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Structural Insights on Recalcitrance during Hydrothermal Hemicellulose Extraction from Wood
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. (Wallenberg Wood Science Center)ORCID iD: 0000-0003-4266-0720
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0002-8614-6291
2017 (English)In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 5, no 6, p. 5156-5165Article in journal (Refereed) Published
Abstract [en]

Hydrothermal extraction of hemicelluloses from lignocellulosic biomass for conversion to renewable materials or fuels has captured attention. The extraction is however partial and some lignin is codissolved. Herein, we investigated the role of molecular structure in the recalcitrance. Wood meal of Spruce and Birch were subjected to pressurized hydrothermal extraction at 160 °C for 2 h, which extracted 68–75% of the hemicelluloses. 2D heteronuclear single quantum coherence (HSQC) NMR, HSQC-TOCSY, and 13C NMR were applied for structural studies of both extracts and residues. Subsequent to the known partial hydrolysis of native carbon-2 and carbon-3 acetates in hemicellulose, some acetylation of primary alcohols on hemicelluloses and lignin was observed. Lignin carbohydrate complexes (LCC) were detected in both the extracts and residues. In Spruce extracts, only the phenyl glycoside-type of LCC was detected. Birch extracts contained both the phenyl glycoside and benzyl ether-types. In the hydrothermal wood residues of both species, benzyl ether- and gamma (γ)-ester-LCC were present. Structural changes in lignin included decrease in aryl ether (βO4) content and increases in resinol- (ββ) and phenyl coumaran (β5) contents. On the basis of the overall analysis, the mechanisms and contribution of molecular structure to recalcitrance is discussed.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017. Vol. 5, no 6, p. 5156-5165
Keywords [en]
13C NMR, 2D HSQC, Autohydrolysis, HSQC-TOCSY, LCC repolymerization, Lignin carbohydrate complexes (LCC), Recalcitrance, trans-Acetylation
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-208164DOI: 10.1021/acssuschemeng.7b00511ISI: 000402950000076Scopus ID: 2-s2.0-85020212464OAI: oai:DiVA.org:kth-208164DiVA, id: diva2:1104425
Funder
Knut and Alice Wallenberg Foundation, 8107
Note

QC 20170613

Available from: 2017-06-01 Created: 2017-06-01 Last updated: 2018-05-14Bibliographically approved
In thesis
1. Fundamental Aspects of Lignin Carbohydrate Complexes (LCC): Mechanisms, Recalcitrance and Material concepts
Open this publication in new window or tab >>Fundamental Aspects of Lignin Carbohydrate Complexes (LCC): Mechanisms, Recalcitrance and Material concepts
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Covalent bonds between lignin and carbohydrates, forming a matrix referred to as lignin carbohydrate complexes (LCC), remain one of the most controversial topics in wood chemistry. A key issue is whether they are formed during chemical and mechanical pretreatments of the compact wood structure or actually present in wood prior to isolation. A fundamental understanding of their origin and reactivity is vital to unravel their role in wood formation and recalcitrance. Recalcitrance, specifically, has affected the successful development of effective and clean fractionation of wood polymers.

To address the above-mentioned concerns, we have developed a novel mild universal and quantitative fractionation protocol of LCC that, when combined with robust spectroscopic analytical tools, including a variety of NMR techniques, GC MS and SEC, reveals deeper insights into the molecular structure of LCC.

This method was applied to both hardwood and softwood LCCs and revealed interesting findings on molecular-level regulatory mechanism for lignin carbohydrate (LC) bond formation such as the role of acetylation in hemicelluloses. Moreover, the role of LC bonds on recalcitrance during subcritical water extraction was unveiled.

Bio-mimicking in vitro lignin polymerization was adopted to investigate whether LC bonds are native or formed during isolation from wood. For the first time, direct evidence lending support that they are formed in wood cells was demonstrated, thus corroborating the mechanisms suggested in the literature.  

Furthermore, based on the overall LCC study, we suggest a sequence for how LC bonds may form in vitro.

Finally, of special interest to material science, the unveiled LC bond formation mechanism inspired a green, biomimetic, one-pot synthesis of functionalized lignin starting from monomeric components. Excellent selectivity of functionalization is reported and production of lignin-based recyclable materials, based on the premise of this functionalization philosophy, is discussed.

Abstract [sv]

Existensen av kovalenta bindningar mellan lignin och kolhydrater, som bildar en matris som kallas ligninkolhydratkomplex (LCC), förblir ett av de mest kontroversiella ämnena inom träkemi. En viktig fråga är om de bildas under isolering eller faktiskt finns närvarande i trä före isolering (där isolering innefattar kemiska och mekaniska förbehandlingar av den kompakta trästrukturen). Djupare insikter om deras ursprung och reaktivitet är avgörande för att utröna deras roll i träbildning och deras bidrag till extraktionssvårighet. Lignins bidrag till extraktionssvårighet är av särskilt intresse, då den länge hämmat den framgångsrika utvecklingen av effektiv och ren fraktionering av träpolymerer.För att ta itu med ovan nämnda problem har vi utvecklat ett nytt, milt, universellt och kvantitativt fraktioneringsprotokoll av LCC som i kombination med robusta spektroskopiska analysverktyg (vilka innefattar ett flertal NMR-tekniker samt GC MS och SEC) ger djupare insikt om LCCs molekylära struktur. Detta protokoll applicerades på både barr- och lövved och ledde till intressanta upptäckter beträffande de molekylära regler-mekanismerna för bildandet av lignin-kolhydrat-bindningar (LC). Dessa upptäckter berörde även vikten av hemicellulosors acetylering. Vidare presenterades hur LC-bindningar bidrar till extractionssvårighet under subkritisk vattenutvinning.Biomimetisk in vitro-ligninpolymerisation användes för att vidare undersöka huruvida LC-bindningar finns närvarande innan isolering av trä eller bildas under denna. I denna avhandling har för första gången direkta bevis till stöd för att de bildas nativt i träceller presenterats. Detta korroborerar tidigare mekanismer som föreslagits i litteraturen. Vidare erhölls djupare insikter på molekylär nivå för att föreslår en sekvens för hur LC-bindningar bildas in vitro.Slutligen, av särskilt intresse för materialvetenskap, inspirerade den framtagna LC-bindningsmedelsmekanismen en grön, biomimetisk enstegssyntes av funktionaliserat lignin utgående från monomera komponenter. Utmärkt funktionaliseringsselektivitet uppvisades och en produktion av ligninbaserade återvinningsbara material baserade på denna funktionaliseringsfilosofi diskuteras.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 95
Series
TRITA-CBH-FOU ; 2018:18
Keywords
Lignin Carbohydrates Complexes; Phenyl Glycosides; Benzyl Ethers; Benzyl and γ-esters; Universal Mild Quantitative fractionation; LCC mechanism formation, Extracellular lignin; Dehydogenation polymer; Autohydrolysis; Recalcitrance; Acetylation role; HSQC, HMBC, HSQC-TOCSY, 13C, 31P NMR, Thioacidolysis-GC; SEC; Green, Biomimetic, One-pot-lignin functionalization; Lignin platform material.
National Category
Wood Science
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-227865 (URN)978-91-7729-771-0 (ISBN)
Public defence
2018-06-11, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180514

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2018-05-21Bibliographically approved

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Giummarella, NicolaLawoko, Martin

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