JPH0530846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a propylene block copolymer. Specifically, the present invention relates to a method for removing polymerization heat during batch polymerization when producing a propylene block copolymer by combining continuous polymerization and batch polymerization.

Conventional technology In order to improve the impact resistance of polypropylene, propylene is copolymerized alone or a small amount of ethylene and propylene are copolymerized (first stage polymerization part), and then ethylene and propylene are copolymerized (second stage polymerization part) to produce so-called propylene. The production of block copolymers is widely practiced on an industrial scale.

It is also known that the copolymerization of ethylene and propylene in the latter stage can be carried out under desired conditions in a bulk polymerization method using propylene itself as a medium by carrying out the first stage polymerization continuously and the second stage polymerization batchwise (for example, JP-A-57-145114, JP-A-57-145115, JP-A-57-
149319, Japanese Patent Application Publication No. 149320).

Problems to be Solved by the Invention The method described above in which at least the first stage polymerization is carried out continuously by bulk polymerization and the second stage polymerization is carried out batchwise has the advantage that a variety of block copolymers can be produced with a small number of polymerization vessels. Although this is an extremely excellent method, the post-polymerization portion accounts for several percent to several +% of the total, and in order to carry out the reaction in a short time while strictly controlling the reaction ratio and reaction amount of ethylene and propylene, The calorific value in the polymerization section and the calorific value change greatly depending on the reaction ratio, and with ordinary methods of controlling the temperature of the polymerization tank, it is impossible to control the polymerization temperature of the polymerization tank on an industrial scale, and the polymerization reaction cannot be carried out under the desired conditions. It was difficult to do so.

The inventors of the present invention have conducted intensive studies on methods for solving the above-mentioned problems, and have found that the above-mentioned problems can be solved by implementing a specific control method, and have completed the present invention.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method of combining continuous polymerization and batch polymerization to perform batch polymerization with good controllability when producing block copolymers.

Means for Solving the Problems That is, the present invention provides a method for producing a propylene block copolymer by copolymerizing propylene alone or with a small amount of ethylene and then batchwise copolymerizing ethylene and propylene. The heat of polymerization is removed in a polymerization tank where polymerization is carried out in batches by evaporating the volatile liquid medium and condensing the vapor in a reflux condenser, and the amount of refrigerant introduced into the reflux condenser is adjusted to the reaction ratio of ethylene and propylene. and a method for producing a propylene block copolymer, which is characterized by controlling the heat generation pattern determined by the amount of reaction.

In the present invention, propylene alone or copolymerization of a small amount of ethylene and propylene also includes copolymerization of a small amount of other α-olefins such as butene-1 and hexene-1.

In addition, copolymerization of ethylene and propylene means that in addition to ethylene and propylene, butene-1 and hexene-1 are copolymerized.
It also includes copolymerizing 1.

In the present invention, any known catalyst can be used in the above polymerization, and any catalyst system used in the stereoregular polymerization of propylene can be used without particular limitation. That is, it is a catalyst system consisting of a commonly used reduction metal compound and an organometallic compound,
Specifically, titanium halides or titanium halides supported on carriers such as magnesium halide, silica, alumina, and especially titanium trichloride or titanium tetrachloride supported on magnesium chloride are preferably used, and organic aluminum, organic It can be used as a suitable catalyst by combining an organometallic compound of magnesium with a stereoregularity improver if necessary.

As a method for producing a block copolymer combining continuous polymerization and batch polymerization in the present invention, the method disclosed in JP-A-57-149320 mentioned above can be employed as is. A preferred embodiment is a bulk polymerization method using propylene itself as a liquid medium, in which propylene alone or a small amount of ethylene and propylene are copolymerized (preliminary polymerization section) by connecting one or more tank-type polymerization machines, preferably two or more tanks. A reactor or a loop reactor is used to continuously polymerize the continuously produced polypropylene slurry, and preferably two or more tank-type polymerizers are installed in parallel to the reactor that continuously polymerizes the continuously produced polypropylene slurry. Accepted into each connected tank type polymerization machine,
Ethylene is added to the received slurry, and propylene is added as necessary to carry out the copolymerization reaction (second stage polymerization part) in batches.

The reaction time allowed for batchwise copolymerization can be increased by increasing the volume of the reaction tank or by increasing the number of reaction tanks connected in parallel, but either way However, the cost required for the equipment becomes large, which is not preferable.

In order to provide a propylene block copolymer with the characteristics of a good balance between impact resistance and rigidity, the reaction ratio of ethylene and propylene in the first stage polymerization section should be 6/94 or less by weight, and the second stage polymerization section should have a reaction ratio of 6/94 or less by weight. It is necessary that the weight ratio in the polymerization section is 15/85 to 95/5, and the ratio of the first stage polymerization section to the second stage polymerization section is 60 to 95:40 to 5 by weight.

The polymerization temperature in the first stage polymerization section is room temperature to 90℃, preferably 50 to 90℃ from the point of view of removing the reaction heat, and the reaction pressure is low in the presence of a gas phase to reduce the concentration of comonomers, hydrogen, and inert hydrocarbons. Once the quantity is determined, it is determined. In addition, in full-liquid polymerization, the pressure can be freely set above the pressure under which the gas phase exists.

In order to produce a propylene block copolymer with a good balance of impact resistance and rigidity, it is necessary to polymerize 40 to 50% by weight of the total in the latter stage polymerization section, that is, the batch polymerization section. If batch polymerization is carried out in a reaction tank with a volume corresponding to the reaction ratio without increasing the volume of the reaction tank or the number of reaction tanks connected in parallel, the change in calorific value can be controlled using the usual temperature control method. In other words, it cannot be followed by detecting the internal temperature and changing the amount of cooling water so that the internal temperature remains constant.

In contrast, the process according to the invention is characterized in that: 1) the cooling is carried out using a reflux condenser, preferably using propylene as the evaporating medium; and 2)
The objective is to control the amount of refrigerant introduced into the reflux condenser by a heat generation pattern determined by the relationship between the reaction ratio and reaction amount of ethylene and propylene.

The method of cooling by passing cooling water through a jacket covering the reaction tank cannot keep up with large changes in calorific value (due to differences in the heat of polymerization of ethylene and propylene and changes in reaction rate) caused by changing the reaction ratio of ethylene and propylene. Therefore, it is necessary to use a reflux condenser to control the temperature. (However, this does not negate the use of a jacket to remove heat for the purpose of removing part of the polymerization heat.) In the present invention, what is more important is that the amount of cooling water introduced into the reflux condenser is adjusted to The method is to change the heat generation pattern depending on the reaction ratio and reaction amount of the copolymerization reaction carried out in the section.

This relationship will be explained using the drawings. FIG. 1 shows the relationship between the elapsed time from the start of polymerization in the batch polymerization section, the reaction ratio of ethylene and propylene, and the amount of heat generated at that time. FIG. 1 shows a case where two-stage polymerization is carried out with different reaction ratios of ethylene and propylene, and then the reaction is carried out without adding ethylene. The initial reaction was carried out at an ethylene/propylene reaction ratio of 0.8 for 12 minutes, then the reaction at an ethylene/propylene reaction ratio of 1.6 was carried out for 2 minutes (one minute was required to change the reaction ratio), and the ethylene reaction was continued for another 2 minutes. The reaction was continued without any addition, and then a quencher was added to stop the reaction (marked with a circle in the drawing). In this case, the relationship between the reaction with a reaction ratio of 0.8 and the subsequent reactions is approximately 0.4 in terms of reaction time, assuming that the reaction with a reaction ratio of 0.8 is 1.
The calorific value is approximately 1.3, and the reaction amount is approximately 1.1.

In the present invention, the polymerization reaction is carried out by predetermining the pattern of the amount of cooling water according to the exothermic pattern (broken line in FIG. 1) determined by the reaction pattern determined according to the reaction ratio and reaction amount. The pattern of the amount of cooling water is determined according to the relationship between the amount of cooling water and the amount of heat removed, which is specific to the reflux condenser being used. The pattern of the amount of cooling water can be determined by determining the amount of excess cooling water that should be introduced in order to reach a steady state in a short time during the transfer and the time for introducing that amount of water.

In this case, the reaction ratio of ethylene and propylene and/or
Or, when performing batch polymerization of reactions with large differences in hydrogen concentration, in addition to the relationship between the amount of cooling water and heat removal specific to the reflux condenser used, consider changes in heat removal due to the concentrations of ethylene and hydrogen in the gas phase. It is desirable to do so. This is because when the ethylene concentration in the gas phase, especially the hydrogen concentration in the gas phase, increases, the amount of heat removed decreases significantly.

Effect The reason why the method of the present invention is extremely effective in producing a block copolymer by combining two consecutive batches is that when the latter stage polymerization is carried out in batch polymerization, the reaction ratio changes in a relatively short period of time. In the copolymerization of ethylene and propylene, the calorific value changes significantly by changing the reaction ratio (the reaction rate and calorific value per unit polymer weight change, and the apparent calorific value is due to a synergistic effect). )
While the method of controlling the polymerization temperature by detecting the normal temperature cannot control the temperature to a constant temperature, the method of the present invention controls the amount of cooling water according to a predetermined heat generation pattern. Therefore, it is presumed that the temperature can be kept constant.

Example A block copolymer was produced using a 40 m ³ reaction tank in the latter stage polymerization section.

FIG. 1 shows the reaction ratio pattern of ethylene and propylene in batch polymerization and the heat generation pattern at that time. FIG. 2 shows the relationship between the amount of cooling water depending on the heat generation pattern. FIG. 2 shows the change in temperature when batch polymerization was carried out using this cooling water pattern. 50±0.4
Polymerization was possible at a nearly constant temperature of ℃. On the other hand, FIG. 3 shows an example in which the polymerization temperature is controlled by detecting the internal temperature and changing the amount of cooling water. In particular, it can be seen that in the latter stage of polymerization, the temperature could not be followed closely and the temperature rose to 52°C.

The amount of ethylene/propylene copolymer polymerized in the above reaction tank is 450Kg/batch, which is approximately 12Mcal/min in a reaction with a reaction ratio of 0.8 and 40Mcal/min in subsequent reactions.
A fever of min has been observed.

Effects By carrying out the method of the present invention, it is possible to produce a block copolymer of constant quality, which is extremely valuable industrially.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the elapsed time of batch polymerization, the ethylene/propylene reaction ratio, and the calorific value, and Figure 2 is a diagram showing the relationship between the internal temperature of the reaction tank and the amount of cooling water when the method of the present invention is carried out. FIG. 3 is a diagram showing the relationship between the elapsed time of batch polymerization, and FIG. 3 is a diagram showing the relationship between the internal temperature and the amount of cooling water and the elapsed time of batch polymerization when controlled by internal temperature for comparison.

Claims (1)

[Claims] 1. A method for producing a propylene block copolymer by continuously copolymerizing propylene or a small amount of ethylene and propylene, and then batchwise copolymerizing ethylene and propylene,
The heat of polymerization is removed in a polymerization tank where polymerization is carried out in batches by evaporating the volatile liquid medium and condensing the vapor in a reflux condenser, and the amount of refrigerant introduced into the reflux condenser is adjusted to the reaction ratio of ethylene and propylene. and a method for producing a propylene block copolymer, characterized in that the heat generation pattern is controlled by a predetermined heat generation pattern based on the relationship between the reaction amount and the reaction amount.