JP2005281659A - Method for producing vinyl chloride polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a vinyl chloride polymer which suppresses foaming by adding an antifoaming agent to the contents of a polymerizer in a timely manner when the liquid level rises due to foaming.
A method of producing a vinyl chloride polymer comprising polymerizing a vinyl chloride monomer or a mixture of the monomer and a monomer copolymerizable therewith in an aqueous medium in a polymerization vessel equipped with a reflux condenser. Because
At least from the start to the end of heat removal by the reflux condenser, a radio wave level gauge that emits microwaves of 4 to 20 GHz provided in the polymerization vessel is used to measure the liquid contents in the polymerization vessel. Monitoring the liquid level, and
A production method comprising adding an antifoaming agent to the liquid content when a polymerization conversion rate is in a range of 30 to 60% and the liquid level is a predetermined height or more.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a vinyl chloride polymer by monitoring the liquid level of the contents of a polymerization vessel using a radio wave level gauge and suppressing foaming due to operation of a reflux condenser by adding an antifoaming agent.

  Conventionally, a method for producing a vinyl chloride polymer that can improve productivity without impairing the quality of a product has been proposed and put into practical use from many viewpoints. The vinyl chloride polymer is usually produced by a batch method. Therefore, productivity is improved by shortening the time required for the entire batch, particularly the polymerization reaction step, and increasing the number of batches per unit time. Further, productivity is improved by increasing the size of the polymerization vessel.

  For this reason, it is common practice to remove the heat of polymerization reaction as efficiently as possible by using a reflux condenser in addition to a cooling jacket (if necessary, further cooling baffles and cooling coils). Since heat removal by the reflux condenser can be performed more economically than heat removal by the cooling jacket, cooling baffle, and cooling coil, the rate of heat removal by the reflux condenser with respect to the total heat removal tends to increase.

  Heat removal by the reflux condenser is performed by condensation of vaporized monomer. As a result, the pressure in the gas phase decreases in the polymerization vessel, and a foaming phenomenon inevitably occurs on the surface of the liquid phase. If the heat removal amount in the reflux condenser is increased more than necessary, scales are likely to be generated on the inner surface of the polymerization vessel near the gas-liquid interface, and polymer particles are blown up to the reflux condenser and the like together with bubbles and adhere to the surface. . Further, the scale generated in this manner is mixed into the product at the next batch, and fish eyes are increased. Therefore, measures for solving these problems have been studied.

  For example, the amount of foam is suppressed by adding an antifoaming agent when it is detected that the amount of foam on the liquid phase surface has reached a certain level or more by the foam sensor installed in the gas phase part of the polymerization vessel. Has been proposed (see Patent Document 1). Since the capacitance type sensor used as the bubble sensor in this method is a contact type sensor, the polymer particles adhere to the sensor part and the measurement accuracy is lowered. In recent years, various varieties of vinyl chloride polymers have been produced. The optimum amount of foam for adding an antifoaming agent in the above method varies depending on the varieties. However, since the position of the bubble sensor is fixed in the above method, only a certain amount of bubbles can be measured. Thus, the above method can only detect the optimal amount of foam for some varieties.

  In addition, a method for suppressing scale generation and the like by controlling the gas-liquid interface within a predetermined range has been proposed (see Patent Document 2). In this method, a polymerization vessel equipped with a liquid level gauge that continuously measures the liquid level in the polymerization vessel is used, and the cooling water temperature or flow rate to the reflux condenser is changed based on the measured liquid level. As a result, the amount of the monomer refluxed by the reflux condenser increases and decreases, and the gas-liquid interface is controlled so that it is constantly stirred and flown within a predetermined range and does not stay stationary. The disadvantage of this method is that the absolute amount of heat removal is low and it is difficult to make the best use of the heat removal capability of the reflux condenser.

  Furthermore, a method has been proposed in which an optimum antifoaming agent is selected and added at a certain time when the reflux condenser is used, so that the heat removal ability of the reflux condenser can be effectively used without deteriorating the quality (patent) Reference 3). However, this method has the same drawbacks as Patent Document 1. Further, this method is very inefficient because the addition amount and the addition timing are determined by observing the position of the polymer particles adhering in the vessel after polymerization.

  When a non-contact type liquid level gauge is used, there are the following problems. Usually, in order to increase the measurement accuracy, the non-contact type liquid level gauge is installed so that the tip of the sensor protrudes from the inner wall surface of the upper mirror portion of the polymerization vessel toward the inside of the vessel. In this case, if the amount of heat removed by the reflux condenser increases too much, the scale will adhere to the sensor tip. In order to prevent bubbles from adhering to the sensor tip, it is necessary to limit the upper limit value of the heat removal amount by the reflux condenser to suppress the height of the foam layer generated in the polymerization reaction step. As a result, it becomes impossible to maximize the heat removal capability of the reflux condenser. The scale can be prevented from adhering to the tip of the sensor by forming a recess on the inner wall surface of the upper mirror part of the polymerization vessel and placing it in the recess. The reflection of the microwave from the side wall surface of the recess is received. When the sensor receives the microwave reflected from the side wall surface, an error occurs in the measurement of the liquid level, and the measurement accuracy of the liquid level may be lowered.

Japanese Unexamined Patent Publication No. 4-130103 Japanese Unexamined Patent Publication No. 7-25909 JP-A-9-169805

  An object of the present invention is to add a defoaming agent to the contents of the polymerization vessel in a timely manner when the liquid level rises due to foaming, thereby suppressing foaming and maximizing the heat removal capability of the reflux condenser. It is to provide a method for producing a vinyl polymer.

As a means for solving the above problems, the present invention polymerizes a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer copolymerizable therewith in an aqueous medium in a polymerization vessel equipped with a reflux condenser. A method for producing a vinyl chloride polymer comprising:
At least from the start to the end of heat removal by the reflux condenser, a radio wave level gauge that emits microwaves of 4 to 20 GHz provided in the polymerization vessel is used to measure the liquid contents in the polymerization vessel. Monitoring the liquid level, and
Provided is a production method comprising adding an antifoaming agent to the liquid content when the polymerization conversion is in the range of 30 to 60% and the liquid level is not less than a predetermined height.

  In this specification, the liquid level means the surface of the liquid content in the polymerization vessel, and when the upper part of the liquid content is composed of a foam layer, it means the surface of the foam layer.

  According to the method of the present invention, the level of the content of the polymerization vessel is monitored using a reflux condenser by using a radio wave level gauge that emits microwaves of 4 to 20 GHz, and the level of the liquid rises due to foaming. Occasionally an antifoaming agent is added to the contents to suppress foaming to maximize the heat removal capability of the reflux condenser. Specifically, when the antifoaming agent is not added, the ratio of the heat removal amount by the reflux condenser to the total required heat removal amount is about 15 to 25%, whereas when the antifoaming agent is added by the method of the present invention The ratio can be increased to 30% or more (30 to 60%). Thus, the method of the present invention can drastically improve the amount of heat removed by the reflux condenser by monitoring the liquid level and adding an antifoaming agent. By the method of the present invention, the amount of heat removed from the condenser can be increased when the reaction heat at the end of polymerization reaches a peak. As a result, the polymerization time can be shortened, energy can be saved, and productivity can be improved.

  In the method of the present invention, foaming during the polymerization reaction can be suppressed by adding an antifoaming agent, so that the polymer particles are blown up to the reflux condenser together with the foam and adhered to the surface, thereby producing scale. Can be prevented. In addition, since the radio wave level gauge used in the present invention can be installed away from the liquid level, it is possible to prevent bubbles and scales from adhering to the sensor portion. As a result, the measurement accuracy can be maintained when the liquid level is monitored, and the maintenance frequency can be minimized even if the radio wave level gauge is used for a long period of time. Furthermore, the sensor unit of the radio wave level gauge can be installed at an optimum position within a range where bubbles and scales do not adhere to the sensor unit.

  Hereinafter, the present invention will be described in detail.

-Polymerization reactor-
The polymerization vessel used to carry out the method of the present invention is equipped with a reflux condenser as a cooling means. A radio wave level gauge is provided as means for monitoring the liquid level. In addition to this, it is usually desirable to provide a jacket for heating and cooling, and a baffle, a coil and the like having a cooling ability, although not essential. Also, a so-called external heat exchange device may be installed in which the mixture slurry in the polymerization vessel is extracted by a pump and returned to the polymerization vessel through a heat exchanger installed outside the polymerization vessel. Although there is no restriction | limiting in particular in the shape of a superposition | polymerization device, For example, it is preferable to use the superposition | polymerization device which has a cylindrical straight body part.

  An example of the polymerization reaction apparatus used in the method of the present invention is shown in FIG. For example, a heating / cooling jacket (not shown) is provided on the outer periphery of the polymerization vessel 1, and a medium such as hot water or cooling water is introduced into the jacket through a line (not shown). . If necessary, a cooling baffle 2 and a cooling coil (not shown) may be provided in the polymerization vessel 1. A reflux condenser 3 is provided in the upper part of the polymerization vessel 1, and a refrigerant such as cooling water is also conducted to the reflux condenser 3 through a line (not shown). The reflux condenser 3 condenses the monomer vapor generated in the polymerization vessel 1, liquefies it, and refluxes it into the polymerization vessel 1.

  In the polymerization vessel 1, an aqueous medium charging line 4 such as ion-exchanged water, a polymerization initiator charging line 5, a monomer charging line 6, a line 7 for collecting unreacted monomers after the completion of the polymerization reaction, an antifoaming agent addition Line 8 is connected. In addition, since the polymerization vessel 1 is equipped with a stirrer 9 having paddle blades so as to be rotated by the drive motor 10, the contents 11 charged in the polymerization vessel 1 can be agitated by the agitator 9. In the illustrated example, a level gauge 12 is provided at the top of the polymerization vessel 1.

  As materials for the inner surface of the polymerization vessel, baffle, paddle blade, shaft, etc. used in the polymerization apparatus of the present invention, stainless steels such as high chromium high purity ferritic stainless steel, duplex stainless steel, and austenitic stainless steel are preferred.

-Features of the method of the present invention-
Heat removal by reflux condenser A feature of the present invention is that heat generated by polymerization is removed using the reflux condenser.

  In suspension polymerization of a vinyl chloride monomer or a monomer mixture containing the same, an aqueous medium, a dispersing agent (suspension agent), a polymerization initiator, and various other additives as necessary are usually contained in a polymerization vessel. Then, the temperature in the polymerization vessel is raised to a predetermined polymerization reaction temperature by passing hot water through the jacket to start polymerization. Thereafter, the polymerization reaction is advanced while maintaining the reaction mixture in the polymerization reactor at a predetermined reaction temperature by removing the heat of polymerization reaction using a cooling means such as a reflux condenser. Normally, when removing heat with a reflux condenser, in order not to suddenly change the temperature in the polymerization vessel or the jacket temperature or affect the foaming of the mixture in the polymerization vessel, a predetermined removal from the beginning of the heat removal from the condenser is required. Generally, the heat removal amount is gradually increased until the heat amount is reached. In the method of the present invention, the polymerization reaction is usually carried out at 20 to 80 ° C, preferably 35 to 75 ° C, more preferably 45 to 70 ° C.

  Heat removal by the reflux condenser is started after the temperature of the reaction mixture in the polymerization vessel is raised to a predetermined polymerization reaction temperature and the temperature of the reaction mixture in the polymerization vessel reaches the predetermined polymerization reaction temperature. The heat removal by the reflux condenser may be started immediately after the temperature of the reaction mixture in the polymerization vessel reaches a predetermined polymerization reaction temperature, or after a certain time has elapsed after reaching the predetermined polymerization reaction temperature. Heat removal by the reflux condenser is preferably started at a polymerization conversion of 10 to 15%. The heat removal by the reflux condenser may be continued until the polymerization is completed, but may be completed before that. Heat removal by the reflux condenser is preferably terminated at a polymerization conversion of 60 to 80%. Further, the heat removal by the reflux condenser is preferably performed during the polymerization at a polymerization conversion rate of 10 to 80%, particularly at a polymerization conversion rate of 15 to 70%.

[Polymerization initiator]
The polymerization initiator used in the method of the present invention is not particularly limited, and may be those used in the production of conventional vinyl chloride polymers. For example, peroxycarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate; t-butyl peroxypivalate, t-hexyl peroxypivalate, t- Peroxyester compounds such as butylperoxyneodecanoate and α-cumylperoxyneodecanoate; acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, 3,5, Peroxides such as 5-trimethylhexanoyl peroxide; azo compounds such as azobis-2,4-dimethylvaleronitrile and azobis (4-methoxy-2,4-dimethylvaleronitrile); potassium persulfate, ammonium persulfate, Examples thereof include hydrogen oxide. These can be used singly or in combination of two or more.

  The addition amount of the polymerization initiator is usually in the range of 0.01 to 1 part by mass, preferably 0.03 to 0.2 part by mass, per 100 parts by mass of all monomers. The method for charging the polymerization initiator may be the same as the conventional method.

[At the end of polymerization]
In the present invention, when the polymerization is completed, the polymerization reaction is stopped by adding a sufficient amount of a polymerization inhibitor (a substance having a polymerization inhibiting ability) to the polymerization vessel to stop the polymerization reaction. It is. Usually, after this, recovery of the unreacted monomer is started.

[Polymerization inhibitor]
As the polymerization inhibitor used in the method of the present invention, those generally used for the production of vinyl chloride polymers can be used. For example, 2-t-butylphenol, 2-aminophenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-diisopropyl-p-cresol, n-octadecyl-3- (3,5-di-t- Butyl-4-hydroxyphenyl) propionate, 3,5-di-t-butyl-4-hydroxytoluene, triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate ], T-butylhydroxyanisole, t-butylhydroquinone, 4,4'-butylidenebis (3-methyl-6-t-butylphenol), 2,2'-methylene-bis (4-methyl-6-t-butylphenol) 2,2'-methylene-bis (4-ethyl-6-t-butylphenol), 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol 2,6-di-t-butyl-4-hydroxymethylphenol, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-thiobi Phenol compounds such as (6-t-butyl-m-cresol), tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane; cyclic neopentanetetraylbis Phosphorus compounds such as (octadecyl phosphite); sulfur such as dilauryl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate, alkali metal sulfate, alkali metal bisulfite, alkali metal thiosulfate Compound; Nitrogen compounds such as N, N-diethylhydroxylamine and sodium nitrite are listed. These can be used singly or in combination of two or more. Among these, n-octadecyl-3- (3,5-di-t-butyl-4 is preferred because of its low scale adhesion to the polymerization vessel and good anti-initial colorability of the resulting polymer. -Hydroxyphenyl) propionate, 3,5-di-tert-butyl-4-hydroxytoluene, triethylene glycol-bis- [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 2 , 2'-methylenebis (4-ethyl-6-t-butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol), t-butylhydroxyanisole, t-butylhydroquinone, N, N- Diethylhydroxylamine is preferred.

  The addition amount of the polymerization inhibitor is usually 0.001 to 0.3 parts by mass, preferably 0.003 to 0.1 parts by mass, and more preferably 0.005 to 0. The range is 05 parts by mass. The method for charging the polymerization inhibitor may be the same as the conventional method.

-Monitoring the liquid level with a radio wave level gauge Further, the feature of the present invention is that at least from the start to the end of heat removal by the reflux condenser, the microwave of 4 to 20 GHz provided in the polymerization vessel is radiated. It is to monitor the liquid level of the liquid content in the polymerization vessel using a radio wave level gauge.

  Since the above monitoring can be performed continuously and accurately, the optimal timing and amount of antifoaming agent corresponding to fluctuations in the liquid level due to changes in the amount of heat removed from the condenser can be determined by using a radio wave level gauge. I can do things. As a result, the heat removal capability of the reflux condenser can be used effectively.

  The period during which the liquid level is monitored by the radio wave level gauge only needs to include the period from the start to the end of heat removal by the reflux condenser. In other words, the monitoring of the liquid level may be started before the start of heat removal by the reflux condenser, or may be continued after the heat removal by the reflux condenser is completed.

[Liquid level indicator]
In the present invention, it is possible to continuously monitor the liquid level in the polymerization vessel, and it has the advantage of being non-contact type and not restricted by the pressure in the polymerization vessel. Use a surface meter.

  The radio wave level gauge used in the method of the present invention irradiates the liquid level of the contents of the polymerization vessel with microwaves and receives the microwave reflected from the microwaves as a measurement object. The wavelength of the microwave used is usually 4 to 20 GHz, preferably 5 to 10 GHz. When using microwaves that exceed 20 GHz and less than 30 GHz, the level of the liquid level that changes relatively gently due to stirring, etc. can be monitored. As a result, it may be difficult to monitor. In addition, when microwaves of 30 GHz or higher are used, it is almost impossible to monitor the level of a liquid level that varies greatly due to stirring or a liquid level that is strongly foamed. On the other hand, when a microwave of less than 4 GHz is used, the measurement accuracy is lowered, and it is difficult to accurately monitor the liquid level.

  The radio wave level gauge used in the method of the present invention has the following structural features. The main body of the radio wave level gauge is a sensor unit including a microwave transmission / reception unit. In order to reliably receive the microwave reflected from the liquid level of the contents of the polymerization vessel, it is preferable to attach a horn antenna to the tip of the sensor unit. Although it depends on the installation conditions, the measurement accuracy can be improved by installing a horn antenna as large as possible. Moreover, it is preferable to connect a horn antenna and a sensor part with a waveguide. By appropriately adjusting the length of the waveguide, the horn antenna can be accurately installed at a more preferable position. Further, if the tip opening of the horn antenna is installed parallel to the liquid surface, the installation angle of the waveguide and the sensor unit is not particularly limited, and there is no problem even if it is inclined with respect to the liquid surface. In order to receive microwaves, it is sufficient that the tip opening of the horn antenna protrudes to the inside of the polymerization vessel.

  As long as the liquid level can be monitored, the radio wave level gauge may be installed at any position in the polymerization vessel. It can be installed at an optimum position according to the polymerization conditions and the like.

  An outline of an example of the radio wave level gauge is shown in FIG. The radio wave level gauge 13 includes a microwave transceiver 14, a waveguide 15, and a horn antenna 16. The radio wave level gauge is used in a form as shown in FIGS. 3 (a) and 3 (b), for example. It is illustrated that the installation angle of the waveguide and the microwave transmitting / receiving unit is not limited if the tip opening 17 of the horn antenna is installed in parallel to the liquid surface.

-Addition of antifoaming agent Further, the present invention is characterized in that the polymerization conversion rate is in the range of 30 to 60%, and the liquid level of the liquid content in the polymerization vessel is equal to or higher than a predetermined height. An antifoaming agent is added to the liquid content to defoam.

  The measured value of the liquid level measured using the radio wave level gauge is compared with a preset height, and when it is detected that the liquid level exceeds the predetermined height, A foaming agent is added. These operations can be performed manually, but can also be automated using, for example, a computer. Considering the height to suppress the carryover phenomenon to the condenser, it is preferable to keep the liquid level below the height below the condenser. Within this range, set the liquid level to be monitored in advance. Just keep it.

  The addition of the antifoaming agent is started based on a signal that the liquid level has become equal to or higher than the predetermined height. After the start of the addition, a predetermined amount of the antifoaming agent may be added over a certain period of time. Further, the addition may be stopped when the liquid level detected by the radio wave type level gauge becomes lower than the predetermined height after the start of the addition. It is preferable to add each time the liquid level becomes equal to or higher than the predetermined height. These illustrated operations can be easily automated by appropriate programming. When the antifoaming agent is added, the polymerization conversion rate is usually 30 to 60%, preferably 40 to 50%.

[Defoamer]
The antifoaming agent used in the present invention is not particularly limited as long as a sufficient antifoaming effect is obtained. As an antifoaming agent that can be used in the present invention, it is preferable to use a copolymerized polyether. More specifically, the copolymerized polyether is a copolymer having a weight average molecular weight of 1.5 million to 2 million, preferably 1.7 million to 2 million, and a molar ratio of ethylene oxide to propylene oxide of 78/22 to 82/18. Polymerized polyether can be used.

  When the molecular weight is less than 1,500,000, the action of the copolymerized polyether that lowers the interfacial tension of bubbles generated in the polymerization system and breaks bubbles is reduced. Therefore, the antifoaming effect cannot be obtained sufficiently, and the amount of the antifoaming agent needs to be increased. As a result, there arises a problem that the quality of the obtained polymer is lowered. On the other hand, when the molecular weight exceeds 2 million, the defoaming effect is lowered because the polymer slurry tends to increase in viscosity.

  The amount of the copolymerized polyether added is 0.001 to 0.008 parts by mass, preferably O.003 to O.008 parts by mass with respect to 100 parts by mass of all monomers charged in the polymerization vessel. If the amount of copolymerized polyether used relative to all monomers is less than 0.001 part by mass, no defoaming effect will occur. Moreover, when it exceeds 0.008 mass part, since a polymer slurry will thicken, an antifoaming effect will fall.

  The copolymer polyether is preferably added as an aqueous solution to the polymerization reaction system. The concentration of the aqueous solution is usually 0.1 to 10% by mass, preferably O.5 to 3% by mass.

  The antifoaming agent, for example, the aqueous copolymer polyether solution, has a polymerization conversion rate in the range of 30 to 60%, and the liquid level of the liquid content in the polymerization vessel is not less than the predetermined height. Sometimes it is preferred to add to this liquid content. More preferably, it is added to the polymerization reaction system when the polymerization conversion rate is in the range of 40 to 50% and the liquid level is not less than the predetermined height. Since the polymer particle formation is insufficient before the polymerization conversion rate reaches 30%, the addition of the antifoaming agent at this point may adversely affect the particle size distribution. Further, if the antifoaming agent is added at such an early stage of the polymerization reaction, the defoaming effect may not be sustained until the foaming of the liquid surface becomes the most intense at the end of the polymerization. On the other hand, in the case of a polymerization reaction in which heat is removed by a reflux condenser, the foaming of the polymer slurry has already progressed considerably when the polymerization conversion rate exceeds 60%. Therefore, even if an antifoaming agent is added to the polymerization reaction system at this time, the antifoaming agent only adheres to the foam and does not sufficiently mix with the entire reaction solution, and the defoaming effect may be difficult to be exhibited. At this time, if the antifoaming agent is to be sufficiently mixed with the entire reaction solution, an extra operation such as increasing the number of revolutions of the stirrer in the polymerization vessel becomes necessary.

  The antifoaming agent can be added intermittently or continuously. When the addition of the antifoaming agent is performed intermittently, the interval between additions may be regular or irregular. Based on the persistence of the antifoaming effect, it can be determined whether the antifoaming agent is added intermittently or continuously. The pre-copolymerized polyether has not only a small influence on the quality, but also is superior to other antifoaming agents in the sustainability of the antifoaming effect, so that it can be added intermittently.

-Other conditions-
The other conditions of the method of the present invention are not particularly limited, and normal conditions used for aqueous suspension polymerization of a vinyl chloride monomer or a mixture mainly containing it and other polymerizable monomers should be adopted. Can do.

[Monomer]
The monomer used in the present invention is vinyl chloride or a monomer mixture mainly composed of vinyl chloride. The monomer mixture mainly composed of vinyl chloride is a mixture comprising at least 50% by mass of vinyl chloride and a monomer copolymerizable with vinyl chloride. Examples of monomers that can be copolymerized with vinyl chloride include vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid esters such as methyl acrylate and ethyl acrylate; or methacrylic acid esters; ethylene and propylene. Olefins; maleic anhydride; acrylonitrile; styrene; vinylidene chloride and the like. These can be used singly or in combination of two or more.

[Dispersant]
In the method of the present invention, the dispersant used in the case of polymerizing vinyl chloride or the like in an aqueous medium is not particularly limited, and may be one used for the production of a conventional vinyl chloride polymer. Examples of the dispersant include water-soluble cellulose ethers such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose, water-soluble partially saponified polyvinyl alcohol, water-soluble polymers such as polyacrylic acid, polymethacrylic acid, and gelatin; sorbitan mono Oil-soluble emulsifiers such as laurate, sorbitan trioleate, glycerin tristearate, ethylene oxide-propylene oxide block copolymer; water-soluble emulsifiers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, sodium laurate, etc. Is mentioned. These can be used singly or in combination of two or more.

[Antioxidant]
The antioxidant used in the present invention is not particularly limited, and may be one generally used in the production of vinyl chloride polymers. For example, 2,2-di (4′-hydroxyphenyl) propane, hydroquinone, p-methoxyphenol, t-butylhydroxyanisole, n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl ) Propionate, t-butylhydroquinone, 2,5-di-t-butylhydroquinone, 4.4'-butylidenebis (3-methyl-6-t-butylphenol), 3,5-di-t-butyl-4-hydroxytoluene, 2,2′methylene-bis (4-ethyl-6-t-butylphenol), triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], pentaerythrityl- Tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,6-di-t-butyl-4-sec-butylphenol, 2,6-di-t-butyl-4 -Methylphenol, phenol compounds such as t-butylcatechol, 4,4′-thiobis (6-t-butyl-m-cresol), tocopherol, nordihydroguaiaretic acid; semicarbazide, and 1-acetylsemicarbazide, 1-chloroacetylsemicarbazide, Semicarbazide derivatives such as 1-dichloroacetyl semicarbazide, 1-benzoyl semicarbazide, semicarbazone; derivatives of thiocarbazide such as carbohydrazide, thiosemicarbazide, thiosemicarbazone; phenylnaphthylamine, N, N′-diphenyl-P-phenylenediamine, 4 Amine compounds such as 4,4'-bis (dimethylbenzyl) diphenylamine; nitro or nitroso compounds such as nitrosoanisole, N-nitrosodiphenylamine, nitroaniline, N mononitrosophenylhydroxylamine aluminum salt; Riphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, 4,4'-butylidene-bis (3-methyl-6-t-butylphenyl-di-tridecyl) phosphite, cyclic isopentanetetrayl bis ( Octadecyl phosphite), tris (nonylphenyl) phosphite, phosphorus compounds such as tris (dinonylphenyl) phosphite; dilauryl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate, dodecyl mercaptan, And sulfur compounds such as 1,3-diphenyl-2-thiourea. These can be used singly or in combination of two or more. Among these, 3,5-di-tert-butyl-4-hydroxytoluene, triethylene glycol-bis [3 in that the anti-initial colorability of the obtained polymer is good and the scale adhesion to the polymerization vessel is small. -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], t-butylhydroxyanisole, t-butylhydroquinone, 2,6-di-t-butyl-4-sec-butylphenol, n-octadecyl -3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate is preferred.

[Scale adhesion inhibitor]
The scale adhesion preventing agent used in the present invention may be a known one, for example, a self-condensation product of polyhydric phenols and polyhydric naphthols; a condensate of 1-naphthol and formaldehyde; a phenol compound and aldehydes; Condensates of quinone-amine compounds and organic silica sols; naphthol sulfide compounds; mixtures and / or reaction products of electron-donating dyes and aryl sulfonic acids; phenothiazine derivatives; quinone compounds and / or their reductions Processed product; Reaction product of ketone resin and phenolic compound; Dye, pigment, aromatic compound having 5 or more conjugated π bonds, heterocyclic compound having 5 or more conjugated π bonds; polyaromatic amine; cation Salts of compounds and anionic compounds; reaction products of polyvinyl alcohol and aminobenzoic acid; phenols and alcohols Examples thereof include an initial condensation product with aldehydes. The method of applying the coating liquid to the inner wall surface of the polymerization vessel is not particularly limited, and includes, for example, brush coating, spray coating, steam coating, and a method of drawing out after filling the polymerization vessel with a polymer scale adhesion inhibitor. Various coating methods can be used.

  In the recent production of vinyl chloride polymers, the coating method using steam as the medium has been the mainstream for the application of the scale adhesion preventing agent. It is also preferable to use self-condensates of polyvalent naphthols, condensates of 1-naphthol and formaldehyde, and naphthol sulfide compounds.

[Other optional ingredients]
In the method of the present invention, if necessary, a polymerization degree adjusting agent, a chain transfer agent, a pH adjusting agent, a gelation improving agent, an antistatic agent, and a crosslinking agent that are generally used for the production of vinyl chloride polymers. , Stabilizers, fillers and the like may be used as appropriate. In addition, an antioxidant may be added to the polymerization system before the start of polymerization, during the polymerization, or after the completion of the polymerization for the purpose of controlling the polymerization reaction and preventing deterioration of the produced polymer.

[Other conditions]
In addition, other conditions in the polymerization, for example, an aqueous medium such as ion-exchanged water to the polymerization vessel, a monomer mixture containing vinyl chloride or vinyl chloride, a method of charging a dispersing agent, or a charging ratio are the same as in the past. Good.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

In the examples and comparative examples, the apparatus shown in FIG. 1 was used. As the polymerization vessel 1, a polymerization vessel having a cylindrical straight body portion was used. In FIG. 1, the upper horizontal surface of the cylindrical body of the polymerization vessel 1 is indicated by “TL line”. A horizontal plane 0.5 m higher than the horizontal plane indicated by the TL line is indicated by “B line”. The internal volume of the polymerization vessel 1 is 130 m ³ . By applying a scale adhesion preventing agent in advance, a scale adhesion preventing coating film was formed on the inner wall surface of the polymerization vessel 1. As the radio wave level gauge 12, a radio wave level gauge that is equipped with a horn antenna and radiates a microwave of 5.8 GHz was used. The surface of the front end opening of the horn antenna coincides with the horizontal plane indicated by the “B line” and is parallel to the liquid level of the contents of the polymerization vessel. The diameter of the tip opening of the horn antenna is 241 mm, and the diameter of the waveguide is 40 mm. The radio wave level gauge 12 was connected to a computer (not shown), and a signal detected by the radio wave level gauge was input to the computer. The computer was programmed so that the antifoam was added from the antifoam addition line 8 under the conditions described below in response to the signal.

  The polymerization conversion rate at a certain point in the polymerization performed in the examples and comparative examples is that the polymerization is actually performed under the specific polymerization conditions, and the polymerization is stopped by adding an antioxidant to the polymerization system at a specific time, The amount of polymer produced at that time was measured, and the polymerization conversion rate at that time was measured from the measured value. A number of similar polymerizations were performed in which the time until the termination of polymerization was extended by 0.5 hours, and the polymerization conversion rate was measured for each. Thus, the relationship between the time and the polymerization conversion rate was determined in advance for each specific polymerization condition, and the polymerization conversion rate at a certain point was specified based on the relationship.

[Example 1]
When the radio wave level gauge 12 detects that the liquid level is equal to or higher than the height corresponding to a position of 0.3 m vertically below the B line, the defoamer is automatically added to the reaction mixture. The computer was programmed to be added. Monitoring of the liquid level with the radio wave level gauge 12 can be performed from before the polymerization mixture is charged, through the charging, polymerization, extraction of the polymer slurry after the polymerization, water washing of the polymerization vessel, and all subsequent processes. The result is always displayed on the display, for example. Polymerizer 1 was charged with 54,900 kg of ion-exchanged water, 13.8 kg of partially saponified polyvinyl alcohol, and 9.2 kg of hydroxypropyl methylcellulose. Next, after evacuating with a vacuum pump until the internal pressure reached 7.98 kPa (gauge pressure), 47,700 kg of vinyl chloride monomer was charged. While stirring, 25.3 kg of di-2-ethylhexyl peroxydicarbonate was injected as a polymerization initiator into the polymerization vessel. Next, warm water was passed through the heating / cooling jacket to raise the liquid phase temperature in the polymerization vessel to 53 ° C. Thereafter, the polymerization reaction was continued while maintaining this temperature. Heat removal by the reflux condenser was started when the polymerization conversion rate was 15%, and the heat removal amount was increased so that the heat removal amount by the reflux condenser became 8370 MJ / hr when the polymerization conversion rate was 40%. Thereafter, this heat removal amount was maintained and the reaction was continued. When the liquid level becomes higher than the above level, according to the above program, as a defoaming agent, a copolymer polyether having a weight average molecular weight of 1,500,000 and a molar ratio of ethylene oxide to propylene oxide of 80/20 is used. 120 kg of 2% aqueous solution was continuously added to the reaction mixture over 2 minutes. At this time, the polymerization conversion rate reached 50%. When the internal pressure of the polymerization vessel reaches 588 kPa (gauge pressure), 5.0 g of triethylene glycol bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is added as a polymerization inhibitor Then, the polymerization was stopped and unreacted monomers were recovered. While the obtained polymer slurry was taken out of the polymerization vessel, the polymerization vessel was washed with water. The heat removal by the reflux condenser was completed when the polymerization conversion was 80%.

The stirring power at the start of the polymerization was 1.3 × 10 ³ W (130 kg · m / s) per mass (t) of the content of the polymerization vessel. The stirring rotation speed was 86 rpm from the start of stirring to the time of slurry extraction. The ratio of the heat removal amount of the reflux condenser to the total heat removal amount per unit time showed a maximum value of 55% when the polymerization conversion rate was 75%.

[Example 2]
When the polymerization conversion rate was 25%, the heat removal amount was increased so that the heat removal amount by the reflux condenser was 8370 MJ / hr, and when the antifoaming agent was added, the polymerization conversion rate reached 30%. Except for the above, polymerization, extraction and washing with water were carried out in the same manner as in Example 1.

[Example 3]
Using 35.3 kg of di-2-ethylhexyl peroxydicarbonate as a polymerization initiator, and increasing the heat removal amount so that the heat removal amount by the reflux condenser is 12,600 MJ / hr when the polymerization conversion rate is 40% Polymerization, extraction, and water washing were performed in the same manner as in Example 1 except that the above procedure was performed.

[Comparative Example 1]
Except that the heat removal amount was increased so that the heat removal amount by the reflux condenser was 8370 MJ / hr when the polymerization conversion rate was 40%, and no antifoam was added, as in Example 1. Then, polymerization, extraction, and water washing were performed.

[Comparative Example 2]
When the polymerization conversion rate was 55%, the heat removal amount was increased so that the heat removal amount by the reflux condenser was 8370 MJ / hr, and when the antifoaming agent was added, the polymerization conversion rate reached 65%. Except for the above, polymerization, extraction and washing with water were carried out in the same manner as in Example 1.

[Comparative Example 3]
When the polymerization conversion rate was 10%, the heat removal amount was increased so that the heat removal amount by the reflux condenser was 6278 MJ / hr, and when the antifoaming agent was added, the polymerization conversion rate reached 15%. Except for the above, polymerization, extraction and washing with water were carried out in the same manner as in Example 1.

[Comparative Example 4]
Polymerization, extraction, and water washing were performed in the same manner as in Example 3 except that no antifoam was added.

[Evaluation results]
For the above Examples and Comparative Examples, the bulk specific gravity, particle size distribution (# 600 pass%, # 100 pass%, # 200 pass%) of the obtained polymer, the number of fish eyes, and the inside of the polymerization vessel after the polymerization reaction The state of scale adhesion was investigated. The results are shown in Table 1.

Bulk specific gravity
Measured according to JIS K-6721.

Particle size distribution
According to the particle size distribution measurement method of JIS Z-8801, the mass% of the sample that passed through the sieves of # 60, # 100, and # 200 was determined.

Number of fish eyes 100 parts by weight of polymer obtained, DOP 50 parts by weight, barium stearate O.1 part by weight, cadmium stearate 0.1 part by weight, cetanol 0.8 part by weight, tin-based stabilizer 2.O parts by weight, titanium dioxide A mixture of 0.5 part by mass and 0.1 part by mass of carbon black was kneaded at 140 ° C. for 5 minutes by a 6-inch roll mill. Thereafter, it was formed into a sheet having a thickness of O.3 mm, and the number of white transparent particles (fish eyes) in 100 cm ^{2 of} this sheet was measured.

Scale adhesion status The scale adhesion status in the polymerization vessel was evaluated according to the following criteria.
A… There is almost no scale adhesion.
B: A portion of scale attached to the inner surface of the polymerization vessel near the gas-liquid interface was observed.
C: Locations where scales adhered to the top of the baffle and the inner surface of the polymerization vessel near the gas-liquid interface were observed.

It is the schematic which shows an example of the superposition | polymerization device used for this invention method. It is the schematic of the radio wave type liquid level gauge used by the Example and the comparative example. (a) It is a figure which shows an example of the application form of a radio wave type level gauge. (b) It is a figure which shows another example of the application form of a radio wave type level gauge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polymerizer 2 Cooling baffle 3 Reflux condenser 4 Aqueous medium preparation line 5 Polymerization initiator preparation line 6 Monomer preparation line 7 Unreacted monomer recovery line 8 Defoamer addition line 9 Stirrer 10 Stirrer drive motor 11 Contents of polymerizer Object 12 Liquid level gauge 13 Radio wave type liquid level gauge 14 Microwave transmitter / receiver 15 Waveguide 16 Horn antenna 17 Horn antenna tip opening

Claims (4)

A method for producing a vinyl chloride polymer comprising polymerizing a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer copolymerizable therewith in an aqueous medium in a polymerization vessel equipped with a reflux condenser Because
At least from the start to the end of heat removal by the reflux condenser, a radio wave level gauge that emits microwaves of 4 to 20 GHz provided in the polymerization vessel is used to measure the liquid contents in the polymerization vessel. Monitoring the liquid level, and
A production method comprising adding an antifoaming agent to the liquid content when a polymerization conversion rate is in a range of 30 to 60% and the liquid level is a predetermined height or more.   The antifoaming agent is an aqueous solution of a copolymerized polyether having a weight average molecular weight of 1.5 to 2 million and a molar ratio of ethylene oxide to propylene oxide of 78/22 to 82/18. Manufacturing method.   The production method according to claim 2, wherein the addition amount of the antifoaming agent is 0.001 to 0.008 parts by mass as a copolymerized polyether with respect to 100 parts by mass of all monomers. The method according to any one of claims 1 to 3, wherein the antifoaming agent is added intermittently or continuously.

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