Process for polymerization of olefins

Details Process for polymerization of olefins Process for polymerization of olefins

1997-05-14

2001-02-13

Wu, David W. (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S153000, C526S281000, C526S282000, C526S308000, C526S943000, C526S348200, C526S348400, C526S348500, C526S348600, C502S152000

Reexamination Certificate

active

06187882

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for polymerization of olefins. More particularly, it relates to an improved process of polymerization and copolymerization using a solid catalyst capable of giving olefin polymers and copolymers with high catalyst activity especially at high temperatures. Still more particularly, it relates to the process using an improved metallocene catalyst supported with the magnesium halide and silica.
DESCRIPTION OF THE RELATED ART
U.S. Pat. No. 5,032,562, describes the preparation of a solid supported catalyst, by the reaction of dibutyl magnesium, a zirconium based neutral metallocene and a compound of a transition metal halide such as titanium tetrachloride and impregnating the said precursor presence onto silica in the of an aluminoxane activator. However, this catalyst results in bimodal distribution of molecular weights, which is not desirable in most of the applications where polyethylene is used.
JP 04,96,908, describes another supported solid catalyst prepared by reacting aqueous magnesium halides in the presence of silica, metallocene and an organoaluminum activator, which shows only moderate activity towards ethylene polymerization at 80° C.
Eur.Pat.No.EP 613,908, describes a silica-magnesium chloride supported metallocene catalyst which in the presence of an organoboron compound polymerizes ethylene with high yield. However, the catalyst prepared according to this method is not very stable to storage and handling.
During the course of their research the inventors of the present invention have found that the presence of small amounts of anhydrous magnesium chloride (<3%) in the silica supported metallocene catalysts effects unexpected benefits in terms of catalyst activity, molecular weight and molecular weight distributions.
Anhydrous magnesium chloride, commonly used as a support in high activity olefin polymerization catalyst is, often not convenient because it is very brittle and undergoes attrition in the polymerization reactor very easily. Silica is a well known support for gas phase as well as fluidized bed polymerization of olefins using titanium based Ziegler-Natta catalysts; however, when used with metallocene-type catalysts silica supports show low polymerization activities. Therefore, a combination of the two, namely, silica and anhydrous magnesium chloride, offers a good balance to prepare catalysts with high activity, controlled particle size and good attrition strength.
SUMMARY OF THE INVENTION
Therefore, the present invention provides a process for polymerization and copolymerization of olefins using the said solid catalyst capable of producing high catalyst activity. In addition, the process could be carried out especially at high temperatures and capable of being used either in gas or slurry phase.
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes a process for the preparation of improved supported metallocene catalyst which is capable of being employed for the polymerization of the olefins especially ethylene. The said catalyst comprises of atoms of Mg, halides more particularly Cl, an electron donor compound such as tetrahydrofuran, a neutral metallocene and a solid support based on a refractory oxide.
In other words, the solid catalyst prepared as per the present process essentially comprises,
a) a particulate carrier composed of an oxide of at least one selected from among those belonging to the groups II, III, IV of the Periodic Table having a surface area of about 300 m
2
/g and containing at least 3 mmol of hydroxyl group per gram of the oxide.
b) a transition metal compound of a metal belonging to the group IVB of the Periodic Table containing a ligand having a cyclopentadienyl skeleton.
c) a particulate compound magnesium halide has the structure MgX
2
where, X is selected from the group containing Cl, Br, or I.
wherein the magnesium halide and the transition metal compound are supported on the particulate carrier.
Another object of the present invention is to provide a process for the preparation of a solid catalyst capable of being employed for the polymerization of the olefins especially ethylene, said catalyst comprising atoms of Mg, Cl, an electron donor compound such as tetrahydrofuran, a neutral metallocene and a solid support based on a refractory oxide.
Accordingly, the present invention provides a process for the preparation of a supported metallocene catalyst which comprises, preparing a precursor catalyst material which consists of preparing the solution of magnesium halide compound in an electron donor solvent in which the magnesium halide will be completely soluble, heating the solution to a temperature in the range of 65° C. to the boiling point of the respective electron donor for a period ranging between 10 to 60 minutes, separately preparing the solution of the metallocene compound into the same electron donor solvent, heating the solution to a temperature in the range of 25° C. to 70° C. for a period ranging between 0.1 to 0.5 hrs., mixing the two solutions to obtain the homogenous solution of catalyst precursor compound, stirring and maintaining this resulting homogenous solution at a temperature in the range of 50° C. to 70° C. for a period of 0.5 to 2 hrs., separately preparing the slurry of the support in the liquid hydrocarbon medium, heating the slurry to a temperature in the range of 50° C. to 75° C. and stirring it for a period of 0.25 to 2 hrs., mixing the homogenous solution of the catalyst precursor compound with the slurry of the support, stirring the slurry for 0.5 to 3 hrs maintaining at a temperature ranging between 50° C. to 70° C., cooling the resultant slurry to room temperature under inert atmosphere, separating the solid by conventional methods, washing the solid by hydrocarbon solvent, drying the solid under vacuum to obtain the product.
The electron donor solvent used for the preparation of the solution of the magnesium halide may be alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones, alkyl esters of C1 to C4 saturated aliphatic carboxylic acids; alkyl esters of C7 to C8 aromatic carboxylic acids; C2 to C6 or more preferably C3 to C4 aliphatic ethers; C3 to C4 cyclic ethers, C4 mono or di ether are preferred. Most preferred being methyl formate, ethyl acetate, butyl acetate, hexyl ether, tetrahydrofuran, and dioxane.
The magnesium halide used may be such as magnesium chloride, magnesium bromide and magnesium iodide, preferably magnesium chloride.
Further, the metallocene compound used in the above catalyst has a general formula
(Cp)a(Cp)′bMXx
Cp and Cp′ designate each an unsaturated hydrocarbonic radical having a cyclopentadienyl skeleton with a central atom M. The groups Cp and Cp′ can be obtained by a covalent bridge (bond).
M indicates the transition metal which are chosen from the groups IIIB, IVB, VB and VIB of the Periodic Table.
a, b and x designate the integral numbers such as a+b+x=m, x>0, and a and/or b not equal to zero.
m indicates the valency of the transition metal M
X designates a halogen selected from Cl, Br and I.
The transitional element in the metallocene compound may be such as scandium, titanium, zirconium, hafnium and vanadium, preferably zirconium.
The Cp and Cp′ groups in the metallocene compound are a mono- or a polycyclic group having a cyclopentadienyl skeleton substituted with 5 to 50 carbon atoms such as cyclopentadienyl, indenyl, or a fluorenyl radical or a derivative substituted by this radical containing up to 10 carbon atoms, or a radical derived from the elements chosen from the group VA of the Periodic Table, such as N or P.
Refractory oxide support contains hydroxyl functional groups and may have a specific surface area (BET) of 50 to 1000 m
2
/g, especially, from 100 to 400 m
2
/g and a pore vol. of 0.5 to 5 ml/g preferably, from 1 to 3 ml/g.
In yet another embodiment of the present invention, the support may be selected from inert porous materials such as dry powders of oxides of silicon o

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