Mixture separation method

Abstract

Provided is a mixture separation method or the like that is excellent in productivity and economic efficiency and that easily separates at least one component A selected from the group consisting of polyesters and protein fibers and at least one component B selected from the group consisting of polyurethanes, nylons, and acrylic fibers, from a mixture that contains the component A and the component B. A mixture separation method according to the present disclosure at least includes: a step for impregnating, at temperature below 50°C and with an acid treatment liquid, a mixture that includes at least one component A selected from the group consisting of polyesters and protein fibers and at least one component B selected from the group consisting of polyurethanes, nylons, and acrylic fibers, to thereby acquire an impregnation-treated mixture including a solid-state component A and a liquid-state component B; and a step for separating the solid-state component A and the liquid-state component B from the impregnation-treated mixture. The acid treatment liquid is an aqueous solution containing at least one selected from the group consisting of sulfuric acid, phosphoric acid, and polyphosphoric acid. The amount of water contained in the aqueous solution is 20 mass% or less.

Description

Method for separating mixtures

[0001] The present invention relates to a method for separating a mixture, in which a predetermined component is separated from the mixture under relatively low-temperature treatment conditions of less than 50°C.

[0002] Due to its excellent properties, polyester (e.g., polyethylene terephthalate (PET)) has traditionally been widely used as fibers, films, clothing, resins, and the like. Due to the large amount of polyester used, the development of recycling technologies has been actively considered in recent years. In particular, chemical recycling, in which polyester is recycled under basic conditions to a polyester monomer (e.g., bis(2-hydroxyethyl) terephthalate, dimethyl terephthalate, etc.) and then polycondensed again to produce recycled polyester, is known as a method for obtaining high-quality recycled polyester, and its application to recycled fibers, recycled bottles, recycled films, recycled containers, recycled rags, recycled automotive interior materials, and the like, is being considered.

[0003] To obtain high-quality recycled polyester through chemical recycling using discarded clothing as a raw material, it is necessary to sort and separate various additives such as coloring pigments, dyes, stabilizers, and antistatic agents, as well as other materials such as nylon, polyurethane, protein fibers, cotton, and polyolefins, and other components from the various recovered products. Low-molecular-weight components such as coloring pigments can be removed using cleaning solutions or solvent washing, while non-hydrolyzable other materials such as cotton can be removed as solids by filtration or the like when the polyester is depolymerized to regenerate liquid polyester monomers (see Patent Documents 1 to 3).

[0004] In this specification, the polyester monomer refers to a dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid obtained by alcoholysis or hydrolysis of polyester, or an ester thereof.

[0005] JP 2004-300115 A JP 2007-045874 A JP 2020-176258 A

[0006] However, if recycled materials containing polyester contain hydrolyzable nitrogen-containing resins such as nylon or polyurethane, the resins can be reduced in molecular weight during the polyester monomer recycling process, making separation from the polyester monomer difficult and causing quality degradation such as discoloration, making it difficult to obtain high-quality recycled polyester. To avoid this, it is necessary to pre-sort and separate the hydrolyzable nitrogen-containing resins from recycled materials containing polyester before chemical recycling. Conventionally, such sorting and separation have been performed physically by hand, which requires considerable effort and cost, and improvements have been sought.

[0007] Moreover, in recent years, an increasing number of products have been produced in which polyester and hydrolyzable nitrogen-containing resins are composited in a form that makes physical sorting and separation difficult. Examples of such composites include blended yarns of polyester and polyurethane, and laminated films of a PET layer and a gas-barrier nylon layer. Therefore, there is a need for an industrially simple method for removing hydrolyzable nitrogen-containing resins contaminated in mixtures containing polyester. In particular, there is a strong need for a method for removing hydrolyzable nitrogen-containing resins that have a significant impact on the coloration of recycled polyester.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for separating a mixture, which can industrially and easily separate component A and component B from a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers, and which is excellent in productivity and economy.

[0009] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by acidifying a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers, with a predetermined acidic treatment solution, and have thus completed the present invention. That is, the present invention provides various specific embodiments as shown below.

[0010] <1> A method for separating a mixture, the method comprising at least the steps of: impregnating a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers, with an acidic treatment liquid at a temperature lower than 50°C to obtain an impregnation treatment mixture containing the solid component A and the liquid component B; and separating the solid component A and the liquid component B from the impregnation treatment mixture, wherein the acidic treatment liquid is an aqueous solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, and polyphosphoric acid, and the aqueous solution contains 20 mass% or less of water.

[0011] <2> The method for separating a mixture according to <1>, wherein the acidic treatment liquid contains at least one selected from the group consisting of phosphoric acid and polyphosphoric acid.

[0012] <3> The method for separating a mixture according to <1> or <2>, wherein the mixture contains 20 parts by mass or more and 99 parts by mass or less of the component A and 1 part by mass or more and 40 parts by mass or less of the component B, relative to 100 parts by mass of the mixture.

[0013] <4> The method for separating a mixture according to any one of <1> to <3>, further comprising the step of adding a liquid component to the liquid component B separated from the solid component A, and solidifying and recovering at least one of the components B.

[0014] <5> The method for separating a mixture according to <4>, wherein the liquid component contains one or more selected from the group consisting of water, methanol, ethanol, propanol, isopropyl alcohol, and ethylene glycol.

[0015] <6> The method for separating a mixture according to any one of <1> to <5>, wherein the component A is contained in one or more selected from the group consisting of fibers, fiber-reinforced resins, bottles, containers, films, and multilayer films, and the component B is contained in one or more selected from the group consisting of fibers, fiber-reinforced resins, bottles, containers, films, and multilayer films.

[0016] <7> The method for separating a mixture according to any one of <1> to <6>, further comprising a step of washing the component A obtained by separating the liquid component B with one or more selected from the group consisting of the acidic treatment liquid, methanol, ethanol, propanol, isopropyl alcohol, ethylene glycol, and water.

[0017] According to the present invention, it is possible to easily separate components A and B industrially from a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers under relatively low-temperature treatment conditions of less than 50°C, thereby improving productivity and economic efficiency and, as a result, enabling the production of high-quality recycled polyester.

[0018] FIG. 1 is a flow chart illustrating a method for separating a mixture according to one embodiment.

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited to these. In other words, the present invention can be implemented with any modifications within the scope of the gist of the present invention. In this specification, for example, when a numerical range is expressed as "1 to 100," it is intended to include both the lower limit "1" and the upper limit "100." The same applies to other numerical ranges.

[0020] [Polyester Recovery Method] Figure 1 is a flowchart showing a mixture separation method and a polyester chemical recycling method according to this embodiment. The mixture separation method according to this embodiment includes at least a step (S12) of impregnating a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers, with an acidic treatment solution at less than 50°C to obtain an impregnation treatment mixture containing the solid component A and the liquid component B, and a step (S13) of separating the solid component A and the liquid component B from the impregnation treatment mixture. The polyester chemical recycling method according to this embodiment also includes a step (S21) of depolymerizing the polyester of component A obtained by the mixture separation method according to this embodiment. Each step is described in detail below.

[0021] <Step (S12) of Preparing Impregnation Mixture> In step S12, a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers, is impregnated with an acidic treatment solution at less than 50°C to obtain an impregnation mixture containing solid component A and liquid component B. The mixture introduced into the acidic treatment solution may take various forms. Examples include, but are not limited to, fibers, fiber-reinforced resins, bottles, containers, films, and multilayer films. The mixture introduced into the acidic treatment solution may be any combination and ratio of two or more types selected from these forms.

[0022] The polyester of component A refers to one having an ester bond formed by dehydration condensation of a polycarboxylic acid and a polyol; an ester bond formed by dehydration condensation of a hydroxycarboxylic acid; an ester bond formed by dehydration condensation of a combination of these; or an ester exchange reaction of a polycarboxylic acid. Specific examples of polyesters include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), glycol-modified polyethylene terephthalate (PETG), polyethylene succinate (PES), polybutylene succinate (PBS), polylactic acid, polyglycolic acid, polycaprolactone, and polyhydroxyalkanoate, but are not particularly limited thereto. These may be used alone or in any combination and ratio of two or more.

[0023] The protein fiber of component A refers to a naturally-derived or artificial protein fiber, which is a fiber primarily composed of protein. Specific examples of protein fibers include, but are not limited to, sheep's wool, goat's hair (mohair, cashmere, angora, and corn), alpaca, camel, horse, and rabbit hair, and artificial protein fibers. These may be used alone or in any combination and ratio of two or more.

[0024] Component A includes one or more types selected from the group consisting of polyester and protein fiber. Component A may be only one of these, or a combination of two or more selected from these. In one aspect, component A preferably contains either polyester or protein fiber as an essential component. In another aspect, component A preferably contains polyester and protein fiber as an essential component. It is more preferable that component A contains polyester as an essential component. In recent years, there has been an increase in products that use composite materials containing polyester (e.g., blended fibers, etc.), and the method of this embodiment has extremely high industrial utility value in that it can easily separate polyester from such composite materials.

[0025] Furthermore, component B includes one or more selected from the group consisting of polyurethane, nylon, and acrylic fiber. Component B may be only one of these, a combination of two or more selected from these, or three of polyurethane, nylon, and acrylic fiber. In one aspect, component B preferably contains either polyurethane or nylon as an essential component. In another aspect, component B preferably contains polyurethane and nylon as an essential component, and preferably contains polyurethane as an essential component. In recent years, an increasing number of products have been made using composite materials (e.g., blended fibers) containing polyester and polyurethane. The method of this embodiment has great industrial utility value in that it can easily separate polyester and polyurethane from such composite materials. In this case, nylon or acrylic fiber may or may not be further included.

[0026] The polyurethane of component B is a polyurethane obtained by polyaddition of polyisocyanates and polyols, and examples thereof include polyurethane elastic fibers (spandex, elastane), but are not limited thereto. The polyurethane may contain additives such as a chain extender, a light stabilizer, and an antioxidant. These may be used alone or in any combination and ratio of two or more.

[0027] Examples of nylons for component B include nylon 6, nylon MXD6, nylon 6,6, nylon 6,6,6, nylon 7, nylon 8, nylon 9, nylon 10, nylon 11, nylon 12, nylon 6,10, nylon 10,10, nylon 6,9, nylon 4,6, nylon 4,10, nylon 5,6, nylon 5,10, nylon 6I, nylon 6T, nylon 6I / 6T, nylon 6-3-T, nylon 6 / MXDI, nylon 6 / 6I, polyamide 4, polyamide 6, polyamide 10, polyamide 11, polyamide 12, polyamide 4, 6, polyamide 6,6, polyamide 6,10, polyamide 6T, polyamide 9T, polyamide 6IT, polymetaxylylene adipamide (polyamide MXD6), isophthalic acid copolymerized polymetaxylylene adipamide (polyamide MXD6I), polymetaxylylene sebacamide (polyamide MXD10), polymetaxylylene dodecanamide (polyamide MXD12), poly 1,3-bisaminocyclohexane adipamide (polyamide BAC6), polyparaxylylene sebacamide (polyamide PXD10), and the like, but are not particularly limited thereto.

[0028] Examples of acrylic fibers of component B include, but are not limited to, polyacrylonitrile, which is made primarily from acrylonitrile, and poly(meth)acrylic acid ester, which is a polymer of (meth)acrylic acid ester. These may be used alone or in any combination and ratio of two or more.

[0029] The above-mentioned components A and B may be contained in a mixture, and the form of their mixture is not particularly limited. For example, the polyester or protein fiber of component A may be contained in any one of fibers, fiber-reinforced resins, bottles, containers, films, multilayer films, etc., or may be contained in two or more of these. Similarly, the polyurethane, nylon, or acrylic fiber of component B may be contained in any one of fibers, fiber-reinforced resins, bottles, containers, films, multilayer films, etc., or may be contained in two or more of these. Furthermore, components A and B may be contained in the mixture as fibers such as blended yarns, blended yarns, or composite yarns, as laminated films such as woven fabrics, woven fabrics, or nonwoven fabrics, or as two-color molded bodies or multi-color molded bodies, etc.

[0030] The content ratios in the mixture can be set appropriately depending on the required performance and are not particularly limited, but in one embodiment, the mixture preferably contains 20 to 99 parts by mass of component A and 1 to 40 parts by mass of component B per 100 parts by mass of the mixture. The mixture more preferably contains 30 to 99 parts by mass of component A and 1 to 40 parts by mass of component B per 100 parts by mass of the mixture, and more preferably contains 40 to 99 parts by mass of component A and 1 to 40 parts by mass of component B per 100 parts by mass of the mixture.

[0031] The content ratio in the mixture can be appropriately set taking into consideration the composition of the recovered polyester and is not particularly limited, but from the viewpoint of obtaining high-quality recycled polyester, it is preferable that the polyester is 50 parts by mass or more and 99 parts by mass or less, and the protein fiber and component B are 1 part by mass or more and 50 parts by mass or less in total, relative to 100 parts by mass of the mixture. More preferably, the polyester is 75 parts by mass or more and 99 parts by mass or less, and the protein fiber and component B are 1 part by mass or more and 25 parts by mass or less in total, relative to 100 parts by mass of the mixture. Even more preferably, the polyester is 90 parts by mass or more and 99 parts by mass or less, and the protein fiber and component B are 1 part by mass or more and 10 parts by mass or less in total, relative to 100 parts by mass of the mixture.

[0032] The mixture may contain components other than the above-described component A and component B (hereinafter, these may be referred to as "contaminant components"). The content of the contaminant components is not particularly limited, but from the viewpoint of obtaining high-quality recycled polyester, it is preferably less than 50% by mass, more preferably less than 40% by mass, even more preferably less than 35% by mass, even more preferably less than 10% by mass, particularly preferably less than 5% by mass, and most preferably less than 1% by mass, relative to 100 parts by mass of the mixture. It goes without saying that the lower limit is 0% by mass or more. Examples of impurity components include, but are not limited to, fiber materials other than the above-mentioned Components A and B (e.g., cotton, linen, silk, cellulose, rayon, acetate, triacetate, cupra, lyocell, etc.), resin materials other than the above-mentioned Components A and B (e.g., polyolefin, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polystyrene, polycarbonate, etc.), metals, paper, inorganic fillers, release improvers such as higher fatty acids, higher fatty acid esters, higher fatty acid amides, higher fatty acid metal salts, polysiloxanes, and fluororesins; colorants such as dyes and pigments; organic fillers; antioxidants; heat stabilizers; light stabilizers; ultraviolet absorbers; flame retardants; antistatic agents; surfactants; rust inhibitors; antifoaming agents; fluorescent agents; and surface finishing agents. The content of impurity components is not particularly limited, but is preferably less than 8% by mass, more preferably less than 5% by mass, more preferably less than 3% by mass, and even more preferably less than 1% by mass, relative to 100 parts by mass of the mixture. In addition, cellulose such as cotton, rayon, and hemp, which are impurity components, can be pulverized by an acidic treatment solution or solubilized by a chemical reaction, etc., so when the method of this embodiment is applied, these can be separated as fine powder or liquid components.

[0033] The acidic treatment liquid is impregnated into the mixture to enable separation of the above-mentioned components A and B. The acidic treatment liquid is not particularly limited, but a solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, and polyphosphoric acid is preferably used from the viewpoints of the solubility and liquefaction of the above-mentioned component B. Such an acidic treatment liquid may be a solution containing an inorganic acid, and preferably an inorganic acid solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, and polyphosphoric acid. Among these, from the viewpoint of low corrosiveness, sulfuric acid, phosphoric acid, and polyphosphoric acid are more preferred, phosphoric acid and polyphosphoric acid are even more preferred, and phosphoric acid is particularly preferred. In particular, phosphoric acid and polyphosphoric acid, unlike hydrochloric acid and nitric acid, are suitable for separating polyester and polyurethane at a relatively low temperature of 50°C. In this specification, polyphosphoric acid refers to condensed phosphoric acid. Polyphosphoric acid may include orthophosphoric acid, pyrophosphoric acid, or linear condensed phosphoric acid, or may be a mixture containing cyclic or branched condensed phosphoric acid, but is not particularly limited thereto. Commercially available polyphosphoric acid products include 116% polyphosphoric acid and 105% polyphosphoric acid manufactured by Rasa Kogyo Co., Ltd., and various polyphosphoric acids manufactured by Nippon Chemical Industry Co., Ltd., Taihei Chemical Industry Co., Ltd., and Fujifilm Wako Pure Chemical Industries, Ltd. Polyphosphoric acid having an orthophosphoric acid equivalent of 105 to 120% by weight can be used, for example, or polyphosphoric acid having an orthophosphoric acid equivalent outside the range of 105 to 120% by weight can also be used in combination. In addition to polyphosphoric acid, orthophosphoric acid, phosphorus pentoxide, water, etc. can also be used in combination.

[0034] The content of the acidic treatment solution is not particularly limited as long as it contains one or more selected from the group consisting of sulfuric acid, phosphoric acid, and polyphosphoric acid. The acidic treatment solution may contain only one of these, a combination of any two or more selected from these, or all three of sulfuric acid, phosphoric acid, and polyphosphoric acid. In one embodiment, the acidic treatment solution preferably contains either sulfuric acid, phosphoric acid, or polyphosphoric acid-sulfuric acid as an essential component. In another embodiment, the acidic treatment solution preferably contains phosphoric acid or polyurethane as an essential component, and preferably contains phosphoric acid as an essential component. From the viewpoints of solubility and economy, the acidic treatment solution is preferably an aqueous solution containing at least water, and more preferably an aqueous solution containing the aforementioned inorganic acid. For example, the acidic treatment solution may be an aqueous sulfuric acid solution, an aqueous phosphoric acid solution, or an aqueous polyphosphoric acid solution, or a mixed aqueous solution of sulfuric acid and phosphoric acid, a mixed aqueous solution of sulfuric acid and polyphosphoric acid, a mixed aqueous solution of phosphoric acid and polyphosphoric acid, or a mixed aqueous solution of sulfuric acid, phosphoric acid, and polyphosphoric acid.

[0035] Furthermore, when the acidic treatment solution is an aqueous solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, and polyphosphoric acid, the water content in the aqueous solution is preferably 20% by mass or less, more preferably 18% by mass or less, even more preferably 16% by mass or less, particularly preferably 13% by mass or less, and particularly preferably 11% by mass or less. The lower limit of the water content in the aqueous solution is not particularly limited, but is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 9% by mass or more. When the water content is within the above range, the separation ability of the above-mentioned components A and B tends to be improved. The acidic treatment solution may contain a solvent other than water. Examples of solvents other than water include, but are not limited to, methanol, ethanol, isopropyl alcohol, and mixtures thereof.

[0036] The acid concentration of the acidic treatment solution varies depending on the type of acid used, but is preferably 80% by mass or more. For example, in the case of sulfuric acid, the acid concentration is preferably 80% by mass or more, more preferably 82% by mass or more, and even more preferably 85% by mass or more. The upper limit is not particularly limited, but is preferably 95% by mass or less, more preferably 93% by mass or less. In the case of phosphoric acid, the acid concentration is more preferably 80% by mass, more preferably 82% by mass, and even more preferably 85% by mass or more. The upper limit is not particularly limited, but is preferably 95% by mass or less, more preferably 93% by mass or less. In the case of polyphosphoric acid, the acid concentration is more preferably 80% by mass, more preferably 82% by mass, and even more preferably 85% by mass or more. The upper limit is not particularly limited, but is preferably 95% by mass or less, more preferably 93% by mass or less. In the case of a mixed aqueous solution, the acid concentration is preferably 80% by mass or more in total, more preferably 82% by mass or more in total, and even more preferably 85% by mass or more in total. The upper limit is not particularly limited, but is preferably 95% by mass or less in total, and more preferably 93% by mass or less in total.

[0037] The method for impregnating the mixture with the acidic treatment solution may be any method and is not particularly limited. For example, the acidic treatment solution may be sprayed or applied to the mixture. From the viewpoints of solubility and economy, a method in which the mixture is immersed in a bath of the acidic treatment solution is preferred. An impregnated mixture can be obtained by impregnating the mixture containing the above-mentioned component A and component B with the acidic treatment solution.

[0038] It is preferable to include a step S12a of pulverizing or cutting the mixture prior to preparing the impregnation treatment mixture. By pulverizing or cutting the mixture in this manner, the volume of the mixture can be reduced and the surface area to be treated increases, which tends to promote the decomposition or liquefaction of the above-mentioned component B. The pulverization or cutting of the mixture can be carried out using a known method. In this case, known processing equipment such as a pulverizer, ball mill, bead mill, flake crusher, hammer mill, pin mill, bantam mill, jet mill, cyclone mill, fret mill, pan mill, edge runner, roller mill, mix miller, vibration mill, sample mill, pulverizer, cutter, shredder, air cutter, or cutter can also be used.

[0039] Furthermore, prior to preparing the impregnation mixture, an elution treatment S12b may be performed before pulverization or impregnation of the mixture, or after pulverization or impregnation, to extract impurities such as disperse dyes and halogen atoms from the mixture with a solvent. By performing this solvent extraction treatment in advance, separation and recovery with higher purity is possible. Known solvents such as methylene chloride, xylene, and alkylene glycol can be used in the solvent extraction treatment. The treatment temperature is not particularly limited, and the optimum temperature varies depending on the type of extraction solvent used, but is preferably 120°C or higher but lower than 210°C, more preferably 120°C or higher but lower than 180°C. The solvent extraction treatment may be performed batchwise or continuously in a countercurrent system.

[0040] <Step of Separating Components A and B (S13)> In step S13, the above-described components A and B are separated from the impregnation treatment mixture. In addition to the above-described components A and B, the impregnation treatment mixture may contain liquid components or fine powder of impurity components. Therefore, by removing the liquid components and fine powder from the impregnation treatment mixture, it is possible to obtain component A with reduced impurity components. In this step, known solid-liquid separation methods such as pressure filtration using a pressure filter or nitrogen gas, vacuum suction filtration, and centrifugation can be used.

[0041] In this specification, the polyester obtained after the separation step (S13) of components A and B refers to a solid component containing the polyester recovered from the impregnation treatment mixture. This solid component is not particularly limited, but may contain the polyester and a hydrolyzable non-nitrogen-containing resin and / or impurity components. These hydrolyzable non-nitrogen-containing resin and / or impurity components can be separated from the polyester as liquid components or fine powders by applying a known solid-liquid separation method such as pressure filtration using a pressure filter or nitrogen gas, vacuum suction filtration, or centrifugation.

[0042] In this separation step of components A and B, from the viewpoint of improving productivity and economy by eliminating the high-temperature treatment exceeding 50°C that has conventionally been required, the separation operation is preferably carried out at a temperature below 50°C, more preferably 45°C or lower, even more preferably 40°C or lower, particularly preferably 35°C or lower, and most preferably 30°C or lower. The lower limit of the treatment temperature is not particularly limited, but from the viewpoints of productivity and economy, it is preferably 0°C or higher, more preferably 5°C or higher, even more preferably 10°C or higher, and particularly preferably 15°C or higher. The treatment time is not particularly limited, but from the viewpoints of productivity and economy, it is preferably 10 hours or lower, more preferably 5 hours or lower, even more preferably 3 hours or lower, and most preferably 1 hour or lower. The lower limit of the treatment time is not particularly limited as long as the treatment capacity is satisfied, but can be, for example, 1 minute or longer, or 5 minutes or longer. The treatment of the impregnation treatment mixture may be carried out either batchwise or continuously in a countercurrent system. For the same reason, when solid-liquid separation such as filtration or centrifugation is performed, it is preferable to wash with water or the above-mentioned acidic treatment liquid, methanol, ethanol, isopropyl alcohol, or a mixture thereof at a temperature of less than 50°C, as described above.

[0043] From the viewpoint of promoting the decomposition or liquefaction of component B and improving productivity and economy, it is preferable to treat this impregnation mixture by immersing the mixture in a bath of the acidic treatment solution and flowing the acidic treatment solution through the mixture. The method of flowing the treatment solution can be carried out using a known method such as a stirring blade. The rotation speed of the stirring blade in this case is not particularly limited, but is preferably 10 to 150 rpm.

[0044] After the impregnation treatment mixture is treated, a washing treatment S13a, for example, may be performed as necessary. The washing treatment can be performed based on a conventional method, and the type of washing treatment is not particularly limited. For example, a liquid component can be added to liquid component B separated from solid component A, and at least one of the components B can be solidified and recovered. The liquid component used in this case is not particularly limited, but can be, for example, one or more selected from the group consisting of the above-mentioned acid treatment solution, methanol, ethanol, propanol, isopropyl alcohol, ethylene glycol, and water.

[0045] As described above, the mechanism by which component A remains solid while part or all of component B becomes a liquid component by performing acid treatment at a relatively low temperature of less than 50°C is not clear, but it is presumed that the relatively high-concentration, highly polar acid treatment liquid functions as a dispersant, making component B easily dispersible. However, the function of the present invention is not limited to these assumptions.

[0046] After the separation step of components A and B, a washing treatment and / or a drying treatment may be further carried out as necessary. The washing treatment can be carried out based on a conventional method, and the type thereof is not particularly limited. When the separation operation is carried out using water or an acidic treatment solution, methanol, ethanol, isopropyl alcohol, or a mixture thereof, it is preferable to carry out a washing treatment with water, ethanol, isopropyl alcohol, or a mixture thereof from the viewpoint of removing inorganic acids. Then, if necessary, the washed component A can also be subjected to a drying treatment at 50°C or higher and 150°C or lower as necessary.

[0047] The component A obtained after the separation process (hereinafter, sometimes referred to as "recovered component A") has a particularly reduced content of component B. Depending on the composition of the mixture before treatment, recovered component A may contain polyester and / or protein fibers. When the mixture before treatment contains polyester, recovered component A is industrially important as a raw material for recycled polyester. The content of polyester in the obtained recovered component A can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and even more preferably 90 parts by mass or more, per 100 parts by mass of the total. Furthermore, the content of components other than polyester can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the total.

[0048] Note that recovered component A may contain polyester and protein fibers, depending on the composition of the mixture before treatment. When recovered component A contains polyester and protein fibers, removing the protein fibers from recovered component A can result in a higher-quality recovered component C with an increased polyester content. Here, the method for removing protein fibers from recovered component A can be carried out based on conventional methods, and the type is not particularly limited. For example, a method of hydrolyzing, separating, and removing protein fibers using a basic hydrolyzing agent (JP 2017-503067 A), a method of decomposing protein fibers including wool by heat treatment in the presence of an organic acid and separating them from polyester fibers (JP 2019-35022 A), and a method of treating protein fibers such as wool with subcritical water at 200°C to 220°C for a predetermined time to decompose them, producing amino acids, which are then separated from polyester fibers (JP 2008-255554 A), etc., are known, and any known method can be applied without particular limitation.

[0049] [Method for Chemically Recycling Polyester] The method for chemically recycling polyester according to this embodiment involves depolymerizing a polyester monomer using recovered component A or component C containing polyester obtained by the separation and recovery method as a raw material for depolymerization. That is, the method for chemically recycling polyester according to this embodiment includes at least the steps of: obtaining the impregnation mixture described above (S12); separating component A and component B from the impregnation mixture (S13); and depolymerizing the obtained component A (recovered component A or component C) as a raw material for depolymerization to obtain a polyester monomer (S21). Steps S12 and S13 have already been described, so redundant description will be omitted. Step S21 will be described in detail below.

[0050] <Polyester depolymerization step (S21)> In this step S21, the polyester that may be contained in the component A (recovered component A or recovered component C) obtained as described above is used as a raw material for recycled polyester, i.e., as a depolymerization raw material, to depolymerize the polyester to obtain a polyester monomer.

[0051] For the depolymerization of polyester, known methods can be applied, and the type thereof is not particularly limited. For example, known methods such as a method of reacting an alcohol under acidic or alkaline conditions, a method of transesterification with methanol in the presence of a transesterification catalyst, a method of reacting an amine compound in the presence of a catalyst, a method of reacting a supercritical or subcritical fluid (water or methanol), and a method of hydrolysis in the presence of an enzyme can be applied. Furthermore, after the polyester depolymerization step, terephthalic acid, dimethyl terephthalate, alkylene glycol, etc. can be purified by a purification method such as distillation, crystallization, or activated carbon treatment to obtain high-purity products.

[0052] As described above in detail, the separation method of this embodiment enables easy industrial separation of components A and B from a mixture containing one or more components A selected from the group consisting of polyesters and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers, under relatively low-temperature treatment conditions of less than 50°C, thereby reducing significant labor and costs compared to conventional techniques. Therefore, the separation method of this embodiment is highly productive and economical on an industrial scale. Furthermore, by chemically recycling the component A separated in this manner, it is also possible to obtain high-quality recycled polyester with excellent productivity and economic efficiency.

[0053] The features of the present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the spirit of the present invention. Furthermore, the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limits in the embodiments of the present invention, and preferred numerical ranges may be defined by combining the above-mentioned upper or lower limits with the values ​​of the following examples or values ​​between the examples.

[0054] Example 1: 1.03 g of a polyester and polyurethane blended fiber (Fast Retailing Co., Ltd., product number 444128, 88% by weight polyester, 12% by weight polyurethane) was weighed and placed in a glass vial along with a stirrer. Next, 30 mL of 85% phosphoric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) was weighed using a measuring cylinder and placed in the glass vial to obtain an impregnation treatment mixture. After stirring for 120 minutes at 25°C, the contents of the vial became a cloudy liquid containing polyester-containing solids. After stirring, the contents of the vial were filtered and washed at 25°C using 85% phosphoric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) as a washing solution, and the solids were collected by filtration. The solids were then washed with ultrapure water and collected by filtration. The collected solids were air-dried overnight and then dried for 3 hours in a dryer set at 80°C, and the mass of the polyester-containing solids after drying was measured. The ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fibers before being placed in the vial is shown in Table 1. The polyester recovery rate is also shown in Table 1.

[0055] (Examples 2 and 3) Each treatment was carried out in the same manner as in Example 1, except that the amount of blended fiber used was changed as shown in Table 1 and the acid treatment conditions and washing treatment conditions were changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0056] (Examples 4 to 6) Treatments were carried out in the same manner as in Examples 1 to 3, except that the amount of blended fiber used was changed as shown in Table 1, the acid treatment solution was changed from 85% phosphoric acid to 89% phosphoric acid (industrial grade, manufactured by Rasa Kogyo Co., Ltd.), the washing solution was changed from 85% phosphoric acid to the 89% phosphoric acid, and the acid treatment conditions and washing treatment conditions were changed to those shown in Table 1. Table 1 shows the ratio (%) of the mass of polyester-containing solids recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0057] Example 7: 535.0 g of a polyester and polyurethane blended fiber (Fast Retailing Co., Ltd., product number 444128, 88% polyester by mass, 12% polyurethane by mass) was weighed and placed in a 5 L glass separable flask. Next, 3,500 mL of 89% phosphoric acid (Rasa Kogyo Co., Ltd., industrial grade) was weighed using a measuring cylinder and placed in the separable flask to obtain an impregnation treatment mixture. After immersion for 180 minutes at 25°C, the contents of the separable flask became a cloudy white liquid containing polyester-containing solids. After immersion, the polyester-containing solids were removed from the separable flask, wrung out by hand, and then dehydrated for 3 minutes in an electric dehydrator (HiSmart Japan Co., Ltd., model HS-S60A). The dehydrated polyester-containing solids were washed at 25°C using 89% phosphoric acid (Rasa Kogyo Co., Ltd., industrial grade) as a cleaning solution, wrung out by hand, and then dehydrated for 3 minutes in a dehydrator. This washing treatment with 89% phosphoric acid (Rasa Kogyo Co., Ltd., industrial grade) was performed a total of three times. The final solid was then washed with ultrapure water, squeezed by hand, and dehydrated in a spin dryer. The recovered solid was air-dried overnight and then dried for 3 hours in a dryer set at 80°C, and the mass of the polyester-containing solid after drying was measured. Table 1 shows the ratio (%) of the mass of the polyester-containing solid recovered after drying to the mass of the blended fiber before being placed in the separable flask. Table 1 also shows the polyester recovery rate.

[0058] (Examples 8 to 10) Treatments were carried out in the same manner as in Example 1, except that the amount of blended fiber used was changed as shown in Table 1, the acid treatment solution was changed from 85% phosphoric acid to a mixed solution of 89% phosphoric acid (manufactured by Rasa Kogyo Co., Ltd., industrial grade), sulfuric acid (manufactured by Kishida Chemical Co., Ltd., special grade reagent), and ultrapure water (the concentrations of each compound in the mixed solution are shown in Table 1), the cleaning solution was changed from 85% phosphoric acid to the mixed solution, and the acid treatment conditions and cleaning treatment conditions were changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of polyester-containing solids recovered after drying to the mass of blended fiber before charging into the vial. Table 1 also shows the polyester recovery rate.

[0059] (Example 11) The same procedure as in Example 1 was repeated, except that the amount of blended fiber used was changed as shown in Table 1, and the contents of the vial were filtered after the stirring process was completed, and the washing solution was changed from 85% phosphoric acid to methanol (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the solid content was washed at 25°C and recovered by filtration. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0060] (Examples 12 and 13) The same procedure as in Example 11 was repeated, except that the amount of blended fiber used was changed as shown in Table 1, and the washing solution was changed from methanol to ethanol (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) or isopropanol (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and washing was performed at 25°C, followed by filtration and recovery of the solid content. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0061] (Examples 14 to 16) Treatments were carried out in the same manner as in Examples 4 to 6, except that the blended fiber was changed to a blended fiber of polyester and polyurethane (manufactured by AEON Co., Ltd., product number TV158SA3302C, 90% by mass of polyester and 10% by mass of polyurethane) and the amount of blended fiber used was changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0062] (Examples 17 to 21) The same procedure as in Example 1 was repeated, except that the blended fiber was changed to a blended fiber of polyester and nylon (product number 3-3412-02, manufactured by AS ONE Corporation, 75% by mass of polyester and 25% by mass of polyurethane), the amount of blended fiber used was changed as shown in Table 1, and the acid treatment conditions and washing treatment conditions were changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0063] Example 22 The same procedures as in Example 1 were repeated, except that the blended fibers were changed to blended fibers of polyester, polyurethane, acrylic fiber, and rayon (Fast Retailing Co., Ltd., product number 450528, 39% by mass of polyester, 8% by mass of polyurethane, 32% by mass of acrylic fiber, and 21% by mass of rayon), the amount of blended fiber used was changed as shown in Table 1, and the acid treatment conditions and washing treatment conditions were changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of polyester-containing solids recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0064] (Comparative Examples 1 to 3) Treatments were carried out in the same manner as in Examples 1 to 3, except that the amount of blended fiber used was changed as shown in Table 1, the acid treatment solution was changed from 85% phosphoric acid to 75% phosphoric acid (prepared by diluting the above 85% phosphoric acid with ultrapure water), the cleaning solution was changed from 85% phosphoric acid to the above 75% phosphoric acid, and the acid treatment conditions and cleaning treatment conditions were changed to those shown in Table 1. The content of the vial after stirring was a mixed solution containing a polyester-containing solid content. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial.

[0065] Comparative Example 4 The same procedure as in Example 1 was used except that the amount of blended fiber used was changed as shown in Table 1, the acid treatment solution was changed from 85% phosphoric acid to a mixed solution of 89% phosphoric acid (manufactured by Rasa Kogyo Co., Ltd., industrial grade), sulfuric acid (manufactured by Kishida Chemical Co., Ltd., special grade reagent), and ultrapure water (the concentrations of each in the mixed solution are shown in Table 1), the cleaning solution was changed from 85% phosphoric acid to the mixed solution, and the acid treatment and cleaning treatment conditions were changed to those shown in Table 1. The contents of the vial after stirring was a mixed solution containing polyester-containing solids. Table 1 shows the ratio (%) of the mass of the polyester-containing solids recovered after drying to the mass of the blended fiber before being placed in the vial.

[0066] Comparative Example 5 The same procedure as in Example 1 was used except that the blended fiber was changed to a blended fiber of polyester and polyurethane (manufactured by AEON Co., Ltd., product number TV158SA3302C, 90% polyester by mass, 10% polyurethane by mass), the amount of blended fiber was changed as shown in Table 1, the acid treatment solution was changed from 85% phosphoric acid to 75% phosphoric acid (prepared by diluting the above 85% phosphoric acid with ultrapure water), the cleaning solution was changed from 85% phosphoric acid to the above 75% phosphoric acid, and the acid treatment and cleaning treatment conditions were changed as shown in Table 1. The contents of the vial after stirring were a mixed solution containing polyester-containing solids. Table 1 shows the ratio (%) of the mass of the polyester-containing solids recovered after drying to the mass of the blended fiber before charging into the vial.

[0067] Comparative Example 6 The same procedures as in Example 1 were repeated except that the blended fibers were changed to blended fibers of polyester, polyurethane, acrylic fiber, and rayon (Fast Retailing Co., Ltd., product number 450528, 39% by mass of polyester, 8% by mass of polyurethane, 32% by mass of acrylic fiber, and 21% by mass of rayon), the amount of blended fiber used was changed as shown in Table 1, and the acid treatment conditions and washing treatment conditions were changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial.

[0068] Reference Example 1 0.94 g of a polyester and polyurethane blended fiber (Fast Retailing Co., Ltd., product number 444128, 88% by weight polyester, 12% by weight polyurethane) was weighed and placed in a glass vial along with a stirrer. Next, 30 mL of 85% phosphoric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special-grade reagent) was weighed using a measuring cylinder and placed in the glass vial to obtain an impregnation treatment mixture. The glass vial was then heated in an oil bath set at 80°C while stirring for 30 minutes, and the contents of the vial became a mixture containing polyester-containing solids. After completion of the heat treatment, the contents of the vial were hot filtered at 80°C, washed with 85% phosphoric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special-grade reagent), and then further washed with 80°C ultrapure water to filter and recover the solids. The contents of the vial after heating were a mixture containing polyester-containing solids. The recovered solids were air-dried overnight and then dried for 3 hours in a dryer set at 80°C, and the mass of the polyester-containing solids after drying was measured. The ratio (%) of the mass of the polyester-containing solids recovered after drying to the mass of the blended fibers before being placed in the vial is shown in Table 1. The polyester recovery rate is also shown in Table 1.

[0069] (Reference Example 2) The same procedure as in Reference Example 1 was repeated, except that the amount of blended fiber used was changed as shown in Table 1, and after the heat treatment, the contents of the vial were filtered at 25°C, washed with 85% phosphoric acid (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at 25°C, and then washed with ultrapure water at 25°C to recover the solid content by filtration. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0070] (Reference Example 3) Treatment was carried out in the same manner as in Reference Example 2, except that the blended fiber was changed to a blended fiber of polyester and polyurethane (manufactured by AEON Co., Ltd., product number TV158SA3302C, 90% by mass of polyester and 10% by mass of polyurethane) and the amount of blended fiber used was changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial. Table 1 also shows the polyester recovery rate.

[0071] (Reference Example 4) Treatments were carried out in the same manner as in Example 1, except that the blended fibers were changed to blended fibers of polyester, polyurethane, acrylic fiber, and rayon (manufactured by Fast Retailing Co., Ltd., product number 450528, 39% by mass of polyester, 8% by mass of polyurethane, 32% by mass of acrylic fiber, and 21% by mass of rayon), the amount of blended fiber used was changed as shown in Table 1, and the acid treatment conditions and washing treatment conditions were changed as shown in Table 1. Table 1 shows the ratio (%) of the mass of the polyester-containing solid content recovered after drying to the mass of the blended fiber before being placed in the vial.

[0072]

[0073] In Comparative Examples 1 to 6, separation of components A and B was not even achieved, and almost all of them were recovered as solids. In contrast, in Examples 1 to 22, almost all of component B was separated as a liquid component, and almost all of component A was recovered as a solid. Comparing Examples 1 to 22 with Comparative Examples 1 to 6, it can be seen that by impregnating a mixture of components A and B with an acidic treatment solution having a relatively high acid concentration (an acidic treatment solution with a relatively low water content), components A and B can be separated even under relatively low-temperature treatment conditions of less than 50°C. Furthermore, while Reference Examples 1 to 4 require heat treatment at 80°C or higher, it can be seen that in Examples 1 to 22, components A and B can be separated without such high-temperature heat treatment.

[0074] Next, in order to understand the ability of the acidic treatment solution to separate component A and component B, the following experiment was carried out using a single material of component A or component B. The single materials of component A and component B used here were as follows: Polyester: white polyester cloth (white cloth attached for color fastness test, conforming to JIS L0803) Protein fiber such as wool: white wool cloth (white cloth attached for color fastness test, conforming to JIS L0803) Polyurethane: polyurethane thread (Lycra, T-127, manufactured by Toray Opelontech Co., Ltd.) Nylon: white nylon cloth (white cloth attached for color fastness test, conforming to JIS L0803) Acrylic fiber: white acrylic cloth (white cloth for dye test, acrylic muslin)

[0075] (Experimental Example 1) Experimental Examples 1a-1d Each of the individual materials of Component A or Component B, weighed as shown in Table 2, was placed in a glass vial together with a stirrer. Next, 75% phosphoric acid (prepared by diluting the above-mentioned 85% phosphoric acid with ultrapure water) was weighed as shown in Table 2 as an acidic treatment solution and placed in each glass vial to obtain an impregnation treatment mixture. Then, each was stirred at 25°C for 300 minutes. After stirring, the contents of the vial were a colorless, transparent liquid containing the individual materials in the shape they were in when placed in the vial, for both the individual materials of Component A (polyester, protein fiber) and the individual materials of Component B (polyurethane, nylon, acrylic fiber). Table 2 shows the ratio (%) of the mass of the solids recovered after drying to the mass of the individual materials before placement in the vial.

[0076] Experimental Example 2 Experimental Examples 2a-2e Using the individual materials of Component A or Component B weighed as shown in Table 2, treatment was carried out in the same manner as in Experimental Example 1, except that the acidic treatment solution was changed from 75% phosphoric acid to 85% phosphoric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), and the amount of acidic treatment solution used and the acidic treatment conditions were changed as shown in Table 2. After stirring, the contents of the vial were colorless and transparent liquids containing the individual materials of Component A (polyester, protein fiber) in the shape they had when added, and yellowish and transparent liquids containing swollen solids for the individual materials of Component B (polyurethane, nylon, acrylic fiber). Table 2 shows the ratio (%) of the mass of the solids recovered after drying to the mass of the individual materials before addition to the vial.

[0077] Experimental Example 3 Experimental Examples 3a-3e Using the individual materials of Component A or Component B weighed as shown in Table 2, treatment was carried out in the same manner as in Experimental Example 1, except that the acid treatment solution was changed from 75% phosphoric acid to 89% phosphoric acid (manufactured by Rasa Kogyo Co., Ltd., industrial grade), and the amount of acid treatment solution used and the acid treatment conditions were changed as shown in Table 2. After stirring, the contents of the vial were colorless and transparent liquids containing the individual materials of Component A (polyester, protein fiber) in the shape they were in when added, and yellowish and transparent liquids containing swollen solids for the individual materials of Component B (polyurethane, nylon, acrylic fiber). Table 2 shows the ratio (%) of the mass of the solids recovered after drying to the mass of the individual materials before addition to the vial.

[0078]

[0079] Comparing Experimental Example 1 with Experimental Example 2-3, it can be seen that in Experimental Example 2-3, in which the acid concentration of the acidic treatment solution was relatively high (the water content in the acidic treatment solution was relatively low), separation of Components A and B was possible using the acidic treatment solution even at a low temperature of less than 50° C. This is because, under conditions in which the acid concentration of the acidic treatment solution was relatively high (the water content in the acidic treatment solution was relatively low), Component A was substantially insoluble in the acidic treatment solution with a residual solid fraction exceeding 99% by mass, whereas Component B was dissolved or liquefied in the acidic treatment solution with a residual solid fraction of less than 5.0% by mass, and solid-liquid separation, for example, by filtration, was possible based on the difference in solubility or liquefaction of the two components.

[0080] (Experimental Example 4) Experimental Examples 4a-4w Component B (polyurethane) weighed as shown in Table 3 was used and placed in a glass vial together with a stirrer. Next, a mixed solution of 89% phosphoric acid (manufactured by Rasa Kogyo Co., Ltd., industrial grade), sulfuric acid (manufactured by Kishida Chemical Co., Ltd., special grade reagent), and ultrapure water as shown in Table 3 was weighed as shown in Table 3 and placed in a glass vial to obtain an impregnation treatment mixture. Then, each mixture was stirred at 25°C for 300 minutes. Table 3 shows the ratio (%) of the mass of the solid content recovered after drying to the mass of the single material before placement in the vial.

[0081]

[0082] The results of Experimental Example 4 show that when a mixed chemical solution in which the acid concentration of the acidic treatment solution is relatively high (the water content in the acidic treatment solution is relatively low) is used, the polyurethane of component B can be dissolved or liquefied by the acidic treatment solution even at low temperatures below 50° C. Therefore, under conditions in which the acid concentration of the acidic treatment solution is relatively high (the water content in the acidic treatment solution is relatively low), component A is substantially insoluble in the acidic treatment solution with a solid residual rate of more than 99% by mass, whereas component B dissolves or liquefies in the acidic treatment solution with a solid residual rate of less than 5.0% by mass, and solid-liquid separation, for example, by filtration, is possible based on the difference in solubility or liquefaction between the two.

[0083] (Experimental Examples 5-7) Experimental Examples 5a-5b / Experimental Examples 6a-6c / Experimental Examples 7a-7b Component B (polyurethane) weighed as shown in Table 4 was used and placed in a glass vial together with a stirrer. Next, as the acidic treatment solution, sulfuric acid (Kishida Chemical Co., Ltd., special reagent grade, prepared by diluting 98% with ultrapure water), hydrochloric acid (Fujifilm Wako Pure Chemical Co., Ltd., special reagent grade, prepared by diluting 35% hydrochloric acid with ultrapure water), and nitric acid (Fujifilm Wako Pure Chemical Co., Ltd., special reagent grade, prepared by diluting 60% nitric acid with ultrapure water) were weighed as shown in Table 4 and placed in a glass vial, respectively, to obtain an impregnation treatment mixture. Then, each mixture was stirred at 25 ° C. for 300 minutes. Table 4 shows the ratio (%) of the mass of the solid content recovered after drying to the mass of the single material before placement in the vial.

[0084]

[0085] The results of Experimental Examples 5 to 7 show that, unlike hydrochloric acid and nitric acid, sulfuric acid cannot dissolve or liquefy polyurethane of component B when the acid concentration is relatively low (relatively high water content), but can dissolve or liquefy polyurethane of component B when the acid concentration is relatively high (relatively low water content). Therefore, even when sulfuric acid with a high acid concentration is used as the acidic treatment liquid, solid-liquid separation is possible based on the difference in solubility or liquefaction ability between component A and component B. On the other hand, it was suggested that it is difficult to dissolve or liquefy polyurethane of component B even when hydrochloric acid or nitric acid is used as the acidic treatment liquid.

[0086] According to the present invention, it is possible to easily separate components A and B industrially from a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers under relatively low-temperature treatment conditions of less than 50°C, thereby improving productivity and economic efficiency and, as a result, enabling the production of high-quality recycled polyester. Therefore, the present invention can be widely and effectively used, for example, in the field of recycled polyester materials.

Claims

1. A method for separating a mixture, comprising at least the steps of: impregnating a mixture containing one or more components A selected from the group consisting of polyester and protein fibers, and one or more components B selected from the group consisting of polyurethane, nylon, and acrylic fibers, with an acidic treatment liquid at less than 50°C to obtain an impregnation treatment mixture containing the solid component A and the liquid component B; and separating the solid component A and the liquid component B from the impregnation treatment mixture, wherein the acidic treatment liquid is an aqueous solution containing one or more selected from the group consisting of sulfuric acid, phosphoric acid, and polyphosphoric acid, and the aqueous solution contains 20 mass% or less of water.

2. The method for separating a mixture according to claim 1, wherein the acidic treatment solution contains at least one selected from the group consisting of phosphoric acid and polyphosphoric acid.

3. The method for separating a mixture according to claim 1, wherein the mixture contains 20 to 99 parts by mass of component A and 1 to 40 parts by mass of component B per 100 parts by mass of the mixture.

4. The method for separating a mixture according to claim 1, further comprising the step of adding a liquid component to the liquid component B separated from the solid component A, and solidifying and recovering at least one of the components B.

5. The method for separating a mixture according to claim 4, wherein the liquid component comprises one or more selected from the group consisting of water, methanol, ethanol, propanol, isopropyl alcohol, and ethylene glycol.

6. The method for separating a mixture according to claim 1, wherein component A is contained in one or more selected from the group consisting of fibers, fiber-reinforced resins, bottles, containers, films, and multilayer films, and component B is contained in one or more selected from the group consisting of fibers, fiber-reinforced resins, bottles, containers, films, and multilayer films.

7. The method for separating a mixture according to claim 1, further comprising a step of washing component A obtained by separating liquid component B with one or more selected from the group consisting of the acidic treating solution, methanol, ethanol, propanol, isopropyl alcohol, ethylene glycol, and water.

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