JPH0356242B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention continuously removes volatile substances such as unreacted monomers, solvents, chain transfer agents, and low molecular weight polymers from a polymerization liquid composition containing a styrenic polymer,
The present invention relates to a method of producing a devolatilized polymer. Conventionally, methods for continuously removing volatile substances from a polymerization liquid composition include a method of preheating or foaming using a shell-and-tube heat exchanger, and then flashing it into a vacuum tank, for example, as described in Japanese Patent Publication No. 1973 −31678,
It is known from Japanese Patent Publication No. 48-29798, Japanese Patent Publication No. 51-134781, etc. However, in the case of these conventional techniques, heating of the polymerization liquid composition containing volatile substances using a preheater and increasing the vacuum degree of the vacuum chamber as a means of reducing volatile substances are as follows. For various reasons, there are limitations, and it has been extremely difficult to reduce the volatile substances remaining in the polymer, such as unreacted monomers, solvents, chain transfer agents, and low molecular weight polymers, beyond a certain level. That is, as the temperature of the polymerization liquid composition is increased, the remaining monomers mainly polymerize in the preheater, resulting in an increase in the amount of low molecular weight polymer in the polymer and a decrease in the heat resistance of the molded product. It also causes defects such as oily substances (tar) adhering to the mold during molding. On the other hand, increasing the degree of vacuum in the vacuum chamber
This causes a dramatic increase in the gas volumetric flow rate of the volatile material, increases the pressure drop in the piping and condenser, and makes such a device extremely expensive to manufacture. Moreover, it is practically difficult to construct such an apparatus when the amount of volatile substances to be evaporated off is large. For these reasons, in order to further reduce the residual volatile substances in the product polymer, it is known to use, for example, an extruder with a vent, a thin film evaporator, etc. in combination. However, such a method is economically disadvantageous due to increased equipment costs and power consumption, and manufacturing costs, so there is a need to improve these drawbacks. The present invention dramatically improves the ability to remove volatile substances in a vacuum chamber, and enables the production of polymers from which volatile substances have been efficiently removed from polymerization liquid compositions without using other equipment as described above. The object of the present invention is to provide a manufacturing method. In order to achieve this goal, the present inventors first foamed and devolatilized the molten polymer in a multi-tubular heat exchanger, extracted the molten polymer stored at the bottom of the vacuum chamber to the outside, and added the molten polymer to the molten polymer. They discovered that adding and mixing a neutral medium and then heating it to cause secondary foaming, or flashing, in a vacuum chamber was extremely effective in removing volatile substances from the polymer, and completed the present invention. I came to the conclusion. That is, in the present invention, when a volatile substance is removed from a polymerization liquid composition containing a styrene polymer obtained by solution polymerization or bulk polymerization to produce a devolatilized polymer, the polymerization liquid composition is subjected to multi-tube heat exchange. heating through a vessel, then flashing into a vacuum chamber, volatile substances are gasified and distilled from the vacuum chamber, and the devolatilized molten polymer is extracted from the bottom of the vacuum chamber;
A devolatilized polymer characterized in that, at the same time, a part of the polymer is taken out as a product, a molten polymer and a medium that is not mutually soluble are added and mixed to the remaining part, and then heated and circulated to the vacuum chamber to flash. This is the manufacturing method. Hereinafter, the method for producing the devolatilized polymer of the present invention will be described in detail with reference to FIG. A polymerization liquid composition containing a styrenic polymer obtained by solution polymerization or bulk polymerization is supplied from the polymerization zone via an inlet valve 1. The inlet valve 1 has the function of maintaining the pressure in the polymerization zone higher than the vapor pressure of the polymerization liquid composition at the reaction temperature. Further, the pressure at the head 2 of the multi-tubular heat exchanger 5 having the heat medium inlet 3 and the heat medium outlet 4 is lower than the vapor pressure at the reaction temperature of the supplied polymerization liquid composition. Since conditions such as heating medium temperature and flow rate are selected, the pressure of the polymerization liquid composition containing the styrenic polymer is reduced, volatile substances in the polymerization liquid composition evaporate, and foaming occurs significantly. Furthermore, since the latent heat of vaporization is removed at the same time, the temperature of the polymerization liquid composition in the head 2 of the multi-tubular heat exchanger is lowered, and the formation of low molecular weight polymers is suppressed. This foamed polymeric liquid composition passes through the heat exchange part of the multi-tubular heat exchanger 5 while being heated, and flows down to the vacuum tank 24 provided below due to gravity and pressure gradient. In this case, it is desirable that the heat medium in the multi-tubular heat exchanger 5 be at a low temperature as long as it does not impair the fluidity of the flowing polymer. Volatile components in the polymerization liquid composition 6 that foams while flowing down and is heated are evaporated inside the vacuum chamber and separated from the polymer, and then passed through the upper piping 23 of the vacuum chamber 24 with a refrigerant. It is condensed in a cooled condenser 18 and recovered in liquid form through a pipe 19. Hereinafter, this operation will be referred to as a primary devolatilization operation. The molten polymer 8 from which most of the volatile substances have been removed by the primary devolatilization operation is discharged out of the vacuum chamber by a screw type pump 9 provided at the bottom of the vacuum chamber. A medium that has no mutual solubility with the molten polymer discharged outside the vacuum chamber and that causes foaming in the molten polymer within the vacuum chamber is added from the addition port 12, and the medium is added using the static mixer 13. Thoroughly disperse and mix into the molten polymer. After being heated by the preheater 15 to a temperature higher than that of the polymerization liquid composition flowing down from the multi-tubular heat exchanger 5, it is transferred into the vacuum chamber from the redispersion nozzle 17 provided in the redispersion nozzle piping 16. Reflash. Hereinafter, this operation will be referred to as a secondary devolatilization operation. The medium added in this secondary devolatilization operation is a highly volatile substance that is incompatible with the molten polymer and has a boiling point lower than that of the remaining volatile components in the molten polymer, such as water or methanol. is considered appropriate. The amount of the medium to be added is suitably 2 to 30 times, and preferably 5 to 20 times, in molar ratio the amount of volatile substances expected to remain in the polymer only after the primary devolatilization operation. Furthermore, in order to enhance the effect of removing volatile substances, it is necessary to disperse the medium well in the molten polymer, and it is preferable to use an appropriate mixing means, such as a static mixer. A static mixer is a mixer that does not have a driving part; for example, the product name Static Mixer (manufactured by Kenix Co., Ltd.) and the Static Mixing Element listed in "Chemical Equipment 21(3)20 (1979)" are examples. Examples of mixer elements include the Ross ISG mixer (manufactured by Sulzer), the Ross ISG mixer (manufactured by Charles Ross), and the Hi Mixer (manufactured by Toray Industries). One or more of these mixer elements are usually installed in the flow direction of the molten polymer in the tube. The redispersion nozzle piping 16 and the redispersion nozzle 17 can have shapes as shown in FIGS. 2 and 3, for example, and the number and diameter of the holes are determined depending on the viscosity and flow rate of the molten polymer. As the heat exchanger used as the preheater 15, for example, a commonly used multi-tubular heat exchanger can be used, and it is desirable to allow the molten polymer to flow inside the tubes and to reduce pressure loss as much as possible. The molten polymer thus circulated by the screw type pump 9 foams significantly at the redispersion nozzle 17 inside the vacuum chamber due to the dispersion and mixing of the medium, promoting surface renewal, and the above-mentioned primary removal. The remaining volatile components that could not be completely evaporated by the volatilization operation alone are evaporated together with the medium. The gasified medium and volatile components are partially condensed and recovered in the condenser 18 via the vacuum chamber upper pipe 23, and the uncondensed gas is sent to the next process via the control valve 20. Here, using the same exhaust piping and condenser as in the primary devolatilization operation increases the devolatilization effect. That is, it is effective in renewing the atmosphere on the gas phase side at the surface of the polymerization liquid composition flowing down while foaming from the multi-tubular heat exchanger 5 during the primary devolatilization operation, and the residual volatilization in the molten polymer is reduced. It is presumed that the devolatilization effect is increased because the diffusion of the chemical components becomes easier. Furthermore, a part of the molten polymer whose volatile components have been reduced in this way is continuously extracted by a gear pump 10 and made into a product via a piping 11. In this case, the ratio of the amount of molten polymer taken out as a product by the gear pump 10 to the weight of the molten polymer circulated by the screw pump 9 is suitably 1/10 to 1/2, preferably 1/5 to 1/2. /3. The styrenic polymers to which the method of the present invention is applied include styrene, alkylstyrenes such as methylstyrene, ethylstyrene, and isopropylstyrene, halogenated styrenes such as chlorostyrene and bromustyrene, and styrenic monomers such as halogenated alkylstyrenes. Copolymers consisting of at least one of these styrene monomers and at least one of acrylic monomers such as acrylonitrile, methacrylonitrile, methyl acrylate, etc. ; At least one of these styrene monomers or at least one acrylic monomer, polybutadiene, copolymers of butadiene and styrene, acrylonitrile, methyl methacrylate, natural rubber, polychloroprene, ethylene propylene, etc.; copolymers with at least one type of rubbery polymers such as polymers, ethylene propylene diene monomer copolymers; and at least one type of styrenic monomer, at least one type of acrylic monomer, and rubbery It is a copolymer with at least one type of polymer. Examples of solvents used in solution polymerization include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and octane. Examples of chain transfer agents include aliphatic and aromatic mercaptans, pentaphenylethane, and α-methylstyrene dimer. According to the method for producing a devolatilized polymer of the present invention, a polymer containing volatile substances such as an unreacted monomer, a chain transfer agent, and a low molecular weight polymer can be produced at a concentration so low as to be difficult to achieve using conventional techniques. It was possible to obtain
Furthermore, the polymer thus obtained had improved heat resistance and fewer defects (stain) during molding. Example 1 52.5% by weight of polystyrene with an intrinsic viscosity of 1.04 and 1.2% by weight of methanol soluble content, ethylbenzene
A polymerization liquid composition containing 10% by weight and the remainder being unreacted styrene was prepared by thermal polymerization at a temperature of 135°C. This polymerization liquid composition was heated to 4.0 kg/cm ² g at a temperature of 135°C.
It was continuously fed into the apparatus of FIG. 1 via inlet valve 1 at a flow rate of 6.3 Kg/Hr under a pressure of . The upper pressure of the multi-tubular heat exchanger 5 in which the heat medium circulates outside is
The pressure was reduced to 0.6 kg/cm ² and the polymerization liquid composition foamed, and the temperature in this area was 125°C. The temperature of the heating medium circulating through the jacket was 230°C, and the temperature of the foamed polymer liquid composition 6, which was flashed into the vacuum chamber while being heated, was 210°C. Here, the pressure inside the vacuum chamber is
The temperature was maintained at 50 m/mHg, and the mantle was kept warm by flowing a heating medium at 235°C. The polymer liquid composition flowing down from the multi-tubular heat exchanger 5 is flashed into a vacuum tank and separated into a gas phase and a liquid phase, and the molten polymer in the liquid phase flows down through the gap in the redispersion nozzle piping group 16. and accumulates at the bottom of the vacuum chamber. This molten polymer was mixed with the molten polymer 7 flashed (secondary devolatilization operation) from the redispersion nozzle, and its temperature rose to 230°C.
The molten polymer accumulated at the bottom of the vacuum chamber was discharged at a rate of about 24 Kg/Hr by a screw pump 9 rotated by a drive motor 21, and water at room temperature was added through the addition port 12 at a rate of 0.13 Kg/Hr. . The piping and the jacket of the static mixer 13 were maintained at 235°C, but the temperature at the static mixer outlet 14 was 228°C.
The temperature decreased slightly with the addition of water. A multi-tubular heat exchanger 15 in which this molten polymer was kept at 260℃
The temperature was raised to 240° C. and flashed from the redispersion nozzle 17 into the vacuum chamber. On the other hand, the molten polymer was discharged from the gear pump 10 at a rate of 3.3 Kg/Hr to produce a product. Table 1 shows the analytical values of the obtained polystyrene product. Using this polystyrene, continuous molding was carried out for 2 hours in an injection molding machine, and the degree of resin adhesion to the mold was observed, and it was found that there was little resin adhesion and it was very good. Comparative Example 1 Example 1 except that water was not added from the addition port 12 and the jacket temperature of the external heat exchanger 15 was 235°C.
Volatile substances were removed under the same conditions. As shown in Table 1, the results showed that the methanol soluble content was higher than in Example 1, and the degree of resin adhesion to the mold, which was a defect during molding, was severe. Comparative Example 2 An experiment was conducted under the same conditions as in Example 1, except that water was not added through the addition port 12 and the temperature of the outer heat exchanger 15 was 260°C. As shown in Table 1, the methanol soluble content was higher than in Example 1, and the degree of resin adhesion to the mold, which was a defect during molding, was also severe. Example 2 Except that the discharge flow rate of the molten polymer at the bottom of the vacuum chamber by the screw type pump 9 was approximately 12 Kg/Hr.
Volatile substances were removed under the same conditions as in Example-1. The results are shown in Table-1. Although some resin adhesion to the mold was observed during molding, it was better than Comparative Examples 1 and 2. Example 3 Volatile substances were removed under the same conditions as in Example 1, except that the amount of water added through the addition port 12 was reduced to 0.07 Kg/Hr. The results are shown in Table-1. Some resin adhesion to the mold was observed during molding, but compared to the comparative example -
It was better than 1 and 2. Comparative Example 3 Water was added together with the polymerization liquid composition via the inlet valve 1 without adding water through the addition port 12.
The experiment was conducted in the same manner as in Example 1, except that 1.5Kg/Hr was added, the discharge rate of the screw type pump 9 was set to 3.3Kg/Hr, and the secondary devolatilization operation was eliminated, and the results are shown in Table 1. However, although the residual monomer, solvent, and methanol soluble content were small, there was significant tar adhesion to the mold.

[Table] *4 Mold: flat spiral flow, continuous 2 hour molding

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus suitable for carrying out the manufacturing method of the present invention, FIG. 2 is an enlarged view of the redispersion nozzle piping section taken from the A-A cross section, and FIG. FIG. 3 is an enlarged view of the redispersion nozzle taken along the line B-B'. 1... Inlet valve, 2... Shell-and-tube heat exchanger head, 3... Heat medium inlet, 4... Heat medium outlet, 5... Shell-and-tube heat exchanger, 6... Polymerization liquid composition, 7... Molten polymer, 8... Melt polymer, 9... Screw type pump, 10... Gear pump, 11... Piping,
12...addition port, 13...static mixer, 14...
...Static mixer outlet, 15... Preheater, 16...
Piping for redispersion nozzle, 17...Redispersion nozzle, 1
8... Condenser, 19... Piping, 20... Control valve, 21... Drive motor, 22...
Heat medium flow section, 23... Vacuum chamber upper piping, 24...
Vacuum tank.

Claims (1)

[Claims] 1. When removing volatile substances from a polymerization liquid composition containing a styrenic polymer obtained by solution polymerization or bulk polymerization to produce a devolatilized polymer, the polymerization liquid composition is heated through a shell-and-tube heat exchanger. ,
Next, it is flashed into a vacuum chamber, and the volatile substances are gasified and distilled off from the vacuum chamber.The devolatized molten polymer is extracted from the lower part of the vacuum chamber, and a part of it is taken out as a product, while the remaining part is melted. A method for producing a devolatilized polymer, which comprises adding and mixing a polymer and a medium that is not mutually soluble, and then heating and circulating the mixture to the vacuum chamber to flash it.