JP2006241648A - Apparatus for recovering unreacted monomer from aqueous coagulant in pan-based fiber spinning - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for recovering monomer designed to prevent a washing machine from halting caused by condenser cloggings. <P>SOLUTION: In a system comprising a distillation section and a condensation section, wherein the distillation section functions to vaporize and separate unreacted monomer and monomer from an aqueous coagulant containing undecomposed radical initiator which occur in producing polyacrylonitrile-based fiber by spinning a polyacrylonitrile-based polymer that is obtained by homogeneous solution polymerization using a radical initiator, and the condensation section functions to condense the vaporized monomer component and water, the apparatus for recovering the monomer has only multiple condensers and functions to automatically switch a condenser in question to another condenser on sensing the condensation section's cloggings based on the divergence of a cooling water control valve. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an unreacted monomer / solution / undecomposed radical initiator / initiation generated when a PAN fiber is obtained by spinning a polyacrylonitrile (PAN) polymer obtained by homogeneous solution polymerization using a radical initiator. The present invention relates to an apparatus for recovering a monomer by vaporizing and separating a monomer from an aqueous coagulant containing an agent decomposition product, water, and other additives, and a method for recovering the monomer by condensing the vaporized monomer component and water.

Generally, polymerization of acrylonitrile is radical polymerization, and industrial processes for obtaining PAN-based polymers are roughly classified into solution polymerization as a homogeneous system and aqueous suspension polymerization as a heterogeneous system. In homogeneous solution polymerization, the reaction rate of radical polymerization generally becomes slower as the progress of the reaction progresses. Therefore, in order to obtain a high conversion rate, a large apparatus or a long reaction time is required, which is industrially disadvantageous. Therefore, it is economically advantageous to cut the conversion rate around 90%. For this reason, the polymer solution contains unreacted monomers. Since solution polymerization is homogeneous polymerization, there is an advantage that there is no separation, drying, and dissolution steps of a polymer required for aqueous heterogeneous polymerization, and the process is simpler than that of aqueous heterogeneous polymerization. The removal of unreacted monomer in solution polymerization is generally a method in which the polymerization is terminated, and a polymer solution containing the unreacted monomer is supplied as a thin film on the inner wall of the degassed tank, and the unreacted monomer is removed. is there. The obtained polymerization solution is spun into an aqueous coagulant to obtain a PAN fiber.
This water-based coagulant contains unreacted monomers, solutions, undecomposed radical initiators, initiator decomposition products, water, and other additives. When the monomer is vaporized and separated from the aqueous coagulant and the monomer component and water are condensed to recover the unreacted monomer, a distillation column is used, but the unreacted monomer and the unreacted radical initiator are sublimated in the condenser. Precipitates and polymerizes to form a condenser.
As a conventional method, there is a method in which a plurality of monomer recovery facilities are provided and the operation is continued while shifting the washing time, but this is not preferable because the facility cost increases.

  Furthermore, as described in Patent Document 1, a polymerization inhibitor is added to a condenser to suppress polymerization, but precipitation of sublimated unreacted radical initiator cannot be prevented, and condensation is caused by precipitation / polymerization. When the vessel is clogged, you are forced to stop washing. In addition, since the inhibitor is added in the order of ppm, it is difficult to add it uniformly when the treatment amount varies greatly.

Moreover, as a thing which predicts clogging of a condenser, there exists a thing which estimates clogging in a refrigerant | coolant passage pipe | tube from the temperature and the amount of water of a refrigerant like patent document 2. However, this is a clogging alarm in the pipe, and even if it is used as an alarm in a process in which the unreacted radical initiator and monomer are polymerized and clogged in the condensing part, it is useful for determining the cleaning time. It cannot be a way to avoid it.
JP 2003-292528 A JP 60-149857 A

  In view of the background of the prior art, an object of the present invention is to provide a monomer recovery apparatus and method for preventing a washing stoppage due to a clogged condenser.

  The present invention employs the following means in order to solve such problems.

  That is, a monomer from an aqueous coagulant containing an unreacted monomer and an undecomposed radical initiator, which is produced when a polyacrylonitrile polymer obtained by uniform solution polymerization with a radical initiator is spun to obtain a polyacrylonitrile fiber. In the system consisting of a distillation section that vaporizes and separates the condensed monomer component and water, the clogging of the condensation section is detected from the opening of the cooling water control valve, and the condenser is automatically removed. It is a monomer recovery device having a plurality of only condensers, characterized by switching to the other condenser.

  According to the present invention, as described below, in the method for recovering the unreacted monomer component during the polymerization of the acrylonitrile-based monomer, when removing the monomer from the process liquid containing the unreacted monomer, the condenser is significantly clogged than before. It is possible to prevent the stoppage due to washing.

  Exemplary embodiments of the present invention will be described in detail with reference to the drawings.

  The present invention relates to an unreacted monomer, solution, unreacted radical initiator, initiator decomposition product, which is produced when a PAN-based polymer obtained by homogeneous solution polymerization with a radical initiator is spun to obtain a PAN-based fiber. The present invention relates to a technique for vaporizing and separating a monomer component from an aqueous coagulant containing water and other additives, and preventing a washing stop due to a condenser in a system for condensing the vaporized monomer component and water.

FIG. 2 schematically shows all conventional monomer recovery steps.
First, an aqueous coagulant is supplied from the spinning process 1 to the distillation column 2. This water-based coagulant is an unreacted monomer / solution / unreacted radical initiator / initiator decomposition product produced by spinning a PAN polymer obtained by solution homogeneous polymerization with a radical initiator to obtain a PAN fiber. -An aqueous solution containing water and other additives.

In the distillation column 2, the monomer / water is distilled and vaporized by a direct distillation method, and is introduced into the condenser 3 to become a mixture of unreacted monomer components and water. The mixed liquid of the monomer component and water liquefied by the condenser 3 is separated through the decanter 6 and recovered by the monomer component and water.
The condenser 3 keeps operating while monitoring the temperature of the outlet side mixed liquid with the thermometer 5 and adjusting the cooling water amount with the cooling water amount adjusting valve 4.

  By the way, the gas mixture which is vaporized and sent to the condenser 3 contains a slight amount of sublimated unreacted radical initiator in addition to the monomer component and water. The unreacted radical initiator sublimated precipitates upon cooling and functions as a polymerization initiator for the monomer component. The precipitate and the polymer of the monomer component cause the condenser 3 to be clogged. The clogging hinders the heat transfer effect of the device, the amount of cooling water before clogging does not allow sufficient cooling, the temperature of the thermometer 5 rises, and the cooling water amount adjustment valve 4 opens to return to the original state. Increase the amount of cooling water.

  Eventually, even if the cooling water amount adjusting valve 4 is fully opened, the temperature cannot be lowered, and the washing must be stopped to remove clogging.

FIG. 1 shows an example of a monomer recovery apparatus in the present invention.
In the present invention, it is possible to have a plurality of condensers. However, in order to minimize equipment costs, the number of condensers is two in this embodiment.
First, an aqueous coagulant is supplied from the spinning process 1 to the distillation column 2.
In the distillation column 2, the monomer / water is distilled and vaporized by a direct distillation method, and is introduced into the condenser 3 a via the switching valve 7 a that flows only in one direction to become a mixture of unreacted monomer components and water. The mixed liquid of the monomer component and water liquefied by the condenser 3a is supplied to the decanter 6 via the switching valve 7b that flows only from one direction. Thereafter, the mixed solution is separated by the decanter 6 and recovered by the monomer component and water.
The condenser 3a continues to operate while monitoring the temperature of the outlet side mixture with the thermometer 5a and adjusting the amount of cooling water with the cooling water amount adjusting valve 4a.
When the condenser 3a is clogged, the temperature of the thermometer 5a rises, and the cooling water amount adjustment valve 4a opens to increase the cooling water amount in order to restore the temperature.
Eventually, the temperature will not drop even if the cooling water amount adjusting valve 4a is fully opened. At this time, the switching valve 7a that flows only in one direction and the switching valve 7b that flows only from one direction are switched to the condenser 3b side with a signal indicating that the cooling water amount adjusting valve 4a is fully opened. Thereafter, the condenser 3b monitors the temperature 5b and can continue the operation by adjusting the amount of cooling water with the cooling water amount adjusting valve 4b. Accordingly, the clogging of the condenser 3a can be removed without stopping the entire monomer recovery apparatus including the distillation tower.

(Example 1) 99.7 mol% of acrylonitrile and 0.3 mol% of itaconic acid were polymerized using dimethyl sulfoxide (DMSO) as a solvent, and a polymer concentration containing 1.7 wt% of unreacted monomer was 19.7 wt% at 45 ° C. A monomer recovery device that produces a PAN fiber by spinning a DMSO solution of an acrylic polymer with a viscosity of 600 poise into an aqueous coagulation bath. A recovery operation was performed. Even after the above operation was continued for 10 months, there was no washing stop due to clogging of the condenser.
(Comparative Example 1) As shown in FIG. 2, the monomer operation was carried out in the same manner as in Example 1 except that it had only a single condenser and no switching operation was performed. It became impossible to condense and was forced to stop washing.

The monomer recovery apparatus which is an example of embodiment of this invention. It is the figure which showed the conventional monomer collection | recovery apparatus.

Explanation of symbols

1: Spinning process 2: Distillation column 3, 3a, 3b: Condenser 4, 4a, 4b: Cooling water amount adjusting valve 5, 5a, 5b: Thermometer 6: Decanter 7a, 7b: Switching valve

Claims (2)

Vaporization of monomer from water-based coagulant containing unreacted monomer and undegraded radical initiator generated when spinning polyacrylonitrile-based polymer obtained by homogeneous solution polymerization with radical initiator to obtain polyacrylonitrile-based fiber In a system consisting of a distillation unit for separation and a condensation unit for condensing vaporized monomer components and water, clogging of the condensation unit is detected from the opening of the cooling water control valve, and the condenser is automatically condensed to other condensation units. A monomer recovery apparatus having a plurality of condensers alone, wherein the apparatus is switched to a condenser. 2. A monomer recovery method according to claim 1, wherein the condenser is automatically switched when the cooling water amount adjusting valve is fully opened.

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