CN1009100B - Process for the continuous polymerization of propylene - Google Patents

Abstract

In the continuous polymerization of propylene using a catalyst supported on magnesium chloride, the catalyst is pretreated with diethylaluminum chloride and introduced into the polymerization reactor in admixture with the gas stream at a velocity of at least 3 m/s.

Description

The present invention relates to a process for the continuous polymerization of propylene using a catalyst system comprising:

(a) A highly active solid catalyst component containing titanium tetrachloride, magnesium chloride, alkoxy groups and an electron donor.

(b) the compound AlR ₃ , wherein R represents an alkyl group containing 2 to 8 carbon atoms and,

(c) Selectivity control agents.

For the convenience of description, the titanium-containing solid component catalyst system is referred to as the "procatalyst" (Procatalyst), and the compound AlR ₃ is referred to as the "cocatalyst", and the selectivity control agent (such as aromatic ester) is the energy and cocatalyst Lewis bases that form complexes.

Improving the polymerization activity of the corresponding catalyst systems is a first object of the present invention. According to this main object, the improvement of the polymerization activity of the catalyst is achieved by contacting the procatalyst with certain dialkylaluminum chlorides under the conditions defined hereinafter. Here, this contact process is referred to as "pretreatment".

Pretreatment can improve the performance of the catalyst, making its activity 40-80% higher than that of the untreated main catalyst. However, such pretreated procatalysts have such high polymerization activity that they present certain problems in handling and transporting them to polymerization vessels. The general method of injecting the unpretreated solid procatalyst component into the polymerization vessel is to suspend the procatalyst in an inert hydrocarbon diluent and inject it into the reactor. However, if such a method is used on pretreated fresh catalyst, polymerization will occur at the outflow end of the injection system, which will eventually clog the injection system. Due to the high activity, very little catalyst is needed to supply continuous polymerization, so in the main catalyst supply line, the flow rate of the suspension is so low that at the end of the supply line, propylene monomer can diffuse from the polymerization reactor to the injection the rear of the catheter. Therefore, it is a second object of the present invention to establish a new method for injecting these very active pretreated catalysts into the polymerization reactor.

Thus, the present invention relates to a process for the continuous polymerization of propylene in a reactor with a catalyst system, the process comprising:

(a) Highly active solid catalyst components containing titanium tetrachloride, magnesium chloride, alkoxy groups and electron donors.

(b) the compound AlR ₃ , wherein R represents an alkyl group containing 2 to 8 carbon atoms, and

(c) selectivity control agent (SCA, selectivity control agent),

It is characterized in that, in the absence of propylene and the (b) and (c) components of the catalyst system, before being used in the propylene polymerization reaction, the above solid catalyst component (a) is mixed with chlorine at 10-55°C Dialkylaluminum chlorides (wherein each alkyl group contains 2 to 8 carbon atoms) are contacted for at least 4 minutes. Next, in the presence of an inert liquid hydrocarbon diluent, the above-mentioned catalyst component (a) in the diluent or its mixture with hydrogen, nitrogen, methane, ethane, propane, isopropane, n-butane or a mixture thereof is mixed with a conduit In the form of a vapor stream, it is introduced into the above-mentioned reaction vessel at a velocity of at least 3 m/s.

Procatalysts improved by pretreatment with dialkylaluminum chloride can be prepared by known methods, for example in U.S. Patent No. 4,329,253, European Patent Specification 19,330, British Patent Specification 1,550,195 , 1,554,340, 1,559,194 and 1,603,724 disclosed in those methods. Such a procatalyst is formed by reacting alkoxymagnesium (preferably diethoxymagnesium) with titanium tetrachloride in the presence of an electron donor aromatic ester, or Those prepared by adding the electron donor aromatic ester after the reaction. Preferably the reaction is in the presence of a liquid halohydrocarbon such as chlorobenzene or carbon tetrachloride, or subsequent treatment with a liquid halohydrocarbon, or the reaction in the presence of a liquid halohydrocarbon followed by subsequent treatment with a liquid halohydrocarbon. To prepare the combination of tetravalent titanium chloride, magnesium chloride and the electron donor, the resulting solid is further treated with titanium tetrachloride at elevated temperature. It is best to treat it one or more times in the presence of benzoyl chloride. Suitable main catalyst general formula is as follows:

In the formula, R is an alkyl group containing 2 to 8 carbon atoms, preferably ethyl; ED (electron donor) is an electron donor, preferably an aromatic ester;

x=5～40, preferably 9～20;

y=10～100, preferably 20～40;

z=0.01～1.0, preferably 0.02～0.2; and

a=0.5-10, preferably 0.6-3.5.

Various electron-donor compounds disclosed in previous catalytic techniques as suitable for the preparation of supported coordinating procatalysts can be used as ED compounds. Good procatalysts can be prepared with ethyl benzoate, ethyl p-toluate or ethyl p-ethoxybenzoate. According to the present invention, the pretreatment main catalyst is preferably diethylaluminum chloride (DEAC).

The reaction of the main catalyst of dialkylaluminum chloride is not an instantaneous reaction, the shortest time is 4 minutes, and it must be contacted with the main catalyst. On the other hand, however, this contact should not be unduly prolonged. It has been found that after six days at room temperature, the activity of the catalyst decreases to the same extent as that of the unpretreated procatalyst after the catalyst has been kept in an inert diluent for six days. The decrease in activity was accompanied by a change in the color of the procatalyst from light brown after 30 minutes of exposure to a very dark brown after six days. The appearance of this change is caused by excessive chemical reduction of titanium in the main catalyst.

Typical contact times are about 4 minutes to 1 hour. The most suitable contact temperature is within 30°C. It has been found that when dealing with relatively dilute procatalyst suspensions, in an inert diluent (the most suitable is a paraffinic mineral oil), at 25 ° C, DEAC and the procatalyst are contacted for 5 to 30 minutes, and excellent activity can be obtained. catalyst. Increasing the concentration of the catalyst suspension from 5% to 40% by weight required an increase in the minimum contact time from approximately 5 minutes to 10 minutes.

Pretreatment must be carried out in the absence of propylene monomer. If the procatalyst is combined with DEAC in propylene at room temperature, the desired improvement in the activity of the procatalyst cannot be obtained.

DEAC is used in an amount of 5 to 35 moles, preferably about 10 to 25 moles of DEAC/gram atom of Ti, per gram atom of titanium in the procatalyst. The pretreatment of the procatalyst is carried out in a liquid hydrocarbon diluent which is inert with respect to the polymerization reaction mixture. Saturated liquid hydrocarbons such as propane, isopentane, n-heptane, paraffins boiling in the gasoline or kerosene range, and highly refined mineral oils are suitable diluents.

As (B) component, the cocatalyst used together with the pretreated procatalyst is a trialkylaluminum compound _AlR₃ , wherein R is an alkyl group containing 2 to 8 carbon atoms, preferably ethyl. The cocatalyst may form a complex with the selectivity control agent prior to introduction to the polymerization reactor. However, it is not necessary to form a complex. In the process of the present invention, the preferred method of operation is that the pretreated main catalyst, cocatalyst and selectivity control agent are introduced into the reactor through separate feed lines, therefore, three feed lines are used in the entire catalyst feed system. Wire.

Various electron donor compounds useful as selectivity control agents can be used as the (c) component of the catalyst. Such compounds are well known in previous polymerization techniques. A preferred class of electron donor compounds are aromatic carboxylic acid esters. For example, ethyl p-ethoxybenzoate, methyl and ethyl benzoate, methyl p-methoxybenzoate, and methyl and ethyl p-toluate are preferred compounds.

Propylene polymerization can be carried out in the gas phase or in the liquid phase. An inert hydrocarbon diluent can be used as the liquid medium for carrying the polypropylene suspension, and propylene monomer can also be used as the liquid medium.

In the continuous reaction system, the reaction area is kept under the reaction conditions (temperature 50-85 ° C, pressure 100-500 kPa), monomers are continuously added to the reaction area, and the components of the catalyst are also continuously added. The reaction mixture was discharged continuously. The total amount of alkylaluminum compound in the polymerization mixture is in the range of 15 to 130 moles per gram atom of titanium, and the molar ratio of cocatalyst to selectivity control agent is suitably in the range of 0.5:1 to 10:1.

A second novel aspect of the present invention pertains to the method of injecting pretreated procatalyst components into a polymerization reactor. This method involves mixing the pretreated procatalyst with a gaseous stream and injecting the mixture into a reaction vessel at a velocity in excess of 3 m/s. This velocity refers to the velocity of the gas/suspension mixture through the injection port at the end of the injection conduit.

The flow rate of the gas/suspension mixture is important to ensure a steady introduction of the catalyst into the reactor, keeping the injection port at the outflow end of the injection conduit free of polymer buildup. The most suitable flow rate range It is 30 to 200 m/s.

Hydrogen is the most suitable gas medium. Since hydrogen is used to control the molecular weight in propylene polymerization, all the hydrogen required for molecular weight control can be fed into the reactor as a carrier gas through the procatalyst injection conduit. However, it is preferable to use only a part of the hydrogen used for molecular weight control as a carrier gas injected into the conduit, and the remaining part is separately fed to the polymerization reactor.

The carrier gas and the suspension of procatalyst in the inert hydrocarbon diluent can be conveniently and efficiently mixed in the injection tube when using a gas injection nozzle capable of injecting a conically diffused gas flow at a predetermined angle to the inner wall of the introduction tube. If the velocity of the gas leaving the nozzle is high enough, the flow film of the procatalyst suspension will be reduced to a mist of fine liquid particles, leaving a substantially "dry" inner wall in the outflow portion of the injection conduit.

Thus, under the conditions relevant to the process, the gas/suspension mixture enters the gas injection port as a "mist loop" (i.e., a stream of gas surrounded by ejected liquid particles) through the open end of the conduit. This condition is preferable and easily attainable when the carrier gas is passed through the gas injection nozzle at a velocity of 30 m/s or higher.

Claims (6)

1, the method for propylene successive polymerization, this method are to carry out in the reactor with the catalyst system that comprises following component:

A) comprise the active solid catalyst component of titanium tetrachloride, magnesium chloride, alkoxyl group and electron donor.

B) compd A lR ₃, wherein R is C _2～8Alkyl,

C) selective control agent, this control agent is a Lewis base, it and components b) form title complex, the characteristics of present method are, component is a) before being used for propylene polymerization, do not having propane, components b) and c) exist, and have inert liq hydrocarbon attenuant to exist, and (alkyl respectively is C with the chlorination aluminum dialkyl under 10～55 ℃ the condition _2～8Alkyl) contact is 4 minutes～1 hour, then, with component A by conduit with its be selected from hydrogen, nitrogen, methane, ethane, propane, different propane, the form of the mixture of the air-flow of normal butane and composition thereof imports reactor, the speed of importing is 3～200 meter per seconds.

2, according to the method for claim 1, characteristics are that said flow is a hydrogen.

3, according to the method for claim 1 or 2, wherein, the speed of described logistics is 30～200 meter per seconds.

4, method according to claim 1, chlorination aluminum dialkyl wherein is a diethylaluminum chloride.

5, method according to claim 1, wherein, added hydrogen is to add in the above-mentioned reactor separately.

6, method according to claim 1, wherein (a) component in the catalyst system, (b) component and (c) component introduce above-mentioned reactor respectively by conduit.