Method for producing refined carbon black

Abstract

To provide a method for producing purified carbon black with effectively reduced ash content.SOLUTION: A method for producing purified carbon black includes the following step (1) and step (2). Step (1): loading particles including carbon black and an oxidizer into a solvent, bringing them into contact with each other. Step (2): loading particles including carbon black and a base into a solvent, bringing them into contact with each other.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing purified carbon black.

Background Art

[0002] In recent years, in order to realize a recycling-oriented society, even the tire industry is required to have a higher level of sustainability. As an example of a method for using used tires, there is a method in which used tires are pyrolyzed, the oilified components are used as petrochemical raw materials, and the carbon black recovered as a solid component is reused. For example, Patent Document 1 aims to provide a method for producing a reinforcing filler that has performance not much inferior to that of commercially available carbon black, in addition to decomposing and recovering heavy and light oil components and gas components from waste tires. When producing a reinforcing filler by pyrolyzing waste tires in a high-temperature non-oxidizing atmosphere to decompose heavy and light oil components, gas components and carbides, the pyrolysis is carried out for a sufficient time so that the acetone extract of the produced carbide is 1% by weight or less, and the obtained produced carbide is rapidly cooled in an atmosphere that blocks the intrusion of air. A method for producing a reinforcing filler from waste tires is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, carbon black recovered from such waste tires contains a large amount of ash as an impurity, consisting of silica and metal components used in tire manufacturing. When the recovered carbon black is applied to various products, it can negatively affect the physical properties of those products. For example, when reused as a tire material, a high ash content can negatively impact rubber properties such as tensile strength. Therefore, it is necessary to reduce the ash content of recovered carbon black. This invention relates to a method for producing refined carbon black with effectively reduced ash content. [Means for solving the problem]

[0005] The present invention relates to the following [1]. [1] A method for producing refined carbon black, comprising the following steps (1) and (2). Step (1) A step in which particles containing carbon black and an oxidizing agent are charged into a solvent and brought into contact. Step (2) Step of charging particles containing carbon black and a base into a solvent and bringing them into contact. [Effects of the Invention]

[0006] The present invention provides a method for producing refined carbon black in which the ash content is effectively reduced. [Modes for carrying out the invention]

[0007] [Method for producing refined carbon black] The present invention provides a method for producing purified carbon black, comprising the following steps (1) and (2). Process (1) A process in which particles containing carbon black (hereinafter also referred to as "recovered carbon black") and an oxidizing agent are charged into a solvent and brought into contact (hereinafter also referred to as the "oxidizing agent contact process"). Step (2) A step in which particles containing carbon black and a base are charged into a solvent and brought into contact (hereinafter also referred to as the "base contact step"). The present invention provides a method for producing refined carbon black in which the ash content is effectively reduced.

[0008] The detailed reasons why the above effects are achieved are unknown, but some explanations are as follows. Generally, particles containing carbon black recovered by the thermal decomposition of rubber products such as tires contain ash containing metal compounds and silicon compounds as impurities, as described later. By treating such recovered carbon black with an oxidizing agent, the metal compounds are converted into solvent-soluble chemical substances, and by treating it with a base, the silicon compounds are converted into solvent-soluble chemical substances. This makes it possible to dissolve the ash in the recovered carbon black into the solvent, and by removing the solvent along with the dissolved ash, it is possible to remove the ash. Furthermore, the mechanism by which the effects of the present invention are obtained is not limited to this. The following describes each step.

[0009] <Particles containing carbon black> In the present invention, the particles containing carbon black are not particularly limited as long as they contain carbon black. A single particle may be a particle in which carbon black and other components described later are aggregated. The particle group may contain particles consisting only of carbon black and particles consisting only of other components. These particles may also be mixed together. The average particle size of carbon black-containing particles (recovered carbon black used as raw material) is preferably 10 nm to 1000 nm, from the viewpoint of ease of handling and ease of solvent penetration. The average particle size of the recovered carbon black can be measured by, for example, a transmission electron microscope, specific surface area measurement, X-ray scattering, or dynamic light scattering.

[0010] Examples of such recovered carbon black include that derived from rubber products such as tires, rubber tracks, vibration damping rubber, and conveyor belts, or from waste rubber generated during the manufacture or processing of rubber products. Among these, recovered carbon black is preferably derived from used rubber products (especially used tires), and more preferably recovered from used rubber products (especially used tires) by thermal decomposition. This is because rubber products such as tires are discarded in large quantities annually, and recycling is desired from the standpoint of environmental protection and sustainability, and such rubber products often contain carbon black as a reinforcing material.

[0011] Other components besides carbon black contained in recovered carbon black include ash. Here, "ash" refers to the inorganic substances remaining after the thermal decomposition of recovered or refined carbon black. The amount of ash is measured by the method described in the examples below. Examples of such ash include metal compounds such as ZnO, ZnS, Al2O3, and CaO, silicon compounds such as SiO2, and mixtures thereof. In particular, when used tires are used as raw materials, it is thought that a large amount of ZnO, ZnS, and SiO2 derived from the tire's constituent components is present. The carbon black content in the recovered carbon black is, for example, 60% to 95% by mass of the total recovered carbon black (total amount of particles containing carbon black). The ash content (content of inorganic substances other than carbon black) is, for example, 5% to 40% by mass of the total recovered carbon black. Among these, an ash content of 10% by mass or more is preferable because it significantly reduces the amount of ash using the manufacturing method of the present invention. Furthermore, in the present invention, the contact-treated particles containing carbon black refer to particles containing carbon black that have been subjected to at least one of the contact steps (1) and (2).

[0012] <Oxidizing agent contact process (Process (1))> Step (1) is a step in which particles containing carbon black and an oxidizing agent are placed in a solvent and brought into contact with each other. The oxidizing agent used in step (1) is preferably one or more selected from the group consisting of hydrogen peroxide and organic peracids, from the viewpoint of availability and ease of handling. Examples of organic peracids include lower aliphatic percarboxylic acids (e.g., those with 1 to 4 carbon atoms) such as performic acid, peracetic acid, perpropionic acid, trifluoroperacetic acid, and perbutyric acid, and aromatic percarboxylic acids such as perbenzoic acid and perphthalic acid. When using organic peracids as oxidizing agents, the organic peracid may be added directly, or, as will be described later, an oxidizing agent such as hydrogen peroxide and an organic peracid precursor such as an organic acid that can react with the oxidizing agent to form an organic peracid may be added to the system to generate the organic peracid. Combinations of oxidizing agents and acids that can generate organic peracids will also be described later.

[0013] The amount of oxidizing agent added is not particularly limited, and varies depending on the type of oxidizing agent and the amount of ash in the recovered carbon black. However, it is preferably 0.25 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of recovered carbon black, and preferably 10,000 parts by mass or less, more preferably 2,000 parts by mass or less, and even more preferably 500 parts by mass or less. Adding the oxidizing agent within this range allows for more effective removal of ash. Furthermore, if an organic peracid precursor such as an organic acid is added in addition to the oxidizing agent to generate an organic peracid in the system, the amount of oxidizing agent added refers to the amount of oxidizing agent that reacts with the organic peracid precursor, not the amount of organic peracid generated.

[0014] When the oxidizing agent is dissolved in a solvent for use, the addition amount of the solvent containing the oxidizing agent (hereinafter also referred to as "treatment liquid 1") is, when carried out in a batch system, from the viewpoints of ease of handling, solubility of ash, etc., preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, still more preferably 2 parts by mass or more, per 1 part by mass of the recovered carbon black, and preferably 100 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 20 parts by mass or less. The batch system will be described in the section of the washing step (4) described later. Also, from the same viewpoints, the total amount of the solvent used in step (1) is preferably within the above range.

[0015] Also, the concentration of the oxidizing agent in the treatment liquid ¹ at that time is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 1.0% by mass or more, from the viewpoints of ease of handling, reactivity between the ash in the recovered carbon black and the oxidizing agent, etc., and preferably 70% by mass or less, more preferably 40% by mass or less, still more preferably 20% by mass or less.

[0016] Also, step (1) is preferably a step of further charging and contacting an organic acid in the solvent. As described above, in this case, the organic acid becomes a peroxy acid by the oxidizing agent, and the recovered carbon black and the peroxy acid as the oxidizing agent come into contact in the solvent. Therefore, as the organic acid, those that react with the oxidizing agent to generate a peroxy acid are preferable. Examples of the organic acid include aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, and halogenated acetic acid (for example, trifluoroacetic acid), and aromatic carboxylic acids such as benzoic acid and phthalic acid. Among these, from the viewpoints of not increasing the ash content, high water solubility, being soluble in an aqueous solvent so that excess organic acid can be easily removed by solid-liquid separation or washing with an aqueous solvent, and easy handling, preferably lower aliphatic carboxylic acids such as formic acid, acetic acid, propionic acid, and butyric acid (for example, having 1 to 4 carbon atoms), more preferably formic acid and acetic acid, and still more preferably formic acid. Also, the pKa of the organic acid is preferably 0.1 or more, more preferably 1.0 or more, still more preferably 2.0 or more, even more preferably 3.5 or more, and preferably 6.0 or less, more preferably 5.0 or less. When the pKa is within such a range, the handling property is good and ash removal is possible.

[0017] In addition, examples of the combination of the oxidizing agent and the organic acid include a combination of hydrogen peroxide and an organic acid that reacts with hydrogen peroxide to generate a peroxy acid. Among these, a combination of hydrogen peroxide and a lower aliphatic carboxylic acid is preferable, a combination of hydrogen peroxide and formic acid or a combination of hydrogen peroxide and acetic acid is more preferable, and a combination of hydrogen peroxide and formic acid is still more preferable. According to such a combination, since a peroxy acid is generated, it is considered that ash can be removed more effectively than hydrogen peroxide alone. Further, with such an oxidizing agent and organic acid, the ash is not increased, and moreover, it has high water solubility and dissolves in an aqueous solvent, so that the used chemicals (oxidizing agent, organic acid) can be easily removed by solid-liquid separation or washing treatment with an aqueous solvent, and the handling becomes easy.

[0018] Note that the purpose of adding the organic acid is not limited to the generation of peroxy acid. For example, it may be added for the purpose of improving the stability of a system containing peroxy acid or increasing the solubility of a product generated by the reaction of a metal compound in ash with an oxidizing agent in a solvent, and is not particularly limited. The molar ratio of the organic acid added to the oxidizing agent (hydrogen peroxide / organic acid (molar ratio)) is preferably 0.1 or more, more preferably 0.3 or more, still more preferably 0.5 or more, and preferably 10 or less, more preferably 2 or less, still more preferably 1.3 or less, even more preferably less than 1.0, and even more preferably 0.8 or less.

[0019] Furthermore, when using treatment solution 1 by dissolving the oxidizing agent and organic acid in a solvent, the concentration of the organic acid in treatment solution 1 immediately after preparation is preferably 0.05% by mass or more, more preferably 0.2% by mass or more, even more preferably 1.0% by mass or more, and preferably 70% by mass or less, more preferably 40% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of ease of handling and ease of producing organic peracids.

[0020] The order and method of charging and contacting the recovered carbon black, oxidizing agent, and optionally organic acid in a solvent are not particularly limited. For example, the recovered carbon black, oxidizing agent, and optionally organic acid may be added to the solvent simultaneously and mixed to bring them into contact. Alternatively, a treatment solution 1 may be prepared by pre-dissolving (or suspending) the oxidizing agent and optionally organic acid in the solvent, and then this treatment solution 1 may be mixed with the recovered carbon black to bring them into contact. Alternatively, the recovered carbon black may be pre-suspended in the solvent, and then the oxidizing agent and optionally organic acid may be mixed and brought into contact (in this case, the oxidizing agent and optionally organic acid may also be prepared in advance as part of treatment solution 1). Furthermore, the organic acid and recovered carbon black may be mixed in the solvent, then the oxidizing agent may be added, mixed, and brought into contact. Alternatively, the oxidizing agent and recovered carbon black may be mixed in the solvent, then the organic acid may be added, mixed, and brought into contact. In addition, the recovered carbon black may be brought into contact with a container (e.g., a column) containing the recovered carbon black by passing the treatment solution 1 containing the oxidizing agent and optionally organic acid through it.

[0021] Among these methods, from the viewpoint of ease of manufacture and effective reduction of metal compounds, it is preferable to prepare a treatment solution 1 and then mix it with the recovered carbon black to bring them into contact. Furthermore, from the viewpoint of further improving contactability, it is preferable to suspend the recovered carbon black in a solvent beforehand and then mix it with a separately prepared treatment solution 1 to bring them into contact. Also, from the viewpoint of effectively utilizing nascent organic peracids, it is preferable to mix the oxidizing agent and the recovered carbon black, then add the organic acid, mix, and bring them into contact. Moreover, from the viewpoint of being able to continuously perform the solid-liquid separation step (3), washing step (4), and base contact step (2) described later, and having good processing efficiency, it is preferable to pack the recovered carbon black into a packed container such as a column and pass the treatment solution 1 containing the oxidizing agent and, if necessary, an organic acid through it.

[0022] Furthermore, during contact, it is preferable to stir as needed. Conventional known stirring methods can be used, such as stirring using impellers or rotors, stirring with ultrasound or electromagnetic waves, shaking, and bubbling. From an industrial standpoint, stirring using impellers is preferred from the viewpoint of stirring efficiency.

[0023] The solvent used in the present invention is not particularly limited as long as it is a commonly used solvent that does not impair the effects of the present invention. It may be an organic solvent or an aqueous solvent, but an aqueous solvent is preferred from the viewpoint of being environmentally friendly and easy to handle. Such an aqueous solvent can preferably be 100% by mass of water, but it may also be a mixed solvent of water with an organic solvent having water affinity, such as alcohols such as methanol, ethanol, and propanol, or ketones such as acetone. From the viewpoint of being environmentally friendly and easy to handle, the water content is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to the total amount of the aqueous solvent, and may be 100% by mass, with 100% by mass being even more preferable.

[0024] The water used in the present invention is not particularly limited and can include distilled water, deionized water, deaerated water, tap water, well water, etc. However, from the viewpoint of the stability of the oxidizing agent during treatment, deionized water and distilled water are preferred, and deionized water is more preferred. Other additives, such as dispersants, may be added to the aqueous solvent, as long as they do not interfere with the effects of the present invention. Furthermore, the present invention can achieve effective results even without including nitrogen hydrides (compounds having NH bonds) as dispersants.

[0025] The contact temperature (reaction temperature) in step (1) is preferably 10°C or higher, more preferably 20°C or higher, even more preferably 35°C or higher, and even more preferably 50°C or higher, and preferably less than 100°C, more preferably 90°C or lower, even more preferably 80°C or lower, and even more preferably 70°C or lower, from the viewpoint of handling and workability. Furthermore, from the viewpoint of efficiently reducing ash content, it is preferable to bring the materials into contact under normal pressure or under pressurized pressure. More specifically, from the viewpoint described above, the pressure is preferably 0.1 MPa or higher, and preferably 0.3 MPa or lower. Moreover, from the viewpoint of ease of manufacturing, it is more preferable to bring the materials into contact under normal pressure (0.1 MPa). Furthermore, the contact time (reaction time) is preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 3 hours or less.

[0026] <Base Contact Process (Process (2))> Step (2) is the process of placing particles containing carbon black and a base into a solvent and bringing them into contact. The base used in step (2) is not particularly limited as long as it is a base that is normally used, but examples include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; aliphatic amines such as tetramethylamine; aromatic amines; hydroxides of ammine complexes such as diamminesilver hydroxide and tetraamminecopper hydroxide; and guanidines. These bases may be used individually or in combination of two or more. Among these, sodium hydroxide, potassium hydroxide, and more preferably sodium hydroxide are preferred from the viewpoint of being water-soluble, allowing for easy removal of excess base by solid-liquid separation or washing with an aqueous solvent, and effectively removing ash.

[0027] The amount of base added is not particularly limited and varies depending on the type of base and the amount of ash in the recovered carbon black, but is preferably 0.4 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 10 parts by mass or more per 100 parts by mass of recovered carbon black, and preferably 4000 parts by mass or less, more preferably 800 parts by mass or less, and even more preferably 200 parts by mass or less. Adding the base within this range allows for more effective removal of ash.

[0028] Furthermore, when using a base dissolved in a solvent, the amount of solvent containing the base (hereinafter also referred to as "treatment solution 2") added is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, and preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 20 parts by mass or less, from the viewpoint of ease of handling and solubility of ash in treatment solution 2, when using a batch method. Furthermore, from a similar viewpoint, it is preferable that the total amount of solvent used in step (2) is also within the above range. Furthermore, the concentration of the base in the aqueous solution is preferably 0.1 M or higher, more preferably 0.5 M or higher, even more preferably 0.8 M or higher, and preferably 20 M or lower, more preferably 5 M or lower, and even more preferably 2 M or lower, from the viewpoint of ease of handling and reactivity between ash and the base. Furthermore, the pKa of the base (conjugate acid) is preferably 9 or higher, more preferably 10 or higher, and preferably 20 or lower, and more preferably 15 or lower. When the pKa is within this range, it is easy to handle and ash removal is facilitated.

[0029] The solvent used in step (2) is the same as the solvent used in step (1) described above. Furthermore, the order and method of charging the recovered carbon black and the base into the solvent and bringing them into contact are not particularly limited. For example, the recovered carbon black and the base may be added to the solvent simultaneously and mixed to bring them into contact. Alternatively, a treatment solution 2 may be prepared by dissolving (or suspending) the base in the solvent, and then this treatment solution 2 may be mixed with the recovered carbon black to bring them into contact. Alternatively, the recovered carbon black may be suspended in the solvent beforehand, and then the base may be mixed in to bring them into contact (in this case, the base may also be prepared in advance as treatment solution 2). Furthermore, the recovered carbon black may be brought into contact with a container (e.g., a column) containing it by passing the treatment solution 2 containing the dissolved base through it.

[0030] As for contact methods, from the viewpoint of ease of manufacture and effective reduction of ash content, it is preferable to prepare the treatment solution 2 and then mix it with the recovered carbon black to bring them into contact. Furthermore, from the viewpoint of further improving contactability, it is preferable to suspend the recovered carbon black in a solvent beforehand and then mix it with the separately prepared treatment solution 2 to bring them into contact. Moreover, from the viewpoint of being able to continuously perform the aforementioned oxidizing agent contact step (1), and the solid-liquid separation step (3) and washing step (4) described later, and having good processing efficiency, it is preferable to pack the recovered carbon black into a packed container such as a column and pass the treatment solution 2 containing the base through it. Furthermore, it is preferable to stir the mixture as needed during contact. Examples of stirring methods include known methods similar to those described in the oxidizing agent contact step (1).

[0031] The contact temperature (reaction temperature) in step (2) is not particularly limited and varies depending on the type of base used, but from the viewpoint of handling and workability, it is preferably 10°C or higher, more preferably 20°C or higher, even more preferably 35°C or higher, and even more preferably 50°C or higher, and preferably less than 100°C, more preferably 90°C or lower, even more preferably 80°C or lower, and even more preferably 70°C or lower. Furthermore, from the viewpoint of efficiently reducing ash content, it is preferable to bring the materials into contact under normal pressure or under pressurized pressure. More specifically, from the viewpoint described above, the pressure is preferably 0.1 MPa or higher, and preferably 0.3 MPa or lower. Moreover, from the viewpoint of ease of manufacturing, it is even more preferable to bring the materials into contact under normal pressure (0.1 MPa). Furthermore, the contact time (reaction time) is preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 3 hours or less.

[0032] The order of steps (1) and (2) is not particularly important; step (2) may be performed after step (1), or step (1) may be performed after step (2). From the viewpoint of effectively removing ash, it is preferable to perform step (2) after step (1). Furthermore, steps (1) and (2) may be repeated, or the same series of processes may be repeated after processing in the order of step (1) to step (2), or similarly, the same series of processes may be repeated after processing in the order of step (2) to step (1).

[0033] <Solid-liquid separation process (step (3))> Preferably, after each of steps (1) and (2), or after the completion of all steps (1) and (2), there is a step (3) in which the solvent after the contact treatment is separated into solid and liquid to obtain contact-treated particles containing carbon black. According to this step, ash dissolved in the solvent by the contact treatment, excess oxidizing agent after the contact treatment, and possibly organic acids, bases, and other chemicals can be easily removed by removing the solvent through solid and liquid separation, making it possible to obtain contact-treated particles containing carbon black with reduced ash content, i.e., purified carbon black. Step (3) may be performed after each of steps (1) and (2), that is, after step (1) and after step (2). Alternatively, after the completion of all steps of steps (1) and (2), that is, after step (1), step (2) may be performed without performing step (3), and then step (3) may be performed, or after step (2), step (1) may be performed without performing step (3), and then step (3) may be performed. From the viewpoint of further reducing impurities, it is preferable to perform step (3) after each of steps (1) and (2), that is, to perform step (3) after step (1) and step (3) after step (2), or to perform step (3) after step (2) and step (3) after step (1).

[0034] The solid-liquid separation in step (3) can be carried out by known solid-liquid separation methods such as sedimentation, filtration, centrifugation, and membrane separation. By using such solid-liquid separation methods, excess oxidizing agents dissolved in the solvent, organic acids added as needed, excess bases, and ash are removed along with the solvent, making it possible to easily remove impurities such as oxidizing agents, organic acids, bases, and ash from particles containing carbon black. Among these methods, vacuum filtration and pressure filtration using filters are preferred from the viewpoint of enabling efficient and simple solid-liquid separation. The pore size of the filter used is not particularly limited and can be appropriately selected according to the particle size of the recovered carbon black used as raw material. Furthermore, from the viewpoint of simplifying the work process, a method using a column is also preferable. With column-based processing, recovered carbon black is packed into a container as the solid phase of the column, and processing liquid 1 or processing liquid 2 is passed through it, making it possible to perform solid-liquid separation (step (3)) simultaneously with the contact treatment in step (1) or step (2).

[0035] <Washing process (Process (4))> It is preferable to have a step (4) to wash the particles to be treated after step (3). Washing the particles to be treated yields purified carbon black of higher purity. One cleaning method involves cleaning the particles to be treated with a new solvent (hereinafter also referred to as the "cleaning solution") and then separating the cleaning solution from its solid-liquid state. Such a cleaning process may be repeated once or two or more times. Furthermore, the removal of the cleaning solution by solid-liquid separation in cleaning step (4) can also be carried out using the same solid-liquid separation means as described in step (3) above. The cleaning solution used in the cleaning process is not particularly limited as long as it is a solvent that can remove impurities from the particles to be treated in contact. Preferably, it is a solvent that can dissolve the ash after contact treatment, the oxidizing agent used in step (1), the organic acid used if necessary, and / or the base used in step (2). More preferably, it is a solvent that can dissolve the ash after contact treatment, the oxidizing agent used in step (1), the organic acid used if necessary, and the base used in step (2). Such a solvent makes it possible to remove impurities adhering to the particles to be treated in contact after solid-liquid separation.

[0036] Specifically, the solvents described in step (1) can be used as such cleaning solutions. Furthermore, the solvents used in steps (1), (2), and (4) may be the same or different. From the viewpoint of workability and efficiency, it is preferable to use the same solvent. As such a single solvent, from the viewpoint of ease of handling, an aqueous solvent is preferably used, and water is more preferable. By performing steps (1), (2), and (4) with the same aqueous solvent (preferably water), the equipment and work can be simplified, costs can be reduced, and chemicals such as oxidizing agents and ash used in the treatment of steps (1) and (2) can be removed efficiently. In particular, when performing steps (1) to (4) in a continuous method such as a column as described later, it is preferable to use the same aqueous solvent because additional washing operations such as passing different solvents through the process become unnecessary.

[0037] The processing method for steps (1) to (4) may be either a batch method or a continuous method. Here, the batch method is a method in which, for example, the required amount of solvent (or processing solution 1 or 2) is added to the container during the processing of step (1) or step (2). More specifically, for example, recovered carbon black, an oxidizing agent, and an organic acid as needed are stirred and mixed in the solvent in the container (step (1)), followed by solid-liquid separation (step (3)), and washing as needed (step (4)). Then, the recovered carbon black obtained after these processing steps (Note: Recovered carbon black that has undergone only one of the processing steps (1) or (2), and has gone through the processing steps (3) and, if necessary, step (4), will also be referred to below as "crudely purified carbon black") and a base are stirred and mixed in the solvent in the container (step (2)), followed by solid-liquid separation (step (3)), and washing as needed (step (4)). Furthermore, the continuous method here refers to a method of continuously supplying and discharging the processing solution used in steps (1) and (2), and the washing solution used in step (4) as needed, using, for example, a column. More specifically, for example, the column is packed with recovered carbon black as a solid phase, processing solution 1, in which an oxidizing agent and, if necessary, an organic acid are dissolved in a solvent, is passed through the column (steps (1) and (3)), then the washing solution is passed through as needed (step (4)), then processing solution 2, in which a base is dissolved in a solvent, is passed through (steps (2) and (3)), and then the washing solution is passed through as needed (step (4)).

[0038] <Drying process (process (5))> It is preferable to have a step (step (5)) to dry the particles to be treated after step (3) or step (4) described above. In particular, it is preferable that the drying step be performed after the completion of steps (1) to (4). Sufficient drying allows the particles to be suitably used in various products. There are no particular restrictions on the drying method, and conventionally known methods can be used, such as natural drying, vacuum drying, hot air drying, freeze drying, and spray drying. The conditions such as temperature, pressure, and time during drying are also not particularly limited and are determined appropriately depending on the drying method. For example, when drying the residue after washing and vacuum filtration by standing, conditions such as 80°C and a drying time of 120 minutes or more can be used.

[0039] The present invention's method for producing refined carbon black may further include a step of recovering carbon black-containing particles from used tires. As for methods for recovering carbon black-containing particles from used tires, conventionally known methods such as pyrolysis can be used. Furthermore, the recovered carbon black used in this invention may be commercially obtained.

[0040] The refined carbon black obtained by the manufacturing method of the present invention can be suitably used, for example, as a black pigment in paints and inks, or as a reinforcing material for rubber products such as tires. [Examples]

[0041] Unless otherwise specified, "%" indicates "mass%". The oxidizing agent, acid, and base used in steps (1) and (2) were each prepared in advance using deionized water to obtain aqueous solutions of the concentrations listed in Table 1. Hereinafter, the aqueous solution of the acid used in step (1) and the aqueous solution of the acid and oxidizing agent will be referred to as "treatment solution 1," and the aqueous solution of the base used in step (2) will be referred to as "treatment solution 2."

[0042] Examples 1-2, 4 and Comparative Example 3 • Experimental procedures As particles containing carbon black, we used recycled carbon black (manufactured by Bolder Industries, product name "BolderBlack", ash content 17.7%) recovered from used tires. Step (1): 5 g of recovered carbon black and 50 g of processing solution 1 (prepared so that the concentrations of each component immediately after preparation match the values ​​shown in Table 1) were placed in a 200 mL vial and stirred with a magnetic stirrer at 60°C for 1 hour. The obtained slurry was filtered under reduced pressure using a 0.1 μm PTFE filter to separate the solid matter (contact-treated particles) (step (3)). The solid matter was then washed with 100 mL of deionized water and filtered under reduced pressure (step (4)) to obtain crude purified carbon black.

[0043] Step (2): The entire amount of crude purified carbon black obtained above, along with 50 g of treatment solution 2 (1 M NaOH), was placed in a 200 mL vial and stirred with a magnetic stirrer at 60°C for 1 hour. The slurry was filtered under reduced pressure through a 0.1 μm PTFE filter (step (3)). The resulting solid was left on the PTFE filter, and while maintaining reduced pressure, 100 mL of deionized water was passed through the PTFE filter for washing (step (4)). Then, at room temperature, the solid was left on the PTFE filter, and while maintaining reduced pressure, it was allowed to stand for 60 minutes to dry (step (5)) to obtain purified carbon black.

[0044] • Evaluation method The purified carbon black obtained by the above process was dried under reduced pressure at 100°C for 12 hours. The dried refined carbon black was placed in an alumina crucible and heated in an electric furnace at 550°C for 4 hours. The ash content in the refined carbon black was calculated using the following formula. Ash content (mass%) in refined carbon black = (mass of residue / mass of refined carbon black after drying) × 100

[0045] Reference example 1 The ash content in the untreated recovered carbon black, which did not undergo processes (1) and (2), was calculated using the evaluation method of Example 1.

[0046] Comparative Example 1 The procedure was the same as in Example 1, except that the treatment in step (1) was omitted, and the treatment in step (2) was performed using treatment solution 2 (1M NaOH) as described in Table 1.

[0047] Comparative Example 2 The procedure was carried out in the same manner as in Example 1, except that the treatment in step (1) was performed using treatment solution 1 (10% H2O2) as shown in Table 1, and the treatment in step (2) was not performed. Example 1~ 2、4 Reference Example 1, Comparative Example 1~ 3 The results are shown in Table 1.

[0048] [Table 1]

[0049] From these results, it was found that treatment with an oxidizing agent or treatment with a base alone did not sufficiently reduce the ash content, but treatment with both an oxidizing agent and a base significantly reduced the ash content. Furthermore, in Example 1, where the material was treated with an organic acid and an oxidizing agent in step (1), an even more significant reduction in ash content was observed.

Claims

1. Including the following steps (1) and (2), Process (1) A process in which particles containing carbon black and an oxidizing agent are charged into a solvent and brought into contact. Step (2) Step of charging particles containing carbon black and a base into a solvent and bringing them into contact. After step (1), perform step (2), The aforementioned step (1) is a step of further adding an organic acid to a solvent and bringing it into contact with the solvent. The molar ratio [oxidizing agent / organic acid] of the organic acid added to the oxidizing agent is 0.3 or more and 10 or less. A method for producing refined carbon black.

2. A method for producing purified carbon black according to claim 1, further comprising step (3) after each of steps (1) and (2), or after the completion of all steps (1) and (2), the solvent after contact treatment is subjected to solid-liquid separation to obtain contact-treated particles containing carbon black.

3. A method for producing purified carbon black according to claim 2, further comprising a step (4) of washing the particles to be contacted after step (3).

4. A method for producing purified carbon black according to claim 2 or 3, further comprising a step (5) of drying the particles to be contacted after step (3) or step (4).

5. The method for producing purified carbon black according to claim 1, wherein the solvent is an aqueous solvent.

6. The method for producing purified carbon black according to claim 1, wherein the particles containing the carbon black are derived from used tires.

7. A method for using refined carbon black obtained by the manufacturing method described in Claim 1 as a tire reinforcing material.

8. A method for manufacturing a tire using refined carbon black obtained by the manufacturing method described in Claim 1 as a tire reinforcing material.

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