Ethanol from Softwood - Process Development Based on Steam Pretreatment and SSF

Kerstin Stenberg

Research output: ThesisDoctoral Thesis (compilation)


Fuel ethanol can be produced from lignocellulosics by the enzymatic hydrolysis process, which consists of a pretreatment step prior to hydrolysis, followed by fermentation and finally refining. This thesis deals with the development of the enzymatic process using softwood as raw material. The focus has not only been on how to obtain high yields, but also on how to solve problems, which can arise in an industrial process, such as inhibition and contamination.

The pretreatment step was evaluated using steam pretreatment and impregnation with an acid catalyst, either sulphur dioxide or sulphuric acid. Both impregnation methods resulted in approximately the same yield, 65% of the theoretical of fermentable sugars, i.e. glucose and mannose, after enzymatic hydrolysis. However, impregnation with sulphur dioxide, resulted in higher ethanol productivity and yield in the fermentation.

Simultaneous saccharification and fermentation (SSF) was investigated using various substrate and cellulase concentrations. An overall ethanol yield of 70% of the theoretical was obtained using the whole slurry from the pretreatment step at an insoluble dry weight content of 5%, which was shown to be optimal. SSF resulted in both higher productivity and higher ethanol yield than in separate hydrolysis and fermentation, but proved to be more sensitive to infection by lactic aid bacteria.

More complex process integration, in the form of recirculation of process streams, which is desirable in an industrial process, was investigated using bench-scale equipment. A reduction in the fresh-water demand of 50%, from 3 kg/kg dry raw material to 1.5 kg/kg dry raw material, was found to be possible without any negative effects on either hydrolysis or fermentation.

A techno-economic evaluation of different process configurations in a process applying SSF was also performed. It was found that the ethanol production cost could be reduced by 20% by internal energy integration and by another 15% by recirculation to the same extent that was shown to give no negative effects in the recirculation study.
Original languageEnglish
Awarding Institution
  • Division of Chemical Engineering
  • Zacchi, Guido, Supervisor
Award date1999 Jun 4
ISBN (Print)91-628-3583-1
Publication statusPublished - 1999

Bibliographical note

Defence details

Date: 1999-06-04
Time: 10:15
Place: Chemical Center, Lund

External reviewer(s)

Name: Lidén, Gunnar
Title: Dr
Affiliation: Chalmers University of Technology, Göteborg


Article: I. Stenberg, K., Tengborg, C., Galbe, M. and Zacchi, G. 1998 Optimisation of steam pretreatment of SO2-impregnated mixed softwoods for ethanol production. J. Chem. Technol. Biotechnol. 71: 299-308

Article: II. Tengborg, C., Stenberg, K., Galbe, M., Zacchi, G., Larsson, S., Palmqvist, E. and Hahn-Hägerdal, B. 1998 Comparison of SO2 and H2SO4 impregnation of softwood prior to steam pretreatment on ethanol production. Appl. Biochem. Biotechnol. 70-72: 3-15

Article: III. Stenberg, K., Bollók, M., Réczey, K., Galbe, M. and Zacchi, G. The effect of substrate and cellulase concentration in simultaneous saccharification and fermentation (SSF) of steam-pretreated softwood for ethanol production. Biotechnol. Bioeng. (Submitted)

Article: IV. Stenberg, K., Galbe. M. and Zacchi, G. The influence of lactic acid formation on the simultaneous saccharification and fermentation (SSF) of softwood to ethanol. Enzyme Microb. Technol. (Submitted)

Article: V. Stenberg, K., Tengborg, C., Galbe, M., Zacchi, G., Palmqvist, E. and Hahn-Hägerdal, B. 1998 Recycling of process streams in ethanol production from softwoods based on enzymatic hydrolysis. Appl. Biochem. Biotechnol. 70-72: 697-708

Subject classification (UKÄ)

  • Chemical Engineering

Free keywords

  • economy
  • infection
  • inhibition
  • recirculation
  • S. cerevisiae
  • SSF
  • steam pretreatment
  • ethanol production
  • process development
  • softwood
  • Carbochemistry
  • petrochemistry
  • fuels and explosives technology
  • Petrokemi
  • bränslen
  • sprängämnen


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