JP3972427B2 - Apparatus and method for recovering unreacted monomer in vinyl chloride polymerization facility - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, after producing a vinyl chloride polymer using a polymerization reaction tank, the contents containing the vinyl chloride polymer and unreacted monomer after the polymerization reaction are withdrawn from the reaction tank, and at the same time, The present invention relates to a method for recovering the unreacted monomer from the contents.
[0002]
[Prior art]
As industrial production methods for vinyl chloride polymers, aqueous suspension polymerization, bulk polymerization, emulsion polymerization, and the like are performed, and aqueous suspension polymerization and emulsion polymerization using water as a dispersion medium are the most widely performed. (These are called aqueous polymerization). In addition to the vinyl chloride homopolymer, the vinyl chloride polymer may be a copolymer of a monomer copolymerizable with a vinyl chloride monomer, such as a vinyl chloride / vinyl acetate copolymer, Olefin-based polymers and further graft polymers of vinyl chloride, for example, those obtained by graft polymerization on ethylene / vinyl acetate copolymers are known.
[0003]
Conventionally, in the method for producing a vinyl chloride polymer, if 70 to 95% of the vinyl chloride monomer charged in the polymerization reaction vessel is polymerized, the subsequent reaction becomes extremely slow. After stopping the reaction and recovering only a certain amount of unreacted monomer from the pipe connected to the top in the polymerization reaction tank, the produced vinyl chloride polymer and unreacted monomer are recovered. Were collected from the reaction vessel. However, the method of sufficiently collecting unreacted monomers in the reaction tank in advance requires time for the operation. Since the method for producing a vinyl chloride polymer is generally performed in a batch system, the next batch cannot be polymerized while the polymerization reaction vessel is closed. Therefore, even if the polymerization reaction itself is completed in a short time, spending a lot of time for the subsequent recovery process leads to a decrease in the production amount of the vinyl chloride polymer product. For the purpose of shortening the time required for this recovery operation, the state where the polymerization reaction tank is kept at a sufficiently high pressure without sufficiently performing the operation of recovering unreacted monomers in the reaction tank after the polymerization reaction, i.e., high A method is also considered in which the unreacted monomer at a concentration is still contained, and is immediately extracted into another tank. However, with this method, the concentration of the unreacted vinyl chloride monomer contained in the extracted content is high, so the concentration of the unreacted vinyl chloride monomer in the content is high. In addition to the fact that the difference in height of the product becomes large, the operation in the subsequent devinylation monomer process becomes unstable, and in the conventional recovery equipment, unreacted vinyl chloride contained in the contents As the amount of the monomer increased, the tank required to store or pass the recovered contents was required to have high pressure resistance, which increased the costs associated with high pressure design and forced the construction cost to rise. .
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a vinyl chloride polymer and a low-pressure low-pressure blow-down tank without substantially or completely recovering unreacted monomers in a reaction tank. By making it possible to recover a high concentration of unreacted monomer, the overall production cost including the production efficiency of the vinyl chloride polymer is improved.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have devised a unique structure and instrumentation for the transfer pipe and the blow-down tank, thereby enabling a low-pressure design of the blow-down tank, and a vinyl chloride polymer. It has been found that the production efficiency can be improved, and the present invention has been completed. That is, this invention has the following aspect.
(1) (a) a polymerization reactor for producing a vinyl chloride polymer by polymerizing a vinyl chloride monomer or a mixture of vinyl chloride and a copolymerizable monomer; and (b) A transfer pipe for transferring the content containing the vinyl chloride polymer after polymerization reaction and the unreacted monomer from the reaction tank; and (c) temporarily transferring the content transferred through the transfer pipe. A blow-down tank having an internal volume of 1 to 3 times the internal volume of the polymerization reaction tank and a permissible pressure resistance of 1 kg / cm ² G or less, (d A) a vent pipe provided at the outlet of the blow-down tank; and (e) a pressure adjusting means for adjusting a flow rate in the transfer pipe at the inlet of the blow-down tank so that the pressure in the blow-down tank is equal to or lower than the allowable pressure-resistant pressure. (F) Move through the vent pipe An unreacted monomer recovery device having a gas holder for holding gas containing unreacted monomer, wherein the inner diameter of the vent pipe is 1.5 to 4 times the inner diameter of the transfer pipe, And the inner periphery of the side surface of the blowdown tank is circular, and the transfer pipe connected from the polymerization reaction tank to the blowdown tank is connected along the tangential direction with respect to the inner periphery of the side surface of the blowdown tank. An apparatus for recovering unreacted monomers in a vinyl chloride polymerization facility.
(2) The recovery device according to (1), wherein the internal volume of the blowdown tank is 1.5 to 2.5 times the internal volume of the polymerization reaction tank.
(3) The recovery device according to (1) or (2), wherein an inner diameter of the vent pipe is 2 to 3 times an inner diameter of the transfer pipe.
(4) A method for recovering unreacted monomer in a vinyl chloride polymerization facility using the recovery device according to any one of (1) to (3), wherein the vinyl chloride monomer or vinyl chloride is In a state in which a mixture with a copolymerizable monomer is charged into a polymerization reactor and 80% by weight or more of the monomer is polymerized, and then 50% by weight or more of the unreacted monomer remains. When the pressure in the polymerization reaction tank is 3 kg / cm ² G or more, the contents of the polymerization reaction tank containing the remaining unreacted monomer and the vinyl chloride polymer are recovered in a blow-down tank, An unreacted unit in a vinyl chloride polymerization facility is characterized in that the gas containing the unreacted monomer is recovered from the blowdown tank to a gas holder while maintaining the pressure in the down tank at 1 kg / cm ² G or less. How to recover the mass.
(5) The content including the remaining unreacted monomer and the vinyl chloride polymer is collected in a blowdown tank in a state where 90% by weight or more of the unreacted monomer remains. The recovery method according to (4) above.
(6) The recovery method according to (4), wherein when the pressure in the polymerization reaction tank is 5 kg / cm ² G or more, the contents of the reaction tank are recovered into the blowdown tank.
[0006]
An example of the recovery facility of the present invention is shown in FIGS. 1 and 2, and the recovery method of the present invention will be specifically described. However, the present invention is not limited to this.
The apparatus of the present invention comprises a polymerization reaction tank 1 for producing a vinyl chloride polymer by polymerizing a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer copolymerizable therewith, A transfer pipe 2 for transferring contents from the reaction tank 1 and a blowdown with a pressure allowable pressure for temporarily storing or passing the contents transferred through the transfer pipe 2 of 1 kg / cm ² G or less A tank 3, a vent pipe 4 provided at the outlet of the blow-down tank 3, a pressure gauge 7 for detecting the pressure in the blow-down tank 3, and the pressure detected by the pressure gauge 7 A pressure regulating valve 6 for adjusting the flow rate in the transfer pipe 2 at the inlet of the blow-down tank 3 so as to be equal to or lower than the pressure-resistant allowable pressure, and the gaseous unreacted monomer moving through the vent pipe 4 are retained. Gas holder 5. Reference numeral 8 denotes a seal pot provided in the middle of the vent pipe 4. This seal pot has the function of draining water accumulated in the vent pipe 4 and the function of degassing when the gas pressure rises abnormally. Connected to the bottom of the blow-down tank 3 is a pipe 9 for transferring a liquid substance such as a vinyl chloride polymer and water from the contents in the blow-down tank to a device for removing full-scale vinyl chloride monomer. The valve 10 is installed.
The polymerization reaction tank 1 used in the present invention may be any one that is used for the polymerization of ordinary vinyl chloride polymers. Further, the transfer pipe 2 used in the present invention may also be used for the production of ordinary vinyl chloride polymers.
The allowable pressure resistance of the blowdown tank 3 used in the recovery facility of the present invention is 1 kg / cm ² G or less. Moreover, the capacity | capacitance is 1-3 times the capacity | capacitance of a polymerization reaction tank, Preferably, it is 1.5-2.5 times. Since no high-pressure tank is required, the equipment cost is low. In the present invention, the vent pipe 4 connecting the blowdown tank 3 and the gas holder 5 preferably has a sufficiently larger diameter than the transfer pipe 2, and is 1.5 to 4 times the inner diameter of the transfer pipe 2, preferably 2 ˜3 times, in terms of dimensions, 200 to 500 mm, preferably 250 to 400 mm. Further, the length of the vent pipe should be short, preferably 150 m or less. In the polymerization reaction tank 1, the unreacted monomer is not sufficiently recovered in advance or not recovered at all, so that a large amount of the content is recovered in a short time in the blow-down tank in which such contents are recovered. Although the unreacted vinyl chloride monomer will evaporate, the flow resistance of the fluid when moving from the blowdown tank to the gas holder is reduced by having a sufficiently large pipe diameter and short pipe length. As a result, the processing pressure in the blowdown tank can be kept at 1 kg / cm ² G or less.
[0007]
Furthermore, it is preferable that a pressure gauge 7 is installed in the blowdown tank 3 and an adjustment valve 6 capable of adjusting the pressure is installed in the transfer pipe. As a result, when the processing pressure in the blowdown tank 3 is likely to exceed the allowable pressure resistance, the recovery amount can be finely adjusted, which contributes to stable operation. Further, preferably, if the regulating valve 6 is installed in the immediate vicinity of the blow-down tank 3, the flash evaporation is minimized so that the pipe is not damaged by the impact generated by flash evaporation of the unreacted monomer in the pipe. It becomes possible to limit to the limit. In addition, as shown in FIG. 2, if the transfer pipe 2 is connected along the inner circumference of the side surface of the blowdown tank 3 along the tangential direction, the polymerization system is recovered through the transfer pipe to the blowdown tank. It is effective in preventing damage to equipment due to the impact of the contents being discharged at once.
[0008]
The gas holder 5 used in the present invention may be one used in ordinary vinyl chloride polymer recovery equipment, for example, a water-sealed container provided upside down in a water tank. Usually, the capacity is preferably sufficiently larger than the blowdown tank 3.
[0009]
Recovery facility of the present invention, the polymerization of more than 80 wt% of the salt of the vinyl monomer were charged vinyl chloride monomer in a polymerization reaction vessel, the pressure of the polymerization reaction tank is 3 kg / cm ² G or more It is desirable to start collection at this point. The effect of the present invention is great when the pressure in the polymerization reaction tank at the start of recovery is 3 kg / cm ² G or more, and more preferably 5 kg / cm ² G or more. It may be when the pressure in the polymerization reaction tank at the start of the recovery is the pressure indicated during the main reaction of the polymerization. In the present invention, among the vinyl chloride monomers initially charged in the polymerization reaction tank, less than 50% by weight of the unreacted monomer that has not been polymerized is preliminarily supplied from a pipe provided at the top of the polymerization reaction tank. You may employ | adopt the method of collect | recovering all the remaining contents to a blowdown tank after performing operation to collect | recover. In the present invention, when adopting a method of starting recovery of the contents from the polymerization reaction tank at a stage where 50% by weight or more of the unreacted vinyl chloride monomer is present in the polymerization reaction tank, The effect is great, more preferably when 90% by weight or more is present. In the present invention, it is possible to recover all the contents in the reaction tank to the blow-down tank without substantially recovering the unreacted vinyl chloride monomer in the polymerization reaction tank. The effect is most preferable when this method is adopted. As described above, in the present invention, since the operation of recovering unreacted monomers in the reaction vessel usually performed after the polymerization reaction can be reduced or omitted at all, the polymerization reaction is terminated and the process until the next batch polymerization is started. It becomes possible to shorten the time lag effectively. As a result, the actual operation rate of the polymerization reaction tank can be increased, which contributes to improving the production efficiency of the vinyl chloride polymer. In addition, if recovery is performed using the recovery equipment of the present invention, the pressure in the tank in the blowdown tank can be reduced, and the concentration of unreacted monomer contained in the recovered content is low. As a result, the variation in local pressure fluctuation in the contents is reduced. For this reason, while being able to reduce the load in the removal process of the full-scale unreacted vinyl chloride monomer in the next process, there is an excellent effect that the operation management in the removal process is stabilized. That is, when the concentration of unreacted monomer in the contents of the blowdown tank is high, the unreacted monomer is removed at the entrance of the apparatus related to the above-described full-scale unreacted vinyl chloride monomer removal process. Since the momentum of flash evaporation is strong, the vinyl chloride polymer particles scatter and adhere to the inner wall of the apparatus, and as a result of being exposed for a long time at a high temperature close to 100 ° C., the polymer particles are colored. This peels off and mixes into the product particles, reducing the product quality. According to the examination results of the present inventors, the contents can be obtained without recovering the unreacted monomer in the polymerization reaction tank by using the equipment normally used without using the recovery equipment of the present invention. When recovered in a tank at once, the concentration of the vinyl chloride monomer in the polymerization system content after the above-described full-scale vinyl chloride monomer removal step was 530 ppm at the maximum, When recovery was performed in the same manner using the apparatus of the present invention, the concentration of the vinyl chloride monomer was stable at 10 ppm or less.
[0010]
【Example】
The present invention will be described below in more detail based on examples, but these do not limit the present invention.
[0011]
Example 1
Both have a gas holder with a volume of 2,500 m ³ in water with a design pressure of 1,000 mm and a blow-down tank of 100 m ³ , and the gap between the gas phase parts is 2.5 times the diameter of the transfer pipe, with a diameter of about 250 mm. It has a seal pot that is connected by a vent pipe having a distance of 80 m and draws condensed water therebetween. The volume of the polymerization reaction tank is 60 m ³ , and the transfer pipe is connected to the blowdown tank via a pump and PIC (blowdown tank pressure regulating valve). This connecting portion is connected in a tangential direction to the inner periphery of the side surface of the blowdown tank. Using this apparatus, at a polymerization temperature of 57 ° C., a vinyl chloride monomer charge amount of 20,000 kg, a water charge amount of 24,000 kg, 440 ppm of partially saponified polyvinyl alcohol as a dispersant with respect to the vinyl chloride monomer, Polymerization was carried out by adding 300 ppm of t-butylperoxydecanoate and 200 ppm of cumylperoxyneodecanoate as polymerization initiators, and when the pressure in the polymerization reaction vessel dropped to 5 kg / cm ³ G (single vinyl chloride) When 91.8% by weight of the body was polymerized), the contents were collected into the blowdown tank via the transfer tube. At this time, the pressure in the blowdown tank was controlled to be 300 mm or less. At this time, the time required for the polymerization process was 545 minutes, the yield was 91.8%, and the productivity was 26 T / m ³ · M (the volume of the vinyl chloride polymer that can be produced per 1 m ^{3 of the} polymerization vessel and 30 days). Tonnage).
[0012]
Example 2
When the pressure in the polymerization reaction tank was reduced to 6.5 kg / cm ³ G, only the unreacted monomer was recovered in the polymerization reaction tank, and the pressure in the polymerization reaction tank was further reduced to 5 kg / cm ³ G. This was carried out in the same manner as in Example 1 except that the polymerization content was collected in the blowdown tank at the time (91.2% by weight of the vinyl chloride monomer was polymerized). The amount of the vinyl chloride monomer recovered in the polymerization reaction tank is the amount of unreacted vinyl chloride monomer present in the reaction tank when the pressure in the reaction tank was 6.5 kg / cm ³ G. The amount was less than 50% by weight. The pressure in the blow-down tank during recovery was controlled below 300 mm water column. The time required for the polymerization process was 510 minutes, the yield was 91.2%, and the productivity was 28.2 T / m ³ · M.
[0013]
Example 3
When the pressure in the polymerization reaction tank dropped to 6.5 kg / cm ³ G (when 90.4% by weight of the vinyl chloride monomer was polymerized), the polymerization system content was recovered in the blowdown tank. Except for the above, it was carried out according to Example 1. Also at this time, the pressure of the blowdown tank was controlled to be 300 mm or less. The time required for the polymerization process was 437 minutes, the yield was 90.4%, and the productivity was 32.8 T / m ³ · M.
[0014]
The present invention is a recovery device that combines high polymerization productivity and low construction costs, and by using this device to recover the polymerization system content, The operation in the removal process is stabilized, and the residual concentration of the vinyl chloride monomer in the vinyl chloride resin product is stabilized at a low value, thereby contributing to the improvement of the product quality.
[Brief description of the drawings]
[Fig. 1] Vinyl chloride polymer recovery facility [Fig. 2] View of blowdown tank from above [Explanation of symbols]
1 .... Polymerization reactor, 2 .... Transfer pipe, 3 .... Blowdown tank,
4 .... Vent pipe, 5 .... Gas holder, 6 ... Control valve,
7. Pressure gauge, 8. Seal pot

Claims (6)

(A) a polymerization reaction vessel for producing a vinyl chloride polymer by polymerizing a vinyl chloride monomer or a mixture of vinyl chloride and a copolymerizable monomer; and (b) the reaction vessel. A transfer pipe for transferring the content containing the vinyl chloride polymer after polymerization reaction and the unreacted monomer, and (c) temporarily storing the contents transferred through the transfer pipe or A blow-down tank having an internal volume of 1 to 3 times the internal volume of the polymerization reaction tank and a pressure-resistant allowable pressure of 1 kg / cm ² G or less; A vent pipe provided at the outlet of the down tank, and (e) a pressure adjusting means for adjusting the flow rate in the transfer pipe at the inlet of the blow-down tank so that the pressure in the blow-down tank is equal to or lower than the allowable pressure-resistant pressure; ) Unwarped moving through the vent pipe A recovery device of unreacted monomers have a gas holder for holding a gas containing a monomer, an inner diameter of the vent tube is 1.5 to 4 times the inner diameter of the transfer tube, and The inner circumference of the side surface of the blowdown tank is circular, and the transfer pipe connecting from the polymerization reaction tank to the blowdown tank is connected to the inner circumference of the side surface of the blowdown tank so as to follow the tangential direction. An unreacted monomer recovery device in a vinyl chloride polymerization facility. The recovery device according to claim 1 , wherein the internal volume of the blowdown tank is 1.5 to 2.5 times the internal volume of the polymerization reaction tank . The recovery device according to claim 1 or 2, wherein an inner diameter of the vent pipe is 2 to 3 times an inner diameter of the transfer pipe . It is a collection | recovery method of the unreacted monomer in the vinyl chloride polymerization equipment using the collection | recovery apparatus of any one of Claims 1-3, and the monomer which can be copolymerized with this with a vinyl chloride monomer or vinyl chloride In the polymerization reaction tank, with 80% by weight or more of the monomer remaining in the polymerization reaction tank and 50% by weight or more of the unreacted monomer remaining. When the pressure is 3 kg / cm ² G or more, the contents of the polymerization reaction tank containing the remaining unreacted monomer and the vinyl chloride polymer are recovered in a blowdown tank, and the pressure in the blowdown tank is reduced. A method for recovering unreacted monomer in a vinyl chloride polymerization facility, wherein the gas containing the unreacted monomer is recovered from the blow-down tank to a gas holder while maintaining the pressure at 1 kg / cm ² G or less. The content of the remaining unreacted monomer and the vinyl chloride polymer is collected in a blowdown tank in a state where 90% by weight or more of the unreacted monomer remains. Item 5. The recovery method according to Item 4. The pressure in the polymerization reactor is 5 kg / cm ² The recovery method according to claim 4, wherein the content of the reaction tank is recovered to the blow-down tank when G or more.

Images