Method for degrading and recycling a polyurethane and the degradation product thereof

Abstract

The present invention relates to the field of polyurethanes, in particular to a method for degrading and recycling a polyurethane comprising UV / VIS light irradiation in the presence of a photocatalyst under an oxygen-containing condition. The recycling in particular comprising a recovery of valuable products, such as polyols. The present invention also relates to a polyurethane degradation product obtained by the method for degrading and recycling, which degradation product comprises a polyol.

Description

[0001] Method for degrading and recycling a polyurethane and the degradation product thereof

[0002] Technical Field

[0003] The present invention relates to the field of polyurethanes, in particular to a method for degrading and recycling a polyurethane comprising UV / V1S light irradiation in the presence of a photocatalyst under an oxygen-containing condition. The recycling in particular comprises a recovery of valuable products, such as polyols. The present invention also relates to a polyurethane degradation product obtained by the method for degrading and recycling, which degradation product comprises a polyol.

[0004] Prior art

[0005] In the past decades, the degradation and recycling of polyurethane (PU), a chemical waste that needs to be transformed in the environment, has attracted more and more attention. Chemical decomposition is one of the most promising recovery technologies to promote polyurethane recycling and reduce waste and greenhouse gas emissions. The challenges presented by the nucleophilic addition of carbamates make it difficult to achieve reactions with high selectivity under mild reaction conditions, which results in the limited existing chemical methods with few technical differences and no substantial improvement therebetween.

[0006] Study on degradation of polyurethane began in the 1990s. Xue et al. reported a method for ammonolysis and glycolysis of rigid polyurethane foams in Cell. Polym. 1994, 13, 125-136 and J. Appl. Polym. Sci. 1995, 56, 127-134, respectively. The ammonolysis of polyurethane may be a base- catalyzed process. Chuayjuljit et. al. reported in Miner. Met. Mater. Ser. 2002, 12, 1, 19-22 that in the presence of diethylenetriamine (DETA) as a degradation agent and sodium hydroxide as a strong base, the ammonolysis product 4,4'-methylenedianiline was successfully recovered as the raw material for further polymer synthesis.

[0007] Polyurethane flexible foams comprising polymeric polyols may also be recovered by glycolysis. The reaction may be carried out by using a glycol, such as diethylene glycol (DEG) as a glycolysis agent and stannous octanoate as a catalyst {Polym. Degrad. Stab. 2014, 109, 115-121). The recovered polyols were proved to be suitable for the synthesis of polyurethane foams. However, the reaction should be carried out under nitrogen atmosphere at high temperature of 190°C to 230°C in presence of a toxic catalyst.

[0008] Motokucho et al. reported that polyurethane can be hydrolyzed under high pressure and carbon dioxide atmosphere {Polym. Sci., Part A: Polym. Chem. 2017, 55, 2004-2010). The reaction has a relatively high hydrolysis rate and no by-products. The compounds obtained are 4,4'- methylenedianiline (MDA) and 1 ,4-butanediol (BD), which are easy to separate. Skrydstrup et al. (T. JACS Au. 2021, 1 (4), 517-524) reported that the reaction may be carried out at a milder temperature of 50°C, when an iridium composite catalyst Ir-lPrMACHO was used for hydrolysis, and polyurethane wastes such as discarded refrigerators, skating wheels and shoes could be well degraded to produce aniline and polyols having relatively high value. However, the reaction still should be carried out at a high pressure of 30 bar.

[0009] Only a few of chemical degradation methods known in the prior art could be used in large-scale industrial production for a long time.

[0010] The degradation and recovery of polyurethane wastes is a problem to be solved. The strict reaction conditions in the existing degradation methods make it difficult to meet the requirements of environmental protection. It is well known that visible light-induced photocatalysis can be carried out under mild reaction conditions and the energy is renewable. In recent years, the development in the field of photochemistry provides a potential for the green degradation of polyurethanes.

[0011] CN 111909336A discloses a method for degradation of polyurethane solid waste, wherein the polyurethane solid waste is crushed into powder of 0.1-1 mm, and mixed with a degradation agent, and then the mixture is subject to preliminary photodegradation treatment with a xenon lamp light source. Then, the mixture after photodegradation and water are degraded in an autoclave at 150 to 170°C and 5 to 20MPa for 20 to 40 minutes to obtain the final degradation product. In this degradation method, the polyurethane is disintegrated by the combination of the degradation agent and the xenon lamp irradiation, and then hydrolyzed at high temperature and high pressure to finally complete the degradation of polyurethane. Xenon lamp irradiation mainly plays a role in promoting the degradation effect of the degradation agent, and cannot complete the degradation of polyurethane independently. The degradation of polyurethane still depends on the hydrolysis reaction with strict reaction conditions.

[0012] CN 113828353 A relates to a catalyst for chemically recycling waste polyurethane and a preparation method thereof. The catalyst is prepared in a multiple-step sequence, comprising (1) pulverizing ash deposited in an incinerator, dissolving it in an oxidant and obtaining after reaction and drying a magnetic carrier, (2) allowing the magnetic carrier to react with an amine reagent and drying to obtain an amine-functionalized magnetic carrier; and (3) grinding the amine-functionalized magnetic carrier together with 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA), followed by a high- temperature treatment to obtain the actual catalyst. Polyurethanes are degraded using this catalyst in a glycolysis reaction (e.g. with ethylene glycol, propylene glycol or butylene glycol) under the influence of irradiation (e.g. with 750 nm monochromatic light) at high temperature (e.g. 160°C). PTCDA nanostructures are known to show strong UV / V1S absorption in the range of 400 to 600 nm (see Y. Han et al., “Preparation, optical and electrical properties of PTCDA nanostructures ’’ , Nanoscale 2015, 7, 17116 - 17121).

[0013] Therefore, it is necessary to develop a environmental degradation technology suitable for polyurethane materials.

[0014] Summary of the invention

[0015] On the one hand, the present invention provides a method for degrading and recycling a polyurethane, in particular with recovery of a polyol, comprising the following step: degrading the polyurethane by light irradiation with visible light and / or ultraviolet light in the presence of a photocatalyst under an oxygen-containing condition, wherein the photocatalyst comprises one or more of a noble metal photocatalyst of the Formula 1, aromatic ketones, anthracenes, fused ring compounds containing at least two naphthyl groups, aryl-substituted pyryliums, xanthenes, cerium-containing compounds selected from the group consisting of organic salts and inorganic salts containing cerium(lll) or cerium(lV), thiochrome, 2,4,5,6-tetrakis(diphenylamino)-isophthalonitrile and methylene blue;

[0016] Formula 1 wherein,

[0017] R1 is selected from ruthenium and iridium,

[0018] R2 and R10 are each independently selected from hydrogen and nitrogen,

[0019] R3, Rs, Ro, R7, Rs and R9 are each independently selected from hydrogen, C1-4 alkyls and halogen,

[0020] R4 is selected from hydrogen and C1-4 haloalkyls, n is an integer of 1-2.

[0021] It is particularly preferred that the fused ring compounds containing at least two naphthyl groups comprise compounds as shown in Formulae 11, 12 and 13 hereinbelow.

[0022] The above mentioned photocatalysts exhibit absorption of light (as determined by the method as described hereinbelow) in at least a part of a wavelength range of from 330 nm to < 400 nm, in particular 330 nm to 395 nm. On the other hand, the present invention provides a polyurethane recovery product obtained by the inventive method for degradation and recovery.

[0023] Embodiments

[0024] General definitions and terms

[0025] The method of determining the absorption properties of the photocatalyst is as follows:

[0026] A suitable solvent is chosen for the photocatalyst that allows obtaining a solution of the photocatalyst in a concentration range of from 0.01 mg / ml to 10 mg / ml that can be measured using a common UV / V1S spectrometer. For baseline calibration, blank solvent is measured first. The actual sample of the photocatalyst solution is measured in a wavelength range of 200 nm to 800 nm. The measurements are done at 20 °C to 25 °C. The above mentioned photocatalysts exhibit absorption in at least a part of the wavelength range of from 330 nm to < 400 nm, in particular 330 nm to 395 nm. The absorption in this wavelength range may be, but does not have to be, the maximum absorption observed in the range of 200 nm to 800 nm.

[0027] Methanol, ethanol, acetonitrile or water maybe used as solvents.

[0028] Any commercially available UV / V1S spectrometer may be used for the measurement, for example a Shimadzu UV-2600 UV / visible spectrometer.

[0029] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. In case of conflict, the definition provided herein shall prevail.

[0030] Unless stated otherwise, all percentages, parts, proportions, etc. are by weight. Those skilled in the art should understand that the sum of all components in the composition may be appropriately 100%. When the quantity, concentration or other values or parameters are given as ranges, preferred ranges or preferred upper and lower limit values or specific values, it should be understood that all ranges formed by the paired values of any upper limit range or preferred value and any lower limit range or preferred value are specifically disclosed, regardless of whether the ranges are separately disclosed. When a numerical range is cited herein, the range includes its endpoints, and all integers and fractions within the range, unless stated otherwise.

[0031] The term “a polyol” as used herein may refer to a single polyol or a mixture of polyols.

[0032] The term “isocyanate recovery products” as used herein refers to products obtained in the inventive degradation and recycling method from the isocyanate component used to prepare the original polyurethane. Terms like “anthracenes”, “xanthenes” and the like include derivatives of the respective base compounds (“anthracene”, “xanthene”, etc.) in which the carbon backbone bears substituents. For example, photocatalyst 23 mentioned below contains a cyano (CN) group at each of central carbon atoms of an anthracene carbon backbone.

[0033] The term “fused aryl” or “fused phenyl” refers to an aryl or phenyl which is fused to one or more aryl, cycloalkyl, non-aromatic heterocyclic, or heteroaryl ring, in particular aryl, across two positions, e.g. a and b positions, or a, b and c positions hereinbelow.

[0034] When the term "about" or "approximately" is used with a numerical variable, it generally means that the value of the variable and all values of the variable are within the experimental error (for example, within the 95% confidence interval of the mean values) or within ± 10% of the specified value, or within a wider range.

[0035] The term "optional" or "optionally" as used herein refers to the event or situation described later that may or may not occur, which includes the occurrence and non-occurrence of the event or situation, as well as the optional selection of the content described later. For example, when the content of a component herein is of 0% to 5%, it means that the component may be optionally present, that is, both the cases of absence (0%) and presence (>0-5%) are covered.

[0036] The terms "including", "comprising", "having", "containing" or "involving" and other variations thereof herein are inclusive or open, and do not exclude other elements or process steps not listed. Those skilled in the art should understand that the above terms such as "including" cover the meaning of "consisting of'. The expression "consisting of' excludes any unspecified elements, steps or ingredients. The expression "substantially consisting of' means that the scope is limited to the specified elements, steps or components, as well as optional elements, steps or components that will not materially affect the basic and new features of the subject matter to be protected. It should be understood that the expression "comprising" covers the expressions "substantially consisting of' and "consisting of'. The term "selected from..." refers to one or more elements in the group listed below, which are selected independently, and may include a combination of two or more elements thereof.

[0037] The term "one or more" or "at least one" as used herein refers to one, two, three, four, five, six, seven, eight, nine or more.

[0038] The terms "and / or" used herein include "and" and "or". A plurality of elements, parts or steps defined by "and / or" represent any one of the elements, parts or steps and any combination thereof. For example, A and / or B covers A, B and A+B; A, B and / or C covers A, B, C, A+B, A+C, B+C and A+B+C. Unless stated otherwise, the terms "combinations thereof', "any combination thereof and "mixtures thereof refer to multi-component mixtures of the said elements, such as mixtures of two, three, four and up to the maximum possible amount of components.

[0039] In addition, if no number is indicated in front of the part or component of the present invention, it means that there is no limit on the number of the part or component that occurs (or exists). Therefore, it should be interpreted as including one or at least one, and the singular form of the part or component also includes the plural form, unless the number clearly indicates the singular form.

[0040] Herein, "more" means two or more, unless specified otherwise. Unless explicitly stated in the context, "a" may cover the singular and plural forms. in the benzene ring may be linked with the group R to form a chemical bond.

[0041] The present invention provides a method for degrading and recycling a polyurethane, comprising the following step: degrading the polyurethane by light irradiation with visible light and / or ultraviolet light in the presence of a photocatalyst under an oxygen-containing condition, wherein the photocatalyst comprises one or more of a noble metal photocatalyst of the Formula 1, aromatic ketones, anthracenes thereof, fused ring compounds containing at least two naphthyl groups, aryl- substituted pyryliums, xanthenes, cerium-containing compounds selected from the group consisting of organic salts and inorganic salts containing cerium(lll) or cerium(lV), thiochrome, 2, 4,5,6- tetrakis(diphenylamino)-isophthalonitrile and methylene blue;

[0042] Formula 1 wherein,

[0043] R1 is selected from ruthenium and iridium,

[0044] R2 and R10 are each independently selected from hydrogen and nitrogen, Rs, RS, R<>, R7, Rs and R9 are each independently selected from hydrogen, C1-4 alkyls and halogens, preferably selected from hydrogen, methyl, ethyl, fluorine, chlorine and bromine, more preferably selected from hydrogen, methyl and fluorine,

[0045] R4 is selected from hydrogen and C1-4 haloalkyls, preferably selected from hydrogen and halomethyls, more preferably trifluoromethyl -CF3, n is an integer of 1-2.

[0046] The polyurethane of the present invention refers to any and all materials or products containing polyurethane commonly used in the art. In terms of chemical structure, polyurethane is a polymer containing carbamate repeat units. In the sense of the present invention, it includes the addition products of polyftmctional isocyanates and polyols (sometimes, although not completely correct, also called polycondensation products). In addition to the basic polyurethane structure mentioned above, polyurethane products usually comprise other structures, such as those with urea bond. The polyurethane with the basic polyurethane structure and these structures other than the pure basic polyurethane structure is also included in the scope of the polyurethane of the present invention, and does not deviate from scope of the present invention.

[0047] In the present invention, the term "isocyanate" comprises all isocyanates known to those skilled in the art in polyurethane chemistry, especially such as toluene diisocyanate (TD1; prepared from toluene diamine TDA), diisocyanates and polyisocyanates of the diphenylmethane series (MD1; prepared from diamine and polyamine of diphenylmethane series MDA), pentane-l,5-diisocyanate (PD1; prepared from 1,5-pentanediamine PDA), hexamethylene diisocyanate (HD1; prepared from 1,6-hexamethylene diamine HAD), 1,5 -naphthalene diisocyanate (ND1; prepared from 1,5- naphthalene diamine NDA), isophorone diisocyanate (1PD1; prepared from isophorone diamine 1PDA), p-xylylene diisocyanate (XD1; prepared from p-xylylene diamine XDA), methylcyclohexyl diisocyanate (HTD1), 4,4'- dicyclohexylmethane diisocyanate, p-phenylene diisocyanate (PPD1) or tetramethylxylylene diisocyanate (TMXD1).

[0048] The term "isocyanate" also covers certainly the embodiments of using two or more different isocyanates (such as a mixture of MD1 and TD1) in the production of polyurethane. This is also the case within a category of isocyanate (thus it also applies to different MD1 types, for example). All isocyanates for producing polyurethane are called isocyanate components of polyurethane. The isocyanate components comprise at least one isocyanate. The isocyanate may comprise various isomers, such as TD1 isomers 2,4-TDl and 2,6-TDl, MD1 isomers 2,4'-MDl and 4,4'-MDl.

[0049] All polyols for preparing polyurethane are called polyol components of polyurethane. The polyol components comprise at least one polyol. The term "polyol" comprises all polyols known to those skilled in the art in polyurethane chemistry, especially polyether polyols, polyester polyols, polyether ester polyols and polyether carbonate polyols. The expression "polyol" also covers certainly the embodiments of using two or more different polyols in the production of polyurethane. This is also the case within a category of polyol. Therefore, when "polyether polyol" (or "polyester polyol", etc.) is mentioned below, for example, the term also covers the embodiments of using two or more different polyether polyols (or two or more different polyester polyols, etc.) in the production of polyurethane. Polyetherpolyols are particularly preferred.

[0050] The polyurethane of the present invention comprises the polyurethane at all stages of use, such as unused or untreated polyurethane, used polyurethane, recycled polyurethane, and polyurethane waste, etc. The polyurethane of the present invention may be present in various forms, such as polyurethane foams (comprising flexible and rigid foams), polyurethane particles, polyurethane coatings, adhesives, sealants and elastomers, etc.

[0051] The method for degradation and recovery of the present invention is not limited by the form of polyurethane products, which may be in various forms of conventional polyurethane products in the art, such as shoe materials, thermal insulation materials, and automobile interiors, etc.

[0052] In order to achieve the mild photodegradation of polyurethane, the inventors chose a group of photocatalysts with good photodegradation effect for polyurethane. The photocatalyst according to the present invention comprises in particular one or more of a noble metal photocatalyst of the Formula 1, aromatic ketones, anthracenes, fused ring compounds containing at least two naphthyl groups, aryl-substituted pyryliums, xanthenes, cerium-containing compounds selected from the group consisting of organic salts and inorganic salts containing cerium(lll) or cerium(lV), thiochrome, methylene blue and 2,4,5,6-tetrakis(diphenylamino)-isophthalonitrile;

[0053] Formula 1 wherein,

[0054] R1 is selected from ruthenium and iridium, R2 and R10 are each independently selected from hydrogen and nitrogen,

[0055] R3, R5, R6, R7, R8 and R9 are each independently selected from hydrogen, C1-4 alkyls and halogens, preferably selected from hydrogen, methyl, ethyl, fluorine, chlorine and bromine, more preferably selected from hydrogen, methyl and fluorine,

[0056] R4 is selected from hydrogen and C1-4 haloalkyls, more preferably selected from hydrogen and halomethyl, more preferably trifluoromethyl -CF3, n is an integer of 1-2.

[0057] In a preferred embodiment of the present invention, the photocatalyst comprises the noble metal catalyst shown in Formula 1, wherein

[0058] R1 is selected from iridium and n is 1 ,

[0059] R2 and R10 are selected from hydrogen,

[0060] R3, R5, R6, R7, Rs and R9 are each independently selected from C1-4 alkyls and halogens, preferably methyl and fluorine,

[0061] R4 is selected from C1-4 haloalkyls, preferably selected from halomethyls, more preferably trifluoromethyl.

[0062] In a more preferred embodiment of the present invention, the photocatalyst comprises the noble metal catalyst shown in Formula 1, wherein

[0063] R1 is selected from iridium and n is 1 ,

[0064] R2 and R10 are selected from hydrogen,

[0065] R3 and Rs are identical, and selected from C1-4 alkyls and halogens, preferably methyl and fluorine, R4 is selected from C1-4 haloalkyls, preferably selected from halomethyls, more preferably trifluoromethyl,

[0066] R6, R7, R8 and R9 are identical, and selected from halogens, preferably fluorine.

[0067] In a preferred embodiment of the present invention, the photocatalyst comprises the noble metal catalyst shown in Formula 1, wherein

[0068] R1 is selected from ruthenium and n is 2,

[0069] R2 and R10 are each independently selected from hydrogen and nitrogen,

[0070] R3, R5, R6, R7, R8 and R9 are each independently selected from hydrogen and C1-4 alkyls, preferably hydrogen,

[0071] R4 is selected from hydrogen.

[0072] In a more preferred embodiment of the present invention, the photocatalyst comprises the noble metal catalyst shown in Formula 1, wherein

[0073] R1 is selected from ruthenium and n is 2, R2 is selected from hydrogen and nitrogen,

[0074] R3, Rs, Re, R7, Rs and R9 are each independently selected from hydrogen and C1-4 alkyls, preferably hydrogen,

[0075] R4 is selected from hydrogen, R10 is selected from nitrogen.

[0076] The aromatic ketones of the present invention are aromatic compounds containing at least one carbonyl group in the art, in which the carbon atom of the carbonyl group is connected with at least one aromatic hydrocarbon group, which may be represented by Ar-CO-Ar' or Ar-CO-R respectively, wherein Ar is an aromatic hydrocarbon group.

[0077] Aromatic ketones within the sense of the present invention also comprise derivatives such as heteroatom-substituted, alkane-substituted, aromatic hydrocarbon-substituted, fused aromatic hydrocarbon-substituted, halogen-substituted, nitro-substituted, amino-substituted, and hydroxyl- substituted aromatic ketones, etc.

[0078] In a preferred embodiment of the present invention, the aromatic ketones comprise one or more compounds as shown in Formulae 2, 3, 4 and 5 shown in Scheme 1 :

[0079] Scheme 1 : Some possible structures of aromatic ketones useful as photocatalysts.

[0080] In Scheme 1, in Formula 2, Rn and Rn are each independently selected from hydrogen, halogens, nitro, hydroxyl, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls and C6-18 fused aryls, wherein the fused aryl preferably forms a ring structure with the two carbon atoms shown as a and b in Formula 2, or in Formula 3, RB is selected from carbon, oxygen and sulfur, and Ru is selected from hydrogen, C1- 4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls and C6-18 fused aryls, and the fused aryl preferably forms a ring structure with the three carbon atoms shown as a, b and c in Formula 3, or in Formula 4, RB and RB are each independently selected from hydrogen, amino and C1-4 alkyl- substituted amino.

[0081] In a preferred embodiment of the present invention, in Formula 2, Rn and R12 are each independently selected from hydrogen, bromine, nitro and hydroxyl.

[0082] In a preferred embodiment of the present invention, in Formula 2, Rn and R12 are each independently selected from hydrogen, halogens, nitro, hydroxyl, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls, and Rn and R12 are respectively connected with the carbon atoms shown as b or c, as shown in Formula 2'. formula 2’

[0083] In a more preferred embodiment of the present invention, in Formula 2', Rn and Rn are each independently selected from hydrogen, bromine, nitro and hydroxyl.

[0084] In a preferred embodiment of the present invention, in Formula 2', Rn and Rn are identical, and selected from hydrogen, halogens, nitro, hydroxyl, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls.

[0085] In a more preferred embodiment of the present invention, in Formula 2’, Rn and R12 are identical, and selected from hydrogen, bromine, nitro and hydroxyl.

[0086] In a preferred embodiment of the present invention, in Formula 2, R 12 is selected from hydrogen, and Rn is C6-18 fused aryl, preferably fused phenyl, Rn preferably forms a ring structure with the two carbon atoms shown as a and b.

[0087] In a preferred embodiment of the present invention, in Formula 3, RB is selected from carbon, oxygen and sulfur, preferably selected from carbon and sulfur; and Ru is selected from hydrogen and C6-18 fused aryls. In a more preferred embodiment of the present invention, in Formula 3, RB is selected from carbon, oxygen and sulfur, preferably selected from carbon and sulfur; and R u is selected from hydrogen.

[0088] In a more preferred embodiment of the present invention, in Formula 3, RB is selected from carbon; Ru is selected from C6-18 fused aryls, preferably fused phenyls, and the fused aryl preferably forms a ring structure with the three carbon atoms shown as a, b and c in Formula 3.

[0089] In a preferred embodiment of the present invention, in Formula 4, RB and RB are each independently selected from hydrogen and dialkyl-substituted amino, wherein the alkyl is methyl or ethyl.

[0090] In a more preferred embodiment of the present invention, in Formula 4, RB and RB are each independently selected from hydrogen and dialkyl-substituted amino, wherein the alkyl is methyl or ethyl, and RB and RB are connected with the carbon atoms shown as a or b, respectively.

[0091] In a more preferred embodiment of the present invention, in Formula 4, RB and RB are identical and selected from hydrogen and dialkyl-substituted amino, wherein the alkyl is methyl or ethyl, and RB and RB are connected with the carbon atoms shown as a or b, respectively.

[0092] In one embodiment, the aromatic ketones comprise quinones . Such quinones comprise in particular phenanthraquinones, anthraquinones, benzoquinones, naphthoquinones, acenaphthoquinones, and mixtures thereof, preferably comprise one or more compounds as shown in Formulae 6, 7, 8 and 9 shown in Scheme 2:

[0093] Formula 6 Formula 7 Formula 8 Formula 9

[0094] Scheme 2: Further possible structures of aromatic ketones useful as photocatalysts.

[0095] In Scheme 2, in Formula 6 or 7, Rn, RB, R19 and R20 are each independently selected from hydrogen, halogens and C1-4 alkyls, in Formula 8, R21 and R22 are each independently selected from hydrogen, halogens, C1-4 alkyls, and C6-18 fused aryls, and the fused aryl preferably forms a ring structure with the two carbon atoms shown as b and c in Formula 8, in Formula 9, R23 and R24 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6,. is aryls, C7-12 alkaryls, C7-12 aralkyls and C6-18 fused aryls, and the fused aryl preferably forms a ring structure with the two carbon atoms shown as a and b in Formula 9.

[0096] In a preferred embodiment of the present invention, in Formula 6, R 17 and Fix are each independently selected from hydrogen, halogens and C1-4 alkyls, preferably hydrogen and bromine.

[0097] In a preferred embodiment of the present invention, in Formula 6, Rn and Fix are identical, and selected from hydrogen and halogens, preferably hydrogen and bromine.

[0098] In a preferred embodiment of the present invention, in Formula 6, F 17 and Fix are each independently selected from hydrogen, halogens and C1-4 alkyls, and R17 and Fix are respectively connected with the carbon atom shown as a or b, as shown in Formula 6'.

[0099] Formula 6'

[0100] In a preferred embodiment of the present invention, in Formula 6', F 17 and Fix are each independently selected from hydrogen and halogens, preferably hydrogen and bromine.

[0101] In a more preferred embodiment of the present invention, in Formula 6', Rn and Fix are identical, and selected from hydrogen and halogens, preferably hydrogen and bromine.

[0102] In a preferred embodiment of the present invention, in Formula 7, R19 and R20 are each independently selected from hydrogen, preferably R19 and R20 are identical.

[0103] In a preferred embodiment of the present invention, in Formula 8, R21 and R22 are each independently selected from hydrogen and C1-4 alkyls, preferably hydrogen and butyl.

[0104] In a preferred embodiment of the present invention, in Formula 8, R21 and R22 are identical, and selected from hydrogen and C1-4 alkyls, preferably hydrogen and butyl. In a preferred embodiment of the present invention, in Formula 8, R21 and R22 are each independently selected from hydrogen, halogens and C1-4 alkyls, preferably hydrogen and butyl, and R21 and R22 are respectively connected with the carbon atom shown as a or b, as shown in Formula 8'.

[0105] Formula 8'

[0106] In a preferred embodiment of the present invention, in Formula 8', R21 and R22 are each independently selected from hydrogen and C1-4 alkyls, preferably hydrogen and butyl.

[0107] In a more preferred embodiment of the present invention, in Formula 8', R21 and R22 are identical, and selected from hydrogen and C1-4 alkyls, preferably hydrogen and butyl.

[0108] In a preferred embodiment of the present invention, in Formula 8, R21 is selected from hydrogen and C1-4 alkyls, preferably hydrogen and methyl; R22 is selected from C6-18 fused aryls, wherein the fused aryl forms a ring structure with the two carbon atoms shown as b and c in Formula 8.

[0109] In a more preferred embodiment of the present invention, in Formula 8, R21 is selected from hydrogen and methyl, and R22 is selected from fused phenyls, wherein the fused phenyl forms a ring structure with the two carbon atoms shown as b and c in Formula 8.

[0110] In a preferred embodiment of the present invention, in Formula 9, R23 and R24 are each independently selected from hydrogen, halogens and C1-4 alkyls.

[0111] In a more preferred embodiment of the present invention, in Formula 9, R23 and R24 are identical, and selected from hydrogen, halogens and C1-4 alkyls.

[0112] In a preferred embodiment of the present invention, in Formula 9, R23 and R24 are each independently selected from hydrogens, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls, and R23 and R24 are respectively connected with the carbon atom shown as b or c, as shown in Formula 9'.

[0113]

[0114] In a preferred embodiment of the present invention, in Formula 9', R23 and R24 are each independently selected from hydrogen, halogens and C1-4 alkyls, preferably hydrogen and t-butyl.

[0115] In a more preferred embodiment of the present invention, in Formula 9', R23 and R24 are identical, and selected from hydrogen, halogens and C1-4 alkyls, preferably hydrogen and t-butyl.

[0116] In a preferred embodiment of the present invention, in Formula 9, R23 is selected from hydrogen and C1-4 alkyls, and R24 is C6-18 fused aryl, and R24 preferably forms a ring structure with the two carbon atoms shown as a and b.

[0117] In a preferred embodiment of the present invention, in Formula 9, R23 is selected from hydrogen and C1-4 alkyls, and R24 is C6-18 fused phenyl, and R24 forms a ring structure with the two carbon atoms shown as a and b.

[0118] In another embodiment of the present invention, the photocatalyst comprises anthracenes. The anthracenes are conventional fused aromatic hydrocarbons with three rings in the art. One or more hydrogen atoms in any benzene ring thereof maybe replaced by another atom, i.e. the anthracenes may be heteroatom-substituted, alkane-substituted, aromatic hydrocarbon-substituted, fused aromatic hydrocarbon-substituted, halogen-substituted, nitro-substituted, amino-substituted, cyano- substituted, acyl-substituted, or hydroxyl-substituted anthracenes.

[0119] The anthracenes preferably comprise a compound as shown in Formula 10 shown in Scheme 3 below.

[0120] Scheme 3: Some possible structures of anthracenes useful as photocatalysts.

[0121] In Scheme 3, R25 and R26 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, C6-18 fused aryls, cyano and C1-4 acyls.

[0122] In a more preferred embodiment of the present invention, R25 and R26 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, C6-18 fused aryls, cyano and C1-4 acyls, and R25 and R26 are respectively connected with the carbon atom shown as a or b, as shown in Formula 10'.

[0123] In a preferred embodiment of the present invention, in Formula 10, R25 is selected from hydrogen, and R26 is selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, G,. is fused aryls, cyano and C1-4 acyls, preferably from hydrogen, bromine, C6-18 aryls, Ce-12 fused aryls, cyano and acetyl.

[0124] In a more preferred embodiment of the present invention, in Formula 10', R25 is selected from hydrogen, and R26 is selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, C6-18 fused aryls, cyano and C1-4 acyls.

[0125] In a more preferred embodiment of the present invention, in Formula 10', R25 is selected from hydrogen, and R26 is selected from hydrogen, bromine, C6-18 aryls, Ce-12 fused aryls, cyano, formyl and acetyl, and R26 is further preferably selected from hydrogen, bromine, phenyl, benzyl, tolyl, naphthyl, cyano, formyl and acetyl.

[0126] In a preferred embodiment of the present invention, in Formula 10', R25 and R26 are identical, and selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, C6-18 fused aryls, cyano and C1-4 acyls. In a more preferred embodiment of the present invention, in Formula 10', R25 and R26 are identical, and selected from hydrogen, bromine, C6-18 aryls, Ce-12 fused aryls, cyano, formyl and acetyl, and further preferably selected from hydrogen, bromine, phenyl, benzyl, tolyl, naphthyl, cyano, formyl and acetyl.

[0127] In yet another embodiment of the present invention, the photocatalyst comprises fused ring compounds containing at least two naphthyl groups. The naphthalenes are conventional fused aromatic hydrocarbons containing two rings in the art, wherein one or more hydrogen in any naphthyl group may be substituted by other groups, such as heteroatom-substituted, alkane-substituted, aromatic hydrocarbon-substituted, fused aromatic hydrocarbon-substituted, halogen-substituted, nitro-substituted, amino-substituted, or hydroxyl-substituted.

[0128] The fused ring compounds containing two naphthyl groups preferably comprise perylenes and naphthacenes. The fused ring compounds containing two naphthyl groups are preferably the compounds as shown in Formulae 11, 12 and 13 shown in Scheme 4.

[0129] Formula 11 Formula 12 Formula 13

[0130] Scheme 4: Some possible structures of fused ring compounds containing two naphthyl groups useful as photocatalysts.

[0131] In Scheme 4, in Formula 11, R27, R28, R29 and R30 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls, or in Formula 12, R31, R32, R33 and R34 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls and hydrogenated naphthalenones (1-tetralones).

[0132] In a preferred embodiment of the present invention, in Formula 11, R27, R28, R29 and R30 are each independently selected from hydrogen and C6-18 aryls, preferably hydrogen and phenyl.

[0133] In a more preferred embodiment of the present invention, in Formula 11, R27, R28, R29 and R30 are identical and selected from hydrogen and C6-18 aryls, preferably hydrogen and phenyl. In a preferred embodiment of the present invention, in Formula 12, R31, R32, R33 and R34 are each independently selected from hydrogen and halogens, preferably hydrogen, bromine and chlorine.

[0134] In a more preferred embodiment of the present invention, in Formula 12, R31, R32, R33 and R34 are identical and selected from hydrogen and halogen, preferably hydrogen, bromine and chlorine.

[0135] In a preferred embodiment of the present invention, in Formula 12, R32 and R33 are both selected from hydrogen, R31 and R34 are both selected from tetrahydrogenated naphthalenones (1-tetralones), R31 forms a ring structure with the two carbon atoms shown as a and b, R34 forms a ring structure with the two carbon atoms shown as c and d, as shown in Formula 12'.

[0136] Formula 12'

[0137] In the present invention, the aryl-substituted pyryliums are conventional pyrylium salts in the art, in which at least one carbon atom, preferably at least three carbon atoms, in the pyrylium ring are replaced by aromatic hydrocarbons. The aryl-substituted pyryliums include preferably a compound as shown in Formula 14,

[0138] Formula 14 wherein

[0139] R35, R36 and R37 are each independently selected from C6-12 aryls, C6-12 haloaryls, C7-13 alkaryls and C7-

[0140] 13 alkoxy-substituted aryls,

[0141] X is a substituted or unsubstituted sulfonate or borate, preferably an unsubstituted sulfonate or haloborate. In a preferred embodiment of the present invention, R35, R36 and R37 are each independently selected from phenyl, fluorophenyl and C7-9 alkaryls and methoxy-substituted phenyls.

[0142] In a preferred embodiment of the present invention, R35, R36 and R37 are each independently selected from phenyl, fluorophenyl, C7-9 alkaryls and methoxy-substituted phenyls, and X is a halogen- substituted borate or sulfonate.

[0143] In a preferred embodiment of the present invention, R35, R36 and R37 are identical and selected from phenyl, fluorophenyl, tolyl and methoxy-substituted phenyls, and X is a tetrafluoroborate.

[0144] The xanthenes in the present invention include dibenzo- y-pyran and preferably such derivatives of xanthenes as shown in Formula 15 shown in Scheme 5 with details of possible substituents at “a” being shown in Scheme 5a.

[0145] Formula 15

[0146] Scheme 5: Some possible structures of xanthenes useful as photocatalysts.

[0147] Formula 16 Formula 17

[0148] Scheme 5a: Possible structures of substituents at “a” in Formula 15.

[0149] In Schemes 5 / 5a, R39 and Rsx are each independently selected from hydrogen, C1-4 alkyls, a group as shown in Formula 16, or R39 and R38 form a ring as shown in Formula 17,

[0150] R40 and R41 are each independently selected from diphenylphosphino (-PPI12), C1-4 alkyls and halogens, R42 and R45 are each independently selected from hydrogen, hydroxyl, C1-4 alkyls and halogens, R43 and R44 are each independently selected from hydrogen, C1-4 alkyls and halogens, R46 is selected from halogens.

[0151] In a preferred embodiment of the present invention, in Formula 15, R39 and Rxx are each independently selected from hydrogen and C1-4 alkyls, preferably hydrogen and methyl, R40 and R41 are diphenylphosphino (-PPI12), and R42, R43, R44 and R45 are each independently selected from hydrogen and C1-4 alkyls, more preferably hydrogen.

[0152] In a more preferred embodiment of the present invention, in Formula 15, R39 and R sx are identical, and selected from hydrogen and C1-4 alkyls, preferably methyl, R40 and R41 are diphenylphosphino (-PPI12), and R42, R43, R44 and R45 are identical, and selected from hydrogen and C1-4 alkyls, more preferably hydrogen.

[0153] In a preferred embodiment of the present invention, in Formula 15, R39 is hydrogen, Rxx is a group as shown in Formula 16, R40 and R41 are each independently selected from C1-4 alkyls and halogens, R42 and R45 are each independently selected from hydroxyl, hydrogen and halogens, and R43 and R44 are each independently selected from hydrogen and halogens.

[0154] In a more preferred embodiment of the present invention, in Formula 15, R39 is hydrogen, Rxx is a group as shown in Formula 16, R40 and R41 are each independently selected from C1-4 alkyls and halogen, R42 and R45 are each independently selected from hydroxyl, hydrogen and halogens, and R43 and R44 are each independently selected from hydrogen and halogens, and R46 is selected from halogens.

[0155] In a more preferred embodiment of the present invention, in Formula 15, R39 is hydrogen, Rxx is a group as shown in Formula 16, R40 and R41 are identical, and selected from C1-4 alkyls, preferably methyl, R42 and R45 are identical, and selected from hydroxyl, and R43 and R44 are each independently selected from hydrogen and halogens, and R46 is selected from halogens, preferably chlorine.

[0156] In a preferred embodiment of the present invention, in Formula 15, R39 and R xx form a ring as shown in Formula 17, R40 and R41 are identical, and selected from halogens, R42 and R45 are identical, and selected from hydroxyl and halogens, and R43 and R44 are identical, and selected from hydrogen and halogens.

[0157] The cerium-containing compounds of the present invention include organic salts and inorganic salts containing cerium, preferably chlorides, substituted or unsubstituted sulfonates, substituted or unsubstituted nitrates, and substituted or unsubstituted ammonium salts of cerium, preferably one or more of ammonium cerium nitrate, cerium chloride and cerium trifluoromethanesulfonate. In a preferred embodiment of the present invention, when ceric ammonium nitrate is used as the photocatalyst, benzoic acid derivatives are also used to improve the catalytic performance. The benzoic acid derivatives comprise those, in which at least one carbon atom, preferably two or three carbon atoms in the benzene ring are replaced, wherein the substituents are preferably selected from C1-4 alkyls, C1-4 haloalkyls, C1-4 cycloalkyls and C1-4 alkyl-substituted silane groups. The benzoic acid derivatives are preferably as shown in Formula 18,

[0158] Formula 18 wherein R47, ICx and R49 are each independently selected from hydrogen, C1-4 alkyls, C1-4 haloalkyls, C1-4 cycloalkyls and C1-4 alkyl-substituted silane groups, and preferably selected from hydrogen, trifluoromethyl, methyl, isopropyl, cyclohexyl and trimethylsilyl.

[0159] In a preferred embodiment of the present invention, the benzoic acid derivatives are selected from one or more of 2,4,6-triisopropylbenzoic acid (CAS 49623-71-4), 2,6-bis (trifhioromethyl)benzoic acid (CAS 24821-22-5), 2,4,6-tricyclohexylbenzoic acid (CAS 1839076-17-3) and 2-methyl-6- trimethylsilylbenzoic acid (CAS 1821231-94-0).

[0160] There is no special restriction on the amount of benzoic acid derivatives in the present invention, which is preferably 1 to 20 times the weight of ceric ammonium nitrate, preferably 1 to 5 times.

[0161] The thiochrome in the present invention is a compound having a structural Formula 19 with CAS number of 51827-51-1.

[0162] Formula 19

[0163] The methylene blue in the present invention is a compound having a structural Formula 20 with CAS number of 61-73-4.

[0164] Formula 20

[0165] 2,4,5,6-Tetrakis(diphenylamino)-isophthalonitrile in the present invention is a compound having a structural Formula 21, also known as 4DPA1PN, with CAS number of 1846598-27-3.

[0166] Formula 21

[0167] In the present invention, the amount of the photocatalyst may be selected as the conventional amount in the photocatalytic degradation reaction, preferably 0.5% by weight or more, further preferably 0.5 to 10% by weight, more preferably 0.5 to 5% by weight, calculated as mass percentage relative to the mass of polyurethane.

[0168] In an embodiment of the present invention, the photocatalyst is selected from one or more of aromatic ketones as shown in Formula 2' and Formula 2" (see Scheme 6 for these and other formulae; details of possible substituents at “a” are shown in Scheme 6a), aromatic ketones as shown in Formula 3', benzanthrone, benzophenone, benzil, phenanthraquinones as shown in Formula 6', anthraquinones as shown in Formula 7, p-benzoquinones as shown in Formula 8' and Formula 8", anthraquinones as shown in Formula 9', 1 ,2-benzanthraquinone and anthracenes as shown in Formula 10', fused ring compounds containing two naphthyl groups as shown in Formulae 11 and 12, compounds as shown in Formula 13, aryl-substituted pyryliums as shown in Formula 14, xanthenes as shown in Formula 15, thiochrome and methylene blue.

[0169]

[0170] Formula 13 Formula 14 Formula 15

[0171] Scheme 6 Some structures of photocatalysts used in an embodiment of the invention.

[0172] Formula 16 Formula 17

[0173] Scheme 6a: Possible structures of substituents at “a”.

[0174] In Schemes 6 / 6a, Rn and Rn are each independently selected from hydrogen, halogens, nitro, hydroxyl, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls, preferably hydrogen, bromine, nitro and hydroxyl, more preferably hydrogen and bromine; preferably, Rn and R12 are identical;

[0175] RB is selected from carbon, oxygen and sulfur, preferably carbon and sulfur;

[0176] Rn and Rix are each independently selected from hydrogen, halogens and C1-4 alkyls, preferably hydrogen and halogens, more preferably hydrogen and bromine; preferably, Rn and R is are identical; R19 and R20 are each independently selected from hydrogen, halogens and C1-4 alkyls, preferably hydrogen;

[0177] R21 and R22 are each independently selected from hydrogen, halogens and C1-4 alkyls, preferably hydrogen and butyl; preferably, R21 and R22 are identical;

[0178] R23 and R24 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls, preferably hydrogen, halogens and C1-4 alkyls, more preferably hydrogen and t-butyl; preferably, R23 and R24 are identical;

[0179] R25 and R26 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, C6-18 fused aryls, cyano and C1-4 acyls, preferably hydrogen, bromine, C6-18 aryls, C6-12 fused aryls and cyano, formyl and acetyl, more preferably hydrogen, bromine, phenyl, benzyl, tolyl, naphthyl, cyano, formyl and acetyl; wherein R25 and R26 are preferably identical, or preferably, R25 is selected from hydrogen and R26 is selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, C6-18 fused aryls, cyano and C1-4 acyls, and R26 is more preferably selected from hydrogen, bromine, phenyl, benzyl, tolyl, naphthyl, cyano, formyl and acetyl;

[0180] R27, R28, R29 and R30 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls, preferably hydrogen and C6-18 aryls, more preferably hydrogen and phenyl; preferably, R27, R28, R29 and R30 are identical;

[0181] R31, R32, R33 and R34 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls and C7-12 aralkyls, preferably hydrogen; and preferably, R31, R32, R33 and R34 are identical; R35, R36 and R37 are each independently selected from C6-12 aryls, C6-12 haloaryls, and C7-13 alkaryls, preferably phenyl, halophenyls and C7-9 alkaryls, more preferably phenyl, florophenyl and tolyl; and X is a substituted or unsubstituted sulfonate or borate, preferably borate; preferably R35, R36 and R37 are identical;

[0182] Rxx and R39 are each independently selected from hydrogen, C1-4 alkyls, a group as shown in Formula 16, or Rxx and R39 forms a ring structure as shown in Formula 17;

[0183] R40 and R41 are each independently selected from diphenylphosphino, C1-4 alkyls and halogens, preferably diphenylphosphino, methyl and bromine; preferably, R40 and R41 are identical;

[0184] R42 and R45 are each independently selected from hydroxyl and hydrogen;

[0185] R43 and R44 are each independently selected from hydrogen and halogens, preferably chlorine, bromine and iodine;

[0186] R46 is selected from halogens, preferably chlorine; preferably, R39 and Rxx are each independently selected from hydrogen and C1-4 alkyls, preferably hydrogen and methyl, R40 and R41 are diphenylphosphino, and R42, R43, R44 and R45 are each independently selected from hydrogen and C1-4 alkyls; preferably, R39 is hydrogen, and Rxx is a group as shown in Formula 16, R40 and R41 are each independently selected from C1-4 alkyls and halogens, R42 and R45 are each independently selected from hydroxyl, hydrogen and halogens, and R43 and R44 are each independently selected from hydrogen and halogens, and R46 is selected from halogens.

[0187] Preferably, R39 and Rxx form a ring as shown in Formula 17, R40 and R41 are identical, and selected from halogens, R42 and R45 are identical, and selected from hydroxyl and halogens, and R43 and R44 are identical, and selected from hydrogen and halogens.

[0188] The photocatalyst of the present invention may be selected from any one in the following table or mixtures thereof.

[0189] The “oxygen-containing condition” in the present invention refers to an environment having oxygen. In order to maintain the oxygen-containing condition, the conventional method for maintaining the oxygen-containing condition in the art may be used, as long as it is not obviously contrary to the photodegradation reaction of the present invention or has no obvious adverse effect. Useful methods comprise introducing oxygen, oxygen-containing gas mixtures, such as air, or liquids that can release oxygen, such as hydrogen peroxide solutions, into the reaction system. In the reaction process of the present invention, it is preferable to maintain a constant flow of the oxygen or oxygen-containing gas introduced to facilitate the mixing of solid and liquid phases in the reaction system.

[0190] In a preferred embodiment of the present invention, when the oxygen-containing condition comprises introducing oxygen or oxygen-containing gas mixtures, etc., there is no special restriction on the amount of the oxygen or oxygen-containing gas mixtures, and it is preferred to introduce the oxygen or oxygen-containing gas mixtures at 1-3 standard atmosphere pressure (atm; 1.013 to 3.040 bar).

[0191] The light irradiation in the present invention may be carried out by any light source commonly used in the field of light irradiation provided that it emits visible light and / or ultraviolet light, preferably ultraviolet A and / or visible light, more preferably a light source with wavelength of 330 nm to 500 nm, preferably 360 nm to 500 nm.

[0192] In a preferable embodiment of the present invention, the light source is xenon lamp, LED lamp, incandescent lamp, energy-saving lamp, and halogen lamp, etc.

[0193] In the present invention, the time for the light irradiation is not specially limited, as long as there is no special impact on the degradation and recovery. Generally, the degradation and recovery efficiency will be improved by prolonging the time for irradiation, and there will be no negative impact on the degradation and recovery. Taking account of the efficiency and effect, preferably is 1 to 20 hours, more preferably 2 to 10 hours, and most preferably 3 to 8 hours in the present invention.

[0194] In the present invention, the degradation may be carried out under mild conditions without excessively high reaction temperature, preferably at 0°C to 115°C, more preferably at 0°C to 80°C, even more preferably at 10°C to 50°C, and most preferably at room temperature, i.e. of 15 to 25°C. In the present invention, in order to improve the degradation effect and promote the dispersion of polyurethane, the degradation may be carried out in a solvent to achieve full dispersion of polyurethane. The preferred solvent of the present invention comprises one or more of monohydric alcohols, water, acetone and ethyl acetate, preferably methanol, ethanol and acetone. It should be noted that the degradation of the present invention is not a simple alcoholysis or hydrolysis reaction, as can clearly be seen from examples 11 and 12.

[0195] The material or product comprising polyurethane in the present invention may be ground before the degradation and then degraded and recycled, or directly degraded without grinding.

[0196] In a preferred embodiment of the present invention, the method for degradation and recycling comprises the following steps: degrading the polyurethane by light irradiation in a solvent in the presence of a photocatalyst under the atmosphere of oxygen or oxygen-containing gas, wherein the photocatalyst comprises one or more of the compounds as shown in Formulae 1 to 15 and Formulae 18 to 21.

[0197] In another embodiment of the present invention, the method for degradation and recovery of polyurethane comprises the following steps: degrading the polyurethane by light irradiation in a solvent in the presence of a photocatalyst under the atmosphere of oxygen or oxygen-containing gas, wherein the photocatalyst comprises aromatics ketone as shown in Formula 2 'and Formula 2", aromatic ketones as shown in Formula 3', benzanthrone, benzophenone, benzil, phenanthraquinones as shown in Formula 6', anthraquinones thereof as shown in Formula 7, p-benzoquinones as shown in Formula 8' and Formula 8", anthraquinones as shown in Formula 9', 1 ,2-benzanthraquinone, anthracenes as shown in Formula 10', fused ring compounds containing two naphthyl groups as shown in Formulae 11 and 12, compounds as shown in Formula 13, aryl-substituted pyryliums as shown in Formula 14, xanthenes as shown in Formula 15, thiochrome and methylene blue, wherein the definitions of R11-R46 and X are identical to those given for Scheme 6.

[0198] In a more preferred embodiment of the present invention, the method for degradation and recycling comprises the following steps: degrading the polyurethane by light irradiation in a solvent in the presence of a photocatalyst under the atmosphere of oxygen or oxygen-containing gas, wherein the photocatalyst comprises one or more of the compounds of Formulae 1 to 15 and Formulae 18 to 21; and the light irradiation is carried out with a light source with a wavelength of 330 nm to 500 nm, preferably 360 nm to 500 nm.

[0199] In yet another embodiment of the present invention, the method for degradation and recycling comprises the following step: degrading the polyurethane by light irradiation in a solvent in the presence of a photocatalyst under the atmosphere of oxygen or oxygen-containing gas, wherein the light irradiation is carried out with a light source with a wavelength of 330 nm to 500 nm, preferably 360 nm to 500 nm, and the photocatalyst comprises aromatic ketones as shown in Formula 2' and Formula 2", aromatic ketones as shown in Formula 3', benzanthrone, benzophenone, benzil, phenanthraquinones as shown in Formula 6', anthraquinones as shown in Formula 7, p- benzoquinones as shown in Formula 8' and Formula 8", anthraquinones as shown in Formula 9', 1,2- benzanthraquinone, anthracenes as shown in Formula 10', fused ring compounds containing two naphthyl groups as shown in Formulae 11 and 12, compounds as shown in Formula 13, aryl- substituted pyryliums as shown in Formula 14, xanthenes as shown in Formula 15, thiochrome and methylene blue, wherein the definitions of R11-R46 and X are identical to those given for Scheme 6.

[0200] In a more preferred embodiment of the present invention, the method for degradation and recovery of polyurethane comprises the following steps: mixing the polyurethane with a solvent while introducing oxygen or oxygen-containing gas at a temperature of 10 to 50°C, and degrading by light irradiation in the presence of a photocatalyst, wherein the photocatalyst comprises one or more of the compounds of Formulae 1 to 15 and Formulae 18 to 21; and the light irradiation is carried out with a light source with a wavelength of 330 nm to 500 nm, preferably 360 nm to 500 nm.

[0201] In a further embodiment of the present invention, the method for degradation and recycling comprises the following steps: mixing the polyurethane with a solvent while introducing oxygen or oxygen- containing gas at a temperature of 10 to 50°C, and degrading by light irradiation in the presence of a photocatalyst, wherein the light irradiation is carried out with a light source with a wavelength of 330 nm to 500 nm, preferably 360 nm to 500 nm, and the photocatalyst comprises aromatic ketones as shown in Formula 2' and Formula 2", aromatic ketones as shown in Formula 3', benzanthrone, benzophenone, benzil, phenanthraquinones as shown in Formula 6', anthraquinones as shown in Formula 7, p-benzoquinones as shown in Formula 8' and Formula 8", anthraquinones as shown in Formula 9', 1 ,2-benzanthraquinone, anthracenes as shown in Formula 10', fused ring compounds containing two naphthyl groups as shown in Formulae 11 and 12, compounds as shown in Formula 13, aryl-substituted pyryliums as shown in Formula 14, xanthenes as shown in Formula 15, thiochrome and methylene blue, wherein the definitions of R11-R46 and X are identical to those given for Scheme 6.

[0202] The method for degradation and recovery according to the present invention may adopt a conventional method for post-treatment in the art, and may further comprise the steps of (a) solid / liquid phase separation, (b) extraction of the liquid phase with a suitable extracting agent, (c) collection of the organic phase and the aqueous phase respectively, wherein the organic phase comprises a polyol. In step (a) of the present invention, the solid / liquid separation may be carried out by a conventional solid / liquid separation method in the art, such as filtration. The obtained solid residue is undegraded polyurethane residue.

[0203] Suitable extracting agents for step (b) include an organic solvent or a mixture of an organic solvent and water. It is, for example, possible to mix the liquid phase obtained in step (a) with water, followed by addition of an organic solvent, intense mixing and phase separation. The pH of any water or aqueous solution used may be adjusted as necessary for the specific recycling task. Thus, in step (b) of the present invention, the liquid phase may be treated in a base such as an alkali metal hydroxide solution, for example aqueous sodium hydroxide solution for a period of time before extraction, and then extracted with an organic solvent. The concentration of the aqueous sodium hydroxide solution is not specially defined, preferably 1-10 mol / L. The treatment may be stirring in the aqueous sodium hydroxide solution for a period of time, preferably 2 to 10 hours, more preferably 4 to 8 hours. This basic treatment facilitates recovery of the polyol, but it is not strictly necessary. The organic solvent for extraction preferably comprises halogenated organic solvents, in particular dichloromethane (DCM) and / or chloroform.

[0204] In step (c) of the present invention, the collected organic phase comprises a polyol. The collected aqueous phase comprises isocyanate recovery products, i.e. derivatives / conversion products of isocyanate monomers and polymers, or isocyanate-derived moieties and fragments, etc. It may be processed further to yield or isolate the corresponding amines.

[0205] In a preferred embodiment of the present invention, the method for degradation and recycling comprises the following steps: (1) degrading the polyurethane by light irradiation in a solvent in the presence of a photocatalyst under the atmosphere of oxygen or oxygen-containing gas, wherein the photocatalyst comprises one or more of the compounds of Formulae 1 to 15 and Formulae 18 to 21; (2) post-treating as follows: (a) solid / liquid phase separation, (b) extraction of the liquid phase, (c) collection of the organic phase and the aqueous phase respectively, wherein the organic phase comprises a recovered polyol.

[0206] In yet another embodiment of the present invention, the method for degradation and recovery comprises the following steps: (1) degrading the polyurethane by light irradiation in a solvent in the presence of a photocatalyst under the atmosphere of oxygen or oxygen-containing gas, wherein the photocatalyst comprises aromatic ketones as shown in Formula 2' and Formula 2", aromatic ketones as shown in Formula 3', benzanthrone, benzophenone, benzil, phenanthraquinones as shown in Formula 6', anthraquinones as shown in Formula 7, p-benzoquinones as shown in Formula 8' and Formula 8", anthraquinones as shown in Formula 9', 1,2-benzanthraquinone, anthracenes as shown in Formula 10', fused ring compounds containing two naphthyl groups as shown in Formulae 11 and 12, compounds as shown in Formula 13, aryl-substituted pyryliums as shown in Formula 14, xanthenes as shown in Formula 15, thiochrome and methylene blue, wherein the definitions of Rn- R46 and X are identical to those given for Scheme 6; (2) post-treating as follows: (a) solid / liquid phase separation, (b) extraction of the liquid phase, (c) collection of the organic phase and the aqueous phase respectively, wherein the organic phase comprises a recovered polyol.

[0207] By the method for degradation and recovery of the present invention, the amount of non-degraded solid residue is very low of only 0-5%, and the recovery rate of polyols may be up to 90% or more.

[0208] The present invention also provides a polyurethane recovery product obtained by the method for degradation and recovery of polyurethane, wherein the recovery product comprises a polyol, and may also comprise isocyanate recovery products.

[0209] Beneficial effects

[0210] The existing methods for polyurethane degradation are chemical degradation methods, which have to be carried out under strict conditions of high temperature and high pressure, and cannot be applied industrially. In the present invention, the nitrogen functional groups of polyurethane (such as the aliphatic functional group of HD1, the aromatic functional group of TD1, and the aromatic functional group of MD1, etc.) can be selectively activated by photo-induced single electron transfer, and photocatalysts particularly effective for polyurethane are selected, so that the carbamate can be easily decomposed under mild conditions, and polyols are recovered and can be directly used for subsequent applications. By the method for degradation and recovery of the present invention, the amount of non-degraded solid residue is very low of only 0-5%, and the recovery rate of polyols may be up to 90% or more.

[0211] Examples

[0212] The present invention is further described in combination with specific examples. However, it should be understood that these examples are only used to illustrate the present invention and do not limit the scope of the present invention.

[0213] The test methods without indicating of specific conditions in the following examples are usually carried out according to the conventional conditions or the conditions recommended by the manufacturers. Unless stated otherwise, all percentages and parts are by weight.

[0214] Materials, instruments and test methods

[0215] Description of test methods:

[0216] Recovery rate of polyol = mass of recovered polyol mixture / mass of polyol component in polyurethane x 100%

[0217] Conversion rate = (mass of polyurethane - mass of solid residue) / mass of polyurethane x 100%

[0218] Test methods for number average molecular weight Mn and dispersity PD1: gel permeation chromatography (GPC) was used to determine the molecular weight distribution (Mn) and the dispersity of polyols. The measurement was carried out with Waters 1515 gel permeation chromatograph having three columns in series (Waters Styragel HR2, HR4 and HR6) and using ImL / min DMF as eluent at 25°C, and equipped with Waters 2414 differential refractive detector.

[0219] 1[ I NMR is tested with 400M NMR Bruker Avance NEO 400.

[0220] Description of raw materials:

[0221] 4,4'-Methylene diphenyl diisocyanate was available from Adamas Reagent Co., Ltd.

[0222] N,N-dimethylformamide was available from Beijing J&K Scientific.

[0223] Butanediol was available from Anhui Zesheng Technology Co., Ltd.

[0224] Methanol was available from Sinopharm Group Co. Ltd.

[0225] 2.4.6-triisopropylbenzoic acid LI (CAS 49623-71-4) was available from Alfa Aesar (China) Chemical Co., Ltd.

[0226] 2.6-bis(trifluoromethyl)benzoic acid L2 (CAS 24821-22-5) was available from Alfa Aesar (China) Chemical Co., Ltd.

[0227] 2.4.6-tricyclohexylbenzoic acid L3 (CAS 1839076-17-3) was prepared according to the following method:

[0228] A 100 mL two-neck flask was baked and the air was replaced with argon, so that it was under the argon atmosphere. At -40°C, cyclohexyl bromide (80 mmol) and benzene (20 mmol) were mixed, and aluminum trichloride (40 mmol) was gradually added through a solid feeder. After the reaction was completed according to TLC detection, water and ethyl acetate were added for extraction and liquid separation. The organic phase was washed with saturated sodium chloride solution, and dried over anhydrous sodium sulfate. The crude intermediate a was obtained by removing ethyl acetate with a rotary evaporator and was directly used for the next reaction.

[0229] A 500 mL flask was baked and the air was replaced with argon, so that it was under the argon atmosphere. Acetonitrile (100 mL) solution of the intermediate a was added to the flask at 0°C, and acetonitrile (100 mL) solution of NBS (20 mmol) was added dropwise slowly to the flask. It was warmed to room temperature and stirred for 2 hours. After the reaction was completed according to TLC detection, water and ethyl acetate were added for extraction and liquid separation. The organic phase was washed with saturated sodium chloride solution, and dried over anhydrous sodium sulfate. The intermediate b (6.03 g, 74.9%) was obtained by separating in column with pure petroleum ether.

[0230] A 500 mL flask was baked and the air was replaced with argon, so that it was under the argon atmosphere. Tetrahydro furan THF (100 mL) solution of the intermediate b was added to the flask at -78°C, and N-butyl lithium (23 mmol) was added dropwise slowly to the flask. It was stirred for 2 hours. Dry ice was added slowly, and it was stirred for 1 hour. After the reaction was completed according to TLC detection, water and ethyl acetate were added for extraction and liquid separation. The organic phase was washed with saturated sodium chloride solution, and dried over anhydrous sodium sulfate. The final product (4.12 g, 73.9%) was obtained by separating in column with pure ethyl acetate EA.

[0231] 2-methyl-6-trimethylsilylbenzoic acid L4 (CAS 1821231-94-0) was prepared according to the method described by Yasushi Tsuji, et al. in J. Org. Chem. 2015, 80, 11618 - 11623.

[0232] Polyurethane flexible foam FFSL-3210 was available from Covestro, wherein the number average molecular weight of polyether polyol was about 3100, the polyol content was about 60.22% by weight, and the TD1 content was about 39% by weight.

[0233] Polyurethane rigid foam FFSL-CERF02 was available from Covestro, wherein the number average molecular weight of polyether polyol was about 500, the polyol content was about 36.23% by weight, and the MD1 content was about 60% by weight.

[0234] The sources of photocatalysts 1-47 are shown in the following table:

[0235] Polyurethane samples 5-042-3000, 5-046-6000, 5-061-10000 were prepared as follows:

[0236] Polyurethane sample 5-042-3000: A mixture of 4,4'-methylene diphenyl diisocyanate (1 equivalent, 20 g) and 1 ,4-butanediol (1.063 equivalent) was heated to 80°C in N,N-dimethylformamide (DMF, 0.5M) with stirring. After 2.5 hours of reaction, methanol was added to form a white solid residue, which was filtered to give a white solid. It was washed 3 times with methanol (100 ml), until DMF was not detected by 'H NMR. The white solid was dried at 100°C for 12 hours to give a white powder of polyurethane (22 g) with Mn measured by GPC =33328, PD1=1.893, and polyol content: 26.4%.

[0237] Polyurethane samples 5-046-6000: A mixture of 4,4'-methylene diphenyl diisocyanate (1 equivalent, 20 g) and 1 ,4-butanediol (1.063 equivalent) was heated to 90°C in N,N-dimethylformamide (DMF, 0.6M) with stirring. After 3.5 hours of reaction, methanol was added to form a white solid residue, which was filtered to give a white solid. It was washed 3 times with methanol (100 ml), until DMF was not detected by 'H NMR. The white solid was dried at 100°C for 12 hours to give a white powder of polyurethane (21.5g) with Mn measured by GPC =51686, PD1=1.936, and polyol content: 26.4%.

[0238] Polyurethane samples 5-061-10000: A mixture of 4,4'-methylene diphenyl diisocyanate (1 equivalent, 20 g) and 1 ,4-butanediol (1.025 equivalent) was heated to 120°C in N,N-dimethylformamide (DMF, 0.8M) with stirring. After 3 hours of reaction, methanol was added to form a white solid residue, which was filtered to give a white solid. It was washed 3 times with methanol (100 ml), until DMF was not detected by 'H NMR. The white solid was dried at 100°C for 12 hours to give a white powder of polyurethane (20.8g) with Mn measured by GPC =86207, PD1=1.827, and polyol content: 26.4%. Example 1

[0239] The powder of Polyurethane 5-042-3000 (250mg) was dispersed in 40mL methanol solution to obtain a dispersion. The photocatalyst 1 (9-fluorenone) was added to the mixture in an amount of 1 % by weight of the polyurethane powder. The mixture was kept under the oxygen atmosphere (1 bar). After irradiating with a blue LED lamp (wavelength of 400 nm to 500 nm) at 25°C for 6 hours, the reaction mixture was filtered, and the solid was washed with methanol, and dried at 100°C for 12 hours to obtain 20.2 mg of solid residue, with a conversion rate of 91.9%. The filtrate was continuously stirred in aqueous sodium hydroxide solution (3M, 10ml) for 4 hours. The mixture was extracted with DCM (40ml) for 3 times, and then washed with distilled water. The organic phase was collected and rotary evaporated to obtain 52.9mg of yellow liquid with a recovery rate of 86%. *H NMR analysis of the yellow liquid indicated that it was a polyol mixture. *H NMR (DMSO-de, 400 MHz): 5 4.36(t, 2H), 3.41-3.35 (m, 4H), 1.46-1.39 (m, 4H).

[0240] Example 2

[0241] The powder of Polyurethane 5-046-6000 was degraded according to the method in Example 1. The results are shown in Table 1.

[0242] Example 3

[0243] The powder of Polyurethane 5-061-10000 was degraded according to the method in Example 1. The results are shown in Table 1.

[0244] Table 1

[0245] Example 4-7

[0246] The powder of Polyurethane 5-061-10000 was degraded according to the method in Example 3. The amount of photocatalyst was of 0.5% by weight, 2% by weight, 3% by weight and 5% by weight respectively, relative to the mass of polyurethane powder. Other conditions remained unchanged. The results are shown in Table 2. Table 2

[0247] Example 8

[0248] The powder of Polyurethane 5-061-10000 was degraded according to the method in Example 3. The gas introduced was air (1 bar), and other conditions remained unchanged. The results are shown in Table 3.

[0249] Table 3

[0250] Examples 9-12

[0251] The powder of Polyurethane 5-061-10000 was degraded according to the method in Example 3. The polyurethane powder was dispersed in ethanol and water. The gas introduced was air (1 bar). Other conditions remained unchanged. The results are shown in Table 4.

[0252] Table 4 Examples 13-16

[0253] The powder of Polyurethane 5-061-10000 was degraded according to the method in Example 3. LEDs of 360nm, 390nm, 400nm and 450nm were used as light sources respectively. Other conditions remained unchanged. The results are shown in Table 5.

[0254] Table 5

[0255] Examples 17-19

[0256] The powder of Polyurethane 5-061-10000 was degraded according to the method in Example 3. The irradiation was conducted at 10°C, 35°C and 50°C respectively. Other conditions remained unchanged. The results are shown in Table 6.

[0257] Table 6 Example 20

[0258] The powder of Polyurethane 5-061-10000 was degraded without catalyst and with photocatalysts 1- 47 according to the method in Example 3. The effect of photocatalysts was evaluated. Other conditions remained unchanged. The results are shown in Table 7. Table 7

[0259] Example 21

[0260] The polyurethane flexible foam FFSL-3210 was ground into powder (250mg) and dispersed in 40mL methanol solution to obtain a dispersion. No catalyst and photocatalysts 1-47 (each 0.0025g) were added to the mixture respectively. Under the oxygen atmosphere, after irradiating with a blue LED lamp (wavelength of 400 nm to 500 nm) at 25°C for 4 hours, the reaction mixture was filtered. The filtered solid residue was washed with methanol, and dried at 100°C for 12 hours. The filtrate was treated with aqueous sodium hydroxide solution (3M, 10ml) and stirred for 4 hours. The mixture was extracted with DCM (40ml) for three times and then washed with distilled water. The organic phase was collected and concentrated to obtain a yellow liquid, i.e. a polyol mixture. The data of degradation effect are shown in Table 8. Table 8

[0261] Example 22

[0262] The polyurethane rigid foam FFSL-CERF02 was ground into powder (0.5g) and dispersed in a mixed solution of 20 rnL methanol and 20 mL acetone to obtain a dispersion. Photocatalyst 3 (0.005g) was added to the mixture respectively. In oxygen atmosphere, after irradiating with a blue LED lamp (wavelength of 400 nm to 500 nm) at 25°C for 8 hours, the reaction mixture was filtered. The filtered solid residue (83.7mg) was washed with methanol, and dried at 100°C for 12 hours. The filtrate was treated with aqueous sodium hydroxide solution (3M, 10ml) and stirred for 4 hours. The mixture was extracted with DCM (40ml) for three times and then washed with distilled water. The organic phase was collected and concentrated to obtain a yellow liquid, i.e. a polyol mixture (110.6 mg, recovery rate of 61%).

[0263] Example 23

[0264] The powder of Polyurethane 5-061-10000 was degraded with photocatalyst 32 according to the method in Example 3. The time for irradiation was 12 hours. Other conditions remained unchanged. The solid residue was of 67.5 mg, and the polyol mixture was of 45.7 mg, with a recovery rate of 69%.

[0265] It can be seen from the above data that the method for degradation and recovery of the present invention has good effect on the degradation of polyurethane powder, polyurethane rigid foam and flexible foam. The recovery rate of polyols may be up to 50% or even more. The degradation may be carried out under mild conditions without high pressure and high temperature. Good effect on degradation and recovery can be achieved at a range of 10-50°C.

[0266] The photocatalysts 1 to 45 in the present invention have very good effect on the photodegradation of polyurethane. Compared with the reaction without catalyst, the catalysts 46 and 47 in the comparative examples have certain effect on the reaction, which is, however, far inferior to the catalysts selected in the present invention. In addition, the prolonged irradiation time has good effect on improving the recovery effect of the selected catalysts. Thus, it is proved that the catalysts of the present invention can achieve good degradation effect.

Claims

Claims:

1. A method for degrading and recycling a polyurethane, comprising the following step: degrading the polyurethane by light irradiation with visible light and / or ultraviolet light in the presence of a photocatalyst under an oxygen-containing condition, wherein the photocatalyst comprises one or more of a noble metal photocatalyst of Formula 1, aromatic ketones, anthracenes, fused ring compounds containing at least two naphthyl groups, aryl-substituted pyryliums, xanthenes, cerium- containing compounds selected from the group consisting of organic salts and inorganic salts containing cerium(lll) or cerium(lV), thiochrome, methylene blue and 2, 4,5,6- tetrakis(diphenylamino)-isophthalonitrile;Formula 1 wherein,R1 is selected from ruthenium and iridium,R2 and R10 are each independently selected from hydrogen and nitrogen,R3, Rs, R6, R7, Rs and R9 are each independently selected from hydrogen, C1-4 alkyls and halogens, preferably selected from hydrogen, methyl, ethyl, fluorine, chlorine and bromine, more preferably selected from hydrogen, methyl and fluorine,R4 is selected from hydrogen and C1-4 haloalkyls, preferably selected from hydrogen and halomethyls, more preferably trifluoromethyl -CF3, n is an integer of 1-2.

2. The method according to claim 1, characterized in that the aromatic ketones comprise quinones, wherein the quinones include phenanthraquinones, anthraquinones, benzoquinones, naphthoquinones, acenaphthoquinones, and mixtures thereof; and / or, the fused ring compounds containing at least two naphthyl groups include perylenes and naphthacenes; and / or, at least one carbon atom in the pyran ring of the aryl-substituted pyryliums is replaced by aromatics, preferably three carbon atoms are replaced by aromatics.

3. The method according to claim 1 or 2, characterized in that the aromatic ketones comprise one or more compounds as shown in Formulae 2, 3, 4 and 5,Formula 2 Formula 3 Formula 4 Formula 5 wherein, in Formula 2, Rn and Rn are each independently selected from hydrogen, halogens, nitro, hydroxyl, Ce-18 aryls, C7-12 alkaryls, C7-12 aralkyls and C6-18 fused aryls, wherein the fused aryl preferably forms a ring structure with the two carbon atoms shown as a and b in Formula 2, or in Formula 3, RB is selected from carbon, oxygen and sulfur, and RM is selected from hydrogen, C1- 4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls and C6-18 fused aryls, wherein the fused aryl preferably forms a ring structure with the three carbon atoms shown as a, b and c in Formula 3, or in Formula 4, R15 and RM are each independently selected from hydrogen, amino and C1-4 alkyl- substituted amino; and / or the quinones comprise one or more compounds as shown in Formulae 6, 7, 8 and 9,wherein, in Formula 6 or 7, Rn, Ris, R19 and R20 are each independently selected from hydrogen, halogens and C1-4 alkyls, or in Formula 8, R21 and R22 are each independently selected from hydrogen, halogens, C1-4 alkyls, and C6-18 fused aryls, wherein the fused aryl preferably forms a ring structure with the two carbon atoms shown as b and c in Formula 8, or in Formula 9, R23 and R24 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6- 18 aryls, C7-12 alkaryls, C7-12 aralkyls and C6-18 fused aryls, wherein the fused aryl preferably forms a ring structure with the two carbon atoms shown as a and b in Formula 9; and / orthe anthracenes thereof comprise a compound as shown in Formula 10,Formula 10 wherein,R25 and R26 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls, C6-18 fused aryls, cyano and C1-4 acyls; and / or the fused ring compounds containing at least two naphthyl groups comprise compounds as shown in Formulae 11, 12 and 13,Formula 11 Formula 12 Formula 13 wherein, in Formula 11, R27, R28, R29 and R30 are each independently selected from hydrogen, halogens, C1-4 alkyls, Ce-18 aryls, C7-12 alkaryls and C7-12 aralkyls, or in Formula 12, R31, R32, R33 and R34 are each independently selected from hydrogen, halogens, C1-4 alkyls, C6-18 aryls, C7-12 alkaryls, C7-12 aralkyls and hydrogenated naphthalenones (1-tetralones); and / or, the aryl-substituted pyryliums include a compound as shown in Formula 14,Formula 14 wherein,R35, R36 and R37 are each independently selected from C6-12 aryls, C6-12 haloaryls, C7-13 alkaryls and C7- 13 alkoxy-substituted aryls, and X is a substituted or unsubstituted sulfonate or borate, more preferably an unsubstituted sulfonate or haloborate; and / or, the xanthenes and include preferably a compound as shown in Formula 15,Formula 15 Formula 16 Formula 17 wherein,R ix and R39 are each independently selected from hydrogen, C1-4 alkyls, a group as shown in Formula16, or R39 and Rxx form a ring as shown in Formula 17,R40 and R41 are each independently selected from diphenylphosphino, C1-4 alkyls and halogens,R42 and R45 are each independently selected from hydrogen, hydroxyl, C1-4 alkyls and halogens,R43 and R44 are each independently selected from hydrogen, C1-4 alkyls and halogens,R46 is selected from halogens; and / or, the cerium-containing compounds comprise one or more of ceric ammonium nitrate, cerium chloride and cerium trifluoromethanesulfonate.

4. The method according to any one of claims 1 to 3, characterized in that the amount of the photocatalyst is 0.5% by weight or more, preferably 0.5 to 10% by weight, more preferably 0.5 to 5% by weight, calculated as mass percentage relative to the mass of polyurethane.

5. The method according to any one of claims 1 to 4, characterized in that the oxygen-containing condition refers to the introduction of oxygen, oxygen-containing gas mixtures or liquids that can release oxygen, preferably the introduction of oxygen or oxygen-containing gas mixtures at 1 atm to 3 atm (1.013 bar to 3.040 bar).

6. The method according to any one of claims 1 to 5, characterized in that the light irradiation is carried out by means of ultraviolet A and / or visible light, and preferably by means of a light source with a wavelength of 330 nm to 500 nm, preferably 360 nm to 500 nm.

7. The method according to any one of claims 1 to 6, characterized in that the degradation is carried out at a temperature of 0°C to 115°C, preferably 0°C to 80°C, more preferably 10°C to 50°C, most preferably 15°C to 25°C.

8. The method according to any one of claims 1 to 7, characterized in that the degradation is carried out in one or more of monohydric alcohols, water, acetone and ethyl acetate, preferably methanol, ethanol and acetone.

9. The method according to any one of claims 1 to 8, further comprising the following steps to be carried out after the degrading of the polyurethane: (a) removing any solids by solid / liquid phase separation to obtain a solid phase and a liquid phase, (b) extraction of the liquid phase to obtain an organic phase and an aqueous phase, and (c) collection of the organic phase and the aqueous phase respectively, wherein the organic phase comprises a recovered polyol.

10. The method according to claim 9, wherein the aqueous phase is processed further to obtain an amine.

11. A polyurethane recovery product obtained by the method according to any one of claims 1 to 10, characterized in that the recovery product comprises a polyol.

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