Method for producing diamine and dicarboxylic acid, method for recycling polyamide, and polyamide

Abstract

A method for producing a diamine and a dicarboxylic acid, said method comprising: a pretreatment step for obtaining a crude polyamide by subjecting waste containing polyamide to at least one treatment selected from the group consisting of pulverization, washing, and foreign matter separation; a depolymerization step in which the crude polyamide is introduced into an acid-containing aqueous solution in a reactor in a closed system, heated to a target temperature of 90-160 DEG C, and then heated at a temperature near the target temperature to depolymerize 80 mass% or more of the total polyamide and decompose the polyamide into a diamine and a dicarboxylic acid; a separation step in which components other than the diamine and the derivative of the diamine, and the dicarboxylic acid and the derivative of the dicarboxylic acid are removed from the reaction liquid obtained in the depolymerization step to obtain the diamine and the derivative of the diamine, and the dicarboxylic acid and the derivative of the dicarboxylic acid; and a purification step in which the diamine and the dicarboxylic acid are individually separated and purified from each of the diamine and the derivative of the diamine and the dicarboxylic acid and the derivative of the dicarboxylic acid obtained in the separation step.

Description

Technical Field

[0001] The present invention relates to a method for producing a diamine and a dicarboxylic acid, a method for recycling a polyamide, and a polyamide. Background Art

[0002] The mechanical properties of polyamides, namely mechanical strength, rigidity, impact resistance, etc., are excellent, and heat resistance and chemical resistance are also excellent. Therefore, they have been used in various industrial fields such as clothing, industrial materials, automobiles, electrical and electronic components, and other industrial products.

[0003] On the other hand, in recent years, in the plastics industry, there has also been a demand to respond to a resource recycling society, and there has been a demand to establish a recycling technology for polyamides.

[0004] Recycling generally includes three types: material recycling, chemical recycling, and thermal recycling. At present, in the automotive applications that account for most of the uses of polyamides, most of the polyamides in waste automobiles are incinerated in the form of thermal recycling and are not effectively utilized as resources. There is a demand to effectively utilize the polyamides through the above-mentioned material recycling and chemical recycling.

[0005] In addition, from the viewpoint of reducing GHG (greenhouse gas) emissions, there is also a demand for material recycling and chemical recycling of polyamides.

[0006] However, polyamide resin compositions and molded articles for automotive applications contain, in addition to polyamides, various additives such as inorganic fillers such as glass fibers, heat stabilizers, pigments, dyes, etc. (for example, refer to Patent Document 1). Therefore, the polyamides obtained by material recycling have a problem that it is difficult to maintain practically sufficient mechanical properties after recycling. Therefore, chemical recycling in which polyamides are depolymerized and decomposed into diamines and dicarboxylic acids as monomers and these monomers are polymerized again is promising and is being researched and developed.

[0007] As a technique related to the above-mentioned chemical recycling, a technique for producing monomers by decomposing polyamides by ammonolysis using a Lewis acid catalyst is proposed in Patent Document 2. In addition, a method is proposed in Patent Document 3: separating polyamides from a molded article of a polyamide resin composition containing glass fibers using an aqueous phosphoric acid solution, and then decomposing the polyamides into monomers. In addition, the depolymerization of polyamide 66 using microwaves is proposed in Non-Patent Document 1.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Patent No. 6839266 Gazette

[0011] Patent Document 2: Japanese Patent No. 3571723 Gazette

[0012] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2000-80199

[0013] Non-Patent Document

[0014] Non-Patent Document 1: Urska Cesarek et al., “Chemical Recycling of Alipahatic Polyamides by Microwave-Assisted Hydrolysis for Efficient Monomar Recovery”, ACS Sutainable Chem. Eng. 2020, 8, 16274-16282 Summary of the Invention

[0015] Problems to be Solved by the Invention

[0016] However, the method described in Patent Document 2 has a problem of low monomer yield.

[0017] In addition, in the method described in Patent Document 3, in a specific example using polyamide 66, the dissolution of polyamide and glass fiber takes 200 minutes. Furthermore, in Patent Document 3, there is no specific description of the depolymerization method. In addition, since the dissolution of the above polyamide and glass fiber takes 200 minutes, it is assumed that when further depolymerizing the polyamide after dissolving the molded product of the polyamide resin composition, the total time becomes even longer, having the problem of lack of practicality.

[0018] In addition, the method described in Non-Patent Document 1 uses a high-concentration hydrochloric acid of 17% by mass or more and uses microwaves to adjust to a high-temperature state of 170 °C or more, thereby achieving depolymerization of polyamide in a short time and with a high yield. Therefore, although microwave irradiation can be carried out using a glass reaction vessel at the laboratory level, when considering implementation at the industrial level, by using a high-concentration hydrochloric acid at a high temperature of 170 °C or more, corrosion of the reaction tank occurs, so the materials for the reaction tank are extremely limited. For example, as described in Non-Patent Document 2 (Corrosion Resistance of New Metal Materials, Akira Takamura, Corrosion Prevention Technology, Vol. 16 (1967), No. 3, pp. 97-106), even titanium, which is generally known to have high corrosion resistance, has a corrosion problem in a high-concentration hydrochloric acid of 5% or more at 100 °C or more.

[0019] As described above, in the methods described in Patent Documents 2 and 3, there are problems such as low monomer yield, lack of practicality in the time for recovering and depolymerizing monomers. In addition, in the method described in Non-Patent Document 1, there is a problem of corrosion of the reaction apparatus, which is not practical industrially. Further, when carried out under conditions such as high temperature and high pressure in order to shorten the above time, there is a problem that the energy required for the process becomes large and it is not practical from the viewpoint of reducing greenhouse gas (GHG) emissions.

[0020] Therefore, in the present invention, in view of the problems of the above prior art, an object thereof is to provide a method for producing a diamine and a dicarboxylic acid, a method for recycling a polyamide, and a polyamide obtained by the above method. Even when the method for producing a diamine and a dicarboxylic acid is carried out industrially, it can be safely carried out under a high-pressure environment, the degree of corrosion of the reaction apparatus is small, the diamine and the dicarboxylic acid can be recovered with high yield and high purity, and a polyamide having physical properties and quality equivalent to those of a polyamide from a petrochemical raw material can be obtained as a polymerization raw material.

[0021] Means for Solving the Problems

[0022] The present inventors repeatedly conducted in-depth studies to solve the above problems of the prior art, and as a result, found that: by depolymerizing a polyamide, a polyamide resin composition, and their molded articles by heating in a specified solvent within a specified temperature range, separating and removing impurities from the recycling raw material and foreign substances used in the recycling process or generated as by-products, and purifying the diamine and the dicarboxylic acid, the above problems can be solved, and thus the present invention was completed.

[0023] That is, the present invention is as follows.

[0024] [1] A method for producing a diamine and a dicarboxylic acid, wherein the production method has the following steps:

[0025] A pretreatment step of performing one or more treatments selected from the group consisting of pulverization, cleaning, and foreign substance separation on waste containing a polyamide to obtain a crude polyamide;

[0026] A depolymerization step of putting the crude polyamide into an aqueous acid solution in a reactor of a closed system, raising the temperature to a target temperature of 90°C or higher and 160°C or lower, and then heating near the target temperature to depolymerize more than 80% of the amide groups in all the polyamides contained in the crude polyamide into a diamine and a dicarboxylic acid;

[0027] Separation step: removing components other than the diamine, the derivatives of the diamine, the dicarboxylic acid, and the derivatives of the dicarboxylic acid from the reaction solution obtained through the depolymerization step to obtain the diamine, the derivatives of the diamine, the dicarboxylic acid, and the derivatives of the dicarboxylic acid; and

[0028] Purification step: separately separating and purifying the diamine and the dicarboxylic acid from the diamine, the derivatives of the diamine, the dicarboxylic acid, and the derivatives of the dicarboxylic acid obtained through the separation step.

[0029] [2] The method for producing a diamine and a dicarboxylic acid according to [1] above, wherein, in the depolymerization step, in a state where there is a space above the reactor that is not filled with an aqueous solution containing the crude polyamide, microwaves are irradiated from above the reactor through a waveguide and the unfilled space using a microwave emitting device.

[0030] [3] The method for producing a diamine and a dicarboxylic acid according to [1] or [2] above, wherein, in the depolymerization step, the heating rate during heating is 25°C / minute or less.

[0031] [4] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to [3] above, wherein, in the depolymerization step, the reactor is equipped with a device for monitoring the pressure inside the reactor and exhausting gas when the pressure is higher than the reference pressure.

[0032] [5] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to [4] above, wherein, in the separation step, the following steps are included: removing components other than the diamine, the derivatives of the diamine, the dicarboxylic acid, and the derivatives of the dicarboxylic acid, which are insoluble substances, from the reaction solution in a state where a part or all of the dicarboxylic acid and / or the derivatives of the dicarboxylic acid and the diamine and the derivatives of the diamine are dissolved in the reaction solution.

[0033] [6] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to [5] above, wherein the pKa of the acid is 0 or less.

[0034] [7] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to [6] above, wherein the amount of the acid is such that the molar ratio of the amide group of the crude polyamide to the proton of the acid is crude polyamide amide group: acid proton = 1:1 to 1:5.5.

[0035] [8] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to [7] above, wherein the acid is hydrochloric acid.

[0036] [9] The method for producing a diamine and a dicarboxylic acid according to [8] above, wherein the concentration of hydrochloric acid in the aqueous solution is 5% by mass or more and 25% by mass or less.

[0037]

[10] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to [9] above, wherein the main component of the polyamide in the waste containing polyamide is polyamide 66.

[0038]

[11] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to

[10] above, wherein in the depolymerization step, a reactor having an inner surface made of a material containing glass lining, zirconium or tantalum is used.

[0039]

[12] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to

[11] above, wherein in the separation step, when removing components other than the diamine, the derivatives of the diamine, the dicarboxylic acid and the derivatives of the dicarboxylic acid, hot filtration and centrifugal separation are carried out.

[0040]

[13] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to

[12] above, wherein in the purification step, the dicarboxylic acid is purified by crystallization.

[0041]

[14] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to

[13] above, wherein in the purification step, the diamine is purified by distillation.

[0042]

[15] The method for producing a diamine and a dicarboxylic acid according to any one of [2] to

[14] above, wherein a partition window for separating the reactor from the microwave emitting device is provided in the middle of the waveguide.

[0043]

[16] The method for producing a diamine and a dicarboxylic acid according to

[15] above, wherein the partition window comprises quartz glass.

[0044]

[17] The method for producing a diamine and a dicarboxylic acid according to any one of [2] to

[16] above, wherein the frequency of the microwave when heating with the microwave is 0.8 GHz to 6 GHz.

[0045]

[18] The method for producing a diamine and a dicarboxylic acid according to any one of [1] to

[17] above, wherein in the purification step, the content of Si element is adjusted to 1 mass ppm or more and 200 mass ppm or less with respect to the total amount of the dicarboxylic acid.

[0046]

[19] A method for recycling a polyamide, wherein a diamine and a dicarboxylic acid are obtained by the method for producing a diamine and a dicarboxylic acid according to any one of [1] to

[18] above, and the method has a polymerization step of polymerizing the diamine and the dicarboxylic acid to obtain a polyamide.

[0047]

[20] A polyamide, which is a polyamide obtained by the method for recycling a polyamide according to

[19] above, wherein the polyamide contains 1 mass ppm or more and 100 mass ppm or less of Si element with respect to the total amount of the polyamide.

[0048] Advantages of the Invention

[0049] According to the present invention, it is possible to provide a method for producing a diamine and a dicarboxylic acid, a method for recycling a polyamide, and a polyamide obtained by this method. Even when the method for producing a diamine and a dicarboxylic acid is carried out industrially, it can be safely carried out under a high-pressure environment, the degree of corrosion of the reaction apparatus is small, the diamine and the dicarboxylic acid can be recovered with high yield and high purity, and a polyamide having physical properties and quality equivalent to those of a polyamide derived from a petrochemical raw material can be obtained by using the obtained monomers as polymerization raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a diagram showing the flow of the method for recycling a polyamide. DETAILED DESCRIPTION OF THE INVENTION

[0051] Hereinafter, the mode for carrying out the present invention (hereinafter, referred to as "the present embodiment") will be described in detail.

[0052] The following present embodiment is an illustration for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be appropriately modified and implemented within the scope of its gist.

[0053] [Method for Producing a Diamine and a Dicarboxylic Acid]

[0054] The method for producing a diamine and a dicarboxylic acid of the present embodiment has the following steps:

[0055] A pretreatment step of performing one or more treatments selected from the group consisting of pulverization, cleaning, and foreign matter separation on the waste containing polyamide to obtain a crude polyamide;

[0056] Depolymerization step: The crude polyamide is put into an aqueous solution containing an acid in a reactor of a closed system, heated to a target temperature of above 90°C and below 160°C, and then heated near the target temperature to depolymerize more than 80% of the amide groups in all the polyamides contained in the crude polyamide into diamines and dicarboxylic acids;

[0057] Separation step: Components other than the diamines, derivatives of the diamines, dicarboxylic acids, and derivatives of the dicarboxylic acids are removed from the reaction solution obtained through the depolymerization step to obtain the diamines, derivatives of the diamines, dicarboxylic acids, and derivatives of the dicarboxylic acids; and

[0058] Purification step: The diamines and the dicarboxylic acids are separately separated and purified from the diamines, derivatives of the diamines, dicarboxylic acids, and derivatives of the dicarboxylic acids obtained through the separation step.

[0059] In addition, in the present embodiment, polyamide is recycled by polymerizing the diamines and dicarboxylic acids obtained by the above method.

[0060] According to the method for manufacturing diamines and dicarboxylic acids and the method for recycling polyamide of the present embodiment, even when implemented industrially, it can be safely implemented in a high-pressure environment, the degree of corrosion of the reaction device is small, diamines and dicarboxylic acids can be recovered with high yield and high purity, and high-quality polyamide can be obtained.

[0061] (Pretreatment step)

[0062] In the method for manufacturing diamines and dicarboxylic acids of the present embodiment, in the pretreatment step, the waste containing polyamide is subjected to one or more treatments selected from the group consisting of crushing, cleaning, and foreign matter separation to obtain crude polyamide.

[0063] <Waste containing polyamide>

[0064] In the method for manufacturing diamines and dicarboxylic acids of the present embodiment, waste containing polyamide is used. Here, the waste does not mean the waste specified in the law (laws related to the treatment and cleaning of waste), but is defined as a general term for waste that is no longer used as a product, waste that cannot be used as a product, etc. As the waste containing polyamide, in addition to polyamide, molded products of polyamide resin compositions, etc., it also includes polyamide and polyamide resin compositions as products.

[0065] Specifically, examples include: unnecessary in-process scraps and non-conforming products discharged from the manufacturing process of polyamide fibers; unnecessary in-process scraps and non-conforming products discharged from the molding process using polyamide; unnecessary in-process scraps and non-conforming products discharged from processes such as weaving and sewing using polyamide fibers; airbags, carpets, clothing products obtained from polyamide fibers, molded products of polyamide discarded after actual use, final products containing polyamide fibers discarded after actual use, and the like.

[0066] Hereinafter, these will be collectively referred to as waste containing polyamide.

[0067] Figure 1 The figure shows a flowchart specifically illustrating the method for recycling polyamide according to this embodiment.

[0068] [Polyamide]

[0069] Polyamide refers to a polymer having an amide bond (-NHCO-) in the main chain.

[0070] As polyamide, polyamides obtained by polymerizing a diamine and a dicarboxylic acid are preferred. Examples of polyamides include: polyamide 46 (polybutylene adipamide), polyamide 56 (polyhexamethylene adipamide), polyamide 66 (polyhexamethylene adipamide), polyamide 410 (polybutylene sebacamide), polyamide 412 (polydodecanedioyl butanediamide), polyamide 610 (polyhexamethylene sebacamide), polyamide 612 (polydodecanedioyl hexanediamide), polyamide 1010 (polydecamethylene sebacamide), polyamide 1012 (polydodecanedioyl decanediamide), polyamide 6T (polyhexamethylene terephthalamide), polyamide 9T (polynonamethylene terephthalamide), polyamide 6I (polyhexamethylene isophthalamide), and copolymers or mixtures thereof, but are not limited thereto.

[0071] In particular, as polyamide, it is preferred to use one or more selected from the group consisting of polyamide 66, polyamide 66 / 6I, polyamide 610, polyamide 612, polyamide 6I, and polyamide 6 as the main component, and more preferably polyamide 66, polyamide 66 / 6I, or a mixture of polyamide 66 and polyamide 6I.

[0072] Here, the main component means a component that accounts for more than 50% by mass relative to the total 100% by mass of the polymer components.

[0073] Polyamide 66 is a polyamide obtained by polycondensation of hexamethylenediamine and adipic acid, and has excellent heat resistance, mechanical strength, and creep characteristics, and is therefore suitable as a material for functional parts of automobiles, machinery, and electrical products or as a high-strength fiber.

[0074] [Polyamide resin composition]

[0075] The polyamide resin composition is a resin composition containing the above polyamide and, as required, inorganic fillers such as glass fiber, lubricants, heat stabilizers, flame retardants, pigments, dyes and other components as other additives.

[0076] 〈Inorganic filler〉

[0077] The polyamide resin composition and its molded article may contain an inorganic filler. Thus, the polyamide resin composition and its molded article tend to have excellent mechanical strength and rigidity.

[0078] Examples of the inorganic filler include, but are not limited to: glass fiber, carbon fiber, calcium silicate fiber, potassium titanate, aluminum borate, glass flake, glass bead, talc, kaolin, mica, hydrotalcite, calcium carbonate, zinc carbonate, zinc oxide, calcium hydrogen phosphate, wollastonite, silica, zeolite, alumina, boehmite, aluminum hydroxide, titanium oxide, silicon oxide, magnesium oxide, calcium silicate, sodium aluminosilicate, magnesium silicate, Ketjen black, acetylene black, furnace black, carbon nanotube, graphite, brass, copper, silver, aluminum, nickel, iron, calcium fluoride, mica, montmorillonite, swelling fluoromica, apatite, etc.

[0079] These inorganic fillers may be used alone or in combination of two or more.

[0080] 〈Lubricant〉

[0081] The polyamide resin composition and its molded article may further contain a lubricant in addition to the above polyamide resin and inorganic filler. Thus, the polyamide resin composition and its molded article tend to have excellent fluidity and appearance.

[0082] 〈Other additives〉

[0083] The polyamide resin composition and its molded article may further contain other additives in addition to the above polyamide, inorganic filler and lubricant.

[0084] Examples of other additives include, but are not limited to: antioxidants, ultraviolet absorbers, heat stabilizers, light degradation inhibitors, plasticizers, mold release agents, nucleating agents, flame retardants, colorants, other thermoplastic resins, etc.

[0085] [Molded article]

[0086] The molded article of the polyamide or polyamide resin composition used in the present embodiment is manufactured by molding by various known methods such as injection molding. The molded article of the present embodiment may be a fiber of the polyamide or polyamide resin composition.

[0087] Polyamides are made into products in various forms such as fibers and films, and are used in a wide range of applications including clothing, carpets, packaging material films, automotive parts, and industrial parts, with an annual usage of over 2 million tons.

[0088] The higher the ratio of polyamide in products suitable for chemical recycling or in polyamide waste from fibers, the higher the recycling efficiency, so it is preferred. For example, about 90% of the base fabric of an airbag made of polyamide 66 is polyamide 66, which is optimal. In addition, polyamide 66 fibers for clothing, bags and other accessories, outdoor goods, sportswear, etc. can also be used.

[0089] In addition, in molded products, there are binding tapes which are one of the representative uses of non-reinforced polyamides.

[0090] On the other hand, in parts for automotive products, glass fiber-reinforced polyamide resin compositions are usually used from the viewpoints of strength and physical properties, and the mass ratio of glass fiber in the molded product is at most 30 mass% - 40 mass%. Therefore, the polyamide component is about 60 mass% - about 70 mass%, and the recycling efficiency of polyamide waste is reduced.

[0091] From such viewpoints, as polyamide waste for chemical recycling, suitable wastes include: the base fabric of airbags, binding tapes, the pile part of carpets, radiator tanks with a glass fiber ratio of about 30 mass% in automotive parts, etc. In addition, compared with used market recycled products, scraps generated in the factory during the manufacturing process are less affected by environmental foreign substances, decomposition products due to deterioration, etc., so they are more preferred.

[0092] As Figure 1 shown, in this embodiment, a pretreatment process is performed on the above polyamide-containing waste.

[0093] In the pretreatment process, the polyamide-containing waste is subjected to one or more treatments selected from the group consisting of crushing, washing, and foreign matter separation to produce crude polyamide. Thus, crude polyamide with a large surface area and capable of more efficiently performing the subsequent depolymerization process is obtained. In this pretreatment process, metals, stones, glass, sand, etc. as inclusions are removed. In washing and foreign matter separation, for example, washing water can be added and specific gravity separation treatment can be used. However, when the purity of polyamide in the polyamide-containing waste is high and there are no obvious inclusions, the washing and foreign matter separation processes can be simplified or omitted.

[0094] By performing the subsequent depolymerization process after the pretreatment process, monomers can be produced with high efficiency.

[0095] <Depolymerization process>

[0096] As Figure 1As shown, after the pretreatment process, a depolymerization process is carried out.

[0097] In the depolymerization process, the above-mentioned crude polyamide obtained in the above-mentioned pretreatment process is put into an aqueous solution containing an acid in a reactor of a closed system, heated to a target temperature of 90 °C or higher and 160 °C or lower, and then heated near the target temperature to depolymerize more than 80% of the amide groups in all the polyamides contained in the above-mentioned crude polyamide, obtaining a reaction solution decomposed into diamine and dicarboxylic acid.

[0098] It should be noted that the above-mentioned "near the target temperature" refers to the temperature range in which the depolymerization reaction continuously occurs stably.

[0099] The cleavage of the amide bond of polyamide requires the supply of energy required to break the amide bond from the outside, so heating is required.

[0100] The heating method is not particularly limited. For example, steam, electric heaters, etc. can be cited. In addition, by using microwaves, depolymerization can be carried out with low energy, and the depolymerization process can be safely implemented even in a high-pressure environment.

[0101] In addition, in order to promote depolymerization, an acid needs to be added. Specific acids will be described later.

[0102] According to the above-mentioned depolymerization process, polyamide, polyamide resin composition, and their molded products can be made into monomers with high yield with low energy, and chemical recycling can be carried out.

[0103] [Reactor]

[0104] In the depolymerization process, a reactor of a closed system is used as the reactor.

[0105] Specifically, due to the gasification of water in the reaction system, the generation of gas evolution caused by the decomposition of organic substances other than polyamide contained in the crude polyamide used as a raw material, and the generation of hydrogen based on the reaction of metals that may be contained as foreign substances in the waste containing polyamide with an acid, etc., the pressure in the reactor may become high, so a pressure-resistant container of a closed system is preferred.

[0106] When microwaves are used in the depolymerization process, in order to efficiently irradiate microwaves into the system, it is preferred to provide a microwave emitting device (magnetron) and a waveguide above the reactor, and adjust it to a state where the reactor is not completely filled with an aqueous solution containing crude polyamide, but has an unfilled portion that does not contain the aqueous solution containing the above-mentioned crude polyamide.

[0107] By irradiating microwaves from the microwave emitting device through the waveguide and the space of the unfilled portion in this state, microwaves can be uniformly irradiated, and there is a tendency for the heating in the system to become more uniform.

[0108] It should be noted that preferably there is a partition window in the middle of the above waveguide that separates the above reactor and the above microwave generating device, allows microwaves to pass through but physically blocks them.

[0109] The above partition window is preferably designed to withstand the increase in internal pressure in the reactor. Specifically, the partition window is preferably made of quartz glass.

[0110] In addition, from the perspective of preventing abnormal increase in internal pressure and reactor breakage caused by sudden gas generation, the above reactor preferably has a device that continuously monitors the internal pressure and exhausts gas when the pressure is higher than the reference pressure.

[0111] [Solvent]

[0112] In the depolymerization process, an aqueous solution containing an acid is used. That is, water is used as the solvent. This is because diamines, dicarboxylic acids, and their derivatives generated by depolymerization are water-soluble, and when removing impurities from the recycled polyamide in subsequent processes, it is easy to physically remove components insoluble in water, such as inorganic fillers like glass fibers, carbon black, pigments, additives, etc. However, as long as an appropriate process for removing impurities from the recycled polyamide can be constructed in subsequent processes, organic solvents such as ethylene glycol and methanol can also be used. In addition, in the depolymerization process, it is not necessary for the crude polyamide, i.e., the waste containing polyamide, to be completely dissolved in the solvent in the form of a polymer. As long as it is partially dissolved and decomposed into monomers in the depolymerization process. During the depolymerization process, since the crude polyamide does not need to be completely dissolved in the solvent in the form of a polymer, it also has the advantages of low thickening in the depolymerization process and the ability to introduce a large amount of crude polyamide into the solvent.

[0113] [Inorganic salt]

[0114] In the depolymerization process, for the purpose of improving the solubility of the crude polyamide, i.e., the waste containing polyamide, in water, an inorganic salt can be added to the aqueous solution. By using an aqueous solution containing an inorganic salt, there is a tendency to further improve the solubility by weakening the hydrogen bonds between the polymer chains of the polyamide.

[0115] Inorganic salts are a general term for salts composed only of inorganic components. For example, metal salts obtained by replacing the hydrogen atoms of an acid with metal ions can be cited.

[0116] As the above metal salts, for example, from the perspective of being suitable for depolymerization, calcium, zinc, lithium, chromium, iron, and cobalt halides can be cited. Specifically, calcium chloride, zinc chloride, zinc bromide, chromium bromide, iron bromide, lithium chloride, lithium bromide, cobalt chloride, etc. can be cited, but it is not limited thereto. From the perspectives of availability and safety, calcium chloride, zinc chloride, and lithium chloride are preferred.

[0117] [Acid]

[0118] In the depolymerization step, the crude polyamide is put into an aqueous solution containing an acid.

[0119] It is considered that the acid acts as a catalyst for the hydrolysis of the polyamide.

[0120] Examples of the acid include organic acids such as methanesulfonic acid, trifluoromethanesulfonic acid, p-toluenesulfonic acid, and trifluoroacetic acid; inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; Sc(OTf) 3 , Yb(OTf) 3 , Nb 2 O 5 , CeO 2 and other Lewis acids, etc., but not limited thereto. They can be used alone or in combination of multiple kinds. However, in order to obtain a high depolymerization rate during depolymerization, an acid with a pKa of 0 or less is preferred.

[0121] In addition, from the viewpoints of reaction efficiency, reduction of impurities, and reduction of waste that is difficult to regenerate, the above acid is preferably hydrochloric acid.

[0122] The amount of the acid (number of moles of protons released) used in the depolymerization step is preferably in excess relative to the number of moles of amide groups in the polyamide. On the other hand, when a significantly excessive amount of acid is used, the amount of polyamide input in the depolymerization step will inevitably become relatively small. Therefore, from the viewpoint of productivity, it is preferred that the amount of acid is not excessive. In particular, as the amount of acid increases, the amount of water in the system increases. Therefore, the load of the water removal process during the purification of diamine in the subsequent process becomes high, resulting in an increase in cost and an increase in GHG emissions. In addition, when a significantly excessive amount of acid is used, a large amount of salt is generated in the neutralization step after the depolymerization step, resulting in an increase in the load and cost of the salt treatment process. From the above viewpoints, it is also preferred that the amount of acid is not excessive.

[0123] From the above viewpoints, the molar ratio of the amide group in the crude polyamide to the proton of the acid is preferably crude polyamide amide group∶acid proton = 1∶1 to 1∶5.5, more preferably 1∶1 to 1∶3, and further preferably 1∶1.15 to 1∶2.

[0124] Regarding the concentration of the acid in the above aqueous solution in the depolymerization step, as a result of analysis based on the Arrhenius formula, as the concentration of hydrochloric acid increases, the activation energy Ea decreases, making the reaction easier to proceed, but at the same time, as the number of water molecules decreases, the frequency factor A decreases, making the reaction difficult to proceed. Therefore, there is an optimal range for the hydrochloric acid concentration, which is preferably 5% by mass or more and preferably 25% by mass or less.

[0125] More preferably, it is 10% by mass to 25% by mass, and further preferably 12% by mass to 22% by mass.

[0126] [Temperature increase]

[0127] In the depolymerization process, the crude polyamide is put into an aqueous solution containing an acid, and the temperature is raised to a target temperature of 90 °C or higher and 160 °C or lower.

[0128] From the viewpoint of achieving a good balance between the input energy during temperature increase and the energy required to maintain a specified temperature after reaching the specified temperature, and optimizing the equipment efficiency, the heating rate during the above-mentioned temperature increase is preferably 25 °C / min or less, more preferably 20 °C / min or less, and further preferably 15 °C / min or less.

[0129] In addition, from the viewpoint of preventing the generation of outgassing due to the decomposition of organic substances other than polyamide contained in the crude polyamide, that is, waste containing polyamide, or preventing the abnormal increase in internal pressure due to the generation of hydrogen gas resulting from the reaction of metals that may be contained as foreign substances with the acid, and thus preventing the reactor from being damaged, the heating rate is also preferably set to a certain value or less within the above-mentioned numerical range. If the internal pressure abnormally rises, in the case of microwave heating, if the power supply is stopped, the heating will immediately stop. Therefore, from the viewpoint of safety, it is also preferable to use microwaves.

[0130] In addition, from the viewpoint of shortening the time of the depolymerization process, the heating rate during the above-mentioned heating is preferably 1 °C / min or more, more preferably 2 °C / min or more, and further preferably 3 °C / min or more.

[0131] From the viewpoints of suppressing side reactions and the corrosion resistance of the reactor, the target temperature is set to 90 °C or higher and 160 °C or lower, preferably 95 °C to 150 °C, more preferably 100 °C to 145 °C, and further preferably 110 °C to 140 °C.

[0132] From the viewpoints of shortening the heating time and the effect of reducing GHG, the heating method for temperature increase preferably uses microwaves. In addition, any of the known methods such as steam and electric heaters can also be used. These methods can be used alone or in combination of two or more.

[0133] [Heating]

[0134] In the above-mentioned depolymerization process, after the temperature is raised to the target temperature as described above, heating is carried out near the target temperature.

[0135] Near the target temperature means that the temperature difference between the temperature inside the system during heating and the target temperature is within 10 °C. During heating, it is preferably 90 °C or higher and 160 °C or lower, more preferably 95 °C to 150 °C, further preferably 100 °C to 145 °C, and further more preferably 110 °C to 140 °C.

[0136] The heating method can be any of the well-known methods such as using steam, electric heaters, etc. From the perspective of shortening the heating time and reducing the effect of GHG, the method using microwaves is preferably used.

[0137] [Microwave irradiation]

[0138] As the irradiation output power of the microwaves during the above heating, the output power capable of heating to the above temperature can be appropriately selected. There is no particular limitation on the upper limit of the above irradiation output power.

[0139] There is no particular limitation on the frequency of the microwaves. For example, it is preferably set to 0.8 GHz to 6 GHz. From the perspective of making it easier for the microwaves to reach inside the system of the depolymerization process, the above frequency is more preferably 0.8 GHz to 2.5 GHz, further preferably 0.8 GHz to 1.5 GHz, further more preferably 0.8 GHz to 1 GHz, and even more preferably 0.9 GHz to 0.95 GHz.

[0140] [Corrosion resistance]

[0141] In the depolymerization process, as the reactor, a reactor with a small degree of corrosion and industrial practicality is preferably used. Specifically, a reactor with an inner surface made of materials such as glass-lined, zirconium, and tantalum is preferably used. The corrosion resistance can be judged, for example, according to the data described in "Properties of Tantalum for Applications in the Chemical Process Industry: F.J. Hunkeler (USA) ASTM STP849, 1984, P28 - 49".

[0142] [Degree of depolymerization of polyamide in the depolymerization process]

[0143] In the depolymerization process, in the manufacturing method of diamine and dicarboxylic acid of the present embodiment, from the perspective of achieving a high recovery rate, more than 80% of the amide groups in all the polyamides contained in the crude polyamide are depolymerized.

[0144] On the other hand, from the perspective of the recovery of decomposition products, the dicarboxylic acid, diamine, and their derivatives as decomposition products are 80% by mass or more in all the polyamides contained in the crude polyamide.

[0145] The residual rate of polyamide is preferably 10% or less, more preferably 7% or less, further preferably 5% or less, and even more preferably 1% or less, based on the amide groups in all the polyamides contained in the crude polyamide.

[0146] Regarding the depolymerization rate, among all the polyamides contained in the crude polyamide, it is preferable to depolymerize 85% or more of the amide groups, more preferably 90% or more, and still more preferably 95% or more.

[0147] The depolymerization rate of the above polyamide, the amount of the decomposition products, and the residual rate of the polyamide can be controlled within the above numerical ranges by adjusting the concentration of the acid, the reaction time, and the temperature.

[0148] <Separation step>

[0149] As Figure 1 shown, in the present embodiment, the separation step is carried out after the above depolymerization step.

[0150] In the separation step, from the reaction solution obtained through the above depolymerization step, in a state where a part or all of the above dicarboxylic acid and / or the derivative of the above dicarboxylic acid is dissolved in the reaction solution, components other than the above diamine, the derivative of the above diamine, the above dicarboxylic acid, and the derivative of the above dicarboxylic acid are removed as insoluble matters, and the above diamine, the derivative of the above diamine, the above dicarboxylic acid, and the derivative of the dicarboxylic acid are obtained.

[0151] In the waste containing polyamide and the crude polyamide obtained in the pretreatment step, there are sometimes impurities from dirt such as glass fiber, carbon fiber, other inorganic fillers, various coating agents having a water-repellent function, and sand. They remain as solids insoluble in the reaction solution after the depolymerization step, so most of them are removed in the separation step. The separation method is not particularly limited, and examples thereof include sedimentation separation of insoluble matters, centrifugal separation, filtration, etc.

[0152] As a specific method for separating components other than diamine, the derivative of the above diamine, dicarboxylic acid, and the derivative of the above dicarboxylic acid, for example, known methods such as filtration using a filter, methods using an ion exchange membrane, an ion exchange resin, etc. can be used according to the object to be removed. However, usually, metals, glass, glass fiber, sand, etc. are contained in the waste containing polyamide. Therefore, from the viewpoints of process efficiency and energy saving, it is preferable to remove these foreign matters by hot filtration or the like during the period when the temperature of the reaction solution is high after the depolymerization step. The temperature of the hot filtration is preferably a temperature at which the diamine, the derivative of the above diamine, the dicarboxylic acid, and the derivative of the above dicarboxylic acid do not precipitate. Therefore, it is preferably 55°C or higher, more preferably 60°C or higher, and still more preferably 65°C or higher.

[0153] In the present embodiment, in order to improve the recovery rates of diamines and dicarboxylic acids, in the separation step, it is preferable to separate insoluble substances in a state where a part or all of the dicarboxylic acid and / or the derivative of the dicarboxylic acid and a part or all of the diamine and the derivative of the diamine are dissolved in the reaction liquid obtained in the above depolymerization step, for example, within the temperature range in which they are dissolved in the reaction liquid, and it is more preferable to separate insoluble substances in a state where all amounts are dissolved.

[0154] It should be noted that in the separation step, it is not necessarily required to remove all amounts of insoluble substances, and a small amount of residual solids can also be removed again in the purification step described later for separating and purifying diamines and dicarboxylic acids.

[0155] In the present embodiment, it is also preferable to remove insoluble solids simultaneously with the dicarboxylic acid precipitated from the reaction liquid in the purification step described later. In this case, in subsequent steps, the dicarboxylic acid can be selectively dissolved completely in a solvent from the mixture of the dicarboxylic acid and the insoluble solids, and only the insoluble substances can be separated from this solution to remove the solids.

[0156] <Purification step>

[0157] As Figure 1 shown, in the present embodiment, the purification step is carried out after the separation step.

[0158] In the purification step, diamines and dicarboxylic acids are separately separated and purified from the diamines and derivatives of diamines and dicarboxylic acids and derivatives of dicarboxylic acids obtained through the above separation step.

[0159] In the purification step of separately separating and purifying diamines and dicarboxylic acids, known methods can be used without particular limitation, and for example, the following methods can be cited.

[0160] [Separation and purification process of diamines]

[0161] In the method for separating and purifying diamines in the purification step, the diamine is dissolved in the liquid after the above separation step in the form of a diamine salt of a dicarboxylic acid (such as adipic acid) or an acid (such as hydrochloric acid). As a method for separating the diamine from the solution containing the diamine salt, neutralization treatment can be cited. By adjusting the pH to within the range of 7 to 14, the diamine can be liberated from the diamine salt. The base used in the neutralization treatment only needs to have a pKa larger than that of the diamine to be separated as the target substance. As the above base, for example, sodium hydroxide, calcium hydroxide, potassium hydroxide, etc. are generally used industrially.

[0162] As a method for purifying the liberated diamine to a purity suitable for polymerization of polyamide, for example, purification by distillation can be mentioned. Purification by distillation can also remove the residues contained in the crude polyamide. When the reaction solution after the above separation step contains a compound having a carboxylic acid, during the heating of distillation, the diamine polymerizes with the carboxylic acid, resulting in a decrease in the yield of the diamine and fouling on the apparatus. Therefore, it is preferable to remove the carboxylic acid by methods such as crystallization, physical adsorption using activated carbon or ion exchange resin, and membrane separation before distillation.

[0163] In addition, as other methods for purifying diamines, extraction using a solvent forming an organic phase, a method using membrane separation, etc. can be mentioned.

[0164] [Separation and purification process of dicarboxylic acid]

[0165] In the method for separating and purifying dicarboxylic acid in the purification process, purification by crystallization is preferably carried out after the above separation step.

[0166] As purification by crystallization, for example, the following method can be mentioned: precipitating the dicarboxylic acid from the reaction solution obtained in the above separation step, performing crystallization by recrystallization, obtaining crude dicarboxylic acid crystals by solid-liquid separation, then adding the obtained crude dicarboxylic acid crystals to pure water and dissolving them, performing crystallization and solid-liquid separation, and drying to obtain purified dicarboxylic acid.

[0167] During crystallization, the solution can be stirred or heated to dissolve the crude dicarboxylic acid crystals, or it can be aged for an appropriate time for crystal growth. The drying conditions can be appropriately selected as long as they are below the melting point of the dicarboxylic acid.

[0168] The dicarboxylic acid obtained in the above separation step is different from the dicarboxylic acid produced by the usual production method, and metal compounds and organic compounds from additives and pigments remain as impurities. These impurities cause the coloring of the dicarboxylic acid and act as polymerization inhibitors when polymerized into polyamide again. Therefore, it is preferable to remove these impurities by crystallization in this separation and purification process. For example, washing the dicarboxylic acid obtained by crystallization with inorganic acids such as nitric acid, sulfuric acid, and hydrochloric acid, physical adsorption using ion exchange resin or activated carbon, membrane separation, etc. can be mentioned as suitable methods.

[0169] For the dicarboxylic acid purified in this way, the remaining water can be dried and recovered in the form of dicarboxylic acid crystals, or it can be mixed with diamine without drying and used as a dicarboxylic acid-diamine salt.

[0170] It should be noted that in this embodiment, as Figure 1As shown, it is preferred to first separate the dicarboxylic acid from the reaction solution obtained in the separation step, and then separate the diamine after treating the residual catalyst, and purify the above-mentioned dicarboxylic acid and diamine respectively.

[0171] [Content of Si element]

[0172] In the above purification step, from the viewpoints of appropriate viscosity of the polyamide and stabilization of the polymerization when producing the polyamide by polymerizing the dicarboxylic acid and the diamine, and good processability of the obtained polyamide, it is preferred to adjust the content of the Si element to 1 mass ppm or more relative to the total amount of the above-mentioned dicarboxylic acid. In addition, from the viewpoint of preventing polymerization inhibition when producing the polyamide by polymerizing the dicarboxylic acid and the diamine, it is preferred to adjust the content of the Si element to 200 mass ppm or less.

[0173] The content of the Si element is more preferably 1 mass ppm to 150 mass ppm, further preferably 1 mass ppm to 120 mass ppm, and still further preferably 1 mass ppm to 100 mass ppm.

[0174] The Si element comes from waste polyamide, and by adjusting the purification step, it can be controlled within the above numerical range.

[0175] [Method for recycling polyamide]

[0176] In the method for recycling polyamide of the present embodiment, as Figure 1 shown, there is a polymerization step of polymerizing the diamine and the dicarboxylic acid obtained by the method for producing the diamine and the dicarboxylic acid of the above-mentioned present embodiment to obtain a polyamide. Thus, the polyamide can be recycled. Regarding the polymerization step, a known method can be used, and there is no particular limitation. For example, the following methods can be cited.

[0177] (Polymerization step)

[0178] In the polymerization step, a method is usually often used in which an aqueous solution or a water suspension of a dicarboxylic acid-diamine salt or a mixture of a dicarboxylic acid and a diamine is heated and polymerized while maintaining a molten state (hereinafter, also referred to as "thermal melt polymerization method"), but it is not limited thereto, and polymerization can be carried out by a known method such as solid-phase polymerization method or solution method.

[0179] As specific production methods of polyamide using the purified diamine and dicarboxylic acid, for example, various methods exemplified below can be cited.

[0180] (1)A method of heating an aqueous solution or a water suspension of a dicarboxylic acid-diamine salt or a mixture of a dicarboxylic acid and a diamine and performing polymerization while maintaining a molten state (hereinafter, also referred to as "thermal melt polymerization method").

[0181] (2)A method of increasing the degree of polymerization while maintaining a solid state of the polyamide obtained by the thermal melt polymerization method at a temperature below the melting point (hereinafter, also referred to as "thermal melt polymerization-solid phase polymerization method").

[0182] (3)A method of polymerizing a dicarboxylic acid-diamine salt or a mixture of a dicarboxylic acid and a diamine while maintaining a solid state (hereinafter, also referred to as "solid phase polymerization method").

[0183] (4)A method of polymerizing using a dicarboxylic acid acyl halide component equivalent to a dicarboxylic acid and a diamine component (hereinafter, also referred to as "solution method").

[0184] Among them, a production method preferably including the thermal melt polymerization method is preferred. When producing a polyamide by the thermal melt polymerization method, it is preferred to maintain a molten state until the polymerization is completed. In order to maintain a molten state, it is necessary to carry out production under polymerization conditions suitable for the polyamide composition. For example, it can be cited: controlling the polymerization pressure in the thermal melt polymerization method to 14 kg / cm 2 ~25 kg / cm 2 (gauge pressure), while continuously heating, reducing the pressure for more than 30 minutes until the pressure in the tank reaches atmospheric pressure (gauge pressure is 0 kg / cm 2 ).

[0185] As the polymerization method of the polyamide, there is no particular limitation, and it can be a batch type or a continuous type.

[0186] As the polymerization apparatus used in the production of the polyamide, there is no particular limitation, and a known apparatus can be used. For example, it can be cited: an autoclave type reactor, a drum type reactor, and an extruder type reactor such as a kneader, etc.

[0187] Hereinafter, as a method for producing a polyamide, a method for producing a polyamide by an intermittent thermal melt polymerization method is specifically shown, but the method for producing a polyamide is not limited thereto.

[0188] First, for example, an aqueous solution containing about 40% to about 60% by mass of a raw material component of a polyamide (dicarboxylic acid, diamine, and lactam and / or aminocarboxylic acid as required) is concentrated to about 65% to about 90% by mass in a concentration tank operated at a temperature of 110°C to 180°C and a pressure of about 0.035 MPa to about 0.6 MPa (gauge pressure) to obtain a concentrated solution.

[0189] Next, transfer the obtained concentrated solution to an autoclave and continue heating until the pressure in the autoclave reaches about 1.2 MPa to about 2.2 MPa (gauge pressure).

[0190] Then, in the autoclave, while withdrawing water and / or gas components, maintain the pressure at about 1.2 MPa to about 2.2 MPa (gauge pressure). When the temperature reaches about 220 °C to about 260 °C, reduce the pressure to atmospheric pressure (gauge pressure is 0 MPa).

[0191] After reducing the pressure in the autoclave to atmospheric pressure, perform decompression as needed, whereby by-products of water can be effectively removed.

[0192] Then, pressurize the autoclave with an inert gas such as nitrogen and extrude the polyamide melt from the autoclave in the form of a strand. Cool and cut the extruded strand to obtain polyamide pellets.

[0193] Regarding the polyamide obtained by the above polyamide recycling method, from the viewpoint that the viscosity does not become too high when adding additives and performing melt-kneading, and the processability of the melt-kneaded product is good, the content of Si element is preferably adjusted to 1 mass ppm or more relative to the total amount of the above polyamide. In addition, from the viewpoint of suppressing the decrease in the molecular weight of the polyamide, the content of Si element is preferably adjusted to 100 mass ppm or less.

[0194] More preferably, it is 1 mass ppm to 50 mass ppm, and further preferably 1 mass ppm to 30 mass ppm.

[0195] In the polyamide obtained by the above polymerization step, as Figure 1 shown, various additives can be blended according to the desired physical properties. By melt-kneading this polyamide, the target recycled polyamide is finally obtained.

[0196] Examples

[0197] Hereinafter, specific examples and comparative examples are listed to explain the present invention in more detail, but the present invention is not limited by the following examples and comparative examples at all.

[0198] Purified monomers and polymers were obtained in the examples and comparative examples using the following raw materials, etc. through the following processes, and evaluated by the following methods.

[0199] [Polyamide for chemical recycling, polyamide resin composition, waste containing polyamide]

[0200] (Polyamide)

[0201] A: Polyamide 66 (manufactured by Asahi Kasei Corporation, model: LEONA 1300)

[0202] (Polyamide resin composition)

[0203] B: Polyamide 66 resin composition (manufactured by Asahi Kasei Corporation, model: LEONA 14G33, glass fiber ratio is 33%)

[0204] In the following Examples and Comparative Examples, mainly from the viewpoints of scrap utilization and inventory recycling, these polyamides and polyamide resin compositions are also used as "waste containing polyamide" and "crude polyamide" in the same way as the following waste.

[0205] (Waste of molded product of polyamide resin composition)

[0206] The cover of a discarded automotive recycled radiator tank.

[0207] It is engraved with >PA66+GF30<, with polyamide 66 as the main component and containing 30% by mass of glass fiber.

[0208] (Waste of cloth-like polyamide fiber)

[0209] Discarded automotive recycled airbags.

[0210] It is embossed with PA66, with polyamide 66 as the main component.

[0211] Note that both colored airbags (with silicone coating) and plain (without silicone coating) are used.

[0212] [Pretreatment process for producing crude polyamide by crushing waste containing polyamide]

[0213] (Crushing of molded product of polyamide resin composition)

[0214] The molded product of the polyamide resin composition is crushed using a crusher "PFS-40" manufactured by CIM of Japan. After crushing, it becomes resin flakes with an irregular shape having a length of 3 mm to 6 mm.

[0215] (Crushing of cloth-like waste of polyamide fiber (airbag))

[0216] The airbag scraps and waste airbags are cut into appropriate sizes.

[0217] The cut size is preferably a size with a side length of about 1 cm to about 10 cm, but it varies depending on the equipment used and the processing amount, so there is no particular limitation on the cut size of the airbag scraps and waste airbags.

[0218] (Treatment of polyamide 66 and polyamide 66 resin composition)

[0219] Regarding the above polyamide 66 (manufactured by Asahi Kasei Corporation, model: LEONA 1300) and polyamide 66 resin composition (manufactured by Asahi Kasei Corporation, model: LEONA 14G33, glass fiber ratio: 33%), they are used as crude polyamides in the form of granules.

[0220] [Solvent used in the depolymerization process]

[0221] (Acid)

[0222] The following inorganic acids and organic acids are used as acids.

[0223] Hydrochloric acid (special grade, purity 35% - 37%), manufactured by Kanto Chemical Co., Inc.

[0224] Sulfuric acid (special grade, purity > 96%), manufactured by Kanto Chemical Co., Inc.

[0225] Phosphoric acid (special grade, purity 85%), manufactured by Hayashi Pure Chemical Industries, Ltd.

[0226] Methanesulfonic acid, manufactured by TCI

[0227] p-Toluenesulfonic acid monohydrate, manufactured by TCI

[0228] [Base used in the purification process for separating and purifying diamine]

[0229] (Base)

[0230] As the base used to neutralize the acid in the purification process, the following sodium hydroxide is used.

[0231] Sodium hydroxide, manufactured by TCI

[0232] [Preparation of the sample solution used in the depolymerization process]

[0233] In a 20 mL glass pressure test tube (Reaction Vial G30 manufactured by Anton Paar), weigh inorganic acid or organic acid, water, polyamide, polyamide resin composition, and crude polyamide according to Tables 1 - 3 below.

[0234] It should be noted that in the case of the polyamide resin composition, the resin component amount after removing the mass of the inorganic filler is used as the polyamide amount, which is consistent with the polyamide amount in other systems.

[0235] The compositions of sample solutions 1 - 18 used in each example and comparative example are shown in Tables 1 - 3.

[0236] [Table 1]

[0237]

[0238] [Table 2]

[0239]

[0240] [Table 3]

[0241]

[0242] [Examples 1 to 37][Comparative Examples 1 to 16]

[0243] Using each of the sample solutions 1 to 18 shown in Tables 1 to 3, a depolymerization step was carried out under the conditions of Tables 4 to 8 and Table 10.

[0244] Table 9 shows the analysis results of purified hexamethylenediamine and adipic acid and the analysis results of the polymerized polyamide 66.

[0245] [Depolymerization Step]

[0246] [Microwave Heating]

[0247] A magnetic stir bar, a specified amount of polyamide, polyamide resin composition, or crude polyamide was placed into a pressure test tube, and 37% hydrochloric acid and distilled water were added to achieve a desired mass percentage. Using a microwave synthesis reactor (Monowave 450 manufactured by Anton Paar GmbH), the mixture was stirred at a specified temperature for a desired time. It should be noted that the temperature increase process until the specified temperature was fixed at a temperature increase time of 16 minutes, and the rotation speed of the magnetic stir bar was set at 600 rpm.

[0248] Depolymerization was carried out at a specified temperature for a desired time, and then the mixture was naturally cooled inside the apparatus. The pressure test tube was taken out when the temperature dropped to 70 °C.

[0249] It should be noted that when the scale for obtaining monomers for polymerization shown in Examples 28 to 32 was increased, depolymerization was carried out under the following conditions using StartSYNTH of Milestone General Co., Ltd.

[0250] A magnetic stir bar, 30 g of polyamide, polyamide resin composition, or crude polyamide was placed into a pressure vessel, and 37% hydrochloric acid and distilled water were added to make it 11% hydrochloric acid. The mixture was stirred at 140 °C for 1 hour. It should be noted that the temperature increase process until the specified temperature was fixed at a temperature increase time of 20 minutes, depolymerization was carried out, and then the mixture was naturally cooled inside the apparatus. The pressure vessel was taken out when the temperature dropped to 80 °C.

[0251] In addition, in Examples 28 to 32, the actual recovery rates of adipic acid and hexamethylenediamine actually recovered after purification were calculated by the following method. The mass of the pure polyamide component in the polyamide, polyamide resin composition, and crude polyamide input was calculated. The theoretically maximum recovery mass obtained by depolymerizing 100% of the pure polyamide component, generating 100% diamine and dicarboxylic acid without secondary reactions after depolymerization, and recovering 100% without physical loss during purification was set as 100%. The ratio of the mass of the actually recovered adipic acid and hexamethylenediamine to the theoretically maximum recovery mass was used as the actual recovery rate (%).

[0252] <Normal heating>

[0253] A magnetic stirrer, a specified amount of polyamide, polyamide resin composition, and crude polyamide were put into a PTFE pressure-resistant container (a microwave / material decomposition container manufactured by Toei Co., Ltd., temperature measurement type), and 37% hydrochloric acid and distilled water were added to achieve a desired mass percentage. Stirring was carried out at a specified temperature for a desired time using an oil bath.

[0254] It should be noted that the depolymerization time is the time starting from when the internal temperature reaches the specified temperature. The heating-up times using the oil bath for each example are shown in Tables 4 and 10.

[0255] In microwave heating and normal heating, the depolymerization time was fixed at 1 hour, and the results of varying the depolymerization temperature are shown in Table 4.

[0256] In addition, the results of varying the depolymerization time and depolymerization temperature in microwave heating and normal heating are shown in Table 5.

[0257] <Measurement of depolymerization rate>

[0258] [Evaluation of the amount of hexamethylenediamine (HMD) and its derivatives relative to the polyamide before the depolymerization process and evaluation of the amount of adipic acid (ADA) and its derivatives relative to the polyamide before the depolymerization process]

[0259] A sample of the reaction solution after the depolymerization process was taken and measured by the NMR method to calculate the depolymerization rate (%) of the polyamide.

[0260] The hydrolyzed solutions obtained in the examples and comparative examples were added to an NMR tube with a diameter of 5 mm. Then, an NMR special sample tube N-502B (manufactured by Nippon Precision Science Co., Ltd.) filled with benzene-d6 in the measurement part was inserted into the NMR tube with a diameter of 5 mm. Measurement was carried out using an NMR apparatus (ECZ-500) manufactured by JEOL Ltd., with 1H as the observed nucleus, at a measurement temperature of 25°C and a cumulative number of 1024 times.

[0261] The depolymerization rate of the polyamide was calculated as (integral value of hexamethylenediamine) / (integral value of hexamethylenediamine + integral value of amide bond) from the integral values of hexamethylenediamine and amide bond.

[0262] [Separation process]

[0263] The solution after the depolymerization process was heated and hot filtered at 85 °C to remove solid matter (including glass fiber, silicon coating, metal sheet, etc.) as insoluble matter.

[0264] Next, the filtrate was cooled to room temperature, and thus the dicarboxylic acid precipitated in the form of crystals. The dicarboxylic acid crystals and the filtrate were separated by filtration.

[0265] [Purification process]

[0266] (Purification of dicarboxylic acid)

[0267] The dicarboxylic acid crystals obtained in the above separation process were dissolved in water in an amount more than the mass of the crystals, heated to 80 °C to dissolve them in water, and after dissolution, cooled by standing to recrystallize the dicarboxylic acid. The precipitated dicarboxylic acid crystals were recovered by filtration.

[0268] (Purification of diamine)

[0269] Sodium hydroxide was slowly added to the filtrate obtained in the above separation process, and sodium hydroxide in an amount equimolar or more relative to hydrochloric acid was added. Salt precipitation was confirmed. The neutralized reaction solution was distilled using a Kugelrohr. After heating at 100 °C and 300 mbar, the temperature was slowly raised and the pressure was reduced to 110 °C and 160 mbar, held for 3 hours, further raised the temperature and reduced the pressure to 140 °C and 80 mbar, held for about 1 hour, and finally the target diamine was recovered.

[0270] (Analysis of monomers)

[0271] The NMR of the purified diamine and dicarboxylic acid was measured, and it was confirmed that they were the target substances.

[0272] In addition, trace impurities were confirmed by ICP - AES semi - quantitative method. It should be noted that as the analytical device, an ICP emission spectrometry device, SPS3520UV - DD manufactured by Hitachi (SII) was used.

[0273] [Polymerization method of polyamide]

[0274] The polymerization reaction of polyamide was carried out as follows by the "thermal melting polymerization method".

[0275] 150 g of an equimolar salt of adipic acid and hexamethylenediamine recovered in the above-described manner was dissolved in 150 g of distilled water to prepare a 50 mass% homogeneous aqueous solution of equimolar raw material monomers. This aqueous solution was put into an autoclave with an internal volume of 0.5 L and purged with nitrogen.

[0276] While stirring at a temperature of 110°C to 150°C, water vapor was slowly removed and concentrated until the solution concentration reached 70 mass%. Then, the internal temperature was raised to 220°C. At this time, the autoclave was pressurized to 1.8 MPa. This state was maintained for 1 hour until the internal temperature reached 245°C, and while slowly removing water vapor and maintaining the pressure at 1.8 MPa, the reaction was carried out for 1 hour.

[0277] Next, the pressure was reduced over 1 hour.

[0278] Then, the inside of the autoclave was maintained under a reduced pressure of 650 Torr (86.66 kPa) for 10 minutes using a vacuum device. At this time, the final internal temperature of the polymerization was 265°C.

[0279] Then, it was pressurized with nitrogen, formed into a strand shape from the lower spinneret (nozzle), water-cooled and cut, discharged in granular form, and dried in a nitrogen atmosphere at 100°C for 12 hours to obtain polyamide. Mw = 35000, Mw / Mn = 2.0.

[0280] (Analysis of Polyamide)

[0281] The NMR of the obtained polyamide was measured, and it was confirmed that it was polyamide 66.

[0282] Trace impurities were confirmed by ICP-AES semi-quantitative analysis. As an analytical device, an ICP emission spectroscopic analyzer, SPS3520UV-DD manufactured by Hitachi (SII), was used.

[0283] [Evaluation of Corrosion Resistance]

[0284] The corrosion resistance was evaluated based on the example of zirconium in the graph of hydrochloric acid concentration and temperature described in "Properties of Tantalum for Applications in the Chemical Process Industry: F.J. Hunkeler (USA) ASTM STP849, 1984, P28-49".

[0285] When the corrosion of the wire exceeded 5 mpy (5 mils / year), it was evaluated as ×, when it was near the 5 mpy line, it was evaluated as △, and when it was away from the 5 mpy line downward, it was evaluated as 〇, ◎.

[0286] [Table 4]

[0287]

[0288] [Table 5]

[0289]

[0290] [Table 6]

[0291]

[0292] [Table 7]

[0293]

[0294] [Table 8]

[0295]

[0296] [Table 9]

[0297]

[0298] [Table 10]

[0299]

[0300] In each of the examples, by depolymerizing at a depolymerization rate of 80% or more, through separation and purification, a high recovery efficiency of the actual monomers was achieved. Specifically, as shown in Examples 28 to 32, the recovery efficiency of the actual monomers was 82% or more. It should be noted that in the comparative examples, even in Comparative Example 7 with the highest depolymerization rate, it was 75%. Even if all 75% decomposed without secondary reactions changing entirely to adipic acid and hexamethylenediamine and could be recovered without physical losses during purification, the actual recovery rate would not exceed 75%. Therefore, it is considered that it would not exceed 83%, the lowest actual recovery rate in the examples.

[0301] In addition, in each of the examples, it was confirmed that the corrosion degree of the reaction apparatus was small, high-purity hexamethylenediamine and adipic acid could be obtained in high yields from various polyamide-containing waste materials, and furthermore, polyamide 66 could be polymerized using the purified hexamethylenediamine and adipic acid.

[0302] This application is based on a Japanese patent application (Japanese Patent Application No. 2023-165285) filed with the Japan Patent Office on September 27, 2023, the content of which is incorporated herein by reference.

[0303] Industrial Applicability

[0304] The method for producing a diamine and a dicarboxylic acid of the present invention and the method for recycling a polyamide have industrial applicability as an efficient recycling method for polyamide resins, polyamide fibers, polyamide resin compositions, and molded articles used in automotive parts and various industrial parts.

Claims

1. A method for producing a diamine and a dicarboxylic acid, wherein: The manufacturing method comprises the following steps: A pre-treatment step of subjecting the waste containing polyamide to one or more treatments selected from the group consisting of crushing, washing, and foreign matter separation to obtain crude polyamide; a depolymerization step of placing the crude polyamide into an aqueous solution containing an acid in a reactor of a closed system, raising the temperature to a target temperature of 90° C. to 160° C., and then heating at about the target temperature to depolymerize more than 80% of the amide groups of all the polyamides contained in the crude polyamide into diamines and dicarboxylic acids; a separation step of removing components other than the diamine and the diamine derivative and the dicarboxylic acid and the dicarboxylic acid derivative from the reaction solution obtained in the depolymerization step to obtain the diamine and the diamine derivative and the dicarboxylic acid and the dicarboxylic acid derivative; as well as A purification step of isolating and purifying the diamine and the dicarboxylic acid from the diamine and the diamine derivative and the dicarboxylic acid and the dicarboxylic acid derivative obtained in the separation step.

2. The method for producing a diamine and a dicarboxylic acid according to claim 1, wherein: In the depolymerization step, in a state where there is a space above the reactor that is not filled with the aqueous solution containing the crude polyamide, microwaves are irradiated from above the reactor through a waveguide and the unfilled space using a microwave emitting device.

3. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: In the depolymerization step, the temperature increase rate during the temperature increase is 25° C. / min or less.

4. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: In the depolymerization step, the reactor has a device for monitoring the pressure in the reactor and venting the reactor when the pressure exceeds a reference pressure.

5. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: The separation step includes the step of removing components other than the diamine and the diamine derivative and the dicarboxylic acid and the dicarboxylic acid derivative as insoluble matter from the reaction solution while a part or all of the dicarboxylic acid and / or the dicarboxylic acid derivative and the diamine and the diamine derivative are dissolved in the reaction solution.

6. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: The pKa of the acid is 0 or less.

7. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: The amount of the acid is calculated as a ratio of the molar number of the amide group of the crude polyamide to the proton of the acid, amide group of the crude polyamide:proton of the acid=1:1 to 1:5.

5.

8. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: The acid is hydrochloric acid.

9. The method for producing a diamine and a dicarboxylic acid according to claim 8, wherein: The concentration of the hydrochloric acid in the aqueous solution is 5 mass % or more and 25 mass % or less.

10. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: The main component of the polyamide in the polyamide-containing waste is polyamide 66.

11. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: In the depolymerization step, a reactor having an inner surface made of a material including glass lining, zirconium or tantalum is used.

12. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: In the separation step, hot filtration and centrifugal separation are performed when removing components other than the diamine and the diamine derivative and the dicarboxylic acid and the dicarboxylic acid derivative.

13. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: In the purification step, the dicarboxylic acid is purified by crystallization.

14. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: In the purification step, the diamine is purified by distillation.

15. The method for producing a diamine and a dicarboxylic acid according to claim 2, wherein: A partition window is provided in the middle of the waveguide to separate the reactor from the microwave emitting device.

16. The method for producing a diamine and a dicarboxylic acid according to claim 15, wherein: The separation window comprises quartz glass.

17. The method for producing a diamine and a dicarboxylic acid according to claim 2, wherein: The frequency of the microwaves used for heating is 0.8 GHz to 6 GHz.

18. The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2, wherein: In the purification step, the content of the Si element is adjusted to 1 mass ppm or more and 200 mass ppm or less relative to the total amount of the dicarboxylic acid.

19. A method for recycling polyamide, wherein: The method for producing a diamine and a dicarboxylic acid according to claim 1 or 2 comprises a polymerization step of obtaining a polyamide by polymerizing the diamine and the dicarboxylic acid.

20. A polyamide obtained by the polyamide recycling method according to claim 19, wherein: The polyamide contains Si element in an amount of 1 mass ppm or more and 100 mass ppm or less based on the total amount of the polyamide.

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