Claims
- 1. A method for the removal of lactide from polylactide which comprises evaporating and recovering lactide from a lactide containing gas, wherein a polymer melt traveling through a nozzle forms thin threads the surface area of which is so large that in normal-pressure or vacuum evaporators the lactide evaporates from the polymer rapidly into a hot carrier-gas flow and the polymer settles under gravity on a collecting device, and the hot lactide-containing gas is cooled rapidly in a crystallisation chamber to a temperature below 100° C., where upon the lactide crystallises from gas, forming lactide crystals, which are separated from the gas.
- 2. A method according to claim 1, wherein the nozzle is a perforated nozzle.
- 3. A method according to claim 1, wherein the diameter of the nozzle perforations is 0.1-1.0 mm.
- 4. A method according to claim 1, wherein the diameter of the nozzle perforations is 0.2-0.3 mm.
- 5. A method according to claim 1, wherein the nozzle is a film nozzle.
- 6. A method according to claim 1, wherein the evaporation gas used is hot nitrogen or air.
- 7. A method according to claim 1, wherein the velocity of the drying gas relative to the melt threads is approx. 0.5-1 m/s.
- 8. A method according to claim 1, wherein the retention time of the polymer melt in the dryer is less than 10 s.
- 9. A method according to claim 1, wherein during evaporation the temperature is 150-300° C.
- 10. A method according to claim 1, wherein the cooling is carried out by directing the gas mixture to a gas mixer to which cold air is fed simultaneously.
- 11. A method according to claim 1, wherein the gas mixture is cooled to a temperature of 20-40° C.
- 12. A method according to claim 1, wherein the mixture of crystallized lactide and gas is sprayed into a crystallization chamber, where the lactide crystallizes.
- 13. A method according to claim 1, wherein the crystallized lactide is separated by filtration.
- 14. A method according to claim 1, wherein the recovered lactide is so pure at it can be recycled directly to the process.
- 15. A polylactide from which lactide has been removed by a method according to claim 1 so that the concentration of lactide in the polymer is less than 4% by weight.
- 16. A method according to claim 1, wherein the retention time of the polymer melt in the dryer is less than 5 s.
- 17. A method according to claim 1, where during evaporation the temperature is 200-260° C.
- 18. A polylactide from which lactide has been removed by a method according to claim 1, so that the concentration of lactide in the polymer is less than 2% by weight.
Priority Claims (2)
Number |
Date |
Country |
Kind |
970649 |
Feb 1997 |
FI |
|
970650 |
Feb 1997 |
FI |
|
Parent Case Info
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/FI98/00139 which has an International filing date of Feb. 13, 1998 which designated the United States of America.
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
102e Date |
371c Date |
PCT/FI98/00139 |
|
WO |
00 |
8/13/1999 |
8/13/1999 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO98/36012 |
8/20/1998 |
WO |
A |
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
5378801 |
Reichert et al. |
Jan 1995 |
|
Foreign Referenced Citations (3)
Number |
Date |
Country |
0499747A2 |
Dec 1991 |
EP |
0664309A2 |
Jul 1995 |
EP |
0755956A2 |
Jan 1997 |
EP |