Processes and apparatus for bimodal slurry polymerization

Patent metadata

Field	Value
Publication number	US-11117979-B2
Application number	US-202016998251-A
Country	US
Kind code	B2
Filing date	Aug 20, 2020
Priority date	Sep 13, 2019
Publication date	Sep 14, 2021
Grant date	Sep 14, 2021

Abstract

Processes and apparatus for preparing bimodal polymers are provided. In some embodiments, processes include introducing a monomer, a first diluent, a catalyst, hydrogen, at a first hydrogen concentration, and optional comonomer, to a first loop reactor to produce, under polymerization conditions, a first slurry of polymer solids. Processes may also include continuously discharging the first slurry of polymer solids from the loop reactor as a first polymerization effluent to a first flash tank; separating the first polymerization effluent in the first flash tank to provide a first concentrated polymer slurry with significantly lower hydrogen concentration; and transferring the first concentrated polymer slurry from the flash tank to a re-slurry mixer. Processes may further include introducing a re-slurry mixer diluent to the first concentrated polymer slurry to form a second concentrated polymer slurry in the re-slurry mixer that can be pumped to a second slurry loop reactor.

First claim

What is claimed is:

1. A process for preparing polymers comprising:
introducing a monomer, a first diluent, a catalyst, hydrogen and optional comonomer to a first loop reactor to produce, under polymerization conditions, a first slurry of polymer solids having a first hydrogen concentration and comprising polymers having a molecular weight;
discharging the first slurry of polymer solids from the loop reactor as a first polymerization effluent to a first flash tank, wherein the first flash tank has a seal chamber configured to maintain a volume of a first concentrated polymer slurry to maintain a seal;
separating the first polymerization effluent in the first flash tank to vaporize from about 50% to about 100% of the first diluent and provide a flash vapor comprising the first diluent and unreacted monomer, and to provide the first concentrated polymer slurry, wherein hydrogen is present in the first concentrated polymer slurry at a second hydrogen concentration that is lower than the first hydrogen concentration;
transferring the first concentrated polymer slurry from the first flash tank to a re-slurry mixer;
introducing a second diluent to the first concentrated polymer slurry to form a second concentrated polymer slurry in the re-slurry mixer; and
discharging the second concentrated polymer slurry from the re-slurry mixer into a second loop reactor.

2. The process of claim 1 , wherein introducing the monomer, the first diluent, the catalyst, and hydrogen is performed at a temperature of from about 50° C. to about 120° C. and/or a pressure of from about 200 psig to about 800 psig.

3. The process of claim 1 , wherein the monomer is ethylene; and further wherein the first and second diluent are each a C 3 -C 5 saturated aliphatic hydrocarbon.

4. The process of claim 3 , wherein the first and second diluent are each isobutane.

5. The process of claim 1 , further comprising introducing a co-catalyst to the first loop reactor, wherein the co-catalyst is selected from trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tripropylaluminum, or tributylaluminum.

6. The process of claim 1 , further comprising introducing a reversible poison to the polymer slurry stream exiting the first loop reactor.

7. The process of claim 6 , wherein the reversible poison is carbon monoxide.

8. The process of claim 1 , wherein introducing the monomer comprises operating the first loop reactor at a space time yield of about 2.6 lbs/hr-gal or greater.

9. The process of claim 1 , wherein the first slurry of polymer solids comprises a homopolymer having a GPC molecular weight distribution with a Mw value of from 10,000 g/mol to about 100,000 g/mol, Mn value of from 3,000 g/mol to about 30,000 g/mol, Mz value of from about 20,000 to about 200,000 g/mol, and PDI of from 2.0 to 8.0, and a density of from about 0.930 g/cm 3 to about 0.980 g/cm 3 .

10. The process of claim 1 , wherein separating the first polymerization effluent comprises operating the first flash tank at a pressure of from about 75 psig to about 200 psig.

11. The process of claim 1 , further comprising transferring the flash vapor from an overhead portion of the first flash tank to a separator and condensing the flash vapor without compression.

12. The process of claim 11 , wherein condensing the flash vapor is performed using a heat exchanger, and wherein the process further comprises introducing a condensed liquid to an accumulator and venting the accumulator to remove one or more poisons, wherein condensing the flash vapor forms the condensed liquid, and wherein the condensed liquid is returned to the first loop reactor.

13. The process of claim 12 , further comprising removing one or more catalyst poisons from the condensed liquid accumulator drum before the condensed liquid is returned to the first loop reactor.

14. The process of claim 1 , wherein discharging the first slurry of polymer solids further comprises heating the first polymerization effluent in a line heater before the first polymerization effluent enters the first flash tank.

15. The process of claim 1 , wherein introducing the second diluent to the first concentrated polymer slurry comprises operating the re-slurry mixer at a pressure equal to or lower than the pressure of the first flash tank.

16. The process of claim 1 , further comprising:
introducing a second monomer, a comonomer and a third diluent, to the second loop reactor, to produce, under polymerization conditions, a second slurry of polymer solids comprising copolymers having a second molecular weight, wherein the second slurry of polymer solids has a third hydrogen concentration lower than the first hydrogen concentration; and
introducing a second co-catalyst to the second loop reactor, wherein the second co-catalyst is selected from trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tripropylaluminum, or tributylaluminum.

17. The process of claim 16 , wherein the second monomer is ethylene and the comonomer is one or more C 4 -C 8 alpha-olefin comonomers; and further wherein the third diluent is isobutane.

18. The process of claim 16 , further comprising.

19. A process for preparing polymers comprising:
introducing a first monomer, a first diluent, a catalyst, co-catalyst, optional comonomer, and optional hydrogen in a first loop reactor to produce, under polymerization conditions, a first slurry of polymer solids comprising a first polymer;
discharging the first slurry of polymer solids from the first loop reactor as a first polymerization effluent to a first flash tank, wherein the first flash tank has a seal chamber configured to maintain a volume of a first concentrated polymer slurry to maintain a seal;
separating the first polymerization effluent in the first flash tank to provide a first flash vapor comprising the first diluent and unreacted first monomer, and to provide a first concentrated polymer slurry in the first flash tank seal chamber;
transferring the first concentrated polymer slurry from the first flash tank seal chamber to a re-slurry mixer;
introducing a second diluent to the first concentrated polymer slurry to form a second concentrated polymer slurry;
transferring the second concentrated polymer slurry from the re-slurry mixer to a second loop reactor via one or more pumps in series;
introducing a second monomer and hydrogen to a third diluent in the second loop reactor to produce a second slurry of polymer solids comprising a second polymer; and
discharging the second slurry of polymer solids from the second loop reactor as a second polymerization effluent to a second flash tank.

20. The process of claim 19 , further comprising:
separating the second polymerization effluent in the second flash tank to provide a second flash vapor comprising the third diluent and unreacted second monomer, and to provide a third concentrated polymer slurry in a seal chamber of the second flash tank; and
transferring the second concentrated polymer slurry from the seal chamber to a third flash tank or a low pressure purge column.

21. The process of claim 20 , wherein high molecular weight polymers are formed in the first loop reactor and low molecular weight polymers are formed in the second loop reactor; and further wherein the second slurry of polymer solids comprises a bimodal polymer composition of the first polymer and the second polymer.

22. The process of claim 19 , wherein:
the first p

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Trapp Keith W
• Roger Scott T
• Kendrick James A
• Smith Edward F

Classifications

• C08F210/16

  Copolymers of ethene with alpha-alkenes, e.g. EP rubbers · CPC title

• C08F110/02

  Ethene · CPC title

• C08F10/02 Primary

  Ethene · CPC title

• C08F10/00

  Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond · CPC title

• C08F6/10

  Removal of volatile materials, e.g. solvents {(C08F6/001, C08F6/003, C08F6/005, C08F6/006, C08F6/008, C08F6/02, C08F6/04 take precedence)} · CPC title