Bioethanol Production: Pretreatment and Enzymatic Hydrolysis of Softwood

Research output: ThesisDoctoral Thesis (compilation)


The enzymatic hydrolysis process can be used to produce bioethanol from softwood, which are the dominating raw material in the Northern hemisphere. This thesis deals with the development of the process focusing on the pretreatment and the enzymatic hydrolysis stages.

The influence of pretreatment conditions on sugar yield, and the effect of inhibitors on the ethanol yield, were investigated for spruce and pine. The maximum yields of hemicellulose sugars and glucose were obtained under different pretreatment conditions. This indicates that two-stage pretreatment may be preferable. The added catalysts, H2SO4 and SO2, resulted in similar total sugar yields about 40 g/100 g dry raw material. However, the fermentability of SO2-impregnated material was better. This pretreatment resulted in the formation of inhibitors to the subsequent process steps, e.g. sugar and lignin degradation products.

The glucose yield in the enzymatic hydrolysis stage was affected by various parameters such as enzyme loading, temperature, pH, residence time, substrate concentration, and agitation. To decrease the amount of fresh water used and thereby waste water produced, the sugar-rich pre-hydrolysate from the pretreatment step was included in the enzymatic hydrolysis of the solid fraction, resulting in a reduction in the cellulose conversion of up to 36%. Different prehydrolysate detoxification methods, such as treatment with Ca(OH)2, laccase, and fermentation using yeast, were investigated. The latter was shown to be very efficient. The amount of fresh water used can be further reduced by recycling various process streams. This was simulated experimentally in a bench-scale process. A reduction in fresh water demand of 50% was obtained without any further negative effects on either hydrolysis or fermentation.


  • Charlotte Tengborg
Research areas and keywords

Subject classification (UKÄ)

  • Chemical Engineering


  • recirculation of process streams, detoxification, inhibition, hydrolysis conditions, enzymatic hydrolysis, Ethanol production, steam pretreatment, softwood, Carbochemistry, petrochemistry, fuels and explosives technology, Petrokemi, bränslen, sprängämnen
Original languageEnglish
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date2000 May 26
  • Professor Guido Zacchi, Department of Chemical Engineering 1, Lund University
Print ISBNs91-7874-069-X
Publication statusPublished - 2000
Publication categoryResearch

Bibliographic note

Defence details Date: 2000-05-26 Time: 10:15 Place: Kemicentrum, Getingevägen 60, Lund, hörsal A External reviewer(s) Name: Saddler, John N. Title: Professor Affiliation: Department of Wood Science, University of British Columbia, Vancouver, BC, Canada --- Article: Stenberg, K., Tengborg, C., Galbe, M. and Zacchi, G. Optimisation of steam pretreatment of SO2-impregnated mixed softwoods for ethanol production.J. Chem. Technol. Biotechnol. 1998, 71, 299-308. Article: Tengborg, C., Stenberg, K., Galbe, M., Zacchi, G., Larsson, S., Palmqvist, E. and Hahn-Hägerdal, B. Comparison of SO2 and H2SO4 impregnation of softwood prior to steam pretreatment on ethanol production.Appl. Biochem. Biotechnol. 1998, 70-72, 3-15. Article: Tengborg, C., Galbe, M. and Zacchi, G. Influence of enzyme loading and physical parameters on the enzymatic hydrolysis of steam-pretreated softwood. Biotechnol. Prog. (Submitted) Article: Tengborg, C., Galbe, M. and Zacchi, G. Reduced inhibition of enzymatic hydrolysis of steam-pretreated softwood. Enzyme Microb. Technol. (Submitted) Article: Tengborg, C., Galbe, M., Zacchi, G. and Kruus, K. Detoxification of prehydrolysate from steam-pretreated spruce prior to enzymatic hydrolysis. J. Ind. Microbiol. (Submitted) Article: Stenberg, K., Tengborg, C., Galbe, M., Zacchi, G., Palmqvist, E. and Hahn-Hägerdal, B. Recycling of process streams in ethanol production from softwoods based on enzymatic hydrolysis. Appl. Biochem. Biotechnol. 1998, 70-72, 697-708.