Chemical recycling of PLA by alcoholysis
A process for recycling a polymer blend necessarily containing PLA, comprising grinding, compacting, dissolving in a solvent of PLA, removing the undissolved contamining polymers, alcoholysis depolymerisation reaction and purification steps.
1. A process for recycling a polymer blend comprising PLA, characterised in that it comprises the steps of:
a) dissolving the ground and/or compacted polymer blend in a solvent of PLA in order to separate PLA from the other polymers;
b) recovering undissolved polymers for separate and subsequent processing;
c) recovering the PLA solution with a weight ratio PLA/solvent between about 0.5 and about 3.0 and subjecting it to a catalytic alcoholysis reaction, at a temperature between about 80° C. and about 180° C. and a pressure between about 0.05 and about 10 bars, in order to transform PLA into lactic ester; and
d) purifying the lactic ester thus recovered.
2. The process according to claim 1 wherein said solvent of PLA is a lactic ester.
3. The process according to claim 1 , characterised in that dissolving the polymer blend in a lactic ester is carried out at a temperature between the boiling temperature of water and the boiling temperature of the ester at operating pressure, for a period of time sufficient to obtain a weight ratio of PLA/lactic ester between about 0.5 and about 3.0.
4. The process according to claim 3 , characterised in that the operating pressure is between about 0.05 and about 10 bars.
5. The process according to claim 2 , characterised in that the lactic ester is an alkyl lactate, wherein the alkyl radical of the alkyl lactate contains from 1 to 12 carbon atoms.
6. The process according to claim 4 , characterised in that the alkyl lactate is selected from the group consisting of methyl, ethyl, isopropyl, butyl or hexyl lactate.
7. The process according to claim 1 , characterised in that the catalytic alcoholysis reaction is performed in the presence of a basic catalyst.
8. The process according to claim 7 , characterised in that the basic catalyst is a guanidine.
9. A process for recycling PLA by depolymerising it the PLA into a monomer or a derivative thereof, comprising dissolving it PLA in a solvent, catalytically alcoholysing the dissolved PLA into a lactic ester, and purifying the lactic ester thus recovered, characterised in that dissolving PLA is performed in a lactic ester at a temperature between the boiling temperature of water and the boiling temperature of the lactic ester at the operating pressure for a period of time sufficient to obtain a weight ratio of PLA/lactic ester between about 0.5 and about 3.0.
10. The process according to claim 9 , characterised in that the operating pressure is between about 0.05 and about 10 bars.
11. The process according to claim 9 , characterised in that the lactic ester is an alkyl lactate, wherein the alkyl radical of the alkyl lactate contains from 1 to 12 carbon atoms.
12. The process according to claim 11 , characterised in that the alkyl lactate is selected from the group consisting of methyl, ethyl, isopropyl, butyl or hexyl lactate.
13. The process according to claim 9 , characterised in that the catalytic alcoholysis reaction is performed in the presence of a basic catalyst.
14. The process according to claim 13 , characterised in that the basic catalyst is a guanidine.
15. The process according to claim 3 , characterised in that the weight ratio of PLA/lactic ester is between about 0.75 and about 2.0.
16. The process according to claim 8 , characterised in that the guanidine is triazabicyclodecene or a derivative thereof.
17. The process according to claim 9 , characterized in that the weight ratio of PLA/lactic ester is between about 0.75 and about 2.0.
18. The process according to claim 14 , characterised in that guanidine is triazabicyclodecene or a derivative thereof.
19. A process for recovering lactic acid, characterised in that it compromises the steps of:
a) dissolving the ground and/or compacted polymer blend in a solvent of PLA in order to separate PLA from the other polymers;
b) recovering undissolved polymers for separate and subsequent processing;
c) recovering the PLA solution with a weight ratio PLA/solvent between about 0.5 and about 3.0 and subjecting it to a catalytic alcoholysis reaction, at a temperature between about 80° C. and about 180° C. and a pressure between about 0 . 05 and about 10 bars, in order to transform PLA into lactic ester;
d) purifying the lactic ester thus recovered; and
e) hydrolyzing the lactic ester into lactic acid.
20. The process according to claim 19 , characterised in that the hydrolyzing is performed in the presence of a catalyst.
21. The process according to claim 19 , characterised in that the hydrolyzing is performed via extraction of alcohol.
22. The process according to claim 1 comprising a step of grinding and/or compacting the polymer blend until a weight/volume ratio between about 0.05 and about 1.4 t/m 3 is obtained, prior to dissolution.
23. The process according to claim 19 comprising a step of grinding and/or compacting the polymer blend until a weight/volume ratio between about 0.05 and about 1.4 t/m 3 is obtained, prior to dissolution.
24. The process according to claim 9 comprising a step of grinding and/or compacting PLA prior to dissolution of the PLA.