| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 23.11.1999 |
| PATENT TITLE |
Process for polymerising olefin with a Ziegler-Natta catalyst |
| PATENT ABSTRACT |
The present invention relates to a process for (co-)polymerizing olefin(s) comprising introducing into a polymerization medium the olefin(s), a titanium-based catalyst of Ziegler-Natta type, an organometallic cocatalyst and a halogenated hydrocarbon compound in an amount effective for increasing the catalyst activity in the (co-)polymerization, the amount being such that the molar ratio of the quantity of the halogenated hydrocarbon compound to that of titanium is comprised between 0.01 and 0.1, or between 0.001 and 0.15 when the (co-)polymerization is carried out continuously. The process is particularly useful in a continuous gas-phase (co-)polymerisation of olefin(s). |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | January 27, 1997 |
| PATENT REFERENCES CITED |
Translation of Toyo --Japanese No. 61-127703. English translation furnished |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
I claim: 1. Process for increasing the catalyst activity of a gas-phase (co-)polymerisation of ethylene or ethylene with at least one C.sub.3 -C.sub.8 olefin, comprising introducing into the gas-phase (co-)polymerisation medium the olefin(s), a titanium based catalyst of the Ziegler-Natta type essentially containing atoms of titanium, halogen and magnesium, and optionally a refractory oxide, and an alkylaluminium cocatalyst, wherein the (co-)polymerisation is conducted continuously in the gas phase and a mono- or polyhalogenated saturated hydrocarbon compound is continuously introduced into the gas-phase (co-)polymerisation medium in an amount such that the molar quantity of the mono- or polyhalogenated saturated hydrocarbon compound to that of titanium introduced into the gas-phase polymerisation medium is from 0.03 to 0.095. 2. Process according to claim 1, characterized in that the halogenated hydrocarbon compound is introduced in a quantity such that the molar ratio of the quantity of the halogenated hydrocarbon compound to that of titanium introduced into the polymerization medium is in the range from 0.031 to 0.091. 3. Process according to claim 1, characterized in that the alkylaluminum cocatalyst is introduced in a quantity such that the molar ratio of the quantity of the halogenated hydrocarbon compound to that of the alkylaluminum cocatalyst introduced into the polymerization medium is comprised between 0.001 and 0.5. 4. Process according to claim 1, characterized in that the halogenated hydrocarbon is selected amongst the group consisting of methylene chloride, chloroform, carbon tetrachloride, trichloro-1,1,1 ethane and dichloro-1,2 ethane. 5. Process according to claim 1, characterized in that the catalyst is prepared by a method comprising: (1) a reaction between a magnesium metal, a halogenated hydrocarbon and at least one tetravalent titanium compound, (2) or bringing a granular support into contact with (a) a dialkylmagnesium and optionally a trialkylaluminium, (b) a halogenated hydrocarbon and (c) a tetravalent titanium compound, (3) or bringing a magnesium chloride support into contact with (a) an alkylaluminum compound suitable for reducing a titanium compound and (b) a tetravalent titanium compound. 6. A process as defined in claim 1 wherein said polyhalogenated hydrocarbon is chloroform. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
The present invention relates to a process for polymerizing olefin(s) in the presence of a catalyst of Ziegler-Natta type and particularly to the use of halogenated hydrocarbon compounds as catalyst activating agents in an olefin polymerization in the presence of titanium-based catalyst of Ziegler-Natta type. It is known to polymerize olefins e.g. ethylene, especially by a gas phase polymerization process with the aid of a catalyst of Ziegler-Natta type and an organometallic cocatalyst. When the catalyst is highly active, especially when it is employed in the presence of a large quantity of cocatalyst, a formation of polymer agglomerates, which may be considerable, can be observed. Patent Application EP-A-0 529 977 discloses a gas phase polymerization of ethylene carried out with the aid of a Ziegler-Natta type catalyst containing titanium, in the presence of a halogenated hydrocarbon compound which enables the formation of ethane to be substantially reduced. Under the conditions used in the process disclosed by this Patent Application, no substantial variation of the average activity of the catalyst is observed. A process has now been found which makes it possible to increase appreciably the activity of a catalyst for olefin polymerization. When the process is carried out, practically no formation of polymer agglomerates is found, even when the catalyst is highly active and is used in the presence of a relatively large quantity of cocatalyst. The subject of the present invention is therefore a process for (co-)polymerizing one or more olefins, comprising introducing into a polymerization medium the olefin(s), a titanium-based catalyst of Ziegler-Natta type, an organometallic cocatalyst and a halogenated hydrocarbon compound, characterized in that the (co-)polymerization is carried out continuously and the halogenated hydrocarbon compound is introduced in an amount effective for increasing the catalyst activity in the (co-)polymerization, the amount being such that the molar ratio of the quantity of the halogenated hydrocarbon compound to that of titanium introduced into the polymerization medium is comprised between 0.001 and 0.15, e.g. greater than 0.001 and lower than 0.15. According to another aspect, the present invention relates to a process for (co-)polymerizing one or more olefins, comprising introducing into a polymerization medium the olefin(s), a titanium-based catalyst of Ziegler-Natta type, an organometallic cocatalyst and a halogenated hydrocarbon compound, characterized in that the halogenated hydrocarbon compound is introduced in an amount effective for increasing the catalyst activity in the (co-)polymerization, the amount being such that the molar ratio of the quantity of the halogenated hydrocarbon compound to that of titanium introduced into the polymerization medium is comprised between 0.01 and 0.1, e.g. greater than 0.01 and lower than 0.1. Preferably, the (co-)polymerization is carried out continuously. According to another embodiment, the present invention also relates to the use of a halogenated hydrocarbon compound as a catalyst activating agent in a (co-)polymerization of one or more olefin(s) carried out in the presence of a titanium-based catalyst of Ziegler-Natta type and an organometallic cocatalyst, the halogenated hydrocarbon compound being used in an amount such that the molar ratio of the quantity of the halogenated hydrocarbon compound to that of titanium is comprised between 0.001 and 0.15, e.g. greater than 0.001 and lower than 0.15. Preferably, the (co-)polymerization is carried out continuously. FIG. 1 diagrammatically represents a fluidized bed reactor for performing a gas phase (co-)polymerization of ethylene according to Example 1 of the present specification. FIG. 2 represents a graph of the catalyst activity (expressed in gramme of (co-)polymer produced per millimole of titanium, per hour of reaction and per 0.1 MPa of ethylene) versus the molar ratio of chloroform to titanium introduced into the polymerization medium during Runs A to F of Example 3 of the present specification. According to the process of the invention a halogenated hydrocarbon compound is employed to increase the activity of a titanium-based catalyst of Ziegler-Natta type. This activity represents the quantity of polymer manufactured under given reaction conditions. For example, the catalyst activity can be measured as the quantity of polymer manufactured per millimole of titanium, per hour of reaction and per 0.1 MPa of olefin pressure. The halogenated hydrocarbon compound may be a chlorinated or brominated hydrocarbon. It may be a monohalogenated hydrocarbon, e.g. corresponding to the general formula R-X in which R denotes an alkyl group containing from 1 to 10, preferably from 1 to 4 carbon atoms, an aralkyl or aryl group containing from 6 to 14, preferably from 6 to 10 carbon atoms, and X denotes a halogen atom such as chlorine or bromine. The halogenated hydrocarbon compound may also be a polyhalogenated hydrocarbon, preferably containing 2 to 6, e.g. 2 to 4 halogen atoms such as chlorine or bromine, and 1 to 14, e.g. 1 to 4 carbon atoms per 1 molecule. Preferably it may also be a mono- or poly halogenated saturated hydrocarbon, such as the halogenated hydrocarbon compounds previously mentioned, e.g. methylene chloride, chloroform, carbon tetrachloride, trichloro-1,1,1 ethane or dichloro-1,2 ethane. Chloroform is employed most frequently. The halogenated hydrocarbon compound may be introduced into the polymerization medium as it is or preferably diluted in a liquid hydrocarbon such as an alcane e.g. isopentane, n-pentane, n-hexane or n-heptane. The halogenated hydrocarbon compound is very advantageously employed in a (co-)polymerization reaction in a quantity such that the molar ratio of the quantity of halogenated hydrocarbon to the quantity of titanium introduced into the polymerization medium is comprised between 0.001 and 0.15, preferably between 0.01 and 0.1 or between 0.03 and 0.1, and more particularly from 0.03 to 0.095, e.g. from 0.031 to 0.091. When these quantities of the halogenated hydrocarbon compound are used, a large increase in the activity of the catalyst is found, surprisingly. It is in general at least 10%. In most cases it may be greater than 20% and even greater than 100%. The increase in the activity of the catalyst is found in particular when the (co-)polymerization reaction is carried out continuously, especially in a gas phase polymerization process. A continuous (co-)polymerization of one or more olefins e.g. containing from 2 to 8 carbon atoms, such as ethylene or ethylene with at least one C.sub.3 -C.sub.8 olefin, generally comprises continuously introducing the olefin(s) into the polymerization medium which is preferably at a temperature below the melting point of the (co-)polymer, e.g. from 30 to 120.degree. C., preferably from 50 to 110.degree. C. or from 60 to 100.degree. C., and under a pressure of from 0.1 to 5 MPa, preferably from 0.5 to 4 MPa, e.g. from 1 to 3 MPa. It also comprises continuously or semi-continuously, e.g. intermittently, introducing the catalyst and the organometallic cocatalyst into the polymerization medium, and continuously or semi-continuously, e.g. intermittently, discharging the polymer produced from the polymerization medium. If required, a molecular weight regulator, e.g. hydrogen, may be continuously introduced into the polymerization medium. Preferably, the catalyst and the halogenated hydrocarbon compound may be used or introduced into the polymerization medium in order to maintain the molar ratio of the quantity of the halogenated hydrocarbon compound to that of titanium introduced at a substantially constant value selected in the above-mentioned ranges. The polymerization medium may be a liquid hydrocarbon diluent which forms with the catalyst and the (co-)polymer a suspension. It may be an alcane or a cycloalcane or a mixture of alcanes or cycloalcanes, e.g. containing from 3 to 10, preferably from 4 to 8 carbon atoms, e.g. n-hexane. It also may be a gaseous phase containing one or more olefins, optionally mixed with hydrogen and inert gas. Preferably the polymerization process is a continuous gas-phase (co-)polymerization of one or more olefins e.g. containing from 2 to 8 carbon atoms, such as ethylene or ethylene with at least one C.sub.3 -C.sub.8 olefin. In that case, the polymerization medium comprises an olefin stream upwardly passing through an agitated bed of finely divided (co-)polymer, with removal of the heat of the (co-)polymerization by cooling the olefin stream which is then recycled to the agitated bed. The agitated bed may be a stirred bed or preferably a fluidized bed wherein the olefin stream is the fluidization gas maintaining the finely divided (co-)polymer in a fluidized state. The olefin stream may comprise one or more olefins, e.g. ethylene or a mixture of ethylene with at least one C.sub.3 -C.sub.8 olefin, a molecular weight regulator, e.g. hydrogen, and an inert gas e.g. nitrogen or at least one C.sub.1 -C.sub.8 alcane, preferably at least one C.sub.2 -C.sub.6 alcane. In the present invention, particularly when a continuous (co-)polymerization of olefin(s) is carried out, the halogenated hydrocarbon compound preferably is continuously introduced into the polymerization medium, e.g. in the form of a solution in a liquid hydrocarbon such as an alcane, a cycloalcane or a mixture thereof e.g. containing from 3 to 10, preferably from 4 to 8 carbon atoms. The halogenated hydrocarbon compound may be used in the form of a solution of from 0.1 to 100%, preferably from 1 to 50% by weight in a liquid alcane or cycloalcane. When the molar ratio of the quantity of the halogenated hydrocarbon compound to the quantity of titanium introduced into the polymerization medium is too high, it is found that the activity of the catalyst is not appreciably modified, or even is substantially reduced, particularly in a continuous polymerization process. When this ratio is too low, no substantial modification in the catalyst activity is found compared with a process carried out in the absence of halogenated hydrocarbon compound. Furthermore, the halogenated hydrocarbon compound may also be employed in a quantity such that the molar ratio of the quantity of the halogenated hydrocarbon compound to the total quantity of cocatalyst introduced into the polymerization medium is comprised between 0.001 and 0.5, preferably between 0.005 and 0.25 and in particular between 0.005 and 0.15, e.g. from 0.01 to 0.15. Preferably, the cocatalyst and the halogenated hydrocarbon compound may be used or introduced into the polymerization medium in order to maintain the molar ratio of the quantity of the halogenated hydrocarbon compound to that of the cocatalyst introduced at a substantially constant value selected in the above-mentioned ranges. The polymerization catalyst is a titanium-based catalyst, which means that it contains substantially no other transition metals and in particular that it contains substantially no vanadium. The catalyst may be a catalyst containing essentially atoms of titanium, halogen and magnesium and optionally a refractory oxide e.g. silica or alumina. It may be prepared by a method comprising a reaction between magnesium metal, at least one halogenated hydrocarbon and at least one tetravalent titanium compound. Such a method is described, for example, in French Patents No. 2,099,311 and No. 2,116,698. The catalyst may comprise a granular support based especially on a refractory oxide such as, for example, silica and/or alumina. Such a catalyst can be prepared by a method comprising bringing the granular support into contact with (a) a dialkylmagnesium and optionally a trialkylaluminium, (b) a halogenated hydrocarbon e.g. a monohalogenated hydrocarbon, (c) and a tetravalent titanium compound. Such a method is described in European Patent Application EP-A-453,088. The catalyst may also contain a magnesium chloride support and in particular a preactived support such as that described in European Patent Application EP-A-336,545. A catalyst of this type can be prepared by a method comprising bringing a magnesium chloride support into contact with (a) an organometallic compound which is a reducing agent for titanium, (b) a tetravalent titanium compound and c) optionally one or more electron-donor compounds. Such a method is described in French Patent Application FR-A-2,669,640. The catalyst may be used in the form of a solid as it is or in the form of a prepolymer, especially when it is used in a gas phase polymerization. The prepolymer is obtained by bringing the catalyst into contact with one or more of olefins e.g. containing from 2 to 8 carbon atoms such as, for example, ethylene or a mixture of ethylene with C.sub.3 -C.sub.8 olefin(s) in the presence of an organometallic cocatalyst. In general, the prepolymer obtained contains from 0.1 to 200 g preferably from 10 to 100 g of polymer per millimole of titanium. The catalyst is employed with an organometallic cocatalyst which may be chosen from organoaluminium, organomagnesium and organozinc compounds. In most cases the organometallic cocatalyst is an alkylaluminium such as, for example, trimethylaluminium, triethylaluminium, tri-n-octylaluminium or else a mixture of these compounds. According to the invention the organometallic cocatalyst may be employed in a relatively large quantity and in particular so that the molar ratio of the total quantity of the organometallic cocatalyst to the quantity of titanium introduced into the polymerization medium is comprised between 0.5 and 100, preferably between 0.7 and 40, more particularly between 1.2 and 20 e.g. between 1.5 and 10. The organometallic cocatalyst may be introduced continuously or semi-continuously, i.e. intermittently, into the polymerization medium as a mixture with the catalyst as, for example, in a prepolymer, or separately from the catalyst. According to a particular method, a portion of the organometallic cocatalyst is introduced into the polymerization medium as a mixture with the catalyst and another portion is introduced separately from the catalyst. It is possible, for example, to employ a prepolymer containing a quantity of the organometallic cocatalyst such that the molar ratio of the quantity of the organometallic cocatalyst to the quantity of titanium is comprised between 0.5 and 5 preferably between 1 and 4 and to add to the polymerization medium separately a quantity of the organometallic cocatalyst such that the molar ratio of the added quantity of the cocatalyst to the quantity of titanium is between 1 and 10. The (co-)polymerization reaction may be carried out in suspension in a liquid hydrocarbon. However, it is very advantageously carried out in gaseous phase, according to known processes, in a reactor containing a mechanically stirred and/or fluidized bed, especially in the equipment described in French Patents No. 2,207,145 and No. 2,335,526. In a gas phase (co-)polymerization, the olefin stream may contain hydrogen in a quantity such that the molar ratio of the quantity of hydrogen to the total quantity of olefin(s) used is comprised between 0.05 and 1, preferably between 0.15 and 0.5. However, this ratio may be higher than 1 particularly when a (co-)polymer of a high melt index is manufactured, for example a (co-)polymer of a melt index MI.sub.2.16 (measured at 190.degree. C. under a 2.16 kg load) higher than 50 g/10 minutes. According to the process of the invention it is possible to prepare ethylene (co-)polymers containing optionally one or more alpha-olefins, e.g. containing from 3 to 8 carbon atoms such as, for example, 1-butene, 1-hexene, 4-methyl-1-pentene or 1-octene. These (co-)polymers may have a density ranging from 0.965 to 0.910. The invention is particularly advantageous for manufacturing copolymers of ethylene with at least one alpha-olefin e.g. C.sub.3 -C.sub.8 alpha-olefin, copolymers having a density ranging from 0.948 to 0.960 and a melt index MI.sub.2.16 ranging from 2 to 25 g/10 minutes. It also makes it possible to manufacture, in good conditions, ethylene copolymers which have a density ranging from 0.914 to 0.930 and a melt index MI.sub.2.16 ranging from 0.5 to 25 g/10 minutes. The (co)polymers obtained by the process have a particularly low titanium content which may be lower than 15 ppm, or even lower than 10 ppm and, in most cases, lower than 5 ppm e.g. from 1 to 5 ppm. Furthermore, these (co)polymers surprisingly have a higher melt index when compared with the (co-)polymers obtained in identical conditions but in the absence of the halogenated hydrocarbon compound. In particular, the melt index measured at 190.degree. C. under a 2.16 kg load may be doubled. The melt index may vary in parallel with the activity of the catalyst. Furthermore, the (co)polymers obtained by the process of the invention may also have a content of soluble polymer which is lower than the (co)polymers obtained in the absence of the halogenated hydrocarbon compound. This result is observed in particular when the (co)polymers are obtained with the aid of a catalyst essentially containing atoms of titanium, halogen and magnesium e.g. prepared by a reaction between magnesium metal, a halogenated hydrocarbon and at least one compound of tetravalent titanium. The drop in the content of soluble polymer may be greater than 20%. According to the present invention the content of soluble polymer of a (co)polymer is measured after the (co)polymer has been kept in n-hexane at 50.degree. C. for 2 hours. This content is expressed in weight %. Advantageously, the (co-)polymers obtained by the process of the invention may also have a content of oligomers substantially reduced compared to (co-)polymers obtained in the absence of the halogenated hydrocarbon compound. In most cases, it was also found that the molecular weight distribution of the (co-)polymers is narrowed compared to (co-)polymers obtained in the absence of the halogenated hydrocarbon compound. The following examples illustrate the present invention. |
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