Evaluation of Pretreatment and Process Configurations for Combined Ethanol and Biogas Production from Lignocellulosic Biomass
Sammanfattning: In view of global climate change and the increasing energy demand there is a need for renewable energy resources. This thesis discusses an energy-driven biorefinery concept based on the agricultural residues corn stover and wheat straw. The work is divided into two main parts. The first part is concerned with the effects of steam pretreatment and choice of acid catalyst on ethanol and biogas production, as well as the overall energy yield. The second part focuses on the combination of acetic-acid-catalysed steam pretreatment and simultaneous saccharification and co-fermentation (SSCF) and the role of process configuration on SSCF.Steam pretreatment was found to be a useful instrument to improve access of the main components of corn stover. This pretreatment resulted in high energy recovery. The choice of catalyst during steam pretreatment affected the overall energy recovery and product yield. Steam pretreatment with acetic acid or sulphuric acid improved the energy recovery compared with steam pretreatment with no catalyst or phosphoric acid. Phosphoric acid had toxic effects on ethanol and biogas production, while acetic acid was toxic only to ethanol production. The toxic effects on ethanol production were overcome by increasing the pH from 5.0 to 5.5. Process configuration also influenced the total energy recovery and product yield. This showed that not only the type of pretreatment, but also the process configuration, is important in an energy-driven biorefinery.Acetic acid is a known inhibitor during ethanol production. Using the S. cerevisiae strain KE6-12b resulted in ethanol production from both glucose and xylose, despite the fact that acetic-acid-catalysed steam pretreatment was used. Fed-batch improved SSCF in terms of ethanol yield and final ethanol concentration. Increasing the water insoluble solids (WIS) concentration from 10% to 11.7% improved the ethanol concentration, but the higher amount of inhibitors had a negative effect on the ethanol yield. Increasing the yeast concentration improved the results with higher WIS, but improvements are still required to increase the ethanol yield and concentration.
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