Method for decomposing crosslinked rubber

Abstract

The present invention addresses the problem of providing a method for decomposing a crosslinked rubber with which it is possible to improve the yield of C4-10 chemical products. The means for solving the problem is a method for decomposing a crosslinked rubber, said method comprising: a first decomposition step in which a crosslinked rubber containing a diene-based rubber is decomposed using the catalysts in formulas (1) to (3) [In the formulas: M is ruthenium, molybdenum, or the like; X1 and X2, and L1, L2 and L3 each independently represent a ligand; R1, R2 and R3 are each independently hydrogen, an alkyl group, an alkenyl group, an aryl group, or the like (these groups may be substituted with an alkyl group, a halogen, or the like); L1 and L2, R1 and R2, and L1 and R1 may be bonded to each other to form a ring]; and a second decomposition step in which the temperature of the decomposition product obtained in the first decomposition step is raised at a heating rate of 800°C / min or more from 100°C to 450°C in an inert gas atmosphere and in the absence of a catalyst, and the decomposition product is thermally decomposed at 450-950°C.

Description

Method for decomposing crosslinked rubber

[0001] The present invention relates to a method for decomposing crosslinked rubber.

[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, and for example, a technique for thermally decomposing cross-linked rubber at high temperatures is known. Furthermore, Patent Document 1 listed below discloses a method for decomposing polyisoprene-based rubber using microorganisms.

[0003] JP 2009-247241 A

[0004] As described above, there are various methods for decomposing crosslinked rubber, but from the viewpoint of further enhancing the recyclability of crosslinked rubber, it is important to increase the yield of chemical products obtained by decomposition, particularly diene monomers. However, as described above, when crosslinked rubber is thermally decomposed at high temperatures, the decomposition products gasify or become polycyclic aromatic compounds, resulting in a decrease in the yield of C4-C10 chemical products, particularly diene monomers. Furthermore, when crosslinked rubber is decomposed using microorganisms, as in the technology disclosed in Patent Document 1, the decomposition takes a long time, and furthermore, there are problems in that the yield of C4-C10 chemical products, particularly diene monomers, is low.

[0005] Therefore, an object of the present invention is to provide a method for decomposing crosslinked rubber that can solve the above-mentioned problems of the conventional technology and improve the yield of C4 to C10 chemical products, particularly diene monomers.

[0006] The gist of the method for decomposing crosslinked rubber of the present invention, which solves the above problems, is as follows.

[0007] [1] A crosslinked rubber containing a diene rubber represented by the following general formula (1), (2), or (3): wherein M is ruthenium, titanium, molybdenum, or tungsten; １and X ２ each independently represents a ligand; １ , L ２ and L ３ each independently represents a ligand; R １ , R ２ and R ３ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl 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); L １ and L ２ may be bonded to each other to form a ring, R １ and R ２ may be bonded to each other to form a ring, １ and R １ may be bonded to each other to form a ring]; and a second decomposition step of heating the decomposition product obtained in the first decomposition step from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposing the decomposition product at 450 to 950°C.

[0008] [2] A method for decomposing a crosslinked rubber, comprising: a first decomposition step of decomposing a crosslinked rubber containing a diene rubber using a catalyst represented by the above general formula (1), (2), or (3); and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 800°C / min or more from 100°C to 600°C in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposing the decomposed product at 600 to 950°C.

[0009] [3] A method for decomposing a crosslinked rubber, comprising: a first decomposition step of decomposing a crosslinked rubber containing a diene rubber using a catalyst represented by the above general formula (1), (2), or (3); and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000°C / min or more from 100°C to 450°C in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposing the decomposed product at 450 to 950°C.

[0010] [4] A method for decomposing a crosslinked rubber, comprising: a first decomposition step of decomposing a crosslinked rubber containing a diene rubber using a catalyst represented by the above general formula (1), (2), or (3); and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000°C / min or more from 100°C to 600°C in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposing the decomposed product at 600 to 950°C.

[0011] [5] The method for decomposing a crosslinked rubber according to any one of [1] to [4], wherein the thermal decomposition in the second decomposition step is carried out at 650 to 850°C.

[0012] [6] The method for decomposing a crosslinked rubber according to any one of [1] to [5], wherein, after the first decomposition step, 80% by mass or more of the diene rubber in the crosslinked rubber is decomposed into diene oligomers having a weight average molecular weight of 100 to 50,000.

[0013] [7] The method for decomposing a crosslinked rubber according to [6], wherein 30 mass% or more of the diene oligomer is decomposed into chemical products of C4 to C10 through the second decomposition step.

[0014] [8] The method for decomposing crosslinked rubber according to any one of [1] to [7], wherein 20 mass% or more of the diene rubber in the crosslinked rubber is decomposed into C4 to C10 chemical products through the first decomposition step and the second decomposition step.

[0015] [9] The method for decomposing a crosslinked rubber according to any one of [1] to [8], wherein the first decomposition step is carried out at a temperature of 20°C or higher and 200°C or lower.

[0016]

[10] The method for decomposing crosslinked rubber according to any one of [1] to [9], wherein the diene rubber comprises at least one selected from the group consisting of isoprene skeleton rubber, styrene-butadiene rubber, and butadiene rubber.

[0017]

[11] The method for decomposing a crosslinked rubber according to any one of [1] to

[10] , wherein the crosslinked rubber further contains carbon black.

[0018]

[12] The method for decomposing a crosslinked rubber according to any one of [1] to

[11] , wherein the crosslinked rubber further contains sulfur.

[0019] According to the present invention, it is possible to provide a method for decomposing crosslinked rubber that can improve the yield of C4 to C10 chemical products, particularly diene monomers.

[0020] The method for decomposing crosslinked rubber of the present invention will be described in detail below by way of example based on embodiments thereof.

[0021] [Definitions] The compounds described herein may be derived in part or in whole from fossil resources, biological resources such as plant resources, recycled resources such as used tires, or a mixture of two or more of fossil, biological, and recycled resources.

[0022] [Method for Decomposing Crosslinked Rubber] The method for decomposing a crosslinked rubber of the present invention comprises decomposing a crosslinked rubber containing a diene rubber into a compound represented by the following general formula (1), (2) or (3): wherein M is ruthenium, titanium, molybdenum, or tungsten; １ and X ２ each independently represents a ligand; １ , L ２ and L ３ each independently represents a ligand; 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, 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); L １ and L ２ may be bonded to each other to form a ring, R １ and R ２ may be bonded to each other to form a ring, １ and R １may be bonded to each other to form a ring], and a second decomposition step in which the decomposition product obtained in the first decomposition step is heated from 100° C. to 450° C. at a heating rate of 800° C. / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposed at 450 to 950° C. In one preferred embodiment, the method includes a first decomposition step in which a crosslinked rubber containing a diene rubber is decomposed using a catalyst represented by general formula (1), (2), or (3), and a second decomposition step in which the decomposition product obtained in the first decomposition step is heated from 100° C. to 600° C. at a heating rate of 800° C. / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposed at 600 to 950° C. In another preferred embodiment, the method includes a first decomposition step of decomposing a crosslinked rubber containing a diene rubber using a catalyst represented by the general formula (1), (2), or (3), and a second decomposition step of heating the decomposition product obtained in the first decomposition step from 100° C. to 450° C. at a heating rate of 2000° C. / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposing the product at 450 to 950° C. In yet another preferred embodiment, the method includes a first decomposition step of decomposing a crosslinked rubber containing a diene rubber using a catalyst represented by the general formula (1), (2), or (3), and a second decomposition step of heating the decomposition product obtained in the first decomposition step from 100° C. to 600° C. at a heating rate of 2000° C. / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposing the product at 600 to 950° C.

[0023] The catalyst represented by the above general formula (1), (2), or (3) used in the first decomposition step of the method for decomposing a crosslinked rubber of the present invention can promote metathesis decomposition, causing metathesis decomposition at unsaturated bonds in the diene rubber, thereby decomposing the diene rubber. Unlike normal thermal decomposition, metathesis decomposition does not require high temperatures, so the diene rubber can be decomposed under mild conditions. Furthermore, metathesis decomposition can suppress the conversion of the decomposition products to polycyclic aromatic compounds, and can improve the retention rate of the monomer skeleton (isoprene skeleton, butadiene skeleton, etc.) in the diene rubber compared to normal thermal decomposition. Furthermore, in the method for decomposing crosslinked rubber of the present invention, in the second decomposition step, the decomposition product obtained in the first decomposition step is rapidly heated from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposed at 450 to 950°C. This reduces the rate of decomposition during heating (i.e., at a temperature lower than the target decomposition temperature), suppresses the generation and volatilization of decomposition products with higher molecular weights than the C4-C10 chemical products from the decomposition product obtained in the first decomposition step, and further suppresses hydrogenation of double bonds in the skeletons of the constituent monomers of the diene rubber (isoprene skeleton, butadiene skeleton, etc.) and oxidation of the decomposition products, while decomposing the decomposition products (intermediate decomposition products) into C4-C10 chemical products (particularly diene monomers) in high yield. Therefore, the decomposition method for crosslinked rubber of the present invention can improve the yield of C4-C10 chemical products, particularly diene monomers, finally obtained from the crosslinked rubber.

[0024] <First Decomposition Step> The method for decomposing a crosslinked rubber of the present embodiment includes a first decomposition step of decomposing a crosslinked rubber containing a diene rubber using a catalyst represented by the above general formula (1), (2), or (3).

[0025] (Crosslinked Rubber) The crosslinked rubber to be decomposed by the decomposition method of the present embodiment contains a diene rubber, and may further contain carbon black, sulfur, and the like.

[0026] The crosslinked rubber to be used for decomposition may be grouped by the type of diene rubber previously compounded, and then thermally decomposed for each group. Alternatively, the rubber may be grouped by the type of filler previously compounded (e.g., the type of carbon black, the type of silica, the mixing ratio of carbon black and silica, etc.), and then thermally decomposed for each group. Furthermore, the rubber may be grouped by both the type of diene rubber and the type of filler, and then thermally decomposed for each group. When thermally decomposing for each group in this way, recycled carbon black, regenerated silica, etc. with 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 decomposition is derived from tires, the tires may be grouped in advance by type (e.g., for passenger cars, trucks, buses, large vehicles such as off-road vehicles, aircraft, agricultural vehicles, etc.), and then pyrolysis 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 pyrolysis may be carried out for each group. Furthermore, the tires may be grouped both by type and by tire component, and then pyrolysis may be carried out for each group. When pyrolysis is carried out for each group in this way, recycled carbon black or the like 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] --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. While the diene-based rubber in the crosslinked rubber is typically present in a crosslinked state, it may be partially uncrosslinked. Specific examples of diene-based monomers (diene-based compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds. Specific examples of the aromatic vinyl compounds include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. Examples of the diene rubber include isoprene-skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). 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 comprises at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber. When the diene rubber comprises at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber, easily recyclable diene monomers such as isoprene and butadiene can be obtained. The content of the diene rubber in the crosslinked rubber is not particularly limited, and is preferably in the range of 10 to 100% by mass, for example. From the viewpoint of further improving the yield of butadiene and isoprene, a range of 30 to 100% by mass is more preferable.

[0031] --Carbon Black-- The crosslinked rubber may further contain carbon black. In the method for decomposing a crosslinked rubber of the present invention, in the first decomposition step, metathesis decomposition is performed using a catalyst represented by the above general formula (1), (2), or (3), thereby decomposing the diene rubber and reducing its molecular weight, for example, to a liquid polymer or liquid oligomer. Therefore, even if the crosslinked rubber contains carbon black, the carbon black can be easily separated and recovered after the first decomposition step, for example, by solid-liquid separation. By recovering the carbon black before the thermal decomposition in the second decomposition step, it can be reused as high-quality carbon black. Furthermore, even if the crosslinked rubber contains carbon black, the crosslinked rubber can be efficiently decomposed. The content of carbon black 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.

[0032] --Sulfur-- The crosslinked rubber may further contain sulfur. Note that, in the crosslinked rubber, sulfur is usually present in a state where the diene rubber is crosslinked (as a crosslink for the diene rubber), but some of it may be free. In the method for decomposing a crosslinked rubber of the present invention, in the first decomposition step, metathesis decomposition is performed using a catalyst represented by the above general formula (1), (2), or (3), thereby decomposing the diene rubber and reducing its molecular weight, for example, to a liquid polymer or liquid oligomer. Therefore, even if the crosslinked rubber contains sulfur, the sulfur can be easily recovered after the first decomposition step, for example, by solid-liquid separation. By recovering the sulfur before the thermal decomposition in the second decomposition step, the sulfur can be reused. Furthermore, even if the crosslinked rubber contains sulfur, the crosslinked rubber can be efficiently decomposed. The sulfur content 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.

[0033] --Other Components--The crosslinked rubber may contain, in addition to the diene rubber, carbon black, and sulfur described above, 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.

[0034] (Catalyst) In the method for decomposing a crosslinked rubber according to the present embodiment, in the first decomposition step, the crosslinked rubber is decomposed by a catalyst represented by the following general formula (1), (2) or (3): The catalyst represented by the general formula (1), (2), or (3) can promote metathesis decomposition, and can decompose diene rubber simply (under mild conditions) and quickly.

[0035] 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.

[0036] 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 ２ Examples 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 ２may 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 ) ２ CO, 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).

[0037] 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 , L２ 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 ３ are 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 H４ ) 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 (CH ２ 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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:

[0045] 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.

[0046] (Reaction Conditions, etc.) The first decomposition step is preferably carried out at a temperature of 20° C. or higher and 200° C. or lower. By carrying out the first decomposition step 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 first decomposition step at 200° C. or lower, decomposition of the catalyst (metathesis catalyst) represented by the above general formula (1), (2), or (3) can be suppressed, and after 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 first decomposition step is more preferably 25° C. or higher, and from the viewpoint of suppressing decomposition of the metathesis catalyst and improving the selectivity of the product maintaining the monomer skeleton, it is more preferably 100° C. or lower.

[0047] The first decomposition step can be carried out at any pressure, including reduced pressure, normal pressure, and increased 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.

[0048] In the method for decomposing a crosslinked rubber according to this embodiment, the catalyst represented by the general formula (1), (2), or (3) may be dissolved in a solvent, and the crosslinked rubber may be immersed in the solvent to carry out the first decomposition step. By allowing the catalyst to act on the crosslinked rubber in the solvent, the decomposition reaction of the diene rubber in the crosslinked rubber is 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 is facilitated. The amount of the solvent used is preferably 10 mL or more, more preferably 50 mL or more, and is preferably 500 mL or less, and 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.

[0049] The first decomposition step 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.

[0050] (Decomposition Products (Intermediate Decomposition Products)) In the method for decomposing a crosslinked rubber of this embodiment, it is preferable to decompose 80% by mass or more of the diene rubber in the crosslinked rubber into diene oligomers having a weight average molecular weight of 100 to 50,000 through the first decomposition step. By decomposing 80% by mass or more of the diene rubber in the crosslinked rubber into diene oligomers having a weight average molecular weight of 100 to 50,000 through the first decomposition step, the yield of C4-C10 chemical products, particularly diene monomers, can be further improved through the second decomposition step described below. From the viewpoint of the yield of diene monomers after the second decomposition step, it is more preferable to decompose 85% by mass or more of the diene rubber in the crosslinked rubber into diene oligomers having a weight average molecular weight of 100 to 50,000 through the first decomposition step. Here, in this specification, oligomer refers to one having a weight average molecular weight of 50,000 or less and containing two or more monomer units. The diene oligomer is an oligomer containing two or more units derived from a diene monomer (diene units). The weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC).

[0051] <Second Decomposition Step> The method for decomposing a crosslinked rubber according to this embodiment includes a second decomposition step in which the decomposition product obtained in the first decomposition step is heated from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposed at 450 to 950°C. In one preferred embodiment, the decomposition product obtained in the first decomposition step is heated from 100°C to 600°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposed at 600 to 950°C. In another preferred embodiment, the decomposition product obtained in the first decomposition step is heated from 100°C to 450°C at a heating rate of 2000°C / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposed at 450 to 950°C. In still another preferred embodiment, the decomposition product obtained in the first decomposition step is heated from 100°C to 600°C at a heating rate of 2000°C / min or more in an inert gas atmosphere and in the absence of a catalyst, and then thermally decomposed at 600 to 950°C.

[0052] The method for decomposing crosslinked rubber according to the present embodiment may involve mixing the decomposition product obtained in the first decomposition step with at least one medium selected from organic solvents, fatty acid esters, and hydrocarbons, and thermally decomposing the mixture.

[0053] The organic solvent can be any solvent that does not inhibit the decomposition reaction, including, for example, aromatic hydrocarbons (aromatic solvents), chlorinated hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, nitriles, esters, etc. Specific examples of these include aromatic hydrocarbons such as toluene, xylene, ethylbenzene, trimethylbenzene, and propylbenzene. Specific examples of chlorinated hydrocarbons include chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethene, chlorobenzene, and dichlorobenzene. Specific examples of aliphatic hydrocarbons include pentane, hexane, and octane. Specific examples of alicyclic hydrocarbons include cyclohexane and cyclooctane. Specific examples of ethers include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and dioxane. Specific examples of nitriles include benzonitrile. Specific examples of esters include ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, and butyl propionate. Among these, aromatic hydrocarbons are preferred from the viewpoints of reaction rate, availability, etc. Specific examples of these include toluene, xylene, and ethylbenzene. Among aromatic hydrocarbons, ethylbenzene is more preferable than toluene in terms of reaction rate.

[0054] Examples of the fatty acid ester include esters of fatty acids and alcohols such as glycerin or aliphatic alcohols. Examples of the fatty acids include myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, and erucic acid. The fatty alcohol preferably has 12 to 24 carbon atoms. Specific examples of the fatty acid ester include rapeseed oil, soybean oil, olive oil, sunflower oil, safflower oil, corn oil, castor oil, jojoba oil, and palm oil. These may be hydrogenated (hydrogenated), and examples of hydrogenated fatty acid esters include hydrogenated rapeseed oil and hydrogenated jojoba oil. These fatty acid esters may be recycled or discarded, such as waste cooking oil. When the alcohol is glycerin, the fatty acid ester may be a triglyceride, as well as a monoglyceride or a diglyceride. The fatty acid moiety of the fatty acid ester preferably has 8 or more carbon atoms, more preferably 12 or more carbon atoms, and preferably 24 or less carbon atoms, more preferably 18 or less carbon atoms. When the fatty acid moiety of the fatty acid ester has 8 or more carbon atoms, the fatty acid ester is present in the reaction field during thermal decomposition, allowing it to fully exert its effect. In addition, the amount of hydrogen generated when the fatty acid ester is decomposed increases, providing more hydrogen to the liquid polymer and accelerating the decomposition of the liquid polymer. Furthermore, when the fatty acid moiety of the fatty acid ester has 24 or less carbon atoms, it is easily miscible with the liquid polymer.

[0055] Examples of the hydrocarbon include liquid paraffin, microcrystalline wax, asphalt-mixed naphthenic oil, polyethylene, polypropylene, etc., of which liquid paraffin and microcrystalline wax are preferred, and microcrystalline wax is more preferred. The hydrocarbon preferably has 12 or more carbon atoms, more preferably 20 or more carbon atoms, and preferably 80 or less carbon atoms, more preferably 60 or less carbon atoms. When the hydrocarbon has 12 or more carbon atoms, it is present in the reaction field during thermal decomposition, allowing it to fully exert its effects. In addition, the amount of hydrogen generated during the decomposition of the hydrocarbon increases, providing more hydrogen to the liquid polymer and promoting the decomposition of the liquid polymer. Furthermore, when the hydrocarbon has 80 or less carbon atoms, it is easily miscible with the liquid polymer.

[0056] (Temperature-Raising Conditions) In the method for decomposing a crosslinked rubber according to the present embodiment, the decomposition product obtained in the first decomposition step or the mixture is heated from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst (temperature-raising step). If the heating rate from 100°C to 450°C is less than 800°C / min, the proportion of decomposition occurring during heating increases, and decomposition products having higher molecular weights than the C4-C10 chemical products from the decomposition product obtained in the first decomposition step or the mixture are generated and volatilized during heating (i.e., at a temperature lower than the target decomposition temperature), resulting in a decrease in the yield of the final C4-C10 chemical products (particularly diene monomers). The temperature rise rate from 100°C to 450°C is preferably 2000°C / min or more. When the temperature rise rate is 2000°C / min or more, the generation of decomposition products obtained in the first decomposition step or high-molecular-weight decomposition products from the mixture can be further suppressed, and the yield of C4 to C10 chemical products (particularly diene monomers) can be further improved.

[0057] In a preferred embodiment, the decomposition product or the mixture obtained in the first decomposition step is heated from 100°C to 600°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst (heating step). When the heating rate from 100°C to 600°C is 800°C / min or more, the rate of decomposition during heating is reduced, and the generation and volatilization of higher molecular weight decomposition products than the C4-C10 chemical products from the decomposition product or the mixture obtained in the first decomposition step during heating (i.e., at a temperature lower than the target decomposition temperature) can be suppressed, thereby improving the yield of the final C4-C10 chemical products (particularly diene monomers). The heating rate from 100°C to 600°C is preferably 2000°C / min or more. When the heating rate is 2000°C / min or more, the generation of high molecular weight decomposition products from the decomposition product or the mixture obtained in the first decomposition step can be further suppressed.

[0058] (Reaction Conditions, etc.) In the second decomposition step of the method for decomposing a crosslinked rubber according to this embodiment, after the temperature increase, thermal decomposition is performed at 450 to 950°C in an inert gas atmosphere in the absence of a catalyst (thermal decomposition step). By performing the thermal decomposition in the second decomposition step at 450°C or higher, the rate of decomposition reaction of the decomposition product or the mixture obtained in the first decomposition step is increased, thereby improving the yield of the final C4-C10 chemical products (particularly diene monomers). Furthermore, by performing the thermal decomposition in the second decomposition step at 950°C or lower, gasification and polycyclic aromatics formation of the decomposition product can be suppressed, and after decomposition, the retention rate (selectivity) of the skeleton of the constituent monomers of the diene oligomer (liquid component) obtained in the first decomposition step is improved, thereby improving the yield of the final C4-C10 chemical products (particularly diene monomers). The temperature of the thermal decomposition in the second decomposition step is preferably 600°C or higher, more preferably 650°C or higher, from the viewpoint of improving the decomposition reaction rate of the decomposition product obtained in the first decomposition step or the mixture. Furthermore, the temperature of the thermal decomposition in the second decomposition step is preferably 850°C or lower, from the viewpoint of improving the selectivity of the product that maintains the monomer skeleton. Therefore, by carrying out the thermal decomposition in the second decomposition step at 600 to 950°C, the yield of C4-C10 chemical products (particularly diene monomers) obtained from the decomposition product obtained in the first decomposition step or the mixture is further improved, and by carrying out the thermal decomposition at 650 to 850°C, the yield of C4-C10 chemical products (particularly diene monomers) obtained from the decomposition product obtained in the first decomposition step or the mixture is further improved.

[0059] The time for thermal decomposition in the second decomposition step is not particularly limited. As an example, the heating time after reaching the target temperature for thermal decomposition in the second decomposition step is preferably 0.1 seconds to 5 minutes, more preferably 0.1 seconds to 1 minute. By performing the thermal decomposition in the second decomposition step for 0.1 seconds or more, the decomposition rate of the decomposition product or the mixture obtained in the first decomposition step is improved. On the other hand, if the decomposition time is too long, the skeletons (double bonds, etc.) of the constituent monomers of the diene oligomer (liquid component) obtained in the first decomposition step are decomposed, and the decomposition product is gasified or converted into polycyclic aromatic compounds. However, by performing the thermal decomposition in the second decomposition step for 5 minutes or less, the decomposition of the monomer skeleton and the gasification or conversion into polycyclic aromatic compounds of the decomposition product can be suppressed, and the retention rate (selectivity) of the skeletons of the constituent monomers of the diene oligomer (liquid component) obtained in the first decomposition step after decomposition is improved.

[0060] Such rapid pyrolysis methods are not particularly limited, but examples thereof include batch, fixed bed, moving hearth, rotary kiln, fluidized bed, entrained bed, microwave heating, plasma heating, high-temperature liquid spray, single-screw extrusion, twin-screw extrusion, free fall, electrified spatiotemporal heating, and wire mesh heating (Hoekstra et al., Chem. Eng. J., 191, 45 (2012)).

[0061] The temperature increase and thermal decomposition in the second decomposition step are carried out in an inert gas atmosphere. By carrying out the temperature increase and thermal decomposition in the second decomposition step in an inert gas atmosphere, oxidation and reduction of the decomposition product or the mixture obtained in the first decomposition step and the decomposition product produced in the second decomposition step can be suppressed, and in particular, hydrogenation of double bonds in the diene monomers produced can be suppressed. Examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0062] To carry out the temperature increase and thermal decomposition in the second decomposition step 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 temperature increase and thermal decomposition in the second decomposition step, the generated hydrogen is not taken into consideration when determining the atmosphere for the temperature increase and thermal decomposition in the second decomposition step.

[0063] The temperature increase and thermal decomposition in the second decomposition step can be carried out at any pressure, and can be carried out under reduced pressure, normal pressure, or increased pressure, but is preferably carried out under reduced pressure or normal pressure. As an example, the pressure for the temperature increase and thermal decomposition in the second decomposition step is preferably 1000 kPa to 65 kPa. By carrying out the temperature increase and thermal decomposition under reduced pressure or normal pressure, polymerization (repolymerization) of oligomers and diene monomers in the decomposition product can be suppressed.

[0064] Furthermore, when the second decomposition step is carried out, for example, under pressure, the decomposition product or the mixture obtained in the first decomposition step may be thermally decomposed in a solvent. 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, 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 more preferably 200 mL or less per gram of the decomposition product or the mixture obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step). If the amount of the solvent used is 10 mL or more per 1 g of the decomposition product or the mixture obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step), the decomposition reaction will proceed further. Furthermore, if the amount of the solvent used is 500 mL or less per 1 g of the decomposition product or the mixture obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step), this is preferable from the standpoint of cost.

[0065] The second decomposition step is carried out in the absence of a catalyst (i.e., no catalyst is used). Not using a catalyst in the second decomposition step 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 reaction system of the second decomposition step.

[0066] (Decomposition Products) In the method for decomposing a crosslinked rubber according to the present embodiment, C4 to C10 chemical products (particularly diene monomers) and the like are obtained as decomposition products in the second decomposition step.

[0067] In the method for decomposing crosslinked rubber according to this embodiment, it is preferable that the second decomposition step decomposes 20% by mass or more of the diene oligomers having a weight average molecular weight of 100 to 50,000 obtained in the first decomposition step into C4-C10 chemical products. By improving the yield of C4-C10 chemical products, the yield of reusable monomers and oligomers is improved, further improving the economic and environmental value of the decomposition method. From the viewpoint of the yield of reusable monomers and oligomers, it is even more preferable that the second decomposition step decomposes 30% by mass or more of the diene oligomers having a weight average molecular weight of 100 to 50,000 obtained in the first decomposition step into C4-C10 chemical products.

[0068] Here, the total amount of C4-C10 chemical products, particularly diene monomers, in the decomposition products obtained in the second decomposition step may depend not only on the reaction conditions described above but also on the reaction apparatus used. In this embodiment, the preferred range of the total amount of C4-C10 chemical products, particularly diene monomers, is the preferred range when the reaction apparatus described in the Examples below is used. When a reaction apparatus more suitable for the present invention is used, the total amount of C4-C10 chemical products, particularly diene monomers, may be even greater.

[0069] Furthermore, in the method for decomposing a crosslinked rubber of this embodiment, it is preferable to decompose 0.1% by mass or more of the diene rubber in the crosslinked rubber into C4-C10 chemical products through the first decomposition step and the second decomposition step. By improving the yield of C4-C10 chemical products, the yield of reusable monomers is improved, further improving the economic and environmental value of the decomposition method. Note that, from the viewpoint of the yield of reusable monomers, it is even more preferable to decompose 20% by mass or more of the diene rubber in the crosslinked rubber into C4-C10 chemical products through the first decomposition step and the second decomposition step.

[0070] The C4-C10 chemical products as decomposition products vary depending on the type of diene rubber in the crosslinked rubber to be decomposed, but examples include hydrocarbons having 4 to 10 carbon atoms and derivatives thereof, such as 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, benzene, toluene, ethylbenzene, xylene, and limonene, with 1,3-butadiene and isoprene being preferred. The proportion of the C4-C10 chemical products, particularly the total amount of diene monomers, in the decomposition products can be controlled by, for example, the reaction conditions in the second decomposition step, such as the reaction temperature and reaction time.

[0071] <Others> The method for decomposing a crosslinked rubber according to this embodiment may further include another step in addition to the first and second decomposition steps described above. Such steps include a pretreatment step for the crosslinked rubber (for example, a cutting step or a pulverization step). Furthermore, when the crosslinked rubber contains carbon black, it is preferable to include a step of recovering the carbon black from the decomposition product (intermediate decomposition product) between the first and second decomposition steps.

[0072] The decomposition method for crosslinked rubber according to this embodiment can be carried out in either a batch reactor or a flow reactor. The decomposition product after the decomposition reaction can be separated and recovered by filtration, distillation, or the like, or recovered by precipitation using a poor solvent, and can be reused. The diene monomer finally obtained from the crosslinked rubber can be reused as a raw material for diene rubber (polymer).

[0073] 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.

[0074] <Measurement of Molecular Weight> The polystyrene-equivalent weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (D=Mw / Mn) of the degradation products (intermediate degradation products) were determined by 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) using monodisperse standard polystyrene as a standard. The measurement temperature was 40°C.

[0075] <Decomposition rate in the first decomposition step> The decomposition rate in the first decomposition step was calculated based on the following formula, in which the unreacted solid rubber after the reaction was recovered and weighed, and the ratio to the weight of the rubber before the reaction was used. The decomposition rate was set to 100% when no solid rubber remained after the reaction. Decomposition rate in the first decomposition step (%) = {1 - (weight of unreacted solid rubber after the reaction / weight of rubber before the reaction)} x 100

[0076] <Structural Formula of Catalyst Used> The structural formula of the catalyst used in the first decomposition step is as follows.

[0077] <Preparation of Crosslinked Rubber Samples> (Crosslinked Rubber Sample A) A rubber composition was prepared by blending 50.0 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 100.1 parts by mass of natural rubber. The rubber composition was then heated and crosslinked to prepare a crosslinked rubber. The resulting crosslinked rubber was cut to approximately 2 to 6 mm on a side to prepare a crosslinked rubber sample. Furthermore, crosslinked rubber samples (approximately 1 mm on a side or less) were also prepared by further freeze-pulverization after cutting.

[0078] (Crosslinked Rubber Sample B) A rubber composition was prepared by blending 50.0 parts by mass of carbon black, 2.0 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 1.0 part by mass of antioxidant trimethyldihydroquinoline polymer, 2.0 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 0.6 parts by mass of vulcanization accelerator (N-cyclohexyl-2-benzothiazolylsulfenamide), and 1.8 parts by mass of sulfur with 100.0 parts by mass of natural rubber, and the rubber composition was heated and crosslinked to prepare a crosslinked rubber. The obtained crosslinked rubber was cut and further freeze-pulverized to prepare crosslinked rubber samples (approximately 1 mm on a side).

[0079] Example of the First Decomposition Step Example 1-1 10 mL of tetrahydrofuran (THF) was added to 0.125 g of the crosslinked rubber sample A (a sample that had only been cut), and the mixture was stirred at 25°C for 24 hours to swell the rubber. 24 mg of a second-generation Grubbs catalyst (G2) was added, and the mixture was stirred at 25°C for an additional 24 hours to carry out a metathesis decomposition reaction. After the reaction, the reaction was stopped by adding 10 mL of methanol and 2.5 mL of ethyl vinyl ether. Since no rubber sample remained after the reaction, the decomposition rate of the rubber sample was calculated to be 100%. Subsequently, the solvent was distilled off under reduced pressure to obtain a liquid polymer and carbon black. A portion of the mixture was taken, tetrahydrofuran was added, and the carbon black was removed by filtration using a syringe filter. The molecular weight of the liquid polymer was measured by GPC analysis. The results are shown in Table 1.

[0080] The reaction conditions (type and amount of catalyst, type and amount of solvent, and reaction scale) were changed, and the reaction of the first decomposition step was carried out in the same manner as in Example 1-1. The results are shown in Table 1.

[0081] (Examples 1-11) 10 mL of tetrahydrofuran and 24 mg of second-generation Grubbs catalyst (G2) were added to 0.125 g of the crosslinked rubber sample A (a sample that was freeze-pulverized after cutting), and the mixture was stirred at 25°C for 24 hours to carry out a metathesis decomposition reaction. After the reaction, the reaction was stopped by adding 10 mL of methanol and 2.5 mL of ethyl vinyl ether. Since no rubber sample remained after the reaction, the decomposition rate of the rubber sample was calculated to be 100%. Subsequently, the solvent was distilled off under reduced pressure to obtain a liquid polymer and carbon black. A portion of the mixture was taken, and tetrahydrofuran was added. The carbon black was removed by filtration using a syringe filter, and the molecular weight of the liquid polymer was measured by GPC analysis. The results are shown in Table 1.

[0082] (Example 1-12) 10 mL of tetrahydrofuran was added to 0.125 g of the crosslinked rubber sample A (a sample that had only been cut), and the mixture was stirred at room temperature for 24 hours to swell the rubber. Subsequently, 40 mg of cis-1,4-diacetoxy-2-butene was added as a chain transfer agent (CTA), and 24 mg of a second-generation Grubbs catalyst (G2) was added, and metathesis degradation was carried out for 24 hours. After the reaction, the reaction was terminated by adding 10 mL of methanol and 2.5 mL of ethyl vinyl ether. Since no rubber sample remained after the reaction, the decomposition rate of the rubber sample was calculated to be 100%. Subsequently, the solvent was distilled off under reduced pressure to obtain a liquid polymer and carbon black. A portion of the reaction mixture was sampled, tetrahydrofuran was added, and the carbon black was removed by filtration using a syringe filter. The molecular weight of the liquid polymer was measured by GPC analysis. The results are shown in Table 1.

[0083] (Example 1-13) 10 mL of tetrahydrofuran and 8 mg of second-generation Grubbs catalyst (G2) were added to 0.125 g of the crosslinked rubber sample B (a sample that was freeze-pulverized after cutting), and the mixture was stirred at 25°C for 24 hours to carry out a metathesis decomposition reaction. Since no rubber sample remained after the reaction, the decomposition rate of the rubber sample was calculated to be 100%. The reaction solution was diluted with tetrahydrofuran, and the carbon black was separated by centrifugation and washed with tetrahydrofuran. The initial supernatant and the washings were combined and concentrated under reduced pressure to obtain a liquid polymer. A portion was sampled and the molecular weight of the liquid polymer was measured by GPC analysis. The results are shown in Table 1.

[0084] The reaction conditions (amount of catalyst, type and amount of solvent, and reaction scale) were changed, and the reaction of the first decomposition step was carried out in the same manner as in Example 1-13. The results are shown in Table 1.

[0085]

[0086] (Notes for Table 1) 1) In Examples 1-1 to 1-10 and 1-12, samples were used in which only the crosslinked rubber was cut, and in Examples 1-11 and 1-13 to 1-23, samples were used in which the crosslinked rubber was cut and then freeze-pulverized. When the freeze-pulverized sample was used, the step of swelling the rubber was omitted. 2) GPC was not measured.

[0087] <Examples of the Second Decomposition Step> (Examples 2-1 to 2-3) A reaction tube was filled with 0.1 g of a liquid rubber sample (Kuraray Co., Ltd., liquid polyisoprene LIR-30) wrapped in quartz wool (Tosoh, fine fiber diameter: 2 to 6 μm), and quartz wool was filled upstream and downstream of the sample. A helium introduction line was installed upstream of the reaction tube, and a cooling trap filled with chloroform (60% ethylene glycol aqueous solution, cooled to -20°C) was installed downstream, and gas passing through the trap was collected using a gas bag. Under conditions of a helium flow rate of 50 mL / min, the liquid rubber sample in the reaction tube was slid onto a heating site in an electric furnace heated to 500°C, 600°C, or 700°C, and heated at that temperature for 3 minutes to perform thermal decomposition. During this process, the temperature of the crosslinked rubber sample was monitored with a thermocouple, and the heating rate was determined. After the reaction was completed, the reaction tube was cooled, and the products precipitated in the reaction tube and trap were collected. Gas products were also collected using a gas bag. The mass proportions (yields) of each product are shown in Table 2. Furthermore, the yields of isoprene, limonene, toluene, xylene, and other aromatic compounds, as well as other aliphatic compounds, in the liquid product were measured by gas chromatography (GC), and the total yield of C4-C10 chemical products was calculated. The results are summarized in Table 2.

[0088] Example 2-4: The liquid rubber sample was changed to liquid polyisoprene LIR-50 manufactured by Kuraray Co., Ltd., and 0.1 g of liquid polyisoprene was supported on 0.5 g of quartz sand instead of quartz wool. Heating was performed at the heating rate shown in Table 2. The same procedures as in Example 2-3 were used to recover the product, and the gaseous product was also recovered using a gas bag. The mass proportions (yields) of each product are shown in Table 2. Furthermore, the yields of isoprene, limonene, toluene, xylene, and other aromatic compounds, as well as other aliphatic compounds, in the liquid product were measured by gas chromatography (GC), and the total yield of C4-C10 chemical products was calculated. The results are summarized in Table 2.

[0089] (Example 2-5) The product was recovered in the same manner as in Example 2-4, except that the liquid rubber sample was changed to liquid polyisoprene LIR-30 manufactured by Kuraray Co., Ltd., and the gas product was also recovered using a gas bag. The mass proportion (yield) of each product is shown in Table 2. Furthermore, the yields of isoprene, limonene, toluene, xylene, other aromatic compounds, and other aliphatic compounds in the liquid product were measured by gas chromatography (GC), and the total yield of chemical products from C4 to C10 was calculated. The results are summarized in Table 2.

[0090] (Example 2-6) The product was recovered in the same manner as in Example 2-4, except that the liquid rubber sample was replaced with the liquid polymer obtained in Example 1-23, and the gaseous product was also recovered using a gas bag. The mass proportion (yield) of each product is shown in Table 2. Furthermore, the yields of isoprene, limonene, toluene, xylene, and other aromatic compounds, as well as other aliphatic compounds in the liquid product were measured by gas chromatography (GC), and the total yield of chemical products from C4 to C10 was calculated. The results are summarized in Table 2.

[0091]

[0092] *1 Yield of gaseous product: A value calculated from the amount of decomposition products recovered by gas bag. *2 Yield of liquid product: A value calculated from the amount of components that could be qualitatively analyzed by gas chromatography (GC) out of the total amount of (1) the decomposition products recovered by a cooling trap and (2) the components that were dissolved in chloroform out of the components that adhered to the reaction tube. *3 Yield of oligomer: A value calculated from the amount of components that could not be qualitatively analyzed by gas chromatography (GC) out of the total amount of (1) the decomposition products recovered by a cooling trap and (2) the components that were dissolved in chloroform out of the components that adhered to the reaction tube. *4 Yield of solid product: A value calculated from the total amount of (1) the residue of the thermal decomposition reaction minus the carbon black content in the crosslinked rubber sample, and (2) the amount of the components that were not dissolved in chloroform out of the components that adhered to the reaction tube.

[0093] Table 2 shows that by increasing the temperature from 100°C to 450°C at a rate of 800°C / min or more and then performing thermal decomposition at 450 to 950°C, it is possible to obtain C4-C10 chemical products, particularly isoprene (diene monomer), in high yield.

[0094] From the results of Examples 1-1 to 1-23 (first decomposition step) and Examples 2-1 to 2-6 (rapid temperature-rising pyrolysis of liquid polymer), it is presumed that by heating the decomposition product obtained in the first decomposition step of the method for decomposing crosslinked rubber of the present invention in an inert gas atmosphere and in the absence of a catalyst from 100°C to 450°C at a heating rate of 800°C / min or more and then pyrolyzing it at 450 to 950°C, C4 to C10 chemical products, in particular isoprene (diene monomer) can be obtained in high yield.

Claims

1. A crosslinked rubber containing a diene rubber represented by the following general formula (1), (2) or (3): [In the formula, M is ruthenium, titanium, molybdenum or tungsten; X １ and X ２ each independently represents a ligand; L １ , L ２ and L ３ each independently represents a ligand; R １ , R ２ and R ３ each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl 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); L １ and L ２ may be bonded to each other to form a ring, R １ and R ２ may be bonded to each other to form a ring, L １ and R １ may be bonded to each other to form a ring], and a second decomposition step of heating the decomposition product obtained in the first decomposition step from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst, and thermally decomposing the decomposition product at 450 to 950°C.

2. A crosslinked rubber containing a diene rubber represented by the following general formula (1), (2) or (3): [In the formula, M is ruthenium, titanium, molybdenum or tungsten; X １ and X ２ each independently represents a ligand; L １ , L ２ and L ３ each independently represents a ligand; R １ , R ２ and R ３ each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl 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); L １ and L ２ may be bonded to each other to form a ring, R １ and R ２ may be bonded to each other to form a ring, L １ and R １ may be bonded to each other to form a ring], and a second decomposition step of heating the decomposition product obtained in the first decomposition step from 100°C to 600°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the absence of a catalyst, to thermally decompose the decomposition product at 600 to 950°C.

3. A crosslinked rubber containing a diene rubber represented by the following general formula (1), (2) or (3): [In the formula, M is ruthenium, titanium, molybdenum or tungsten; X １ and X ２ each independently represents a ligand; L １ , L ２ and L ３ each independently represents a ligand; R １ , R ２ and R ３ each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl 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); L １ and L ２ may be bonded to each other to form a ring, R １ and R ２ may be bonded to each other to form a ring, L １ and R １ may be bonded to each other to form a ring], and a second decomposition step of heating the decomposition product obtained in the first decomposition step from 100°C to 450°C at a heating rate of 2000°C / min or more in an inert gas atmosphere and in the absence of a catalyst, to thermally decompose the decomposition product at 450 to 950°C.

4. A crosslinked rubber containing a diene rubber represented by the following general formula (1), (2) or (3): [In the formula, M is ruthenium, titanium, molybdenum or tungsten; X １ and X ２ each independently represents a ligand; L １ , L ２ and L ３ each independently represents a ligand; R １ , R ２ and R ３ each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl 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); L １ and L ２ may be bonded to each other to form a ring, R １ and R ２ may be bonded to each other to form a ring, L １ and R １ may be bonded to each other to form a ring], and a second decomposition step of heating the decomposition product obtained in the first decomposition step from 100°C to 600°C at a heating rate of 2000°C / min or more in an inert gas atmosphere and in the absence of a catalyst, to thermally decompose the decomposition product at 600 to 950°C.

5. The method for decomposing crosslinked rubber according to any one of claims 1 to 4, wherein the thermal decomposition in the second decomposition step is carried out at 650 to 850°C.

6. A method for decomposing crosslinked rubber according to any one of claims 1 to 4, wherein after the first decomposition step, 80 mass% or more of the diene rubber in the crosslinked rubber is decomposed into diene oligomers having a weight average molecular weight of 100 to 50,000.

7. The method for decomposing crosslinked rubber according to claim 6, wherein 30 mass % or more of the diene oligomers are decomposed into chemical products having a molecular weight of C4 to C10 through the second decomposition step.

8. A method for decomposing crosslinked rubber described in any one of claims 1 to 4, wherein 20 mass% or more of the diene rubber in the crosslinked rubber is decomposed into chemical products of C4 to C10 through the first decomposition step and the second decomposition step.

9. A method for decomposing crosslinked rubber according to any one of claims 1 to 4, wherein the first decomposition step is carried out at a temperature of 20°C or higher and 200°C or lower.

10. The method for decomposing crosslinked rubber according to any one of claims 1 to 4, wherein the diene rubber comprises at least one selected from the group consisting of isoprene skeleton rubber, styrene-butadiene rubber, and butadiene rubber.

11. The method for decomposing crosslinked rubber according to any one of claims 1 to 4, wherein the crosslinked rubber further contains carbon black.

12. The method for decomposing crosslinked rubber according to any one of claims 1 to 4, wherein the crosslinked rubber further contains sulfur.

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