Methods for controlling aluminum alkyl feed to a slurry polymerization process

Patent metadata

Field	Value
Publication number	US-9896520-B2
Application number	US-201515305047-A
Country	US
Kind code	B2
Filing date	Apr 28, 2015
Priority date	Apr 28, 2014
Publication date	Feb 20, 2018
Grant date	Feb 20, 2018

Abstract

The present disclosure generally relates to a slurry polymerization process for the preparation of polyethylene in the presence of a Ziegler catalyst and aluminum alkyl co-catalyst in at least one polymerization reactor, in which process suspension medium comprising a concentration of aluminum alkyl co-catalyst is recycled to the polymerization, the concentration of aluminum alkyl co-catalyst in the recycled suspension medium is determined; and the amount of fresh aluminum alkyl co-catalyst fed to the polymerization is adjusted to maintain a targeted aluminum alkyl co-catalyst concentration in the recycled suspension medium.

First claim

We claim:

1. A slurry polymerization process for the preparation of polyethylene in a one polymerization reactor set-up or in a reactor cascade of two or more polymerization reactors comprising the steps of:
a) feeding ethylene, a Ziegler catalyst, fresh aluminum alkyl co-catalyst, a diluent selected from fresh diluent, recycled suspension medium comprising a concentration of aluminum alkyl co-catalyst and mixtures thereof, and optionally amounts of hydrogen and optionally amounts of one or more C 3 to C 10 alpha-olefins to a polymerization reactor;
b) contacting the ethylene, Ziegler catalyst, fresh aluminum alkyl co-catalyst, diluent and optionally the hydrogen and the C 3 to C 10 alpha-olefins in the polymerization reactor at a reactor temperature from 60° C. to 95° C. and a reactor pressure from 0.15 MPa to 3 MPa, thereby forming a slurry product comprising particulate polyethylene and a suspension medium;
c) withdrawing the slurry product from the polymerization reactor;
d) optionally feeding the slurry product to a second polymerization reactor of the reactor cascade, feeding additional amounts of ethylene, diluent selected from fresh diluent, recycled suspension medium comprising a concentration of aluminum alkyl co-catalyst, and mixtures thereof, and optionally additional amounts of hydrogen and of C 3 to C 10 alpha-olefins to the polymerization reactor; contacting the slurry product fed to the polymerization reactor and the additional amounts of ethylene, diluent, and optionally hydrogen and C 3 to C 10 alpha-olefins in the polymerization reactor at a reactor temperature from 60° C. to 95° C. and a reactor pressure from 0.15 MPa to 3 MPa, thereby forming an additional amount of polyethylene in the slurry product;
and withdrawing the slurry product from the polymerization reactor;

e) optionally feeding the slurry product obtained in step d) to a third polymerization reactor of the reactor cascade and repeating the activities of step d);
f) optionally repeating step e) for additional polymerization reactors of the reactor cascade;
g) feeding the slurry product withdrawn from the polymerization reactor of the one polymerization reactor set-up or from the last polymerization reactor of the reactor cascade to a separator;
h) separating in the separator the particulate polyethylene from the suspension medium;
i) recycling at least a part of the suspension medium separated from the slurry product in the separator as recycled suspension medium to the polymerization reactor of the one polymerization reactor set-up or to at least one polymerization reactor of the reactor cascade;
j) determining the concentration of aluminum alkyl co-catalyst in the recycled suspension medium; and
k) adjusting the amount of fresh aluminum alkyl co-catalyst fed to the polymerization reactor of the one polymerization reactor set-up or to the first polymerization reactor of the reactor cascade to maintain a targeted aluminum alkyl co-catalyst concentration in the recycled suspension medium.

2. The process of claim 1 , wherein the targeted aluminum alkyl co-catalyst concentration in the recycled suspension medium is from 0.05 mmol/L to 3 mmol/L.

3. The process of claim 1 , wherein the fresh aluminum alkyl co-catalyst comprises one or more trialkylaluminum compounds.

4. The process of claim 3 wherein the trialkylaluminum compounds are selected from trimethylaluminum, triethylaluminum, tri-isobutylaluminum, and tri-n-hexylaluminum.

5. The process of claim 4 wherein the fresh aluminum alkyl co-catalyst comprises tri-isobutylaluminum or triethylaluminum.

6. The process of claim 5 wherein the fresh aluminum alkyl co-catalyst comprises triethylaluminum.

7. The process of claim 1 , wherein the slurry polymerization process is carried out in a one polymerization reactor set-up.

8. The process of claim 1 , wherein the slurry polymerization process is carried out in a reactor cascade.

9. The process of claim 8 , wherein the reactor cascade system has two reactors.

10. The process of claim 8 , wherein the reactor cascade system has three reactors.

11. The process of claim 8 , wherein the diluent fed to the first reactor of the reactor cascade is fresh diluent.

12. The process of claim 1 , wherein the slurry product withdrawn from the polymerization reactor of the one polymerization reactor set-up or from the last polymerization reactor of the reactor cascade is combined as a first slurry product comprising a first particulate polyethylene and a first suspension medium with at least one additional slurry product comprising a second particulate polyethylene and a second suspension medium, thereby forming a combined slurry product, and the combined slurry product is fed to the separator, thereby separating in the separator the combined particulate polyethylene comprising the first polyethylene and the second polyethylene from the combined suspension medium comprising the first suspension medium and the second suspension medium and recycling at least a part of the combined suspension medium separated from the combined slurry product as recycled suspension medium to the polymerization reactor of the one polymerization reactor set-up or to at least one polymerization reactor of the reactor cascade.

13. The process of claim 1 , wherein the polyethylene has a density in the range of from 0.935 g/cm 3 to 0.970 g/cm 3 .

14. A slurry polymerization process for the preparation of polyethylene in a one polymerization reactor set-up or in a reactor cascade of two or more polymerization reactors comprising the steps of:
a) feeding amounts of ethylene, a Ziegler catalyst, fresh aluminum alkyl co-catalyst, a diluent which is selected from fresh diluent, recycled suspension medium comprising a concentration of aluminum alkyl co-catalyst, and mixtures thereof, and optionally amounts of hydrogen and optionally amounts of one or more C 3 to C 10 alpha-olefins to a polymerization reactor;
b) contacting the amounts of the ethylene, the Ziegler catalyst, the fresh aluminum alkyl co-catalyst, the diluent and optionally the hydrogen and the C 3 to C 10 alpha-olefins in the polymerization reactor at a reactor temperature from 60° C. to 95° C. and a reactor pressure from 0.15 MPa to 3 MPa, thereby forming a slurry product comprising particulate polyethylene and a suspension medium;
c) withdrawing the slurry product from polymerization the reactor;
d) optionally feeding the slurry product to a second polymerization reactor of the reactor cascade, feeding additional amounts of ethylene, diluent selected from fresh diluent, recycled suspension medium comprising a concentration of aluminum alkyl co-catalyst, and mixtures thereof, and optionally additional amounts of hydrogen and of C 3 to C 10 alpha-olefins to the polymerization reactor;
contacting the slurry product fed to the polymerization reactor and the additional amounts of ethylene, diluent, and optionally hydrogen and C 3 to C 10 alpha-olefins in the polymerization reactor at a reactor temperature from 60° C. to 95° C. and a reactor pressure from 0.15 MPa to 3 MPa, thereby forming an additional amount of polyethylene in the slurry product;
and withdrawing the slurry product from the polymerization reactor;
e) optionally feeding the slurry product obtained in step d) to a third polymerization reactor of the reactor cascade and repeating the activities of step d);
f) optionally repeating step e) for additional polymerization reactors of the reactor cascade;
g) feeding the slurry product withdrawn from the polymerization reactor of the one polymerization reactor set-up or from the last polymerization reactor of the

Assignees

• Basell Polyolefine Gmbh

Inventors

• Kuehl Reinhard
• Carvajal Rodrigo
• Meier Gerhardus
• Damm Elke
• Pyman Phil

Classifications

• C08F10/02 Primary

  Ethene · CPC title

• C08F2/01

  characterised by special features of the polymerisation apparatus used · CPC title

• C08F2500/18

  Bulk density · CPC title

• C08F6/003

  from polymer solutions, suspensions, dispersions or emulsions without recovery of the polymer therefrom · CPC title

• C08F2400/02

  Control or adjustment of polymerization parameters · CPC title