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- Ismail, Mohamed, et al.
(författare)
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Closing the loop for poly(butylene-adipate-co-terephthalate) recycling: depolymerization, monomers separation, and upcycling
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Ingår i: Green Chemistry. - 1463-9270.
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Tidskriftsartikel (refereegranskat)abstract
- Efficient recycling and upcycling strategies to retain the material in the economy and away from the ecosystems are important to achieve a sustainable plastic system. Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable polyester that has gained considerable interest for various applications. Here, we report a study on enzymatic depolymerization of PBAT, recovery and purification of its monomers, and feasible routes for their recycling/upcycling. PBAT films (15 g L−1) were completely hydrolysed employing a leaf-branch compost cutinase variant (LCC-WCCG, 1.4 mg per gram polymer) to its monomers at a rate of 0.49 g L−1 h−1. LCC-WCCG kinetics were superior to that of other enzymes engineered for PBAT hydrolysis; the data were supported by in silico investigations. The released monomers were separated using membrane filtration and precipitation techniques and recovered with purity exceeding 95%. To close the loop, the monomers were re-polymerized and successfully cast into PBAT films. Moreover, adipic acid was reacted with hexamethylene diamine using Novozym®435 to form a polyamide, while 1,4-butanediol was oxidized to 4-hydroxybutyrate using Gluconobacter oxydans cells. The current study exemplifies a high-impact scientific approach toward a circular plastics economy.
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- Pyo, Sang Hyun, et al.
(författare)
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A facile process for adipic acid production in high yield by oxidation of 1,6-hexanediol using the resting cells of Gluconobacter oxydans
- 2022
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Ingår i: Microbial Cell Factories. - : Springer Science and Business Media LLC. - 1475-2859. ; 21
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Tidskriftsartikel (refereegranskat)abstract
- Background: Adipic acid (AA) is one of the most important industrial chemicals used mainly for the production of Nylon 6,6 but also for making polyurethanes, plasticizers, and unsaturated polyester resins, and more recently as a component in the biodegradable polyester poly(butylene adipate terephthalate) (PBAT). The main route for AA production utilizes benzene as feedstock and generates copious amounts of the greenhouse gas NO2. Hence, alternative clean production routes for AA from renewable bio-based feedstock are drawing increasing attention. We have earlier reported the potential of Gluconobacter oxydans cells to oxidize 1,6-hexanediol, a potentially biobased diol to AA. Results: The present report involves a study on the effect of different parameters on the microbial transformation of 1,6-hexanediol to adipic acid, and subsequently testing the process on a larger lab scale for achieving maximal conversion and yield. Comparison of three wild-type strains of G. oxydans DSM50049, DSM2003, and DSM2343 for the whole-cell biotransformation of 10 g/L 1,6-hexanediol to adipic acid in batch mode at pH 7 and 30 °C led to the selection of G. oxydans DSM50049, which showed 100% conversion of the substrate with over 99% yield of adipic acid in 30 h. An increase in the concentrations of the substrate decreased the degree of conversion, while the product up to 25 g/L in batch and 40 g/L in fed-batch showed no inhibition on the conversion. Moreover, controlling the pH of the reaction at 5–5.5 was required for the cascade oxidation reactions to work. Cell recycling for the biotransformation resulted in a significant decrease in activity during the third cycle. Meanwhile, the fed-batch mode of transformation by intermittent addition of 1,6-hexanediol (30 g in total) in 1 L scale resulted in complete conversion with over 99% yield of adipic acid (approximately 37 g/L). The product was recovered in a pure form using downstream steps without the use of any solvent. Conclusion: A facile, efficient microbial process for oxidation of 1,6-hexanediol to adipic acid, having potential for scale up was demonstrated. The entire process is performed in aqueous medium at ambient temperatures with minimal greenhouse gas emissions. The enzymes involved in catalyzing the oxidation steps are currently being identified.
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- Örn, Oliver Englund, et al.
(författare)
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Enhanced Protocatechuic Acid Production From Glucose Using Pseudomonas putida 3-Dehydroshikimate Dehydratase Expressed in a Phenylalanine-Overproducing Mutant of Escherichia coli
- 2021
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Ingår i: Frontiers in Bioengineering and Biotechnology. - : Frontiers Media SA. - 2296-4185. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Protocatechuic acid (PCA) is a strong antioxidant and is also a potential platform for polymer building blocks like vanillic acid, vanillin, muconic acid, and adipic acid. This report presents a study on PCA production from glucose via the shikimate pathway precursor 3-dehydroshikimate by heterologous expression of a gene encoding 3-dehydroshikimate dehydratase in Escherichia coli. The phenylalanine overproducing E. coli strain, engineered to relieve the allosteric inhibition of 3-deoxy-7-phosphoheptulonate synthase by the aromatic amino acids, was shown to give a higher yield of PCA than the unmodified strain under aerobic conditions. Highest PCA yield of 18 mol% per mol glucose and concentration of 4.2 g/L was obtained at a productivity of 0.079 g/L/h during cultivation in fed-batch mode using a feed of glucose and ammonium salt. Acetate was formed as a major side-product indicating a shift to catabolic metabolism as a result of feedback inhibition of the enzymes including 3-dehydroshikimate dehydratase by PCA when reaching a critical concentration. Indirect measurement of proton motive force by flow cytometry revealed no membrane damage of the cells by PCA, which was thus ruled out as a cause for affecting PCA formation.
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