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Optimal conditions for alkaline detoxification of dilute-acid lignocellulose hydrolysates.
Karlstad University, Faculty of Technology and Science.
Karlstad University, Faculty of Technology and Science.
STFI-Packforsk, Stockholm, Sweden.
Karlstad University, Faculty of Technology and Science.
2006 (English)In: Applied Biochemistry and Biotechnology, ISSN 0273-2289, E-ISSN 1559-0291, Vol. 129-132, p. 599-611Article 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.

Place, publisher, year, edition, pages
2006. Vol. 129-132, p. 599-611
Identifiers
URN: urn:nbn:se:kau:diva-3294DOI: 10.1385/ABAB:130:1:599PubMedID: 16915672OAI: oai:DiVA.org:kau-3294DiVA, id: diva2:134148
Available from: 2009-01-19 Created: 2009-01-16 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Ethanol from lignocellulose: Management of by-products of hydrolysis
Open this publication in new window or tab >>Ethanol from lignocellulose: Management of by-products of hydrolysis
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. p. 71
Series
Karlstad University Studies, ISSN 1403-8099 ; 2009:7
Keywords
Ethanol, Lignocellulose, Detoxification, Genetic engineering, Enzyme production
National Category
Other Chemistry Topics
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-3314 (URN)978-91-7063-228-0 (ISBN)
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
2. Ethanol from lignocellulose: Alkali detoxification of dilute-acid spruce hydrolysates
Open this publication in new window or tab >>Ethanol from lignocellulose: Alkali detoxification of dilute-acid spruce hydrolysates
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Detoxification of dilute-acid lignocellulose hydrolysates by treatment with Ca(OH)2 (overliming) efficiently improves the production of fuel ethanol, 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 possibility that the ammonium ions from the NH4OH treatments gave a positive effect as an extra source of nitrogen during the fermentations was excluded after experiments in which NH4Cl was added to the medium. 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.

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2006. p. 38
Series
Karlstad University Studies, ISSN 1403-8099 ; 2006:30
National Category
Other Chemistry Topics
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-2632 (URN)91-7063-061-5 (ISBN)
Presentation
(English)
Available from: 2010-03-29 Created: 2010-03-29 Last updated: 2011-10-05Bibliographically approved

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