Monday, April 30, 2007

Improving AFEX pretreatment using concentrated aqueous ammonia

Bryan D. Bals, Hasan Alizadeh, Derek J. Marshall, Elizabeth D. Newton, Venkatesh Balan, and Bruce E. Dale. Chemical Engineering and Material Science, Michigan State University, 2527 Engineering Building, East Lansing, MI 48823

Previous studies with Ammonia Fiber Expansion (AFEX) have focused on charging anhydrous ammonia into the reaction vessel at high (1g/g dry biomass) loadings, while adjusting moisture content of the biomass as needed.  We have recently suggested that a modified ammonia recovery approach and reactor that uses concentrated aqueous ammonia can significantly reduce the costs associated with biomass processing.  In addition, recent findings suggest that using concentrated ammonia can reduce the ammonia loading required for an effective pretreatment.

We present a complete investigation into using concentrated aqueous ammonia under pressure in AFEX pretreatment with corn stover.  The complex relationship between ammonia loading, ammonia concentration, and moisture content of the biomass is studied, using subsequent enzymatic hydrolysis as a measure of the effectiveness of the pretreatment.  AFEX pretreatment parameters are reoptimized at the lowest ammonia loading that still maintains high sugar yields.  In addition, the role of reaction pressure is examined, with particular emphasis on maintaining ammonia in the liquid phase.  After reoptimizing AFEX pretreatment at lower ammonia loadings, a complete comparison to the optimal high ammonia loading conditions is made, including sugar yields, hydrolysis rates, microbial tolerance at high solid loadings, inhibition and degradation products, and fermentability of the resulting hydrolysate.