Sulfiding agent and method for producing polyarylene sulfide resin

Abstract

To provide a method for producing a sulfidizing agent having high purity by removing an alkali metal carbonate from waste water discharged when a polyarylene sulfide resin (PAS resin) is subjected to polymerization reaction, and then is washed with water or hot water.SOLUTION: There is provided a method for producing a sulfidizing agent that includes the steps of: bringing a mixture (A) containing at least a PAS resin, an alkali metal halide, an alkali metal carbonate and a sulfidizing agent into contact with water, then solid-liquid separating the mixture, to obtaining an aqueous solution (B); adding a metal salt containing at least one Group-II element to the aqueous solution (B) to produce a water- insoluble carbonate; separating and removing the produced water-insoluble carbonate to obtain an aqueous solution (C); adding an acid to the aqueous solution (C) to produce hydrogen sulfide; recovering the produced hydrogen sulfide; and reacting the recovered hydrogen sulfide with an alkali metal hydroxide. There is also provided a method for producing a PAS resin using the sulfidizing agent.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a sulfiding agent and a method for producing a polyarylene sulfide resin using the same. More specifically, it relates to a method for removing an alkali metal carbonate, which is an impurity, from wastewater discharged in the production process of a polyarylene sulfide resin, separating and purifying a high-purity sulfiding agent, and a method for producing a polyarylene sulfide resin that reuses the obtained sulfiding agent as part of a raw material.

Background Art

[0002] Polyarylene sulfide resins (hereinafter sometimes abbreviated as PAS resins), typified by polyphenylene sulfide resin (hereinafter sometimes abbreviated as PPS resin), are excellent in heat resistance, chemical resistance, etc., and are widely used in applications such as electric and electronic parts, automotive parts, water heater parts, fibers, and films. In particular, in applications such as lithium-ion battery packings and gasket members, in recent years, especially high-molecular-weight PAS resins have been widely used because of their excellent toughness and moldability.

[0003] PAS resins are obtained by, for example, a method of polymerizing a polyhaloaromatic compound with an alkali metal sulfide and / or an alkali metal hydrosulfide (hereinafter sometimes abbreviated as a sulfiding agent) in an aprotic polar solvent such as N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as NMP). Together with the target PAS resin, a crude reaction product containing a sulfiding agent such as an alkali metal hydrosulfide or an alkali metal sulfide that remained without undergoing a polymerization reaction, an alkali metal halide typified by sodium chloride, other alkali metal-containing inorganic salts, by-products such as oligomers and their derivatives generated by side reactions is obtained. The crude reaction product after the polymerization reaction is taken out into an appropriate container, and the solvent in the crude reaction product is separated and recovered by a solvent removal treatment using an appropriate solid-liquid separation device such as a solvent drying device, a filter, or a centrifuge (this operation is referred to as solvent removal).

[0004] Furthermore, since the reaction product obtained after the desolvation treatment contains alkali metal halides, other alkali metal-containing inorganic salts, and by-products together with the target PAS resin, washing with water and filtration are repeated to remove these. Generally, there are a water washing method performed at a temperature below 100°C and a hot water washing method performed under high temperature and high pressure of 100°C or higher. The polyarylene sulfide obtained after water washing or hot water washing is separated by a filter, a centrifugal filter, etc., and then dried, and heat-treated as necessary to perform a cross-linking reaction to obtain a product.

[0005] On the other hand, the wastewater obtained after water washing or hot water washing has been treated as industrial waste and has not been effectively utilized. However, since the COD load of the wastewater is high, in order to reduce the environmental load, it has been required to reduce the COD substances.

[0006] When the wastewater discharged by water washing or hot water washing after the polymerization reaction was examined in detail, it was found that the sulfidizing agent remaining unreacted remained at about 3 to 5 mol% of the charged amount in terms of sulfur atoms, and this unreacted sulfidizing agent was one of the factors increasing the COD value of the wastewater. Furthermore, it was clarified that it was the cause of the loss of sulfur atoms (decrease in the raw material unit).

[0007] Therefore, a method has been proposed to reduce the COD value of the wastewater by gasifying the unreacted sulfidizing agent contained in the wastewater and separating and recovering it (see Patent Document 1). However, in this method, when adding an acid to the wastewater to gasify the unreacted sulfidizing agent, even the alkali metal carbonate contained as an impurity in the raw material is gasified at the same time. Therefore, when repeating the polymerization step using the sulfidizing agent recovered from the wastewater, there is a disadvantage that the impurity alkali metal carbonate accumulates in the wastewater. Also, due to this, there were problems in terms of production, such as blockage of the piping.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, the problem to be solved by the present invention is to reduce the alkali metal carbonate, which is an impurity, from the aqueous solution (hereinafter sometimes referred to as waste water) obtained by washing with water or hot water after the polymerization reaction of PAS resin, and to provide a method for producing a high-purity sulfidizing agent. Furthermore, there is provided a method for producing a PAS resin in which the sulfidizing agent obtained by the above production method is reused as a polymerization raw material of the PAS resin, thereby providing a method for suppressing the loss of sulfur atoms (decrease in raw material unit).

Means for Solving the Problems

[0010] As a result of various studies, the inventors of the present application have found that by adding a metal salt containing at least one Group 2 element among magnesium, calcium, strontium, and barium to the waste water discharged by washing with water or hot water after the polymerization reaction, a carbonate insoluble in water is formed from the alkali metal carbonate, which is an impurity, and by gasifying and separating and recovering the unreacted sulfidizing agent from the waste water from which it has been separated and removed, a high-purity sulfidizing agent can be produced, and that the COD of the waste water can be reduced and it can be reused as a raw material for producing PAS resin, thus arriving at a solution to the above problems.

[0011] That is, the present invention provides: [1] a step (1) of bringing a mixture (A) containing at least a PAS resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent into contact with water, and then separating and removing the PAS resin to obtain an aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent; a step (2) of adding a metal salt containing at least one Group 2 element among magnesium, calcium, strontium, and barium to the aqueous solution (B) to form a carbonate insoluble in water; Step (3) of separating and removing the carbonate insoluble in the generated water from the aqueous solution (B) to obtain an aqueous solution (C) containing at least an alkali metal halide and a sulfidizing agent. Step (4) of adding an acid to the aqueous solution (C) to generate hydrogen sulfide. Step (5) of recovering the generated hydrogen sulfide, and Step (6) of reacting the recovered hydrogen sulfide with an alkali metal hydroxide. It relates to a method for producing a sulfidizing agent, characterized by comprising the above steps.

[0012] Further, the present invention relates to the production method described in [1] above, characterized by having, after step (6) of reacting the recovered hydrogen sulfide with an alkali metal hydroxide, step (7) of adding hydrogen sulfide to the unreacted alkali metal hydroxide and reacting the hydrogen sulfide with the unreacted alkali metal hydroxide.

[0013] Further, the present invention relates to [3] the mixture (A) containing at least a PAS resin, an alkali metal halide, an alkali metal carbonate and a sulfidizing agent, It is a crude reaction mixture containing at least a PAS resin, an alkali metal halide, the aprotic polar solvent and a sulfidizing agent, obtained after reacting a polyhaloaromatic compound with a sulfidizing agent in an aprotic polar solvent, or a reaction mixture obtained by solid-liquid separation of the aprotic polar solvent from the crude reaction mixture, and relates to the production method described in [1] above.

[0014] Furthermore, the present invention relates to the production method described in [3] above, characterized in that the sulfidizing agent used when reacting a polyhaloaromatic compound with a sulfidizing agent in an aprotic polar solvent is obtained through a dehydration step of dehydrating a hydrous sulfidizing agent in the presence of at least an aprotic polar solvent.

[0015] Furthermore, the present invention relates to a method for producing a sulfiding agent, characterized by having a step of reacting hydrogen sulfide generated in the dehydration step described in [5] above with an alkali metal hydroxide to obtain a sulfiding agent after recovering the hydrogen sulfide.

[0016] Furthermore, the present invention relates to the method for producing a sulfiding agent described in [5] above, characterized by having a step of adding hydrogen sulfide to the unreacted alkali metal hydroxide and reacting the hydrogen sulfide with the unreacted alkali metal hydroxide after the step of reacting with an alkali metal hydroxide to obtain a sulfiding agent.

[0017] Furthermore, the present invention relates to a method for producing a PAS resin, in which a sulfiding agent obtained by dehydrating a hydrous sulfiding agent in the presence of an organic amide solvent is reacted with a polyhaloaromatic compound in the presence of an organic amide solvent to produce a PAS resin. The method for producing a PAS resin is characterized by having a step of adding a sulfiding agent obtained by the production method according to any one of [1] to [4] above as the hydrous sulfiding agent or the sulfiding agent and / or a sulfiding agent obtained by the production method according to [5] or [6] above.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a method for efficiently removing alkali metal carbonates contained in wastewater discharged by water washing or hot water washing after the polymerization reaction of a PAS resin, recovering unreacted sulfiding agent, and reducing the COD value of the wastewater. Furthermore, a method for producing a PAS resin in which the recovered unreacted sulfiding agent is reused as a polymerization raw material of the PAS resin can be provided, thereby providing a method for suppressing the loss of sulfur atoms (decrease in raw material unit).

Embodiments for Carrying Out the Invention

[0019] Method for Producing Sulfiding Agent The method for producing a sulfiding agent of the present invention is as follows. After contacting a mixture (A) containing at least a PAS resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent with water, the PAS resin is separated and removed to obtain an aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent in step (1). In step (2), a metal salt containing at least one Group 2 element among magnesium, calcium, strontium, and barium is added to the aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent to form a carbonate insoluble in water. In step (3), the formed carbonate insoluble in water is separated and removed from the aqueous solution (B) to obtain an aqueous solution (C) containing at least an alkali metal halide and a sulfidizing agent. In step (4), an acid is added to the aqueous solution (C) containing at least an alkali metal halide and a sulfidizing agent to generate hydrogen sulfide. In step (5), the generated hydrogen sulfide is recovered, and in step (6), the recovered hydrogen sulfide is reacted with an alkali metal hydroxide. It is characterized by having the above steps.

[0020] Step (1) Step (1) is a step in which, after contacting a mixture (A) containing at least a PAS resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent with water, it is separated into an aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent and the PAS resin, and then the PAS resin is removed to obtain an aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent (hereinafter sometimes referred to as wastewater).

[0021] The mixture (A) used in the process (1) is not particularly limited as long as it contains at least a PAS resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent, but preferably, a reaction mixture containing at least a PAS resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent obtained in the method for producing a PAS resin used in the present invention described below is used.

[0022] The method for contacting the mixture (A) with water to remove the PAS resin from the mixture (A) and obtain an aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent is not particularly limited as long as the effects of the present invention are not impaired, but examples include a method of solid-liquid separation by filtering the PAS resin after contacting with water (hereinafter sometimes referred to as "water washing").

[0023] Examples of the method for solid-liquid separation by filtering the PAS resin after water washing the mixture (A) include, for example, a method of adding water to a reaction slurry obtained by solid-liquid separating an aprotic polar solvent from a crude reaction mixture obtained in a PAS production process described below, stirring, and then filtering using a filtration device; a method of adding water again to a filtration residue containing water (hereinafter abbreviated as "water-containing cake") obtained by the above filtration to form a slurry and then filtering; or a method of adding water again and filtering while the water-containing cake is held in a filter.

[0024] When performing the water washing, the amount of water added to the mixture (A) is preferably in the range of 2 to 10 times the theoretical yield of the finally obtained PAS resin, which is preferable from the viewpoint of washing efficiency. It is preferable to subject the water in the above amount to water washing by dividing it into 2 to 10 times, preferably 2 to 4 times. The water washing is preferably performed in a nitrogen or air atmosphere at a water temperature in the range of 20°C to 300°C. From the viewpoint of good washing efficiency, it is more preferably performed in the range of 50°C to 100°C, and most preferably performed in the range of 70°C to 90°C. The water washing can be performed once or repeatedly. When performing repeated water washing a plurality of times, the atmosphere and temperature conditions may be the same or different.

[0025] In the filtered PAS resin, a trace amount of alkali metal halide or sulfidizing agent may remain without being thoroughly washed. Therefore, after further contacting with water in the range of 100°C to 280°C and then performing solid-liquid separation (hereinafter sometimes referred to as "hot water washing"), the PAS resin is separated and removed by filtration or the like, and the obtained filtrate can be added to the aqueous solution (B), which is preferable from the viewpoint of reducing the COD load and suppressing the loss of sulfur atoms (decrease in raw material unit).

[0026] The temperature of the hot water washing is preferably in the range of 100 to 280°C, for example, and more preferably in the range of 120 to 275°C from the viewpoint of good extraction efficiency of the alkali metal halide and sulfidizing agent remaining in the resin. More specifically, it is preferable to perform the extraction treatment with hot water at 140 to 260°C under the condition that the pressure of the gas phase in the reactor is under pressure, more preferably 0.2 to 4.6 MPa (gauge pressure).

[0027] Specific methods for performing such hot water washing include a method of washing the PAS resin filtered after the above-described water washing with water under stirring under predetermined pressure and temperature conditions in a pressure vessel. The amount of water during hot water washing is preferably 1.5 to 10 times the mass of the polyarylene sulfide from the viewpoint of good extraction efficiency of the alkali metal halide and the sulfidizing agent, and hot water washing may be performed by dividing this amount of hot water into two or more times. For example, when hot water washing is repeated twice, filtration is preferably performed between the first hot water washing and the second hot water washing to filter and separate the alkali metal halide and the sulfidizing agent extracted by the first hot water washing from the PAS resin. Further, filtration may be performed after performing hot water washing once, and the above-described water washing may be performed. By this operation, separation and removal of the alkali metal halide and the sulfidizing agent from the PAS resin can be further promoted. Although the conditions of the first hot water washing step and the second hot water washing step can be arbitrarily selected from the above conditions, the temperature of the first hot water washing step is set, for example, to a temperature in the range of 120°C to 200°C, and first, the highly alkaline filtrate is filtered and removed, and then the temperature of the second hot water washing step is set to a temperature higher than the temperature of the first hot water washing step, for example, a temperature in the range of 150°C to 275°C, which is preferable from the viewpoint of the chemical resistance of the apparatus used for the hot water washing.

[0028] In addition, in step (1), an acid or a base can be added to the aqueous solution (B) to adjust the pH, and it is particularly preferable to control the pH after hot water washing to be in the range of 11.0 or more and less than 13.0. Examples of the acid used at that time include hydrochloric acid, sulfuric acid, carbonic acid, acetic acid, oxalic acid, etc., and among these, carbonic acid, acetic acid, and oxalic acid are preferable. Further, carbon dioxide gas may be introduced and contacted under normal pressure or under pressure. On the other hand, examples of the base include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, or sodium carbonate, ammonium carbonate, sodium phosphate, etc., and among these, sodium hydroxide is preferable.

[0029] Step (1) can be carried out using a water washing tank with a stirrer and a centrifuge for solid-liquid separation, but it can also be carried out in a container having a mixing function with a stirring blade inside the container and a filtration filter disposed at the bottom. Also, even for hot water washing exceeding 100°C, it is possible to use a water washing tank with a stirrer for hot water washing and a centrifuge for subsequent filtration at 20 to 100°C, but it can also be carried out in a sealed or sealable container having a mixing function with a stirring blade inside the container and a filtration filter disposed at the bottom. In the present invention, water washing or hot water washing may be carried out continuously or batchwise.

[0030] Step (2) Step (2) is a step of adding a metal salt containing at least one Group 2 element in the periodic table among magnesium, calcium, strontium, and barium to an aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent to form a water-insoluble carbonate and precipitate it in the aqueous solution (B). The metal salt used at this time is not particularly limited as long as it is a metal salt containing at least one Group 2 element in the periodic table among magnesium, calcium, strontium, and barium. Examples include chlorides, hydroxides, bromides, acetates, etc. Among these, chlorides are desirable, and calcium chloride and barium chloride are more desirable. The addition amount of the metal salt is not particularly limited as long as it is in a range where a water-insoluble carbonate is formed by the addition, but it is preferably in a range of 0.1 mol or more, more preferably 0.3 mol or more, preferably 5 mol or less, and more preferably 3 mol or less with respect to 1 mol of the alkali metal carbonate in the aqueous solution (B).

[0031] Step (3) Step (3) is a step of separating and removing the carbonate insoluble in the generated water from the aqueous solution (B) to obtain an aqueous solution (C) containing at least an alkali metal halide and a sulfiding agent. The method for separating and removing the carbonate insoluble in the generated water is not particularly limited as long as the effects of the present invention are not impaired, but examples thereof include a method of performing solid-liquid separation by filtering off the carbonate insoluble in the generated water. Examples of the method of performing solid-liquid separation by filtering off the carbonate insoluble in the generated water include a method of filtering using a filtration device, a method of adding water again to the filtration residue containing water obtained by the above-described filtration (hereinafter abbreviated as "water-containing cake") to form a slurry and then filtering, or a method of adding water again and filtering while the water-containing cake is held on a filter. By step (3), 90% by mass or more of the carbonate generated and precipitated in the aqueous solution (B) in step (2) can be separated and removed.

[0032] Step (4) Step (4) is a step of adding an acid to an aqueous solution (C) containing at least an alkali metal halide and a sulfiding agent to generate hydrogen sulfide. Examples of the acid used at this time include hydrochloric acid, sulfuric acid, carbonic acid, acetic acid, etc., and among these, hydrochloric acid is preferred. The pH range of the aqueous solution (C) is not particularly limited as long as hydrogen sulfide is generated by adding an acid, but it is preferably carried out in the range of 2.5 to 5.5 because it is a condition in which hydrogen sulfide is more likely to be generated, and more preferably in the range of 3.5 to 4.5. In addition, the addition of the acid is preferably carried out in the range of 0 to 60 °C, more preferably in the range of 10 to 40 °C, and preferably carried out in the range of a pressure of 0 to 1.0 Pa (gauge pressure).

[0033] Steps (5) and (6) In step (5), since the hydrogen sulfide generated in step (4) volatilizes as a gas, subsequently, it is a step of recovering the generated hydrogen sulfide. Further, step (6) is a step of reacting the obtained hydrogen sulfide with an alkali metal hydroxide. Step (5) and step (6) can be carried out simultaneously or separately.

[0034] When performing step (5) and step (6) simultaneously, for example, there is a method of discharging the volatilized hydrogen sulfide out of the system, absorbing and recovering it in an aqueous solution containing an alkali metal hydroxide, and at the same time, reacting hydrogen sulfide with the alkali metal hydroxide to generate a sulfidizing agent. In this case, as the alkali metal hydroxide to be used, the same one as that used in the above-described PAS polymerization step can be used. Since the amount of the alkali metal hydroxide used varies depending on the temperature and pressure during the absorption of hydrogen sulfide, it cannot be generally specified, but it is desirable that the amount be not less than the amount sufficient to fully absorb and react with the total amount of the volatilized hydrogen sulfide. Generally, when absorbing and reacting hydrogen sulfide at normal temperature and normal pressure, it is preferably not less than 1 mol, more preferably in the range of 1 to 2 mol, per 1 mol of the sulfur atom of the volatilized hydrogen sulfide. Also, since the concentration of the alkali metal hydroxide in the aqueous solution varies depending on the temperature and pressure during the absorption and reaction of hydrogen sulfide, it cannot be generally specified, but it is preferably in the range of 5 to 49 wt%, more preferably in the range of 10 to 45 wt%. Further, since the temperature during the absorption and reaction of hydrogen sulfide in the aqueous solution containing an alkali metal hydroxide varies depending on the pressure, it cannot be generally specified, but the range of 0 to 200°C is preferable, and the range of 10 to 150°C is more preferable. Also, since the pressure during the absorption and reaction of hydrogen sulfide in the aqueous solution containing an alkali metal hydroxide varies depending on the temperature, it cannot be generally specified, but the range of 0 to 1.0 Pa (gauge pressure) is preferable, and the range of 0 to 0.5 Pa (gauge pressure) is more preferable.

[0035] On one hand, when steps (5) and (6) are carried out separately, for example, after performing a step of discharging the volatilized hydrogen sulfide out of the system and absorbing it into a solvent known to absorb hydrogen sulfide, such as an organic amide solvent, and then recovering it, a method can be mentioned in which an alkali metal hydroxide is added to the recovered solvent containing hydrogen sulfide to react hydrogen sulfide with the alkali metal hydroxide to produce an alkali metal hydrosulfide. In this case, examples of the solvent known to absorb hydrogen sulfide include organic amide solvents. Further, examples of the organic amide solvents include amides and ureas such as formamide, acetamide, N-methylformamide, N,N-dimethylacetamide, tetramethylurea, N-methyl-2-pyrrolidone, 2-pyrrolidone, N-methyl-ε-caprolactam, ε-caprolactam, hexamethylphosphoramide, N-dimethylpropyleneurea, and 1,3-dimethyl-2-imidazolidinone acid. Among these, amides having an aliphatic cyclic structure such as N-methyl-2-pyrrolidone, 2-pyrrolidone, N-methyl-ε-caprolactam, ε-caprolactam, hexamethylphosphoramide, N-dimethylpropyleneurea, and 1,3-dimethyl-2-imidazolidinone acid are preferred, and N-methyl-2-pyrrolidone is more preferred.

[0036] Although the amount of the solvent known to absorb hydrogen sulfide cannot be generally specified because it varies depending on the temperature and pressure at the time of absorbing hydrogen sulfide, it is desirable that the amount be not less than the amount sufficient to fully absorb the total amount of the volatilized hydrogen sulfide. Generally, when absorbing hydrogen sulfide at normal temperature and pressure, it is preferably in the range of 1 to 30 kg with respect to 1 mol of the sulfur atom of the volatilized hydrogen sulfide. Although the temperature and pressure at the time of absorbing hydrogen sulfide into the solvent known to absorb hydrogen sulfide cannot be generally specified, the absorption temperature is preferably in the range of 0 to 200°C, more preferably in the range of 10 to 150°C. On the other hand, the pressure is preferably in the range of 0 to 1.0 Pa (gauge pressure), more preferably in the range of 0 to 0.5 Pa (gauge pressure). Thereafter, an alkali metal hydroxide is added to the solvent containing the recovered hydrogen sulfide to react hydrogen sulfide with the alkali metal hydroxide to produce an alkali metal hydrosulfide. At this time, it is desirable that the amount of the alkali metal hydroxide added be not less than the amount sufficient to fully react with the total amount of the hydrogen sulfide absorbed in the solvent. Generally, when absorbing hydrogen sulfide at normal temperature and pressure, it is preferably not less than 1 mol, more preferably in the range of 1 to 2 mol, with respect to 1 mol of the sulfur atom of the hydrogen sulfide absorbed in the solvent. Although the concentration of the alkali metal hydroxide in the aqueous alkali solution added to the solvent also varies depending on the temperature and pressure at the time of absorbing hydrogen sulfide and thus cannot be generally specified, it is preferably in the range of 5 to 49 wt%, more preferably in the range of 10 to 45 wt%. Further, although the temperature at the time of reacting the hydrogen sulfide absorbed in the solvent with the alkali metal hydroxide varies depending on the pressure and thus cannot be generally specified, the temperature is preferably in the range of 0 to 200°C, more preferably in the range of 10 to 150°C. Also, although the pressure cannot be generally specified, it is preferably in the range of 0 to 1.0 Pa (gauge pressure), more preferably in the range of 0 to 0.5 Pa (gauge pressure).

[0037] The process (5) can be either a continuous process or a batch process. Since the absorption rate of hydrogen sulfide in an aqueous solution of an alkali metal hydroxide or an organic amide solvent is high, a general apparatus such as a packed tower with a circulation pump may be used, and a liquid injection type, a bubbling type, etc. can also be sufficiently used. When the processes (5) and (6) are carried out simultaneously, the process (6) can be carried out in the same apparatus as the process (5). When the processes (5) and (6) are carried out separately, even if the process (6) is carried out in the same apparatus as the process (5), after transferring the hydrogen sulfide recovered in the process (5) to another apparatus, for example, a reaction tank with a stirring blade, a vessel, a drum, etc., an alkali metal hydroxide may be added and reacted.

[0038] Process (7) As described above, in the processes (5) and (6), since an alkali metal hydroxide in an amount sufficient to absorb and react all of the recovered hydrogen sulfide is used, excess alkali metal hydroxide remains unreacted in the system. Therefore, after the process (6), it is preferable to have a process (7) in which hydrogen sulfide is added to the unreacted alkali metal hydroxide to react the unreacted alkali metal hydroxide with the hydrogen sulfide. The amount of hydrogen sulfide to be added is preferably in the range of 0.5 to 1 mole per 1 mole of the alkali metal hydroxide remaining unreacted. By reacting with hydrogen sulfide in this range, 0.5 to 1 mole of alkali metal hydrosulfide and / or alkali metal sulfide is generated per 1 mole of the remaining alkali metal hydroxide.

[0039] Note that the ratio of the alkali metal hydrosulfide and the alkali metal sulfide generated through the process (6) or the process (7) varies depending on the amount of the alkali metal hydroxide reacted with hydrogen sulfide, the reaction time, the temperature, the pressure, etc., and thus cannot be generally defined. Also, since both the alkali metal hydrosulfide and the alkali metal sulfide can be reused as a sulfidizing agent, which is a polymerization raw material of the PAS resin described later, the ratio of the alkali metal hydrosulfide and the alkali metal sulfide may be any ratio within the range of 0 / 100 to 100 / 0 on a mass basis.

[0040] Method for producing PAS resin At least, the mixture (A) containing a PAS resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent can be obtained by the following method for producing a PAS resin. Further, the alkali metal hydrosulfide and / or alkali metal sulfide obtained through the above steps (1) to (6) or steps (1) to (7) can be used as a sulfidizing agent in the following method for producing a PAS resin as at least a part of the polymerization raw materials.

[0041] PAS polymerization step That is, the method for producing a PAS resin used in the present invention comprises mixing an aprotic polar solvent, a polyhaloaromatic compound, and a sulfidizing agent, and subjecting the polyhaloaromatic compound and the sulfidizing agent to a polymerization reaction in the aprotic polar solvent to obtain a crude reaction mixture containing at least a PAS resin, a sulfidizing agent remaining unpolymerized, an alkali metal halide, and an aprotic polar solvent; and a PAS / solvent solid-liquid separation step of obtaining a reaction mixture containing at least a PAS resin, a sulfidizing agent remaining unpolymerized, and an alkali metal halide, which is obtained by solid-liquid separating the aprotic polar solvent from the crude reaction mixture.

[0042] Here, in the present invention, the polyhaloaromatic compound is, for example, a halogenated aromatic compound having two or more halogen atoms directly bonded to an aromatic ring. Specifically, examples include dihaloaromatic compounds such as p-dichlorobenzene, o-dichlorobenzene, m-dichlorobenzene, trichlorobenzene, tetrachlorobenzene, dibromobenzene, diiodobenzene, tribromobenzene, dibromonaphthalene, triiodobenzene, dichlorodiphenylbenzene, dibromodiphenylbenzene, dichlorobenzophenone, dibromobenzophenone, dichlorodiphenyl ether, dibromodiphenyl ether, dichlorodiphenyl sulfide, dibromodiphenyl sulfide, dichlorobiphenyl, dibromobiphenyl, and mixtures thereof. These compounds may be block copolymerized. Among these, dihalogenated benzenes are preferred, and those containing 80 mol% or more of p-dichlorobenzene are particularly preferred. Further, for the purpose of increasing the viscosity of the PAS resin by forming a branched structure, a polyhaloaromatic compound having three or more halogen substituents in one molecule may be used as a branching agent as desired. Examples of such polyhaloaromatic compounds include 1,2,4-trichlorobenzene, 1,3,5-trichlorobenzene, 1,4,6-trichloronaphthalene, etc. Furthermore, polyhaloaromatic compounds having a functional group with active hydrogen such as an amino group, a thiol group, a hydroxyl group, etc. can be mentioned. Specifically, dihaloanilines such as 2,6-dichloroaniline, 2,5-dichloroaniline, 2,4-dichloroaniline, 2,3-dichloroaniline; trihaloanilines such as 2,3,4-trichloroaniline, 2,3,5-trichloroaniline, 2,4,6-trichloroaniline, 3,4,5-trichloroaniline; dihaloaminodiphenyl ethers such as 2,2'-diamino-4,4'-dichlorodiphenyl ether, 2,4'-diamino-2',4-dichlorodiphenyl ether, and compounds in which the amino group in these mixtures is replaced by a thiol group or a hydroxyl group, etc. are exemplified.In addition, active hydrogen-containing polyhaloaromatic compounds in which the hydrogen atoms bonded to the carbon atoms forming the aromatic rings in these active hydrogen-containing polyhaloaromatic compounds are substituted with other inert groups, such as hydrocarbon groups such as alkyl groups, can also be used.

[0043] Among these various active hydrogen-containing polyhaloaromatic compounds, preferred are active hydrogen-containing dihaloaromatic compounds, and particularly preferred is dichloroaniline.

[0044] Examples of the polyhaloaromatic compounds having a nitro group include mono- or dihalonitrobenzenes such as 2,4-dinitrochlorobenzene and 2,5-dichloronitrobenzene; dihalonitrodiphenyl ethers such as 2-nitro-4,4'-dichlorodiphenyl ether; dihalonitrodiphenyl sulfones such as 3,3'-dinitro-4,4'-dichlorodiphenyl sulfone; mono- or dihalonitropyridines such as 2,5-dichloro-3-nitropyridine and 2-chloro-3,5-dinitropyridine; or various dihalonitronaphthalenes and the like.

[0045] In addition, in the present invention, examples of the sulfidizing agent include alkali metal sulfides and / or alkali metal hydrosulfides.

[0046] Examples of the alkali metal sulfide include lithium sulfide, sodium sulfide, rubidium sulfide, cesium sulfide, and mixtures thereof. Such alkali metal sulfides can be used as hydrates, aqueous mixtures, or anhydrides. In addition, alkali metal sulfides can also be derived by the reaction of alkali metal hydrosulfides and alkali metal hydroxides. Incidentally, usually, in order to react with trace amounts of alkali metal hydrosulfides and alkali metal thiosulfates present in the alkali metal sulfide, a small amount of alkali metal hydroxide may be added without any problem.

[0047] In addition, examples of the alkali metal hydrosulfide include lithium hydrosulfide, sodium hydrosulfide, rubidium hydrosulfide, cesium hydrosulfide, and mixtures thereof. Such alkali metal hydrosulfides can be used as hydrates, aqueous mixtures, or anhydrides.

[0048] Further, the alkali metal hydrosulfide is used in combination with an alkali metal hydroxide. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, etc. These may be used alone or in combination of two or more. Among these, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferred because they are easily available, and sodium hydroxide is particularly preferred.

[0049] As described above, the alkali metal hydrosulfide and / or alkali metal sulfide obtained through the above steps (1) to (6) or steps (1) to (7) can also be reused as a sulfidizing agent and as a raw material in the polymerization reaction of the PAS resin.

[0050] In the method for producing the PAS resin used in the present invention, a hydrous sulfidizing agent can also be used as a raw material. In that case, it is preferable to subject the hydrous sulfidizing agent to a dehydration step in the presence of at least an aprotic polar solvent and then use it in the polymerization reaction of the PAS resin. Further, when the charged amount of the aprotic polar solvent is small, for example, less than 1 mol per 1 mol of the sulfur atom of the sulfidizing agent, it is preferable to dehydrate the hydrous sulfidizing agent and the aprotic polar solvent in the presence of a polyhaloaromatic compound.

[0051] The dehydration process involves charging at least an aprotic polar solvent, an aqueous alkali metal sulfide or an aqueous alkali metal hydrosulfide and an alkali metal hydroxide as a hydrous sulfidizing agent into a reaction vessel equipped with a distillation apparatus, and heating to a temperature at which water is removed by azeotropy, specifically in the range of 300 °C or lower, preferably in the range of 80 to 220 °C, more preferably in the range of 100 to 200 °C, and discharging water out of the system by distillation. In the dehydration process, it is preferable to dehydrate until the amount of water in the system where the polymerization reaction is carried out is in the range of 5 moles or less, more preferably in the range of 0.01 to 2.0 moles, per mole of sulfur atom of the sulfidizing agent.

[0052] Also, in the dehydration process, the alkali metal sulfide or the alkali metal hydrosulfide reacts with water to generate hydrogen sulfide gas in equilibrium. Therefore, after recovering the generated hydrogen sulfide, it is preferable to react it with an alkali metal hydroxide to obtain an alkali metal hydrosulfide and / or an alkali metal sulfide. Specifically, the generated hydrogen sulfide is preferably discharged out of the reaction system together with water or an azeotropic mixture, separated from water or the azeotropic mixture by a distillation apparatus, and then recovered by the same method as in the above step (5). Further, it is preferable to react the recovered hydrogen sulfide with an alkali metal hydroxide by the same method as in the above step (6) to produce an alkali metal hydrosulfide and / or an alkali metal sulfide. Also, after the step of reacting the hydrogen sulfide recovered in the dehydration process with an alkali metal hydroxide to produce an alkali metal hydrosulfide and / or an alkali metal sulfide, it preferably has a step of adding hydrogen sulfide to the unreacted alkali metal hydroxide and reacting the unreacted alkali metal hydroxide with the hydrogen sulfide by the same method as in step (7). The alkali metal hydrosulfide and / or the alkali metal sulfide obtained in the dehydration process are also preferably used as part of the raw materials in the method for producing a PAS resin as a sulfidizing agent.

[0053] In the present invention, aprotic polar solvents include amides, ureas, and lactams such as formamide, acetamide, N-methylformamide, N,N-dimethylacetamide, tetramethylurea, N-methyl-2-pyrrolidone, 2-pyrrolidone, N-methyl-ε-caprolactam, ε-caprolactam, hexamethylphosphoramide, N-dimethylpropyleneurea, and 1,3-dimethyl-2-imidazolidinone; sulfolanes such as sulfolane and dimethylsulfolane; nitriles such as benzonitrile; ketones such as methyl phenyl ketone; and mixtures thereof. Among these, amides having an aliphatic cyclic structure such as N-methyl-2-pyrrolidone, 2-pyrrolidone, N-methyl-ε-caprolactam, ε-caprolactam, hexamethylphosphoramide, N-dimethylpropyleneurea, and 1,3-dimethyl-2-imidazolidinone are preferred, and N-methyl-2-pyrrolidone is more preferred.

[0054] In the PAS polymerization process, the polymerization reaction of the PAS resin involves reacting the above-mentioned alkali metal sulfide as a sulfidizing agent with a polyhaloaromatic compound in the presence of these aprotic polar solvents. Alternatively, the polymerization reaction of the PAS resin involves reacting the above-mentioned alkali metal hydrosulfide and alkali metal hydroxide as sulfidizing agents with a polyhaloaromatic compound in the presence of these aprotic polar solvents. The polymerization conditions generally range from 200 to 330 °C in terms of temperature, and the pressure should be in a range that substantially maintains the polymerization solvent and the polyhaloaromatic compound, which is the polymerization monomer, in the liquid phase. Generally, it is selected from the range of 0.1 to 20 MPa, preferably from the range of 0.1 to 2 MPa. The charged amount of the polyhaloaromatic compound is adjusted to be in the range of 0.2 mol to 5.0 mol, preferably in the range of 0.8 to 1.3 mol, and more preferably in the range of 0.9 to 1.1 mol, per 1 mol of the sulfur atom of the above-mentioned sulfidizing agent. Also, the charged amount of the aprotic polar solvent is adjusted to be in the range of 1.0 to 6.0 mol, preferably in the range of 2.5 to 4.5 mol, per 1 mol of the sulfur atom of the sulfidizing agent. Note that the polymerization reaction is preferably carried out in the presence of a small amount of water, and the ratio thereof is preferably adjusted as appropriate in consideration of the polymerization method, the molecular weight of the resulting polymer, and productivity. Specifically, a dehydration operation is performed so that it is in the range of 2.0 mol or less, preferably 1.6 mol or less, per 1 mol of the sulfur atom of the sulfidizing agent. However, when the dehydration operation is further carried out in the presence of the polyhaloaromatic compound (for example, the method of "5)" in the following specific embodiments), the dehydration operation may be carried out so that it is in the range of 0.9 mol or less, preferably 0.05 to 0.3 mol, and more preferably 0.01 to 0.02 mol or less.

[0055] As specific embodiments of polymerizing a sulfidizing agent and a polyhaloaromatic compound in the presence of the above-mentioned aprotic polar solvents, for example, 1) A method using a polymerization aid such as an alkali metal carboxylate or lithium halide; 2) A method using a branching agent such as an aromatic polyhalogen compound; 3) A method of carrying out the polymerization reaction in the presence of a small amount of water and then adding water to further polymerize; 4) A method of cooling the gas phase part of the reaction kettle during the reaction of an alkali metal sulfide and an aromatic dihalogen compound to condense a part of the gas phase in the reaction kettle and reflux it to the liquid phase. 5) In the presence of a polyhaloaromatic compound, a step of reacting an alkali metal sulfide, or a hydrous alkali metal hydrosulfide and an alkali metal hydroxide with an amide, urea or lactam having an aliphatic cyclic structure while dehydrating to produce a slurry containing a solid alkali metal sulfide. After producing the slurry, a step of further adding a polar organic solvent such as NMP and distilling off water for dehydration. Then, in the slurry obtained through the dehydration step, a polyhaloaromatic compound, an alkali metal hydrosulfide, and an alkali metal salt of a hydrolysis product of the amide, urea or lactam having the aliphatic cyclic structure are reacted with the water content existing in the reaction system being 0.02 mol or less per 1 mol of the polar organic solvent such as NMP to carry out polymerization. A method for producing a PAS resin having this as an essential production step.

[0056] Among these, in the case of producing a PAS resin by the polymerization methods of 1) to 5), particularly 1) to 4), when the aprotic polar solvent is NMP and the polyhaloaromatic compound is p-dichlorobenzene as production raw materials, as a side reaction product of the polymerization reaction, the following general formula (1)

[0057]

Chemical formula

[0058] The crude reaction mixture containing at least a PAS resin, an alkali metal hydrosulfide and / or an alkali metal sulfide remaining as an unreacted sulfidizing agent, an alkali metal halide, an alkali metal carbonate, and a non-protic polar solvent obtained through the above PAS polymerization step can be used as the mixture (A).

[0059] PAS / solvent solid-liquid separation step The crude reaction mixture containing at least a PAS resin, an alkali metal halide, an alkali metal hydrosulfide and / or an alkali metal sulfide remaining as an unreacted sulfidizing agent, an alkali metal carbonate, and a non-protic polar solvent obtained through the PAS polymerization step is subsequently a step of subjecting the non-protic polar solvent to solid-liquid separation from the crude reaction mixture to obtain a reaction mixture containing at least a PAS resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent. The obtained reaction mixture can also be used as the mixture (A).

[0060] The solid-liquid separation can be roughly divided into two types: the flash method and the quench method, which will be described later. The flash method is a method of evaporating the solvent to recover the solvent and simultaneously recovering the solid matter. Generally, it is carried out by heating under reduced pressure to distill off the solvent.

[0061] On the other hand, the quench method is a method of cooling the polymerization reactant to recover particulate PAS resin. Generally, after cooling the reaction slurry in the reaction kettle, crystallizing the PAS resin and then separating the solid and liquid can be mentioned. The solid-liquid separation in the quench method includes methods such as separating using a centrifuge such as filtration or a screw decanter, adding water directly to the obtained filtration residue to form a slurry, and then repeating the solid-liquid separation, or heating the obtained filtration residue in a non-oxidizing atmosphere to remove the remaining solvent. The flash method is preferable in that the solid matter can be recovered relatively simply. The quench method is preferable in that it is easy to control the particle size of the PAS resin and it is difficult for impurities such as alkali metal halides and sulfidizing agents to be incorporated into the polymer particles during crystallization, so that a high-purity polymer can be obtained.

[0062] Subsequently, the reaction mixture is separated into a PAS resin and an aqueous solution containing at least an alkali metal halide and a sulfidizing agent through the purification step by water washing or hot water washing according to the present invention. This purification step can be carried out in the same manner as in step (1). When producing the PAS resin, the filtered PAS resin may be recovered.

[0063] The filtered PAS resin is recovered. Then, it may be dried as it is and used as PAS resin powder, or after further washing treatment, solid-liquid separation is carried out and drying is performed to prepare powdery or granular PAS resin.

[0064] Composition, use, etc. As described above, the PAS resin polymerized by recycling at least a part of the raw materials with the sulfidizing agent obtained through the steps (1) to (6) or steps (1) to (7) of the present invention may contain additives such as a release agent, a colorant, a heat stabilizer, an ultraviolet stabilizer, a foaming agent, a rust preventive, a flame retardant, a lubricant, a coupling agent, and a filler, as long as the effects of the present invention are not impaired. Further, synthetic resins and elastomers as described below can be mixed and used in the same manner. Examples of these synthetic resins include polyester, polyamide, polyimide, polyetherimide, polycarbonate, polyphenylene ether, polysulfone, polyethersulfone, polyetheretherketone, polyetherketone, polyarylene, polyethylene, polypropylene, polytetrafluoroethylene, polydifluoroethylene, polystyrene, ABS resin, epoxy resin, silicone resin, phenol resin, urethane resin, liquid crystal polymer, etc., and examples of the elastomer include polyolefin rubber, fluororubber, silicone rubber, etc.

[0065] Furthermore, the PAS resin polymerized by recycling at least a part of the raw materials with the sulfidizing agent obtained through the steps (1) to (6) or steps (1) to (7) of the present invention is excellent in heat resistance, moldability, dimensional stability, etc. by various melt processing methods such as injection molding, extrusion molding, compression molding, blow molding. Therefore, for example, it can be widely used as injection-molded and compression-molded products such as electric and electronic parts such as connectors, printed circuit boards, and encapsulated molded products, automotive parts such as lamp reflectors and various electrical parts, interior materials for various buildings, aircraft, automobiles, etc., or precision parts such as OA equipment parts, camera parts, watch parts, etc., or extrusion-molded and drawn-molded products such as fibers, films, sheets, pipes, etc.

[0066] According to the present invention, by separating and recovering the alkali metal hydrosulfide remaining as a reusable high-purity unreacted sulfidizing agent from the wastewater obtained after water washing or hot water washing in the manufacturing process of the PAS resin, it is possible to reduce the COD value of the wastewater, reduce the environmental load due to the reduction of industrial waste, suppress the loss of sulfur atoms (reduction of raw material unit), and improve the productivity of the PAS resin.

Example

[0067] The present invention will be specifically described below with reference to examples. These examples are illustrative and not limiting. Unless otherwise specified, "% " and "parts" are based on mass hereinafter.

[0068] <Evaluation>

[0069] (1) Quantification of sodium carbonate concentration, sodium hydrogen sulfide concentration, and sodium sulfide concentration in wastewater and sulfiding agent recovery solution For each of the wastewater and sulfiding agent recovery solutions obtained in each run of each example and comparative example, an aqueous barium chloride solution was added, and after confirming the formation of a precipitate of barium carbonate, the slurry-like solution was subjected to neutralization titration with 0.5 mol / L hydrochloric acid using a potentiometric automatic titrator. The sodium sulfide concentration was calculated from the titration volume at the first equivalence point. Next, the sodium hydrogen sulfide concentration was calculated from the difference between the titration volume at the second equivalence point and the titration volume at the first equivalence point, and the sodium carbonate concentration was calculated from the difference between the third equivalence point and the second equivalence point.

[0070] (2) Measurement of pH when adding hydrochloric acid to wastewater In each sulfiding agent recovery step of each example and comparative example, the pH when adding hydrochloric acid to the wastewater was measured using a "Personal pH Meter PH72" manufactured by Yokogawa Electric Corporation. The electrodes were calibrated using pH 4 and pH 7 standard solutions.

[0071] <Examples 1 - 9, Comparative Examples 1 - 4>

[0072] Example (1 - 1) PPS polymerization and production of wastewater A 150 - liter autoclave with a stirrer blade and a bottom valve connected to a condenser, a pressure gauge, a thermometer, and a gas absorption bottle charged in advance with 1.88 kg of a 20 wt% aqueous sodium hydroxide solution was charged with 60.33 wt% Na 219.403 kg of S-flake raw material (150 mol of sulfur atoms, "60% sodium sulfide product" manufactured by Nagao Co., Ltd., sodium carbonate content 0.35 wt%) and 45.0 kg (454 mol) of NMP were charged. While stirring under a nitrogen stream, the temperature was raised to 209 °C, and 4.815 kg of water was distilled off. The hydrogen sulfide scattered during dehydration was absorbed into an aqueous sodium hydroxide solution using a gas absorption bottle. Then, the autoclave was sealed and cooled to 180 °C, and 22.185 kg (151 mol) of p-dichlorobenzene and 18.0 kg (182 mol) of NMP were charged. Using nitrogen gas, the pressure was increased to 0.1 MPa at a gauge pressure at a liquid temperature of 150 °C, and the temperature increase was started. The reaction was advanced while stirring at a liquid temperature of 260 °C for 3 hours, and the upper part of the autoclave was cooled by sprinkling water. Next, the temperature was decreased, and the cooling of the upper part of the autoclave was stopped. After the slurry obtained after the reaction was cooled to room temperature, it was dried at 150 °C under reduced pressure for 3 hours using a vacuum dryer to distill off NMP. Next, 93 kg of warm water at 70 °C was added and stirred, then filtered, and further 53 kg of warm water at 70 °C was added and filtered. Each filtrate was collected to obtain 136 kg of waste water (1a-1). The concentrations of sodium carbonate and sulfidizing agents (sodium hydrogen sulfide and sodium sulfide) contained in the waste water (1a-1) were measured by neutralization titration. The results are shown in Table 1.

[0073] Example (1-2) Filtration of waste water and recovery of sulfidizing agent contained in the waste water To the waste water (1a-1), 0.50 mol of calcium chloride was added per 1 mol of dissolved sodium carbonate, and the generated white precipitate was filtered to obtain 136 kg of waste water (1a-2). The waste water (1a-2) was subjected to neutralization titration to determine the amounts of sodium carbonate and sulfidizing agent. The results are shown in Table 1. Then, a gas absorption bottle containing an aqueous sodium hydroxide solution that had absorbed hydrogen sulfide obtained in Example (1-1) was connected to a container equipped with a stirrer, a pH meter, a gas introduction tube, and a dropping funnel. 136 kg of the waste water (1a-2) was charged into the container, and N 2While stirring, gas (50 ml / min) was introduced, hydrochloric acid was added to adjust the pH to 3.0, and stirring was carried out for 60 minutes to generate a gas containing hydrogen sulfide. The generated hydrogen sulfide gas was absorbed into an aqueous sodium hydroxide solution to obtain 2.17 kg of a sulfiding agent recovery solution (1a). The sulfiding agent recovery solution (1a) was measured by neutralization titration to determine the concentrations of sodium carbonate and the sulfiding agent. The results are shown in Table 2.

[0074] Example (1-3) Production of PPS using a sulfiding agent recovery solution The raw materials charged into the autoclave were, instead of "19.413 kg of 60.33 wt% Na 2 S flakes raw material", "18.918 kg of 60.33 wt% Na 2 S flakes raw material (146.25 moles of sulfur atoms), 0.997 kg of the sulfiding agent recovery solution (1a) (3.75 moles of sulfur atoms, and the usage ratio of the sulfiding agent recovery solution to the total number of moles of sulfur atoms charged was 2.5 mol%), and a mixture of 0.259 kg (3.18 moles) of 49.21 wt% sodium hydroxide". Except for this, the same procedure as in Example (1-1) was carried out to obtain wastewater (1b-1). The amounts of the sulfiding agent and sodium carbonate in the raw materials charged in the production of PPS are shown in Table 3.

[0075] Example (1-4) Filtration of wastewater and recovery of the sulfiding agent contained in the wastewater (second time) In the same procedure as in Example (1-2), 0.50 mol of calcium chloride was added to the wastewater (1b-1) per 1 mol of sodium carbonate in the wastewater, and the generated white precipitate was filtered to obtain wastewater (1b-2). Then, hydrochloric acid was added to the obtained wastewater (1b-2), and the gas containing hydrogen sulfide generated was absorbed into an aqueous sodium hydroxide solution to obtain a sulfiding agent recovery solution (1b). The sulfiding agent recovery solution (1b) was measured by neutralization titration to determine the concentrations of sodium carbonate and the sulfiding agent. The results are shown in Table 4.

[0076] Example (1-5) Repeated test Thereafter, PPS production using the sulfidizing agent recovery solution was repeated in the same manner as in Examples (1-3), and filtration of the same wastewater as in (1-4) and recovery of the sulfidizing agent contained in the wastewater were repeated. In each process, sulfidizing agent recovery solutions (1c) to (1j) were obtained respectively. The concentrations of sodium carbonate and the sulfidizing agent contained in each sulfidizing agent recovery solution were determined by neutralization titration. The results are shown in Table 4.

[0077] Examples (2-1 to 2-5) In Example (1-3), the procedure was the same as in Example (1), except that the ratio of the sulfidizing agent recovery solution used to the total number of moles of sulfur atoms charged was changed from 2.5 mol% to 5.0 mol%. The results obtained are shown in Tables 1 to 4.

[0078] Examples (3-1 to 3-5) In Example (1-2), the procedure was the same as in Example (1), except that the amount of calcium chloride added to the wastewater was changed from 0.50 mol per 1 mol of sodium carbonate to 1.00 mol. The results obtained are shown in Tables 1 to 4.

[0079] Examples (4-1 to 4-5) In Example (2-2), the procedure was the same as in Example (2), except that the amount of calcium chloride added to the wastewater was changed from 0.50 mol per 1 mol of sodium carbonate to 1.00 mol. The results obtained are shown in Tables 1 to 4.

[0080] Examples (5-1 to 5-5) In Example (2-2), the procedure was the same as in Example (2), except that the amount of calcium chloride added to the wastewater was changed from 0.50 mol per 1 mol of sodium carbonate to 2.00 mol. The results obtained are shown in Tables 1 to 4.

[0081] Examples (6-1 to 6-5) In Example (4-2), the procedure was the same as in Example (4), except that the metal salt added to the wastewater was changed from calcium chloride to calcium acetate. The results obtained are shown in Tables 1 to 4.

[0082] Examples (7-1 to 7-5) In Example (4-2), the procedure was the same as in Example (4), except that calcium hydroxide was used as the metal salt added to the wastewater instead of calcium chloride. The respective obtained results are shown in Tables 1 to 4.

[0083] Examples (8-1 to 8-5) In Example (4-2), the procedure was the same as in Example (4), except that barium chloride was used as the metal salt added to the wastewater instead of calcium chloride. The respective obtained results are shown in Tables 1 to 4.

[0084] Examples (9-1 to 9-5) In Example (4-2), the procedure was the same as in Example (4), except that strontium chloride was used as the metal salt added to the wastewater instead of calcium chloride. The respective obtained results are shown in Tables 1 to 4.

[0085] Comparative Examples (1-1 to 1-5) In Example (1-2), the procedure was the same as in Example (1), except that hydrochloric acid treatment was performed without adding a metal salt to the wastewater. The respective obtained results are shown in Tables 1 to 4.

[0086] Comparative Examples (2-1 to 2-5) In Example (2-2), the procedure was the same as in Example (2), except that hydrochloric acid treatment was performed without adding a metal salt to the wastewater. The respective obtained results are shown in Tables 1 to 4. In the production of the sulfiding agent, the concentration of sodium carbonate exceeded 10 wt% at the fourth time, and due to concerns about sodium carbonate precipitation, the subsequent production of PPS was stopped.

[0087] Comparative Examples (3-1 to 3-5) In Example (4-2), the procedure was the same as in Example (4), except that calcium carbonate was used as the metal salt added to the wastewater instead of calcium chloride. The respective obtained results are shown in Tables 1 to 4. In the production of the sulfiding agent, the concentration of sodium carbonate exceeded 10 wt% at the fourth time, and due to concerns about sodium carbonate precipitation, the subsequent production of PPS was stopped.

[0088] Comparative Examples (4-1 to 4-5) In Comparative Example (4-2), the procedure was the same as in Example (4), except that potassium chloride was used instead of calcium chloride as the metal salt added to the wastewater. No precipitate was observed in the wastewater after the addition of potassium chloride. Therefore, hydrochloric acid was added without performing subsequent filtration. The results obtained are shown in Tables 1 to 4. In the production of the sulfiding agent, the concentration of sodium carbonate exceeded 10 wt% at the fourth time, and due to concerns about sodium carbonate precipitation, the subsequent production of PPS was stopped.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] [Table 4]

[0093] From the results in Table 1, it was confirmed that in the examples, the concentration of sodium carbonate in the wastewater after filtration could be reduced compared with the comparative examples. From the results in Table 2, since the concentration of sodium carbonate in the wastewater of the examples was low, when the hydrogen sulfide gas generated by adding hydrochloric acid to the waste liquid was recovered in the aqueous sodium hydroxide solution, it was found that the carbon dioxide gas derived from sodium carbonate generated together was small and the sodium carbonate in the sulfiding agent recovery liquid was small. When the production of PPS was repeated by reusing the sulfiding agent recovery liquid in the amount shown in Table 3, it became clear from Table 4 that the concentration of sodium carbonate in the sulfiding agent recovery liquid remained low in the examples.

Claims

1. After contacting a mixture (A) containing at least a polyarylene sulfide resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent with water, the polyarylene sulfide resin is separated and removed to obtain an aqueous solution (B) containing at least an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent (Step 1), A metal salt selected from chlorides, hydroxides, bromides, or acetates, which contains at least one Group 2 element among magnesium, calcium, strontium, and barium, is added to the aqueous solution (B) to form a carbonate insoluble in water (Step 2), The carbonate insoluble in water formed is separated and removed from the aqueous solution (B) to obtain an aqueous solution (C) containing at least an alkali metal halide and a sulfidizing agent (Step 3), An acid is added to the aqueous solution (C) to generate hydrogen sulfide (Step 4), Step (5) of recovering the generated hydrogen sulfide, and Step (6) of reacting the recovered hydrogen sulfide with an alkali metal hydroxide, A method for producing a sulfidizing agent, characterized by comprising the above steps.

2. After step (6) of reacting the recovered hydrogen sulfide with an alkali metal hydroxide, hydrogen sulfide is added to the unreacted alkali metal hydroxide to react the hydrogen sulfide with the unreacted alkali metal hydroxide (Step 7). The method for producing a sulfidizing agent according to Claim 1, characterized by comprising this step.

3. The mixture (A) containing at least a polyarylene sulfide resin, an alkali metal halide, an alkali metal carbonate, and a sulfidizing agent is A crude reaction mixture containing at least a polyarylene sulfide resin, an alkali metal halide, the aprotic polar solvent, and a sulfidizing agent, which is obtained by reacting a polyhaloaromatic compound with a sulfidizing agent in an aprotic polar solvent, or a reaction mixture obtained by solid-liquid separation of the aprotic polar solvent from the crude reaction mixture. The method for producing a sulfidizing agent according to Claim 1, characterized by this.

4. The sulfidizing agent used when reacting a polyhaloaromatic compound with a sulfidizing agent in an aprotic polar solvent is obtained through a dehydration step of dehydrating a hydrous sulfidizing agent in the presence of at least an aprotic polar solvent. The method for producing a sulfidizing agent according to Claim 3, characterized by this.

5. A method for producing a sulfiding agent, comprising a step of reacting hydrogen sulfide generated in the dehydration step according to Claim 4 with an alkali metal hydroxide to obtain a sulfiding agent after recovering the hydrogen sulfide.

6. The method for producing a sulfiding agent according to Claim 5, further comprising a step of adding hydrogen sulfide to the unreacted alkali metal hydroxide and reacting the hydrogen sulfide with the unreacted alkali metal hydroxide after the step of reacting with the alkali metal hydroxide to obtain a sulfiding agent.

7. In a method for producing a polyarylene sulfide resin, wherein a sulfiding agent obtained by dehydrating a hydrous sulfiding agent in the presence of an organic amide solvent is reacted with a polyhaloaromatic compound in the presence of the organic amide solvent to produce a polyarylene sulfide resin, The method for producing a polyarylene sulfide resin, comprising a step of adding a sulfiding agent obtained by the method for producing a sulfiding agent according to any one of Claims 1 to 4 and / or a sulfiding agent obtained by the method according to Claim 5 or 6 as at least a part of the hydrous sulfiding agent or the sulfiding agent.

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