Method for polymerising ethylene

Details Method for polymerising ethylene Method for polymerising ethylene

2003-05-05

2004-06-01

Cheung, William (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S074000, C526S128000, C526S129000, C526S234000, C526S236000

Reexamination Certificate

active

06743871

ABSTRACT:

The present invention relates to a process for polymerizing ethylene.
It is known to polymerize ethylene by means of metallocene catalysts. Such processes result in the manufacture of polyethylenes having a low bulk density (BD).
Moreover, the use of antistatic agents in industrial polymerization processes is well known. These antistatic agents reduce electrical charges and thus prevent the formation of agglomerates and of deposits on the walls of the polymerization reactors. Patent applications WO 99/61486 and WO 96/11960 disclose processes for polymerizing ethylene using a supported metallocene, an aluminoxane, a trialkylaluminum and a nonionic antistatic agent chosen from diethoxylated tertiary alkylamines, which do not cause coating. Patent application EP 0 803 514 discloses a process for (co)polymerizing propylene using a supported metallocene catalyst, an aluminoxane, a trialkylaluminum and an ionic antistatic agent, which does not cause coating nor the formation of agglomerates.
A process has now been discovered for polymerizing ethylene which makes it possible to obtain polyethylenes of high bulk density with a high catalytic activity and without the walls of the reactor being fouled.
For this purpose, the present invention relates to a process for manufacturing ethylene homopolymers or ethylene copolymers comprising at least 90 mol % of units derived from ethylene, in which process ethylene, and optionally the other monomers, are brought into contact, under polymerizing conditions, with a catalytic system comprising:
(a) a catalytic solid comprising a metallocene of a transition metal of Groups 4 to 6 of the Periodic Table, which contains at least one cyclopentadiene ligand, possibly substituted, deposited on a support;
(b) at least one organoaluminum compound chosen from compounds satisfying the general formula (1)
AlT
x
(Y′)
y
X′
z
  (1)
in which:
T is a hydrocarbon group containing from 1 to 30 carbon atoms,
Y′ is a group chosen from —OR′, —SR′ and NR′R″, where R′ and R″ represent, independently, a hydrocarbon group containing from 1 to 30 carbon atoms,
X′ is a halogen atom,
x is a number satisfying the condition
0<x≦3,
y is a number satisfying the condition 0≦y<3,
z is a number satisfying the conditions 0≦z<3 and x+y+z=3; and
(c) at least one ionic antistatic agent.
According to the present invention, the expression “process for polymerizing ethylene” is understood to mean a process for manufacturing ethylene homopolymers and ethylene copolymers comprising at least 90 mol % of units derived from ethylene. The preferred copolymers are those of ethylene with another alpha-olefin comprising from 3 to 8 carbon atoms. Particularly preferred are ethylene/1-butene and/or ethylene/1-hexene copolymers.
The metallocene used in the process according to the present invention is usually chosen from compounds satisfying the formula
Q
a
(C
5
H
5-d-b
R
1
b
)(C
5
H
5-d-c
R
2
c
)MeXY  (2)
in which:
Q represents a divalent linking group between the two cyclopentadiene ligands (C
5
H
5-d-b
R
1
b
) and (C
5
H
5-d-c
R
2
c
);
a equals 0 or 1;
b, c and d are integers satisfying the conditions 0≦b≦5, 0≦c≦5 and 0≦d≦5 when a equals 0, and 0≦b≦4, 0≦c≦4 and 0≦d≦4 when a equals 1;
R
1
and R
2
each represent hydrocarbon groups containing from 1 to 20 carbon atoms and able to be linked to the cyclopentadiene ring in the form of a monovalent group or able to be connected to each other so as to form a ring adjacent to the cyclopentadiene ring, halogen atoms, alkoxy groups having from 1 to 12 carbon atoms, silicon-containing hydrocarbon groups of formula —Si(R
4
)(R
5
)(R
6
), phosphorus-containing hydrocarbon groups of formula —P(R
4
)(R
5
), nitrogen-containing hydrocarbon groups of formula —N(R
4
)(R
5
) or boron-containing hydrocarbon groups of formula —B(R
4
)(R
5
) in which R
4
, R
5
and R
6
represent hydrocarbon groups containing from 1 to 24 carbon atoms, as long as when b, c or d equals 2 or more and/or a plurality of groups R
1
or R
2
exist, the latter may be identical or different;
Me represents a transition metal of Groups 4 to 6 of the Periodic Table; and
X and Y, which are identical or different, each represent a hydrogen atom, a halogen atom, a hydrocarbon group, an alkoxy group, an amino group, a phosphorus-containing hydrocarbon group or a silicon-containing hydrocarbon group having from 1 to 20 carbon atoms.
The preferred transition metal compounds of formula (2) are generally such that:
Q represents an alkylene group containing 1 or 2 carbon atoms, possibly substituted with alkyl or aryl groups containing from 1 to 10 carbon atoms, or a dialkylgermanium or dialkylsilicon group containing from 1 to 6 carbon atoms;
a equals 0 or 1;
b, c and d are integers satisfying the conditions 0≦b≦5, 0≦c≦5 and 0≦d≦5 when a equals 0, and 0≦b≦4, 0≦c≦4 and 0≦d≦4 when a equals 1;
R
1
and R
2
represent alkyl, alkenyl, aryl, alkylaryl, alkenylaryl or arylalkyl groups containing from 1 to 20 carbon atoms, it being possible for several groups R
1
and/or several groups R
2
to be linked to each other so as to form a ring containing from 4 to 8 carbon atoms;
Me is zirconium, hafnium or titanium; and
X and Y represent halogen atoms or hydrocarbon groups chosen from alkyls, aryls and alkenyls containing from 1 to 10 carbon atoms.
Particularly preferred are metallocenes of formula (2) in which Q is a linking group chosen from dimethylsilyl and diphenylsilyl, ethylene and methylenes and ethylenes substituted with alkyl or aryl groups containing from 1 to 8 carbon atoms. Particularly suitable compounds of formula (2) are compounds in which the ligands (C
5
H
5-d-b
R
1
b
) and (C
5
H
5-d-c
R
2
c
) are chosen from cyclopentadienyls, indenyls and fluorenyls, these possibly being substituted. The catalytic solid (a) usually also includes an activator. The activator is generally chosen from aluminoxanes and ionizing agents.
The term “aluminoxanes” is understood to mean compounds satisfying the formula R
7
—(AlR
7
—O)
m
—AlR
7
2
and the cyclic compounds satisfying the formula (—AlR
7
—O—)
m+2
in which m is a number from 1 to 40 and R
7
is an alkyl or aryl group containing from 1 to 12 carbon atoms. The preferred compounds are chosen from methyaluminoxanes, ethylaluminoxanes, isobutylaluminoxanes and mixtures thereof, and more particularly those in which m is a number from 2 to 20. Most particularly preferred is methylaluminoxane (MAO) in which m is a number from 10 to 18.
The term “ionizing agents” is understood to mean compounds comprising a first part which has the properties of a Lewis acid and is capable of ionizing the metallocene and a second part which is inert with respect to the ionized metallocene and is capable of stabilizing it. As examples of such compounds, mention may be made of triphenylcarbenium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilium tetrakis(pentafluorophenyl)borate, tri(n-butyl)ammonium tetrakis(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, triphenylboron, trimethylboron, tri(trimethylsilyl)boron and organoboroxines.
The amount of activator in the catalytic solid depends on the type of activator used. When the activator is an aluminoxane, the amount of aluminoxane is usually such that the atomic ratio of aluminum coming from the aluminoxane to the transition metal coming from the metallocene is from 2 to 5000. Preferably, this ratio is at least 5, more particularly at least 10. Good results are obtained when this ratio is at least 20. Usually the aluminoxane is employed in amounts such that the aluminum/transition metal atomic ratio is at most 2000, more particular at most 1500. Atomic ratios of aluminum coming from the aluminoxane of [sic] the transition metal of at most 1000 are most particularly preferred. Ratios of at most 300 give good results. When the activator is an ionizing agent, the amount of ionizing agent is usually such that the molar ratio of the

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