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Structure and antioxidant relation of water-acetone fractionated Beechwood lignins
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. (Biochemical Process Engineering)
Department of Earth and Environmental Sciences, University of Milano-Bicocca.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. (Biochemical process engineering)
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. (Biochemical Process Engineering)
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The viability of second generation biorefineries relies on value-added utilization of all the components present in lignocellulose. Till today, lignin presents the largest room for improvement in such sense. Meanwhile, the lignin structural characteristics are complex, disperse, and largely dependent on extraction conditions and factors such as severity. Herein, two beechwood lignins best described as largely native and non-native are isolated through organosolv processing in absence and presence of H2SO4. The behavior of the two parental lignins are further investigated through post-organosolv water-acetone fractionation with accompanied functional group analysis, size distribution characterization, and solubility trials. The original parental lignin chemistry alongside the fraction size-distribution determines properties such as solubility in aqueous acetone solutions. Finally, to correlate the lignin extract chemistry with value-added down-stream properties, the DPPH radical scavenging properties of the parent and fractionated lignins were evaluated alongside their UV absorption in solution. It was found that the preference of the lignins to generate solution aggregates is a result of extraction conditions, which eventually influences not only solubility, but also their display of antioxidant properties.    

National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
URN: urn:nbn:se:ltu:diva-105288OAI: oai:DiVA.org:ltu-105288DiVA, id: diva2:1855138
Available from: 2024-04-29 Created: 2024-04-29 Last updated: 2024-05-02
In thesis
1. Structure and property oriented organosolv lignin extraction
Open this publication in new window or tab >>Structure and property oriented organosolv lignin extraction
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this Thesis, organosolv fractionation of softwood (spruce), hardwood (birch and beech), and herbaceous crops (wheat straw) was performed by applying various organosolv process conditions. Among these were a novel steam-explosion/organosolv hybrid mode, and two ternary solvent systems utilizing water/ethanol/acetone, and water/acetone/acetic acid. In addition, the effect of using inorganic acidic catalyst (H2SO4) was investigated for all raw material classes. Also, alkaline catalyst (NaOH) was investigated for wheat straw due to its reported high content of inorganics which presence adds additional structural complexity to the lignocellulosic recalcitrance. Following the organosolv fractionation, structural characterization was performed (content of cellulose, hemicellulose, lignin) in the isolated product fractions. Additionally, in-depth characterization of the isolated lignins was performed by combining Pyrolysis-Gas Chromatography Mass Spectroscopy (Pyr-GC/MS), Gel Permeation Chromatography (GPC), and different modes of Nuclear Magnetic Resonance (NMR; 13C, 1H-13C, 31P). Complementary analytics, such as content of monomeric/oligomeric sugars, dehydration products, total phenolics, and Size-Exclusion Chromatography (SEC) of the isolated product liquor, were performed to provide a comprehensive understanding of the process. Special attention was given the lignin structural changes occurring throughout the organosolv process. This was done as the use of lignin for higher-value application is considered crucial for the economic viability and development of a modern biorefinery. For this reason, significant focus was given to study how the lignin characteristics translate into physical properties such as solubility. The latter property was measured through solubility trials in binary aqueous acetone solutions, as well as solvent-based fractionation (acetone-water system). A coherent picture was aimed for, where structural motifs and lignin characteristics were correlated to reductions/enhancements in solubility at various water contents. To finally bridge this with a potential down-stream application, DPPH radical scavenging was performed in DMSO with and without intercalating Lithium Bromide (LiBr) for a selection of organosolv lignins, as well as their acetone/water fractionated lignins. This was complemented with a UV absorption study of the lignin solutions.The results provide a descriptive span of chemical characteristics related to organosolv lignins, where they range between highly native, to non-native. Whereas the former lignins are largely comprised of inter-unit motifs such as β-O-4’, β-β’ and β-5’, the non-native lignins are instead better characterized by a high content of oxidized sidechains, biaryls and bifurans, as well as showing strong indications of having quaternary cross-linkers originating from ketone functionalities. The ketones are also found to undergo aldol condensation with aldehydes formed throughout the process. Interestingly, these two extremes in lignin characteristics yield highly varying physical properties, where the predominantly native and non-native lignins for example display low and high solubility in pure acetone, respectively. Simultaneously, the latter is more prone towards water-induced precipitation, whereas the former instead require water to display complete (~100%) solubility at specific concentrations. These properties and findings are eventually consistent with recent literature where lignin aggregates also dominate their dissolved state, and the interunit motifs dictate the affinity on forming such aggregates which are important for both their dissolution, precipitation, but also their display of functionality such as antioxidant activity.                    

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Chemical Process Engineering
Research subject
Biochemical Process Engineering
Identifiers
urn:nbn:se:ltu:diva-105316 (URN)978-91-8048-564-7 (ISBN)978-91-8048-565-4 (ISBN)
Public defence
2024-09-20, C305, Luleå University of Technology, Luleå, 12:00 (English)
Opponent
Supervisors
Available from: 2024-05-02 Created: 2024-05-02 Last updated: 2024-06-10Bibliographically approved

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