JPH1121311A - Method of removal of volatile matter in polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of removing volatile matter in a polymer produced during solution polymerization or bulk polymerization remarkably, efficiently and industrially advantageously. SOLUTION: After a polymer is fed to the first degassing vessel equipped with a plate-fin type or shell-and-tube type heat exchanger 22a and is degassed to decrease the content of volatile matter to not more than 5,000 ppm by weight, the polymer is fed to the second degassing vessel equipped with a shell-and-tube type heat exchanger 21b having the diameter of inner pipe of 5-15 mm to decrease the content of volatile matter to not more than 500 ppm by weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for removing volatile substances in a polymer, and more particularly, to a method for removing volatile substances in a polymer such as a styrene-based polymer obtained by solution polymerization or bulk polymerization. The present invention relates to an efficient and industrially advantageous method of removing.

[0002]

2. Description of the Related Art A solution polymerization method or a bulk polymerization method is used.
When a monomer such as styrene is polymerized, it is rarely polymerized completely. Contains sexual substances. Such volatile substances cause deterioration or deterioration of the quality of the polymer, and further deteriorate the quality of the product obtained from the polymer. Need to be removed. Therefore, the polymer transferred from the polymerization step is processed by a volatile substance removing device. As a method for removing volatile substances in a polymer, various methods have been used to suppress the deterioration of the quality of the polymer at high temperatures and to efficiently remove volatile substances to about 500 ppm by weight or less. Devices and methods have been proposed.

[0003] As a general method, a multistage devolatilization method in which devolatilization tanks are arranged in multiple stages in series and devolatilization is employed. For example, in the case of a two-stage type, usually, in the first-stage devolatilization step, a volatile substance remaining in the polymer in an amount of about 15 to 25% by weight is reduced to a polymer temperature of about 200 to 240 ° C. and a vacuum degree of
Flash evaporation is performed under conditions of about 100 torr, and devolatilization treatment is performed until the residual amount of volatile substances in the polymer becomes about 2 to 6% by weight. Next, in the second-stage devolatilization step, a volatile substance remaining in the polymer in an amount of about 2 to 6% by weight is removed at a polymer temperature of about 240 to 260 ° C. and a degree of vacuum of 4 to 5 t.
Flash evaporation is performed under conditions of about orr, and devolatilization treatment is performed until the residual amount of volatile substances in the polymer becomes 500 ppm by weight or less.

In such a two-stage devolatilization method, usually, both the first stage and the second stage use a flash drum incorporating a plate fin type preheater having high heat transfer efficiency and low pressure loss. in use. However, when such a flash drum is scaled up, the drum diameter is increased to an unrealistic level, and it may not be possible to manufacture the flash drum. Further, since the plate fin type is a special heat exchanger, there is a problem that the cost per unit area is basically higher than the multi-tube type, and the plate fin type is large and requires a large installation area. It is also known that a volatile substance can be easily removed by mixing and dispersing a low-boiling point foaming substance such as water in a polymer and flash-evaporating the polymer together with the volatile substance. Even if the boiling point foaming material is mixed and dispersed in the polymer in advance, the plate fin type heater has a small pressure loss, so that the low boiling point foaming material is easily separated from the polymer at the inlet, and as a result, the low boiling point There is also a problem that the effect of mixing and dispersing the foamable substance in the polymer is not sufficiently exhibited.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for removing volatile substances in a polymer obtained by solution polymerization or bulk polymerization very efficiently and industrially advantageously under such circumstances. The purpose is to provide.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, adopted a two-stage devolatilization method. Using a devolatilization tank with a small-loss heat exchanger (plate fin type or multi-tube type), a large amount of volatile substances was flash-evaporated to reduce the residual amount of volatile substances in the polymer to a certain value or less. Then, as the second-stage devolatilization tank, using a devolatilization tank having a multi-tube heat exchanger of a thin tube with a large pressure loss, flash-evaporated volatile substances in a state in which they are more easily diffused, and polymerized It has been found that the object can be achieved by reducing the residual amount of volatile substances in the resin to a certain value or less.
In particular, by using a heat exchanger having a large pressure loss in the devolatilization tank of the second stage, when a low boiling point foaming substance is mixed and dispersed in the polymer in the upstream of the devolatilization tank, the inlet or the heat exchanger It has been found that the separation of the low boiling point foaming substance inside is suppressed, and the volatile substance is effectively devolatilized. The present invention has been completed based on such findings. That is, in the present invention, in removing volatile substances in a polymer obtained by solution polymerization or bulk polymerization, the polymer is subjected to a first-stage devolatilization tank having a plate-fin or multi-tube heat exchanger. And devolatilized so that the volatile substance in the polymer becomes 5000 ppm by weight or less, and then the inner diameter of the tube is 5 to 1
The polymer is supplied to a second-stage devolatilization tank having a 5 mm multitubular heat exchanger and devolatilized so that volatile substances in the polymer become 500 ppm by weight or less. A method for removing volatile substances is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polymer to which the method of the present invention is applied is not particularly limited as long as it is a polymer obtained by solution polymerization or bulk polymerization, and various polymers can be used. Styrenic polymers are preferred. Examples of the styrene-based polymer include homopolymers of styrene-based monomers such as styrene, vinyltoluene and α-methylstyrene, copolymers obtained from two or more of these, or styrene-based monomers and acrylonitrile or acrylic acid. Copolymers with monomers such as methyl and methyl methacrylate, and copolymers with a styrene-based monomer and a copolymerizable rubber-like material are exemplified. The content of the volatile substance in these polymers varies depending on the polymerization method and the type of the polymer, but is usually 5 to 40% by weight, preferably 10 to 40% by weight.
The range is 30% by weight, more preferably 15 to 25% by weight. In the method of the present invention, a two-stage devolatilization method is adopted, and in the first-stage devolatilization tank, a plate having a high heat transfer efficiency and a small pressure loss is used for flash evaporation of a large amount of volatile substances. A devolatilization tank having a fin-type heat exchanger or a multi-tube heat exchanger is used.

In the first devolatilization tank, the temperature of the polymer is 180 to 270 ° C., and the degree of vacuum is 30 to 150 torr.
It is preferable to perform the deaeration treatment under the following conditions. If the temperature of the polymer is 1
If the temperature is lower than 80 ° C., devolatilization may be insufficient.
If it exceeds 0 ° C., the polymer tends to deteriorate. On the other hand, if the degree of vacuum is less than 30 torr, the equipment cost is high, which is not preferable. If the degree of vacuum exceeds 150 torr, devolatilization may be insufficient. In consideration of devolatilization, suppression of polymer deterioration, equipment costs, and the like, more preferable devolatilization conditions are a polymer temperature in the range of 200 to 240 ° C. and a degree of vacuum of 50 to 100 ° C.
torr range. In the first-stage devolatilization tank, the devolatilization treatment should be performed so that the volatile substance in the polymer becomes 5000 ppm by weight or less. This volatile substance is 5
If it exceeds 000 ppm by weight, devolatilization in the second devolatilization tank may be insufficient. In addition, devolatilization treatment in this first stage until the amount of volatile substances becomes too low is not preferable from a practical viewpoint. From the viewpoint of devolatilization and practicality in the second-stage devolatilization tank, in this first-stage devolatilization tank, the amount of volatile substances in the polymer was 100%.
It is advantageous to perform the devolatilization treatment so as to be in the range of 0 to 3000 ppm by weight.

When a devolatilization tank having a plate fin type heat exchanger is used as the first-stage devolatilization tank, the devolatilization tank preferably has a structure shown in FIG. 1, for example. . FIG. 1 is a side sectional view showing an outline of an example of a devolatilization tank having a plate-fin type heat exchanger that can be used as a first-stage devolatilization tank in the method of the present invention. Heat exchanger 3 in a body 1 having a jacket 2 provided with a supply port 4 and a discharge port 5 thereof.
Is provided. This heat exchange device 3 can be provided outside the main body 1. A plate fin type heat exchanger 6 is used for the heat exchange device 3, and the fins of the plate fin type heat exchanger include, for example, a plain type (flat fin), a louver type, and a serrate type (flaky type). Fins), perforate type (perforated fins), helibone type (corrugated fins), and the like, and serrate type is particularly preferable. The flow system may be any of a cross-flow type, a counter-flow type, a parallel-flow type, and a combination thereof, but a cross-flow type is particularly preferable from the structural point of view. Here, a cross-flow type plate fin type heat exchanger will be described as an example.

The heat exchanger 6 has a horizontal passage through which the heat medium H passes and a vertical passage through which the polymer P passes. The heat passage H is supplied from the supply pipe 7 to the horizontal passage, and the discharge pipe is provided. 8
Discharge more. The polymer P is supplied to the inlet nozzle 10 and the pipe 11
Is supplied to the polymer supply chamber 9 provided above the heat exchanger 6 through the heat exchanger 6, and is dispersed and heated through the vertical passage of the heat exchanger 6, and then the main body 1 is in a decompressed state. Is discharged as a polymer stream P. In addition,
Reference numeral 14 denotes a temperature detection end. FIG. 2, FIG. 3 and FIG.
FIG. 3 is a side view, a plan view, and a bottom view of an example of the heat exchange device 3. The heat exchange device 3 is provided with heat medium chambers 15 on both sides of a lateral passage of the plate-fin heat exchanger 6. The supply pipe 7 and the discharge pipe 8 are connected. A polymer supply chamber 9 is provided at the upper portion on the side of the vertical passage, and a pipe 11 for supplying the polymer P is connected.

FIG. 5 is an enlarged view of a portion A in FIG. 4, and FIG.
FIG. 6 is a cross-sectional view taken along the arrow Y in FIG.
Is a structure in which metal plates (fins) 16A and 17A each having a cross section formed in an uneven shape or a corrugated shape are orthogonally connected via a partition plate 18, and the metal plate (fin) 16
A, a number of vertical passages 16 are formed, and a metal plate (fin) 17 is formed.
A forms a number of lateral passages 17. Therefore, the vertical and horizontal passages are opened in a honeycomb shape.
In view of 6, the polymer flows into the heat exchanger 6 in the form of a number of cords, and is discharged at the outlet of the vertical passage 16 in the form of a sheet or a thick cord. Further, since the horizontal passage 17 of the heat medium H separated by the partition plate 18 is arranged adjacent to both sides of the vertical passage 16 through which the polymer P passes, heat transfer is extremely good. Polymer P
Is a heat exchanger 3 via an inlet nozzle 10 and a pipe 11
Is supplied to the inside of the polymer supply chamber 9, and is heated to a predetermined temperature by the high-temperature heat medium H in the horizontal passage 17 while passing through the vertical passage 16, and is opened at the lower part of the heat exchange device 3. The liquid is discharged from the open end of the vertical passage 16 into the main body 1 held in a reduced pressure state.

In this case, the polymer P is efficiently heated by the heat medium H passing through the adjacent horizontal passage 17 while passing through the vertical passage 16 and its viscosity is reduced to a predetermined range. Volatile substances are easily discharged. When the polymer P having such reduced viscosity is discharged as a polymer stream P into the main body 1 maintained in a reduced pressure state, volatile substances are instantaneously evaporated (flashed) from the inside thereof, so that heavy The merged flow P descends into the main body 1 as if it were a thin sheet or a string, and is discharged from a discharge port 12 provided at a lower portion thereof. On the other hand, the volatile substance B evaporated from the polymer stream P is discharged from the outlet 13. In the method of the present invention, as the second-stage devolatilization tank, a devolatilization tank having a multi-tube heat exchanger having a large pressure loss and consisting of a thin tube having an inner diameter of 5 to 15 mm is used. If the inner diameter of the tube in this multi-tube heat exchanger is less than 5 mm, the pressure loss becomes too large and is not practical. If the inner diameter of the tube exceeds 15 mm, the pressure loss becomes too small, and as a result, foaming of volatile substances easily occurs inside the heat exchanger, and a low-boiling-point foaming substance is mixed and dispersed in the polymer in the upstream of the heat exchanger. In this case, the low-boiling-point foamable substance is likely to be separated at the inlet or inside of the heat exchanger, and the volatile substance may not be sufficiently devolatilized. From the point of pressure loss, the inside diameter of this pipe is 7 to 10 mm
Is preferable. By using such a multi-tube heat exchanger, low heat efficiency is good, miniaturization is possible, and flash efficiency is high.

In the second-stage devolatilization tank, devolatilization treatment is preferably performed under the conditions of a polymer temperature of 220 to 270 ° C. and a degree of vacuum of 5 torr or less. Polymer temperature 220 ° C
If it is less than 270 ° C., devolatilization may be insufficient, and if it exceeds 270 ° C., the polymer tends to deteriorate. From the viewpoints of devolatilization and prevention of deterioration of the polymer, the temperature of the polymer is preferably 24
The range of 0-260 degreeC is preferable. In addition, the degree of vacuum is 5 to
If it exceeds rr, devolatilization may be insufficient. In this second-stage devolatilization tank, the volatile substance in the polymer is devolatilized so as to be 500 ppm by weight or less. When the residual amount of the volatile substance exceeds 500 ppm by weight, the quality of the polymer is likely to deteriorate or deteriorate, and the quality of the product obtained from the polymer is likely to deteriorate,
The object of the present invention cannot be achieved.

In the method of the present invention, the polymer extracted from the first-stage devolatilization tank is charged with a low-boiling-point foaming substance of 0.1 to 0.1.
After adding 1% by weight and mixing and dispersing, it is desirable to supply this to the second-stage devolatilization tank. At this time, the low boiling point foaming substance is not particularly limited as long as it has a lower boiling point than the monomers and the solvent contained in the polymer and does not adversely affect the polymer. Examples of such a low boiling point foaming substance include water, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and butanol. These may be used alone.
Two or more kinds may be used in combination. By mixing and dispersing such a low boiling point foaming substance in the polymer, the volatile substance is flash-evaporated together with the volatile substance in the second-stage devolatilization tank, and the volatile substance is effectively devolatilized. If the amount of the low boiling point foaming substance is less than 0.1% by weight with respect to the polymer, the added effect is not sufficiently exhibited, and if it exceeds 1% by weight, the effect is improved for the amount. Is not recognized, but rather the energy consumption increases, which is economically disadvantageous.
Considering the effect and economy, the preferred amount of the low-boiling foamable substance is in the range of 0.3 to 0.6% by weight based on the polymer.

There is no particular limitation on the mixing device for the low-boiling-point foaming substance, but a static mixer in which a plurality of mixing elements having no movable parts therein are fixed, such as a Sulzer-type tubular mixer and a Kenix-type static mixer. And the like are preferably used. Next, the method of the present invention will be described with reference to the accompanying drawings. FIG. 7 is a schematic diagram of an example of an apparatus for carrying out the method of the present invention. The polymer P containing
And the multi-tubular heat exchanger 22A attached to the first-stage devolatilizing tank 21A (the above-described plate-fin heat exchanger may be used instead of the multi-tubular heat exchanger). .). The polymer P is usually 180 to 270 ° C., preferably 200 to 240 ° C. by the heat exchanger 22A.
° C, and then is usually heated to 30 ° C by a decompression device 23A.
Is discharged into the first-stage devolatilization tank 21A which is reduced to 150 torr, preferably 50 to 100 torr,
Most of the volatiles in the polymer flash evaporate, leaving less than 5000 ppm by weight of volatiles.

The polymer in the first-stage devolatilization tank 21A passes through a pipe 27 by a gear pump 24A, and has an inner diameter of 5 to 15 m attached to the second-stage devolatilization tank 21B.
m, preferably 7 to 10 mm, is supplied to the multitubular heat exchanger 22B. At this time, if necessary, the low-boiling-point foamable substance W is polymerized by the static mixer 25 provided in the middle of the pipe 27. About 0.1 to 1% by weight, preferably 0.3 to 1% by weight.
After being mixed and dispersed at a ratio of 0.6% by weight, the mixture may be supplied to the multitubular heat exchanger 22B. The polymer is heated to usually 220 to 270 ° C., preferably 240 to 260 ° C. by the multitubular heat exchanger 22B, and then depressurized by the pressure reducing device 23B to the second stage, which is usually reduced to 5 torr or less. Volatile substances discharged into the tank 21B and in the polymer are:
Flash evaporates with the optional addition of low boiling point foaming material to 500 ppm by weight or less. The polymer in the second-stage devolatilization tank 21B is taken out of the system as a product polymer Q through a pipe 28 by a gear pump 24B.

[0017]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Examples 1 to 5 and Comparative Examples 1 and 2
Was carried out using the apparatus shown in FIG. However, in Examples 1 to 5 and Comparative Example 1, as the multi-tube heat exchanger of the first-stage devolatilizing tank, one having 20 tubes with an inner diameter of 1 inch and a length of 1.5 m was used. As the multi-tube heat exchanger of the second-stage devolatilization tank, a tube heat exchanger having 13 tubes with an inner diameter of 7 mm and a length of 1.2 m was used. In Comparative Example 2, the multi-tubular heat exchanger in the first-stage devolatilization tank was the same as described above, but the multi-tubular heat exchanger in the second-stage devolatilization tank had a pipe inner diameter of 1 mm. The one having 13 tubes of 1.5 inches in length and 1.5 inches was used. In Example 6, in the apparatus shown in FIG. 7, Examples 1 to 5 were performed except that the above-mentioned plate-fin type heat exchanger was used instead of the multitubular heat exchanger of the first-stage devolatilization tank. The test was performed using the same apparatus as described above.

EXAMPLE 1 18% by weight of volatile substances such as styrene and ethylbenzene
The polystyrene melt containing the polystyrene was extracted from the polymerization reactor at the previous stage by a gear pump, and the apparatus shown in FIG. 7 (first stage multitubular heat exchanger: tube inner diameter 1 inch, length 1.5 m,
The number of tubes was 20, and the second-stage multitubular heat exchanger: tube inner diameter 7 mm, length 1.2 m, number 13), and devolatilization was performed under the conditions shown in Table 1. Table 1 shows the quality of the obtained products. Example 2 and Comparative Example 1 The procedure was performed in the same manner as in Example 1 except that devolatilization was performed under the conditions shown in Table 1. Table 1 shows the quality of the obtained products. Examples 3 to 5 The same procedure as in Example 1 was carried out, except that the amount of water shown in Table 1 was added to the polymer upstream of the second-stage devolatilization tank. Table 1 shows the quality of the obtained products. Comparative Example 2 In Example 1, as the second-stage multitubular heat exchanger,
The procedure was carried out in the same manner as in Example 1 except that a tube having an inner diameter of 1 inch, a length of 1.5 m, and 13 tubes was used. Table 1 shows the quality of the obtained products. Example 6 Example 1 was performed in the same manner as in Example 1 except that the plate-fin type heat exchanger described in the specification was used instead of the first-stage multitubular heat exchanger. . Table 1 shows the quality of the obtained products.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, it is possible to reduce the size of a devolatilizer and to remove volatile substances in a polymer such as a styrene-based polymer obtained by solution polymerization or bulk polymerization in a very short time. It can be efficiently and industrially advantageously removed.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an outline of an example of a devolatilization tank having a plate-fin type heat exchanger that can be used as a first-stage devolatilization tank in the method of the present invention.

FIG. 2 is a side view of an example of a heat exchange device used in a first-stage devolatilization tank.

FIG. 3 is a plan view of the heat exchange device of FIG.

FIG. 4 is a bottom view of the heat exchange device of FIG.

FIG. 5 is an enlarged view of a portion A of the heat exchange device of FIG.

FIG. 6 is a sectional view taken along the line YY of FIG. 5;

FIG. 7 is a schematic diagram of an example of an apparatus for performing the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main body 2 Jacket 3 Heat exchanger 6 Plate fin type heat exchanger 9 Polymer supply chamber 10 Polymer inlet nozzle 12 Polymer outlet 15 Heat medium chamber 16 Vertical passage 17 Horizontal passage 21A First-stage devolatilization tank 21B Second-stage devolatilization tank 22A First-stage multitubular heat exchanger 22B Second-stage multitubular heat exchanger 25 Static mixer P Polymer H Heat medium h Heat medium Q Product polymer W low boiling point foaming substance

Claims (4)

[Claims] In removing a volatile substance in a polymer obtained by solution polymerization or bulk polymerization, the polymer is placed in a first-stage devolatilization tank having a plate-fin or multi-tube heat exchanger. After supplying and devolatilizing the volatile matter in the polymer so as to be 5000 ppm by weight or less, the inner diameter of the tube is 5 to 1%.
The polymer is supplied to a second-stage devolatilization tank having a 5 mm multitubular heat exchanger and devolatilized so that volatile substances in the polymer become 500 ppm by weight or less. Volatile substance removal method. 2. In the first-stage devolatilization tank, devolatilization is performed at a polymer temperature of 180 to 270 ° C. and a degree of vacuum of 30 to 150 torr. The method for removing volatile substances in a polymer according to claim 1, wherein the devolatilization is carried out under the conditions of -270 ° C and a degree of vacuum of 5 torr or less. 3. A low-boiling point foaming substance of 0.1 to 1% by weight is added to the polymer extracted from the first-stage devolatilization tank, mixed and dispersed, and then added to the second-stage. The method for removing volatile substances in a polymer according to claim 1, which is supplied to a devolatilizing tank. 4. The method according to claim 1, wherein the polymer is a styrenic polymer.