Comparison of Lab, Pilot, and Commercial Scale Low Consistency Mechanical Refining for Improvements in Enzymatic Digestibility of Pretreated Hardwood

Mechanical refining has been shown to improve biomass enzymatic digestibility. In this study industrial high-yield sodium carbonate hardwood pulp and was subjected to lab, pilot and industrial refining to determine if the mechanical refining improves the enzymatic hydrolysis sugar conversion efficiency differently at different refining scales. Lab, pilot and industrial refining increased the biomass digestibility for lignocellulosic biomass relative to the unrefined material. The sugar conversion was increased from 47% to 72% at 5 FPU/g of biomass with refining at 67.0 kWh/t. There is a maximum in the sugar conversion with respect to the amount of refining energy. Water retention value is a good predictor of improvements in sugar conversion for a given fiber source and composition. Improvements in biomass digestibility with refining due to lab, pilot plant and industrial refining were similar with respect to water retention value. The effects of various mechanical refining operating conditions will be discussed in detail.  These conditions including refiner plate design, refiner plate gap, refining energy input and other energy considerations, refining consistency (especially high consistency refining), and refiner operation costs and economics.  Fundamental studies of how particle size and surface area change with refining and how different fractions contribute toward the enzymatic hydrolysis efficiency will also be presented.