Polymerisation of olefins using a Ziegler-Natta catalyst and two organometallic compounds.

DESCRIPTION

The present invention relates to a process for the production of polyolefins by polymerization or copolymerization, mainly in the gas phase, of low-pressure alpha-olefins, by means of Ziegler-Natta catalytic systems.

It is known that the catalytic systems for the polymerization and copolymerization of olefins, known as Ziegler-Natta systems, consist, on the one hand, as a catalyst, of transition metal compounds belonging to groups IV, V or VI of the Periodic Table of the Elements and, on the other hand, as cocatalysts, in organometallic compounds of metals of groups II or III of said Table. The most frequently used catalysts are halogenated derivatives of titanium and vanadium, preferably associated with magnesium compounds. In addition, the most frequently used cocatalysts are organoaluminum compounds or organocinc.

Polymerization of alpha-olefins in the gas phase is known, for example, in a fluid bed reactor where the solid polymer, in the course of its formation is maintained in a fluid state by means of an ascending gas stream comprising the alpha-gases. olefins to polymerize. The gaseous reaction mixture leaving the reactor is generally cooled before being recycled to the reactor, adding a supplementary amount of alpha-olefins corresponding to the amount consumed. The fluidization rate must be sufficiently high to provide homogeneity of the fluidized bed and to provide adequate cooling of said bed. The polymerization can be carried out by means of a Ziegler-Natta type catalytic system introduced continuously or semicontinuously into the fluid bed reactor.

The obtained polymer extraction can also be carried out continuously or semi-continuously.

It is known that, prior to its use for gas phase polymerization, the catalytic system can be converted into a prepolymer which is obtained during an operation known as "prepolymerization", consisting of bringing the catalyst and cocatalyst into contact with a or alpha-olefins. The catalytic system converted into a prepolymer should be adapted to the gas phase polymerization conditions, especially with respect to the particle size of the prepolymer and its catalytic activity.

The gas phase polymerization processes can be used to prepare polyolefins with high productivity (in terms of polymer weight produced per unit weight of catalyst per hour). In order to prepare, to commercially useful production rates, polyolefins containing small amounts of catalytic residues, and which can be converted into products without the need for a catalyst separation step, it is convenient to use highly active catalytic systems. By using highly active catalytic systems it is possible to obtain relatively high polymerization rates in the gas phase, even when the alpha-olefin monoomers are maintained at relatively low partial pressures. The ability of such highly active catalytic systems to polymerize alpha-olefins at relatively low partial pressures can provide a useful means to prevent or reduce the condensation of monoomers associated with the gas phase polymerization or copolymerization of easily condensible alpha-olefins.

It is known that the activity of certain Ziegler catalytic systems can be improved by increasing the amount of organometallic compound used as cocatalyst. In this case, it is generally necessary to use relatively large amounts of organometallic compounds as cocatalysts in the polymerization medium. However, this involves disadvantages, including safety concerns, with respect to the fact that these organometallic compounds spontaneously ignite after contact with air.

On the other hand, the processes for the polymerization of alpha-olefins in the gas phase normally employ a chain transfer agent in the reaction gas mixture, for example hydrogen, in order to reduce the average molecular weight of the polyolefins obtained. However, it has been found that the simultaneous use of hydrogen and large amounts of organometallic compounds favors the hydrogenation reaction of alpha-olefins to form alkanes, to the detriment of the polymerization reaction. Although they are inert with respect to the catalytic systems used, the roasted alkanes formed accumulate in the reaction gas mixture and decrease the productivity of the polymerization process.

Several techniques have already been proposed for the introduction of the cocatalyst, for example, the direct introduction of the cocatalyst into the polymerization reactor or the contact of the catalyst with the cocatalyst before its introduction into the polymerization medium. In the latter case, however, and considering the fact that the catalytic systems used normally have a maximum activity at the beginning of the polymerization, it can be difficult to avoid displacement of the reaction prone to involve the formation of hot spots and polymer agglomerates. molten.

Likewise, it is possible to combine the two cocatalyst introduction techniques mentioned above, by introducing an additional amount of cocatalyst into the polymerization reactor with respect to the prior contact with the catalyst. However, it has been observed that, under these conditions, it is necessary to use a relatively large amount of cocatalyst in the polymerization medium, which leads to the aforementioned disadvantages, the amount of the atomic ratio of the total amount of metal being such in the cocatalyst the amount of transition metal in the catalyst is 10 to 500, generally 20 to 100.

The present invention relates especially to a process for the polymerization of alpha-olefins in the gas phase using a Ziegler-Natta type catalytic system,

000 598 comprising a prepolymer-shaped catalyst and a cocatalyst comprising at least two different organometallic compounds used separately in the polymerization process and in defined amounts. Surprisingly, it has been found that by using this process it is possible to achieve a high production rate of polyolefins without forming hot spots or agglomerates in the reactor and simultaneously obtaining a decrease in the hydrogenation reaction of the olefins to alkanes. In this way polyolefins can be prepared having a relatively low content in catalytic residues.

The present invention provides a process for the polymerization of alpha-olefins comprising the steps of (A) preparing a prepolymer base catalyst, contacting one or more of the alpha olefins with a ZieglerNatta type catalyst system consisting, on the one hand, in a Catalyst that comprises baitically aitoms of halogen, magnesium and a transition metal belonging to groups IV, Voí VI of the Periodic Table of the Elements and, on the other hand, in a cocatalyst based on one or more organometallic compounds of a metal belonging to groups II or III of said Table, and (B) contacting the prepolymer base catalyst, under conditions of gas phase polymerization, with one or more alpha olefins in presence of organometallic cocatalyst; characterized in that:

(1) The cocatalyst used in step (A) is at least one low volatility organometallic compound (a) having a vapor pressure at 80 ° C less than 65 Pa, in an amount such that the atoimic ratio of the amount of metal in the organometallic compound (a) to the amount of transition metal in the catalyst is at least 0.5 and at most 2.5, preferably at least 0.8, and at most 2.

(2) The cocatalyst used in step (B) is at least one volatile organometallic compound (b) having a vapor pressure at 80 ° C equal to or greater than 65 Pa, in an amount such that the atoimic ratio of the amount of metal in the organometallic compound (b) to the amount of transition metal in the prepolymer base catalyst is at least 0.5 and the atomic ratio of the total amount of metal in the organometallic compound (a) and (b) the amount of transition metal in the catslizer is at least 0.5 and at most 9, preferably at least 3 and at most 7, the organometallic compound (b) being introduced into the polymerization medium separately from the prepolymer base catalyst.

The organometallic compound (a) used in the Process of the invention preferably comprises at least one low volatility organometallic compound of the general formula:

Al Rn X3 -n where R is an alkyl group of 4 to 20 carbon athems, X is a hydrogen or halogen atom or an alcoholate group and n is an integer or fraction that can have any value of 1 to 3. This Organometallic compound (a) may be selected in particular from one or mine of the following: tri-n-butyl aluminum, tri-n-hexyl

- aluminum, tri-n-octyl-aluminum, diisobutyl aluminum hydride and diisobutyl aluminum chloride. Polymeric organoaluminum compounds obtained by reaction between a trialkyl aluminum or an alkyl aluminum hydride and isoprene (for example, compounds known as "Isoprenyl Aluminum") are also suitable.

The organometallic compound (a) has a vapor pressure at 80 ° less than 65 Pa, preferably less than 40 Pa.

The organometallic compound (b) used in the process of the present invention preferably comprises one or more organoaluminum compounds of general formula:

When R'n X3-n where R 'is an alkyl group of 1 to 3 carbon atoms, X is an hydrogen or halogen atom or an alcoholate group and n is an integer or fraction that can have any value of 1 to 3 Preferably, one or mine of the following is chosen: triethyl aluminum, trin propyl aluminum, diethyl aluminum chloride and ethyl sesquichloride

- aluminum. Likewise, as organometallic compound (b), one or mine volatile organocinc compounds such as diethyl zinc can be selected.

Preferably, the organomethyl compound (b) has a vapor pressure of 80^°C greater than 100 Pa more preferably of the order of 100 to 2,000 Pa

Preferably, the organometallic compound (b) is introduced into the polymerization reactor at a different point from that at which the prepolymer base catalyst (hereinafter referred to as "prepolymer") is introduced, preferably at a comparatively point distant. It can be introduced into the polymerization medium continuously or semi-continuously, following various known methods. For example, it can be introduced in a liquid state or as a solution in an omission of liquid alpha-olefins or in liquid saturated aliphatic hydrocarbons comprising, for example, 4 to 6 carbon atoms.

The catalyst used in accordance with the invention preferably corresponds in particular to the general formula:

Mgm Men M (OR1) p (R2) q Xr Ds where Me is an aluminum and / or zinc atom, M is an atom of a transition metal belonging to groups IV, V or VI Periodic Table of the Elements, with preferably a titanium and / or vanadium atom, R1 is an alkyl group of 1 to 14 carbon atoms, R2 is an alkyl group of 2 to 12 carbon atoms, X is a chlorine and / or bromine atom, D is a compound

000 598 electron donor comprising at least one atom of oxygen or sulfur or nitrogen or phosphorus, where m is between 0.5 and 50, preferably between 1 and 10, n is between 0 and 1, preferably between 0 and 0.5, p was between 0 and 3, which was between 0 and 1, preferably between 0 and 0.5, r was between 2 and 104, preferably between 3 and 24, and sestia between 0 and 1 60, preferably between 0 and 20.

The catalyst can be obtained by several processes, for example those in which a magnesium compound, such as magnesium chloride, is milled in the presence of at least one transition metal compound, or where a magnesium compound is precipitated thereto. time that one or mine transition metal compounds. for example, the catalyst can be obtained by reacting an organomagnesium compound and a titanium compound taken at its maximum valence, optionally in the presence of an electron donor compound D, chosen, for example, from amines, amides, phosphines, sulphioxides and aliphatic ethers.

Preferably, the catalyst is obtained by reaction, at temperatures between -20 and 150 ^ C, of ​​1 or more compounds of tetravalent titanium of formula

TiX4-t (OR1) t where X is an chlorine or bromine atom, he is an alkyl group of 2 to 14 carbon atoms and t is an integer or fraction between 0 and 3, and an arganomagnesium compound of formula R2 MgX I heard of Mg (R2) 2 formula where X is an chlorine or bromine atom, and R2 is an alkyl group of 2 to 12 carbon atoms. The reaction between the tetravalent titanium compound or compound and the organomagnesium compound was conveniently carried out in the presence of an alkyl halide of the form F2 in which R2 and X are defined as above, and optionally in the presence of the electron donor compound D.

Another technique for preparing the catalyst is to react, at temperatures between -20 and 150 ^ C, metallic magnesium with one alkyl halide or more tetravalent titanium compounds, these last compounds corresponding to the R2X and TiX4-t ( OR1) t defined respectively above, optionally in the presence of electron donor compound D. In this case, the reactants can be used in molar ratios such that: TiX4-t (OR1) t / Mg is between 0.05 and 0.5, preferably between 0.1 and 0.33; R2 X / Mg is between 0.5 and 8, preferably between 1.5 and 5; Y

D / TiX4-t (OR1) t is between 0 and 0.5, preferably between 0 and 0.2.

The catalyst can also be prepared by precipitating a transition metal compound on solid particles consisting biasically of magnesium chloride.

Silicate magnesium chloride particles can be prepared, for example, by reacting an organomagnesium compound and a chlorinated organe compound, using the following conditions:

- The organomagnesium compound is a diakyl

- magnesium of form R3 Mg R4 or an organomagnesium derivative of formula R3 Mg R4, xAl (R5) 3, encuyasfíormulas R3, R4 and R5 are the same or different and represent alkyl groups of 2 to 12 carbon atoms and x is a number between 0.01 and 1.

- The chlorinated organic compound is an alkyl chloride of the formula R6 Cl in which R6 is a secondary or preferably tertiary alkyl group having 3 to 12 carbon atoms.

- The reaction was carried out in the presence of an electron donor compound D which, for example, can be selected from amines, phosphines, sulphioxides, sulfones or aliphatic ethers.

Precipitation of the transition metal compound on solid magnesium chloride particles can be accomplished by a reduction reaction of a transition metal compound such as titanium or vanadium, taken at its maximum valence, by means of organometallic metal compounds of the Groups II and III of the Periodic Table of the Elements. Preferably, a titanium compound of TiX4-t formula (OR1t wherein R1, Xyt is defined as above, is used, the reduction being effected by means of a reducing agent chosen from organomagnesium compounds of form R3 Mg R4 where R3 and R4 are defined as before, organocinc compounds of the formula Zn (R7) 2-and Xy, wherein R7 is an alkyl group of 2 to 12 carbon atoms, X is an chlorine or bromine atom and and is 0 1, or a fraction between 0 and 1, and organoaluminum compounds of the formula Al (R8) 3-z Xz wherein R8 is an alkyl group of 2 to 12 carbon atoms, X is a chlorine or bromine atom and z is 0, 1 or 2, or a fraction between 0 and 2 .

In the reduction reaction it is preferable to use an amount of organometallic compound (ie, organomagnesium compound, organoincine or organoaluminum) sufficient to reduce the titanium compound to a lower valence state. If an excess of said organometallic compound is used, it is preferably separated from the catalyst before carrying out the prepolymerization step.

Said reduction reaction may optionally be carried out in the presence of an electron donor compound D as described above, at a temperature between

- 30 and 100 ^ C, with stirring, in a liquid hydrocarbon medium. For the purpose of polymerizing propylene or copolymerizing propylene with ethylene or other alpha-olefins, the catalyst should not only have a satisfactory polymerization activity. but also a high stereospecificity. In this case, one of the preferred methods for the preparation of the catalyst is to impregnate, with titanium tetrachloride, particles

000 598 magnesium chloride solids such as, for example, those obtained according to the method described above, the impregnation being performed preferably in the presence of an electron donor compound D.

Conveniently, the preparation of said catalyst can be carried out by a process comprising the following two steps:

(a) Treatment of solid magnesium chloride particles using an electron donor compound D chosen in particular from the aromatic acid oresters or aromatic ethers.

(b) Impregnition of the solid magnesium chloride particles treated using titanium tetrachloride.

The amount of electron donor compound D used during the first stage was generally between 0.06 and 0.2 moles of electron donor compound per mole of magnesium compound and the treatment temperature can be between 20 and 50^or C approximately. In the second stage, the magnesium chloride solid particles are impregnated with pure used titanium tetrachloride or in a liquid hydrocarbon medium. One of the methods consists in particular of grinding the solid particles of magnesium chloride in the presence of titanium tetrachloride. The amount of titanium tetrachloride should be sufficient to fix, on these particles, 0.5 to 3 gram atoms of titanium per 100 atoms - gram of magnesium, it being possible that the impregnation temperature is between 80 and 150^orC approximately.

The catalyst, prepared according to any of the above-described methods, is generally in the form of solid particles with a particle size generally less than 50 microns and with a polymerization activity that is normally unsatisfactory for direct use without fluid bed polymerization olefin gas.

To solve this problem, the catalyst becomes a prepolymer.

The prepolymer conversion consists in contacting one or more alpha-olefins with the catalyst and at least one organometallic compound (a) used as a cocatalyst, in amounts such that the atoomic ratio of the amount of metal in the organometallic compound (a) to the amount of transition metal in the catalyst is at least 0.5 and at most 2.5, preferably at least 0.8 and at most 2. However, a portion of the amount of the organometallic compound used (a) may be added to the prepolymer at the conversion term. The prepolymerization can be carried out in suspension in a liquid medium, such as aliphatic hydrocarbons or liquid alpha-olefins, or in the gas phase. The prepolymerization stops when the prepolymer contains 2 x 10^-3 a10^-1, preferably x 10³ a3x 10^-2 Oatomos - milligrams of transition metal per gram. When the prepolymerization was carried out in suspension in a liquid medium, the prepolymer can then be isolated in the form of a powder after drying in an inert gas atmosphere, at temperatures between 50 and 80^orC. The powder prepolymer obtained consists of solid particles having an average mass diameter between 50 and 300 microns, preferably between 70 and 250 microns, whose dimensions are compatible with the use for gas phase polymerization, especially by means of a fluid bed.

The gas phase polymerization can be carried out, for example, in a stirred reactor or preferably in a fluid bed reactor where the polymer particles in the course of their formation are maintained in a fluid state by means of an upward, driven gas stream. at a speed of 2 to 10 times, preferably 5 to 8 times, the minimum rate of fluidification, that is, generally between 15 and 80 cm / second, preferably between 40 and 60 cm / second. The upstream gas stream comprises the monomer material to be polymerized, optionally with other components, for example hydrogen (chain transfer agent) and / or inert gases, for example methane, ethane, propane or nitrogen. The monomeric material comprises the alpha-olefin or alpha-olefins to be polymerized and optionally a diene. The alpha-olefin or alpha-olefins to be polymerized generally comprise from 2 to 12 carbon atoms. As it passes through the fluidized bed, only part of the alpha-olefin or alpha-olefins polymerizes in contact with the developing polymer particles. The fraction of alphaolefins that has not been in reaction leaves the fluid bed and passes through a cooling system to absorb the heat produced during the reaction before being recycled to the fluid bed reactor by means of a compressor.

The average pressure in the reactor may be close to atmospheric, but is preferably higher in order to increase the polymerization rate. For example, it can be 0.5 to 5 MPa.

The temperature is maintained in the reactor at a level sufficient for rapid polymerization, but without being too close to the softening temperature of the polymer, in order to avoid in this last case, the formation of hot spots and polymeric agglomerates. In general it was between 50 and 110^orC, preferably between 70 and 100^orC.

The catalytic system previously converted into a prepolymer is introduced continuously or semicontinuously into the polymerization reactor. The extraction of the obtained polymer can also be carried out continuously or semicontinuously according to known methods. The polymer can be removed from the reactor in particular by means of various mechaonic devices. The preferred device consists in providing the lower part of the reactor with an opening capable of being closed and communicating with a chamber in which a lower gas pressure is maintained than the pressure of the reactor. The opening of said opening during a given period allows the discharge into this chamber of the desired amount of polymer. Once the opening has been closed again, the polymeric product can be recovered from the

000 598 chamber.

The process of the invention makes it possible to obtain polyolefins with a bath contained in catalytic residues, not only of transition metal compounds but also of organometallic compounds used as cocatalysts. The polyolefins preferably contain less than 3 x 10-4 atoms - milligram of transition metal per gram, but preferably less than 2 x 10^-4 aotomes - milligram of transition metal. It is possible to produce, under very advantageous and satisfactory industrial conditions, a large number of different qualities of alpha-olefin polymers, for example, high density polyethylenes (density greater than 0.940), among which are ethylene homopolomers and copolymers of ethylene and alpha olefins that have 3 to 12 carbon atoms, linear low density polyethylenes (density less than 0.940) consisting of copolymers of ethylene and alpha-olefin atoms that have 3 to 12 carbon atoms, with a weight content of ethylene-derived units greater than 80%, elastomeric terpolymers of ethylene , propylene and dienes, elastomeric copolymers of ethylene and propylene having a weight content of units derived from approximately 30 to 70% ethylene, isotactic polypropylenes and, copolymers of propylene and ethylene and other alpha-olefins, which have a weight content of units derived from propylene greater than 90%, copolymers of propylene and 1-butene that have a weight content of units derived from 1

- Butene between 10 and 40%.

The process of the invention makes it possible to obtain high rates of polyolefin production using relatively small amounts of cocatalysts, under conditions of gas phase polymerization, stable and reproducible. These conditions are especially advantageous in solving certain safety problems and in reducing the formation of alkanes by hydrogenation of alphaolefins in the presence of hydrogen.

The following non-limiting examples illustrate the present invention.

Example 1:

Catalyst Preparation

In a 1-liter glass flask, equipped with an agitator system and with a heating and cooling device, 500 ml of n-hexane, 8.8 g of magnesium in the form are introduced under a nitrogen atmosphere at 20 ° C of powder and 1.2 g of iodine, successively. With stirring, the reaction mixture is heated to 80 ° C and 9.1 g of titanium tetrachloride and 13.7 g of tetrapropyl titanate are introduced rapidly and then slowly for 4 hours, 74.5 g of n chloride

- butyl. At the end of this time, the reaction mixture thus obtained is maintained for 2 hours with stirring at 80 ° and then cooled to room temperature (20 °). The precipitate obtained is then washed three times with n-hexane to give the solid catalyst (A) ready for use. The analysis of the catalyst (A) obtained shows that it contains, per atom - gram of titanium in total:

0.9 atoms - gram of trivalent titanium,

0.1 grams of tetravalent titanium,

3.7 atoms - gram of magnesium and

7.7 aotomes - gram of chlorine and that the catalyst composition (A) corresponds to the general formula:

Mg3.7 Ti (OC3H7) 2 (C4H9) 0.7 Cl7.7

In a 5-liter stainless steel reactor, equipped with a stirrer that rotates at 750 revolutions per minute, 3 liters of n-hexane heated to 70 are introduced under nitrogen^°C, 14 ml of a molar solution of tri-n-octyl-aluminum (TnOA) in n-hexane and an amount of catalyst (A) prepared in the formula described above and containing 14 atoms-milligram of titanium, these amounts being such that the Al: Ti ratio is equal to 1.0. TnOA is an organoaluminum compound, liquid under the conditions of polymerization or copolymerization in the gas phase, which has a vapor pressure at 80^°C less than 0.13 Pa. The reactor is then closed and hydrogen is introduced to a pressure of 0.5 MPa and ethylene with a flow rate of 160 g / hour for 3 hours. The prepolymer obtained (B) is then dried in a rotary evaporator at 70^°C under a stream of nitrogen. It contains 0.029 aortos milligram of titanium per gram.

Copolymerization in fluid bed.

In a fluid bed reactor with a diameter of 45 cm., Provided in its lower part with a fluidization grid, it is circulated at 80^°, a rising gas stream at a rate of 45 cm / second and consisting of a reaction gas mixture comprising hydrogen, ethylene, 1-butene and nitrogen, under the following partial pressures (pp):

pp hydrogen: 0.23 MPa pp ethylene: 0.64MPa pp 1 - butene: 0.09 MPa pp nitrogen: 0.66 MPa.

100 Kg of an inert anhydrous polyethylene powder is introduced into the reactor as a loading powder, after which, sequentially, approximately 5 g of prepolymer (B) every 210 seconds.

Also, a 0.05 molar solution of triethylaluminum (TEA) in n-hexane, at a regular flow rate corresponding to 14 millimoles of TEA per hour, is introduced into the fluid bed reactor at a point below the fluidization grid . The TEA has a steam pressure of 80^°C equal to 455 Pa and is essentially in a gaseous state under the conditions of polymerization or copolymerization of alpha-olefins in the gas phase. The total amount of organoaluminum compound present in the fluid bed is such that the non-toxic ratio Al: Ti is equal to 6.6.

After a period of stabilization of the production conditions of the copolymer of ethylene and 1-butene, approximately 25 kg / hour of powdered copolymer are collected by sequential removal, while maintaining the weight of the fluid bed at a value of 75 Kg. Thus, and at a relatively high production rate, equal to 95 Kg of copolymer per hour and per m³ fluid bed, you get a

000 598 powder copolymer having the following characteristics:

- Titanium content: 1.00 x 10^-4 atoms - mg of titanium per gram.

- Fusion index (MI₂,₁₆, measured at 190 ° C under a load of 2.16 kg: 5.8 g / 10 minutes.

- Density (at 20^°C): 0.937.

Under these conditions, it has also been found that ethane is formed in a relatively small amount, so that the reaction gas mixture comprises 4.5% by volume of ethane.

The results are summarized in Table I. Example 2:

Copolymerization in fluid bed

In the fluid bed reactor used in example 1, it is circulated at 80^°C, an ascending gas stream driven at a speed of 45 cm / second and consisting of a reaction gas mixture comprising hydrogen, ethylene, 1 butene and nitrogen, under the following partial pressures (pp):

pp hydrogen: 0.20 MPa pp ethylene: 0.56 MPa pp 1 - butene: 0.80 MPa pp nitrogen: 0.70 MPa

100 kg of an inert anhydrous polyethylene powder is then introduced into the reactor as a filler powder, and then, approximately every 120 seconds, in sequence, approximately 5 g of prepolymer (B) is introduced.

Likewise, a 0.05 molar solution of triethyl aluminum (TEA) in n-hexane, at a regular flow rate corresponding to 12.5 mmol, is introduced into the fluid bed reactor at a point below the fluidization grid. of ASD per hour. The total amount of organoaluminum compounds present in the fluid bed is such that the atomic ratio Al: Ti is equal to 3.8.

After a period of stabilization of the production conditions of the copolymer of ethylene and 1-butene, approximately 30 kg / hour of powdered copolymer are collected by sequential removal, while maintaining the weight of the fluid bed at a value of 75 Kg. Thus, and with a high production rate equal to 110 Kg of copolymer per hour and per m³ With a fluid bed, a powder copolymer is obtained that has the following characteristics:

- Titanium content: 1.46x10^-4 Atoms - mg of titanium per gram.

- Melt index (MI2,16, measured at 190^°Under a load of 2.16 Kg: 5.7 g / 10 minutes.

- Density (at 20^°C: 0.938.

Under these conditions, it has also been found that a relatively small amount of ethane is formed, so that the reaction gas mixture comprises 4% by volume of ethane.

The results are given in table I. Example 3:

Copolymerization in fluid bed

In the fluid bed reactor used in example 1, it is circulated at 80^°C, an ascending gas stream driven at a speed of 45 cm / second and consisting of a reaction gas mixture comprising hydrogen, ethylene, 1 butene and nitrogen, under the following partial pressures (pp):

pp hydrogen: 0.17 Mpa pp ethylene: 0.48 MPa pp 1 - butene: 0.07 MPa pp nitrogen: 0.74 MPa.

100 Kg of an inert anhydrous polyethylene powder is then introduced into the reactor as a filler powder, and then, every 155 seconds, in sequence, approximately 5 g of prepolymer (B) is introduced.

Likewise, a 0.0 * molar solution of triethylaluminum (TEA) in n-hexane, at a regular flow rate corresponding to 6 mmol of TEA, is introduced into the fluid bed reactor at a point below the fluidization grid. per hour. The total amount of organoaluminum compound present in the fluid bed is such that the atoimic ratio Al: Ti is equal to 2.8.

After a period of stabilization of the production conditions of the copolymer of ethylene and 1-butene, approximately 20 kg per hour of powdered copolymer are collected by sequence, while maintaining the weight of the fluid bed at a value of 80 Kg. Thus, and with a high production rate equal to 65 Kg of copolymer per hour and per m³ With a fluid bed, a powder copolymer is obtained that has the following characteristics:

- Titanium content: 1.67 x 10^-4 Atoms - mg of titanium per gram.

- Melt index (MI2,16), measured at 190^°Under a load of 2.16 kg: 5.6 g / 10 minutes.

- density at 20^°C 0.938.

Under these conditions, it has also been found that a relatively small amount of ethane is formed, so that the reaction gas mixture comprises 2.5% by volume of ethane.

The results are given in table I. Example 4 (comparative):

Copolymerization in fluid bed.

It operates exactly as in Example 1, except that instead of introducing 14 mmol of TEA per hour into the fluid bed reactor, 42.2 mmol of TEA are introduced per hour, so that the total amount of organoaluminum compounds present in the fluid bed it corresponds to an atoimic relation Al: Ti equal to 18.

After a period of stabilization of the production conditions of the copolymer of ethylene and 1-butene, approximately 12 Kg / hour of powdered copolymer are collected in sequence, while maintaining the weight of the fluid bed at a value of 72 Kg. Thus, at a relatively low production rate equal to 45 Kg of copoimer per hour and per m³ fluid bed, you get a

000 598 copolymer powder having the following characteristics:

- Titanium content: 2.07 x 10^-4 atoms - mg of titanium per g.

- MI fusion index₂,₁₆), measured at 190 ° C under a load of 2.16 kg: 6.8 g / 10 minutes.

- Density (at 20^°C: 0.939.

Under these conditions, in which relatively large amounts of TEA are introduced into the fluid bed, it has been found that a large amount of ethane is formed, such that the reaction gas mixture comprises 12.5% ​​by volume of ethane. The large amount of ASD introduced into the fluid bed also has an unfavorable action on the volume production rate of the copolymer which also has a relatively high titanium content.

The results are given in table I. Example 5 (comparative):

Copolymerization in fluid bed

It is operated exactly as in Example 1, except that instead of introducing a 0.05 molar TEA solution into the fluid bed reactor at a speed of 14 mmol TEA per hour, a 0.05 molar TnOA solution is introduced at a speed of 14 mmol of TnOA per hour.

After 48 hours of production of ethylene and 1-butene copolymer, the formation of a liquid reservoir is found in the reactor base, below the fluidization grid, also observing the deposit of molten copolymer agglomerates on the grid of fluidization, which makes it necessary to terminate the copolymerization.

The results are given in table I. Example 6 (comparative):

Preparation of the prepolymer

It operates exactly as in Example 1, except that instead of introducing 14 mmol of TnOA into the reactor, 75.6 mmol of TnOA are introduced. The amounts of catalyst and cocatalyst used to prepare the prepolymer are therefore such that the atomic ratio Al: Ti is 5.4.

In this way, a prepolymer (C) is obtained containing 0.029 aitoms - mg of titanium per gram.

Copolymerization in fluid bed.

It is operated exactly with Example 1, except that instead of using the prepolymer (B) and introducing into the fluid bed reactor 14 mmol of TEA per hour, the prepolymer (C) prepared above is used and introduced into the reactor of fluid bed 3 mmol of TEA per hour. The total amount of organoaluminium compound present in the fluid bed is then such that the atomic ratio Al: Ti is the same as that used in example 1, that is, 6.6.

As soon as the production of the copolymer of ethylene and 1-butene begins, agglomerates of molten copolymers are deposited on the fluidization grid, causing the copolymerization to stop.

The results are given in table I. Example 7 (comparative):

Preparation of the prepolymer

It operates exactly as in Example 1, except that instead of introducing 14 mmol of TnOA into the reactor, 14 mmol of TEA are introduced. The amounts of catalyst and cocatalyst used to prepare the prepolymer are therefore identical to those of Example 1, that is, they are such that the Al: Ti atoimic ratio is 1.0.

In this way, a prepolymer (D) is obtained containing 0.029 aitoms - mg of titanium per gram.

Copolymerization in fluid bed.

It is operated exactly as in Example 2, except that instead of using prepolymer (B), prepolymer (D) prepared above is used.

After a period of stabilization of the production conditions of the copolymer of ethylene and 1-butene, 16 kg / hour of powdered copolymer are collected in sequence, while maintaining the weight of the fluid bed at a value of 78 Kg. Thus, already a production regime of 55 Kg of copolymer per hour and per m³ With a fluid bed, a powder copolymer is obtained that has the following characteristics:

- Titanium content: 5.00 x 10^-4 íatomos - mg of titanium per gram.

- Fusion index (MI2,16): 2.6 g / 10 minutes.

- Density (at 20^°C): 0.937.

Under these conditions, in which the pre-polymer comprises a relatively volatile organoaluminum compound, it is found that the velocity produced is relatively small, that the titanium content of the copolymer obtained is high and that the melt index of this copolymer is relatively low. . The results are offered in Table I.

Example 8:

Copolymerization in fluid bed

In a fluid bed reactor of a diameter of 90 cm, provided in its lower part with a fluidizing grid, an upwardly driven gas stream is circulated at a speed of 45 cm / second and consisting of a reaction gas mixture comprising Hydrogen, ethylene, 4-methyl-pentene (4MPI) and nitrogen, under the following partial pressures (pp):

pp hydrogen: 0.05 MPa pp ethylene: 0.32 MPa pp 4MPI: 0.80 MPa pp nitrogen: 1.15 MPa.

The polymerization temperature is 80^°C and the temperature of the recycled gas is 63^°C. The dew point of recycled gas is 48^°C.

A powder load of 160 kg of an inert anhydrous powder of a copolymer of ethylene and 4MPI produced in a previous operation is then introduced, after which, every 125 seconds, 40 g of prepolymer (B) are directly introduced into the fluid bed .

A 0.1 molar solution of triethylaluminum (TEA) in n-hexane, at a regular flow rate corresponding to 6.6 mmol of TEA, is also introduced into the fluid bed reactor at a point below the fluidization grid. by

000 598 hour. The total amount of organoaluminum compounds present in the fluid bed is such that the non-toxic ratio Al: Ti is equal to 3.

After a period of stabilization of the production conditions of the ethylene copolymer and 4MPI, approximately 160 kg per hour of powdered copolymer are collected by sequencing while maintaining the weight of the fluid bed at a value of 350 kg The cop olomer powder has the following characteristics:

- Titanium content: 2 x 10^-4 atoms - mg of titanium per gram.

- Fusion index (MI2,16), measured at 190^orUnder a load of 2.16 kg: 0.9 g / 10 minutes;

- Density (at 20^orC): 0.918.

Example 9:

Copolymerization in fluid bed

It is operated as in Example 8, except that the prepolymer contains such an amount of tri n-octylaluminum that the al: Ti atoomic ratio is equal to 1.5 and that triethylaluminum is not introduced into the reactor. Prepolymer D is introduced into the reactor in a proportion of 40 g every 110 seconds.

The gaseous reaction mixture comprises hydrogen, ethylene, 4MPI and nitrogen under the following partial pressures (pp): hydrogenic pp: 0.13 MPa pp ethylene: 0.70 MPa pp 4MPI: 0.175 MPa pp nitrogen: 0.595 MPa The polymerization temperature it's 80^orC and the temperature of the recycled gas is 71^orC. The dew point of recycled gas is 70^orC.

After a period of stabilization of the production conditions of the copolymer of ethylene and 4MPI, approximately 100 kg / hour of copolymer are collected by sequence removal, while maintaining the weight of the fluid bed at a value of 350 kg.

The powder copolymer has the following characteristics:

- Titanium content: 3.7 x 10^-4 aotomes - mg of titanium per gram.

- Fusion index (MI2,16), measured at 190^orUnder a load of 2.16 kg: 0.9 g / 10 minutes.

- Density (at 20^orC): 0.918.

Described sufficiently the nature of the invention, as well as the way of carrying it out in practice, it should be noted that the provisions described above are subject to modifications in detail, as long as they do not alter its fundamental principle.

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