On-line control of molecular weight in continuous solid state polymerization processes
View Patent ↗Methods of on-line control of molecular weight in continuous solid state polymerization processes. The solid state polymerization process can be a polyester process or to a polyamide process, and more specifically a poly(ethylene terephthalate) (PET) or a poly(butylene terephthalate) (PBT) or a nylon 6,6 continuous solid-state polymerization (SSP) process. An in-line viscometer melts and measures the molecular weight of the SSP resin and adjusts one or more of the process variables, i.e. reactor time, inert gas purity and inert gas temperature to maintain a constant resin molecular weight.
1. A method of controlling the molecular weight of a solid phase polymerized polycondensation polymer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP polymer chips from the exit of a SSP reactor,
b) controlling the SSP reactor residence time with the melt viscosity output value, and
c) repeating steps a and b to.
2. The method of claim 1 wherein said polymer is a polyester.
3. The method of claim 2 wherein said polyester is poly(ethylene terephthalate).
4. The method of claim 2 wherein said polyester is a copolyester of poly(ethylene terephthalate) containing up to 15 mole % of a comonomer.
5. The method of claim 1 wherein said polymer is a polyamide.
6. The method of claim 5 wherein said polyamide is selected from poly(hexamethylene adipamide) and poly(caprolactam).
7. A method of controlling the molecular weight of a solid phase polymerized polycondensation polymer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP polymer chips from the exit of a SSP reactor,
b) controlling the SSP reactor inert gas purity with the melt viscosity output value,
c) and repeating steps a and b.
8. The method of claim 7 wherein said polymer is a polyester.
9. The method of claim 8 wherein said polyester is poly(ethylene terephthalate).
10. The method of claim 8 wherein said polyester is a copolyester of poly(ethylene terephthalate) containing up to 15 mole % of a comonomer.
11. The method of claim 7 wherein said polymer is a polyamide.
12. The method of claim 11 wherein said polyamide is selected from poly(hexamethylene adipamide) and poly(caprolactam).
13. The method of claim 7 wherein the said inert gas is nitrogen.
14. A method of controlling the molecular weight of a solid phase polymerized polycondensation polymer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP polymer chips from the exit of a SSP reactor,
b) controlling the SSP reactor inert gas temperature with the melt viscosity output value, and
c) repeating steps a and b.
15. The method of claim 14 wherein the polymer is a polyester.
16. The method of claim 15 wherein said polyester is poly(ethylene terephthalate).
17. The method of claim 15 wherein said polyester is a copolyester of poly(ethylene terephthalate) containing up to 15 mole % of a comonomer.
18. The method of claim 14 wherein said polymer is a polyamide.
19. The method of claim 18 wherein said polyamide is selected from poly(hexamethylene adipamide) and poly(caprolactam).
20. The method of claim 14 wherein said inert gas is nitrogen.
21. A method of controlling the molecular weight of a solid phase polymerized polycondensation polymer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP polymer chips from the exit of a SSP reactor, and
b) controlling the at least two SSP reactor values selected from the group consisting of: (i) reactor residence time; (ii) inert gas temperature; and (iii) inert gas purity, with the melt viscosity output value, and
c) repeating steps a and b.
22. The method of claim 21 wherein said polymer is polyester.
23. The method of claim 22 wherein said polyester is poly(ethylene terephthalate).
24. The method of claim 22 wherein said polyester is a copolyester of poly(ethylene terephthalate) containing up to 15 mole % of a comonomer.
25. The method of claim 21 wherein said polymer is a polyamide.
26. The method of claim 25 wherein said polyamide is selected from poly(hexamethylene adipamide) and poly(caprolactam).
27. The method of claim 21 wherein said inert gas is nitrogen.
28. A method of controlling the molecular weight of a solid phase polymerized PET or PET copolyesters using a SSP viscometer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP PET or PET copolyester polymer chips from the exit of a SSP reactor,
b) controlling the SSP reactor residence time with the melt viscosity output value, and
c) repeating steps a and b,
wherein the PET or PET copolyester has a more than 20% reduction in a coefficient of variation of the average daily solution IV over a 120 day time period compared to the coefficient of variation of the average daily solution IV of the PET or PET copolyester over the same time period, not using the SSP viscometer to control the molecular weight.
29. A method of controlling the molecular weight of a solid phase polymerized PET or PET copolyesters using a SSP viscometer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP PET or PET copolyester polymer chips from the exit of a SSP reactor,
b) controlling the SSP reactor inert gas purity with the melt viscosity output value, and
c) repeating steps a and b,
wherein the PET or PET copolyester has a more than 20% reduction in a coefficient of variation of the average daily solution IV over a 120 day time period compared to the coefficient of variation of the average daily solution IV of the PET or PET copolyester over the same time period, not using the SSP viscometer to control the molecular weight.
30. The method of claim 29 wherein the said inert gas is nitrogen.
31. A method of controlling the molecular weight of a solid phase polymerized PET or PET copolyesters using a SSP viscometer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP PET or PET copolyester polymer chips from the exit of a SSP reactor,
b) controlling the SSP reactor inert gas temperature with the melt viscosity output value, and
c) repeating steps a and b,
wherein the PET or PET copolyester has a more than 20% reduction in a coefficient of variation of the average daily solution IV over a 120 day time period compared to the coefficient of variation of the average daily solution IV of the PET or PET copolyester over the same time period, not using the SSP viscometer to control the molecular weight.
32. The method of claim 31 wherein the said inert gas is nitrogen.
33. A method of controlling the molecular weight of a solid phase polymerized PET or PET copolyesters using a SSP viscometer, comprising:
a) generating a melt viscosity output value by measuring the melt viscosity of SSP PET or PET copolyester polymer chips from the exit of a SSP reactor,
b) controlling at least two SSP reactor values selected from the group consisting of: (i) reactor residence time; (ii) inert gas temperature; and (iii) inert gas purity with the melt viscosity output value, and
c) repeating steps a and b,
wherein the PET or PET copolyester has a more than 20% reduction in a coefficient of variation of the average daily solution IV over a 120 day time period compared to the coefficient of variation of the average daily solution IV of the PET or PET copolyester over the same time period, not using the SSP viscometer to control the molecular weight.
34. The method of claim 33 wherein the said ineli gas is nitrogen.
35. The method of claim 33 , wherein the melt viscosity output value is IVt-x.
36. The method of claim 33 , wherein the melt viscosity output value is IVt-0.
37. The method of claim 33 , wherein the controlling step is done using an open loop control process.
38. The method of claim 1 , wherein controlling the SSP reactor residence time with the melt viscosity output value comprises increasing the SSP reactor residence time when the melt viscosity output value is below a target value, or decreasing the SSP reactor residence time when the melt viscosity output value is above the target value.
39. The method of claim 7 , wherein controlling the SSP reactor inert gas purity with the melt viscosity output value comprises increasing the SSP reactor inert gas purity when the melt viscosity output value is below a target value, or decreasing the SSP reactor inert as purity when the melt viscosity output value is above the target value.
40. The method of claim 1 , wherein repeating steps a and b maintains an hourly coefficient of variation of the melt viscosity output value of less than 0.06%.
41. The method of claim 7 , wherein repeating steps a and b maintains an hourly coefficient of variation of the melt viscosity output value of less than 0.06%.
42. The method of claim 14 , wherein repeating steps a and b maintains an hourly coefficient of variation of the melt viscosity output value of less than 0.06%.
43. The method of claim 21 , wherein repeating steps a and b maintains an hourly coefficient of variation of the melt viscosity output value of less than 0.06%.