Cooling and pelletizing process for semi-crystalline polymers

Patent metadata

Field	Value
Publication number	US-9296837-B2
Application number	US-201213466182-A
Country	US
Kind code	B2
Filing date	May 8, 2012
Priority date	Jun 17, 2011
Publication date	Mar 29, 2016
Grant date	Mar 29, 2016

Abstract

Methods and systems for pelletizing low molecular weight semi-crystalline polymers are provided herein. Polymer compositions comprising the semi-crystalline polymer and a solvent are provided to a devolatilizing device, where the solvent is at least partially evaporated under vacuum conditions, resulting in removal of heat from the polymer by evaporative cooling and crystallization of the polymer. Once the polymer has reached the desired temperature, the polymer exits the devolatilizer and is pelletized. Semi-crystalline polymers that may be used in the present invention include propylene-based copolymers, such as propylene-ethylene and propylene-hexene copolymers having a heat of fusion, Hf, from about 5 to about 75 J/g and a weight average molecular weight, Mw, from about 10,000 to about 200,000 g/mol.

First claim

We claim:

1. A process for pelletizing a semi-crystalline polymer, the process comprising:
a. providing a vessel having an inlet and an outlet;
b. introducing a first polymer composition comprising a semi-crystalline polymer and a solvent into the inlet of the vessel;
c. subjecting the first polymer composition to a vacuum in the vessel such that at least a portion of the solvent is removed from the first polymer composition and the temperature of the first polymer composition is reduced, forming a second polymer composition comprising the semi-crystalline polymer and having a lower solvent content and a lower temperature than the first polymer composition;
d. discharging the second polymer composition from the outlet of the vessel;
e. feeding the second polymer composition to a pelletizer; and
f. discharging a pelletized polymer product from the pelletizer,
wherein the second polymer composition comprises less than or equal to about 1 wt % solvent, and the relationship between the temperature of the second polymer composition at the outlet of the vessel (Tf) and the first crystallization temperature of the semi-crystalline polymer (Tc1) satisfies the formula Tf≦Tc1+60 wherein Tf and Tc1 are in degrees Celsius.

2. The process of claim 1 , wherein the semi-crystalline polymer has a melting point of greater than 30° C. and a heat of fusion greater than 5 J/g and less than about 70 J/g.

3. The process of claim 1 , wherein the semi-crystalline polymer has viscosity at 190° C. of less than 20,000 cP.

4. The process of claim 1 , wherein the pelletizer comprises a pelletization die and wherein the pelletization die temperature (Td) satisfies the formula Tc1−30≦Td≦Tc1+30 wherein Td is in degrees Celsius.

5. The process of claim 1 , wherein the semi-crystalline polymer has an Mw from about 10,000 to about 200,000.

6. The process of claim 1 , wherein the second polymer composition has a viscosity from about 5,000 to about 500,000 cP.

7. The process of claim 1 , wherein the relationship between the temperature of the second polymer composition at the outlet of the vessel (Tf) and the crystallization temperature of the first semi-crystalline polymer (Tc1) satisfies the formula Tc1−30≦Tf≦Tc1+60.

8. The process of claim 1 , wherein the vessel further comprises:
a. at least one vacuum port and at least one stirrer shaft port;
b. a stirrer shaft passing through the at least one stirrer shaft port, wherein the stirrer shaft has an external portion outside of the vessel and an internal portion extending into the vessel, the internal portion of the stirrer shaft comprising an agitating means;
c. a stirrer shaft seal associated with each stirrer shaft port for sealing against the stirrer shaft; and
d. at least one motor located outside the vessel for rotating the stirrer shaft.

9. A process for the production of polymer pellets comprising:
a. providing a devolatizer having an inlet and an outlet;
b. providing a polymer composition comprising a semi-crystalline polymer and a solvent to the inlet of the devolatizer;
c. conveying the polymer composition through the devolatizer from the inlet to the outlet;
d. maintaining the temperature and pressure within the devolatizer such that a vacuum is created sufficient to remove at least a portion of the solvent from the polymer composition by evaporation and such that the temperature of the polymer composition at the outlet of the devolatizer is lower than the temperature of the polymer composition at the inlet of the devolatizer;
e. removing the polymer composition from the outlet of the devolatizer; and
f. pelletizing the polymer composition.

10. The process of claim 9 , wherein the relationship between the temperature of the polymer composition at the outlet of the vessel (Tf) and the first crystallization temperature of the semi-crystalline polymer (Tc1) satisfies the formula Tf≦Tc1+60.

11. The process of claim 9 , wherein the temperature of the polymer composition at the outlet of the devolatizer is at least about 10° C. lower than the temperature of the polymer composition at the inlet of the devolatizer.

12. The process of claim 9 , wherein the polymer composition at the outlet of the vessel comprises less than 1 wt % solvent.

13. The process of claim 9 , wherein the polymer composition is pelletized in an underwater pelletizer.

14. The process of claim 9 , wherein the semi-crystalline polymer comprises propylene and has an Mw from about 10,000 to about 200,000, a melting point from about 30° C. to about 110° C., and a heat of fusion from about 5 to about 70 J/g.

15. The process of claim 14 , wherein the semi-crystalline polymer is a copolymer of propylene and ethylene, a copolymer of propylene and hexene, or a mixture thereof.

16. The process of claim 9 , wherein the viscosity of the polymer composition at the outlet of the devolatizer is from about 5,000 to about 500,000 cP.

Assignees

• Wang Yu F
• Mitchell Cynthia A
• Venditte Lisa B V
• Rodriguez George
• Datta Sudhin
• Exxonmobil Chem Patents Inc

Inventors

• Wang Yu F
• Mitchell Cynthia A
• Venditte Lisa B V
• Rodriguez George
• Datta Sudhin

Classifications

• C08J3/12

  Powdering or granulating · CPC title

• B29C48/39

  a first extruder feeding the melt into an intermediate location of a second extruder · CPC title

• B29B9/065

  under-water, e.g. underwater pelletizers · CPC title

• C08J2323/14

  Copolymers of propene (C08J2323/16 takes precedence) · CPC title

• C08F6/005 Primary

  from solid polymers · CPC title