JPH0629291B2 - Vinyl chloride fluidized gas phase polymerization equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a vinyl chloride monomer (hereinafter abbreviated as VCM).
Alternatively, the present invention mainly relates to a reactor suitable for continuous polymerization in a gas flow gas phase polymerization with a copolymerizable comonomer by a stirring gas flow system.

Regarding the gas phase polymerization of VCM, Japanese Patent Publication No. 48-1466
No. 6,48,918, US Pat. No. 3,578,646, etc., but the quality of the obtained product is insufficient.

As a result of earnest studies, the inventors of the present invention have conducted a continuous polymerization method or a semi-continuous polymerization method to obtain a product having a quality sufficiently comparable to the product obtained by the conventional suspension polymerization method or the two-stage bulk polymerization method by the gas phase polymerization method. I found that it was possible.

That is, 1) Conditions for preparing seed polymer The properties of the seed polymer, which is a carrier for the initiator of the gas phase polymerization, have a considerably dominant influence on the properties of the product of the gas phase polymerization.

In order to improve the properties of this kind of polymer, in bulk prepolymerization, for example, in the polymerization with a polymerization rate of 14 to 20%, the particle size distribution is sharpened and the internal structure of the particles is modified to obtain a porous polymer. In addition, in the gas phase polymerization, a specific additive having the function of preventing the polymerization inside the particles as much as possible is added, and further, at the end of the bulk prepolymerization, a characteristic of Coating the additive to prevent the infiltration of the initiator inside the gas phase polymerization,
Polymerization inside the particles is prevented, and aggregation between particles is prevented.

Furthermore, when unreacted VCM is recovered and powdered seed polymer is obtained, sufficient stirring shear and heat are applied to reduce irregularities on the particle surface, and it is necessary to make a good powdered seed polymer with a bulk specific gravity of 0.32 or more. There is.

2) Gas phase polymerization In carrying out gas phase polymerization using the above-mentioned seed polymer, gas phase polymerization is Pr (= polymerization pressure kg / cm ³ / saturated vapor pressure at the polymerization temperature).
kg / cm ³ ) is less than 1.0 and 0.5 or more, but with Pr 0.75 or more, the reactivity becomes significantly higher as Pr becomes higher,
Further, the bulk specific gravity also becomes large, the particle size distribution becomes sharp, and the coarse particle generation rate also decreases. Furthermore, the hue and thermal stability during processing are also improved. However, the fish eye characteristic (hereinafter abbreviated as FE characteristic) is significantly deteriorated.

Therefore, in order to keep the FE characteristics at a good level and the other characteristics at a practical level, it is necessary to carry out the gas phase polymerization with Pr 0.65 to 0.85, preferably 0.70 to 0.80.

Still, the growth ratio [(gas phase polymerization amount + seed polymer amount) / seed polymer amount. same as below. ) Exceeds 5 to 6 times, the quality gradually deteriorates. In order to prevent this and maintain a constant quality level, it is necessary to feed new seed polymer and keep the growth ratio in the range of 4-5 times.

However, even if the production conditions of these seed polymers and the values of Pr and the growth ratio in the gas phase polymerization are satisfied, various technical problems remain in the gas phase polymerization. That is, (1) in the gas phase polymerization, when the polymerized slurry is spray-supplied as a means for supplying the seed polymer, the gas phase polymerized particles aggregate to form coarse particles.

(2) A method is known in which the heat of polymerization is removed by the latent heat of vaporization of the monomer liquid, but the supply amount of the monomer liquid becomes excessive only by this method.

The present invention is intended to solve these problems, and its gist is to have (a) an upper portion, (b) a spray nozzle for a monomer liquid, and a spray nozzle for a slurry (comprising a monomer liquid and a seed polymer). It is a fluidized gas phase polymerization apparatus for homopolymerization or copolymerization of VCM, which comprises a central part and (c) a bottom part having a monomer gas blowing port, a cooler and an anchor type stirring blade.

The details of the present invention will be described below.

After starting the polymerization, it is most processwise to supply the polymerization slurry having a polymerization rate of 14 to 20% by the bulk prepolymerization as the seed polymer to be supplied to the polymerization apparatus and the VCM diluted to a solid concentration of 7.0% to 12%. Reasonable, but there are some problems. Among them, a major problem is that aggregate coarse particles are likely to occur.

The particles of the above-mentioned polymerized slurry have a smaller particle size and are softer than the powdered seed polymer, so that they adhere to the particles during the gas phase polymerization and act as a binder to generate agglomerated coarse particles. It is considered easy.

As a result of diligently studying the prevention of the formation of aggregate coarse particles, it was found that it is important to apply a shearing force at the initial stage of aggregation to redisperse the particles. In a simple gas flow polymerization tank, when the gas flow velocity is increased, the movement of particles in the vertical direction becomes active in the means, but shearing force between particles is hardly applied.

In the present invention, as shown in FIG. 1, a stirring blade is attached to the lower part, whereby a shearing force is applied to the particles to redisperse the agglomerated particles in the initial stage, thereby preventing the generation of coarse particles. The stirring blade is an anchor type and low speed stirring of 150 rpm or less is desirable.

Monomer inlet for fluidizing polymer particles 4,
For No. 5, it is desirable to insert a porous ring-shaped diffuser tube in the lower part of the fluidized bed.

In the perforated plate type dispersion plate, powder leakage occurs when the polymerization reaction rises and stops when compared with the perforated plate. In particular, at the time of start-up, during the operation for deoxidizing the system, powder leakage easily occurs, which causes trouble. Further, although a powder such as a sintered plate does not leak, it is clogged with fine particles contained in the circulating gas, which causes an increase in pressure loss and makes continuous polymerization difficult. Insertion of a porous ring-shaped air diffuser enables continuous polymerization which causes powder leakage and clogging.

An internal cooling pipe is provided at the bottom as the most effective means for removing the heat of polymerization generated.

Since the cooling pipe is at the bottom, that is, in the fluidized bed, it prevents partial flow due to blow-through phenomenon in the initial stage of flow, and suppresses abnormal phenomena such as slagging and channeling when the fluidized bed height rises or the gas flow velocity is increased, In addition to homogenizing the flow, by passing cooling water inside, fine condensed monomer droplets are generated on the surface of the pipe, the gas phase polymer particles are wiped off, and it is evaporated and gasified by the heat of polymerization. In addition to frictional heat transfer of particles, condensation heat transfer is added to it, and therefore, it has a large heat transfer capacity, so the removal capacity for polymerization heat is extremely high, that is, the production capacity can be increased.

However, if the gap between the adjacent cooling pipes is 40 mm or less, the flow is obstructed and lumps are easily formed. Further, if the length is 100 mm or more, the number of pieces that can be stored is small, which is not preferable. 50 mm ~
100 mm is a preferable range.

The partition plate 8 is vertically inserted in the middle part. When it is two or more, insert a plurality of partition plates in parallel with each other, or intersect at the center of the circle of the cross section to divide the circle into two or more and divide into two or more and five or less, and then the initiator and seed slurry are added. In addition to the first partition, the next partition, and so on by overflow,
It is possible to control the residence time distribution in continuous polymerization by moving to the next compartment and withdrawing the product from the final compartment.

It is also possible to change the fluidization speed of each chamber to some extent by setting the VCM gas injection pipe at the bottom.

It should be noted that the partition plate may not be completely partitioned, but 1/4 to 3/4 from the upper part of the fluidized bed may be shared by the lower part.

The initiator is usually added to the monomer liquid and supplied by spraying, but if sprayed from the upper part of the fluidized bed, there is an upward flow from the lower side, the fine droplets do not contact the powder, and are blown upward,
There is a risk that the efficiency of the initiator will be reduced, and there is a risk of scaling in the gas phase. Therefore, in order to avoid these drawbacks, the monomer liquid spray nozzle is immersed in the fluidized bed and sprayed.

Since it is necessary for the spray nozzle 10 for polymerized slurry to divide and disperse the polymerized slurry into individual polymer particle levels as much as possible, it is desirable to spray from above the fluidized bed level.

In the upper part of the fluidized bed, in order to prevent particles from being entrained in the circulating gas, the cross-sectional area of the upper part is set to 2 to the cross-sectional area of the middle part.
It is quadrupled and the flow velocity is expanded so that it is less than 1/2 of the superficial velocity in the fluidized bed. That is, in the case of a cylindrical shape, the inner diameter is set to be 2 times or more and 2 times or less that of the fluidized bed.

As described above, even if the cross-sectional area of the upper part is increased, it is inevitable that fine particles are entrained in the exhaust gas, so it is desirable to separate with a cyclone provided as shown in FIG. The fine particles adsorb the monomer and have a large angle of repose, so they do not return at the vibrator or air knocker position. If they accumulate, the separation efficiency will decrease, and powder will mix into the circulation line, causing scaling and other problems.

As a result of various studies, for example, a part of the circulation flow of the monomer gas is divided, and the monomer gas is connected to the bottom of the cyclone via the automatic valve 15. On the other hand, open the automatic valve 12 under the cyclone for a certain time,
The separated fine powder is put into a pipe 13 with a bile letter or a knocker, after the automatic valve 12 is closed, the automatic valve 12 is opened, the automatic valve 15 is immediately opened, and the fine powder is forcibly blown into the fluidized tank by a partial flow of the monomer gas, After a certain time, the automatic valve 14 is closed, and then the automatic valve 15 is also closed. It becomes possible to forcibly return the fine powder separated by the cyclone to the fluidized bed in an intermittent valve sequence in which the automatic valve 12 opens again.

[Brief description of drawings]

1 and 2 are cross-sectional views of an embodiment of the device of the present invention. Bottom, middle part of monomer liquid spray nozzle, upper part of polymerized slurry spray nozzle, extraction pipe, monomer gas injection pipe, automatic valve, stirring blade, pipe cooler, automatic valve partition plate, automatic valve diversion pipe

Claims (7)

[Claims] 1. Vinyl chloride comprising (a) an upper part, (b) a middle part having a spray nozzle for a monomer solution and a spray nozzle for a slurry, and (c) a bottom part having a monomer gas inlet, a cooler and a stirring blade. A fluidized gas phase polymerization apparatus for homopolymerization or copolymerization of. 2. The polymerization apparatus according to claim 1, wherein the stirring blade is an anchor type stirring blade. 3. The polymerization apparatus according to claim 1 or 2, wherein the cooler comprises a group of cooling tubes, and the distance between adjacent cooling tubes is 40 to 100 mm. 4. The spray nozzle for monomer liquid is located below the fluidized bed level, and the spray nozzle for slurry is located above the fluidized bed level, (1), (2) or (3). The polymerization apparatus according to the item. 5. The polymerization apparatus according to any one of (1) to (4), wherein the monomer gas blowing port is a porous ring-shaped air diffusing tube. 6. The polymerization apparatus according to any one of (1) to (5), wherein the middle part is divided vertically into two to five chambers by a partition plate. 7. The polymerization apparatus according to any one of (1) to (6), wherein the cross-sectional area of the upper portion is 2 to 4 times that of the middle portion.