Monday, April 30, 2007 - 2:10 PM

Power consumption in a scraped surface reactor for batch and fed-batch enzymatic hydrolysis of pretreated corn stover slurries

Rajesh K. Dasari and R. Eric Berson. Chemical Engineering, University of Louisville, J.B. Speed School of Engineering, Chemical Engineering Department, Belknap Campus, Louisville, KY 40292

High solids processing allows for operation of bioreactors with high substrate content while keeping the processing volume the same. This provides the following benefits: reduction of waste stream volume, reduction in use of water and utilities, and reduction of processing time. However, high solids processing poses mixing problems above a certain solids concentration (~15% for pretreated corn stover solids).  Also, higher solids content implies higher slurry viscosity which leads to higher power consumption. A semi-batch approach is employed to reduce the power consumption without sacrificing processing with higher solids content. The power consumption is compared in an 8 liter scraped surface reactor (SSR) for the enzymatic hydrolysis of PCS in batch and semi-batch mode. The study by some of the researchers in the past proved that SSR improves the heat and mass transfer in fluids, especially with high solids concentration. It is observed that scraping of blades against wall without loaded material accounts for above 50% of the total power consumption. The correlation of the power consumption to rotor speed, reactor geometry, and material properties is developed. Higher glucose production rates are observed in the SSR than in laboratory shake flasks, which is contradictory to many reactor scale-up cases in the literature.  This is attributed to the improved mixing and heat transfer abilities of the SSR.