Sunday, May 3, 2009
3-95
Effects of Mixing on the Enzymatic Hydrolysis and Simultaneous Saccharification and Fermentation of Pretreated Spruce
Magnus Wiman, Benny Palmkvist, and Gunnar Lidén. Department of Chemical Engineering, Lund University, Getingevägen 60, SE-221 00, Lund, Sweden
Simultaneous saccharification and fermentation (SSF) has proved to be a promising option for ethanol production from lignocellulosic materials. Separation costs for recovery of ethanol in the fermentation is quite significant, and for this reason a high content of water insoluble solids (WIS) is needed in the SSF. Concentrated fiber suspensions are, however, characterized by both a high viscosity and a non-newtonian flow behavior, which may lead to poor mixing and/or high power consumptions in large-scale operation. It is therefore important both to rheologically characterize the material, and also to study the consequences of mixing in the SSF process.
In the current work, enzymatic hydrolysis (EH) and SSF experiments of pretreated spruce (10% WIS) were carried out in lab-scale reactors at different stirring speeds. As expected, the initial rate of hydrolysis increased with increasing stirring speed. This positive effect was more pronounced in the range of low stirring speeds (<100 rpm). Surprisingly, however, the initial ethanol productivity in the SSF experiments showed the opposite trend. A higher ethanol productivity was observed when the stirring speed was lowered. Possible explanations of these results were investigated by several sets of separate experiments in order to consider different individual effects of mixing in SSF.
In the current work, enzymatic hydrolysis (EH) and SSF experiments of pretreated spruce (10% WIS) were carried out in lab-scale reactors at different stirring speeds. As expected, the initial rate of hydrolysis increased with increasing stirring speed. This positive effect was more pronounced in the range of low stirring speeds (<100 rpm). Surprisingly, however, the initial ethanol productivity in the SSF experiments showed the opposite trend. A higher ethanol productivity was observed when the stirring speed was lowered. Possible explanations of these results were investigated by several sets of separate experiments in order to consider different individual effects of mixing in SSF.