Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond

Definitions

• the present invention relates to a process for the preparation of a catalyst of the Ziegler-Natta type. It also relates to an olefin polymerisation process using the prepared catalyst.
• French Patents no 2 116 698 and no 2 099 311 it is known to prepare a catalyst of the Ziegler-Natta type which can be employed for the polymerisation of olefins and especially for the polymerisation of ethylene.
• French Patent no 2 116 698 it is prepared by the reaction of magnesium in the metallic state with a monohalogenated hydrocarbon, an ether and a derivative of a transition metal in a valency state of at least 4. According to
• a catalyst is prepared by the reaction of activated magnesium, with a monohalogenated hydrocarbon and a derivative of a transition metal in a valency state of at least 4.
• Such catalysts are effective but have a catalytic activity which increases rapidly with increasing polymerisation temperature, especially in the temperature range generally employed for olefin polymerisation reactions.
• a small change in the reaction temperature can entail a relatively large change in the activity of the catalyst and consequently in the rate of polymerisation. This phenomenon is particularly troublesome when starting a polymerisation reaction, where temperature changes can occur in an unpredictable manner.
• a change in the rate of polymerisation can promote the formation of polymer agglomerates, especially in a gas phase polymerisation process, for example in a fluidised bed.
• the present invention relates to the preparation of a polymerisation catalyst which overcomes or at least mitigates the problems associated with these known catalysts.
• the catalyst prepared according to the present invention has a relatively stable activity over the desired range of temperature, that is to say a slight change in the temperature does not result in a large change in the catalyst activity. This ensures that the catalyst is better adapted to use in a large scale commercial reactor.
• the subject of the present invention is therefore a process for the preparation of a catalyst of the Ziegler-Natta type characterised in that it comprises contacting a solid component comprising atoms of halogen, magnesium and a transition metal of groups IV, V or VI of the Periodic Classification of the Elements, with an electron donor compound.
• the solid component used according to the invention preferably corresponds to the general formula: in which Me is an atom of aluminium and/or zinc, M is an atom of a transition metal belonging to groups IV, V, or VI of the Periodic Classification of the Elements, preferably an atom of titanium and/or vanadium, R ⁇ is an alkyl group comprising from 1 to 14 carbon atoms, R ⁇ is an alkyl group comprising from 1 to 12 carbon atoms, X is an atom of chlorine and/or bromine, D is an electron donor compound comprising preferably atoms of oxygen, sulphur, nitrogen, or phophorus, and where, m is from 1.5 to 50, preferably from 2 to 10, n is from 0 to 2, preferably from 0 to 1, p is from 0 to 4, preferably from 0 to 3, q is from 0 to 1, preferably from 0 to 0.5, r is from 4 to 110, preferably from 5 to 27, and s is from 0 to 0.5, preferably from 0 to 0.2
• the invention is particularly suitable for use with a solid component prepared by a reaction between magnesium in the metallic state, at least one monohalogenated hydrocarbon and at least one compound of a transition metal of groups IV, V or VI of the Periodic Classification of the Elements, taken in a valency state of at least 4, optionally in the presence of an electron donor compound.
• the solid component can be prepared without magnesium derivative compounds.
• the solid component can advangeously be prepared as described in French Patent no 2 099 311 or n° 2 116 698. Generally, the solid component prepared according to these patents consists of particles which have an irregular shape.
• the transition metal of groups IV, V, or VI of the Periodic Classification of the Elements is preferably titanium and/or vanadium.
• Titanium compounds employed are advantageously the tetravalent compounds of titanium of formula TiX4_ t (OR 3 ) t in which X denotes a halogen atom, generally chlorine or bromine, R ⁇ an alkyl radical which can contain from 2 to 8 carbon atoms and t a whole or fractional number which can take any value from 0 to 4, for example from 0 to 3 and preferably equal to or close to 2.
• titanium compounds corresponding to this definition are titanium tetrachloride, alkyl tetratitanates of formula Ti(OR ⁇ ) 4 in which ⁇ is a radical corresponding to the above formula, or a mixture of titanium tetrachloride and of an alkyl tetratitanate.
• the magnesium used in the preparation of the solid component is preferably solid metallic magnesium.
• the magnesium is used in the form of powder or turnings.
• the magnesium preferably comprises magnesium of high puritity.
• the magnesium is preferably reacted in an active form, that is to say in a form which is substantially free from impurities e.g. due to oxidation of the metal.
• Preliminary activation of the magnesium can be effected, for example, by grinding the metal in an inert atmosphere or within an inert liquid such as an aliphatic solvent.
• the activation ...n be effected by treating the magnesium with iodine vapor.
• a substance can represent by weight less than 10 % and preferably less than 5 % of the quantity of magnesium used.
• the monohalogenated hydrocarbon compound is preferably selected from chlorinated or brominated derivatives of saturated aliphatic hydrocarbons. It can have the general formula R 4 -Z in which Z is bromine or chlorine and R 4 is an alkyl group having from 1 to 10 carbon atoms.
• the monohalogenated hydrocarbon is ethyl chloride, propyl chloride, butyl chloride, pentyl chloride.
• the reaction for preparing the solid component can be effected using different modes of operation. Thus, for example, the different reactants can be introduced into an inert solvent at a temperature which is sufficiently low for the reaction not to be initiated.
• the reaction mixture if necessary after the addition of a magnesium activating agent such as iodine crystals, is then heated with agitation, at a temperature which is generally from -20 to 150°C, preferably from 40 to 100°C, for a period of a few minutes to 30 hours. During the reaction no milling operation is needed.
• the solid component is advantageously washed with a liquid hydrocarbon, at a temperature from 10 to 50°C and preferably at a temperature close to 20°C. It is preferred not to heat the solid product obtained to a temperature higher than 100°C, and preferably not higher than 90°C.
• the solid component by reacting amounts of reactants such that, the molar ratio between the monohalogenated hydrocarbon and the magnesium is between 0.5 and 10 preferably between 1 and 4, the molar ratio between the transition metal and the magnesium is less than 1 and preferably less than 0.5.
• the process of the invention comprises contacting the solid component with an electron donor compound.
• the latter is an organic compound.
• it is free from labile hydrogen atom. It can be chosen, for example, from amongst aliphatic ethers, tertiary phosphines, tertiary amines, secondary amides and organosilicon compounds.
• dimethylformamide or hexamethylphosphoro- triamide is employed.
• the contact operation between the solid component and the electron donor compound is generally brought about in a liquid hydrocarbon which is kept stirred and under conditions such that a maximum quantity of electron donor compound becomes bound to the solid.
• the liquid hydrocarbon can be an alkane or a cycloalkane which has, for example, from 4 to 10 carbon atoms, or an aromatic hydrocarbon which has, for example, from 6 to 14 carbon atoms.
• This contact operation is in most cases brought about at a temperature ranging from 20 to 100°C, preferably from 40 to 90°C.
• the operation can be carried out in various ways, for example by adding the electron donor compound to the solid component in suspension in the liquid hydrocarbon. This addition is preferably performed slowly so as to bind the electron donor compound homogeneously. It can last, for example, between 10 and 600 minutes and in most cases between 15 and 30 minutes. Following this addition, the stirring of the obtained suspension can last from 30 minutes to 5 hours.
• This contact operation is generally brought about in the absence of any cocatalysts such as organoaluminium compounds and in the absence of any olefins.
• the quantity of electron donor compound remaining in the free state in the liquid hydrocarbon can be nil or relatively small. It is preferable, however, to wash the solid product resulting from this contact in order to remove all the impurities present in the liquid hydrocarbon.
• a solid catalyst which has a catalytic activity substantially constant over a useful range. This range is generally from 85 to 95°C.
• the catalyst prepared according to the process of the present invention is used in the presence of a cocatalyst in a process for the polymerisation of olefins containing from 2 to 8 carbon atoms.
• the catalyst is advantageously used for the polymerisation of ethylene optionally mixed with an alpha-olefin such as 1-butene, with a view to the manufacture of a high density, a linear low density or a very low density polyethylene.
• This polyethylene has a density which can range from 0.890 to 0.965.
• the polymerisation temperature is preferably chosen in the temperature range where the catalyst activity has stabilised.
• the polymerisation temperature is generally from 70 to 100°C, preferably from 70 to 90°C for preparing linear low density polyethylene ⁇ , and preferably from 85 to 95°C for preparing high density polyethylenes.
• the olefin polymerisation can be performed within a liquid in which the catalyst is dispersed and which can be an olefin in the liquid state or a saturated aliphatic hydrocarbon.
• the polymerisation can also be performed in the gaseous phase according to known techniques in a gas phase polymerisation reactor which may be a reactor with a fluidised and/or mechanically stirred bed like those described in French Patent n° 2 207 145 or French Patent no 2 335 526.
• the catalyst is advantageously used in the form of a prepolymer prepared beforehand by bringing the catalyst into contact with ethylene optionally mixed with one or more olefins, the contact being brought about in the presence of a cocatalyst and optionally in the presence of hydrogen.
• a prepolymer obtained with the catalyst of the invention contains a relatively small quantity of fine particles. This quantity is, in particular, smaller than that obtained under identical prepolymerisation conditions with a catalyst prepared without contact with an electron donor compoud.
• the cocatalyst is chosen from the organometallic compounds of metals of groups II or III of the Periodic Classification of the elements, such as organoaluminium, organomagnesium or organozinc compounds. Typically, the cocatalyst is a trialkylaluminium.
• the cocatalyst can be introduced into the polymerisation reactor within a prepolymer or separately.
• Figure 1 shows diagrammatically a fluidised bed reactor consisting essentially of a vertical cylinder surmounted by a disengagement chamber which is used in Examples 1 and 2.
• Figure 2 shows curves of the catalytic activity of two different catalysts as a function of the temperature : the lower curve corresponds to a catalyst according to the invention and the upper curve to a comparative catalyst.
• Figure 1 shows diagrammatically a fluidised bed reactor consisting essentially of a vertical cylinder (2) surmounted by a disengagement chamber (3), provided in its lower part with a fluidisation grid (4) and with a recycle conduit (5) connecting the top of the disengagement chamber to the lower part of the reactor which is situated under the fluidisation grid, which is equipped with a heat exchanger (6) a compressor (7) and feed conduits for ethylene (8) comonomer e.g. 1-butene (9) and chain transfer agent e.g. hydrogen (10).
• the reactor is also equipped with a feed conduit for catalyst (11) and a conduit for drawing off polymer (12).
• n-hexane 5.5 kg of iodine, 3160 moles of magnesium, 29 moles of isobutanol, 60 moles of n-propyl titanate and 60 moles of n-butyl chloride were introduced into a reactor 10 m 3 in volume provided with a mechanical stirring system rotating at 100 revolutions per minute.
• the reactor was then heated to a temperature of 85°C until the reaction began and then the temperature was maintained to 80°C.
• 340 moles of n-propyl titanate, 400 moles of titanium tetrachloride, and then 4700 moles of n-butyl chloride were introduced into the reactor over 240 minutes.
• the reactor contained a fluidised bed of particles of ethylene polymer being formed.
• the bed had a height of 2 m and was traversed by an upward stream of a reaction gas mixture.
• the gas mixture had an upward velocity of 50 cm/s.
• the total pressure was 1.7 MPa and the temperature measured at the exit of the disengagement chamber was 90°C.
• the reaction gas mixture comprised, by volume, 30 % of ethylene, 1.6 % of 1-butene, 21 % of hydrogen and 47.4 % of nitrogen.
• the reactor was fed with the prepolymer prepared previously at a rate of 600 g/hour. It was also separately fed with triethylaluminium in a quantity such that the molar ratio of the added aluminium to the titanium of the prepolymer was 1.2.
• the polyethylene had a relative density of 0.960, a titanium content of 10 ppm and contained approximately 1 % by weight of 1-butene.
• Example 2 a) Preparation of a solid component The solid component was prepared as for the catalyst in Example 1 (a) except that no dimethylformamide was used. b) Preparation of a prepolymer
• the reactor contained a fluidised bed of particles of ethylene polymer being formed.
• the bed had a height of 2 m and was traversed by an upward stream of a reaction gas mixture.
• the reaction gas mixture had an upward velocity of 50 cm/s.
• the total pressure was 1.7 MPa and the temperature measured at the exit of the disengagement section was 80°C.
• the reaction gas mixture comprised, by volume, 30 % of ethylene, 13.5 % of 1-butene, 6 % of hydrogen and 50.5 % of nitrogen.
• the reactor was fed with the prepolymer prepared previously at a rate of 600 g/hour. It was also separately fed with triethylaluminium in a quantity such that the molar ratio of the added aluminium and the titanium of the prepolymer was 1.2. Under these conditions a polyethylene is drawn off at a rate of 70 kg/hour which had a relative density of 0.918, a titanium content of 10 ppm and which contained approximately 8 % by weight of 1- butene.
• Example 3 Measurement of the catalyst activity
• Two series of gas-phase ethylene polymerisation reactions were carried out in a 2.5-litre stainless steel reactor provided with a stirring system rotating at 300 revolutions per minute and with a temperature control system.
• the first series was performed with the aid of a prepolymer prepared with the catalyst of Example 1, in which the molar ratio of aluminium to titanium is 1.5 and which contained 40 g of polyethylene per millimole of titanium.
• the second series was performed with the aid of a prepolymer prepared with a comparative catalyst prepared as in Example 1 except for the fact that no dimethylformamide was employed, and in which the molar ratio of aluminium to titanium was 1.2 and which contained 40 g of polyethylene per millimole of titanium.
• each series a number of polymerisation reactions were carried out at different temperatures.
• each reaction there were introduced into the reactor 200 g of polyethylene as charge powder, a quantity of prepolymer containing 0.5 millimole of titanium, a quantity of hydrogen such as to have a partial pressure of 0.1 MPa and ethylene so as to maintain a total pressure of 0.4 MPa.
• the activity of the catalyst was measured in the case of each reaction, that is to say the quantity of polyethylene produced in grams per millimole of titanium present in the reactor and per hour of reaction.

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• 1992
  • 1992-06-04 FR FR9207150A patent/FR2691970B1/fr not_active Expired - Fee Related
• 1993
  • 1993-06-02 WO PCT/GB1993/001166 patent/WO1993024542A1/en not_active Application Discontinuation
  • 1993-06-02 SK SK113-94A patent/SK11394A3/sk unknown
  • 1993-06-02 BR BR9305539A patent/BR9305539A/pt not_active Application Discontinuation
  • 1993-06-02 PL PL30231593A patent/PL302315A1/xx unknown
  • 1993-06-02 JP JP6501842A patent/JPH07502300A/ja active Pending
  • 1993-06-02 CZ CZ94189A patent/CZ18994A3/cs unknown
  • 1993-06-02 EP EP93913271A patent/EP0598094A1/en not_active Withdrawn
  • 1993-06-02 HU HU9400312A patent/HU212974B/hu not_active IP Right Cessation
  • 1993-06-03 TW TW82104428A patent/TW226383B/zh active
  • 1993-06-04 CN CN 93108275 patent/CN1083820A/zh active Pending
  • 1993-06-04 MX MX9303367A patent/MX9303367A/es not_active Application Discontinuation

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