Method for the enzymatic degradation of polyethylene terephthalate
The present invention relates to a process for enzymatic depolymerization of polyethylene terephthalate (PET), in particular contained in a plastic material. The process according to the invention can in particular be implemented on an industrial or semi-industrial scale.
1 . A process for enzymatic depolymerization of semi-crystalline polyethylene terephthalate (PET) comprising bringing said semi-crystalline PET into contact with an enzyme capable of depolymerizing said semi-crystalline PET, said enzyme selected from cutinases comprising an amino acid sequence having at least 75% identity with SEQ ID NO:1, and further comprising at least one mutation combination selected from: (i) F208I+D203C+S248C+Y92G, (ii) F208W+D203C+S248C+Y92G, or (iii) F208I+D203C+S248C+V170I+Y92G, corresponding to the residues of SEQ ID NO:1, wherein:
a) the semi-crystalline PET has an initial degree of crystallinity of at most 25%;
b) the depolymerization step is carried out at a temperature T equal to the Tg+10° C. of said semi-crystalline PET; and
c) the enzyme has a depolymerization time (tD) of the semi-crystalline PET that is less than the crystallization time (tR) of said semi-crystalline PET, wherein the time tD represents the time required for said enzyme to depolymerize at least 80% of said semi-crystalline PET at said temperature T, and the time tR represents the time required for said semi-crystalline PET to reach a degree of crystallinity of at most 35% at said temperature T.
2 . The depolymerization process as claimed in claim 1 , wherein the temperature T is between the Tg−10° C. and the Tg+5° C. of the semi-crystalline PET.
3 . The depolymerization process as claimed in claim 1 , wherein the temperature T is between 66° C. and 80° C.
4 . The depolymerization process as claimed in claim 1 , wherein the crystallization time of the semi-crystalline PET is measured prior to the depolymerization step, on a sample of said semi-crystalline PET.
5 . The depolymerization process as claimed in claim 1 , wherein the selected enzyme has a time tD less than or equal to 20 h.
6 . The depolymerization process as claimed in claim 1 , wherein the enzyme is selected from enzymes having a melting temperature (Tm) strictly higher than the temperature T.
7 . The depolymerization process as claimed in claim 1 , wherein the initial degree of crystallinity of the semi-crystalline PET is less than 20%.
8 . The depolymerization process as claimed in claim 1 , wherein the depolymerization time (tD) is between 1 h and 16 h.
9 . The depolymerization process as claimed in claim 1 , wherein the semi-crystalline PET is subjected to an amorphization step prior to the depolymerization step.
10 . The depolymerization process as claimed in claim 1 , wherein the time tD represents the time required for said enzyme to depolymerize at least 90% of said semi-crystalline PET at said temperature T, and the time tR represents the time required for said semi-crystalline PET to reach a degree of crystallinity of at most 30% at said temperature T.
11 . The depolymerization process as claimed in claim 1 , wherein:
a) the semi-crystalline PET has an initial degree of crystallinity of at most 25% and a Tg between 65° C.±1° C. and 80° C.±1° C.;
b) the depolymerization step is carried out at a temperature T of 72° C.±1° C.; and
c) the enzyme has a depolymerization time (tD) of the semi-crystalline PET that is less than the crystallization time (tR) of said semi-crystalline PET, wherein the time tD represents the time required for the selected enzyme to depolymerize at least 80% of said semi-crystalline PET at said temperature T, and the time tR represents the time required for said semi-crystalline PET to reach a degree of crystallinity of at most 35% at said temperature T.
12 . The depolymerization process as claimed in claim 1 , wherein:
a) a plastic material is selected from fibers and/or fiber and/or textile waste comprising semi-crystalline PET with an initial degree of crystallinity of at most 25% and a Tg between 60° C.±1° C. and 75° C.±1° C.;
b) the depolymerization step is carried out at a temperature T of 65° C.±1° C.; and
c) the enzyme capable of degrading semi-crystalline PET has a depolymerization time (tD) of the semi-crystalline PET that is less than the crystallization time (tR) of said semi-crystalline PET, wherein the time tD represents the time required for the selected enzyme to depolymerize at least 80% of said semi-crystalline PET at said temperature T, and the time tR represents the time required for said semi-crystalline PET to reach a degree of crystallinity of at most 35% at said temperature T.
13 . The depolymerization process as claimed in claim 1 , wherein the temperature T is between 68° C. and 73° C.
14 . The depolymerization process as claimed in claim 1 , wherein the depolymerization time (tD) is between 1 h and 10 h.
15 . The depolymerization process as claimed in claim 1 , wherein the cutinase has at least 75% identity with SEQ ID NO:1 and comprises the mutation combination F208I+D203C+S248C+Y92G, corresponding to the residues of SEQ ID NO:1.
16 . The depolymerization process as claimed in claim 1 , wherein the cutinase has at least 75% identity with SEQ ID NO:1 and comprises the mutation combination F208W+D203C+S248C+Y92G, corresponding to the residues of SEQ ID NO: 1.
17 . The depolymerization process as claimed in claim 1 , wherein the cutinase has at least 75% identity with SEQ ID NO:1 and comprises the mutation combination selected from: (i) F208I+D203C+S248C+Y92G, or (iii) F208I+D203C+S248C+V170I+Y92G, corresponding to the residues of SEQ ID NO:1.