Mechanical refining to enhance enzymatic hydrolysis of pretreated biomass

Production of fermentable sugars from lignocellulosic biomass to produce biofuels and platform chemicals still remains expensive.  To make the overall process more economically attractive, mechanical refining has been suggested as a viable strategy to reduce enzyme dosage and enhance digestibility of pretreated biomass.  In addition to enzyme reduction, fermentation inhibitors can be significantly reduced and reactor metallurgy can be replaced by inexpensive material with the decreased pretreatment severity.  Mechanical refining is a proven technology in pulp and paper industry for several decades and handles ~1000 od ton biomass per day depending on the size of refiner.

Since mechanical refining has been optimized in pulp and paper industry, there are a few questions to be answered.  Can this handle high insoluble-solid content to produce a final product with a high concentration?  What is the operational energy cost at high insoluble-solid content?  What variables can be controlled to optimize mechanical refining?

To address these questions, a pilot-scale refiner at NC State (12-inch disk refiner) was tested to study the effect of refining variables such as disk gap size and consistency on refining energy and digestibility.  In addition, the scale-up feasibility of refining technology was evaluated at Andritz (36-inch disk refiner) using NREL’s pretreated corn stover.  Strong correlations were found among measured pore volume, refining energy consumption, and biomass digestibility.  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 use and hydrolysis yield.