13-04: Mechanical refining to enhance enzymatic hydrolysis of pretreated biomass

Enzymatic hydrolysis remains an expensive process and thus, the amount of charged enzyme must be reduced to make the overall process more economically attractive.  Mechanical refining of biomass has been suggested as a viable strategy to reduce enzyme dosage and enhance digestibility of pretreated biomass.  This proven technology can be applied to any type of biomass and pretreatment to reduce pretreatment severity, which could benefit the downstream biological processes.  Additionally, the economic value of reducing enzyme cost and hydrolysis time is coupled with a relatively low operation cost of mechanical refining.  With a lab-scale refiner (PFI mill and Valley Beater), mild–alkaline pretreated (green liquor, kraft, and Na₂CO₃) hardwood and softwood were tested.  It was found that mechanical refining enhanced sugar recovery of all pretreated biomass samples.  Enzymatic sugar recovery of alkaline pretreated hardwood increased from 66.9% to 89.3% at 5 FPU/g.  An enzyme reduction of 32.3% was realized at a level of sugar conversion over 90.5%.  In some cases, 5 FPU/g enzymatic hydrolysis of alkaline pretreated softwood achieved over 100% improvement in total sugar conversion.  Pore volume and surface area were evaluated in a wet state using Simons’ staining and DSC thermoporometry methods. A strong correlation was found between biomass digestibility and measured properties.  Furthermore, a pilot-scale refiner with a 12-inch disk was tested to demonstrate the scale-up feasibility of refining technology.  We will discuss the opportunity in refining plate design in terms of refining actions (cutting vs. fibrillation) and the optimization of refining energy use and hydrolysis yield.