Method for decomposing organic material

Abstract

The present invention addresses the problem of providing a method for decomposing a crosslinked rubber or an uncrosslinked rubber, the method being capable of suppressing gelling of a decomposition product. A means for solving the problem is a method for decomposing an organic material by mixing an organic material selected from among a crosslinked rubber and an uncrosslinked rubber containing a diene-based rubber with a solvent and a disulfide compound so as to decompose the organic material. The method is characterized in that the disulfide compound has only one disulfide bond in the molecule.

Description

Methods for decomposing organic materials

[0001] This invention relates to a method for decomposing organic materials.

[0002] Traditionally, rubber products primarily made from cross-linked rubber, such as vulcanized rubber, have been difficult to recycle. After their lifespan, they are often reused as fuel, particularly in cement factories. However, with the growing environmental concerns, there is a growing demand for the development of methods to reuse materials obtained by decomposing rubber products, rather than burning them as fuel. Furthermore, uncross-linked rubber materials are sometimes discarded as scraps during the rubber product manufacturing process, and there is a need for the development of methods to reuse such uncross-linked rubber. Various methods exist for decomposing cross-linked and uncross-linked rubber. For example, a technology for thermal decomposition of cross-linked and uncross-linked rubber at high temperatures is known. In addition, Patent Document 1 below discloses a method for decomposing polyisoprene rubber using microorganisms.

[0003] Japanese Patent Publication No. 2009-247241

[0004] As described above, there are various methods for decomposing crosslinked rubber and uncrosslinked rubber, but from the viewpoint of improving the recyclability of crosslinked rubber and uncrosslinked rubber, it is important to increase the yield of chemicals obtained by decomposition, especially monomers. However, as described above, when organic materials such as crosslinked rubber and uncrosslinked rubber are thermally decomposed at high temperatures, the decomposition products tend to gasify or become aromatized, and the yield of monomers cannot be sufficiently increased. Furthermore, when decomposing crosslinked rubber using microorganisms, as in the technology disclosed in Patent Document 1, there are problems such as the fact that decomposition takes a long time and the yield of monomers is low.

[0005] In response to this, the inventors have found that by decomposing organic materials such as crosslinked rubber and uncrosslinked rubber at a lower temperature than conventional thermal decomposition, a liquid polymer (i.e., a partially decomposed rubber product) can be obtained, and by further thermal decomposition (depolymerization) of this liquid polymer, monomers can be obtained. However, further investigation by the inventors revealed that when organic materials such as crosslinked rubber and uncrosslinked rubber are decomposed into liquid polymers, in particular when crosslinked rubber and uncrosslinked rubber are decomposed into liquid polymers in a solvent, the decomposition products tend to gel. In particular, when the crosslinked rubber or uncrosslinked rubber contains butadiene-based rubber, the decomposition products are more likely to gel, and even when the crosslinked rubber or uncrosslinked rubber contains isoprene-based rubber, gelation occurs when decomposition is carried out under oxygen-free conditions.

[0006] Therefore, the object of the present invention is to provide a method for decomposing crosslinked rubber and uncrosslinked rubber that can solve the problems of the above-mentioned prior art and suppress the gelation of decomposition products.

[0007] The gist of the present invention's method for decomposing organic materials, which solves the above problems, is as follows.

[0008] [1] A method for decomposing an organic material, comprising mixing an organic material selected from crosslinked rubber and uncrosslinked rubber containing diene rubber with a solvent and a disulfide compound, wherein the disulfide compound has only one disulfide bond in its molecule.

[0009] [2] The method for decomposing an organic material according to [1], wherein the solvent is at least one selected from the group consisting of toluene, xylene, cyclohexane, and butyl acetate.

[0010] [3] The method for decomposing an organic material according to [1] or [2], wherein the disulfide compound is at least one selected from the group consisting of aromatic disulfides and aliphatic disulfides.

[0011] [4] The method for decomposing an organic material according to any one of [1] to [3], wherein the disulfide compound is at least one selected from the group consisting of diphenyl disulfide, di-p-tolyl disulfide, bis(4-hydroxyphenyl) disulfide, 4,4'-dichlorodiphenyl disulfide, dicyclohexyl disulfide, dioctyl disulfide, didodecyl disulfide, and bis(phenylacetyl) disulfide.

[0012] [5] The method for decomposing an organic material according to any one of [1] to [4], wherein the amount of the disulfide compound is 5% by mass or more and 20% by mass or less of the amount of diene rubber in the organic material.

[0013] [6] A method for decomposing an organic material according to any one of [1] to [5], wherein the decomposition temperature is 150°C to 300°C.

[0014] [7] A method for decomposing an organic material according to any one of [1] to [6], wherein the decomposition time is 1 hour to 48 hours.

[0015] [8] The method for decomposing an organic material according to any one of [1] to [7], wherein the diene rubber comprises at least butadiene rubber.

[0016] According to the present invention, it is possible to provide a method for decomposing crosslinked rubber and uncrosslinked rubber that can suppress the gelation of decomposition products.

[0017] The method for decomposing organic materials according to the present invention will be described in detail below, based on its embodiments.

[0018] <Definitions> The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, or recycled resources.

[0019] <Method for Decomposing Organic Materials> In the method for decomposing organic materials of this embodiment, an organic material selected from crosslinked rubber and uncrosslinked rubber containing diene rubber is decomposed by mixing it with a solvent and a disulfide compound. Furthermore, in the method for decomposing organic materials of this embodiment, the disulfide compound is characterized in that it has only one disulfide bond (S-S bond) in its molecule.

[0020] As described above, when crosslinked rubber or uncrosslinked rubber is decomposed into liquid polymers, particularly when crosslinked rubber or uncrosslinked rubber is decomposed into liquid polymers in a solvent, the decomposition products tend to gel. This gelation is especially likely when the crosslinked rubber or uncrosslinked rubber contains butadiene-based rubber. To address this problem, the organic material decomposition method of this embodiment adds a disulfide compound having only one disulfide bond to the solvent in order to eliminate gelation during decomposition. While we do not wish to be constrained by theory, it is believed that in the organic material decomposition method of this embodiment, the disulfide compound having only one disulfide bond acts on the decomposition products, thereby suppressing re-crosslinking of the decomposition products and thus suppressing gelation of the decomposition products. Therefore, according to the organic material decomposition method of this embodiment, it is possible to suppress gelation of the decomposition products. Furthermore, according to the organic material decomposition method of this embodiment, the decomposition of the organic material is promoted by the addition of a disulfide compound having only one disulfide bond, and by depolymerizing the resulting decomposition products, the yield of the final diene-based monomer can be improved.

[0021] (Organic Material) In the method for decomposing an organic material of this embodiment, the organic material to be decomposed is selected from crosslinked rubber and uncrosslinked rubber. These organic materials may be a single type or a mixture of two or more types.

[0022] The aforementioned crosslinked rubber and uncrosslinked rubber may contain diene rubber as a rubber component, and may further contain compounding agents such as carbon black and sulfur.

[0023] The crosslinked and uncrosslinked rubbers used for decomposition may be grouped beforehand based on the type of diene rubber they contain, and then decomposed separately for each group. Alternatively, they may be grouped based on the type of filler they contain (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then decomposed separately for each group. Furthermore, they may be grouped both by the type of diene rubber and the type of filler, and then decomposed separately for each group. When decomposition is performed by group in this way, recycled carbon black, recycled silica, etc. with more uniform physical properties can be obtained, resulting in a rubber composition with better performance when they are re-combined into the rubber composition.

[0024] Furthermore, if the cross-linked rubber used for decomposition is derived from tires, it may be grouped beforehand by tire type (for example, passenger car tires, truck and bus tires, heavy off-road vehicle tires, aircraft tires, agricultural vehicle tires, etc.) and then decomposed separately for each group. Alternatively, it may be grouped beforehand by tire component (for example, tread rubber, sidewall rubber, bead rubber, steel cord coated rubber, organic fiber coated rubber, pad rubber, cushion rubber, etc.) and then decomposed separately for each group. In addition, it may be grouped by both tire type and tire component, and then decomposed separately for each group. When decomposition is performed group by group in this way, recycled carbon black with more uniform physical properties can be obtained, resulting in a rubber composition with better performance when it is again incorporated into a rubber composition.

[0025] The form of the crosslinked rubber is not particularly limited and may be, for example, powdered rubber. This powdered rubber can be obtained by cutting and crushing used rubber products such as waste tires. The crushing process may include multiple steps such as a preliminary crushing process and a fine crushing process, and the particle size of the powdered rubber to be used may be adjusted by a classification process after the crushing process.

[0026] The form of the uncrosslinked rubber is not particularly limited, and examples include scraps of unvulcanized rubber sheets discarded during the manufacturing process of rubber products.

[0027] The aforementioned cross-linked rubber may be recycled waste rubber, used rubber products, etc. Waste rubber refers to all discarded rubber, including not only rubber generated from rubber products, but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is, for example, fine rubber generated in the buffing process of retreading tires, where the tread portion remaining on the base tire is scraped off. Peeling rubber is, for example, long pieces of rubber, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by scraping the surface of rubber products such as tires using a U-shaped or V-shaped knife like a peeler. Rubber products include, for example, final products such as tires and rubber hoses, and rubber parts or components at the manufacturing stage of final products. Used tires may be, for example, retreaded tires, or tires that have been discarded for any reason, such as tire replacements, scrapped vehicles, or End-of-Life Tires (ELTs) that have reached the end of their lifespan as tires.

[0028] The collected rubber products such as tires may undergo a "dismantling and downsizing" process. Dismantling and downsizing is a series of processes that crush rubber products such as tires and separate them into individual materials. Dismantling and downsizing may further involve the following processes in this order: "separation," "cutting," "chipping," "crushing," and "grinding." Separation is the process of separating the rubber product into individual materials (rubber and metal, etc.). Cutting is the process of cutting the rubber product into fragments according to its parts (tread and sidewall, etc.). Chipping is the process of scraping or drilling holes in the rubber product. Crushing is the process of crushing the rubber product into chips of several inches in size. Grinding is the process of grinding the rubber product into granules.

[0029] The separation methods mentioned above include pulling, induction heating, punch cutting, magnetic separation, cutting separation, mechanical separation, cooling, and water jetting. Pulling is a method of pulling the bead out of the tire by hooking it with a hook or the like. Induction heating is a method of separating the metal bead and rubber by reducing the adhesive force between them through induction heating. Punch cutting is a method of removing the bead from the tire by making a series of overlapping punch cuts (holes) in the tire sidewall around the bead. Magnetic separation is a method of separating the metal bead and rubber by utilizing magnetic force. Cutting separation is a method of cutting and separating the metal bead and rubber using a blade, cutter blade, knife, or rotary milling machine. Mechanical separation is a method of separating the metal and rubber by applying sufficient mechanical force to separate them. Cooling is a method of separating the rubber after it has been embrittled by cooling with liquid nitrogen or the like. Water jetting is a method of separating the rubber and metal by spraying water at high pressure.

[0030] The aforementioned cutting methods include rotary blades, blade cutters, L-shaped knives, water jets, and pneumatic cutting. Rotary blades are a method of cutting by applying a rotating blade (including blades, circular saws, etc.) to the object. Blade cutters are a method of cutting using a blade or cutter blade. L-shaped knives are a method of cutting using an L-shaped knife. Water jets are a method of cutting by spraying water (including water containing sand) at high pressure. Pneumatic cutting is a method of cutting using compressed air.

[0031] The aforementioned methods of cutting include punch cutting and filing. Punch cutting is a method of making holes using a punch blade. Filing is a method of filing down the tire using a file.

[0032] As the method of crushing, a rotary blade, a blade cutter, and a cutting wheel can be mentioned. The rotary blade is a method of crushing by applying a rotated blade (including a blade, a circular saw, etc.) to an object. The blade cutter is a method of crushing using a blade or a cutter blade. The cutting wheel is a method of crushing by arranging a cutting blade on a wheel-shaped crushing part and applying it to an object.

[0033] As the method of pulverization, a roller mill, a pin mill, and a water jet can be mentioned. The roller mill is a method of pulverization by the "grinding and crushing action" in which the compressive force due to the centrifugal force of the roller and the shearing force due to the rotation of the roller overlap. The pin mill is a method of pulverization by attaching dozens of pins to the surfaces of two facing disks and rotating them at high speed. The water jet is a method of pulverization by spraying water at high speed and causing it to collide with an object.

[0034] Furthermore, for the separation described above, the following separation methods may be selected depending on the object to be separated. If the object to be separated is metal, magnetic separation, "drawing, peeling, tearing", melting, crushing, punching, high-pressure jetting, cutting / machining, sedimentation, and centrifugal classification may be selected. Magnetic separation is a method of separating metal and rubber using magnetic force. Drawing, peeling, and tearing is a method of separating metal such as bead wire from rubber by drawing it out, peeling it off, and tearing it. Melting includes vibration melting, superheated steam, and induction heating. Vibration melting is a method of separating metal components while melting the tire by vibrating it with ultrasound or the like. Superheated steam is a method of melting the rubber by blowing superheated steam and separating the metal cords. Induction heating is a method of heating the tire by electromagnetic induction and separating the metal cords. Crushing is a method of separating the metal cords from rubber by crushing the tire with rollers or the like. Punching is a separation method that removes metal cords from tires by creating a series of overlapping punching cuts in a circumferential pattern on the tire sidewall around the bead. High-pressure jetting is a method that separates metal and rubber by spraying water or other materials at high pressure. Cutting and machining is a method that separates metal and rubber parts by mechanically cutting and machining them. Sedimentation is a method that separates rubber and wires that have settled at the bottom by placing them in a water-soluble polyol at a temperature exceeding 160°C for several hours to tens of hours. Centrifugal classification is a type of wind classification that separates metal and rubber using centrifugal force.

[0035] When the object to be separated is a fiber, screening, vibrating screen, melting, air classification, centrifugal classification, gravity classification, friction, "pulling out, peeling off, tearing", high-pressure jet, electrostatic separation, mechanical thermal control, cutting may be selected. Screening is a method of separating fibers and rubber using a sieve. A vibrating screen is a separation method that performs screening by vibrating the sieve up and down. Melting includes heated steam and induction heating. Heated steam is a method of melting rubber by spraying heated steam and separating the metal cord. Induction heating is a method of heating the tire by electromagnetic induction and separating the metal cord. Air classification is a method of separating fibers and rubber powder by utilizing the differences in the hydrodynamic behavior (centrifugal force, gravity, inertial force, etc.) of particles. Centrifugal classification is a type of air classification and is a method of separating fibers and rubber using centrifugal force. Gravity classification is a type of air classification and is a method of separating fibers and rubber using gravity. Friction is a method of applying pressure to the tire to generate friction, forming aggregates from the fibers, and separating the aggregates and rubber granules using a sieve or the like. Pulling out, peeling off, and tearing are methods of separating from the rubber by pulling out, peeling off, and tearing the fiber reinforcement part. A high-pressure jet is a method of separating fibers and rubber by spraying water or the like at high pressure. Electrostatic separation is a method of charging particles using electrostatic force and separating fibers and rubber based on the differences in their charge amounts or electric field strengths. Mechanical thermal control is a method of separating rubber from the fiber reinforcement element under controlled thermal conditions. Cutting is a method of mechanically cutting and separating the fiber part and the rubber part.

[0036] When the object to be separated is a sealant, mechanical anti-friction after solidification and the use of processing aids may be selected. Mechanical anti-friction after solidification is a separation method of removing the sealant layer by mechanical anti-friction after solidifying using liquid nitrogen or the like. The use of processing aids is a separation method of removing the sealant layer using water or a soap solution.

[0037] When the material to be separated is resin, crushing, cutting, melting, or peeling may be selected. Crushing is a method of separating the resin from the rubber by crushing the tire with a roller or the like. Cutting is a method of separating the resin by cutting along the interface between the rubber layer and the resin. Melting includes vibration melting. Vibration melting is a method of separating the resin while melting the tire by vibrating it with ultrasound or the like. Peeling is a separation method in which the unfoamed rubber is foamed by heating, and a peeling force is applied between the rubber and the resin component to separate the resin component from the rubber.

[0038] -Diene-based rubber- The diene-based rubber is a rubber containing units derived from diene monomers (diene units), and may further contain units derived from copolymerizable comonomers. The units derived from diene monomers enable crosslinking (vulcanization) of the diene-based rubber and can exhibit rubber-like elongation and strength. In crosslinked rubber, the diene-based rubber usually exists in a crosslinked state, but some parts may not be crosslinked. Specific examples of diene monomers (diene compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and among these, 1,3-butadiene and isoprene are preferred, with isoprene being particularly preferred. On the other hand, examples of copolymerizable comonomers include aromatic vinyl compounds. Examples of the aromatic vinyl compound include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene.

[0039] Examples of the diene-based rubber include isoprene-based rubber and butadiene-based rubber. Isoprene-based rubber is rubber containing isoprene units, while butadiene-based rubber is rubber containing butadiene units. Examples of isoprene-based rubber include isoprene-skeleton rubber and styrene-isoprene rubber (SIR). Examples of butadiene-based rubber include styrene-butadiene rubber (SBR) and butadiene rubber (BR). Other examples of diene-based rubber include chloroprene rubber (CR). Here, isoprene-skeleton rubber is rubber whose main skeleton is isoprene units, and specifically, examples include natural rubber (NR) and synthetic isoprene rubber (IR). Among these, the diene-based 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, easily recyclable diene monomers such as isoprene and butadiene can be obtained by decomposing the crosslinked or uncrosslinked rubber.

[0040] The diene rubber may also contain butadiene rubber. As described above, when crosslinked or uncrosslinked rubber contains butadiene rubber, the decomposition products tend to gel. However, in the organic material decomposition method of this embodiment, by using a disulfide compound having only one disulfide bond, the gelation of the decomposition products can be suppressed. Therefore, even if the organic material to be decomposed contains butadiene rubber as the diene rubber, decomposition can be carried out without pretreatment such as removing or reducing the butadiene rubber. For this reason, the organic material decomposition method of this embodiment has a wide range of organic materials to be decomposed, and even when the diene rubber contains at least butadiene rubber, the pretreatment steps can be reduced.

[0041] The diene rubber may also contain isoprene rubber. As mentioned above, even if the crosslinked rubber or uncrosslinked rubber contains isoprene rubber, if decomposition is carried out under oxygen-free conditions, the decomposition products will gel. However, in the organic material decomposition method of this embodiment, by using a disulfide compound having only one disulfide bond, the gelation of the decomposition products can be suppressed. Therefore, even if the organic material to be decomposed contains isoprene rubber as the diene rubber, decomposition can be carried out under oxygen-free conditions while suppressing gelation. Furthermore, even if the organic material to be decomposed contains isoprene rubber as the diene rubber, the gelation problem does not occur if decomposition is carried out in the presence of oxygen. However, by adding a disulfide compound having only one disulfide bond, an improvement in the yield of isoprene skeleton in the decomposition product (liquid polymer) can be expected.

[0042] The content of the diene-based rubber in the crosslinked rubber and the uncrosslinked rubber is not particularly limited, but is preferably in the range of 10 to 100% by mass, and more preferably in the range of 30 to 100% by mass from the viewpoint of further improving the yield of the liquid polymer containing the diene-based monomer in the backbone and the diene-based monomer after depolymerization.

[0043] -Carbon Black- The crosslinked rubber and uncrosslinked rubber may further contain carbon black. The carbon black is not particularly limited, and examples of grades of carbon black include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. According to the organic material decomposition method of this embodiment, the diene rubber in the organic material to be decomposed (crosslinked rubber, uncrosslinked rubber) can be decomposed to a low molecular weight, for example, a liquid polymer. Therefore, even if the crosslinked rubber or uncrosslinked rubber contains carbon black, the carbon black can be easily separated and recovered after decomposition by, for example, centrifugation or filtration, and the recovered carbon black can be reused. Furthermore, according to the organic material decomposition method of this embodiment, the decomposition of the diene rubber in the organic material to be decomposed (crosslinked rubber, uncrosslinked rubber) can be promoted, so the residual organic content in the recovered carbon black can be reduced. By reusing the recovered carbon black, which has reduced residual organic matter, in the rubber composition, a deterioration in the physical properties of the rubber composition can be suppressed. The carbon black content in the organic material is not particularly limited, and is, for example, in the range of 10 to 150 parts by mass, preferably in the range of 30 to 120 parts by mass, per 100 parts by mass of diene rubber. Furthermore, the carbon black content in the organic material is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 40% by mass or less, and even more preferably 35% by mass or less. When the carbon black content in the organic material is 20% by mass or more, the amount of carbon black that can be recovered increases.

[0044] -Sulfur- The crosslinked rubber and uncrosslinked rubber may further contain sulfur. In the crosslinked rubber, sulfur usually exists in a crosslinked state of the diene rubber (as a bridge for the diene rubber), but some may be free. According to the organic material decomposition method of this embodiment, the diene rubber in the organic material to be decomposed (crosslinked rubber, uncrosslinked rubber) can be decomposed to a low molecular weight, for example, a liquid polymer. Therefore, even if the crosslinked rubber or uncrosslinked rubber contains sulfur, the sulfur can be easily recovered after decomposition by, for example, centrifugation or filtration, and the recovered sulfur can be reused. The sulfur content in the organic material is not particularly limited, and for example, it is in the range of 0.1 to 10 parts by mass, and preferably in the range of 1 to 5 parts by mass, per 100 parts by mass of diene rubber.

[0045] -Other Components- In addition to the diene rubber, carbon black, and sulfur mentioned above, the organic material (crosslinked rubber, uncrosslinked rubber) may also contain various components commonly used in the rubber industry, such as rubber components other than diene rubber, 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 oxide), vulcanization accelerators, crosslinking agents other than sulfur (peroxide, etc.).

[0046] (Solvent) In the organic material decomposition method of this embodiment, the organic material (crosslinked rubber, uncrosslinked rubber) is decomposed in a solvent to which a disulfide compound described later is added. When the organic material is decomposed in a solvent, the organic material swells due to the solvent. By decomposing the organic material under solvent swelling, gasification and aromatization of the decomposition products can be suppressed, and decomposition products (liquid polymers) with a higher retention rate of the skeletons (isoprene skeleton, butadiene skeleton, etc.) of the constituent monomers of diene rubber can be obtained compared to normal high-temperature thermal decomposition.

[0047] Various solvents having the effect of swelling crosslinked rubber and / or uncrosslinked rubber can be used as the solvent, for example, aromatic solvents, chlorinated hydrocarbons, aliphatic solvents, alicyclic solvents, ether solvents, ester solvents, nitriles, etc. Aromatic solvents include benzene, toluene, xylene, benzonitrile, diethylbenzene, o-dichlorobenzene, p-cymene, 1,2,4-trimethylbenzene, etc. Specific examples of chlorinated hydrocarbons include chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethene, chlorobenzene, dichlorobenzene, etc. Aliphatic solvents include pentane, hexane, heptane, etc. Alicyclic solvents include cyclopentane, cyclohexane, etc. Ether solvents include tetrahydrofuran (THF), cyclopentyl methyl ether, 4-methyltetrahydropyran, etc. Ester solvents include ethyl acetate, butyl acetate, methyl benzoate, etc. Nitriles include benzonitrile, acetonitrile, etc. Among these, the solvent is preferably at least one selected from the group consisting of toluene, xylene, benzonitrile, diethylbenzene, o-dichlorobenzene, p-cymene, 1,2,4-trimethylbenzene, cyclohexane, and butyl acetate, more preferably at least one selected from the group consisting of toluene, xylene, cyclohexane, and butyl acetate, and particularly preferably toluene. When toluene, xylene, cyclohexane, or butyl acetate is used as the solvent, a decomposition product (liquid polymer) with a high retention rate of the skeleton (isoprene skeleton, butadiene skeleton, etc.) of the constituent monomers of the diene rubber can be obtained.

[0048] The amount of solvent used is preferably 1 mL or more per gram of organic material to be decomposed, more preferably 5 mL or more, more preferably 500 mL or less, and more preferably 200 mL or less. If the amount of solvent used is 10 mL or more per gram of organic material to be decomposed, the decomposition reaction of the diene rubber in the organic material proceeds further, and if the amount of solvent used is 500 mL or less per gram of organic material to be decomposed, it is preferable in terms of cost.

[0049] (Disulfide Compound) In the organic material decomposition method of this embodiment, the organic material and the solvent are mixed with a disulfide compound to carry out the decomposition. The order in which the disulfide compound is added is arbitrary. For example, the organic material may be added to the solvent first, and then the disulfide compound may be added to the solvent first, and then the organic material may be added, or the organic material and the disulfide compound may be mixed first, and then the resulting mixture may be added to the solvent.

[0050] The aforementioned disulfide compound has only one disulfide bond (S-S bond) in its molecule. While we do not wish to be constrained by theory, it is thought that using a disulfide compound with multiple S-S bonds would result in an abundance (excess) of sulfur radicals being generated at the terminals of the decomposition products, promoting the re-crosslinking reaction of the decomposition products and making them more prone to gelation. In contrast, it is thought that a disulfide compound with only one disulfide bond would suppress the generation of radicals at the terminals of the decomposition products, thereby suppressing the re-crosslinking of the decomposition products and thus suppressing the gelation of the decomposition products.

[0051] Preferred disulfide compounds include aromatic disulfides and aliphatic disulfides. By using at least one selected from the group consisting of aromatic disulfides and aliphatic disulfides as the disulfide compound, it is possible to further suppress the gelation of the decomposition product. Specific examples of aromatic disulfides include diphenyl disulfide, dibenzyl disulfide, di-p-tolyl disulfide, bis(4-hydroxyphenyl) disulfide, 4,4'-dichlorodiphenyl disulfide, 4,4'-dibromodiphenyl disulfide, bis(phenylacetyl) disulfide (also called "dibenzoyl disulfide"), and bis(2-benzamidophenyl) disulfide. Furthermore, specific examples of the aliphatic disulfide include dibutyl disulfide, diamyl disulfide, diisoamyl disulfide, dicyclohexyl disulfide, dioctyl disulfide, didecyl disulfide, and didodecyl disulfide. Among these, diphenyl disulfide, di-p-tolyl disulfide, bis(4-hydroxyphenyl) disulfide, 4,4'-dichlorodiphenyl disulfide, dicyclohexyl disulfide, dioctyl disulfide, didodecyl disulfide, and bis(phenylacetyl) disulfide are preferred as the disulfide compound. By using at least one disulfide compound selected from the group consisting of diphenyl disulfide, di-p-tolyl disulfide, bis(4-hydroxyphenyl) disulfide, 4,4'-dichlorodiphenyl disulfide, dicyclohexyl disulfide, dioctyl disulfide, didodecyl disulfide, and bis(phenylacetyl) disulfide, it is possible to further suppress the gelation of the decomposition products.

[0052] In the organic material decomposition method of this embodiment, the amount of the disulfide compound is preferably 5% by mass or more and 20% by mass or less of the amount of diene rubber in the organic material (crosslinked rubber, uncrosslinked rubber). When the amount of the disulfide compound is 5% by mass or more of the amount of diene rubber in the organic material, the effect of adding the disulfide compound is fully exerted, and the gelation of the decomposition product can be further suppressed. When the amount of the disulfide compound is 20% by mass or less of the amount of diene rubber in the organic material, the re-crosslinking of the decomposition product is suppressed, and the gelation of the decomposition product can be further suppressed. Therefore, if the amount of the disulfide compound is 5% by mass or more and 20% by mass or less of the amount of diene rubber in the organic material, it is possible to further suppress the gelation of the decomposition product.

[0053] (Reaction Conditions, etc.) In the organic material decomposition method of this embodiment, the decomposition temperature is preferably 150 to 300°C. By performing decomposition at 150°C or higher, the rate of the decomposition reaction of diene rubber in the organic material (crosslinked rubber, uncrosslinked rubber) is improved, and by performing decomposition at 300°C or lower, gasification and aromatization of the decomposition products can be suppressed, and after decomposition, the retention rate (selectivity) of the skeleton of the constituent monomer of the diene rubber in the organic material (crosslinked rubber, uncrosslinked rubber) is improved. Therefore, by setting the decomposition temperature within the range of 150°C to 300°C, it is possible to improve the rate of the decomposition reaction while improving the retention rate (selectivity) of the skeleton of the constituent monomer of the diene rubber in the organic material. From the viewpoint of improving the rate of the decomposition reaction of the organic material, the decomposition temperature is preferably 160°C or higher, and more preferably 180°C or higher. Furthermore, from the viewpoint of improving the selectivity of the product that maintains the monomer skeleton, it is preferably 280°C or lower, and more preferably 250°C or lower.

[0054] In the organic material decomposition method of this embodiment, the decomposition time is not particularly limited. For example, the decomposition time is preferably 1 to 48 hours, and more preferably 3 to 18 hours. Decomposition for 1 hour or more improves the decomposition rate of the organic material (crosslinked rubber, uncrosslinked rubber). On the other hand, if the decomposition time is too long, the skeleton (double bonds, etc.) of the constituent monomers of the diene rubber may be decomposed, or the decomposition products may be gasified or aromatized. However, by performing decomposition for 48 hours or less, the decomposition of the monomer skeleton and the gasification and aromatization of the decomposition products can be suppressed, and the retention rate (selectivity) of the skeleton of the constituent monomers of the diene rubber in the organic material after decomposition is improved. Therefore, by setting the decomposition time within the range of 1 to 48 hours, it is possible to improve the retention rate (selectivity) of the skeleton of the constituent monomers of the diene rubber while improving the decomposition rate of the organic material to be decomposed.

[0055] In the organic material decomposition method of this embodiment, the decomposition may be carried out under an inert gas atmosphere or in the presence of oxygen. Examples of inert gases include nitrogen, carbon dioxide, argon, and helium. Carrying out the decomposition under an inert gas atmosphere (particularly in an oxygen-free environment) improves process safety. On the other hand, carrying out the decomposition in the presence of oxygen improves the decomposition efficiency of the organic material and also improves the retention rate of the skeletons (isoprene skeleton, butadiene skeleton) of the constituent monomers of the diene rubber.

[0056] To carry out the aforementioned decomposition under an inert gas atmosphere or in the presence of oxygen, for example, when using a batch reactor, the atmosphere charged into the reactor should be an inert gas or an oxygen-containing gas, and when using a flow-through reactor, the atmosphere circulating through the reactor should be an inert gas or an oxygen-containing gas. Here, air is preferred as the oxygen-containing gas. Although hydrogen may be generated during decomposition, the generated hydrogen is not taken into consideration when determining the decomposition atmosphere.

[0057] The aforementioned decomposition can be carried out at any pressure, including under reduced pressure, at atmospheric pressure, or under pressurized 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.

[0058] The aforementioned decomposition may or may not involve the use of a catalyst, but it is preferable not to use a catalyst. By not using a catalyst for decomposition, costs can be reduced. If a catalyst is used, any catalyst that promotes the decomposition reaction of crosslinked rubber and / or uncrosslinked rubber can be used.

[0059] The aforementioned decomposition may or may not involve the use of a decomposition aid, but it is preferable not to use one. By not using a decomposition aid, costs can be reduced. If a decomposition aid is used, any decomposition aid that promotes the decomposition reaction of crosslinked rubber and / or uncrosslinked rubber can be used.

[0060] (Decomposition Products (Liquid Polymers)) According to the method for decomposing organic materials of this embodiment, a liquid polymer is obtained as a decomposition product by the decomposition. Herein, in this specification, a liquid polymer refers to a material that is liquid at room temperature (23°C) and contains two or more diene monomer units.

[0061] The liquid polymer preferably has a weight-average molecular weight (Mw) of 500 to 300,000, and more preferably 1,000 to 250,000. When the weight-average molecular weight (Mw) is 500 or more, the decomposition has not progressed too far, making it easy to maintain a retention rate of 30% by mass or more of the diene monomer skeleton. On the other hand, when the weight-average molecular weight (Mw) is 300,000 or less, the decomposition has progressed sufficiently, and when obtaining the diene monomer from the liquid polymer by further decomposition (for example, depolymerization described later), side reactions are less likely to proceed, and the yield of the diene monomer is easily improved. In this specification, the weight-average molecular weight (Mw) can be measured by gel permeation chromatography (GPC).

[0062] The liquid polymer preferably has a retention rate of 30% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more, of the diene monomer skeleton of the diene rubber in the organic material to be decomposed. 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 (depolymerization, etc.). In this specification, the retention rate of the diene monomer skeleton (isoprene skeleton, butadiene skeleton, etc.) is １ Measured using H-NMR.

[0063] As the diene monomer skeleton of the aforementioned diene rubber, at least one selected from the group consisting of an isoprene skeleton and a butadiene skeleton is preferred. From liquid polymers with a high retention rate of the isoprene skeleton and / or butadiene skeleton, easily reusable diene monomers such as isoprene and butadiene can be obtained in high yield by further decomposition (depolymerization, etc.).

[0064] When the aforementioned organic material (crosslinked rubber, uncrosslinked rubber) contains a diene rubber containing an isoprene skeleton, it is preferable that the retention rate of the isoprene skeleton is 30% by mass or more, and more preferably 50% by mass or more, relative to the mass of the isoprene skeleton of the diene rubber in the organic material before decomposition. From liquid polymers 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 (depolymerization, etc.).

[0065] When the aforementioned organic material (crosslinked rubber, uncrosslinked rubber) contains a diene rubber containing a butadiene skeleton, it is preferable that the retention rate of the butadiene skeleton is 30% by mass or more relative to the mass of the butadiene skeleton of the diene rubber in the organic material before decomposition. From a 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 (depolymerization, etc.).

[0066] Furthermore, if the organic material (crosslinked rubber, uncrosslinked rubber) contains carbon black together with the diene rubber, a mixture of liquid polymer and recycled carbon black can be obtained by undergoing the aforementioned decomposition. The recycled carbon black in the mixture can be recovered and reused.

[0067] (Depolymerization step) The organic material decomposition method of this embodiment may include a step of further decomposing (depolymerizing) the decomposition product (liquid polymer) obtained as described above. The further decomposition method (depolymerization method) of the decomposition product (liquid polymer) obtained as described above is not particularly limited, but examples include: (i) a method of thermally decomposing the decomposition product (liquid polymer) at 600°C to 950°C in the absence of a catalyst (first depolymerization method), (ii) a method of thermally decomposing the decomposition product (liquid polymer) at 300°C to 950°C in the presence of a catalyst (second depolymerization method), etc. These depolymerization methods will be described in detail below. In the following description of the depolymerization methods, the decomposition product (liquid polymer) obtained as described above may be simply referred to as "decomposition product (liquid polymer)".

[0068] -First Depolymerization Method- In the first depolymerization method, by performing the decomposition (depolymerization) of the decomposition product (liquid polymer) at 600°C or higher, the rate of the decomposition reaction of the decomposition product (liquid polymer) is greatly improved, and the monomer yield is greatly improved. Furthermore, by performing the decomposition (depolymerization) of the decomposition product (liquid polymer) at 950°C or lower, gasification and aromatization of the decomposition product can be suppressed, and the selectivity of the product that maintains the monomer skeleton can be improved. From the viewpoint of improving the decomposition reaction rate and improving the monomer yield, the decomposition (depolymerization) is preferably performed at 700°C or higher. Furthermore, by performing the decomposition (depolymerization) at 700°C to 900°C, it is possible to improve the rate of the decomposition reaction of the decomposition product (liquid polymer) while improving the selectivity of the product that maintains the monomer skeleton.

[0069] Furthermore, in a preferred embodiment of the first depolymerization method, the decomposition product (liquid polymer) is heated from 100°C to 450°C at a heating rate of 800°C / min or more under an inert gas atmosphere, 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 high molecular weight decomposition products such as oligomers is suppressed, and after decomposition, the retention rate (selectivity) of the skeleton of the constituent monomers of the decomposition product (liquid polymer) is further improved, and the yield of diene monomers is further improved.

[0070] Furthermore, in another preferred embodiment of the first depolymerization method, the decomposition product (liquid polymer) is heated from 100°C to 450°C at a heating rate of 2000°C / min or more under an inert gas atmosphere, 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 high molecular weight decomposition products such as oligomers is further suppressed, and after decomposition, the retention rate (selectivity) of the skeleton of the constituent monomers of the decomposition product (liquid polymer) is further improved, and the yield of diene monomers is further improved.

[0071] Furthermore, in another preferred embodiment of the first depolymerization method, the decomposition product (liquid polymer) is heated from 100°C to 600°C at a heating rate of 800°C / min or more under an inert gas atmosphere, and then 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 high molecular weight decomposition products such as oligomers is further suppressed, and after decomposition, the retention rate (selectivity) of the skeleton of the constituent monomers of the decomposition product (liquid polymer) is further improved, and the yield of diene monomers is further improved.

[0072] Furthermore, in another preferred embodiment of the first depolymerization method, the decomposition product (liquid polymer) is heated from 100°C to 600°C at a heating rate of 2000°C / min or more under an inert gas atmosphere, and then 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 high molecular weight decomposition products such as oligomers is further suppressed, and after decomposition, the retention rate (selectivity) of the skeleton of the constituent monomers of the decomposition product (liquid polymer) is further improved, and the yield of diene monomers is further improved.

[0073] Furthermore, in another preferred embodiment of the first depolymerization method, the decomposition product (liquid polymer) is mixed with a medium selected from fatty acid esters and hydrocarbons, and then thermally decomposed at 600 to 950°C under an inert gas atmosphere and in the absence of a catalyst. By thermally decomposing the decomposition product (liquid polymer) after mixing it with a medium, the decomposition of the decomposition product (liquid polymer) into diene monomers is promoted, and diene monomers can be obtained in high yield.

[0074] The first depolymerization method described above is preferably carried out under an inert gas atmosphere. By carrying out the decomposition (depolymerization) 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 of the decomposition products can be suppressed. Examples of inert gases include nitrogen, carbon dioxide, argon, and helium. To carry out the decomposition (depolymerization) under an inert gas atmosphere, for example, when using a batch reactor, the atmosphere charged into the reactor should be an inert gas, and when using a flow-through reactor, the atmosphere circulated through the reactor should be an inert gas. Although hydrogen may be generated during the decomposition (depolymerization), the generated hydrogen is not taken into consideration when determining the atmosphere for the decomposition (depolymerization).

[0075] The aforementioned decomposition (depolymerization) can be carried out at any pressure, including under reduced pressure, at atmospheric pressure, or under pressure, but it is preferable to carry it out under reduced pressure or at atmospheric pressure. As an example, the reaction pressure for the aforementioned decomposition (depolymerization) is preferably 1000 kPa to 65 kPa. By carrying out the aforementioned decomposition (depolymerization) under reduced pressure or at atmospheric pressure, polymerization (repolymerization) of the monomers of the decomposition products can be suppressed.

[0076] The reaction time for the decomposition (depolymerization) is not particularly limited. For example, the reaction time for the decomposition (depolymerization) is preferably 0.001 seconds to 1000 seconds, and more preferably 0.01 seconds to 1000 seconds.

[0077] The aforementioned decomposition (depolymerization) is carried out in the absence of a catalyst (i.e., without using a catalyst). By not using a catalyst in the aforementioned decomposition (depolymerization), costs can be reduced. Here, "in the absence of a catalyst" means that there is no catalyst in the reaction system of the aforementioned decomposition (depolymerization) that has the effect of promoting the decomposition reaction.

[0078] -Second Depolymerization Method- In the second depolymerization method, the rate of the decomposition reaction of the decomposition product (liquid polymer) is improved by performing the decomposition (depolymerization) of the decomposition product (liquid polymer) at 300°C or higher, and the selectivity of the product that maintains the monomer skeleton is improved by performing the decomposition (depolymerization) of the decomposition product (liquid polymer) at 950°C or lower. From the viewpoint of improving the rate of the decomposition reaction, a temperature of 500°C or higher is more preferable, and from the viewpoint of improving the selectivity of the product that maintains the monomer skeleton, a temperature of 900°C or lower is more preferable.

[0079] The second depolymerization method described above is preferably carried out under an inert gas atmosphere. By carrying out the decomposition (depolymerization) 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 of the decomposition products can be suppressed. Examples of inert gases include nitrogen, carbon dioxide, argon, and helium. To carry out the decomposition (depolymerization) under an inert gas atmosphere, for example, when using a batch reactor, the atmosphere charged into the reactor should be an inert gas, and when using a flow reactor, the atmosphere circulated through the reactor should be an inert gas. Although hydrogen may be generated during the decomposition (depolymerization), the generated hydrogen is not taken into consideration when determining the atmosphere for the decomposition (depolymerization).

[0080] When the decomposition (depolymerization) is carried out under pressure, for example, the decomposition product (liquid polymer) may be thermally decomposed in a solvent. Here, as the solvent, any solvent that does not inhibit the decomposition reaction can be used, and examples thereof include ethers, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons (aromatic solvents), and the like. More specifically, as the solvent, tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, and xylene are preferable, and toluene and tetrahydrofuran are more preferable. The amount of the solvent used is preferably 5 mL or more, more preferably 10 mL or more, even more preferably 50 mL or more, per 1 g of the decomposition product (liquid polymer), and is preferably 500 mL or less, more preferably 200 mL or less. When the amount of the solvent used is 10 mL or more per 1 g of the decomposition product (liquid polymer), the decomposition reaction further proceeds, and when the amount of the solvent used is 500 mL or less per 1 g of the decomposition product (liquid polymer), it is preferable in terms of cost.

[0081] The second depolymerization method is carried out in the presence of a catalyst. Here, the catalyst may be an acidic catalyst, a neutral catalyst, or a basic catalyst, and among these, a basic catalyst is preferable. Also, TiO 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 ３ It is more preferably carried out in the presence of at least one basic catalyst selected from the group consisting of. By carrying out the decomposition (depolymerization) in the presence of these basic catalysts, the rate of the decomposition reaction (depolymerization reaction) of the decomposition product (liquid polymer) is improved, and the selectivity of the product maintaining the monomer skeleton is also improved. These catalysts may be used alone or in combination of two or more.

[0082] The amount of 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 also preferably 8,000 parts by mass or less, even more preferably 4,000 parts by mass or less, and even more preferably 500 parts by mass or less, per 100 parts by mass of the decomposition product (liquid polymer). If the amount of catalyst used is 100 parts by mass or more per 100 parts by mass of the decomposition product (liquid polymer), the decomposition reaction proceeds further, and if the amount of catalyst used is 500 parts by mass or less per 100 parts by mass of the raw material, it is preferable in terms of cost.

[0083] -Depolymerization Products- Depolymerization yields monomers (particularly diene monomers) as decomposition products. The decomposition products obtained by depolymerization preferably contain 15% by mass or more of hydrocarbon compounds having 5 or fewer carbon atoms and limonene (particularly hydrocarbon compounds having 2 to 4 carbon atoms, isoprene, and limonene), more preferably 20% by mass or more, and even more preferably 25% by mass or more. Improving the yield of hydrocarbon compounds having 5 or fewer carbon atoms and limonene (particularly hydrocarbon compounds having 2 to 4 carbon atoms, isoprene, and limonene) improves the yield of reusable monomers, further improving the economic and environmental value of the decomposition method. From the viewpoint of the yield of reusable monomers, it is even more preferable that the decomposition products obtained by depolymerization contain 40% by mass or more of hydrocarbon compounds having 5 or fewer carbon atoms. Here, the total amount of hydrocarbon compounds having 5 or fewer carbon atoms and limonene (particularly hydrocarbon compounds having 2 to 4 carbon atoms, isoprene, and limonene) in the decomposition products obtained by the depolymerization may depend on the reaction apparatus used, in addition to the reaction conditions described above. Furthermore, the hydrocarbon compounds having 5 or fewer carbon atoms as decomposition products vary depending on the type of diene rubber in the organic material to be decomposed (crosslinked rubber, uncrosslinked rubber), but examples include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc., with 1,3-butadiene and isoprene being preferred. The proportion of hydrocarbon compounds having 5 or fewer carbon atoms in the decomposition products can be controlled, for example, by reaction conditions such as the reaction temperature and reaction time of the depolymerization.

[0084] (Other) The organic material decomposition method of this embodiment may include other steps in addition to the steps described above. Such steps include pretreatment steps for crosslinked rubber or uncrosslinked rubber (for example, cutting steps, grinding steps, etc.). Furthermore, if the crosslinked rubber or uncrosslinked rubber contains carbon black, it is preferable to include a step for recovering carbon black from the decomposition product (liquid polymer) between the first decomposition step and the second decomposition step.

[0085] The organic material decomposition method of this embodiment can be carried out in either a batch reactor or a flow-through reactor. Furthermore, the decomposition products after the decomposition reaction can be separated and recovered by filtration, distillation, centrifugation, etc., or recovered by precipitation using a poor solvent, and reused. In addition, the monomers (especially diene monomers) finally obtained from the organic material to be decomposed can be reused as raw materials for diene rubber (polymer).

[0086] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0087] (1) Method for measuring the amount of gel The yellow transparent component adhering to the wall of the reaction vessel after the rubber decomposition reaction was defined as the gel component, and the amount of gel component relative to the amount of rubber used was calculated as the amount of gel.

[0088] (2) Method for analyzing the retention rate of monomer skeletons in diene rubbers Using a nuclear magnetic resonance spectrometer (NMR spectrometer) manufactured by JEOL Ltd., product name "JNM-ECA-500", the decomposition products (liquid polymers) obtained were analyzed to calculate the retention rate of isoprene skeletons and / or butadiene skeletons derived from natural rubber and / or butadiene rubber contained in each crosslinked rubber sample.

[0089] (3) Method for Analyzing the Weight-Average Molecular Weight (Mw) of Liquid Polymers The weight-average molecular weight (Mw) of the decomposition products (liquid polymers) in polystyrene equivalent was determined using gel permeation chromatography (hereinafter sometimes referred to as GPC analysis. Liquid delivery unit: Shimadzu LC-20AB, Column: combination of Showa Denko KF-803 and KF-804 or combination of Tosoh G2000HXL and G4000HXL, Detector: Shimadzu differential refractometer RID-10A, Analysis system: Shimadzu LabSolutions, Eluent: Tetrahydrofuran), with monodisperse standard polystyrene as the reference. The measurement temperature was 40°C.

[0090] (4) Method for analyzing the organic content of carbon black Using the product name "STA7220" manufactured by Hitachi High-Tech Science Corporation, the mass (m) of carbon black after heating it to 120°C and holding it for 1 hour was determined by thermogravimetric analysis (TGA). ０ ) and the mass (m) obtained when the temperature was then raised to 550°C at 40°C / min and held for 2 hours. １ ) and the following formula is used: Organic content (mass%) = (m ０ -m １ ) / m ０ The organic content of carbon black was calculated according to the formula ×100.

[0091] (Preparation of Crosslinked Rubber Sample A) A rubber composition was prepared by blending 40 parts by mass of natural rubber and 60 parts by mass of butadiene rubber [manufactured by UBE Elastomer Co., Ltd., trade name "UBEPOL BR150L"] with 50 parts by mass of carbon black, 1.0 part by mass of the 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 the vulcanization accelerator (N-cyclohexyl-2-benzothiazolyl sulfenamide), and 4.5 parts by mass of sulfur. The rubber composition was then heated and crosslinked to prepare crosslinked rubber. The obtained crosslinked rubber was cut into a shape of 3 mm × 3 mm × 2 mm to prepare crosslinked rubber sample A.

[0092] (Preparation of Crosslinked Rubber Sample B) Crosslinked rubber sample B was prepared in the same manner as crosslinked rubber sample A, except that 100 parts by mass of natural rubber was added instead of 40 parts by mass of natural rubber and 60 parts by mass of butadiene rubber.

[0093] (Examples 1-7) 0.4 g of crosslinked rubber sample A, 4 mL of toluene, and 40 mg of disulfide compound were added to a reactor and stirred at 200°C for 9 hours under an air atmosphere to carry out the decomposition reaction. The types of disulfide compounds used in each example are shown in Table 1. After the reaction, the mixture was separated into solvent (toluene) soluble components and solvent-insoluble components (solids). The solvent-soluble components consisted mainly of liquid polymer, while the solvent-insoluble components (solids) consisted mainly of carbon black (recycled carbon black). The amount of gel was calculated using the method described above. For the obtained solvent-soluble components (liquid polymer), １ ¹H-NMR analysis was performed to calculate the retention rates of the diene monomer skeletons (isoprene skeleton and butadiene skeleton). Furthermore, the expected yield of diene monomers (expected yield of isoprene and expected yield of butadiene) was calculated from the product of the liquid polymer yield and the retention rates of the diene monomer skeletons. In addition, the weight-average molecular weight (Mw) of the liquid polymer was analyzed by GPC analysis. The organic content of the obtained carbon black was also calculated using the above method. The results are shown in Table 1.

[0094] (Comparative Example 1) The decomposition reaction was carried out in the same manner as in Examples 1 to 7, except that the disulfide compound was not added, and the amount of gel produced by the decomposition product was calculated. １ ¹H-NMR analysis was used to calculate the retention rate of the diene monomer skeleton in the decomposition products, and the expected yield of the diene monomer was also calculated. Furthermore, GPC analysis was used to analyze the weight-average molecular weight (Mw) of the liquid polymer, and the organic content of the carbon black was calculated. The results are shown in Table 1.

[0095]

[0096] (Examples 8 and 9) Except for changing the amount of disulfide compound (diphenyl disulfide) added, and changing the amount of disulfide compound relative to the amount of crosslinked rubber sample A as shown in Table 2, the decomposition reaction was carried out in the same manner as in Example 1, and the amount of gel of the decomposition product was calculated, and, １ ¹H-NMR analysis was used to calculate the retention rate of the diene monomer skeleton in the decomposition products, and the expected yield of the diene monomer was also calculated. Furthermore, GPC analysis was used to analyze the weight-average molecular weight (Mw) of the liquid polymer, and the organic content of the carbon black was calculated. The results are shown in Table 2.

[0097]

[0098] (Examples 10-15 and Comparative Example 2) Except for using cross-linked rubber sample B instead of cross-linked rubber sample A as the target for decomposition, the decomposition reaction was carried out in the same manner as in Examples 1-4 and 6-7 or Comparative Example 1, and the amount of gel produced from the decomposition product was calculated. １ ¹H-NMR analysis was used to calculate the retention rate of the isoprene skeleton in the decomposition products, and the expected isoprene yield was also calculated. Furthermore, GPC analysis was used to analyze the weight-average molecular weight (Mw) of the liquid polymer, and the organic content of the carbon black was calculated. The results are shown in Table 3. In Comparative Example 2, the gel amount was 0%, but although some gel components remained in the reaction vessel, it was not possible to recover a weighable amount.

[0099]

[0100] Tables 1 to 3 show that the method for decomposing organic materials according to the present invention can suppress the gelation of decomposition products.

Claims

1. A method for decomposing an organic material, comprising mixing an organic material selected from crosslinked rubber and uncrosslinked rubber containing diene rubber with a solvent and a disulfide compound, wherein the disulfide compound has only one disulfide bond in its molecule.

2. The method for decomposing an organic material according to claim 1, wherein the solvent is at least one selected from the group consisting of toluene, xylene, cyclohexane, and butyl acetate.

3. The method for decomposing an organic material according to claim 1, wherein the disulfide compound is at least one selected from the group consisting of aromatic disulfides and aliphatic disulfides.

4. The method for decomposing an organic material according to claim 1, wherein the disulfide compound is at least one selected from the group consisting of diphenyl disulfide, di-p-tolyl disulfide, bis(4-hydroxyphenyl) disulfide, 4,4'-dichlorodiphenyl disulfide, dicyclohexyl disulfide, dioctyl disulfide, didodecyl disulfide, and bis(phenylacetyl) disulfide.

5. The method for decomposing an organic material according to claim 1, wherein the amount of the disulfide compound is 5% by mass or more and 20% by mass or less of the amount of diene rubber in the organic material.

6. The method for decomposing an organic material according to claim 1, wherein the decomposition temperature is 150°C to 300°C.

7. The method for decomposing an organic material according to claim 1, wherein the decomposition time is 1 hour to 48 hours.

8. The method for decomposing an organic material according to claim 1, wherein the diene rubber comprises at least butadiene rubber.

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