioned problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for depolymerization of plastics, which can efficiently carry out catalytic depolymerization of plastics, produce high purity monomer products, is applicable to the processing of various plastics, and uses a catalyst that is easy to obtain, has good catalytic effect and strong stability.

[0011] Solution for solving the problem

[0012] To address the aforementioned problems, the inventors conducted long-term and in-depth research, attempting to use readily available, highly effective, and stable metal complexes as catalysts for the depolymerization of plastics. As a result, it was discovered that the above-mentioned technical problems could be solved by using specific transition metal complex catalysts to depolymerize plastics such as polyester, polycarbonate, polyamide, and polyurethane.

[0013] Specifically, the present invention solves the problems of the present invention through the following solutions.

[0014] [1] A method for depolymerizing a plastic, wherein the plastic is subjected to a depolymerization reaction in the presence of a depolymerization agent and a catalyst.

[0015] The plastic is selected from one or more of polyester, polycarbonate, polyamide, and polyurethane.

[0016] The catalyst is selected from one or more mononuclear metal Salen complexes and mononuclear metal phthalocyanine complexes.

[0017] The mononuclear metal Salen-like complex has the structure shown in the following general formula (1):

[0018]

[0019] In the general formula (1), M represents a metal atom and is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, or Pd. M exhibits a divalent or trivalent oxidation state.

[0020] When M is divalent, X does not exist; when M is trivalent, X exists and X is selected from NO3. - Cl - ,Br - OAc - OTf - OH - BF4 - PF6 - or ClO4 - ,

[0021] R1, R2, R3, R4, R1', R2', R3', and R4' are each independently selected from H, alkyl groups having 1 to 6 carbon atoms, halogens, alkoxy groups having 1 to 6 carbon atoms, or trialkylsilyl groups having 3 to 18 carbon atoms, or R1 and R1' are bonded to each other to form -O-CH2CH2-(OCH2CH2). n -OCH2CH2O-, where n is 1 or 2.

[0022] Y is selected from linear or branched alkylene groups having 1 to 6 carbon atoms, cycloalkylene groups having 3 to 10 carbon atoms, aryl groups having 6 to 20 carbon atoms, or heterocyclic groups having 4 to 10 carbon atoms, wherein the substituent is selected from the group consisting of hydroxyl, phenyl, and cycloalkyl groups having 4 to 8 carbon atoms.

[0023] The mononuclear metal phthalocyanine complex has the structure shown in the following general formula (2):

[0024]

[0025] In the general formula (2), M represents a metal atom and is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, or Pd. M is divalent or trivalent.

[0026] When M is divalent, X does not exist; when M is trivalent, X exists and X is selected from NO3. - Cl - ,Br - OH - BF4 - PF6 - or ClO4 - ,

[0027] R5, R6, R7 and R8 are each independently selected from H, hydroxyl, alkyl with 1 to 6 carbon atoms, halogen, alkoxy with 1 to 6 carbon atoms, amino, sulfonic acid or nitro, and each R5 may be the same as or different from each other, each R6 may be the same as or different from each other, each R7 may be the same as or different from each other, and each R8 may be the same as or different from each other.

[0028] [2] According to the depolymerization method of the plastic described in [1], wherein the depolymerization reagent is selected from alcohol, water, ammonia or amine; preferably, the depolymerization reagent is alcohol.

[0029] [3] The depolymerization method for plastics according to [1] or [2], wherein,

[0030] In the general formula (1), in the definitions of R1, R2, R3, R4, R1', R2', R3', and R4', the alkyl group having 1 to 6 carbon atoms is selected from methyl, ethyl, isopropyl, or tert-butyl; the halogen is selected from fluorine, chlorine, or bromine; the alkoxy group having 1 to 6 carbon atoms is selected from methoxy, ethoxy, or propoxy; the trialkylsilyl group having 3 to 18 carbon atoms is selected from triethylsilyl or triisopropylsilyl; and Y is selected from -CH2-CH2-, -CH2CH2CH2-, -CH2CH(OH)CH2-, ... In the structural formula, * represents a bonding site;

[0031] In the general formula (2), in the definitions of R5, R6, R7 and R8, the alkyl group having 1 to 6 carbon atoms is selected from methyl, ethyl, isopropyl or tert-butyl, the halogen is selected from fluorine, chlorine or bromine, and the alkoxy group having 1 to 6 carbon atoms is selected from methoxy, ethoxy or propoxy.

[0032] [4] The method for depolymerizing the plastic according to any one of [1] to [3], wherein,

[0033] In the general formula (1), M is selected from Mn, Fe, Co, or Ni.

[0034] When M is trivalent, X is Cl. - or Br - ,

[0035] R1, R2, R3, R4, R1', R2', R3' and R4' are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl, fluorine, chlorine, methoxy or ethoxy; preferably, R1, R2, R3, R4, R1', R2', R3' and R4' are each independently selected from H, fluorine or methoxy.

[0036] Y is selected from -CH2-CH2-, -CH2CH2CH2-, -CH2CH(OH)CH2-, In the structural formula, * represents a bonding site; preferably, Y is selected from -CH2-CH2-, -CH2CH2CH2-, ... In the structural formula, * represents a bonding site;

[0037] In the general formula (2), M represents Mn, Fe, Co, or Ni.

[0038] When M is trivalent, X is Cl. - or Br - ,

[0039] R5, R6, R7 and R8 are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl, chlorine or bromine; preferably, R5, R6, R7 and R8 are each independently selected from H or chlorine.

[0040] [5] A method for depolymerizing plastics according to any one of [1] to [4], wherein the catalyst is one or more catalysts selected from the following formulas (1-1) to (1-5) and (2-1) to (2-2):

[0041]

[0042] [6] A method for depolymerizing a plastic according to any one of [1] to [5], wherein the molar ratio of the depolymerizing agent to the total molar ratio of the structural units in the plastic is 100:1 to 7:1.

[0043] [7] A method for depolymerizing plastic according to any one of [1] to [6], wherein the amount of catalyst used is from 0.0015 mol / L to 0.2 mol / L based on the volume of the depolymerizing agent.

[0044] [8] The depolymerization method of plastic according to any one of [1] to [7], wherein the temperature of the depolymerization reaction is 25°C to 280°C, preferably 60°C to 240°C, more preferably 70°C to 210°C; the time of the depolymerization reaction is 0.5 hours to 12 hours, preferably 0.7 hours to 10 hours, more preferably 0.8 hours to 8 hours; and stirring is carried out during the depolymerization reaction, wherein the stirring rate is 300 r / min to 600 r / min.

[0045] [9] The method for depolymerizing the plastic according to any one of [1] to [8], wherein,

[0046] The polyester is selected from one or more of the following: polymers obtained by polycondensation of polyols and polyacids, polymers obtained by ring-opening polymerization of lactones, and polymers obtained by polycondensation of compounds having both hydroxyl and carboxyl groups.

[0047] Preferably, the polyol is an aliphatic polyol, more preferably an aliphatic polyol with 2 to 6 carbon atoms; the polyacid is an aliphatic polyacid or an aromatic polyacid, preferably an aliphatic polyacid with 2 to 6 carbon atoms, and preferably an aromatic polyacid with 8 to 14 carbon atoms; the lactone is an aliphatic lactone, more preferably an aliphatic lactone with 6 to 10 carbon atoms; and the compound having both hydroxyl and carboxyl groups is lactic acid.

[0048] The polycarbonate is bisphenol A type polycarbonate;

[0049] The polyamide is selected from one or more aliphatic polyamides and aromatic polyamides;

[0050] The polyurethane is selected from one or more types of polyester polyurethane and polyether polyurethane.

[0051]

[10] The depolymerization method of the plastic according to any one of [1] to [9], wherein the plastic is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polybutylene adipate, polybutylene adipate, polybutylene succinate, polyethylene adipate, polybutylene succinate, polycaprolactone, polylactic acid, polyamide 6, polyamide 66, polyamide 46, polyamide 12, polyamide 69, polyamide 6-10 and polyurethane formed by polymerization of polybutylene adipate diol and diphenylmethane diisocyanate (MDI); preferably, the plastic is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polyamide 6, polyamide 66 and polyurethane formed by polymerization of polybutylene adipate diol and diphenylmethane diisocyanate (MDI).

[0052] The effects of the invention

[0053] The depolymerization method for plastics of the present invention can efficiently perform catalytic depolymerization of plastics, produce high purity monomer products, simplify post-processing, and is applicable to the processing of various plastics. Furthermore, the catalyst used is readily available, has good catalytic effect, and is highly stable. Attached Figure Description

[0054] Figure 1 The liquid chromatography of the BHET product obtained in Example 1 and the liquid chromatography of a commercially available BHET standard are shown.

[0055] Figure 2 The NMR spectra of the BHET product obtained in Example 1 are compared with those of a commercially available BHET standard.

[0056] Figure 3 The NMR carbon spectra of the BHET product obtained in Example 1 and the NMR carbon spectra of a commercially available BHET standard are shown. Detailed Implementation

[0057] The present invention will now be described in detail. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

[0058] <Terminology and Definitions>

[0059] In this instruction manual, "room temperature" refers to a temperature range of 20 to 30°C, such as 25°C.

[0060] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0061] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0062] In this specification, the use of "can" or "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0063] In this specification, the terms "optionally" or "optionally" are used to indicate the use or non-use of certain substances, components, procedures, application conditions, etc.

[0064] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" used refers to weight or mass percentage content.

[0065] In this specification, references to "preferred embodiments," "implementation methods," etc., mean that a specific element (e.g., feature, structure, property, and / or characteristic) related to that embodiment is included in at least one of the embodiments described herein, and may or may not be present in other embodiments. Furthermore, it should be understood that the elements may be combined in any suitable manner in various embodiments.

[0066] The purpose of this invention is to provide a method for depolymerizing plastics, wherein the plastics undergo a depolymerization reaction in the presence of a depolymerization agent and using a specific mononuclear metal complex catalyst.

[0067] The plastic is selected from one or more of polyester, polycarbonate, polyamide and polyurethane.

[0068] The depolymerization method of this invention enables plastics to depolymerize efficiently in the presence of a depolymerization reagent and a specific catalyst, thereby depolymerizing the plastics into oligomers or monomers. While achieving the goals of efficient catalytic depolymerization of plastics, high purity of monomer products, and the ability to depolymerize a wide variety of plastics, the depolymerization method of this invention also has the following advantages: the specific catalyst used is readily available, and some catalysts can be purchased directly from the market, reducing costs.

[0069] The following describes in detail various aspects of the depolymerization method of the present invention.

[0070] <Catalyst>

[0071] The catalyst used in the depolymerization method of the plastic of the present invention is a mononuclear metal complex. Specifically, the catalyst is selected from one or more mononuclear metal Salen complexes and mononuclear metal phthalocyanine complexes.

[0072] Mononuclear metal Salen-type complexes have the structure shown in the following general formula (1):

[0073]

[0074] In general formula (1), M represents a metal atom and is selected from transition metals such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh or Pd, preferably selected from Mn, Fe, Co or Ni; M is divalent or trivalent.

[0075] When M is divalent, X does not exist (in this case, general formula (1) can be expressed as general formula (1'). In general formula (1'), the definitions of R1, R2, R3, R4, R1', R2', R3', R4' and Y are the same as those in general formula (1); when M is trivalent, X exists and X is an anion, which can be selected from NO3. - Cl -,Br - OAc - OTf - OH - BF4 - PF6 - or ClO4 - Cl is preferred - or Br - X can be axially coordinated at the metal center or act as a complex anion. Among the metal atoms that M can be selected from, namely Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, and Pd, when M is Cr, M is trivalent; when M is Mn, M can be divalent or trivalent; when M is selected from Ti, V, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, or Pd, M is divalent.

[0076]

[0077] R1, R2, R3, R4, R1', R2', R3', and R4' are each independently selected from H, alkyl groups having 1 to 6 carbon atoms, halogens, alkoxy groups having 1 to 6 carbon atoms, or trialkylsilyl groups having 3 to 18 carbon atoms, or R1 and R1' are bonded to each other to form -O-CH2CH2-(OCH2CH2). n -OCH2CH2O-, where n is 1 or 2.

[0078] In a preferred embodiment, in the definitions of R1, R2, R3, R4, R1', R2', R3', and R4', the alkyl group having 1 to 6 carbon atoms is selected from methyl, ethyl, isopropyl, or tert-butyl; the halogen is selected from fluorine, chlorine, or bromine; the alkoxy group having 1 to 6 carbon atoms is selected from methoxy, ethoxy, or propoxy; and the trialkylsilyl group having 3 to 18 carbon atoms is selected from triethylsilyl or triisopropylsilyl.

[0079] In a preferred embodiment, R1, R2, R3, R4, R1', R2', R3', and R4' are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl, fluorine, chlorine, methoxy, or ethoxy.

[0080] In a preferred embodiment, R1, R2, R3, R4, R1', R2', R3', and R4' are each independently selected from H, fluorine, or methoxy.

[0081] Y is selected from linear or branched alkylene groups having 1 to 6 carbon atoms, cycloalkylene groups having 3 to 10 carbon atoms, aryl groups having 6 to 20 carbon atoms, or heterocyclic groups having 4 to 10 carbon atoms, wherein the substituent is selected from the group consisting of hydroxyl, phenyl, and cycloalkyl groups having 4 to 8 carbon atoms.

[0082] In a preferred embodiment, Y is selected from -CH2-CH2-, -CH2CH2CH2-, -CH2CH(OH)CH2-, ... In the structural formula, * represents the bonding site.

[0083] In a preferred embodiment, Y is selected from -CH2-CH2-, -CH2CH2CH2-, ... In the structural formula, * represents the bonding site.

[0084] In the definition of Y above, the alkylene group having 1 to 6 carbon atoms with substituents refers to the number of carbon atoms in the alkylene skeleton, and does not include the number of carbon atoms in the substituents (i.e., the substituents selected from the group consisting of hydroxyl, phenyl and cycloalkyl groups having 4 to 8 carbon atoms) of the alkylene group.

[0085] In general formula (1), R1 and R1' are bonded together as -O-CH2CH2-(OCH2CH2). n Examples of mononuclear metal Salen-like complexes of -OCH2CH2O- (n is 1 or 2) are given by the complex shown in the following formula (1”) (where M in general formula (1) is Mn and X is OAc). - R2, R3, R4, R2', R3', and R4' are H, R1 and R1' are bonded together to form -O-CH2CH2-OCH2CH2-OCH2CH2O-, and Y is -CH2-CH2-):

[0086]

[0087] In one embodiment, the mononuclear metal Salen-type complex is selected from one or more complexes shown in formulas (1-a) to (1-i):

[0088]

[0089]

[0090] In equations (1-a) to (1-i), the definitions of M, X, R1, R2, R3, R4, R1', R2', R3' and R4' are the same as those in the general equation (1) above.

[0091] In one implementation, the mononuclear metal Salen-type complex is the complex shown in formula (1-j):

[0092]

[0093] Mononuclear metal phthalocyanine complexes have the structure shown in the following general formula (2):

[0094]

[0095] In the general formula (2), M represents a metal atom and is selected from transition metals such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh or Pd, preferably selected from Mn, Fe, Co or Ni; M is divalent or trivalent.

[0096] When M is divalent, X does not exist (in this case, general formula (2) can be expressed as general formula (2'). In general formula (2'), the definitions of R5, R6, R7 and R8 are the same as those in general formula (2); when M is trivalent, X exists and X is an anion, which can be selected from NO3. - Cl - ,Br - OH - BF4 - PF6 - or ClO4 - Cl is preferred - or Br - X can be axially coordinated at the metal center or act as a complex anion. Among the metal atoms that M can be selected from, namely Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, and Pd, when M is Cr, M is trivalent; when M is Mn, M can be divalent or trivalent; when M is selected from Ti, V, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, or Pd, M is divalent.

[0097]

[0098] R5, R6, R7 and R8 are each independently selected from H, hydroxyl, alkyl with 1 to 6 carbon atoms, halogen, alkoxy with 1 to 6 carbon atoms, amino, sulfonic acid or nitro, and each R5 may be the same as or different from each other, each R6 may be the same as or different from each other, each R7 may be the same as or different from each other, and each R8 may be the same as or different from each other.

[0099] In a preferred embodiment, in the definitions of R5, R6, R7 and R8, the alkyl group having 1 to 6 carbon atoms is selected from methyl, ethyl, isopropyl or tert-butyl, the halogen is selected from fluorine, chlorine or bromine, and the alkoxy group having 1 to 6 carbon atoms is selected from methoxy, ethoxy or propoxy.

[0100] In a preferred embodiment, R5, R6, R7 and R8 are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl, chlorine or bromine, and each R5 may be the same as or different from each other, each R6 may be the same as or different from each other, each R7 may be the same as or different from each other, and each R8 may be the same as or different from each other.

[0101] In a preferred embodiment, R5, R6, R7 and R8 are each independently selected from H or chlorine, and each R5 may be the same as or different from each other, each R6 may be the same as or different from each other, each R7 may be the same as or different from each other, and each R8 may be the same as or different from each other.

[0102] In this invention, the coordination configurations of mononuclear metal Salen-type complexes having a structure represented by general formula (1) and mononuclear metal phthalocyanine-type complexes having a structure represented by general formula (2) are similar. Furthermore, the similarities between the two in various aspects are summarized as follows:

[0103] 1. Similarity of Coordination Centers. Core Structure: Both metal Salen and metal phthalocyanine possess stable structures formed by the coordination of polydentate ligands with the central metal ion. The metal center of metal Salen, represented by general formula (1), provides a four-coordinate structure with two oxygen atoms from phenoxy groups and two imine nitrogen atoms, forming an M-N2O2 coordination. Metal phthalocyanine, represented by general formula (2), provides a four-coordinate environment with four nitrogen atoms, forming an M-N4 coordination. This similarity of coordination centers allows both to stably bind metal ions and provides similar electronic environments, promoting the depolymerization process of plastics.

[0104] 2. π-conjugated system: Both ligands contain π-conjugated structures, which can enhance electron mobility and stabilize reaction intermediates, thus providing an effective electron transfer channel for plastic depolymerization reaction.

[0105] 3. Correlation of catalytic functions: Both have adjustable redox potentials and can regulate reaction pathways and change catalytic performance by altering the type of central metal ion or modifying ligands.

[0106] 4. Similarity in structural rigidity: Both have highly rigid ligand frameworks (macrocyclic or bis-Schiff base structures). This rigidity ensures the stability of active sites during catalysis and reduces the loss of catalytic activity caused by ligand dissociation.

[0107] In a preferred embodiment, the catalyst is one or more catalysts selected from those shown in formulas (1-1) to (1-5) and (2-1) to (2-2).

[0108]

[0109]

[0110] <Depolymerization reagent>

[0111] The depolymerization agent used in this invention is an alcohol, water, ammonia, or an amine. Preferably, the depolymerization agent is an alcohol.

[0112] alcohol

[0113] In this invention, the alcohol used as the depolymerization agent can be any alcohol conventionally used in the art, without any particular limitation.

[0114] Preferably, the alcohol is selected from one or more monohydric alcohols and dihydric alcohols; more preferably, the alcohol is a dihydric alcohol; even more preferably, the alcohol is selected from one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentanediol, 1,6-hexanediol, 1,2-cyclohexanediethanol, 1,3-cyclohexanediethanol, 1,4-cyclohexanediethanol, 2,2,2,2-tetramethyl-1,3-cyclobutanediol, 2-methyl-2,4-pentanediol, and p-xylylenediol.

[0115] water

[0116] In this invention, the water used as the depolymerization reagent can be ion-exchanged water or deionized water. When water is used as the depolymerization reagent, the depolymerization reaction can be carried out under conditions known in the art, such as acidic or alkaline conditions. Therefore, optionally, acidic components such as hydrochloric acid and acetic acid are added to the water to make the aqueous solution weakly acidic (pH about 5.5 to 6.7), or alkaline components such as sodium hydroxide and potassium hydroxide are added to the water to make the aqueous solution weakly alkaline (pH about 8.0 to 10.0).

[0117] ammonia or amine

[0118] In this invention, there are no particular restrictions on the ammonia or amine used as depolymerization agents.

[0119] Ammonia can be used in a suitable form, such as in ammonia water or liquid ammonia. The preferred amine is a diamine.

[0120] Examples of ammonia or amines include, but are not limited to, liquid ammonia (NH3), ethylenediamine, propylenediamine, butanediamine, hexamethylenediamine, and ethanolamine.

[0121] <Depolymerization Temperature>

[0122] The depolymerization method of the present invention can be carried out in a wide depolymerization temperature range of 25°C to 280°C, and the depolymerization temperature can be adjusted according to the types of both the plastic to be depolymerized and the depolymerization reagent.

[0123] From the perspective of reaction efficiency, the depolymerization temperature of the present invention is preferably 50°C or higher, and even more preferably 60°C or higher, such as 70°C or higher, 80°C or higher, or 90°C or higher.

[0124] Furthermore, considering ease of operation, volatility of the depolymerization reagent, reduced equipment requirements, and prevention of high-temperature carbonization of the plastic and depolymerization products, the depolymerization temperature of the present invention is preferably below 270°C, more preferably below 260°C, even more preferably below 240°C, and even more preferably below 210°C. Specifically, for example, it is below 270°C, below 250°C, below 230°C, below 220°C, or below 200°C.

[0125] In one embodiment, the depolymerization temperature is 50°C to 280°C, preferably 60°C to 240°C, and more preferably 70°C to 210°C.

[0126] <Depolymerization reaction>

[0127] In the depolymerization method of the present invention, the depolymerization reaction can be carried out by mixing a depolymerization agent, a catalyst, and plastic together, and heating the mixture to the depolymerization temperature described above while stirring the mixture. During this depolymerization reaction, the plastic depolymerizes into oligomers and / or monomers, and the amount of monomers as depolymerization products gradually increases as the depolymerization reaction proceeds.

[0128] In this invention, there is no particular limitation on the depolymerization reaction time, which can be selected according to the amount of material and the depolymerization temperature. Typically, the depolymerization reaction time can be from 0.5 hours to 12 hours, preferably from 0.7 hours to 10 hours, and more preferably from 0.8 hours to 8 hours. Specifically, the depolymerization reaction time can be, for example, 0.9 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0129] In one embodiment, the depolymerization agent is an alcohol, and the depolymerization reaction is carried out under a nitrogen atmosphere.

[0130] In one embodiment, during the depolymerization reaction, the stirring rate of the mixture is 300 r / min to 600 r / min, preferably 350 r / min to 500 r / min, for example 400 r / min.

[0131] In one embodiment, the molar ratio of the depolymerization agent to the total molar ratio of the structural units in the plastic is 100:1 to 7:1, preferably 90:1 to 8:1, and even more preferably 85:1 to 10:1.

[0132] In the above text, the "total number of moles of structural units" used to describe plastics refers to the sum of the moles of all structural units in the plastic (i.e., polymer). In the case of polymer mixtures and copolymers, it refers to the sum of the moles of structural units of each polymer in the mixture. In this text, the structural unit of a polymer has its usual meaning in the art and is used synonymously with a repeating unit.

[0133] Generally, for polyesters, the number of moles of structural units is basically the same as the number of moles of ester groups; for polycarbonates, the number of moles of structural units is basically the same as the number of moles of carbonate groups; for polyamides, the number of moles of structural units is basically the same as the number of moles of amide groups; and for polyurethanes, the number of moles of structural units is basically the same as the number of moles of urethane groups.

[0134] In one embodiment, the amount of catalyst used is from 0.0015 mol / L to 0.2 mol / L, based on the volume of the depolymerization agent (25°C); preferably from 0.0020 mol / L to 0.2 mol / L; more preferably from 0.0020 mol / L to 0.1 mol / L.

[0135] <Separation of Depolymerization Products>

[0136] In the depolymerization method of the present invention, optionally, the depolymerization product is separated from the reaction system after the depolymerization reaction is completed. There are no particular limitations on the separation method for the depolymerization product; any suitable separation method known in the art can be used. Specifically, if the monomers generated during depolymerization are dissolved in the depolymerization reaction system, extraction can be used, for example. Furthermore, if the monomers generated during depolymerization precipitate from the depolymerization reaction system and there is no solid residue in the polymer raw material, methods such as decantation, filtration, or centrifugation can be used.

[0137] Optionally, the separated monomers can be washed several times (e.g., 3 times, 5 times) with a solvent, dried, etc., to improve the purity of the monomers. The solvent used for washing can be an alcohol, such as methanol, ethanol, etc.; or an ether, such as dimethyl ether, diethyl ether, etc.

[0138] <Plastics>

[0139] In this invention, the plastic is selected from one or more of polyester, polycarbonate, polyamide and polyurethane.

[0140] Polyester

[0141] In this invention, polyester includes saturated polyester and unsaturated polyester. Polyester can be a polymer obtained by polycondensation of polyols and polyacids, or a polymer obtained by ring-opening polymerization of lactones, or a polymer obtained by polycondensation of compounds simultaneously having hydroxyl and carboxyl groups. The polyol is preferably an aliphatic polyol, more preferably an aliphatic polyol with 2 to 6 carbon atoms. The polyacid is an aliphatic polyacid or an aromatic polyacid, wherein the aliphatic polyacid is preferably an aliphatic polyacid with 2 to 6 carbon atoms; the aromatic polyacid is preferably an aromatic polyacid with 8 to 14 carbon atoms, more preferably terephthalic acid, phthalic acid, or isophthalic acid. The lactone is preferably an aliphatic lactone, preferably an aliphatic lactone with 6 to 10 carbon atoms. The compound simultaneously having hydroxyl and carboxyl groups is preferably lactic acid (lactide), etc.

[0142] In one embodiment, the polyester is a linear polymer obtained by polycondensation of a diol and a diacid. The diol is preferably selected from one or more aliphatic diols, more preferably from one or more aliphatic diols having 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butanediol, pentanediol, and hexanediol. The diacid can be selected from one or more aliphatic or aromatic diacids, preferably including aromatic diacids, for example, diacids simultaneously including both aromatic and aliphatic diacids. Aromatic diacids include, for example, terephthalic acid and phthalic acid. Aliphatic diacids include, for example, succinic acid, glutaric acid, and adipic acid.

[0143] In one embodiment, the polyester is a polymer obtained by ring-opening polymerization of a lactone, such as polycaprolactone.

[0144] In one embodiment, the polyester is a polymer obtained by polycondensation of a compound having both hydroxyl and carboxyl groups, such as polylactic acid (polylactide).

[0145] In a preferred embodiment, the polyester is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polybutylene adipate, polybutylene adipate, polybutylene succinate, polyethylene adipate, polybutylene succinate, polycaprolactone, and polylactic acid; more preferably, the polyester is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polylactic acid, and polybutylene adipate.

[0146] In one embodiment, the weight-average molecular weight of the polyester is 10,000 to 200,000, preferably 15,000 to 150,000.

[0147] polycarbonate

[0148] In this invention, the polycarbonate can be aliphatic polycarbonate, aromatic polycarbonate, or aliphatic-aromatic polycarbonate.

[0149] In one embodiment, the polycarbonate is an aromatic polycarbonate, more preferably a bisphenol A type polycarbonate. Bisphenol A type polycarbonate can be synthesized by reacting bisphenol A with carbonyl chloride (COCl2). Currently, the most commonly used synthesis method is the melt transesterification method, which involves the synthesis of bisphenol A with diphenyl carbonate through transesterification and polycondensation.

[0150] In one embodiment, the polycarbonate has a weight-average molecular weight of 10,000 to 50,000, preferably 20,000 to 40,000.

[0151] Bisphenol A type polycarbonate has the following structure (end groups not shown):

[0152]

[0153] Where n represents the number of structural units within the brackets, typically 80 to 200.

[0154] polyamide

[0155] Polyamides can be aliphatic polyamides, aromatic polyamides, and semi-aromatic polyamides.

[0156] Examples of polyamides include, but are not limited to, polyamide 6 (Nylon 6), polyamide 66 (Nylon 66), polyamide 46, polyamide 12, polyamide 69 and polyamide 6-10.

[0157] In one embodiment, the polyamide has a weight-average molecular weight of 5,000 to 20,000, preferably 8,000 to 16,000.

[0158] polyurethane

[0159] Polyurethane refers to "polyurethane," a polymer obtained by the condensation polymerization of polyols and polyisocyanates. Polyurethane can be polyether-type polyurethane or polyester-type polyurethane, preferably polyester-type polyurethane.

[0160] Polyether polyurethane is a reaction product of polyether polyol and polyisocyanate, wherein the polyether polyol is preferably an aliphatic diol, such as polyethylene glycol, polypropylene glycol, polybutanediol, and their block or random copolymers.

[0161] Polyester-type polyurethane is a reaction product of polyester polyol and polyisocyanate, wherein the polyester polyol is preferably an aliphatic polyester polyol, such as an oligomer of aliphatic diol and aliphatic dicarboxylic acid, specific examples include polyethylene adipate diol (PEA), polyethylene adipate-propylene adipate diol, polyethylene adipate-diethylene adipate diol (PDA), polybutylene adipate diol, polyhexane adipate diol, polyethylene succinate diol, polypropylene succinate diol, polybutylene succinate diol, etc.

[0162] The aforementioned polyisocyanate is selected from one or more of aliphatic and aromatic polyisocyanates. Preferably, the aforementioned polyisocyanate is a diisocyanate, more preferably selected from one or more of aliphatic and aromatic diisocyanates. Particularly preferably, the diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, and dicyclohexylmethane diisocyanate.

[0163] In a preferred embodiment, the polyurethane is the reaction product of polybutylene adipate diol and diphenylmethane diisocyanate (MDI).

[0164] In one embodiment, the polyurethane has a weight-average molecular weight of 100,000 to 500,000, preferably 200,000 to 400,000.

[0165] In one embodiment, the plastic is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polybutylene adipate, polybutylene adipate, polybutylene succinate, polyethylene adipate, polybutylene succinate, polycaprolactone, polylactic acid, polyamide 6, polyamide 66, polyamide 46, polyamide 12, polyamide 69, polyamide 6-10, and polyurethanes formed by polymerizing polybutylene adipate diol with diphenylmethane diisocyanate (MDI); preferably, the plastic is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polyamide 6, polyamide 66, and polyurethanes formed by polymerizing polybutylene adipate diol with diphenylmethane diisocyanate (MDI).

[0166] The depolymerization method for plastics of the present invention achieves efficient catalytic depolymerization of plastics, high purity of monomer products, simple post-processing, and applicability to the processing of various plastics. It also has the following advantages: the catalyst used is easy to obtain and some catalysts are commercially available, and the catalytic effect is good and the stability is strong.

[0167] Example

[0168] The following specific embodiments further illustrate the present invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by this invention.

[0169] The raw materials used in the following examples are described below:

[0170] Polyethylene terephthalate (PET): Mw≈20,000, crystallinity 38%. Brand: Maclean.

[0171] Polybutylene terephthalate (PBT): Mw≈100,000, crystallinity 30%, brand name: Maclean.

[0172] Bisphenol A type polycarbonate (BPA-PC, hereinafter referred to as PC): Mw≈26,000, crystallinity 10%, brand: Maclean. The structural formula is shown below:

[0173]

[0174] Where n≈102.

[0175] Ethylene glycol, analytical grade, brand owner: Sinopharm Shanghai Experimental, product number: 10009818.

[0176] Manganese chloride tetrahydrate (MnCl2·4H2O), CAS No.: 13446-34-9, purchased from Aladdin.

[0177] Anhydrous manganese acetate (Mn(OAc)2), CAS No.: 638-38-0, purchased from Aladdin.

[0178] Manganese phthalocyanine (II) (Mn(II)Pc) (structural formula is (2-1) above), CAS No.: 14325-24-7, purchased from Bid Pharmaceutical.

[0179] Mn(III)PcCl (structural formula (2-2) above), trade name: manganese phthalocyanine chloride (III), CAS number: 53432-32-9, product number: BD01202416, purchased from Bid Pharmaceutical.

[0180] Mn(Salen)Cl (structural formula (1-1) above), trade name EUK-8, purchased from Bid Pharmaceuticals.

[0181] Mn(Salen)Cl-a (structural formula (1-2) above), trade name EUK-134, CAS number: 81065-76-1, purchased from Bid Pharmaceutical.

[0182] Fe(Salen) (structural formula is (1-3) above), trade name N,N'-disalicylaldehyde ethylenediamine iron (II), CAS number: 14167-12-5, purchased from Bid Pharmaceutical.

[0183] Co(Salen) (structural formula (1-4) above), trade name N,N′-disalicylaldehyde ethylenediamine cobalt(II) hydrate, CAS number: 207124-68-3, purchased from Bid Pharmaceutical.

[0184] Ni(Salen) (structural formula (1-5) above) can be synthesized using the method described in Dalton Transactions, 2014, 43, pp. 16745-16753. The specific synthesis procedure is as follows: 2 mL of an ethanol solution of Ni(OAc)₂·4H₂O (2 mmol) was added to 9 mL of an ethanol solution containing N,N'-bis(salicylic acid)-ethylenediamine (1 mmol). After reflux for 1 hour, a light brown solid precipitated from the solution. The precipitate was filtered and collected, and dried at 100 °C for 1 hour to obtain Ni(Salen), yield: 80%.

[0185] In the above explanation, "Mw" represents the weight-average molecular weight.

[0186] In the following examples, the depolymerization of plastic was carried out as follows: a certain amount of catalyst, plastic and depolymerization reagent were added to a reaction flask, and the mixture was heated to a specified reaction temperature while stirring at a speed of 400 rpm / min under a nitrogen atmosphere.

[0187] In the following examples and comparative examples, unless otherwise specified, the depolymerization reaction time is 1 hour. After 1 hour of depolymerization, the plastic depolymerizes into oligomers and / or monomers.

[0188] Test methods and evaluation criteria

[0189] The test methods and evaluation criteria involved in the embodiments and comparative examples described below are described in detail below.

[0190] 1) Conversion rate, conversion rate, yield, and monomer selectivity

[0191] The conversion rate, conversion efficiency, yield, and monomer selectivity in the following examples were calculated according to the following test methods and formulas:

[0192] 1.1) Plastic conversion rate

[0193] Plastic conversion rate % = (1 - amount of unreacted plastic / initial amount of plastic) × 100

[0194] The amount of unreacted plastic was determined based on the amount of solids after hot filtration.

[0195] The amount of solid obtained after hot filtration was determined by the following method: the reaction system was filtered while hot after the reaction was completed, and the obtained solid was dried and weighed.

[0196] 1.2) Conversion rate of plastics

[0197] Unless otherwise specified, the conversion rate (mmol / h) of plastics mentioned below refers to the average conversion rate during the first hour of the reaction.

[0198] Plastic conversion rate (mmol / h) = Plastic conversion rate × Initial amount of plastic added (mmol) / 1h

[0199] 1.3) Monomer Yield

[0200] Monomer yield % = Amount of monomer in actual reaction solution / Theoretical amount of monomer after complete depolymerization of plastic

[0201] The amount of monomer in the actual reaction solution is determined by the following liquid chromatography, and the theoretical amount of monomer after the plastic is completely depolymerized is calculated based on the molar mass of the plastic.

[0202] Specifically, during or at the end of the depolymerization reaction, a trace amount of the reaction solution is taken and the amount of monomer products from polymer depolymerization is detected by liquid chromatography, and the monomer yield is calculated according to the above formula.

[0203] 1.3.1) Liquid Chromatography

[0204] Liquid chromatography was used to determine the amount of monomer in the actual reaction solution.

[0205] The liquid chromatography instrument and testing conditions used are as follows:

[0206] The liquid chromatograph model is Agilent 1260 Infinity II.

[0207] C18 reversed-phase chromatographic column,

[0208] The detector is an ultraviolet detector.

[0209] The detection method for bis(2-hydroxyethyl) terephthalate (BHET), a monomer product of PET ethylene glycol hydrolysis, is as follows: the detection wavelength is 254 nm, the mobile phase is 40 v% water + 60 v% methanol, and the flow rate is 0.5 mL / min.

[0210] The detection method for bisphenol A (BPA), a monomer product of ethylene glycol hydrolysis of polycarbonate, is as follows: the detection wavelength is 210 nm, the mobile phase is 40 v% water + 60 v% acetonitrile, and the flow rate is 1 mL / min.

[0211] 1.4) Monomer selectivity

[0212] The selectivity (%) of monomer product BHET = amount of monomer product BHET in the actual reaction solution (mmol) / conversion amount of plastic (mmol). Wherein, the amount of monomer product BHET in the actual reaction solution is determined by the method described in 1.3.1) above; the conversion amount of plastic = initial amount of plastic added - amount of unreacted plastic, the determination of the amount of unreacted plastic is described in 1.1) above.

[0213] 2) Measurement and characterization of purity

[0214] The purity of the monomer products in the examples and comparative examples was measured or characterized by one or more of liquid chromatography (using the same instruments and test conditions as described in 1.2.1 above), 1H NMR, and 1C NMR.

[0215] 2.1) Monomer purity was measured using liquid chromatography.

[0216] The purity of BHET was assessed by liquid chromatography analysis (the instruments and test conditions used were the same as those described above).

[0217] 1.3.1) The same procedure was followed, and a known amount of m1 g of the monomer product BHET was dissolved in ethylene glycol. The amount of BHET obtained by liquid chromatography was m2 g.

[0218] BHET purity (%) = (m2 / m1) × 100%.

[0219] 2.2) Characterize monomer purity using 1H NMR and / or 1C NMR.

[0220] The nuclear magnetic resonance spectrometer used was a Bruker AVANCEⅢ400M.

[0221] The sample was dissolved in deuterated dimethyl sulfoxide (DMSO-d6) for testing.

[0222] In the following examples, the molar amounts given for polymers are the total molar amounts of structural units (repeating units) in the polymer. For details, please refer to the specific descriptions of various polymers above.

[0223] Example 1

[0224] The plastic processed in this embodiment is PET; the catalysts used are Mn(Salen)Cl, Mn(Salen)Cl-a, MnCl2·4H2O and Mn(OAc)2, respectively.

[0225] Example 1-1

[0226] Depolymerization conditions: 0.192 g (i.e., 1 mmol) of 100-mesh PET powder, 0.01 mmol of catalyst Mn(Salen)Cl, and 4.5 mL of ethylene glycol were added to a reaction flask. The reaction temperature was 180 °C, and the reaction time was 1 hour. Afterward, the reaction system was cooled to room temperature and then placed at 4 °C overnight. Bis(2-hydroxyethyl) terephthalate (BHET), the monomer product of PET alcoholysis, precipitated as white crystals. The crystals were filtered, washed twice with ethanol, and dried to obtain the BHET product. The measurement results of the alcoholysis product monomer BHET in this example are shown in Table 1 below. Figures 1-3 As shown in the image.

[0227] Purity of BHET products

[0228] (1) Liquid Chromatography Analysis

[0229] The PET alcoholysis product BHET obtained in this embodiment ( Figure 1 Liquid chromatography of b) and commercially available BHET standards ( Figure 1 The liquid chromatography chromatogram of a) in section a) is as follows: Figure 1 As shown, the BHET standard from this commercial source is branded Aladdin and has a purity of 95%. Figure 1 As can be seen, the liquid chromatography chromatogram of the BHET product obtained in this embodiment is exactly the same as that of the liquid chromatography chromatogram of the commercially available BHET standard. Figure 1 The liquid chromatography chromatogram of the BHET product showed that the recovered BHET product had high purity and no obvious BHET dimer signal.

[0230] (2) Nuclear magnetic resonance hydrogen spectroscopy and nuclear magnetic resonance carbon spectroscopy analysis

[0231] The PET alcoholysis product BHET obtained in this example was dissolved in deuterated dimethyl sulfoxide (DMSO-d6), and its 1H NMR and 1C NMR spectra were measured, as shown in the figures. Figure 2 and Figure 3 In the middle. For example Figure 2 and Figure 3 As shown, the BHET product obtained in this embodiment ( Figure 2 and Figure 3 (b) and commercially sourced BHET standard ( Figure 2 and Figure 3 The hydrogen and carbon NMR spectra of a) in the data are completely consistent. Figure 2 and Figure 3 The BHET standard from this commercial source is branded Aladdin and has a purity of 95%. Figure 2 and Figure 3 The 1H NMR and 1C NMR spectra of the BHET products both indicate that the recovered BHET products have high purity and no obvious BHET dimer signal.

[0232] Examples 1-2

[0233] Except that 0.01 mmol of catalyst Mn(Salen)Cl-a was used instead of 0.01 mmol of catalyst Mn(Salen)Cl, the alcoholysis of PET was carried out in the same manner as in Example 1-1. After the alcoholysis reaction was completed in 1 hour, the BHET product was obtained by the same series of operations as in Example 1-1.

[0234] Comparative Example 1-1

[0235] Except that 0.01 mmol of catalyst Mn(Salen)Cl was used instead of 0.01 mmol of catalyst MnCl2·4H2O, the alcoholysis of PET was carried out in the same manner as in Example 1-1.

[0236] Comparative Examples 1-2

[0237] The alcoholysis of PET was carried out in the same manner as in Examples 1-1, except that 0.01 mmol of catalyst Mn(OAc)2 was used instead of 0.01 mmol of catalyst Mn(Salen)Cl.

[0238] Comparative Examples 1-3

[0239] The PET was hydrolyzed in the same manner as in Examples 1-1, except that no catalyst was used.

[0240] The results of each embodiment and comparative example are shown in Table 1.

[0241] Table 1

[0242]

[0243] Note: "-" indicates that the BHET purity data was not determined. Comparative Examples 1-1 and 1-2, which used MnCl2·4H2O and Mn(OAc)2, and Comparative Example 1-3, which did not use a catalyst, had too slow reaction rates and the products were not separated.

[0244] As shown in Table 1, the conversion rate and BHET yield of PET when using Mn(Salen)Cl and Mn(Salen)Cl-a as catalysts (Examples 1-1 and 1-2) were significantly higher than those when using simple metal salts of Mn (MnCl2·4H2O, Mn(OAc)2) as catalysts (Comparative Examples 1-1 and 1-2) and when no catalyst was used (Comparative Example 1-3). This demonstrates the advantage of the unique structure of Mn(Salen) for this reaction. Furthermore, the purity of the BHET products obtained after washing and drying with ethanol in Examples 1-1 and 1-2 was as high as 99.0%.

[0245] Example 2

[0246] The plastic processed in this embodiment is PET; the catalysts used are Fe (Salen), Co (Salen) and Ni (Salen).

[0247] Example 2-1

[0248] Depolymerization conditions: 0.192 g (i.e., 1 mmol) of 100-mesh PET powder, 0.01 mmol of catalyst Fe (Salen) and 4.5 mL of ethylene glycol were added to a reaction flask. The reaction temperature was 180 °C and the reaction time was 1 hour.

[0249] Example 2-2

[0250] The alcoholysis of PET was carried out in the same manner as in Example 2-1, except that 0.01 mmol of catalyst Co (Salen) was used instead of 0.01 mmol of catalyst Fe (Salen).

[0251] Example 2-3

[0252] Except that 0.01 mmol of catalyst Ni (Salen) was used instead of 0.01 mmol of catalyst Fe (Salen), the alcoholysis of PET was carried out in the same manner as in Example 2-1.

[0253] Comparative Example 2

[0254] Except that no catalyst was used, the PET was hydrolyzed in the same manner as in Example 2-1.

[0255] The results of each embodiment and comparative example are shown in Table 2.

[0256] Table 2

[0257]

[0258] As shown in Table 2, the PET conversion rate and BHET yield when Fe(Salen), Co(Salen), and Ni(Salen) were used as catalysts (Examples 2-1 to 2-3) were much higher than those when no catalyst was used (Comparative Example 2), demonstrating the general advantage of transition metal Salen-type catalysts for this reaction.

[0259] Example 3

[0260] The plastic processed in this embodiment is PET; the catalyst used is Mn(Salen)Cl.

[0261] Example 3-1

[0262] Depolymerization conditions: 1 mmol of 100-mesh PET powder, 0.01 mmol of catalyst Mn(Salen)Cl and 4.5 mL of ethylene glycol were added to a reaction flask. The reaction temperature was 180 °C and the reaction time was 1 hour.

[0263] Example 3-2

[0264] Except that the amount of PET was changed to 5 mmol, the alcoholysis of PET was carried out in the same manner as in Example 3-1.

[0265] Example 3-3

[0266] Except that the amount of PET was changed to 10 mmol, the alcoholysis of PET was carried out in the same manner as in Example 3-1.

[0267] The results of each embodiment and comparative example are shown in Table 3.

[0268] Table 3

[0269]

[0270] As shown in Table 3, Mn(Salen)Cl-catalyzed PET glycololysis can be carried out over a wide range of PET solid content. The PET conversion rate increases with the amount of PET added, and the selectivity of the monomer product BHET is higher than 95%.

[0271] Example 4

[0272] The plastic processed in this embodiment is PET; the catalyst used is Mn(Salen)Cl.

[0273] Example 4-1

[0274] Depolymerization conditions: 2 mmol of 100-mesh PET powder, 0.01 mmol of catalyst Mn(Salen)Cl and 4.5 mL of ethylene glycol were added to a reaction flask. The reaction temperature was 100 °C and the reaction time was 1 hour.

[0275] Example 4-2

[0276] Except that the reaction temperature was changed to 160°C, the alcoholysis of PET was carried out in the same manner as in Example 4-1.

[0277] Example 4-3

[0278] Except for changing the reaction temperature to 200°C, the alcoholysis of PET was carried out in the same manner as in Example 4-1.

[0279] The results of each embodiment and comparative example are shown in Table 4.

[0280] Table 4

[0281]

[0282] As shown in Table 4, the Mn(Salen)Cl-catalyzed PET glycololysis can be carried out over a wide temperature range. The PET conversion rate and the BHET yield after 1 hour of reaction both increase with increasing reaction temperature, and the selectivity of the monomer product BHET is higher than 85%.

[0283] Example 5

[0284] The plastics processed in this embodiment are PET, PBT, and PC; the catalysts used are Mn(II)Pc and Mn(III)PcCl, respectively.

[0285] Example 5-1

[0286] Depolymerization conditions: 1 mmol of 100-mesh PET powder, 0.01 mmol of catalyst Mn(II)Pc and 4.5 mL of ethylene glycol were added to a reaction flask. The reaction temperature was 180 °C and the reaction time was 1 hour.

[0287] Example 5-2

[0288] Except that 1 mmol of 100-mesh PET powder was replaced with 1 mmol of 100-mesh PBT powder, the alcoholysis of PBT was carried out in the same manner as in Example 5-1.

[0289] Example 5-3

[0290] Except that 1 mmol of 100-mesh PET powder was replaced with 1 mmol of 100-mesh PC powder and the reaction temperature was changed to 120°C, the alcoholysis of PC was carried out in the same manner as in Example 5-1.

[0291] Example 5-4

[0292] Except that 0.01 mmol of catalyst Mn(II)Pc was replaced with 0.01 mmol of catalyst Mn(III)PcCl, the alcoholysis of PET was carried out in the same manner as in Example 5-1.

[0293] Example 5-5

[0294] The alcoholysis of PBT was carried out in the same manner as in Examples 5-2, except that 0.01 mmol of catalyst Mn(II)Pc was replaced with 0.01 mmol of catalyst Mn(III)PcCl.

[0295] Examples 5-6

[0296] Except that 0.01 mmol of catalyst Mn(II)Pc was replaced with 0.01 mmol of catalyst Mn(III)PcCl, the alcoholysis of PC was carried out in the same manner as in Examples 5-3.

[0297] Comparative Example 5-1

[0298] Except that no catalyst was used, the PET was hydrolyzed in the same manner as in Example 5-1.

[0299] Comparative Example 5-2

[0300] The PBT was hydrolyzed in the same manner as in Examples 5-2, except that no catalyst was used.

[0301] Comparative Example 5-3

[0302] The alcoholysis of PC was carried out in the same manner as in Examples 5-3, except that no catalyst was used.

[0303] The results of each embodiment and comparative example are shown in Table 5.

[0304] Table 5

[0305]

[0306] As shown in Table 5, commercially available manganese phthalocyanine complexes can catalyze the ethylene glycolation of various plastics (Examples 5-1 to 5-6), and the conversion rate of the plastics is increased by orders of magnitude compared to the blank group (Comparative Examples 5-1 to 5-3).

[0307] As can be seen from the comparison between the above embodiments and comparative examples, the depolymerization method of the present invention can perform catalytic depolymerization of plastics more efficiently, the obtained monomer product has high purity, is suitable for the processing of various plastics, and the catalyst used has excellent catalytic effect and is easy to obtain; the conversion rate of plastics, monomer yield and monomer selectivity can be controlled as needed by adjusting the amount of plastic, reaction temperature and other factors.

[0308] Industrial availability

[0309] The depolymerization method for plastics of the present invention can be widely used in the industrial processing of plastics.

Claims

1. A method for depolymerizing plastics, characterized in that, In the presence of a depolymerization agent and a catalyst, the plastic undergoes a depolymerization reaction. The plastic is selected from one or more of polyester, polycarbonate, polyamide, and polyurethane. The catalyst is selected from one or more mononuclear metal Salen complexes and mononuclear metal phthalocyanine complexes. The mononuclear metal Salen-type complex has the structure shown in the following general formula (1): In the general formula (1), M represents a metal atom and is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, or Pd. M exhibits a divalent or trivalent oxidation state. When M is divalent, X does not exist; when M is trivalent, X exists and X is selected from NO3. - Cl - ,Br - OAc - OTf - OH - BF4 - PF6 - or ClO4 - , R1, R2, R3, R4, R1', R2', R3', and R4' are each independently selected from H, alkyl groups having 1 to 6 carbon atoms, halogens, alkoxy groups having 1 to 6 carbon atoms, or trialkylsilyl groups having 3 to 18 carbon atoms, or R1 and R1' are bonded to each other to form -O-CH2CH2-(OCH2CH2). n -OCH2CH2O-, where n is 1 or 2. Y is selected from linear or branched alkylene groups having 1 to 6 carbon atoms, cycloalkylene groups having 3 to 10 carbon atoms, aryl groups having 6 to 20 carbon atoms, or heterocyclic groups having 4 to 10 carbon atoms, wherein the substituent is selected from the group consisting of hydroxyl, phenyl, and cycloalkyl groups having 4 to 8 carbon atoms. The mononuclear metal phthalocyanine complex has the structure shown in the following general formula (2): In the general formula (2), M represents a metal atom and is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr, Ru, Rh, or Pd. M is divalent or trivalent. When M is divalent, X does not exist; when M is trivalent, X exists and X is selected from NO3. - Cl - ,Br - OH - BF4 - PF6 - or ClO4 - , R5, R6, R7 and R8 are each independently selected from H, hydroxyl, alkyl with 1 to 6 carbon atoms, halogen, alkoxy with 1 to 6 carbon atoms, amino, sulfonic acid or nitro, and each R5 may be the same as or different from each other, each R6 may be the same as or different from each other, each R7 may be the same as or different from each other, and each R8 may be the same as or different from each other.

2. The method for depolymerizing plastics according to claim 1, characterized in that, The depolymerization agent is selected from alcohol, water, ammonia or amine; preferably, the depolymerization agent is an alcohol.

3. The method for depolymerizing plastics according to claim 1 or 2, characterized in that, In the general formula (1), for the definitions of R1, R2, R3, R4, R1', R2', R3', and R4', the alkyl group having 1 to 6 carbon atoms is selected from methyl, ethyl, isopropyl, or tert-butyl; the halogen is selected from fluorine, chlorine, or bromine; the alkoxy group having 1 to 6 carbon atoms is selected from methoxy, ethoxy, or propoxy; and the trialkylsilyl group having 3 to 18 carbon atoms is selected from triethylsilyl or triisopropylsilyl. Y is selected from -CH2-CH2-, -CH2CH2CH2-, -CH2CH(OH)CH2-, In the structural formula, * represents a bonding site; In the general formula (2), in the definitions of R5, R6, R7 and R8, the alkyl group having 1 to 6 carbon atoms is selected from methyl, ethyl, isopropyl or tert-butyl, the halogen is selected from fluorine, chlorine or bromine, and the alkoxy group having 1 to 6 carbon atoms is selected from methoxy, ethoxy or propoxy.

4. The method for depolymerizing plastic according to any one of claims 1 to 3, characterized in that, In the general formula (1), M is selected from Mn, Fe, Co, or Ni. When M is trivalent, X is Cl. - or Br - , R1, R2, R3, R4, R1', R2', R3' and R4' are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl, fluorine, chlorine, methoxy or ethoxy; preferably, R1, R2, R3, R4, R1', R2', R3' and R4' are each independently selected from H, fluorine or methoxy. Y is selected from -CH2-CH2-, -CH2CH2CH2-, -CH2CH(OH)CH2-, In the structural formula, * represents a bonding site; preferably, Y is selected from -CH2-CH2-, -CH2CH2CH2-, ... In the structural formula, * represents a bonding site; In the general formula (2), M represents Mn, Fe, Co, or Ni. When M is trivalent, X is Cl. - or Br - , R5, R6, R7 and R8 are each independently selected from H, methyl, ethyl, isopropyl, tert-butyl, chlorine or bromine; preferably, R5, R6, R7 and R8 are each independently selected from H or chlorine.

5. The method for depolymerizing plastic according to any one of claims 1 to 4, characterized in that, The catalyst is selected from one or more catalysts shown in formulas (1-1) to (1-5) and (2-1) to (2-2):

6. The method for depolymerizing plastic according to any one of claims 1 to 5, characterized in that, The molar ratio of the depolymerization agent to the total molar ratio of the structural units in the plastic is 100:1 to 7:

1.

7. The method for depolymerizing plastic according to any one of claims 1 to 6, characterized in that, Based on the volume of the depolymerization agent, the amount of catalyst used is from 0.0015 mol / L to 0.2 mol / L.

8. The method for depolymerizing plastic according to any one of claims 1 to 7, characterized in that, The temperature of the depolymerization reaction is 25℃~280℃, preferably 60℃~240℃, more preferably 70℃~210℃; the time of the depolymerization reaction is 0.5 hours to 12 hours, preferably 0.7 hours to 10 hours, more preferably 0.8 hours to 8 hours; stirring is carried out during the depolymerization reaction, and the stirring rate is 300r / min~600r / min.

9. The method for depolymerizing plastic according to any one of claims 1 to 8, characterized in that, The polyester is selected from one or more of the following: polymers obtained by polycondensation of polyols and polyacids, polymers obtained by ring-opening polymerization of lactones, and polymers obtained by polycondensation of compounds having both hydroxyl and carboxyl groups. Preferably, the polyol is an aliphatic polyol, more preferably an aliphatic polyol with 2 to 6 carbon atoms; the polyacid is an aliphatic polyacid or an aromatic polyacid, preferably an aliphatic polyacid with 2 to 6 carbon atoms, and preferably an aromatic polyacid with 8 to 14 carbon atoms; the lactone is an aliphatic lactone, more preferably an aliphatic lactone with 6 to 10 carbon atoms; and the compound having both hydroxyl and carboxyl groups is lactic acid. The polycarbonate is bisphenol A type polycarbonate; The polyamide is selected from one or more aliphatic polyamides and aromatic polyamides; The polyurethane is selected from one or more types of polyester polyurethane and polyether polyurethane.

10. The method for depolymerizing plastic according to any one of claims 1 to 9, characterized in that, The plastic is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polybutylene adipate, polybutylene adipate, polybutylene succinate, polyethylene adipate, polybutylene succinate, polycaprolactone, polylactic acid, polyamide 6, polyamide 66, polyamide 46, polyamide 12, polyamide 69, polyamide 6-10, and polyurethane formed by polymerizing polybutylene adipate diol with diphenylmethane diisocyanate (MDI); preferably, the plastic is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polyamide 6, polyamide 66, and polyurethane formed by polymerizing polybutylene adipate diol with diphenylmethane diisocyanate (MDI).

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