Non-unified effects of cellulose allomorphs on fast pyrolysis and enzymatic hydrolysis

Abstract

Saccharification is a vital process to release sugar monomers from cellulose before the production of biofuels and fine chemicals. In this study, four distinct crystalline allomorphs of Cellulose (I–IV) are synthesized to examine the impact of crystalline structure and degree of crystallinity on cellulose depolymerization in pyrolysis and hydrolysis. It is found that cellulose with higher crystallinity produces higher yields of levoglucosan. Specifically, Cellulose II and III exhibit lower crystallinity index and levoglucosan yields compared to Cellulose I and IV. Notably, despite Cellulose IV having a higher crystallinity index than Cellulose I, the differences in crystalline structure and hydroxyl group level lead to a lower levoglucosan yield in pyrolysis. Thermogravimetric kinetics analysis suggests that cellulose with high crystallinity yields more anhydro-sugars through dehydration reactions, whereas amorphous cellulose predominantly produces lower molecular weight molecules through ring scission reactions. It is found that Cellulose II yields the maximum amount of glucose, while higher crystallinity levels have a negative impact on the sugar yield in general. This study provides a fundamental insight for modulating cellulose crystallinity towards effective utilization of biomass.