Liquid polymer, mixture of liquid polymer and recycled carbon black, and method for recovering diene-based monomer

Abstract

The present invention addresses the problem of providing a liquid polymer obtained by the decomposition of a crosslinked rubber and capable of obtaining a diene-based monomer in a high yield. The solution is a liquid polymer obtained by the decomposition of a crosslinked rubber containing a diene-based rubber, and is characterized in that the weight-average molecular weight is 500 to 300,000, and the retention rate of a diene-based monomer skeleton of the diene-based rubber in the crosslinked rubber is 30 mass% or more with respect to the mass of the diene-based monomer skeleton before the decomposition. The diene-based monomer skeleton of the diene-based rubber is preferably at least one skeleton selected from the group consisting of an isoprene skeleton and a butadiene skeleton.

Description

Liquid polymer, mixture of liquid polymer and recycled carbon black, and method for recovering diene monomer

[0001] The present invention relates to a liquid polymer, a mixture of a liquid polymer and recycled carbon black, and a method for recovering a diene monomer.

[0002] Conventionally, rubber products primarily made of cross-linked rubber such as vulcanized rubber have been difficult to reuse, and after the end of their product life, they have often been reused as fuel, particularly in cement factories. However, with the recent rise in environmental concerns, there has been a demand for the development of methods for recycling materials obtained by decomposing rubber products, rather than burning them as fuel. There are various methods for decomposing cross-linked rubber. For example, Patent Document 1 listed below discloses the thermal decomposition of organic materials such as used tires at 550 to 800°C, and further discloses the incorporation of carbon black obtained by thermal decomposition into a rubber mixture as a filler.

[0003] EP 3427975

[0004] Generally, rubber products made of crosslinked rubber use a rubber composition in which a filler such as carbon black is blended with a diene rubber, and therefore, by decomposing the crosslinked rubber, carbon black can be recovered as described in the above-mentioned Patent Document 1. The present inventors have also found that by selecting the decomposition conditions of the crosslinked rubber, constituent monomers and oligomers (liquid polymers) of the diene rubber can be obtained in addition to carbon black.

[0005] However, the liquid polymers obtained by the present inventors so far have not been able to sufficiently maintain the skeleton of the constituent monomers of the diene rubber, and there is a problem in that the diene monomer cannot be obtained from the liquid polymer in a sufficient yield.

[0006] Therefore, an object of the present invention is to provide a liquid polymer that can be obtained by decomposing crosslinked rubber and that can produce a diene monomer in high yield. Another object of the present invention is to provide a mixture of such a liquid polymer and recycled carbon black, and a method for recovering the diene monomer.

[0007] The liquid polymer, the mixture of the liquid polymer and recycled carbon black, and the method for recovering diene monomers of the present invention, which solve the above problems, are outlined as follows.

[0008] [1] A liquid polymer obtained by decomposition of a crosslinked rubber containing a diene rubber, the liquid polymer having a weight average molecular weight of 500 to 300,000, and characterized in that the retention rate of the diene monomer skeleton of the diene rubber in the crosslinked rubber before the decomposition is 30 mass% or more.

[0009] [2] The liquid polymer according to [1], wherein the diene-based monomer skeleton of the diene-based rubber is at least one selected from the group consisting of an isoprene skeleton and a butadiene skeleton.

[0010] [3] The liquid polymer according to [1] or [2], wherein the crosslinked rubber contains a diene rubber containing an isoprene skeleton, and the retention rate of the isoprene skeleton is 30 mass% or more relative to the mass of the isoprene skeleton of the diene rubber in the crosslinked rubber before decomposition.

[0011] [4] The liquid polymer according to any one of [1] to [3], wherein the crosslinked rubber contains a diene rubber containing a butadiene skeleton, and the retention rate of the butadiene skeleton is 30 mass% or more relative to the mass of the butadiene skeleton of the diene rubber in the crosslinked rubber before decomposition.

[0012] [5] The liquid polymer according to any one of [1] to [4], wherein the retention rate of the diene monomer skeleton is 50 mass% or more relative to the mass of the diene monomer skeleton of the diene rubber in the crosslinked rubber before decomposition.

[0013] [6] The liquid polymer according to any one of [1] to [5], wherein the retention rate of the diene monomer skeleton is 70 mass% or more relative to the mass of the diene monomer skeleton of the diene rubber in the crosslinked rubber before decomposition.

[0014] [7] The liquid polymer according to any one of [1] to [6], wherein the crosslinked rubber is a sulfur crosslinked rubber.

[0015] [8] A mixture of a liquid polymer and recycled carbon black obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black, wherein the liquid polymer is the liquid polymer described in any one of [1] to [7].

[0016] [9] A mixture of a liquid polymer and recycled carbon black obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black, wherein the liquid polymer is obtained by removing part or all of the components having a molecular weight of 5,000 or less from the liquid polymer according to any one of [1] to [7], and the proportion of components having a molecular weight of 15,000 or less is 30 mass % or less.

[0017]

[10] A method for recovering a diene monomer, comprising pyrolyzing the liquid polymer according to any one of [1] to [7] at 300 to 950°C in an inert gas atmosphere and in the presence of a catalyst.

[0018]

[11] A method for recovering a diene monomer, comprising thermally decomposing the liquid polymer according to any one of [1] to [7] at 300 to 450°C in an inert gas atmosphere and in the absence of a catalyst.

[0019]

[12] A method for recovering a diene monomer, comprising pyrolyzing the liquid polymer according to any one of [1] to [7] at 600 to 950°C in an inert gas atmosphere and in the absence of a catalyst.

[0020] The present invention provides a liquid polymer that can be obtained by decomposing a crosslinked rubber and that can produce a diene monomer in high yield. The present invention also provides a mixture of the liquid polymer and recycled carbon black, and a method for recovering the diene monomer.

[0021] The liquid polymer, the mixture of the liquid polymer and the recycled carbon black, and the method for recovering a diene monomer of the present invention will be described in detail below with reference to the embodiments.

[0022] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0023] <Liquid Polymer> The liquid polymer of the present embodiment is a liquid polymer obtained by decomposition of a crosslinked rubber containing a diene rubber, and is characterized in that the weight average molecular weight is 500 to 300,000, and the retention rate of the diene monomer skeleton is 30 mass% or more relative to the mass of the diene monomer skeleton of the diene rubber in the crosslinked rubber before the decomposition.

[0024] The liquid polymer of this embodiment has a sufficiently low molecular weight, with a weight average molecular weight of 500 to 300,000, and the retention rate of the diene monomer skeleton of the diene rubber in the crosslinked rubber before decomposition is 30 mass% or more, so that by further decomposing the liquid polymer, diene monomers can be obtained in high yield. Here, in this specification, the liquid polymer refers to one that is liquid at room temperature (23°C) and contains two or more diene monomer units.

[0025] (Crosslinked Rubber) The liquid polymer of the present embodiment is obtained by decomposition of a crosslinked rubber, and the crosslinked rubber contains a diene rubber and may further contain carbon black or the like.

[0026] The crosslinked rubber to be used for decomposition may be grouped according to the type of diene rubber previously compounded, and then the decomposition step may be carried out for each group. Alternatively, the crosslinked rubber may be grouped according to the type of filler previously compounded (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then the decomposition step may be carried out for each group. Furthermore, the crosslinked rubber may be grouped according to both the type of diene rubber and the type of filler, and then the decomposition step may be carried out for each group. When the decomposition step is carried out for each group in this way, liquid polymers, recycled carbon black, regenerated silica, etc. having more uniform physical properties can be obtained, and therefore, when compounded again into a rubber composition, a rubber composition with better performance can be obtained.

[0027] Furthermore, when the crosslinked rubber used for degradation is derived from tires, the tires may be grouped in advance by type (e.g., for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and then the decomposition process may be carried out for each group. Alternatively, the tires may be grouped in advance by tire component (e.g., tread rubber, sidewall rubber, bead rubber, steel cord-coated rubber, organic fiber-coated rubber, pad rubber, cushion rubber, etc.), and then the decomposition process may be carried out for each group. Furthermore, the tires may be grouped both by type and by tire component, and then the decomposition process may be carried out for each group. When the decomposition process is carried out for each group in this way, a liquid polymer or recycled carbon black having more uniform physical properties can be obtained, and therefore, when blended again into a rubber composition, a rubber composition with better performance can be obtained.

[0028] The form of the crosslinked rubber is not particularly limited, and may be, for example, powdered rubber. The powdered rubber can be obtained by cutting and pulverizing used rubber products such as scrap tires. The pulverization step may include multiple steps such as a preliminary pulverization step and a fine pulverization step, and the particle size of the powdered rubber to be used may be adjusted by a classification step after the pulverization step.

[0029] The crosslinked rubber may be recycled waste rubber, used rubber products, etc. Waste rubber refers not only to rubber generated from rubber products, but also to all discarded rubber, including unnecessary scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process of scraping off the tread portion remaining on the base tire, for example, during tire retreading. Peeled rubber is a long piece of rubber, for example, 1 to 2 cm wide, peeled off from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Rubber products include, for example, final products such as tires, rubber hoses, and rubber conveyor belts, as well as rubber parts or components used in the manufacturing process of final products. Used tires may be, for example, tires to be retreaded, or may be tires discarded for some reason, such as waste tires generated as a result of tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their life as tires.

[0030] The crosslinked rubber is preferably a sulfur-crosslinked rubber, which is easily available and from which a liquid polymer made from the sulfur-crosslinked rubber can be further decomposed to obtain a diene monomer in a higher yield.

[0031] -Diene-Based Rubber- The diene-based rubber is a rubber containing units derived from a diene-based monomer (diene-based units) and may further contain units derived from a copolymerizable comonomer. The units derived from the diene-based monomer enable the diene-based rubber to be crosslinked (vulcanized) and to exhibit rubber-like elongation and strength. Note that, although the diene-based rubber is usually present in a crosslinked state in the crosslinked rubber, a portion of it may not be crosslinked. Specific examples of diene-based monomers (diene-based compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc., and among these, 1,3-butadiene and isoprene are preferred, with isoprene being particularly preferred. On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds, etc. Specific examples of the aromatic vinyl compound include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene.

[0032] Examples of the diene rubber include isoprene-skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). Here, the isoprene-skeleton rubber is a rubber whose main skeleton is an isoprene unit, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). Among these, the diene rubber preferably includes at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber, with isoprene-skeleton rubber being particularly preferred. When the diene rubber includes at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber, decomposition of the crosslinked rubber produces a liquid polymer containing easily recyclable diene monomers, such as isoprene or butadiene, in its skeleton, along with recycled carbon black.

[0033] Furthermore, when the crosslinked rubber contains an isoprene skeleton rubber and a butadiene rubber as diene-based rubbers, the proportion of the butadiene rubber in the total amount of the isoprene skeleton rubber and the butadiene rubber is preferably 50% by mass or less. When the proportion of the butadiene rubber in the total amount of the isoprene skeleton rubber and the butadiene rubber is 50% by mass or less, gelation can be suppressed during decomposition, and a decomposition product (liquid polymer) with a high retention rate of the isoprene skeleton can be obtained. Note that when the crosslinked rubber contains a butadiene rubber as a diene-based rubber, particularly when the proportion of the butadiene rubber in the diene-based rubber exceeds 50% by mass, it is preferable to prevent re-crosslinking by using an antioxidant, a decomposition accelerator, or the like.

[0034] The content of the diene rubber in the crosslinked rubber is not particularly limited, and is preferably, for example, in the range of 10 to 100 mass %, and more preferably in the range of 30 to 100 mass % from the viewpoint of further improving the yield of a liquid polymer containing a diene monomer in the skeleton, and of butadiene and isoprene.

[0035] -Carbon Black- The crosslinked rubber may further contain carbon black. The carbon black is not particularly limited, and examples of carbon black grades include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. The carbon black content in the crosslinked rubber is not particularly limited, and is, for example, in the range of 10 to 150 parts by mass, preferably 30 to 120 parts by mass, per 100 parts by mass of the diene rubber. The carbon black content in the crosslinked rubber is preferably 20% by mass or more, more preferably 30% by mass or more, and is preferably 40% by mass or less, and even more preferably 35% by mass or less. When the carbon black content in the crosslinked rubber is 20% by mass or more, a larger amount of carbon black can be recovered.

[0036] -Sulfur- As described above, the crosslinked rubber is preferably a sulfur-crosslinked rubber, that is, the crosslinked rubber preferably contains sulfur. In the sulfur-crosslinked rubber, sulfur is usually present in a state in which the diene rubber is crosslinked (as a crosslink for the diene rubber), but a portion of the sulfur may be free. The content of sulfur in the crosslinked rubber is not particularly limited, and is, for example, in the range of 0.1 to 10 parts by mass, preferably 1 to 5 parts by mass, per 100 parts by mass of the diene rubber.

[0037] -Other Components- In addition to the diene rubber, carbon black, and sulfur described above, the crosslinked rubber may contain various components commonly used in the rubber industry, such as rubber components other than diene rubbers, fillers other than carbon black (silica, calcium carbonate, etc.), silane coupling agents, antioxidants, softeners, processing aids, resins, surfactants, organic acids (stearic acid, etc.), zinc oxide (zinc white), vulcanization accelerators, crosslinking agents other than sulfur (peroxides, etc.), and the like.

[0038] (Weight-Average Molecular Weight) The liquid polymer of this embodiment has a weight-average molecular weight (Mw) of 500 to 300,000, preferably 1,000 to 250,000. If the weight-average molecular weight (Mw) is less than 500, decomposition will proceed too far, making it difficult to achieve a diene monomer skeleton retention rate of 30% by mass or more. On the other hand, if the weight-average molecular weight (Mw) exceeds 300,000, decomposition will not proceed sufficiently, and further decomposition will likely cause side reactions to occur when obtaining a diene monomer from the liquid polymer, resulting in a decrease in the yield of the diene monomer. In this specification, the weight-average molecular weight (Mw) is measured by gel permeation chromatography (GPC).

[0039] (Retention rate of diene monomer skeleton) In the liquid polymer of this embodiment, the retention rate of the diene monomer skeleton relative to the mass of the diene monomer skeleton of the diene rubber in the crosslinked rubber before decomposition is 30% by mass or more, preferably 50% by mass or more, and more preferably 70% by mass or more. When the retention rate of the diene monomer skeleton is 70% by mass or more, diene monomers can be obtained from the liquid polymer in high yield by further decomposition. In this specification, the retention rate of the diene monomer skeleton (isoprene skeleton, butadiene skeleton, etc.) is １ Measured by H-NMR.

[0040] The diene monomer skeleton of the diene rubber is preferably at least one selected from the group consisting of an isoprene skeleton and a butadiene skeleton. From the liquid polymer having a high retention rate of the isoprene skeleton and / or butadiene skeleton, easily recyclable diene monomers such as isoprene and butadiene can be obtained in high yields by further decomposition.

[0041] When the crosslinked rubber contains a diene rubber containing an isoprene skeleton, the retention rate of the isoprene skeleton is preferably 30 mass% or more relative to the mass of the isoprene skeleton of the diene rubber in the crosslinked rubber before decomposition. From a liquid polymer with a high retention rate of the isoprene skeleton, isoprene that can be easily reused as a monomer can be obtained in high yield by further decomposition.

[0042] When the crosslinked rubber contains a diene rubber containing a butadiene skeleton, the retention rate of the butadiene skeleton is preferably 30 mass% or more relative to the mass of the butadiene skeleton of the diene rubber in the crosslinked rubber before decomposition. From the liquid polymer with a high retention rate of the butadiene skeleton, butadiene that can be easily reused as a monomer can be obtained in high yield by further decomposition.

[0043] (Method for Producing Liquid Polymer) The method for producing the liquid polymer of this embodiment is not particularly limited, but can be obtained, for example, by decomposing a crosslinked rubber, such as by: (i) a method for decomposing a crosslinked rubber using a metathesis catalyst (first decomposition method); (ii) a method for thermally decomposing a crosslinked rubber at 150°C or higher and 400°C or lower (second decomposition method); (iii) a method for decomposing a crosslinked rubber in a solvent (third decomposition method); or (iv) a method for decomposing a crosslinked rubber using a radical initiator (fourth decomposition method). These first, second, third, and fourth decomposition methods involve decomposition at lower temperatures than conventional high-temperature thermal decomposition of crosslinked rubber, thereby suppressing gasification and aromatization of the decomposition products. Furthermore, compared to conventional high-temperature thermal decomposition, liquid polymers can be obtained that retain a higher percentage of the skeletons (isoprene skeletons, butadiene skeletons, etc.) of the constituent monomers of the diene rubber. The first, second, third, and fourth decomposition methods are described in detail below.

[0044] -First Decomposition Method (Metathesis Decomposition)- In the first decomposition method, the crosslinked rubber is decomposed using a metathesis catalyst. Here, the metathesis catalyst is a compound represented by the following general formula (1), (2), or (3): The catalysts represented by the general formula (1), (2) or (3) are excellent in promoting metathesis decomposition, and can decompose diene rubbers simply (under mild conditions) and quickly.

[0045] In the above general formulas (1), (2), and (3), M is ruthenium (Ru), titanium (Ti), molybdenum (Mo), or tungsten (W). Among these, ruthenium is preferred as M from the viewpoint of promoting the decomposition reaction of the diene rubber in the crosslinked rubber.

[0046] In the above general formulas (1) and (2), X １ and X ２ Each independently represents a ligand, and is preferably an anionic ligand. １ and X ２Examples of the X include hydrogen, halogen, pseudohalogen, a linear or branched alkyl group having 1 to 30 carbon atoms, an aryl group having 6 to 24 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryloxy group having 6 to 24 carbon atoms, an alkyldiketonate having 3 to 20 carbon atoms, an aryldiketonate having 6 to 24 carbon atoms, a carboxylate having 1 to 20 carbon atoms, an alkylsulfonate having 1 to 20 carbon atoms, an arylsulfonate having 6 to 24 carbon atoms, an alkylthiol group having 1 to 20 carbon atoms, an arylthiol group having 6 to 24 carbon atoms, an alkylsulfonyl group having 1 to 20 carbon atoms, and an alkylsulfinyl group having 1 to 20 carbon atoms. １ and X ２ may be substituted with one or more further groups, for example, a halogen (preferably fluorine), an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or an aryl group having 6 to 24 carbon atoms, wherein these groups may also be further substituted with one or more substituents selected from the group consisting of a halogen (preferably fluorine), an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and a phenyl group. １ and X ２ are the same or different, and each is a halogen (particularly fluorine, chlorine, bromine or iodine), a benzoate, a carboxylate having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms, a phenoxy group, an alkoxy group having 1 to 5 carbon atoms, an alkylthiol group having 1 to 5 carbon atoms, an arylthiol group having 6 to 24 carbon atoms, an aryl group having 6 to 24 carbon atoms, or an alkylsulfonate having 1 to 5 carbon atoms. １ and X ２ are identical and each represents a halogen (especially chlorine), CF ３ COO, CH ３ COO, CFH ２ COO, (CH ３ ) ３ CO, (CF ３ ) ２ (CH ３ ) CO, (CF ３ ) (CH ３ ) ２CO, PhO (phenoxy), MeO (methoxy), EtO (ethoxy), tosylate (p-CH ３ -C ６ H ４ -SO ３ ), mesylate (2,4,6-trimethylphenyl) or CF ３ SO ３ (trifluoromethanesulfonate).

[0047] In the above general formulas (1), (2) and (3), L １ , L ２ and L ３ each independently represents a ligand, preferably a neutral (uncharged) electron donor (also called an "electron-donating neutral ligand"). １ , L ２ and L ３ can be, for example, independently of one another, a phosphine, sulfonated phosphine, phosphate, phosphinite, phosphonit, arsine, stibine, ether, amine, amide, aryloxy, sulfonate, sulfoxide, carboxyl, nitrosyl, pyridine, thioether or imidazolidine ligand. １ , L ２ and L ３are each independently an arylphosphine ligand having 6 to 24 carbon atoms, an alkylphosphine ligand having 1 to 10 carbon atoms or a cycloalkylphosphine ligand having 3 to 20 carbon atoms, a sulfonated arylphosphine ligand having 6 to 24 carbon atoms or a sulfonated alkylphosphine ligand having 1 to 10 carbon atoms, an aryl phosphinite ligand having 6 to 24 carbon atoms or an alkyl phosphinite ligand having 1 to 10 carbon atoms, an arylphosphonite ligand having 6 to 24 carbon atoms or an alkylphosphonite ligand having 1 to 10 carbon atoms, an aryl phosphite ligand having 6 to 24 carbon atoms or an alkyl phosphite ligand having 1 to 10 carbon atoms, an aryl arsine ligand having 6 to 24 carbon atoms or an alkyl phosph ... is preferably an alkylarsine ligand having 1 to 10 carbon atoms, an arylamine ligand having 6 to 24 carbon atoms or an alkylamine ligand having 1 to 10 carbon atoms, a pyridine ligand, an arylsulfoxide ligand having 6 to 24 carbon atoms or an alkylsulfoxide ligand having 1 to 10 carbon atoms, an arylether ligand having 6 to 24 carbon atoms or an alkylether ligand having 1 to 10 carbon atoms, or an arylamide ligand having 6 to 24 carbon atoms or an alkylamide ligand having 1 to 10 carbon atoms, each of which may be substituted with a phenyl group, and the phenyl group may also be optionally further substituted with a halogen, an alkyl group having 1 to 5 carbon atoms or an alkoxy group having 1 to 5 carbon atoms. The term "phosphine" includes, for example, PPh ３ , P(p-Tol) ３ , P(o-Tol) ３ , PPh(CH ３ ) ２ , P(CF ３ ) ３ , P(p-FC ６ H ４ ) ３ , P(p-CF ３ C ６ H ４ ) ３ , P(C ６ H ４ -SO ３ Na) ３ , P(CH ２ C ６ H ４ -SO ３ Na) ３ , P(isopropyl) ３ , P(CHCH ３ (CH２ CH ３ )) ３ , P(cyclopentyl) ３ , P (cyclohexyl) ３ , P (neopentyl) ３ and P(neophenyl) ３ The term "phosphinite" includes, for example, triphenyl phosphinite, tricyclohexyl phosphinite, triisopropyl phosphinite, and methyldiphenyl phosphite. The term "phosphite ester" includes, for example, triphenyl phosphite, tricyclohexyl phosphite, tri-tert-butyl phosphite, triisopropyl phosphite, and methyldiphenyl phosphite. The term "stibine" includes, for example, triphenylstibine, tricyclohexylstibine, and trimethylstibine. The term "aryloxy" includes, for example, 2-tert-butyl-4,5-dimethylphenyloxy. The term "sulfonate" includes, for example, trifluoromethanesulfonate, tosylate, and mesylate. The term "sulfoxide" includes, for example, (CH ３ ) ２ S(=O) and (C ６ H ５ ) ２ The term "thioether" includes, for example, CH ３ SCH ３ , C ６ H ５ SCH ３ , C.H. ３ OCH ２ CH ２ SCH ３and tetrahydrothiophene. The term "pyridine" includes, for example, pyridine, picolines (α-, β-, and γ-picoline), lutidines (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-lutidine), collidine (2,4,6-trimethylpyridine), trifluoromethylpyridine, phenylpyridine, 4-(dimethylamino)pyridine, chloropyridines, bromopyridines, nitropyridines, quinoline, pyrimidine, pyrrole, imidazole, and phenylimidazole. In the imidazolidine ligand, hydrogen atoms bonded to carbon atoms or nitrogen atoms constituting the imidazolidine ring may be substituted with a linear or branched alkyl group having 1 to 30 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aryl group having 6 to 24 carbon atoms, a carboxylate having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an alkenyloxy group having 2 to 20 carbon atoms, an alkynyloxy group having 2 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, an alkoxycarbonyl group having 2 to 20 carbon atoms, an alkylthio group having 1 to 20 carbon atoms, an arylthio group having 6 to 20 carbon atoms, an alkylsulfonyl group having 1 to 20 carbon atoms, an alkylsulfonate having 1 to 20 carbon atoms, an arylsulfonate having 6 to 20 carbon atoms, or an alkylsulfinyl group having 1 to 20 carbon atoms.

[0048] In the above general formulas (1), (2) and (3), R １ , R ２ and R ３each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, a carboxylate group, an alkoxy group, an alkenyloxy group, an alkynyloxy group, an aryloxy group, an alkoxycarbonyl group, an alkylamino group, an alkylthio group, an arylthio group, an alkylsulfonyl group, or an alkylsulfinyl group, wherein these groups are optionally substituted with one or more alkyl groups, halogens, alkoxy groups, aryl groups, or heteroaryl groups. Furthermore, the alkyl group is preferably an alkyl group having 1 to 30 carbon atoms, the cycloalkyl group is preferably a cycloalkyl group having 3 to 20 carbon atoms, the alkenyl group is preferably an alkenyl group having 2 to 20 carbon atoms, the alkynyl group is preferably an alkynyl group having 2 to 20 carbon atoms, the aryl group is preferably an aryl group having 6 to 24 carbon atoms, the aralkyl group is preferably an aralkyl group having 7 to 24 carbon atoms, the carboxylate group is preferably a carboxylate group having 1 to 20 carbon atoms, the alkoxy group is preferably an alkoxy group having 1 to 20 carbon atoms, and the alkenyloxy group is preferably an alkenyloxy group having 2 to 20 carbon atoms. As the alkynyloxy group, an alkynyloxy group having 2 to 20 carbon atoms is preferred, as the aryloxy group, an aryloxy group having 6 to 24 carbon atoms is preferred, as the alkoxycarbonyl group, an alkoxycarbonyl group having 2 to 20 carbon atoms is preferred, as the alkylamino group, an alkylamino group having 1 to 30 carbon atoms is preferred, as the alkylthio group, an alkylthio group having 1 to 30 carbon atoms is preferred, as the arylthio group, an arylthio group having 6 to 24 carbon atoms is preferred, as the alkylsulfonyl group, an alkylsulfonyl group having 1 to 20 carbon atoms is preferred, and as the alkylsulfinyl group, an alkylsulfinyl group having 1 to 20 carbon atoms is preferred. In one embodiment, R １ and R ２one of the groups is hydrogen, and the other is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 10 carbon atoms, alkenyl having 2 to 20 carbon atoms, alkynyl having 2 to 20 carbon atoms, aryl having 6 to 24 carbon atoms, aralkyl having 7 to 24 carbon atoms, carboxylate having 1 to 20 carbon atoms, alkoxy having 1 to 20 carbon atoms, alkenyloxy having 2 to 20 carbon atoms, alkynyloxy having 2 to 20 carbon atoms, aryloxy having 6 to 24 carbon atoms, alkoxycarbonyl having 2 to 20 carbon atoms, alkylamino having 1 to 30 carbon atoms, alkylthio having 1 to 30 carbon atoms, arylthio having 6 to 24 carbon atoms, alkylsulfonyl having 1 to 20 carbon atoms, or alkylsulfinyl having 1 to 20 carbon atoms, each of which is optionally substituted with one or more alkyl groups, halogens, alkoxy groups, aryl groups, or heteroaryl groups.

[0049] In the above general formulas (1), (2) and (3), L １ and L ２ may be bonded to each other to form a ring. １ and L ２ The ring formed by the combination of may be aliphatic or aromatic and may be optionally substituted and contain one or more heteroatoms, such as oxygen, sulfur, nitrogen, phosphorus, etc.

[0050] In the above general formulas (1), (2) and (3), R １ and R ２ may be bonded to each other to form a ring. １ and R ２ However, these R １ and R ２ The ring formed together with the common carbon atom to which it is attached may be aliphatic or aromatic and may be optionally substituted and contain one or more heteroatoms.

[0051] In the above general formulas (1), (2) and (3), L １ and R １ may be bonded to each other to form a ring. １ and R １The ring formed by the combination of may be aliphatic or aromatic and may be optionally substituted and contain one or more heteroatoms, such as oxygen, sulfur, nitrogen, phosphorus, etc.

[0052] The catalyst represented by the general formula (1) above includes those represented by the following structural formulas (1-1) to (1-3): [In the formula, Cy represents a cyclohexyl group, and Mes represents a mesityl group (also called a "2,4,6-trimethylphenyl group")]. The catalyst represented by structural formula (1-1) is called a Grubbs first-generation catalyst, the catalyst represented by structural formula (1-2) is called a Grubbs second-generation catalyst, and the catalyst represented by structural formula (1-3) is called a Grubbs-Hoveyda second-generation catalyst. When a catalyst represented by any of structural formulas (1-1) to (1-3) is used, the decomposition reaction (metathesis decomposition) of the diene rubber in the crosslinked rubber proceeds more rapidly.

[0053] The catalyst represented by the general formula (2) above is represented by the following structural formula (2-1): The catalyst represented by structural formula (2-1) is called a Grubbs third generation catalyst. When the catalyst represented by structural formula (2-1) is used, the decomposition reaction (metathesis decomposition) of the diene rubber in the crosslinked rubber proceeds more rapidly.

[0054] The catalyst represented by the general formula (3) above is represented by the following structural formula (3-1): Examples of the catalyst include those represented by the following formula:

[0055] The amount of the catalyst used is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of the diene rubber. If the amount of the catalyst used is 0.1 part by mass or more per 100 parts by mass of the diene rubber, the decomposition reaction of the diene rubber will further proceed, and if the amount of the catalyst used is 10 parts by mass or less per 100 parts by mass of the diene rubber, it is preferable from the standpoint of cost.

[0056] The decomposition by the metathesis catalyst (hereinafter sometimes simply referred to as "metathesis decomposition") is preferably carried out at a temperature of 20°C or higher and 200°C or lower. By carrying out the metathesis decomposition at 20°C or higher, the rate of the decomposition reaction of the diene rubber in the crosslinked rubber is improved, and by carrying out the metathesis decomposition at 200°C or lower, the decomposition of the catalyst (metathesis catalyst) represented by the above general formula (1), (2), or (3) can be suppressed, and the retention rate (selectivity) of the monomer skeleton of the diene rubber in the crosslinked rubber after the decomposition is improved. From the viewpoint of improving the decomposition reaction rate of the diene rubber, the metathesis decomposition temperature is more preferably 25°C or higher, and from the viewpoint of suppressing the decomposition of the metathesis catalyst and improving the selectivity of the product retaining the monomer skeleton, it is more preferably 100°C or lower.

[0057] The metathesis decomposition can be carried out at any pressure, including reduced pressure, normal pressure, and elevated pressure. For example, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 1 MPa, and even more preferably 50 kPa to 500 kPa.

[0058] In the metathesis decomposition, the catalyst represented by the above-mentioned general formula (1), (2), or (3) may be dissolved in a solvent, or the crosslinked rubber may be immersed in the solvent. By allowing the catalyst to act on the crosslinked rubber in a solvent, the decomposition reaction of the diene rubber in the crosslinked rubber can be facilitated. Any solvent that does not inhibit the decomposition reaction can be used as the solvent, and examples thereof include ethers, aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons (aromatic solvents). More specifically, the solvent is preferably tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, or xylene, and more preferably toluene or tetrahydrofuran. When the solvent is selected from tetrahydrofuran, hexane, cyclohexane, pentane, cyclopentane, toluene, or xylene, the decomposition reaction of the diene rubber in the crosslinked rubber can be facilitated. The amount of the solvent used is preferably 10 mL or more, more preferably 50 mL or more, and preferably 500 mL or less, more preferably 200 mL or less, per 1 g of the crosslinked rubber. If the amount of the solvent used is 10 mL or more per 1 g of the crosslinked rubber, the decomposition reaction of the diene rubber in the crosslinked rubber will further proceed, and if the amount of the solvent used is 500 mL or less per 1 g of the crosslinked rubber, it is preferable from the standpoint of cost.

[0059] The metathesis degradation may be carried out in the presence of a chain transfer agent (CTA). Examples of the chain transfer agent include cis-1,4-diacetoxy-2-butene and cis-1,4-dibenzyloxy-2-butene. The amount of the chain transfer agent used is preferably in the range of 1 to 100 mol per 1 mol of the catalyst.

[0060] - Second Decomposition Method (Low-Temperature Pyrolysis) - In the second decomposition method, the crosslinked rubber is thermally decomposed at a temperature of 150°C or higher and 400°C or lower. By carrying out the thermal decomposition at 150°C or higher, the rate of the decomposition reaction of the diene rubber in the crosslinked rubber is improved, and by carrying out the thermal decomposition at 400°C or lower, gasification and aromatization of the decomposition products can be suppressed, and after the decomposition, the retention rate (selectivity) of the monomer skeleton of the diene rubber in the crosslinked rubber is improved. From the viewpoint of improving the decomposition reaction rate of the diene rubber, the thermal decomposition temperature is preferably 175°C or higher, and more preferably 190°C or higher. Furthermore, from the viewpoint of improving the selectivity of products that maintain the monomer skeleton, the thermal decomposition temperature is preferably 350°C or lower, and more preferably 300°C or lower.

[0061] The second decomposition method is preferably carried out under an inert gas atmosphere. By carrying out the thermal decomposition under an inert gas atmosphere, oxidation and reduction of the decomposition products can be suppressed, and in particular, hydrogenation of double bonds in oligomers and monomers in the decomposition products can be suppressed. Furthermore, oxidation of the recycled carbon black can also be suppressed. Examples of inert gases include nitrogen, carbon dioxide, argon, and helium.

[0062] To carry out the pyrolysis under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that although hydrogen may be generated during pyrolysis, the generated hydrogen is not taken into consideration when determining the pyrolysis atmosphere.

[0063] The thermal decomposition can be carried out at any pressure, whether under reduced pressure, normal pressure, or increased pressure, but is preferably carried out under reduced pressure or normal pressure. For example, the reaction pressure for the thermal decomposition is preferably 1000 kPa to 65 kPa. By carrying out the thermal decomposition under reduced pressure or normal pressure, polymerization (repolymerization) of oligomers and monomers in the decomposition products can be suppressed.

[0064] The reaction time of the thermal decomposition is not particularly limited. For example, the reaction time of the thermal decomposition is preferably 1 minute to 180 minutes, more preferably 3 minutes to 60 minutes, and even more preferably 5 minutes to 30 minutes.

[0065] The thermal decomposition may or may not use a catalyst, but it is preferable not to use a catalyst. Not using a catalyst for thermal decomposition can reduce costs. When a catalyst is used, any catalyst that has the effect of accelerating the decomposition reaction of the crosslinked rubber can be used.

[0066] -Third Decomposition Method (Solvent Decomposition)- In the third decomposition method, the crosslinked rubber is decomposed in a solvent. When the decomposition of the crosslinked rubber is carried out in a solvent, the crosslinked rubber swells due to the solvent. By decomposing the crosslinked rubber under solvent swelling, gasification and aromatization of the decomposition products can be suppressed, and a decomposition product (liquid polymer) can be obtained that retains a higher percentage of the skeletons of the constituent monomers of the diene rubber (isoprene skeleton, butadiene skeleton, etc.) than in normal high-temperature thermal decomposition.

[0067] As the solvent, various solvents that have the effect of swelling the crosslinked rubber can be used, such as aromatic solvents, aliphatic solvents, alicyclic solvents, ester solvents, ethers, etc. Examples of aromatic solvents include benzene, toluene, xylene, etc.; aliphatic solvents include pentane, hexane, heptane, etc.; alicyclic solvents include cyclopentane, cyclohexane, etc.; ester solvents include ethyl acetate, propyl acetate, butyl acetate, etc.; and ethers include tetrahydrofuran (THF). Among these, the solvent is preferably at least one selected from the group consisting of toluene, xylene, and cyclohexane, and toluene is particularly preferred. Using toluene, xylene, or cyclohexane as the solvent allows for the production of a liquid polymer with a higher retention rate of the skeleton (isoprene skeleton, butadiene skeleton, etc.) of the constituent monomers of the diene rubber.

[0068] The amount of the solvent used is preferably 1 mL or more, more preferably 5 mL or more, and is preferably 500 mL or less, more preferably 200 mL or less, per gram of the crosslinked rubber. If the amount of the solvent used is 10 mL or more per gram of the crosslinked rubber, the decomposition reaction of the diene rubber in the crosslinked rubber will further proceed, and if the amount of the solvent used is 500 mL or less per gram of the crosslinked rubber, this is preferred from the standpoint of cost.

[0069] The temperature for decomposition in the solvent is preferably 150 to 300°C. By carrying out the decomposition in the solvent at 150°C or higher, the rate of the decomposition reaction of the diene rubber in the crosslinked rubber is improved. Furthermore, by carrying out the decomposition in the solvent at 300°C or lower, gasification and aromatization of the decomposition products can be suppressed, and after the decomposition, the retention rate (selectivity) of the structural monomer skeleton of the diene rubber in the crosslinked rubber is improved. Furthermore, for example, when the crosslinked rubber contains carbon black, it can be recovered and reused as high-quality carbon black. From the viewpoint of improving the decomposition reaction rate of the crosslinked rubber, the decomposition in the solvent is preferably 150°C or higher, more preferably 280°C or higher. Furthermore, from the viewpoint of improving the selectivity of products that maintain the monomer skeleton, it is preferably 180°C or lower, more preferably 250°C or lower.

[0070] The decomposition time in the solvent is not particularly limited. As an example, the decomposition time in the solvent is preferably 1 hour to 48 hours, and more preferably 3 hours to 18 hours. By carrying out the decomposition in the solvent for 1 hour or more, the decomposition rate of the crosslinked rubber is improved. On the other hand, if the reaction time is too long, the skeleton (double bond, etc.) of the constituent monomer of the diene rubber is decomposed, and the decomposition products are gasified or aromatized. However, by carrying out the decomposition in the solvent for 48 hours or less, the decomposition of the monomer skeleton and the gasification or aromatization of the decomposition products can be suppressed, and the retention rate (selectivity) of the skeleton of the constituent monomer of the diene rubber in the crosslinked rubber after the decomposition is improved.

[0071] The decomposition in the solvent is preferably carried out under an inert gas atmosphere. By carrying out the decomposition in the solvent under an inert gas atmosphere, the active species (oxygen, hydrogen, etc.) dissolved in the solvent can be reduced, and the oxidation and reduction of the decomposition products can be suppressed, and in particular, hydrogenation of the double bonds in the oligomers and monomers in the decomposition products can be suppressed. Furthermore, when the crosslinked rubber contains carbon black, oxidation of the carbon black can also be suppressed. Here, examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0072] To carry out the decomposition in the solvent under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that, although hydrogen may be generated during the decomposition in the solvent, the generated hydrogen is not taken into consideration when determining the atmosphere for the decomposition in the solvent.

[0073] The decomposition in the solvent can be carried out at any pressure, such as reduced pressure, normal pressure, or increased pressure. For example, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 5 MPa, and even more preferably 50 kPa to 2 MPa.

[0074] The decomposition in the solvent may or may not involve the use of a catalyst, but it is preferable not to use a catalyst. Not using a catalyst in the decomposition in the solvent can reduce costs. When a catalyst is used, any catalyst that has the effect of accelerating the decomposition reaction of the crosslinked rubber can be used.

[0075] -Fourth Decomposition Method (Radical Decomposition)- In the fourth decomposition method, a radical initiator is reacted with a crosslinked rubber in an atmosphere containing oxygen gas. The radical initiator is thought to act mainly on crosslinking sites caused by sulfur, severing the crosslinked bonds. Therefore, in the case of diene rubber, it is thought that its main chain structure is basically maintained even after the decomposition reaction.

[0076] As the radical initiator, various known compounds can be used, but from the viewpoint of reaction efficiency, peroxides and azo compounds are preferred, and peroxides are more preferred. Examples of peroxides include acyl peroxide, percarboxylic acid, dialkyl peroxide, and alkyl hydroperoxide. Among these, from the viewpoint of reaction rate, acyl peroxide and percarboxylic acid are preferred, and acyl peroxide is more preferred. Specific examples of acyl peroxides include benzoyl peroxide, toluoyl peroxide, chlorobenzoyl peroxide, dichlorobenzoyl peroxide, methoxybenzoyl peroxide, phthaloyl peroxide, acetyl peroxide, propanoyl peroxide, caprylyl peroxide, decanoyl peroxide, lauroyl peroxide, myristoyl peroxide, and stearoyl peroxide. Among acyl peroxides, benzoyl peroxide, lauroyl peroxide, and acetyl peroxide are preferred from the viewpoints of reaction rate, cost, and availability. From the viewpoints of reaction rate and peroxide stability, lauroyl peroxide is preferred over benzoyl peroxide. Examples of percarboxylic acids include perbenzoic acid, chloroperbenzoic acid, peracetic acid, and perpropionic acid. Examples of dialkyl peroxides include di-tert-butyl peroxide, dicumyl peroxide, and tert-butylcumyl peroxide. Examples of alkyl hydroperoxides include tert-butyl hydroperoxide and cumene hydroperoxide. Examples of azo compounds include azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate. These radical initiators may be in the form of a hydrate from the viewpoints of safety, availability, and the like. By using a suitable initiator, crosslinked rubber can be efficiently decomposed under mild conditions.

[0077] The amount of the radical initiator used is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the crosslinked rubber. If the amount of the radical initiator used is 0.1 part by mass or more per 100 parts by mass of the crosslinked rubber, the decomposition reaction of the crosslinked rubber proceeds more quickly, and if the amount of the radical initiator used is 30 parts by mass or less per 100 parts by mass of the crosslinked rubber, it is preferable from the standpoint of cost.

[0078] The fourth decomposition method is carried out in an atmosphere containing oxygen gas. The concentration (volume %) of oxygen gas in the reaction atmosphere is typically 1 to 100%, preferably 1 to 80%, and more preferably 5 to 50%, including the atmospheric oxygen concentration of approximately 20%. When the oxygen gas concentration is not 100%, an inert gas such as nitrogen gas can be used as the remaining gas component. The decomposition reaction in the fourth decomposition method is generally more advantageous as the oxygen concentration increases, but because undesirable side reactions are more likely to occur, it is preferable to appropriately control the reaction time, reaction temperature, etc. when the oxygen concentration is high. On the other hand, using atmospheric air with an oxygen concentration of approximately 20% eliminates the need for separate oxygen gas, which is advantageous in terms of equipment and economy. In a reaction under an air atmosphere, when the amount of crosslinked rubber is small, the reaction can proceed even in a sealed container with a sufficiently large internal volume. In this case, the internal volume of the reaction container is generally 50 parts by volume or more, more preferably 100 parts by volume or more, per 1 part by volume of crosslinked rubber. When the fourth decomposition method is carried out in a closed system, a large amount of crosslinked rubber requires a reaction vessel with a large internal volume, which is not desirable from the standpoint of equipment. Therefore, from the standpoint of equipment, it is preferable to carry out the reaction in a non-closed system that allows the flow of air, etc. In order to make the reaction system a non-closed system, methods such as opening a portion of the reaction vessel, installing a membrane that allows the flow of air, etc., or allowing air, etc., to overflow can be considered. Another advantageous embodiment is a method in which the reaction is carried out while continuously or intermittently blowing air, etc. into the solution. In this case, the blowing rate is not particularly limited, but is usually 1 to 1000 mL / min, preferably 2 to 500 mL / min, and more preferably 3 to 200 mL / min per gram of crosslinked rubber.

[0079] In the fourth decomposition method, the radical initiator may be dissolved in a solvent, or the crosslinked rubber may be immersed in a solvent to perform the decomposition. By allowing the radical initiator to act on the crosslinked rubber in a solvent, the decomposition of the crosslinked rubber can be facilitated. Any solvent that does not inhibit the decomposition reaction can be used as the solvent, and examples thereof include aromatic hydrocarbons (aromatic solvents), chlorinated hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, etc. Specific examples of aromatic hydrocarbons include toluene, xylene, ethylbenzene, trimethylbenzene, and propylbenzene. Chlorinated hydrocarbons include chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethene, chlorobenzene, and dichlorobenzene. Aliphatic hydrocarbons include pentane, hexane, and octane. Alicyclic hydrocarbons include cyclopentane, cyclohexane, and cyclooctane. Ethers include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and dioxane. Among these, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoints of reaction rate, availability, etc. Specific examples thereof include toluene, xylene, ethylbenzene, chloroform, chlorobenzene, dichlorobenzene, etc. Among aromatic hydrocarbons, ethylbenzene is preferred over toluene from the viewpoint of reaction rate. The solvent suitable for the decomposition reaction also depends on the type of crosslinked rubber. For example, when the crosslinked rubber is an NR-based, IR-based, or BR-based crosslinked rubber, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoints of reaction rate, solubility of the product, etc., specific examples thereof include toluene, ethylbenzene, chloroform, chlorobenzene, etc. On the other hand, when the crosslinked rubber is an SBR-based crosslinked rubber, chlorinated hydrocarbons are more preferred from the viewpoint of reaction rate, etc., specific examples thereof include chloroform, chlorobenzene, etc. Use of a preferred solvent facilitates the decomposition of the crosslinked rubber, allowing for more efficient production of a liquid polymer. The amount of the solvent used is preferably 2 mL or more, more preferably 10 mL or more, per 1 g of the crosslinked rubber, and is preferably 100 mL or less, more preferably 50 mL or less.If the amount of solvent used is 2 mL per 1 g of crosslinked rubber, the decomposition reaction of the crosslinked rubber is promoted, and if the amount of solvent used is 50 mL or less per 1 g of crosslinked rubber, this is preferable from the standpoint of cost.

[0080] The fourth decomposition method is preferably carried out at a temperature of 0°C or higher and 200°C or lower. By carrying out the fourth decomposition method at a temperature of 0°C or higher, the rate of decomposition reaction of the crosslinked rubber is improved, and by carrying out the fourth decomposition method at a temperature of 200°C or lower, the retention rate (selectivity) of the monomer skeleton in the crosslinked rubber is improved. In terms of improving the decomposition reaction rate of the crosslinked rubber, the fourth decomposition method is more preferably carried out at a temperature of 10°C or higher, and more preferably at a temperature of 150°C or lower, from the viewpoint of improving the selectivity of the product that retains the monomer skeleton. Furthermore, when a peroxide-based radical initiator is used, the decomposition efficiency is high, so the reaction proceeds at a low temperature of 60°C or lower. Another advantage of using a peroxide-based radical initiator is that the reaction proceeds smoothly even at around room temperature (20 to 30°C), so no special equipment for heating or cooling is required.

[0081] The fourth decomposition method can be carried out under any pressure, including reduced pressure, normal pressure, and increased pressure. Specifically, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 1 MPa, and even more preferably 50 kPa to 500 kPa.

[0082] In the fourth decomposition method, it is important to efficiently stir the raw materials, namely, the crosslinked rubber, the radical initiator, and the solvent. As a stirring method, various conventionally known methods can be used, such as a method using a magnetic stirrer, a method using a mechanical stirrer, or a method using a shaker. Furthermore, to promote the reaction, ultrasonic irradiation, microwave irradiation, light irradiation, or the like may be used in combination. These methods can also be used in combination.

[0083] -Other decomposition methods- The method for decomposing the crosslinked rubber to obtain the liquid polymer of this embodiment is not limited to the above-mentioned first, second, third, and fourth decomposition methods, and any decomposition method that preserves 30% or more of the basic structure of the polymer is sufficient. Furthermore, a decomposition method that preserves 50% or more of the polymer structure is more preferred, and a decomposition method that preserves 70% or more of the polymer structure is even more preferred.

[0084] <Mixture of Liquid Polymer and Recycled Carbon Black> The mixture of liquid polymer and recycled carbon black according to the first embodiment of the present invention is a mixture of liquid polymer and recycled carbon black obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black. The mixture of liquid polymer and recycled carbon black according to the first embodiment is characterized in that the liquid polymer is the liquid polymer according to the present embodiment described above.

[0085] The mixture of liquid polymer and recycled carbon black of the first embodiment can be obtained after the decomposition of the crosslinked rubber described above, without separating and recovering the recycled carbon black. By blending the mixture of liquid polymer and recycled carbon black into a rubber composition without separating and recovering the recycled carbon black, the productivity of the rubber composition can be improved. Furthermore, when the mixture of liquid polymer and recycled carbon black of the first embodiment is reused in a rubber composition, the liquid polymer acts as a softener, facilitating the kneading of the rubber composition.

[0086] A second embodiment of the present invention provides a mixture of a liquid polymer and recycled carbon black obtained by decomposing a crosslinked rubber containing a diene rubber and carbon black. The mixture of a liquid polymer and recycled carbon black of the second embodiment is characterized in that the liquid polymer is obtained by removing some or all of the components with a molecular weight of 5,000 or less from the liquid polymer of the present embodiment, and the proportion of components with a molecular weight of 15,000 or less is 30% by mass or less.

[0087] The mixture of liquid polymer and recycled carbon black of the second embodiment can be obtained by removing some or all of the low-molecular-weight components from the liquid polymer after decomposition of the crosslinked rubber described above, without separating and recovering the recycled carbon black. Blending the mixture of liquid polymer and recycled carbon black into a rubber composition without separating and recovering the recycled carbon black can improve the productivity of the rubber composition. Furthermore, by removing some or all of the low-molecular-weight components from the liquid polymer, the plasticizing effect of the low-molecular-weight components can be suppressed when blending the mixture of liquid polymer and recycled carbon black into a rubber composition, making it easier to obtain a rubber composition with desired physical properties.

[0088] In the mixture of the liquid polymer and recycled carbon black of the second embodiment, the liquid polymer preferably contains 30% by mass or less of components with a molecular weight of 15,000 or less. When the proportion of components with a molecular weight of 15,000 or less is 30% by mass or less, plasticization is suppressed, making it easier to obtain a rubber composition with desired physical properties. Here, the molecular weight is measured using gel permeation chromatography (GPC).

[0089] As described above, the mixture of the liquid polymer and recycled carbon black can be compounded into a rubber composition. In addition to the mixture of the liquid polymer and recycled carbon black, the rubber composition may contain a rubber component and compounding agents commonly used in the rubber industry, such as fillers (carbon black, silica, calcium carbonate, etc.), silane coupling agents, antioxidants, waxes, softeners, processing aids, resins, surfactants, organic acids (stearic acid, etc.), zinc oxide (zinc white), vulcanization accelerators, and crosslinking agents (sulfur, peroxides, etc.). The rubber composition can be used in a variety of rubber products, including tires, rubber crawlers, and seismic isolation rubber.

[0090] <Method for recovering diene monomer> -Method for recovering diene monomer of first embodiment- The method for recovering diene monomer of the first embodiment of the present invention is characterized in that the liquid polymer of the present embodiment described above is thermally decomposed in an inert gas atmosphere and in the presence of a catalyst at 300 to 950° C. According to the method for recovering diene monomer of the first embodiment, the diene monomer can be recovered in high yield.

[0091] By carrying out the pyrolysis at 300° C. or higher, the rate of the decomposition reaction of the liquid polymer is increased, and by carrying out the pyrolysis at 950° C. or lower, the selectivity of the product in which the monomer skeleton is maintained is increased. The temperature of the pyrolysis is preferably 500° C. or higher from the viewpoint of increasing the decomposition reaction rate, and preferably 900° C. or lower from the viewpoint of increasing the selectivity of the product in which the monomer skeleton is maintained.

[0092] In a preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 450° C. at a heating rate of 800° C. / min or more, and thermally decomposed at 450 to 950° C. When the heating rate from 100° C. to 450° C. is 800° C. / min or more, the generation of decomposition products such as oligomers having higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, thereby further improving the yield of the diene monomer.

[0093] In another preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 450° C. at a heating rate of 2000° C. / min or more, and thermally decomposed at 450 to 950° C. When the heating rate from 100° C. to 450° C. is 2000° C. / min or more, the generation of decomposition products such as oligomers having higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, and the yield of the diene monomer is further improved.

[0094] In another preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 600° C. at a heating rate of 800° C. / min or more, and thermally decomposed at 650 to 950° C. When the heating rate from 100° C. to 600° C. is 800° C. / min or more, the generation of decomposition products such as oligomers having higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, and the yield of the diene monomer is further improved.

[0095] In another preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 600° C. at a heating rate of 2000° C. / min or more, and thermally decomposed at 650 to 950° C. When the heating rate from 100° C. to 600° C. is 2000° C. / min or more, the generation of decomposition products such as oligomers that have higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, thereby further improving the yield of the diene monomer.

[0096] In another preferred embodiment of the thermal decomposition, the liquid polymer is mixed with a medium selected from a fatty acid ester and a hydrocarbon, and then thermally decomposed in an inert gas atmosphere in the presence of a catalyst at 300 to 950° C. By mixing the liquid polymer with the medium and then thermally decomposing it, the decomposition of the liquid polymer into diene monomers is promoted, and the diene monomers can be obtained in a high yield.

[0097] The pyrolysis is carried out under an inert gas atmosphere. By carrying out the pyrolysis under an inert gas atmosphere, oxidation and reduction of the decomposition products can be suppressed, and in particular, hydrogenation of double bonds in the monomers in the decomposition products can be suppressed. Examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0098] To carry out the pyrolysis under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that although hydrogen may be generated during the pyrolysis, the generated hydrogen is not taken into consideration when determining the pyrolysis atmosphere.

[0099] For example, when the thermal decomposition is carried out under pressure, the liquid polymer may be thermally decomposed in a solvent. The solvent may be any solvent that does not inhibit the decomposition reaction, such as ethers, aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons (aromatic solvents). More specifically, tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, and xylene are preferred, with toluene and tetrahydrofuran being more preferred. The amount of the solvent used is preferably 10 mL or more, more preferably 50 mL or more, and more preferably 500 mL or less, and even more preferably 200 mL or less, per 1 g of the liquid polymer. When the amount of the solvent used is 10 mL or more per 1 g of the liquid polymer, the decomposition reaction proceeds further, and when the amount of the solvent used is 500 mL or less per 1 g of the liquid polymer, this is preferred from the viewpoint of cost.

[0100] The thermal decomposition is carried out in the presence of a catalyst. The catalyst may be an acidic catalyst, a neutral catalyst, or a basic catalyst, and among these, a basic catalyst is preferred. ２ , ZrO ２ , MgO, La ２ O ３ , CeO ２ , Y ２ O ３ , Li ２ CO ３ , Na ２ CO ３ , Rb ２ CO ３ , and Cs ２ CO ３It is more preferable to carry out the thermal decomposition in the presence of at least one basic catalyst selected from the group consisting of: (i) a basic catalyst selected from the group consisting of (ii) a basic catalyst selected from the group consisting of (iii) a basic catalyst selected from the group consisting of (iv) a basic catalyst selected from the group consisting of (v) a basic catalyst selected from the group consisting of (vi ...

[0101] The amount of the catalyst used is preferably 1 part by mass or more, more preferably 10 parts by mass or more, even more preferably 100 parts by mass or more, and is preferably 8,000 parts by mass or less, more preferably 4,000 parts by mass or less, and even more preferably 500 parts by mass or less, relative to 100 parts by mass of the liquid polymer. If the amount of the catalyst used is 100 parts by mass or more relative to 100 parts by mass of the liquid polymer, the decomposition reaction will proceed further, and if the amount of the catalyst used is 500 parts by mass or less relative to 100 parts by mass of the liquid polymer, it is preferable from the standpoint of cost.

[0102] - Method for recovering diene monomer according to a second embodiment - The method for recovering diene monomer according to a second embodiment of the present invention is characterized in that the liquid polymer according to the present embodiment described above is thermally decomposed in an inert gas atmosphere in the absence of a catalyst at 300 to 450° C. The method for recovering diene monomer according to the second embodiment also makes it possible to recover diene monomers in high yield.

[0103] By carrying out the pyrolysis at 300°C or higher, the rate of the decomposition reaction of the liquid polymer is increased, and the yield of the monomer is improved, while by carrying out the pyrolysis of the liquid polymer at 450°C or lower, gasification and aromatization of the decomposition products can be significantly suppressed, and the selectivity of products that maintain the monomer skeleton is significantly improved. The pyrolysis is preferably carried out at 320°C or higher from the viewpoint of increasing the decomposition reaction rate and improving the monomer yield, and preferably at 380°C or lower from the viewpoint of suppressing gasification and aromatization of the decomposition products.

[0104] The pyrolysis is carried out under an inert gas atmosphere. By carrying out the pyrolysis under an inert gas atmosphere, oxidation and reduction of the decomposition products can be suppressed, and in particular, hydrogenation of double bonds in the monomers in the decomposition products can be suppressed. Examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0105] To carry out the pyrolysis under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that although hydrogen may be generated during the pyrolysis, the generated hydrogen is not taken into consideration when determining the pyrolysis atmosphere.

[0106] The thermal decomposition can be carried out at any pressure, whether under reduced pressure, normal pressure, or increased pressure, but is preferably carried out under reduced pressure or normal pressure. As an example, the reaction pressure for the thermal decomposition is preferably 1000 kPa to 67 kPa. By carrying out the thermal decomposition under reduced pressure or normal pressure, polymerization (repolymerization) of the monomer in the decomposition product can be suppressed.

[0107] The reaction time of the thermal decomposition is not particularly limited. For example, the reaction time of the thermal decomposition is preferably 3 to 60 minutes, and more preferably 5 to 30 minutes.

[0108] The thermal decomposition is carried out in the absence of a catalyst (i.e., no catalyst is used). Not using a catalyst in the thermal decomposition can reduce costs. Here, "in the absence of a catalyst" means that no catalyst that has the effect of promoting the decomposition reaction is present in the thermal decomposition reaction system.

[0109] - Method for recovering diene monomer according to a third embodiment - A method for recovering diene monomer according to a third embodiment of the present invention is characterized in that the liquid polymer according to the present embodiment described above is thermally decomposed in an inert gas atmosphere in the absence of a catalyst at 600 to 950° C. The method for recovering diene monomer according to the third embodiment also makes it possible to recover diene monomers in high yield.

[0110] By carrying out the pyrolysis at 600°C or higher, the rate of the decomposition reaction of the liquid polymer is significantly increased, resulting in a significantly improved monomer yield. Furthermore, by carrying out the pyrolysis at 950°C or lower, gasification and aromatization of the decomposition products can be suppressed, and the selectivity of products that maintain the monomer skeleton is improved. From the viewpoints of improving the decomposition reaction rate and improving the monomer yield, the pyrolysis is preferably carried out at 700°C or higher. Furthermore, by carrying out the pyrolysis at 700 to 900°C, the rate of the decomposition reaction of the liquid polymer can be increased, while the selectivity of products that maintain the monomer skeleton can be improved.

[0111] In a preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 450° C. at a heating rate of 800° C. / min or more, and then thermally decomposed at 600 to 950° C. When the heating rate from 100° C. to 450° C. is 800° C. / min or more, the generation of decomposition products such as oligomers having higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, thereby further improving the yield of the diene monomer.

[0112] In another preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 450° C. at a heating rate of 2000° C. / min or more, and then thermally decomposed at 600 to 950° C. When the heating rate from 100° C. to 450° C. is 2000° C. / min or more, the generation of decomposition products such as oligomers having higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, thereby further improving the yield of the diene monomer.

[0113] In another preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 600° C. at a heating rate of 800° C. / min or more, and thermally decomposed at 650 to 950° C. When the heating rate from 100° C. to 600° C. is 800° C. / min or more, the generation of decomposition products such as oligomers having higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, and the yield of the diene monomer is further improved.

[0114] In another preferred embodiment of the thermal decomposition, the liquid polymer is heated in an inert gas atmosphere from 100° C. to 600° C. at a heating rate of 2000° C. / min or more, and thermally decomposed at 650 to 950° C. When the heating rate from 100° C. to 600° C. is 2000° C. / min or more, the generation of decomposition products such as oligomers that have higher molecular weights than the diene monomer is suppressed, and after the decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the liquid polymer is further improved, thereby further improving the yield of the diene monomer.

[0115] In another preferred embodiment of the thermal decomposition, the liquid polymer is mixed with a medium selected from a fatty acid ester and a hydrocarbon, and then thermally decomposed in an inert gas atmosphere in the absence of a catalyst at 600 to 950° C. By mixing the liquid polymer with the medium and then thermally decomposing it, the decomposition of the liquid polymer into diene monomers is promoted, and the diene monomers can be obtained in a high yield.

[0116] The pyrolysis is carried out under an inert gas atmosphere. By carrying out the pyrolysis under an inert gas atmosphere, oxidation and reduction of the decomposition products can be suppressed, and in particular, hydrogenation of double bonds in the monomers in the decomposition products can be suppressed. Examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0117] To carry out the pyrolysis under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that although hydrogen may be generated during the pyrolysis, the generated hydrogen is not taken into consideration when determining the pyrolysis atmosphere.

[0118] The thermal decomposition can be carried out at any pressure, whether under reduced pressure, normal pressure, or increased pressure, but is preferably carried out under reduced pressure or normal pressure. As an example, the reaction pressure for the thermal decomposition is preferably 1000 kPa to 65 kPa. By carrying out the thermal decomposition under reduced pressure or normal pressure, polymerization (repolymerization) of the monomer in the decomposition product can be suppressed.

[0119] The reaction time of the thermal decomposition is not particularly limited. For example, the reaction time of the thermal decomposition is preferably 0.001 seconds to 1000 seconds, and more preferably 0.01 seconds to 1000 seconds.

[0120] The thermal decomposition is carried out in the absence of a catalyst (i.e., no catalyst is used). Not using a catalyst in the thermal decomposition can reduce costs. Here, "in the absence of a catalyst" means that no catalyst that has the effect of promoting the decomposition reaction is present in the thermal decomposition reaction system.

[0121] - Uses - The diene monomer obtained by the diene monomer recovery method can be reused as a raw material for diene rubber (polymer). Note that the diene monomer obtained varies depending on the type of diene rubber in the crosslinked rubber to be decomposed, but examples thereof include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc., with 1,3-butadiene and isoprene being preferred.

[0122] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0123] (1) Method for Analyzing Retention Rate of Monomer Skeleton in Diene Rubber The obtained liquid polymer was analyzed using an NMR apparatus under the trade name "Nuclear Magnetic Resonance Spectrometer JNM-ECA-500" manufactured by JEOL Ltd., and the retention rate of the isoprene skeleton and / or butadiene skeleton derived from the natural rubber and / or butadiene rubber contained in each crosslinked rubber sample was calculated.

[0124] (2) Method for Analyzing Weight-Average Molecular Weight (Mw) of Liquid Polymer The polystyrene-equivalent weight-average molecular weight (Mw) of the liquid polymer was determined using gel permeation chromatography (hereinafter sometimes referred to as GPC analysis; solution delivery unit: LC-20AB manufactured by Shimadzu Corporation; column: a combination of KF-803 and KF-804 manufactured by Showa Denko K.K. or a combination of G2000HXL and G4000HXL manufactured by Tosoh Corporation; detector: differential refractometer RID-10A manufactured by Shimadzu Corporation; analysis system: LabSolutions manufactured by Shimadzu Corporation; eluent: tetrahydrofuran) at a temperature of 40°C.

[0125] (Preparation of Crosslinked Rubber Sample A) A rubber composition was prepared by blending 50 parts by mass of carbon black, 1.0 part by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 2.0 parts by mass of stearic acid, 2.5 parts by mass of zinc oxide, 1.5 parts by mass of vulcanization accelerator (N-cyclohexyl-2-benzothiazolylsulfenamide), and 4.5 parts by mass of sulfur with 100 parts by mass of natural rubber, and the rubber composition was then heat-crosslinked to prepare a crosslinked rubber. The resulting crosslinked rubber was cut into a shape of 3 mm x 3 mm x 2 mm to prepare crosslinked rubber sample A.

[0126] (Preparation of Crosslinked Rubber Sample B) Crosslinked rubber sample B was prepared in the same manner as crosslinked rubber sample A, except that 60 parts by mass of natural rubber and 40 parts by mass of butadiene rubber (manufactured by UBE Elastomers Co., Ltd., product name "UBEPOL BR150L") were compounded instead of 100 parts by mass of natural rubber.

[0127] (Preparation of Crosslinked Rubber Sample C) Crosslinked rubber sample C was prepared in the same manner as crosslinked rubber sample A, except that 40 parts by mass of natural rubber and 60 parts by mass of butadiene rubber (manufactured by UBE Elastomers Co., Ltd., product name "UBEPOL BR150L") were compounded instead of 100 parts by mass of natural rubber.

[0128] (Examples 1-1 to 1-7) 0.4 g of crosslinked rubber sample A and 4 mL of toluene were added to a reactor, and the mixture was stirred under an Ar atmosphere at 200°C or 240°C for 3, 6, 9 or 18 hours to carry out a decomposition reaction. After the reaction, the mixture was separated into a solvent (toluene) soluble component and a solvent insoluble component. The solvent soluble component was mainly composed of a liquid polymer, while the solvent insoluble component was mainly composed of carbon black. The obtained solvent soluble component (liquid polymer) was subjected to the following steps: １ H-NMR analysis was performed to calculate the retention rate of the diene monomer skeleton. The expected diene monomer yield was calculated from the product of the liquid polymer yield and the retention rate of the diene monomer skeleton. Furthermore, the weight average molecular weight (Mw) of the liquid polymer was analyzed by GPC analysis.

[0129] (Examples 2-1 to 2-7) A decomposition reaction was carried out in the same manner as in Example 1, except that crosslinked rubber sample B was used as the decomposition target instead of crosslinked rubber sample A. １ The retention rate of the diene monomer skeleton in the product was calculated by H-NMR analysis, and the expected diene monomer yield was also calculated. Furthermore, the weight average molecular weight (Mw) of the liquid polymer was analyzed by GPC analysis.

[0130] (Examples 3-1 to 3-8) A decomposition reaction was carried out in the same manner as in Example 1, except that crosslinked rubber sample C was used as the decomposition target instead of crosslinked rubber sample A. １ The retention rate of the diene monomer skeleton in the product was calculated by H-NMR analysis, and the expected diene monomer yield was also calculated. Furthermore, the weight average molecular weight (Mw) of the liquid polymer was analyzed by GPC analysis.

[0131] (Examples 4-1 to 4-7) A decomposition reaction was carried out in the same manner as in Example 1, except that cyclohexane was used as the solvent instead of toluene. １ The retention rate of the diene monomer skeleton in the product was calculated by H-NMR analysis, and the expected diene monomer yield was also calculated. Furthermore, the weight average molecular weight (Mw) of the liquid polymer was analyzed by GPC analysis.

[0132] (Examples 5-1 to 5-7) A decomposition reaction was carried out in the same manner as in Example 1, except that xylene was used as the solvent instead of toluene. １ The retention rate of the diene monomer skeleton in the product was calculated by H-NMR analysis, and the expected diene monomer yield was also calculated. Furthermore, the weight average molecular weight (Mw) of the liquid polymer was analyzed by GPC analysis. The results of Examples 1-1 to 5-8 are shown in Tables 1 to 5, respectively.

[0133]

[0134]

[0135]

[0136]

[0137]

[0138] Recovery of Diene Monomer Example 6 A 3.0 mg portion of the reaction mixture obtained in Example 1-1 (first decomposition step) (a reaction mixture obtained by concentrating the filtrate obtained by filtering the reaction solution of Example 1-1 under reduced pressure) was dissolved in 0.60 mL of tetrahydrofuran. A 5.0 μL portion of this solution was placed in a stainless steel container, and the solvent was distilled off under reduced pressure. 0.025 mg of the reaction mixture from the first decomposition step obtained after solvent distillation was heated to 700°C using a pyrolyzer (PY-3030D, manufactured by Frontier Labs), and the resulting pyrolysis product was analyzed using a gas chromatograph mass spectrometer and a gas chromatograph analyzer (a GCMS-QP2010Plus manufactured by Shimadzu Corporation and a GC-2014, manufactured by Shimadzu Corporation, respectively, both equipped with an UltraALLOY UA-1 capillary column manufactured by Frontier Labs). The yields were estimated to be 34.8% isoprene, 1.3% limonene, 17.3% hydrocarbons with 1 to 4 carbon atoms, and 38.8% hydrocarbons with 5 to 10 carbon atoms (other than isoprene and limonene).

[0139] (Examples 7 to 10) The pyrolysis reaction was carried out in the same manner as in Example 6, except that the decomposition target and heating temperature were changed as shown in Table 6. The obtained pyrolysis products were analyzed using a gas chromatograph mass spectrometer and a gas chromatograph analyzer, and the results were estimated.

[0140]

[0141] *1 Yield of hydrocarbons with 1 to 4 carbon atoms (other than butadiene) *2 Yield of hydrocarbons with 5 to 10 carbon atoms (other than isoprene and limonene)

[0142] From Table 6, it is predicted that diene monomers can be obtained in high yield from the liquid polymers of the present invention.

[0143] The liquid polymer of the present invention can be used as a raw material for diene monomers, which in turn can be used as a raw material for rubber components of rubber products such as tires, rubber crawlers, and seismic isolation rubber.

Claims

1. A liquid polymer obtained by decomposition of a crosslinked rubber containing a diene rubber, the liquid polymer having a weight average molecular weight of 500 to 300,000, and characterized in that the retention rate of the diene monomer skeleton of the diene rubber in the crosslinked rubber before the decomposition is 30 mass% or more.

2. The liquid polymer according to claim 1, wherein the diene monomer skeleton of the diene rubber is at least one selected from the group consisting of an isoprene skeleton and a butadiene skeleton.

3. The liquid polymer according to claim 1, wherein the crosslinked rubber contains a diene rubber containing an isoprene skeleton, and the retention rate of the isoprene skeleton is 30 mass% or more relative to the mass of the isoprene skeleton of the diene rubber in the crosslinked rubber before decomposition.

4. The liquid polymer according to claim 1, wherein the crosslinked rubber contains a diene rubber containing a butadiene skeleton, and the retention rate of the butadiene skeleton is 30 mass% or more relative to the mass of the butadiene skeleton of the diene rubber in the crosslinked rubber before decomposition.

5. The liquid polymer according to claim 1, wherein the retention rate of the diene monomer skeleton is 50 mass% or more relative to the mass of the diene monomer skeleton of the diene rubber in the crosslinked rubber before decomposition.

6. The liquid polymer according to claim 1, wherein the retention rate of the diene monomer skeleton of the diene rubber in the crosslinked rubber before decomposition is 70 mass % or more.

7. The liquid polymer according to claim 1, wherein the crosslinked rubber is a sulfur crosslinked rubber.

8. A mixture of a liquid polymer and recycled carbon black obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black, characterized in that the liquid polymer is the liquid polymer described in any one of claims 1 to 7.

9. A mixture of a liquid polymer and recycled carbon black obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black, characterized in that the liquid polymer is obtained by removing some or all of the components having a molecular weight of 5,000 or less from the liquid polymer described in any one of claims 1 to 7, and the proportion of components having a molecular weight of 15,000 or less is 30 mass% or less.

10. A method for recovering a diene monomer, comprising pyrolyzing the liquid polymer according to any one of claims 1 to 7 at 300 to 950°C in an inert gas atmosphere and in the presence of a catalyst.

11. A method for recovering a diene monomer, comprising pyrolyzing the liquid polymer according to any one of claims 1 to 7 at 300 to 450°C in an inert gas atmosphere and in the absence of a catalyst.

12. A method for recovering a diene monomer, comprising pyrolyzing the liquid polymer according to any one of claims 1 to 7 at 600 to 950°C in an inert gas atmosphere and in the absence of a catalyst.

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