Method for recovering carbon fiber from material composition containing carbon fiber-reinforced resin and glass fiber-reinforced resin

Abstract

To provide new technical means enabling suppression of mixing of a glass fiber into an obtained carbon fiber, in a method for recovering a carbon fiber from a material composition including carbon fiber-reinforced resin and glass fiber-reinforced resin.SOLUTION: A method for recovering a carbon fiber from a material composition includes: a step (1) of preparing a material composition which includes a carbon fiber-reinforced resin containing a carbon fiber and a matrix resin and a glass fiber-reinforced resin, and is immersed in molten liquid containing an alkali metal compound; and a step (2) of separating the carbon fiber from the molten liquid.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for recovering carbon fibers from a material composition that includes a carbon fiber reinforced resin and a glass fiber reinforced resin. [Background technology]

[0002] Carbon fiber reinforced resins containing carbon fibers and a matrix resin have the excellent characteristics of being lightweight and having high strength and durability, and are therefore used in a variety of fields, such as the sports industry, general industry, and aerospace industry. In recent years, material compositions containing carbon fiber reinforced resins and glass fiber reinforced resins have also been used in the manufacture of hydrogen tanks and the like.

[0003] The production volume of carbon fiber reinforced resin is increasing year by year, and the amount of waste from used products containing a material composition containing carbon fiber reinforced resin and glass fiber reinforced resin is also increasing year by year. However, due to its excellent durability, it is difficult to process this waste in a conventional incinerator. For this reason, most of this waste is crushed and pulverized and then landfilled, but there is a shortage of disposal sites for landfill treatment. In addition, carbon fiber is expensive because its production requires a large amount of energy. Therefore, there is a need for technology to process waste material compositions containing carbon fiber reinforced resin and glass fiber reinforced resin and to recover carbon fiber from the waste.

[0004] It is known that when a material composition containing carbon fiber reinforced resin and glass fiber reinforced resin is heated under normal conditions, glass fibers remain in the resulting residue (carbon fiber). If glass fibers remain in the resulting carbon fiber, problems may arise when the resulting carbon fiber is processed to produce recycled carbon fiber or carbon fiber reinforced resin (for example, problems such as the inability to obtain high-purity carbon fiber).

[0005] For example, Patent Document 1 proposes a method of making incisions in a material composed of a layer containing carbon fiber reinforced resin and a layer containing glass fiber reinforced resin, penetrating a heated phosphoric acid-containing solution through the incisions to separate the layer containing carbon fiber reinforced resin and the layer containing glass fiber reinforced resin, and recovering carbon fibers from the separated layer containing carbon fiber reinforced resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-65205 Summary of the Invention

[0007] The method proposed in Patent Document 1 can prevent glass fibers from being mixed into carbon fibers, but it requires physical separation of the layer containing carbon fiber reinforced resin, which means that it is extremely difficult to apply this method to materials in which the layer containing carbon fiber reinforced resin and the layer containing glass fiber reinforced resin cannot be separated, and therefore it was not satisfactory.

[0008] Therefore, one object of the present disclosure is to provide a new technical means capable of suppressing the inclusion of glass fibers in the obtained carbon fibers in a method for recovering carbon fibers from a material composition containing carbon fiber reinforced resin and glass fiber reinforced resin.

[0009] The present inventors have found that immersing a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin in a melt containing an alkali metal compound can prevent glass fibers from being mixed into the carbon fibers. The present disclosure is based on this finding.

[0010] According to one embodiment of the present disclosure, (1) preparing a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin, the material composition containing carbon fibers and a matrix resin being immersed in a melt containing an alkali metal compound; and (2) Separating the carbon fibers from the melt a method for recovering carbon fibers from the material composition, comprising: is provided.

[0011] According to the present disclosure, in a method for recovering carbon fibers from a material composition containing carbon fiber reinforced resin and glass fiber reinforced resin, it is possible to prevent glass fibers from being mixed into the obtained carbon fibers. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing the amount of fuel gas recovered in Examples 1 to 3. FIG. [Figure 2] 1 is a graph showing the residual ratios of carbon fibers obtained in Examples 1 to 3. FIG. [Figure 3] 1 is a photograph of the appearance of carbon fibers obtained in Example 24. [Figure 4] 1 is a photograph of the appearance of the geopolymer obtained in Example 25. Specific Description of the Invention

[0013] In this disclosure, "A to B" indicating a range of values ​​includes the values ​​A and B written before and after "to" as the lower and upper limits, respectively. For example, "1 to 10" means a range of values ​​from 1 to 10.

[0014] According to one embodiment of the present disclosure, in a method for recovering carbon fibers from a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin, the method comprising: (1) a step of preparing a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin, the material composition containing carbon fiber and a matrix resin being immersed in a melt containing an alkali metal compound (also referred to as "step (1)" in the present disclosure); and (2) A step of separating the carbon fibers from the melt (also referred to as “step (2)” in the present disclosure). A method is carried out comprising:

[0015] According to one embodiment of the present disclosure, the use of a melt containing an alkali metal compound advantageously enables not only partial or substantially complete removal of the matrix resin contained in the material composition, but also partial or substantially complete removal of the glass fibers contained in the material composition. It is a completely unexpected fact that partial or substantially complete partitioning (e.g., dissolution) of the glass fibers into the melt. Furthermore, according to a preferred embodiment of the present disclosure, even when the material composition contains a metal (e.g., aluminum) and / or calcium carbonate, etc., it is particularly advantageous in that partial or substantially complete partitioning of the metal and / or calcium carbonate, etc. can be achieved. It is a completely unexpected fact that the metal and calcium carbonate, etc., which may be contained in the material composition, can be partitioned (e.g., dissolved) into the melt. The method of the present disclosure is described in detail below.

[0016] [Process (1)] In step (1), a material composition containing carbon fiber reinforced resin and glass fiber reinforced resin, which contains carbon fiber and a matrix resin, is prepared by immersing the material composition in a melt containing an alkali metal compound. In step (1), the material composition may be immersed in a melt containing an alkali metal compound, or the material composition may be immersed in the melt by heating under conditions in which the material composition and a solid alkali metal compound coexist, causing the alkali metal compound to reach its melting point and become molten. Immersing the material composition in the melt decomposes and / or gasifies the matrix resin contained in the material composition, and enables the glass fiber contained in the material composition to be separated. Another advantage of step (1) is that it does not require separating the carbon fiber reinforced resin layer from the glass fiber reinforced resin layer in the material composition.

[0017] The process of immersing or immersing the material composition in the melt (also referred to as "immersion process" in the present disclosure) may be either a batch process or a continuous process. The batch process is a process in which a predetermined amount of the melt is charged into a reactor, a predetermined amount of the material composition is added thereto, an immersion process is performed, and carbon fibers are extracted. In the batch process, multiple material compositions may be added to the reactor multiple times. The continuous process is a process in which the melt is continuously supplied to and discharged from a reactor to circulate, while the material composition is continuously introduced into the reactor, the immersion process is performed, and carbon fibers are extracted.

[0018] In step (1), the material composition is heated by immersing it in a melt containing an alkali metal compound. The melt is, for example, a melt of the alkali metal compound. For the avoidance of doubt, the "immersion treatment" in this disclosure is different from a dissolution treatment method in which the material composition is immersed in an organic solvent (e.g., an alcohol solvent, an ether solvent, a ketone solvent, an ester solvent, or an amide solvent) and heated to decompose and dissolve the matrix resin.

[0019] The immersion treatment can be carried out in a conventionally known reactor. Examples of the reactor include a silicon carbide vessel. Examples of methods for heating the alkali metal compound to a molten state include convection heating using gas, etc.; radiation heating using infrared rays, far infrared rays, microwaves, etc.; conduction heating such as by contact with a hot plate; and any combination of two or more of these. During the immersion treatment, the melt may be stirred.

[0020] According to one embodiment of the present disclosure, step (1) includes a step of immersing the material composition in the melt.

[0021] In one embodiment of the present disclosure, the temperature of the melt containing the alkali metal compound in the immersion treatment is not particularly limited as long as it is a temperature at which the immersion treatment can be performed (for example, a temperature above the melting point of the alkali metal compound). From the viewpoint of efficiently suppressing the incorporation of glass fibers into the obtained carbon fiber, the temperature of the melt is preferably above 200°C, more preferably above 250°C, and even more preferably above 300°C. Furthermore, from the viewpoint of suppressing deterioration of the recovered carbon fiber, the temperature of the melt is preferably below 600°C, more preferably below 500°C, even more preferably below 400°C, and even more preferably below 300°C. According to a preferred embodiment of the present disclosure, the temperature of the melt is above 200°C and below 300°C, preferably 250°C to 300°C.

[0022] According to one embodiment of the present disclosure, the matrix resin is decomposed into low-molecular-weight compounds such as phenolic compounds and dissolved in the melt. According to one embodiment of the present disclosure, the matrix resin can be decomposed even at the above-mentioned temperature. Therefore, compared with conventional pyrolysis or combustion treatments that require high-temperature heating above 600°C, carbon fibers with less degradation and high strength and durability can be recovered. Furthermore, according to one embodiment of the present disclosure, glass fibers that could not be removed even with conventional pyrolysis or combustion treatments that require high-temperature heating above 600°C can be advantageously separated even at the above-mentioned temperature.

[0023] The immersion time of the material composition in the melt during the immersion treatment is appropriately set depending on the heating temperature. The immersion time is preferably 1 minute or longer, more preferably 3 minutes or longer, and even more preferably 5 minutes or longer. If the immersion time is equal to or longer than the lower limit, decomposition and / or gasification of the matrix resin and separation of the glass fibers can proceed. The upper limit of the immersion time is not particularly limited, but is, for example, 24 hours or shorter, preferably 10 hours or shorter, and more preferably 5 hours or shorter.

[0024] The immersion treatment can be carried out in the melt, which can prevent the carbon fibers from coming into contact with air and inhibit oxidation degradation of the carbon fiber surface, and is therefore advantageous in that it can recover carbon fibers with strength (e.g., tensile strength) comparable to that of virgin materials. The immersion treatment can be carried out in an air atmosphere or a non-oxidizing gas atmosphere, but is preferably carried out in an air atmosphere because the immersion treatment can prevent contact between the carbon fibers and air and can reduce costs. The immersion treatment can be carried out under normal pressure, or under reduced or increased pressure. The immersion treatment is preferably carried out under normal pressure.

[0025] The non-oxidizing gas atmosphere is an atmosphere that does not contain oxygen gas or an atmosphere that does not substantially contain oxygen gas. The atmosphere that does not substantially contain oxygen gas does not include an atmosphere to which oxygen gas is intentionally added when heating the carbon fiber reinforced resin, but does include an atmosphere to which oxygen gas is inevitably mixed. Examples of non-oxidizing gases include inert gases such as nitrogen gas and argon gas.

[0026] Since the immersion treatment in step (1) can be carried out in an air atmosphere, it is easy to enlarge the reactor that contains the melt. Because the reactor can be enlarged, a large-sized material composition (e.g., a material composition containing long fibers, large waste materials, or process waste materials) can be used as the treatment target.

[0027] The viscosity of the melt is not particularly limited as long as the object of the present disclosure can be achieved. The viscosity of the melt may be, for example, 50 mPa·s or less, preferably 20 mPa·s or less, and more preferably 10 mPa·s or less. The viscosity of the melt may be adjusted to fall within the above range by adjusting the type and amount of the alkali metal compound described below. Setting the viscosity of the melt within the above range is advantageous in that it can reduce the amount of alkali metal compound adhering to or remaining on the carbon fibers after separation from the melt.

[0028] The amount of the alkali metal compound in the melt is not particularly limited as long as the object of the present disclosure can be achieved. The amount of the alkali metal compound in the melt is, for example, about 80 to 100% by mass, preferably about 85 to 100% by mass, more preferably about 88 to about 99% by mass, and even more preferably about 90 to about 98% by mass, relative to the total mass of the melt. When the amount is less than 100% by mass, at least a portion of the remainder may be an impurity contained in the active pharmaceutical ingredient of the alkali metal compound (e.g., potassium hydroxide).

[0029] <Material composition> The "material composition" in this disclosure includes a carbon fiber reinforced resin containing carbon fiber and a matrix resin, and a glass fiber reinforced resin.

[0030] The material composition may be a composite of the carbon fiber reinforced resin and the glass fiber reinforced resin, each of which may be separable from the other. When the material composition is a composite, the material composition may be, for example, a laminate of a layer containing carbon fiber reinforced resin and a layer containing glass fiber reinforced resin, or a mixture of carbon fiber reinforced resin and glass fiber reinforced resin. According to one embodiment of the present disclosure, the material composition is a composite of the carbon fiber reinforced resin and the glass fiber reinforced resin.

[0031] The material composition may contain components other than the carbon fiber reinforced resin and the glass fiber reinforced resin. Examples of the other components include reinforcing fibers other than the carbon fiber reinforced resin and the glass fiber reinforced resin, various metals (e.g., iron, copper, aluminum, alloys, etc.), and the like. According to one embodiment of the present disclosure, the material composition contains a metal (preferably aluminum). Even when the material composition contains a metal (preferably aluminum), this embodiment of the present disclosure is particularly advantageous in that it is possible to prevent the metal from being mixed into the recovered carbon fibers.

[0032] The shape of the material composition is not particularly limited, and examples thereof include a plate, a sheet, a square pipe, a round pipe, an L-shaped cross section, a T-shaped cross section, a C-shaped cross section, an H-shaped cross section, and any other three-dimensional shape.

[0033] The carbon fiber reinforced resin, the glass fiber reinforced resin, and / or the material composition may be in the form of an intermediate material, such as pellets, prepregs (sheets of semi-cured thermosetting resin obtained by impregnating carbon fibers with a thermosetting resin) and laminates thereof, or stampable sheets (sheets obtained by impregnating carbon fibers with a thermoplastic resin) and laminates thereof, or may be in the form of a finished product. The carbon fiber reinforced resin, the glass fiber reinforced resin, and / or the material composition may be waste materials from used products, or process waste materials such as scraps and scraps generated during the manufacturing process of intermediate materials or products. The carbon fiber reinforced resin, the glass fiber reinforced resin, and / or the material composition are preferably waste materials from used products or process waste materials generated during the manufacturing process of intermediate materials or products. According to one embodiment of the present disclosure, the waste materials that are difficult to process in conventional incinerators can be easily processed in an energy-saving and low-cost manner.

[0034] When the material composition is a large intermediate material or product, the material composition may be cut into appropriate sizes using a cutter as needed. When cutting the material composition containing long fibers, the material composition may be cut along the longitudinal direction of the long fibers contained in the material composition so that the long fibers can be recovered in as long a length as possible.

[0035] When the material composition is a product, the entire product may be the material composition, or a part of the product may be the material composition. That is, the target in step (1) may be any product as long as it contains the material composition, and may be, for example, a composite of the material composition with other components. Examples of other components include fiber-reinforced resins containing reinforcing fibers other than carbon fiber and glass fiber, resin molded products containing no reinforcing fibers, metals, ceramics, etc.

[0036] Examples of products include products in the sports industry, general industry, and aerospace industry. Examples of products in the sports industry include golf club shafts, fishing rods, ski poles, tennis and badminton racket frames, baseball bats, hockey sticks, and other components. Examples of products in general industry include structural materials, drive shafts, flywheels, leaf springs, and components for automobiles, ships, and railway vehicles; various containers (high-pressure tanks, filtration tanks, etc.), rollers, cables, roofing materials, wind turbine blades, and other components. Examples of products in the aerospace industry include components for aircraft (such as structural materials used in main wings, tails, and fuselages), rockets, and the like.

[0037] <Carbon fiber reinforced resin> Carbon fiber reinforced resin is a fiber reinforced resin that contains carbon fiber and a matrix resin, and usually contains carbon fiber as a reinforcing material in the matrix resin. Carbon fiber reinforced resin is also commonly called carbon fiber reinforced plastic (CFRP).

[0038] (carbon fiber) Examples of carbon fibers include polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers such as coal pitch or petroleum pitch, rayon-based carbon fibers, and vapor-grown carbon fibers, with PAN-based carbon fibers and pitch-based carbon fibers being preferred. The carbon fiber reinforced resin can contain one or more types of carbon fibers.

[0039] The carbon fiber preferably has an average diameter (average fiber diameter) of 0.1 to 30 μm, more preferably 1 to 20 μm, per single fiber. The diameter of the carbon fiber can be determined by a test method conforming to JIS R7607 "Carbon Fiber - Test Method for Diameter and Cross-Sectional Area of ​​Single Fiber." The carbon fiber may be either a long fiber or a short fiber. The average fiber length of the carbon fiber is not particularly limited and is, for example, 100 mm or less. The average diameter and fiber length can be calculated based on 100 fibers arbitrarily selected from the carbon fibers obtained by the method of the present disclosure.

[0040] Examples of carbon fiber forms include fiber bundles (filaments or tows) in which multiple single fibers are aligned in one direction, chopped yarns in which fiber bundles are cut to any length, milled yarns in which the fiber bundles are cut even finer than chopped yarns, and carbon fiber substrates such as unidirectional materials (UD materials), woven fabrics, knitted fabrics, and nonwoven fabrics. Carbon fiber reinforced resins can contain one or more types of carbon fiber. Carbon fiber reinforced resins can also contain one or more carbon fiber substrates.

[0041] The carbon fiber content in the carbon fiber reinforced resin is, for example, 20 to 90 mass%, preferably 30 to 85 mass%, and more preferably 50 to 80 mass%, based on the total mass of the carbon fiber reinforced resin. The carbon fiber content can be determined, for example, by differential thermal analysis or thermogravimetric analysis. If such analysis is difficult, the carbon fiber content can also be determined by a test method in accordance with JIS K7075 "Test method for fiber content and void content of carbon fiber reinforced plastics."

[0042] (matrix resin) Examples of the matrix resin include a resin formed from a thermosetting resin and a resin formed from a thermoplastic resin. As the matrix resin, a resin formed from a thermosetting resin is preferred, and a resin formed by thermal curing of a thermosetting resin is more preferred. The carbon fiber reinforced resin can contain one or more matrix resins.

[0043] Examples of thermosetting resins include epoxy resins, phenolic resins, unsaturated polyester resins, vinyl ester resins, melamine resins, urea resins, cyanate ester resins, and thermosetting polyimide resins, and epoxy resins are preferred, with epoxy resins being more preferred, since the alkali metal compound decomposes smoothly in the melt. The matrix resin may be formed from one type of thermosetting resin, or may be formed from two or more types of thermosetting resins.

[0044] The thermosetting resin may be a resin that is cured by heating, or a resin that is cured by heating and the action of a curing agent. In the case of an epoxy resin, examples of the curing agent include an acid anhydride curing agent, an amine curing agent, and a phenol resin curing agent.

[0045] Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, alicyclic epoxy resins, linear aliphatic epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, diglycidyl ethers of biphenol, diglycidyl ethers of naphthalenediol, diglycidyl ethers of phenols, diglycidyl ethers of alcohols, and alkyl-substituted, halogenated, and hydrogenated products thereof.

[0046] Examples of thermoplastic resins include polyolefin resins, acrylic resins, polystyrene resins, acrylonitrile-butadiene-styrene copolymer resins, polyester resins, polycarbonate resins, polyacetal resins, polyamide resins, polyether ketone resins, polyether ether ketone resins, and polyphenylene sulfide resins. The matrix resin may be formed from one type of thermoplastic resin or two or more types of thermoplastic resins.

[0047] According to one embodiment of the present disclosure, the matrix resin is preferably a resin in which a crosslinked structure is formed by thermal curing of a thermosetting resin, and the crosslinked structure contains functional groups such as ester bonds and amide bonds. It is believed that the functional groups of the matrix resin having such a crosslinked structure are more easily decomposed by an alkali metal compound such as an alkali metal hydroxide, resulting in low molecular weight compounds even at low temperatures.

[0048] The content of the matrix resin in the carbon fiber reinforced resin is, for example, 5 to 60 mass %, preferably 10 to 50 mass %, and more preferably 15 to 40 mass %, based on the total mass of the carbon fiber reinforced resin.

[0049] The carbon fiber reinforced resin may contain components other than the carbon fiber and the matrix resin, such as additives such as antioxidants, heat stabilizers, weathering agents, release agents, lubricants, pigments, dyes, plasticizers, antistatic agents, and flame retardants, which may be used alone or in any combination of two or more.

[0050] The amount of carbon fiber reinforced resin contained in the material composition may be, for example, 40 to 99 mass %, preferably 50 to 95 mass %, and more preferably 60 to 90 mass %, based on the total mass of the material composition.

[0051] <Glass fiber reinforced resin> The term "glass fiber reinforced resin" as used herein refers to a fiber reinforced resin that contains glass fibers and a matrix resin, and typically contains glass fibers as a reinforcing material in the matrix resin. Glass fiber reinforced resin is also commonly called glass fiber reinforced plastic (GFRP).

[0052] (glass fiber) The glass fibers contained in the glass fiber reinforced resin are not particularly limited, and may be any glass fibers such as, for example, A glass, E glass, alkali-resistant glass compositions containing a zirconia component, chopped strands, or glass roving, and these may be used alone or in any combination of two or more types.

[0053] The average fiber diameter of the glass fiber is not particularly limited and may be, for example, 1 μm to 50 μm, preferably 5 μm to 20 μm. When the glass fiber is a strand formed by twisting glass filaments together, the average fiber diameter may refer to the average diameter of the filaments constituting the strand, rather than the diameter of the strand itself.

[0054] The content of glass fibers in the glass fiber reinforced resin is, for example, 5 to 70 mass %, more preferably 10 to 50 mass %, and more preferably 20 to 40 mass %, based on the total mass of the glass fiber reinforced resin.

[0055] (matrix resin) The matrix resin contained in the glass fiber reinforced resin is not particularly limited, and may be, for example, the matrix resin described above for the carbon fiber reinforced resin.

[0056] The content of the matrix resin in the glass fiber reinforced resin is, for example, 5 to 70 mass %, more preferably 10 to 50 mass %, and even more preferably 20 to 40 mass %, based on the total mass of the glass fiber reinforced resin.

[0057] The glass fiber reinforced resin may contain other components in addition to the glass fibers and the matrix resin, such as various metals, fillers (e.g., calcium carbonate), and the "other components" described above for the carbon fiber reinforced resin.

[0058] The amount of glass fiber reinforced resin contained in the material composition may be, for example, 0.1 to 40 mass %, preferably 1 to 30 mass %, and more preferably 1 to 20 mass %, based on the total mass of the material composition.

[0059] The mass ratio of the carbon fiber reinforced resin to the glass fiber reinforced resin contained in the material composition (carbon fiber reinforced resin / glass fiber reinforced resin) may be, for example, 1-100, preferably 2-40, and more preferably 3-20.

[0060] ≪Optional ingredients≫ The material composition may contain optional components other than the carbon fiber reinforced resin and the glass fiber reinforced resin. Examples of optional components that may be contained in the material composition include antioxidants, heat stabilizers, weathering agents, release agents, lubricants, pigments, dyes, plasticizers, antistatic agents, flame retardants, and various metals (e.g., aluminum). These may be used alone or in any combination of two or more. According to one embodiment of the present disclosure, the material composition contains a metal (preferably aluminum).

[0061] When the material composition contains a metal (e.g., aluminum), the metal can be recovered together with the carbon fibers or separately from the carbon fibers by appropriately adjusting the conditions of the method of the present disclosure (e.g., the temperature of the melt, the immersion time, the amount of the alkali metal compound, etc.). According to one embodiment of the present disclosure, when the material composition contains a metal, it is advantageous in that the metal can be recovered together with the carbon fibers or separately from the carbon fibers.

[0062] <Alkali metal compounds> The term "alkali metal compound" used in the present disclosure is not particularly limited as long as it is a compound of an alkali metal. Examples of alkali metal compounds include, but are not limited to, compounds of alkali metals such as lithium, sodium, potassium, rubidium, and cesium (e.g., hydroxides, alcoholates, phenolates, inorganic acid salts (e.g., phosphates, carbonates, sulfates, and nitrates), and organic acid salts of alkali metals), which may be used alone or in any combination of two or more. Without being bound by theory, it is believed that the alkali metal compound acts as a decomposition catalyst for the matrix resin during the immersion treatment.

[0063] Among these, from the viewpoint of enabling the decomposition of the matrix resin to proceed satisfactorily at low temperatures (for example, 600°C or less, preferably 500°C or less, more preferably 300°C or less), alkali metal hydroxides are preferred, and those containing at least one selected from the group consisting of sodium hydroxide and potassium hydroxide are more preferred, with potassium hydroxide being particularly preferred.

[0064] To further lower the temperature of a melt containing an alkali metal compound, a method can be used in which the freezing point (melting point) of the alkali metal compound is lowered by using a combination of multiple alkali metal compounds. For example, an alkali metal compound containing sodium hydroxide and potassium hydroxide in a molar ratio of 3:7 to 7:3 can be used. Alternatively, to further lower the temperature of a melt containing an alkali metal compound, the alkali metal compound can be made to coexist with other substances (e.g., impurities contained in the alkali metal compound).

[0065] When potassium hydroxide is approximately 100% pure, its melting point is approximately 360°C. However, in the presence of other substances (e.g., alkali metal compounds other than potassium hydroxide, impurities, etc.), the melting point can drop to 300°C or lower (preferably 280°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower). Note that the term "impurity" used in this context refers to an unintentional substance that may be contained in a potassium hydroxide drug substance (e.g., a reagent). Therefore, substances that may be intentionally allowed to coexist with potassium hydroxide (e.g., sodium hydroxide, as described below) are not considered "impurities." When potassium hydroxide contains impurities, the purity of the potassium hydroxide is less than 100% (i.e., the remainder is impurities). In one embodiment of the present disclosure, potassium hydroxide is preferably less than 100% pure (i.e., contains impurities), more preferably 85% or more but less than 100%, and even more preferably 85% or more but less than 99% pure. Potassium hydroxide with a purity of less than 100% is available from, for example, Fujifilm Wako Pure Chemical Industries, Ltd., Sigma-Aldrich, etc.

[0066] Examples of the impurities include, but are not limited to, potassium salts other than potassium hydroxide (e.g., chlorides such as potassium carbonate and potassium chloride, phosphates such as potassium phosphate, and silicates such as potassium silicate), metals such as sodium, magnesium, calcium, zinc, aluminum, iron, copper, nickel, chromium, manganese, and rubidium, and salts of these metals (e.g., hydroxides, chlorides, carbonates, phosphates, etc.).

[0067] The melting point of potassium hydroxide can also be lowered in the presence of sodium hydroxide. For example, potassium hydroxide with a purity of about 100% has a melting point of about 360°C when used alone, as described above. However, in the presence of sodium hydroxide with a purity of about 100%, the melting point can be lowered to about 300°C or lower (preferably about 280°C or lower, more preferably about 250°C or lower, and even more preferably about 200°C or lower). The melting point when potassium hydroxide and sodium hydroxide coexist can vary depending on their ratio (e.g., mass ratio, molar ratio, etc.). For such melting points, reference may be made to known literature, information, etc. For example, referring to https: / / www.metallab.net / chemsoc / alloys.php?id=19, when the molar ratio of potassium hydroxide to sodium hydroxide is about 4:1 to about 1:19 (i.e., the mass ratio of potassium hydroxide to sodium hydroxide is about 1:14 to about 7:1), a melt can be formed even at about 300°C or below (preferably, about 300°C or below and about 170°C or above). Alternatively, a person skilled in the art can experimentally measure the melting point at a desired ratio, for example, by referring to a known melting point measurement method (e.g., visual observation, thermal analysis, etc.). When sodium hydroxide and sodium hydroxide coexist, the melting point can be further lowered by the additional presence of the above-mentioned impurities.

[0068] According to one embodiment of the present disclosure, the amount of potassium hydroxide contained in the alkali metal compound is 45% by mass or more, preferably 72.5% by mass or more, and more preferably 85% by mass or more, based on the total mass of the alkali metal compound. Setting the amount of potassium hydroxide in the alkali metal compound within this range is advantageous in that it can more efficiently suppress the contamination of glass fibers into the resulting carbon fiber. Furthermore, from the viewpoint of the viscosity of the melt, setting the amount of potassium hydroxide in the alkali metal compound within this range is advantageous in that it can obtain a melt with a low viscosity (e.g., a viscosity of 50 mPa·s or less, preferably 10 mPa·s or less) even at a low temperature (e.g., 400°C or less, preferably 300°C or less).

[0069] When the alkali metal compound contains potassium hydroxide and sodium hydroxide, the ratio of potassium hydroxide to sodium hydroxide contained in the alkali metal compound (in other words, the ratio of potassium hydroxide to sodium hydroxide in the melt) is, in terms of mass ratio, for example, 3:1 to 1:3.5, preferably 3:1 to 1:3, more preferably 3:1 to 1:1.5, and more preferably 3:1 to 1:1. Furthermore, in the alkali metal compound, the amount of sodium hydroxide per part by mass of potassium hydroxide is, for example, 0.3 parts by mass or more and 3.5 parts by mass or less, preferably 0.3 parts by mass or more and less than 3.5 parts by mass, more preferably 0.3 parts by mass or more and 1.2 parts by mass or less, and even more preferably 0.3 parts by mass or more and 1 part by mass or less. In one embodiment of the present disclosure, the molar ratio of potassium hydroxide to sodium hydroxide in the alkali metal compound (in other words, the molar ratio of potassium hydroxide to sodium hydroxide in the melt) is, for example, 3:1 to 1:5, preferably 2.5:1 to 1:4, more preferably 2.2:1 to 1:2, and even more preferably 2:1 to 1:1. Setting the ratio and / or amount of potassium hydroxide to sodium hydroxide within the above range is advantageous from the viewpoint of more efficiently suppressing the incorporation of glass fibers into the resulting carbon fibers. Setting the ratio and / or amount of potassium hydroxide to sodium hydroxide within the above range is also advantageous from the viewpoint of more efficiently recovering the metal (e.g., aluminum) together with the carbon fibers when the material composition contains the metal (e.g., aluminum).

[0070] The amount of alkali metal compound used is, from the viewpoint of ensuring good decomposition of the matrix resin, for example, 10 parts by mass or more, preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 200 parts by mass or more, even more preferably 300 parts by mass or more, and particularly preferably 500 parts by mass or more, relative to 100 parts by mass of the material composition. While there is no particular upper limit on the amount of alkali metal compound used, from the viewpoint of cost, the amount of alkali metal compound used is, for example, 10,000 parts by mass or less, preferably 5,000 parts by mass or less, more preferably 4,000 parts by mass or less, and even more preferably 3,000 parts by mass or less, relative to 100 parts by mass of the material composition. When multiple material compositions are added to a reactor multiple times, it is desirable to adjust the amount of material composition added each time so that the amount of alkali metal compound used each time is the above-mentioned amount.

[0071] The amount of the melt containing the alkali metal compound in the reactor into which the material composition is introduced is, from the viewpoint of ensuring good decomposition of the matrix resin, for example, 10 parts by mass or more, preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 200 parts by mass or more, even more preferably 300 parts by mass or more, particularly preferably 500 parts by mass or more, and particularly preferably 800 parts by mass or more, 1,000 parts by mass or more, 1,100 parts by mass or more, 1,200 parts by mass or more, 1,300 parts by mass or more, 1,400 parts by mass or more, or 1,500 parts by mass or more, relative to 100 parts by mass of the material composition introduced, but is not particularly limited, and is, for example, 10,000 parts by mass or less, preferably 5,000 parts by mass or less, relative to 100 parts by mass of the material composition introduced. In the case of a continuous reactor, the feed rate of the melt to the reactor and the discharge rate of the melt from the reactor are not particularly limited.

[0072] [Process (2)] In step (2), the carbon fibers are separated from the melt after step (1). The separation method is not particularly limited, but examples include a method in which the carbon fibers are removed from the melt and, if necessary, washed with a washing liquid. The separated melt can be reused as is or via step (3), which will be described later. According to one embodiment of the present disclosure, the alkali metal compound used as a decomposition catalyst for the matrix resin can be recovered after the immersion treatment and reused repeatedly, which is advantageous in that the running costs of the method of the present disclosure are lower than those of conventional techniques.

[0073] Examples of the cleaning method include immersion cleaning, ultrasonic cleaning, spray cleaning, shower cleaning, and jet cleaning, and two or more of these methods may be combined. In the case of immersion cleaning and ultrasonic cleaning, the carbon fibers are immersed in a cleaning solution, stirred as necessary, and then separated from the cleaning solution. Examples of the separation method include filtration, sedimentation separation, and centrifugation.

[0074] In the case of immersion washing, although not limited thereto, for example, the material composition placed in a mesh container (e.g., wire mesh) may be immersed or kept immersed in a melt of an alkali metal compound, and after a desired time has elapsed, the mesh container containing the carbon fibers may be removed from the melt and immersed in a washing liquid, etc. Alternatively, the material composition and a solid alkali metal compound may be placed in a furnace such as a kiln, and the furnace may be heated to immerse or keep immersed in a melt of an alkali metal compound, and after a desired time has elapsed, the kiln may be rotated, tilted, etc. to recover the carbon fibers, which may then be immersed in a washing liquid, etc.

[0075] Examples of cleaning solutions include water and organic solvents. Examples of organic solvents include alcohol solvents such as methanol, ethanol, propanol, benzyl alcohol, and ethylene glycol monomethyl ether; ether solvents such as dipropyl ether, diisopropyl ether, and dibutyl ether; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate, propyl acetate, and γ-butyrolactone; and amide solvents such as N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylacetamide, and N-methylpyrrolidone. A mixture of water and an organic solvent may be used as the cleaning solution, or one or more organic solvents may be used. A cleaning solution containing at least water is preferred, and a cleaning solution containing 50% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more of water is more preferred. An acidic aqueous solution such as an aqueous solution of hydrochloric acid or phosphoric acid may also be used as the cleaning solution. The pH of the cleaning solution can be adjusted appropriately by those skilled in the art.

[0076] The conditions for washing are not particularly limited. The temperature of the washing liquid may be room temperature, or may be a temperature at which the washing liquid remains liquid; for example, the temperature may be increased to increase the amount of matrix resin-derived components and alkali metal compounds dissolved. For example, when a washing liquid containing at least water is used, the temperature of the washing liquid is preferably 5 to 90°C, more preferably 10 to 80°C. The washing time is also not particularly limited.

[0077] The above-mentioned cleaning method makes it possible to easily remove matrix resin-derived components and alkali metal compounds that may adhere to the carbon fibers without deteriorating the carbon fibers, compared to methods that apply mechanical forces such as compressive stress, tensile stress, and shear stress to the carbon fibers.

[0078] After washing the carbon fibers, the carbon fibers may be dried using a dryer such as an oven.

[0079] [Step (3) and Step (4)] According to one embodiment of the present disclosure, the method may further include a step (also referred to as "step (3)" in the present disclosure) of heating the melt after separation of the carbon fibers in step (2) to decompose and gasify components derived from the matrix resin dissolved in the melt, and recovering a melt with a reduced content of the components.

[0080] According to one embodiment of the present disclosure, the method may further include a step of recovering the gas gasified in step (3) (also referred to as "step (4)" in the present disclosure).

[0081] When the material composition is immersed in the melt in step (1), typically, at least a portion of the matrix resin decomposes to form low molecular weight compounds. Examples of low molecular weight compounds derived from the matrix resin include phenolic compounds, although they vary depending on the type of matrix resin. The low molecular weight compounds are dissolved in the melt. The low molecular weight compounds may be one type or two or more types.

[0082] The melt containing the matrix resin-derived components is heated to decompose and / or gasify the matrix resin-derived components dissolved in the melt, thereby recovering a melt containing alkali metal compounds with few impurities and reusing it as the melt in step (1). That is, the melt obtained in step (3) can be recycled and used as the melt in step (1). Note that, since the carbon fibers have already been separated and recovered from the melt, the heating in step (3) does not cause deterioration of the carbon fibers.

[0083] Furthermore, gases obtained by decomposing matrix resin-derived components may include usable fuel gases such as hydrogen gas (H) and methane gas (CH), depending on the type of matrix resin. In the decomposition of epoxy resin, hydrogen (H) and methane (CH) are typically produced. Therefore, according to one embodiment of the present disclosure, not only carbon fibers but also fuel gases usable as fuel can be recovered. The above gases may be one type or two or more types.

[0084] The heating temperature of the melt in step (3) is preferably 400°C or higher, more preferably 450°C or higher, even more preferably 500°C or higher, particularly preferably 550°C or higher or 600°C or higher, and is preferably lower than the boiling point of the alkali metal compound, more preferably 1000°C or lower, even more preferably 900°C or lower, particularly preferably 800°C or lower.

[0085] The heating time of the melt in step (3) is appropriately set depending on the heating temperature. The heating time is preferably 10 minutes or more, more preferably 20 minutes or more, and even more preferably 30 minutes or more. If the heating time is equal to or longer than the lower limit, the decomposition and gasification of the matrix resin-derived components can be sufficiently promoted. The upper limit of the heating time is not particularly limited, but is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

[0086] [Process (5)] According to one embodiment of the present disclosure, the method may further include a step of recovering a geopolymer (also referred to as "step (5)" in the present disclosure), which includes a step of mixing the melt after the carbon fiber separation with aluminum silicate. The inclusion of step (5) is particularly advantageous in that it allows not only carbon fibers but also industrially useful geopolymers to be recovered.

[0087] The melt after the carbon fiber separation may be the melt in step (2) or step (3).

[0088] Examples of aluminum silicate include, but are not limited to, kaolin, clay, fly ash, silica fume, and ground granulated blast furnace slag. These may be used alone or in any combination of two or more. The aluminum silicate may be in the form of a powder or a solid. According to one embodiment of the present disclosure, the aluminum silicate includes fly ash.

[0089] Fly ash, also known as coal ash, is the ash remaining after burning coal, and there are no particular limitations on its composition. Coal ash can have any composition. Coal ash usually contains large amounts of calcium aluminate (CaO·Al2O3) and silica (SiO2).

[0090] The amount of aluminum silicate to be mixed is not particularly limited as long as it is an amount that can form a geopolymer. The amount of aluminum silicate may be, for example, 0.1 to 200 parts by mass, preferably 1 to 100 parts by mass, and more preferably 10 to 60 parts by mass, per 100 parts by mass of the melt. The amount of aluminum silicate may be, for example, 0.1 to 500 parts by mass, preferably 1 to 300 parts by mass, and more preferably 10 to 100 parts by mass, per 100 parts by mass of the material composition.

[0091] The conditions (temperature, pressure, time, etc.) for mixing aluminum silicate with the melt can be appropriately adjusted by a person skilled in the art. By mixing aluminum silicate with the melt, a powdery geopolymer is usually obtained.

[0092] The obtained powdered geopolymer may be mixed with water, other ingredients, etc., and heated as necessary to produce a solidified geopolymer.

[0093] [Method for producing recycled carbon fiber] According to another embodiment of the present disclosure, there is provided a method for producing recycled carbon fibers, comprising a step of obtaining carbon fibers as recycled carbon fibers from the material composition using the method for recovering carbon fibers of the present disclosure.

[0094] The recycled carbon fibers produced as described above can be used as they are. Alternatively, the recycled carbon fibers produced as described above may be subjected to a conventionally known sizing treatment to improve the handleability of the fibers. The sizing treatment is, for example, a treatment agent (sizing agent) for bundling carbon fibers applied to the surface of the carbon fibers, and heated as necessary to bond the sizing agent to the carbon fibers. Examples of sizing agents include urethane resins, epoxy resins, polyester resins, and polyamide resins. The amount of sizing agent attached to the recycled carbon fibers is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the recycled carbon fibers.

[0095] In order to improve the adhesion between the carbon fibers and the matrix resin, the recycled carbon fibers may be subjected to a surface treatment in which the carbon fiber surface is oxidized by anodic electrolytic oxidation or ozone oxidation to introduce oxygen-containing functional groups.

[0096] The recycled carbon fiber obtained by the above method can be used, if necessary, in combination with non-recycled carbon fiber (virgin material) or various inorganic or organic fibers such as aramid fiber, nylon fiber, polyester fiber, glass fiber, boron fiber, alumina fiber, and silicon nitride fiber.

[0097] [Method for manufacturing carbon fiber reinforced resin] According to another embodiment of the present disclosure, a method for producing recycled carbon fibers according to the present disclosure, A step of producing a carbon fiber reinforced resin using the recycled carbon fiber and resin. A method for producing a carbon fiber reinforced resin is provided, comprising:

[0098] Examples of methods for producing carbon fiber reinforced resin using recycled carbon fibers include, but are not limited to, the methods exemplified below.

[0099] Examples of methods for producing pellets include a method in which carbon fibers such as fiber bundles (filaments or tows) in which multiple single fibers are aligned in one direction, chopped yarns in which fiber bundles are cut to any length, and milled fibers in which the fiber bundles are cut even finer than chopped yarns are impregnated with a resin that forms a matrix resin to form a composite.

[0100] Examples of resin impregnation methods include methods using a single-screw extruder, a twin-screw extruder, a press, a high-speed mixer, or an injection molding machine. When forming the composite, additives may be used together with the resin, if necessary. Examples of additives include antioxidants, heat stabilizers, weathering agents, mold release agents, lubricants, pigments, dyes, plasticizers, antistatic agents, and flame retardants.

[0101] Resins used to produce carbon fiber reinforced resins include, for example, the thermosetting resins and thermoplastic resins described in the above (Matrix Resin) section, with thermosetting resins being preferred, epoxy resins and phenolic resins being more preferred, and epoxy resins being even more preferred.

[0102] The carbon fiber reinforced resin obtained by the above method may be in the form of an intermediate material such as pellets, prepregs and laminates thereof, stampable sheets and laminates thereof, or may be in the form of a product. In the case of a product, the entire product may be carbon fiber reinforced resin, or only a portion of the product may be carbon fiber reinforced resin. For example, it may be a composite of carbon fiber reinforced resin and other components. Examples of other components include fiber reinforced resins containing reinforcing fibers other than carbon fiber, resin molded products containing no reinforcing fibers, metals, and ceramics.

[0103] Carbon fiber reinforced resin products can be obtained, for example, by molding the pellets using methods such as injection molding, extrusion molding, press molding, blow molding, compression molding, injection compression molding, and foam injection molding.

[0104] Examples of methods for producing a prepreg include a method in which a thermosetting resin is applied onto a release sheet to prepare a resin film, and then the resin film and a carbon fiber substrate are overlapped and heated and pressurized to impregnate the carbon fiber substrate with the semi-cured thermosetting resin; a method in which a thermosetting resin is heated to reduce its viscosity, and then the carbon fiber substrate is impregnated with the resin; and a method in which a thermosetting resin is dissolved in a solvent to obtain a resin solution, and the carbon fiber substrate is immersed in the solution, then pulled out, and the solvent is evaporated using an oven or the like.

[0105] Carbon fiber reinforced resin products can be obtained by, for example, the autoclave method, hand layup method, filament winding method, sheet winding method, pultrusion molding method, resin transfer molding method, or sheet molding compound press molding method.

[0106] For example, a carbon fiber reinforced resin product can be obtained by, for example, heating and pressurizing a prepreg, or by laminating multiple prepregs and then heating and pressurizing them to sufficiently cure a semi-cured thermosetting resin.

[0107] [Melt composition] According to another embodiment of the present disclosure, there is provided a melt composition for recovering carbon fibers, the melt composition comprising a melt containing an alkali metal compound, carbon fibers, a component derived from the matrix resin contained in the carbon fiber reinforced resin (a component derived from the matrix resin) dissolved in the melt, and a component derived from the glass fiber reinforced resin. The melt composition may be obtained, for example, by immersing the material composition in a melt containing an alkali metal compound. Carbon fibers can be recovered by separating the carbon fibers from the melt composition. Details of each of these components, the conditions for the immersion treatment, and the method for separating the carbon fibers are as described above. The melt composition may be cooled to form a solid.

[0108] Examples of components derived from glass fiber reinforced resin include components derived from the matrix resin contained in the glass fiber reinforced resin (components derived from the matrix resin), glass fibers, other substances, and the like.

[0109] In the melt composition, the amount of the alkali metal compound is, for example, 10 parts by mass or more, preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 200 parts by mass or more, still more preferably 300 parts by mass or more, and particularly preferably 500 parts by mass or more, relative to 100 parts by mass of the material composition to be immersed. There is no particular upper limit on the amount of the alkali metal compound, but from the viewpoint of cost, the amount of the alkali metal compound is, for example, 10,000 parts by mass or less, preferably 5,000 parts by mass or less, more preferably 4,000 parts by mass or less, and even more preferably 3,000 parts by mass or less, relative to 100 parts by mass of the material composition to be immersed.

[0110] For example, by heating the melt composition or a solidified product thereof at an appropriate temperature, the matrix resin-derived components can be decomposed and / or gasified and removed. The heating conditions may be the same as those used in fuel gas recovery from the composition for fuel gas recovery described below. This results in a melt composition containing an alkali metal compound with little impurities (e.g., matrix resin). The melt composition may be cooled to form a solidified product. The resulting melt composition can be used as a melt containing an alkali metal compound in the method of the present disclosure.

[0111] The definitions of each term, preferred embodiments, etc. are as described above in this specification.

[0112] [Fuel gas recovery composition] According to another embodiment of the present disclosure, there is provided a composition for fuel gas recovery obtained by separating carbon fibers from the melt composition or a solidified product thereof. The composition for fuel gas recovery may be in a molten state or a solid state. For example, the melt composition after carbon fiber separation may be cooled to obtain a solidified composition for fuel gas recovery. Details of the carbon fiber separation method and the like are as described above.

[0113] By heating the fuel gas recovery composition at an appropriate temperature, the matrix resin-derived components contained in the fuel gas recovery composition are decomposed and / or gasified to produce fuel gases such as hydrogen gas (H2) and methane gas (CH4).

[0114] The heating temperature of the fuel gas recovery composition during fuel gas recovery is preferably 400°C or higher, more preferably 450°C or higher, even more preferably 500°C or higher, particularly preferably 550°C or higher or 600°C or higher, and is preferably below the boiling point of the alkali metal compound, more preferably 1000°C or lower, even more preferably 900°C or lower, particularly preferably 800°C or lower.

[0115] The heating time of the composition for fuel gas recovery during fuel gas recovery is appropriately set depending on the heating temperature. The heating time is preferably 10 minutes or more, more preferably 20 minutes or more, and even more preferably 30 minutes or more. The upper limit of the heating time is not particularly limited, but is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 2 hours or less.

[0116] The definitions of each term, preferred embodiments, etc. are as described above in this specification.

[0117] [Geopolymer manufacturing composition] According to another embodiment of the present disclosure, a geopolymer production composition is provided, which is obtained by separating carbon fibers from the molten composition or a solidified product thereof. The geopolymer production composition may be in a molten state or a solid state. For example, the molten composition after carbon fiber separation may be cooled to obtain a solidified geopolymer production composition. Details of the carbon fiber separation method are as described above.

[0118] A powdered geopolymer can be obtained by mixing the geopolymer production composition with aluminum silicate. The amounts of the geopolymer production composition and aluminum silicate are not particularly limited. For example, the amount of aluminum silicate may be 0.1 to 200 parts by mass, preferably 1 to 100 parts by mass, and more preferably 10 to 60 parts by mass per 100 parts by mass of the geopolymer production composition.

[0119] In addition, the powdered geopolymer can be mixed with water, other components, etc., and heated as necessary to produce a solidified geopolymer.

[0120] [Geopolymer manufacturing method] According to another embodiment of the present disclosure, (1) preparing a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin, the material composition containing carbon fibers and a matrix resin, which is immersed in a melt containing an alkali metal compound; (2) separating the carbon fibers from the melt; and (5) A step of mixing the melt after separating the carbon fibers with aluminum silicate. A method for producing a geopolymer is provided, comprising:

[0121] The definitions of each term, preferred embodiments, etc. in this embodiment are as described above in this specification.

[0122] The present disclosure encompasses the following. [1] (1) A step of preparing a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin, the material composition containing carbon fiber and a matrix resin, immersed in a melt containing an alkali metal compound; (2) Separating the carbon fibers from the melt a method for recovering carbon fibers from the material composition, comprising: [2] The method according to [1], wherein the step (1) includes a step of immersing the material composition in the melt. [3] The recovery method according to [1] or [2], wherein the temperature of the melt in step (1) is higher than 200°C. [4] The recovery method according to any one of [1] to [3], wherein the temperature of the melt in the step (1) is 600° C. or lower. [5] The method according to any one of [1] to [4], wherein the temperature of the melt in step (1) is higher than 200°C and not higher than 300°C. [6] The method according to any one of [1] to [5], wherein the viscosity of the melt in step (1) is 50 mPa·s or less. [7] The method according to any one of [1] to [6], wherein the alkali metal compound comprises a hydroxide of an alkali metal. [8] The method according to any one of [1] to [7], wherein the alkali metal compound comprises potassium hydroxide or sodium hydroxide. [9] The method according to any one of [1] to [8], wherein the alkali metal compound comprises potassium hydroxide.

[10] The method according to [9], wherein the amount of potassium hydroxide contained in the alkali metal compound is 45 mass % or more based on the total mass of the alkali metal compound.

[11] The method according to [9] or

[10] , wherein the amount of potassium hydroxide contained in the alkali metal compound is 72.5 mass % or more based on the total mass of the alkali metal compound.

[12] (3) A step of heating the melt after the separation of the carbon fibers to decompose and gasify components derived from the matrix resin dissolved in the melt, and recovering a melt having a reduced content of the components. The method according to any one of [1] to

[11] , further comprising:

[13] (4) A step of recovering the gas gasified in the above step (3). The method according to

[12] , further comprising:

[14] (5) A step of recovering a geopolymer, which includes a step of mixing the melt after the carbon fiber separation with aluminum silicate. The method according to any one of [1] to

[13] , further comprising:

[15] A process for obtaining recycled carbon fibers from a material composition containing a carbon fiber reinforced resin containing carbon fibers and a matrix resin and a glass fiber reinforced resin, using the method according to any one of [1] to

[14] . A method for producing recycled carbon fiber, comprising:

[16]

[15] A process for producing recycled carbon fibers by the method described in

[16]

[15] ; and A step of producing a carbon fiber reinforced resin using the recycled carbon fiber and resin. A method for producing a carbon fiber reinforced resin, comprising:

[17] A melt composition for recovering carbon fibers, or a solidified product thereof, comprising: a melt containing an alkali metal compound; carbon fibers; a component derived from a matrix resin contained in a carbon fiber reinforced resin dissolved in the melt; and a component derived from a glass fiber reinforced resin dissolved in the melt.

[18] A composition for fuel gas recovery obtained by separating the carbon fibers from the melt composition according to

[17] or a solidified product thereof.

[19] A composition for producing a geopolymer obtained by separating the carbon fiber from the molten composition or its solidified product according to

[17] . [Example]

[0123] The method of the present disclosure will be described in more detail below using examples. However, the following examples are not intended to limit the method of the present disclosure in any way. Unless otherwise specified, percentages and ratios described herein are by mass. Furthermore, unless otherwise specified, units and measurement methods described herein are in accordance with the provisions of the Japanese Industrial Standards (JIS).

[0124] [Test piece manufacturing] (Test piece 1) Test piece 1 was a sample made by combining 1 part by mass of domestically produced glass fiber reinforced resin waste (glass fiber: 33% by mass, matrix resin: 32% by mass, filler (mainly calcium carbonate): 35% by mass), 9 parts by mass of carbon fiber reinforced resin waste (carbon fiber: 75% by mass, matrix resin consisting of epoxy resin: 25% by mass), and 1 part by mass of aluminum.

[0125] (Test piece 2) A part of the waste material of a high-pressure hydrogen tank was shredded (a material composition containing glass fiber reinforced resin and carbon fiber reinforced resin) to prepare test piece 3.

[0126] [Production of salts containing alkali metal compounds] Potassium hydroxide (KOH, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 85% or higher) and sodium hydroxide (NaOH, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 97% or higher) were mixed in a mass ratio of 3:1, 1:1, or 1:3 (i.e., about 0.3 parts by mass, about 1 part by mass, or about 3 parts by mass of sodium hydroxide per 1 part by mass of potassium hydroxide), heated at 400°C for 1 hour, and then allowed to cool, to obtain a mixed salt. Similarly, potassium hydroxide alone or sodium hydroxide alone was heated at 400°C for 1 hour and then allowed to cool, to produce a salt mixture. Assuming that the purities of the potassium hydroxide and sodium hydroxide used are 85% and 97%, respectively, the converted mass ratios for 3:1, 1:1, and 1:3 are approximately 2.6:1, approximately 1:1.2, and approximately 1:3.4, respectively (i.e., approximately 0.4 parts by mass, approximately 1.2 parts by mass, and approximately 3.4 parts by mass of sodium hydroxide per 1 part by mass of potassium hydroxide). Furthermore, the amount of potassium hydroxide contained in the mixed salt is 72.2 mass%, 45.6 mass%, and 23.2 mass%, based on the total mass of the mixed salt, when the mass ratios are 3:1, 1:1, and 1:3, respectively (calculated based on the converted masses assuming that the purities of the potassium hydroxide and sodium hydroxide used are 85% and 97%, respectively). The mass ratio of potassium hydroxide to sodium hydroxide described below indicates the ratio before conversion.

[0127] The viscosity of the obtained alkali metal salt was measured at each temperature (apparatus: DV-1, manufactured by Brookfield / pressure: atmospheric pressure). The results are shown in Table 1 below.

[0128] [Table 1]

[0129] [Example 1: Carbon fiber recovery 1-1] 2.2 g of test piece 1 and 60 g of the salt containing the alkali metal compound prepared above (potassium hydroxide and sodium hydroxide in a 1:1 mass ratio) were placed in a stainless steel container and heated at 300°C for 1 hour under a nitrogen atmosphere. In this method, the salt was in a molten state, so test piece 1 was immersed in the solution. The gas generated during heating was collected in a gas pack and analyzed using a gas chromatograph (apparatus: GC-8A, manufactured by Shimadzu Corporation; column oven: approximately 400°C; detector: thermal conductivity detector; column: SHINCARBON ST (50 / 80 mesh) stainless steel column, 6 m, manufactured by Shinwa Chemical Industry Co., Ltd.; column temperature: 150°C; carrier gas: argon (50 mL / min)). The results are shown in Figure 1. After cooling, 300 mL of 8 M nitric acid was added to the container to dissolve the salt, obtaining a solution. The resulting solution was filtered to recover a residue containing carbon fibers and the remaining liquid. The residue was dried and its mass was measured. The amounts of silicon and calcium contained in the resulting residual liquid were measured using an inductively coupled plasma analyzer (apparatus: Avio 500, PerkinElmer) under the conditions shown in Table 2. The amount of aluminum contained in the resulting residual liquid was measured using an atomic absorption analyzer (apparatus: A Analyst 200, PerkinElmer) under the conditions shown in Table 3. The residual percentage of the residue was calculated based on the mass of test piece 1 before the test began. In addition, the proportions of silicon, calcium, and aluminum remaining in the residue were calculated from the amounts of silicon, calcium, and aluminum contained in the residual liquid. The results are shown in Figure 2. The tensile strength of the recovered residue was measured using a strength tester (ZTA-500N, Imada Co., Ltd.). The strength tester was attached to an electric test stand (MX2-500N, Imada Co., Ltd.), and the test speed and direction were uniform. A bundle (carbon fiber bundle) was made from the recovered carbon fibers, and the mass of the carbon fiber bundle was measured. Both ends of the carbon fiber bundle were solidified with adhesive and fixed to a mount. The carbon fiber bundle was then fixed to the strength tester via the mount, and a tensile test was performed at a test speed of 50 mm / min, and the tensile strength at the time the carbon fiber bundle broke was measured. The results are shown in Table 4.

[0130] [Table 2]

[0131] [Table 3]

[0132] [Example 2: Carbon fiber recovery 1-2] A similar method to Example 1 was carried out, except that the salt containing an alkali metal compound was a mixture of potassium hydroxide and sodium hydroxide in a mass ratio of 3:1. In this method, the salt was in a molten state, and therefore test piece 1 was immersed in the solution. The results are shown in Figures 1 and 2 and Table 4.

[0133] [Example 3: Carbon fiber recovery 1-3] A similar method to Example 1 was carried out, except that the salt containing an alkali metal compound was a mixture of potassium hydroxide and sodium hydroxide in a mass ratio of 1:0. In this method, the salt was in a molten state, and therefore test piece 1 was immersed in the solution. The results are shown in Figures 1 and 2 and Table 4.

[0134] [Table 4]

[0135] [Example 4: Carbon fiber recovery 1-4] A similar method to Example 1 was carried out, except that a mass ratio of potassium hydroxide to sodium hydroxide of 1:3 was used as the salt containing an alkali metal compound. In this method, the salt was in a molten state, so the test piece 1 was immersed. Although a residue (carbon fiber) with reduced glass fiber contamination could be recovered, the amount of glass fiber contamination in the residue was slightly higher than in Examples 1 to 3.

[0136] [Example 5: Carbon fiber recovery 1-5] A similar method to Example 1 was carried out, except that a mass ratio of potassium hydroxide to sodium hydroxide of 0:1 was used as the salt containing an alkali metal compound. In this method, the salt was in a molten state, and therefore test piece 1 was immersed in it. Although a residue (carbon fiber) with reduced glass fiber contamination could be recovered, the amount of glass fiber contamination in the residue was slightly higher than in Examples 1 to 3.

[0137] [Examples 6 to 8: Carbon fiber recovery 2-1] The same method as in Example 1 was carried out, except that heating was carried out at 400°C, 500°C, and 600°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. As in Example 1, a residue (carbon fiber) with reduced glass fiber contamination could be recovered.

[0138] [Examples 9-11: Carbon fiber recovery 2-2] The same method as in Example 2 was carried out, except that heating was carried out at 400°C, 500°C, and 600°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. As in Example 2, a residue (carbon fiber) with reduced glass fiber contamination could be recovered.

[0139] [Examples 12 to 14: Carbon fiber recovery 2-3] The same method as in Example 3 was carried out, except that heating was carried out at 400°C, 500°C, and 600°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. As in Example 3, a residue (carbon fiber) with reduced glass fiber contamination could be recovered.

[0140] [Examples 15 to 17: Carbon fiber recovery 2-4] The same method as in Example 4 was carried out, except that heating was carried out at 400°C, 500°C, and 600°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. As in Examples 1 to 3, a residue (carbon fiber) with reduced glass fiber contamination could be recovered.

[0141] [Examples 18-20: Carbon fiber recovery 2-5] The same method as in Example 5 was carried out, except that heating was carried out at 400°C, 500°C, and 600°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. As in Examples 1 to 3, a residue (carbon fiber) with reduced glass fiber contamination could be recovered.

[0142] [Example 21: Carbon fiber recovery 3-1] The same method as in Example 1 was carried out, except that heating was performed at 200°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. Although a residue (carbon fiber) with reduced glass fiber contamination could be recovered, the amount of glass fiber remaining in the residue was greater than in Examples 1 to 3.

[0143] [Example 22: Carbon fiber recovery 3-2] The same method as in Example 2 was carried out, except that heating was performed at 200°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. Although a residue (carbon fiber) with reduced glass fiber contamination could be recovered, the amount of glass fiber remaining in the residue was greater than in Examples 1 to 3.

[0144] [Example 23: Carbon fiber recovery 3-3] The same method as in Example 3 was carried out, except that heating was performed at 200°C instead of 300°C. In this method, the salt was in a molten state, so the test piece 1 was immersed. Although a residue (carbon fiber) with reduced glass fiber contamination could be recovered, the amount of glass fiber remaining in the residue was greater than in Examples 1 to 3.

[0145] [Reference Example 1: Carbon fiber recovery 3-4] The same method as in Example 4 was carried out, except that heating was performed at 200°C instead of 300°C. In this method, the salt was in a solid state, so Test Piece 1 was not immersed. Little or no glass fibers in the residue could be removed.

[0146] [Reference Example 2: Carbon fiber recovery 3-5] The same method as in Example 5 was carried out, except that heating was performed at 200°C instead of 300°C. In this method, the salt was in a solid state, so the test piece 1 was not immersed. Little or no glass fibers in the residue could be removed.

[0147] [Comparative Examples 1 to 4: Recovery of Carbon Fiber 4] Test piece 1 was heated in an electric furnace in an air atmosphere under atmospheric pressure at 300°C, 400°C, 500°C or 600°C for 60 minutes. Under all conditions, little or no glass fibers could be removed from the residue.

[0148] [Example 24: Carbon fiber recovery 5] 600 g of the alkali metal salt (mass ratio of potassium hydroxide to sodium hydroxide: 1:0) prepared above was placed in a stainless steel container and heated under a nitrogen atmosphere. After the temperature reached 300°C (the alkali metal salt was in a molten state), 70 g of test piece 2 was immersed in the molten alkali metal salt and heated at 300°C for 30 minutes. The residue was collected and washed with nitric acid and water. The collected residue (carbon fiber) is shown in Figure 3. The mass of the dried residue was measured to be 50.23 g. After cooling, water was added to the molten salt to dissolve it, and the amount of silicon contained in the solution was measured in the same manner as in Example 1, and was found to be 102.8 mg.

[0149] [Example 25: Production of geopolymer from melt] 300 g of the salt containing the alkali metal compound produced above (mass ratio of potassium hydroxide to sodium hydroxide: 1:0) was placed in a silicon carbide container and heated to 300°C (molten state) under a nitrogen atmosphere. 2.2 g of test piece 1 was placed therein and heated at 300°C for 30 minutes. The residue (carbon fiber) was removed, and 10 g of fly ash was added to the remaining liquid (molten state) to obtain a powder. 3 g of this powder was mixed with 2.4 g of water and heated at 80°C for 24 hours to obtain a geopolymer (solidified body). The results are shown in Figure 4.

[0150] From the results of Examples 1 to 23, it is believed that by immersing a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin in a melt containing an alkali metal compound, it is possible to recover a residue (carbon fiber) from which some or substantially all of the glass fibers have been removed.From the results of Examples 1 to 23, it is believed that by setting the temperature of the melt containing the alkali metal compound to above 200°C, it is possible to more efficiently suppress the inclusion of glass fibers.

[0151] The results of Examples 1 to 3 show that the method of the present disclosure is advantageous in that it is possible to recover industrially useful fuel gases such as hydrogen and / or methane (FIG. 1).

[0152] The results of Examples 1 to 3 show that a residue with a residual rate of approximately 60 to 80% was obtained (Figure 2). Since the amount of carbon fiber based on the total mass of the test piece 1 used was approximately 60 to 65 mass%, it is believed that almost all of the carbon fiber contained in the test piece 1 was recovered. Furthermore, while test piece 1 is believed to contain approximately 30 mg of elemental silicon, the residual liquid obtained in Examples 1 to 3 contained 22.3 to 34.2 mg of elemental silicon, which suggests that most of the elemental silicon contained in the test piece 1 was removed (Table 4, Figure 2). Furthermore, when the mass ratio of potassium hydroxide to sodium hydroxide is more than 3:1 (preferably 1:0), it is particularly advantageous in that the inclusion of aluminum and other substances (calcium carbonate, etc.) in the carbon fibers can be more efficiently suppressed (FIG. 2).Further investigations by the present inventors have revealed that by immersing a glass fiber reinforced resin in a molten liquid containing an alkali metal compound at a temperature above 200°C (preferably 300°C or higher), it is possible to remove most (preferably substantially all) of the silicon dioxide and calcium carbonate contained in the glass fiber reinforced resin.

[0153] The results of Examples 1 to 3 show that the recovered carbon fibers had good tensile strength.

[0154] Without being bound by theory, when the viscosity of the alkali metal salt melt is low (for example, 50 mPa·s or less, preferably 30 mPa·s or less, more preferably 10 mPa·s or less), the amount of melt adhering to or remaining on the recovered residue is reduced, which is advantageous in that post-treatment of the residue (for example, washing, etc.) can be facilitated.

[0155] Furthermore, the results of Example 25 show that geopolymer could be produced from the melt after carbon fiber recovery.

[0156] In conventional techniques (e.g., the method described in Patent Document 1), carbon fiber reinforced resin is separated from a material composition to prevent glass fiber from being mixed into the recovered carbon fiber. On the other hand, one embodiment of the present disclosure is advantageous in that a method for recovering carbon fibers from a material composition containing carbon fiber reinforced resin and glass fiber reinforced resin does not require separation or isolation of the carbon fiber reinforced resin from the material composition. Another embodiment of the present disclosure is advantageous in that it enables simultaneous removal of carbon fiber reinforced resin-derived components and glass fiber reinforced resin-derived components from the material composition. One embodiment of the present disclosure is advantageous in that it can contribute to improved operational efficiency, reduced costs, and / or energy savings when recovering large amounts of carbon fiber industrially, compared to conventional techniques.

[0157] JP 2023-177341 A discloses a technique for recovering carbon fibers by immersing a carbon fiber reinforced resin in a melt containing an alkali metal compound. However, JP 2023-177341 A does not state or suggest that glass fibers can be removed from a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin. As described above, it was common technical knowledge that in order to prevent glass fibers from being mixed into the carbon fibers separated from the material composition, it was necessary to separate (e.g., physically separate) the carbon fiber reinforced resin from the material composition. According to one embodiment of the present disclosure, it is possible to suppress the incorporation of glass fibers into carbon fibers without the need to separate the carbon fiber reinforced resin from the material composition, which is a completely unexpected fact, given the invention described in JP 2023-177341 A. Furthermore, according to a preferred embodiment of the present disclosure, even if the material composition contains optional components (e.g., metals such as aluminum), it is possible to suppress the incorporation of optional components into carbon fibers without the need to separate these optional components, which is a completely unexpected fact, given the invention described in JP 2023-177341 A. According to a further preferred embodiment of the present disclosure, the carbon fiber reinforced resin, glass fiber reinforced resin, and optional components (e.g., metals such as aluminum) contained in the material composition can be processed simultaneously, and therefore, it is possible to simultaneously recycle the carbon fiber reinforced resin, glass fiber reinforced resin, and optional components (e.g., metals such as aluminum). This is a completely unexpected fact, given the invention described in JP 2023-177341 A.

Claims

1. (1) preparing a material composition containing a carbon fiber reinforced resin and a glass fiber reinforced resin, the material composition containing carbon fiber and a matrix resin, immersed in a melt containing an alkali metal compound; and (2) A step of separating the carbon fibers from the melt a method for recovering carbon fibers from the material composition, comprising:

2. The method of claim 1 , wherein step (1) comprises immersing the material composition in the melt.

3. The recovery method according to claim 1, wherein the temperature of the melt in step (1) is greater than 200°C.

4. 2. The method according to claim 1, wherein the temperature of the melt in step (1) is 600°C or less.

5. 2. The method according to claim 1, wherein the temperature of the melt in step (1) is greater than 200°C and less than or equal to 300°C.

6. 2. The method according to claim 1, wherein the viscosity of the melt in step (1) is 50 mPa·s or less.

7. The method of claim 1 , wherein the alkali metal compound comprises an alkali metal hydroxide.

8. The method of claim 1 , wherein the alkali metal compound comprises potassium hydroxide or sodium hydroxide.

9. The method of claim 1 , wherein the alkali metal compound comprises potassium hydroxide.

10. 10. The method according to claim 9, wherein the amount of potassium hydroxide contained in the alkali metal compound is 45% by mass or more based on the total mass of the alkali metal compound.

11. 10. The method according to claim 9, wherein the amount of potassium hydroxide contained in the alkali metal compound is 72.5% by mass or more based on the total mass of the alkali metal compound.

12. (3) A step of heating the melt after the separation of the carbon fibers to decompose and gasify components derived from the matrix resin dissolved in the melt, and recovering a melt with a reduced content of the components. The method of claim 1 further comprising:

13. (4) A step of recovering the gas gasified in the step (3). The method of claim 12 further comprising:

14. (5) A step of recovering a geopolymer including a step of mixing the melt after the carbon fiber separation with aluminum silicate. The method of claim 1 further comprising:

15. A process for obtaining recycled carbon fibers from a material composition containing a carbon fiber reinforced resin containing carbon fibers and a matrix resin and a glass fiber reinforced resin, using the method according to any one of claims 1 to 14. A method for producing recycled carbon fiber, comprising:

16. Producing recycled carbon fibers by the method of claim 15; and A step of producing a carbon fiber reinforced resin using the recycled carbon fiber and a resin. A method for producing a carbon fiber reinforced resin, comprising:

17. A melt composition for recovering carbon fibers, or a solidified product thereof, comprising: a melt containing an alkali metal compound; carbon fibers; a component derived from a matrix resin contained in a carbon fiber reinforced resin dissolved in the melt; and a component derived from a glass fiber reinforced resin dissolved in the melt.

18. A composition for fuel gas recovery, obtained by separating the carbon fibers from the melt composition according to claim 17 or a solidified product thereof.

19. A geopolymer production composition obtained by separating the carbon fiber from the molten composition according to claim 17 or a solidified product thereof.

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