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Sustainable, highly selective, and metal-free thermal depolymerization of poly-(3-hydroxybutyrate) to crotonic acid in recoverable ionic liquids
Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University, S-90187 Umeå, Sweden.ORCID iD: 0000-0002-3458-939X
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0002-4628-3857
Industrial Chemistry & Reaction Engineering, Department of Chemical Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, FI-20500 Åbo-Turku, Finland.
Technical Chemistry, Department of Chemistry, Chemical-Biological Centre, Umeå University, S-90187 Umeå, Sweden.
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2022 (English)In: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 24, no 10, p. 4130-4139Article in journal (Refereed) Published
Abstract [en]

Valorization of renewable and biodegradable biopolymers to value added chemicals and green fuels is currently considered as an important research topic aiming at reducing the dependency on fossil derived feedstocks as well as their negative consequences on the environment. In this report, we are introducing an ionic liquid (IL) mediated, sustainable, and green synthesis of crotonic acid (CA) from poly-(3-hydroxybutyrate, PHB), a biopolymer derived from microbial fermentation. In this actual case, imidazolium cation comprising ILs have been used in the synthesis, where the influence of various reaction parameters such as reaction temperature and types of ILs as well as the amount of polymer, water, and IL in the reaction mixture were examined. The conversion of PHB to CA in IL took place by a base catalyzed depolymerization with formation of crotonyl terminated polymeric entities as intermediates, a mechanism that was confirmed by NMR analysis of the reaction mixtures sampled when the reactions were carried out at various temperatures. The rate of CA formation via the IL mediated base catalyzed depolymerization increased with increasing temperature in the tested interval, and 97% yield of CA was obtained after 90 min at 140 degrees C. The [EMIM][AcO] IL applied as solvent and catalyst is capable of completely depolymerizing PHB to CA in 5 h at 120 degrees C up to a polymer loading of 40 wt%. At higher loadings the depolymerization became incomplete, which is attributed to a deactivation of the IL due to hydrogen bonding interactions with the in situ formed CA, confirmed by NMR and DSC techniques. Since the depolymerization is base catalyzed, the only tested ILs that were able to form CA were based on acetate anions, whereas the less basic or neutral [EMIM][Cl] IL was found to be inactive. Finally, more than 90% of CA as well as [EMIM][AcO] IL were recovered in high purity by solvent extraction with brine (saturated aqueous NaCl) and 2-methyl tetrahydrofuran (2-Me-THF). Most importantly, here we introduce a sustainable, metal free, and single solvent based reaction approach for selective depolymerization of PHB to industrially valuable CA in basic and recoverable ILs.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2022. Vol. 24, no 10, p. 4130-4139
National Category
Analytical Chemistry Polymer Chemistry Energy Systems
Research subject
Engineering Materials
Identifiers
URN: urn:nbn:se:ltu:diva-90716DOI: 10.1039/d2gc00621aISI: 000792782700001Scopus ID: 2-s2.0-85131448220OAI: oai:DiVA.org:ltu-90716DiVA, id: diva2:1660448
Funder
Swedish Research Council, 2016-02011 MISTRAKnut and Alice Wallenberg Foundation
Note

Validerad;2022;Nivå 2;2022-05-24 (hanlid)

Available from: 2022-05-24 Created: 2022-05-24 Last updated: 2022-07-11Bibliographically approved

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Nikjoo, Dariush

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