| 1. |
- Larsson, S, et al.
(författare)
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The generation of fermentation inhibitors during dilute acid hydrolysis of softwood
- 1999
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 24:3-4, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the severity of dilute sulfuric acid hydrolysis of spruce (softwood) on sugar yield and on the fermentability of the hydrolysate by Saccharomyces cerevisiae (Baker's yeast) was investigated. Fermentability was assessed as the ethanol yield on fermentable sugars (mannose and glucose) and the mean volumetric productivity (4 h). The hydrolysis conditions, residence time, temperature, and sulfuric acid concentration were treated as a single parameter, combined severity (CS). When the CS of the hydrolysis conditions increased, the yield of fermentable sugars increased to a maximum between CS 2.0-2.7 for mannose, and 3.0-3.4 for glucose above which it decreased. The decrease in the yield of monosaccharides coincided with the maximum concentrations of furfural and 5-hydroxymethylfurfural (5HMF). With the further increase in CS, the concentrations of furfural and 5-HMF decreased while the formation of formic acid and levulinic acid increased The yield of ethanol decreased at approximately CS 3; however, the volumetric productivity decreased at lower CS. The effect of acetic acid, formic acid, levulinic acid furfural, and 5-HMF on fermentability was assayed in model fermentations Ethanol yield and volumetric productivity decreased with increasing concentrations of acetic acid, formic acid, and levulinic acid. Furfural and 5-HMF decreased the volumetric productivity but did not influence the final yield of ethanol. The decrease in volumetric productivity was more pronounced when 5-HMF was added to the fermentation, and this compound was depleted at a lower rate than furfural. The inhibition observed in hydrolysates produced in higher CS could not be fully explained by the effect of the by-products furfural, 5-HMF, acetic acid, formic acid: and levulinic acid. (C) 1998 Elsevier Science Inc.
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| 2. |
- Palmqvist, E, et al.
(författare)
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Design and operation of a bench-scale process development unit for the production of ethanol from lignocellulosics
- 1996
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Ingår i: Bioresource Technology. - 1873-2976. ; 58:2, s. 171-179
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Tidskriftsartikel (refereegranskat)abstract
- A bench-scale unit for the development of an enzymatic process for the bioconversion of lignocellulosics to ethanol has been used to study the recycling of waste-water streams to minimize fresh-water requirements and reduce effluent streams. Willow, after impregnation with sulphur dioxide, was steam-pretreated, enzymatically hydrolysed, and the sugars produced were fermented using S. cerevisiae. The fermentation broth was distilled and the stillage was fractionated by evaporation into six separate condensate fractions and a residue. The overall yield of ethanol from willow was 65% of the theoretical yield based on total fermentable sugars. The inhibitory effect of the evaporation condensates was assessed by fermentation using S. cerevisiae. The non-volatile residue of the stillage was found to be inhibitory to fermentation. The ethanol yield decreased from 0.37 g/g in a pure sugar reference to 0.31 g/g in the residue and the average ethanol fermentation rate decreased fi om 6.3 g/(l h) to 2.7 g/(l h), respectively. The evaporation condensates, containing the volatile components, showed no negative effects on fermentation. The intermediate evaporation condensate fractions, fractions 4 and 5, had the lowest chemical oxygen demand (GOD), 1560 and 1120 mg/l, compared with 33 300 mg/l for the stillage. Therefore, these fractions can be released directly into the effluent without further treatment. Copyright (C) 1997 Elsevier Science Ltd.
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| 3. |
- Palmqvist, E, et al.
(författare)
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Simultaneous detoxification and enzyme production of hemicellulose hydrolysates obtained after steam pretreatment
- 1997
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 20:4, s. 286-293
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Tidskriftsartikel (refereegranskat)abstract
- In the process of making ethanol from lignocellulosic materials, compounds inhibitory to microorganisms are generated during steam pretreatment of the wood. Water-soluble inhibitors and pentoses are liberated and washed from the cellulose structure which is further enzymatically hydrolyzed. To make the process economically feasible, rite pentoses have to be fermented to ethanol. A major drawback with the pentose-fermenting organisms that have been suggested for this purpose is that they do not tolerate an inhibitory environment and there fore, the pentose stream has to be detoxified prior to fermentation. An alternative use of the hemicellulose hydrolysate obtained after steam;pretreatment of willow is to use it for. enzyme production by the cellulolytic fungus Trichoderma reesei. The sugars in the pentose function are almost completely utilized, and simultaneously the hemicellulose hydrolysate is detoxified and can be recirculated in rite process to minimize the need for freshwater. (C) 1997 by Elsevier Science Inc.
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| 4. |
- Palmqvist, E, et al.
(författare)
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The effect of water-soluble inhibitors from steam-pretreated willow on enzymatic hydrolysis and ethanol fermentation
- 1996
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 19:6, s. 470-476
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Tidskriftsartikel (refereegranskat)abstract
- In the process of producing ethanol from lignocellulosic materials, compounds inhibitory to enzymatic hydrolysis and fermentation are generated during the pretreatment of the wood. In an industrial process, these compounds will accumulate due to the recirculation of process streams. The inhibitory effects of the accumulation of volatile and nonvolatile compounds released during stream pretreatment on enzymatic hydrolysis and fermentation were studied. The volatile compounds did not affect either the enzymatic hydrolysis or the fermentation significantly even at high concentrations. In contrast, the nonvolatile compounds severely affected both the hydrolysis and the fermentation: the effect was more pronounced in the latter case. For the effective use of a lignocellulosic material as a substrate for ethanol production, the nonvolatile compounds must thus be removed.
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| 5. |
- Stenberg, K, et al.
(författare)
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Recycling of process streams in ethanol production from softwoods based on enzymatic hydrolysis
- 1998
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 70-2, s. 697-708
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Tidskriftsartikel (refereegranskat)abstract
- In ethanol production from lignocellulose by enzymatic hydrolysis and fermentation, it is desirable to minimize addition of fresh-water and waste-water streams, which leads to an accumulation of substances in the process. This study shows that the amount of fresh water used and the amount of waste water thereby produced in the production of fuel ethanol from softwood, can be reduced to a large extent by recycling of either the stillage stream or part of the liquid stream from the fermenter. A reduction in fresh-water demand of more than 50%, from 3 kg/kg dry raw material to 1.5 kg/kg dry raw material was obtained without any negative effects on either hydrolysis or fermentation. A further decrease in the amount of fresh water, to one-fourth of what was used without recycling of process streams, resulted in a considerable decrease in the ethanol productivity and a slight decrease in the ethanol yield.
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| 6. |
- Tengborg, C, et al.
(författare)
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Comparison of SO2 and H2SO4 impregnation of softwood prior to steam pretreatment on ethanol production
- 1998
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 70-2, s. 3-15
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Tidskriftsartikel (refereegranskat)abstract
- The pretreatment of softwood with sulfuric acid impregnation in the production of ethanol, based on enzymatic hydrolysis, has been investigated. The parameters investigated were: H2SO4 concentration (0.5-4.4% w/w liquid), temperature (180-240 degrees C), and residence time (1-20 minutes). The combined severity (log Ro-pH) was used to combine the parameters into a single reaction ordinate. The highest yields of fermentable sugars, i.e., glucose and mannose, were obtained at a combined severity of 3. At this severity, however, the fermentability declined and the ethanol yield decreased. In a comparison with previous results, SO2 impregnation was found to be preferable, since it resulted in approximately the same sugar yields, but better fermentability.
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