Production of low-cost sugar using mechanical refining of pretreated biomass

Production of fermentable sugars from lignocellulosic biomass still remains expensive. To make the overall process more economically attractive, mechanical refining has been suggested to overcome biomass recalcitrance and process complexity for the following reasons. a) Sugar conversion can be enhanced by 10-20% with commercially attractive levels of enzymes and enzyme dosage can be reduced since the substrate is more digestible. b) Pretreatment severity (e.g. dilute-acid treatment) can be greatly reduced to achieve the same level of sugar conversion, resulting in lower concentrations of inhibitors for fermentation or catalytic upgrading. c) Mechanical refining technology can be installed in conjunction with any type of pretreatment scheme. d) Mechanical refining is a commercially proven technology at process flows of ~2,000 dry tons/day of biomass.

The 12-inch disk refiner was used to study the effect of refining variables such as gap size and solid content on refining energy and digestibility. It was found that there was a maximum in sugar conversion with respect to the amount of refining energy. To evaluate the energy consumption, the 36-inch refiner was tested at 33% solid content and the sugar conversion was increased from 69% to 79% at 130 kWh/dry ton biomass. For the 42-inch refiner, the sugar conversion was increased from 47% to 72% at 5 FPU/g with refining energy at 67 kWh/dry ton biomass. We will discuss the opportunity in refining plate design in terms of refining actions (external fibrillation, internal delamination, and cutting) and the optimization of refining energy in terms of high-solid enzymatic hydrolysis.