AUTHOR=Coffman Philip , McCaffrey Nicole , Gardner James , Bhagia Samarthya , Kumar Rajeev , Wyman Charles E. , Tanjore Deepti 

TITLE=In Situ Rheological Method to Evaluate Feedstock Physical Properties Throughout Enzymatic Deconstruction

JOURNAL=Frontiers in Energy Research

VOLUME=Volume 6 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2018.00053

DOI=10.3389/fenrg.2018.00053

ISSN=2296-598X

ABSTRACT=Feedstock physical properties determine not only downstream flow behavior, but also downstream process yields. Enzymatic treatment of pretreated feedstocks greatly dependent on upstream feedstock physical properties and choice of pre-processing technologies. Currently available enzyme assays have been developed to study biomass slurries at low concentrations of ≤ 1% w/w. At commercially relevant biomass concentrations of ≥ 15% w/w, pretreated feedstocks have sludge-like properties, where low free water restricts movement of unattached enzymes. This work is an account of the various steps taken to develop a method that helps identify the time needed for solid-like biomass slurries transition into liquid-like states during enzymatic hydrolysis. A pre-processing technology that enables feedstocks in achieving this transition sooner will greatly benefit enzyme kinetics and thereby overall process economics. 
Through this in situ rheological properties determining method, we compared a model feedstock, Avicel®PH101 cellulose, and acid pretreated corn stover. We determined that 25% (w/w) Avicel when treated with Novozymes Cellic®CTec2 (80 mg protein/g glucan) can reduce from solid-like to liquid-like state in 5.5 h, as the phase angles rise beyond 45° at this time. The same slurry needed 5.3 h to achieve liquid-like state with Megazyme endoglucanase (40 mg protein/g glucan). After 10.8 h, CTec2 slurry reached a phase angle of 89° or complete liquid-like state but Megazyme slurry peaked only to 64.7°, possibly due to inhibition by cello-oligomers. Acid pretreated corn stover at 30% (w/w) with a CTec2 protein loading of 80 mg/g glucan exhibited a solid-like to liquid-like transition at 37.8 h, which reflects the combined inhibition of low water activity and presence of lignin. The acid pretreated slurry also never achieved complete liquid-like state due to the presence of biomass residue. This method is applicable in several scenarios comparing varying combinations of pre-processing technologies, feedstock types, pretreatment chemistries, and enzymes. Using this method, we can generate a process chain with optimal flow behavior at commercially-relevant conditions.