Strategies to improve copper-catalyzed alkaline hydrogen peroxide pretreatment of woody biomass

We previously demonstrated that copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment of hybrid poplar substantially improves delignification and the subsequent sugar yields following enzymatic hydrolysis relative to uncatalyzed AHP.  In this current study, a combination of strategies was employed to improve further the Cu-AHP process by efficiently utilizing the H₂O₂ and by reducing the chemical inputs.  In the first strategy, an alkali pre-extraction step was added prior to the Cu-AHP process, and this two-stage pretreatment improved glucose yields relative to standard Cu-AHP from 63% to 86 %.  Secondly, to utilize the H₂O₂ more efficiently, fed-batch addition of H₂O₂ was performed over the course of 10 h.  This also resulted in an increase in the glucose yields (75 %) compared to the standard Cu-AHP pretreatment (63 %).  Interestingly, combining both of these strategies (i.e. alkali pre-extraction followed by fed-batch Cu-AHP) resulted in very high glucose yields (96 % of theoretical maximum).  Experiments were also performed to evaluate the impact of different concentrations of enzyme, H₂O₂, and catalyst loading on the modified fed-batch, two-stage Cu-AHP pretreatment process.  Our results demonstrated that we could substantially lower the chemical inputs while still maintaining high product yields.  The pretreatment also delivered a relatively pure lignin stream consisting of ≥90% Klason lignin.  Preliminary characterizations of the purified lignin demonstrated that it was high molecular weight and relatively unmodified.  Overall, the improved Cu-AHP process not only provided higher sugar yields while using lower chemical inputs, but also preserved the lignin for potential valorization.