OPTIMIZATION OF STEAM PRETREATMENT OF SO2-IMPREGNATED MIXED SOFTWOODSFOR ETHANOL-PRODUCTION

Pretreatment of mixed softwoods with SO2 impregnation and steam for pr oduction of ethanol has been investigated. The optimal conditions, bot h for sugar yield and ethanol yield, to assess the effect of inhibitor s formed in the pretreatment, have been determined. The parameters inv estigated 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). T o investigate fermentability, the hydrolysed filtrate was fermented us ing 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 inf luence on the ethanol production rate. (C) 1998 SCI.