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Liquefaction of lignocellulose at high solids concentrations.

Jørgensen H, Vibe-Pedersen J, Larsen J, Felby C

Department of Forestry and Forest Products, Danish Centre for Forest, Landscape and Planning, The Royal Veterinary and Agricultural University, Rolighedsvej 23, DK‐1958 Frederiksberg, Denmark.

To improve process economics of the lignocellulose to ethanol process a reactor system for enzymatic liquefaction and saccharification at high solids concentrations was developed. The technology is based on free fall mixing employing a horizontally placed drum with a horizontal rotating shaft mounted with paddlers for mixing. Enzymatic liquefaction and saccharification of pretreated wheat straw was tested with up to 40 (w/w) % initial DM. In less than 10 h, the structure of the material was changed from intact straw particles (length 1-5 cm) into a paste/liquid that could be pumped. Tests revealed no significant effect of mixing speed in the range 3.3 to 11.5 rpm on the glucose conversion after 24 h and ethanol yield after subsequent fermentation for 48 h. Low power inputs for mixing are therefore possible. Liquefaction and saccharification for 96 h using an enzyme loading of 7 FPU (g DM)(-1) and 40 % DM resulted in a glucose concentration of 86 g kg(-1). Experiments conducted at 2 to 40 (w/w) % initial DM revealed that cellulose and hemicellulose conversion decreased almost linearly with increasing DM. Performing the experiments as simultaneous saccharification and fermentation also revealed a decrease in ethanol yield at increasing initial DM. Saccharomyces cerevisiae was capable of fermenting hydrolysates up to 40 % DM. The highest ethanol concentration, 48 g kg(-1), was obtained using 35 (w/w) % DM. Liquefaction of biomass with this reactor system unlocks the possibility of 10 (w/w) % ethanol in the fermentation broth in future lignocellulose to ethanol plants. (c) 2006 Wiley Periodicals, Inc.

Published 25 July 2006 in Biotechnol Bioeng.
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