Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
To understand cellulosic biomass complex structure and effect of lignin removal on biomass digestibility, two methods employing sodium chlorite/acetic acid (SC/AA) and peracetic acid (PAA) are often used. These methods are well established and are reportedly highly selective. However, results are mostly reported for highly recalcitrant and non-pretreated softwood and hardwood species, and information on less recalcitrant lignocellulosics, such as agricultural residues, energy crops, and pretreated biomass is scarce. In addition, effects on cellulose structure and reactivity are not documented. Thus, in this study, delignification kinetics and selectivity of two delignification methods (SC/AA and PAA) were evaluated when applied to untreated switchgrass, poplar, corn stover, and pine, and poplar pretreated by AFEX, controlled pH, lime, and SO2 pretreatments. Cellulose model compounds (Avicel PH101, α-cellulose, cotton linter, and filter paper) were also subjected to these delignification methods, and untreated and delignified solids were enzymatically hydrolyzed. It was found that both methods, irrespective of substrate and pretreatment types, were effective in removing > 90% of lignin, but selectivity of lignin and carbohydrates removal varied. For untreated biomass, PAA was more selective in removing lignin than SC/AA and had less pronounced impact on cellulose structure as determined by gel permeation chromatography. However, both methods were found to be less selective for pretreated solids. Enzymatic digestibility of solids prepared by both methods revealed that although lignin removal enhanced enzymatic digestibility several fold, the effect was substrate dependent. The effects of PAA and SC/AA on cellulose molecular structure and enzymatic hydrolysis will also be discussed.