Method for decomposing polyarylene sulfide resin, method for producing oligomers of polyarylene sulfide resin, and the oligomer

Abstract

The present invention aims to provide a method for decomposing polyarylene sulfide resin, a method for producing the oligomer using the decomposition method, and the oligomer produced by the production method, which can produce a polyarylene sulfide resin oligomer that can be used for chemical recycling, particularly for the repolymerization of polyarylene sulfide resins, in high yield under mild conditions. [Solution] A method for decomposing polyarylene sulfide resin, characterized by comprising: a dehydration step of reacting a hydrated alkali metal hydroxide, a hydrated alkali metal sulfide, or a hydrated alkali metal hydroxide and alkali metal hydroxide with an aliphatic cyclic compound that can be ring-opened by hydrolysis, while dehydrating the reaction; and a decomposition step of contacting the product obtained in the dehydration step with a polyarylene sulfide resin at 200-210°C in the presence of an aliphatic cyclic compound that can be ring-opened by hydrolysis.

Description

Technical Field

[0001] The present invention relates to a method for decomposing a polyarylene sulfide resin, a method for producing an oligomer of a polyarylene sulfide resin, and the oligomer. Background Art

[0002] Polyarylene sulfide resins, represented by polyphenylene sulfide resin (hereinafter, "polyphenylene sulfide" may be abbreviated as "PPS") (hereinafter, "polyarylene sulfide" may be abbreviated as "PAS"), belong to super engineering plastics. They have excellent mechanical strength, rigidity, heat resistance, flame retardancy, chemical resistance, electrical properties and dimensional stability, and thus are widely used in various applications such as electrical and electronic parts, home appliance parts, automotive parts and mechanical parts. In recent years, demand for sustainable products has increased rapidly, and reuse of PAS resin has been studied. PAS resin is often used after being mixed with fillers and the like, and the composition of the mixture is generally unknown in general waste, making material recycling difficult. Therefore, chemical recycling is desired, in which PAS resin is depolymerized through a chemical reaction to separate mixtures such as fillers and recover them as chemical raw materials.

[0003] Due to the high stability of PAS resin, there are almost no chemical decomposition methods available, and very few examples of implementation of chemical recycling exist at present. For example, Patent Document 1 describes a method for decomposing a polyphenylene sulfide resin, which comprises a step of reacting a polyphenylene sulfide resin with hydrosilane in the presence of a palladium complex catalyst having a ligand, and describes that benzene and bis(trialkylsilyl) sulfide can be obtained in high yields as decomposition products. Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Patent Publication No. 2022-170457 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the decomposition method described in Patent Document 1 makes it difficult to use the resulting decomposition product for the repolymerization of polyphenylene sulfide resin, and it is also costly because it uses an expensive palladium complex catalyst. Therefore, the present invention aims to provide a method for decomposing polyarylene sulfide resin, a method for producing the oligomer using the decomposition method, and the oligomer produced by the production method, which can produce a polyarylene sulfide resin oligomer that can be used for chemical recycling, particularly for the repolymerization of polyarylene sulfide resin, in high yield under mild conditions. [Means for solving the problem]

[0006] As a result of diligent research conducted by the inventors to solve the above problems, they discovered that the above problems can be solved by reacting a product obtained by dehydrating a hydrated alkali metal hydroxide, a hydrated alkali metal sulfide, or an aliphatic cyclic compound that can be ring-opened by hydrolysis with a hydrated alkali metal hydroxide and alkali metal hydroxide, with a polyarylene sulfide resin at a specific temperature in the presence of an aliphatic cyclic compound that can be ring-opened by hydrolysis, and thus completed the present invention.

[0007] In other words, the present invention is as follows. [1] A hydrated alkali metal hydroxide and an aliphatic cyclic compound that can be ring-opened by hydrolysis, A hydrated alkali metal sulfide and an aliphatic cyclic compound that can be ring-opened by hydrolysis, or Hydrated alkali metal hydroxides and alkali metal hydroxides, and aliphatic cyclic compounds that can be ring-opened by hydrolysis, A dehydration process in which the reaction is carried out while dehydrating, A decomposition step in which the product obtained in the dehydration step is brought into contact with a polyarylene sulfide resin at 200-210°C in the presence of an aliphatic cyclic compound that can be ring-opened by hydrolysis. A method for decomposing polyarylene sulfide resin, characterized by including [a certain element]. [2] The method for decomposing polyarylene sulfide resin according to [1], wherein the dehydration step is performed at 200 to 210°C. [3] The method for decomposing a polyarylene sulfide resin according to [1] or [2], wherein the number average molecular weight (Mn) of the polyarylene sulfide resin is 1,000 or more and 50,000 or less. [4] The dehydration step is a step of producing at least anhydrous alkali metal hydroxide, a method for decomposing polyarylene sulfide resin according to any one of [1] to [3]. [5] A method for decomposing a polyarylene sulfide resin according to any one of [1] to [4], wherein in the decomposition step, the amount of the product obtained in the dehydration step added is 0.3 molar equivalents or more as the amount of sulfur atoms relative to the repeating units of the polyarylene sulfide resin. [6] A method for decomposing polyarylene sulfide resin according to any one of [1] to [5], wherein a catalyst is further added in the decomposition step. [7] A method for producing an oligomer of a polyarylene sulfide resin, characterized by decomposing the polyarylene sulfide resin by any of the methods described in [1] to [6] to obtain an oligomer. [8] An oligomer of polyarylene sulfide resin, characterized by being manufactured by the method described in [7]. [Effects of the Invention]

[0008] According to the present invention, there can be provided a method for decomposing a polyarylene sulfide resin, which is capable of producing an oligomer of a polyarylene sulfide resin that can be used for chemical recycling, particularly for repolymerization of polyarylene sulfide resin, under mild conditions in high yield; a method for producing the oligomer using the decomposition method; and the oligomer produced by the production method. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [Figure 1] Differential molecular weight distribution curves obtained by high-temperature GPC measurement for the PPS resin before decomposition and the solid content (decomposition product) recovered in Examples 2, 4 and 5 are shown. [Figure 2] The FD-MS analysis result (FD-MS spectrum) of the solid content (decomposition product) recovered in Example 5 is shown. MODES FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (referred to as "the present embodiment") will be described in detail. However, the present disclosure is not limited to the following description, and can be implemented with various modifications within the scope of the gist thereof.

[0011] [Method for Decomposing Polyarylene Sulfide Resin] The method for decomposing a polyarylene sulfide resin according to the present embodiment comprises: a dehydration step of subjecting a hydrous alkali metal hydrosulfide, a hydrous alkali metal sulfide, or a hydrous alkali metal hydrosulfide and an alkali metal hydroxide to a dehydration reaction with an aliphatic cyclic compound that can be ring-opened by hydrolysis (hereinafter sometimes simply referred to as "aliphatic cyclic compound"); and a decomposition step of decomposing the polyarylene sulfide resin by bringing the product obtained in the dehydration step into contact with the polyarylene sulfide resin at 200 to 210°C in the presence of the aliphatic cyclic compound that can be ring-opened by hydrolysis.

[0012] [Dehydration Step (Dissolution Step)] The dehydration step is a step of reacting water-containing alkali metal hydrosulfide, water-containing alkali metal sulfide, or water-containing alkali metal hydrosulfide and alkali metal hydroxide with an aliphatic cyclic compound while performing dehydration, to remove water from the water-containing alkali metal sulfide or water-containing alkali metal hydrosulfide. In the dehydration step, at least anhydrous alkali metal hydrosulfide is produced. In addition, when a water-containing alkali metal sulfide, or water-containing alkali metal hydrosulfide and alkali metal hydroxide is reacted with an aliphatic cyclic compound, anhydrous alkali metal hydrosulfide is produced, and at the same time, part of the aliphatic cyclic compound may undergo ring-opening via hydrolysis to produce the alkali metal salt thereof. In the dehydration step, water that has not been used for hydrolysis of the aliphatic cyclic compound is discharged out of the reaction system. In addition, since the produced anhydrous alkali metal hydrosulfide dissolves in the aliphatic cyclic compound, the dehydration step is also a step of dissolving the sulfur source for the subsequent decomposition step (decomposition of the PAS resin). In the dehydration step, it is preferable to perform dehydration until substantially all of the water in the water-containing alkali metal sulfide or water-containing alkali metal hydrosulfide is removed.

[0013] Examples of the water-containing alkali metal sulfide include liquid or solid hydrates (hydrated products) of compounds such as lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesium sulfide, and mixtures of two or more of these. The solid content concentration thereof is preferably 10 to 80% by mass, and particularly preferably 35 to 65% by mass. Among these, from the viewpoint of reactivity, a hydrate of sodium sulfide is preferable. The water-containing alkali metal sulfide can also be obtained by the reaction between water-containing alkali metal hydrosulfide and alkali metal hydroxide. In addition, usually, a small amount of alkali metal hydroxide may be added to react with the trace amounts of water-containing alkali metal hydrosulfide and alkali metal thiosulfate that are normally present in water-containing alkali metal sulfide, which is acceptable. Furthermore, when using hydrated alkali metal sulfides as a sulfur source for the subsequent decomposition process (decomposition of PAS resin), it is preferable to add alkali metal hydroxides in addition to the hydrated alkali metal sulfides and perform dehydration treatment, as this further promotes the formation of solid alkali metal sulfides.

[0014] Examples of the above-mentioned hydrated alkali metal hydrosulfides include compounds such as lithium hydrosulfide (lithium hydrogen sulfide), sodium hydrosulfide (sodium hydrogen sulfide), potassium hydrosulfide (potassium hydrogen sulfide), rubidium hydrosulfide (rubidium hydrogen sulfide), and cesium hydrosulfide (cesium hydrogen sulfide), as well as liquid or solid hydrated substances (hydrates) of mixtures of two or more of these, with a solid content concentration of 10 to 80% by mass being preferred. Among these, hydrated lithium hydrosulfide and hydrated sodium hydrosulfide are preferred from the viewpoint of reactivity, and hydrated sodium hydrosulfide is particularly preferred. Hydrated alkali metal hydroxides may be used alone or in combination with alkali metal hydroxides.

[0015] Examples of the alkali metal hydroxides mentioned above include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, and aqueous solutions thereof. These may be used individually or in mixtures of two or more. When using aqueous solutions, it is preferable that the aqueous solution has a concentration of 20% by mass or higher, as this facilitates the dehydration process. Among these, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferred due to their availability, with sodium hydroxide being particularly preferred. The amount of alkali metal hydroxide used is preferably in the range of 0.8 to 1.2 moles, and more preferably in the range of 0.9 to 1.1 moles, per mole of hydrated alkali metal hydroxide, in order to promote the formation of solid alkali metal sulfides through the reaction between the alkali metal hydroxide and the hydrated alkali metal hydroxide.

[0016] In this embodiment, any known aliphatic cyclic compound that can be ring-opened by hydrolysis can be used without particular limitation. Specific examples of such aliphatic cyclic compounds include aliphatic cyclic amide compounds such as N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as "NMP"), N-cyclohexyl-2-pyrrolidone, N-methyl-ε-caprolactam, 2-pyrrolidone, ε-caprolactam, and 1,3-dimethyl-2-imidazolidinone, as well as amidourea and lactams. Among these, aliphatic cyclic amide compounds, particularly NMP, are preferred due to their good reactivity.

[0017] The following are specific examples of methods for performing dehydration in the dehydration process. (Method 1) A method for dehydrating by charging an aliphatic cyclic compound that can be ring-opened by hydrolysis and a hydrated alkali metal hydroxide in a reaction vessel and heating under atmospheric pressure to a temperature above the boiling point of the hydrated alkali metal hydroxide and to a temperature at which water is removed by azeotrope. Specifically, the heating temperature is preferably 80°C or higher, more preferably 100°C or higher, even more preferably 200°C or higher, preferably 220°C or lower, and more preferably 210°C or lower. In Method 1, at least anhydrous alkali metal hydroxide is produced. (Method 2) A method for dehydrating a reaction vessel by charging an aliphatic cyclic compound that can be ring-opened by hydrolysis with a hydrated alkali metal sulfide and heating it under atmospheric pressure to a temperature above the boiling point of the hydrated alkali metal sulfide and at which water is removed by azeotropy. Specifically, the heating temperature is preferably 80°C or higher, more preferably 100°C or higher, even more preferably 200°C or higher, preferably 220°C or lower, and more preferably 210°C or lower. In method 2, at least anhydrous alkali metal hydroxide is produced. At the same time, a portion of the aliphatic cyclic compound may be ring-opened by hydrolysis to produce its alkali metal salt. Alternatively, an aliphatic cyclic compound, a hydrated alkali metal hydroxide, and an alkali metal hydroxide may be charged into a reaction vessel, and simultaneously with this charging, a hydrated alkali metal sulfide may be produced by the reaction of the hydrated alkali metal hydroxide with the alkali metal hydroxide, and the produced hydrated alkali metal sulfide may be reacted with the aliphatic cyclic compound. This reaction can be carried out by adjusting the amount of aliphatic cyclic compound charged to the hydrated alkali metal hydroxide and alkali metal hydroxide. (Method 3) A method for dehydrating by charging an aliphatic cyclic compound that can be ring-opened by hydrolysis, a hydrated alkali metal hydroxide, and an alkali metal hydroxide into a reaction vessel and heating under atmospheric pressure to a temperature above the boiling point of the hydrated alkali metal hydroxide and to a temperature at which water is removed by azeotropy. Specifically, the heating temperature is preferably 80°C or higher, more preferably 100°C or higher, even more preferably 200°C or higher, preferably 220°C or lower, and more preferably 210°C or lower. In method 3, at least anhydrous alkali metal hydroxide is produced. In addition, a portion of the aliphatic cyclic compound may be ring-opened by hydrolysis to produce its alkali metal salt.

[0018] The amount of aliphatic cyclic compound used in the dehydration step is not particularly limited as long as it is in excess of the hydrated alkali metal sulfide (Method 2) or hydrated alkali metal hydrosulfide (Methods 1 and 3). For example, per mole of hydrated alkali metal sulfide (Method 2) or hydrated alkali metal hydrosulfide (Methods 1 and 3), the lower limit is preferably more than 1 mole, more preferably 2 moles or more, and even more preferably 3 moles or more. The upper limit is not particularly limited, but since the dehydration effect is significant, it is preferably 100 moles or less, more preferably 50 moles or less, and even more preferably 10 moles or less.

[0019] Apparatus that can be used for dehydration treatment includes, for example, a dehydration apparatus equipped with a reaction vessel (dehydration vessel) containing a stirrer, a steam distillation line, a condenser, a decanter, a distillate return line, an exhaust line, a hydrogen sulfide capture device, and a heating device. Furthermore, while the reaction vessel used in the dehydration treatment reaction is not particularly limited, it is preferable to use a reaction vessel in which the wetted parts are made of titanium, chromium, or zirconium. In addition, the dehydration treatment can employ any of the conventional methods used in dehydration treatment, such as a batch method, a batch method, or a continuous method. The dehydration process may be carried out under normal pressure or under pressurized pressure. Furthermore, the dehydration process is preferably carried out under an inert gas atmosphere. Examples of inert gases that can be used include nitrogen, helium, neon, and argon, with nitrogen being preferred in terms of economy and ease of handling.

[0020] The dehydration step is preferably carried out in the absence of polyhalo-aromatic compounds, as this promotes the subsequent decomposition step (depolymerization reaction). Polyhalo-aromatic compounds are monomer components that do not have repeating units. For example, p-dihalobenzene, m-dihalobenzene, o-dihalobenzene, 1,2,3-trihalobenzene, 1,2,4-trihalobenzene, 1,3,5-trihalobenzene, 1,2,3,5-tetrahalobenzene, 1,2,4,5-tetrahalobenzene, 1,4,6-trihalonaphthalene, 2,5-dihalotoluene, 1,4-dihalonaphthalene, 1-methoxy-2,5-dihalobenzene, 4,4'-dihalobiphenyl, 3,5-dihalobenzoic acid Examples include acids, 2,4-dihalobenzoic acid, 2,5-dihalonitrobenzene, 2,4-dihalonitrobenzene, 2,4-dihaloanisole, p,p'-dihalodiphenyl ether, 4,4'-dihalobenzophenone, 4,4'-dihalodiphenyl sulfone, 4,4'-dihalodiphenyl sulfoxide, 4,4'-dihalodiphenyl sulfide, and compounds having an alkyl group with 1 to 18 carbon atoms as a nuclear substituent on the aromatic ring of each of the above compounds. Examples of halogen atoms contained in each of the above compounds include chlorine atoms and bromine atoms.

[0021] [Disassembly process] The decomposition step involves depolymerizing the PAS resin by contacting the product obtained in the dehydration step, i.e., at least anhydrous alkali metal hydroxide, with the PAS resin in the presence of an aliphatic cyclic compound that can be ring-opened by hydrolysis as a solvent.

[0022] (Polyarylene sulfide resin) The PAS resin used in this embodiment is a polymer whose main constituent unit is a repeating unit represented by "-(Ar-S)-" (where Ar is an arylene group). The arylene group is a divalent aromatic group containing at least one carbon 6-membered ring, and examples include p-phenylene group, m-phenylene group, o-phenylene group, substituted phenylene group, p,p'-diphenylene sulfone group, p,p'-biphenylene group, p,p'-diphenylene ether group, p,p'-diphenylene carbonyl group, naphthalene group, etc. In this disclosure, the term "major constituent unit" refers to a constituent unit that accounts for 50 mol% or more of the total constituent units derived from all constituent monomers, with the sum of all constituent units derived from all constituent monomers being defined as 100 mol%.

[0023] The form of the PAS resin is not particularly limited and may be powder, granules, pellets, fibers, films, molded articles, etc.

[0024] The number-average molecular weight (Mn) of the PAS resin depends on the raw materials and methods used, and is not particularly limited, but may be, for example, 1,000 or more, 2,000 or more, or 5,000 or more. Furthermore, the number-average molecular weight (Mn) of the PAS resin may be, for example, 50,000 or less, 20,000 or less, or 10,000 or less. The number-average molecular weight (Mn) of PAS resin is the polystyrene-based molecular weight obtained by high-temperature GPC (gel permeation chromatography) measurement.

[0025] The following describes polyphenylene sulfide resin, a typical example of PAS resin.

[0026] ((Polyphenylene sulfide resin)) The PPS resin used in this embodiment is a polymer whose main constituent unit is a monomer unit (p-phenylene sulfide unit) represented by the following formula (1). In addition to the p-phenylene sulfide unit, it may also contain phenylene sulfide sulfone units and phenylene sulfide ketone units, and may be a random copolymer, block copolymer, or mixture thereof. [ka]

[0027] The form of the PPS resin is not particularly limited and may be powder, granules, pellets, fibers, films, molded products, etc.

[0028] The number-average molecular weight (Mn) of the PPS resin is not particularly limited, as it depends on the raw materials and methods used, but may be, for example, 1,000 or more, 2,000 or more, or 5,000 or more. Furthermore, the number-average molecular weight (Mn) of the PPS resin may be, for example, 50,000 or less, 20,000 or less, or 10,000 or less. The number-average molecular weight (Mn) of the PPS resin is the polystyrene-based molecular weight obtained by high-temperature GPC (gel permeation chromatography) measurement, and can be specifically determined by the method described in the examples below.

[0029] (Product obtained in the dehydration process) In the PAS resin decomposition reaction of this embodiment, the PAS resin is depolymerized using the product obtained in the dehydration step in the presence of an aliphatic cyclic compound. As described above, by using the product obtained in the dehydration step, i.e., at least anhydrous alkali metal hydroxide, in the presence of an aliphatic cyclic compound, the PAS resin, which is difficult to decompose due to its high stability, can be efficiently decomposed to oligomers under mild conditions as described later. Furthermore, because anhydrous alkali metal hydroxide, which is also used in the polymerization reaction of PAS resin, is used as a monomer, the PAS resin can be decomposed without disrupting the repeating units of the polymer. Furthermore, the product obtained in the dehydration step may be used in the decomposition step after separating the product from the reaction solution, or it may be used in the decomposition step as is (in the state in which the anhydrous alkali metal hydroxide is dissolved in the aliphatic cyclic compound) without separating the product from the reaction solution.

[0030] In the decomposition step, the amount of product obtained in the dehydration step added is preferably 0.1 molar equivalents or more, more preferably 0.3 molar equivalents or more, and even more preferably 0.5 molar equivalents or more, as the amount of sulfur atoms relative to the repeating units of the PAS resin. When the amount of product obtained in the dehydration step added is within the above range, the PAS resin can be efficiently decomposed, and oligomers can be obtained as decomposition products in high yield. Furthermore, there is no particular upper limit to the amount of product obtained in the dehydration step added, but for example, it may be 20 molar equivalents or less, 10 molar equivalents or less, or 5 molar equivalents or less. The repeating units of the PAS resin mentioned above refer to all monomer units, including not only the main constituent unit, the p-arylene sulfide unit (for example, in the case of PPS resin, not only the p-phenylene sulfide unit but also the phenylene sulfide sulfone unit, phenylene sulfide ketone unit, etc.). One equivalent is defined as the amount at which the PAS resin is completely decomposed into monomers by the product obtained in the dehydration process.

[0031] In this embodiment, the decomposition reaction of the PAS resin uses an aliphatic cyclic compound that can be ring-opened by hydrolysis as the solvent. The aliphatic cyclic compound can be the same as the aliphatic cyclic compound used in the dehydration step described above, or the same aliphatic cyclic compound used in the dehydration step may be used, such as when the reaction solution from the dehydration step described later is used as is. The aliphatic cyclic compound is preferably N-methyl-2-pyrrolidone. Although hexamethyl phosphate triamide (HMPA, boiling point 235°C) is also known as a solvent, NMP has lower toxicity and higher practicality compared to HMPA. The amount of aliphatic cyclic compound used is preferably 1 to 50 parts by mass, more preferably 2 to 20 parts by mass, and even more preferably 3 to 10 parts by mass, per 1 part by mass of PAS resin. When the amount of aliphatic cyclic compound used is within the above range, the PAS resin can be efficiently decomposed, and oligomers can be obtained in high yield as decomposition products. Furthermore, if the reaction solution from the dehydration step is used as is (in the state in which anhydrous alkali metal hydroxide is dissolved in an aliphatic cyclic compound), it is preferable to adjust it to fall within the above range, taking into account the amount of aliphatic cyclic compound added to the reaction system in the dehydration step. If the amount of aliphatic cyclic compound added in the dehydration step is insufficient, it is preferable to add more aliphatic cyclic compound to the reaction system.

[0032] (catalyst) The decomposition reaction of the PAS resin in this embodiment may use a catalyst. Examples of catalysts include benzyl sulfide ((C6H5CH2)2S) and other sulfide compounds soluble in aliphatic cyclic compounds such as N-methyl-2-pyrrolidone. The amount of catalyst added is preferably 0.1 to 30 mol%, more preferably 0.5 to 20 mol%, and even more preferably 1 to 10 mol%, per 100 mol% of PAS resin. When the amount of catalyst added is within the above range, the PAS resin tends to be decomposed more efficiently.

[0033] (Reaction conditions) The reaction temperature for the PAS resin decomposition reaction is 200-210°C, which is around the boiling point of aliphatic cyclic compounds, particularly NMP (202°C), under normal pressure. Preferably, it is 203-208°C, and more preferably 205-207°C. By setting the reaction temperature within this range, the decomposition reaction can be carried out efficiently. Furthermore, the reaction time for the PAS resin decomposition reaction is preferably 3 to 35 hours, more preferably 5 to 30 hours, and even more preferably 5 to 25 hours. When the reaction time is within the above range, the PAS resin can be sufficiently decomposed, and oligomers as decomposition products tend to be obtained in high yield. The PAS resin decomposition reaction may be carried out under atmospheric pressure, or under pressure using an autoclave or the like. The above reaction temperature range is for under atmospheric pressure, but when the reaction is carried out under pressure using an autoclave or the like, the temperature range may be converted from the above range derived from the vapor pressure curve. The reaction is preferably carried out under an inert gas atmosphere such as nitrogen or argon. The apparatus that can be used for the decomposition reaction is not particularly limited, and known apparatuses can be used, and may be equipped with a reflux mechanism. For example, a reflux apparatus equipped with a stirrer, a steam distillation line, a condenser, a decanter, a distillate return line, an exhaust line, a hydrogen sulfide capture device, and a heating device in the reaction vessel can be used. Furthermore, the reaction vessel used is not particularly limited, but it is preferable to use a reaction vessel in which the wetted parts are made of titanium, chromium, or zirconium. In addition, the decomposition process can employ a conventional method used in decomposition treatment, such as a batch method, a batch method, or a continuous method. Furthermore, the decomposition process is preferably carried out under an inert gas atmosphere. Examples of inert gases that can be used include nitrogen, helium, neon, and argon, with nitrogen being preferred in terms of economy and ease of handling.

[0034] [Refining process] The method for decomposing PAS resin according to this embodiment may further include a purification step for isolating and purifying PAS resin oligomers (hereinafter also referred to as "PAS oligomers") from the decomposition products obtained in the decomposition step. The isolation and purification method is not particularly limited, and known methods can be used. For example, PAS oligomers can be obtained by adding an aqueous HCl solution to the decomposition products obtained in the decomposition step to neutralize them, then adding ion-exchanged water to wash and perform vacuum filtration, filtering and recovering the solid components, and drying them.

[0035] (decomposition products) As described above, the method for decomposing PAS resin in this embodiment is a decomposition reaction that does not break down the repeating units of the polymer, and therefore the resulting decomposition products include PAS oligomers. The PAS oligomers obtained as decomposition products are, for example, mixtures of 2 to 10 oligomers, preferably mixtures of 3 to 8 oligomers, with both ends being thiol groups (-SH groups) or alkali metal salts thereof. Oligomers with thiol groups or alkali metal salts thereof at both ends have high reuse value, such as being usable in the repolymerization of PAS resin. Furthermore, because they contain oligomers with relatively large molecular weights (e.g., 5 to 10 oligomers), the amount of raw material used can be reduced when repolymerizing PAS resin using these decomposition products as raw materials.

[0036] [Method for producing polyarylene sulfide resin oligomers] The method for producing PAS resin oligomers in this embodiment is a method for producing PAS oligomers by decomposing PAS resin using the PAS resin decomposition method of this embodiment described above. The method for producing PAS oligomers according to this embodiment may further include a step of separating and recovering unreacted PAS resin. Unlike decomposition products, PAS resin is insoluble in organic solvents, so unreacted PAS resin in aliphatic cyclic compounds can be easily recovered. By recovering and reusing unreacted PAS resin, the yield of PAS oligomers can be further increased.

[0037] [Polyarylene sulfide resin oligomers] The PAS resin oligomer of this embodiment can be manufactured by the method for manufacturing the PAS resin oligomer of this embodiment described above. PAS oligomers are, for example, mixtures of 2 to 10 thiols, preferably mixtures of 3 to 8 thiols, with both ends being thiol groups (-SH groups) or alkali metal salts thereof. Oligomers with thiol groups or alkali metal salts thereof at both ends have high reusability, such as being usable in the repolymerization of PAS resins. Furthermore, because they contain oligomers with relatively large molecular weights (e.g., 5 to 10 thiols), the amount of raw material used can be reduced when repolymerizing PAS resins using these oligomers as raw materials. [Examples]

[0038] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples unless it exceeds the scope of its essence.

[0039] The measurement methods used in the examples and comparative examples are as follows.

[0040] [High-temperature GPC measurement] PPS resin and its decomposition products were measured using high-temperature GPC under the following conditions. Using a calibration curve prepared in advance with polystyrene as the standard substance, the number-average molecular weight (Mn) and peak-top molecular weight (Mp) in polystyrene equivalent were determined. The Mn and Mp values ​​of the PPS resin before decomposition were 4,684 and 23,930, respectively. Measuring device: "HLC-8321GPC / HT" (manufactured by Tosoh Corporation) Columns: The following columns manufactured by Tosoh Corporation were used, connected in series. "TSKgel Guard Column H HR (S) HT2” x 1 TSKgel GMH HR -H(S)HT2” x 1 "TSKgel H HR HT-RC” x 1 Detector: RI (Differential Refractometer) Data processing: Tosoh Corporation 8321GPC-WS Column temperature: 220℃ Solvent: 1-Chloronaphthalene Flow rate: 1.0mL / min Standard: Polystyrene Sample: Approximately 20 mg of resin solids covered with an aluminum sheet and dissolved in 1-chloronaphthalene at 220°C. Injection volume: 300μL Standard material: A calibration curve was prepared using the following monodisperse polystyrene manufactured by Tosoh Corporation. "TSKgel Standard Polystyrene A-500" "TSKgel Standard Polystyrene A-1000" "TSKgel Standard Polystyrene A-2500" "TSKgel Standard Polystyrene A-5000" "TSKgel Standard Polystyrene F-1" "TSKgel Standard Polystyrene F-2" "TSKgel Standard Polystyrene F-4" "TSKgel Standard Polystyrene F-10" "TSKgel Standard Polystyrene F-20" "TSKgel Standard Polystyrene F-40" "TSKgel Standard Polystyrene F-80" "TSKgel Standard Polystyrene F-128"

[0041] [FD-MS measurement] The decomposition products of PPS resin were subjected to FD-MS spectral measurements using the following measuring equipment and conditions. From these results, a mass peak corresponding to the PPS oligomer was confirmed. Measurement device: "JMS-T200GC AccuTOF" (manufactured by JEOL Ltd.) Measurement conditions Measurement range: m / z = 50.00~3200.00 Rate of change: 25.6 mA / min Final current value: 40mA Cathode voltage: -10kV Recording interval: 2 min

[0042] [Example 1] (Synthesis and dehydration of hydrated Na2S) 100g of NMP was placed in a separable flask equipped with a stirrer, to which 20g of a 20% by mass NaOH aqueous solution and 20g of a 28% by mass aqueous NaSH aqueous solution were added. Next, a distillation mechanism was attached to the separable flask, and heating was started using an oil bath while flowing nitrogen. The temperature of the oil bath was gradually increased until it reached 230°C. When the liquid temperature reached 205°C, heating was stopped, and the oil bath temperature was reset to 150°C. (PPS resin decomposition process) After the liquid temperature reached 150°C by air cooling, 10g of PPS resin (neat polymer) and 40g of NMP were added, and the distillation mechanism was reconfigured into a reflux mechanism. The oil bath was heated to 230°C, and the decomposition reaction was initiated when the liquid temperature exceeded 200°C. After 6 hours, the heating of the oil bath was stopped, and the decomposition reaction was stopped at that point. The liquid temperature during the reaction was maintained at 205±2°C by reflux. (Purification process of decomposition products) After allowing the liquid to cool naturally to room temperature, 62.5 g of a 4 mmol / g HCl aqueous solution was added to neutralize it. The generated H2S gas was collected using a gas trap. After neutralization, the solution was diluted to approximately 1 L with deionized water, and then filtered under reduced pressure using a 40 μm membrane filter to recover the solid. The solid was then dispersed again in approximately 1 L of deionized water for washing, and then filtered under reduced pressure using a 40 μm membrane filter to recover the solid. The recovered solid was dried in a vacuum dryer at 40°C for 24 hours or more, and the mass was measured to calculate the yield. Furthermore, high-temperature GPC analysis was performed on the recovered solid component, and the molecular weight distribution was compared with that of pre-decomposition PPS resin, which had also undergone high-temperature GPC analysis. A decrease in molecular weight was confirmed. Additionally, FD-MS analysis confirmed that the recovered solid component contained 2-6 mer PPS oligomers, with thiol groups at both ends.

[0043] [Examples 2-7] The decomposition reaction of PPS resin was carried out in the same manner as in Example 1, except that the reaction conditions were changed as shown in Table 1. In Examples 2 and 4, the reaction was carried out by adding benzyl sulfide ((C6H5CH2)2S) at concentrations of 5 mol% and 1 mol%, respectively, per 100 mol% of the PPS resin during the PPS resin decomposition process. In all of the solid components recovered in Examples 2-7, high-temperature GPC measurement confirmed that the molecular weight was lower compared to the PPS resin before decomposition. Furthermore, FD-MS analysis of the solid components recovered in Examples 2-7 confirmed that they contained 3-8 mer PPS oligomers with thiol groups at both ends. The reaction conditions and measurement results are shown in Tables 1 and 2.

[0044] Figure 1 also shows the differential molecular weight distribution curves of the solid components recovered in Examples 2, 4, and 5. The solid line represents the differential molecular weight distribution curve of the PPS resin before decomposition. Furthermore, Figure 2 shows the FD-MS analysis results (FD-MS spectrum) of the solid recovered in Example 5. The measurement confirmed the presence of 3-6 mer PPS oligomers, each having at least two thiol groups at both ends.

[0045] [Comparative Example 1] The decomposition reaction of PPS resin was carried out in the same manner as in Example 1, except that the reaction conditions were changed as shown in Table 1, Na2S·9H2O was used instead of the synthesized hydrated Na2S, the dehydration step was performed at 150-155°C, and the decomposition step was performed at 173±2°C. Analysis by FD-MS confirmed that the recovered solid contained 3-8 mer PPS oligomers with thiol groups at both ends. The reaction conditions and measurement results are shown in Tables 1 and 2.

[0046] [Table 1] *1 Molar equivalent as the amount of sulfur atoms relative to the repeating units of PPS resin. *2 As Na2S

[0047] [Table 2]

[0048] As shown in Tables 1 and 2, the methods of Examples 1 to 7 allowed for the efficient decomposition of PPS resin under mild conditions (atmospheric pressure, reaction temperature 200-210°C), yielding 3-8 mer PPS oligomers with thiol groups at both ends in high yield. On the other hand, in the method of Comparative Example 1, the decomposition step (depolymerization) was carried out at 171-175°C, which prevented the efficient decomposition of the PPS resin, and thus it was not possible to obtain PPS oligomers of 3-8 moers with thiol groups at both ends in high yield.

Claims

1. A hydrated alkali metal hydroxide and an aliphatic cyclic compound that can be ring-opened by hydrolysis, A hydrated alkali metal sulfide and an aliphatic cyclic compound that can be ring-opened by hydrolysis, or Hydrated alkali metal hydroxides and alkali metal hydroxides, and aliphatic cyclic compounds that can be ring-opened by hydrolysis, A dehydration process in which the reaction is carried out while dehydrating, A decomposition step in which the product obtained in the dehydration step is brought into contact with a polyarylene sulfide resin at 200 to 210°C in the presence of an aliphatic cyclic compound that can be ring-opened by hydrolysis. A method for decomposing polyarylene sulfide resin, characterized by including [a certain element].

2. The method for decomposing polyarylene sulfide resin according to claim 1, wherein the dehydration step is performed at 200 to 210°C.

3. The method for decomposing a polyarylene sulfide resin according to claim 1, wherein the number-average molecular weight (Mn) of the polyarylene sulfide resin is 1,000 or more and 50,000 or less.

4. The method for decomposing a polyarylene sulfide resin according to claim 1, wherein the dehydration step is a step of generating at least anhydrous alkali metal hydroxide.

5. The method for decomposing a polyarylene sulfide resin according to claim 1, wherein in the decomposition step, the amount of the product obtained in the dehydration step added is 0.3 molar equivalents or more as the amount of sulfur atoms relative to the repeating units of the polyarylene sulfide resin.

6. The method for decomposing polyarylene sulfide resin according to claim 1, further comprising adding a catalyst in the decomposition step.

7. A method for producing an oligomer of a polyarylene sulfide resin, characterized by obtaining an oligomer by decomposing the polyarylene sulfide resin by the method described in any one of claims 1 to 6.

8. An oligomer of polyarylene sulfide resin, characterized by being manufactured by the method described in claim 7.

Images