JP2782826B2 - Method for producing propylene-ethylene block copolymer - Google Patents

Description

The present invention relates to a method for producing a propylene-ethylene block copolymer having excellent low-temperature impact resistance.

[Conventional technology]

To improve the impact resistance of crystalline polypropylene at low temperatures, a method of blending with a rubber component, or a method of copolymerizing propylene with a small amount of ethylene, or a so-called block copolymer in which propylene homopolymerization is followed by ethylene-propylene copolymerization Polymerization and the like are performed. As a general continuous production method of a propylene-ethylene block copolymer, a method in which two polymerization tanks are connected in series, propylene is polymerized in a first tank, and ethylene and propylene are copolymerized in a second tank. Is well known.

However, polymers obtained by a continuous production method using two tanks still tend to have poor low-temperature impact resistance as compared with those obtained by a batch method. This is considered to be due to the formation of gel by particles having a high ethylene-propylene copolymer component composition attributed to the particles obtained by short-passing the first propylene polymerization tank. Therefore, a method in which a large number of polymerization tanks are connected in series to make the residence time distribution of the catalyst itself close to that of a batch system (Japanese Patent Publication No. 49-12589).
A method of concentrating and classifying polypropylene particles in a tank to remove short-path catalyst particles, small-sized particles having insufficient growth, and the like (Japanese Patent Laid-Open No. 51-135787, 55-116716), or a method in a first-stage polymerization tank. Is withdrawn from the reactor wall with stirring, and the withdrawn slurry is countercurrently washed with a fresh medium of the same kind as the slurry medium to obtain a slurry having substantially less small particle components. A method of supplying the solution to a tank (JP-A-55-106533) is known.

Regarding these methods, in a simple multi-tank series system,
Not only is the equipment complicated and expensive, but the installation area is also large, which may increase the cost of the product.Although the simple classification process method has some improvement in impact resistance, it is still inferior to the batch type. Such disadvantages still existed.

On the other hand, the present inventors have proposed a classification system in the present invention in Japanese Patent Application Laid-Open No. Sho 58-49716.

Furthermore, in recent years, technological development of gas phase polymerization has progressed, and various gas phase polymerization processes have been proposed for producing a propylene block copolymer.

However, in the above method proposed by the present inventors, when the propylene polymer slurry is directly supplied from the classification system to the gas phase polymerization tank, the liquid propylene and a small amount of an inert solvent accompany the inside of the gas phase polymerization tank. However, there has been a tendency for troubles such as a temperature distribution to occur or a uniform flow state to be not obtained. On the other hand, a method using a degassing tank for evaporating liquefied propylene has also been proposed, but mere degassing alone results in adhesion due to particles having a high copolymer component attributed to the residence time distribution in the gas phase polymerization reactor. Particles were formed, resulting in poor flow, adhesion to vessel walls, and agglomeration, and stable movement was not always easy.

[Problems to be solved by the present invention]

The present inventors have conducted various process studies in order to solve the above-mentioned problems, and as a result, by combining a propylene polymerization tank classification system and a degassing system and controlling the operation under certain specific conditions, The inventors have found that the problem can be easily solved and a product excellent in low-temperature impact resistance can be stably manufactured, and have reached the present invention.

[Means for solving the problem]

The feature of the present invention is that first, in the presence of a stereoregular catalyst,
In the step, propylene is polymerized in one or two or more serially connected polymerization tanks in the presence of liquefied propylene and hydrogen, and then the propylene polymer slurry obtained in the second step is fed to an ethylene / propylene copolymerization tank. In a continuous production method of a propylene-ethylene block copolymer in which ethylene-propylene copolymerization is carried out in a gas phase substantially free of an inert solvent and liquefied propylene, (i) a classification system is provided by a propylene polymerization tank. At least one set is provided between the propylene polymerization tank and the ethylene-propylene copolymerization tank, and a slurry containing a large amount of coarse particles and a slurry containing a large amount of fine particles are obtained from the slurry extracted from the propylene polymerization tank, and a large amount of the coarse particles are contained. The slurry is supplied to the subsequent ethylene / propylene copolymerization tank, and the slurry containing a large amount of fine particles Should be returned to the original propylene polymerization tank.

(Ii) The polymer slurry containing a large amount of coarse particles removed from the classification system is introduced into a degassing system maintained under pressure, and the unreacted liquefied propylene is adjusted so that the flash rate becomes 5% or more and 80% or less. Is vaporized and then supplied to a subsequent ethylene / propylene gas phase copolymerization reactor.

And a method for producing a propylene-ethylene block copolymer.

 Hereinafter, the present invention will be described in more detail.

The propylene homopolymerization in the first stage is a stereoregular catalyst, in which one polymerization tank or two or more polymerization tanks are connected in series.
An organic aluminum compound, (a third component for improving stereoregularity if necessary), hydrogen, and liquefied propylene are continuously supplied to perform substantial homopolymerization using propylene itself as a solvent. The propylene polymerization in the first stage may include homopolymerization of propylene and copolymerization of propylene with a small amount of an α-olefin other than propylene, for example, ethylene. In this case, the amount of the α-olefin other than propylene is usually 5% by weight or less based on propylene,
It is preferably at most 3% by weight.

Here, the stereoregular catalyst is composed of a titanium-containing solid catalyst component and an organic aluminum compound, but is not particularly limited, and a known catalyst is used. The titanium-containing solid catalyst component may be a known titanium trichloride type or a carrier-supported type catalyst, and is not particularly limited.

As a catalyst containing titanium trichloride as a main component, conventionally known titanium trichloride can be used. For example, titanium trichloride which has been activated by ball mill pulverization, titanium trichloride obtained by extracting it with a solvent, β-type titanium trichloride is treated with a complexing agent such as ethers, and further treated with titanium tetrachloride. In the presence of titanium trichloride and an ether having an atomic ratio of 0.15 or less with respect to Ti, titanium tetrachloride is treated with an organoaluminum compound to form a liquid, which is further heated to obtain a solid having an Al content of Ti. And titanium trichloride having an atomic ratio of 0.15 or less.

Particularly preferred among these titanium trichlorides, the aluminum content is 0.15 or less in terms of the atomic ratio of aluminum to titanium, preferably 0.1 or less, more preferably 0.05 or less.
2 or less and contains a complexing agent.

For the titanium-containing solid catalyst component, the organoaluminum compound used as a cocatalyst has a general formula of AlR ¹ _m X _3-m
(Wherein, R ¹ represents a hydrocarbon group having 1 to 20 carbon atoms, X represents a halogen, and m represents a number satisfying 3 ≧ 3> 1.5). If the titanium-containing solid catalyst component is the carrier-supported type catalyst component containing a magnesium compound solid, AlR ¹ ₃
Or it preferred to use a mixture of AlR ¹ ₃ and AlR ¹ ₂ X. On the other hand, titanium-containing solid catalyst component, three if the titanium chloride as the main component is to use AlR ¹ ₂ X, in particular, usually the diethylaluminum chloride, di-n-propyl aluminum chloride, dihexyl aluminum chloride, And so on.

The third component, which is used as necessary to improve the stereoregularity, includes various electron-donating compounds including N, O, P or Si, and aromatic compounds such as benzene, toluene and xylene. Is preferably used.

The above-mentioned titanium-containing solid catalyst component may be used for polymerization as it is. However, if a small amount of olefin is preliminarily polymerized and used in the presence of an organoaluminum compound, the powder properties of the polymer (eg, bulk density) Is improved. For this pretreatment, known conditions can be employed as they are. The former-stage propylene-based polymerization is performed in liquefied propylene, and may be performed by connecting a plurality of reactors in series.
Since the effect of the method of the present invention is remarkable, one tank can sufficiently achieve the purpose. The amount of this propylene homopolymer is
The polymerization temperature and the polymerization time are selected so as to be 70 to 95% by weight of the total amount of the polymer.

Standard polymerization temperature is 40-100 ° C, preferably 55-80 ° C
It is. The polymerization pressure is the sum of the partial pressure of liquefied propylene, the pressure of hydrogen used as a molecular weight regulator and the partial pressure of an inert hydrocarbon used as a diluent for a catalyst component, but is usually 5 to 40 kg / cm. ^2- G.

The classification operation according to the present invention is performed on the slurry in which the propylene polymerization in the first stage has been completed.
In the case where the polymerization is carried out in one or more polymerization tanks, the effect is greater when the polymerization is carried out during the propylene polymerization in the first tank or the second tank. Although one set of the classification system according to the present invention is sufficient, two or more sets can be used for more assurance.

The classification system is not particularly limited, and may be constituted by, for example, a hydrocyclone. Preferably, the slurry extracted from the propylene polymerization tank (1) (see FIG. 1) is converted into a slurry having a high slurry concentration and a slurry having a low slurry concentration. It comprises a concentrator (3) for separation and a hydraulic classifier (4) for obtaining a slurry containing a large amount of coarse particles and a slurry containing a large amount of fine particles by bringing the high- and low-concentration slurries into countercurrent contact. Among them, as the concentrator, a liquid cyclone, a centrifugal separator, a filter and the like are used, but in the case of continuous operation, the liquid cyclone is excellent in operability, and the apparatus is small, inexpensive, and requires a small installation area. Used. A plurality of hydrocyclones are installed in series,
If the low-concentration slurry from the cyclone is supplied to the second cyclone, the slurry concentration of the low-concentration slurry discharged from the second cyclone can be further reduced as compared with the case of only one unit, so that the classification efficiency in the hydraulic classifier is further improved. Increase. In the liquid cyclone (3), the weight ratio of the low-concentration slurry (slurry at the top of the cyclone) and the high-concentration slurry (slurry at the bottom of the cyclone) is determined by the weight ratio of the polymer particles and the solvent combined.
It is preferably 50/50 to 1/99. Under suitable conditions, the particle concentration in the low-concentration slurry portion can be made almost zero, and at this time, the effect of the present invention is maximized.

The high-concentration slurry extracted from the lower part of the hydrocyclone (3) is supplied to the upper part of the settling liquid classifier (4), and is extracted from the upper part of the hydrocyclone and supplied from the lower part of the sedimentation liquid classifier. It comes into countercurrent contact with the slurry in the classifier.

Slurry containing coarse particles (sufficiently grown particles) among the polymer particles is settled as particles in the classifier against the countercurrent liquid, and then sent to the downstream side from the body outlet.

On the other hand, slurry containing fine particles (particles with insufficient growth)
It is extracted from the upper part of the classifier along with the countercurrent liquid and returned to the original propylene polymerization tank (1).

The greater the ratio of the slurry containing fine particles returned to the original propylene polymerization tank (1) from the upper part of the classifier to the slurry containing coarse particles sent from the lower part of the classifier to the downstream, the greater the effect of the present invention. However, this is determined by the production rate, the slurry pump capacity, the pressure balance that can be employed, and the like.
It is usually operated in the range 30/70 to 99/1, preferably 50/50 to 98/2.

It is also possible to mix and use the same fresh medium as the medium at the time of polymerization in the low-concentration slurry supplied to the lower part of the classifier. In any case, in this classification system, in order to ensure stable operation and maintain high classification efficiency, it is most important to strictly control the flow rate of the low-concentration slurry supplied to the lower part of the classifier.

The slurry containing coarse particles thus obtained, i.e., the slurry containing polymer particles having a uniform particle size by classification, is transferred to the subsequent degassing system, and the polymer that evaporates the liquid olefin under pressure to a solid state is formed. The powder is subjected to a subsequent gas phase copolymerization. The degassing system preferably comprises a double tube heat exchanger and a fluidized flash tank.

In the present invention, when the liquid olefin is vaporized and vaporized to separate the solid polymer powder, the degassing tank is maintained under pressure, and the conditions are such that the flash rate is 5 to 80%. is important.

Here, the flash rate (f) is a measure of the gasification rate of liquid propylene in the slurry, and is defined and calculated as follows, assuming an adiabatic state.

t ₁ : temperature of slurry in polymerization tank (° C.) t ₂ : saturated liquid temperature of propylene under pressure condition of degassing tank (° C.) _pp ; average specific heat of polypropylene powder between t ₁ and t ₂ (kcal / kg)・ ℃) ΔH ₁ ; enthalpy of liquid propylene in polymerization tank (temperature t ₁ , pressure P ₁ ) (kcal / kg) ΔH ₂ ; enthalpy of liquid propylene in saturated liquid temperature of propylene in degassing tank (kcal / kg) ΔH ₃ ; same as above Steam propylene enthalpy (kcal / k
g) [PP]; Slurry concentration from the polymerization tank (wt%) Also, prior to feeding to the degassing tank, if it differs from an adiabatic system such as heating in advance, of course, the contribution (f _i ) of those contributions The flash rate (f) is obtained as a sum.

f = .SIGMA.f _i For example, prior to supply to the degassing vessel, if the slurry was heated by a double pipe heat exchanger, the contribution of the flash rate by which (f ₂₎ is, t ₃ ; Double tube heat exchanger outer tube hot water inlet temperature (° C) t ₂ ; Double tube heat exchanger outer tube hot water outlet temperature (° C); Average of heating medium between t _{1 and} t ₂ Specific heat (kcal / kg · ° C) W ₁ ; circulation amount of heating medium in double-tube heat exchanger (kg / H) W ₂ ; inflow of slurry from polymerization tank (kg / H)

That is, when a sudden degassing was performed, such as flash drying to an atmospheric pressure system in which the flash ratio exceeded 80%, it was dissolved in the liquid phase propylene or included in the polymer particles. Amorphous polymer precipitates and adheres unevenly on the polymer particle surface, causing agglomeration phenomenon between the particles, causing poor flow in the subsequent gas phase polymerization tank and adhesion to the vessel wall,
It causes agglomeration. In some cases, the performance of gas-phase polymerization may be significantly impaired due to scattering and deterioration of the organoaluminum compound and the third component, which are catalyst components.
When the flash rate is less than 5%, the effect of the degassing system is not recognized.

As the degassing device used in the present invention, various types such as a fluidized dryer type using only gas flow, a stirred fluidized tank type using both gas flow and mechanical stirring, and a mixing tank type using only mechanical mixing can be applied. Heat of evaporation, heating with a jacket, a method using the sensible heat of the flowing gas as a heating source, or
It is given in advance by a method of heating with a double tube heat exchanger or the like, but using the sensible heat of the flowing gas as a heating source,
It is preferable to use. In the case of the stirred fluidized-tank type, the amount of gas for assisting fluidization and mixing is smaller than that of the fluidized-dryer type, and it is sufficient to provide a very small superficial linear velocity of about 1.0 to 2 times the flow start velocity.

The operating conditions of this degassing tank are a pressure of 5 to 30 kg / cm ² , preferably 10 to 25 kg / c ² , a temperature of 30 to 90 ° C., preferably 60 to 90 ° C.
The conditions under which the olefin does not condense in the system are selected.

In addition, the average residence time of the powder in this degassing tank can be arbitrarily set, but if it is too long, it is not only economically disadvantageous, but also causes gel or fish eye due to post-polymerization here. It is not preferable because it becomes
120 minutes, preferably about 3 to 30 minutes is employed.

Hereinafter, a preferred example of the present invention will be described with reference to FIG. 1, but the present invention is not limited to this example.

A slurry of polymer particles having a uniform particle size by the above-described classification system is first sent to a double-tube heat exchanger (5),
Here, a part of the liquefied olefin evaporates.

The most desirable flash rate at the outlet of the double tube heat exchanger is 80% or less. If the flash ratio exceeds 80%, the powder properties deteriorate significantly, which is undesirable. Therefore, it is preferable to adjust the heat transfer area, the amount of superheated steam, the jacket heating temperature, and the like so as to obtain desirable flash conditions.

The slurry which has been flushed to some extent in the double tube heat exchanger is further completely flushed in the fluidized flush tank (6). The temperature of the fluidized flash tank may be maintained at 30 to 90 ° C., which is equal to or higher than the liquefaction temperature of the olefin, and the temperature may be controlled by a method that does not inactivate the catalyst component contained in the polymer particles. For example, a method in which olefin vaporized in a fluidized flash tank is reheated in a heat exchanger and recirculated to the flash tank has good thermal efficiency and is suitable. First
In the case of the process as shown in the figure, it is necessary to adjust the temperature and the amount of the heating medium flowing through the outer tube of the double tube heat exchanger (5) and the temperature of the heat exchanger (11) of the flow flash system. Can be.

On the other hand, the operating pressure is 5 to 30 KG, and by assembling a process such that the pressure is sequentially reduced in the first stage propylene polymerization tank, flash tank, and gas phase polymerization tank which is the second stage copolymerization tank,
A very advantageous transfer of slurry or solids is possible.
The residence time in the fluidized flash tank can be determined as appropriate, but is preferably about 10 minutes in order to improve the powder properties.

In the present invention, the copolymerization of ethylene and propylene is carried out in the gas phase. At this time, an α-olefin other than propylene may be contained. Examples of these α-olefins include α-olefins having 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms.
-Olefins. The conditions for gas phase polymerization are usually 30
The polymerization or copolymerization is carried out at a temperature of -100 ° C and 1-50 kg / cm ² , and the polymerization ratio in the whole polymer is 3-50% by weight, preferably 10-30% by weight. When an ethylene-propylene mixed gas which is a more preferred embodiment is used, the composition of the gas (propylene / (ethylene + propylene))
Is usually 10 to 90 mol%, preferably 20 to 80 mol%.

Further, the subsequent gas phase polymerization can be performed in multiple stages, and the polymerization temperature, hydrogen concentration, monomer composition, and reaction amount ratio can be changed in each reactor.

In the present invention, the apparatus used for the subsequent gas-phase polymerization is not particularly limited, and a known apparatus such as a fluidized bed, a stirring tank, a fluidized bed with a stirrer, or a moving bed is preferably used to continuously perform polymerization. Can be. Among these, it is particularly preferable to use a stirred fluidized tank.

After completion of the gas phase polymerization, the polymer continuously taken out is
If necessary, an inactivation treatment or demineralization treatment with an alkylene oxide, an alcohol, or hydrogen, or removal of an amorphous polymer with a solvent may be performed.

〔Example〕

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

As in the process illustrated in Example 1 Figure 1, the internal volume 1.7 m ³ and 2
During the m ³ of reactor ((1) and (8)), hydrocyclone (3) and consisting of sedimentation liquid force classifier (4) classification system and double-pipe heat exchanger (5) and fluidized flash Tank (6)
A propylene-ethylene block copolymer was produced by a process incorporating a degassing system consisting of In the propylene polymerization tank (1), liquefied propylene and hydrogen were charged so that the hydrogen composition in the gas phase was 6 mol%, and diethyl aluminum monochloride and methyl methacrylate were charged in the same manner as in Example 1 of JP-A-59-12905. The titanium trichloride-type catalysts prepared as described above were supplied in a molar ratio of 5,0.3, respectively. The polymerization temperature was 65 ° C., the pressure was 28 kg / cm ² G, and the liquid volume in the polymerization tank was adjusted to 1 m ³ . The slurry polymerized in this polymerization tank had a slurry concentration of about 35%, and was pressurized by the slurry pump (2) and supplied to the liquid cyclone (3) at a flow rate of about 10 m ³ / H. From the upper part of the cyclone, a supernatant liquid containing almost no solid particles was taken out, and supplied at 2 m ³ / H from the lower part of the hydraulic classifier (4).

The high-concentration slurry extracted from the lower part of the cyclone was supplied to the upper part of the classifier as it was, and was brought into contact with the above-mentioned supernatant and countercurrent liquid. Since the slurry extracted from the upper part of the classifier contains fine powder, it is circulated to the original propylene polymerization tank, and the concentration of the slurry extracted from the lower part of the classifier is about 35%.
The slurry mainly containing coarse particles of was supplied at 0.15 m ³ / H to a downstream flash tube of a double-tube heat exchanger.

First, while adjusting the flash rate at the outlet of the double-pipe heat exchanger (5) to be 50 to 55% by heating with hot water in the outer pipe, the fluidized flash tank is heated propylene gas supplied from the lower part. (Approximately 100 ° C) to reduce the pressure in the tank to 15kg / cm
² G, temperature was maintained at 60 ° C. As a result, the liquefied propylene in the slurry supplied to the flash tank was heated and vaporized by the heated propylene gas into gaseous propylene, and was recycled.

The obtained solid polypropylene powder was sent to a gas phase polymerization tank (8), where a copolymer of propylene and ethylene was obtained. In the gas phase polymerization tank (8), a mixed gas of ethylene, propylene and hydrogen was circulated by a gas blower (10) to the polymerization tank provided with an auxiliary stirring blade for improving mixing.
The polymerization temperature was controlled at 60 ° C. and the pressure was controlled at 14.0 kg / cm ² by circulating gas. The average residence time was about 2 hours. As a result, melt flow rate MFR = 2.5 / 10mi
n, bulk density ρ _B = 0.46 g / cc, ethylene content 6 wt%, gel
Propylene-ethylene block copolymers of about 100/250 cm ² could be produced stably for a long period of time. The results are shown in Table 1.

The gel was evaluated by adding 0.1% by weight of BHT (2,6-di-t-butyl-4-methylphenol) to the obtained product powder,
anox1010,0.1 wt%, was added 0.1 wt% calcium stearate, polyethylene terephthalate was formed into pellets at 230 ° C. with a pelletizer having an inner diameter of 40 mm, and molded into air-cooled inflation film having a thickness of 23 .mu.m, the diameter of this film 250 cm ² per 0.05
The measurement was performed by measuring the number of gels having a size of not less than mm.

Comparative Example 1 Example 1 was repeated except that the degassing system was not provided and the propylene polymer extracted from the classification system was directly supplied to the gas phase reactor without separating unreacted liquefied propylene and solid polymer particles. A propylene-ethylene block copolymer was produced in the same manner as described above. The results are shown in Table 1. In this case, it can be seen that the bulk density of the obtained polymer powder is low.

Comparative Example 2 A propylene-ethylene block copolymer was produced in the same manner as in Example 1 except that the flush ratio at the outlet of the double tube heat exchanger (5) was set to 90%. The results are shown in Table 1. In this case, many gels were generated, and stable production was not possible in terms of process and quality.

Comparative Example 3 Same as Example 1 except that there was no classification system. The results are shown in Table 1. In this case, the generation of gel increased, and the physical properties also deteriorated remarkably. The powder properties were not satisfactory.

[Effects of the Invention] According to the present invention, a propylene-ethylene block copolymer having little gel generation, that is, excellent in low-temperature impact resistance, can be continuously and stably produced.

[Brief description of the drawings]

FIG. 1 is a flow diagram illustrating one embodiment of the present invention. The numbers in the figure represent the following. 1 ... Propylene polymerization tank, 2 ... Slurry pump, 3 ...
... Concentrator, 4 ... Hydro classifier, 5 ... Double tube heat exchanger, 6 ... Flow flash tank, 7 ... Gas blower, 8
... gas phase polymerization tank, 9 ... cyclone, 10 ... gas blower.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-263107 (JP, A) JP-A-59-47209 (JP, A) JP-A-58-213011 (JP, A) JP-A-58-210 49716 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08F 293/00-297/08 C08F 2/00 C08F 10/00-10/14 C08F 110/00-110/14 C08F 210/00-210/18

Claims (8)

(57) [Claims] (1) In the presence of a stereoregular catalyst, propylene is firstly polymerized in one or more series polymerization tanks in the presence of liquefied propylene and hydrogen in a first stage, and then in a second stage. The propylene polymer slurry obtained as above is fed to an ethylene / propylene copolymerization tank, and the ethylene / propylene copolymerization is carried out in a gas phase substantially free of an inert solvent and liquefied propylene.
In the method for continuously producing an ethylene block copolymer, (i) a slurry system provided between a propylene polymerization tank or at least one set between a propylene polymerization tank and an ethylene / propylene copolymerization tank, and a slurry extracted from the propylene polymerization tank; A slurry containing a large amount of coarse particles and a slurry containing a large amount of fine particles are obtained from, and the slurry containing a large amount of coarse particles is supplied to a subsequent ethylene / propylene copolymerization tank, and the slurry containing a large amount of fine particles is returned to an original propylene polymerization tank. . (Ii) The polymer slurry containing a large amount of coarse particles taken out from the classification system is introduced into a degassing system maintained under pressure, and the unreacted liquefied propylene is adjusted so that the flash rate becomes 5% or more and 80% or less. Is vaporized and then supplied to a subsequent ethylene / propylene gas phase copolymerization reactor. A method for producing a propylene-ethylene block copolymer. 2. The weight ratio of the slurry returned to the original propylene polymerization tank to the slurry supplied to the subsequent polymerization tank in the classification system is in the range of 30/70 to 99/1. 2. The method for producing a propylene-ethylene block copolymer according to item 1. 3. A classification system comprising a concentrator and a sedimentation liquid classifier, wherein a slurry extracted from a propylene polymerization tank is first supplied to a concentrator to be divided into a high-concentration slurry and a low-concentration slurry. 3. A slurry containing a large amount of coarse particles and a slurry containing a large amount of fine particles by contacting both slurries countercurrently in a settling hydraulic classifier. The method for producing a propylene-ethylene block copolymer according to any one of the above. 4. The method for producing a propylene-ethylene block copolymer according to claim 1, wherein the concentrator in the classification system is a hydrocyclone. 5. The propylene-ethylene according to claim 1, wherein the degassing system comprises a combination of a double tube heat exchanger and a fluidized tank. A method for producing a block copolymer. 6. A process for producing a propylene-ethylene block copolymer according to claim 1, wherein the process is carried out in a fluidized tank for stirring the gas phase polymerization in the second stage. . 7. The method according to claim 1, wherein a pressure difference is provided between each of the propylene polymerization tank, the degassing system, and the gas phase polymerization tank, and the slurry or solid is transferred by the force. A method for producing a propylene-ethylene block copolymer according to any one of claims 6 to 13. 8. A stereoregular catalyst comprising a solid titanium trichloride-based catalyst complex having an aluminum content of 0.15 or less in terms of an atomic ratio of aluminum to titanium and containing a complexing agent, and an organoaluminum compound. The method for producing a propylene-ethylene block copolymer according to any one of claims 1 to 7, wherein the catalyst system comprises: