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Comparison of [HSO4](-), [Cl](-) and [MeCO2](-) as anions in pretreatment of aspen and spruce with imidazolium-based ionic liquids
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2017 (English)In: BMC Biotechnology, ISSN 1472-6750, E-ISSN 1472-6750, Vol. 17, article id 82Article in journal (Refereed) Published
Abstract [en]

Background: Ionic liquids (ILs) draw attention as green solvents for pretreatment of lignocellulose before enzymatic saccharification. Imidazolium-based ILs with different anionic constituents ([HSO4], [Cl], [MeCO2]) were compared with regard to pretreatment of wood from aspen and spruce. The objective was to elucidate how the choice of anionic constituent affected the suitability of using the IL for pretreatment of hardwood, such as aspen, and softwood, such as spruce. The investigation covered a thorough analysis of the mass balance of the IL pretreatments, the effects of pretreatment on the cell wall structure as assessed by fluorescence microscopy, and the effects of pretreatment on the susceptibility to enzymatic saccharification. Torrefied aspen and spruce were included in the comparison for assessing how shifting contents of hemicelluloses and Klason lignin affected the susceptibility of the wood to IL pretreatment and enzymatic saccharification.

Results: The glucose yield after IL pretreatment increased in the order [Cl] < [HSO4] < [MeCO2] for aspen, but in the order [HSO4] < [Cl] < [MeCO2] for spruce. For both aspen and spruce, removal of hemicelluloses and lignin increased in the order [Cl] < [MeCO2] < [HSO4]. Fluorescence microscopy indicated increasingly disordered cell wall structure following the order [HSO4] < [Cl] < [MeCO2]. Torrefaction of aspen converted xylan to pseudo-lignin and changed the glucose yield order to [HSO4] < [Cl] < [MeCO2].

Conclusions: The acidity of [HSO4] caused extensive hydrolysis of xylan, which facilitated pretreatment of xylan-rich hardwood. Apart from that, the degree of removal of hemicelluloses and lignin did not correspond well with the improvement of the enzymatic saccharification. Taken together, the saccharification results were found to mainly reflect (i) the different capacities of the ILs to disorder the cell wall structure, (ii) the recalcitrance caused by high xylan content, and (iii) the capacity of the [HSO4]-based IL to hydrolyze xylan.

Place, publisher, year, edition, pages
BioMed Central, 2017. Vol. 17, article id 82
Keywords [en]
Hardwood, Softwood, Pretreatment, Ionic liquid, Enzymatic saccharification, Torrefaction, Xylan, ason lignin, Pseudo-lignin
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-142457DOI: 10.1186/s12896-017-0403-0ISI: 000415149600001PubMedID: 29141617OAI: oai:DiVA.org:umu-142457DiVA, id: diva2:1162490
Available from: 2017-12-04 Created: 2017-12-04 Last updated: 2018-06-09Bibliographically approved
In thesis
1. Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability
Open this publication in new window or tab >>Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lignocellulose is an inexpensive and abundant renewable resource that can be used to produce advanced biofuels, green chemicals, and other bio-based products. Pretreatment and efficient enzymatic saccharification are essential features of bioconversion of lignocellulosic biomass. The aims of the research were to achieve a better understanding of the recalcitrance of woody biomass to bioconversion, to explore different pretreatment techniques that can be used to decrease the recalcitrance of the biomass and improve the digestibility of the cellulose, and to investigate by-products of acid pretreatment that cause enzymes and microorganisms to work less efficiently.

The recalcitrance of wood from aspen, birch, and spruce was investigated before and after acid pretreatment. Before pretreatment, birch exhibited the highest recalcitrance, which was attributed to structural factors. After pretreatment, spruce showed the highest recalcitrance, which was attributed to chemical factors, such as high lignin content. Deacetylation of hybrid aspen in planta by a CE5 acetyl xylan esterase decreased the recalcitrance, and the glucose yield of enzymatic saccharification of non-pretreated wood increased with 27%.

Pretreatment options based on ionic liquids and steam explosion were further explored. The effects of the anionic constituents of a series of imidazolium-based ionic liquids on pretreatment of aspen and spruce were investigated. [HSO4]− was efficient only for aspen, which was attributed to acid degradation of xylan. [MeCO2]− was efficient for both aspen and spruce, which was attributed to its capability to create a disordered cell wall structure rather than to removal of lignin and hemicellulose. A comparison was made between using sulfuric acid and sulfur dioxide for pretreatment of spruce. Although sulfur dioxide resulted in a pretreatment liquid that was more inhibitory to both enzymes and yeast, it was still superior to pretreatment with sulfuric acid, a phenomenon that was attributed to the particle size of the pretreated material.

In a comparison of microbial inhibitors in pretreatment liquids from steam explosion of spruce, formaldehyde was found to be the most important inhibitor of yeast. Enzyme inhibition by catalytically non-productive adsorption to lignins and pseudo-lignin was investigated using quantitative proteomics. The results indicate that protein adsorption to pseudo-lignin can be as extensive as adsorption to real lignin. 

Place, publisher, year, edition, pages
Umeå: Umeå University, 2018. p. 59
Keywords
Recalcitrance, Pretreatment, Enzymatic saccharification, Ionic liquid, Steam explosion, Enzyme inhibition, Non-productive binding, Microbial inhibitors
National Category
Bioprocess Technology Wood Science Biochemicals
Identifiers
urn:nbn:se:umu:diva-145045 (URN)978-91-7601-853-8 (ISBN)
Public defence
2018-03-16, KBC-huset, Lilla Hörsalen, KB.E3.01, Umeå, 10:00 (English)
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Supervisors
Available from: 2018-02-23 Created: 2018-02-19 Last updated: 2018-06-09Bibliographically approved

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