11-32: Relevance of crystalline cellulose III formation to the Extractive-AFEXTM (E-AFEXTM) process

Recent studies have shown that reorganizing the hydrogen bonding network within crystalline cellulose using ammonia to produce cellulose III can enhance fungal cellulase activity by up to 5-fold (Chundawat et al, 2011, JACS, 133:11163; Igarashi et al, 2011, Science, 333:1279). These findings have prompted development of a novel ammonia treatment process designated as Extractive-AFEX^TM (E-AFEX^TM) that facilitates formation of cellulose III during pretreatment of lignocellulosic biomass. However, further process optimization of E-AFEX^TM would be facilitated by a deeper understanding of the mechanism of cellulose crystal structure alteration by ammonia and other co-solvents. Detailed studies were carried out to explore the impact of ammonia-water-organic solvent systems, residence time and reaction temperature on the crystal structure of cellulose. The substrates were characterized using suitable diffraction methods. Finally, the substrates were subjected to enzymatic hydrolysis by various combinations of Trichoderma reesei cellulases at low and high solids loading, to additionally mimic industrially-relevant biomass refining scenarios. Theoretical modeling was utilized to gain a mechanistic understanding of cellulose crystal structure disruption by solvents like ammonia and its subsequent enzymatic deconstruction. These studies shed new light into the mechanism of cellulose crystal structure modification by ammonia and its deconstruction to fermentable sugars.