Factors that contribute to cellulose III conversion and associated impact on enzymatic digestibility of cellulose

Recent advances in ammonia-based pretreatment of lignocellulosic biomass led to the creation of the Extractive Ammonia (EA) pretreatment. This novel technology converts the naturally occurring cellulose I (CI) to more easily-hydrolysed cellulose III (CIII) while also removing up to 50% of the lignin present. Little is known about the factors that contribute to CIII formation and the associated consequences on enzymatic digestibility of cellulose. Thus systematic studies are needed to further understand this phenomenon. For this purpose, a new reaction system was built to control the formation of the ammonia-cellulose complex (i.e., temperature, ammonia concentration, liquid to solid ratio and time) and likewise to control conditions during assembly of CIII crystals (i.e., temperature and solvent system). Also, deconvolution methods were developed to calculate the relative proportions of CI, CIII and amorphous cellulose in a given sample. By applying these methods, we better understand how CIII is formed as a function of pretreatment conditions and the key factors that impact CIII conversion including solvent type, solvent concentration, temperature and residence time. The kinetics of CIII conversion was also analyzed as a function of temperature and concentration of ammonia in two different solvent systems. The degree of CIII conversion and crystallinity of cellulose achieved under various pretreatment regimes was correlated with enzymatic hydrolysis yields. From these studies, we found that higher CIII crystallinity actually improves enzymatic hydrolysis yields, contradicting the current paradigm for the effects of crystallinity on cellulose hydrolysis.