JPH05163302A - Production of polymer and polymerization device - Google Patents

Abstract

PURPOSE:To prevent scale deposition in polymerizing an ethylenic monomer in water while keeping the monomer in a polymerization vessel partly circulated through an external circulation line, by injecting water into the line at points where the reaction mixture resides. CONSTITUTION:A circulating pump 4 and a heat exchanger 2 are connected to a polymerization vessel 1 through a circulation line 3. An ethylenic monomer (e.g. vinyl chloride) is introduced into the vessel 1 along with an aqueous medium, a dispersant, a polymerization initiator, etc. The mixture is heated to initiate polymerization. The polymerization is then conducted while keeping the reaction mixture partly withdrawn through the bottom of the vessel 1 by means of the pump 4, cooled in the exchanger 2, and then returned to the vessel 1. During the polymerization, water is injected into the line 3 at points where the reaction mixture resides, through lines 7 and 8, etc. Thus, scale deposition within the line 3 is prevented and, hence, clogging of the line 3 is prevented and the amount of fish eyes contained in the polymer product is prevented from increasing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polymer by polymerizing a monomer having an ethylenic double bond, in which the reaction mixture is circulated in a heat exchanger installed separately from the polymerizer. And a polymerization apparatus.

[0002]

2. Description of the Related Art Conventionally, the polymerization of a monomer having an ethylenic double bond is carried out by using a polymerization medium such as water, a monomer having an ethylenic double bond, in a polymerization vessel equipped with a jacket and a reflux condenser. A method of controlling the reaction system to a constant temperature by charging a polymerization initiator, a dispersant, and other various additives as necessary, and circulating cooling water through a jacket and a reflux condenser during the reaction to remove heat of polymerization reaction. Has been carried out by.

In recent years, in order to improve productivity, a method of enlarging the polymerization vessel and shortening the polymerization time per batch have been adopted. However, since the ratio of the heat transfer area to the reaction mixture has decreased with the increase in size of the polymerization vessel, the conventional heat removal method described above lacks the ability to remove the heat of polymerization reaction. Further, when the polymerization time per batch is shortened, the heat generation rate due to the polymerization reaction per unit time increases, so that the heat removal capacity becomes further insufficient.

Therefore, measures have been taken, such as increasing the size of the reflux condenser to increase the amount of heat removed, or cooling the water flowing through the jacket of the polymerization vessel through a refrigerator to further cool it. However, the former method of increasing the size of the reflux condenser has the disadvantages that scale is attached to the inside of the polymerization vessel due to carryover due to foaming of the reaction mixture, the heat removal capacity is reduced, and fish eyes in the product increase. Accompany. In addition, this method has a restriction that it cannot be used as a heat removal means from the start of polymerization because the particle size of the polymer becomes coarse when used at a time when the polymerization rate is low. The latter method using a refrigerator is too costly and economically inefficient. Further, when producing a polymer having a high degree of polymerization, it is necessary to keep the polymerization temperature low,
In that case, it is necessary to further lower the temperature of the cooling water in order to increase the cooling capacity, but this is difficult, and thus the heat removal capacity cannot be improved even by using this method.

An alternative method to these methods has been proposed, in which the reaction mixture is circulated through a heat exchanger provided outside the polymerization vessel (Japanese Patent Laid-Open Nos. 54-24991 and 56-47410).
No. 58-32606 and JP-B No. 64-11642), this method is extremely efficient in that the ratio of the heat transfer area to the reaction mixture can be increased, and is used from the beginning of polymerization. It can be used for producing a polymer having a high degree of polymerization. However, according to this method, the block-shaped polymer which is presumed to be produced in the circulation line composed of the heat exchanger and the circulation pipe connecting the heat exchanger and the polymerization vessel, causes the tube of the heat exchanger to flow. There is a problem of blockage and increase of fish eyes in the product.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a polymerization vessel, a heat exchanger provided outside the polymerization vessel, and to exit the polymerization vessel and to pass through the heat exchanger to the polymerization vessel. In a polymerization apparatus equipped with a circulation line composed of a return circulation pipe, it is possible to prevent the generation of scale and block-like polymers in the circulation line and obtain a polymer with less fish eyes, an ethylenic double bond To provide a method for producing a polymer and a polymerization apparatus by polymerizing a monomer having

[0007]

Means for Solving the Problems The present inventors have solved the above problems as a result of intensive studies. The present invention, when polymerizing a monomer having an ethylenic double bond in an aqueous medium, the reaction mixture in the polymerization vessel, the polymerization vessel, a heat exchanger provided outside the polymerization vessel and the polymerization. In the method for producing a polymer by polymerizing a monomer having an ethylenic double bond, which has a step of circulating a circulation line composed of a circulation pipe returning from the vessel through the heat exchanger and returning to the polymerization vessel, Provided is a method for producing a polymer, which comprises injecting water into a reaction mixture retention site in the circulation line.
Further, the present invention comprises a polymerization vessel, a heat exchanger provided outside the polymerization vessel, and a circulation line composed of a circulation pipe that exits from the polymerization vessel and returns to the polymerization vessel via the heat exchanger. A polymerization apparatus provided with a means for injecting water into a reaction mixture retention location in the circulation line.

The studies conducted by the inventors of the present invention have confirmed that the scale-like and block-like polymers in the circulation line are generated especially at the residence points of the flow of the reaction mixture in the circulation line. The scale and block-like polymer generated at the retention point were peeled off and mixed into the reaction mixture, and as a result, the tube of the heat exchanger was blocked or the fish eye of the product was increased. As a countermeasure, it is possible to prevent the generation of scale and block-like polymer in the circulation line by injecting water by means for injecting water into the reaction mixture retention location in the circulation line, for example, by providing a water injection port. I found that I could do it.

Examples of the staying place in the circulation line include side wall recesses in the circulation line. For example, a water injection pipe is connected to the most recessed portion of the side wall recess to provide a water injection port, and water can be injected into the side wall recess to prevent retention.

As a typical example of the side wall recessed portion, a pipe of a line branched from the circulation pipe of the circulation line, for example, a pipe of a branch line such as a slurry recovery line, a drain line, a bypass line, etc., can be cited as a retention point. That is,
While the reaction mixture is being circulated, the valves such as the slurry recovery line, drain line, and bypass line are closed, so that the reaction mixture easily stays in the pipe from the circulation pipe to the valve (so-called dead space). .. To prevent stagnation by installing a water injection pipe in the pipe from the circulation pipe to the valve, preferably at a position as close to the valve as possible so long as it does not hinder the piping work of the pipe, and to inject water into the dead space. You can

The present invention will be described in detail below with reference to the drawings illustrating the polymerization apparatus of the present invention. FIG. 1 illustrates an overall schematic view of a polymerization apparatus according to the present invention.
The polymerization apparatus of the present invention comprises a polymerization vessel 1, a heat exchanger 2 for heating or cooling a reaction mixture, and a circulation pipe 3 for returning from the bottom of the polymerization vessel 1 to the polymerization vessel 1 via the heat exchanger 2. ..
Further, the polymerization apparatus of the present invention is equipped with the circulation pump 4 in the middle of the circulation pipe 3. In the polymerization apparatus of the present invention, an aqueous reaction mixture such as a monomer, an aqueous medium, a dispersant, and an oil-soluble polymerization initiator charged in the polymerization vessel 1 is extracted from the bottom of the polymerization vessel 1 by the circulation pump 4. After passing through the circulation pipe 3, it reaches the heat exchanger 2, where it is cooled or heated and then returned again to the gas phase part or the liquid phase part in the polymerization vessel 1 through the circulation pipe 3.

Further, the polymerization apparatus of the present invention is provided with a slurry recovery pipe 5 and a drain pipe 6, and water injection pipes 7 and 8 are provided in the respective pipes. FIG. 2 is an enlarged view of the portion of the slurry recovery pipe 5 in FIG. While the reaction mixture circulates in the circulation line (in the direction of arrow 11 in FIG. 2), the valve 9 of the slurry recovery pipe is closed, so the dead space 12 (hatching from the branch point with the circulation pipe to the valve 9). Although water is likely to accumulate in the portion (marked with a mark), the water injection pipe 7 is connected to the pipe 5 above the valve 9, and the water injection port 7a is opened in the dead space 12 at a position from the valve 9. By pouring water from the water injection port 7a in the direction of the arrow 13, it is possible to prevent the dead space 12 from staying. Similarly, FIG. 3 is an enlarged view of the drain pipe 6 portion of FIG. 1, and while the reaction mixture is circulating in the circulation line (in the direction of arrow 11 in FIG. 3), the valve 10 of the drain pipe is closed. Because there is circulation pipe to valve 10
Up to the dead space 14 (hatched portion) easily accumulates, but the water injection pipe 8 is connected to the drain pipe 6 in the same manner as the pipe 5, the water injection port 8a is provided, and from the water injection port, By injecting water in the direction of arrow 15, retention in dead space 14 can be prevented.

In the present invention, the amount of water to be injected into the reaction mixture retention site in the circulation line is, for example, preferably about 0.1 to 20 L / min, although it depends on the size of the pipe and the like.
It is preferably about 0.1 to 10 L / min. The water injection may be started at the same time as or before the start of circulation of the reaction mixture, and the injection is preferably ended after the polymerization is completed and the polymer slurry is withdrawn from the circulation line.

Polymerizer 1 in the polymer production apparatus of the present invention
As the above, a conventionally known type equipped with a stirrer, a reflux condenser, a baffle, a jacket or the like can be used. As the stirrer, stirrer blades such as paddles, foulers, bull margins, propellers and turbines are used, if necessary, in combination with flat plates, cylinders and baffles such as hairpin coils.

As the heat exchanger 2, a generally used one such as a multi-tube type, a coil type, a spiral type, or a thrombone cooler can be applied, and steam is used as a medium for heating and cooling the heat exchanger 2. Cooling water and brine are used.
Alternatively, the circulation pipe 3 itself may be a double pipe, and cooling water or brine may be passed through the gap on the outside thereof to increase the efficiency of heat removal. From the point of heat transfer and corrosion resistance, the heat exchanger 2, the circulation pipe 3, the circulation pump 4, and other parts where the reaction mixture comes into contact are 18-8 austenite type, 13 chromium ferrite type, martensite type, 18 chromium ferrite type. ,
It is preferable to use stainless steel such as high-chromium ferrite-based or two-phase austenite-ferrite-based stainless steel. In addition, a conventionally known scale inhibitor may be applied to these places or may be added to the aqueous suspension mixture.

The circulation pump 4 is preferably of a low shear type, and is preferably a pump having a structure in which a conical hub is provided with an impeller composed of a single blade. Examples of the pump having such a structure include those commercially available under the trade name of Hydrostal Pump (manufactured by Taiheiyo Metal Co., Ltd.).

Examples of the monomer having an ethylenic double bond to be polymerized by the polymerization apparatus of the present invention include vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid and methacrylic acid. Examples thereof include acids and esters or salts thereof; maleic acid, fumaric acid, and esters or anhydrides thereof; diene-based monomers such as butadiene, chloroprene and isoprene; styrene, acrylonitrile, vinylidene halides, vinyl ethers and the like. The polymerization apparatus of the present invention is particularly suitable for producing a vinyl chloride polymer such as vinyl chloride among the above monomers. The vinyl chloride polymer includes, in addition to vinyl chloride homopolymer, a copolymer of vinyl chloride and another vinyl monomer (usually 50% by weight or more of vinyl chloride). As the comonomer copolymerized with vinyl chloride, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1
Α-olefins such as decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene; acrylic acid such as acrylic acid, methyl acrylate and ethyl acrylate, or esters thereof; methacrylic acid, methyl methacrylate, methacryl Methacrylic acid or its ester such as ethyl acid acid; Maleic acid or its ester; Vinyl ester such as vinyl acetate and vinyl propionate; Vinyl ether such as lauryl vinyl ether and isobutyl vinyl ether; Maleic anhydride; Acrylonitrile; Styrene; Vinylidene chloride; Other vinyl chloride And the like, which may be used alone or in combination of two or more.

The polymerization method using the polymerization apparatus of the present invention is suitable for polymerization in an aqueous medium such as suspension polymerization and emulsion polymerization. Hereinafter, taking as an example the case of suspension polymerization and emulsion polymerization,
A general polymerization method will be specifically described.

First, water and a dispersant are charged into a polymerization vessel, and then a polymerization initiator is charged. Next, exhaust the inside of the polymerization vessel.
After reducing the pressure to 0.1 to 760 mmHg, the monomers are charged (at this time, the internal pressure of the polymerization vessel is usually 0.5 to 30 kgf / cm ² · G), and then polymerization is carried out at a reaction temperature of 30 to 150 ° C. During the polymerization, one or more of water, a dispersant, and a polymerization-facilitating agent are added as needed. The reaction temperature during polymerization is
Depending on the type of monomer to be polymerized, for example, in the case of vinyl chloride polymerization, the polymerization is performed at 30 to 80 ° C, and in the case of styrene polymerization, the polymerization is performed at 50 to 150 ° C. In polymerization, when the internal pressure of the polymerization vessel dropped to 0 to 7 kgf / cm ² · G, or there was almost no difference between the inlet temperature and the outlet temperature of the cooling water flowing in and out of the jacket equipped on the outer periphery of the polymerization vessel. When (that is, when the heat generated by the polymerization reaction disappears)
It is judged that it is completed. Water charged during polymerization,
The dispersant and the polymerization initiator are usually 20 to 500 parts by weight of water, 0.01 to 30 parts by weight of the dispersant, and 0.01 to 5 parts by weight of the polymerization initiator with respect to 100 parts by weight of the monomer.

Other conditions adopted in this polymerization, for example, a method of charging an aqueous medium, a monomer, a polymerization initiator or a dispersion aid, and a charging ratio to the polymerization vessel may be the same as in the conventional case. Further, in this polymerization system, if necessary,
Polymerization regulators, chain transfer agents, pH regulators, gelation improvers, antistatic agents, cross-linking agents, stabilizers, fillers, antioxidants, buffers and scale inhibitors, which are appropriately used for vinyl chloride-based polymerization. Etc. is also optional.

[0021]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Example 1 A stainless steel jacketed polymerization vessel having an internal volume of 2.1 m ³ , a shell-and-tube type multi-tube heat exchanger having a heat transfer area of 5.0 m ² , and a circulation pump of 5 m ³ / Hr × 2 m hydro. A stall pump (with a variable flow rate device by an inverter) was connected through piping, valves, etc., as shown in FIGS. 840k deionized water in the polymerization vessel
g, 240 g of partially saponified polyvinyl alcohol and 160 g of cellulose ether were added as an aqueous solution. 50 inside
After degassing to mmHg, 670 kg of vinyl chloride monomer was charged, and while stirring, 2010 g of di-2-ethylhexyl peroxydicarbonate was further press-fitted with a pump.
After that, hot water was passed through the jacket of the polymerization vessel to raise the temperature.
After starting the polymerization reaction, cooling water was passed through the jacket, and after 30 minutes, circulation to the outside was started, and at the same time, cooling water at 30 ° C. was supplied to the heat exchanger at a rate of 10 m ³ / hr. 7a, 8a
Then, the injection of water was started at a flow rate of 0.5 L / min. Polymerization was continued while maintaining the inner temperature of the polymerization vessel at 55 ° C. The internal pressure of the polymerization vessel is 6.5 kg
Unreacted monomer was recovered at the time when it fell to / cm ² G, and the vinyl chloride polymer produced was taken out of the reactor in slurry form,
After the injection of water was completed, the vinyl chloride polymer slurry was dehydrated and dried. The total amount of water injected was 120 liters. The bulk specific gravity, particle size distribution, plasticizer absorption amount and fish eye of the obtained vinyl chloride polymer were measured by the following methods. The results are shown in Table 1.

(1) Bulk Specific Gravity: Measured according to JIS K-6721. (2) Particle size distribution: ^# 60, ^# 80, ^# 100 according to JIS Z-8801
, ^# 150, ^# 200 sieves were used for sieving, and the passing amount (% by weight) was measured. (3) Absorption amount of plasticizer: Glass fiber is packed in the bottom of an aluminum alloy container having an inner diameter of 25 mm and a depth of 85 mm, and 10 g of a vinyl chloride polymer sample is put into the container. To this, 15 cc of dioctyl phthalate (hereinafter referred to as DOP) is added and left for 30 minutes to allow the DOP to sufficiently permeate the polymer. Then 1500G
Excess DOP was centrifuged under the acceleration of 10 g, and the amount of DOP absorbed in 10 g of the polymer was measured and converted per 100 g of the polymer. (4) Fish eye: prescription of 100 parts by weight of vinyl chloride polymer, 50 parts by weight of dioctyl phthalate, 0.5 part by weight of tribasic lead sulfate, 1.5 parts by weight of lead stearate, 0.1 part by weight of titanium oxide and 0.05 part by weight of carbon black. 25 g of the mixture prepared in (1) was kneaded with a 6-inch roll for kneading at 140 ° C. for 5 minutes to prepare a sheet having a width of 15 cm and a thickness of 0.2 mm. The number of transparent particles per 100 cm ^{2 of the} obtained sheet was counted and used as the number of fish eyes. In addition, Table 1 shows the results of examining the state of scale adhesion in the circulation line after completion of the polymerization.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that water was not injected. The results are shown in Table 1.

[0024]

[Table 1]

[0025]

According to the present invention, it is possible to prevent the generation of scale or block polymer in the circulation line.
Therefore, it is possible to prevent clogging of the circulation line and increase of fish eyes in the product, so that the polymer can be efficiently produced with high productivity.

[Brief description of drawings]

FIG. 1 is a view exemplifying a schematic view of an entire polymerization apparatus of the present invention.

FIG. 2 is an enlarged view of a portion of a slurry recovery pipe 5 shown in FIG.

FIG. 3 is an enlarged view of a drain pipe 6 portion of FIG.

[Explanation of symbols]

 1 Polymerizer 2 Heat exchanger 3 Circulation pipe 5 Slurry recovery pipe 6 Drain pipe 7 Water injection pipe 8 Water injection pipe

Claims (2)

[Claims] 1. When polymerizing a monomer having an ethylenic double bond in an aqueous medium, the reaction mixture in the polymerization vessel is
Ethylene having a step of circulating a polymerization vessel, a heat exchanger provided outside the polymerization vessel, and a circulation line composed of a circulation pipe that exits from the polymerization vessel and returns to the polymerization vessel via the heat exchanger A method for producing a polymer by polymerizing a monomer having a polymerizable double bond, comprising injecting water into a reaction mixture retention site in the circulation line. 2. A polymerization vessel, and a circulation line constituted by a heat exchanger provided outside the polymerization vessel and a circulation pipe that exits from the polymerization vessel and returns to the polymerization vessel via the heat exchanger. The polymerization apparatus is provided with a means for injecting water into the reaction mixture retention location in the circulation line.