JP5817560B2 - Aprotic polar solvent recovery method and aprotic polar solvent recovery apparatus - Google Patents

Description

  The present invention relates to a method for efficiently extracting an aprotic polar solvent from an aqueous solution containing at least an alkali halide and / or an organic salt and an aprotic solvent, and separating and removing the alkali halide.

  Aprotic polar solvents are widely used as solvents for organic reactions because they are excellent in organic compound solubility, mutual solubility with water, and can improve nucleophilic substitution reactivity. It is also useful as a polymerization solvent in the production of a PPS resin excellent in heat resistance, chemical resistance, flame retardancy, molding processability and dimensional stability. Among them, N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is widely used industrially. This NMP is more expensive than a normal organic solvent and becomes a high source of CODMn when discharged as an aqueous solution. Therefore, it is generally recovered, purified and reused industrially. However, since NMP dissolves infinitely with water, it is difficult to efficiently recover NMP, and various recovery methods have been proposed.

  For example, Patent Document 1 discloses a method of recovering NMP by liquid-liquid extraction. However, since salt removal is insufficient and the purity of recovered NMP is not sufficient, further efficiency is improved. A new method was required.

  Patent Document 2 discloses a method of combining both of maintaining an alkali halide concentration after extraction at a certain level and maintaining a temperature at the time of extraction at 70 ° C. or higher. However, salt as a by-product is extracted. Since it may precipitate in a post process and cause clogging troubles, each time cleaning and removal are required, so the operation stability is insufficient.

  Patent Document 3 discloses a method of extracting from an aqueous solution containing an inorganic salt and / or organic salt and an aprotic polar solvent with a halogen-based solvent. However, most of the salt is removed by washing the extracted halogen-based solvent layer with a lot of water. At this time, the extraction efficiency deteriorates due to the back-extraction of the aprotic polar solvent again. There was a drawback.

Japanese Patent Publication No. 6-53728 JP 2007-269638 A JP 2002-1008 A

  The present invention has been achieved as a result of intensive studies to solve the above-described problems in the prior art.

  Therefore, the present invention is industrially developed from an aqueous solution (hereinafter referred to as slurry) containing at least an alkali halide and / or an organic salt and an aprotic solvent in the production of PAS represented by polyphenylene sulfide (hereinafter abbreviated as PPS). It is another object of the present invention to provide a stable process by efficiently recovering an aprotic polar solvent with high purity and suppressing the introduction of salt into step 2 and subsequent steps.

  As a result of intensive studies to solve the above problems, the present inventors cooled the extract when extracting and recovering an aprotic polar solvent from a slurry in PAS production with a non-halogen aliphatic organic compound. As a result, it was found that the salt concentration in the extract can be suppressed without impairing the extraction efficiency by controlling the phase equilibrium and allowing the stationary separation, thereby completing the present invention.

That is, the present invention
1. A method for recovering an aprotic polar solvent, comprising the following three steps.
(Step 1) In the production of polyarylene sulfide , an aqueous solution containing at least an alkali halide and / or an organic salt and an aprotic solvent is used as n-hexane, n-hexanol, n-hexanal, n-hexanone, 2-methyl-1 -Pentane, 2-methyl-1-pentanol, 2-methyl-1-pentanal, 2-methyl-1-pentanone, 3-methyl-1-hexane, 3-methyl-1-hexanol, 3-methyl-1- Organic containing an aprotic polar solvent by contacting at least one non-halogen aliphatic organic compound having 6 or more carbon atoms selected from hexanal and 3-methyl-1-hexanone at 50 ° C. or higher and 100 ° C. or lower. Extracting phase 1;
(Step 2) Step of cooling the organic phase 1 to 20 ° C. or higher and lower than 50 ° C., and extracting the organic phase 2 containing an aprotic polar solvent by phase separation;
(Step 3) A step of distilling the organic phase 2.
2. 2. The method for recovering an aprotic polar solvent according to 1, wherein the step 2 is repeated twice or more.
3. In the step 2, the cooled organic phase 1 is supplied to a stationary tank through an internal tube provided with pores having a diameter of 10 mm or less at the tip of the nozzle to perform phase separation 1 or 2 A method for recovering the described aprotic polar solvent.
4). The method for recovering an aprotic polar solvent according to 1 to 3, wherein the aprotic polar solvent is a recovery solvent obtained by separating the polyarylene sulfide from the polyarylene sulfide polymerization reaction solution,
5. The method for recovering an aprotic polar solvent according to any one of 1 to 4, wherein the alkali halide is sodium chloride.
6). The method for recovering an aprotic polar solvent according to any one of 1 to 5, wherein the organic compound is n-hexanol.
7). In the manufacturing method of the polyarylene sulfide which polymerizes at least a polyhalogenated aromatic compound and a sulfidizing agent in an aprotic polar solvent, the aprotic polar solvent is any one of claims 1 to 6. A method for producing polyarylene sulfide, which comprises using the recovered aprotic polar solvent according to the method for recovering an aprotic polar solvent.
8). An aqueous solution containing at least an alkali halide and / or an organic salt and an aprotic solvent is added to n-hexane, n-hexanol, n-hexanal, n-hexanone, 2-methyl-1-pentane, 2-methyl-1- Pentanol, 2-methyl-1-pentanal, 2-methyl-1-pentanone, 3-methyl-1-hexane, 3-methyl-1-hexanol, 3-methyl-1-hexanal, and 3-methyl-1- An extraction facility for extracting the organic phase 1 containing an aprotic polar solvent by contacting at least one non-halogen aliphatic organic compound having 6 or more carbon atoms selected from hexanone at 50 ° C. or higher and 100 ° C. or lower is provided. ,
The organic phase 1 is cooled to 20 ° C. or higher and lower than 50 ° C., and a stationary tank for extracting the organic phase 2 containing an aprotic polar solvent by phase separation is provided.
An apparatus for recovering an aprotic polar solvent in the production of polyarylene sulfide, comprising a distillation facility for distilling the organic phase 2.
9. And wherein the tube interposed between the static置槽and the extraction equipment is internal tube provided with a plurality of previously diameter 10mm or less of the pores in the nozzle, the polyarylene sulfide according to 8 An aprotic polar solvent recovery apparatus in production.

  In the present invention, the aprotic polar solvent is industrially efficiently recovered from the slurry in the PAS production, and further, by separating and recovering the salt, the introduction of the salt into the step 2 and subsequent steps is suppressed, thereby stabilizing. The purpose is to provide a process.

It is the schematic of an aprotic polar solvent collection | recovery apparatus in this invention. 2 is a graph showing the influence of extraction temperature on NMP distribution equilibrium in Example 1. FIG.

[Polyarylene sulfide]
The aprotic polar solvent recovery method of the present invention is mainly intended to recover the aprotic polar solvent from the waste liquid containing the aprotic polar solvent generated in the PAS production process and the purification process. PAS is a homopolymer or copolymer having a repeating unit of the formula, — (Ar—S) —, as the main constituent unit, and preferably containing 80 mol% or more of the repeating unit. Ar includes units represented by the following formulas (A) to (K), among which the formula (A) is particularly preferable.

  R1 and R2 are substituents selected from hydrogen, an alkyl group, an alkoxy group, and a halogen group, and R1 and R2 may be the same or different.

  As long as this repeating unit is a main structural unit, it can contain a small amount of branching units or crosslinking units represented by the following formulas (L) to (N). The amount of copolymerization of these branched units or cross-linked units is preferably in the range of 0 to 1 mol% with respect to 1 mol of-(Ar-S)-units.

  The PAS in the present invention may be any of a random copolymer, a block copolymer and a mixture thereof containing the above repeating unit.

  Furthermore, the molecular weight of various PASs is not particularly limited, but a range in which the melt viscosity is usually 5 to 5,000 Pa · s (300 ° C., shear rate 200 / second) can be exemplified as a preferable range.

  Typical examples thereof include polyphenylene sulfide (PPS), polyphenylene sulfide sulfone, polyphenylene sulfide ketone, random copolymers, block copolymers, and mixtures thereof. Particularly preferred PASs include polyphenylene sulfide (PPS) containing 80 mol% or more, particularly 90 mol% or more of the following p-phenylene sulfide units as the main structural unit of the polymer, as well as polyphenylene sulfide sulfone and polyphenylene sulfide ketone.

[Polyarylene sulfide production method]
A method for producing PAS will be described below, but the method is not limited to the following method as long as the PAS having the above structure is obtained. First, the polyhalogen aromatic compound, sulfidizing agent, polymerization solvent and polymerization aid used in the production of PAS will be described.

  Usually, the PAS having the above structure is obtained by reacting at least one polyhalogenated aromatic compound and at least one sulfidizing agent under a conventionally known polymerization condition in an aprotic polar organic solvent. This will be described in detail below.

[Polyhalogenated aromatic compounds]
The polyhalogenated aromatic compound used as a raw material for PAS is, for example, two or more halogenated aromatic compounds directly bonded to an aromatic ring, such as p-dichlorobenzene, o-dichlorobenzene, m-dichlorobenzene, Trichlorobenzene, tetrachlorobenzene, dibromobenzene, diiodobenzene, tribromobenzene, triiodobenzene, dichloronaphthalene, dibromonaphthalene, dichlorodiphenylbenzene, dibromodiphenylbenzene, dichlorobenzophenone, dibromobenzophenone, dibromo Examples thereof include polyhaloaromatic compounds such as chlorodiphenyl ether, dibromodiphenyl ether, dichlorodiphenyl sulfide, dibromodiphenyl sulfide, dichlorobiphenyl, dibromodiphenyl, and mixtures thereof. Among these, preferred is one containing 80 mol% or more of p-dichlorobenzene with respect to the number of moles of all polyhalogenated aromatic compounds to be used.

[Sulfiding agent]
The sulfiding agent is not particularly limited, and can be used as an anhydride or hydrate of an alkali metal sulfide or an aqueous solution, such as lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide and cesium sulfide, or these These may be used alone or in combination of two or more. Among the alkali metal sulfides, sodium sulfide and potassium sulfide are preferable from the viewpoint of excellent reactivity, and sodium sulfide is particularly preferable.

  Usually, a small amount of alkali metal hydroxide may be added to react with alkali metal hydrosulfide or alkali metal thiosulfate present in a trace amount in the alkali metal sulfide.

  In addition, these sulfidizing agents react NMP and alkali metal hydrosulfide, or alkali metal hydrosulfide and alkali metal hydroxide, or hydrogen sulfide and alkali metal hydroxide before the polymerization reaction. In addition to the vessel, it can also be obtained by performing a dehydration reaction in which water in the system is distilled out of the system while raising the temperature, and it can be transferred to a polymerization tank and used for polymerization.

  The alkali metal hydrosulfide is not particularly limited, and the alkali metal hydrosulfide can be used as an anhydride, hydrate, or aqueous solution of the alkali metal hydrosulfide. Examples of the alkali metal hydrosulfide include lithium hydrosulfide, sodium hydrosulfide, potassium hydrosulfide, rubidium hydrosulfide, and cesium hydrosulfide. Among them, sodium hydrosulfide is preferable. These may be used alone or in admixture of two or more.

  Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, etc. Among them, lithium hydroxide, sodium hydroxide, potassium hydroxide are preferable, Sodium hydroxide is particularly preferred. These may be used alone or in admixture of two or more. Further, the alkali metal hydrosulfide and the alkali metal hydroxide may be used for the reaction in any form such as a solid state, a liquid state, and a molten state, and there is no particular limitation.

[Polymerization solvent]
In the present invention, an aprotic polar solvent is used as the polymerization solvent. Specific examples include N-alkylpyrrolidones such as N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone (NMP), caprolactams such as N-methyl-ε-caprolactam, 1,3-dimethyl-2, and the like. -Aprotic organic solvents represented by imidazolidinone, N, N-dimethylacetamide, N, N-dimethylformamide, hexamethylphosphoric triamide, dimethyl sulfone, tetramethylene sulfoxide, etc., and mixtures thereof, etc. Are preferably used because of their high reaction stability. Among these, NMP is particularly preferably used because of excellent stability and easy handling. Hereinafter, NMP will be described as an example of an aprotic polar solvent.

  The amount of NMP used in the polymerization is selected in the range of 2.0 to 10 mol, preferably 2.25 to 6.0 mol, more preferably 2.5 to 5.5 mol per mol of the sulfidizing agent. The

[Polymerization aid]
In the present invention, it is also a preferred embodiment to use a polymerization aid for adjusting the degree of polymerization. Here, the polymerization assistant means a substance having an action of increasing the viscosity of the obtained PPS resin. Specific examples of such polymerization aids include, for example, organic carboxylates, water, alkali metal chlorides, organic sulfonates, alkali metal sulfates, alkaline earth metal oxides, alkali metal phosphates and alkaline earths. Metal phosphates and the like. These may be used alone or in combination of two or more. Of these, organic carboxylates, water, and alkali metal chlorides are preferable, and sodium and lithium carboxylates and / or water are particularly preferably used.

  Specific examples of the alkali metal carboxylate include, for example, lithium acetate, sodium acetate, potassium acetate, sodium propionate, lithium valerate, sodium benzoate, sodium phenylacetate, potassium p-toluate, and mixtures thereof. Can be mentioned.

  The alkali metal carboxylate is an organic acid and one or more compounds selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates, and are allowed to react by adding approximately equal chemical equivalents. You may form by. Among the alkali metal carboxylates, lithium salts are highly soluble in the reaction system and have a large auxiliary effect, but are expensive, and potassium, rubidium and cesium salts are insufficiently soluble in the reaction system. Therefore, sodium acetate, which is inexpensive and has an appropriate solubility in the polymerization system, is most preferably used.

  When using these alkali metal carboxylates as polymerization aids, the amount used is usually 0.01 mol with respect to 1 mol of the charged sulfidizing agent from the viewpoint of obtaining a PPS resin having a viscosity suitable for processing and oligomer low elution. The range of ˜2 mol is preferable, and the range of 0.010 to 0.088 mol is preferable from the viewpoint of achieving both the degree of polymerization useful for the present invention and the low oligomer property. In the case of the above range, a PPS resin having the above-described melt viscosity in a preferable range can be obtained.

  In addition, when water is used as a polymerization aid, the addition amount is usually in the range of 0.3 to 15 mol with respect to 1 mol of the charged sulfidizing agent, and 0.6 to 10 in the sense of obtaining a higher degree of polymerization. The molar range is preferable, and the range of 1 to 5 mol is more preferable. Of course, two or more kinds of these polymerization aids can be used in combination. For example, when an alkali metal carboxylate and water are used in combination, a higher molecular weight can be obtained in a smaller amount.

  There is no particular designation as to the timing of addition of these polymerization aids, which may be added at any time during the previous step, polymerization start, polymerization in the middle to be described later, or may be added in multiple times. When using an alkali metal carboxylate as a polymerization aid, it is more preferable to add it at the start of the previous step or at the start of the polymerization from the viewpoint of easy addition. When water is used as a polymerization aid, it is effective to add the polyhalogenated aromatic compound during the polymerization reaction after charging.

[Polymerization reaction]
A PAS resin is produced by reacting a sulfidizing agent and a polyhalogenated aromatic compound in a temperature range of 200 ° C. or higher and lower than 290 ° C. in NMP.

  When starting the polymerization reaction step, NMP, a sulfidizing agent, and a polyhalogenated aromatic compound are desirably mixed in an inert gas atmosphere at a temperature ranging from room temperature to 240 ° C., preferably 100 to 230 ° C. A polymerization aid may be added at this stage. The order in which these raw materials are charged may be out of order or may be simultaneous.

  The mixture is usually heated to a temperature in the range of 200 ° C to 290 ° C. Although there is no restriction | limiting in particular in a temperature increase rate, Usually, the speed of 0.01-5 degreeC / min is selected, and the range of 0.1-3 degreeC / min is more preferable.

  In general, the temperature is finally raised to a temperature of 250 to 290 ° C., and the reaction is usually carried out at that temperature for 0.25 to 50 hours, preferably 0.5 to 20 hours.

  In the stage before reaching the final temperature, for example, a method of reacting at 200 to 260 ° C. for a certain time and then raising the temperature to 270 to 290 ° C. is effective in obtaining a higher degree of polymerization. Under the present circumstances, as reaction time in 200 to 260 degreeC, the range of 0.25 to 20 hours is normally selected, Preferably the range of 0.25 to 10 hours is selected. In order to obtain a polymer having a higher degree of polymerization, it may be effective to perform polymerization in multiple stages. When the polymerization is performed in a plurality of stages, it is effective that the conversion of the polyhalogenated aromatic compound in the system at 245 ° C. reaches 40 mol% or more, preferably 60 mol%. For this polymerization, usual polymerization methods such as a batch method and a continuous method can be employed. Further, the atmosphere during the polymerization is preferably a non-oxidizing atmosphere, and it is preferably performed in an inert gas atmosphere such as nitrogen, helium or argon, and nitrogen is particularly preferable from the viewpoint of economy and ease of handling. .

  The reaction pressure is not particularly limited because it cannot be defined unconditionally depending on the type and amount of the raw material and solvent used, or the reaction temperature.

[cooling]
After completion of the polymerization, cooling is performed for the purpose of recovering a solid from a polymerization reaction product containing a polymer, a polymerization solvent and the like. PAS means that a granular PAS resin is obtained, and a method of slowly cooling after completion of the polymerization reaction to recover the particulate polymer is preferable. Although there is no restriction | limiting in particular in the slow cooling rate in this case, Usually, it is about 0.1 degree-C / min-about 3 degree-C / min. There is no need for slow cooling at the same rate in the entire process of the slow cooling step, and a method of slow cooling at a rate of 0.1 to 1 ° C./minute until the polymer particles crystallize and then 1 ° C./minute or more is used. You may employ | adopt and finally cool to 220 degrees C or less.

[Recovery / cleaning process]
After the polymerization step, PAS is recovered from the PAS slurry obtained in the polymerization step by solid-liquid separation, and an aqueous solution containing NMP as a main component is separated. Separation may be a commonly used solid-liquid separation method, and specific examples include filtration, vibration sieving, centrifugation, sedimentation separation, and the like. In the present invention, NMP can be recovered and reused from the separated aqueous solution containing NMP.

  The separated and recovered solid matter is preferably washed with NMP and / or water, and NMP can be recovered from the washing waste liquid by the method of the present invention and reused.

  As a method of washing with NMP, there is a method of immersing PAS in an organic solvent, and it is possible to appropriately stir or heat as necessary. There is no restriction | limiting in particular about washing | cleaning temperature, Arbitrary temperature of about normal temperature-about 300 degreeC can be selected. Although the cleaning efficiency tends to increase as the cleaning temperature increases, a sufficient effect is usually obtained at a cleaning temperature of room temperature to 150 ° C.

  The amount of NMP used at the time of washing is preferably selected as a bath ratio of 1 kg or more with respect to 300 g of PAS.

  The washed PAS is recovered by solid-liquid separation, and an aqueous solution containing NMP as a main component is separated. The separation may be a commonly used solid-liquid separation method, as in the case of the separation after polymerization. Specific examples include filtration, vibration sieving, centrifugal separation, sedimentation separation, and the like.

  Further, in order to remove the residual organic solvent and ionic impurities from the solid containing the PAS resin, it is preferable to further wash several times with water or warm water. As a method for washing PAS with water or warm water, there is a method of immersing PAS in water or warm water, and it is possible to appropriately stir or heat as necessary.

  The washing temperature when washing PAS with water or warm water is preferably 20 ° C to 220 ° C, more preferably 50 ° C to 200 ° C. If it is less than 20 ° C., it is difficult to remove by-products, and if it exceeds 220 ° C., the pressure becomes high, which is not preferable for safety.

  The water used in the water or warm water washing is preferably distilled water or deionized water. Formic acid, acetic acid, propionic acid, butyric acid, chloroacetic acid, dichloroacetic acid, acrylic acid, crotonic acid, benzoic acid, Organic acidic compounds such as salicylic acid, oxalic acid, malonic acid, succinic acid, phthalic acid, fumaric acid and their alkali metal salts, alkaline earth metal salts, inorganic acidic compounds such as sulfuric acid, phosphoric acid, hydrochloric acid, carbonic acid, silicic acid, and ammonium An aqueous solution containing ions or the like may be used.

  The operation of the hot water treatment is usually performed by charging a predetermined amount of PAS into a predetermined amount of water, and heating and stirring at normal pressure or in a pressure vessel.

  The PAS thus washed is recovered by solid-liquid separation, and an aqueous solution containing NMP is separated. Separation may be a commonly used solid-liquid separation method, and specific examples include filtration, vibration sieving, centrifugation, sedimentation separation, and the like.

[Other post-processing]
The PAS thus obtained is dried under normal pressure and / or reduced pressure. The drying temperature is preferably in the range of 120 to 280 ° C, more preferably in the range of 140 to 250 ° C. The drying atmosphere may be any of an inert atmosphere such as nitrogen, helium and reduced pressure, an oxidizing atmosphere such as oxygen and air, and a mixed atmosphere of air and nitrogen, preferably under reduced pressure, particularly under normal pressure. It is preferable to dry again under reduced pressure after drying to remove moisture and the like. The drying time is preferably 0.5 to 50 hours, preferably 1 to 30 hours, and more preferably 1 to 20 hours.

[Aqueous solution containing aprotic polar solvent]
The aprotic polar solvent in the present invention refers to a recovery solvent obtained by separating PAS from a PAS polymerization reaction solution. Accordingly, examples of the aqueous solution containing an aprotic polar solvent include the filtrate separated when solid-liquid separation is performed in the PAS recovery step and the washing waste liquid obtained in the step of washing the filtered PAS. It is more efficient to collectively use the aprotic polar solvents obtained in the PAS polymerization step in (Step 1) which is a constituent of the present invention.

  In addition to the aprotic polar solvent, the aqueous solution containing the aprotic polar solvent contains at least an alkali halide and / or an organic salt obtained as a by-product in the polymerization step of water and PAS. The alkali halide contained in the aqueous solution containing the aprotic polar solvent varies depending on the types of the polyhalogenated aromatic compound, sulfidizing agent, polymerization solvent and polymerization aid used as a raw material. Metal halides such as sodium bromide, sodium iodide, potassium chloride, potassium bromide and potassium iodide, metal carbonates such as sodium carbonate and potassium carbonate, metal sulfates such as sodium sulfate and potassium sulfate, sodium nitrate and potassium nitrate Examples thereof include metal nitrates and the like. When the alkali halide is a chloride salt, it is considered that the extraction efficiency of the aprotic polar solvent extraction step of the present invention is increased due to the salting out effect.

  The organic salt contained in the aqueous solution containing the aprotic polar solvent also varies depending on the type of raw material used in the production of PAS. Specifically, organic base hydrochlorides such as triethylamine hydrochloride and pyridine hydrochloride, tetrabutyl bromide Quaternary ammonium salts such as ammonium and trimethylbenzylammonium, and phosphonium salts such as tetramethylphosphonium bromide and triphenylbenzylphosphonium bromide may be contained. Any substance that dissolves in water and an aprotic polar solvent can be removed by the process of the present invention. These alkali halides and / or organic salts may be used singly or in combination.

[Aprotic polar solvent recovery process]
A schematic diagram is shown in FIG. 1 as an example of an apparatus for recovering an aprotic polar solvent in the present invention.

[Step 1 (extraction step)]
In step 1, an aqueous solution containing at least an alkali halide and / or an organic salt and an aprotic polar solvent is brought into contact with a non-halogen aliphatic organic compound having 6 or more carbon atoms at 50 ° C. or higher and 100 ° C. or lower. Extract the organic phase 1 containing the aprotic polar solvent. The above process may use a general liquid-liquid extraction facility, and can be used either batchwise or continuously. Specific examples include a mixer-settler extractor, a spray tower, a packed tower, a perforated plate extraction tower, a baffle tower, a shovel tower, a rotating disk extraction tower, a vibrating plate tower, and an alternating pulsating flow extraction tower.

  As an extraction solvent to be contacted with an aqueous solution containing at least an alkali halide and / or an organic salt and an aprotic polar solvent, from the viewpoints of affinity and hydrophobicity with the aprotic polar solvent, two-layer separation, and distillation recovery A non-halogen aliphatic organic compound having 6 or more carbon atoms is used. Since the halogen solvent has a specific gravity greater than 1, the halogen solvent layer after extraction is the lower layer, and when the salt concentration is high, the precipitated inorganic salt is likely to settle and mix, and the extracted halogen solvent layer is washed with a lot of water. Not suitable because it needs to be done. Furthermore, there is a drawback that the extraction efficiency is poor because the aprotic polar solvent is back-extracted again during extraction. Specific examples of non-halogen aliphatic organic compounds having 6 or more carbon atoms include n-hexane, n-hexanol, n-hexanal, n-hexanone, 2-methyl-1-pentane, and 2-methyl-1-pentanol. 2-methyl-1-pentanal, 2-methyl-1-pentanone, 3-methyl-1-hexane, 3-methyl-1-hexanol, 3-methyl-1-hexanal, 3-methyl-1-hexanone, etc. N-hexanol is more preferably used.

  The amount of the extraction solvent used is in the range of 0.5 to 2, preferably 0.7 to 1.5, by weight with respect to the aprotic polar solvent.

  The higher the extraction temperature of the present invention, the better the extraction efficiency and the better. However, water is boiled at a temperature higher than 100 ° C, and if it is lower than 50 ° C, the extraction efficiency is reduced. There is a need to do. Preferably it is 70-100 degreeC.

  A non-halogen aliphatic organic compound having 6 or more carbon atoms is supplied to the lower layer of a general extraction facility, and an aqueous solution containing at least an alkali halide and / or organic salt and an aprotic polar solvent is supplied to the upper layer. And make AC contact. At this time, it is preferable to install a disperser or the like in order to prevent drift, because the extraction efficiency is improved. Although there is no restriction | limiting in particular as an installation position, It is preferable that it is a position lower than the position which supplies the aqueous solution containing an aprotic polar solvent.

  When the above process is performed, for example, in a packed column, the non-halogen aliphatic organic phase (organic phase 1) containing at least an alkali halide and / or an organic salt and an aprotic polar solvent becomes an upper layer and is recovered from the top of the column. The aqueous phase (aqueous phase 1) after the extraction operation is drained from the tower bottom as waste liquid. In the organic phase 1, in addition to the aprotic polar solvent, there are at least water, an alkali halide and / or an organic salt that cannot be removed in this step. In the present invention, in order to reduce the alkali halide and / or organic salt contained in the organic phase 1, washing with water may be performed by further adding water or warm water.

[Step 2 (phase separation)]
In step 2, the organic phase 1 is cooled to 20 ° C. or higher and lower than 50 ° C., whereby the organic phase 2 containing the aprotic polar solvent is phase-separated and liquid-liquid extracted.

  In the organic phase 1 extracted in Step 1, there are still water and alkali halide and / or organic salts that cannot be removed in Step 1. In this step, the aprotic polar solvent is efficiently recovered with high purity by further removing water and alkali halide and / or organic salt.

  The organic phase 1 extracted in the step 1 is cooled using a heat exchanger. By cooling, the solubility of water partially contained in the organic phase 1 is lowered, and when the saturation is reached, the water is separated from the organic phase 1. The water separated from the organic phase 1 contains a large amount of alkali halide and / or organic salt, but the partition ratio of the alkali halide and / or organic salt to the aqueous phase is often much higher than that of the organic phase. Therefore, since this moves to the aqueous phase, the alkali halide and / or organic salt in the organic phase 1 can be further separated and removed. However, when the cooling temperature is lower than 20 ° C., the distribution of NMP is biased toward the aqueous phase, so that the NMP in the organic phase 1 is back-extracted into the aqueous phase, and the NMP extraction efficiency deteriorates. Further, when the temperature is 50 ° C. or higher, it is difficult to remove the alkali halide and / or the organic salt using the difference from the extraction temperature in Step 1.

  For this reason, the temperature after cooling is preferably 20 ° C. or higher and lower than 50 ° C. Specific examples of heat exchangers include spiral heat exchangers, plate heat exchangers, double tube heat exchangers, multi-tube cylindrical heat exchangers, multiple tube heat exchangers, and spiral tube heat exchangers. Among these, a spiral heat exchanger is particularly preferable because of its excellent compactness and high performance. These may be used alone or in combination of two or more. The medium for heat exchange is not particularly limited, but water is preferable.

  After cooling, the extract is allowed to stand to cause phase separation into an organic phase 2 and an aqueous phase 2. In this case, a stationary tank may be used for phase separation. A stationary tank may use a general tank, and the organic phase 2 and the water phase 2 can be phase-separated from the organic phase 1 by supplying the cooled organic phase 1 to the said stationary tank. The organic phase 2 has a smaller amount of water and alkali halide and / or organic salt than the organic phase 1. The cooled organic phase 1 is supplied to the stationary tank through a pipe interposed between the extraction equipment and the stationary tank, and the pipe is not particularly limited. It is preferable to use the one provided with a plurality of pores at the tip of the nozzle of the internal pipe. Providing a plurality of pores at the nozzle tip of the internal pipe is preferable because the contact area is increased by supplying with oil droplets and the extraction efficiency is improved. The diameter of the pores is not particularly limited, but is preferably 20 mm or less, and more preferably 10 mm or less, in order to increase the contact area and improve the extraction efficiency.

  The stationary tank may have one or two or more, and if there are a plurality of the stationary tanks, the number of extraction stages increases, so that the extraction efficiency is improved. Since the aqueous phase 2 contains at least an aprotic polar solvent in addition to moisture, an alkali halide and / or an organic salt, the extraction efficiency is improved by supplying it again to the upper layer of Step 1 and performing re-extraction. preferable.

  When supplying the aqueous phase 2 to the packed tower, or when supplying the organic phase 1 extracted again in the packed tower to the stationary tank, water may be added. It becomes possible to reduce organic salt.

  Since the alkali halide and / or organic salt contained in the organic phase 2 obtained in the step 2 causes a blockage trouble in the distillation facility, the content thereof is preferably 1% or less. Specifically, it is 0.5% or less, more preferably 0.1% or less. As a result, the amount of salt brought into the subsequent process is reduced, and blockage troubles in the distillation facility can be reduced, and the process can be stabilized.

[Step 3 (distillation)]
Step 3 includes a distillation facility, and recovers the aprotic polar solvent by distilling the organic phase 2.

  Distillation should be carried out by dividing the distillation column into several columns for each boiling point of each solvent in order to recover non-halogen aliphatic organic compounds, aprotic polar solvents, alkali halides and / or organic salts, and other impurities. Is possible. Further, it may be at normal pressure or under reduced pressure. It is sufficient to select the conditions that do not cause decomposition of the non-halogen aliphatic organic compound and the aprotic polar solvent. As described above, since the organic phase 2 contains almost no alkali halide and / or organic salt, the aprotic polar solvent recovered by distilling the organic phase 2 is very pure. Is expensive. Therefore, in the method for producing polyarylene sulfide in which at least a polyhalogenated aromatic compound and a sulfidizing agent are polymerized in an aprotic polar solvent, the aprotic polar solvent recovered by distillation in the aprotic polar solvent Can be used. It can also be reused for cleaning. The recovered non-halogen aliphatic organic compound can be reused as the extraction solvent in step 1.

[Composition analysis of NMP aqueous solution]
In the present invention, it is important that the composition of the aqueous solution containing NMP is in the above range, but the NMP concentration and water concentration of the aqueous solution containing NMP are values obtained by gas chromatography using an internal standard substance. After weighing the sample, 20 μL of dimethylaniline is added as an internal standard substance, weighed, and dissolved in acetone. The NMP concentration is calculated from the peak area ratio by measuring at a column temperature of 170 ° C. and an injection temperature of 300 ° C. by a gas chromatograph using a packed column. As the water concentration, a value obtained by subtracting the sum of all peak component concentrations detected by gas chromatography and the alkali halide concentration from 100% by weight is used.

  The concentration of the alkali halide contained in the extracted aqueous layer is determined by a general potentiometric titrator. A 0.1N silver nitrate solution is used as the titration solution.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the scope of the present invention is not limited to an Example at all.

The NMP concentration and the alkali halide concentration in the NMP aqueous solution were measured by the following methods. Weigh about 0.3 g of NMP concentration / material into a 5 ml sample bottle.
・ Add about 20 μl of the internal standard substance dimethylaniline and weigh.
Add about 4 ml of acetone and mix.
-1.0 microliter was inject | poured into the micro syringe and it measured on condition of the following.
Column: PEG6000 on shimaliteTPA
4φ × 3φ × 4m SUS
N2 pressure 50 kpa
H2 pressure 50 kpa
air pressure 50 kpa
Column temperature 170 ° C (constant temperature)
INJ temperature 300 ℃
Injection volume 1.0μL
Concentration of alkali halide Measured using the following apparatus.

KYOTO ELECTRONICS
AT-400 (automatic bullet)
AT-410 (Titration device)

Reference example 1
NMP was mixed with 10% by weight saline (distilled water was used), and 500 g of an arbitrary mixture of NMP 0.5-80 wt% was prepared. A 1.2-fold amount (600 g) of n-hexanol was added at a weight ratio, and the mixture was stirred for 15 minutes and then allowed to stand and separate. The n-hexanol phase, which is the upper layer, and the aqueous phase, which is the lower layer, were collected, and the NMP concentration was analyzed by gas chromatography. From the obtained results, the influence of the extraction temperature on the NMP distribution equilibrium is shown in FIG. The higher the extraction temperature, the higher the NMP concentration in the oil phase (n-hexanol phase), and more efficient extraction is performed.

Comparative Example 1
In a 10 liter autoclave equipped with a stirrer, 789 g of hydrous sodium sulfide having a purity of 98.9 wt% (sodium sulfide 780 g, water 9 g), 96% sodium hydroxide 20.8 g, NMP 2970 g, anhydrous sodium acetate 24. 6 g and 1490 g of p-dichlorobenzene (p-DCB) were charged. The water content per mole of sulfur component of sodium sulfide used as a sulfidizing agent was 0.05 mol.

  After sealing the reaction vessel under nitrogen gas, the temperature was raised to 220 ° C. while stirring at 400 rpm, the reaction was performed at 220 ° C. for 2 hours, and then 180 g of water was added by press-fitting over 10 minutes. At this stage, the water content in the system per 1 mol of the sulfur component of the sulfidizing agent charged was 1.0 mol. Thereafter, the temperature was raised to 270 ° C., and the reaction was continued at 270 ° C. for 1 hour. After cooling from 270 ° C. to 200 ° C. at an average rate of 1 ° C./min, the polymer was rapidly recovered to around 100 ° C. The liquid was separated.

  Further, the polymer was washed using 4375 g of NMP, and the liquid was separated by filtration. Next, 3810 g of water was divided into four times to wash the polymer, and filtered to separate the liquid. Finally, it was dried to obtain about 950 g of polymer. All of the separated liquids were mixed to obtain an NMP aqueous solution of NMP: 42% by weight, water: 49% by weight, NaCl: 8.8% by weight.

  Next, a packed tower having a tower diameter of 200 mm, an upper filling portion of 3400 mm, and a lower filling portion of 4000 mm is filled with a metal 25A interlock saddle packing, and an NMP aqueous solution heated to 90 ° C. from the supply port at 125 kg / hr. N-Hexanol was supplied at 157 Kg / Hr from the 4000 mm part below the supply port, and heated at 90 K from the 3000 mm part above the supply port at 17 Kg / Hr for extraction. . As a result of sampling and measuring the internal liquid from the 3000 mm portion nozzle below the supply port, the NMP concentration was 0.1 wt% or less. Further, the column bottom liquid and the column top liquid were sampled and the NaCl concentration was measured. As a result, they were 17.2 wt% and 0.7 wt%, respectively. The temperature of the column top liquid at this time was 78 ° C.

Example 1
The tower top liquid of Comparative Example 1 is supplied to a spiral heat exchanger, cooled to 38.5 ° C. by heat exchange with water, supplied to a stationary tank via an internal tube, and allowed to stand to leave an organic phase. (Upper layer) and aqueous phase (lower layer) were phase-separated. The lower layer was continuously supplied again to the extraction tower supply port. As a result of sampling the upper layer and measuring the NaCl concentration, it was 0.23% by weight.

Example 2
The upper layer of Example 1 was supplied to another stationary tank via an internal tube and allowed to stand to cause phase separation into an organic phase (upper layer) and an aqueous phase (lower layer). The lower layer was continuously supplied to the stationary tank of Comparative Example 1. As a result of sampling the upper layer and measuring the NaCl concentration, it was 0.08% by weight.

Claims (9)

A method for recovering an aprotic polar solvent, comprising the following three steps.
(Step 1) In the production of polyarylene sulfide , an aqueous solution containing at least an alkali halide and / or an organic salt and an aprotic solvent is used as n-hexane, n-hexanol, n-hexanal, n-hexanone, 2-methyl-1 -Pentane, 2-methyl-1-pentanol, 2-methyl-1-pentanal, 2-methyl-1-pentanone, 3-methyl-1-hexane, 3-methyl-1-hexanol, 3-methyl-1- Organic containing an aprotic polar solvent by contacting at least one non-halogen aliphatic organic compound having 6 or more carbon atoms selected from hexanal and 3-methyl-1-hexanone at 50 ° C. or higher and 100 ° C. or lower. Extracting phase 1;
(Step 2) Step of cooling the organic phase 1 to 20 ° C. or higher and lower than 50 ° C., and extracting the organic phase 2 containing an aprotic polar solvent by phase separation;
(Step 3) A step of distilling the organic phase 2.   The method for recovering an aprotic polar solvent according to claim 1, wherein step 2 is repeated twice or more. The phase separation is performed by supplying the cooled organic phase 1 to the stationary tank through an internal tube having pores having a diameter of 10 mm or less at the tip of the nozzle in the step 2. 3. The method for recovering an aprotic polar solvent according to 2.   The method for recovering an aprotic polar solvent according to any one of claims 1 to 3, wherein the aprotic polar solvent is a recovery solvent obtained by separating polyarylene sulfide from a polyarylene sulfide polymerization reaction solution.   The method for recovering an aprotic polar solvent according to any one of claims 1 to 4, wherein the alkali halide is sodium chloride. The method for recovering an aprotic polar solvent according to claim 1, wherein the organic compound is n-hexanol.   In the manufacturing method of the polyarylene sulfide which polymerizes at least a polyhalogenated aromatic compound and a sulfidizing agent in an aprotic polar solvent, the aprotic polar solvent is any one of claims 1 to 6. A method for producing polyarylene sulfide, which comprises using the recovered aprotic polar solvent according to the method for recovering an aprotic polar solvent. An aqueous solution containing at least an alkali halide and / or an organic salt and an aprotic solvent is added to n-hexane, n-hexanol, n-hexanal, n-hexanone, 2-methyl-1-pentane, 2-methyl-1- Pentanol, 2-methyl-1-pentanal, 2-methyl-1-pentanone, 3-methyl-1-hexane, 3-methyl-1-hexanol, 3-methyl-1-hexanal, and 3-methyl-1- An extraction facility for extracting the organic phase 1 containing an aprotic polar solvent by contacting at least one non-halogen aliphatic organic compound having 6 or more carbon atoms selected from hexanone at 50 ° C. or higher and 100 ° C. or lower is provided. ,
The organic phase 1 is cooled to 20 ° C. or higher and lower than 50 ° C., and a stationary tank for extracting the organic phase 2 containing an aprotic polar solvent by phase separation is provided.
An apparatus for recovering an aprotic polar solvent in the production of polyarylene sulfide, comprising a distillation facility for distilling the organic phase 2. Said tube interposed between the extraction equipment and the static置槽, characterized in that it is an internal pipe which is provided a plurality ahead the following pore diameters 10mm nozzle, poly claim 8 An aprotic polar solvent recovery device for the production of arylene sulfide.

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