PROCESS FOR CONTINUOUS POLYMERIZATION OF PROPENE

Abstract: In the continuous polymerization of propene with a magnesiumchloride supported catalyst the latter is pre­ reacted with DEAC and introduced into the polymerization reactor in admixture with a gaseous stream at a velocity of at least 3 m.sec⁻¹.

Description: PROCESS FOR CONTINUOUS POLYMERIZATION OF PROPENE This invention relates to a process for continuous polymerization of propene using a catalyst system comprising: (a) a highly active solid catalyst component comprising titanium tetrachloride, magnesium chloride, alkoxy groups and an electron donor, (b) a compound AlR3 where R represent an alkyl group of from 2 to 8 carbon atoms, and (c) a selectivity control agent. For convenience of reference, the solid titanium-containing constituent of such catalyst systems is referred to herein as "procatalyst" and compound A1R3, is referred to herein as "cocatalyst". The selectivity control agent (SCA) is a Lewis base which is able to form a complex with the cocatalyst, e.g. an aromatic ester. It is a first object of the present invention to improve the polymerization activity of the relevant catalyst systems and in accordance with an important aspect of this invention this is achieved by contacting the procatalyst with certain dialkyl aluminium chlorides under conditions defined hereinafter. This contacting is referred to herein as "pretreatment". The pretreatrent modifies the procatalyst to make it about 40 to 80% more active than untreated procatalyst. However, the pretreated procatalyst has such an enhanced polymerization activity, that it presents certain problems in handling and in supplying it to the polymerization reactor vessel. The standard method for mDecting non-pretreated solid procatalyst components into the polymerization reactor vessel involved using a stream of a suspension of procatalyst in an inert hydrocarbon diluent. However, if such method is used for the new pretreated catalyst, polymerization occurs in the downstream end of the injection system, which polymerization will eventually clog the system. Because of the very enhanced activity only very little procatalyst needs to be supplied to the continuous polymerization, so the flcw rate of the suspension in the procatalyst supply line is so low that at the end of the supply line propene neeceer can diffuse from the polymerization reactor into the last section of the injection conduit. It 1S therefore a second object of this invention to create a new system for injecting these very active pretreated procatalysts into the polymerization reactor. Accordingly, this invention is concerned with a process for the continuous polymerization of propene in a reactor with a catalyst system comprising: (a) a highly active solid catalyst component comprising titanium tetrachloride, magnesium chloride, alkoxy groups and an electron donor, (b) a compound A1R3 where R represents an alkyl group of fran 2 to 8 carbon atoms, and (c) a selectivity control agent, characterized in that, said solid catalyst component (a), prior to employing it in prspene polymerization, is contacted at a temperature of fran 10 to 55 C with a dialkylaluminium chloride in which the alkylgroups each have fran 2 to 8 carton atoms, for at least 4 min in the absence of propene and system components (b) and (c) and in the presence of an inert liquid hydrocarbon diluent and in which said catalyst component (a) is subsequently introduced into said reactor vessel via a conduit in admixture with a gaseous stream of hydrogen, nitrogen, methane, ethane, propane, isopropane, n-butane and mixtures thereof, at a velocity of at least 3 m.sec-1 The procatalysts which are improved by pretreatment with dilkylaluminium chloride may be produced by methods knawn per se, e.g. those disclosed in U.S. Patent No. 4,329,253, European Patent Spec. 19,330, British Patent Spec. 1,550,195, 1,554,340, 1,559,194 and 1,603,724. Such procatalysts are prepared by reacting a magnesium alkoxide, suitably magnesium diethoxide, with titanium tetrachloride in the presence of or with subsequent addition of an aranatic ester electron donor, preferably in the presence of and/or with subsequent treatment with a halohydrocarbon liquid such as clorobenzene or carbon tetrachloride, to produce a caroosition of combined tetravalent titanium chloride carpounds, magnesium chloride and the electron donor, and further treating the resulting solid at an elevated terrperature with titanium tetrachloride, optionally in the copresence of benzoyl chloride, in one or more contacts. Preferred procatalysts have the general formula TiMgxCly(OR)z.aED wherein R is an alkyl group of 2-8 carbon atans, preferably ethyl; ED is an electron donor, preferably an aranatic ester; x = 5-40 and preferably 9-20; y = 10-100 and preferably 20-40; z = 0.01-1.0 and preferably 0.02-0.2; and a = 0.5-10 and preferably 0.6-3.5. A variety of electron donor compounds, disclosed in the prior art as useful in the preparation of supported coordination procatalysts may be employed as compound ED. Very good procatalysts can be made using ethyl benzoate, ethyl-p-toluate or ethyl-p ethoxybenzoate. In the pretreatment of a procatalyst in accordance with this invention the use of diethyl aluminium chloride (DEK:) is preferred. The reaction of dialkylaluminiumchloride with procatalyst is not instantaneous. A minium ot time i.e. 4 min, rrust be allowed for contact with procatalyst. On the other hand, the contacting should not be prolonged excessively, it was found that at roan terperature and in an inert diluent after holding for six days catalyst activity was reduced compared to use of the same procatalyst without pretreatment. This decrease ot activity was accarpied by change of colour of the procatalyst frcm pale brown after 30 minutes contact to very dark brown atter 6 days. It appears that this is due to chemical over-reduction of titanium in the procatalyst. Contact tines of about 4 minutes to one hour will generally be useful. Preterred contacting temperatures do not exceed 30 OC. It was wound that excellent results are obtained by contacting DEAC and procatalyst in an inert diluent liquid, suitably a paraffinic mineral oil, tor 5 to 30 minutes at 25 C when a relatively dilute slurry of procatalyst is treated. Increasing the slurry density fran 5% to 40% by weight required an increase of minimum of contact tine fran about 5 minutes to about 10 minutes. The pretreatment must be conducted in the absence of propene r:rner. When combining the procatalyst with DEPf at artbient temperature in propylene the desired improvement of the procatalyst is not obtained. The amount of DEAC employed is fran 5 to 35 moles per atan of titanium in the procatalyst and preferably fran about 10 to about 25 moles DEAC/atom Ti. The pretreatment of the procatalyst is conducted in a liquid hydrocarbon diluent which is inert in the polymerization reaction mixture. Saturated hydrocarbon liquids are suitable, e.g., profane, isopentane, n-beptane, paraffinic hydrocarbon m the gasoline or kerosene boiling range, and highly retined mineral oil. Cocatalysts used as carpent (b) with the pretreated procatalysts are trialkyl aluminium compounds AlR3' wherein R' is an alkyl group of 2 to 8 carbon atans, preferably ethyl. Before addition to the polymerization reactor, they may be carplexed with a selectivity control agent. However, this is not necessary and in a preferred way of operating the process of this invention each of pretreated procatalyst, cocatalyst and SCA are introduced into the reactor through separate feed lines thus usmg three lines in all to supply the total catalyst system. A variety or electron donor compounds tor use as selectivity control agents may be employed as catalyst component (c). Such compounds are well known in the prior art, preferred species are esters of aromatic carboxylic aclds, preferred are e.g. ethyl-p- ethoxybenzoate, methyl and ethylbenzoate, methyl-p-methoxybenzoate and methyl- and ethyl-p-toluate. The polymerization of propene may be carried out in gas phase or in liquid phase, either employing an inert hydrocarbon diluent as the liquid rnedium carrying the polypropene suspension or empoying propene monomer as the liquid medium. In a continuous reaction system, the reaction zone is maintained at reaction conditions (temperature 50 to 85 OC, pressure 100 to 5000 kPa), monomer is continuously charged to the reactor zone, catalyst components are also charged continuously and reaction mixture which contains polymer is withdrawn continuously. The total amount or aluminium alkyl compounds in the polymerization reaction mixture is in the range of from IS to 130 moles per stem of titanium, the molar ratio of cocatalyst to SCA agent is suitably in the range tran 0.5:1 to 10:1. The second novel aspect of the present invention deals with the method by which the pretreated prooatalyst conent is injected into the polymerization reactor. This method comprises mixing the pretreated procatalyst with a gaseous stream and injecting the mixture into the reactor vessel at a velocity in excess of 3 m.sec-1. This injection velocity is the velocity at which the gas/slurry mixture passes through the injection opening situated at the end of the inlection conduit. The velocity of the gas-slurry mixture is important to insure steady introduction of catalyst into the reactor and to keep the downstream end of the injection conduit and the injection orifice free of polymer bild-up. Preferred ranges tor velocity are between 30 and 200 m.sec-1 Hydrogen is the preferred gaseous medium since it is used in the polymerization of prcpene to control molecular weight. If desired, all of the hydrogen needed for molecular weight control can be added to the reactor as the carrier gas in the procatalyst injection conduit. However, it is is preferred to use only part of the hydrogen needed for molecular weight control as gas carrier in the injection conduit and to add the remaining part separately to the polymerization reactor. The admixing of the carrier gas and the procatalyst slurry in inert liquid hydrocarbon diluent in the injection conduit is cooveniently effected when employing a gas injection nozzle which projects a conically divereent stream of gas under a predetermined angle to the inner wall of the conduit. If the velocity of The gas leaving the nozzle is high enough this will cause the streaming film of procatalyst slurry liquid to be transformed in a mist of fine liquid particles, leaving a substantially "dry" inner wall m the downstream section of the injection conduit. The gas/slurry mixture thus passes tran the gas-injection point to the endening of the conduit under conditions which are referred to in the art as "mist annular flow", i.e. a gaseous streaming which is surrouned by a spray of liquid particles. This condition is preferred and it is easily achieved when letting the carrier gas pass the gas-injection nozzle at a linear flow- velocity of 30 m.sec.-Ú or more.

Claims: CLAIMS 1. Process for the continuous polymerization of propene in a reactor with a catalyst system corprising: (a) a highly active solid catalyst ccnponent comprising titanium tetrachloride, magnesium chloride, alkoxy groups and an electron donor, (b) a compound A1R3 where R represents an alkyl group of fran 2 to 8 carbon atoms, and (c) a selectlvity control agent, characterized in that, said solid catalyst carponent (a), prior to employing it in propene polymerization, is contacted at a temperature of fran 10 to 55 C with a dialkylaluminium chloride in which the alkyl groups each have fran 2 to 8 carbon atoms, for at least 4 min in the absence of profane and system components (b) and (c) and in the presence of an inert liquid hydrocarbon diluent, and in which said catalyst component (a) is subseguently introduced into said reactor vessel via a conduit in adixure with a gaseous stream of hydrogen, nitrogen, methane, ethane, propane, isopropane, n-butane and mixtures thereot, at a velocity of at least 3 m.sec.-Ú 2. A process according to claim 1, wherein said gaseous stream is hydrogen. 3. A process according to claim 1 or 2 wherein said velocity is between 30 and 200 m.sec. 1. 4. A process as claimed in any of claims 1 to 3, in which the dialkyl aluminium chloride is diethylaluminium chloride. 5. A process as claimed in claim 2 wherein additional hydrogen is added separately to said reactor vessel. 6. A process as claimed in any ot claims 1 to 5 wherein the catalyst system carponents (a), (b), and (c) are each introduced into said reactor vessel via a separate conduit. 7. A process as claimed in any of claims 1 to 6, wherein catalyst component (a), before contacting with dialkylaluminiumchloride has the general formula TiMgxCly(OR)z.aED wherein R is an alkyl group of 2-8 carbon atans; ED is an aranatic ester, x = 9-20; y = 20-40; z = 0.02-0.2; a = 0.6-3.5. 8. Polypropene whenever obtained with a process as claimed in any of claims 1 to 7.

Inventors: BECKER, PHILLIP CAREY, HARRIS, RONALD DAVID, MCCOY, NED ROGER, JR.
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1984
Main classification: C08F10
IPC codes: C08F4, C08F10