Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Reexamination Certificate
1995-11-09
2002-11-26
Wu, David W. (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...
C502S111000, C502S115000, C502S117000, C502S120000, C502S125000, C526S114000, C526S119000, C526S124500, C526S124600, C526S129000, C526S160000, C526S943000
Reexamination Certificate
active
06486089
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the production of bimetallic catalyst systems for ethylene polymerization reactions. The catalysts contain two types of transition metals and produce polyethylene resins with broad and/or bimodal molecular weight distribution (MWD) in a single reactor. In a preferred embodiment, the invention relates to the production of titanium/zirconium-based bimetallic catalyst systems that produce broad and/or bimodal MWD polyethylene resins in a single reactor. In the most preferred embodiment, the low molecular weight (LMW) component in the resin is produced by the Zr active centers, while the high molecular weight (HMW) component is produced by the Ti active centers. The relative productivity of the two active centers determines the ratio of the HMW and the LMW components in the final resin.
This invention particularly relates to a new procedure for preparing bimetallic catalysts. This procedure results in bimetallic catalysts with a more uniform inter-particle distribution of the metals. With increasing uniformity in inter-particle distribution of the metals, the gel content in polyethylene resins decreases. The bimetallic catalysts are used in (co)polymerization reactions to produce high molecular weight polyethylene product. Gels are attributable to high molecular weight components in the resins which are substantially greater in molecular weight than the surrounding matrix resin. The presence of gels in a resin results in poor appearance when the resin is fabricated into film. The presence of gels also interferes with the uniform printing on films. Films possessing very high gel levels also suffer in some film performance characteristics, such as tensile strength.
SUMMARY OF THE INVENTION
This invention relates to supported titanium-zirconium bimetallic catalysts with an improved inter-particle metal distribution of the Zr active centers and facilitates the scale-up of the catalysts.
This invention also includes a new procedure for preparing bimetallic catalysts. This procedure results in bimetallic catalysts with a more uniform inter-particle distribution of transition metal(s). The process comprises
(1) providing silica which is porous and has a particle size of 1 to 250 microns, having pores which have an average diameter of 50 to 500 Angstroms and having a pore volume of 0.5 to 5.0 cc/g;
(2) slurrying the silica in an aliphatic solvent having a boiling point lower than 110° C.;
(3) providing a volume of a solution comprising a metallocene complex, alumoxane of formulas R—(Al(R)—O—)
x
—AlR
2
for oligomeric linear alumoxanes and (—Al(R)—O—)
y
for cyclic alumoxanes wherein x is 1-40, y is 3-40, and R is a C
1
-C
8
alkyl group in an aromatic solvent wherein the volume of the solution is lower than that required to form a slurry of said silica;
(4) contacting the silica with said volume of said solution (3) and allowing the solution to impregnate the pores of silica, and to disperse the metallocene complex in and on the carrier;
(5) evaporating solvents from the impregnated silica slurry, to recover dry free-flowing catalyst particles.
Catalyst Composition
The invention relates to a supported olefin (co)polymerization catalyst composition which is synthesized to uniformly disperse at least one transition metal component on the support. In preferred embodiments, the catalysts contain at least two transition metals, at least one in the form of a metallocene complex. A second transition metal on the support may be in the form of a non-metallocene component or a second metallocene complex, different from the first mentioned metallocene complex, but is preferably a non-metallocene compound. The catalyst compositions of the invention comprise a cocatalyst comprising an alkyl aluminum compound, such as a trialkylaluminum, free of alumoxane and free of oxygen-containing oligomers and polymers of the alkyl aluminum compounds, and a catalyst precursor comprising a carrier, an alumoxane and at least one metallocene; in one embodiment the catalysts further include a second transition metal source.
In accordance with the invention, these catalysts are made by a process for forming a carrier material impregnated with alumoxane and derivatives thereof comprising the steps
(1) providing silica which is porous and has a particle size of 1 to 250 microns, having pores which have an average diameter of 50 to 500 Angstroms and having a pore volume of 0.5 to 5.0 cc/g;
(2) slurrying the silica in an aliphatic solvent having a boiling point less than 110° C., preferably by stirring at a temperature in the range of 20 to 25° C.;
(3) providing a volume of a solution comprising a metallocene, alumoxane of formulas R—(Al(R)—O—)
x
—AlR
2
for oligomeric linear alumoxanes and (—Al(R)—O—)
y
for cyclic alumoxanes wherein x is 1-40, y is 3-40, and R is a C
1
-C
8
alkyl group in an aromatic solvent, wherein the concentration of alumoxane, expressed as Al weight percent is 5 to 20; and wherein the volume of the solution is sufficient to impregnate the pores of silica without forming a slurry of the silica in the solvent;
(4) contacting the silica with said volume of said solution (3);
(5) evaporating solvents from the impregnated silica to recover dry free-flowing catalyst particles.
The metallocene complex becomes more uniformly distributed throughout the support as a result of steps (2) and (4). When two transition metal sources exhibiting different hydrogen responses in ethylene polymerization reactions are supported on the carrier subjected to the process of the invention, the result of the catalyst preparation process is an olefin polymerization catalyst composition which produces less gels in the polyethylene film produced from the polyethylene prepared with the catalyst composition. In the process of the invention, step (2) may be undertaken prior to or after (4).
The carrier material is a solid, particulate, porous, preferably inorganic material, such as an oxide of silicon and/or of aluminum. The carrier material is used in the form of a dry powder having an average particle size of from about 1 micron to about 500 microns, preferably from about 10 microns to about 250 microns. The surface area of the carrier is at least about 3 square meters per gram (m
2
/g), and preferably at least about 50 m
2
/g up to about 350 m
2
/g. The carrier material should be free of absorbed water. Drying of the carrier material can be effected by heating at about 100° C. to about 1000° C., preferably at about 600° C. When the carrier is silica, it is heated to at least 200° C., preferably about 200° C. to about 850° C. and most preferably at about 600° C. The carrier material must have at least some active hydroxyl (OH) groups to produce the catalyst composition of this invention.
In the most preferred embodiment, the carrier is silica which, prior to the use thereof in the first catalyst synthesis step, has been dehydrated by fluidizing it with nitrogen and heating at about 600° C. for about 4-16 hours to achieve a surface hydroxyl group concentration of about 0.7 mmol/g. The silica of the most preferred embodiment is a high surface area, amorphous silica (surface area=300 m
2
/g; pore volume of about 1.65 cm
3
/g), and it is a material marketed under the tradenames of Davison 952 or Davison 955 by the Davison Chemical Division of W. R. Grace and Company. The silica is in the form of spherical particles and obtained by the spray-drying process. As procured, these silicas are not calcined; and this must be dehydrated, as indicated above.
The catalyst synthesis is undertaken under inert conditions in the absence of water and oxygen.
The carrier material having said OH groups is slurried in a non-polar solvent. The slurry of the carrier material is prepared by introducing the carrier into the solvent, preferably while stirring, and heating the mixture to about 25 to about 70° C., preferably to about 40 to about 60° C. Temperature of the slurry is critical with respect to the activity of the catalyst components added to it. All catalyst precursor synthesis steps should
Kissin Yury V.
Mink Robert I.
Nowlin Thomas E.
Schregenberger Sandra D.
Shirodkar Pradeep P.
ExxonMobil Oil Corporation
Milbank Mandi B.
Prodnuk Stephen D.
Rabago R.
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