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Ethanol from lignocellulose: Management of by-products of hydrolysis
Karlstad University, Faculty of Technology and Science, Department of Chemistry and Biomedical Sciences.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fuel ethanol can be produced from lignocellulosic materials, such as residues from agriculture and forestry. The polysaccharides of lignocellulose are converted to sugars by hydrolysis and the sugars can then be fermented to ethanol using microorganisms. However, during hydrolysis a wide range of by-products are also generated. By-product formation can affect ethanol yield and productivity. Management of by-products of hydrolysis is therefore important in the development of commercially viable production of cellulosic ethanol.

Detoxification of inhibitory dilute-acid lignocellulose hydrolysates by treatment with Ca(OH)2 (overliming) efficiently improves the fermentability, but is associated with drawbacks like sugar degradation and CaSO4 precipitation. In factorial designed experiments, in which pH and temperature were varied, dilute-acid spruce hydrolysates were treated with Ca(OH)2, NH4OH or NaOH. The concentrations of sugars and inhibitory compounds were measured before and after the treatments. The fermentability was examined using the yeast Saccharomyces cerevisiae and compared with reference fermentations of synthetic medium without inhibitors. The treatment conditions were evaluated by comparing the balanced ethanol yield, which takes both the degradation of sugars and the ethanol production into account. Treatment conditions resulting in excellent fermentability and minimal sugar degradation were possible to find regardless of whether Ca(OH)2, NH4OH or NaOH was used. Balanced ethanol yields higher than those of the reference fermentations were achieved for hydrolysates treated with all three types of alkali. As expected, treatment with Ca(OH)2 gave rise to precipitated CaSO4. The NH4OH treatments gave rise to a brownish precipitate but the amounts of precipitate formed were relatively small. No precipitate was observed in treatments with NaOH. The findings presented can be used to improve the effectiveness of alkali detoxification of lignocellulose hydrolysates and to minimize problems with sugar degradation and formation of precipitates.

Overexpression of different S. cerevisiae genes was investigated with the aim to engineer a biocatalyst with increased inhibitor tolerance. Overexpression of YAP1, a gene encoding a transcription factor, conveyed increased resistance to lignocellulose-derived inhibitors as well as to a dilute-acid hydrolysate of spruce.

Recombinant Aspergillus niger expressing the Hypocrea jecorina endoglucanase Cel7B was cultivated on spent lignocellulose hydrolysate (stillage). The fungus simultaneously removed inhibitors present in the stillage and produced higher amounts of endoglucanase than when it was grown in a standard medium with comparable monosaccharide content. The concept can be applied for on-site production of enzymes in a cellulose-to-ethanol process and facilitate recycling of the stillage stream.

Place, publisher, year, edition, pages
Karlstad: Karlstad University , 2009. , 71 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2009:7
Keyword [en]
Ethanol, Lignocellulose, Detoxification, Genetic engineering, Enzyme production
National Category
Other Chemistry Topics
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kau:diva-3314ISBN: 978-91-7063-228-0 (print)OAI: oai:DiVA.org:kau-3314DiVA: diva2:134165
Public defence
2009-02-27, Ericssonsalen, 9C 204, Karlstad Universitet, Karlstad, 13:15 (English)
Opponent
Supervisors
Available from: 2009-02-09 Created: 2009-01-19 Last updated: 2011-10-05Bibliographically approved
List of papers
1. Critical conditions for improved fermentability during overliming of acid hydrolysates from spruce.
Open this publication in new window or tab >>Critical conditions for improved fermentability during overliming of acid hydrolysates from spruce.
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2005 (English)In: Applied Biochemistry and Biotechnology, ISSN 0273-2289, E-ISSN 1559-0291, Vol. 121-124, 1031-44 p.Article in journal (Refereed) Published
Abstract [en]

Bioethanol can be produced from wood via acid hydrolysis, but detoxification is needed to achieve good fermentability. Overliming was investigated in a factorial designed experiment, in which pH and temperature were varied. Degradation of inhibitory furan aldehydes was more extensive compared to monosaccharides. Too harsh conditions led to massive degradation of sugars and formation of inhibiting acids and phenols. The ethanol productivity and yield after optimal overliming reached levels exceeding reference fermentations of pure glucose. A novel metric, the balanced ethanol yield, which takes both ethanol production and losses of fermentable sugars into account, was introduced and showed the optimal conditions within the investigated range. The findings allow process technical and economical considerations to govern the choice of conditions for overliming.

National Category
Natural Sciences
Identifiers
urn:nbn:se:kau:diva-3309 (URN)10.1385/ABAB:124:1-3:1031 (DOI)15930579 (PubMedID)
Available from: 2009-01-19 Created: 2009-01-19 Last updated: 2017-12-14Bibliographically approved
2. Ammonium hydroxide detoxification of spruce acid hydrolysates.
Open this publication in new window or tab >>Ammonium hydroxide detoxification of spruce acid hydrolysates.
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2005 (English)In: Applied Biochemistry and Biotechnology, ISSN 0273-2289, E-ISSN 1559-0291, Vol. 121-124, 911-22 p.Article in journal (Refereed) Published
Abstract [en]

When dilute-acid hydrolysates from spruce are fermented to produce ethanol, detoxification is required to make the hydrolysates fermentable at reasonable rates. Treatment with alkali, usually by overliming, is one of the most efficient approaches. Several nutrients, such as ammonium and phosphate, are added to the hydrolysates prior to fermentation. We investigated the use of NH4OH for simultaneous detoxification and addition of nitrogen source. Treatment with NH4OH compared favorably with Ca(OH)2, Mg(OH)2, Ba(OH)2, and NaOH to improve fermentability using Saccharomyces cerevisiae. Analysis of monosaccharides, furan aldehydes, phenols, and aliphatic acids was performed after the different treatments. The NH4OH treatments, performed at pH 10.0, resulted in a substantial decrease in the concentrations of furfural and hydroxymethylfurfural. Under the conditions studied, NH4OH treatments gave better results than Ca(OH)2 treatments. The addition of an extra nitrogen source in the form of NH4Cl at pH 5.5 did not result in any improvement in fermentability that was comparable to NH4OH treatments at alkaline conditions. The addition of CaCl2 or NH4Cl at pH 5.5 after treatment with NH4OH or Ca(OH)2 resulted in poorer fermentability, and the negative effects were attributed to salt stress. The results strongly suggest that the highly positive effects of NH4OH treatments are owing to chemical conversions rather than stimulation of the yeast cells by ammonium ions during the fermentation.

National Category
Other Chemistry Topics
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-3310 (URN)10.1385/ABAB:124:1-3:0911 (DOI)15930570 (PubMedID)
Available from: 2009-01-19 Created: 2009-01-19 Last updated: 2017-12-14Bibliographically approved
3. Optimal conditions for alkaline detoxification of dilute-acid lignocellulose hydrolysates.
Open this publication in new window or tab >>Optimal conditions for alkaline detoxification of dilute-acid lignocellulose hydrolysates.
2006 (English)In: Applied Biochemistry and Biotechnology, ISSN 0273-2289, E-ISSN 1559-0291, Vol. 129-132, 599-611 p.Article in journal (Refereed) Published
Abstract [en]

Alkaline detoxification strongly improves the fermentability of dilute-acid hydrolysates in the production of bioethanol from lignocellulose with Saccharomyces cerevisiae. New experiments were performed with NH4OH and NaOH to define optimal conditions for detoxification and make a comparison with Ca(OH)2 treatment feasible. As too harsh conditions lead to sugar degradation, the detoxification treatments were evaluated through the balanced ethanol yield, which takes both the ethanol production and the loss of fermentable sugars into account. The optimization treatments were performed as factorial experiments with 3-h duration and varying pH and temperature. Optimal conditions were found roughly in an area around pH 9.0/60 degrees C for NH4OH treatment and in a narrow area stretching from pH 9.0/80 degrees C to pH 12.0/30 degrees C for NaOH treatment. By optimizing treatment with NH4OH, NaOH, and Ca(OH)2, it was possible to find conditions that resulted in a fermentability that was equal or better than that of a reference fermentation of a synthetic sugar solution without inhibitors, regardless of the type of alkali used. The considerable difference in the amount of precipitate generated after treatment with different types of alkali appears critical for industrial implementation.

Identifiers
urn:nbn:se:kau:diva-3294 (URN)10.1385/ABAB:130:1:599 (DOI)16915672 (PubMedID)
Available from: 2009-01-19 Created: 2009-01-16 Last updated: 2017-12-14Bibliographically approved
4. Overexpression of Saccharomyces cerevisiae transcription factor and multidrug resistance genes conveys enhanced resistance to lignocellulose-derived fermentation inhibitors.
Open this publication in new window or tab >>Overexpression of Saccharomyces cerevisiae transcription factor and multidrug resistance genes conveys enhanced resistance to lignocellulose-derived fermentation inhibitors.
2010 (English)In: Process Biochemistry, ISSN 1359-5113, E-ISSN 1873-3298, Vol. 45, no 2, 264-271 p.Article in journal (Refereed) Published
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-3312 (URN)10.1016/j.procbio.2009.09.016 (DOI)000273897400017 ()
Available from: 2009-01-19 Created: 2009-01-19 Last updated: 2017-12-14Bibliographically approved
5. Cellulase Production from Spent Lignocellulose Hydrolysates with Recombinant Aspergillus niger.
Open this publication in new window or tab >>Cellulase Production from Spent Lignocellulose Hydrolysates with Recombinant Aspergillus niger.
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2009 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 75, no 8, 2366-2374 p.Article in journal (Refereed) Published
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kau:diva-3313 (URN)10.1128/AEM.02479-08 (DOI)
Available from: 2009-01-19 Created: 2009-01-19 Last updated: 2017-12-14Bibliographically approved

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