JPS5835202B2 - Propylene removal process - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously carrying out homopolymerization of propylene, random copolymerization of propylene and ethylene, or block copolymerization of propylene and ethylene.

More specifically, the present invention relates to a method of carrying out the above polymerization using a horizontal polymerizer having a structure in which most of the parts are divided into classrooms by partition plates.

Conventionally, a vertical stirring polymerization vessel has been well known as a polymerization vessel used in the single polymerization of propylene or the copolymerization of propylene and ethylene.

When this polymerization vessel is used, it has the advantage of relatively stable continuous operation and a large amount of polymerization per unit time, but on the other hand, the catalyst and polymer remain in the vessel because stirring is performed close to complete mixing inside the polymerization vessel. Since the time distribution is wide, it has the following problems.

■ Among the catalysts, the catalysts with short residence times that are still highly active are discharged, so the amount of polymerization per catalyst is approximately 1% compared to the batch method.
Decreases by 0φ.

■ When performing so-called block copolymerization using two polymerization vessels in series, in which propylene is polymerized in the first polymerization vessel and then copolymerized with ethylene in the second polymerization vessel, the distribution of catalyst residence time is wide and Since the amount of polymerization per particle varies depending on the residence time in the polymerization vessel, the amount of polymerized propylene in the first stage and the amount of copolymerization with ethylene in the second stage of each polymer particle vary independently from each other. The resulting block copolymer has an extremely wide compositional distribution.

For example, even if the ratio of the total amount of polymerization in the first stage to the total amount of polymerization in the second stage is 80/20, if you think about it in an extreme way, the composition distribution of the polymer will range from 100% propylene polymer particles to ethylene-propylene random copolymer. This means that there are variations even down to the polymer particles having a combined diameter of 100φ.

The quality of polymers with such non-uniform composition is not desirable.

For example, the intrinsic viscosity (5) of the polymer in the first stage and the copolymer in the second stage
Since there is generally a difference in the molecular weight, a wide distribution of composition corresponds to a wide distribution of molecular weight, and processing the polymer into a film is unsuitable because it results in a large number of fish eyes.

Furthermore, when used for injection molding, the impact resistance of the molded product at low temperatures is significantly reduced and whitening is likely to occur upon impact.

It is known that as a method for improving these drawbacks, it is effective to (1) carry out batch polymerization and (2) carry out continuous series polymerization in multiple tanks.

However, in the batch polymerization method (2), a homogeneous polymer can be obtained and the catalyst efficiency is high, but it takes time to charge raw materials and discharge the polymer, and the polymerization rate is not constant, so it is necessary to always maintain the highest polymerization rate. Therefore, it has the disadvantage that the amount of polymer per unit time is significantly lower than that in the continuous polymerization method.

In addition, method (2) uses a large number of polymerization vessels in series to make polymerization continuous and compensate for the disadvantages of the batch system. Since it is necessary to install necessary equipment such as control equipment and a polymer suspension transfer device, it is disadvantageous because it increases equipment costs, increases area, and complicates operation.

As a result of various studies, the present inventors have constructed one or two horizontal polymerization vessels that have a structure that is divided into at least three or more chambers by partition plates, and that have a built-in stirrer that has a shape that reduces the effect of backflow mixing. The inventors have discovered that the above-mentioned problems can be solved by carrying out polymerization using a group, and have thus arrived at the present invention.

According to the present invention, one polymerization vessel can perform operations equivalent to at least three conventional polymerization vessels, and the horizontal structure facilitates stable operation.

A multistage vertical polymerization vessel is also described in U.S. Pat. The mold structure has disadvantages in that if the heat of polymerization is insufficiently removed in each chamber, air bubbles may be generated or temperature distribution may occur between the chambers.

Due to the high polymerization rate of polymerization in liquid propylene, on an industrial scale, it is often insufficient to remove the polymerization heat simply by cooling the jacket attached to the wall of the polymerization vessel; A reflux condenser is usually installed at the top of the polymerization reactor as a container.

However, in the case of a multi-stage vertical polymerization reactor, only the top chamber has a gas phase, so even if an external cooler is installed, it is not possible to maintain a constant temperature in all chambers, making stable operation extremely difficult. It has drawbacks that make it difficult to carry out.

In the present invention, since a horizontal polymerization reactor is used, the gas phase exists in the upper part of each chamber, and if polymerization is carried out in the propylene liquid phase, the vapor pressure of propylene, which is a factor that determines the polymerization temperature, can be controlled in any chamber of the polymerization reactor. Because they are the same, the temperature in each chamber of the polymerization vessel can be kept constant in a self-controlled manner, and even if the amount of polymerization differs depending on the chamber, propylene evaporates depending on the amount of polymerization, forming the same gas phase and polymerizing. The temperature can always be maintained at a constant value.

The evaporated gas is condensed in a flux condenser installed outside the polymerization vessel, and the condensate is circulated back to the polymerization vessel.

In this way, the present invention does not have the drawbacks found in vertical polymerization vessels.

To further describe the present invention, the catalyst used in the present invention is a Ziegler-Natsuta catalyst that is generally used for the polymerization of propylene, and is composed of a combination of an organoaluminium compound a and a transition metal compound S. a: An organoaluminum compound and a catalytic transition metal compound of groups ① to ② of the periodic table, or a complex compound of the compound and a metal compound of groups ① to ② of the periodic table.

It is a catalyst system mainly consisting of a combination of catalyst C:
The system may also include the use of third components such as amines, ethers, esters, sulfur, halogens, benzene derivatives, organic and inorganic compounds such as nitrogen and phosphorus.

In addition, the conditions used for polymerization may be those in which propylene exists as a liquid phase, but industrially the polymerization pressure is 16 to 4
6 kg/ffl and a polymerization temperature in the range of 40 to 90°C are adopted.

Under such conditions, the polymer is obtained suspended in liquid propylene.

Also, industrially, propane is usually used for propylene with a diameter of 1 to 30 mm.
However, the present invention can be suitably carried out using such propylene.

In order to further clarify the present invention, the present invention will be explained below using drawings.

1 and 2 are schematic diagrams of an example of an apparatus used in the present invention, and FIG. 3 is a side view of a typical example of a stirring blade used in the present invention.

In Figure 1, the polymerization vessel 1 installed horizontally has a horizontal stirring shaft 2.
It is sealed by a polymerizer and a mechanical seal, fixed at both ends or in the middle as the case may be, and rotated by a tag electric motor 5.

A stirring blade 3 having a small back-mixing effect and a rotary plate 4 which partitions the polymerization vessel 1 into multiple chambers are attached to the stirring shaft 2 as necessary.

In addition to using rotating plates as partitions, it is also possible to use fixed partitions.

The polymerization vessel 1 is supplied with liquid propylene from a nozzle 6, catalyst a from a nozzle 7, catalyst b from a nozzle 8, hydrogen from a nozzle 9, and ethylene from a nozzle 10.

The polymer is discharged from the discharge port 11 as a suspension.

In the polymerization vessel 1, as the polymerization progresses, the polymer moves toward the discharge port 11 through the gaps between the partition plates by the stirring blades 3 and the flow of the liquid.

Propylene and propane gases evaporated by the heat generated by polymerization are extracted from the nozzle 12, condensed in the reflux condenser 13, and returned to the polymerization vessel through the nozzle 14.

A non-condensable gas such as hydrogen or ethylene is drawn out from the flux condenser 13, compressed by a compressor 15, and circulated through a nozzle 16 to the polymerizer 1.

Nozzles 14 and 16 are preferably mounted in each chamber so that each flow rate is regulated and distributed.

A portion of the polymerization heat is transferred to the jacket 1 attached to the wall of the polymerization vessel.
7 also removes heat.

FIG. 2 shows a method for performing block copolymerization using the two polymerization vessels shown in FIG. Propylene is polymerized by supplying hydrogen, and then the polymer suspension is transferred to the polymerization vessel 19 through the pipe 24, and copolymerization of propylene and ethylene is carried out while adding liquid propylene from the nozzle 25 and ethylene from the nozzle 26. This is carried out continuously to obtain a block copolymer.

The block copolymer is extracted from the outlet 27 and sent to the next step E.

The polymerization vessels 18 and 19 have the same structure, have the same stirring type, and have the same type of flux condenser compressor, but the volumes are not necessarily the same.

Generally, the polymerization vessel 19 is smaller than the polymerization vessel 18 because the amount of polymerization in the polymerization vessel 19 is smaller and the polymerization rate is faster.

The stirring rotation speed does not need to be strong enough to uniformly disperse the polymer particles in each chamber.

Empirically, it is enough to simply prevent the polymer particles from adhering to each other, as long as the circumferential velocity is 0.3 m/secC or more.

Intense stirring is undesirable because it increases the mixing within each chamber due to the discharge flow from the stirring blades and increases the mixing in the chamber definitions.

Typical shapes of stirring blades are paddle types (A, B) and horizontal blades (C, D) with twist angles of 0 to 5 degrees, as shown in FIG.

The stirring shaft may be eccentric as shown in FIG. 1 or may have a central shaft.

The position of the stirring shaft can be determined depending on the shape of the stirring blades and the partition plate.

Next, the present invention will be explained using examples.

Example I A stirring shaft was inserted through the central shaft into a horizontal polymerization vessel with L/D = 2.5 (L: length, D: inner diameter) and an internal volume of 20 OA, and each chamber had one D-type stirring device in Fig. 3. The interior of the polymerization vessel was divided into four parts by attaching wings and three fan-shaped notches cut out from 1/12 of a rotating disk to the partition plate.

The stirring rotation speed is 25 r, p, m and the peripheral speed is 0.671 LA.
It was ec.

Diethylaluminum chloride 4 g/as catalyst a
h r and titanium trichloride as catalyst 1.29/h
The mixture was intermittently mixed with heptane at intervals of once every 10 minutes.

Titanium trichloride is obtained by reducing TiCl2 with diethylaluminum, followed by diisoamyl ether treatment, and then T
+cA! 4 treatments were used.

Liquid propylene was continuously supplied at a rate of 14 ky, 4, and hydrogen was added so that the gas phase concentration in the polymerization vessel was 3.2.

Polymerization was carried out at a polymerization temperature of 60° C., a polymerization pressure of 25.8 kg/cTL, and an average residence time of 35 hours.

Heat was removed using the jacket of the polymerization vessel.

The obtained polymer had an M, r of 6.5, a polymer yield of 6.2 kg/hr, and a polymerized amount of 5.2 kg per 1 g of titanium trichloride.

Comparative Example 1 A vertical polymerization vessel with /D=1.8 and an internal volume of 20OA was used.

The stirrer was a turbine blade, rotating at 150 r, p, m.

Four baffle plates were attached to the inner wall of the polymerization vessel.

The polymer obtained by polymerization under exactly the same conditions as in Example 1 had an MI of 5.6 and a polymer weight of 5.6 kg/h.
It was r.

The amount of polymerization per 1 g of titanium trichloride was 4.7 kg.

Example 2 Two polymerization vessels identical to those in Example 1 were used in series, and the front polymerization vessel was operated in the same manner as in Example 1.

Ethylene 0.6 kg/hr and propylene 1 kg/hr were charged into the second stage polymerization vessel, and the polymerization temperature was set at 45°.
Copolymerization was carried out at a C1 polymerization pressure of 19 kg/-.

The yield of the obtained polymer was 7.8 kg/hr.

The physical property values are shown in Table 1. It was found that the sheet had a greater effect of improving the falling weight impact strength at low temperatures than Comparative Example 2.

Comparative Example 2 Two polymerization vessels identical to those of Comparative Example were used in series, and the same operation as in Actual Case 2 was carried out.

Polymerization temperature in the second stage polymerization vessel: 45℃, polymerization pressure: 18.8kg/
-It was.

The yield of the obtained polymer was 7.6 kg/hr. The physical property values are shown in Table 1.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an example of an apparatus used for homopolymerization of propylene or copolymerization with ethylene according to the present invention. FIG. 2 is a schematic diagram of a polymerization apparatus in which propylene is polymerized in a first stage polymerization vessel and copolymerized with ethylene in a second stage polymerization vessel. FIG. 3 is a side view of a typical example of the stirring blade used. 1: Polymerization vessel, 2: Stirring shaft, 3: Stirring blade, 4 Two partition plates,
18: Polymerization vessel (first stage), 19: Polymerization vessel (second stage).

Claims (1)

[Claims] 1. In a propylene liquid phase using one or two horizontal polymerization vessels that have a structure in which the interior is divided into at least three chambers by partition plates and a built-in stirrer that has a shape that reduces the effect of backflow mixing. A method characterized by homopolymerization of propylene, copolymerization with ethylene, or polymerization of propylene and copolymerization with ethylene in series to perform block copolymerization.