Method for treating rubber waste and method for producing recycled carbon black

Abstract

A method for treating rubber waste according to the present invention comprises (a) decomposing rubber waste with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the obtained carbon black. A method for producing recycled carbon black according to the present invention comprises decomposing rubber waste with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the carbon black as recycled carbon black. The rubber waste is, for example, a waste tire.

Description

Method for treating rubber waste and method for producing recycled carbon black

[0001] The present invention relates to a method for treating rubber waste and a method for producing recycled carbon black.

[0002] In recent years, rubber waste has been increasing worldwide, and its disposal has become a challenge. While efforts are being made by governments, industries, and manufacturers in various countries to deal with waste tires, much of the waste remains untreated. Problems caused by abandoned tires include tire fires, air pollution, and pest damage, making recycling them a challenge.

[0003] A typical method for recycling waste tires is a thermal treatment method. In the thermal treatment method, for example, waste tires are heated in an oxygen-free environment, whereby the rubber component is thermally decomposed and recovered as oil, and carbon black, which is a filler, can also be recovered. This allows the oil and carbon black to be recovered from the waste tires and recycled.

[0004] However, recycled products recovered from discarded tires using the heat treatment method, particularly carbon black, have the problem of insufficient quality. The deterioration in quality of carbon black recovered using the heat treatment method is due to the formation of a rubber adsorption layer, called bound rubber, with a thickness of about several nanometers, around the carbon black during tire molding. This bound rubber is carbonized during pyrolysis and remains integrated with the carbon black. Therefore, the particle size of the carbon black recovered as a recycled product becomes larger, resulting in a decrease in performance, such as reinforcing effect.

[0005] Techniques have also been proposed for suppressing deterioration in the quality of carbon black recovered by heat treatment. For example, Patent Document 1 describes how recycled carbon black with improved quality can be obtained by quickly removing rubber residues adhering to the surface of recycled carbon black obtained by heat treatment through oxidative decomposition using a high-temperature flame.

[0006] Patent No. 7409752

[0007] However, the technology disclosed in Patent Document 1 further heat-treats the carbon black recovered by the heat-treatment method. Therefore, it is difficult to solve the problem of the deterioration in quality of the carbon black (i.e., the increase in particle size) due to the carbonization of the bound rubber mentioned above. Furthermore, since an additional treatment is required in addition to the treatment of the rubber waste, the treatment cost increases. As such, no treatment method has been established to recover high-quality carbon black from rubber waste such as discarded tires.

[0008] An object of the present invention is to provide a novel method for treating rubber waste that can recover carbon black of superior quality to carbon black recovered by treating rubber waste using conventional heat treatment methods.A further object of the present invention is to provide a method for producing recycled carbon black that can provide recycled carbon black of superior quality to recycled carbon black produced from rubber waste using conventional heat treatment methods.

[0009] The present invention provides a method for treating rubber waste, comprising: (a) subjecting rubber waste to a decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the obtained carbon black.

[0010] Viewed from another aspect, the present invention provides a method for producing recycled carbon black, comprising: subjecting rubber waste to a decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the carbon black as recycled carbon black.

[0011] According to the method for treating rubber waste of the present invention, it is possible to recover carbon black having superior quality to carbon black recovered by treating rubber waste using conventional heat treatment methods. Furthermore, according to the method for producing recycled carbon black of the present invention, it is possible to provide recycled carbon black having superior quality to recycled carbon black produced from rubber waste using conventional heat treatment methods.

[0012] FIG. 1 is a flowchart showing a method for treating rubber waste according to a first embodiment of the present invention. FIG. 2 is a flowchart showing a method for treating rubber waste according to a second embodiment of the present invention. FIG. 3 is a flowchart showing a method for producing recycled carbon black according to a third embodiment of the present invention. FIG. 4 is a transmission electron microscope (TEM) image of the recovered material obtained in Example 1. FIG. 5 is a TEM image of the recovered material obtained in Example 2. FIG. 6 is a TEM image of the recovered material obtained in Example 3. FIG. 7 is a TEM image of the recovered material obtained in Example 5. FIG. 8 is a TEM image of the recovered material obtained in Example 6. FIG. 9 is a TEM image of the recovered material obtained in Example 7. FIG. 10 is a TEM image of the recovered material obtained in Example 8. FIG. 11 is a TEM image of the recovered material obtained in Example 9. FIG. 12 is a TEM image of the recovered material obtained in Example 10. FIG. 13 is a TEM image of the recovered material obtained in Example 11. FIG. 14 is a TEM image of the recovered material obtained in Example 12. FIG. 15 is a TEM image of the recovered material obtained in Example 13. FIG. 16 is a TEM image of the recovered material obtained in Example 14. FIG. 17 is a TEM image of the recovered material obtained in Example 15. FIG. 18 is a TEM image of the recovered material obtained in Example 16. FIG. 19 is a TEM image of the recovered material obtained in Example 17. FIG. 20 is a TEM image of the recovered material obtained in Example 18. FIG. 21 is a TEM image of the recovered material obtained in Comparative Example 1. FIG. 22 is a TEM image of non-recycled carbon black. FIG. 23 is a graph showing the results of thermogravimetric analysis of the recovered material of Example 2 and comparative non-recycled carbon black. FIG. 24 is a graph showing the results of stress-strain measurement of rubber compositions to which the recovered materials of Examples 3 and 19 (recycled carbon black) have been added, comparative rubber compositions to which non-recycled carbon black has been added, and comparative rubber compositions to which no carbon black has been added.

[0013] A method for treating rubber waste according to a first aspect of the present invention includes: (a) subjecting rubber waste to a decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the obtained carbon black.

[0014] In a second aspect of the present invention, for example, in the treatment method according to the first aspect, in the step (a), the rubber waste is brought into contact with supercritical water, subcritical water, or superheated steam at a temperature of 200°C or higher and 600°C or lower and a pressure of 5 MPa or higher and 100 MPa or lower for 10 minutes or longer to obtain the carbon black.

[0015] In a third aspect of the present invention, for example, in the treatment method according to the second aspect, in the step (a), the rubber waste is brought into contact with heated steam at a temperature of 400°C or more and 500°C or less and a pressure of 5 MPa or more and 20 MPa or less, for 20 minutes or more, to obtain the carbon black.

[0016] In a fourth aspect of the present invention, for example, the treatment method according to any one of the first to third aspects further includes: (b) subjecting the rubber waste to a decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain oil, and recovering the obtained oil, and (b) is carried out before (a).

[0017] In a fifth aspect of the present invention, for example, in the treatment method according to the fourth aspect, in (b), the rubber waste is brought into contact with supercritical water at a temperature of 400°C or more and 500°C or less and a pressure of 40 MPa or more and 50 MPa or less for 0.5 minutes or more and less than 30 minutes to obtain the oil.

[0018] In a sixth aspect of the present invention, for example, in the treatment method according to the fourth or fifth aspect, (a) is carried out consecutively after (b).

[0019] In a seventh aspect of the present invention, for example, in the treatment method according to any one of the first to sixth aspects, the rubber waste is waste tires.

[0020] In an eighth aspect of the present invention, for example, in the treatment method according to any one of the first to seventh aspects, in (a), the carbon black obtained by the decomposition treatment of the rubber waste with supercritical water, subcritical water, or superheated steam has an average particle size of less than 100 nm.

[0021] A method for producing recycled carbon black according to a ninth aspect of the present invention includes: subjecting rubber waste to a decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain carbon black; and recovering the carbon black as recycled carbon black.

[0022] In a tenth aspect of the present invention, for example, in the production method according to the ninth aspect, the carbon black is obtained by bringing the rubber waste into contact with supercritical water, subcritical water, or superheated steam at a temperature of 200°C or higher and 600°C or lower and a pressure of 5 MPa or higher and 100 MPa or lower for 10 minutes or longer.

[0023] In an eleventh aspect of the present invention, for example, in the production method according to the tenth aspect, the carbon black is obtained by bringing the rubber waste into contact with superheated steam at a temperature of 400°C or more and 500°C or less and a pressure of 5 MPa or more and 20 MPa or less for 20 minutes or more.

[0024] In a twelfth aspect of the present invention, for example, in the manufacturing method according to any one of the ninth to eleventh aspects, the rubber waste is waste tires.

[0025] In a thirteenth aspect of the present invention, for example, in the production method according to any one of the ninth to twelfth aspects, the recycled carbon black has an average particle size of less than 100 nm.

[0026] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented in any modified form without departing from the gist of the present invention.

[0027] (First embodiment) One embodiment of the method for treating rubber waste of the present invention will be described.

[0028] As shown in FIG. 1 , the method for treating rubber waste according to the first embodiment includes: (a) subjecting rubber waste to a decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the obtained carbon black (S11).

[0029] In the treatment method of the first embodiment, rubber waste is decomposed using supercritical water, subcritical water, or superheated steam. This method can gasify the rubber components attached to the periphery of the carbon black contained in the rubber waste while preventing carbonization of the rubber components. As a result, the treatment method of the first embodiment can prevent the increase in particle size due to carbonization of bound rubber, which is a factor in the deterioration of the quality of carbon black recovered from rubber waste treatment using conventional heat treatment methods, and extract high-quality carbon black from the rubber waste while maintaining almost its original performance. Here, in this specification, high-quality carbon black that maintains almost its original performance refers to carbon black with a particle size similar to that of the original carbon black, in which the increase in particle size due to the adhesion of charred rubber components such as bound rubber to the surface has been suppressed.

[0030] In the treatment method of the first embodiment, the carbon black obtained by decomposing rubber waste using supercritical water, subcritical water, or superheated steam has an average particle size of, for example, less than 100 nm. According to the treatment method of the first embodiment, it is possible to obtain carbon black with an average particle size of 30 nm or less, and even carbon black with an average particle size of 20 nm or less. Carbon black with such an average particle size has a particle size similar to that of carbon black used, for example, as a tire reinforcing material. Furthermore, as described above, according to the treatment method of the first embodiment, the adhesion of charred rubber components to the surface of the recovered carbon black is reduced or absent, and the surface condition of the resulting carbon black is substantially the same as that of the original carbon black. Therefore, when the carbon black recovered by the treatment method of the first embodiment is reused as a reinforcing material for rubber products such as tires, it can achieve the same reinforcing effect as the original, non-recycled carbon black.

[0031] In this specification, the average particle size of carbon black is determined by measuring the particle sizes (maximum particle diameters) of 20 arbitrarily selected carbon black particles in an electron microscope image (e.g., a TEM image) of the carbon black and calculating the average value.

[0032] The rubber waste to be treated in the treatment method of the first embodiment is, for example, waste rubber products containing carbon black, such as tires and rubber belts. In particular, waste tires are increasing worldwide, and there is a demand for recovering recycled products from waste tires. Therefore, the rubber waste in the treatment method of the first embodiment is preferably, for example, waste tires. According to the treatment method of the first embodiment, carbon black having excellent quality can be extracted and recovered from waste tires, and the carbon black can be reused in tire production.

[0033] In order to efficiently obtain high-quality carbon black that substantially retains its original performance, the temperature conditions for the decomposition treatment of rubber waste with supercritical water, subcritical water, or superheated steam carried out in the above step (a) are, for example, 200° C. or higher, or may be 350° C. or higher, or may be 400° C. or higher. The upper limit of the temperature conditions for this decomposition treatment is not particularly limited, but may be 600° C. or lower, or 500° C. or lower, for example, for reasons of improving energy efficiency.

[0034] In order to efficiently obtain carbon black of excellent quality that substantially retains its original performance, the pressure conditions for the decomposition treatment of rubber waste with supercritical water, subcritical water, or superheated steam carried out in the above step (a) are, for example, 5 MPa or more, and may be 10 MPa or more. The upper limit of the pressure conditions for this decomposition treatment is, for example, 100 MPa or less, and may be 35 MPa or less, 20 MPa or less, or 15 MPa or less, in order to efficiently obtain carbon black of excellent quality that substantially retains its original performance.

[0035] The time for the decomposition treatment of rubber waste with supercritical water, subcritical water, or superheated steam carried out in the above step (a) can be appropriately determined taking into consideration the temperature and pressure conditions. The treatment time is, for example, 10 minutes or more, and may be 20 minutes or more, in order to efficiently obtain high-quality carbon black that substantially retains its original performance. By extending the treatment time, the rubber component can be sufficiently decomposed and gasified, thereby obtaining high-quality carbon black. On the other hand, the treatment time may be, for example, 30 minutes or less, as this is sufficient treatment time to gasify the rubber component adhering to the periphery of the carbon black.

[0036] In the above step (a), carbon black is preferably obtained by contacting the rubber waste with supercritical water, subcritical water, or superheated steam at a temperature of 200° C. to 600° C. and a pressure of 5 MPa to 100 MPa for 10 minutes or longer. Treating the rubber waste under these temperature and pressure conditions for this treatment time makes it possible to efficiently obtain high-quality carbon black that retains most of its original performance.

[0037] In the above step (a), it is more preferable to obtain carbon black by contacting the rubber waste with superheated steam at a temperature of 400° C. to 500° C. and a pressure of 5 MPa to 20 MPa (preferably 5 MPa to 15 MPa) for 20 minutes or longer. Treating the rubber waste under these temperature and pressure conditions for this treatment time makes it possible to more reliably and efficiently obtain high-quality carbon black that retains most of its original performance.

[0038] In the treatment method of the first embodiment, a pretreatment step may be carried out in advance to cut or crush the rubber waste into small pieces so that the decomposition treatment of the rubber waste in (a) above can be carried out efficiently and reliably.

[0039] The decomposition treatment of rubber waste with supercritical water, subcritical water, or superheated steam in (a) above can be carried out using, for example, a known supercritical water reactor or subcritical water reactor. The apparatus used is preferably an apparatus capable of controlling the internal temperature and pressure of a reaction vessel in which the material to be treated (in the first embodiment, rubber waste) is housed and decomposed. For example, it is preferable to use an apparatus in which the material to be treated is continuously supplied to the reaction vessel and decomposed with supercritical water, subcritical water, or superheated steam within the reaction vessel. The use of such an apparatus capable of continuous treatment can improve treatment efficiency. The reaction vessel may be provided with an outlet through which the recovered product obtained by the decomposition treatment can be removed.

[0040] For example, rubber waste and water are supplied to a reaction vessel, and the temperature and pressure inside the vessel are increased to bring the water into a supercritical state above the critical point, or into a subcritical state below the critical temperature and above the saturated water vapor pressure, or into superheated steam above the critical temperature and below the critical pressure, and the rubber waste is decomposed with the supercritical water, subcritical water, or superheated steam.

[0041] Second Embodiment An embodiment of the method for treating rubber waste of the present invention will be described.

[0042] The rubber waste treatment method of the second embodiment is the rubber waste treatment method of the first embodiment, further comprising: (b) subjecting the rubber waste to a decomposition treatment with supercritical water, subcritical water or superheated steam to obtain oil, and recovering the obtained oil. The step (b) is carried out before the step (a) described in the first embodiment.

[0043] That is, as shown in FIG. 2 , the method for treating rubber waste according to the second embodiment includes: (b) subjecting the rubber waste to decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain oil, and recovering the obtained oil (S21); and (a) after the above (b), subjecting the rubber waste to decomposition treatment with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the obtained carbon black (S22).

[0044] In the processing method of the second embodiment, in addition to carbon black, oil can also be recovered from the rubber waste. The oil recovered from the rubber waste may be used, for example, as a raw material for producing new carbon black. In this case, the carbon black produced using oil as fuel can be mixed with natural rubber to produce rubber products such as tires that do not rely on petroleum.

[0045] Hereinafter, the decomposition treatment using supercritical water, subcritical water, or superheated steam to obtain oil in (b) above will be referred to as a first decomposition treatment, and the decomposition treatment using supercritical water, subcritical water, or superheated steam to obtain carbon black in (a) above will be referred to as a second decomposition treatment.

[0046] In the second embodiment, the waste rubber is subjected to a first decomposition treatment to produce and recover oil from the waste rubber. The first decomposition treatment for producing oil from the waste rubber is carried out under conditions that do not cause the waste rubber to be decomposed too much and the rubber component to be gasified.

[0047] For example, in the first decomposition treatment (b) above, oil can be obtained by contacting rubber waste with supercritical water at a temperature of 400°C or higher and 500°C or lower and a pressure of 40 MPa or higher and 50 MPa or lower for 0.5 minutes or longer and less than 30 minutes.

[0048] In the above example, the first decomposition treatment is carried out under high pressure, and therefore, in this case, in order to prevent excessive decomposition of the rubber component of the rubber waste, the time for which the rubber waste is in contact with supercritical water at a temperature of 400°C or more and 500°C or less and a pressure of 40 MPa or more and 50 MPa or less is preferably 20 minutes or less, more preferably 10 minutes or less, and even more preferably 3 minutes or less.

[0049] In the treatment method of the second embodiment, a second decomposition treatment is carried out after the first decomposition treatment to obtain carbon black. That is, in the treatment method of the second embodiment, the rubber waste in the second decomposition treatment is the remainder after the oil is recovered by the first decomposition treatment. Note that the details of the second decomposition treatment are the same as those described in the first embodiment, and therefore will not be described here. As in the first embodiment, the treatment method of the second embodiment also makes it possible to obtain carbon black of excellent quality that substantially retains its original performance.

[0050] The above (a) may be carried out consecutively after the above (b). This allows oil and carbon black to be efficiently obtained from rubber waste. In this case, for example, after recovering oil by the first decomposition treatment, the temperature and pressure during the first decomposition treatment may be directly changed to the temperature and pressure for the second decomposition treatment, or after the first decomposition treatment, the temperature and pressure conditions for bringing water to a supercritical or subcritical state may be temporarily released, and then the temperature and pressure may be changed again to bring water to a supercritical or subcritical state for the second decomposition treatment.

[0051] In the treatment method of the second embodiment, as in the first embodiment, the rubber waste to be treated is, for example, waste rubber products containing carbon black, such as tires and rubber belts. The rubber waste in the treatment method of the second embodiment is preferably, for example, waste tires. According to the treatment method of the second embodiment, oil can be extracted and recovered from the waste tires in addition to high-quality carbon black.

[0052] The first decomposition treatment and the second decomposition treatment in the treatment method of the second embodiment can be carried out, as in the first embodiment, using, for example, a known supercritical water reaction apparatus or subcritical water reaction apparatus, and it is preferable that the reaction vessel in which the material to be treated is accommodated and decomposed is an apparatus capable of controlling the internal temperature and pressure.

[0053] Third Embodiment One embodiment of the method for producing recycled carbon black of the present invention will be described.

[0054] As shown in FIG. 3 , the method for producing recycled carbon black according to the third embodiment includes decomposing rubber waste with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the carbon black as recycled carbon black (S31).

[0055] In the manufacturing method of the third embodiment, recycled carbon black is produced by decomposing rubber waste with supercritical water, subcritical water, or superheated steam. This manufacturing method can gasify the rubber components attached to the carbon black contained in the rubber waste while preventing carbonization of the rubber components. As a result, the manufacturing method of the third embodiment can prevent the increase in particle size due to carbonization of bound rubber, which is a factor that reduces the quality of recycled carbon black produced by treating rubber waste using conventional heat treatment methods, and produce recycled carbon black of high quality that largely retains its original performance. Here, in this specification, "high-quality recycled carbon black that largely retains its original performance" refers to recycled carbon black that has a particle size similar to that of the original carbon black, but in which the increase in particle size due to the adhesion of charred rubber components such as bound rubber to the surface has been suppressed.

[0056] The average particle size of the recycled carbon black produced by the production method of the third embodiment is, for example, less than 100 nm. According to the production method of the third embodiment, it is possible to obtain carbon black with an average particle size of 30 nm or less, and even carbon black with an average particle size of 20 nm or less. Recycled carbon black with such average particle size has a particle size similar to that of carbon black used, for example, as a tire reinforcing material. Furthermore, as described above, according to the production method of the third embodiment, recycled carbon black can be obtained in which adhesion of charred rubber components to the surface of the recycled carbon black is minimized or absent, resulting in a surface condition that is substantially the same as that of the original carbon black. Therefore, when the recycled carbon black produced by the production method of the third embodiment is reused as a reinforcing material for rubber products such as tires, it can achieve the same reinforcing effect as the original, non-recycled carbon black.

[0057] In this specification, the average particle size of recycled carbon black is determined by the same method as the average particle size of carbon black described in the first embodiment.

[0058] The rubber waste used as a raw material in the production method of the third embodiment is, for example, waste rubber products containing carbon black, such as tires and rubber belts. The rubber waste used as a raw material in the production method of the third embodiment is desirably, for example, discarded tires. According to the production method of the third embodiment, recycled carbon black having excellent quality can be produced using discarded tires as a raw material, and the recycled carbon black can be reused in the production of tires.

[0059] In order to efficiently produce recycled carbon black of excellent quality that retains most of the original performance, the temperature conditions for the decomposition treatment of rubber waste with supercritical water, subcritical water, or superheated steam are, for example, 200° C. or higher, or alternatively, 350° C. or higher, or even 400° C. or higher. The upper limit of the temperature conditions for this decomposition treatment is not particularly limited, but may be 600° C. or lower, or 500° C. or lower, for example, for reasons of improving energy efficiency.

[0060] In order to efficiently produce recycled carbon black of excellent quality that retains almost all of its original performance, the pressure conditions for the decomposition treatment of rubber waste with supercritical water, subcritical water, or superheated steam are, for example, 5 MPa or more, and may be 10 MPa or more. The upper limit of the pressure conditions for this decomposition treatment is, for example, 100 MPa or less, and may be 35 MPa or less, 20 MPa or less, or 15 MPa or less, in order to efficiently produce recycled carbon black of excellent quality that retains almost all of its original performance.

[0061] The time for decomposing rubber waste with supercritical water, subcritical water, or superheated steam can be appropriately determined taking into account the temperature and pressure conditions. The treatment time is, for example, 10 minutes or more, and may be 20 minutes or more, in order to efficiently produce high-quality recycled carbon black that retains most of its original performance. By extending the treatment time, the rubber component can be sufficiently decomposed and gasified, thereby producing high-quality recycled carbon black. On the other hand, the treatment time may be, for example, 30 minutes or less, as this is sufficient treatment time to gasify the rubber component adhering to the periphery of the carbon black.

[0062] In the production method of the third embodiment, carbon black is preferably obtained by contacting rubber waste with supercritical water, subcritical water, or superheated steam at a temperature of 200° C. to 600° C. and a pressure of 5 MPa to 100 MPa for 10 minutes or longer. Treating rubber waste under such temperature, pressure, and treatment time conditions allows for efficient production of recycled carbon black of excellent quality that retains most of the original performance.

[0063] In the production method of the third embodiment, it is more preferable to obtain carbon black by bringing rubber waste into contact with superheated steam at a temperature of 400° C. to 500° C. and a pressure of 5 MPa to 20 MPa (preferably 5 MPa to 15 MPa) for 20 minutes or longer. Treating rubber waste under such temperature and pressure conditions and for such a treatment time makes it possible to more reliably and efficiently produce recycled carbon black of excellent quality that largely retains the original performance.

[0064] In the manufacturing method of the third embodiment, a pre-treatment step of cutting or pulverizing the rubber waste may be carried out in advance so that the decomposition treatment of the rubber waste can be carried out efficiently and reliably.

[0065] The decomposition treatment of rubber waste with supercritical water, subcritical water, or superheated steam in the production method of the third embodiment can be carried out using, for example, a known supercritical water reactor, subcritical water reactor, or superheated steam reactor. The apparatus used is preferably an apparatus capable of controlling the internal temperature and pressure of a reaction vessel in which the raw rubber waste is accommodated and decomposed. For example, it is preferable to use an apparatus in which the raw rubber waste is continuously supplied to the reaction vessel and decomposed with supercritical water, subcritical water, or superheated steam within the reaction vessel. The use of such an apparatus capable of continuous treatment can improve the production efficiency of recycled carbon black. The reaction vessel may be provided with an outlet through which the produced recycled carbon black can be removed.

[0066] For example, recycled carbon black is produced by supplying rubber waste and water to a reaction vessel, increasing the temperature and pressure inside the vessel to bring the water into a supercritical state above the critical point, or into a subcritical state below the critical point, or by converting the water into superheated steam, and then decomposing the rubber waste with the supercritical water, subcritical water, or superheated steam.

[0067] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples.

[0068] [Treatment of Rubber Waste] (Examples 1 to 3) In Examples 1 to 3, rubber waste was decomposed using superheated steam.

[0069] The following three types of rubber waste samples were prepared. Example 1: Waste tires made from a rubber composition in which 100 parts by mass of styrene butadiene rubber (SBR) was compounded with 65 parts by mass of HAF (High Abrasion Furnace) carbon black (hereinafter referred to as "HAF65") Example 2: Waste truck tires made from a rubber composition in which natural rubber was compounded with tire carbon black (hereinafter referred to as "TB") Example 3: Waste passenger car tires made from a rubber composition in which SBR was compounded with tire carbon black (hereinafter referred to as "PC")

[0070] HAF65 in Example 1 was a sheet-like material having a composition in which 100 parts by mass of SBR was mixed with 65 parts by mass of carbon black from HAF, 3 parts by mass of ZnO, 1.5 parts by mass of stearic acid, and 2 parts by mass of an accelerator. This sheet-like material was cut into a size of 10 mm x 5 mm and used as a sample.

[0071] Both TB in Example 2 and PC in Example 3 were in the form of powder.

[0072] The rubber waste samples from Examples 1 to 3 were decomposed using superheated steam. Specifically, each sample and distilled water were placed in a reaction tube approximately 150 mm long and 1 / 2 inch in outer diameter, and then sealed. The amount of distilled water placed in the reaction tube was determined so that the pressure inside the reaction tube would be 10 MPa when the predetermined reaction temperature (450°C in this example) was reached. The amounts of sample and distilled water placed in the reaction tube are shown in Table 1. The reaction tube containing the sample and distilled water was placed in a salt bath heated to 450°C. After 30 minutes, the reaction tube was removed from the salt bath and immersed in water for rapid cooling. The contents of the reaction tube were then recovered with 10 mL of distilled water.

[0073]

[0074] Example 4 In Example 4, rubber waste was decomposed using supercritical water, and oil was recovered by decomposing the rubber waste using supercritical water. In Example 4, TB was used as the rubber waste, and the rubber waste was decomposed using supercritical water using a supercritical fluid reactor (manufactured by AKICO Corporation). Specifically, 40 g of a rubber waste sample and 160 g of distilled water were charged into a 300 cc reaction tube and sealed. The reaction tube containing the sample and distilled water was heated to 450°C and pressurized to 45 MPa. After maintaining the 450°C and 45 MPa conditions for approximately 1 minute, the temperature and pressure inside the reaction tube were reduced. As a result, oil production was confirmed. Note that in Example 4, the remainder after oil recovery was not further treated with supercritical water, subcritical water, or superheated steam. That is, in Example 4, only the first decomposition treatment was performed to confirm oil production.

[0075] Examples 5 to 18 In Examples 5 to 18, PC was used as rubber waste, and samples of the rubber waste were decomposed using superheated steam under the conditions shown in Table 2. Specifically, similar to Examples 1 to 3, each sample and distilled water were charged into a reaction tube with a tube length of approximately 150 mm and an outer diameter of ½ inch, and then sealed. The amount of distilled water charged into the reaction tube was determined so that the pressure inside the reaction tube would be the pressure shown in Table 2 when the reaction temperature was raised to the predetermined reaction temperature (the reaction temperature shown in Table 2). The reaction tube containing the sample and distilled water was placed in a salt bath heated to the predetermined reaction temperature (the reaction temperature shown in Table 2). After the predetermined treatment time (the treatment time shown in Table 2) had elapsed, the reaction tube was removed from the salt bath and immersed in water for rapid cooling. The contents of the reaction tube were then recovered with 10 mL of distilled water.

[0076]

[0077] Example 19 In Example 19, rubber waste was decomposed using supercritical water. In Example 19, TB was used as the rubber waste, and similarly to Example 4, the rubber waste was decomposed using supercritical water using a supercritical fluid reactor (manufactured by AKICO Corporation). Specifically, first, 40 g of a rubber waste sample and distilled water were charged into a 300 cc reaction tube and sealed. The amount of distilled water was determined so that the pressure would be 40 MPa at 450°C. Next, the reaction tube containing the sample and distilled water was heated to 450°C and pressurized to 40 MPa. The 450°C and 40 MPa conditions were maintained for approximately 20 minutes, and then the temperature and pressure inside the reaction tube were reduced.

[0078] Comparative Example 1: Rubber waste was treated by a heat treatment method. The rubber waste used was waste tires from trucks and buses. The rubber waste was heat treated at 600°C for 30 minutes, and the reaction product was collected.

[0079] [Analysis of the Composition of the Recovered Materials] Thermogravimetric analysis (TGA) was performed to analyze the components of the recovered materials in Examples 1 to 3 and 5 to 19. The analysis results showed that 99% of the recovered materials were carbon black.

[0080] [TEM Observation of Recovered Materials] TEM observation was performed on the recovered materials recovered by the treatment of rubber waste with supercritical water in Examples 1 to 3 and 5 to 18, and the recovered material recovered by the treatment of rubber waste using the heat treatment method in Comparative Example 1. FIG. 4 is a TEM image of the recovered material obtained in Example 1, FIG. 5 is a TEM image of the recovered material obtained in Example 2, FIG. 6 is a TEM image of the recovered material obtained in Example 3, and FIGS. 7 to 20 are TEM images of the recovered materials obtained in Examples 5 to 18, respectively. FIG. 21 is a TEM image of the recovered material obtained in Comparative Example 1. For comparison, FIG. 22 is a TEM image of non-recycled carbon black (N330, manufactured by Cabot Corporation). From the TEM images in FIGS. 4 to 20 and 22, it was confirmed that the recovered materials recovered in Examples 1 to 3 and 5 to 18 had particle sizes similar to those of non-recycled carbon black. The average particle size of the recovered materials in Examples 1 to 3 and 5 to 18 was determined using the TEM images in Figures 4 to 20, and all were found to be less than 100 nm. On the other hand, as shown in Figure 21, the recovered material in Comparative Example 1 had particles that had fused together to form large clumps, and it was clear that the recovered material was composed of particles with particle sizes exceeding 100 nm. Similarly, the average particle size of the recovered material obtained in Example 19 was determined from the TEM image, and was found to be less than 100 nm.

[0081] [Thermogravimetric analysis (TGA) of recovered material] Thermogravimetric analysis was performed on the recovered material of Example 2. For comparison, thermogravimetric analysis was also performed on non-recycled carbon black (N330, manufactured by Cabot Corporation). Specifically, the thermogravimetric analysis was performed as follows. Using a thermogravimetric analyzer "TGA-50" manufactured by Shimadzu Corporation, measurements were performed at a heating rate of 10°C / min in an Ar atmosphere. Figure 23 is a graph showing the thermogravimetric analysis results for the recovered material (rCB) of Example 2 and non-recycled carbon black (N330) for comparison.

[0082] [Reinforcing Effect of Recycled Carbon Black 1] The reinforcing effect was evaluated using the recycled carbon black recovered in Example 2. Specifically, the reinforcing effect was evaluated by the following method. 0.25 g of the recovered recycled carbon black was mixed with 1.0 g of SBR, and after vulcanization, the plateau modulus was measured by linear viscoelasticity measurement. The modulus was found to be equivalent to that of a sample obtained by mixing the same amount of non-recycled carbon black N330 with SBR and vulcanizing it.

[0083] [Reinforcing Effect of Recycled Carbon Black 2] The reinforcing effect was evaluated using the recycled carbon black recovered in Examples 3 and 19. Specifically, the reinforcing effect was evaluated by the following method. A rubber composition was prepared by kneading a mixture of 100 parts by mass of SBR, 35 parts by mass of the recovered recycled carbon black, 3 parts by mass of ZnO, 2 parts by mass of stearic acid, 1.5 parts by mass of sulfur, and 2 parts by mass of a vulcanization accelerator. The kneading was performed by repeatedly folding and compressing the mixture until the mixture was uniform. The obtained rubber composition was vulcanized and cut into a size of 5 mm wide, 25 mm long, and 1 mm thick, which was used as a sample. Using a Tensilon universal testing machine (RTF1350) manufactured by A&D Co., Ltd., the sample was pulled in the longitudinal direction at a tensile speed of 600 mm / min at 20°C, and a stress-strain curve was obtained. For comparison, stress-strain curves were also obtained for samples prepared by mixing non-recycled carbon black N330 and N660 with SBR, ZnO, stearic acid, sulfur, and a vulcanization accelerator, as in Examples 3 and 19, and vulcanizing the mixture. For comparison, stress-strain curves were also obtained for samples prepared by mixing only SBR, ZnO, stearic acid, sulfur, and a vulcanization accelerator in the same compositional ratios as in Examples 3 and 19, without adding carbon black (CB). Figure 24 is a graph showing the results of stress-strain measurements for the rubber compositions of Examples 3 and 19 containing recycled carbon black, a comparative rubber composition containing non-recycled carbon black, and a comparative rubber composition containing no carbon black. As shown in Figure 24, the recycled carbon blacks of Examples 3 and 19 were confirmed to have reinforcing power equal to or greater than that of carbon black N660. In particular, it was found that the recycled carbon black of Example 3, which was treated with superheated steam at a pressure of 20 MPa or less, had a high reinforcing power comparable to that of carbon black N330.

[0084] The technology of the present disclosure is useful as a recycling technology for rubber waste, particularly waste tires.

Claims

1. A method for treating rubber waste, comprising: (a) decomposing rubber waste with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the obtained carbon black.

2. The method for treating rubber waste according to claim 1, wherein in (a), the carbon black is obtained by contacting the rubber waste with supercritical water, subcritical water, or superheated steam at a temperature of 200°C or higher and 600°C or lower and a pressure of 5 MPa or higher and 100 MPa or lower for 10 minutes or longer.

3. The method for treating rubber waste according to claim 2, wherein in (a), the carbon black is obtained by contacting the rubber waste with superheated steam at a temperature of 400°C or higher and 500°C or lower and a pressure of 5 MPa or higher and 20 MPa or lower for 20 minutes or longer.

4. The method for treating rubber waste according to claim 1, further comprising: (b) subjecting the rubber waste to a decomposition treatment with supercritical water, subcritical water or superheated steam to obtain oil, and recovering the obtained oil, wherein (b) is carried out before (a).

5. The method for treating rubber waste according to claim 4, wherein in (b), the oil is obtained by contacting the rubber waste with supercritical water at a temperature of 400°C or higher and 500°C or lower and a pressure of 40 MPa or higher and 50 MPa or lower for 0.5 minutes or longer and shorter than 30 minutes.

6. The method for treating rubber waste according to claim 4, wherein (a) is carried out continuously after (b).

7. The method for treating rubber waste according to claim 1, wherein the rubber waste is waste tires.

8. The method for treating rubber waste according to claim 1, wherein in (a), the carbon black obtained by decomposing the rubber waste with supercritical water, subcritical water, or superheated steam has an average particle size of less than 100 nm.

9. A method for producing recycled carbon black, comprising: decomposing rubber waste with supercritical water, subcritical water, or superheated steam to obtain carbon black, and recovering the carbon black as recycled carbon black.

10. The method for producing recycled carbon black according to claim 9, wherein the carbon black is obtained by contacting the rubber waste with supercritical water, subcritical water, or superheated steam at a temperature of 200°C or higher and 600°C or lower and a pressure of 5 MPa or higher and 100 MPa or lower for 10 minutes or longer.

11. The method for producing recycled carbon black according to claim 10, wherein the carbon black is obtained by contacting the rubber waste with superheated steam at a temperature of 400°C or higher and 500°C or lower and a pressure of 5 MPa or higher and 20 MPa or lower for 20 minutes or longer.

12. The method for producing recycled carbon black according to claim 9, wherein the rubber waste is waste tires.

13. The method for producing recycled carbon black according to claim 9, wherein the recycled carbon black has an average particle size of less than 100 nm.

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