JP2762600B2 - Device for devolatilizing polymer solution and method for devolatilizing polymer solution using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for removing volatile substances such as unreacted monomers and solvents from a polymerization solution in a final step of a facility for producing a thermoplastic resin such as a styrene-based polymer. The present invention relates to a devolatilizer for a polymer solution that is continuously and efficiently removed, and a method for devolatilizing a polymer solution using the device.

[Conventional technology]

When styrene is used alone or in bulk polymerization or solution polymerization with other copolymerizable monomers, generally about 40 to
The polymerization reaction is stopped when 90% by weight has been polymerized, and unreacted monomers remaining in the obtained polymerization solution and, in the case of solution polymerization, volatiles such as a solvent are usually separated and removed from the polymerization solution. It is. Above all, styrene polymers used for tableware, containers, food packaging containers and the like are required to have a particularly low residual volatile content due to hygienic problems. In carrying out this devolatilization operation, care must be taken not to proceed with the polymerization further, and care should be taken not to expose the polymerization solution to a high temperature for a long time. It is important to prevent deterioration and the like due to crosslinking of the rubber phase in order to obtain a high quality polymer.

A device that removes volatiles from a styrene-based polymer solution usually provides the heat required for evaporation of the volatiles, and heat exchange in which the polymer solution is heated after evaporation of the volatiles so that the polymer still has an appropriate fluidity. And a devolatilization tank connected to a vacuum device for evaporating volatiles contained in the polymerization liquid. To obtain a good quality polymer, minimize the distance between the heat exchanger and the devolatilization tank and reduce the unit volume of the polymerization liquid in the devolatilization tank in order to minimize the degradation of the polymer at high temperatures. It is desirable to increase the surface area per unit area and increase the evaporation amount of volatiles.

As a method for minimizing the distance between the heat exchanger and the vacuum devolatilization tank, JP-A-59-166506 and JP-A-61-228012 disclose a method for heating a polymerization liquid taken out from a polymerization step. It has been proposed that a vertical multitubular heat exchanger is installed on a devolatilization tank, and the polymer solution that has passed through the heat exchanger immediately flows into the devolatilization tank while foaming. Here, a foaming agent such as water or alcohol is mixed into the polymerization liquid to improve the devolatilization efficiency.

[Problems to be solved by the invention]

However, in these methods, since the evaporation surface area of the polymerization liquid is limited by the number and diameter of the tubes of the heat exchanger, there is a limit to the reduction of the amount of residual volatiles in the polymer after the devolatilization treatment. If the temperature of the polymerization solution is raised to reduce the amount of volatiles, a low molecular weight substance is generated, and the quality is degraded. In order to solve this, two devolatilizations
Although there is a method of performing steps in three or three steps, the effect is not sufficient.

An object of the present invention is to provide an efficient devolatilizer capable of reducing the concentration of residual volatiles in a polymer to 300 ppm or less without significant capital investment and energy consumption, and a method for devolatilizing a polymerization solution using the same. Is to develop.

[Means for solving the problem]

The present inventors have conducted intensive studies in view of such a situation, and as a result, connected a devolatilization tank connected to a vacuum unit below a heat exchanger for heating a polymerization liquid, and provided a divider therebetween. It has been found that the use of a devolatilizer for a polymerization solution eliminates the above-mentioned disadvantages, and the present invention has been completed.

That is, the present invention connects a devolatilization tank connected to a vacuum device below a heat exchanger for heating a polymerization liquid,
Furthermore, a devolatilizer for a polymer solution characterized by providing a divider between the heat exchanger and the devolatilization tank, and a devolatilization method for a polymer solution characterized by using the devolatilizer are provided. Is what you do.

The heat exchanger used in the present invention is not particularly limited as long as it heats the polymerization liquid, but a vertical multi-tube heat exchanger is particularly preferable. When the content of volatile matter such as unreacted monomer and solvent is more than 1% by weight, especially 5% by weight or more, the heat exchanger is used to mix the polymerization liquid and prevent the flow from being biased. For this reason, it is preferable to use one in which a plurality of mixing elements having no movable parts are fixed in each tube. However, in the case of a polymerization liquid having a volatile matter content of 1% by weight or less, a pressure increase in the tube becomes large.

Examples of the plurality of mixing elements include those that mix the polymerization liquid by repeating the division of the flow of the polymerization liquid flowing into the tube, the change in the flow direction or the division direction, and the merge of the divided flows. For example, there are a Sulzer type tubular mixer and a Kenix type static mixer.

The divider used in the present invention may be any as long as it can divide the flow path of the polymerization liquid and can withstand the pressure received during the division, for example, a plate having many slits or circular openings. One. The shape of the opening is not particularly limited and includes, for example, a slit shape, a circular shape, a polygon having more than a triangle, a star shape, a rhombus shape, an array shape, and the like. However, considering the balance between processing cost and performance, a simple circular hole having no change in the cross-sectional area of the opening is preferable.

The size, number and arrangement of the openings, such as slits and holes, provided in the division part are such that the surface area with respect to the flow rate per unit time of the polymer solution divided through the divider is directly devolatilized from the heat exchanger. It is necessary that the surface area of the polymerization liquid per unit time when extruded into the vessel be sufficiently larger than that of the polymerization liquid and that excessive pressure is not applied to the divider. Further, it is preferable that a large difference does not occur in the flow rate of the polymerization liquid passing through each opening. For example, when a vertical multi-tube heat exchanger using a tube having an inner diameter a of 10 to 50 mm and a divider having a circular opening is used as the heat exchanger, the inner diameter b of the circular opening is usually It is determined within a range where 3 <a / b <10 is satisfied. Specifically, 3 to 5 m in diameter per tube
The number of circular openings of m is preferably 4 to 10. The arrangement of the openings is preferably such that no opening is provided at the center of the divider, since the flow rate of the polymer solution passing through each opening can be easily made uniform.

The method of attaching the divider is not particularly limited. For example, a method of attaching to a tube plate of a heat exchanger via a steel bar, a gusset plate, a bolt, or the like, or a method of attaching directly to each of the outlets of the tubes of the heat exchanger by welding or the like. And the like.

In the latter mounting method, the polymer solution that has passed through the tubes of the heat exchanger is led directly to the splitter without merging, making it easy to equalize the flow rate of the polymer solution at the outlet of the splitter. In addition, the polymerization liquid can be divided and devolatilized while maintaining the mixed state of the polymerization liquid in the heat exchanger,
This is preferable in that the devolatilization efficiency hardly fluctuates or decreases.

In the former mounting method, the polymer solution that has passed through the tubes of the heat exchanger is merged and then guided to the splitter. A change in the mixing state of the polymerization liquid due to a pressure drop or the like at the time of merging, for example, partial separation of the foaming agent from the polymerization liquid, and the like are more likely to occur than in the latter method. In order to prevent this, the distance between the tube sheet and the disperser is reduced to, for example, 40 mm or less, and the volume created by the tube sheet and the disperser becomes 10% or less with respect to the total volume of the heat exchanger. It is preferred that

The devolatilization tank used in the present invention is connected below the heat exchanger, and is connected to a vacuum device such as a vacuum pump for maintaining the inside of the devolatilization tank under vacuum or reduced pressure. For example, those conventionally used in an apparatus for producing a styrene-based resin can be used. As the vacuum device, a device capable of maintaining the pressure in the devolatilization tank at 10 to 100 mmHg is usually used.

In the apparatus of the present invention, since a divider is provided between the heat exchanger and the devolatilization tank, the polymer solution flowing down from the heat exchanger passes through the divider, for example, into a film or plate. It is directly supplied to the devolatilization tank in a state where it has a large surface area such as a shape or a thin columnar shape and is deformed into a shape suitable for devolatilization, and then foams, so that the devolatilization efficiency is remarkably improved.
In addition, when a heat retention tube is provided in the devolatilization tank, the polymerization liquid supplied into the devolatilization tank is temporarily received by the heat retention tube and is heated and then dropped, thereby further improving the devolatilization efficiency. Can be preferred.

The devolatilization apparatus for a polymerization liquid of the present invention is used for devolatilization of a polymerization liquid of a thermoplastic resin containing volatile substances such as unreacted monomers and solvents, but a rubber-modified or unmodified styrene-based polymer is used. It is preferable to use for devolatilization of the polymerization liquid. Among them, a polymerization conversion of a styrene-based polymer liquid obtained by polymerization until the polymerization conversion rate becomes relatively high as 80 to 95% by weight, a rubber-modified or not, is used. When used for devolatilization, efficient devolatilization becomes possible in a state in which a low-molecular-weight polymer is hardly produced, which is particularly preferable.

In order to perform devolatilization by the devolatilization method of the present invention, the devolatilizer for a polymer solution of the present invention may be appropriately used instead of the conventional devolatilizer for a polymer solution. For example, a polymerization solution having a polymerization conversion rate of 40 to 90% by weight is devolatilized using a conventional polymerization solution devolatilizer in one or two stages until the volatile matter concentration becomes 1% by weight or less. Then, after adding and mixing a foaming agent such as water or alcohol, using a devolatilizer for a polymerization solution of the present invention, for example, a temperature of 200 to 270 ° C., and a pressure of 10 to 30 in a devolatilization tank.
A method of devolatilizing a polymerization solution under the condition of mmHg, a polymerization solution having a polymerization conversion of 80 to 95% by weight, a devolatilization device for a polymerization solution of the present invention, preferably a plurality of mixing elements having no movable parts. Using a one-stage or two-stage polymerization liquid devolatilizer having a heat exchanger fixed in a tube, at a temperature of 200 to 250 ° C and a pressure of 10
Under conditions of ~ 100mmHg, the volatile content is devolatilized to 1% by weight or less, preferably 0.2 to 0.5% by weight, and then, if necessary, after adding and mixing a foaming agent such as water or alcohol,
A method of performing devolatilization in the same manner as the above method may be used. A device for mixing a foaming agent such as water or alcohol is not particularly limited, for example, a tubular mixer having a structure in which a plurality of mixing elements having no movable parts therein are fixed,
For example, a Sulzer-type tubular mixer, a Kenix-type static mixer, or the like is preferable. The amount of the foaming agent is usually 0 to 5 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the solid polymer.

Among these, the polymerization conversion rate is particularly 80 to 95% by polymerization.
Of the polymerization solution of the present invention in one or two stages
It is preferable to use a stage for devolatilization until the volatile substance concentration becomes 1% by weight or less, then add and mix a foaming agent, and then perform devolatilization using the devolatilizer for a polymerization liquid of the present invention. At this time, in the initial stage of performing devolatilization to a volatile matter concentration of 1% by weight or less, a devolatilizer for a polymerization solution is used.
Using a plurality of mixing elements without moving parts in the heat exchanger fixed in each tube, and in the devolatilization after mixing the blowing agent, without the mixing element in the heat exchanger It is preferable to use

〔Example〕

The devolatilizer for a polymerization liquid of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing an example of a devolatilizer for a polymerization liquid according to the present invention. In this apparatus, a devolatilization tank (3) is connected below a vertical multitubular heat exchanger (2) through which a polymerization liquid supplied from a polymerization step is supplied from a conduit (1).
Further, a splitter (5) is attached to the lower part of the tube sheet (4) on the lower side of the vertical multi-tube heat exchanger (2).
The devolatilization tank (3) is connected to a vacuum device (6) for keeping the inside of the devolatilization tank under vacuum or reduced pressure. A plurality of heat insulation pipes (7) capable of being installed are installed horizontally. Next, a gear pump (8) is connected below the devolatilization tank (3) to take out a polymer from which volatile substances have been separated into a conduit (9). In addition, a mixing element (not shown) having no movable part may be fixed in the pipe (10) in the vertical multitubular heat exchanger (2).

2 to 5 are partially enlarged longitudinal sectional views showing specific examples of a mounting portion of the divider (5).

FIG. 2 shows an example in which a divider (5) having a large number of openings (11) is attached via a stay (12).
One end of 2) is welded and fixed to the tube sheet (4) of the heat exchanger (2), and the other end is fixed to the splitter (5) by welding. ) Indicates that the side plate (13) is fixed by welding (however, a welded portion is not shown; the same applies hereinafter).

FIG. 3 shows a state in which a stay bolt (14) fixed by welding to a tube sheet (4) is used, and a divider (5) having a side plate (13) is attached by a nut (15).

FIG. 4 shows a heat exchanger (2) in which a divider (5) is directly welded and fixed to the outlet of a pipe (10).

FIG. 5 shows a heat exchanger (2) in which a screw fitting (16) is welded and fixed to an outlet portion of a pipe (10), and a splitter (5) having threaded side plates is attached thereto.

3 and 5 are preferable in that the divider (5) can be easily removed and replaced.

6 to 8 are plan views showing specific examples of the arrangement of the opening (11) of the divider (5) attached to the outlet of the pipe (10) of the heat exchanger (2). As the arrangement, an arrangement as shown in FIGS. 7 and 8 in which there is no opening at the center of the tube where the flow rate of the polymerization solution is the fastest is preferable in order to make the flow rate of the polymerization solution uniform.

9 to 13 are plan views showing specific examples of the shape (except for a circle) and arrangement of the opening (11) of the divider (5) attached to the outlet of the pipe (10) of the heat exchanger (2). FIG. FIG. 9 shows a slit-shaped opening, FIG. 10 shows a triangular opening,
FIG. 11 shows a star-shaped opening, FIG. 12 shows a diamond-shaped opening, FIG.
The figure has an array of openings.

Hereinafter, a devolatilizer (A) for a polymerization liquid of the present invention similar to FIG. 1 except that there is no heat retaining pipe (7) and a splitter (5) similar to FIG. ) And the second
1 except that a divider (5) was attached in the same manner as in the figure, or a volatilizer (B) for a polymerization liquid of the present invention similar to FIG. A test was performed using the same devolatilizer (C) for the polymerization liquid as a control for comparison as in FIG. 1, and the results are shown.

A device in which a raw material composed of 95% by weight of styrene and 5% by weight of toluene is polymerized to a polymerization conversion rate of 85% by weight, and as a heat exchanger, a plurality of mixing elements without moving parts are fixed in each tube (B). ) With volatile matter concentration of 2700ppm
After obtaining a polymerization solution of water, water was added to the polymerization solution at 2% by weight.
In addition, a device (A), (B) or (C), which is obtained by mixing a mixing element having no moving parts in a mixer (Sluzer mixer SMX) fixed inside, is used as a heat exchanger. A plurality of mixing elements with no moving parts therein are not fixed in each tube.)
After transporting 00l and raising the temperature to 230 ° C in a heat exchanger (2) with a tube inner diameter of 20 mm, each of the devices (A) and (B) has three openings of 3 mm in diameter per tube of the heat exchanger. After passing through the divider and passing through the divider in the apparatus (C), the volatile matter was removed while maintaining the pressure in the devolatilization tank at 20 mmHg, the mixture was sent out from a gear pump to obtain devolatilized polystyrene.

The residual volatile matter concentration of polystyrene obtained using the apparatus (A) of the present invention was 177 ppm, and the residual volatile matter concentration of polystyrene obtained using the apparatus (B) was 233 ppm. The residual volatile matter concentration of the polystyrene obtained using C) was 394 ppm.

〔The invention's effect〕

According to the devolatilization method using the devolatilizer for a polymerization liquid of the present invention, the polymerization liquid containing volatiles is heated by a heat exchanger, and then immediately separated by a divider into a film, plate, thin column, or the like. Since the surface area is large, it is divided into a shape suitable for devolatilization and supplied into a vacuum devolatilization tank, and then foamed, efficient devolatilization can be performed without causing deterioration of the polymer.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a devolatilizer for a polymerization liquid according to the present invention, FIGS. 2 to 5 are partially enlarged longitudinal sectional views showing specific examples of a mounting portion of a divider, and FIGS. 9 to 13 are plan views showing specific examples of the arrangement of the openings of the divider, and FIGS. 9 to 13 are plan views showing specific examples of the shape and arrangement of the openings of the divider. 1: conduit, 2: vertical multi-tube heat exchanger, 3: devolatilization tank, 4: tube sheet,
5: Divider, 6: Vacuum device, 7: Insulation tube, 8: Gear pump, 9: Conduit, 10: Tube, 11: Opening, 12: Stay, 13: Side plate, 14: Stay bolt, 15: Nut, 16 : Screw fitting.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C08F ⁶ /06-6/12 B01D 1/00-1/30

Claims (14)

(57) [Claims] 1. A devolatilization tank connected to a vacuum device is connected below a heat exchanger for heating a polymerization liquid, and a divider is provided between the heat exchanger and the devolatilization tank. A devolatilizer for a polymerization liquid, comprising: 2. The apparatus according to claim 1, wherein the heat exchanger is a vertical multi-tube heat exchanger. 3. The apparatus according to claim 1, wherein the heat exchanger is a vertical multi-tube heat exchanger in which a plurality of mixing elements having no moving parts are fixed in each tube. 4. The heat exchanger according to claim 1, wherein the heat exchanger is a vertical multi-tube heat exchanger, and the splitter is directly attached to each outlet of each tube of the vertical multi-tube heat exchanger. Equipment. 5. The apparatus according to claim 4, wherein each of said dividers has 4 to 10 circular openings having a diameter of 3 to 5 mm. 6. The apparatus according to claim 5, wherein the divider has no central opening. 7. A devolatilization tank connected to a vacuum device is connected to a lower part of a heat exchanger for heating a polymerization liquid of a thermoplastic resin containing a volatile substance, and further includes a divider. A method for devolatilizing a polymer solution, comprising devolatilizing using a polymer solution devolatilizer provided between the heat exchanger and the devolatilization tank. 8. The method according to claim 7, wherein the polymerization liquid is a polymerization liquid of a styrenic polymer. 9. The method according to claim 7, wherein the heat exchanger is a vertical multitubular heat exchanger. 10. The method according to claim 9, wherein the heat exchanger is a vertical multi-tube heat exchanger having a plurality of mixing elements without moving parts fixed in respective tubes. 11. The heat exchanger is a vertical multi-tube heat exchanger,
The method according to claim 9 or 10, wherein the splitter is directly attached to each of the outlets of each tube of the vertical multi-tube heat exchanger. 12. The method according to claim 7, wherein the polymerization liquid is a polymerization liquid of a styrenic polymer which has been devolatilized until the volatile matter concentration has become 1% by weight or less. 13. A devolatilization tank connected to a vacuum device is connected below a heat exchanger of a vertical multi-tube heat exchanger in which a plurality of mixing elements having no movable parts are fixed in respective tubes. Using a polymerization liquid devolatilizer provided with a divider between the heat exchanger and the devolatilization tank, the polymerization liquid is devolatilized until the volatile matter concentration becomes 1% by weight or less. After the addition and mixing, a devolatilization tank connected to a vacuum device was connected below the vertical multi-tube heat exchanger heat exchanger having no mixing element in each tube, and further a splitter was provided. 12. The method according to claim 7, 8 or 11, wherein the devolatilization is carried out by using a polymerization liquid devolatilizer provided between the heat exchanger and the devolatilization tank. 14. A devolatilizer having a mixing element fixed in a heat exchanger and a devolatilizer having no mixing element in the heat exchanger, wherein a plurality of mixing elements having no moving parts therein are provided. 14. The method according to claim 13, wherein a tubular mixer having a fixed structure is arranged to add and mix the foaming agent.