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Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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 [en]
Recalcitrance, Pretreatment, Enzymatic saccharification, Ionic liquid, Steam explosion, Enzyme inhibition, Non-productive binding, Microbial inhibitors
National Category
Bioprocess Technology Wood Science Biochemicals
Identifiers
URN: urn:nbn:se:umu:diva-145045ISBN: 978-91-7601-853-8 (print)OAI: oai:DiVA.org:umu-145045DiVA, id: diva2:1183813
Public defence
2018-03-16, KBC-huset, Lilla Hörsalen, KB.E3.01, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-02-23 Created: 2018-02-19 Last updated: 2018-06-09Bibliographically approved
List of papers
1. Chemical and structural factors influencing enzymatic saccharification of wood from aspen, birch and spruce
Open this publication in new window or tab >>Chemical and structural factors influencing enzymatic saccharification of wood from aspen, birch and spruce
2018 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 109, p. 125-134Article in journal (Refereed) Published
Abstract [en]

The susceptibility of untreated and sulfuric-acid-pretreated aspen, birch, and spruce to analytical enzymatic saccharification was studied in relation to their chemical composition and physical-structural features. The analytical data collected covered the mass fractions of lignin, carbohydrates, and extractives, the release of acetic acid, formic acid, and uronic acids by acid and alkaline hydrolysis, crystallinity and crystallite size, syringyl: guaiacyl (S:G) ratio of lignin, cellulose accessibility, FTIR spectra, images from SEM and fluorescence microscopy, and susceptibility to enzymatic saccharification using enzyme mixtures with and without supplementary xylanase.In the absence of pretreatment the mass fraction yield of Glc on the original dry wood in the analytical enzymatic saccharification increased in the order birch (16 g kg−1) < spruce (35 g kg−1) < aspen (150 g kg−1). After acid pretreatment, the order changed to spruce (170 g kg−1) < aspen (290 g kg−1), birch (290 g kg−1). The relatively high recalcitrance of untreated birch was not possible to relate to mass fraction of lignin, S:G ratio, cellulose crystallinity, or mass fraction of acetyl, but rather to structural features, such as a more compact surface structure with high density and low cellulose accessibility. The relatively high sugar yields from both untreated and pretreated aspen suggest that aspen wood is well suited as feedstock for production of liquid biofuels and green chemicals in forest-based biorefineries.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Hardwood, Softwood, Chemical composition, Dilute-acid pretreatment, Enzymatic saccharification, Physical structure
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:umu:diva-143889 (URN)10.1016/j.biombioe.2017.12.020 (DOI)000424939200015 ()
Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-08-06Bibliographically approved
2. Bioprocessing properties of hybrid aspen expressing a Carbohydrate Esterase Family 5 acetyl xylan esterase under control of a wood-specific promoter
Open this publication in new window or tab >>Bioprocessing properties of hybrid aspen expressing a Carbohydrate Esterase Family 5 acetyl xylan esterase under control of a wood-specific promoter
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(English)Manuscript (preprint) (Other academic)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:umu:diva-145113 (URN)
Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-06-09Bibliographically approved
3. Comparison of [HSO4](-), [Cl](-) and [MeCO2](-) as anions in pretreatment of aspen and spruce with imidazolium-based ionic liquids
Open this publication in new window or tab >>Comparison of [HSO4](-), [Cl](-) and [MeCO2](-) as anions in pretreatment of aspen and spruce with imidazolium-based ionic liquids
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
Keywords
Hardwood, Softwood, Pretreatment, Ionic liquid, Enzymatic saccharification, Torrefaction, Xylan, ason lignin, Pseudo-lignin
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-142457 (URN)10.1186/s12896-017-0403-0 (DOI)000415149600001 ()29141617 (PubMedID)
Available from: 2017-12-04 Created: 2017-12-04 Last updated: 2018-06-09Bibliographically approved
4. Effects of impregnation of softwood with sulfuric acid and sulfur dioxide on chemical and physical characteristics, enzymatic digestibility, and fermentability
Open this publication in new window or tab >>Effects of impregnation of softwood with sulfuric acid and sulfur dioxide on chemical and physical characteristics, enzymatic digestibility, and fermentability
2018 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 247, p. 200-208Article in journal (Refereed) Published
Abstract [en]

Hydrothermal pretreatment improves bioconversion of lignocellulose, but the effects of different acid catalysts are poorly understood. The effects of sulfuric acid (SA) and sulfur dioxide (SD) in continuous steam pretreatment of wood of Norway spruce were compared in the temperature range 195 degrees C-215 degrees C. The inhibitory effects of the pretreatment liquid on cellulolytic enzymes and Saccharomyces cerevisiae yeast were higher for SD-than for SApretreated material, and the inhibitory effects increased with increasing pretreatment temperature. However, the susceptibility to cellulolytic enzymes of wood pretreated with SD was 2.0-2.9 times higher than that of wood pretreated with SA at the same temperature. Data conclusively show that the superior convertibility of SDpretreated material was not due to inhibition phenomena but rather to the greater capability of the SD pretreatment to reduce the particle size through partial delignification and cellulose degradation. Particle size was shown to be correlated with enzymatic digestibility (R-2 0.97-0.98).

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Hydrothermal pretreatment, Sulfuric acid, Sulfur dioxide, Inhibition, Enzymatic digestibility
National Category
Polymer Technologies
Identifiers
urn:nbn:se:umu:diva-143712 (URN)10.1016/j.biortech.2017.09.081 (DOI)000417841800026 ()28950127 (PubMedID)
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2018-06-09Bibliographically approved
5. Formation of microbial inhibitors in steam-explosion pretreatment of softwood impregnated with sulfuric acid and sulfur dioxide
Open this publication in new window or tab >>Formation of microbial inhibitors in steam-explosion pretreatment of softwood impregnated with sulfuric acid and sulfur dioxide
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2018 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 262, p. 242-250Article in journal (Refereed) Published
Abstract [en]

Wood chips of Norway spruce were pretreated by steam explosion at 195–215 °C after impregnation with either sulfuric acid (SA) or sulfur dioxide (SD). The effects of different pretreatment conditions on formation of microbial inhibitors were investigated, and the inhibitory effects on yeast of pretreatment liquids and of specific inhibitors that were found in the pretreatment liquids were elucidated. Whereas the concentrations of most inhibitors increased with increasing pretreatment temperatures, there were exceptions, such as formaldehyde and p-hydroxybenzaldehyde. The highest concentration of each inhibitor was typically found in SD-pretreated material, but formic acid was an exception. The toxic effects on yeast were studied using concentrations corresponding to loadings of 12 and 20% total solids (TS). Among individual inhibitors that were quantitated in pretreatment liquids, the concentrations of formaldehyde were by far most toxic. There was no or minimal yeast growth in the formaldehyde concentration range (5.8–7.7 mM) corresponding to 12% TS.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Lignocellulose, Pretreatment, Sulfuric acid, Sulfur dioxide, Microbial inhibitors
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:umu:diva-145114 (URN)10.1016/j.biortech.2018.04.074 (DOI)000433219500030 ()29709843 (PubMedID)
Note

Originally included in thesis in manuscript form.

Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-06-25Bibliographically approved
6. Comparison of catalytically non-productive adsorption of fungal proteins to lignins and pseudo-lignin using isobaric mass tagging
Open this publication in new window or tab >>Comparison of catalytically non-productive adsorption of fungal proteins to lignins and pseudo-lignin using isobaric mass tagging
(English)Manuscript (preprint) (Other academic)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:umu:diva-145115 (URN)
Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-06-09

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