Method for the separation of volatile compounds from viscous products by means of a thin-film evaporator, and polylactide resin

Patent metadata

Field	Value
Publication number	US-11447604-B2
Application number	US-201716346899-A
Country	US
Kind code	B2
Filing date	Nov 3, 2017
Priority date	Nov 8, 2016
Publication date	Sep 20, 2022
Grant date	Sep 20, 2022

Abstract

A method for removing compounds in the gaseous aggregate state from PLA-containing products in the viscous aggregate state by means of a thin-film evaporator. The compounds may be present in the liquid or solid aggregate state in the products under standard conditions. The invention further relates to a polylactide resin prepared in accordance with the method of the invention.

First claim

What is claimed is:

1. A method for removing compounds in gaseous aggregate state from a polymer melt containing polylactide and/or a poly(co)lactide, said melt comprising said compounds in liquid or solid aggregate state, with a thin-film treatment apparatus comprising:
a housing having a heatable and/or coolable housing jacket which surrounds a rotationally symmetrical treatment chamber extending in an axial direction,
at least one inlet port, arranged in an inlet region of the housing, for introducing material to be treated into the treatment chamber,
at least one outlet port arranged in an outlet region of the housing, for discharging the material from the treatment chamber, and
a drivable rotor shaft arranged in the treatment chamber and extending coaxially therewith, for generating a film of the material on an inside face of the housing jacket and for conveying the material from the inlet region to the outlet region, the rotor shaft comprising a central rotor shaft body with rotor blades arranged on the periphery of said body, radially outermost ends of said blades being spaced a distance from the inside face of the housing jacket, and
at least one temperature sensor arranged on the rotor shaft in the treatment chamber for measuring the temperature of the film of material, wherein the at least one temperature sensor is positioned on the rotor shaft for submersion in the film during operation of the thin-film treatment apparatus, the method comprising:
carrying the polymer melt in a viscous aggregate state having a viscosity in a range of 1 to 50,000 Pa·s into the treatment chamber via the at least one inlet port,
generating a film of the polymer melt on the inside face of the housing jacket,
converting at least a portion of the compounds present in the liquid or solid aggregate state in the polymer melt into the gaseous aggregate state,
discharging at least a portion of the compounds in the gaseous aggregate state from the thin-film treatment apparatus,
discharging the polymer melt after treatment in the thin-film treatment apparatus via the at least one outlet port from the thin-film treatment apparatus, and
determining a local temperature value of the film at one or more location with the at least one temperature sensor that is disposed on the rotor shaft and is submerged in the film.

2. The method of claim 1 , including comparing the temperature value determined with a setpoint value and regulating an amount of heat to be removed from or added to the polymer melt depending on the deviation from the setpoint value.

3. The method of claim 2 , including regulating the amount of heat to be removed from or added to the polymer melt at least partly by way of the amount of heat to be removed from or added to the housing jacket and/or by way of a rotary speed of the rotor shaft.

4. The method of claim 1 , wherein the compounds to be removed are selected from the group consisting of lactide, lactic acid, lactic acid dimers, and lactic acid oligomers that are in gaseous form under operating conditions in the thin-film treatment apparatus, water and additives of the polymer synthesis.

5. The method of claim 4 wherein the additives include one or more of catalysts, initiators, or stabilizers.

6. The method of claim 1 , wherein the thin-film treatment apparatus is in the form of a thin-film evaporator, a thin-film drier, or a thin-film reactor.

7. The method of claim 1 , including assigning a signal line to the at least one temperature sensor and passing a signal indicative of temperature from the at least one temperature sensor to an external signal processing apparatus.

8. The method of claim 1 , including a plurality of temperature sensors distributed over the length of the treatment chamber.

9. The method of claim 1 , wherein the rotor blades are operated with a rotary speed of about 0.1 to 10 m/s, and/or the rotor blades are used to set a shear rate of not more than 1000 l/s, the shear rate being the ratio of the peripheral speed to the distance of the rotor blades from the inside wall of the treatment chamber.

10. The method of claim 9 , wherein the rotor blades are operated with a rotary speed of from 0.5 to 2 m/s.

11. The method of claim 9 , wherein the rotor blades are used to set a shear rate of not more than 300 l/s.

12. The method of claim 1 , wherein the interior of the housing jacket includes a housing jacket cavity which is traversed by a flow of a heat transfer medium for the purpose of heating and/or cooling.

13. The method of claim 1 , wherein the housing jacket comprises at least two housing jacket segments which are heated and/or cooled independently of one another.

14. The method of claim 13 , wherein the housing jacket segments each surround a corresponding treatment chamber zone, and temperature sensors are distributed over different treatment chamber zones.

15. The method of claim 1 , wherein the temperature value obtained from the polymer melt is used to adjust the temperature of the heatable and/or coolable housing jacket to a setpoint value, the housing jacket includes at least two housing jacket segments that each possess at least one temperature sensor, and a separate adjustment of the temperature takes place in each of the at least two housing jacket segments by means of a respective measurement value of the temperature of the film of the polymer melt in each respective housing jacket segment.

16. The method of claim 15 , wherein a viscosity of the polymer melt carried into the treatment chamber is at least 300 Pa·s, and further comprising:
adjusting a pressure which is reduced relative to standard conditions to a pressure of below 100 mbar,
discharging compounds in the gaseous aggregate state via the vapour port, and
recovering the discharged compounds in a downstream apparatus configured to recover gaseous compounds from the gaseous aggregate state by condensation and/or desublimation,
wherein the residence time of the polymer melt in the thin-film treatment apparatus is from about 2 to 4 min, and/or the temperature of each of the housing jacket segments is adjusted to a temperature lower than the temperature of the polymer melt fed into the treatment chamber, and temperature-conditioned to a temperature of 130 to 250° C.

17. The method of claim 1 , wherein before the polymer melt is carried into the treatment chamber, one or more of deactivators, additives, stabilizers,_ or mixtures thereof are fed into the polymer melt via a static mixer which is engaged upstream of the thin-film treatment apparatus.

18. The method of claim 1 , including:
reducing a pressure in the thin-film treatment apparatus to less than 100 mbar; and
feeding an inert gas into the atmosphere in the interior of the thin-film treatment apparatus.

19. The method of claim 1 , wherein the amount of the compounds in the polymer melt after passage through the thin-film treatment apparatus is not more than 0.2 times the amount of the compounds before passage through the thin-film treatment apparatus,
wherein the residual lactide content of the polymer melt after passage through the thin-film treatment apparatus is less than 0.5% by weight,
the yellowing of the polymer melt, measured as b* value, during the conduct of the method is increased by not more than 4 scale values,
the yellow coloration of the polymer melt, measured as b* value, after passage through the thin-film evaporator is less than 15, and
during the method a maximum of 50 black specks are formed per kilogram of discharged polymer melt, and/or
the weight-average

Assignees

• Uhde Inventa Fischer Gmbh
• Thyssenkrupp Ag

Inventors

• Mühlbauer Udo
• Hagen Rainer

Classifications

• C08G63/785

  characterised by the apparatus used · CPC title

• C08G63/90 Primary

  Purification; Drying · CPC title

• B01D1/065

  by film evaporating · CPC title

• B01D1/0082

  Regulation; Control · CPC title

• C08G63/08

  Lactones or lactides · CPC title