Process for polymerization in a fluidized bed reactor
A polymerization process for stable gas phase reactor start-up when making ethylene copolymers having relatively high molecular weight distribution and melt flow ratio.
1. A process for polymerization in a gas phase reactor, the process comprising:
a) fluidizing a bed of polymer particles in a reactor with a gas mixture comprising ethylene and one or more alpha olefin at a first hydrogen concentration [H 2 ] A ;
b) introducing a single site catalyst system to the reactor to initiate a polymerization reaction;
c) polymerizing the ethylene and the one or more alpha olefin at a first reactor temperature, T A to give a first ethylene copolymer with a first melt index, I 2 A , a first melt flow ratio, (I 21 /I 2 ) A , and a first density, d A , until at least one reactor bed volume has turned over, where a reactor bed volume is defined as the volume of the reactor from a reactor distributor bed plate to the top of the fluidized bed; and
d) subsequently reducing the hydrogen concentration and the reaction temperature to a second hydrogen concentration [H 2 ] B and a second reactor temperature T B , respectively, to give a second ethylene copolymer with a second melt index, I 2 B , a second melt flow ratio, (I 21 /I 2 ) B , and a second density, d B ; wherein the first melt index, I 2 A is greater than the second melt index, I 2 B .
2. The process of claim 1 wherein the second melt flow ratio, (I 21 /I 2 ) B is greater than the first melt flow ratio, (I 21 /I 2 ) A .
3. The process of claim 1 wherein the first and second ethylene copolymers each have a melt flow ratio, (I 21 /I 2 ) of from 20 to 50.
4. The process of claim 2 wherein the first and second ethylene copolymers each have a melt flow ratio, (I 21 /I 2 ) of from 20 to 50.
5. The process of claim 1 wherein the first melt flow ratio, (I 21 /I 2 ) A is at least 25.
6. The process of claim 1 wherein the second melt flow ratio, (I 21 /I 2 ) B is at least 30.
7. The process of claim 5 wherein the second melt flow ratio, (I 21 /I 2 ) B is at least 30.
8. The process of claim 1 wherein the first melt flow ratio, (I 21 /I 2 ) A is less than 33.0.
9. The process of claim 1 wherein the second ethylene copolymer has a second melt flow ratio, (I 21 /I 2 ) B of at least 33.0.
10. The process of claim 8 wherein the second ethylene copolymer has a second melt flow ratio, (I 21 /I 2 ) B of at least 33.0.
11. The process of claim 1 wherein the first melt index, I 2 A is greater than 1 g/10 min.
12. The process of claim 1 wherein the second melt index, I 2 B is less than 1 g/10 min.
13. The process of claim 11 wherein the second melt index, I 2 B is less than 1 g/10 min.
14. The process of claim 1 wherein the first density, d A is greater than the second density, d B .
15. The process of claim 1 wherein the first and second ethylene copolymers each have a density of from 0.912 to 0.937 g/cm 3 .
16. The process of claim 14 wherein the first and second ethylene copolymers each have a density of from 0.912 to 0.937 g/cm 3 .
17. The process of claim 1 wherein the second ethylene copolymer has a molecular weight distribution (M w /M n ) which is greater than the molecular weight distribution (M w /M n ) of first ethylene copolymer.
18. The process of claim 1 wherein the first and second ethylene copolymers each have a molecular weight distribution (M w /M n ) of from 3.5 to 6.0.
19. The process of claim 17 wherein the first and second ethylene copolymers each have a molecular weight distribution (M w /M n ) of from 3.5 to 6.0.
20. The process of claim 1 wherein the first reactor temperature, T A and the second reactor temperature, T B differ by at least 2° C.
21. The process of claim 1 wherein the first hydrogen concentration [H 2 ] A and the second hydrogen concentration [H 2 ] B differ by at least 15 ppm.
22. The process of claim 20 wherein the first hydrogen concentration [H 2 ] A and the second hydrogen concentration [H 2 ] B differ by at least 15 ppm.
23. The process of claim 1 wherein the single site catalyst system comprises a phosphinimine catalyst.
24. The process of claim 1 wherein single site catalyst system comprises a phosphinimine catalyst having the formula: (L)(PI)MX 2 , where M is Ti, Zr or Hf; PI is a phosphinimine ligand having the formula R 3 P═N—, where R is independently selected from hydrogen, halogen, and C 1 -C 20 hydrocarbyl; L is a ligand selected from indenyl, or substituted indenyl; and X is an activatable ligand.
25. The process of claim 1 wherein the single site catalyst system comprises a phosphinimine catalyst having the formula:
(1-R 2 -Indenyl)Ti(N═P( t -Bu) 3 )X 2 ;
wherein R 2 is a substituted or unsubstituted alkyl group, a substituted or an unsubstituted aryl group, or a substituted or unsubstituted benzyl group, wherein substituents for the alkyl, aryl or benzyl group are selected from alkyl, aryl, alkoxy, aryloxy, alkylaryl, arylalkyl and halide substituents; and wherein X is an activatable ligand.