10-40: Maximizing sugar yield by applying kinetics of hemicellulose hydrolysis and sugar degradation in SPORL pretreatment of Douglas-fir

Pretreatment at high severities is often required to achieve high enzymatic digestibility of lignocelluloses. However, high severity can also cause increased sugar degradation to inhibitors to affect downstream processing.  We hypothesize that sugar degradation reaction is more sensitive to temperature than hemicellulose dissolution reactions.  Therefore, it is conceivable to conduct pretreatment at the same severity with a low temperature without affecting the enzymatic digestibility of the resultant substrate, but with significantly reduced inhibitor formation. 

We will present kinetic analysis of the proposed hypothesis along with experimental data from SPORL (Sulfite Pretreatment to Overcome Recalcitrance of lignocelluloses) of Douglas fir at 165 and 180°C.  A combined hydrolysis factor (CHF) and a combined degradation factor (CDF) were developed to illustrate the difference in kinetics between hemicellulose dissolution and sugar degradation.  Fitting the models to the experimental data confirmed hemicellulosic sugar degradation was more sensitive to pretreatment temperature than hemicellulose dissolution.  Specifically,  SPORL pretreatment at 165°C for 75min with the acid and bisulfite dosages of 0.4% and 10%, respectively, produced an enzymatic digestibility of  94%, HMF and furfural of 1.35 g/L and 0.47 g/L, respectively. At the same pretreatment severity using the same chemical loading but at an elevated temperature of 180°C and short time of 30 min, approximately the same enzymatic digestibility of 92% was achieved, but with significantly higher formation of HMF of 3.88 g/L and Furfural of 1.80 g/mL.