# US 7,745,551 B2 · Low gel chromium catalysis

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- Number: US 7,745,551 B2
- Document ID: US7745551B2
- Status: Granted
- Kind: B2
- Application number: 11/501,183
- Filed: 2005-02-08
- Published: 2008-10-16
- Granted: 2010-06-29
- Earliest claimed: 2004-02-13
- Assignees: Total Petrochemicals Research Feluy
- Inventors: Philippe Bodart; Philippe Marechal; Eric Damme
- Web page: https://patentgrep.com/patent/US7745551B2

## CPC

- C08F 10/00: Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F 10/02: Ethene
- C08F 210/16: Copolymers of ethene with alpha-alkenes, e.g. EP rubbers
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS

## Abstract

The present invention discloses the use of a chromium-based catalyst system in two serially connected loop reactors for copolymerising ethylene and a comonomer, at reduced productivity, the final polyethylene having a reduced amount of gel.

## Claims

### Claim 1

A method for the polymerization of ethylene in a double loop reactor system comprising first and second interconnected loop reactors comprising:
a) introducing an ethylene monomer, and a diluent carrier liquid into a first loop reactor of said reactor system;
b) supplying a polymerization catalyst system comprising a supported chromium-based catalyst component to said first loop reactor;
c) circulating said diluent liquid and ethylene monomer through said first loop reactor while polymerizing said ethylene monomer in the presence of said catalyst system to produce a slurry of polymer fluff particles in said diluent carrier liquid;
d) withdrawing said slurry from said first loop reactor and supplying said withdrawn slurry to said second loop reactor;
e) introducing an ethylene monomer and a diluent carrier liquid into said second loop reactor;
f) circulating said diluent liquid and ethylene monomer through said second loop reactor while polymerizing said ethylene monomer in the presence of said catalyst system to produce a slurry of polymer particles in said diluent in said second reactor;
g) controlling the polymerization conditions in said first and second reactors to produce a final ethylene polymer at a productivity of less than 3500 grams of polymer per gram of catalyst component and wherein said first and second reactors are operated under conditions such to produce a polymer having a mono modal polydispersity, such conditions comprising operating the first and second reactors at substantially the same temperature;
h) recovering said ethylene polymer from said second loop reactor.

### Claim 2 (depends on 1)

The method of claim 1 wherein said first and second reactors are operated under polymerization conditions to produce a productivity of less than 2500 grams of polymer per gram of catalyst component.

### Claim 3 (depends on 2)

The method of claim 2 wherein the productivity of said polymerization reaction in said second reactor is less than the productivity of said polymerization reaction in said first reactor.

### Claim 4 (depends on 2)

The method of claim 2 wherein said ethylene polymer is a homopolymer.

### Claim 5 (depends on 1)

The method of claim 1 further comprising supplying a C3+ olefin comonomer into said first and second reactors to produce a copolymer of ethylene and said alpha olefin comonomer.

### Claim 6 (depends on 5)

The method of claim 5 wherein said alpha olefin comonomer has from 3 to 8 carbon atoms.

### Claim 7 (depends on 6)

The method of claim 6 wherein said comonomer is 1-hexene.

### Claim 8 (depends on 1)

The method of claim 1 further comprising processing the ethylene polymer recovered from a said second loop reactor to prepare a film having a gel content of no more than 30 ppm.

### Claim 9 (depends on 1)

The method of claim 1 further comprising processing the ethylene polymer recovered from second loop reactor to prepare a film having a gel content of no more than 600 gels per square meter of said film.

### Claim 10 (depends on 1)

The method of claim 1 wherein said supported catalyst component comprising a titania containing support and has a chromium content in the range of 0.5-5 weight percent.

### Claim 11 (depends on 10)

The method of claim 10 wherein said catalyst component comprises at least 1 weight percent titania.