JPH06200039A - Transfer method for vinyl chloride polymer slurry - Google Patents

Abstract

(57) [Summary] [Construction] In a method for transferring a vinyl chloride polymer slurry from a polymerization vessel to a slurry tank via a transfer pump, the transfer pump comprises a conical hub and a spiral attached to the conical hub. A method for transferring a vinyl chloride polymer slurry, which is a pump comprising an impeller having a single blade. [Effect] After the completion of the polymerization, the time from the start of the collection of the unreacted monomer from the polymerization vessel to the completion of the transfer of the vinyl chloride polymer slurry to the slurry tank can be further shortened. Therefore, it is possible to increase the operating rate of the polymerization vessel and improve the productivity of producing the vinyl chloride polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer method for transferring a vinyl chloride polymer slurry from a polymerization vessel to a slurry tank after the completion of a polymerization reaction when producing a vinyl chloride polymer.

[0002]

2. Description of the Related Art Conventionally, in a method for producing a vinyl chloride-based polymer, the polymerization reaction of a monomer such as vinyl chloride is caused by a polymerization conversion
The polymerization reaction is stopped when 70-95% is reached, and the unreacted monomer is directly recovered from the polymerization vessel, and the resulting vinyl chloride polymer slurry is transferred to improve the operation rate of the polymerization vessel. Was transferred to the slurry tank. The vinyl chloride polymer slurry once stored in the slurry tank was then sequentially transferred to a dehydration step and a drying step to produce a vinyl chloride polymer. A centrifugal pump has been mainly used as the transfer pump.

In recent years, in order to increase the operating rate of the polymerization vessel and improve the productivity of the vinyl chloride polymer production, it has been required to shorten the polymerization cycle per batch. As part of this, it has been attempted to shorten the time from the start of collecting unreacted monomers from the polymerization vessel to the completion of transfer of the vinyl chloride polymer slurry to the slurry tank.

In order to shorten the time from the recovery of the unreacted monomer from the inside of the polymerization vessel to the completion of the transfer of the vinyl chloride polymer slurry to the slurry tank, after the reaction is completed, the unreacted monomer from the polymerization vessel is removed. At the same time, the vinyl chloride polymer slurry is transferred from the polymerization vessel to the slurry tank while being collected. However, in this method, the transfer of the vinyl chloride polymer is started rapidly when the pressure in the polymerization vessel is higher than the pressure in the slurry tank, so the spiral pump used as the transfer pump cannot deliver liquid exceeding the rated value. As a result of being forced, the motor will stop due to overcurrent (so-called trip), or the impeller of the centrifugal pump will subject the vinyl chloride polymer slurry to high shear force and gasify the unreacted monomers in the vinyl chloride polymer slurry. The transfer pump trips or the pump cavitation phenomenon occurs, which increases the transfer time. In a severe case, there arises a problem that the transfer cannot be performed. Therefore, after starting the recovery of unreacted monomers, it is not possible to start the transfer of the vinyl chloride polymer slurry from the polymerization vessel to the slurry tank until the internal pressure of the polymerization vessel becomes less than 0.1 kg / cm ² · G. There was a limitation.

[0005]

Therefore, an object of the present invention is to provide a vinyl chloride polymer slurry even if transfer of the vinyl chloride polymer slurry is started in a state where the internal pressure of the polymerization vessel is higher than the pressure in the slurry tank. It can be smoothly transferred from the polymerization vessel to the slurry tank, and as a result, it is possible to shorten the time from the start of collecting unreacted monomers in the polymerization vessel to the completion of the transfer of the vinyl chloride polymer slurry to the slurry tank. It is an object of the present invention to provide a method for transferring a vinyl chloride polymer slurry capable of carrying out the above.

[0006]

The inventors of the present invention can transfer unreacted monomers in a vinyl chloride polymer slurry without gasification by adopting a special structure described below. It has been found that the above objectives can be achieved.

That is, the present invention relates to a method of transferring a vinyl chloride polymer slurry from a polymerizer to a slurry tank via a transfer pump, wherein the transfer pump is a conical hub and a spiral attached to the conical hub. The present invention provides a method for transferring a vinyl chloride polymer slurry, which is a pump including an impeller having a single blade. Hereinafter, details of the present invention will be described with reference to the accompanying drawings.

FIG. 1 schematically shows the whole of a polymerization vessel and a slurry tank equipped with a means for transferring a vinyl chloride polymer slurry. In FIG. 1, 1 is a polymerization vessel, 2
Is a slurry tank, and 3 is a transfer pipe for transferring the vinyl chloride polymer slurry from the bottom of the polymerizer 1 to the slurry tank 2 from the polymerizer 1 to the slurry tank 2.
Further, 4 is a transfer pump provided in the transfer pipe 3 between the polymerizer 1 and the slurry tank 2. Reference numeral 5 is a pipe for charging a raw material, which is provided in the upper part of the polymerization vessel, 6 is an unreacted monomer recovery pipe, which is provided in the upper part of the polymerization vessel, for recovering unreacted monomer after completion of the polymerization, and 7 is a polymerization vessel. The jackets, 8 and 8 ', are pipes for supplying a medium for heating or cooling to the polymerization vessel jacket 7. 9 is a stirrer provided in the polymerization vessel, and 10 is a stirrer provided at the top of the polymerization vessel.
Is a motor for driving.

Reference numeral 11 is a pipe for transferring the vinyl chloride polymer slurry from the bottom of the slurry tank 2 to the dehydration step,
Reference numeral 12 is an unreacted monomer recovery pipe provided on the upper portion of the slurry tank 2 for recovering unreacted monomer contained in the vinyl chloride polymer slurry. Reference numeral 13 is a stirrer provided in the slurry tank, and 14 is a motor provided at the upper part of the slurry tank for driving the stirrer 13.

In the apparatus shown in FIG. 1, a vinyl chloride monomer, an aqueous medium, a dispersant, an oil-soluble polymerization initiator, etc. are introduced into the inside of the polymerization vessel 1 through a raw material charging pipe 5 provided in the upper portion of the polymerization vessel 1. The raw materials and the like charged into the polymerization vessel 1 are stirred and mixed by a stirrer 9 to form an aqueous suspension mixture.
With stirring, the aqueous suspension mixture is heated and heated by the polymerization vessel jacket 7 to start the polymerization at a predetermined temperature. During the polymerization reaction, the temperature of the polymerization vessel is maintained at a predetermined temperature by cooling from the polymerization vessel jacket 7. The polymerization reaction is stopped when the polymerization reaction of the vinyl chloride-based monomer reaches a polymerization conversion rate of 70 to 95%.

After the completion of the polymerization reaction, the vinyl chloride-based polymer is collected from the inside of the polymerization vessel 1 while collecting the unreacted monomer from the inside of the polymerization vessel 1 through the unreacted monomer collection pipe 6 provided at the upper portion of the polymerization vessel 1. The slurry is transferred to the slurry tank 2 by the transfer pump 4 through the vinyl chloride polymer slurry transfer pipe 3.

If necessary, after the vinyl chloride polymer slurry has been transferred to the slurry tank 2, the vinyl chloride polymer slurry is agitated by the stirrer 13 while the unreacted unit amount contained in the vinyl chloride polymer slurry is agitated. The body may be recovered through the unreacted monomer recovery pipe 12. Further, when collecting the unreacted monomer, a vinyl chloride polymer slurry is predetermined through a heating medium through pipes 16 and 16 'for supplying a medium for heating or cooling to a jacket 15 provided in the slurry tank 2. The unreacted monomer contained in the vinyl chloride-based polymer slurry may be recovered while heating to the above temperature.

According to the present invention, as the transfer pump 4, a pump having a conical hub and an impeller having a single spiral blade mounted on the conical hub is used. The pump concerning FIG. 2 is illustrated.

The pump shown in FIG. 2 comprises a conical hub 21 rotatably provided around a rotary shaft 20, and an impeller 22 consisting of a single blade spirally provided around the hub 21. Have. The diameter of the impeller 22 is small at the tip of the conical hub 21 and gradually increases toward the base. The hub 21 and impeller
The casing that encloses 22 is about half 23 at the base side of the hub 21,
It has a thick disc shape so that an annular space (swirl chamber) 24 is provided around the hub 21. Approximately half 25 of the end of the hub 21 of the casing is frustoconical and has an inner diameter of a spiral impeller.
It is almost in contact with the outer edge of 22. A suction port 25 for the vinyl chloride polymer slurry is opened at the tip of the frustoconical casing 25, and the transfer pipe 3 is connected to the suction port 25. A discharge port 26 for the vinyl chloride polymer slurry is provided on the side wall of the disk-shaped casing portion 23, and is connected to the transfer pipe 3.

In the above pump, the hub 21 and the impeller 22
Rotates in the direction of the arrow 27, and in the region A corresponding to the frustoconical casing portion 25, the impeller 22 mainly adds a screw action to the polymer slurry. The impeller 22 has a screw shape and functions like a volumetric pump, and since it has only one blade, it has a gentle flow, and separation due to centrifugal force and shearing force hardly occurs, and at the same time, the polymer slurry flowing from the suction port 25 It gives a strong suction force. While the impeller 22 is rotating, the impeller 22 faces the disk-shaped casing 23 in the frustoconical casing 25, and its diameter gradually increases. It flows, its peripheral speed is gradually increased, and discharge pressure is added.

In the region B corresponding to the disk-shaped casing portion 23, the centrifugal action is mainly applied to the polymer slurry, and the polymerization reaction liquid is discharged from the discharge port 26 at a high discharge pressure. The pump having this structure is generally commercially available under the trade name of Hydrostal Pump (manufactured by Taiheiyo Metal Co., Ltd.).

The polymerization reaction of vinyl chloride type monomer is usually
The polymerization reaction is stopped when the polymerization conversion rate reaches 70 to 95%. At this stage, the pressure in the polymerization vessel is usually 4.0 to
It is 10.0 kg / cm ² · G. According to the present invention, if the pressure in the polymerization vessel after completion of the polymerization reaction is 7.0 kg / cm ² G or less,
Even when the transfer of vinyl chloride polymer slurry from the polymerization vessel to the slurry tank is started, the transfer pump trips,
It is possible to transfer the vinyl chloride polymer slurry smoothly without causing a problem such as a cavitation phenomenon. After completion of the reaction, the vinyl chloride polymer slurry may be transferred from the polymerization vessel to the slurry tank at the same time as the recovery of the unreacted monomer from the polymerization vessel may be started. After the partial recovery, the vinyl chloride polymer slurry transfer from the polymerization vessel to the slurry tank may be started while continuing the recovery of the unreacted monomer.
Desirably, the transfer of the vinyl chloride polymer slurry from the polymerization vessel to the slurry tank is started at an internal pressure of the polymerization vessel of 5.0 kg / cm ²
・ Transfer will start when it becomes less than G. When the transfer of the vinyl chloride polymer slurry is started when the internal pressure of the polymerization vessel is too high, a foaming phenomenon accompanying the evaporation of the monomer suddenly occurs in the slurry tank and scatters on the monomer recovery line.
Problems such as line blockage may occur.

The internal pressure of the slurry tank when the vinyl chloride polymer slurry is started is preferably 0.1 kg / cm ² · G or less, more preferably 0 kg / cm ² · G or less.

Further, when recovering the unreacted monomer from the polymerization reactor, the pressure in the polymerization reactor is kept from the start of recovering the unreacted monomer.
It is preferable that the exhaust gas velocity per unit weight of the charged monomer is 60 to 300 Nm ³ / Hr / t monomer until the pressure falls to 2.5 kg / cm ² · G. If the exhaust gas velocity at this time is too low, it takes too much time to recover the unreacted monomer, which is not economical. Further, if the recovery rate is too high, carryover of the polymer slurry generated during recovery will occur.

After the pressure in the polymerization vessel is reduced to about 2.5 kg / cm ² · G or less, the exhaust gas velocity is preferably less than 60 Nm ³ / Hr / t monomer. If the pressure in the polymerization vessel at this time is too high, bubbles are remarkably generated, and carry-over of the produced vinyl chloride polymer slurry occurs.

As the polymerization vessel 1 used in the present invention, a conventionally known type equipped with a stirrer, a reflux condenser, a baffle or a jacket is used. For this stirrer, a stirrer of the type such as a paddle, a Fowler, a bull margin, a propeller or the like is used in combination with a baffle such as a flat plate, a cylinder or a hairpin coil, if necessary.

As the slurry tank 2 used in the present invention, a conventionally known type in which a stirrer, a jacket and the like are energized is used. For this stirrer, a stirrer of the same type as in the case of the above-mentioned polymerization vessel is used.

The transfer pipe 3, the transfer pump 4, the unreacted monomer recovery pipes 6 and 12, and other parts where the vinyl chloride polymer such as baffles and the unreacted monomer come into contact with each other are 18 in terms of heat transfer and corrosion resistance. -8 austenite type, 13 chrome ferrite type,
It is preferable to use martensite-based, 18 chromium ferrite-based, high chromium ferrite-based, two-phase austenite, ferritic stainless steel. Conventionally known scale inhibitors may be applied to these places.

The vinyl chloride-based polymer produced by the polymerization apparatus of the present invention is a vinyl chloride homopolymer as well as a copolymer of vinyl chloride and another vinyl-based monomer (usually 50% by weight or more of vinyl chloride). ) Is included. Comonomers copolymerized with this vinyl chloride include ethylene, propylene,
Α-olefins such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene; acrylic Acrylic acid or its ester such as acid, methyl acrylate, ethyl acrylate; Methacrylic acid or its ester such as methacrylic acid or methyl methacrylate; Maleic acid or its ester; Vinyl ester such as vinyl acetate, vinyl propionate; Lauryl vinyl ether , Vinyl ethers such as isobutyl vinyl ether; maleic anhydride; acrylonitrile; styrene; vinylidene chloride; and other monomers copolymerizable with vinyl chloride. These can be used alone or in combination of two or more.

Other conditions used in this polymerization, the method of charging the aqueous medium, the vinyl chloride monomer, the polymerization initiator or the dispersion aid, etc. to the polymerization vessel, the charging ratio, etc. may be the same as in the conventional case. . Further, in this polymerization system, if necessary, a polymerization regulator, a chain transfer agent, a pH regulator, a gelation improver, an antistatic agent, a cross-linking agent, a stabilizer, and a filler which are appropriately used for vinyl chloride-based polymerization. Agents, antioxidants, buffers,
It is also optional to add a scale inhibitor or the like.

[0026]

【Example】

Example 1 As shown in FIG. 1, a polymerization vessel 1 made of stainless steel with an internal volume of 2.1 m ³ and equipped with a jacket and a stirrer and a pressure resistant slurry tank 2 made of stainless steel with an internal volume of 3.4 m ³ and equipped with a jacket and a stirrer were used. Connected via a transfer pipe 3 for transferring the vinyl chloride polymer slurry, and as a transfer pump 4 between them, 15
m ³ / Hr × 5m hydro static Le pump piping by installing a (variable flow rate with apparatus according to the inverter), was connected via a valve or the like.

Deionized water (950 kg), partially saponified polyvinyl alcohol (420 g) and 2-ethylhexyl peroxydicarbonate (280 g) were charged in the above polymerization vessel, and after degassing the inside of the polymerization vessel, 700 kg of vinyl chloride monomer was charged. While stirring the inside of the polymerization vessel, pure water was passed through the polymerization vessel jacket to raise the temperature to 57 ° C. to start the polymerization. During the polymerization reaction, cold water was passed through the polymerization vessel jacket to keep the polymerization reaction temperature at 57 ° C. The polymerization was stopped when the internal pressure in the polymerization vessel dropped to 6.5 kg / cm ² · G. Recovery of unreacted monomers from the polymerization vessel and transfer of the vinyl chloride polymer slurry from the polymerization vessel to the slurry tank were performed as follows.

The pressure in the polymerization vessel is 6.5 kg / cm ² · G to 2.
While decreasing to 5 kg / cm ² G, the exhaust gas velocity of unreacted monomer is controlled to 100 Nm ³ / Hr / t monomer to recover unreacted monomer, and the pressure in the polymerization vessel is 2.5 kg. When the exhaust gas velocity of the unreacted monomer is changed to 20 Nm ³ / Hr / t monomer when it falls below / cm ² · G, until the transfer of the vinyl chloride polymer slurry from the polymerizer to the slurry tank is completed Collection continued. After the start of the recovery of unreacted monomer from the polymerization vessel, the pressure in the polymerization vessel is
At the time when it dropped to 1.5 kg / cm ² · G, the flow rate of the vinyl chloride polymer slurry from the polymerizer to the slurry tank was changed to 16
Started at 000 l / hr. At this time, the inside of the slurry tank was degassed beforehand, and the internal pressure was -0.1 kg / cm ^2.
It was G.

When the transfer was carried out in this manner, the following results were obtained. -Time from start of exhaust gas in polymerization vessel to completion of slurry transfer 40 minutes-Time required to transfer slurry 10 minutes

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that a centrifugal volute pump of 15 m ³ / Hr × 5 m was used as the transfer pump, and the unreacted monomer was recovered from the polymerizer and the polymerizer was used. The vinyl chloride polymer slurry was transferred to the slurry tank.

The following results were obtained. -Time from start of exhaust gas in polymerization vessel to completion of slurry transfer-Time required to transfer slurry- 20 minutes

It should be noted that shortly after the transfer of the vinyl chloride polymer slurry from the polymerization vessel to the slurry tank was started, the discharge pressure of the transfer pump was lowered, and abnormal noise was generated, causing cavitation phenomenon in the transfer pump. Was confirmed. This cavitation phenomenon continued during the transfer. When the inside of the polymerization vessel was inspected after the completion of the transfer, the polymer slurry was partly caked and remained at the bottom of the polymerization vessel.

Comparative Example 2 Polymerization was carried out in the same manner as in Example 1 except that a 15 m ³ / Hr × 5 m centrifugal centrifugal pump was used as the transfer pump. Recovery of unreacted monomers from the polymerization vessel and transfer of the vinyl chloride polymer slurry from the polymerization vessel to the slurry tank were performed as follows.

The pressure inside the polymerization vessel is from 6.5 kg / cm ² · G
The exhaust gas velocity of unreacted monomer was controlled to 100 Nm ³ / Hr / t monomer while it was reduced to 2.5 kg / cm ² · G, and unreacted monomer was recovered. When the pressure in the polymerization vessel dropped to 2.5 kg / cm ² G or less, the exhaust gas velocity of unreacted monomer was changed to 20 Nm ³ / Hr / t monomer, and the pressure in the polymerization vessel was changed to 0.1 kg / The unreacted monomer was continuously collected at the same exhaust gas velocity until it reached cm ² · G.
After the recovery of the unreacted monomer was completed, the transfer of the vinyl chloride polymer slurry to the slurry tank (internal pressure: -0.1 kg / cm ² · G) was started at a transfer rate of 1600 l / Hr.

The following results were obtained. -Time required for recovery of unreacted monomer 40 minutes-Time from start of exhaust gas in polymerization vessel to completion of slurry transfer 50 minutes-Time required for slurry transfer 10 minutes Transfer of vinyl chloride polymer slurry completed The inside of the post-polymerization vessel was inspected, but no slurry remained.

[0036]

According to the present invention, after the completion of polymerization,
The time from the start of collecting the unreacted monomer from the inside of the polymerization vessel to the completion of the transfer of the vinyl chloride polymer slurry to the slurry tank can be further shortened. Therefore, it is possible to increase the operating rate of the polymerization vessel and improve the productivity of producing the vinyl chloride polymer.

[Brief description of drawings]

FIG. 1 is a schematic view showing a polymerization vessel and a slurry tank connected by a polymer slurry transfer pipe.

FIG. 2 shows an example of a pump used in the method of the present invention.

[Explanation of symbols]

 1 Polymerizer 2 Slurry pump 3 Polymer slurry transfer pipe 4 Transfer pump 6 Unreacted monomer recovery pipe 12 Unreacted monomer recovery pipe

Claims (1)

[Claims] 1. A method for transferring a vinyl chloride polymer slurry from a polymerizer to a slurry tank via a transfer pump, wherein the transfer pump comprises a conical hub and a spiral single blade mounted on the conical hub. A method for transferring a vinyl chloride polymer slurry, which is a pump comprising: