JPS6044323B2 - Method for removing volatile substances from polymerization liquid composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for more efficiently removing volatile substances from a polymerization liquid composition.

Conventionally, in the production of various polymers, volatile substances such as unreacted monomers and solvents remain in the product, and the inherent mechanical properties such as strength, thermal properties such as heat resistance, or chemical resistance are affected. Various measures have been taken to remove volatile substances, as they reduce chemical properties such as chemical properties.

For example, when producing a styrene polymer, in solution or bulk polymerization, the polymerization is stopped when 40% by weight of the monomers have been polymerized, and the unreacted monomers remaining in the polymerization solution composition are Alternatively, volatile substances, mainly solvents, are generally removed from the polymerization system.

For example, a method disclosed in Japanese Patent Publication No. 48-29797 as a prior invention is a method in which unreacted monomers or solvent coexisting in a polymerization liquid composition are evaporated in a transfer heat exchanger, and the polymerization liquid composition is In order to reduce the average residence time of the material as it passes through the transfer heat exchanger, and therefore to reduce the contact heating time,
The purpose is to suppress the concentration of low molecular weight polymers produced when volatile substances are removed by evaporation, and to prevent deterioration of mechanical properties such as transparency, tensile strength, hardness, impact strength, etc. of the polymer. . However, in this method, when the concentration of the polymer in the polymerization liquid composition becomes 70% or more, the concentration of volatile substances in the polymerization liquid composition decreases. It is not possible to sufficiently reduce the average residence time of , and the desired effect cannot be achieved. The purpose of the present invention is to provide a method for effectively removing volatile substances from a polymer solution composition, without impairing the physical and mechanical properties of the polymer, and by which these physical properties can be controlled as necessary. It is about providing.

The purpose of the present invention is to remove volatile substances from the polymer solution composition when the concentration of the polymer in the polymer solution composition obtained in the polymerization process is 70% or more. The objective is to provide an innovative method that can process the problem without causing any damage. The above purpose is to remove volatile substances from a polymerization liquid composition by adding a blowing agent that is not mutually soluble to the polymerization liquid composition, and then heating it with a shell-and-tube heat exchanger.
This is achieved by evaporating and separating volatile substances from the polymerization liquid composition together with the blowing agent gas.

Here, the polymer solution composition refers to a polymer obtained by nonaqueous suspension polymerization, solution polymerization, or bulk polymerization, a monomer solvent for this polymer, or a polymer whose main component is a nonaqueous suspension medium. This polymer includes vinyl aromatic compounds such as styrene and alvar methylstyrene, halogenated vinyl compounds such as vinyl chloride and vinylidene chloride, compounds such as butadiene and isoprene, acrylonitrile, and methyl methacrylate. A polymer consisting of an acrylic compound such as olefin such as ethylene propylene, or a copolymer thereof, or a copolymer consisting of this monomer and other copolymerizable monomers with it,
For example, general purpose polystyrene, high impact polystyrene, AB
S resin, polymethyl methacrylate, polyacrylonitrile, styrene-acrylonitrile copolymer, polybutadiene, polyisoprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, styrene -Maleic acid copolymer, styrene-
Examples include butyl acrylate glycidyl methacrylate copolymer. The solvent is one that can dissolve the polymer and form a substantially uniform polymer solution, such as benzene, toluene, methyl ethyl ketone, acetone, dimethylformamide, cellosolve, etc., while a non-aqueous suspension medium is a suspending medium other than water that is substantially incompatible with the polymer polymerized by the suspension polymerization method, such as in the polymerization of polypropylene. Heptane, hexane, etc. in 1. The volatile substances are the monomers, solvents, or non-aqueous suspension media mentioned above, and can be separated and removed from the polymer by evaporation.

Foaming agents that are mutually soluble in the polymerization liquid composition that can be used in the present invention include various gases that are inert to the polymerization liquid composition, such as water or nitrogen, and compounds that can generate such gases;
For example, bicarbonate of soda, ammonia carbonate, etc.

The amount of blowing agent added varies depending on the properties of the polymerization liquid composition.If the polymer content is high and the vapor pressure of the polymerization liquid composition is relatively low, the amount of blowing agent added should be increased; When the vapor pressure is relatively high, such as in a polymerization liquid composition obtained using a polymer or a solvent, the amount added may be reduced.

In the case of a polystyrene polymer solution composition obtained by producing a styrenic polymer such as polystyrene, rubber-modified polystyrene, etc. by bulk or solution polymerization, it is added in an amount of about 5 to 20% by weight based on the polymer solution composition. In the present invention, a blowing agent that is not mutually soluble is added to the polymerization liquid composition in advance, and then introduced into an evaporator capable of evaporating volatile substances by heating, such as a shell-and-tube heat exchanger. Depending on the polymerization conditions of the polymer contained in it, it may be at low temperatures near room temperature, or under pressure by transmitting the pressure of the heating evaporator, so that the gaseous form of the blowing agent is sufficiently absorbed. It may not exist. In such a case, in order to fully exhibit the desired effect, it is preferable to heat the foaming agent when adding it, or to heat the polymerization liquid composition, or to add the foaming agent while lowering the pressure of the heated evaporator. It is best to lower the pressure at the inlet port. Before introducing the polymerization liquid composition to which the blowing agent has been added into the heating evaporator, if a gaseous body of the blowing agent is sufficiently present,
Volatile substances in the polymerization liquid composition evaporate and become contained in the gas of the blowing agent, reducing the concentration of volatile substances such as monomers in the polymerization liquid composition. Increase the total volume of the mixture of composition and blowing agent. For this reason,
When removing volatile substances from a polymer by heating and evaporating, it shortens the heating time, thereby promoting a decrease in the performance of the polymer during heating or a decrease in residual volatile content in the polymer after heating, and further can be effective. As the heating evaporator, a shell-and-tube heat exchanger that can be heated by a heat medium or the like is used.

Shell-and-tube heat exchangers are more effective when installed vertically so that when the polymer is heated to a temperature above which it becomes fluid, it flows down by gravity; in such cases, a blowing agent may be added. The prepared polymerization liquid composition is introduced into the upper end. Its lower end is connected to a gas-liquid separator under reduced pressure to facilitate the separation of polymers and volatile substances, as well as their collection. The heating temperature of the shell-and-tube heat exchanger varies depending on the properties of the polymerization liquid composition, and when the content of volatile substances is high or the boiling point of the volatile substances is high, or when the temperature at which the polymer shows fluidity is high. If the temperature is high, it may be heated to a higher temperature, and if the opposite is the case, it may be heated to a lower temperature.
Heating is performed using heat medium C.

At this time, the temperature of the polymerization liquid composition at the inlet of the shell-and-tube heat exchanger was kept in the range of 120 to 180°C, and the temperature at the outlet was kept in the range of 180 to 280°C. It is preferable to design a shell-and-tube heat exchanger. If it is difficult to heat the polymerization liquid composition using a single-stage shell-and-tube heat exchanger to evaporate and separate the volatile substances from the polymer, such a shell-and-shell heat exchanger may be used in two stages. It is also possible to process by connecting more than one stage in series. It is desirable that the blowing agent introduced together with the polymerization liquid composition be in a gaseous state at the time of introduction, but it may be in a liquid state, and in such a case, the blowing agent can exert the desired effect by being heated and vaporized. do.

The blowing agent that has become a gas contains volatile substances therein, which reduces the content of monomers in the polymerization liquid composition and increases the volume of the gas body, so that the shell-and-tube heat of the polymerization liquid composition is reduced. This will reduce the average residence time through the exchanger. Therefore, it is possible to prevent performance deterioration due to abnormal polymerization of monomers during passage and performance deterioration due to heating of the polymer, and furthermore, it is possible to reduce the amount of volatile substances remaining in the polymer.
Abnormal polymerization of monomers refers to the polymerization of a large amount of monomers to produce excessively low molecular weight polymers, as well as the polymerization of excessively low molecular weight polymers due to the polymerization of monomers at high temperatures due to local overheating. Means the creation of a union. Compared to the conventional method mentioned above,
According to the method of the present invention, abnormal polymerization of monomers can be suppressed to prevent deterioration in the performance of the resulting polymer, but this can be done by reducing the monomer content in the polymerization liquid composition as described above, and Because it increases the volume of gas passing through the shell-and-tube heat exchanger,
This is believed to be because the passing speed can be increased and local overheating can therefore be prevented. As mentioned above, the method of the present invention in which a blowing agent is added and heated to evaporate and remove volatile substances from the polymerization liquid composition has better gloss, heat resistance, and mechanical properties than a method that does not use a blowing agent. It is possible to obtain a polymer which has excellent strength, etc., has a small amount of residual volatile matter in the polymer, and has excellent sanitary properties such as odor and toxicity.

Another important effect of the present invention is that it is possible to control the melt flow index of a polymer, which is one of the important factors in physical properties, without changing the polymerization conditions of the polymer according to market demands. In order to increase the melt flow index, the amount of blowing agent added may be reduced, while in order to lower the melt flow index, the amount of blowing agent added may be increased. The reason why it is possible to control the melt flow index of the produced polymer by changing the amount of blowing agent added is that the amount of produced or evaporated low molecular weight polymer is This is because the amount of blowing agent varies depending on the amount of blowing agent, and therefore the concentration of low molecular weight polymer and the average molecular weight (usually expressed as intrinsic viscosity or reduced viscosity) in the resulting polymer vary. As is well known, as the average molecular weight decreases, the melt flow index of the polymer generally increases. In addition, the low molecular weight polymer has the effect of improving the fluidity of the polymer, similar to an internal lubricant.
Therefore, as the concentration of low molecular weight polymer increases, the melt flow index increases. Furthermore, since the blowing agent according to the present invention has no mutual solubility with the polymerization liquid composition, the final separation of the blowing agent and the removed volatile substances is easy, and the reuse of unreacted monomers and solvent is economical. This is a great advantage of the present invention. The accompanying drawings show flow sheets for carrying out the method of the invention.

The polymerization liquid composition discharged from the polymerization process passes through the gate valve 1 and is continuously introduced into the addition section 4 at a constant rate, while the blowing agent is introduced into the heater 3 freely or by a pump, where it is evaporated or superheated. , the flow rate is controlled to be constant through the control valve 2, and the flow rate is introduced into the addition section 4. The polymerization liquid composition and the blowing agent join the addition section 4 and are introduced into the head of a multi-tubular heat exchanger 6 heated with a heat medium such as steam or Dowsome A, and then distributed uniformly by the dispersion plate 5. It is distributed inside each tube of the shell-and-tube heat exchanger and flows down inside the tubes while measuring the distribution. While flowing down, the polymerization liquid composition is heated, the temperature of the polymer is raised to a temperature above which it exhibits substantial fluidity, and almost all of the volatile substances are evaporated. The foaming agent gas containing the molten polymer and volatile substances is introduced into the gas-liquid separator 8 from the lower end of the multi-tubular heat exchanger 6 and flashed. The gas-liquid separator 8 is connected to a vacuum generator (not shown) by a conduit 7 through a condenser (not shown), and the gas-liquid separator is maintained under reduced pressure and prevents condensation of volatile substances. Therefore, it is heated by a heat medium. The volatile substances and blowing agent flashed into the gas-liquid separator 8 are gaseous and led to the condenser through the conduit 7, where the volatile substances are condensed and recovered. On the other hand, the molten polymer substantially free of volatile substances is discharged from the system by an extruder 9 and pelletized. The various polymers obtained by the present invention are widely used in the field of general resins, but especially when the present invention is applied to styrenic polymers obtained by bulk or solution polymerization, they are excellent molding materials in the field of molding resins. is obtained.

Next, embodiments of the present invention will be described according to the flow sheets of the attached drawings.

Example 1 The intrinsic viscosity was 1.07 and the methanol soluble content was 1.07. Polystyrene 8.5% by weight, ethylbenzene 1% by weight
, the polymerization liquid composition in which the remainder is unreacted styrene was heated to a temperature of 14
It was prepared by thermal polymerization at 5°C.

This polymerization liquid composition was heated to 4.5 kg/CI at a temperature of 145°C.
The mixture was continuously introduced into the addition section 4 through the gate valve 1 at a flow rate of 30 kg/Hr under a pressure of tG. On the other hand, 2.9kg/DG
of saturated steam was continuously introduced into addition 4 through control valve 2 at a flow rate of 3.0 k9/Hr.

The addition section 4 uses a T-shaped tube in which conduits are connected in a T-shape, and the outside is kept warm. did. The polymerization liquid composition to which this foaming agent was added was then introduced into a heating evaporator 6. The temperature of the polymerization liquid composition at the inlet of the heating evaporator was 135°C, and the pressure was 0.7k9/DG due to the pressure transmitted from the gas-liquid separator 8. The inner diameter of the heating evaporator 6 is 14.9! ? A rigid multi-tube heat exchanger was used in which heat exchanger tubes each having a length of 1.2 m were arranged in a staggered manner, and the inlet section was installed at the top. The polymerization liquid composition and the blowing agent were allowed to flow down the tube. Dow Samoo A outside the tube is 235℃
was circulated and heated. The polymerization liquid composition and blowing agent were then flashed to a gas-liquid separator 8. A vacuum tank maintained at a pressure of 507 wtHg was used as the gas-liquid separator.
It was directly connected to the lower end of a rigid multi-tubular heat exchanger, and the jacket was kept warm by circulating Dow Samoo A at 235°C. The temperature of the flashed polystyrene is 215. The temperature of the polystyrene accumulated at the bottom of the vacuum chamber was also 215°C. This revealed that the volatile substances in the polymerization liquid composition were almost completely evaporated at the outlet of the rigid shell-and-tube heat exchanger. The analysis values of the polystyrene taken out from the vacuum chamber were as shown in Table 1. Comparative Example 1 An experiment similar to Example 1 was conducted without adding any blowing agent.

The temperature of the polymerization liquid composition at the inlet of the rigid shell-and-tube heat exchanger was 130°C, and the pressure was 0.5 kg/DG. The temperature of the polystyrene at the outlet of the rigid multi-tubular heat exchanger was 220°C, and the temperature of the polystyrene accumulated at the bottom of the vacuum chamber was 215°C, indicating a decrease in temperature. This revealed that in this example, more volatile substances than polystyrene evaporated in the vacuum chamber. Table 1 shows the analytical values of the polystyrene taken out from the vacuum chamber. Example 3~
4 and Reference Example 1 Experiments exactly the same as in Example 1 were conducted using various polymerization liquid compositions.

Table 1 shows the polymerization liquid composition used, the amount of blowing agent added, and the analytical values of the obtained polymer. Comparative Examples 2 to 4 Experiments were conducted in exactly the same manner as in Examples 2 to 4, except that no blowing agent was added.

Table 1 shows the polymerization liquid composition used and the analytical values of the obtained polymer. Example 5 Example 1 except that the amount of blowing agent added was 1.0k9/Ur.
conducted exactly the same experiment.

The analytical values of the obtained polymer are shown in Table 1. Example 6 Experiments were conducted by changing the type of blowing agent.

Nitrogen gas at a pressure of 5.0 kg/CItG is heated to 14 by heater 3.
An experiment was conducted in exactly the same manner as in Example 1, except that the mixture was heated to 5.0° C. and introduced into the addition section 4 through the regulating valve 2 at a flow rate of 1.5 kg/Hr. The analytical values of the obtained polymer are shown in Table 1. As is clear from the above table, when the method of the present invention is used to remove volatile substances, a polymer with superior mechanical strength can be obtained compared to when no blowing agent is used, and The residual volatile content is reduced, the content of low molecular weight polymers (methanol soluble content) is also significantly reduced, and the heat resistance of the polymer is also improved.

[Brief explanation of the drawing]

The accompanying drawings show flow sheets for implementing the invention.

Claims (1)

[Claims] 1. When removing volatile substances from a polymer solution composition obtained by non-aqueous suspension polymerization, solution polymerization, or bulk polymerization, when the concentration of the polymer in the polymer solution composition is 70% or more,
A blowing agent that is not mutually soluble is added to the polymerization liquid composition in an amount of about 5 to 20% by weight based on the weight of the polymerization liquid composition, and then heated in a shell-and-tube heat exchanger and placed in a gas-liquid separator under reduced pressure. A method for removing volatile substances from a polymerization liquid composition, the method comprising introducing the volatile substances and evaporating and separating the volatile substances together with a blowing agent gas.