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Pretreatment and enzymatic saccharification of lignocellulose: formation and effects of pseudolignin
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Leif Jönsson)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Production of advanced biofuels, green chemicals, and bio-based materials from renewable lignocellulosic biomass would contribute to decreased dependence on fossil resources and to sustainable development. The overall aim of the investigations was to explore how preprocessing and pretreatment technologies affected the chemical composition of cellulosic materials and their susceptibility to enzymatic saccharification, which is one of the major routes for biorefining of lignocellulose. Special attention was given to formation and effects of pseudolignin, an aromatic substance derived from polysaccharides. Pseudolignin is formed during dry thermal preprocessing, such as torrefaction, and during dilute-acid pretreatment, techniques that are highly relevant for biorefining of wood.

The susceptibility of seven fractions of Scots pine to dilute-acid pretreatment and enzymatic saccharification was investigated. Harsh pretreatment conditions led to slow initial conversion, which was tentatively attributed to pseudolignin. Pretreatment with ionic liquids was investigated using substrates consisting of crystalline and amorphous cellulose, hemicelluloses, and wood. The susceptibility of torrefied spruce wood to enzymatic saccharification after pretreatment with acid or ionic liquid was investigated. The results showed that the negative effects of mild torrefaction on enzymatic saccharification were possible to overcome using pretreatment with the ionic liquid. In a subsequent study, the possibility to dissolve pseudolignin with ionic liquids and conventional solvents was explored. The effects of pseudolignin on wood polysaccharides and enzymatic saccharification were further studied using NMR, FTIR, XPS, TOF-SIMS, and SEM. The surface-sensitive analytical methods TOF-SIMS, XPS, and SEM revealed how pseudolignin formed a coat on the surface of the polysaccharide, which could explain the effects on the enzymatic saccharification.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2016. , 67 p.
Keyword [en]
Pretreatment, enzymatic saccharification, ionic liquid, torrefaction, pseudolignin
National Category
Analytical Chemistry
Research subject
Analytical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-126463ISBN: 978-91-7601-575-9 (print)OAI: oai:DiVA.org:umu-126463DiVA: diva2:1033471
Public defence
2016-10-28, KB3B1, KBC-huset, Linnaeus väg 6, 907 36, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2016-10-07 Created: 2016-10-06 Last updated: 2016-10-07Bibliographically approved
List of papers
1. Analysis, pretreatment and enzymatic saccharification of different fractions of Scots pine
Open this publication in new window or tab >>Analysis, pretreatment and enzymatic saccharification of different fractions of Scots pine
2014 (English)In: BMC Biotechnology, ISSN 1472-6750, E-ISSN 1472-6750, Vol. 14, 20Article in journal (Refereed) Published
Abstract [en]

Background: Forestry residues consisting of softwood are a major lignocellulosic resource for production of liquid biofuels. Scots pine, a commercially important forest tree, was fractionated into seven fractions of chips: juvenile heartwood, mature heartwood, juvenile sapwood, mature sapwood, bark, top parts, and knotwood. The different fractions were characterized analytically with regard to chemical composition and susceptibility to dilute-acid pretreatment and enzymatic saccharification. Results: All fractions were characterized by a high glucan content (38-43%) and a high content of other carbohydrates (11-14% mannan, 2-4% galactan) that generate easily convertible hexose sugars, and by a low content of inorganic material (0.2-0.9% ash). The lignin content was relatively uniform (27-32%) and the syringyl-guaiacyl ratio of the different fractions were within the range 0.021-0.025. The knotwood had a high content of extractives (9%) compared to the other fractions. The effects of pretreatment and enzymatic saccharification were relatively similar, but without pretreatment the bark fraction was considerably more susceptible to enzymatic saccharification. Conclusions: Since sawn timber is a main product from softwood species such as Scots pine, it is an important issue whether different parts of the tree are equally suitable for bioconversion processes. The investigation shows that bioconversion of Scots pine is facilitated by that most of the different fractions exhibit relatively similar properties with regard to chemical composition and susceptibility to techniques used for bioconversion of woody biomass.

Place, publisher, year, edition, pages
BioMed Central, 2014
Keyword
Scots pine, Chemical composition, Dilute-acid pretreatment, Enzymatic saccharification
National Category
Microbiology Agricultural Biotechnology
Identifiers
urn:nbn:se:umu:diva-89235 (URN)10.1186/1472-6750-14-20 (DOI)000334881900001 ()
Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
2. Evaluation of four ionic liquids for pretreatment of lignocellulosic biomass.
Open this publication in new window or tab >>Evaluation of four ionic liquids for pretreatment of lignocellulosic biomass.
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2014 (English)In: BMC Biotechnology, ISSN 1472-6750, E-ISSN 1472-6750, Vol. 14, no 1, 34-45 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Lignocellulosic biomass is highly recalcitrant and various pretreatment techniques are needed to facilitate its effective enzymatic hydrolysis to produce sugars for further conversion to bio-based chemicals. Ionic liquids (ILs) are of interest in pretreatment because of their potential to dissolve lignocellulosic materials including crystalline cellulose.

RESULTS: Four imidazolium-based ionic liquids (ILs) ([C=C2C1im][MeCO2], [C4C1im][MeCO2], [C4C1im][Cl], and [C4C1im][HSO4]) well known for their capability to dissolve lignocellulosic species were synthesized and then used for pretreatment of substrates prior to enzymatic hydrolysis. In order to achieve a broad evaluation, seven cellulosic, hemicellulosic and lignocellulosic substrates, crystalline as well as amorphous, were selected. The lignocellulosic substrates included hybrid aspen and Norway spruce. The monosaccharides in the enzymatic hydrolysate were determined using high-performance anion-exchange chromatography. The best results, as judged by the saccharification efficiency, were achieved with [C4C1im][Cl] for cellulosic substrates and with the acetate-based ILs for hybrid aspen and Norway spruce. After pretreatment with acetate-based ILs, the conversion to glucose of glucan in recalcitrant softwood lignocellulose reached similar levels as obtained with pure crystalline and amorphous cellulosic substrates. IL pretreatment of lignocellulose resulted in sugar yields comparable with that obtained with acidic pretreatment. Heterogeneous dissolution with [C4C1im][HSO4] gave promising results with aspen, the less recalcitrant of the two types of lignocellulose included in the investigation.

CONCLUSIONS: The ability of ILs to dissolve lignocellulosic biomass under gentle conditions and with little or no by-product formation contributes to making them highly interesting alternatives for pretreatment in processes where high product yields are of critical importance.

Place, publisher, year, edition, pages
Springer, 2014
Keyword
Ionic liquid, Pretreatment, Lignocellulose, Enzymatic saccharification
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-90622 (URN)10.1186/1472-6750-14-34 (DOI)000335990000001 ()24779378 (PubMedID)
Available from: 2014-06-26 Created: 2014-06-25 Last updated: 2017-12-05Bibliographically approved
3. Biochemical Conversion of Torrefied Norway Spruce After Pretreatment with Acid or Ionic Liquid
Open this publication in new window or tab >>Biochemical Conversion of Torrefied Norway Spruce After Pretreatment with Acid or Ionic Liquid
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2016 (English)In: Bioenergy Research, ISSN 1939-1234, E-ISSN 1939-1242, Vol. 9, no 1, 355-368 p.Article in journal (Refereed) Published
Abstract [en]

The chemical effects of torrefaction and the possibility to combine torrefaction with biochemical conversion were explored in experiments with five preparations of wood of Norway spruce that had been torrefied using different degrees of severity. Compositional analysis and analyses using solid-state CP/MAS C-13 NMR, Fourier-transform infrared (FTIR) spectroscopy, and Py-GC/MS showed small gradual changes, such as decreased hemicellulosic content and increased Klason lignin value, for torrefaction conditions in the range from 260 A degrees C and 8 min up to 310 A degrees C and 8 min. The most severe torrefaction conditions (310 A degrees C, 25 min) resulted in substantial loss of glucan and further increase of the Klason lignin value, which was attributed to conversion of carbohydrate to pseudo-lignin. Even mild torrefaction conditions led to decreased susceptibility to enzymatic hydrolysis of cellulose, a state which was not changed by pretreatment with sulfuric acid. Pretreatment with the ionic liquid (IL) 1-butyl-3-methylimidazolium acetate overcame the additional recalcitrance caused by torrefaction, and the glucose yields after 72 h of enzymatic hydrolysis of wood torrefied at 260 A degrees C for 8 min and at 285 A degrees C for 16.5 min were as high as that of IL-pretreated non-torrefied spruce wood. Compared to IL-pretreated non-torrefied reference wood, the glucose production rates after 2 h of enzymatic hydrolysis of IL-pretreated wood torrefied at 260 A degrees C for 8 min and at 285 A degrees C for 16.5 min were 63 and 40 % higher, respectively. The findings offer increased understanding of the effects of torrefaction and indicate that mild torrefaction is compatible with biochemical conversion after pretreatment with alternative solvents that disrupt pseudo-lignin-containing lignocellulose.

Keyword
Torrefaction, Wood, Acid pretreatment, Ionic liquid, Enzymatic hydrolysis
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:umu:diva-118386 (URN)10.1007/s12155-015-9698-7 (DOI)000370816300032 ()
Available from: 2016-04-22 Created: 2016-03-18 Last updated: 2017-11-30Bibliographically approved
4. Dissolution of pseudolignin in ionic liquid for improved saccharification of cellulose
Open this publication in new window or tab >>Dissolution of pseudolignin in ionic liquid for improved saccharification of cellulose
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-126465 (URN)
Available from: 2016-10-07 Created: 2016-10-07 Last updated: 2016-10-07
5. Pseudolignin formation during dry thermal treatment: analysis of microcrystalline cellulose and beechwood xylan
Open this publication in new window or tab >>Pseudolignin formation during dry thermal treatment: analysis of microcrystalline cellulose and beechwood xylan
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-126467 (URN)
Available from: 2016-10-07 Created: 2016-10-07 Last updated: 2016-10-07

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