JPH0347643B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a propylene-α-olefin block copolymer.

More specifically, the propylene polymer obtained without deactivating the catalyst may adhere between polymer particles or on the inner wall of the reactor, or may clog pipes or solidify in silos or hoppers in subsequent steps. By polymerizing other α-olefins or copolymerizing propylene and other α-olefins in the gas phase without
- A method for producing an olefin block copolymer with high reaction vessel volumetric efficiency.

[Conventional technology]

Regarding the polymerization of α-olefins such as ethylene and propylene, the performance of polymerization catalysts has improved significantly in recent years, and the yield of polymer per catalyst component has dramatically increased. The amount of components is sufficiently small, making it possible to omit the catalyst removal step.

On the other hand, the polymerization methods for these α-olefins include slurry polymerization in an inert hydrocarbon solvent, bulk polymerization in a liquefied monomer such as liquefied propylene, and gas phase polymerization in a gas phase. Although it is legal, in recent years it has become popular because gas phase polymerization does not use a solvent, so there is no need for solvent recovery or purification steps, and it is easy to recover monomers and dry the polymer product. It has started to attract attention.

In the field of propylene and other α-olefin block copolymers, propylene polymer is produced in the first stage, and in the second stage, other α-olefins are polymerized in the gas phase, or propylene and other α-olefins are copolymerized in the gas phase. A block copolymerization method is known.

The gas-phase block copolymerization method has economical reasons as mentioned above, as well as product diversification, compared to methods in which the subsequent polymerization is carried out in an inert hydrocarbon solvent or in liquid propylene. There are also some advantages.

However, in the gas phase polymerization method, the monomer concentration is relatively low, so the reaction is slow, and in order to form a good fluidized bed, a catalyst with good particle properties is required. It has also been pointed out that a catalyst with excellent properties is essential, and that it also involves various difficulties such as problems with equipment for good flow and mixing, heat removal problems, and adhesion problems. In particular, adhesion inside the reactor not only becomes a major hindrance to long-term stable operation, but also causes a decline in quality.

[Problem that the invention seeks to solve]

The present inventors mainly focused on propylene-α in the latter stage.
- Regarding the phenomenon of adhesion and deterioration of powder properties in the olefin gas phase copolymerization reactor, we conducted an intensive study on the causes and countermeasures. As a result, in the gas phase polymerization reactor and its gas circulation system, low molecular weight polymers of ethylene and propylene are likely to be produced due to the action of the organoaluminum component used as a cocatalyst.
In some cases, it may form an oily substance;
It has been found that these low molecular weight polymers are the cause of adhesion within the reactor, agglomeration phenomena, and deterioration of powder properties.

[Means for solving problems]

Therefore, the present inventors investigated various methods for suppressing the production of these low molecular weight polymers, and found that
By supplying a specific compound into the gas-phase polymerization reaction system in the latter stage, it suppresses the production of low molecular weight polymers without affecting the polymerization reaction at all, and reduces the deterioration of powder properties, adhesion inside the reactor, and clumping. The inventors have discovered that this can be prevented, and have arrived at the present invention.

The gist of the present invention is to obtain a propylene polymer by polymerizing propylene or propylene and a small amount of other α-olefin in the presence of a catalyst, and then to obtain a propylene polymer by polymerizing propylene and another α-olefin or other α-olefin in a gas phase. Propylene-α- to be copolymerized or polymerized
A method for producing an olefin block copolymer, characterized in that an aromatic carboxylic acid ester is supplied to a subsequent gas phase polymerization system.
The present invention relates to a method for producing an olefin block copolymer.

The present invention will be sequentially explained below.

In the present invention, the polymerization catalyst used is composed of a titanium-containing solid catalyst component and an organoaluminum compound, but is not particularly limited and any known catalyst can be used.

As the titanium-containing solid catalyst component, a known carrier-supported catalyst component containing a solid magnesium compound, a titanium compound component, and a halogen component can also be used, but a catalyst component containing titanium trichloride as the main component is preferable. As the material containing titanium trichloride as a main component, conventionally known titanium trichloride can be used. For example, titanium trichloride that has been activated by ball milling: titanium trichloride from which it has been extracted as a solvent: beta-type titanium trichloride that has been treated with a complexing agent such as an ether, and then treated with titanium tetrachloride. Titanium trichloride with an Al content of 0.15 or less in atomic ratio to Ti: In the presence of ethers, titanium tetrachloride is treated with an organoaluminum compound to form a liquid, which is then further heated to become a solid to reduce the Al content. One example is titanium trichloride with an atomic ratio of 0.15 or less to Ti.

Among these titanium trichlorides, particularly preferred are those having an aluminum content of 0.15 or less, preferably 0.1 or less, more preferably 0.02 or less in terms of the atomic ratio of aluminum to titanium, and containing a complexing agent.

The content of the complexing agent is the molar ratio of the complexing agent to titanium trichloride in the solid titanium trichloride-based catalyst complex.
It is 0.001 or more, preferably 0.01 or more. Specifically, titanium trichloride, a formula with an atomic ratio of aluminum to titanium of titanium trichloride of 0.15 or less
Aluminum halide represented by AlR ¹ pX ₃ -p (wherein R ¹ is a hydrocarbon group having 1 to 20 carbon atoms, X is a halogen atom, and p is a number of 0≦p≦2) and trichloride Those containing a complexing agent in a molar ratio of 0.001 or more to titanium, such as those with the formula TiCl ₃ (AlR ¹ pX ₃ −
p)a・(C)t (in the formula, R ¹ is a hydrocarbon group having 1 to 20 carbon atoms, X is a halogen atom, and p is 0≦
is a number with p≦2, C is a complexing agent, and a is 0.15
The following numbers, where t is a number greater than or equal to 0.001) are listed, but of course,
In addition to the TiCl ₃ component, the AlR ¹ pX ₃ -p component, and the complexing agent C component, a small amount of iodine, titanium trichloride in which part or all of the chlorine has been replaced with iodine or bromine, or MgCl ₂ , Mgo It may contain inorganic solids for carriers such as olefin polymer powders such as polyethylene and polypropylene. Examples of the complexing agent C include ethers, thioethers, ketones, carboxylic acid esters, amines, carboxylic acid amides, and polysiloxanes, among which ethers and thioethers are particularly preferred.
As an ether or thioether, the general formula
R″-0-R or R″-S-R (in the formula, R″, R
indicates a hydrocarbon group having 15 or less carbon atoms. ). Examples of AlR ¹ pX ₃ -p include AlCl ₃ and AlR ¹ Cl ₂ .

Further, it is particularly preferable that the solid titanium trichloride-based catalyst complex has an X-ray diffraction pattern having a halo of maximum intensity at a position corresponding to the strongest peak position of α-type titanium trichloride (near 2θ=32.9°). Furthermore, during the production of solid titanium trichloride-based catalyst complexes,
Those that have not been subjected to thermal history at temperatures exceeding 150°C are preferred. Furthermore, the cumulative pore volume with a pore radius of 20 Å to 500 Å measured using the mercury porosimeter method is 0.02 Å.
cm ³ /g or more, especially 0.03 cm ³ /g to ^{0.15 cm 3} /g, which is characterized by a pore volume with an extremely fine pore diameter, but in that there is no need to remove the amorphous polymer,
Particularly preferred.

However, such a solid titanium trichloride-based catalyst complex can be prepared from a liquid containing titanium trichloride liquefied in the presence of (a) ether or thioether at 150°C;
Precipitate at the following temperature (b) Easily produce solid titanium trichloride obtained by reducing titanium tetrachloride with an organoaluminum compound or metal aluminum by a method such as treatment with a complexing agent and treatment with a halogen compound. I can do it.
Methods (a) and (b) above have already been used in Japanese Patent Publication No. 57-8451,
No. 55-8452, No. 53-24194, No. 55-8003,
No. 54-41040, No. 54-28316, JP-A-53-
No. 12796, No. 52-91794, No. 55-116626, No. 53
-3356, 52-40348, 58-36928, 59
-12905, 59-13630, etc. Furthermore, in addition to methods (a) and (b), the Special Publication No. 54-27871
As described in the issue, solid titanium trichloride obtained by reducing titanium tetrachloride with an organoaluminum compound is added in a molar ratio of 0.5 to the titanium trichloride.
A product prepared by adding the ether compound No. 5 and heating to 50 to 120° C. and then separating the solid may also be used.

The organoaluminum compound used as a cocatalyst for the titanium-containing solid catalyst component has the general formula AlR ² mX ₃ -m (wherein R ² is a hydrocarbon group having 1 to 20 carbon atoms, and X represents a halogen). , m is 3≧m>
1.5). When the titanium-containing solid catalyst component is a supported catalyst component containing a solid magnesium compound, AlR ² ₃ and
Preference is given to using a mixture of AlR ² ₃ and AlR ² ₂ X. On the other hand, when the titanium-containing solid catalyst component is mainly composed of titanium trichloride, AlR ² ₂ It is preferable to use

The titanium trichloride and organoaluminum compounds shown above are generally organoaluminum compounds/
The molar ratio of titanium trichloride is 1 to 30, preferably 2 to 30.
Used in a range of 15.

In the present invention, the above catalyst may be used as it is, but it is preferable to pre-polymerize a small amount of olefin onto the catalyst made of titanium trichloride and an organoaluminum compound as a pretreatment.

The above method involves adding titanium trichloride and an organoaluminum compound to an inert solvent such as hexane, heptane, etc., and adding propylene, ethylene,
It is sufficient to supply an olefin such as butene-1 or a mixture thereof for polymerization. This pretreatment is generally referred to as prepolymerization, and known polymerization conditions can be used as they are. Polymerization temperature is 30-70°C. The higher the polymerization rate per unit weight of titanium acid chloride, the better; however, from an equipment or economic point of view, it is 0.1 to 100 g-polymer/g-TiCl ₃
Generally, it is within the range of .

Furthermore, a molecular weight regulator such as hydrogen may be added during prepolymerization.

Further, it is preferable that the prepolymerization is carried out uniformly in a batch manner. This prepolymerization is effective in improving polymer properties such as bulk density.

An additive for improving stereoregularity may be used as a third component in the catalyst made of titanium trichloride and an organoaluminum compound described above. For this purpose, various electron-donating compounds and hydrocarbon compounds containing N atoms, O atoms, P atoms, Si atoms, etc. are used. Such electron-donating compounds include compounds containing one or more electron-donating atoms or groups, such as ethers, polyethers, alkylene oxides, furans, amines, trialkylphosphines, triarylphosphines, and pyridines. , quinolines, phosphoric acid esters, phosphoric acid amides, phosphine oxides, trialkylphosphites, triallylphosphites, ketones, carboxylic acid esters, carboxylic acid amides, and the like. Among these, preferred are ethyl benzoate,
Carboxylic acid esters such as methyl benzoate, phenyl acetate, and methyl methacrylate; glycine esters such as dimethylglycine ethyl ester and dimethylglycine phenyl ester; triaryl phosphites such as triphenyl phosphite and trinonyl phenyl phosphite; Can be mentioned.

Furthermore, aromatic hydrocarbons such as benzene, toluene, and xylene may also be used as the third component.

The amount of the third component added is generally 0.0001 to 5, preferably 0.001 to 1 in molar ratio to titanium trichloride.
is within the range of

The polymerization method in the main polymerization of propylene carried out in the first stage can be carried out by known slurry polymerization, slurry polymerization in a liquefied monomer, gas phase polymerization, or the like. These polymerization methods may be either batchwise or continuous, and the reaction conditions are 1 to 100 atm, preferably 5 to 40
The reaction is carried out under atmospheric pressure at a temperature of 50 to 90°C, preferably 60 to 80°C. In slurry polymerization, inert hydrocarbon solvents such as aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, etc. used in normal olefin polymerization are used as the polymerization medium. Preferably normal hexane, normal heptane, cyclohexane,
Benzene and toluene are preferably used. Moreover, propylene itself can also be used as a medium.

Further, as a method for controlling the molecular weight of the produced polymer, a known molecular weight controlling agent such as hydrogen or diethylzinc can be appropriately added to the polymerization reaction.

Although propylene alone may be polymerized in the first stage of the present invention, propylene and a small amount of other α-olefin may be used in combination. Other α-olefins include α-olefins such as ethylene, butene-1, and 4-methylpentene-1, and the amount thereof is small enough that the product does not lose its properties as a propylene polymer. 10% by weight or less.

The propylene polymer obtained by the first-stage polymerization is transferred to the second-stage gas phase polymerization vessel, with or without removing a portion of the reaction medium without deactivating the catalyst contained therein. That is, when the polymer is obtained by a solvent polymerization method, inert hydrocarbons and unreacted monomers are removed using a centrifuge, a liquid cyclone, or the like. Furthermore, when liquid propylene itself is used as a medium, it can be sent directly to a gas phase polymerization vessel in addition to similar known solid-liquid separation means.

The most important technical feature of the present invention is that by newly adding an aromatic carboxylic acid ester to the gas phase polymerization system in the latter stage, a low molecular weight polymer of α-olefin monomers such as ethylene and propylene is produced. As a result, adhesion inside the reactor, clumping phenomenon,
It is possible to prevent deterioration of powder properties, form a good fluidized bed, and achieve stable operation.

Aromatic carboxylic acid esters used in the present invention include benzoic acid esters such as methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, methyl cinnamate, ethyl cinnamate, and benzyl cinnamate. , methyl toluate, ethyl toluate, propyl toluate, butyl toluate, methyl ethylbenzoate, ethyl ethylbenzoate, ethyl xylene carboxylate, methyl anisate, ethyl anisate, methyl ethoxybenzoate,
Nuclear substituted benzoic acid esters such as ethyl ethoxybenzoate, dimethyl phthalate, diethyl phthalate,
Examples include aromatic polycarboxylic acid esters such as dipropyl phthalate and dibutyl phthalate.

Further, although these aromatic carboxylic acid esters are different from the electron-donating compounds used in the propylene polymerization in the previous step, they may be the same.

That is, if it has excellent polymerization properties (polymerization activity, stereoregularity, etc.) in the propylene polymerization system in the first stage, it can be added to the first stage as a third component, and it can also be added to the second stage gas phase polymerization system. I can do it.

The aromatic carboxylic acid ester can be added directly to the gas phase reactor, or it can be dissolved and diluted in an inert hydrocarbon solvent or liquid propylene, or it can be added to an α-olefin or propylene and other α-olefins. It can also be supplied directly in a mixed gas with olefin, or dissolved or diluted in an inert hydrocarbon solvent, liquid propylene, etc.

The amount of aromatic carboxylic acid ester to be used varies depending on the amount of organoaluminum compound present in the gas phase polymerization system, but usually, the amount of aromatic carboxylic acid ester used is based on the amount of organoaluminum compound supplied in the first stage, or in the gas phase polymerization system in the second stage. When adding an aluminum compound (for example, Japanese Patent Publication No. 55-7464, Japanese Patent Publication No. 53-30686,
No. 56-151713, etc.), the molar ratio of aromatic carboxylic acid ester/organoaluminium to the total amount of both is 0.0001 to 1, preferably 0.001 to 0.5.
If the amount added is too large, the polymerization activity in gas phase polymerization will decrease, which is not preferable. On the other hand, if the amount is too small, the effect of suppressing the formation of low molecular weight polymers will not be sufficiently exhibited.

In addition, a method of newly adding inert carbon hydrogen to the gas phase polymerization system in the latter stage (for example, Japanese Patent Application Laid-Open No. 57-31905)
Also, the method of the present invention can be used in combination with a method of adding a silicone compound (for example, Japanese Patent Application No. 1734560/1982) and is effective.

In the present invention, α is polymerized or copolymerized in a gas phase.
- As the olefin, used is an α-olefin having 2 to 8 carbon atoms, preferably ethylene or an ethylene-propylene mixture.

The conditions for gas phase polymerization are usually 30 to 100℃ and 1 to 50℃.
Kg/cm ² , and the polymerization ratio of the α-olefin block copolymerization portion in the subsequent stage to the total polymer is 3.
Polymerization or copolymerization is carried out to 50% by weight, preferably 10 to 30% by weight. When using a more preferred embodiment of ethylene-propylene mixed gas,
The composition of the gas is 10 to 90 mol% propylene based on the sum of ethylene and propylene, preferably 20 to 90 mol%.
It is 80 mol%.

The production method of the present invention basically consists of a first step of polymerizing propylene or propylene and a small amount of other α-olefin to obtain a propylene polymer, and a gas phase polymerization of other α-olefin or propylene and other α-olefin. It consists of a second step. However, in the present invention, the subsequent gas phase polymerization of α-olefin can be carried out in multiple stages, and the polymerization temperature, hydrogen concentration, monomer composition, and reaction amount ratio can also be changed in each reactor. .

In the present invention, the equipment used for the latter stage gas phase polymerization is not particularly limited, and includes a known fluidized bed, a stirring tank,
Apparatus such as a fluidized bed with a stirrer or a moving bed are preferably used to carry out the polymerization continuously or batchwise.

After the completion of gas phase polymerization, the polymer extracted continuously or batchwise is subjected to inactivation treatment or deashing treatment with alkylene oxide, alcohol, water, etc., and removal of amorphous polymer with a solvent, etc., as necessary. It's okay to get old.

The method of the present invention is characterized by the addition of an aromatic carboxylic acid ester to the gas phase polymerization system in the subsequent stage, which suppresses the formation of low molecular weight polymers of α-olefins that cause adhesion and sticking, resulting in good powder properties. , the adhesion to the vessel wall and clumping phenomena are eliminated, a good fluidity state is achieved, long-term stable operation is possible in terms of process and quality, and polymerization such as gas phase polymerization activity is achieved. The reason is that it has almost no effect on behavior.

〔Example〕

The present invention will be described below with reference to Examples, but the present invention is not limited thereto unless it exceeds the gist thereof.

In the following Examples and Comparative Examples, bulk density, n-
The hexane extraction residue was measured by the following method.

(1) Bulk density JIS K-6721 (2) N-hexane extraction residue
Remaining amount (% by weight) after extraction with hexane for 3 hours.

Example 1 (A) Preparation of solid titanium trichloride 5.15 liters of purified triene was placed in a 10 volume autoclave which was sufficiently purged with nitrogen at room temperature.
While stirring, 651 g (5 moles) of n-butyl ether,
949 g (5 mol) of titanium tetrachloride and 286 g (2.4 mol) of diethylaluminum chloride were added,
A brown homogeneous solution was obtained.

Next, the temperature was raised to 40°C, and after 30 minutes, precipitation of a purple fine powder solid was observed, but the temperature was maintained at 40°C for 2 hours.

Then 315g of titanium tetrachloride was added and heated to 98°C.
The temperature rose to . After being kept at 98℃ for about 1 hour, a powdery purple solid was separated and washed with n-hexane to give about 800g.
of solid titanium trichloride was obtained.

(B) Production of titanium trichloride containing propylene polymer (pretreatment) Purified n-hexane 5 was placed in 10 autoclaves that were sufficiently purged with nitrogen, and 195 g of diethylaluminium chloride and the solid titanium trichloride obtained in (A) above were added. After charging 250g of TiCl ₃ , keep the temperature at 40℃ and add propylene gas with stirring.
Contact treatment was carried out by blowing 250 g into the gas phase for about 60 minutes.

The solid components were then allowed to settle, and the supernatant liquid was removed by decantation and washed several times with n-hexane to obtain solid titanium trichloride containing a propylene polymer.

(C) Production of propylene-ethylene block copolymer Two reactors with agitators with capacities of 1,000 and 400 are connected in series, and one stirred fluidized tank type gas phase polymerization tank with a capacity of 1,500 is connected in series. In the first and second reaction tanks, homopolymerization of propylene was carried out in liquefied propylene, and in the third reaction tank, copolymerization of propylene and ethylene was carried out by gas phase polymerization.

The first reaction tank contained liquefied propylene, 4.0 g/hr of the catalyst component obtained in (B) above, 10 g/hr of co-catalyst diethyl aluminum chloride, 0.52 g/hr of methyl methacrylate, and hydrogen as a molecular weight regulator.
0.15Kg/hr was continuously supplied. The polymerization temperature was 70°C in the first tank and 67°C in the second tank, and the slurry was continuously extracted from the first tank and supplied to the second tank. The average residence time is the total of the 1st tank and 2nd tank.
It took 4.0 hours.

The polymer slurry from the second tank is continuously transferred to the third tank.
The mixture was supplied to a tank, and gas phase polymerization was carried out while maintaining the temperature at 60°C and the pressure at 15 kg. The compositions of ethylene and propylene in the gas phase were adjusted to propylene/(ethylene+propylene)=65 mol% and _H2 /(ethylene+propylene)=15 mol%. In addition, 0.78% of methyl toluate was added to the circulating gas of this gas phase polymerization system.
g/hr.

The average residence time in this gas phase reactor is 2.5 hours, and the polymer powder continuously extracted from the third tank is separated from unreacted gas and then treated with propylene oxide vapor to convert the powdered polymer into 45
Obtained at a rate of Kg/hr.

This operation was continued for 14 days, and the entire system was able to operate stably, and when the reactor was opened after the operation, no deposits or lumps were observed inside the reactor, similar to those observed in the comparative example. No oily substance formation was observed.

The average weight ratio of homopolymerization and copolymerization of the polymer obtained during this period was 85/15. In addition, the bulk density of the powder is 0.45g/cc, and the amount remaining after n-hexane extraction is
It was 97.8%.

Comparative Example 1 Continuous operation for 14 days was carried out in the same manner as in Example 1 except that methyl toluate was not supplied to the gas phase polymerization system.

During this period, the formation of oily substances was observed at the bottom of the gas phase reactor distribution plate, and the pressure loss of the distribution plate tended to increase over time. The bulk density of the obtained polymer powder was also low, 0.38 to 0.40 g/cc, and the residual amount after extraction with n-hexane was 92.6%.

Further, after the operation was completed, the reactor was opened, and sticky substances and fine particles were found to be attached to the upper part of the reactor freeboard section, and formation of lumps was observed around the shaft of the stirring blade and around the stay section. Furthermore, deposits were also formed on the dispersion plate.

Example 2 Continuous operation for 14 days was carried out in the same manner as in Example 1 except that the amount of methyl toluate added to the gas phase polymerization system was changed to 0.39 g/hr.

During this period, stable operation of the entire system was achieved, but after the completion of the operation, the reactor was opened, and although some adhesion was observed inside the reactor, no formation of lumps was observed.

Also, the bulk density of the polymer powder obtained during this period was
0.43 g/cc, and the residual amount after n-hexane extraction was 96.8%.

Example 3 Continuous operation for 14 days was carried out in the same manner as in Example 1 except that the aromatic compound added to the gas phase polymerization system in Example 1 was changed to 0.71 g/hr of methyl benzoate.

During this period, stable operation of the entire system was achieved, and when the reactor was opened after the completion of the operation, no adhesion or lumps were observed inside the reactor, and no oily substances were observed as observed in the comparative example.

Also, the bulk density of the polymer powder obtained during this period was
0.44 g/cc, and the residual amount after n-hexane extraction was 97.5%.

〔Effect of the invention〕

According to the present invention, the production of low molecular weight polymers is suppressed without reducing polymerization activity, adhesion to the reactor inner wall and clumping phenomena are eliminated, and a good fluidity state is achieved, resulting in improved process quality. It also enables long-term stable operation.

Claims (1)

[Claims] 1. Propylene is polymerized in the presence of a catalyst, and then α other than propylene is polymerized without deactivating the catalyst.
- A method for polymerizing or copolymerizing olefin or propylene and other α-olefins in a gas phase, characterized in that an aromatic carboxylic acid ester is supplied to the subsequent gas phase polymerization system.
A method for producing an olefin block copolymer. 2. The method according to claim 1, wherein the polymerization catalyst comprises titanium trichloride and dialkyl aluminum chloride. 3. A patent claim characterized in that the polymerization catalyst has an aluminum content in an atomic ratio of aluminum to titanium of 0.15 or less and is composed of a solid titanium trichloride catalyst complex containing a complexing agent and an organoaluminum compound. The method described in Scope 1. 4 The polymerization catalyst is a solid titanium trichloride-based catalyst complex, and the pore radius measured by the mercury porosimeter method is
The method for producing a block copolymer according to claim 1, which uses a block copolymer having a cumulative pore volume of 0.02 cm ³ /g or more between 20 Å and 500 Å. 5 The polymerization catalyst is a solid titanium trichloride catalyst complex,
Claim 1, which is precipitated at a temperature of 150°C or less from a liquid containing titanium trichloride liquefied in the presence of an ether or thioether.
The method for producing the block copolymer described in Section 1. 6 The polymerization catalyst is obtained by treating solid titanium trichloride obtained by reducing titanium tetrachloride with an organic aluminum compound or metal aluminum using a solid titanium trichloride-based catalyst complex, and treating it with a complexing agent and a halogen compound. A method for producing a block copolymer according to claim 1.