3-23: Fractionation and Characterization of Lignin from Extractive Ammonia Pretreated Corn Stover

A novel pretreatment technology called Extractive Ammonia (EA) has been used to simultaneously convert cellulose I to cellulose III and partially remove lignin from lignocellulosic biomass. The resultant EA pretreated feedstocks contain highly digestible carbohydrates and significantly reduced lignin content. Temperature, ammonia concentration and solvent type are the major factors that contribute to selective lignin solubilization and further extraction. Depending on these pretreatment conditions, it is possible to observe variations on the selectivity during lignin solubilization. Some pretreatment conditions tend to solubilize ash and hemicellulose residues along with lignin, while others selectively remove lignin with significantly less carbohydrates. However, since most applications for purified lignin streams require low ash and carbohydrate contents, these extractives have been further fractionated to obtain a cleaner lignin fraction. Thus differences in solubility, precipitation and filtration based methods were applied to get four distinct lignin-rich fractions. In this work, multiple fractions generated from extractives of EA  pretreated corn stover were characterized by several techniques, including GPC, DSC, ¹³C-NMR, ³⁴P-NMR and 2D NMR. Additionally, the level of lignin extraction and cellulose III conversion was correlated with cellulose digestibility for corn stover.