Method for decomposing vulcanized rubber

Abstract

The present invention addresses the problem of providing a method for efficiently decomposing a vulcanized rubber, the method being characterized by comprising: a first decomposition step in which a radical initiator is caused to act on a vulcanized rubber or a composition containing the vulcanized rubber in an atmosphere containing an oxygen gas and convert the same into a soluble decomposition product; and a second decomposition step in which the soluble decomposition product obtained in said decomposition step is thermally decomposed to convert the soluble decomposition product into a low-molecular compound having a carbon number of 10 or less.

Description

How to decompose vulcanized rubber

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

[0002] Conventionally, vulcanized rubber products such as tire rubber have often been recycled as fuel in cement plants, etc., which contributes to increasing carbon dioxide emissions. However, because carbon dioxide emissions promote global warming, there is a need to develop new methods for recycling rubber products from the perspective of reducing carbon dioxide emissions and curbing global warming. In particular, chemical recycling technology, which decomposes rubber products into low-molecular-weight compounds such as soluble polymers or monomers while maintaining their basic structure, and then produces rubber products again, has the advantage of being able to regenerate rubber products with performance equivalent to that of the original rubber product. Known methods for decomposing vulcanized rubber include thermal decomposition of vulcanized rubber at high temperatures (usually 400°C or higher) (Patent Documents 1 and 2, etc.) and decomposition of polyisoprene-based rubber using microorganisms (Patent Document 3).

[0003] U.S. Patent No. 3,704,108 JP 7-310076 JP 2009-247241

[0004] In chemical recycling of vulcanized rubber, it is important to improve the yield of low-molecular-weight compounds, such as soluble polymers and monomers, produced by the decomposition of vulcanized rubber. However, in methods of thermally decomposing vulcanized rubber at high temperatures, product selectivity in thermal decomposition is low, making it difficult to obtain soluble polymers that maintain the basic structure of the rubber product. It is also often difficult to obtain specific low-molecular-weight compounds, such as monomers, in high yields. Furthermore, methods of decomposing vulcanized rubber using microorganisms have problems, such as requiring a very long time, although the decomposition of rubber itself progresses.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a method for decomposing vulcanized rubber that can improve the yield of low molecular weight compounds such as soluble polymers and monomers while maintaining the basic skeleton of the original rubber product.

[0006] As a result of intensive research to solve the above problems, the inventors of the present invention have discovered that by dividing the decomposition process of vulcanized rubber into a first decomposition process in which a radical initiator is reacted with the vulcanized rubber in an oxygen gas-containing atmosphere to solubilize the vulcanized rubber, and a second decomposition process in which the solubilized decomposition product is thermally decomposed, the rubber components in the vulcanized rubber can be decomposed into soluble polymers in the first decomposition process while maintaining the basic skeleton of the original rubber product, and the soluble polymers produced can be efficiently decomposed into low molecular weight compounds such as monomers in the second decomposition process, thereby completing the present invention. The gist of the present invention that solves the above problems is as follows.

[0007] <1> A method for decomposing vulcanized rubber, comprising: a first decomposition step of reacting a radical initiator with vulcanized rubber or a composition containing the same in an oxygen gas-containing atmosphere to convert the vulcanized rubber or a composition containing the same into soluble decomposition products; and a second decomposition step of thermally decomposing the soluble decomposition products obtained in the decomposition step to low-molecular-weight compounds having 10 or less carbon atoms. <2> The decomposition method according to <1>, wherein the rubber component of the vulcanized rubber is a rubber component containing at least one rubber selected from natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR). <3> The decomposition method according to <1> or <2>, wherein the composition containing the vulcanized rubber is a tire rubber composition containing carbon black or silica. <4> The decomposition method according to any one of <1> to <3>, wherein the radical initiator is selected from an azo compound and a peroxide. <5> The decomposition method according to <4>, wherein the peroxide is selected from acyl peroxides. <6> The decomposition method according to <5>, wherein the acyl peroxide is selected from benzoyl peroxide, lauroyl peroxide, and acetyl peroxide. <7> The decomposition method according to any one of <1> to <6>, wherein the thermal decomposition in the second decomposition step is thermal decomposition carried out at a temperature of 400 to 900°C. <8> The decomposition method according to any one of <1> to <7>, wherein the thermal decomposition in the second decomposition step is thermal decomposition carried out in the presence of a catalyst. <9> The decomposition method according to any one of <1> to <8>, wherein the decomposition method in the first decomposition step is a decomposition method using a chlorinated hydrocarbon or an aromatic hydrocarbon as a solvent. <10> The decomposition method according to <9>, wherein the chlorinated hydrocarbon is selected from chloroform or chlorobenzene. <11> The decomposition method according to <9>, wherein the aromatic hydrocarbon is ethylbenzene. <12> The decomposition method according to any one of <1> to <11>, wherein the vulcanized rubber is a vulcanized rubber that has been subjected to a pretreatment step of washing with a solvent.

[0008] In a preferred embodiment of the method for decomposing vulcanized rubber of the present invention, the vulcanized rubber contains carbon black. Even in this case, the vulcanized rubber can be decomposed efficiently and the carbon black can be reused.

[0009] Unlike conventional thermal decomposition, decomposition using a radical initiator does not require high temperatures, and therefore can convert vulcanized rubber into soluble decomposition products under relatively mild conditions. Specifically, soluble decomposition products are soluble polymers derived from the rubber component in the vulcanized rubber and compositions containing them (hereinafter, sometimes referred to as soluble polymer compositions). "Soluble" means that they can be dissolved in a solvent (e.g., the solvent used if a solvent is used in the first decomposition step). Furthermore, because the decomposition reaction does not require high temperatures, it is also possible to improve the retention rate of the monomer skeleton (isoprene skeleton, butadiene skeleton, etc.) in the vulcanized rubber. In the second decomposition step of the vulcanized rubber of the present invention, the soluble products obtained in the first decomposition step are thermally decomposed, thereby decomposing them into low-molecular-weight monomer compounds having 10 or less carbon atoms. Since the first decomposition step of the present invention achieves a high retention rate of the rubber component skeleton, the yield of the final monomer compound obtained can be improved.

[0010] According to the present invention, vulcanized rubber can be converted with high yield into soluble polymers and monomers that maintain the skeleton, and therefore, an efficient method for decomposing vulcanized rubber can be provided.

[0011] The method for decomposing vulcanized rubber of the present invention will be described in detail below by way of example based on an embodiment thereof.

[0012] <First Decomposition Step> The method for decomposing vulcanized rubber according to this embodiment includes a first decomposition step in which a radical initiator is allowed to act on vulcanized rubber or a composition containing the same in an atmosphere containing oxygen gas.

[0013] It is believed that the radical initiator used in the first decomposition step of the present invention acts mainly on cross-linking sites formed by sulfur to sever the cross-linking bonds, and therefore, in the case of diene rubber, it is believed that its main chain skeleton is basically maintained even after the decomposition reaction.

[0014] (Vulcanized Rubber) The vulcanized rubber to be decomposed by the decomposition method of this embodiment contains, for example, a diene rubber having crosslinking sites containing sulfur atoms, and may further contain carbon black, silica, etc. It is believed that the radical initiator used in the first decomposition step basically decomposes the vulcanized rubber by acting on the sulfur crosslinking sites. The form of the vulcanized rubber is not limited, and it may be, for example, powdered rubber. The powdered rubber can be obtained by cutting and pulverizing used rubber products such as waste 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 used may be adjusted through a classification step after the pulverization step. Furthermore, the composition containing the vulcanized rubber may be recycled waste rubber, used rubber products, etc. Waste rubber is not limited to rubber generated from rubber products, but refers to all discarded rubber, including unnecessary scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is fine rubber generated during the buffing process of scraping off the remaining tread portion of a base tire, for example, during tire retreading. Peeling rubber is long pieces of rubber, for example, 1 to 2 cm wide, peeled off from the surface of a rubber product such as a tire. Peeling 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 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 from tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their life as tires. Tire rubber containing carbon black or silica is preferred as a composition containing vulcanized rubber.

[0015] --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 diene-based monomer-derived units enable the diene-based rubber to be crosslinked (vulcanized) and to exhibit rubber-like elongation and strength. While the diene-based rubber is typically present in a crosslinked state in the vulcanized rubber, 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). Here, the isoprene-skeleton rubber is a rubber whose main skeleton is an isoprene unit, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). Among these, it is preferable that the diene rubber contains at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber. When the diene rubber contains 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 the second decomposition step following the first decomposition step. The content of the diene rubber in the vulcanized rubber is not particularly limited, and is preferably, for example, in the range of 10 to 100 mass %, and more preferably in the range of 30 to 100 mass % from the viewpoint of further improving the yield of the monomer compound after the second decomposition step.

[0016] Sulfur: In the vulcanized rubber, sulfur is typically present in a state where the diene rubber is crosslinked (as a crosslinker for the diene rubber), but some sulfur may be free. In the method for decomposing vulcanized rubber of the present invention, in the first decomposition step, decomposition is carried out using a radical initiator, thereby decomposing the diene rubber and converting it into a soluble polymer. Therefore, even if the vulcanized rubber contains sulfur, the sulfur can be easily recovered after the first decomposition step, for example, by solid-liquid separation. Recovering sulfur before the thermal decomposition in the second decomposition step allows the sulfur to be reused. Furthermore, even when a catalyst is used in the second decomposition step, sulfur can be prevented from poisoning the catalyst or from re-vulcanizing the decomposition products. The sulfur content in the vulcanized 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.

[0017] --Carbon Black-- The vulcanized rubber may further contain carbon black. In the method for decomposing vulcanized rubber of the present invention, the diene rubber can be decomposed and converted into a soluble polymer by decomposing the diene rubber using a radical initiator in the first decomposition step. Therefore, even if the vulcanized 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 when a catalyst is used in the second decomposition step, carbon black can be prevented from becoming a catalyst poison or causing coking. Therefore, even if the vulcanized rubber contains carbon black, the vulcanized rubber can be efficiently decomposed. The content of carbon black in the vulcanized 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.

[0018] --Other Components-- In addition to the diene rubber, carbon black, and sulfur described above, the vulcanized rubber may 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 white), vulcanization accelerators, crosslinking agents other than sulfur, etc.

[0019] (Radical initiator in the first decomposition step) In the method for decomposing vulcanized rubber according to this embodiment, a radical initiator is used in the first decomposition step. Various conventionally known radical initiators can be used as the radical initiator, but from the viewpoint of reaction efficiency, peroxides and azo compounds are preferred, with peroxides being more preferred. Examples of peroxides include acyl peroxide, percarboxylic acid, dialkyl peroxide, and alkyl hydroperoxide. Among these, from the viewpoint of reaction rate, acyl peroxide and percarboxylic acid are preferred, with acyl peroxide being more preferred. Specific examples of acyl peroxides include benzoyl peroxide, toluoyl peroxide, chlorobenzoyl peroxide, dichlorobenzoyl peroxide, methoxybenzoyl peroxide, phthaloyl peroxide, acetyl peroxide, propanoyl peroxide, caprylyl peroxide, decanoyl peroxide, lauroyl peroxide, myristoyl peroxide, and stearoyl peroxide. Among acyl peroxides, benzoyl peroxide, lauroyl peroxide, and acetyl peroxide are preferably used from the viewpoints of reaction rate, cost, availability, etc. Lauroyl peroxide is preferred over benzoyl peroxide from the viewpoints of reaction rate and peroxide stability. Examples of percarboxylic acids include perbenzoic acid, chloroperbenzoic acid, peracetic acid, and perpropionic acid. Examples of dialkyl peroxides include di-tert-butyl peroxide, dicumyl peroxide, and tert-butylcumyl peroxide, and examples of alkyl hydroperoxides include tert-butyl hydroperoxide and cumene hydroperoxide. Examples of azo compounds include azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate.

[0020] These radical initiators may be in the form of a water-containing product from the viewpoints of safety, availability, etc. By using a suitable initiator, vulcanized rubber can be efficiently decomposed under mild conditions.

[0021] The amount of the radical initiator used is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and is preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, relative to 100 parts by mass of the vulcanized rubber. If the amount of the radical initiator used is 0.1 part by mass or more relative to 100 parts by mass of the vulcanized rubber, the decomposition reaction of the vulcanized rubber proceeds more quickly, and if the amount of the radical initiator used is 30 parts by mass or less relative to 100 parts by mass of the vulcanized rubber, it is preferable from the standpoint of cost.

[0022] (Reaction Conditions for the First Decomposition Step) The first decomposition step is carried out in an atmosphere containing oxygen gas. The concentration (volume %) of oxygen gas in the reaction atmosphere is typically 1 to 100%, preferably 1 to 80%, and more preferably 5 to 50%, including the atmospheric oxygen concentration of approximately 20%. When the oxygen gas concentration is not 100%, an inert gas such as nitrogen gas can be used as the remaining gas component. Generally, the higher the oxygen concentration, the more advantageous the decomposition reaction. However, since undesirable side reactions are more likely to occur, when the oxygen concentration is high, it is necessary to appropriately control the reaction time, reaction temperature, etc. On the other hand, using atmospheric air with an oxygen concentration of approximately 20% eliminates the need for separate oxygen gas, which is advantageous in terms of equipment and economy. In a reaction under an air atmosphere, when the amount of vulcanized rubber is small, the reaction can proceed even in a sealed container with a sufficiently large internal volume. In this case, the internal volume of the reaction container is generally 50 parts by volume or more, more preferably 100 parts by volume or more, per 1 part by volume of vulcanized rubber. When the decomposition reaction is carried out in a closed system, a large amount of vulcanized rubber requires a reaction vessel with a large internal volume, which is not desirable from an equipment perspective. Therefore, from an equipment perspective, it is preferable to carry out the reaction in a non-closed system that allows the flow of air, etc. To make the reaction system non-closed, methods such as opening a portion of the reaction vessel, installing a membrane that allows the flow of air, etc., or allowing air, etc., to overflow can be considered. Another advantageous embodiment is a method in which the reaction is carried out while continuously or intermittently blowing air, etc. into the solution. In this case, the blowing rate is not particularly limited, but is usually 1 to 1000 mL / min, preferably 2 to 500 mL / min, and more preferably 3 to 200 mL / min per gram of vulcanized rubber.

[0023] In the first decomposition step of the vulcanized rubber of this embodiment, the radical initiator may be dissolved in a solvent, or the vulcanized rubber may be immersed in a solvent to perform the decomposition. By allowing the radical initiator to act on the vulcanized rubber in a solvent, the decomposition of the vulcanized rubber can be facilitated. Any solvent that does not inhibit the decomposition reaction can be used as the solvent, including, for example, aromatic hydrocarbons (aromatic solvents), chlorinated hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, etc. Specific examples of aromatic hydrocarbons include toluene, xylene, ethylbenzene, trimethylbenzene, and propylbenzene. Chlorinated hydrocarbons include chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethene, chlorobenzene, and dichlorobenzene. Aliphatic hydrocarbons include pentane, hexane, and octane. Alicyclic hydrocarbons include cyclopentane, cyclohexane, and cyclooctane. Ethers include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and dioxane. Among these, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoints of reaction rate, availability, etc. Specific examples thereof include toluene, xylene, ethylbenzene, chloroform, chlorobenzene, dichlorobenzene, etc. Among aromatic hydrocarbons, ethylbenzene is preferred over toluene from the viewpoint of reaction rate. The solvent suitable for the decomposition reaction also depends on the type of vulcanized rubber. For example, when the vulcanized rubber is an NR-based, IR-based, or BR-based rubber, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoints of reaction rate, solubility of the product, etc., specific examples of which include toluene, ethylbenzene, chloroform, chlorobenzene, etc. On the other hand, for SBR-based vulcanized rubber, chlorinated hydrocarbons are more preferred from the viewpoint of reaction rate, etc., specific examples of which include chloroform, chlorobenzene, etc. Use of a preferred solvent facilitates the decomposition of the vulcanized rubber, allowing for more efficient production of a soluble polymer.The amount of the solvent used is preferably 2 mL or more, more preferably 10 mL or more, and is preferably 100 mL or less, more preferably 50 mL or less, per gram of the vulcanized rubber. If the amount of the solvent used is 2 mL per gram of the vulcanized rubber, the decomposition reaction of the vulcanized rubber is promoted, and if the amount of the solvent used is 50 mL or less per gram of the crosslinked rubber, this is preferred from the standpoint of cost.

[0024] The first decomposition step is preferably carried out at a temperature of 0°C or higher and 200°C or lower. By carrying out the first decomposition step at a temperature of 0°C or higher, the rate of decomposition reaction of the vulcanized rubber is improved, and by carrying out the first decomposition step at a temperature of 200°C or lower, the retention rate (selectivity) of the monomer skeleton in the vulcanized rubber is improved. From the viewpoint of improving the decomposition reaction rate of the vulcanized rubber, the first decomposition step is more preferably 10°C or higher, and from the viewpoint of improving the selectivity of the product maintaining the monomer skeleton, it is even more preferably 150°C or lower. When a peroxide-based radical initiator is used, the decomposition efficiency is high, so the reaction proceeds at a low temperature of 60°C or lower. Another advantage of using a peroxide-based radical initiator is that the reaction proceeds smoothly even at around room temperature (20 to 30°C), eliminating the need for special heating or cooling equipment.

[0025] The first decomposition step can be carried out under any pressure, such as reduced pressure, normal pressure, or increased pressure. Specifically, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 1 MPa, and even more preferably 50 kPa to 500 kPa.

[0026] In the first decomposition step of the present invention, it is important to efficiently stir the raw materials, i.e., the vulcanized rubber, the radical initiator, and the solvent. Various conventionally known stirring methods can be used, such as a method using a magnetic stirrer, a method using a mechanical stirrer, or a method using a shaker. Furthermore, to promote the reaction, ultrasonic irradiation, microwave irradiation, light irradiation, or the like may be used in combination. These methods can also be used in combination.

[0027] (Product of the First Decomposition Step) In the method for decomposing vulcanized rubber according to this embodiment, the first decomposition step is preferably followed by decomposition into a soluble polymer having a weight-average molecular weight of 200 to 200,000, and more preferably into a soluble polymer having a weight-average molecular weight of 300 to 150,000. By decomposing the vulcanized rubber into a soluble polymer having a weight-average molecular weight of 200 to 200,000 in the first decomposition step, the yield of diene monomers and the like can be further improved in the second decomposition step described below. The weight-average molecular weight (Mw) can be measured, for example, by gel permeation chromatography (hereinafter sometimes referred to as GPC). Furthermore, insoluble carbon black is recovered after the first decomposition step. The recovered carbon black typically contains organic components, such as polymers derived from the vulcanized rubber. The proportion of organic components in the recovered carbon black is preferably 5 to 35% by mass, more preferably 7 to 25% by mass.

[0028] <Second Decomposition Step> The method for decomposing vulcanized rubber according to the present embodiment includes a second decomposition step in which the soluble polymer obtained in the first decomposition step is thermally decomposed to convert it into a low molecular weight compound having 10 or less carbon atoms.

[0029] (Reaction conditions for the second decomposition step) The thermal decomposition in the second decomposition step is generally carried out at 400°C or higher and 900°C or lower. By carrying out the thermal decomposition at 400°C or higher, the rate of the decomposition reaction of the soluble polymer obtained in the first decomposition step is improved, and by carrying out the thermal decomposition at 900°C or lower, undesirable side reactions can be suppressed. From the viewpoint of improving the decomposition reaction rate, the thermal decomposition temperature is more preferably 500°C or higher, and from the viewpoint of suppressing side reactions, it is more preferably 850°C or lower.

[0030] The second decomposition step is preferably carried out in an inert gas or water vapor atmosphere. By carrying out the second decomposition step in an inert gas atmosphere, oxidation of the decomposition products obtained in the first decomposition step can be suppressed. Examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0031] The second decomposition step can be carried out under any of atmospheric pressure, reduced pressure, and increased pressure, but is preferably carried out under atmospheric pressure or reduced pressure from the viewpoint of promoting the progress of the reaction. When carried out under reduced pressure, the pressure is preferably 0.001 to 0.9 atm, more preferably 0.01 to 0.6 atm.

[0032] Various conventionally known reactors can be used for the second decomposition step. However, from the viewpoint of thermal decomposition efficiency, a reactor in which the raw material is introduced into a reactor heated to a high temperature and rapidly heated to thermally decompose the raw material is preferred. An example of such a reactor is the type used in pyrolysis gas chromatography (hereinafter sometimes referred to as Py-GC). In this type, the raw material is thermally decomposed instantaneously at a high temperature, improving the yield of the target product. Fluidized-bed reactors using silica sand, steam, or the like as a heat transfer medium are also preferred because they can rapidly heat the raw material to the thermal decomposition temperature. On the other hand, if the raw material is not thermally decomposed instantaneously, problems such as insufficient decomposition of the raw material or the raw material being distilled out of the reaction system without being decomposed can occur, resulting in a decrease in the yield of the target product.

[0033] (Catalyst for the second decomposition step) In the second decomposition step, a catalyst may be present. As such a catalyst, any catalyst, whether acidic, neutral, or basic, can be used. In addition, although an inorganic solid catalyst can generally be used as the catalyst, various inorganic catalysts, such as non-porous and porous catalysts, can also be used. Examples of non-porous catalysts include MgO, CaO, BaO, Y ２ O ３ , La ２ O ３ , CeO ２ , TiO ２ , ZrO ２ , metal oxides such as ZnO, Li ２ CO ３ , Na ２ CO ３ , K. ２ CO ３ , Rb ２ CO ３ , Cs ２ CO ３Examples of porous materials include silica, alumina, zeolite, montmorillonite, activated carbon, and the like. Metal-supported silica, alumina, zeolite, montmorillonite, activated carbon, and the like can also be used. There are no particular limitations on the type of silica, alumina, zeolite, montmorillonite, activated carbon, and the like, and various commercially available acidic, neutral, and basic products can be used. Zeolites such as USY, SDUSY, beta, ZSM-5, and Y types are preferably used from the viewpoint of activity. The silica / alumina ratio of the zeolite is typically 3 to 2000, preferably 4 to 1000. Zeolites and montmorillonites that have been ion-exchanged with protons or metal cations such as Na and K are also preferably used. Furthermore, silica, alumina, activated carbon, and the like that support metals such as Ru, Co, Rh, Ir, Ni, Pd, Pt, and Cu are also preferably used. The yield and distribution of products can be changed by the type of catalyst, but a basic or neutral catalyst is preferred for the yield of isoprene, a type of diene monomer, and an acidic catalyst is preferred for the production of hydrocarbons having 4 or less carbon atoms. Two or more of the above catalysts may be used in combination.

[0034] The amount of the catalyst used is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 1 part by mass or more, and is preferably 80 parts by mass or less, even more preferably 40 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 1 part by mass of the decomposition product obtained in the first decomposition step (or the intermediate product to be provided to the second decomposition step). If the amount of the catalyst used is 1 part by mass or more relative to 1 part by mass of the decomposition product obtained in the first decomposition step (or the intermediate product to be provided to the second decomposition step), the decomposition reaction proceeds more rapidly, and if the amount of the catalyst used is 5 parts by mass or less relative to 1 part by mass of the decomposition product obtained in the first decomposition step (or the intermediate product to be provided to the second decomposition step), it is preferable from the standpoint of cost.

[0035] (Products of the Second Decomposition Step) In the method for decomposing vulcanized rubber of this embodiment, the soluble polymer obtained in the first decomposition step is decomposed into hydrocarbons having 10 or less carbon atoms in the second decomposition step. Efficient decomposition down to hydrocarbons having 10 or less carbon atoms improves the yield of low-molecular-weight compounds such as reusable monomers, further improving the economic and environmental value of the decomposition method. The decomposition rate of the soluble polymer is preferably 20% by mass or more, and more preferably 30% by mass or more. Note that the hydrocarbons having 10 or less carbon atoms as decomposition products vary depending on the type of rubber in the vulcanized rubber to be decomposed, but examples include ethylene, propylene, 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, benzene, toluene, xylene, ethylbenzene, isopropylbenzene, styrene, and limonene.

[0036] <Others> The method for decomposing vulcanized rubber according to this embodiment may further include other steps in addition to the first decomposition step and the second decomposition step described above. Examples of such steps include pretreatment steps of the vulcanized rubber (e.g., a cutting step and a pulverization step). Examples of pretreatment steps in the first decomposition step include a step of washing with a solvent. Washing with a solvent can remove additives that may inhibit the decomposition reaction, such as antioxidants, remaining in the vulcanized rubber, thereby reducing the amount of initiator used. The type of solvent used in the pretreatment step is not particularly limited, but is preferably a solvent that easily dissolves additives such as antioxidants. Specific examples include hydrocarbons such as toluene, ketones such as acetone, chlorinated hydrocarbons such as chloroform, and ethers such as tetrahydrofuran. Furthermore, the method for decomposing vulcanized rubber according to this embodiment can be carried out using either a batch or flow reactor.

[0037] <Separation and Purification of Products> Separation and purification of the products after the decomposition reaction can be easily carried out in the first decomposition step by operations such as filtration, centrifugation, reprecipitation, and preparative GPC, and in the second decomposition step by operations such as distillation and recrystallization. The soluble polymer product obtained in the first decomposition step can be used as a raw material in the second decomposition step, and can also be reused as a raw material for producing vulcanized rubber, since it maintains the basic skeleton of the vulcanized rubber before decomposition. In addition, the hydrocarbon product having 10 or less carbon atoms obtained in the second decomposition step can also be reused as a raw material for diene rubber, etc.

[0038] 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.

[0039] <Analytical equipment, etc.> Gel permeation chromatography (hereinafter sometimes referred to as GPC): Analysis system: Shimadzu Corporation LabSolutions (liquid delivery unit: Shimadzu Corporation LC-20AB, column: Tosoh Corporation TSKgel Super HM-H × 2, detector: Shimadzu Corporation differential refractometer RID-10A, eluent: tetrahydrofuran, flow rate: 0.6 mL / min, measurement temperature: 40°C, weight average molecular weight (Mw) and number average molecular weight (Mn) are based on standard polystyrene) Nuclear magnetic resonance analyzer (hereinafter sometimes referred to as NMR): Bruker Corporation AVANCE III HD 600 (solvent: CDCl ３ ) Pyrolyzer device (hereinafter may be referred to as Py): PY-3030D manufactured by Frontier Labs Gas chromatograph mass spectrometer (hereinafter may be referred to as GC / MS): GCMS-QP2010Plus manufactured by Shimadzu Corporation (column: UltraALLOY UA-1 capillary column manufactured by Frontier Labs) Gas chromatograph analyzer (hereinafter may be referred to as GC): and GC-2014 manufactured by Shimadzu Corporation (column: UltraALLOY UA-1 capillary column manufactured by Frontier Labs) It should be noted that a pyrolyzer device is generally used by being attached to a gas chromatography mass spectrometer or a gas chromatograph analyzer (hereinafter may be referred to as Py-GC / MS or Py-GC).

[0040] <Preparation of Vulcanized Rubber Sample> (Vulcanized Rubber A) A rubber composition was prepared by blending 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 2 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.6 parts by mass of vulcanization accelerator CBS [N-cyclohexyl-2-benzothiazolylsulfenamide], 1.8 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] per 100 parts by mass of natural rubber, and the rubber composition was then heat-crosslinked to prepare a vulcanized rubber.

[0041] (Vulcanized Rubber B) 60 parts by mass of natural rubber and 40 parts by mass of butadiene rubber were blended with 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 2 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.6 parts by mass of vulcanization accelerator CBS [N-cyclohexyl-2-benzothiazolylsulfenamide], 1.8 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] to prepare a rubber composition, and the rubber composition was heated and crosslinked to prepare a vulcanized rubber.

[0042] (Vulcanized Rubber C) 40 parts by mass of natural rubber and 60 parts by mass of butadiene rubber were blended with 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 2 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.6 parts by mass of vulcanization accelerator CBS [N-cyclohexyl-2-benzothiazolylsulfenamide], 1.8 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] to prepare a rubber composition, and the rubber composition was heated and crosslinked to prepare a vulcanized rubber.

[0043] (Vulcanized Rubber D) A rubber composition was prepared by blending 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 1 part by mass of wax, 1 part by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.3 parts by mass of vulcanization accelerator DPG [1,3-diphenylguanidine], 0.5 parts by mass of vulcanization accelerator MBTS [dibenzothiazolyl disulfide], 0.5 parts by mass of vulcanization accelerator TBBS [N-t-butyl-2-benzothiazole sulfenamide], 1.5 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] with 100 parts by mass of styrene-butadiene rubber, and the rubber composition was heated and crosslinked to prepare a vulcanized rubber. In the first decomposition step of the vulcanized rubber, the obtained vulcanized rubber was cut into pieces (about 5 mm square) or further frozen and crushed into pieces (about 1 to 2 mm square) and used.

[0044] <Example of the first decomposition step> (Calculation of yield) The yield of the first decomposition step was calculated by adding a certain amount of an internal standard substance (hexamethyldisilane) to the reaction solution, then collecting a portion of the reaction solution, １ H NMR measurement was carried out to calculate the weight of the monomer skeleton of the solubilized rubber component, and the weight was calculated from the ratio of the weight of the monomer skeleton in the vulcanized rubber before the reaction (calculated from the vulcanized rubber recipe) according to the following formula: Yield of the first decomposition step (%) = (Weight of the monomer skeleton of the solubilized rubber component after the reaction ÷ Weight of the monomer skeleton of the vulcanized rubber component before the reaction) × 100. For example, in the case of natural rubber, １ H NMR (CDCl ３ In the graph (middle), the proton signals of the internal standard hexamethyldisilane and the proton signals of the isoprene skeleton (alkenyl group) of the solubilized rubber component are observed around 0.04 and 5.13 ppm, respectively. The yield can be calculated from the ratio of the signal integral value of the isoprene skeleton to the signal integral value of hexamethyldisilane. The polyisoprene content of the natural rubber was assumed to be 93%.

[0045] Specific examples are described below. (Example 1) A mixture of 50 mg of the vulcanized rubber sample A, 7.4 mg of benzoyl peroxide (water-containing, 75% purity), and 0.8 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C (room temperature) for one day in a 5 mL Spitz vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement to be 89%. Furthermore, by GPC measurement of the reaction solution, the molecular weight was estimated to be Mw = 41,400, Mn = 16,900, and Mw / Mn = 2.4 (see Table 1).

[0046] (Examples 2 to 57) The decomposition reaction and analysis of the products were carried out in the same manner as in Example 1, while changing the reaction conditions (type of vulcanized rubber, type of radical initiator, type of solvent, reaction temperature, type of container, etc.). The results are shown in Tables 1 to 3.

[0047]

[0048]

[0049]

[0050] (Notes for Tables 1 to 3) 1) The types of reaction vessels used are as follows (all reactions were carried out under sealed conditions): Examples 1 to 23, 34 to 38, 41, Comparative Example 2: 5 mL Spitz-type vials Examples 24 to 33, 39, 40, 42 to 47, Comparative Example 1: 10 mL round-bottom vials Examples 48 and 49: 20 mL round-bottom vials Examples 50 to 57: 150 mL flat-bottom vials 2) The radical initiators used are as follows: BPO: benzoyl peroxide LPO: lauroyl peroxide APO: acetyl peroxide AIBN: azobisisobutyronitrile 3) The solvents used are as follows: PhMe: toluene, Xy: xylene, CyHex: cyclohexane, CHCl ３ : Chloroform, CHCl ２ CH ２ Cl: 1,1,2-trichloroethane, Cl ２ C=CCl ２: tetrachloroethene, DCB: o-dichlorobenzene, PhCl: chlorobenzene, PhCN: benzonitrile, PhOMe: anisole, ｔ BuOMe: tert-butyl methyl ether, PhEt: ethylbenzene, THF: tetrahydrofuran, CDCl ３ : deuterated chloroform 4) In terms of temperature, 25°C indicates decomposition at room temperature, 30°C and 40°C indicate decomposition in a thermostatic bath, and 60°C indicates decomposition in an oil bath or water bath. 90, 120, 130, and 150°C indicate heating in an oil bath (Examples 17, 19-21, 34, 36, and 37) or a microwave irradiation device (Examples 18, 35, and Comparative Example 2). 5) In terms of time, m indicates minutes, h indicates hours, and d indicates days. 6) The numbers in parentheses for the yield in the decomposition reaction of vulcanized rubbers B and C indicate the ratio of the yield of the isoprene skeleton to the yield of the butadiene skeleton. 7) Comparative Examples 1 and 2 show examples of reactions performed under a nitrogen atmosphere using a deoxygenated solvent.

[0051] The results in Tables 1 to 3 demonstrate that compounded vulcanized rubbers containing natural rubber, butadiene rubber, and / or styrene-butadiene rubber and carbon black decompose in various solvents under air with a radical initiator such as acyl peroxide to yield soluble polymers. In particular, when acyl peroxide is used, the decomposition reaction proceeds smoothly even at room temperature. Furthermore, with regard to the type of rubber, styrene-butadiene rubber exhibits a greater solvent effect than natural rubber and butadiene rubber, and the decomposition reaction proceeds more efficiently when a chlorinated hydrocarbon is used as the solvent. For example, with vulcanized rubber D containing styrene-butadiene rubber, the yield was 30% even after four days at 30°C in toluene (Example 47), whereas a high yield of 77% was achieved after one day at 30°C in chloroform (Example 44). In these decomposition reactions, the presence of oxygen is important, as shown in the following comparative example.

[0052] Comparative Example 1 In the reaction of Example 29 (vulcanized rubber A, benzoyl peroxide initiator, toluene solvent, 40°C, 6 hours), the reaction was carried out under a nitrogen atmosphere using a deoxygenated solvent as the solvent. As a result, the yield of the soluble polymer decreased from 83% to 3%.

[0053] Comparative Example 2 In the reaction of Example 35 (vulcanized rubber A, azobisisobutyronitrile initiator, o-dichlorobenzene solvent, 150°C, 20 minutes), the reaction was carried out under a nitrogen atmosphere using a deoxygenated solvent as the solvent. As a result, the yield of the soluble polymer decreased from 95% to 9%.

[0054] The results of Comparative Examples 1 and 2 show that the decomposition reaction proceeds in an air atmosphere, but hardly proceeds in a nitrogen atmosphere. The presence of oxygen in the air is thought to be extremely important for the progress of the decomposition reaction.

[0055] In decomposing compounded rubber containing carbon black, the carbon black can be separated by filtration, centrifugation, etc. to obtain a soluble polymer. Specific examples are shown below.

[0056] (Example 58) A mixture of 50 mg of the vulcanized rubber sample A, 7.4 mg of benzoyl peroxide (water-containing, 75% purity), and 0.8 mL of chlorobenzene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 1 day in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 94%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 42,900, Mn = 17,000, and Mw / Mn = 2.5. Chlorobenzene was added to the reaction solution, and insoluble solids were removed by filtration. The insoluble solids were washed with toluene. The insoluble solids were heated and dried under vacuum to recover the carbon black component (20 mg). Meanwhile, the filtrate and washings were combined and concentrated under reduced pressure to obtain a soluble polymer composition (P1) having an isoprene skeleton (30 mg). A portion of this was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition (P1) was calculated to be 65%, and by GPC measurement, the molecular weight was estimated to be Mw = 45,200, Mn = 18,300, and Mw / Mn = 2.5.

[0057] (Example 59) 150 mg of the vulcanized rubber sample A, 23 mg of benzoyl peroxide (water-containing, 75% purity), and 2.4 mL of chlorobenzene were stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 2 days in a 100 mL round-bottom flask (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 94%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 37,800, Mn = 14,800, and Mw / Mn = 2.6. Chlorobenzene was added to the reaction solution, and insoluble solids were removed by filtration. The insoluble solids were washed with toluene. The insoluble solids were heated and dried under vacuum to recover the carbon black component (40 mg). Meanwhile, the filtrate and washings were combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (100 mg). A portion of this was sampled, and an internal standard (hexamethyldisilane) was added to the solution. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 62%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 41,800, Mn = 15,600, and Mw / Mn = 2.7. Furthermore, in order to purify the soluble polymer composition, a portion of the obtained soluble polymer composition was dissolved in tetrahydrofuran and added dropwise to methanol. The precipitated liquid polymer was separated, washed with methanol, and dried under reduced pressure to obtain purified soluble polymer composition (P2) (65 mg). A portion of it was sampled, and an internal standard substance (hexamethyldisilane) was added to the sample. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the purified soluble polymer composition (P2) was calculated to be 81%, and the molecular weights were estimated to be Mw = 45,800, Mn = 16,100, and Mw / Mn = 2.5 by GPC measurement.

[0058] (Example 60) A mixture of 200 mg of the vulcanized rubber sample A, 30 mg of benzoyl peroxide (water-containing, 75% purity), and 3.2 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 2 days in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and was found to be 89%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 38,300, Mn = 15,300, and Mw / Mn = 2.5. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Tetrahydrofuran was added to the separated insoluble solid, mixed, and further centrifuged to recover the insoluble carbon black component (70 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (147 mg). A portion of the polymer was sampled, and an internal standard (hexamethyldisilane) was added to the sample. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 69%, and by GPC measurement, the molecular weight was estimated to be Mw = 43,700, Mn = 16,300, and Mw / Mn = 2.7.

[0059] (Example 61) A mixture of 200 mg of the vulcanized rubber sample A, 30 mg of benzoyl peroxide (water-containing, 75% purity), and 3.2 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 60°C for 5 hours in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and was found to be 87%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 31,900, Mn = 13,400, and Mw / Mn = 2.4. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Tetrahydrofuran was added to the separated insoluble solid, mixed, and further centrifuged to recover the insoluble carbon black component (67 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (148 mg). A portion of the polymer was sampled, and an internal standard (hexamethyldisilane) was added to the sample. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 68%, and by GPC measurement, the molecular weight was estimated to be Mw = 35,200, Mn = 14,800, and Mw / Mn = 2.4.

[0060] (Example 62) A mixture of 200 mg of the vulcanized rubber sample A, 37 mg of lauroyl peroxide, and 3.2 mL of chloroform was placed in a 20 mL round-bottom vial (sealed) under an air atmosphere at 25°C for 2 days, and stirred with a magnetic stirrer using a Teflon (registered trademark) rotor to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 39,700, Mn = 16,000, and Mw / Mn = 2.5. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Tetrahydrofuran was added to the separated insoluble solid, mixed, and centrifuged again. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (74 mg). Meanwhile, the supernatant after centrifugation was combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (162 mg). A portion of the mixture was sampled, and an internal standard (hexamethyldisilane) was added to the mixture. １As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 61%, and by GPC measurement, the molecular weight was estimated to be Mw = 44,400, Mn = 17,000, and Mw / Mn = 2.6.

[0061] (Example 63) A mixture of 200 mg of the vulcanized rubber sample A, 37 mg of lauroyl peroxide, and 3.2 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 60°C for 5 hours in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and was found to be 87%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 31,900, Mn = 13,400, and Mw / Mn = 2.4. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Toluene was added to the separated insoluble solid, mixed, and centrifuged again. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (76 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (159 mg). A portion of the mixture was sampled, and an internal standard (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 61%, and by GPC measurement, the molecular weight was estimated to be Mw = 27,600, Mn = 12,900, and Mw / Mn = 2.1.

[0062] (Example 64) A mixture of 1,000 mg of the vulcanized rubber sample A, 147 mg of benzoyl peroxide (water-containing, 75% purity), and 16 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 42,400, Mn = 14,900, and Mw / Mn = 2.8. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, and the mixture was further centrifuged. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (368 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (731 mg). A portion of the mixture was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 64%, and by GPC measurement, the molecular weight was estimated to be Mw = 47,000, Mn = 15,600, and Mw / Mn = 3.0.

[0063] (Example 65) A mixture of 1,000 mg of the vulcanized rubber sample A, 147 mg of benzoyl peroxide (water-containing, 75% purity), and 16 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 85%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 25,400, Mn = 10,300, and Mw / Mn = 2.5. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, mixed, and further centrifuged. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (351 mg). Meanwhile, the supernatant after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (731 mg). A portion was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 61%, and by GPC measurement, the molecular weight was estimated to be Mw = 28,900, Mn = 10,700, and Mw / Mn = 2.7.

[0064] (Example 66) A mixture of 1,000 mg of the vulcanized rubber sample A, 183 mg of lauroyl peroxide, and 16 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 85%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 27,100, Mn = 10,900, and Mw / Mn = 2.5. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, mixed, and further centrifuged. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (392 mg). Meanwhile, the supernatant after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (782 mg). A portion was sampled, and an internal standard substance (hexamethyldisilane) was added to the sample. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 58%, and by GPC measurement, the molecular weight was estimated to be Mw = 30,100, Mn = 11,100, and Mw / Mn = 2.7.

[0065] (Example 67) A mixture of 1,000 mg of the vulcanized rubber sample A, 183 mg of lauroyl peroxide, and 16 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 85%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 23,200, Mn = 9,800, and Mw / Mn = 2.4. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, mixed, and centrifuged again. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (381 mg). Furthermore, the supernatant after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (798 mg). A portion of this was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 60%, and by GPC measurement, the molecular weight was estimated to be Mw = 27,200, Mn = 10,500, and Mw / Mn = 2.6.

[0066] (Example 68) A mixture of 6000 mg of the vulcanized rubber sample A, 886 mg of benzoyl peroxide (water-containing product, 75% purity), and 100 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 4 days in a 1000 mL flat-bottom vial (unsealed) equipped with a PTFE membrane having a pore size of 0.2 µm, to carry out a decomposition reaction. １ By H NMR measurement, the yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 45,800, Mn = 14,800, and Mw / Mn = 3.1. The reaction solution was diluted with tetrahydrofuran, and the insoluble solid was separated by centrifugation and dried by heating under vacuum to recover the insoluble carbon black component (2,257 mg). Meanwhile, the supernatant was concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (4,460 mg). By adding an internal standard substance (hexamethyldisilane), １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 66%, and by GPC measurement, the molecular weight was estimated to be Mw = 51,100, Mn = 16,700, and Mw / Mn = 3.1.

[0067] (Example 69) A mixture of 6000 mg of the vulcanized rubber sample A, 886 mg of benzoyl peroxide (water-containing product, 75% purity), and 110 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 4 days in a 1000 mL flat-bottomed vial (unsealed) equipped with a PTFE membrane having a pore size of 0.45 µm, to carry out a decomposition reaction. １ By H NMR measurement, the yield of the soluble polymer composition produced by decomposition of the vulcanized rubber was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 50,400, Mn = 15,900, and Mw / Mn = 3.2. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation and dried by heating under vacuum to recover the insoluble carbon black component (2,304 mg). Meanwhile, the supernatant was concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (4,351 mg). By adding an internal standard (hexamethyldisilane), １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 66%, and by GPC measurement, the molecular weight was estimated to be Mw = 51,400, Mn = 16,200, and Mw / Mn = 3.2.

[0068] The soluble polymer obtained by the first decomposition step of the present invention basically maintains the polymer skeleton in the raw vulcanized rubber. For example, decomposition of vulcanized rubber sample A can selectively obtain cis-polyisoprene.

[0069] For example, the NMR data of the purified soluble polymer composition (P2) obtained by the decomposition reaction of vulcanized rubber sample A in Example 59 was as follows: 1 H NMR (CDCl3): δ(ppm) 1.68 (s, 3H, CH3), 2.00-2.09 (m, 4H, CH2), 5.12 (t, J = 6.2 Hz, 1H, =CH) 13 C NMR (CDCl3): δ(ppm) 23.5, 26.4, 32.2, 125.0, 135.2 observed １ H and １３C NMR data indicates that the resulting soluble polymer has a cis-polyisoprene backbone, maintaining the basic structure of the polymer component in the vulcanized rubber.

[0070] Example of the Second Decomposition Step Example 70 The soluble polymer composition obtained in the first decomposition step (soluble polymer composition (P1) obtained in Example 58) was dissolved in toluene to prepare a 5 mg / mL solution. A 5.0 μL portion of the solution was placed in a stainless steel container, and the solvent was distilled off. 25 μg of the soluble polymer composition obtained after the first decomposition step, obtained after solvent distillation, was heated to 650°C using a pyrolyzer. The resulting pyrolysis products were analyzed by GC / MS and GC (Py-GC / MS and Py-GC). As a result, it was confirmed that isoprene, limonene, hydrocarbons having 1 to 4 carbon atoms, and hydrocarbons having 5 to 10 carbon atoms (other than isoprene and limonene) were produced in yields of 27%, 6%, 5%, and 25%, respectively (see Table 4).

[0071] Examples 71 to 73 The decomposition reaction and analysis of the products were carried out in the same manner as in Example 70, but the reaction conditions (reaction temperature) were changed. The results are shown in Table 4.

[0072] Example 74 The soluble polymer composition obtained in the first decomposition step was purified by reprecipitation to prepare a soluble polymer composition (purified soluble polymer composition (P2) of Example 59) and dissolved in toluene to prepare a 5 mg / mL solution. A 5.0 μL portion of the solution was placed in a stainless steel container, and the solvent was distilled off. 25 μg of the purified soluble polymer composition obtained after the first decomposition step, obtained after solvent distillation, was heated to 650°C using a pyrolyzer. The resulting pyrolysis products were analyzed by GC / MS and GC. As a result, it was confirmed that isoprene, limonene, hydrocarbons having 1 to 4 carbon atoms, and hydrocarbons having 5 to 10 carbon atoms (other than isoprene and limonene) were produced in yields of 31%, 7%, 6%, and 29%, respectively (see Table 4).

[0073] Examples 75 to 77 The decomposition reaction and analysis of the products were carried out in the same manner as in Example 74, but with different reaction conditions (reaction temperature). The results are shown in Table 4.

[0074] Example 78 The soluble polymer composition obtained in the first decomposition step was purified by reprecipitation to prepare a soluble polymer composition (purified soluble polymer composition (P2) of Example 59) in toluene to prepare a 5 mg / mL solution. A 5.0 μL portion of the solution was impregnated onto 1 mg of MgO catalyst placed in a stainless steel container, and the solvent was then distilled off under reduced pressure. The MgO, to which 25 μg of the purified soluble polymer composition obtained after the first decomposition step had adhered, obtained after solvent distillation was heated to 750°C using a pyrolyzer. The resulting pyrolysis products were analyzed by GC / MS and GC. It was confirmed that isoprene, limonene, hydrocarbons having 1 to 4 carbon atoms, and hydrocarbons having 5 to 10 carbon atoms (other than isoprene and limonene) were produced in yields of 38%, 0%, 15%, and 38%, respectively (see Table 4).

[0075] Examples 79 to 99 The decomposition reaction and analysis of the products were carried out in the same manner as in Example 78, but with different reaction conditions (type of catalyst). The results are shown in Table 4.

[0076]

[0077] (Notes for Table 4) 1) In Examples 78 to 86, the solution of the purified soluble polymer composition obtained in the first decomposition step was impregnated into a catalyst placed in a stainless steel container, and the solvent was distilled off under reduced pressure to carry out thermal decomposition. On the other hand, in Examples 87 to 99, the solution of the purified soluble polymer composition obtained in the first decomposition step was placed in a stainless steel container, the solvent was distilled off under reduced pressure, and then the catalyst was added to the stainless steel container to carry out thermal decomposition. 2) The soluble polymers used are as follows: (P1): Soluble polymer composition obtained in Example 58 (P2): Purified soluble polymer composition obtained in Example 59 3) Details of the catalysts used in Examples 87 to 99 are as follows: CP811-E75: CP811-E75 (H-beta zeolite, SiO) manufactured by Zeolyst Co., Ltd. ２ / Al ２ O ３ = 75) CBV780: CBV780 (H-SDUSY type zeolite, SiO ２ / Al ２ O ３= 81) CBV8020: CBV8020 manufactured by Zeolyst (H-ZSM-5 type zeolite, SiO ２ / Al ２ O ３ = 85) CBV8011G: CBV8011G manufactured by Zeolyst (Na-ZSM-5 type zeolite, SiO ２ / Al ２ O ３ =80) CBV28011G: CBV28011G manufactured by Zeolyst (Na-ZSM-5 type zeolite, SiO ２ / Al ２ O ３ = 280) CBV100: CBV100 (Na-Y type zeolite, SiO) manufactured by Zeolyst Co., Ltd. ２ / Al ２ O ３ = 5) HSZ-320NAA: HSZ-320NAA (Na-Y type zeolite, SiO) manufactured by Tosoh Corporation ２ / Al ２ O ３ =6) Activated carbon (032-18091): Activated carbon 032-18091 manufactured by Fuji Film Wako Co., Ltd. Activated carbon (035-18101): Activated carbon 035-18101 manufactured by Fuji Film Wako Co., Ltd. Pd / C (Pd 5 wt%): Activated carbon-supported palladium (5 wt%) 205680 manufactured by Merck (Sigma-Aldrich) Silica gel (37559-79): Silica gel 37559-79 manufactured by Kanto Chemical Co., Ltd. Activated alumina (019-08295): Activated alumina 019-08295 manufactured by Fuji Film Wako Co., Ltd. Montmorillonite K10 (281522): Montmorillonite K10 281522 manufactured by Merck (Sigma-Aldrich) 4) The yields of isoprene and limonene were calculated using the absolute calibration curve method. The yields of hydrocarbons with 1 to 5 carbon atoms and hydrocarbons with 5 to 10 carbon atoms (other than isoprene and limonene) were calculated based on the area ratio of each hydrocarbon peak in gas chromatographic analysis. 5) Hydrocarbons with 1 to 4 carbon atoms. 6) Hydrocarbons with 5 to 10 carbon atoms (other than isoprene and limonene).

[0078] The results in Table 4 show that the isoprene yield is maximized by pyrolysis at a temperature range of about 700 to 750°C, whether using the unpurified soluble polymer composition (P1) or the soluble polymer composition (P2) purified by reprecipitation. ２ CO ３ , K. ２ CO ３ (1) Acidic catalysts based on zeolites (e.g., CP811-E75, CBV780, CBV8020) tend to increase the C1-C4 components (e.g., Examples 87-89).

[0079] (Example 100) A mixture of 100 mg of vulcanized rubber sample A, 14.8 mg of benzoyl peroxide, and 1.6 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 60°C for 1 hour in a 10 mL vial (sealed) to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement to be 68%. Furthermore, the molecular weights were estimated by GPC measurement to be Mw = 57,900, Mn = 15,100, and Mw / Mn = 3.8.

[0080] (Example 101) A decomposition reaction was carried out in the same manner as in Example 100, except that the decomposition reaction time was changed to 2 hours instead of 1 hour, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 87%, and the molecular weights of the soluble polymer were estimated to be Mw = 64,600, Mn = 21,200, and Mw / Mn = 3.0.

[0081] (Example 102) In Example 100, except that 18.4 mg of lauroyl peroxide was used instead of 14.8 mg of benzoyl peroxide, decomposition reaction was carried out in the same manner as in Example 100, and the product was analyzed.As a result, the yield of soluble polymer was calculated to be 85%, and the molecular weight of the soluble polymer was estimated to be Mw=59800, Mn=21600, and Mw / Mn=2.8.Comparing the yield of soluble polymer with the yield of Example 100, when using benzoyl peroxide, it was 68%, but when using lauroyl peroxide, it was 85%, and it was found that the decomposition reaction proceeded faster when using lauroyl peroxide.

[0082] (Example 103) In Example 102, except that the time of decomposition reaction is changed to 2 hours instead of 1 hour, decomposition reaction is carried out in the same manner as in Example 102, and product analysis is carried out.As a result, the yield of soluble polymer can be calculated as 88%, and the molecular weight of soluble polymer is estimated as Mw=37100, Mn=14800, Mw / Mn=2.6.Comparing the molecular weight of soluble polymer with that of Example 101, when using benzoyl peroxide, Mw=64600, Mn=21200, Mw / Mn=3.0, but when using lauroyl peroxide, Mw=37100, Mn=14800, Mw / Mn=2.6, it is found that using lauroyl peroxide makes decomposition reaction proceed faster, and obtains low molecular weight soluble polymer.

[0083] Example 104 A decomposition reaction was carried out in the same manner as in Example 100, except that an ethylbenzene solvent was used instead of the toluene solvent in Example 100, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 87%, and the molecular weight of the soluble polymer was estimated to be Mw = 35,800, Mn = 14,000, and Mw / Mn = 3.0. When the yield of the soluble polymer was compared with the yield in Example 100, the yield was 68% when a toluene solvent was used, but 87% when an ethylbenzene solvent was used, indicating that the decomposition reaction proceeded more quickly when an ethylbenzene solvent was used.

[0084] Example 105: The decomposition reaction was carried out in the same manner as in Example 104, except that the decomposition reaction time was changed to 2 hours instead of 1 hour, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 88%, and the molecular weight of the soluble polymer was estimated to be Mw = 35,300, Mn = 13,900, and Mw / Mn = 2.5. When the molecular weight of the soluble polymer was compared with that of Example 101, when a toluene solvent was used, the values ​​were Mw = 64,600, Mn = 21,200, and Mw / Mn = 3.0, but when an ethylbenzene solvent was used, the values ​​were Mw = 35,300, Mn = 13,900, and Mw / Mn = 2.5. It was found that the decomposition reaction proceeded more quickly when an ethylbenzene solvent was used, and a low molecular weight soluble polymer was obtained.

[0085] (Example 106) A decomposition reaction was carried out in the same manner as in Example 104, except that 18.4 mg of lauroyl peroxide was used instead of 14.8 mg of benzoyl peroxide in Example 104, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 88%, and the molecular weights of the soluble polymer were estimated to be Mw = 43,300, Mn = 17,000, and Mw / Mn = 2.5.

[0086] Example 107 The decomposition reaction was carried out in the same manner as in Example 106, except that the decomposition reaction time was changed to 2 hours instead of 1 hour, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 88%, and the molecular weights of the soluble polymer were estimated to be Mw = 27,600, Mn = 11,700, and Mw / Mn = 2.4.

[0087] (Example 108) As a pretreatment step, 10 g of the vulcanized rubber sample A was immersed in 100 mL of toluene solvent and shaken and stirred at room temperature for one day to dissolve the additives in the vulcanized rubber. After that, the vulcanized rubber was removed from the solution and dried under reduced pressure. A mixture of 200 mg of the vulcanized rubber sample A after the pretreatment step, 7.3 mg of lauroyl peroxide, and 3.2 mL of chloroform was placed in a 30 mL vial (sealed) and stirred with a magnetic stirrer using a Teflon (registered trademark) rotor at room temperature for one day under an air atmosphere to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement and found to be 84%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 70,200, Mn = 20,700, and Mw / Mn = 3.4. Without the pretreatment step, under the same decomposition reaction conditions, the yield of the soluble polymer was 11%, demonstrating that the pretreatment step accelerates the decomposition reaction.

[0088] (Example 109) Pretreatment and decomposition reaction were carried out in the same manner as in Example 108, except that the decomposition reaction time was changed to 2 days instead of 1 day, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 86%, and the molecular weight of the soluble polymer was estimated to be Mw = 57,100, Mn = 17,700, and Mw / Mn = 3.2. When the pretreatment step was not carried out, the yield of the soluble polymer was 13% under the same decomposition reaction conditions, demonstrating that the pretreatment step promotes the decomposition reaction.

[0089] Example 110 Pretreatment and decomposition reaction were carried out in the same manner as in Example 108, except that 40 mL of acetone solvent was used instead of 100 mL of toluene solvent in the pretreatment step of Example 108. As a result, the yield of the soluble polymer was calculated to be 83%, and the molecular weights of the soluble polymer were estimated to be Mw = 67,800, Mn = 21,100, and Mw / Mn = 3.2.

[0090] Example 111 Pretreatment and decomposition reaction were carried out in the same manner as in Example 110, except that the decomposition reaction time was changed to 2 days instead of 1 day, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 84%, and the molecular weights of the soluble polymer were estimated to be Mw = 62,500, Mn = 18,600, and Mw / Mn = 3.4.

[0091] The present invention can provide an efficient method for decomposing vulcanized rubber, which is useful for chemical recycling of vulcanized rubber, and therefore the present invention is highly useful and has great industrial significance.

Claims

1. A method for decomposing vulcanized rubber, comprising: a first decomposition step in which a radical initiator is reacted with vulcanized rubber or a composition containing same in an atmosphere containing oxygen gas to convert it into a soluble decomposition product; and a second decomposition step in which the soluble decomposition product obtained in the decomposition step is thermally decomposed to convert it into a low molecular weight compound having 10 or less carbon atoms.

2. The decomposition method according to claim 1, wherein the rubber component of the vulcanized rubber is at least one rubber component selected from the group consisting of natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR) and styrene-butadiene rubber (SBR).

3. The method according to claim 1, wherein the composition containing vulcanized rubber is a composition selected from tire rubber containing carbon black or silica.

4. The method according to claim 1, wherein the radical initiator is selected from the group consisting of an azo compound and a peroxide.

5. The method according to claim 4, wherein the peroxide is a peroxide selected from acyl peroxides.

6. The method for decomposing according to claim 5, wherein the acyl peroxide is selected from the group consisting of benzoyl peroxide, lauroyl peroxide and acetyl peroxide.

7. The method according to claim 1, wherein the thermal decomposition in the second decomposition step is carried out at a temperature in the range of 400 to 900°C.

8. The method according to claim 1, wherein the thermal decomposition in the second decomposition step is carried out in the presence of a catalyst.

9. The method according to claim 1, wherein the decomposition method in the first decomposition step is a decomposition method using a chlorinated hydrocarbon or an aromatic hydrocarbon as a solvent.

10. The method according to claim 9, wherein the chlorinated hydrocarbon is selected from the group consisting of chloroform and chlorobenzene.

11. The method according to claim 9, wherein the aromatic hydrocarbon is ethylbenzene.

12. The decomposition method according to claim 1, wherein the vulcanized rubber is a vulcanized rubber that has been subjected to a pretreatment step of washing with a solvent.