JPH0341485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing propylene-ethylene copolymers. Specifically, a step of polymerizing a propylene-ethylene copolymer, a step of countercurrently washing the copolymer with a low-boiling hydrocarbon, a step of recovering a low-boiling hydrocarbon for cleaning used in the countercurrent washing, and a step of polymerizing a propylene-ethylene copolymer. The present invention relates to a method for producing a propylene-ethylene copolymer, which comprises the steps of taking out the ethylene copolymer and further recovering a catalyst diluent, propylene, and ethylene monomers.

Since the invention of stereoregular catalysts by Ziegler and Natsuta et al., crystalline polyolefin has become a general-purpose resin with excellent properties such as excellent rigidity, impact resistance, and lightweight molded products, and its production has increased worldwide in recent years. are doing. Among them, crystalline polypropylene has characteristics such as excellent transparency and lightweight molded products, so its production volume is rapidly increasing. However, crystalline polypropylene has the disadvantage of being brittle at low temperatures, so it is difficult to use in applications that require impact resistance at low temperatures. Many studies have already been made on methods to improve this drawback, and various improvement methods have been proposed. Among these, a method of copolymerizing propylene with other olefins, especially ethylene, has been developed as an industrially advantageous method, and has been proposed in, for example, Japanese Patent Publications No. 38-14834, No. 39-1836, and No. 39-15535. Furthermore, as a method to improve the disadvantages of copolymers produced by these methods, such as poor rigidity and transparency of molded products, and whitening of deformed parts when deformed by impact or folding, 3. A method of carrying out block copolymerization in stages was proposed in Japanese Patent Publications No. 44-20621 and No. 49-24593, and the resulting propylene _* ethylene copolymers had very excellent physical properties.

On the other hand, methods for obtaining ethylene-propylene copolymers by bulk polymerization that do not substantially use high-boiling point inert solvents are known, and include Japanese Patent Publications No. 42-17488, No. 49-120986, and No. 52-3684. These methods, proposed by et al., do not substantially use high-boiling point inert solvents, so by combining recent highly active catalysts, the solvent purification step is virtually unnecessary, and catalyst residue is eliminated. is becoming almost unnecessary for polymers used in a considerable number of fields. However, in many fields with the current catalyst performance, it is necessary to use a catalyst in which catalyst residues or low molecular weight and low crystallinity polymers have been removed.

In order to solve these problems without losing the advantages of bulk polymerization using propylene as the polymerization solvent, the propylene _* ethylene copolymer obtained in the polymerization process is catalytically activated with alcohol, alkylene oxide, or diketones. A propylene-ethylene copolymer having excellent physical properties can be obtained by solubilizing the catalyst residue at the same time as deactivating it, and then washing and removing it with a washing solvent containing propylene as a main component. A specific example is Tokko Akira.
51-1274, JP-A-54-142290, etc.

However, these methods use a countercurrent cleaning agent whose main component is propylene in an extremely large amount compared to the propylene used as the polymerization solvent.
A major problem is the recovery and reuse of the propylene-based cleaning solvent used in countercurrent cleaning and the polymerization solvent recovered from the slurry extracted from the lower part of the countercurrent cleaning tower.

Regarding the above-mentioned recovery and reuse, it is of course possible to completely separate all parts into each component using methods such as distillation, separate them to the extent that they can be used for polymerization, and reuse them. Since the solvent and polymerization solvent contain monomers such as ethylene and propylene, and relatively high-boiling hydrocarbons used as catalyst diluents, it is not easy to completely separate each component. In particular, complete separation of ethylene and propylene requires an extremely low temperature medium, and the separation process requires very expensive equipment and operation, which significantly increases the cost of producing the polymer. Become. Furthermore, in reality, as a cleaning solvent for countercurrent cleaning, it is not necessary to completely separate ethylene and propylene, and furthermore, as a monomer used in the polymerization process, it is appropriate to use ethylene as a mixture of ethylene and propylene. There is no particular disadvantage if you choose the conditions. A method of rationally separating and reusing the recovered mixture by dividing it into three parts according to these ideas is shown in Japanese Patent Publication No. 47-42379. According to this method, the part extracted from the upper part of the countercurrent washing tower is separated into a solid part and a gas part using a simple evaporator, part of the gas part is used for countercurrent cleaning, and the remaining part is distilled into parts used for homopolymerization of propylene and copolymerization of ethylene and propylene. A method of separating and reusing it has been proposed. Although the method of the invention represents a very rational method and is a very useful method, one of the problems of the invention is that all the recovered volatile matter is condensed in its entirety, and the condensed matter is A portion is passed through a countercurrent washing tower, and the remaining portion is separated by distillation into a mixture of ethylene and propylene and a highly purified portion of propylene.The entire amount is first turned into a gas, and then the entire amount is pressurized to make it a liquid. and cooling is required, which is disadvantageous in terms of energy.

On the other hand, if only partial condensation is performed, the condensed fraction is passed through a countercurrent washing tower, and the non-condensed fraction is further separated into a mixture of ethylene and propylene and a highly purified portion of propylene, the portion passing through the countercurrent washing tower is The content of relatively high-boiling hydrocarbons increases, and more polymer than necessary is solubilized in the countercurrent washing tower and extracted and removed, resulting in a decrease in the copolymer ratio.

As a result of various studies, the present inventors focused on the fact that the volatile content in the liquid extracted from the upper part of the countercurrent cleaning tower was much larger than the volatile content in the slurry extracted from the lower part. Catalyst residues and soluble polymers are separated from the liquid extracted from the upper part, and the entire volatile content is condensed, and the condensed material is passed to a countercurrent washing tower, but the slurry from the lower part contains propylene-propylene as its non-volatile content. We have discovered that the above problems can be solved by taking the ethylene copolymer out of the system, separating the volatile components into a mixture of ethylene and propylene and a highly purified propylene portion, and reusing each for polymerization. completed.

The purpose of the present invention is to polymerize a propylene-ethylene copolymer using a bulk polymerization method using propylene itself as a solvent, and then remove the soluble catalyst residue and soluble polymer from the copolymer in a countercurrent washing tower to improve its physical properties. The objective is to extract a superior copolymer and to efficiently recover relatively high-boiling saturated hydrocarbons for use in monomers, cleaning solvents, and catalyst dilution.

The present invention is a bulk polymer in which propylene itself is used as a solvent and a small amount of a saturated hydrocarbon having 4 to 10 carbon atoms or an aromatic hydrocarbon is used as a catalyst diluent, and (A) the reaction ratio of ethylene/propylene is 6/94. A propylene-ethylene copolymer is obtained as a slurry in a polymerization step in which mainly propylene is polymerized at a weight ratio of 15/85 to 95/5, and then ethylene/propylene is polymerized at a weight ratio of 15/85 to 95/5, and (B) the above-mentioned The slurry obtained in the polymerization process is introduced into the upper part of the countercurrent washing tower,
A cleaning liquid is introduced from the lower part, the cleaning liquid containing the polymer soluble in the cleaning liquid and catalyst residue is extracted from the upper part, and the countercurrently washed propylene-ethylene copolymer is taken out as a slurry from the lower part. In the method for obtaining a polymer, (C) the washing liquid containing the soluble polymer and catalyst residue extracted from the upper part of the countercurrent washing tower is subjected to single evaporation to convert the soluble polymer and the catalyst residue into non-volatile components. (D) Countercurrently washed propylene-ethylene copolymer extracted from the lower part of the countercurrent cleaning tower. On the other hand, the volatile components are separated in the first separation zone into a portion mainly consisting of the catalyst diluent and a portion mainly consisting of ethylene and propylene, and the fraction mainly consisting of ethylene and propylene is introduced into the second separation zone. , a propylene fraction sufficient to perform polymerization with an ethylene/propylene reaction ratio of 6/94 or less by weight, and ethylene used for polymerization with an ethylene/propylene reaction ratio of 15/85 to 95/5 by weight. This is a method for polymerizing a propylene-ethylene copolymer, which is characterized in that a mixture of propylene is separated into fractions and subjected to a polymerization step (A).

The first element of the present invention is that (A) the polymerization step is carried out by bulk polymerization using propylene itself as a solvent and a small amount of a saturated hydrocarbon having 4 to 15 carbon atoms or an aromatic hydrocarbon as a catalyst diluent. It's about doing. Saturated hydrocarbons or aromatic hydrocarbons having 4 to 15 carbon atoms are used as inert substances to ordinary olefin polymerization catalysts, and specifically,
Gasoline, kerosene, light oil, etc., which are generally available as butane, pentane, hexane, heptane, nonane, decane, cyclohexane, benzene, toluene, xylene, etc., or mixtures thereof, can also be used. The catalyst is not particularly limited and may be a combination of a normal transition metal halide and an organometallic compound, as long as it provides a polymer in a slurry state, and specifically, titanium, panadium chloride, Alternatively, these transition metal compounds can be combined with various carriers such as magnesium, aluminum,
Examples include chlorides or oxides of manganese, etc., and organic metal compounds such as aluminum, zinc, magnesium, etc. are used. Preferably, compounds containing TiCl ₃ as a main component or MgCl ₂ with Ti chloride supported on it,
Combinations of organometallic compounds of aluminum are preferably used.

The second element of the present invention is to mainly polymerize propylene at an ethylene/propylene reaction ratio of 6/94% by weight or less, and then to perform polymerization at an ethylene/propylene reaction ratio of 15/85 to 95/5 by weight. The goal is to obtain a propylene-ethylene copolymer as a slurry in the polymerization process. The temperature of the polymerization is generally
The temperature is 30 to 100°C, and the preferred range varies depending on the catalyst used, but it is usually 40 to 90°C.
Compared to the polymerization temperature when the propylene reaction ratio is 6/94% by weight or less, the ethylene/propylene reaction ratio is
Polymerization at a weight ratio of 15/85 to 95/5 is generally carried out at low temperatures. Polymerization at a reaction ratio of ethylene/propylene of 6/94 or less is a necessary step to maintain high rigidity of the resulting copolymer, and generally accounts for 40 to 95 weight ratio of the total polymerization amount. It is.
Ethylene/propylene reaction ratio is 15/85 to 95/5
The weight ratio polymerization is necessary to increase the impact resistance of the resulting copolymer, and is especially necessary to maintain high impact resistance at low temperatures. In order to maintain a good balance with rigidity, polymerization at this reaction ratio is generally carried out so that the amount of polymerization is 5 to 60% by weight of the total polymerization amount. The pressure during the above polymerization is determined to be a specific value based on the minimum pressure to keep propylene in a liquid state, the reaction ratio of ethylene/propylene, the polymerization temperature, and when hydrogen is used to control the molecular weight, the hydrogen concentration, etc. However, it is usually 10 to 50 kg/cm ² -gauge. The copolymer slurry obtained by the above operation is
Of course, it is possible to pass the product as it is to the next step (C) in the countercurrent washing tower, but in order to increase the effect of uncontrolled polymerization in the countercurrent washing tower or removal of catalyst residue in the countercurrent washing tower, It is preferable to deactivate the catalyst with alcohol, alkylene oxide, diketone, etc., and further solubilize the catalyst residue.

The third element of the present invention is to introduce the slurry in which the catalyst has been deactivated into the upper part of the countercurrent washing tower in the above polymerization step and if necessary, introduce the washing liquid from the lower part, and introduce the slurry which is soluble in the washing liquid from the upper part. The cleaning liquid containing the polymer and catalyst residue is blown out, and the countercurrently washed propylene-ethylene copolymer is taken out as a slurry from the bottom. This element is necessary to improve various physical properties of the resulting polymer, weather resistance, surface stickiness of molded products, voltage resistance of the film when used as a film, and surface condition of the film. This element is particularly effective when the performance of the catalyst is relatively poor. Regarding the condition of the countercurrent cleaning tower, commonly used and well-known ones can be used, and it is not limited to those with a special structure, but it should be a cylindrical pressure-resistant vessel with an inner diameter to height ratio of 1:2 to 1: 50 is common. There are no particular restrictions on the operating temperature of the countercurrent washing tower, but it is generally 10 to 80°C, and in particular, when the countercurrent washing tower is used to deactivate the catalyst and solubilize the catalyst residue, it is relatively low. Although it is preferable to carry out the process at a high temperature, it is usually preferably determined rationally based on the temperature of the slurry received into the countercurrent cleaning tower, the pressure of the cleaning liquid recovery step (C) described below, etc. There is no particular restriction on the operating pressure of the countercurrent washing tower, but it is reasonable to conduct the operation at a pressure lower than that of the polymerization process or catalyst deactivation process without requiring a special device for transferring the slurry, and the preferable pressure range is , can be determined by considering the operating conditions of recovery steps (C) and (D). There are no particular restrictions on the movement speed of the cleaning liquid from the bottom to the top within the countercurrent cleaning tower, as long as the countercurrent cleaning tower can be operated.
For copolymers obtained with ordinary catalysts, generally 0.05 to 5
cm/sec.

The fourth element of the present invention is to remove the soluble polymer and catalyst residue as nonvolatile components by evaporating the cleaning liquid containing the soluble polymer and catalyst residue extracted from the upper part of the countercurrent cleaning tower. The method is to condense all of the water and introduce the condensed recovered cleaning liquid into the lower part of the countercurrent cleaning tower as a cleaning liquid. This is a characteristic feature of the present invention and makes it possible to efficiently recover and reuse the countercurrent cleaning liquid. There are no particular restrictions on the method of evaporating to remove polymers and catalyst residues soluble in the cleaning solution, and any known method can be used. The cleaning solution is flushed into a container kept at a high temperature and low pressure compared to the temperature and pressure, and the cleaning solution is collected as volatile matter from the upper part, and soluble polymer and catalyst residue are collected as non-volatile matter from the lower part. It is common to take it out of the system.
There are no particular restrictions on the temperature and pressure of the container in which the cleaning liquid is flushed, but it is best to keep it at a lower pressure and higher temperature than the pressure and temperature of the countercurrent cleaning tower. It is undesirable to transfer the slurry to the container, which requires special equipment, and the temperature is high enough to vaporize the volatiles, the range of which is determined by the pressure of the vessel. The appropriate temperature will also vary depending on the amount of dissolved polymer in the cleaning solution. Next, the volatile components taken out by the above operation are compressed and/or cooled using a known compressor to condense the entire amount, and can be passed to a countercurrent washing tower. There are no particular restrictions on the condensation conditions, but it is preferable and rational to compress and cool the condensate so that the temperature and pressure are suitable for passing the condensate to a countercurrent washing tower.

The fifth element of the present invention is to convert the countercurrently washed propylene-ethylene copolymer slurry extracted from the lower part of the countercurrent washing tower into non-volatile matter by single evaporation, and take out the propylene-ethylene copolymer from the system.
On the other hand, volatile matter is ()catalyst diluent ()ethylene/
A fraction consisting almost only of propylene used for polymerization with a propylene reaction ratio of 6/94% by weight or less, and
Separate into a mixture of ethylene and propylene used for polymerization at 15/85 to 95/5% by weight, () and () are passed through the (A) polymerization process as is, and () is usually further subjected to appropriate treatment. , to reuse it as a catalyst diluent. There is no particular restriction on the separation method into the above three parts, but usually a distillation column is used to separate the two fractions (), () and (), and the fraction consisting of () and () is separated into two fractions: () and (). Furthermore, it is preferable to separate the fractions () and () using a distillation column.

By using the method of the present invention, each raw material can be used effectively with a simple device, energy-wise, and is very advantageous industrially. Hereinafter, the method of the present invention will be explained in more detail according to the method of the present invention using figures showing one example of the method of the present invention.
This example shows one example of the method of the present invention,
The method of the present invention is not limited, and various attached devices or unnecessary items can be deleted as necessary.

Add explanation according to the diagram. In polymerization tank A~, polymerization is carried out with an ethylene/propylene reaction ratio of 6/94 or less by weight, and in polymerization tank B~, polymerization is carried out with an ethylene/propylene reaction ratio of 15/85 to 95/5 weight ratio, and then In reaction tank C~, an operation to separate hydrogen and an operation to deactivate the catalyst are performed.

A solid catalyst and organoaluminum are charged as a catalyst to the polymerization tanks A through line 1, and propylene is charged through line 4 with a mixture of recovered propylene and new propylene. The slurry from polymerization tanks A to A is continuously transferred to polymerization tank B using a known slurry transfer method, and to polymerization tank B, propylene is supplied from line 3, ethylene is supplied from line 2, and ethylene is supplied from line 6. The recovered mixture of ethylene and propylene is charged through line 6, and ethylene and propylene are copolymerized. The slurry in polymerization tank B is continuously transferred to reaction tank C, and a deactivator is introduced into reaction tank C. In the example shown in Table 1, diethylene glycol monoisopropyl ether is introduced at a rate of 35 kg/day, and hydrogen is further removed from line 17. The slurry from reaction vessel C is continuously introduced into the upper part of countercurrent washing tower D.
The cleaning liquid recovered from line 12 is introduced into countercurrent washing tower D~, and the copolymer washed in countercurrent is taken out from line 13 as an insoluble polymer, and the volatile components are removed in solvent volatilizer G~. It is separated and taken out as a powder from the 18 line. The powder taken out from No. 18 contains 0.8% by weight of propylene, 0.3% by weight of heptane, and 0.1% by weight of diethylene glycol monoisopropyl ether, which can be removed by normal granulation operations or is necessary. Propylene _* ethylene copolymer can be obtained at 7558 kg/day by the process shown in Figure and Table 1, which can be dried in a known dryer if available. The mixture having the composition shown in 14 in Table 1 taken out as a volatile component from the volatile unit G~ is separated in the distillation column H~ which is the first separation zone, and a fraction mainly consisting of heptane is taken out from the lower part of this line 16~ The fraction shown is combined with the heptane portion taken out from line 11, further purified, and used as heptane for diluting the catalyst. The fraction extracted from the upper part of the distillation column H~ is introduced into the second separation zone, the distillation column I~, and a mixture of ethylene and propylene is taken out from the upper part of the distillation column as a fraction to be used in the polymerization tank B~, and is passed through line 6. The polymer is introduced into the polymerization tank B through the steps. On the other hand, the fraction extracted from the lower part of distillation column I is introduced into polymerization tank A through line 5. In addition, the portion extracted from the upper part of the countercurrent washing tower D~ passes through line 10 and is separated from the volatile matter by catalyst residue and soluble polymer in separator E~, and is then extracted from line 11. It is further preferred to use an apparatus to remove heptane as a volatile fraction, purify it together with the portion from line 16, and use it for catalyst dilution. The volatile components taken out from the separators E are condensed in the cooler F, passed through the lines 12, and if necessary, are pressurized with a pressure booster pump and introduced into the lower part of the countercurrent washing tower D. If the composition shown in Table 1 is used, the entire amount can be condensed at a pressure of 26 kg/cm ² -gauge and a temperature of 45°C. There are no difficulties.

Table 1 shows the mass balance when performing the above operations.
Furthermore, Table 2 shows the operating conditions of each device in the recovery system, which is a feature of the present invention.

[Brief explanation of drawings]

The drawing is a flow diagram illustrating one preferred embodiment of the present invention.

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Claims (1)

[Claims] 1. Propylene itself is used as a solvent, and all solvents are
It is a bulk polymerization method that uses 0.1 to 10% by weight of saturated hydrocarbons or aromatic hydrocarbons having 4 to 15 carbon atoms as a diluent for the catalyst. Polymerize propylene, and then the reaction ratio of ethylene/propylene is 15/85 ~
A propylene-ethylene copolymer is obtained as a slurry in a polymerization step in which polymerization is carried out at a weight ratio of 95/5, and (B) the slurry obtained in the above polymerization step is introduced into the upper part of a countercurrent washing tower, and the washing liquid is introduced from the lower part. The cleaning solution containing polymers and catalyst residues soluble in the cleaning solution is extracted from the upper part, and the countercurrently washed propylene-ethylene copolymer is taken out as a slurry from the lower part, thereby converting the propylene-ethylene copolymer. In the method for obtaining (C), the cleaning liquid containing the soluble polymer and catalyst residue extracted from the upper part of the countercurrent cleaning tower is evaporated to remove the soluble polymer and catalyst residue as non-volatile components, and the entire amount of volatile components is condensed. , the entire amount of the condensed recovery liquid is introduced as a cleaning liquid into the lower part of the countercurrent cleaning tower, and (D) the countercurrently washed propylene-ethylene copolymer slurry extracted from the lower part of the countercurrent cleaning tower is evaporated as non-volatile matter. A propylene-ethylene copolymer is obtained, and the volatile components are separated in the first separation zone into a part mainly consisting of (2) catalyst diluent and a part mainly consisting of ethylene and propylene, and a fraction mainly consisting of ethylene and propylene. is introduced into the second separation band, and ()
Sufficient propylene fraction for use in polymerization with an ethylene/propylene reaction ratio of 6/94 weight ratio or less and () an ethylene/propylene reaction ratio of
Production of a propylene-ethylene copolymer characterized by separating a fraction of a mixture of ethylene and propylene sufficient for use in polymerization at a weight ratio of 15/85 to 95/5 and passing it through (A) a polymerization step. Method.