JP4345171B2 - Heat removal method using reflux condenser, polymerization method using the same, stirring tank and polymerization reactor used therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention removes heat generated from a liquid substance such as a reaction liquid in a reaction tank such as a reaction tank of a polymerization reaction apparatus, and efficiently removes heat when performing a reflux cooling operation to control the temperature. The present invention relates to a method, a polymerization method using the method, a stirring tank and a polymerization reaction apparatus used for the method.
[0002]
[Prior art]
The heat removal by the reflux condenser is performed by, for example, cooling the treatment liquid such as the reaction liquid in the reaction tank in the polymerization reaction apparatus such as vinyl chloride resin to control the polymerization temperature in the tank. And is a technique frequently used in industrial operations as means for removing heat generated in the system such as polymerization heat and reaction heat, and there are many practical examples. Conventional reflux condensers are connected and installed mainly outside via a short straight pipe, as described in, for example, Japanese Patent Application Laid-Open No. 08-134107 and Japanese Patent Application Laid-Open No. 07-025909. Has been. This is considered to be simple in terms of manufacturing and structure of the apparatus or maintenance.
[0003]
The reflux cooling operation by the reflux condenser as described above performs heat exchange when the condensable vapor generated from the processing liquid in the tank is indirectly cooled and condensed with the refrigerant of the reflux condenser, This is a technique for removing heat by reducing the amount of heat and returning the condensed liquid to the liquid phase part in the tank. At this time, it is known that if non-condensable gas exists in the cooler, the heat exchange performance is remarkably lowered. Therefore, when performing a reflux cooling operation of a treatment liquid in which a non-condensable gas exists in the gas phase part, in order to prevent the non-condensable gas from staying in the reflux cooler and reducing the cooling performance, The non-condensable gas must be removed from the system. Also, for example, in a polymerization reaction by semi-batch operation accompanied by a change in liquid volume, when a monomer liquid supplied at a low temperature is polymerized at a relatively high temperature, a non-condensable gas dissolved in the monomer liquid, Nitrogen is released into the gas phase part in the tank, and this is mixed into the reflux condenser, which lowers the reflux cooling performance. As described above, once the non-condensable gas is mixed into the reflux condenser, the cooling capacity of the reflux condenser is reduced. Therefore, in order to restore the cooling capacity, it is often the case that non-condensable gas is purged out of the system from the reflux condenser as described above. However, in this case, for environmental measures, it is necessary to recover the condensable vapor coexisting with the purged gas, most of which is an organic solvent or a monomer. Further, when the pressure in the system is equal to or lower than the atmospheric pressure, the non-condensable gas cannot be purged other than using a decompression pump, and the equipment load is large.
[0004]
In addition, when performing a reflux cooling operation of a liquid that causes a scale to adhere to the reflux cooler by entrainment of droplets due to the reflux cooling operation, the scale generated or attached on the cooling surface deteriorates the cooling performance. In addition, conventional reflux condensers often have an efficient flow by being provided at a position different from the steam inlet and the condensate flow outlet. In the reflux device provided separately from the mouth, the inlet of the condensable vapor may be blocked by the attached scale. Further, if the steam inlet and the condensate flow outlet are provided at one location, the heat exchange performance is lowered by the collision of the rising steam and the flow of the condensate flowing down, which is not effective.
[0005]
Furthermore, for example, when a vinyl chloride resin is polymerized, a slurry solution in which the vinyl chloride resin being polymerized is dispersed in an aqueous solution or a vinyl chloride paste (solid) being polymerized is present in a latex form in the aqueous solution. When the reflux cooling operation is performed in the presence of a solid-liquid mixture in which solid fine particles are finely dispersed in a liquid, for example, depending on the properties of the liquid, for example, when the influence of an emulsifier or a dispersant is large The foaming is intense, and in some cases, the solid conveyed by entrainment of droplets or rising of the liquid level may block the steam inlet of the reflux condenser. Thus, when the liquid level rises due to foaming associated with the reflux operation, there are many methods for controlling the rise of the liquid level by suppressing the reflux amount. As a result, the amount of heat removal is limited, and the production efficiency is significantly reduced. There is a method to cope with this by adding a foam breaker or the like, but an increase in cost is unavoidable, and it must be fully studied from the viewpoint of quality degradation.
[0006]
[Problems to be solved by the invention]
In view of the problems in heat removal by the conventional reflux condenser as described above, the present invention, when removing heat from the treatment liquid in the reaction tank of the polymerization reaction apparatus by the reflux condenser, the treatment liquid splashes. Entrainment generates scale in the reflux cooler, liquid phase or gas phase in the tank contains non-aggregating gas that lowers the cooling capacity, or treatment liquid in the tank foams due to reflux cooling operation Even in the case of a heat removal operation involving a semi-batch operation in which the liquid level rises due to the change in the liquid level in the tank, the productivity is reduced, the cost is increased, or the quality is reduced. The object is to enable efficient heat removal by the reflux condenser without lowering.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the heat removal method according to the present invention is configured to remove condensable vapor generated in the tank when the heat generated in the tank containing the treatment liquid is removed by the reflux condenser. In the heat removal method in which heat is removed by cooling, condensing and refluxing with a reflux condenser provided in the tank, the removal in the semi-batch operation in which the amount of the processing liquid in the tank increases and the liquid level in the liquid phase part rises. In the first half of the half-batch operation, heat is removed by the reflux cooling action of the reflux condenser, and in the second half of the half-batch operation, heat is removed by liquid contact heat transfer of the treatment liquid to the reflux condenser. It is characterized by this. In this heat removal method, when the treatment liquid present in the tank is a liquid or a solid-liquid mixture that causes the scale to adhere to the reflux condenser due to entrainment by the reflux cooling operation, a non-condensable gas is present in the gas phase portion in the tank. When removing heat in the presence of 1 vol% or more, when the pressure in the tank before and / or after the reflux cooling operation is below atmospheric pressure, the liquid or solid-liquid mixture in the tank is subjected to the reflux cooling operation. It is effective when the liquid level rises due to accompanying foaming .
[0009]
The heat removal method according to the present invention as described above is suitable, for example, when a polymerization reaction of a vinyl chloride resin or a polymerization reaction of ethylene oxide or propylene oxide is performed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The heat removal method according to the present invention can be used, for example, for a polymerization reaction of vinyl chloride resin, ethylene oxide, propylene oxide, etc., and the treatment liquid includes a solution for polymerization of vinyl chloride resin, ethylene oxide, propylene oxide, and the like. Examples of the polymer solution include a liquid or a solid-liquid mixture such as a solution containing an organic solvent such as hexane. The heat removal method of the present invention is performed in a tank that is sealed to such an extent that the treatment liquid inside the tank generates condensable vapor by heat. In the present invention, the reflux condenser must be installed inside a sealed stirring tank such as a reaction tank of a polymerization reactor. In the case of a normal stirring tank such as a reaction tank, for example, the bottom of the cylindrical straight body has a bottom part with a downwardly convex shape such as a semi-elliptical section or a cone shape, and this tank can be rotated from the outside of the tank. A stirrer provided with a stirring blade is disposed. In the present invention, the installation position of the reflux condenser in the tank may be within such a tank, but preferably the straight body is good, and more preferably, the gas phase flow by the stirring blade is expected to be strong. In the vicinity of the stirring blade. When non-condensable gas is present, if the non-condensable gas is heavier than the reflux target vapor, the reflux cooler is preferably installed above the tank, but usually the non-condensable gas is the reflux target. In many cases, the reflux condenser is lighter than steam, and the reflux condenser is preferably installed above the liquid level and as low as possible in the tank.
[0013]
In the present invention, the reflux condenser installed in the tank is connected to, for example, a cooling unit located in the tank and both ends of the cooling unit, and a cooling liquid supply that supplies the cooling liquid to the cooling unit. A reflux condenser including a pipe and a cooling liquid discharge pipe for discharging the cooling liquid from the cooling unit is provided. When the reflux cooler is provided in the tank in this way, heat exchange is performed on the outer surface of the cooling section by the condensable vapor generated in the tank coming into contact with the outer surface of the cooling section of the reflux cooler. In addition, heat is removed by cooling, condensing, and refluxing the cohesive vapor. As a cooling part of the reflux condenser in this case, a tubular part integrated with a cooling liquid supply pipe and a cooling liquid discharge pipe connected to both ends thereof can be used, and further, by using a serpentine type, A reflux cooling operation by efficient heat exchange can be expected.
[0014]
The treatment liquid handled in the tank is reflux-cooled, such as a liquid or solid-liquid mixture such as a polymerization solution for polymerizing vinyl chloride resin, a polymerization solution for polymerizing by continuously adding ethylene oxide monomer or propylene oxide monomer. The effect of the present invention is particularly great when the liquid or solid-liquid mixture causes the scale to adhere to the reflux condenser by entrainment of droplets due to the operation and / or the liquid or solid-liquid mixture includes a non-condensable gas in the gas phase portion. That is, as described above, in the present invention, the reflux condenser is in the tank, and the outer surface of the reflux condenser is in contact with the condensable vapor to perform reflux cooling. Even in the case of a liquid or a solid / liquid mixture to which the scale is attached, the outer surface of the cooling unit is washed before the scale is generated on the surface of the cooler by the condensate, thereby preventing the generation of the scale. In addition, when a non-condensable gas is included in the gas phase and the non-condensable gas is lighter than the condensable vapor (return target vapor), the conventional reflux cooler installed outside the tank is reflux cooled. Since the non-condensable gas is present in the chamber, the heat transfer performance is significantly reduced.If the non-condensable gas is not removed by the purge operation, the heat transfer performance cannot be restored. Depending on the type of gas to be purged, it is necessary to remove the coexisting substances in the purge gas. Further, when the gas phase pressure in the tank is lower than the atmospheric pressure, the purge operation is performed by using a vacuum pump, etc. The equipment load is heavy. On the other hand, if the reflux cooler is in the tank as in the present invention, the need for a purge operation is greatly reduced, and the above problem can be solved.
[0015]
Further, in the present invention, when the liquid level rises due to foaming accompanying the reflux cooling operation, bubbles can be broken by dripping the condensate condensed by the reflux cooler installed inside the tank, It is possible to keep the production efficiency of the polymerization reaction and the like high because there is no need to limit the reflux amount without causing a rise. In addition, since it is not necessary to use a foam breaker, there is no increase in cost and quality.
[0016]
Further, in the present invention, since the reflux condenser is installed in the tank, the reflux condenser can be used not only for the purpose of the reflux operation but also for the purpose of the heat removal operation by the liquid contact heat transfer. For example, in a semi-batch operation accompanied by a change in the amount of liquid in the tank, a tubular internal coil such as a serpentine internal coil is used as a reflux condenser, and in the first half of the half-batch operation, a part or all of the internal coil is used. Arranged so as to be exposed to the gas phase part, in the first half of the half-batch operation, the internal coil was refluxed and cooled, and in the latter half of the half-batch operation, the internal coil was positioned in the liquid phase part In the state, heat may be removed by liquid contact heat transfer of the liquid in the tank to the internal coil. This heat removal method is particularly effective in polymerization reactions in which the amount of polymer increases in the latter half of the half-batch operation and the amount of condensable vapor decreases compared to the first half, making it difficult to remove heat by reflux cooling. It is.
[0017]
【Example】
EXAMPLES Next, although an Example is given and this invention is demonstrated concretely, these Examples do not restrict | limit this invention at all.
[0018]
Example 1
A cooling water supply pipe 22 and a cooling water discharge pipe whose both ends are connected to the outside as a reflux condenser 2 in an agitation tank 1 having an internal volume 10L shown in FIG. An intermediate portion of a stainless steel tube having an outer diameter of 8 mm, which is 23, is set as a cooling portion 21 so as to surround the stirring shaft 5a of the stirrer 5 so as to be 40 cm in length above the gas phase portion. First, the inside of the tank 1 was evacuated from the vacuum line 3, and then 1 L of hexane was charged as the processing liquid A from the processing liquid supply line 4 so that air did not leak. While stirring the hexane in the tank 1 with the stirrer 5, steam is generated by heating the liquid in the tank (hexane) to 70 ° C. with the temperature raising jacket 6 to raise the temperature in the tank (hexane). When the water temperature of the cooling water supply pipe 22 immediately before entering the tank 1 by flowing 15 ° C. water at a flow rate of 100 L / hr and the water temperature of the cooling water discharge pipe 23 immediately after leaving the tank 1 were measured, At about 3 ° C., the heat removal amount was about 1260 kJ / hr, and heat exchange by the reflux cooling operation in the cooling unit 21 in the gas phase part in the tank 1 was confirmed. Moreover, when the stainless steel tube surface of the cooling part 21 part of the reflux cooler 2 in the tank 1 was observed from the sight glass 7, a large amount of condensate was confirmed.
[0019]
(Example 2)
The same operation as in Example 1 was carried out except that 1 kg of polypropylene glycol having a molecular weight of about 3000 and 200 g of tetrahydrofuran were charged as the treatment liquid A instead of hexane. The gas phase pressure in the tank at this time was not more than atmospheric pressure (about −5 × 10 ⁴ Pa). As a result, as in Example 1, an increase in cooling water temperature of about 2.8 ° C. (heat removal amount: about 1170 kJ / hr) due to heat exchange was confirmed. Further, the condensate was confirmed by observation from the sight glass 7.
[0020]
(Example 3)
After the treatment liquid was charged, the same operation as in Example 2 was performed except that nitrogen was charged at 5 Vol% and 10 Vol% with respect to the initial tank pressure. The amount of heat removal decreased to about 80% (heat removal amount of about 960 kJ / hr) and about 65% (heat removal amount of about 750 kJ / hr), respectively, as compared with Example 2 in which nitrogen was not added.
[0021]
(Example 4)
The same operation as in Example 2 was performed except that polypropylene glycol having a molecular weight of about 10,000 was applied to the outer surface of the stainless steel tube constituting the cooling part 21 of the reflux condenser 2 located in the gas phase part in the tank 1. After starting the reflux operation, it was observed from the sight glass 7 that the polypropylene glycol applied to the outer surface of the cooling unit 21 of the reflux cooler 2 was washed with the condensate, and the heat removal amount was the same as in Example 2 ( About 1170 kJ / hr).
[0022]
(Comparative Example 1)
As shown in FIG. 2, the cooling water supply line to the cooling unit 21a having the same heat transfer area as that of the cooling unit 21 of the stainless steel tube 40 cm having an outer diameter of 8 mm used as the reflux cooler 2 in Examples 1 to 4. The same operation as in Example 3 was performed except that the reflux condenser 2a configured to discharge the cooling water supplied from 22a from the cooling water discharge line 23a was used. Note that the valve at the tip of the cooling unit 21a was normally closed. Compared to the case of Example 2 in which nitrogen was not added, the heat removal amount was about 30% (about 330 kJ / hr) when nitrogen was added at 5 vol% with respect to the initial internal pressure, and a level that could not be detected when 10 vol% was added. (About 10% or less, about 120 kJ / hr or less).
[0023]
【The invention's effect】
As described above, according to the present invention, since the reflux cooling operation is performed by the reflux cooler provided in the tank, scale adhesion to the reflux cooler accompanying the reflux operation can be prevented, Reduced heat transfer performance due to the presence of non-condensable gas and reduced the heat transfer performance due to environmental measures There is no need to perform the purging operation, and there is almost no decrease in cooling performance due to the rise in liquid level due to foaming, which is superior to the conventional heat removal method using a reflux condenser installed outside the tank. This is a practical heat removal method. Moreover, a favorable polymerization reaction can be performed by using this heat removal method.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an agitation tank used in an example in which heat is removed by a reflux condenser provided in the tank.
FIG. 2 is an explanatory view showing an agitation tank used in a comparative example in which heat is removed by a reflux condenser provided outside the tank.
[Explanation of symbols]
1: stirring tank, 2: reflux condenser, 3: vacuum line, 4: treatment liquid supply line, 5: stirrer, 6: temperature rising jacket, 7: sight glass, 21: cooling section, 22: cooling water supply pipe , 23: Cooling water discharge pipe.

Claims (6)

When the heat generated in the tank containing the treatment liquid is removed by the reflux cooler, the condensable vapor generated in the tank is cooled by the reflux cooler provided in the tank, condensed, and then removed by refluxing. In the heat removal method by heating, the heat removal method in a semi-batch operation in which the amount of the processing liquid in the tank increases and the liquid level in the liquid phase rises, and in the first half of the half-batch operation, A heat removal method wherein heat removal is performed by a reflux cooling action, and heat is removed by liquid contact heat transfer of the treatment liquid to the reflux condenser in the second half of the half-batch operation .   The heat removal method according to claim 1, wherein the treatment liquid is a liquid or a solid-liquid mixture in which scale is attached to the reflux condenser by entrainment with droplets by reflux cooling operation.   The heat removal method of Claim 1 performed in the state in which the non-condensable gas exists in the gaseous-phase part in the said tank in 1 vol% or more.   The heat removal method according to claim 1, wherein the pressure in the tank before and / or after the reflux cooling operation is equal to or lower than the atmospheric pressure.   The heat removal method according to claim 1, wherein the treatment liquid is a liquid or a solid-liquid mixture whose liquid level rises due to foaming associated with a reflux cooling operation. The polymerization method performed with the heat removal operation by the heat removal method in any one of Claims 1-5 .

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