FR2680794A1 - Process for gas phase copolymerisation of ethylene with 1-octene - Google Patents

Abstract

Process for copolymerisation of ethylene with 1-octene and optionally with an alpha -olefin containing from 3 to 6 carbon atoms, performed in a gas-phase polymerisation reactor with the aid of a catalyst system of the Ziegler-Natta type consisting of a solid catalyst including titanium, magnesium and a halogen and of a cocatalyst consisting of an organometallic compound of a metal of groups II and III of the Periodic Classification of the elements. This process is such that throughout the gaseous phase present in the reactor the ratio of the pressure of 1-octene to the partial pressure of ethylene is lower than or equal to 0.02.

Description

 The present invention relates to a gas phase copolymerization process of ethylene with octene-1 and optionally with another alpha-olefin.

 According to European patent application EP-A-164 215, there is known a process for the gas phase copolymerization of ethylene with butene-1 and / or propylene and with octene-1. This process is carried out in a fluidized bed polymerization reactor and with the aid of a catalytic system of the Ziegler-Natta type. Furthermore, according to this process during the copolymerization reaction, the ratio between the partial pressure of octene-1 and the partial pressure of ethylene, in the gas phase, must range from 0.05 to 0.2.

 A new gas phase copolymerization process has now been found for 11 ethylene with octene-1, and optionally with an alpha-olefin having 3 to 6 carbon atoms, in which the ratio of octene partial pressure -l and the partial pressure of ethylene in the gas phase. is lower than that recommended in the European patent application EP-A-164 215.

The subject of the present invention is therefore a process for the copolymerization of ethylene with octene-1 and optionally with an alpha-olefin having 3 to 6 carbon atoms, carried out in a gas phase polymerization reactor using a catalytic system of the Ziegler Natta type consisting of a solid catalyst comprising titanium, magnesium and a halogen and a cocatalyst consisting of an organometallic compound of a metal from groups II and
III of the periodic table, characterized in that throughout the gas phase contained in the reactor, the ratio between the partial pressure of octene-1 and the partial pressure of ethylene is less than or equal to 0.02.

 According to the essential characteristic of the invention, the ratio between the partial pressure of octene-1 and the partial pressure of ethylene, in the gas phase used during the copolymerization, must be less than or equal to 0.02. Most often this ratio can range from 0.0015 to 0.02 and more particularly from 0.002 to 0.01. Thus, the present invention is based on the surprising principle that octene-1 has in the gas phase a very great ability to copolymerize with ethylene in the presence of a catalytic system of the Ziegler-Natta type. Thus, it is possible to manufacture copolymers ethylene with octene-1, by copolymerization of ethylene with octene-1, with a gas phase in which the amount of octene1 represents a very small proportion of the amount of ethylene.

 According to a characteristic, which is not essential to the invention, the partial pressure of octene-1 in the gas phase can be low. For example, it can range from 0.001 to 0.015 MPa and more particularly from 0.0012 to 0.006. In this particular case, by varying the conditions of the copolymerization, and in particular the conditions of pressure and temperature, it is observed that the copolymer particles produced contain little octene-1, absorbed in liquid form. In general, these particles contain by weight less than 4% of octene-1 absorbed.

 According to the invention, the copolymerization is carried out using a catalytic system of the Ziegler-Natta type consisting of a solid catalyst comprising titanium, magnesium and a halogen and a cocatalyst consisting of an organometallic compound d 'a metal from groups II and III of the periodic table. This catalytic system can be identical to that described in European patent application EP-A-164 215. Furthermore, in addition to titanium, magnesium and halogen, the catalyst used can comprise a granular support based on a refractory oxide such as silica, alumina or a mixture of these two oxides.

 The catalyst can be introduced into the polymerization reactor as it is. It can also be introduced after a prepolymerization. This prepolymerization consists in bringing the catalytic system into contact with ethylene, optionally in admixture with octene-1 and / or with an alpha-olefin having from 3 to 6 carbon atoms. This prepolymerization can be carried out, according to known techniques, in one or more stages. It is generally stopped when the prepolymer contains from 10 to 300 g of polymer per millimole of titanium.

In addition to the catalytic system, it is advantageously possible to introduce into the reactor, an agent which slows down the activity of the catalyst, such as those described in the European patent application.
EP-A-376559 ..

 The gas phase copolymerization can be carried out in a mechanically stirred and / or fluidized bed reactor, according to known techniques. A fluidized bed reactor essentially consists of a vertical cylinder equipped with a fluidization grid and surmounted by a stilling chamber. Furthermore, it is equipped with an external recycling pipe connecting the top of the stilling chamber to the base of the reactor and which is provided with at least one heat exchanger, a gas compressor and pipes for olefin feed. In a fluidized bed reactor, the fluidization speed of the gas phase passing through the fluidized bed is 2 to 8 times the minimum fluidization speed, that is to say generally between 20 and 120 cm / s.

 The gas phase used for the copolymerization contains ethylene and ltoctene-1. Furthermore, it may contain propylene and / or butene-1. In this case, during the copolymerization, the ratio between the partial pressure of propylene and / or butene-1 and the partial pressure of ethylene is most often between 0.05 and 0.4.

 The gas phase, in addition to the olefins to be copolymerized, generally contains an inert gas such as nitrogen, methane, ethane. The ratio of the partial pressure of all the inert gases to the total pressure of the gas phase can in principle range from 0.2 to 0.8. Furthermore, the gas phase may contain hydrogen in order to regulate the molecular weight of the copolymer produced according to the process. Generally, the ratio between the partial pressure of hydrogen and the partial pressure of ethylene is less than or equal to 0.5.

 During the copolymerization, certain constituents of the gas phase, and in particular ethylene and octene-1, can be introduced continuously into the polymerization reactor. In this case, the copolymerization can be regulated, in particular by keeping the ratio between the partial pressure of octene-1 and the partial pressure of ethylene constant in the gas phase. However, given the low value of this ratio, it is preferable to introduce octene-1 into the reactor so as to keep constant the ratio between the rate of introduction of octene-1 and the rate of introduction of ethylene. .

Thus, a copolymer with a constant content of octene-1 is more easily obtained.

 The copolymerization is carried out at a temperature between 500 and 100 C and preferably between 70 and 90 C and under an absolute total pressure ranging from 0.5 to 5 MPa. The copolymer produced according to the process is advantageously withdrawn from the reactor when it contains less than 20 parts per million of titanium.

The copolymers produced according to the process most often contain between 2 and 15% by weight of octene-1.

According to the present invention, the alpha-olefin having 3 to 6 carbon atoms can be propylene, butene-1, lthexene-1, or alternatively methyl-4pentene-1. Therefore, according to the process of the invention, it is possible to manufacture copolymers containing ethylene, 4-methyl-pentene-1 or hexene, and octene-1. The process of the invention allows in particular to manufacture copolymers of ethylene with butene-1 and with octene-1 having from 85 to 95% by weight of ethylene and from 15 to 5% by weight of butene-1 and of octene-1 and having the following characteristics
- a density which can range from 0.915 to 0.940
- a fluidity index measured at 1900C under a load of 2 kg which can range from 0.1 to 5 g / 10 minutes
- a melting temperature which can range from 120 to 1260C
a distribution of the molecular weights measured by the ratio of the molecular weight by weight Mw to the molecular weight by number Mn, between 3 and 5.

- A content of copolymer soluble in n-hexane at 500C, ranging from 1 to 3% by weight
- a flow index 2'n "calculated by the ratio between the melt index measured at 1900C under a load of 26.1 kg and the melt index measured at 190 C under a load of 2.16 kg ranging from 1.4 to 1.5.

- a titanium content measured by X-ray fluorescence of less than 20 ppm
The copolymers obtained represent in the form of a powder having very good flow properties. It has an apparent density ranging from 0.280 to 0.450 g / cm3.

 The copolymers obtained are particularly adopted in the manufacture of films.

Determination of the flowability of a polymer or copolymer powder
The flowability of a polymer or copolymer powder is determined using a hopper with a volume of 0.286 liters, having the shape of a cone of revolution cone, with a vertical axis. and downwardly angled at the apex having a diameter of the small base of 12.5 mm, a diameter of the large base of 93 mm and a height of 113 mm.

 The hopper opening is closed with a glass slide. Through the upper orifice, the polymer or copolymer powder which has been previously aerated and loosened is poured into the hopper without tamping it. When the hopper is full, the powder is leveled off at the upper orifice of the hopper by horizontal scanning of the excess quantity of the powder poured. Then remove the glass slide closing the lower hole and it is observed whether the free flow of the powder takes place or not. The flowability of a powder is determined by the time required to completely empty the hopper. According to this method, a powder is considered to have good flow properties when the hopper is emptied in less than 25 seconds and as having poor flow properties if the hopper empties in more than 35 seconds.

 The following examples with reference to FIG. 1, which schematically represents a gas phase polymerization reactor with a fluidized bed, illustrate the present invention.

 FIG. 1 schematically represents a gas phase polymerization reactor with a fluidized bed (1) essentially consisting of a vertical cylinder (2) surmounted by a stilling chamber (3) provided in its lower part with a fluidization grid ( 4) as well as a recycling pipe (5) connecting the top of the stilling chamber to the lower part of the reactor located under the fluidization grid, which is equipped with a heat exchanger (6), a compressor (7) and supply lines for ethylene (8), butene-1 (9), octene-1 (10), hydrogen (11) and nitrogen (12). The reactor is also equipped with a prepolymer supply line (13) and a copolymer withdrawal line (14).

Example
The operation is carried out in a gas phase polymerization reactor with a fluidized bed as shown diagrammatically in FIG. 1 consisting of a vertical cylinder 74 cm in diameter and 7 m high.

 The reactor contains, above the fluidization grid, a fluidized bed, maintained at 80 ° C. from a height of 2.5 m and consisting of 285 kg of a powder of ethylene copolymer with octene-1 and the butene-l during training. This fluidized bed is crossed, with an ascending fluidization speed of 51 cm / s, by a gas phase containing by volume 35% ethylene, 8 Y. of butene-l, 0.26% of octene-l, 10 % hydrogen of 46.74 Y. of nitrogen. The total pressure of the gas phase is 1.7 MPa, the partial pressure of ethylene is kept constant at 0.6 MPa, and the partial pressure of octene-1 is 0, oo45 MPa. In this gas phase, the ratio between the partial pressure of octene-1 and the partial pressure of ethylene is 0.0074. Octene-1 is introduced pure and in liquid form into the reactor at a flow rate close to 6.2 liters / hour and in such a way that the ratio between this flow rate and the flow rate of introduction of ethylene is kept constant.

 A catalyst which is identical to that described in Example 1 of European patent application EP-A-164 215 which contains magnesium, chlorine and titanium and is intermittently introduced over time into the reactor which has been previously transformed into a prepolymer containing 35 g of polyethylene per millimole of titanium and an amount of tri-n-octylaluminum (TnOA) such that the Al / Ti molar ratio is equal to 1.05 and consisting of particles having a diameter mass average of 200 microns. The rate of introduction of the prepolymer into the reactor is kept constant at 520 g / hour.

 Triethylaluminum is also introduced into the reactor so as to obtain in the reactor, a molar ratio between the aluminum of the triethylaluminum and the titanium of the catalyst equal to-1.7, and of dimethylformamide so as to obtain in the reactor a ratio molar between dimethylformamide and titanium of the catalyst-equal to 0.05.

Under these conditions, 65 kg / hour of a copolymer containing by weight 90% ethylene, 5% butene-1 and 5 Y. of octene-1 having the following properties is produced.
- density: 0.918
- fludity index measured at 1900C under a load of 2.16 kg: 1.06 g / to minutes
- apparent density of the copolymer powder 0.320 g / cm3
- titanium content: 11 ppm
- melting temperature: 123 C
- flowability: 16.

Example2
The operation is carried out in a gas phase polymerization reactor with a fluidized bed as shown diagrammatically in FIG. 1 consisting of a vertical cylinder 74 cm in diameter and 7 m high.

 The reactor contains above the fluidization grid a fluidized bed, maintained at 80 "C with a height of 2.5 m and consisting of 285 kg of a powder of ethylene copolymer, with octene-1 and butene-1 being formed. This fluidized bed is traversed, with an ascending fluidization speed of 51 cm / s, by a gas phase containing by volume 35% ethylene, 13% butene-1.0.10% octene-1.8 E of hydrogen and 43.9 Y of nitrogen. The total pressure of the gas phase is 1.7 MPa, the partial pressure of ethylene is kept constant at 0.6 MPa, and the partial pressure of octene-1 is 0.0018 MPa. In this gas phase, the ratio between the partial pressure of octene-1 and the partial pressure of ethylene is 0.003.

Octene-1 is introduced pure and in liquid form into the reactor at a flow rate close to 2 liters / hour.

 In the reactor, a catalyst is introduced intermittently over time which is identical to that described in Example i of European patent application EP-A-164 214 which contains magnesium, chlorine and titanium and which has been previously transformed into a prepolymer containing 35 g of polyethylene per millimole of titanium and an amount of tri-n-octylaluminum (TnOA) such that the Al / Ti molar ratio is equal to 0.750 and consisting of particles having an average diameter in mass of 200 microns. The rate of introduction of the prepolymer into the reactor is kept constant at 520 g / hour.

 In the reactor, triethylaluminum is also introduced so as to obtain in the reactor, a molar ratio between the aluminum of the triethylaluminum and the titanium of the catalyst equal to 2, and dimethylformamide so as to obtain in the reactor a molar ratio between the dimethylformamide and the titanium of the catalyst equal to 0.05.

Under these conditions, 65 kg / hour of a copolymer containing 91.4% of ethylene, 6.6% of butene-1, and 2% of octene-1 having the following properties are produced.
- density: 0.918
- melt index measured at 190 C under a load of 2.16 kg: 0.73 g / 10 minutes
- apparent density of the copolymer powder 0.320 g / cm3
- titanium content: 11 ppm
- melting temperature: 1230C
- flowability: 15.

Claims (10)

5 "CLAIMS 1. Process for the copolymerization of ethylene with octene-1 and optionally with an alpha-olefin having 3 to 6 carbon atoms, carried out in a gas phase polymerization reactor using a catalytic system of Ziegler Natta type consisting of a solid catalyst comprising titanium, magnesium and a halogen and a cocatalyst consisting of an organometallic compound of a metal from groups II and III of the periodic table, characterized in that in all the gas phase contained in the reactor, the ratio between the partial pressure of octene-1 and the partial pressure of ethylene is less than or equal to 0.02. 2. Method according to claim 1, characterized in that the ratio between the partial pressure of octene-1 and the partial pressure of ethylene ranges from 0.0015 to 0.02. 3. Method according to claim 1 or 2, characterized in that the partial pressure of octene-l ranges from 0.001 to 0.015 MPa. 4. Method according to any one of claims 1 to 3, characterized in that the polymerization reactor is a fluidized bed reactor. 5. Method according to any one of claims 1 to 4, characterized in that the catalytic system is introduced into the polymerization reactor in the form of a prepolymer. 6. Method according to any one of claims 1 to 5, characterized in that the ethylene and octene-1 are continuously introduced into the polymerization reactor. 7. Process according to claim 6, characterized in that in the gas phase the ratio between the partial pressure of octene1 and the partial pressure of ethylene is kept constant. 8. Method according to claim 6, characterized in that the ratio between the rate of introduction of octene-1 and the rate of introduction of ethylene is kept constant. 9. Method according to any one of claims 1 to 8, characterized in that the alpha-olefin having 3 to 6 carbon atoms is chosen from propylene, butene-1, methyl-4, pentene-1 , and hexene-I. 10. Copolymers containing ethylene, 4-methyl pentene-1 or hexene-1, and octene-1 which can be obtained by the process according to any one of claims 1 to 8.