JP4806213B2 - Separation of acrylonitrile polymer in aqueous suspension polymerization process and separation method of polymer by continuous rotary filter equipped with filter cloth - Google Patents

Description

  The present invention relates to a filter cloth capable of efficiently filtering and separating a polymer from a polymer suspension of an acrylonitrile-based polymer obtained by aqueous suspension polymerization, and a polymer separation method using a continuous rotary filter equipped with the filter cloth.

  Acrylic fibers have properties such as excellent bulkiness similar to wool, texture, and clearness of dyeing, and are used in a wide range of applications. The acrylic fiber is also frequently used as a raw material for carbon fiber. In the spinning method, a raw material acrylic copolymer is dissolved in an organic solvent or an inorganic solvent, and then a staple or filament is formed by a wet spinning method, a dry spinning method, or a semi-dry spinning method. The raw material acrylonitrile-based copolymer is produced by radical polymerization of an acrylonitrile monomer and a nonionic comonomer such as an acrylic ester, methacrylic ester, vinyl acetate, or acrylamide copolymerizable therewith.

  Usually, the acrylonitrile-based copolymer is often produced by a continuous suspension polymerization method using water as a reaction medium. In this continuous suspension polymerization system, the acrylonitrile monomer and comonomer are individually metered from the raw material tank and the monomer recovery step and supplied to the monomer preparation tank. The monomer charge composition in the preparation tank needs to be strictly set to a constant value in consideration of the reactivity ratio of acrylonitrile and comonomer depending on the copolymer composition of the polymer to be produced.

  The polymerization reactor is polymerized by adding a polymerization initiator together with the prepared acrylonitrile, comonomer, water, catalyst and the like. In general, an inorganic initiator is used as the polymerization initiator. As an inorganic initiator, for example, a combination of ammonium persulfate-sodium hydrogen sulfite-ferrous sulfate oxidation-reduction system is often used, and a monomer component mainly composed of acrylonitrile containing the above comonomer is used as a reaction medium. When a polymerization reaction is performed using sulfuric acid acid water that acts, a particulate polymer of several tens of μm is formed, and an acrylonitrile-based polymer is obtained in the state of an aqueous dispersion.

  A polymerization terminator is added to the polymer taken out from the polymerization reaction kettle to stop the reaction. As a polymerization terminator in the case of producing an acrylonitrile-based polymer by aqueous suspension polymerization, it is necessary to maintain the function of neutralizing the acidic aqueous solution of the reaction system. Sodium oxalate, sodium bicarbonate, ethylenediaminetetraacetic acid 2 An aqueous electrolyte solution such as sodium salt is used. In order to inhibit the polymerization of the acrylonitrile monomer during storage or transportation, a polymerization inhibitor such as p-methoxyphenol is usually added to the raw material monomer in advance.

  There is no problem as long as the polymerization terminator for the polymerization reaction is usually used when an acrylonitrile-based polymer is produced by an aqueous suspension polymerization method. After adding a polymerization terminator to the polymer aqueous solution, the unreacted monomer is recovered. At this time, approximately 1 wt% of unreacted monomer remains unpolymerized. As a method for recovering the unreacted monomer, the polymer aqueous solution is directly distilled, and then the unreacted monomer component and water separated from the polymer aqueous solution are sent to the condenser and condensed to form a monomer / water solution. This solution is separated into a monomer component and water by a decanter. The separated unreacted monomer component is returned to the polymerization reaction kettle.

In the polymerization step, the polymerization reaction kettle is not operated with a single group in consideration of the operation efficiency, and usually, polymerization is performed by simultaneously operating a plurality of polymerization reaction kettles. At this time, the polymer / unreacted monomer / water solution taken out from the polymerization reaction kettle is once introduced into a large-sized (volume: 50 m ² ) slurry tank disposed downstream, and is then supplied to a distillation section via a pump. Sent and separated into polymer and unreacted monomer / water as described above. In addition, after the polymerization is stopped, the outlets of a plurality of polymerization reaction kettles are opened all at once, and all the polymer / unreacted monomer / water solutions are discharged to the slurry tank, and the polymerization is resumed in the polymerization reaction kettle. Store up to. Therefore, a polymer / unreacted monomer / water solution is always stored in the slurry tank. Usually, the polymer / unreacted monomer / water solution is stored in the slurry tank for about 2 to 3 hours and then sent to the distillation section.

The polymer suspension composed of polymer / unreacted monomer / water obtained through the distillation section after the polymerization reaction is dehydrated and washed. In this washing and dewatering method, a continuous rotary cylindrical filter, a centrifugal dehydrator, or the like is used, but a continuous rotary cylindrical filter capable of continuous operation is industrially superior. -137106 (Patent Document 1) and JP-A-4-45107 (Patent Document 2) are widely used. The structure is such that a collecting pipe is arranged at the center of rotation of a rotating mesh horizontal cylindrical drum, and a suction part extends from the collecting pipe toward the inner surface of the drum. A filter cloth is wound and fixed on the outer peripheral surface of the cylindrical drum, and the lower half of the drum is immersed in a bat supplied with a polymer suspension and rotates. The suspension is sucked together with air at the suction section, and water is collected in the collecting pipe and led to the outside. On the other hand, the cake-like wet polymer filtered by the filter cloth and adhered to the surface of the filter cloth is scraped by a scraper and sent to the next pellet forming step.
JP-A-3-137106 JP-A-4-45107

  By the way, polypropylene is often used for the filter cloth attached to the continuous rotary cylindrical filter used in the aqueous suspension polymerization method of this type of acrylonitrile polymer. However, in the case of this polypropylene filter cloth, the chemical resistance is excellent, but the mechanical properties are inferior, and the fibrillation of the surface tends to proceed with long-term use. The progress of fibrillation is a filtration method in which adsorption and separation are repeated on the surface of the filter cloth like a continuous rotary cylindrical filter, so that the peelability is greatly deteriorated and the processing efficiency is lowered early. Further, in this type of filtration, the higher the temperature, the higher the filtration efficiency. However, polypropylene is susceptible to temperature increases. Therefore, conventionally, the treatment temperature condition has to be suppressed to around 50 ° C., and there is a limit to the improvement of the filtration efficiency.

  In recent years, attempts have been made to use a finely woven plain weave filter cloth consisting of nylon monofilaments with excellent mechanical properties and excellent chemical resistance and peelability. There is a great deal of pressure on using it. In addition, the filter cloth having this plain weave structure has poor clogging, although it is less clogged and excellent in the amount of filtration. In order to ensure this trapping property, the weave density must be made dense, but when the weave density is increased, the amount of filtration treatment is greatly reduced.

  Accordingly, an object of the present invention is a filter cloth attached to a continuous rotary filter that continuously filters and separates a polymer from a suspension of an acrylonitrile-based polymer and water, and has mechanical properties, heat resistance, and A filter cloth that excels in chemical resistance, exfoliation, and does not stop at alkali resistance even under high-temperature treatment, has excellent acid resistance, and does not lead to an increase in cost. An object of the present invention is to provide a method for efficiently separating a polymer by a continuous rotary filter equipped with a cloth.

The object is to provide a continuous rotating cylinder for separating a polymer having an average particle size of 10 to 40 μm from a polymer suspension having a particle size distribution of 1 to 200 μm in water obtained by the aqueous suspension polymerization step of the acrylonitrile polymer of the present invention. A filter cloth to be mounted on a mold filter, comprising a polyester multifilament thread having a value obtained by dividing the air permeability (cc / cm ² / sec) by the cloth thickness (mm) in the range of 200 to 400 This is effectively achieved by a filter cloth for an acrylonitrile-based polymer, characterized by comprising a plain weave structure woven fabric. The fabric thickness of the woven fabric is preferably 0.3 mm or less. Moreover, it is preferable to make the air permeability of this fabric into the range of 1-6 (cc / cm < ² > / sec). The air permeability is a value measured by JIS L 1096 method A (Fragile type method).

  In order to separate the polymer from the polymer suspension obtained in the aqueous suspension polymerization process of the acrylonitrile-based polymer using a continuous rotary cylindrical filter equipped with such a filter cloth, the polymer suspension has a pH of 4.0 ± 1. The polymer suspension dispersed in water with a particle size distribution of 1 to 200 μm even under the condition of being acidic at 0.0 and maintaining the temperature of the polymer suspension at 60 to 80 ° C. Thus, the polymer having an average particle size of 10 to 40 μm can be efficiently separated through the filter cloth.

  In this separation, a plain woven screen having nylon monofilament as a constituent thread may be interposed between the rotary drum of the rotary cylindrical filter and the filter cloth. At this time, it is preferable that the filament diameter of the monofilament which is the constituent yarn of the screen is 150 to 180 μm and the basis weight is set in the range of 20 to 30 pieces / cm.

Effect

By adopting the material and woven structure as described above as the filter cloth of the present invention, it becomes easier to form an appropriate gap between the single fibers compared to the woven density by flattening the multifilament that is a constituent yarn, The necessary air permeability can be easily supported. In addition, since the material is polyester, there is no fear of fibrillation, it is excellent in chemical resistance, it does not change even under high temperature acidity, and high peelability is maintained over a long period of time. In particular, when the value obtained by dividing the air permeability (cc / cm ² / sec) by the fabric thickness (mm) is 9 or less, although the collection ability of the polymer is improved, the drainage is lowered and clogging is likely to occur. In the case of 55 or more, the drainage is improved, but a part of the polymer passes through the filter cloth together with water, so that not only clear water is obtained but also the average particle size of the separated polymer is increased and the polymer yield is decreased. Leads to. In the present invention, the fabric thickness of the woven fabric is significantly reduced from the conventional fabric thickness of 0.5 to 1 mm. When the cloth thickness exceeds 0.3 mm, the air permeability is relatively small, and thus the drainage is lowered. Also, when the air permeability is 1 (cc / cm ² / sec) or less, the drainage also decreases and clogging increases at the same time. When the air permeability is 6 (cc / cm ² / sec) or more, the trapping property decreases and the polymer passes. Incurs an increase in volume.

By interposing a plain weave structure screen comprising nylon monofilaments between the rotary drum of the rotary cylindrical filter and the filter cloth, the above-described aspect of the present invention is thinner than the normal cloth thickness. At the same time as the decrease in the tensile strength of the filter cloth is reinforced, water passing through the filter cloth smoothly moves to the screen because nylon is hydrophilic. Further, when the wire diameter of the monofilament that is the constituent yarn of the screen is 150 μm or less, the tensile strength required for the monofilament unit cannot be obtained, and when the wire diameter is 180 μm or more, the required water passage performance is obtained. Absent. At this time, if the air permeability of the screen is set in the range of 1 to 6 (cc / cm ² / sec) at the same time, necessary strength and drainage capacity can be obtained.

Hereinafter, typical embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 schematically shows the entire polymerization process of an acrylonitrile-based polymer. First, a predetermined amount of liquid acrylonitrile is charged into the monomer preparation tank 3 while being metered by the first metering pump 2a from the acrylonitrile storage tank 1 as the main raw material. In the present embodiment, 20 to 100 ppm by weight of p-methoxyphenol is added to the acrylonitrile stored in the acrylonitrile storage tank 1 so as not to cause polymerization during storage. As the polymerization inhibitor, hydroquinone, p-t-butylcatechol, diphenylpicrylhydrazyl, benzoquinone, galvinoxyl, 1,3,5-triphenylferdazyl and the like can be used in addition to the p-methoxyphenol.

  The monomer preparation tank 3 is further charged with a comonomer which is a second component copolymerized with acrylonitrile at a predetermined ratio while being measured by the second metering pump 2b from the comonomer storage tank 1a. A solution of acrylonitrile and comonomer, which is charged into the monomer preparation tank 3 at a predetermined ratio and adjusted, is sent to the monomer supply tank 4 by a pump. The viscous raw material liquid prepared in the monomer supply tank 4 is sent to the polymerization reaction kettle 5 through the third metering pump 2c. In addition, a necessary amount of ion-exchanged water ID is supplied to the polymerization reaction kettle 5 and various catalysts, polymerization initiators, and various auxiliary agents are added simultaneously.

  As the polymerization initiator in this embodiment, an inorganic redox initiator is used. The inorganic redox initiator can be selected from ordinary oxidizing agents and reducing agents. In the case of redox consisting of a combination of an oxidizing agent and a reducing agent, typical ones are usually used as an oxidizing agent such as ammonium persulfate, potassium persulfate, sodium persulfate, etc., and the reducing agent is sodium sulfite, Ammonium sulfite, sodium hydrogen sulfite, ammonium hydrogen sulfite, sodium thiosulfate, ammonium thiosulfate, sodium dithionite, sodium formaldehyde sulfoxylate, L-alcorbic acid, dextroses and the like are usually used. Compounds such as ferrous sulfate or copper sulfate can also be used in combination. Among them, a combination of ammonium persulfate-sodium hydrogen sulfite (ammonium) -ferrous sulfate is preferable. Any ratio of the reducing agent and the oxidizing agent is possible, but it is preferable that the equivalent ratio of the reducing agent and the oxidizing agent is 1 to 4 in order to proceed the polymerization more efficiently.

  The acrylonitrile-based polymer used in the present embodiment may be composed of repeating units of an acrylonitrile monomer and a monoolefin monomer copolymerizable therewith. Here, the acrylonitrile-based polymer needs to be composed of at least 60% by weight of acrylonitrile monomer. This is because if the content of the acrylonitrile monomer is less than 60% by weight, the fiber function inherently possessed by the acrylonitrile-based synthetic fiber cannot be retained. Examples of the copolymerizable monoolefinic monomer include acrylic acid, methacrylic acid and esters thereof, acrylamide, vinyl acetate, styrene, vinyl chloride, vinylidene chloride, maleic anhydride, N-substituted maleimide, butadiene, and isoprene. Etc. Moreover, p-sulfonyl methallyl ether, methallyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-sulfoethyl methacrylate and salts thereof are also used as copolymerizable monomers. it can.

  Polymerization of the acrylonitrile monomer is performed under the following conditions. That is, the polymerization reaction temperature is preferably 30 to 80 ° C. When the polymerization temperature exceeds 80 ° C., acrylonitrile evaporates and disperses outside the reaction system, and the polymerization conversion rate decreases. On the other hand, if it is less than 30 ° C., not only the polymerization rate is lowered, the productivity is lowered, but also the polymerization stability is impaired. It is preferable to use ion-exchanged water as the polymerization medium. Furthermore, the ratio of ion-exchanged water to the monomer (hereinafter referred to as water / monomer ratio) can be any ratio, but the water / monomer ratio is preferably in the range of 1.0 to 5.0. The average residence time of the monomer in the polymerization reaction vessel may be a normal time employed when an acrylonitrile-based polymer is produced by an aqueous suspension polymerization method. The hydrogen ion concentration in the polymerization reaction vessel may be in a range in which the catalyst used promptly causes an oxidation / reduction reaction, and is preferably an acidic region having a pH of 2.0 to 3.5.

  A polymerization terminator is added to the aqueous polymer solution taken out from the polymerization reaction kettle 5 to stop the reaction. The terminator for the polymerization reaction is not limited as long as it is usually used when an acrylonitrile-based polymer is produced by aqueous suspension polymerization. After adding a polymerization terminator to the slurry polymer aqueous solution, the unreacted monomer is recovered. The unreacted monomer is recovered as much as possible and recovered in the unreacted monomer recovery tank 1b as long as it is an unrecovered unreacted monomer generated in the entire polymerization process. As a method for recovering the unreacted monomer from the polymer aqueous solution composed of the polymer / unreacted polymer / water obtained in the above-described polymerization reaction vessel 5, in the present embodiment, in the vaporization separation step via the first slurry tank 8 as usual. Instead of introducing into a certain distillation column 7, a method of directly and continuously introducing into the distillation column 7 while performing deaeration through the decylinder unit 6 and performing distillation is employed.

As described above, when the allylonitrile-based polymer is polymerized in sulfuric acid acidic water, among the combination of ammonium persulfate-sodium hydrogen sulfite-ferrous sulfate as a polymerization initiator, sodium hydrogen sulfite as a reducing agent for polymerization initiation reaction (NaHSO ₃ : CD) reacts with acrylonitrile (AN) to produce AAP (Acrilonitril Addition Product) as shown below.

CH = CHCN + NaHSO ₃ → NaO ₃ SCH ₂ CH ₂ CN (Sodium β-Sulfo Propianitrile)
(AN) (CD) (AAP)
Since this AAP is water-soluble, all of it is discharged out of the system as waste water from the bottom of the monomer strip tower (MS tower) and cannot be recovered, which is one of the biggest causes of AN loss.

  Of course, such AAP is also produced in the polymerization reaction kettle, distillation tower and MS tower, but as described above, the polymer / unreacted monomer / water solution obtained in the polymerization process is introduced into the slurry tank. However, when it is stored in the slurry tank for a long time, it has been found that the amount produced is much higher than the amount produced in the polymerization reaction kettle, distillation column and MS column. Incidentally, according to experiments, the amount of AAP generated in the slurry tank reaches 60% of the amount of AAP generated in all processes.

  The present inventors investigated the amount of AAP generated in the polymerization process at three points in the process from the polymerization reaction tank, the slurry tank, and the distillation column to the MS column. As a result, the amount of AAP generated in the slurry tank is the highest, 0.15% bop in the polymerization reactor, 0.31% bop in the slurry tank, and 0.06% bop from the distillation column to the MS column. I understood.

Based on the results of this investigation, it was predicted that one of the causes of AAP was related to the residence time of the polymer / unreacted monomer / water solution containing sodium bisulfite. Then, the test which calculates | requires the relationship between the generation amount of AAP and the residence time of the said solution was done. In this test, sodium bisulfite was added to the polymer / unreacted monomer / water solution obtained from the polymerization reaction kettle, and the solution was placed in a beaker and kept at 45 ° C. for 30 minutes from the start of measurement. The amount of AAP generated was measured every minute and 120 minutes.
FIG. 2 is a graph showing the results at that time.

According to the figure, when the measurement start time is assumed to be zero minutes, the amount of APP generated at 0.75% bop at zero minutes increases almost linearly to 1.75% bop after one hour. After that, it gradually increases between the high generation amounts, and after 2 hours, the generation amount reaches 1.85% bop.
The inventors estimated from this test result that the generation of AAP can be suppressed by shortening the residence time of the solution as much as possible.

  Therefore, first, the first slurry tank 18 was excluded, and an attempt was made to introduce the polymer / unreacted monomer / water solution overflowing from the polymerization reaction vessel 5 directly into the distillation column 7 via the slurry feed pump 8. However, since the slurry feed pump 8 sucked air and a vacuum break occurred in the distillation tower, the operation could not be continued.

  Furthermore, when various test operations were performed, a new recovery of the unreacted monomer component generated in the aqueous suspension polymerization process of the acrylonitrile-based polymer was performed using the polymer / unreacted monomer / water obtained in the polymerization reaction vessel 5. Knowing that the generation of AAP as a whole polymerization process can be greatly reduced by continuously introducing the mixture into the distillation column 7 while degassing it through the decylinder section 6 having the small-bore cylinder 9. It was.

FIG. 3 shows an example of the small-diameter cylindrical body 9. The small-diameter cylindrical body 9 has an inner diameter of 200 to 500 mm, a height of 2000 to 6000 mm, and a capacity of 0.05 to 1.2 m ² . Then, a predetermined amount of the polymer / unreacted monomer / water solution is continuously introduced into the distillation column 7 while being stored in the solution outlet portion inside the cylinder. Further, water may be injected toward the inner wall surface of the decylinder unit 6.

  As described above, the recovery of the acrylonitrile monomer component generated by the aqueous suspension polymerization method according to the present embodiment includes the polymerization reaction vessel 5 and the decylinder unit 6 connected to the polymerization reaction vessel 5 through the flow path. A distillation column 7 connected to the de-cylinder unit 6 via a flow path, for distilling a polymer / unreacted monomer / water mixture to vaporize and separate unreacted monomer components and water from the polymer; And an unreacted monomer component recovery unit for recovering the unreacted monomer component by condensing the unreacted monomer component vaporized and separated with water. At this time, the end of the decylinder unit 6 is arranged in the vertical direction, at least the degassing port 9c at the upper end, and the outlet for the polymer / unreacted monomer / water mixture at the lower end. 9a is provided.

The decylinder unit 6 includes a cylinder 9 having an inner diameter of 200 to 500 mm, a height of 2000 to 6000 mm, and a capacity of 0.05 to 1.2 m ^2, and is composed of polymer / unreacted monomer / water. A liquid feed pump 8 is disposed in a flow path between the solution outlet and the distillation column 7. Further, a water injection port (not shown) directed to the inner wall surface of the de-cylinder unit 6 may be provided at least at the upper end of the de-cylinder unit 6. Further, as shown in FIG. 3, there are provided detecting means 9f and 9g for detecting the liquid level within a predetermined range on the bottom side of the decylinder part 6, and the liquid level is detected based on the detection values of the liquid level detecting means 9f and 9g. A liquid level detector stage LT and a liquid level control unit LIC for controlling the liquid feeding amount of the liquid feeding pump 8 are provided so that the surface position is within the range.

The polymer / unreacted monomer / water solution obtained in the polymerization step overflows from the polymerization reaction vessel 5 and is introduced into the decylinder unit 6 having the small-diameter cylindrical body 9. The air mixed at this time is deaerated from the decylinder part 6 through the deaeration passage. On the other hand, the polymer / unreacted monomer / water solution introduced into the decylinder unit 6 passes through the decylinder unit 6 and is continuously fed into the distillation column 7. As described above, the small-diameter cylindrical body 9 of the decylinder portion 6 has an inner diameter of 200 to 500 mm, a height of 2000 to 6000 mm, and a capacity of 0.05 to 1.2 m ² . Compared with the conventional first slurry tank 18, the small-diameter cylindrical body 9 has an extremely small capacity of 1/60 to 1/125 of the conventional first slurry tank 18. As a result, the exclusive space becomes extremely small, and the decylinder unit 6 can be arranged adjacent to a plurality of polymerization reaction kettles operating simultaneously.

  Incidentally, in the conventional first slurry tank 18, the time for the solution to pass through the decylinder unit 6 according to the present invention is at most about 1 minute, compared to the time for the solution to pass for 2 to 3 hours. As a result, the amount of APP generated is significantly reduced as described above. On the other hand, even in the present embodiment, the conventional first slurry tank 18 is not usually used but left for emergency use.

  When a predetermined amount of the polymer / unreacted monomer / water solution is continuously introduced into the distillation column 7 while being stored in the solution outlet part inside the cylinder, the air is completely exhausted in the decylinder part 6. Thus, when the solution is introduced into the distillation column 7, there is no air mixing, and smooth vaporization and separation without air mixing between the polymer and the unreacted monomer / water is performed. At this time, when water is sprayed toward the inner wall surface of the decylinder portion 6, not only the polymer is not clogged in the slurry outlet 9 a but also it can be prevented from adhering to the inner surface of the cylindrical body 9.

  The de-cylinder unit 6 has an end portion arranged in the vertical direction, and at least an upper end portion thereof is provided with a deaeration port 9c, and a lower end portion thereof is provided with a polymer / unreacted monomer / water solution outlet port 9a. Therefore, a smooth flow of the slurry made of these solutions is obtained. In addition, since the liquid feed pump 18 is disposed in the flow path between the polymer / unreacted monomer / water solution outlet 9a and the distillation column 7, the slurry can be actively fed. In addition, if the output is controlled, the liquid level of the slurry stored in the decylinder unit 9 can always be maintained at an appropriate position.

When this polymer / unreacted monomer / water solution is continuously introduced into the distillation column 7 while being degassed via the decylinder unit 6, and vaporized and separated in the distillation column 7 to recover the unreacted monomer. As described above, the amount of AAP produced by adding sodium bisulfite as a reducing agent is reduced to an amount that is not comparable to that when using the conventional large first slurry tank 18. Can be made. Incidentally, the total length of the decylinder part 6 according to the present embodiment is 5320 mm including various entrances, the inner diameter of the small diameter cylindrical body 9 is 306.5 mm, and the capacity is 0.3 m ² .

  The polymer / unreacted monomer / water aqueous solution introduced into the distillation column 7 is separated into the polymer and the monomer / water, and the monomer / water mixture is distilled in the distillation column 7 and vaporized. It is introduced and condensed to form a mixture of unreacted monomer components and water. The mixed liquid of the monomer component and water liquefied by the condenser 10 is separated through the decanter 11, and the monomer component is returned to the polymerization reaction vessel 5 through the scrubber 8.

  The polymer separated in the distillation column 7 is ion-exchanged in the washing and dehydrating unit 13 equipped with the continuous rotary cylindrical filter 130 having the characteristic configuration of the present invention through the second slurry tank 12 together with water. After being washed with water, it is filtered through a filter cloth, formed into pellets with a pelletizer 14, and then dried with a dryer 15. The aqueous solution discharged from the washing and dehydrating unit 13 is stored in the filter washing tank 16 and the liquid containing unreacted monomer components mainly composed of water is sent to the MS tower (monomer strip tower) 17 for vaporization. The gas and liquid are separated and the waste water is taken out from the bottom of the tower, and water and unreacted monomers are recovered from the top of the tower and returned to the distillation tower 7.

  FIG. 4 schematically shows the configuration of the continuous rotary filter 130. As shown in the figure, the continuous rotary filter 130 according to the present embodiment has the same structure as the conventional one except for the filter cloth portion wound around the circumferential surface of the mesh-shaped rotary drum. That is, the continuous rotary filter 103 is unidirectional with the vat 131 into which a polymer suspension as a filtration stock solution is introduced and the lower half of the vat 131 being substantially immersed in the polymer suspension inside the vat 131. A mesh-shaped horizontal rotary drum 132 that rotates and rotates, a liquid collection pipe 133 disposed on the rotary shaft portion of the rotary drum 132, and a suction that communicates with the collection pipe 133 and extends toward the inner peripheral surface of the rotary drum 132. Part 134. The filter cloth 135 of the present invention is wound and fixed on the outer peripheral surface of the rotating drum 132.

  Further, a plurality of shower nozzles 138 for spraying high-temperature washing water made of ion-exchanged water at 60 to 80 ° C. are arranged on the outer peripheral surface of the rotary drum 132 on which the filter cloth 135 is wound and fixed. ing. Further, a scraper 139 for scraping off a polymer (wet polymer) containing cake-like water adsorbed on the surface of the filter cloth 135 wound around the outer peripheral surface of the rotary drum 132 and sending it to the pellet forming step 14 of the next step is provided. It is arranged.

In this embodiment, as shown in FIGS. 5 and 6, a screen 136 having a required mesh is interposed between the filter cloth 135 and the outer peripheral surface of the rotary drum 132.
The filter cloth 135 is made of polyester multifilament and has a plain weave structure. The fabric thickness is 0.11 mm, and the fineness of the multifilament yarn is 52-58 (d / 17f) for warp, 83-85 (d / 17f) for weft, and 150-160 (for warp). Book / in), weft is 94-100 (books / in), air permeability is 1-6 (cc / cm ² / sec) and weight is 69-73 (g / m ² ). .

  As in this embodiment, when a multifilament is adopted as the constituent yarn of the filter cloth 135, the polymer collecting property is remarkably improved as compared with the case where a monofilament or a twisted yarn is used. However, if the cloth thickness is large, the drainage is reduced and at the same time clogging is likely to occur. However, when the cloth thickness is 0.3 mm or less as in the present invention, the trapping property is ensured and the drainage does not cause any particular problem. However, when the fabric thickness is as extremely thin as 0.11 mm as in this embodiment, it is difficult to ensure the necessary strength. In order to compensate for this decrease in strength, in the present embodiment, a screen 136 having high air permeability and high strength is interposed between the rotary drum 132 and the filter cloth 135 as described above.

The screen 136 is made of a mesh fabric having a plain weave structure using nylon monofilaments as the weft. The wire diameter is 150 to 180 μm, and the fineness of the monofilament yarn is 50 to 55 (d) for warp, 47 to 52 (d) for weft and the thickness of the constituent yarn of the filter cloth 135, Woven density is 152-162 (lines / in) for warp, 102-108 (lines / in) for wefts, air permeability is 20-30 (cc / cm ² / sec), and weight is 58-62 (g) / M ² ) plain fabric. Thus, even if the thickness of the yarn used for the screen 136 is smaller than the thickness of the yarn used for the filter cloth 135, the constituent yarn is a monofilament, so that the strength is higher than that of the multifilament. Stable strength can be obtained.

  In order to wind and fix the filter cloth 135 and the screen 136 around the rotary drum 132, first, the screen 136 is wound around the outer periphery of the rotary drum 132 and the ends are abutted, and the filter cloth along the outer periphery thereof. Wrap 135 in the same way and match the ends. In this state, as shown in FIG. 5, the wire 137 is tightly wound and tightened in the circumferential direction of the rotary drum 132 at intervals of 2 to 3 cm.

  A rotating drum 132, in which a polyester filter cloth 135 and a nylon screen 136 are tightly wound, is driven and rotated in one direction. At the same time, a constant flow rate of polymer / water suspension is continuously introduced into the bat 131 from the second slurry tank 12 via the liquid feed pump, and the polymer / The water suspension is sucked together with air, and the water-containing polymer is adsorbed on the surface of the filter cloth 135 and is accompanied by the rotating drum 132 to reach the scraper 139. The wet polymer containing water adsorbed on the surface of the filter cloth 135 is scraped off by the scraper 139. During this time, the clarified water sucked by the suction part 134 and passed through the filter cloth 135 and the screen 136 is sent to the MS tower (monomer strip tower) 17 through the liquid collection pipe 143. While the rotary drum 132 is rotating, hot water of 60 to 80 ° C. is constantly sprayed from above, and the temperature inside the apparatus is maintained at 60 to 80 ° C. to increase the cleaning efficiency.

In the present embodiment, as described above, the filter cloth 135 having the above-described configuration and the screen are laminated and fixed to the outer peripheral surface of the rotary drum 132. It is flattened and the single fibers are denser than the woven density, and the required polymer collection and air permeability are ensured. In addition, since the material is polyester, the strength is high, there is no fear of fibrillation, the filament surface has been kept smooth for a long period of time, it has excellent chemical resistance, and it is altered even under high temperature acidity. Without being maintained, high peelability is maintained over a long period of time. In particular, since the value obtained by dividing the air permeability 1 to 6 (cc / cm ² / sec) by the cloth thickness 0.11 (mm) is 9 to 55, the necessary collection property of the polymer is ensured, Smooth drainage is obtained and clogging is less likely to occur.

  Further, by inserting a plain weave screen having a monofilament made of nylon between the rotary drum 132 and the filter cloth 135 of the rotary cylindrical filter 130, the thickness of the cloth is less than the normal cloth thickness. At the same time as the decrease in the tensile strength of the thin filter cloth 135 of the present invention is compensated, water passing through the filter cloth 135 easily moves to the screen 136 because nylon is hydrophilic. In addition, despite the fact that the fineness of the monofilaments constituting the screen 136 is smaller than the fineness of the multifilament of the filter cloth 135, the laminate strength of the filter cloth 135 and the screen 136 is extremely high, The collection property of the polymer and the drainage performance by the filter cloth 135 are ensured.

It is process drawing of the superposition | polymerization process of the acrylonitrile-type polymer provided with the monomer collection | recovery system of this invention. It is a graph which shows a time-dependent change of the generation amount of AAP. It is an external view which shows an example of the cylinder removal part applied to a monomer collection | recovery process. It is a side view which shows schematic structure of the continuous rotary filter applied to this invention. It is a schematic perspective view of the rotating drum which wound and fixed the filter cloth of the said continuous rotary filter. It is a schematic side view which expands and shows the lamination | stacking state of the filter cloth wound around a rotating drum, and a screen.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Acrylonitrile storage tank 1a Comonomer storage tank 1b Unreacted monomer recovery tanks 2a to 2c First to third metering pumps 3 Monomer preparation tank 4 Monomer supply tank 5 Polymerization reaction tank 6 Decylinder section 7 Distillation tower 8 Feed pump 9 Small diameter cylindrical body 9a Polymer aqueous solution outlet 9b Lid 9c Deaeration port 9d Polymer aqueous solution inlet 9e Ion exchange water inlet 9f, 9g Liquid level detector 10 Condenser 11 Decanter 12 Second slurry tank 13 Second filter 14 Pelletizer 15 Drying Machine 16 Filtrate tank 17 Monomer strip tower 18 Slurry tank 130 Continuous rotary filter 131 Butt 132 Rotating drum 133 Liquid collecting pipe 134 Suction part 135 Filter cloth 136 Screen 137 Wire 138 Shower nozzle 139 Scraper LT Liquid level detector LIC liquid Control unit

Claims (6)

Mounted on a continuous rotating cylindrical filter that separates a polymer having an average particle size of 10 to 50 μm from a polymer suspension having a particle size distribution of 1 to 200 μm in water obtained by an aqueous suspension polymerization process of an acrylonitrile-based polymer. A filter cloth,
It is characterized by comprising a woven fabric of a plain weave structure comprising polyester multifilament yarns having a value obtained by dividing the air permeability (cc / cm ² / sec) by the fabric thickness (mm) in the range of 9 to 55. Filter cloth for acrylonitrile polymer.   The filter cloth according to claim 1, wherein a thickness of the fabric is 0.3 mm or less. The filter cloth according to claim 1 or 2, wherein the air permeability of the fabric is in the range of 1 to 6 (cc / cm ² / sec). A method for separating a polymer from a polymer suspension obtained in an aqueous suspension polymerization step of an acrylonitrile-based polymer by a continuous rotary cylindrical filter equipped with the filter cloth according to claim 1 or 2,
The polymer suspension is acidic with a pH of 4.0 ± 1.0;
Maintaining the polymer suspension at a liquid temperature of 60 to 80 ° C., and the polymer having an average particle size of 10 to 50 μm from the polymer suspension dispersed in water with a particle size distribution of 1 to 200 μm. Filtering through a filter cloth,
A method for filtering and separating acrylonitrile-based polymers using a continuous rotary cylindrical filter.   5. A filtration separation method according to claim 4, further comprising interposing a plain weave screen comprising nylon monofilaments between the rotary drum of the rotary cylindrical filter and the filter cloth.   The filtration separation method according to claim 5, wherein a monofilament that is a constituent yarn of the screen has a diameter of 150 to 180 μm, and a basis weight of the screen is 20 to 30 pieces / cm.

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