JP2011063553A - Method of reutilizing unreacted monomer content in polymerization of acrylonitrile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique of inhibiting adherent staining caused in facilities to a minimum to enable economical distillation and purification in reutilizing the unreacted monomer content formed in the process for producing PAN-based fibers by solution polymerization using an aprotic polar solvent and a radical initiator. <P>SOLUTION: A method of reutilizing the unreacted monomer content in the polymerization of acrylonitrile (AN) includes a step of performing azeotropy of water and AN, a step of separating a distillate of the azeotropy into an aqueous phase and an organic phase by decantation to recover crude AN including not less than 90 wt.% AN, a step of subjecting the crude AN to reduced-pressure distillation at least once in the presence of a polymerization solvent and a polymerization inhibitor in a distillation column, and a step of recovering highly purified AN having a purity of 97 wt.% or higher, and a step of adding at least part of the purified AN to the polymerization step as a polymerization raw material in separating the unreacted monomer content from an aqueous coagulation bath solution after spinning polyacrylonitrile (PAN). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an unreacted component of a raw material monomer mainly composed of acrylonitrile in a production process of polyacrylonitrile (hereinafter referred to as PAN) fiber by solution polymerization using an aprotic polar solvent and a radical initiator. The present invention relates to a technique for distilling and purifying and again using it as a polymerization raw material.

  PAN-based fibers are used in a wide variety of applications including clothing, and are also used as precursor fibers for producing carbon fibers. In particular, the use of carbon fibers in the automobile and aircraft fields is increasing because they have excellent specific strength and elastic modulus.

  The PAN-based fiber is obtained by polymerizing and spinning a monomer raw material mainly composed of acrylonitrile, and the polymerization method is roughly classified into solution polymerization and suspension polymerization.

  As the reaction proceeds in solution polymerization, the reaction rate of radical polymerization decreases. Therefore, it is possible to operate economically by cutting off the monomer conversion rate around 90%. The polymer solution obtained here is spun into an aqueous coagulation bath to obtain a PAN fiber.

  Monomers that have not contributed to the polymerization in the polymerization step cause the production cost to increase as raw material loss. Further, when the unreacted monomer separated and recovered from the production process is discarded, further costs are incurred. For this reason, in order to reduce the cost of the PAN-based fiber, it is an effective means to establish a technique for recovering and reusing the unreacted monomer.

  As methods for recovering and reusing monomer unreacted components generated in PAN-based fiber production by solution polymerization, there are methods described in Patent Documents 1 and 2.

  Patent Document 1 describes a method of vaporizing and recovering an unreacted monomer from a polymer solution before spinning, and Patent Document 2 reuses the recovered unreacted monomer as a polymerization raw material without purification. A method is described. However, when the recovered unreacted monomer is reused as a raw material without purification, impurities in the raw material are circulated and concentrated, which causes a deterioration in the quality of the PAN fiber. Further, as described in Patent Document 1 and Patent Document 3, in the method of vaporizing and recovering the unreacted monomer from the polymer solution before spinning, the unreacted content cannot be recovered completely and is recovered. The remaining unreacted portion is sent to the spinning process and mixed into the aqueous coagulation bath liquid. For this reason, if technology that reliably recovers and purifies unreacted monomer and technology that reuses unreacted monomer mixed in the aqueous coagulation bath can be established, quality stabilization and cost reduction over existing technologies can be achieved. I can expect.

  Patent Documents 3 and 4 describe techniques for vaporizing and separating the unreacted monomer components from the aqueous coagulation bath liquid. However, these techniques are aimed at removing the monomer in the coagulation bath liquid, and are not considered at all for reuse.

  A technique for reusing the unreacted monomer recovered from the polymerization solution and the coagulation bath is described in Patent Document 5. However, this invention is a technology for adding a polymerization inhibitor for the purpose of improving the stability of the recovered monomer unreacted component, and has been considered for the detailed technology related to the purification of the monomer unreacted component and the quality effect on the PAN fiber. Absent.

  Problems in purifying unreacted monomer components are described in Patent Document 4, and the unreacted monomer components include residual radical initiator, decomposed products of initiators, and other impurities derived from raw materials. Since it is contained, the polymerization reaction easily occurs. Therefore, if the unreacted monomer content is purified by distillation, the inside of the equipment cannot be economically operated because the equipment washing cycle becomes shorter due to contamination of the polymerization reaction product, and problems remain in the control of the polymerization reaction. It was not enough.

  Actually, when distillation purification is performed by the method described in Patent Document 5, deposits that are thought to be derived from the polymerization reaction of the unreacted monomer are generated inside the distillation equipment, so that an economically disadvantageous distillation operation is performed. Will be forced.

  If we ignore the economical operation of refining distillation and the quality effect of PAN-based fibers, it is possible to reuse the unreacted monomer within the technical scope of Patent Documents 4 and 5, but highly functional fibers and carbon. In applications that require high quality stability, such as for fibers, it is substantially problematic to reuse unreacted monomer components that cannot be guaranteed in purity.

  As a technique for purifying acrylonitrile recovered from the reaction system, other than the PAN-based fiber manufacturing process, there are methods described in Patent Documents 6 and 7.

  These are technologies that suppress the polymerization of acrylonitrile by controlling the oxygen concentration or temperature conditions during distillation, and mainly purify unreacted acrylonitrile recovered from the production process of acrylamide derivatives. Yes.

  However, in the study by the present inventors, when the techniques described in Patent Documents 6 and 7 were applied to purify unreacted monomers generated in the PAN-based fiber by solution polymerization using a radical initiator, distillation equipment was used. The deposits generated on the inner wall could not be completely suppressed. The cause of this problem seems to be that, as described in Patent Document 7, the impurities contained in acrylonitrile differ from reaction system to reaction system, so that the effectiveness cannot be applied when purifying all acrylonitrile-containing components. It is.

  For the above reasons, in the production of PAN-based fibers by solution polymerization using an aprotic polar solvent and a radical initiator, there is a demand for technology for distilling and purifying unreacted raw material monomers generated and using them again as polymerization raw materials. It is extremely expensive.

JP 2000-44606 A JP 2000-336115 A JP 2004-91943 A JP 2006-241648 A JP-A-10-87740 JP 7-70036 A JP 7-48335 A

  The present invention relates to adhesive dirt generated in equipment when reusing unreacted monomer in a PAN-based fiber production process by solution polymerization using an aprotic polar solvent and a radical initiator. Therefore, it is possible to provide a technique capable of economically purifying by distillation while minimizing the above.

  As a result of detailed examination of a technique for distilling unreacted monomers generated in a PAN-based fiber production process by solution polymerization using an aprotic polar solvent and a radical initiator, the present inventors have identified Under these distillation conditions, it was found that the system can be operated economically while minimizing adhesive dirt generated in the equipment, and the present invention has been completed.

That is, the invention according to claim 1 is a method for reusing the unreacted monomer component in the polymerization of acrylonitrile, characterized by comprising the following steps for the production of PAN-based fibers.
(1) A step of performing solution polymerization using a radical initiator with 95% by weight or more of the monomer raw material being acrylonitrile and using an aprotic polar solvent as a polymerization solvent.
(2) Polyacrylonitrile (hereinafter referred to as PAN) obtained by solution polymerization is spun into an aqueous coagulation bath. A process in which water and acrylonitrile are azeotroped when the unreacted monomer is separated from the aqueous coagulation bath.
(3) A step of separating the azeotropic fraction into an aqueous phase and an organic phase by decantation and recovering crude acrylonitrile containing 90% by weight or more of acrylonitrile.
(4) A step of recovering purified acrylonitrile purified to a purity of 97% by weight or more by distilling crude acrylonitrile under reduced pressure at least once under the condition that a polymerization solvent and a polymerization inhibitor are present in the distillation column.
(5) A step of returning at least a part of the purified acrylonitrile to the polymerization step as a polymerization raw material.

  The invention according to claim 2 is characterized in that it is dimethyl sulfoxide (hereinafter referred to as DMSO) which is an aprotic polar solvent.

  In the invention according to claim 3, in the step (4), the polymerization inhibitor used for distillation under reduced pressure contains cuperone, and the supply amount of cuperone is 10 ppm (weight basis, below) with respect to the weight of the crude acrylonitrile. The same) and 500 ppm or less.

  In the invention according to claim 4, in the step (4), the operation condition of the vacuum distillation is 22 kPa (absolute pressure, the same shall apply hereinafter) or more and 70 kPa or less, and the temperature of the liquid and gas in the distillation column is 35 ° C. or more and 90 ° C. A fluid having a temperature of 60 ° C. or higher and 105 ° C. or lower is used as a reboiler heating source associated with distillation equipment.

  In the invention according to claim 5, in the step (4), the distillation column for recovering purified acrylonitrile is a distillation column for distilling and recovering purified acrylonitrile, and the concentration of the polymerization solvent at the bottom of the distillation column is 5% by weight or more. 72 wt% or less.

  In the invention according to claim 6, in the step (4), the distillation column for recovering purified acrylonitrile is a distillation column for distilling and recovering purified acrylonitrile, and the concentration of the polymerization solvent at the bottom of the distillation column is 30% by weight or more. 72 wt% or less.

  The invention according to claim 7 is characterized in that, in the step (4), water is added to the bottoms of a distillation column for recovering purified acrylonitrile, and the polymerization solvent is recovered from the bottoms by an extraction operation.

  The distillation technology of the present invention minimizes unreacted monomer generated in the production process of PAN fibers by solution polymerization using an aprotic polar solvent and a radical initiator, and minimizes adherent contamination generated in equipment. Since it can be effectively distilled and purified and reused while limiting to the limit, the production cost of the PAN-based fiber can be reduced while maintaining the stability of quality.

  The present invention is a technique for recovering and purifying a raw material monomer that has not contributed to the reaction in the polymerization of PAN used in a PAN-based fiber, and the raw material monomer is mainly composed of acrylonitrile. The raw material monomer of the present invention may contain a copolymerizable comonomer, provided that the content is 5% by weight or less of the raw material monomer weight. Although there is a possibility that it can be applied to a system containing a comonomer exceeding 5% by weight, the effect is not guaranteed.

  As the comonomer, any compound having an ethylenic double bond can be used without any problem. Specifically, unsaturated organic acids such as acrylic acid, methacrylic acid, and itaconic acid, and esters thereof such as methyl and ethyl Or a salt and also unsaturated amide compounds, such as acrylamide, etc. can be illustrated.

  The polymerization of PAN in the present invention is performed by solution polymerization using a radical initiator with an aprotic polar solvent as a polymerization solvent (step (1)). The conditions for solution polymerization are not particularly limited, and may be a commonly performed method.

  As the radical polymerization initiator, a general radical initiator such as a peroxide such as benzoyl peroxide, an azo compound such as azobisdimethylvaleronitrile or azobisisobutyronitrile, or a redox initiator can be used. There is no particular limitation.

  As the aprotic polar solvent, DMSO, dimethylformamide, dimethylacetamide and the like can be used, but DMSO is preferable from the viewpoint of low toxicity.

  There is no restriction on the conversion rate of the raw material monomer in the polymerization process, but it is economically advantageous to terminate the reaction when 85% to 95% of the charged raw material monomer is consumed to obtain a polymer solution for spinning. It becomes.

  Next, step (2) will be described.

  The polymer solution polymerized in the step (1) is spun by spinning into an aqueous coagulation bath solution.

  The polymer solution after polymerization can evaporate and separate unreacted monomers from the polymer solution before spinning, and the concentration in the solution can be reduced. However, even if this step is omitted, the present invention is not hindered. . In addition, when purifying and reusing the unreacted monomer vaporized and recovered before spinning, the unreacted component is mixed again with the coagulation bath liquid after spinning and purified by distillation in the process described in the present invention. It can be purified and reused.

  The aqueous coagulation bath used for coagulating the PAN obtained by solution polymerization includes a polymerization solvent, an unreacted component of a raw material monomer mainly composed of an acrylonitrile component, a residual radical initiator, a decomposition product of the initiator, Other impurities derived from raw materials are included.

  Since the acrylonitrile component in the coagulation bath liquid has a higher vapor pressure than the polymerization solvent and forms a minimum azeotrope with water, it can be separated from the polymerization solvent in the coagulation bath liquid by a distillation column or an evaporator.

  The acrylonitrile component azeotroped with water is condensed and cooled in a heat exchanger, and when decanted, it is separated into an aqueous phase and an organic phase, and the main component of the organic phase is acrylonitrile (hereinafter referred to as a crude monomer) ((3 ) Process). Usually, since the water | moisture content is saturated with a crude monomer, about 3 weight% of water | moisture content mixes. In addition, components having a low boiling point among impurities in the coagulation bath liquid and impurities formed as a by-product during collection are mixed.

  The acrylonitrile concentration in the crude monomer, which is thus recovered as a purification raw material of the present invention, is usually 90% by weight or more (hereinafter referred to as crude acrylonitrile).

  In the present invention, the crude acrylonitrile thus obtained is distilled at least once under reduced pressure to recover a monomer component (hereinafter referred to as purified acrylonitrile) purified to an acrylonitrile concentration of 97% by weight or more (step (4)). If the purity is less than 97% by weight, impurities remaining in the purified monomer may adversely affect storage, polymerization, or quality.

  The purified acrylonitrile recovered in the present invention can be reused by performing the step (5) which is added to the polymerization step as a PAN-based polymerization raw material. The ratio of purified acrylonitrile in the raw material monomer is not limited, but in order to minimize the influence on the quality of the PAN fiber, the ratio of purified acrylonitrile in the raw material monomer is preferably 20% by weight or less. .

  In the step (4), the crude acrylonitrile is distilled at least once under reduced pressure. As distillation equipment such as distillation tower used for vacuum distillation, the same distillation tower and equipment may be used repeatedly, or a plurality of distillation towers and equipment. May be used. One or more distillation columns to be distilled may have the same distillation form and equipment specifications in each distillation column, or may have different specifications.

  Although there is no restriction on the internal of the distillation column, it is preferable to reduce the amount of liquid retained in the column. From this viewpoint, regular packing or irregular packing with little hold-up, or sieve tray with low liquid retention, etc. Is preferably used.

  Moreover, although there is no restriction | limiting in the number of distillation stages, it is preferable to set it as 40 or less as a theoretical stage. Above that, the equipment cost increases, the pressure loss of the tower increases, and the temperature of the bottom increases, so that it becomes difficult to satisfy the temperature condition recommended in the present invention.

  A reboiler is usually attached to distillation equipment such as a distillation tower used in the present invention. There is no restriction on the type of the reboiler. However, if the liquid stays in the reboiler for a long time, it causes an adhesive stain due to a side reaction. In order to suppress deposits growing on the reboiler wall surface, a structure in which a shearing force is applied to the liquid on the heat transfer surface is preferable. From the above viewpoint, it is preferable to cause the liquid to flow by thermosiphon or forced circulation, and a structure in which a shear force is applied to the liquid on the heat transfer surface by a heat exchanger such as a multi-tube type or a plate type is preferable.

  In the present invention, in order to recover purified acrylonitrile, a low boiling point component, a high boiling point component, and water are separated from the crude acrylonitrile by distillation under reduced pressure. The distillation form can be carried out by either batch distillation or continuous distillation.

  When purifying by continuous distillation, if only one distillation column is installed, the purified monomer is recovered from the middle stage by side cut, and low boiling point impurities are extracted from the top of the column, the capital investment can be reduced. . However, in this case, since the low-boiling component and the high-boiling component are separated with a limited number of stages, the separation of impurities may be deteriorated. The crude acrylonitrile used in the present invention contains various impurities including unidentified impurities, and acrylonitrile and water form the lowest azeotrope, so the separation of acrylonitrile, water and impurities is strictly controlled. It ’s difficult.

  When purified monomers with particularly high purity are required from the viewpoint of the quality of PAN-based fibers, the concentration of impurities can be controlled by performing continuous distillation with two or more distillation facilities or batch distillation as part of the purification process. It becomes easy.

  For the reasons described above, the number of distillation facilities and the selection of batch distillation and continuous distillation can be freely designed from the required purity and recovery cost of the purified monomer.

  In each distillation column, if the internal liquid and gas temperature rises, dirt on the inner wall of the equipment due to side reaction of unreacted monomer will occur, and monomer components will be consumed by side reaction, so purified acrylonitrile The amount recovered may be reduced. For this reason, it is preferable from the point which suppresses a side reaction to perform distillation operation at the liquid and gas temperature in a distillation tower at 90 degrees C or less. In addition, when operation is performed at a liquid and gas temperature of less than 35 ° C in the distillation column, the requirements for the specifications of the incidental equipment (condenser, vacuum generation source, etc.) become strict, making it difficult to operate economically. Therefore, it is desirable to carry out at 35 ° C. or higher.

  In the present invention, the pressure in the distillation tower is distilled under reduced pressure in the range of 22 kPa or more and 70 kPa or less (absolute pressure, the same shall apply hereinafter), so that the temperature of the liquid and gas in the facility falls within the recommended range, and economical operation is achieved. enable.

  In addition, the crude acrylonitrile used in the present invention is mixed with components that particularly lower the stability of the liquid, such as the radical initiator used in the previous solution polymerization. Since this component has a boiling point higher than that of acrylonitrile, the deposit fouling in the equipment mainly occurs near the bottom of the distillation column.

  For this reason, even if the liquid temperature at the bottom of the distillation column is maintained at the temperature recommended in the present invention (60 ° C. or higher and 90 ° C. or lower), if the temperature of the reboiler heat transfer surface is high, adhesion fouling is likely to occur on the wall surface. Become. For this reason, the stability of the bottom liquid can be improved by controlling the temperature of the fluid (heat medium) used as the heating source of the reboiler to 105 ° C. or lower.

  As the heat medium, any of steam, hot water, oil and the like can be used. Although a heating medium dedicated to the distillation facility implemented in the present invention can be prepared, more efficient operation is possible by using waste heat of other processes.

  A polymerization inhibitor is supplied to each distillation facility to prevent runaway polymerization reaction and contamination of the facility. The polymerization inhibitor can be arbitrarily selected from generally known polymerization inhibitors and can be used alone or in combination of two or more, but a strong polymerization inhibition effect can be obtained. It is preferable that cuperone having a low vapor pressure is included. Cuperon has a low vapor pressure, so it concentrates at the bottom of the distillation column and is effective in improving the stability of the liquid. In addition, since cupron is hardly mixed into the purified monomer, it is preferable in that the inhibitor concentration of the polymerization raw material can be easily controlled.

  There is no particular limitation on the supply form of the polymerization inhibitor, and part or all of the polymerization inhibitor can be mixed with the crude acrylonitrile before being supplied to the distillation facility, or may be directly supplied to the distillation facility, In order to suppress contamination occurring in the raw material supply line of the distillation facility, it is preferable to mix at least a portion with the crude acrylonitrile before distillation.

  The amount of cuperone added is preferably 10 ppm or more and 500 ppm or less (weight basis) with respect to the weight of the crude acrylonitrile. By setting it to 10 ppm or more, a sufficient polymerization inhibition effect can be obtained. By making it 500 ppm or less, economical operation is possible, and from the viewpoint of cuperone solubility in acrylonitrile, uniform dispersion is preferable.

  The crude acrylonitrile used in the present invention contains subcomponents at the time of polymerization in addition to impurities derived from the polymerization raw material, so the stability of the liquid is determined by each operation of the polymerization process, spinning process, and crude acrylonitrile recovery process. Varies depending on conditions. For this reason, in order to strictly determine the optimum amount of polymerization inhibitor, use a process liquid collected from the same process in advance, or a model liquid prepared to have the same properties as the process liquid, It is preferable to investigate the relationship between the addition amount of the polymerization inhibitor and the polymerization induction time and confirm that a sufficient induction time is obtained.

  When supply is difficult in the case of using a solid polymerization inhibitor such as cuperon, supply is facilitated by dissolving in a suitable solvent. As the solvent, water, ethanol, methanol, dimethylformamide, dimethylacetamide, DMSO, and the like can be used. Among them, DMSO is a component that is also used as a polymerization solvent, and has a lower vapor pressure than acrylonitrile. This is particularly preferable because it has the effect of increasing the solubility of a polymerization inhibitor such as cuperone.

  In the present invention, it is necessary for the polymerization solvent to be present in the distillation equipment. Since the polymerization solvent has a lower vapor pressure than acrylonitrile, it has the effect of concentrating at the bottom of the distillation column, lowering the acrylonitrile concentration at the bottom, and increasing the stability of the liquid.

  In addition, even when adhering dirt that does not completely dissolve in acrylonitrile occurs due to the addition of a polymerization inhibitor and temperature control, and even if adhering dirt that does not dissolve in acrylonitrile occurs, the adhering dirt is removed by the polymerization solvent present in the distillation column. Since the solubility is increased, an economical operation such as extending the interval of equipment cleaning is possible. In addition, when a polymerization solvent is used, even when the solvent is mixed with purified acrylonitrile, there are significant industrial advantages such as that the polymerization is not affected.

  There is no limitation on the supply form of the polymerization solvent, and a part or all of the crude acrylonitrile can be mixed, or it can be directly supplied to any part of the distillation equipment, but at least a part of the supplied polymerization solvent is It is preferable to reach the bottom of the distillation column.

  Although there is no restriction | limiting in the supply amount of a polymerization solvent, It is preferable to set it as the quantity which satisfy | fills the conditions of temperature and pressure recommended in embodiment of this invention. Specifically, it is preferable to supply the polymerization solvent concentration in the bottoms of the distillation column for recovering purified acrylonitrile so that the concentration is 5% by weight or more and 72% by weight or less. The polymerization solvent concentration of the liquid is 30% by weight or more and 72% by weight or less.

  When the concentration of the polymerization solvent in the bottoms is 5% by weight or more, a sufficient dispersion effect of the polymerization inhibitor can be obtained. Furthermore, when it is 30% by weight or more, in addition to obtaining a sufficient dispersion effect of the polymerization inhibitor, a sufficient dissolution effect of deposits in the distillation column can be obtained.

  On the other hand, when it exceeds 72% by weight, the temperature of the distillation bottom may exceed the temperature recommended in the present invention.

  The recovered purified acrylonitrile can be used as a polymerization raw material, but a polymerization inhibitor can be added to the purified acrylonitrile in order to increase the storage stability until it is used as a polymerization raw material. The polymerization inhibitor to be added and the amount added can be arbitrarily selected in combination that does not affect the polymerization.

  The bottoms of a distillation column for recovering purified acrylonitrile contain an acrylonitrile component, high-boiling impurities mainly composed of a polymer, a polymerization solvent, and the like. The bottoms can be processed as industrial residues, but in this case, the polymerization solvent is lost. Here, if the polymerization solvent can be recovered, further economical purification becomes possible.

  The polymerization solvent can be recovered only by vaporization recovery such as distillation operation of the polymerization solvent. However, as in the case of the monomer distillation equipment, problems such as the occurrence of adhesive soiling and the entry of high-boiling impurities into the polymerization solvent occur. Therefore, the extraction operation is preferably performed as part of the polymerization solvent recovery step.

  Here, since the polymerization solvent used in the present invention has high solubility in water, and the acrylonitrile component and the polymer are difficult to dissolve in water, extraction separation using water as an extractant is an effective means.

  Since the polymerization solvent separated from the acrylonitrile component and the polymer by extraction is recovered as a mixture with water, the polymerization solvent can be recycled by dehydrating it.

  There are no particular limitations on the extraction conditions, but economical conditions can be set based on the recovery rate of the polymerization solvent, the distribution of impurity components, and the amount of heat necessary for dehydration of the polymerization solvent.

  EXAMPLES Hereinafter, although an Example, a comparative example, and a reference example are illustrated and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Example 1]
A distillation experiment apparatus equipped with a glass 200 ml round bottom flask, a Dimroth type cooling agglomerator, and a packed tower corresponding to 5 stages was prepared. From an aqueous coagulation bath solution produced by spinning PAN fiber obtained by solution polymerization of acrylonitrile using azobisisobutyronitrile as a radical disclosure agent using DMSO as a polymerization solvent into an aqueous coagulation bath solution A 100 g sample of unreacted monomer (crude acrylonitrile) recovered using azeotropic distillation of water and acrylonitrile was prepared. This monomer unreacted component is an organic phase obtained by decanting the vaporized component of the aqueous coagulation bath liquid, and the acrylonitrile purity is 95.6% by weight. To the crude acrylonitrile, 0.02 g of cuperone (200 ppm based on the crude acrylonitrile) and 10 g of DMSO were added, and a vacuum batch distillation experiment was conducted. The pressure was controlled between 24 kPa and 29 kPa, heating was performed using an oil bath at 60 ° C., and the reflux ratio was 1. The first distillate 10g was the first distillate, and then 80g was the main distillate. When the main sample was analyzed by FID-GC (Shimadzu Corporation GC-2010), the acrylonitrile purity was 99.2% by weight. This has the same purity as that of acrylonitrile usually used as a polymerization raw material, and can be purified to a purity that does not hinder the addition of the polymerization raw material.

  The time from the start of heating to the end of distillation was 3 hours. During the distillation, the temperature of the liquid in the flask was maintained at 42 to 55 ° C, and the temperature of the gas was maintained at 42 to 49 ° C. After completion of the distillation, no adhesive dirt was generated on the inner wall of the round bottom flask used as a kettle.

The DMSO concentration in the bottoms extracted from the bottom of the distillation apparatus was 55.3% by weight. The DMSO concentration was measured by FID-GC in the same manner as the main distillate sample.
In addition, 5 g of water was added to 10 g (including about 5.5 g of DMSO) of the bottoms, and DMSO was extracted at a liquid temperature of 25 ° C. As a result, 4.4 g of DMSO could be distributed to the aqueous phase side, and acrylonitrile and DMSO could be separated.

[Comparative Example 1]
The same experiment as in Example 1 was performed except that DMSO was not added to the crude acrylonitrile.
When the main fraction sample was analyzed by FID-GC, the acrylonitrile purity was 99.0% by weight, and the purity could be increased as in Example 1.

  The time from the start of heating to the end of distillation was 3 hours. After completion of the distillation, the glass inner surface of the round bottom flask used as a kettle had become white and cloudy, and adhesive dirt was generated. This soil could not be removed by washing with acetone.

[Comparative Example 2]
The same experiment as in Example 1 was performed except that DMSO was not added to the crude acrylonitrile and the oil bath temperature was changed to 160 ° C.

  When about 20 minutes had passed after the start of heating, the glass inner surface of the round bottom flask became cloudy white and adhesive dirt was generated. Thereafter, when about 50 minutes passed, a white solid was generated in the liquid in the kettle, and a polymer was generated. Therefore, it was judged that continuation of distillation was dangerous, and the experiment was stopped.

[Reference Example 1]
A heating experimental apparatus equipped with a 50 ml eggplant-shaped flask, an Allen cooler, and an oil bath was prepared. Kanto Chemical Co., Ltd. deer special grade acrylonitrile (purity 99% by weight or more) was heated in the range of 80 to 160 ° C., and a thermal stability test was conducted for 120 minutes. Table 1 shows the time when the white polymer was generated (polymerization inhibition time). At this time, when heated at 160 ° C., the polymerization inhibiting effect was 10 minutes, whereas at 100 ° C., the polymerization inhibiting effect was extended to 120 minutes or more.

[Reference Example 2]
Using the same apparatus as in Reference Example 1, the polymerization inhibitor cuperon was added to the same crude acrylonitrile used in Example 1 so that it would be 2 to 20 ppm (weight basis), and heated at 160 ° C. A 120 minute thermal stability test was conducted. Table 2 shows the time when the white polymer was generated (polymerization suppression time). When 2 ppm was added, the polymerization inhibitory effect was 40 minutes, whereas when 10 ppm or more was added, the polymerization inhibitory effect was extended to 120 minutes or longer.

[Reference Example 3]
Using an apparatus similar to that of Reference Example 1, Kanto Chemical Co., Ltd. deer special grade acrylonitrile (purity 99 wt. % Or more) was added so that the polymerization solvent DMSO would be 10 to 70% by weight, and a thermal stability test was conducted for 120 minutes under a heating condition of 100 ° C. Table 3 shows the time when the white polymer was generated (polymerization suppression time). When the amount was 10% by weight, the polymerization inhibitory effect was 20 minutes, whereas when added at 30% by weight or more, the polymerization inhibitory effect was extended to 40 minutes or longer. Further, when 50% by weight or 70% by weight was added, it was extended to 120 minutes or more.

According to the present invention, the unreacted content of the raw material monomer mainly composed of acrylonitrile generated in the production process of PAN fiber by solution polymerization using an aprotic polar solvent and a radical initiator is generated in the equipment. Therefore, the production cost of the PAN-based fiber can be greatly reduced while maintaining the quality stability.

Claims (7)

A method for reusing an unreacted monomer component in polymerization of acrylonitrile, comprising the following steps for producing a polyacrylonitrile fiber.
(1) A step of performing solution polymerization using a radical initiator with 95% by weight or more of the monomer raw material being acrylonitrile and using an aprotic polar solvent as a polymerization solvent.
(2) The polyacrylonitrile obtained by solution polymerization is spun into an aqueous coagulation bath. A process in which water and acrylonitrile are azeotroped when the unreacted monomer is separated from the aqueous coagulation bath.
(3) A step of separating the azeotropic fraction into an aqueous phase and an organic phase by decantation and recovering crude acrylonitrile containing 90% by weight or more of acrylonitrile.
(4) A step of recovering purified acrylonitrile purified to a purity of 97% by weight or more by distilling crude acrylonitrile under reduced pressure at least once under the condition that a polymerization solvent and a polymerization inhibitor are present in the distillation column.
(5) A step of adding at least a part of purified acrylonitrile to the polymerization step as a polymerization raw material. 2. The method for reusing monomer unreacted components in the polymerization of acrylonitrile according to claim 1, which is dimethyl sulfoxide as an aprotic polar solvent. In the step (4), the polymerization inhibitor used for distillation under reduced pressure contains cuperone, and the supply amount of cuperone is 10 ppm (weight basis, the same applies hereinafter) or more and 500 ppm or less with respect to the weight of the crude acrylonitrile. 3. A method for reusing an unreacted monomer component in the polymerization of acrylonitrile according to claim 1 or 2. In the step (4), the operation condition of the vacuum distillation is 22 kPa (absolute pressure, the same shall apply hereinafter) to 70 kPa, the temperature of the liquid and gas in the distillation tower is 35 ° C. or more and 90 ° C. or less, and distillation equipment 4. A method for reusing unreacted monomer in the polymerization of acrylonitrile according to claim 1, wherein a fluid having a temperature of 105 [deg.] C. or less is used as a heating source for the reboiler associated therewith. 5. The method according to claim 1, wherein in the step (4), the concentration of the polymerization solvent discharged from the bottom of the vacuum distillation column for recovering the purified acrylonitrile is 5 wt% or more and 72 wt% or less. A method for reusing the unreacted monomer component in the polymerization of acrylonitrile according to 1. The concentration of the polymerization solvent taken out from the bottom of the vacuum distillation column for collecting the purified acrylonitrile in the step (4) is 30 wt% or more and 72 wt% or less. A method for reusing the unreacted monomer component in the polymerization of acrylonitrile according to 1. 7. The process according to claim 1, wherein in the step (4), water is added to the bottoms of a distillation column for recovering purified acrylonitrile, and the polymerization solvent is recovered from the bottoms by an extraction operation. A method for reusing an unreacted monomer component in the polymerization of acrylonitrile.