JPH0912612A - Production of vinyl chloride polymer - Google Patents

Abstract

PURPOSE: To perform the polymerization by using a polymerization tank composed of a polymerization vessel, a clearance room and a cylindrical temperature-controlling element formed in the vessel and a device through which the vessel communicates with the room and introducing an inert gas into the polymerization system in performing the aqueous polymerization of vinyl chloride. CONSTITUTION: A polymerization vessel for (co)polymerizing vinyl chloride in an aqueous medium is used. A temperature-controlling element 5 having a heating medium passage 9 divided by spaced partitions 7 is formed in the space between a double-cylinder formed by inner and outer strips 6 and 8 in the body 1 of the vessel. The top and bottom of the clearance between the element 5 and the body 1 are sealed to form a clearance room 14. The room 14 is allowed to communicate with the vessel through e.g. a communicating pipe. This production process comprises feeding a liquid (e.g. water) into the room 14, feeding an aqueous medium and vinyl chloride, introducing an inert gas into the polymerization system and starting the polymerization. According to this process, the deposition of scales on the wall around the vapor phase, the communication vessel, etc., can be reduced.

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 vinyl chloride polymer, and in particular to a high quality vinyl chloride polymer,
The present invention relates to a method for producing a vinyl chloride polymer that can be produced with high productivity.

[0002]

2. Description of the Related Art Generally, a tank container used for a polymerization reaction of vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers (hereinafter collectively referred to as "vinyl chloride-based monomer") is a container. The main body 1'is formed of a pressure-tight closed container in which dish-shaped end plates are welded to both ends of a cylindrical body, and a jacket 22 for removing heat generation or heating contents is attached to the outside of the main body of the container. A type of tank container (FIG. 4) is used.

[0003] In this type of tank container, since the container body maintains pressure resistance, the plate thickness of the container is generally large, the coefficient of heat transfer through the wall of the container body is low, and a vinyl chloride-based unit quantity which is an exothermic reaction. In the body polymerization, it was difficult to obtain high productivity. Further, in the case of enlarging the tank container, it is necessary to increase the plate thickness of the wall of the container main body from the viewpoint of strength, and there is a disadvantage that the heat transfer coefficient is further lowered.

Therefore, in order to solve this inconvenience in heat conduction, as shown in FIG. 5, partition plates 23 are arranged in parallel at a right angle to the inner surface of the container body 1 ', and between the tips of the partition plates. An inner jacket type vessel container has been proposed in which a spiral flow path 25 partitioned by a partition plate is formed between the inner strip and the inner surface of the container body by straddling the inner strip 24. JP-A-57-147502).
In the tank container of this method, the pressure resistance strength can be increased by making the interval between the partition plates smaller than the inner diameter of the container body, the wall thickness of the inner strip can be reduced, and the heat transfer coefficient can be increased.

However, while the inner jacket type tank container is excellent in thermal conductivity, a large number of welds are present between the inner strips on the inner surface of the tank container where the contents come into contact during the polymerization reaction of the vinyl chloride monomer. There is a disadvantage due to being exposed to. That is, the weld has a rough surface roughness on its construction, and there are welding defects, but in the polymerization reaction of the vinyl chloride-based monomer, the contacting portion of the reaction mixture (hereinafter,
If the surface roughness of the "wetted part" is rough, polymer scale is likely to be produced and adhered, and if the produced scale peels and enters the product, the quality will deteriorate (especially when processed into a film etc.). , Causes so-called fish eyes (FE) in which unmelted material remains in the film. In addition, when trying to prevent the adhesion of polymer scale that causes quality deterioration, it is necessary to extremely smooth the numerous welding lines and to introduce special adhesion prevention / removal technology.
There is an inconvenience that the maintenance cost becomes large.

Further, in the polymerization reaction of vinyl chloride-based monomer, stainless steel is usually used as the material of the inner surface of the tank because of the corrosiveness caused by hydrogen chloride generated as the reaction proceeds. Indicates that residual stress due to welding is concentrated, and when a vinyl chloride monomer polymerization reaction is performed using an internal jacket type tank container in which many welding lines are adjacent to the inner surface of the container, the reaction progresses. There is a concern of stress corrosion cracking due to the accompanying hydrogen chloride (chlorine ion). Therefore, it is necessary to carefully and continuously inspect the degree of deterioration of the welding line, and maintenance is complicated and inspection costs increase.

In order to solve the inconvenience while taking advantage of the advantage of the inner jacket type tank container, the inventors of the present invention have previously proposed, as a method for producing a vinyl chloride polymer in an aqueous medium, which does not have such a problem. Partition plates are arranged side by side at a right angle to the outer surface of the inner cylinder, and an outer strip is laid between the front ends of the partition plates so that the inner cylinder and the outer strip are partitioned by the partition plate. A flow path wall (hereinafter referred to as "temperature control element") having a flow path for a heat medium is formed, and the temperature control element is fixed in the container body with an outer strip side facing the inner surface of the container body with a space therebetween. In addition, in a tank container having a structure in which the upper and lower parts of the gap between the outer strip side of the temperature control element and the inner surface of the container body are sealed to form a gap chamber (hereinafter referred to as "temperature control element type tank container") And the internal pressure of the gap chamber While the difference between the internal pressure of the enclosed by the inner cylinder of the inner surface and the temperature control element of the container body space (hereinafter referred to as "main body chamber") kept small by communicating pipe or the like has proposed a method of performing polymerization.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to manufacture a vinyl chloride polymer in a temperature control element type vessel container while keeping the difference between the internal pressure in the gap chamber and the internal pressure in the main chamber small. Another object of the present invention is to provide a manufacturing method capable of preventing the generation and growth of scale in the gas phase part, the communication pipe, etc., and stably performing polymerization with high quality and high productivity.

[0009]

That is, the gist of the present invention is as follows.
Suspension polymerization of vinyl chloride or a mixture of copolymerizable monomers mainly composed of vinyl chloride in an aqueous medium is performed by arranging partition plates side by side at right angles to the outer surface of the inner cylinder. By straddling an outer strip between the tips, a flow passage wall (temperature control element) having a flow passage for a heat medium partitioned by a partition plate is formed between the inner cylinder and the outer strip,
The temperature control element is fixed in the container body with the outer strip side facing the inner surface of the container body at a distance, and the upper and lower portions of the gap between the outer strip side of the temperature control element and the inner surface of the container body are fixed. It has a structure in which a gap chamber is formed by sealing with a partition wall, and a space (main body chamber) surrounded by the inner surface of the container body and the inner cylinder of the temperature control element and the gap chamber are connected by a communication pipe or a pressure equalizer. When the liquid is charged into the interstitial chamber, the aqueous medium and chloride are added when the liquid is charged into the interstitial chamber (hereinafter collectively referred to as “pressure equalizing pipe”) or in a tank container connected by a communication port provided in the partition above the temperature control element. A method for producing a vinyl chloride polymer, which comprises charging a vinyl monomer and introducing an inert gas into the polymerization system in advance to start the polymerization.

Hereinafter, the present invention will be described in detail. <Tank Container> Tank container main body The temperature control element type tank container used in the method of the present invention has the following structure. That is, as shown in FIG. 2, partition plates 7 are arranged side by side at a right angle on the outer surface of the inner cylinder 6,
By straddling the outer strip 8 between the ends of the partition plate, the temperature control element 5 having the flow path 9 for the heat medium partitioned by the partition plate is formed between the inner cylinder and the outer strip.

The plate thickness of the inner cylinder depends on the required strength and the space between the partition plates. However, since the space between the partition plates is smaller than the body length of the container body, the plate thickness of the inner cylinder should be reduced. Therefore, a high heat transfer coefficient can be obtained. As described above, as the material of the inner cylinder, in consideration of the corrosion resistance of the liquid contact part, a stainless steel material (pure stainless steel material, stainless steel / carbon steel clad material or the like, particularly SUS316L is preferable) or a glass lining material is used. The material is not particularly limited as long as it is a material resistant to stress corrosion cracking due to chlorine ions.

From the viewpoint of preventing scale adhesion, the surface of the inner cylinder is preferably smooth, but as a method for smoothing the surface, methods such as buffing and electropolishing which are usually carried out industrially are used. It is possible and is not particularly limited. The surface roughness is usually 10 μm at the maximum height Ry.
m or less, preferably 3 μm or less, more preferably 1 μm
The following is good. The method defined in JIS B 0601 may be used for the measurement of Ry. Also, the application of commonly used anti-adhesion agents is not limited in the practice of the method of the present invention.

Since the welded portion occupies the inner wall surface of the main body chamber side of the tank container manufactured as described above in a remarkably smaller amount than that of the internal jacket type tank container, the adhesion and formation of polymer scale is small and the product obtained is The quality is also good,
Since there is little concern about stress corrosion cracking, the degree of maintenance / inspection (so-called maintenance) may be the same as that of a normal outer jacket type tank container.

The outer diameter of the temperature control element is made smaller than the inner diameter of the tank container, and the outer strip side of the temperature control element is fixed to the inner surface of the container body 1 with a space therebetween as shown in FIGS. To do. It is preferable to fix the temperature control element so that the center line of the temperature control element and the center line of the container substantially coincide with each other. , A gap corresponding to the difference in diameter between the two is formed, and this becomes substantially uniform in the circumferential direction.

The lower end of the temperature control element may be directly sealed to the bottom end plate 3 around the tank container nozzle 12 by continuous welding as shown in FIG. 1, or may be sealed via a partition wall. Good. On the other hand, as for the upper end of the temperature control element, the partition wall 13 is usually attached to the cylindrical body 2 or the top end plate 4 of the container to seal it. In this way, a gap chamber is formed between the outer surface of the temperature control element fixed inside the container body and the inner surface of the container body. This can prevent the reaction mixture from penetrating into the above-mentioned gap and the scale from adhering and growing.

It is preferable that the partition wall or the like for sealing the upper part and / or the lower part of the gap is provided with an expansion / contraction absorbing part capable of absorbing expansion / contraction of the temperature control element due to heat. It is necessary to have a strength that can withstand the temperature and pressure normally used during the polymerization of the system monomer. Further, in order to prevent the temperature control element and the welding for sealing the upper and lower portions of the gap between the temperature control element and the container body and the partition wall from being destroyed by reaction pressure or the like, the inner surface of the container body (usually,
For safety, it is preferable to minimize the difference between the internal pressure of the space (main body chamber) surrounded by the top end plate and bottom end plate) and the inner cylinder of the temperature control element and the internal pressure of the gap chamber. The pressure resistance of the partition walls is not necessary.

In the method of the present invention, as a method for reducing the difference between the internal pressure of the main body chamber and the internal pressure of the interstitial chamber, the main chamber and the interstitial chamber are connected to each other by, for example, a communicating pipe 15 as shown in FIG. A method of connecting with a pipe via a pressure equalizer 20 as shown in, or a method of providing a communication port in a partition wall that separates the main body chamber and the gap chamber is used.

The pressure equalizer which can be used in the method of the present invention is, for example, a balance piston type such as an air cylinder type or a cylinder type for pressurizing the sealing liquid of a mechanical seal, and a diaphragm type such as a diaphragm type or a bellows type. And the like. These pressure equalizers have a structure such that the pressure difference between the two sides of the pressure equalizer can be kept below a predetermined pressure, for example, 3 Kg / cm ² or less, by means of a sliding piston or a pressure resistant film such as a diaphragm or bellows. Has become. The material of the pressure equalizer is preferably made of stainless steel, but a material having strength and corrosion resistance that can withstand the pressure change during the polymerization reaction of the vinyl chloride-based monomer may be used.

If liquid is sealed in the gap chamber side portion of the pressure equalizer, the gap chamber, and the pipe portion connecting both of them, the displacement amount of the movable portion of the pressure equalizer can be made small, and therefore the pressure equalizer can be reduced. Also, a small scale is sufficient, which is preferable. As a liquid to be sealed, considering mixing with the contents inside the main body due to a leak or the like, water or vinyl chloride monomer, or a polymerization inhibitor such as a radical scavenger added to these It is preferable to use, but it is not particularly limited.

For the above-mentioned reason, the temperature control element type tank container used in the method of the present invention has a pressure equalizing pipe or a communication port (hereinafter collectively referred to as "communicating port" for reducing the difference between the internal pressure of the main chamber and the internal pressure of the gap chamber). It is important to connect the two via a pressure equalizing pipe, etc.) to ensure stable production.
In the case of the polymerization reaction of vinyl chloride-based monomer, the reaction mixture containing the vinyl chloride-based monomer enters the inside of the pressure equalizing pipe, etc., and polymerizes there, or the polymer or the above reaction mixture is scattered by foaming or the like. However, it may adhere to the periphery of the pressure-equalizing pipe or the like or the inner wall, and the scale may gradually grow, eventually leading to the blockage of these, and the pressure difference between the two may not be maintained within a predetermined pressure range. is there.

In the method of the present invention, as described in detail in the section of the charging method, liquid is charged in advance in the gap chamber (including the pipe on the main chamber side of the pressure equalizer when the pressure equalizer is used (hereinafter the same)). By introducing an inert gas into the polymerization system at the time of polymerization, the partial pressure of the vinyl chloride monomer near the gas phase part of the tank container including the pressure equalizing pipe etc., especially the pipe connected to the top end plate and the communication port should be kept low. Therefore, the scale is prevented from adhering to the pressure equalizing pipe or the like.

The flow path of the heat medium in the temperature control element may be a single spiral as shown in FIG. 1 or may be divided into a plurality of spiral or meandering flow paths. Well, it is not particularly limited. As the heat medium flowing in the flow path, steam, hot water or the like is used for heating, normal temperature water such as industrial water for cooling, water cooled separately by a refrigerator or the like, refrigerant such as ethylene glycol, CFC Low temperature boiling point refrigerants such as

Equipment attached to tank container The type and material of the reflux condenser that can be used in the method of the present invention are not particularly limited, and a multi-tube heat exchanger or the like having stainless steel as the material of the liquid contact portion, A reflux condenser generally used for polymerization of vinyl chloride-based monomers may be used. The heat transfer area may be determined according to the required quality of the product type, the degree of heat removal load, and the load control method. The load control method may be a generally used method, such as a method of controlling by the amount of cooling water supplied to the reflux condenser or the temperature of the cooling water.

This reflux condenser is installed in the gas phase part of the tank container, but it is usually installed vertically on the top end plate of the tank container body through a connecting pipe to prevent the accumulation and sticking of scattered polymer. It is suitable for prevention. The shapes of the stirring blades, baffles, etc., which are the auxiliary equipment of other tank containers, are not particularly limited, and the equipment / equipment generally used in the conventional suspension polymerization method can be used. For example, the stirring blades include turbine blades, fan turbine blades, multi-stage turbine blades, Fowler blades, blue margin blades, full zone blades, Maxblend blades, and the like, and the baffle shape includes a plate shape, a rod shape, a D shape, Examples thereof include loop type and finger type.

<Preparation Method> When carrying out the method of the present invention, the tank medium may be charged with the aqueous medium, the vinyl chloride monomer, the polymerization initiator, the dispersant, etc., for example, as follows. it can. In the polymerization reaction of vinyl chloride-based monomers, it is generally necessary to adjust the oxygen concentration in the tank container in order to improve the thermal stability of the product polymer and the particle size distribution. For example, when the polymerization is carried out after the tank container is opened to the atmosphere, the vacuum concentration operation and the introduction of nitrogen gas are performed after the tank container is closed, and the oxygen concentration in the tank container is repeated by repeating these operations as necessary. To a concentration that achieves the desired product quality. By repeating the polymerization without opening the tank container to the atmosphere, if the oxygen concentration in the tank container is kept within the preferred concentration range,
Although it is not necessary to perform operations such as suction and decompression in the tank container as described above, if it is necessary to adjust the oxygen concentration to a high level in terms of product quality, oxygen may be charged into the tank container. It is preferable to dilute the mixture with a solvent such as a mixture. When the concentration of dissolved oxygen in the aqueous medium is high, it may be necessary to reduce the oxygen concentration during the charging or after the charging by performing a decompression operation.

The oxygen concentration in the tank container depends on the target product quality, the type of the polymerization aid used, the operating conditions, etc., but it also includes the oxygen dissolved in the liquid supplied during the polymerization, and the charged vinyl chloride. Generally 100 wt% based on the total amount of monomers
-ppm or less, preferably 70 wt-ppm or less. In the method of the present invention, a liquid is charged in the interstitial chamber prior to charging water, a vinyl chloride-based monomer or the like into the tank container. As a result, the body of the temperature control element or the sealing portion is damaged by the pressure (weight) of the aqueous medium, or the vinyl chloride-based monomer enters the gap chamber through the communication pipe or the communication port,
It is possible to reduce the possibility of causing scale adhesion and the like.

As a liquid used for this purpose, a communication pipe or a communication port is used for ensuring a uniform pressure, and when the liquid is supplied into the main body chamber during the polymerization reaction as described later, the same liquid as this supply liquid is used. Is preferred. When the pressure equalizer is used, it is as described above. The procedure for charging the aqueous medium, the vinyl chloride-based monomer, the dispersant, the polymerization initiator, and the like into the main body chamber and the stirring start time may be in accordance with a conventional method, and are not particularly limited, but vinyl chloride It is preferable that the charging start time of the system monomer is after the vinyl chloride monomer has been charged with an amount of the aqueous medium that can be dispersed in the aqueous medium by the stirring action and the stabilizing action of the dispersant.

These procedures and conditions may be adjusted according to the shape of the stirring blade, the stirring power, the type and amount of the dispersant used. In addition, the charging ratio and charging method of other various polymerization aids are not particularly limited. In the method of the present invention, as described above, after previously introducing an inert gas into the polymerization system,
The polymerization system is heated to a predetermined temperature to start the polymerization. As a result, the partial pressure of the vinyl chloride monomer in the vicinity of the pipe connected to the top end plate including the pressure equalizing pipe and in the vapor phase of the tank container can be kept low, and the adhesion to the pipe and the vicinity of the communication port can be prevented. be able to.

As the inert gas to be used, a non-condensable gas is used. For example, a gas having a lower molecular weight (atomic weight) and a lower boiling point than a vinyl chloride monomer, such as nitrogen, helium, neon, or argon, is used in the tank. It is suitable for the purpose of the present invention because it easily collects in the gas phase portion of the container, particularly in the upper portion thereof. Of these, nitrogen gas is preferable because it is industrially easily available and inexpensive.

The inert gas may be introduced into the polymerization system before the start of the polymerization, but in consideration of reducing the mixing with the vinyl chloride-based monomer vapor in the tank container, the chloride It is preferable to start the charging of the vinyl-based monomer at the same time as the start or as soon as possible after the start. The amount of the inert gas introduced is preferably not more than the volume of the gas phase portion formed in the polymerization system after the completion of charging the polymerization raw materials at the maximum temperature during the polymerization.

The part for introducing the inert gas is preferably on the upper side of the gas phase part of the main body chamber, but it is carried out through a pipe connected to the top end plate or auxiliary equipment such as a reflux condenser or a pressure equalizer. It is preferable in order to effectively prevent the adhesion to the accessory device. In order to prevent clogging of the reflux condenser, pressure equalizing pipe and the like, it is preferable to introduce an inert gas from the top of the reflux condenser into the polymerization system through the pressure equalizing pipe.

Further, as a method of keeping the partial pressure of the inert gas high, a method of cooling the top end plate and the piping and condensing the vapor of the vinyl chloride monomer can be additionally adopted. Examples of the cooling method include an external cooling method using a shower or a double pipe. In the method of the present invention, in order to prevent the entry of the vinyl chloride monomer into the pressure equalizing pipe and / or the gap chamber, the liquid may be supplied to the main chamber through the pressure equalizing pipe during the polymerization reaction period. Good. The liquid to be supplied is preferably of the same quality as water used in the polymerization reaction such as deionized water, but is not particularly limited as long as it does not adversely affect the quality of the vinyl chloride polymer.

The inlet 16 for the liquid to be supplied may be anywhere as long as it is on the gap chamber side from the position where the pressure equalizing pipe opens to the tank container side, and may be provided in the gap chamber as shown in FIG. It may be provided inside the main body chamber or on the pressure equalizing pipe. The supply amount of the liquid is not particularly limited as long as it does not adversely affect the polymerization reaction and the quality, and there is no adverse effect due to overfilling, etc., including the amount of the liquid supplied from other parts to the main chamber,
It is preferable that the total amount of the supplied liquid does not exceed the volume contraction amount due to the polymerization of the vinyl chloride-based monomer.
It is preferable to supply the liquid continuously or intermittently at least during the polymerization reaction period.

<Polymerization prescription> The vinyl chloride-based polymer referred to in the present invention is a polymer containing vinyl chloride as a main constituent unit, which is obtained by polymerizing a vinyl chloride-based monomer in an aqueous medium. Say. Further, the polymerization reaction period as referred to in the present invention, after the reaction system reaches a predetermined polymerization temperature, the internal pressure of the tank container is reduced by a predetermined pressure from the saturated pressure of the vinyl chloride monomer at the temperature of the reaction system, It refers to the time until the collection of unreacted monomers begins. Suspension polymerization of vinyl chloride monomer
Usually, it is carried out by polymerizing a vinyl chloride-based monomer in an aqueous medium containing a dispersant in the presence of an oil-soluble polymerization initiator.

Monomer The vinyl chloride-based monomer used in the method of the present invention includes vinyl chloride monomer alone and a mixture of copolymerizable monomers mainly composed of vinyl chloride monomer. As the other monomer copolymerizable with the vinyl chloride monomer, those generally used in the related art can be used and are not particularly limited. Examples of the above-mentioned other monomers include vinyl acetates such as vinyl acetate, vinyl propionate and vinyl stearate, alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether, lauryl vinyl ether and cetyl vinyl ether, ethylene and the like. Α-olefins, acrylic acid,
Mono-unsaturated acids such as methacrylic acid, alkyl esters of these mono-unsaturated acids such as methyl ester and ethyl ester, di-unsaturated acids such as maleic acid, fumaric acid, itaconic acid, etc. One or a mixture of two or more of alkyl esters such as methyl ester and ethyl ester of saturated acid, vinylidene compound such as vinylidene chloride, unsaturated nitrile such as acrylonitrile and the like can be mentioned. These other monomers are usually 3
It is used in an amount of 0% by weight or less, preferably 20% by weight or less, but there is no particular limitation.

Dispersant The dispersant that can be used in the method of the present invention is not particularly limited, and may be one that is conventionally generally used in the suspension polymerization method of vinyl chloride type monomers. Examples of the dispersant include partially saponified polyvinyl acetate (so-called polyvinyl alcohol), cellulose derivatives such as hydroxypropylmethylcellulose, and water-soluble polymers such as gelatin. In addition, anionic surfactants such as sodium lauryl sulfate and nonionic surfactants such as sorbitan fatty acid esters and glycerin fatty acid esters may be used as the dispersing aid. These dispersants or dispersing agents can be used alone or in combination of two or more. The amount of these dispersants used is not particularly limited, and its type, stirring strength, polymerization temperature,
Depending on the type and composition of other monomers to be copolymerized with the vinyl chloride monomer and the particle size of the intended vinyl chloride polymer, etc. 0.001-2% by weight, preferably 0.03-1
Used in the range of wt%.

Polymerization Initiator The polymerization initiator that can be used in the method of the present invention is not particularly limited and may be one that has been generally used conventionally in each polymerization method of vinyl chloride type monomers. Perester compounds such as t-butylperoxypivalate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, t-hexylperoxyneodecanoate, α-cumylperoxyneodecanoate, dilauroyl Diacyl or dialkyl peroxide compounds such as peroxides, percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, azo compounds such as azobis (2,4-dimethylvaleronitrile), azobisisobutyronitrile, etc. Is mentioned. These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used varies depending on the type of the polymerization initiator, the polymerization temperature, the desired reaction time, etc., but is generally in the range of 0.01 to 1% by weight based on the total amount of the vinyl chloride-based monomer.

Other auxiliaries Further, in the method of the present invention, if necessary, a polymerization degree adjusting agent (chain transfer agent, cross-linking agent), antioxidant, pH used for the polymerization of vinyl chloride-based monomers. Various polymerization aids such as regulators may be added as appropriate, and the amounts of these components charged may be the general conditions conventionally used for the polymerization of vinyl chloride-based monomers.

As the degree-of-polymerization regulator used for the polymerization of vinyl chloride type monomers, trichlorethylene, carbon tetrachloride, chain transfer agents such as 2-mercaptoethanol and octyl mercaptan, diallyl phthalate and triallyl isocyanurate. Examples thereof include cross-linking agents such as ethylene glycol diacrylate and trimethylolpropane trimethacrylate.

<Polymerization Method> Polymerization Initiation Method To initiate the polymerization, a heat medium for heating is circulated through the heat medium flow path of the temperature control element to raise the temperature of the polymerization system to a predetermined reaction temperature to radicalize the polymerization initiator. It is done by decomposing it physically. Examples of the heating medium used for heating at this time include so-called heating mediums such as hot water, steam, and hydrocarbon oil. In the method of the present invention in which the liquid is preliminarily charged in the void chamber, the liquid in the void chamber is also included. Since they are heated at the same time, it is preferable to use a heating medium of a relatively low temperature in order to prevent boiling of the liquid. For example, when the liquid in the interstitial chamber is water, it is preferable to use hot water as the heat medium or steam having a saturated vapor pressure equal to or lower than the vapor pressure of the vinyl chloride monomer at the reaction temperature.

Polymerization temperature : The polymerization temperature employed in the method of the present invention includes the type of polymerization initiator used, the polymerization method, the presence / absence of a polymerization degree modifier,
Generally, it varies from 0 to, although it varies depending on the target degree of polymerization and the like.
90 ° C., especially 40 to 70 ° C. is often used.
Further, in the reaction, even if the polymerization is carried out at a constant temperature,
Alternatively, the polymerization temperature may be changed during the polymerization.

Polymerization Termination Method In the method of the present invention, examples of the method for terminating the polymerization reaction include a method of adding a so-called polymerization inhibitor or a polymerization terminator, a method of recovering unreacted monomers from a vessel container, and the like. .

<Post-Treatment Method> The operations of dehydrating and drying the slurry of the vinyl chloride polymer produced by the suspension polymerization method are generally performed such as centrifugal dehydration and fluidized drying.
Drying means may be used and is not particularly limited.

[0044]

EXAMPLES Next, specific embodiments of the method of the present invention will be described with reference to Examples, but the present invention is not limited as long as the gist thereof is not exceeded.
It is not limited by the following examples. <Example> An internal volume of 400 liters was provided with a stirrer, and the inner wall of the tank container (that is, the surface of the inner cylinder of the temperature control element) was electrolytically polished to about Ry 1.2 μm, and was divided into a gap chamber and a main chamber. As shown in Fig. 1, a stainless steel temperature control element type tank container is equipped with a communication pipe and a liquid inlet, so that liquid can be supplied into the main body chamber, and a pipe for introducing an inert gas is provided in the communication pipe. It was

After closing the tank container, the gap chamber was filled with deionized water while performing vacuum decompression operation, and then charging of 150 kg of deionized water into the main body chamber was started. 60 g of partially saponified polyvinyl acetate was charged as a dispersant, and after the charging of deionized water was completed, the vacuum suction operation was stopped, and charging of 100 kg of vinyl chloride monomer was started. At the same time, 70 liters of nitrogen as an inert gas was introduced into the polymerization system from a pipe 17 provided in the communication pipe and a valve 18.
After charging 40 g of dioctyl peroxydicarbonate as a polymerization initiator, 3 kg / cm ² was added to the temperature control element.
(Gauge pressure) water vapor was circulated to raise the temperature inside the main body chamber to 57 ° C. to start polymerization. Until the recovery of unreacted vinyl chloride monomer was completed, the supply of deionized water (2.5 liters / hour) was continued through the communication tube.

After the polymerization reaction starts (the polymerization reaction starts when the internal temperature of the vessel reaches a predetermined reaction temperature), the heat medium circulating in the temperature control element is switched to cooling water, Polymerization was carried out while maintaining the reaction temperature of 57 ° C. until the polymerization rate was reached. After that, unreacted vinyl chloride monomer was recovered, the produced slurry was extracted, ventilated, and the tank container was opened to observe the situation of scale adhesion to the communication pipe and its periphery.

After observing the scale adhering condition at and around the opening of the communicating tube, the inner wall of the vessel was washed with low-pressure ion-exchanged water, and the test of the next batch was repeated under the same conditions. The experiment was continued for 20 batches. The results of observing the scale adhesion are summarized in the table.

Comparative Example All the vinyl chloride monomer was prepared under the same conditions as in Example 1 except that the operation of charging water into the interstitial chamber was not performed in advance and the introduction of nitrogen gas before the initiation of polymerization was not performed. A polymerization reaction was performed and the same evaluation was performed. The results are shown in the table.

[0049]

[Table 1] Criteria: ○: No adhesion of the opening, almost no adhesion on the inner wall within 10 cm around it △: Slight adhesion is found on the opening. 10 cm around it
Spotted scales are also generated on the inner wall portion within the area .... The adhesion is generated on the opening and the opening is narrowed. In addition, the generation of adhesion is clearly seen in the peripheral area.

[0050]

EFFECTS OF THE INVENTION In a temperature control element type tank container,
The upper and lower parts of the gap between the element and the container body are sealed to form a gap chamber, and the gap chamber and the body chamber are connected by a pressure equalizing pipe or the like such as a communication pipe so that the internal pressure of the gap chamber is increased. When polymerizing vinyl chloride monomers using a tank container that maintains a small difference from the internal pressure of the container body, after charging the liquid into the interstitial chamber, charge the aqueous medium and vinyl chloride monomers. By using the method of the present invention, which is carried out, and preliminarily introducing an inert gas into the polymerization system and then initiating the polymerization, the gas phase part, particularly the main chamber side opening of the pressure equalizing pipe or the like and the scale in the vicinity thereof. Occurrence and growth can be prevented.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view showing an example of a tank container used for carrying out the method of the present invention.

FIG. 2 is an enlarged view of a main part of FIG. 1;

FIG. 3 is a vertical cross-sectional view showing another example of a tank container used for carrying out the method of the present invention.

FIG. 4 is a vertical sectional view showing an example of a conventional tank container.

FIG. 5 is an enlarged vertical sectional view of an essential part showing another example of a conventional tank container.

[Explanation of symbols]

 1, 1'Container body 2 Cylindrical body 3 Bottom mirror plate 4 Top mirror plate 5 Temperature control element 6 Inner cylinder 7 Partition plate 8 Outer strip 9 Heat medium flow passage 10 Heat medium flow passage inlet 11 Heat medium flow passage outlet 12 Tank container Nozzle 13 Partition wall 14 Gap chamber 15 Communication pipe 16 Liquid inlet 17 Pipe for introducing inert gas 18 Automatic valve 19 Pressure equalizing pipe 20 Pressure equalizer 21 Reflux condenser 22 (External) jacket 23 Partition plate 24 Inner strip 25 Heat transfer channel H gap

Claims (9)

[Claims] 1. Suspension polymerization of vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers in an aqueous medium is performed by arranging partition plates side by side at right angles to the outer surface of the inner cylinder. A flow path wall having a flow path of the heat medium partitioned by the partition plate between the inner cylinder and the outer strip by straddling an outer strip between the ends of the partition plate (hereinafter referred to as "temperature control element"). Is formed between the outer strip side of the temperature control element and the inner surface of the container body with the outer strip side facing the inner surface of the container body with the outer strip side facing the inner surface of the container body. And a space surrounded by the inner surface of the container body and the inner cylinder of the temperature control element (hereinafter referred to as "main body chamber"). Connect a communication tube or pressure equalizer to the gap chamber. When the liquid is charged in the interstitial chamber, the aqueous medium and vinyl chloride are used when the liquid is charged into the interstitial chamber (hereinafter collectively referred to as "pressure equalizing pipe") or in the tank container connected by the communication port provided in the partition above the temperature control element. A method for producing a vinyl chloride-based polymer, which comprises charging a system monomer and introducing an inert gas into the polymerization system in advance to start the polymerization. 2. The method for producing a vinyl chloride polymer according to claim 1, wherein the inert gas is introduced through a pipe provided in the upper mirror section or an accessory device installed in the upper mirror section. 3. The method for producing a vinyl chloride polymer according to claim 2, wherein a reflux condenser is provided as an accessory, and an inert gas is introduced through a pipe provided at the top of the reflux condenser. 4. The method for producing a vinyl chloride polymer according to claim 1, wherein the inert gas is introduced from a pipe provided in the pressure equalizing pipe. 5. The method for producing a vinyl chloride polymer according to claim 1, wherein the inert gas is a gas having a lower molecular weight and a lower boiling point than the vinyl chloride monomer. . 6. The method for producing a vinyl chloride polymer according to claim 1, wherein the inert gas is nitrogen. 7. The method for producing a vinyl chloride polymer according to claim 1, wherein a balance piston type pressure equalizer is used as the pressure equalizer. 8. The method for producing a vinyl chloride polymer according to claim 1, wherein a diaphragm type pressure equalizer is used as the pressure equalizer. 9. Water is used as a liquid to be charged into the interstitial chamber, and water vapor having a saturated vapor pressure equal to or lower than the vapor pressure of the vinyl chloride-based monomer at the reaction temperature is passed through the flow path of the temperature control element when the temperature is raised. The method for producing the vinyl chloride polymer according to any one of claims 1 to 8.