Subcritical CO2-H2O hydrolysis of polyethylene terephthalate as a sustainable chemical recycling platform
Osei, Dacosta
;
Gurrala, Lakshmiprasad
;
Sheldon, Aria
, et al.
Green Chem.,2024,26,6436-6445. DOI:
10.1039/d3gc04576e
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Abstract: The development of an efficient and environmentally sustainable chem. hydrolysis process for recycling waste plastics, based on green chem. principles, is a key challenge. In this work, we investigated the role of subcritical CO2 on the hydrolysis of polyethylene terephthalate (PET) into terephthalic acid (TPA) at 180-200 °C for 10-100 min. The addition of CO2 into the reaction mixture led to the in situ formation of carbonic acid that helps to catalyze PET hydrolysis relative to hot compressed H2O (i.e. N2-H2O). The highest TPA yield of 85.0 ± 1.3% was obtained at 200 °C, PET loading of 2.5 g PET in 20 mL H2O for 100 min, and 208 psi of initial CO2 pressure. In addition, the subcritical CO2-H2O system demonstrated high selectivity toward hydrolyzing PET in a mixture with polyethylene (PE) at 200 °C for 100 min, thus providing "molecular sorting" capabilities to the recycling process. The robustness of the process was also demonstrated by the ability to hydrolyze both colored Canada Dry and transparent Pure Life waste PET bottles into high yields of TPA (>86%) at 200 °C. In addition, subcritical CO2-H2O hydrolysis of colored PET bottles resulted in a white TPA product similar to that generated from transparent PET bottles. Overall, this work shows that, under optimized reaction conditions, subcritical CO2 can provide acid tunability to the reaction medium to favor waste PET hydrolysis for subsequent recycling.
Purchased from AmBeed:
1137-99-1
Probing Supercritical CO2 to Improve the Susceptibility of Semicrystalline Polyethylene Terephthalate to Enzymatic Hydrolysis
Lakshmiprasad Gurrala
;
Rafi Anowar
;
Ana Rita C. Morais
ACS Sustain. Chem. Eng.,2024,12(20):7713–7723. DOI:
10.1021/acssuschemeng.3c08286
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Abstract: Enzymatic hydrolysis of semicrystalline poly(ethylene terephthalate) (PET) is hindered by the hydrophobic nature and crystallinity of the substrate, and it highly depends on the available interfacial area between substrate and aqueous phase. While most studies leverage particle size reduction to increase interfacial area, this study investigates the use of supercritical CO2 (scCO2) to increase internal surface area in PET, and its impact on the enzymatic hydrolysis yields. Our work shows that scCO2 pretreatment of semicrystalline PET resulted in up to 2-fold higher terephthalic acid (TPA) yield relative to the untreated counterpart using Humicola insolens cutinase (HiC) enzyme. There is a positive correlation between the total pore surface area in the scCO2-pretreated PET samples and the final TPA yield. In addition, preliminary kinetic studies revealed faster initial production of TPA for scCO2-treated PET relative to untreated PET. ScCO2-treated PET samples showed no significant changes in the crystalline content and thermal properties. However, NMR data indicated that scCO2-treated PET has a slightly higher apparent number-average molecular weight (Mn) relative to that of untreated PET. Overall, scCO2 pretreatment led to increased semicrystalline PET susceptibility to HiC enzyme action, resulting in increased TPA yields.
Keywords:
biocatalysis ; terephthalic acid ; CO2 ; porosity ; cutinase ; interfacial ; sustainability ; plastic recycling/upcycling
Purchased from AmBeed:
1137-99-1
Discovery and rational engineering of PET hydrolase with both mesophilic and thermophilic PET hydrolase properties
Hong, Hwaseok
;
Ki, Dongwoo
;
Seo, Hogyun
, et al.
Nat. Commun.,2023,14(1):4556. DOI:
10.1038/s41467-023-40233-w PubMed ID:
37507390
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Abstract: Excessive polyethylene terephthalate (PET) waste causes a variety of problems. Extensive research focused on the development of superior PET hydrolases for PET biorecycling has been conducted. However, template enzymes employed in enzyme engineering mainly focused on IsPETase and leaf-branch compost cutinase, which exhibit mesophilic and thermophilic hydrolytic properties, respectively. Herein, we report a PET hydrolase from Cryptosporangium aurantiacum (CaPETase) that exhibits high thermostability and remarkable PET degradation activity at ambient temperatures. We uncover the crystal structure of CaPETase, which displays a distinct backbone conformation at the active site and residues forming the substrate binding cleft, compared with other PET hydrolases. We further develop a CaPETaseM9 variant that exhibits robust thermostability with a Tm of 83.2 °C and 41.7-fold enhanced PET hydrolytic activity at 60 °C compared with CaPETaseWT. CaPETaseM9 almost completely decompose both transparent and colored post-consumer PET powder at 55 °C within half a day in a pH-stat bioreactor.
Purchased from AmBeed:
1137-99-1