| 1. |
- Eklund, R, et al.
(författare)
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The Influence of SO2 and H2SO4 Impregnation of Willow Prior to Steam Pretreatment
- 1995
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Ingår i: Bioresource Technology. - 1873-2976. ; 52:3, s. 225-229
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation steam pretreatment of willow with the addition of SO2 or H2SO4 was studied, the aim being to recover both the cellulose and the hemicellulose fr actions. The willow was steamed (1 bar saturated steam) prior to impregnation with 0-3% H2SO4 or 1% SO2 (w/w substrate). The pretreatment experiments were performed at temperatures in the range 160-230 degrees C for 10 min. The highest xylose recovery with H2SO4 impregnation was obtained using 3% H2SO4 at 190 degrees C, where 80% of the available xylose could be recovered by washing. At these pretreatment conditions, a glucose yield after enzymatic hydrolysis of 67%, based on the glucan available in the raw material, was achieved. The maximum glucose yield, 95%, was obtained when the willow was impregnated with 1% SO2 and pretreated at 200 degrees C. At these conditions, 62% of the original xylose was solubilized. As glucan is the main constituent of willow, a high yield of glucose is of more importance than a high yield of xylose, leading to the conclusion that impregnation with SO2 is better than impregnation with H2SO4.
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| 2. |
- Larsson, M, et al.
(författare)
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Recirculation of process water in the production of ethanol from softwood
- 1997
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Ingår i: Bioresource Technology. - 1873-2976. ; 60:2, s. 143-151
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Tidskriftsartikel (refereegranskat)abstract
- In the production of ethanol from lignocellulosics, large quantities of water are needed in various process steps. In industrial processes, recycling of process streams is necessary to minimise fresh water requirements and decrease the amount of wastewater produced. This leads to increases in various substances, both volatile and non-volatile which inhibit fermentation. In the present Study ethanol was produced from softwood in a bench-scale process development unit. The stillage stream from the distillation step was fractionated by evaporation and various evaporation fractions characterised and their inhibitory effect on fermentation investigated. irt was found that the volatile fractions have no negative effect on the fermentation while the non-volatile fraction inhibited fermentation and resulted in a decreased yield. Simulation of a six-effect evaporation unit based on the experimental data shows that the intermediate evaporation condensate fractions are most suited for disposal. The chemical and biological oxygen demands are only about 10% of the value in the stillage stream. Evaporation has been shown to be an effective way to drastically diminish the build-up of inhibitory compounds when process streams are recirculated, but the energy demand is high. Various process configurations to reduce the energy demand are suggested. (C) 1997 Elsevier Science Ltd.
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| 3. |
- 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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| 4. |
- Palmqvist, E, et al.
(författare)
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Evaluation of cell recycling in continuous fermentation of enzymatic hydrolysates of spruce with Saccharomyces cerevisiae and on-line monitoring of glucose and ethanol
- 1998
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 50:5, s. 545-551
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Tidskriftsartikel (refereegranskat)abstract
- The maximum growth rate of Saccharomyces cerevisiae ATCC 96581, adapted to fermentation of spent sulphite liquor (SSL), was 7 times higher in SSL of hardwood than the maximum growth rate of bakers' yeast. ATCC 96581 was studied in the continuous fermentation of spruce hydrolysate without and with cell recycling. Ethanol productivity by ATCC 96581 in continuous fermentation of an enzymatic hydrolysate of spruce was increased 4.6 times by employing cell recycling. On-line analysis of CO2, glucose and ethanol (using a microdialysis probe) was used to investigate the effect of fermentation pH on cell growth and ethanol production, and to set the dilution rate. Cell growth in the spruce hydrolysates was strongly influenced by fermentation pH. The fermentation was operated in continuous mode for 210 h and a theoretical ethanol yield on fermentable sugars was obtained.
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| 5. |
- 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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| 6. |
- Stenberg, K, et al.
(författare)
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Optimisation of steam pretreatment of SO2-impregnated mixed softwoods for ethanol production
- 1998
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Ingår i: Journal of Chemical Technology and Biotechnology. - 0268-2575. ; 71:4, s. 299-308
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Tidskriftsartikel (refereegranskat)abstract
- Pretreatment of mixed softwoods with SO2 impregnation and steam for production of ethanol has been investigated. The optimal conditions, both for sugar yield and ethanol yield, to assess the effect of inhibitors formed in the pretreatment, have been determined. The parameters investigated were: SO2 concentration (1-6% (w/w) dry matter), temperature (190-230 degrees C) and residence time (2-15 min). After pretreatment, the material was separated into a solid residue and a filtrate. The solid residue was enzymatically hydrolysed with 2% dry matter (w/w). To investigate fermentability, the hydrolysed filtrate was fermented using Saccharomyces cerevisiae. The effects of the different parameters are described by response-surface modelling. The highest experimental sugar yield of 42.1 g per 100 g dry matter was obtained at 210 degrees C and 5.5 min residence time. Although the fermentabilities were good for all filtrates with yields greater than 90% of the yield obtained in a pure glucose reference solution, the pretreatment has a clear influence on the ethanol production rate. (C) 1998 SCI.
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| 7. |
- 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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| 8. |
- 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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