Method for decomposing crosslinked rubber

Abstract

The present invention addresses the problem of providing a method for decomposing a crosslinked rubber, which makes it possible to improve the yield of C4-C10 chemical products, especially diene monomers. The method for decomposing a crosslinked rubber is characterized by including a first decomposition step, in which a crosslinked rubber including a diene-based rubber is thermally decomposed at 150-400°C, and a second decomposition step, in which the decomposition products obtained in the first decomposition step are heated in an inert-gas atmosphere in the presence of a catalyst from 100°C to 450°C at a heating rate of 800 °C / min or higher and thermally decomposed at 450-950°C.

Description

Method for decomposing crosslinked rubber

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

[0002] Conventionally, rubber products primarily made of cross-linked rubber such as vulcanized rubber have been difficult to reuse, and after the end of their product life, they have often been reused as fuel, particularly in cement factories. However, with the recent rise in environmental concerns, there has been a demand for the development of methods for recycling materials obtained by decomposing rubber products, rather than burning them as fuel. There are various methods for decomposing cross-linked rubber, and for example, a technique for thermally decomposing cross-linked rubber at high temperatures is known. Furthermore, Patent Document 1 listed below discloses a method for decomposing polyisoprene-based rubber using microorganisms.

[0003] JP 2009-247241 A

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

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

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

[0007] [1] A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 800°C / min or higher from 100°C to 450°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the product at 450 to 950°C.

[0008] [2] A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 800°C / min or higher from 100°C to 600°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the decomposition product at 600 to 950°C.

[0009] [3] A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000°C / min or higher from 100°C to 450°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the decomposed product at 450 to 950°C.

[0010] [4] A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000°C / min or higher from 100°C to 600°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the decomposed product at 600 to 950°C.

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

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

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

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

[0015] [9] The method for decomposing crosslinked rubber according to any one of [1] to [8], wherein the diene rubber comprises at least one selected from the group consisting of isoprene skeleton rubber, styrene-butadiene rubber, and butadiene rubber.

[0016]

[10] The second decomposition step is performed by using 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 The method for decomposing a crosslinked rubber according to any one of [1] to [9], wherein the decomposition is carried out in the presence of at least one basic catalyst selected from the group consisting of:

[0017]

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

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

[0018]

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

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

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

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

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

[0022] [Method for Decomposing Crosslinked Rubber] The method for decomposing crosslinked rubber of the present invention is characterized by comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150° C. or higher and 400° C. or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step in an inert gas atmosphere and in the presence of a catalyst from 100° C. to 450° C. at a heating rate of 800° C. / min or higher, and thermally decomposing the product at 450 to 950° C. In a preferred embodiment, the method comprises: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150° C. or higher and 400° C. or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step in an inert gas atmosphere and in the presence of a catalyst from 100° C. to 600° C. at a heating rate of 800° C. / min or higher, and thermally decomposing the product at 600 to 950° C. In another preferred embodiment, the method includes a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150° C. or higher and 400° C. or lower, and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000° C. / min or higher in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the product at 450 to 950° C. In yet another preferred embodiment, the method includes a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150° C. or higher and 400° C., and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000° C. / min or higher in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the product at 600 to 950° C.

[0023] In the method for decomposing a crosslinked rubber of the present invention, in the first decomposition step, pyrolysis is carried out at a relatively low temperature of 150°C or more and 400°C or less, thereby making it possible to suppress gasification and polycyclic aromatic compounds from the decomposition products, and to improve the retention rate of the monomer skeleton (isoprene skeleton, butadiene skeleton, etc.) in the diene rubber compared to ordinary high-temperature pyrolysis. Furthermore, in the decomposition method for crosslinked rubber of the present invention, in the second decomposition step, the decomposition product obtained in the first decomposition step is rapidly heated from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposed at 450 to 950°C. This reduces the rate of decomposition during temperature rise (i.e., at a temperature lower than the target decomposition temperature), suppresses the generation and volatilization of decomposition products with higher molecular weights than the C4-C10 chemical products from the decomposition product obtained in the first decomposition step, and further suppresses hydrogenation of double bonds in the skeletons of the constituent monomers of the diene rubber (isoprene skeleton, butadiene skeleton, etc.) and oxidation of the decomposition products, while decomposing the decomposition products (intermediate decomposition products) into C4-C10 chemical products (particularly diene monomers) in high yield. Therefore, according to the decomposition method for crosslinked rubber of the present invention, the yield of C4-C10 chemical products, particularly diene monomers, finally obtained from the crosslinked rubber can be improved.

[0024] <First Decomposition Step> The method for decomposing a crosslinked rubber according to the present embodiment includes a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at a temperature of 150°C or higher and 400°C or lower.

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

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

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

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

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

[0030] --Diene-Based Rubber-- The diene-based rubber is a rubber containing units derived from a diene-based monomer (diene-based units) and may further contain units derived from a copolymerizable comonomer. The units derived from the diene-based monomer enable the diene-based rubber to be crosslinked (vulcanized) and to exhibit rubber-like elongation and strength. While the diene-based rubber in the crosslinked rubber is typically present in a crosslinked state, it may be partially uncrosslinked. Specific examples of diene-based monomers (diene-based compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds. Specific examples of the aromatic vinyl compounds include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. Examples of the diene rubber include isoprene-skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). The isoprene-skeleton rubber is a rubber whose main skeleton is an isoprene unit, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). Among these, the diene rubber preferably comprises at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber. When the diene rubber comprises at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber, easily recyclable diene monomers such as isoprene and butadiene can be obtained. The content of the diene rubber in the crosslinked rubber is not particularly limited, and is preferably in the range of 10 to 100% by mass, for example. From the viewpoint of further improving the yield of butadiene and isoprene, a range of 30 to 100% by mass is more preferable.

[0031] --Carbon Black-- The crosslinked rubber may further contain carbon black. In the method for decomposing a crosslinked rubber of the present invention, in the first decomposition step, the diene rubber in the crosslinked rubber can be decomposed to reduce the molecular weight, for example, to a liquid polymer or liquid oligomer. Therefore, even if the crosslinked rubber contains carbon black, the carbon black can be easily separated and recovered after the first decomposition step, for example, by solid-liquid separation. By recovering the carbon black before the thermal decomposition in the second decomposition step, deterioration of the carbon black can be suppressed, and it can be reused as high-quality carbon black. Furthermore, even if the crosslinked rubber contains carbon black, the crosslinked rubber can be efficiently decomposed. The content of carbon black in the crosslinked rubber is not particularly limited, and is, for example, in the range of 10 to 150 parts by mass, preferably 30 to 120 parts by mass, per 100 parts by mass of the diene rubber.

[0032] --Sulfur-- The crosslinked rubber may further contain sulfur. In the crosslinked rubber, sulfur is usually present in a state where the diene rubber is crosslinked (as a crosslink for the diene rubber), but some of it may be free. In the method for decomposing a crosslinked rubber of the present invention, in the first decomposition step, the diene rubber in the crosslinked rubber is decomposed to reduce the molecular weight, for example, to a liquid polymer or liquid oligomer. Therefore, even if the crosslinked rubber contains sulfur, the sulfur can be easily recovered after the first decomposition step, for example, by solid-liquid separation. By recovering the sulfur before the thermal decomposition in the second decomposition step, the sulfur can be reused. Furthermore, even when a catalyst is used in the second decomposition step, sulfur can be prevented from poisoning the catalyst or from re-crosslinking (re-vulcanization) of the decomposition products. Therefore, even if the crosslinked rubber contains sulfur, the crosslinked rubber can be efficiently decomposed. The sulfur content in the crosslinked rubber is not particularly limited, and is, for example, in the range of 0.1 to 10 parts by mass, preferably 1 to 5 parts by mass, per 100 parts by mass of the diene rubber.

[0033] --Other Components--The crosslinked rubber may contain, in addition to the diene rubber, carbon black, and sulfur described above, various components commonly used in the rubber industry, such as rubber components other than diene rubbers, fillers other than carbon black (silica, calcium carbonate, etc.), silane coupling agents, antioxidants, softeners, processing aids, resins, surfactants, organic acids (stearic acid, etc.), zinc oxide (zinc white), vulcanization accelerators, crosslinking agents other than sulfur (peroxides, etc.), and the like.

[0034] (Reaction Conditions, etc.) The first decomposition step is carried out at a temperature of 150°C or higher and 400°C or lower. By carrying out the first decomposition step at 150°C or higher, the rate of decomposition reaction of the diene rubber in the crosslinked rubber is improved. Furthermore, by carrying out the first decomposition step at 400°C or lower, gasification and aromatization of the decomposition products can be suppressed. Furthermore, after the decomposition, the retention rate (selectivity) of the monomer skeleton of the diene rubber in the crosslinked rubber is improved. Furthermore, for example, when the crosslinked rubber contains carbon black, it can be recovered and reused as high-quality carbon black. From the viewpoint of improving the decomposition reaction rate of the diene rubber, the first decomposition step is preferably 175°C or higher, more preferably 190°C or higher. Furthermore, from the viewpoint of improving the selectivity of products that maintain the monomer skeleton, it is preferably 350°C or lower, more preferably 300°C or lower.

[0035] The first decomposition step is preferably carried out under an inert gas atmosphere. By carrying out the first decomposition step under an inert gas atmosphere, oxidation and reduction of the decomposition products can be suppressed, and in particular, hydrogenation of double bonds in oligomers and monomers in the decomposition products can be suppressed. Furthermore, when the crosslinked rubber contains carbon black, oxidation of the carbon black can also be suppressed. Examples of inert gases include nitrogen, carbon dioxide, argon, and helium.

[0036] To carry out the first decomposition step under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that although hydrogen may be generated during the first decomposition step, the generated hydrogen is not taken into consideration when determining the atmosphere for the first decomposition step.

[0037] The first decomposition step can be carried out at any pressure, whether under reduced pressure, normal pressure, or increased pressure, but is preferably carried out under reduced pressure or normal pressure. As an example, the reaction pressure in the first decomposition step is preferably 1000 kPa to 65 kPa. By carrying out the first decomposition step under reduced pressure or normal pressure, polymerization (repolymerization) of oligomers and monomers in the decomposition products can be suppressed.

[0038] The reaction time of the first decomposition step is not particularly limited. For example, the reaction time of the first decomposition step is preferably 1 minute to 180 minutes, more preferably 3 minutes to 60 minutes, and even more preferably 5 minutes to 30 minutes.

[0039] The first decomposition step may or may not use a catalyst, but it is preferable not to use a catalyst. Not using a catalyst in the first decomposition step can reduce costs. When a catalyst is used, any catalyst that has the effect of accelerating the decomposition reaction of the crosslinked rubber can be used.

[0040] (Decomposition Products (Intermediate Decomposition Products)) In the method for decomposing a crosslinked rubber of this embodiment, it is preferable to decompose 80% by mass or more of the diene rubber in the crosslinked rubber into diene oligomers having a weight average molecular weight of 100 to 50,000 through the first decomposition step. By decomposing 80% by mass or more of the diene rubber in the crosslinked rubber into diene oligomers having a weight average molecular weight of 100 to 50,000 through the first decomposition step, the yield of C4-C10 chemical products (particularly diene monomers) can be further improved through the second decomposition step described below. From the viewpoint of the yield of diene monomers after the second decomposition step, it is more preferable to decompose 85% by mass or more of the diene rubber in the crosslinked rubber into diene oligomers having a weight average molecular weight of 100 to 50,000 through the first decomposition step. Here, in this specification, oligomer refers to one having a weight average molecular weight of 50,000 or less and containing two or more monomer units. The diene oligomer is an oligomer containing two or more units derived from a diene monomer (diene units). The weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC).

[0041] <Second Decomposition Step> The method for decomposing a crosslinked rubber according to this embodiment includes a second decomposition step in which the decomposition product obtained in the first decomposition step is heated from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposed at 450 to 950°C. In one preferred embodiment, the decomposition product obtained in the first decomposition step is heated from 100°C to 600°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposed at 600 to 950°C. In another preferred embodiment, the decomposition product obtained in the first decomposition step is heated from 100°C to 450°C at a heating rate of 2000°C / min or more in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposed at 450 to 950°C. In still another preferred embodiment, the decomposition product obtained in the first decomposition step is heated from 100°C to 600°C at a heating rate of 2000°C / min or more in an inert gas atmosphere and in the presence of a catalyst, and then thermally decomposed at 600 to 950°C.

[0042] The method for decomposing crosslinked rubber according to the present embodiment may involve mixing the decomposition product obtained in the first decomposition step with at least one medium selected from organic solvents, fatty acid esters, and hydrocarbons, and thermally decomposing the mixture.

[0043] The organic solvent can be any solvent that does not inhibit the decomposition reaction, including, for example, aromatic hydrocarbons (aromatic solvents), chlorinated hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, nitriles, esters, etc. Specific examples of these include aromatic hydrocarbons such as toluene, xylene, ethylbenzene, trimethylbenzene, and propylbenzene. Specific examples of chlorinated hydrocarbons include chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethene, chlorobenzene, and dichlorobenzene. Specific examples of aliphatic hydrocarbons include pentane, hexane, and octane. Specific examples of alicyclic hydrocarbons include cyclohexane and cyclooctane. Specific examples of ethers include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and dioxane. Specific examples of nitriles include benzonitrile. Specific examples of esters include ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, and butyl propionate. Among these, aromatic hydrocarbons are preferred from the viewpoints of reaction rate, availability, etc. Specific examples of these include toluene, xylene, and ethylbenzene. Among aromatic hydrocarbons, ethylbenzene is more preferable than toluene in terms of reaction rate.

[0044] Examples of the fatty acid ester include esters of fatty acids and alcohols such as glycerin or aliphatic alcohols. Examples of the fatty acids include myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, and erucic acid. The fatty alcohol preferably has 12 to 24 carbon atoms. Specific examples of the fatty acid ester include rapeseed oil, soybean oil, olive oil, sunflower oil, safflower oil, corn oil, castor oil, jojoba oil, and palm oil. These may be hydrogenated (hydrogenated), and examples of hydrogenated fatty acid esters include hydrogenated rapeseed oil and hydrogenated jojoba oil. These fatty acid esters may be recycled or discarded, such as waste cooking oil. When the alcohol is glycerin, the fatty acid ester may be a triglyceride, as well as a monoglyceride or a diglyceride. The fatty acid moiety of the fatty acid ester preferably has 8 or more carbon atoms, more preferably 12 or more carbon atoms, and preferably 24 or less carbon atoms, more preferably 18 or less carbon atoms. When the fatty acid moiety of the fatty acid ester has 8 or more carbon atoms, the fatty acid ester is present in the reaction field during thermal decomposition, allowing it to fully exert its effect. In addition, the amount of hydrogen generated when the fatty acid ester is decomposed increases, providing more hydrogen to the liquid polymer and accelerating the decomposition of the liquid polymer. Furthermore, when the fatty acid moiety of the fatty acid ester has 24 or less carbon atoms, it is easily miscible with the liquid polymer.

[0045] Examples of the hydrocarbon include liquid paraffin, microcrystalline wax, asphalt-mixed naphthenic oil, polyethylene, polypropylene, etc., of which liquid paraffin and microcrystalline wax are preferred, and microcrystalline wax is more preferred. The hydrocarbon preferably has 12 or more carbon atoms, more preferably 20 or more carbon atoms, and preferably 80 or less carbon atoms, more preferably 60 or less carbon atoms. When the hydrocarbon has 12 or more carbon atoms, it is present in the reaction field during thermal decomposition, allowing it to fully exert its effects. In addition, the amount of hydrogen generated during the decomposition of the hydrocarbon increases, providing more hydrogen to the liquid polymer and promoting the decomposition of the liquid polymer. Furthermore, when the hydrocarbon has 80 or less carbon atoms, it is easily miscible with the liquid polymer.

[0046] (Temperature-Raising Conditions) In the method for decomposing a crosslinked rubber according to the present embodiment, the decomposition product obtained in the first decomposition step or the mixture is heated from 100°C to 450°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the presence of a catalyst (temperature-raising step). If the heating rate from 100°C to 450°C is less than 800°C / min, the proportion of decomposition occurring during heating increases, and decomposition products having higher molecular weights than the C4-C10 chemical products from the decomposition product obtained in the first decomposition step or the mixture are generated and volatilized during heating (i.e., at a temperature lower than the target decomposition temperature), resulting in a decrease in the yield of the final C4-C10 chemical products (particularly diene monomers). The temperature rise rate from 100°C to 450°C is preferably 2000°C / min or more. When the temperature rise rate is 2000°C / min or more, the generation of decomposition products obtained in the first decomposition step or high-molecular-weight decomposition products from the mixture can be further suppressed, and the yield of C4 to C10 chemical products (particularly diene monomers) can be further improved.

[0047] In a preferred embodiment, the decomposition product or the mixture obtained in the first decomposition step is heated from 100°C to 600°C at a heating rate of 800°C / min or more in an inert gas atmosphere and in the presence of a catalyst (heating step). When the heating rate from 100°C to 600°C is 800°C / min or more, the rate of decomposition during heating is reduced, and the generation and volatilization of higher molecular weight decomposition products than the C4-C10 chemical products from the decomposition product or the mixture obtained in the first decomposition step during heating (i.e., at a temperature lower than the target decomposition temperature) can be suppressed, thereby improving the yield of the final C4-C10 chemical products (particularly diene monomers). The heating rate from 100°C to 600°C is preferably 2000°C / min or more. When the heating rate is 2000°C / min or more, the generation of high molecular weight decomposition products from the decomposition product or the mixture obtained in the first decomposition step can be further suppressed.

[0048] (Reaction Conditions, etc.) In the second decomposition step of the method for decomposing a crosslinked rubber according to this embodiment, after the temperature increase, thermal decomposition is performed at 450 to 950°C in an inert gas atmosphere and in the presence of a catalyst (thermal decomposition step). By performing the thermal decomposition in the second decomposition step at 450°C or higher, the rate of decomposition reaction of the decomposition product or the mixture obtained in the first decomposition step is increased, thereby improving the yield of the final C4-C10 chemical products (particularly diene monomers). Furthermore, by performing the thermal decomposition in the second decomposition step at 950°C or lower, gasification and polycyclic aromatics formation of the decomposition product can be suppressed, and after decomposition, the retention rate (selectivity) of the structural monomers of the diene oligomer (liquid component) obtained in the first decomposition step is improved, thereby improving the yield of the final C4-C10 chemical products (particularly diene monomers). The temperature of the thermal decomposition in the second decomposition step is preferably 600°C or higher, more preferably 650°C or higher, from the viewpoint of improving the decomposition reaction rate of the decomposition product obtained in the first decomposition step or the mixture. Furthermore, the temperature of the thermal decomposition in the second decomposition step is preferably 850°C or lower, from the viewpoint of improving the selectivity of the product that maintains the monomer skeleton. Therefore, by carrying out the thermal decomposition in the second decomposition step at 600 to 950°C, the yield of C4-C10 chemical products (particularly diene monomers) obtained from the decomposition product obtained in the first decomposition step or the mixture is further improved, and by carrying out the thermal decomposition at 650 to 850°C, the yield of C4-C10 chemical products (particularly diene monomers) obtained from the decomposition product obtained in the first decomposition step or the mixture is further improved.

[0049] The time for thermal decomposition in the second decomposition step is not particularly limited. As an example, the heating time after reaching the target temperature for thermal decomposition in the second decomposition step is preferably 0.1 seconds to 5 minutes, more preferably 0.1 seconds to 1 minute. By performing the thermal decomposition in the second decomposition step for 0.1 seconds or more, the decomposition rate of the decomposition product or the mixture obtained in the first decomposition step is improved. On the other hand, if the decomposition time is too long, the skeletons (double bonds, etc.) of the constituent monomers of the diene oligomer (liquid component) obtained in the first decomposition step are decomposed, and the decomposition product is gasified or converted into polycyclic aromatic compounds. However, by performing the thermal decomposition in the second decomposition step for 5 minutes or less, the decomposition of the monomer skeleton and the gasification or conversion into polycyclic aromatic compounds of the decomposition product can be suppressed, and the retention rate (selectivity) of the skeletons of the constituent monomers of the diene oligomer (liquid component) obtained in the first decomposition step after decomposition is improved.

[0050] The method of such rapid pyrolysis is not particularly limited, but examples thereof include batch type, fixed bed type, moving hearth type, rotary kiln type, fluidized bed type, entrained bed type, microwave heating type, plasma heating type, high-temperature liquid spray type, single-screw extrusion type, twin-screw extrusion type, free fall type, electrified spatiotemporal heating, and wire mesh heating (Hoekstra et al., Chem. Eng. J., 191, 45 (2012)).

[0051] The temperature increase and thermal decomposition in the second decomposition step are carried out in an inert gas atmosphere. By carrying out the temperature increase and thermal decomposition in the second decomposition step in an inert gas atmosphere, oxidation and reduction of the decomposition product or the mixture obtained in the first decomposition step and the decomposition product produced in the second decomposition step can be suppressed, and in particular, hydrogenation of double bonds in the diene monomers produced can be suppressed. Examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0052] To carry out the temperature increase and thermal decomposition in the second decomposition step under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that, although hydrogen may be generated during the temperature increase and thermal decomposition in the second decomposition step, the generated hydrogen is not taken into consideration when determining the atmosphere for the temperature increase and thermal decomposition in the second decomposition step.

[0053] The temperature increase and thermal decomposition in the second decomposition step can be carried out at any pressure, and can be carried out at reduced pressure, normal pressure, or increased pressure. As an example, the pressure for the temperature increase and thermal decomposition in the second decomposition step is preferably 10 kPa to 5 MPa, and more preferably 100 kPa to 1 MPa. Note that by carrying out the temperature increase and thermal decomposition under reduced pressure or normal pressure, polymerization (repolymerization) of oligomers and diene monomers in the decomposition product can be suppressed.

[0054] Furthermore, when the second decomposition step is carried out under pressure, for example, the decomposition product obtained in the first decomposition step may be thermally decomposed in a solvent. Any solvent that does not inhibit the decomposition reaction can be used as the solvent, and examples thereof include ethers, aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons (aromatic solvents). More specifically, the solvent is preferably tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, and xylene, and more preferably toluene and tetrahydrofuran. The amount of the solvent used is preferably 10 mL or more, more preferably 50 mL or more, and more preferably 500 mL or less, and more preferably 200 mL or less, per 1 g of the decomposition product obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step). If the amount of the solvent used is 10 mL or more per 1 g of the decomposition product obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step), the decomposition reaction will proceed further. Furthermore, if the amount of the solvent used is 500 mL or less per 1 g of the decomposition product obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step), this is preferable from the standpoint of cost.

[0055] (Catalyst) The second decomposition step is carried out in the presence of a catalyst. The catalyst may be an acidic catalyst, a neutral catalyst, or a basic catalyst, and among these, a basic catalyst is preferred. In addition, the second decomposition step is carried out in the presence of a catalyst such as 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 preferable to carry out the second decomposition step in the presence of at least one basic catalyst selected from the group consisting of:

[0044] By carrying out the second decomposition step in the presence of such a basic catalyst, the rate of the decomposition reaction (depolymerization reaction) of the decomposition product obtained in the first decomposition step or the mixture 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.

[0056] The amount of the catalyst used is preferably 1 part by mass or more, more preferably 10 parts by mass or more, and even more preferably 100 parts by mass or more, relative to 100 parts by mass of the decomposition product or the mixture obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step), and is preferably 8,000 parts by mass or less, more preferably 4,000 parts by mass or less, and even more preferably 500 parts by mass or less. If the amount of the catalyst used is 100 parts by mass or more relative to 100 parts by mass of the decomposition product or the mixture obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step), the decomposition reaction will proceed further, and if the amount of the catalyst used is 500 parts by mass or less relative to 100 parts by mass of the decomposition product or the mixture obtained in the first decomposition step (or the intermediate product to be subjected to the second decomposition step), it is preferable from the standpoint of cost.

[0057] (Decomposition Products) In the method for decomposing a crosslinked rubber according to the present embodiment, C4 to C10 chemical products (particularly diene monomers) and the like are obtained as decomposition products in the second decomposition step.

[0058] In the method for decomposing crosslinked rubber according to this embodiment, it is preferable that the second decomposition step decomposes 20% by mass or more of the diene oligomers having a weight average molecular weight of 100 to 50,000 obtained in the first decomposition step into C4-C10 chemical products. By improving the yield of C4-C10 chemical products, the yield of reusable monomers and oligomers is improved, further improving the economic and environmental value of the decomposition method. From the viewpoint of the yield of reusable monomers and oligomers, it is even more preferable that the second decomposition step decomposes 30% by mass or more of the diene oligomers having a weight average molecular weight of 100 to 50,000 obtained in the first decomposition step into C4-C10 chemical products.

[0059] Here, the total amount of C4-C10 chemical products, particularly diene monomers, in the decomposition products obtained in the second decomposition step may depend not only on the reaction conditions described above but also on the reaction apparatus used. In this embodiment, the preferred range of the total amount of C4-C10 chemical products, particularly diene monomers, is the preferred range when the reaction apparatus described in the Examples below is used. When a reaction apparatus more suitable for the present invention is used, the total amount of C4-C10 chemical products, particularly diene monomers, may be even greater.

[0060] Furthermore, in the method for decomposing a crosslinked rubber of this embodiment, it is preferable to decompose 0.1% by mass or more of the diene rubber in the crosslinked rubber into C4-C10 chemical products through the first decomposition step and the second decomposition step. By improving the yield of C4-C10 chemical products, the yield of reusable monomers is improved, further improving the economic and environmental value of the decomposition method. Note that, from the viewpoint of the yield of reusable monomers, it is even more preferable to decompose 20% by mass or more of the diene rubber in the crosslinked rubber into C4-C10 chemical products through the first decomposition step and the second decomposition step.

[0061] The C4-C10 chemical products as decomposition products vary depending on the type of diene rubber in the crosslinked rubber to be decomposed, but examples include hydrocarbons having 4 to 10 carbon atoms and derivatives thereof, such as 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, benzene, toluene, ethylbenzene, xylene, and limonene, with 1,3-butadiene and isoprene being preferred. The proportion of the C4-C10 chemical products, particularly the total amount of diene monomers, in the decomposition products can be controlled by, for example, the reaction conditions in the second decomposition step, such as the reaction temperature and reaction time.

[0062] <Others> The method for decomposing a crosslinked rubber according to this embodiment may further include another step in addition to the first and second decomposition steps described above. Such steps include a pretreatment step for the crosslinked rubber (for example, a cutting step or a pulverization step). Furthermore, when the crosslinked rubber contains carbon black, it is preferable to include a step of recovering the carbon black from the decomposition product (intermediate decomposition product) between the first and second decomposition steps.

[0063] The decomposition method for crosslinked rubber according to this embodiment can be carried out in either a batch reactor or a flow reactor. The decomposition product after the decomposition reaction can be separated and recovered by filtration, distillation, or the like, or recovered by precipitation using a poor solvent, and can be reused. The diene monomer finally obtained from the crosslinked rubber can be reused as a raw material for diene rubber (polymer).

[0064] 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.

[0065] <Preparation of Crosslinked Rubber Sample> A rubber composition was prepared by blending 50.0 parts by mass of carbon black, 1.0 part by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 2.0 parts by mass of stearic acid, 2.5 parts by mass of zinc oxide, 1.5 parts by mass of vulcanization accelerator (N-cyclohexyl-2-benzothiazolylsulfenamide), and 4.5 parts by mass of sulfur with 100.1 parts by mass of natural rubber, and the rubber composition was then heat-crosslinked to prepare a crosslinked rubber. The resulting crosslinked rubber was cut to a side length of approximately 2 to 6 mm to prepare a crosslinked rubber sample.

[0066] Example 1-1: Quartz wool was packed into the lower part of the reaction region of a reaction tube equipped with a sample inlet and a nitrogen introduction line on the upstream side. An ice-cooled trap, a first liquid nitrogen trap, and a second liquid nitrogen trap were installed downstream of the reaction tube, and gas passing through the second liquid nitrogen trap was collected using a gas bag. 10 g of the crosslinked rubber sample obtained as described above was supplied to the reaction tube at a supply rate of 1 g / 10 min, and a thermal decomposition reaction (first decomposition step) was carried out at 330°C under a nitrogen flow rate of 600 mL / min. The supplied sample was placed above the quartz wool and subjected to the thermal decomposition reaction. Ten minutes after the completion of sample supply, the reaction tube was cooled, and the highly viscous material (oligomer) precipitated in the reaction tube and trap was directly collected. The recovered oligomer was dark brown and highly viscous, with a recovery amount of 2.4 g. When measured by liquid chromatography in accordance with test standard IP391, the ratio of the mass of aromatic compounds derived from natural rubber in the degradation products (oligomers) to the mass of natural rubber in the crosslinked rubber sample was 25 mass%. At the same time, carbon black derived from the crosslinked rubber sample was recovered. The recovered amount of carbon black was 6.1 g.

[0067] (Examples 1-2 to 1-9) <First decomposition step> 1.5 g of a vulcanized rubber sample cut into 2 mm squares was loaded into an alumina boat and placed in the chamber of an electric furnace (ROP-001PG). Nitrogen gas was then circulated into the electric furnace chamber at a rate of 5 L / min to replace the atmosphere with nitrogen. While circulating nitrogen gas at the same flow rate, the electric furnace was heated to the temperature shown in Table 1 and maintained for the time shown in Table 1 to carry out a thermal decomposition reaction (first decomposition step).

[0068] (Solvent decomposition step) 2 g of deuterated chloroform as a solvent and 0.10 g of precisely weighed hexamethylenedisilazane were added to 20 mg of the heat-treated rubber obtained above, and after ultrasonic dispersion, solid-liquid separation was carried out using a centrifuge to separate into a supernatant and a solid. The amount of polymer component remaining in the solid was determined by heating to 50-700°C in nitrogen using TGA and measuring the weight loss at 300-650°C. The decomposition yield of the polymer component was calculated by subtracting the amount of polymer component remaining in the solid from the weight of the polymer component contained in the rubber. The supernatant was １ H-NMR was measured, and the yield of the isoprene skeleton component in the decomposed polymer component was calculated from the ratio of the amount of hydrogen at the α-position of the isoprene structure to the amount of hydrogen in hexamethylenedisilazane, and is shown in Table 1.

[0069]

[0070] <Second Decomposition Step> (Examples 2-1 to 2-3) A reaction tube was filled with 0.1 g of a liquid rubber sample (Kuraray Co., Ltd., liquid polyisoprene LIR-30) wrapped in quartz wool (Tosoh, fine fiber diameter: 2 to 6 μm), and quartz wool was filled upstream and downstream of the sample. A helium introduction line was installed upstream of the reaction tube, and a cooling trap filled with chloroform (60% ethylene glycol aqueous solution, cooled to -20 ° C) was installed downstream, and the gas that passed through the trap was collected using a gas bag. Under conditions of a helium flow rate of 50 mL / min, the liquid rubber sample in the reaction tube was slid onto a heating site in an electric furnace heated to 500 ° C, 600 ° C, or 700 ° C, and heated at that temperature for 3 minutes to perform thermal decomposition. During this process, the temperature of the liquid rubber sample was monitored with a thermocouple, and the temperature rise rate was determined. After the reaction was completed, the reaction tube was cooled, and the products precipitated in the reaction tube and trap were collected. Gas products were also collected using a gas bag. The mass proportions (yields) of each product are shown in Table 2. Furthermore, the yields of isoprene, limonene, toluene, xylene, and other aromatic compounds, as well as other aliphatic compounds, in the liquid product were measured by gas chromatography (GC), and the total yield of C4-C10 chemical products was calculated. The results are summarized in Table 2.

[0071]

[0072] *1 Yield of gaseous product: A value calculated from the amount of decomposition products recovered by gas bag. *2 Yield of liquid product: A value calculated from the amount of components that could be qualitatively analyzed by gas chromatography (GC) out of the total amount of (1) the decomposition products recovered by a cooling trap and (2) the components that were dissolved in chloroform out of the components that adhered to the reaction tube. *3 Yield of oligomer: A value calculated from the amount of components that could not be qualitatively analyzed by gas chromatography (GC) out of the total amount of (1) the decomposition products recovered by a cooling trap and (2) the components that were dissolved in chloroform out of the components that adhered to the reaction tube. *4 Yield of solid product: A value calculated from the total amount of (1) the residue of the thermal decomposition reaction minus the carbon black content in the crosslinked rubber sample, and (2) the amount of the components that were not dissolved in chloroform out of the components that adhered to the reaction tube.

[0073] Table 2 shows that, in the absence of a catalyst, C4-C10 chemical products, particularly isoprene (diene monomer), can be obtained in high yield by increasing the temperature from 100° C. to 450° C. at a rate of 800° C. / min or more and then performing thermal decomposition at 450 to 950° C. It is also estimated that, even in the presence of a catalyst, C4-C10 chemical products, particularly isoprene (diene monomer), can be obtained in high yield by performing thermal decomposition at a similar rate of increase in temperature and at a similar thermal decomposition temperature.

[0074] From the results of Examples 1-1 to 1-9 (first decomposition step) and Examples 2-1 to 2-3 (rapid temperature-rising pyrolysis of liquid polymer in the absence of a catalyst), it is presumed that C4 to C10 chemical products, in particular isoprene (diene monomer), can be obtained in high yield by heating the decomposition product obtained in the first decomposition step of the method for decomposing crosslinked rubber of the present invention in an inert gas atmosphere and in the presence of a catalyst from 100°C to 450°C at a heating rate of 800°C / min or more and then pyrolyzing it at 450 to 950°C.

Claims

1. A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 800°C / min or higher from 100°C to 450°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the product at 450 to 950°C.

2. A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 800°C / min or higher from 100°C to 600°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the product at 600 to 950°C.

3. A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000°C / min or higher from 100°C to 450°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the product at 450 to 950°C.

4. A method for decomposing crosslinked rubber, comprising: a first decomposition step of thermally decomposing a crosslinked rubber containing a diene rubber at 150°C or higher and 400°C or lower; and a second decomposition step of heating the decomposition product obtained in the first decomposition step at a heating rate of 2000°C / min or higher from 100°C to 600°C in an inert gas atmosphere and in the presence of a catalyst, and thermally decomposing the product at 600 to 950°C.

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

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

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

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

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

10. The second decomposition step is carried out by 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 The method for decomposing a crosslinked rubber according to any one of claims 1 to 4, wherein the decomposition is carried out in the presence of at least one basic catalyst selected from the group consisting of:

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

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