High activity ziegler-natta catalyst for high molecular...

Details High activity ziegler-natta catalyst for high molecular... High activity ziegler-natta catalyst for high molecular...

2001-06-25

2004-04-20

Choi, Ling-Siu (Department: 1713)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Plural component system comprising a - group i to iv metal...

C502S113000, C502S103000, C502S115000, C502S104000, C526S348000, C526S144000, C526S137000, C526S123100, C526S124100, C526S124200, C526S124300

Reexamination Certificate

active

06723677

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for preparing Ziegler-Natta catalyst systems, which also contain magnesium. The resulting catalyst is useful in a solution polymerization process and for the preparation of polymers of ethylene, especially homopolymers of ethylene and copolymers of ethylene and higher alpha-olefins. In particular, the invention relates to a method of sequentially reacting the components used to make the catalyst using specific holding times, concentrations and temperature conditions to control the activity of the catalyst and the structural properties of the polymers prepared. Catalyst concentration was not considered in the prior art an important variable for controlling the catalyst activity and polymer properties.
BACKGROUND OF THE INVENTION
Polymers of ethylene, for example, homopolymers of ethylene and copolymers of ethylene and higher alpha-olefins, are used in large volumes for a wide variety of end-uses, for example, in the form of film, fibers, molded or thermoformed articles, pipe, pipe coating and the like. There are two types of processes for the manufacture of polyethylene that involve the polymerization of monomers in an inert liquid medium in the presence of a coordination catalyst viz. those which operate at temperatures below the melting or solubilization temperature of the polymer and those which operate at temperatures above the melting or solubilization temperature of the polymer. The latter are referred to as “solution” processes, an example of which is described in Canadian Patent 660,869 of A. W. Anderson, E. L. Fallwell and J. M. Bruce, which issued Apr. 9, 1963. In a solution process, the process is operated so that both the monomers and polymer are soluble in the reaction medium.
European Patent 0 606 289 B1 granted May 28, 1997 to Zboril describes three procedures for preparing catalyst for solution polymerization process. The difference among the three procedures was the addition sequence of the initial reagents to form the first catalyst component, which is the result of the reaction of magnesium alkyl, first aluminum alkyl, reactive chloride and titanium compound. The second component is formed from the reaction between a second aluminum alkyl and an alcohol. The combination of the first and second components is the final step of the three procedures; however, no claim on catalyst concentration was made in any of the three procedures. In fact it was stated on page 4 at lines 54 through 58 and on page 5 at line 1 that the concentration of the components of the solutions used in the preparation of the catalyst is not critical.
U.S. Pat. No. 5,589,555 issued Dec. 31, 1996 to Zboril et al. describes a process for controlling a solution polymerization process by controlling the composition of the aluminum alkoxy alkyl used in activating the catalyst. The catalyst is prepared reacting a mixture of a dialkyl magnesium compound and a first aluminum compound with a reactive halide and titanium tetrachloride and optionally a vanadium oxytrihalide to make a first component. The resulting mixture is then reacted with a mixture of a second aluminum alkyl compound. The patent does not teach or suggest heating of the reaction product of the first three components to elevated temperatures from 120° C. to 180° C. before adding a second aluminum component.
The specification teaches at column 2 lines 54 through 64 that, optionally the first component may be prepared by reacting (i) the first aluminum alkyl compound, and (ii) the titanium tetrachloride containing optionally vanadium oxytrihalide at temperature of less than 30° C. and heating the resultant admixture to at temperature of 150-300° C. for a period of 5 seconds to 60 minutes before adding (iii) second aluminum alkyl. No magnesium compound is used in this option and the catalyst concentration is considered to be not critical.
U.S. Pat. No. 5,492,876 issued Feb. 20, 1996 to Gillis et al. teaches a process to prepare a catalyst comprising mixing in an inert organic solvent, aluminum compound of the formula AIR
n
X
3−n
where R is a C
1-20
alkyl, cycloalkyl and aryl radical, X is a halogen and n is 1, 2 or 3; with titanium tetrahalide and vanadium oxytrihalide and heating the resulting solution to a temperature from 180° C. to 250° C. for a time from 15 seconds to 5 minutes and cooling the resulting solution to a temperature of less than 100° C. and adding second vanadium oxytrihalide compound to the cooled mixture and then activating the mixture with an additional aluminum compound, preferably an aluminoxane. The present invention does not contemplate the addition of a vanadium oxytrihalide nor does it contemplate the cooling step. Additionally the reference does not teach the presence of a magnesium compound and the use of catalyst concentration as a variable to control catalyst activity and polymer properties.
Typically in the solution polymerization of ethylene catalyst tends to produce lower molecular weight polymer (which is indicated by a higher melt index) and lose activity at high temperatures. Also in producing ethylene copolymers it is desirable to have more and more uniformly distributed co-monomer incorporation which is reflected by a lower density. It is desirable to find a catalyst having a high activity without significantly reducing the molecular weight of the polymer. The present invention seeks to provide such a catalyst.
SUMMARY OF THE INVENTION
The present invention provides a process for preparing an olefin polymerization catalyst comprising. sequentially mixing:
(i) a mixture of a compound of the formula (R
1
)
2
Mg where in R
1
is selected from the group consisting of C
1-6
alkyl radicals and a compound of the formula Al
1
(R
2
)
3
wherein R
2
is selected from the group consisting of C
1-6
alkyl radicals; and HCl or a reactive organic chloride for example but not limited to R
3
Cl wherein R
3
is selected from the group consisting of C
1-6
alkyl radicals and C
6-12
aromatic radicals; and maintaining the resulting mixture at a temperature from 25° C. to 80° C., preferably 40° C. to 60° C. for a period from 60 to 150 seconds, preferably 90 to 120 seconds, at the concentration of R
3
Cl adjusted to obtain the desired polymer properties and catalyst performance; depending on the equipment it is between 5 to 100 mmol/L, preferably between 8 and 70 mmol/L; then
(ii) adding a titanium compound of the formula (R
4
)
a
TiCl
b−a
wherein R
4
is a C
1-6
alkoxy radical and a and b are integers from 0 to 4 and the sum of a+b is 4 and holding the mixture for a time from 20 to 90 seconds, preferably from 30 to 50 seconds at a temperature from 25° C. to 80° C., preferably 40° C. to 60° C., at the concentration of (R
4
)
a
TiCl
b−a
adjusted to obtain the desired polymer properties and catalyst performance; depending on the equipment it is between 0.1 to 10 mmol/L, preferably between 0.1 and 5 mmol/L, most preferably between 0.5 and 5 mmol/L; and
(iii) adding a compound of the formula (R
5
)
2
Al
2
(R
6
) wherein R
5
is a C
1-6
alkyl radical and R
6
is a C
1-6
alkoxy radical and holding the resulting mixture at a temperature from 25° C. to 80° C., preferably 40° C. to 60° C. for a period of time from 5 to 30 seconds, preferably from 3 to 15 seconds. The concentration of (R
5
)
2
Al
2
(R
6
) is not critical and is primarily governed by practical considerations.
The components are added in amounts to provide: an atomic ratio of Mg:Al
1
is from 3:1 to 8:1, most preferably about 4.5:1; the atomic ratio of Cl:Mg is from 1.5:1 to 2.5:1, most preferably about 2:1; the atomic ratio of Al
1
:Ti is from 0.5:1 to 1.5:1, most preferably 0.8:1 to 1.5:1; the atomic ratio of Mg:Ti is from 3:1 to 8:1, preferably from 4:1 to 8:1, most preferably from 4:1 to 6:1; and the atomic ratio of Al
2
:Ti is from 0.5:1 to 2:1, most preferably from 0.75:1 to 1.5:1.
The present invention also provides a process for the solution polymerization of from 80 to 100% of ethylene with from 0 to 20 weight % of one or more C
3-8
alpha-olefins at a tempe

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