CA1106099A

CA1106099A - Process for producing copolymers of ethylene and higher alpha-olefins

Info

Publication number: CA1106099A
Application number: CA313,065A
Authority: CA
Inventors: Francois Caumartin; Laszlo Havas
Original assignee: Naphtachimie SA
Current assignee: Naphtachimie SA
Priority date: 1977-10-12
Filing date: 1978-10-11
Publication date: 1981-07-28
Also published as: NL184165B; NL184165C; JPS5462292A; GB2006232B; JPS6053044B2; ES474076A1; GB2006232A; DE2844312C2; BE871221A; IT1099775B; LU80350A1; FR2405961B1; DE2844312A1; NL7810217A; IT7828577A0; FR2405961A1

Abstract

ABSTRACT
A process for producing copolymers of ethylene and higher alpha-olefins containing 3 to 6 carbon atoms utilizing a fluidised bed procedure.
A catalyst system comprising a tetravalent titanium compound as catalyst to-gether with a co-catalyst comprising either an organo-magnesium compound or magnesium metal is used. This process is capable of providing a copolymer containing up to 33% by weight of units derived from the higher alpha-olefin, in contrast to previous processes which are limited to about 6% of higher alhpa-olefin. The products of this process find use, in the production of castings by rotary moulding techniques, and in melt-coating procedures.

Description

6~1199 The invention concerns a process for producing in a fluidized bed copolymers of ethylene and a higher alpha-olefin containing from 3 to 6 carbon atoms, which copolymers have a density of from 0.900 to 0.945 g/cm3 and may contain up to 33%
by weight of units derived from the higher alpha-olefin.
It has already been proposed that mixtures of ethylene and but-l-ene may be polymerized in a bed of particles, which is maintained in a fluidized condition by a rising flow of the mix-ture to be polymerized, in contact with a catalyst comprising a chromium compound deposited on a granular carrier, generally of silica. However, it does not seem possible to use this method to produce copolymers which contain more than from 5 to 6% by weight of units derived from but-l-ene. In addition, the result-ing copolymers are characterized by a high value in respect of the breadth of distribution of the molecular weights, which value is generally higher than 6, and by a low coefficient of fluidity under 2.16 kg, of the order of 0.1 to 0.2. The defini-tion of the breadth of distribution of the molecular masses and the coefficient of fluidity appears following the examples.
For the purposes of producing copolymers which have a higher coefficient of fluidity, the use of catalysts contain-ing both a chromium compound and a tetravalent titanium compound has also been proposed. The combination of these compounds, which both have catalytic properties, although of different f~

B

natures, probably results in the combined formation of two types of polymers; indeed, the properties of the copolymers vary according to the residence time of the copolymer in the reactor, by virtue of a different speed of exhaustion of the two catalytic compounds. Moreover, the coefficient of fluidity of the B -la-6~)99 resulting copolymers is still lower than 2 and their breadth of distribution of the molecular weights is even higher than that of the copolymers produced by the above-mentioned method.
A process has now been discovered, which makes it possible, by poly-merisation in a fluidised bed, to produce powders of copolymers of ethylene, which may contain up to 33% by weight of units derived from a higher alpha-olefin, which copolymers have a breadth of distribution of molecular weights which may vary between 2 and 11~ and a coefficient of fluidity which is from 0.1 to 30.
The invention therefore provides a process for the production of pow-ders of copolymers of ethylene and a higher alpha-olefin comprising from 3 to 6 carbon atoms~ such as propylene or but-1-ene~ which copolymers contain from 1 to 33% by weight of units derived from said higher alpha-olefin and have a density of from 0.900 to 0.945 g/cm3, a breadth of distribution of molecular weights of from 2 to 11, and a coefficient of fusion of from 0.1 to 30 at a temperatureof 190C under 2.16 kg, which comprises polymerisation of a gaseous misture which contains the olefins to be polymerised, and, if necessary hydro-gen, and which circulates upwardly through a fluidised bed of the copolymer in the course of formation, wherein the polymerisation is effected in the presence of a catalytic system comprising (i) a co-catalyst formed by at least one or-gano-metallic compound of a metal of group II and III of the periodic table of elements; and ~ a catalyst formed by a solid compound of titanium, magnesium and a halogen, which is produced by reacting at a temperature of from -20 to 150C and preferably from 60 to 90C:
a) one or more tetravalent titanium compounds having the formula TiX4 (OR) , wherein X is a chlorine or a bromine atom, R is an alkyl radical iLl(}6~J~

which may contain from 2 to 8 carbon atoms, and n is an integer or a fraction which may assume any value between 0 and 4~
b) an alkyl halide having the formula RX wherein R and X are as defined above, c) an organo-magnesium compound having the formula RMgX, an organo-magnesium compound having the formula MgR2 or metal magnesium, R and X being as defined above, which various compounds are used in molar ratios such that:
when an organo-magnesium compound having the formuLa RMgX is used as component c);
0.1 ~ TiX4_n(0R)n / RMgX ~ 0-33 and 1 ~ RX / RmgX ~ 2 when an organo-magnesium compound having the formuLa MgR2 is used as component c);

O.l~Tix4 n(OR)n / MgR2~0.33 and 2~ RX / MgR2 ~ 4 when metal magnesium is used as component c).
O1~ TiX4 n(OR)n / Mg ~ 0.33 and 0.5 ~ R~ / Mg ~ 10 or preferably 1.5 ~ RX / Mg ~ 4 In performing the process of the invention, the catalyst may be introduced directly into the p01ymerisation reactor or into the first of the polymerisation reactors when a plurality of reactors is used.
The cata:Lyst may also be introduced into the polymerisation reactor in the form of a prepolymer produced by means of previous polymerisation of one or more olefins in an inert l;quid, such as an aliphatic hydrocarbon, and in the presence of a halogenated titanium and magnesium compound as defined i~a~6q~ss above, and a co-ca~alyst such as an organo-aluminium compound. Prepolymerisa-tion is stopped after a moderate amolmt of polymer has been formed, in most cases such amotmt being from 1 to 500 g per milligram-atom of titanium of the catalyst. After separation from the liquid in which it was prepared, the pre-polymer in which tha halogenated titanium and magnesium compound remains in-cluded may then be used directly as a solid substance with catalytic activity;
however, before the prepolymer is used in the process of the invention, it is desirable for the prepolymer to be subjected to one or more extraction opera-tions by means of a solvent such as an aliphatic hydrocarbon in order to create porosity within the grains of the prepolymer. Such porosity improves the access of the olefins to the catalytic locations.
The copolymer present in the polymerisation reactor is kept in the fluidised condition in a rising flow of the gaseous mixture containing the olefins to be polymerised, and if necessary hydrogen, in proportions which may be up to 70% by volume of the gaseous mixture. The latter advantageously com-prises both the gaseous mixture issuing from the reactor, which is recycled, and, an amount of the olefins to be polymerised, which is introduced into the reaction circuit.
The velocity needed to be imparted to the gaseous mixture to maintain the copolymer present in the reactor in the fluidised condition is related to the physical parameters of the copolymer and the gaseous mixture. Of such parameters, the main ones are the sizes of the particles of the copolymer, the density of the copolymer, and the viscosity and density of the gaseous mixture;
gas velocities of the order of a few decimeters per second are the most usual ones.

The temperature in the reactor is maintained at a sufficient level for polymerisation to be rapid, but without being too close to the temperature at which agg]Lomerates would be formed, which would interfere with or stop polymerisation.
The composition of the gaseous mixture circu]Lating in the polymerisa-tion reactor is se;Lected according to the nature of the comonomer used and according to the desired proportion of comonomer in the copolymer. The total pressure in the reactors is genera~Ly from 1 to 40 bars; however, the process of the invention may be carried out at pressures below 1 bar or above 40 bars.
The gaseous mixture is in contact with the catalyst in the reactors only for a l~nited period of time, which is genera~Ly less than a few tenths of a second. According]Ly, on]Ly a fraction of the olefins introduced into the reactors is polymerised therein, and in consequence it is desirable to recycle to the reactors the gaseous mixture which issues therefrom. In order to ensure that the gaseous mixture does not entrain particles of the polymer or the catalyst upon discharge from the reactor, the reactor may be provided for ex-ample in its upper part with a chamber referred to as a tranquilisation chamber, which is of greater sectional area than the reactor; in this chamber, the speed of rise of the gaseous mixture is lower than in the reactor, which permits at least a fraction of the particles of polymer or catalyst which are entrained to fall back into the reactor. The particles which are entrained by the gaseous mixture may also be separated in a cyclone separator and returned to the re-actor, preferably in the lower part thereof. As polymerisation of olefins causes heat to be produced, it is necessary to remove the heat generated, in order to maintain cL constant temperature in the reactors; this operation of '11(;6~ ~99 removing heat is preferably performed by circulating the gaseous mixture to be recycled through a heat exchanger disposed outside of the reactor.
The operation of polymerising ~he olefins according to the inven-tion may also be performed in a plurality of fluidised bed reactors which are arranged in series. In this case~ only a part of the polymerisation operation is effected in each reactor and the polymer which is in the course of being formed circulates from the head reactor to the tail reactor. In an alternative form, some reactors may be arranged in a parallel arrangement, whereby the polymer which is in the course of being formed and which issues from one reactor is supplied to two or more secondary reactors.
The finished polymer may be discharged from the reactor in which it is produced by means of suitable mechanical or pneumatic arrangements. One discharge arrangement comprises providing the lower part of the reactor with an orifice which is capable of being closed and which communicates with a chamber in which there prevails a pressure lower than that in the reactor.
Opening the orifice for a given period of time allows the desired amount of polymer to be introduced into this chamber. When the orifice has been closed again, it is then sufficient for the chamber to be communicated with the out-side, for the purposes of collecting the polymer.
The process of the invention is preferably performed so that the operating conditions of the reactor or reactors are substantially constant.
This mode of operation may be achieved in practice by circulating in each reactor a gaseous mixture having substantially constant characteristics, which gaseous mixture is provided primarily by the recycled gaseous mixture.
The cocatalysts used in the process of the invention preferably comprise at least one organo-aluminium compound having the mean formula AIRI Y(3 )wherein Rl represents an alkyl group containing from 1 to 12 carbon atoms, and preferably from 6 to 10 carbon atoms, Y represents a hydrogen atom or a halogen such as chlorine or bromine, and x represents an integer or a fraction which may be of any value from 1 to 3.
The catalysts and the cocatalysts are advantageously used in amounts such that the atomic ratio between the metals of groups II and III of the cocatalysts and the titanium of the catalysts is from 1 to 50. The cocatalysts may be introduced into the reactor in different ways. Thus, the organo-aluminium cocatalysts, which are generally liquids under normal temperature and pressure conditions~ may be introduced directly into the reactor in the liquid condition, or may first be vapourised. The cocatalysts may be introduced into the reactor after they have been brought into contact with the catalyst or with the prepolymer.
The copolymers of the invention have a density which is from 0.900 to 0.945 g/cm3, a breadth of distribution of molecular weights of from 2 to 11, and a coefficient of fusion which is capable of being as low as 0.1 or as high as 30.
The properties of these copolymers vary in particular according to their content of units derived from the higher alpha-olefin. Generally, the higher the proportion of higher alpha-olefin, the lower is the density of the copolymers. For example, copolymers which contain from about 1 to 7% by weight of units derived from propylene or but-1-ene have a density which is approxi~
mately from 0.945 to 0.930 g/cm3 and their fusion temperature is about 130 to 120C, these copoly~ers are partially soluble in boiling cyclohexane, and the soluble fraction may represent up to 40~ by weight of the copolymer. When )9'3 thecopol~ners contain from about 7 to 33% by weight of units derived from propylene or but-l-ene~ their density is approximately from 0.930 to 0.900 g/cm and their fnsion temperature is from about 120 to 100C. Copolymers containing from about 7 to 33% by weight of units derived from higher alpha-olefin have a relatively high degree of solubility in boiling cyclohexane, usually from 40 to 80% by weight. Moreover, the greater the proportion of higher alpha-olefin, the higher is the coefficient of fluidity of the cop-olymers in addition, for a given proportion of higher alpha-olefin, it is possible to increase the coefficient of fluidity of the copolymer by increas-ing the hydrogen content of ~he gaseous mixture. Likewise, the breadth of molecular distribution of the copolymers may be modified by the choicc of the titanium compound or compounds used in the production of the catalyst, and by the choice of the cocatalyst. Thus for e~ample catalysts prepared from titanium compounds containing alkoxy groups result in copolymers which have a narrower breadth of molecular distribution than catalysts prepared from tit-anium halides alone.
The process of the invention therefore makes it possible to pro-duce, directly in the form of powders, copolymers whose higher alpha-olefin content may attain 33% by weight and whose properties such as density, melt-ing temperature, breadth of distribution of molecular masses and coefficient of fusion are capable of being very greatly varied. It is not possible to achieve such a wide range of copolymers by means of the previously known fluidised bed polymerisation processes. It should also be noted that cop-olymerisation of the alpha-olefins within an inert liquid such as n-heptane and in the presence of the catalytic systems used in the invention also does 11~6~ 9 not make it possib.le to produce such a range of copolymersO Indeed, this method of polymerisation within a liquid encounters practical difficulties in carrying out the p:rocess, such difficulties being due in particular to the high viscosity of the polymerisation mediwn and the necessity for separating the polymer from the inert liquidO
It is particularly advantageous for the copolymers of the inven-tion to be used for the production of articles by rotary castingO In this process, the polymer is introduced in the form of a powder into a rotary mould which is heated to a temperature higher than the melting temperature of the polymer; the polymer begins to melt, and spreads over the internal surface of the mould. The moulded article is removed from the mould after cooling of the mould and opening thereofO In accordance with the previously known methods, the copolymer produced in the form of granules had to be subjected to an ex-pensive crushing operation before it could be introduced into the rotary mould.
The copolymers of the invention can also be used for coating substrates such as films of plastics material, fabrics or sheets of paper or cardboard, by virtue of their relatively low melting temperature and their good adhesive propertiesO
Example 1 a) Preparation of a catalystO
The following are successively introduced at a temperature of 25C
into a 1 liter glass flask provided with a mechanical stirrer and a heating and cooling means:
- 500 ml of n-heptane - 906 g of magnesium in powder form (0~40 gram-atom) - 1.2 g of iodineO
While the contents of the Xlask are stirred, the contents are heated 1~6q~99 to 80C, and the following are introduced:
- 9.1 g of titaniwn tetrachloride (48 m.moles) - 13.7 g of tetrapropyltitanate (48 m.moles) - and, over a period of 4 hours, 74.5 g of n~butyl ch]Loride (o.805 mole).
The resuLting precipitate is washed 3 times, with intermediate decan-tation, with 200 ml of n-heptane. After drying, the resulting catalyst is analysed; it contains 8% by weight of titanium.
b) Preparation of a prepolymer The following are introduced into a 5 litre stain]Less steel reactor provided with a mechanical stirrer and a heating and cooling means:
- 1 litre of n-heptane

- 2.1 g of the catalyst prepared in a) above - 1.3 g of tri n-octylaluminium.
The contents of the reactor is raised, while being stirred, to a temperature of 70C. Hydrogen is introduced into the reactor, until the rela-ti~e pressure is 1 bar, and then ethylene is introduced at a flow rate of 100 g/h. After 2 hours 30 minutes of polymerisation, 250 g of a prepolymer is collected, which prepolymer is isolated and then re-suspended in a solution of 2.6 g of tri n-octylalw~nium in 500 ml of n-heptane. The n-heptane is then evaporated.
c) ~Luidised bed polymerisationO
100 g of a pre~iously prepared polyethylene powder is introduced into a fluidised bed reactor which is 15 cm in diameter. The polyethylene powder is fluidised by a gas flow at a temperature of 65C which circulates at a speed of rise of 20 cm/s (calcu]Lated in relation to the empty reactor)O This gas q.~

flow compIises a m~Yture, by volume, of 40% ethylene, 40% propylene and 20%
hydrogen. The prc:polymer prepared in b) above is introduced into the reactor in 5 g portions, every 12 minutes. It is noted that about 800 g/h of polymer is formed. A part; of the polymer is periodically removed from the reactor, in order to leave on]y about 2 kg in the reactor~ After 3 hours of polymerisation, a sample of the polymer, in the form of a white non-sticky powder, is drawn off. The physical characteristics of this polymer are set out in Table I.
Examples 2 to 7 Operation is as in 3xample 1 except as regards the composition of the gaseous mixture used in the polymerisation step, This composition~ together with the characteristics of the polymers produced, are set out in Table I.
Examples 8 to 10 Operation is as in Example 1 except as regards the composition of the gaseous mixture used in the polymerisation step, which contains but-1-ene in-stead of propylene. The composition of the gaseous mixture as well as the characteristics of the polymers produced are set out in Table II.
Examples 11 to 13 a) Operation is as in Example la~, except that the catalyst is prepared from 18.2 g (96 m.moles) of titanium tetrachloride (instead of 9.1 g of titanium tetrachloride and 13.7 g of tetrapropyltitanate) and that the temperature at which the catalyst is prepared is 70C instead of 80C. The catalyst produced contains 8.7% by weight of titanium.
b) The prepolymer is prepared in the manner set out in Example lb)~
from 1.9 g of the catalyst above.
c) Polymerisation is effected under the conditions set out in ~11--il~6q~9~

Example 1c). The composition of the gaseous mixture as well as the character-istics of the polyMers produced are set out in Table III
In Tables I to III:
- IF2 is the coefficient of fluidity of the polymer, measured under a load of 2.16 kg, in accordance with Standard ASTM D. 1238.
- % C3 and % C4 de:note the content by weight in the polymer of propylene de-rived units and but~1-ene derived units respectively, as measured by infra-red spectrometry.
- RF is the bending strength, measured in accordance with French Standard BNMP 40-422 A.
- ~is the breadth of molecular distribution, which is equal to the ratio Mw/Mn of the mean molecuLar mass by weight Mw to the mean molecular mass by number Mn, said moLecular masses being calculated after fractionating of the polymer by gel permeation (G.P.C.).

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of powders of copolymers of ethylene and a higher alpha-olefin having from 3 to 6 carbon atoms, which copolymers contain from 1 to 33% by weight of units derived from the higher alpha-olefin and have a density of from 0.900 to 0.945 g/cm3, a breadth of distribution of molecular masses of from 2 to 11, and a coefficient of fusion of from 0.1 to 30 at a temperature of 190°C under 2.16 kg, which comprises polymerisation of a gaseous mixture which contains the olefins to be polymerised and if necessary hydrogen and which circulates upwardly through a fluidized bed of the copolymer in the course of formation, wherein the process is effected in the presence of a catalytic system comprising (i) a co-catalyst formed by at least one organo-metallic compound of a metal group II and III of the periodic table of elements and (ii) a catalyst formed by a solid compound of titanium, magnesium and a halogen, which is produced by reacting at a temperature of from -20 to 150°C
a) one or more tetravalent titanium compounds having the formula TiX4-n(OR)n, wherein X is a chlorine or a bromine atom, R is an alkyl radical which may contain from 2 to 8 carbon atoms, and n is an integer or a fraction which may assume any value between 0 and 4, b) an alkyl halide having the formula RX wherein R and X are as defined above, c) an organo-magnesium compound having the formula RMgX, an organo-magnesium compound having the formula MgR2 or magnesium metal, R and X being as defined above, which various compounds are used in molar ratios such that: when an organo-magnesium compound having the formula RMgX is used as component c);

and when an organo-magnesium compound having the formula MgR2 is used as component c);

and when magnesium metal is used as component c);

and 2. A process as claimed in claim 1 wherein the catalyst is prepared from titanium tetrachloride.

3. A process as claimed in claim 1 wherein the catalyst is prepared from titanium tetrachloride and tetrapropyltitanate used jointly.

4. A process as claimed in claim 1 wherein the higher alpha-olefin is chosen from propylene or but-1-ene.

5. A process as claimed in claim 1 wherein hydrogen is present in the reactor.

5. A process as claimed in claim 1 wherein the solid compound of titanium, magnesium and a halogen are reacted at a temperature of from 60°C to 90°C.

1. A process as claimed in claim 1 wherein when magnesium metal is used as component c) the molar ratios are such that:

and 8. A process as claimed in claim 1 wherein the catalyst is introduced into the reactor in the form of a prepolymer produc-ed by liquid phase polymerization of at least one olefin in an inert liquid in the presence of the halogenated titanium and magnesium compound.

9. A process as claimed in claim 8 wherein the prepolymer contains from 1 g to 500 g of prepolymer per milligram-atom of titanium in the catalyst.

10. A process as claimed in claim 8 wherein the prepolymer containing the catalyst is subjected to at least one solvent extraction step prior to its introduction into the reactor.

11. A process according to claim 1 wherein the pressure within the reactor is from 1 to 40 bars.

12. A process according to claim 1 wherein the co-catalyst comprises at least one organo-aluminum compound of the formula AlR1xY(3-x) wherein R1 represents an alkyl group containing from 1 to 12 carbon atoms, Y represents hydrogen or a halogen, and x represents an integer or a fraction which may be of any value from 1 to 3.

13. Process according to claim 1 or 12 wherein the co-cata-lyst is tri-n-octylaluminum.

14. Process according to claim 1 wherein the catalyst is prepared from magnesium metal and iodine.

15. Process according to claim 1 wherein the catalyst and co-catalyst are used in amounts sufficient to provide an atomic ratio of the metals of groups II and III in the co-catalyst to the titanium in the catalyst of from 1:1 to 1:50.

16. Process according to claim 15 wherein the atomic ratio of the metals in the co-catalyst to the titanium in the catalyst is about 1:3.