A process for energy-efficient high-solids fed-batch enzymatic liquefaction of cellulosic biomass

Enzymatic hydrolysis of cellulosic biomass is a key step of biological routes for production of fuels and chemicals. Economic considerations for large-scale implementation of the process demand operation in the high solids regime. In this regime, the biomass is processed at concentrations of 15% (w/w) or higher, forming a high viscosity slurry which introduces processing challenges especially in the initial stages of hydrolysis (liquefaction). Rheological measurements with rotational rheometers are challenging in these materials due to rapid changes in rheology that require high time resolution, and the large particle sizes which cause gap effects and settling. We employed a non-invasive real-time rheometer based on magnetic resonance imaging velocimetry (FlowScan^TM, Aspect Imaging) to characterize the real-time evolution of yield stress of cellulose undergoing enzymatic hydrolysis in a recycle-flow reactor. Past studies on the liquefaction of biomass have shown that fast initial rheological changes occur, and this was used along with the real-time rheometer to develop an energy-efficient process that enabled high-solids hydrolysis of biomass. Hydrolysis was performed in fed-batch mode, with fibers and enzyme being added at various time points. Each addition of fibers caused a rapid increase followed by a decay in yield stress due to the enzymatic action. The decay of the yield stress was more rapid for the initial loads, becoming slower as the hydrolysis progressed. Additionally, different enzyme feeding schemes were found to impact overall cellulose hydrolysis and process efficiency. Effects of enzyme feeding schemes and opportunities for further optimization for a pre-hydrolysis process will be discussed.