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Effects of impregnation of softwood with sulfuric acid and sulfur dioxide on chemical and physical characteristics, enzymatic digestibility, and fermentability
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.
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. Vol. 247, p. 200-208
Keywords [en]
Hydrothermal pretreatment, Sulfuric acid, Sulfur dioxide, Inhibition, Enzymatic digestibility
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:umu:diva-143712DOI: 10.1016/j.biortech.2017.09.081ISI: 000417841800026PubMedID: 28950127OAI: oai:DiVA.org:umu-143712DiVA, id: diva2:1171852
Available from: 2018-01-08 Created: 2018-01-08 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)
Opponent
Supervisors
Available from: 2018-02-23 Created: 2018-02-19 Last updated: 2018-06-09Bibliographically approved

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