JPH0931123A - Method for producing vinyl chloride polymer - Google Patents

Abstract

(57) [Summary] [Objective] Unreacted vinyl chloride monomer can be efficiently removed from an aqueous dispersion of a vinyl chloride polymer obtained by emulsion polymerization or fine suspension polymerization. Provide a method for producing a small amount of vinyl chloride polymer. [Composition] In recovering and removing unreacted vinyl chloride monomer from an aqueous dispersion obtained by emulsion polymerization or fine suspension polymerization of vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers, a plurality of Coarse polymer particles having a diameter of more than 10 μm contained in the aqueous dispersion using a wet pulverizer when using the recovery equipment connected to the recovery apparatus and transferring the aqueous dispersion between the recovery apparatuses. A method for producing a vinyl chloride-based polymer, which comprises crushing. Even if the demonomerization treatment is carried out under relatively mild conditions, the monomer can be efficiently removed, and a vinyl chloride polymer having a small amount of residual monomer can be easily obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a vinyl chloride-based polymer having a low residual vinyl chloride monomer content, and more specifically to vinyl chloride or a copolymerizable monomer mainly comprising vinyl chloride. Efficiently reacts unreacted vinyl chloride (hereinafter referred to as "monomer") from an aqueous dispersion obtained by emulsion polymerization or fine suspension polymerization of a mixture (hereinafter referred to as "vinyl chloride-based monomer") The present invention relates to a method of recovering and removing (hereinafter referred to as "demonomer treatment") to obtain a vinyl chloride polymer having a small amount of residual monomer.

[0002]

2. Description of the Related Art In a method for industrially producing a vinyl chloride-based polymer by emulsion polymerization or fine suspension polymerization of a vinyl chloride-based monomer, the conversion rate of the vinyl chloride-based monomer is usually 80 to 95. %, And the aqueous dispersion after polymerization contains a considerable amount of unreacted monomer.

When the aqueous dispersion is used as it is for a latex application or when it is dried to produce a powdery vinyl chloride resin, the residual monomer remains hygienic.
It is not preferable in any of the environmental aspects, and therefore it is desired to reduce the residual amount of the monomer in the aqueous dispersion as much as possible. In general, as a method for removing monomers from an aqueous dispersion of a vinyl chloride-based polymer, a method of transferring the dispersion to a monomer recovery facility and removing unreacted monomer under reduced pressure in the recovery device is used. . However, it is difficult to efficiently remove the unreacted monomer by this method, and it is extremely difficult to reduce the residual amount of the monomer in the aqueous dispersion to about 100 to 1000 ppm based on the weight of the polymer.

As a method for improving the above-mentioned demonomer treatment, for example, the degree of decompression at the time of recovering the monomer is increased (the demonomer treatment is performed under a high vacuum), the temperature of the aqueous dispersion is raised, and the aqueous dispersion is strengthened. Methods such as stirring and prolonging the time for demomerization treatment have been proposed. However, in order to increase the degree of pressure reduction, it is necessary to increase the pressure resistance of the recovery device or increase the capacity of the vacuum equipment.On the other hand, if the temperature is increased or the stirring is increased, the emulsification of the aqueous dispersion liquid Stability may be impaired, agglomeration may occur, making it difficult to transfer, or product quality may deteriorate. Also,
Prolonging the processing time is problematic in terms of productivity.

[0005]

In view of the above circumstances, the present invention efficiently removes unreacted monomers from an aqueous dispersion of a vinyl chloride polymer obtained by emulsion polymerization or fine suspension polymerization of a vinyl chloride monomer. An object of the present invention is to provide a method for well recovering / removing, that is, a method for demonomerizing an aqueous dispersion of a vinyl chloride polymer capable of easily reducing the amount of residual unreacted monomer, and a method for producing a vinyl chloride polymer based on the method. I am trying.

[0006]

Means for Solving the Problems As a result of extensive studies conducted by the present inventor in order to achieve the above-mentioned object, the main reason why the monomer is not efficiently removed during the denomer treatment and is likely to remain in the polymer is 3mm diameter generated in the polymerization process,
It has been found that the unreacted monomer contained in the coarse particles having a size of more than 10 mm is not easily removed. Based on this finding, when the monomer dispersion treatment of the aqueous dispersion after polymerization was performed, a recovery facility connected to a plurality of recovery devices was used, and coarse particles contained in the aqueous dispersion were crushed during transfer between the recovery devices. By doing so, it was confirmed that the residual monomer can be efficiently removed, and the present invention was completed.

That is, the gist of the present invention is obtained by emulsion polymerization or fine suspension polymerization of vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers (vinyl chloride-based monomers). When recovering and removing unreacted vinyl chloride (monomer) from the aqueous dispersion (demonomerizing treatment), use a recovery facility that connects multiple recovery devices and transfer the aqueous dispersion between the recovery devices. At this time, the method for producing a vinyl chloride polymer is characterized in that coarse polymer particles contained in the aqueous dispersion are pulverized by using a wet pulverizer (hereinafter referred to as "pulverization treatment").

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous dispersion targeted by the present invention is an aqueous dispersion of a vinyl chloride polymer obtained by emulsion polymerization or fine suspension polymerization of a vinyl chloride monomer (so-called “latex”). )). Emulsion polymerization of vinyl chloride-based monomer is carried out in the presence of an emulsifier and water-soluble polymerization initiator in vinyl chloride-based monomer in an aqueous medium. Is homogenized in the presence of an emulsifier and an oil-soluble polymerization initiator, and then polymerized.

The vinyl chloride-based monomer in the present invention includes vinyl chloride alone and a mixture of vinyl chloride-based copolymerizable monomers. As the other monomer copolymerizable with vinyl chloride, those generally used conventionally can be used and are not particularly limited. Examples of the other monomer 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
-Mono-unsaturated acids such as olefins, acrylic acid and methacrylic acid, alkyl esters such as methyl esters and ethyl esters of these mono-unsaturated acids, di-unsaturated acids such as maleic acid, fumaric acid and itaconic acid Examples thereof include one or a mixture of two or more kinds of acids, alkyl esters such as methyl esters and ethyl esters of these diunsaturated acids, vinylidene compounds such as vinylidene chloride, and unsaturated nitriles such as acrylonitrile. These other monomers are usually used in a proportion of 30% by weight or less, preferably 20% by weight or less, with respect to the vinyl chloride monomer, but there is no particular limitation.

Examples of the emulsifier used for producing the aqueous dispersion targeted by the method of the present invention include higher alcohol sulfate ester salts (alkali metal salts and ammonium salts), alkylbenzene sulfonates (alkali metal salts and ammonium salts). Salts), alkyl sulfonates (alkali metal salts, ammonium salts), higher fatty acid salts (alkali metal salts, ammonium salts) and other anionic surfactants, nonionic surfactants, and / or cationic surfactants. These surfactants may be used alone or in combination of two or more. The amount of emulsifier used is usually 0.1 to 5 with respect to the vinyl chloride monomer.
It is in the range of wt% (preferably 0.3 to 2 wt%).

In the case of emulsion polymerization, the polymerization initiator is, for example, a water-soluble peroxide such as persulfate (sodium salt, potassium salt, ammonium salt), hydrogen peroxide or the like, or a water-soluble peroxide thereof. Oxides and water-soluble reducing agents (eg,
Sodium sulfite, sodium pyrosulfite, sodium bisulfite, ascorbic acid, sodium formaldehyde sulfoxylate, etc.) is used as a water-soluble redox initiator, and in the case of the fine suspension polymerization method, azobisisobutyrate is used. Ronitrile, Azobis (2,4
-Dimethylvaleronitrile), lauroyl peroxide, t-butylperoxypivalate, and other monomer-soluble (oil-soluble) initiators, or a redox system consisting of a combination of these oil-soluble initiators with the aforementioned water-soluble reducing agents An initiator is used.

The amount of these polymerization initiators used is usually about 0.001 to 0.1% by weight based on the vinyl chloride monomer. Furthermore, in the method of the present invention, a polymerization degree adjusting agent (chain transfer agent, cross-linking agent), an antioxidant, a pH adjusting agent, a redox type initiator used for the polymerization of vinyl chloride-based monomers, if necessary. Various polymerization aids such as activators can be appropriately added, and the charging amount of each of these components may be the general conditions conventionally used for the polymerization of vinyl chloride-based monomers. .

Auxiliaries such as emulsifiers and polymerization initiators used in the polymerization reaction may be added to the reaction system all at once before the initiation of the polymerization, or may be added dividedly or continuously during the polymerization reaction. It doesn't matter. The polymerization temperature varies depending on the type of the polymerization initiator used, the polymerization method, the presence / absence of the use of a polymerization degree adjuster, the target degree of polymerization, etc., but it is generally 0 to 90.
C., especially in the range 40 to 70.degree. C. is often used. In the reaction, the polymerization may be performed at a constant temperature, or the polymerization temperature may be changed during the polymerization.

The polymerization pressure varies depending on the type and composition of the vinyl chloride monomer used, or the reaction temperature.
Usually, it is about 4 to 12 kg / cm ² . In addition, the charging ratio of the monomer and water at the time of polymerization is generally about 0.5 to 3 in terms of water / monomer (weight ratio). In addition,
In the polymerization, a separately prepared vinyl chloride polymer may be charged as a seed polymer (seed) and polymerized.

The average degree of polymerization (JIS method) of the vinyl chloride polymer thus obtained is usually 400 to 800.
At about 0, most of the particle size is 10 μm or less. The vinyl chloride polymer aqueous dispersion obtained by the above-mentioned method usually contains 1 to 20% by weight of unreacted monomer, and it is necessary to collect and remove this. As the method of the demomerization treatment, two methods, that is, a batch treatment method and a continuous treatment method are generally used. As the batch treatment method, for example, a method of recovering the vaporized monomer by directly blowing water vapor or the like into the aqueous dispersion in a container, preferably by stirring, or by reducing the pressure while heating by passing through a jacket or the like. Is mentioned. Further, as the continuous treatment method, for example, the aqueous dispersion is sprayed or allowed to flow from the upper part of the tower under reduced pressure, and this is brought into countercurrent contact with water vapor and / or an inert gas introduced from the lower part of the tower to remove vaporized monomers. A method of recovering the gas from the top of the tower can be mentioned.

In the method of the present invention, the demonomer treatment is carried out by using a recovery facility in which a plurality of recovery devices are connected. However, only one of the above batch type or continuous type devices is used. Or both may be used together. The temperature of the demomerization treatment is usually 50 to 100 ° C,
The temperature is preferably 50 to 80 ° C., and the pressure is finally desired to be about the saturated steam pressure at the processing temperature.

In many cases, the residence time in each apparatus for the demonomer treatment is usually 0.5 minutes to 5 hours. When a plurality of recovery devices are connected in series to perform a demonomerization process, the first-stage device is not particularly subjected to a depressurization process, but is simply an aqueous solution after polymerization in a pressurized state by the vapor pressure of the monomer. A method (normal pressure flash method) in which the dispersion liquid is flashed in a normal pressure recovery device to volatilize the monomer may be adopted.

As described above, the size of the polymer particles in the vinyl chloride polymer aqueous dispersion obtained by emulsion polymerization or fine suspension polymerization is mostly 10 μm or less, but contains a small amount of large particle aggregates. Sometimes. The shape of such aggregates is generally spherical or amorphous, but those having a diameter (the maximum diameter in the case of amorphous) exceeding 3 mm, particularly 10 mm, have a particularly bad influence on the removal of monomers.

In the method of the present invention, a recovery facility in which a plurality of recovery devices are connected is used in the demonomer treatment, and a wet pulverizer is used to transfer the aqueous dispersion between the recovery devices. It is characterized in that coarse polymer particles contained in the dispersion liquid are pulverized. The number of recovery devices is not particularly limited, but 2 to 5 units are preferable, and normally 2 units are used by connecting them in series to the flow of the aqueous dispersion.

The position where the wet pulverizer is installed is not particularly limited as long as it is a connecting pipe between the recovery devices. However, the aqueous dispersion is placed in the recovery device installed at the most outflow side (downstream side) of the recovery equipment. Is preferably installed in the pipe for supplying In this case, the concentration of the monomer in the aqueous dispersion subjected to the pulverization treatment is 500 per weight of the polymer contained in the aqueous dispersion.
It is preferable to keep it at 0 ppm or less.

In addition, it is usually sufficient to install one wet pulverizer, but the effect is greater when two or more wet pulverizers are installed, especially one unit between each recovery device. The type of wet pulverizer that can be used in the method of the present invention is, for example, generally composed of a stator that is a screen and a rotor that is a pulverizing blade in the shape of a rod, a plate or a propeller, and in some cases a liner or a cutting blade. It can be a target. The maximum size of the particles after the pulverization treatment is controlled by the opening of the screen. Generally, the finer the opening, the more effective the monomer removal is, and it is preferably at most 3 mm or less. This opening is generally determined in consideration of the maximum particle size to be removed, the filtration resistance, or the strength of the screen.

The liquid temperature during the crushing treatment is not particularly limited, but is usually about 10 to 80 ° C. By carrying out this pulverization treatment, coarse particles, which take a long time to diffuse the monomer in the particles, are eliminated, and the monomer can be promptly removed even in the demonomerization treatment under relatively mild conditions.

If only coarse particles are to be removed, there are methods such as filtration separation and sedimentation separation, but there are problems such as loss of polymer and labor for demomerization of the separated coarse particles, which is an efficient method. That's hard to say. The aqueous dispersion after demonomerization can be used as it is for latex applications, or sent to a drying facility and dried by a conventional method such as spray drying to be a powdery vinyl chloride resin mainly used for paste applications. Is manufactured.

The gas containing the monomer is compressed and / or
Alternatively, the monomer can be cooled and liquefied and recovered for reuse.

[0025]

EXAMPLES Next, the method of the present invention will be explained more specifically with reference to examples, but the present invention is not limited by the following description of the examples unless it exceeds the gist. Example (1) Production of seed polymer A polymerization vessel with an internal volume of 300 liter equipped with a stirrer was heated at a temperature of 5
90 kg of deionized water at 4 ° C., 10 g of potassium persulfate, 50 g of sodium pyrosulfite and 18 g of sodium lauryl sulfate as an initial emulsifier were charged and stirred for about 20 minutes to dissolve these auxiliaries. Next, 60 kg of vinyl chloride was charged and the temperature inside the can was adjusted to 50 ° C. 15 minutes after the completion of the charging of vinyl chloride, the previously dissolved 0.2% aqueous solution of potassium persulfate was used so that the polymerization reaction rate became constant. It is possible to do so by adding). Further, when the polymerization rate reached about 15%, the separately dissolved 10% sodium lauryl sulfate aqueous solution was added at a rate of about 8 ml / min, and the total amount added (as sodium lauryl sulfate) was 360 g. Continued until. 2 kg / c from the saturation pressure of vinyl chloride at a pressure of 50 ° C
When m ² (1960 hPa) was lowered, unreacted vinyl chloride was released to the outside of the system to terminate the reaction. The vinyl chloride polymer particles in the obtained aqueous dispersion have an average particle size of 0.42.
It was a monodisperse particle of μm.

(2) Production of vinyl chloride polymer aqueous dispersion Into a polymerization vessel having the same internal volume of 300 liters as used above, 80 kg of deionized water and 4.8 kg of the seed polymer latex prepared above as a polymer amount were charged. After degassing, 75.2 kg of vinyl chloride was added. Can temperature 5
After heating to 5 ° C, the total amount is 0.05% (vs vinyl chloride)
Hydrogen peroxide-sodium formaldehyde sulfoxylate redox initiator was continuously added. Furthermore,
From when the polymerization rate reached 10% with respect to the total amount of the seed polymer and vinyl chloride, the total solid content was 500 as an emulsifier.
A 10% aqueous solution of sodium lauryl sulfate (g) was continuously added to vinyl chloride at a rate of 0.08% per hour.

When the internal pressure of the can dropped 1 kg / cm ² (980 hPa) from the saturated pressure of vinyl chloride at 55 ° C., the addition of the initiator was stopped to terminate the reaction. The vinyl chloride polymer particles in the obtained aqueous dispersion have a particle size of 0.41.
Two peak distributions of μm and 1.35 μm were shown.

(3) Demonomerization Treatment The above aqueous dispersion is connected in series to two recovery devices with a stirrer having a monomer recovery pipe in the upper gas phase part, and high-speed agitation type wet pulverization is performed in the pipe connecting them. Demonomer treatment was carried out using a monomer recovery facility (with a bypass pipe of a wet pulverizer) equipped with a machine (equipped with a screen having a maximum mesh size of 3 mm, a propeller type pulverization blade, and a cutting blade).

First, half of the aqueous dispersion obtained in (2) above was transferred to the first-stage recovery device. Water vapor (pressure 3 kG) was intermittently supplied at a rate of 1.5 kg / hour from around the bottom of this recovery container, and the desorbed monomer was maintained at a temperature of 68 ± 1 ° C. and the desorbed monomer was 3 m ³ / hour together with water vapor. It was removed out of the system at a rate of (shown as volume under process conditions). This treatment was performed for 2.5 hours, and the liquid temperature was 68.1 ° C and the internal pressure was 282 mmHg (absolute pressure).

Next, the aqueous dispersion was transferred to the second-stage recovery device at a flow rate of 300 liters / hour while being pulverized by the wet pulverizer, and coarse particles contained in the polymer in the aqueous dispersion were pulverized. did. The second stage demonomerization treatment was also performed for 1.5 hours under the same conditions as in the first stage, and the liquid temperature was 68.0 ° C.
The internal pressure became 213 mmHg (absolute pressure).

At the end of the treatments of the first and second stages, a sample was taken to measure the residual monomer amount. The results are shown in the table. The residual amount of the monomer contained in the polymer in the aqueous dispersion is determined by sampling a certain amount of the aqueous dispersion of the vinyl chloride polymer and using this in a measuring flask to prepare tetrahydrofuran (TH
Hydrogen flame ionization detector (FID)
Inject a fixed amount into a gas chromatograph equipped with, and from the peak corresponding to vinyl chloride monomer on the obtained chromatogram, determine the concentration of vinyl chloride monomer in the sample using a calibration curve prepared separately, It was calculated by converting into the amount of monomer per weight of polymer.

Comparative Example The remaining half of the aqueous dispersion obtained in (2) above was transferred to the monomer recovery facility, and the transfer from the first stage to the second stage was carried out using a bypass pipe to a wet pulverizer. The monomer removal treatment was carried out in the same manner as in the example except that the above was not used.

The liquid temperature at the end of the first stage treatment is 68.3 ° C.,
The internal pressure was 279 mmHg (absolute pressure), the liquid temperature at the end of the second stage treatment was 68.1 ° C., and the internal pressure was 215 mmHg (absolute pressure). The amount of residual monomer in the aqueous dispersion was measured in the same manner as above, and the results are also shown in the table.

[0034]

EFFECTS OF THE INVENTION According to the method of the present invention, even if the demonomer treatment is carried out under relatively mild conditions, the demonomer treatment can be efficiently carried out, and the vinyl chloride-based vinyl chloride-based product having a small amount of residual monomer can be easily obtained. Polymers can be produced.

[0035]

[Table 1]

[0036] Processing conditions: 68 ± 1 ° C, steam injection 1.5 kg / hour

Claims (4)

[Claims] 1. Unreacted vinyl chloride is recovered and removed from an aqueous dispersion obtained by emulsion polymerization or fine suspension polymerization of vinyl chloride or a mixture of vinyl chloride-based copolymerizable monomers. In doing so, when using a recovery facility in which a plurality of recovery devices are connected and when transferring the aqueous dispersion between the recovery devices, coarse polymer particles contained in the aqueous dispersion are crushed using a wet crusher. A method for producing a vinyl chloride-based polymer, comprising: 2. The method for producing a vinyl chloride polymer according to claim 1, wherein a wet pulverizer is installed in a pipe for supplying the aqueous dispersion to a recovery device installed on the most outflow side of the recovery facility. 3. The method for producing a vinyl chloride polymer according to claim 1, wherein the polymer particles having a diameter of more than 10 mm in the aqueous dispersion are pulverized. 4. The method for producing a vinyl chloride polymer according to claim 1, wherein a plurality of recovery devices are installed in series with respect to the flow of the aqueous dispersion.