Crosslinked rubber composition for oil recovery by thermal decomposition, oil, and method for producing oil

Abstract

The present invention addresses the problem of providing a crosslinked rubber composition that is used for the purpose of recovering an oil, which contains a component that serves as a starting material for an isoprene skeleton rubber, by means of thermal decomposition. A means for solving the problem is a crosslinked rubber composition for oil recovery by thermal decomposition, the crosslinked rubber composition being characterized in that: the crosslinked rubber composition contains a rubber component and sulfur; the rubber component contains an isoprene skeleton rubber; the content of the isoprene skeleton rubber is 50 parts by mass or more per 100 parts by mass of the rubber component; the content of the sulfur is 8 parts by mass or less with respect to 100 parts by mass of the rubber component; and the mass ratio (isoprene skeleton rubber / sulfur) of the content of the isoprene skeleton rubber to the content of the sulfur is 12 or more.

Description

Crosslinked rubber composition for oil recovery by pyrolysis, oil, and method for producing oil

[0001] The present invention relates to a crosslinked rubber composition for oil recovery by pyrolysis, an oil, and a method for producing the oil.

[0002] Recently, recycling of used rubber products, including used tires, has been promoted from the viewpoint of protecting the global environment. One such recycling method is a technique of pyrolyzing used rubber products and recovering pyrolysis products such as oil and carbon black (carbide). For example, Patent Document 1 listed below discloses a method of recovering carbon and hydrocarbon mixtures from waste tires or similar polymer materials by pyrolysis.

[0003] Special Publication No. 2002-523552

[0004] As described in Patent Document 1 and elsewhere, various studies have been conducted on methods for pyrolyzing used tires, but no study has been conducted on the components in the oil recovered by pyrolysis. Furthermore, since pyrolysis oil from commercially available tires is generally used as fuel, there is no need to consider the components in the pyrolysis oil. Meanwhile, in order to pyrolyze used rubber products and return them to isoprene-based rubbers such as natural rubber and isoprene rubber, which are the main components of rubber products, it is necessary to recover isoprene as a monomer. However, since the pyrolysis oil from commercially available tires contains almost no isoprene, it is difficult to recover isoprene.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional art and to provide a cross-linked rubber composition that can be used to recover oil containing components (monomers such as isoprene, limonene, etc.) that serve as raw materials for isoprene-skeleton rubber by thermal decomposition. Another object of the present invention is to provide oil obtained from such a cross-linked rubber composition and a method for producing oil from such a cross-linked rubber composition.

[0006] The crosslinked rubber composition for oil recovery by thermal decomposition, the oil, and the method for producing the oil of the present invention, which solve the above problems, are outlined as follows.

[0007] [1] A cross-linked rubber composition for oil recovery by thermal decomposition, the cross-linked rubber composition comprising a rubber component and sulfur, the rubber component comprising an isoprene skeleton rubber, the content of the isoprene skeleton rubber being 50 parts by mass or more per 100 parts by mass of the rubber component, the content of the sulfur being 8 parts by mass or less per 100 parts by mass of the rubber component, and a mass ratio of the content of the isoprene skeleton rubber to the content of the sulfur (isoprene skeleton rubber / sulfur) being 12 or more.

[0008] [2] Further containing carbon black, the following formula (1): exp(18.977663905 + 0.0085742124 × A - 0.003867326 × B - 0.028534179 × C - 0.251024648 × D + (C - 3.75) × ((D - 3.948) × 0.0118234107)) / 243316566.160943 + exp(17.436413974+0.0140219114×A−0.00394088×B−0.137558684×D−(A−80)×((A−80)×0.000514996)) / 86230236.8833005≧0.4 (1) [wherein A is the content (parts by mass) of the isoprene skeleton rubber in 100 parts by mass of the rubber component, and B is the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area (m ２ / g), C is the content (parts by mass) of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine per 100 parts by mass of the rubber component, and D is the content (parts by mass) of the sulfur per 100 parts by mass of the rubber component.

[0009] [3] The cross-linked rubber composition according to [1] or [2], wherein the sulfur content is 5 parts by mass or less per 100 parts by mass of the rubber component.

[0010] [4] The cross-linked rubber composition according to any one of [1] to [3], wherein the sulfur content is 3 parts by mass or less per 100 parts by mass of the rubber component.

[0011] [5] The cross-linked rubber composition according to any one of [1] to [4], wherein the content of the isoprene skeleton rubber is 70 parts by mass or more per 100 parts by mass of the rubber component.

[0012] [6] The cross-linked rubber composition according to any one of [1] to [5], wherein the rubber component consists solely of the isoprene skeleton rubber.

[0013] [7] The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​the carbon black is 180 m ２ / g or less.

[0014] [8] The cross-linked rubber composition according to any one of [1] to [7], which does not contain an antioxidant, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

[0015] [9] The cross-linked rubber composition according to any one of [1] to [8], wherein the oil is an oil for producing a rubber composition for tires.

[0016]

[10] An oil recovered by thermally decomposing the crosslinked rubber composition according to any one of [1] to [9].

[0017]

[11] A method for producing an oil, comprising thermally decomposing the cross-linked rubber composition according to any one of [1] to [9].

[0018] According to the present invention, it is possible to provide a cross-linked rubber composition that can be thermally decomposed to recover oil containing components that serve as raw materials for isoprene-skeleton rubber. Furthermore, according to the present invention, it is possible to provide oil obtained from such a cross-linked rubber composition and a method for producing oil from such a cross-linked rubber composition.

[0019] The crosslinked rubber composition for oil recovery by thermal decomposition, the oil, and the method for producing the oil of the present invention will be described in detail below with reference to the embodiments.

[0020] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0021] In this specification, used tires refer to tire products that have been used once or have not been used and are then collected or discarded.

[0022] In this specification, the cross-linked rubber composition refers to a rubber composition after cross-linking a rubber composition, and may also be called a "cross-linked rubber." The cross-linked rubber composition also includes rubber members, rubber fragments, and the like collected from used rubber products such as used tires.

[0023] <Cross-linked Rubber Composition> The cross-linked rubber composition of this embodiment is a cross-linked rubber composition for oil recovery by thermal decomposition. The cross-linked rubber composition of this embodiment is characterized in that it contains a rubber component and sulfur, the rubber component contains an isoprene skeleton rubber, the amount of the isoprene skeleton rubber is 50 parts by mass or more per 100 parts by mass of the rubber component, the amount of sulfur is 8 parts by mass or less per 100 parts by mass of the rubber component, and the mass ratio of the amount of the isoprene skeleton rubber to the amount of sulfur (isoprene skeleton rubber / sulfur) is 12 or more.

[0024] As described above, no study has been conducted to date on the components contained in oil recovered by pyrolysis of used rubber products, including used tires. In response to this, the present inventors conducted extensive research aimed at recovering monomers such as isoprene, which are raw materials for isoprene-skeleton rubber. As a result, they discovered that by pyrolyzing a cross-linked rubber composition containing a rubber component and sulfur, the rubber component containing the isoprene-skeleton rubber being 50 parts by mass or more per 100 parts by mass of the rubber component, the sulfur content being 8 parts by mass or less per 100 parts by mass of the rubber component, and the mass ratio of the isoprene-skeleton rubber to the sulfur content (isoprene-skeleton rubber / sulfur) being 12 or more, it is possible to recover oil containing large amounts of monomers such as isoprene and components such as limonene, which are raw materials for isoprene-skeleton rubber. Limonene is a compound consisting of two isoprene units and is a type of isoprene dimer, so it can be used as a raw material for isoprene-skeleton rubber.

[0025] Here, since the raw materials for the isoprene-skeleton rubber, such as isoprene and limonene, are mainly derived from the isoprene-skeleton rubber contained in the cross-linked rubber composition, the yield of raw materials for the isoprene-skeleton rubber, such as isoprene and limonene, is increased by having the isoprene-skeleton rubber content of 50 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, since sulfur plays a role in cross-linking the rubber component, if the sulfur content is too high, the cross-linked rubber composition becomes less susceptible to thermal decomposition, and the amount of complex decomposition products increases, resulting in a decrease in the yield of raw materials for the isoprene-skeleton rubber, such as isoprene and limonene (components having an isoprene skeleton). In contrast, the sulfur content of 8 parts by mass or less per 100 parts by mass of the rubber component reduces the amount of complex decomposition products produced, thereby increasing the yield of raw materials for the isoprene-skeleton rubber, such as isoprene and limonene. Furthermore, if the sulfur content is too high relative to the isoprene skeleton rubber content, the cross-linked rubber composition becomes difficult to thermally decompose, and the amount of complex decomposition products increases, resulting in a decrease in the yield of components that serve as raw materials for isoprene skeleton rubber, such as isoprene and limonene. In contrast, by setting the mass ratio of the isoprene skeleton rubber content to the sulfur content (isoprene skeleton rubber / sulfur) to 12 or more (i.e., by relatively increasing the isoprene skeleton rubber content), the amount of complex decomposition products produced can be reduced and the yield of components that serve as raw materials for isoprene skeleton rubber, such as isoprene and limonene, can be increased. Therefore, by thermally decomposing the cross-linked rubber composition of this embodiment, monomers such as isoprene, which are raw materials for isoprene skeleton rubber, and oils rich in limonene can be efficiently recovered.

[0026] (Applications) The cross-linked rubber composition of this embodiment is a cross-linked rubber composition for oil recovery by thermal decomposition, in other words, a cross-linked rubber composition used for recovering oil by thermal decomposition. As described above, the cross-linked rubber composition of this embodiment is particularly suitable for applications in which oil is recovered by thermal decomposition because it can efficiently recover monomers such as isoprene, which are raw materials for isoprene-skeleton rubber, and oils containing a large amount of limonene, etc.

[0027] Furthermore, the oil recovered by pyrolysis of the cross-linked rubber composition is preferably oil for producing a rubber composition for tires. Here, the oil for producing a rubber composition for tires refers to oil that can be used as a raw material for isoprene-skeleton rubber, which is the rubber component of the rubber composition for tires. By using the oil recovered by pyrolysis of the cross-linked rubber composition as a raw material for isoprene-skeleton rubber, which is the rubber component of the rubber composition for tires, chemical recycling of the cross-linked rubber composition becomes possible. Furthermore, when the cross-linked rubber composition is collected from used tires, it can be recycled into tires.

[0028] (Rubber Component) The cross-linked rubber composition of the present embodiment contains a rubber component, and the rubber component provides rubber elasticity to the cross-linked rubber composition.

[0029] --Isoprene-skeleton rubber-- The rubber component includes an isoprene-skeleton rubber. The isoprene-skeleton rubber is a rubber whose main skeleton is isoprene units, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). By thermally decomposing a cross-linked rubber composition containing an isoprene-skeleton rubber as the rubber component, it is possible to recover monomers such as isoprene, which are raw materials for the isoprene-skeleton rubber, and oils containing limonene and the like.

[0030] The content of the isoprene skeleton rubber is 50 parts by mass or more, and preferably 70 parts by mass or more, per 100 parts by mass of the rubber component. It is more preferable that the rubber component consists solely of the isoprene skeleton rubber. If the content of the isoprene skeleton rubber is less than 50 parts by mass per 100 parts by mass of the rubber component, the yield of raw materials for the isoprene skeleton rubber, such as isoprene and limonene, decreases. On the other hand, if the content of the isoprene skeleton rubber is 70 parts by mass or more per 100 parts by mass of the rubber component, the yield of raw materials for the isoprene skeleton rubber, such as isoprene and limonene, further increases. Furthermore, if the rubber component consists solely of the isoprene skeleton rubber, the yield of raw materials for the isoprene skeleton rubber, such as isoprene and limonene, further increases.

[0031] --Other Rubber Components-- The rubber component may contain a rubber component other than an isoprene-skeleton rubber. Such a rubber component other than an isoprene-skeleton rubber is preferably a 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 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 compound include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. Examples of diene rubbers other than the isoprene skeleton rubber include styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). Among these, butadiene rubber is preferred as the diene rubber other than the isoprene skeleton rubber. When the diene rubber contains butadiene rubber, easily recyclable diene monomers such as butadiene can be obtained.

[0032] The content of the rubber component other than the isoprene skeleton rubber is 50 parts by mass or less, preferably 30 parts by mass or less, and may be 0 part by mass, per 100 parts by mass of the rubber component.

[0033] (Sulfur) The cross-linked rubber composition of this embodiment contains sulfur. The sulfur has the effect of cross-linking (vulcanizing) the rubber component and improving the strength of the cross-linked rubber composition. As the sulfur, various types of sulfur can be used, such as ordinary sulfur (soluble sulfur (powdered sulfur) and the like) and insoluble sulfur, and oil treat sulfur can also be used.

[0034] The sulfur content is 8 parts by mass or less, preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and preferably 1.4 parts by mass or more, per 100 parts by mass of the rubber component. If the sulfur content exceeds 8 parts by mass per 100 parts by mass of the rubber component, the amount of complex decomposition products produced increases when the crosslinked rubber composition is thermally decomposed, resulting in a decrease in the yield of components (components having an isoprene skeleton) that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene. On the other hand, if the sulfur content is 5 parts by mass or less per 100 parts by mass of the rubber component, the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, further increases. Furthermore, if the sulfur content is 3 parts by mass or less per 100 parts by mass of the rubber component, the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, further increases. Furthermore, when the sulfur content is 1.4 parts by mass or more per 100 parts by mass of the rubber component, the cross-linked rubber composition is sufficiently cross-linked, and various rubber products have excellent strength.

[0035] The mass ratio of the isoprene skeleton rubber content to the sulfur content (isoprene skeleton rubber / sulfur) is 12 or more, preferably 20 or more, and preferably 80 or less. If the mass ratio of the isoprene skeleton rubber content to the sulfur content (isoprene skeleton rubber / sulfur) is less than 12, the amount of complex decomposition products produced when the cross-linked rubber composition is thermally decomposed increases, resulting in a reduced yield of components that serve as raw materials for isoprene skeleton rubber, such as isoprene and limonene. On the other hand, if the mass ratio of the isoprene skeleton rubber content to the sulfur content (isoprene skeleton rubber / sulfur) is 20 or more, the amount of complex decomposition products produced when the cross-linked rubber composition is thermally decomposed can be further reduced, thereby further increasing the yield of components that serve as raw materials for isoprene skeleton rubber, such as isoprene and limonene. Furthermore, if the mass ratio of the isoprene skeleton rubber content to the sulfur content (isoprene skeleton rubber / sulfur) is 80 or less, the cross-linked rubber composition is sufficiently cross-linked and has sufficient strength for use in various rubber products.

[0036] (Carbon Black) The cross-linked rubber composition of this embodiment preferably further contains carbon black. The carbon black reinforces the cross-linked rubber composition, thereby improving the reinforcing properties of the cross-linked rubber composition. The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used alone or in combination of two or more.

[0037] The carbon black content is preferably 30 parts by mass or more, preferably 90 parts by mass or less, and more preferably 80 parts by mass or less, per 100 parts by mass of the rubber component. When the carbon black content is 30 parts by mass or more per 100 parts by mass of the rubber component, the reinforcement of the cross-linked rubber composition can be further improved. When the carbon black content is 90 parts by mass or less per 100 parts by mass of the rubber component, the content of the isoprene skeleton rubber in the entire cross-linked rubber composition relatively increases, and therefore, when the cross-linked rubber composition is thermally decomposed, the yield of components that serve as raw materials for the isoprene skeleton rubber, such as isoprene and limonene, further increases.

[0038] The crosslinked rubber composition of the present embodiment has a crosslinking coefficient of 1.001, which is expressed by the following formula (1): exp(18.977663905+0.0085742124×A−0.003867326×B−0.028534179×C−0.251024648×D+(C−3.75)×((D−3.948)×0.0118234107)) / 243316566.160943 + exp(17.436413974+0.0140219114×A−0.00394088×B−0.137558684×D−(A−80)×((A−80)×0.000514996)) / 86230236.8833005 It is preferable that the following relationship is satisfied: ≧ 0.4 (1) By thermally decomposing a crosslinked rubber composition that satisfies the relationship of the above formula (1) (i.e., the value of the left side of formula (1) is 0.4 or more), the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, is further increased.

[0039] In the cross-linked rubber composition of this embodiment, the value of the left side of the above formula (1) is more preferably 0.6 or more, and even more preferably 1.0 or more. When the value of the left side of the formula (1) of the cross-linked rubber composition is 0.6 or more, the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, is further increased. Furthermore, when the value of the left side of the formula (1) of the cross-linked rubber composition is 1.0 or more, the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, is particularly increased.

[0040] In the above formula (1), A is the content (parts by mass) of the isoprene skeleton rubber in 100 parts by mass of the rubber component. As the content of the isoprene skeleton rubber in the crosslinked rubber composition increases, the amounts of isoprene and limonene produced tend to increase.

[0041] In the above formula (1), B is the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area (m ２ / g). When the crosslinked rubber composition contains two or more types of carbon black, the CTAB adsorption specific surface area is an average value taking into account the mass proportion of each carbon black. In other words, when the crosslinked rubber composition contains n types of carbon black, the nth type of carbon black is referred to as "CB ｎ ", the following formula (2): (average) CTAB adsorption specific surface area (m ２ / g) = Σ(CB ｎ CTAB adsorption specific surface area × CB ｎ Content of CB ｎ (content of carbon black) ... (2) As the CTAB adsorption specific surface area of ​​the carbon black contained in the crosslinked rubber composition increases, the amounts of isoprene and limonene produced tend to decrease. In this specification, the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​carbon black is a value measured in accordance with JIS K6217-3, and is the external surface area of ​​the carbon black excluding micropores, expressed as the specific surface area when CTAB (cetyltrimethylammonium bromide) is adsorbed onto the carbon black.

[0042] In the above formula (1), C represents the content (parts by mass) of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in the crosslinked rubber composition relative to 100 parts by mass of the rubber component. As the content of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in the crosslinked rubber composition increases, the amount of limonene produced tends to decrease. In the crosslinked rubber composition of this embodiment, the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is not an essential component, and the content of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine may be 0 parts by mass. Furthermore, as described below, it is preferable that the crosslinked rubber composition of this embodiment does not contain the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

[0043] In the above formula (1), D is the content (parts by mass) of the sulfur relative to 100 parts by mass of the rubber component. When the content of sulfur in the crosslinked rubber composition increases, the amounts of isoprene and limonene produced tend to decrease.

[0044] In the above formula (1), the term "exp(18.977663905 + 0.0085742124 × A - 0.003867326 × B - 0.028534179 × C - 0.251024648 × D + (C - 3.75) × ((D - 3.948) × 0.0118234107)) / 243316566.160943" (first term on the left side) is a term calculated from the amount of limonene produced when the cross-linked rubber composition is thermally decomposed. The present inventors have found that there is a correlation between the amount of limonene produced when various rubber compositions (specifically, the rubber compositions of the Examples and Comparative Examples described below) are pyrolyzed and A: the content of isoprene-skeleton rubber, B: the CTAB adsorption specific surface area of ​​carbon black, C: the content of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and D: the sulfur content, and have discovered this relationship from a regression equation obtained by multiple regression analysis. Here, the oil obtained by thermally decomposing the crosslinked rubber composition was analyzed with a gas chromatograph mass spectrometer (GC / MS), and the area value (integral value) of the limonene peak in the GC chromatogram was normalized with the concentration of the oil in the sample to be used as the response variable. In addition, multiple regression analysis was performed using A: the content of isoprene-skeleton rubber, B: the CTAB adsorption specific surface area of ​​carbon black, C: the content of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and D: the content of sulfur as explanatory variables to calculate the above relational expression.

[0045] In addition, in the above formula (1), the term "exp(17.436413974 + 0.0140219114 × A - 0.00394088 × B - 0.137558684 × D - (A - 80) × ((A - 80) × 0.000514996)) / 86230236.8833005" (the second term on the left side) is a term calculated from the amount of isoprene produced when the crosslinked rubber composition is thermally decomposed. The present inventors have found a correlation between the amount of isoprene produced when various rubber compositions (specifically, the rubber compositions of the Examples and Comparative Examples described below) are thermally decomposed and A: the content of isoprene-skeleton rubber, B: the CTAB adsorption specific surface area of ​​carbon black, and D: the sulfur content, and have discovered this relationship from the regression equation of multiple regression analysis. Here, the oil obtained by thermally decomposing the crosslinked rubber composition was analyzed by a gas chromatograph mass spectrometer (GC / MS), and the area value (integral value) of the isoprene peak in the GC chromatogram was normalized by the oil concentration in the sample to be used as the response variable. In addition, multiple regression analysis was performed using A: the content of isoprene skeleton rubber, B: the CTAB adsorption specific surface area of ​​carbon black, and D: the content of sulfur as explanatory variables to calculate the above relational expression.

[0046] When the cross-linked rubber composition is thermally decomposed, the amount of limonene produced is considerably larger than the amount of isoprene produced, and as is, the relational expression is strongly influenced by the amount of isoprene produced. Therefore, in order to reflect the influence of the amounts of isoprene and limonene produced approximately equally, normalization was performed to derive the formula (1).

[0047] Specifically, the first term on the left side of the formula, "exp(18.977663905 + 0.0085742124 × A - 0.003867326 × B - 0.028534179 × C - 0.251024648 × D + (C - 3.75) × ((D - 3.948) × 0.0118234107)) / 243316566.160943," represents A: content of isoprene skeleton rubber, B: CTAB adsorption specific surface area of ​​carbon black, and C: antioxidant. The content of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, D: calculated from the sulfur content, is calculated by dividing the result "exp(18.977663905 + 0.0085742124 × A - 0.003867326 × B - 0.028534179 × C - 0.251024648 × D + (C - 3.75) × ((D - 3.948) × 0.0118234107))" by "243316566.160943". Regarding the second term on the left side, "exp(17.436413974 + 0.0140219114 x A - 0.00394088 x B - 0.137558684 x ​​D - (A - 80) x ((A - 80) x 0.000514996)) / 86230236.8833005", A is the content of isoprene-based rubber, B is the content of carbon black. CTAB adsorption specific surface area of ​​the rack, D: "exp(17.436413974 + 0.0140219114 × A - 0.00394088 × B - 0.137558684 × D - (A - 80) × ((A - 80) × 0.000514996))" calculated from the sulfur content is divided by "86230236.8833005".

[0048] Here, the value "243316566.160943" is equal to the value of "exp(18.977663905 + 0.0085742124 × A - 0.003867326 × B - 0.028534179 × C - 0.251024648 × D + (C - 3.75) × ((D - 3.948) × 0.0118234107))" of the sample that produced the most limonene when analyzed by GC / MS. In other words, the value of the first term on the left side of the sample that produced the most limonene has been normalized to 1. The value "86230236.8833005" is equal to the value of "exp(17.436413974+0.0140219114×A-0.00394088×B-0.137558684×D-(A-80)×((A-80)×0.000514996))" of the sample that produced the most isoprene when analyzed by GC / MS. In other words, the value of the second term on the left side of the equation for the sample that produced the most isoprene was normalized to 1.

[0049] The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​the carbon black is 180 m ２ / g or less, and ２ / g or less is more preferable, ２ / g or less is more preferable, and ２ / g or more. The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​the carbon black is preferably 180 m ２ When the carbon black has a specific surface area of ​​90 m / g or less, the yield of components serving as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, can be further increased when the crosslinked rubber composition is thermally decomposed. ２ When the carbon black has a specific surface area of ​​30 m / g or less, the yield of components serving as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, can be further increased when the crosslinked rubber composition is thermally decomposed. ２ When the crosslinked rubber composition has a modulus of 1 / 2 g or more, the crosslinked rubber composition has sufficient strength for use in various rubber products.

[0050] (Antiaging Agent) The crosslinked rubber composition of this embodiment preferably further contains an antioxidant. When the crosslinked rubber composition contains an antioxidant, aging resistance (weather resistance, ozone resistance) is improved, resulting in an excellent life span for various rubber products. Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, N,N'-diphenyl-p-phenylenediamine, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine, N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, and N,N'-dicyclohexyl-p-phenylenediamine.

[0051] The cross-linked rubber composition of this embodiment preferably does not contain the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine. As the content of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in the cross-linked rubber composition increases, the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, tends to decrease when the cross-linked rubber composition is thermally decomposed. Therefore, the lower the content of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in the cross-linked rubber composition, the more preferable, and it is particularly preferable that the cross-linked rubber composition does not contain the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine. By thermally decomposing a cross-linked rubber composition that does not contain the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, can be further increased. In this specification, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is sometimes referred to as "antioxidant 6PPD."

[0052] The content of the antioxidant is preferably 6 parts by mass or less per 100 parts by mass of the rubber component. When the content of the antioxidant is 6 parts by mass or less per 100 parts by mass of the rubber component, the aging resistance of the cross-linked rubber composition is improved, and a decrease in the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, can be sufficiently suppressed when the cross-linked rubber composition is thermally decomposed.

[0053] (Other Compounding Chemicals) In addition to the rubber component, sulfur, carbon black, and antioxidant described above, the crosslinked rubber composition of this embodiment may contain various components commonly used in the rubber industry, as needed, such as fillers other than carbon black (inorganic fillers such as silica and calcium carbonate), silane coupling agents, softeners, zinc oxide (zinc oxide), stearic acid, vulcanization accelerators, crosslinking agents other than sulfur, etc., appropriately selected within the scope that does not impair the object of the present invention. Commercially available products can be suitably used as these compounding agents.

[0054] The content of the zinc white (zinc oxide) is not particularly limited, but is preferably in the range of 0.1 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of the rubber component.

[0055] The content of the stearic acid is not particularly limited, but is preferably in the range of 0.1 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of the rubber component.

[0056] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0057] (Origin of Cross-Linked Rubber Composition) The cross-linked rubber composition of this embodiment may be derived from various rubber products (used rubber products), and may be derived from, for example, tires, hoses, etc. The cross-linked rubber composition of this embodiment preferably contains a cross-linked rubber composition derived from tires. When a cross-linked rubber composition derived from tires is contained, the tires are thermally decomposed to recover monomers such as isoprene, which are raw materials for the isoprene-skeleton rubber, and oil containing a large amount of limonene, etc., and isoprene-skeleton rubber is synthesized from the monomers such as isoprene and limonene in the oil and reused in tires, which makes it possible to recycle the tires and is also preferable from the standpoint of protecting the global environment.

[0058] The crosslinked rubber composition to be used for the thermal decomposition may be grouped by the type of rubber component previously compounded, and then thermally decomposed for each group. Alternatively, the composition may be grouped by the type of filler previously compounded (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then thermally decomposed for each group. Furthermore, the composition may be grouped by both the type of rubber component and the type of filler, and then thermally decomposed for each group. Such thermal decomposition for each group results in oils (e.g., including isoprene, limonene, liquid polymers, etc.), recycled carbon black, regenerated silica, etc., with more uniform physical properties, which results in a rubber composition with better performance when compounded again with rubber.

[0059] Furthermore, when the crosslinked rubber composition used for the pyrolysis 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 performed 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 performed for each group. Furthermore, the tires may be grouped both by type and by tire component, and then pyrolysis may be performed for each group. Such pyrolysis for each group results in oils (e.g., including isoprene, limonene, liquid polymers, etc.) and recycled carbon black with more uniform physical properties, which results in a rubber composition with better performance when blended again into rubber.

[0060] (Method for producing cross-linked rubber composition) The method for producing the rubber composition is not particularly limited, but the rubber composition can be produced, for example, by blending the above-mentioned rubber component and sulfur with various components appropriately selected as necessary, and kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be heated to form a cross-linked rubber composition.

[0061] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0062] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0063] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0064] The apparatus, method, conditions, etc. for carrying out the crosslinking (vulcanization) are not particularly limited and can be appropriately selected depending on the purpose. Examples of apparatuses for carrying out the crosslinking include molding vulcanizers using molds used for vulcanizing rubber compositions. The crosslinking conditions include a temperature of, for example, about 100 to 190°C.

[0065] <Oil> The oil of this embodiment is characterized by being recovered by thermally decomposing the cross-linked rubber composition of this embodiment. Since the oil of this embodiment is recovered by thermally decomposing the cross-linked rubber composition of this embodiment, it contains large amounts of monomers such as isoprene, which are raw materials for isoprene-skeleton rubber, and limonene, etc.

[0066] The oil of this embodiment preferably has an isoprene content of 0.1% by mass or more. The oil of this embodiment preferably has a limonene content of 1% by mass or more. A large amount of isoprene, which is a raw material for isoprene-skeleton rubber, can be obtained from oil having an isoprene content of 0.1% by mass or more and / or an limonene content of 1% by mass or more, and therefore the oil can be easily recycled into isoprene-skeleton rubber.

[0067] Furthermore, the oil of this embodiment is suitable as an oil for producing a rubber composition for tires. The oil recovered by pyrolyzing the cross-linked rubber composition can be used as a raw material for isoprene-skeleton rubber, which is the rubber component of the rubber composition for tires, thereby enabling chemical recycling of the cross-linked rubber composition. Furthermore, when the cross-linked rubber composition is collected from used tires, it can be recycled into tires.

[0068] The method for producing the oil of this embodiment is not particularly limited, but the oil of this embodiment can be obtained by the method for producing the oil of this embodiment described below.

[0069] <Oil Production Method> The oil production method of this embodiment is characterized by thermally decomposing the cross-linked rubber composition of this embodiment described above. Since the oil production method of this embodiment involves thermally decomposing the cross-linked rubber composition of this embodiment described above, it is possible to obtain oil that is rich in monomers such as isoprene, which are raw materials for isoprene-skeleton rubber, and limonene.

[0070] The temperature for thermal decomposition of the crosslinked rubber composition is preferably 300° C. or higher, more preferably 350° C. or higher, and is preferably 800° C. or lower, and more preferably 550° C. or lower. When the thermal decomposition temperature is 350° C. or higher, the decomposition of the crosslinked rubber composition can be sufficiently promoted, and when the temperature is 550° C. or lower, the amount of complex decomposition products produced can be further reduced, and the yield of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene, can be further increased.

[0071] The thermal decomposition is preferably carried out in an inert gas atmosphere, which can prevent oxidation or reduction of the decomposition products. Examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0072] The thermal decomposition can also be carried out in a solvent. Any solvent that does not inhibit the thermal decomposition reaction can be used as the solvent, and examples thereof include ethers, aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons (aromatic solvents). More specifically, examples of the solvent include tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, and xylene.

[0073] The oil production method of this embodiment may further include other steps in addition to the above-mentioned thermal decomposition step, such as a pretreatment step of the cross-linked rubber composition (e.g., a cutting step or a pulverization step).

[0074] The oil production method of this embodiment can be carried out in either a batch reactor or a flow reactor. The oil (cracked product) after thermal cracking can be separated and recovered by filtration, distillation, or the like, or recovered by precipitation using a poor solvent.

[0075] 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.

[0076] <Preparation of Crosslinked Rubber Compositions> Rubber compositions having the formulations shown in Tables 1 and 2 were kneaded to prepare them. Here, kneading was carried out in two stages, with the first kneading stage being carried out at 110°C for 3 minutes and 15 seconds, and the second kneading stage being carried out at 80°C for 1 minute. Furthermore, the vulcanization curve of the obtained rubber composition was measured (JIS K 6300-2), and the composition was heated at 145°C for a time 1.5 times the T90 to prepare a crosslinked rubber composition.

[0077] <Pyrolysis of Crosslinked Rubber Composition> 25 g of the crosslinked rubber composition prepared as described above was charged into a tubular reactor in approximately 1 g portions every 5 minutes, and pyrolysis was carried out under conditions of a temperature of 500°C and a nitrogen flow rate of 100 mL / min, to obtain an oil.

[0078] <Oil Analysis> Measurement samples were prepared by dissolving the oil obtained by pyrolysis in chloroform and analyzed using a gas chromatograph mass spectrometer (GC / MS, Agilent Technologies, product name "7890 GC System 5977B MSD," equipped with Agilent Technologies' "HP-5MS UI (length 30 m, inner diameter 0.25 mm, film thickness 0.25 μm)"). The peak area values ​​(integrated values) of isoprene and limonene were normalized by the oil concentration in the measurement sample, and multiple regression analysis was performed using the peak area values ​​(integrated values) of isoprene and limonene as the objective variable and the blending factors as the explanatory variables, resulting in the relationship shown in Equation (1). The peak area values ​​and area ratios of the produced isoprene and limonene are shown in Tables 1 and 2. The left side of equation (1): exp(18.977663905 + 0.0085742124 × A - 0.003867326 × B - 0.028534179 × C - 0.251024648 × D + (C - 3.75) × ((D - 3.948) × 0.0118234107)) / 243316566.160943 + exp(17.436413974 + 0.0140219114 × A - 0.00394088 × B - 0.137558684 × D - (A - 80) × ((A - 80) × 0.000514996)) / 86230236.8833005 = exp (log limonene) / 243316566.160943 + exp (log isoprene) / 86230236.8833005, and the values ​​of "log limonene" and "log isoprene" are shown in Tables 1 and 2.

[0079]

[0080]

[0081] *1 NR: Contains 0.06 parts by mass of "Noctizer SD" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. per 100 parts by mass of natural rubber. The actual amount of natural rubber is shown in the lower part. *2 BR: Butadiene rubber, manufactured by UBE Elastomers Co., Ltd., product name "UBEPOL BR150L" *3 Carbon black 1: CTAB adsorption specific surface area = 41 m ２ / g * 4 Carbon black 2: CTAB adsorption specific surface area = 74 m ２ / g *5 Carbon black 3: CTAB adsorption specific surface area = 123 m ２ / g *6 Stearic acid: NOF Corporation, trade name "Kiri Brand Stearic Acid" *7 Zinc oxide: Hakusui Tech Co., Ltd., trade name "Zinc Oxide" *8 Antioxidant 6PPD: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac 6C" *9 Vulcanization accelerator CBS: N-cyclohexyl-2-benzothiazolylsulfenamide, Sanshin Chemical Industry Co., Ltd., trade name "Suncerer CM-G" *10 20% oil-containing sulfur: Shikoku Chemical Industry Co., Ltd., trade name "Mucron OT-20 EX", contains 20% oil by mass, the actual amount of sulfur is shown in the lower part *11 Antioxidant TMQ: 2,2,4-trimethyl-1,2-dihydroquinoline polymer, Seiko Chemical Co., Ltd., trade name "Nonflex RD"

[0082] Tables 1 and 2 show that by thermally decomposing the crosslinked rubber compositions of the examples according to the present invention, it is possible to recover oil containing large amounts of components that serve as raw materials for isoprene-skeleton rubber, such as isoprene and limonene.

[0083] The crosslinked rubber composition of the present invention can be thermally decomposed and used to recover monomers such as isoprene, which are raw materials for isoprene-skeleton rubber, and oils rich in limonene and the like.

Claims

1. A cross-linked rubber composition for oil recovery by thermal decomposition, comprising: a rubber component; and sulfur; the rubber component comprises an isoprene skeleton rubber; the amount of the isoprene skeleton rubber is 50 parts by mass or more per 100 parts by mass of the rubber component; the amount of the sulfur is 8 parts by mass or less per 100 parts by mass of the rubber component; and the mass ratio of the isoprene skeleton rubber content to the sulfur content (isoprene skeleton rubber / sulfur) is 12 or more.

2. It further contains carbon black, and the following formula (1) is used: exp(18.977663905 + 0.0085742124 x A - 0.003867326 x B - 0.028534179 x C - 0.251024648 x D + (C - 3.75) x ((D - 3.948) x 0.0118234107)) / 243316566.160943 + exp(17.436413974+0.0140219114×A−0.00394088×B−0.137558684×D−(A−80)×((A−80)×0.000514996)) / 86230236.8833005≧0.4 (1) [wherein, A is the content (parts by mass) of the isoprene skeleton rubber in 100 parts by mass of the rubber component, and B is the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area (m ２ / g), C is the content (parts by mass) of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine relative to 100 parts by mass of the rubber component, and D is the content (parts by mass) of the sulfur relative to 100 parts by mass of the rubber component.

3. The crosslinked rubber composition according to claim 1, wherein the sulfur content is 5 parts by mass or less per 100 parts by mass of the rubber component.

4. The crosslinked rubber composition according to claim 1, wherein the sulfur content is 3 parts by mass or less per 100 parts by mass of the rubber component.

5. The crosslinked rubber composition according to claim 1, wherein the content of the isoprene skeleton rubber is 70 parts by mass or more per 100 parts by mass of the rubber component.

6. The crosslinked rubber composition according to claim 1, wherein the rubber component consists solely of the isoprene skeleton rubber.

7. The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​the carbon black is 180 m ２ The crosslinked rubber composition according to claim 2, wherein the crosslinked rubber composition has a viscosity of 100:1 or less.

8. The crosslinked rubber composition of claim 1 which is free of the antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

9. The crosslinked rubber composition according to claim 1, wherein the oil is an oil for producing a rubber composition for tires.

10. An oil recovered by thermally decomposing the crosslinked rubber composition according to any one of claims 1 to 9.

11. A method for producing oil, comprising pyrolyzing the crosslinked rubber composition according to any one of claims 1 to 9.

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