(111c) Flocculation Assisted Clarification of Enzymatically Hydrolyzed Corn Stover Slurries

Stickel, J. J., National Renewable Energy Laboratory
Lischeske, J. J., National Renewable Energy Laboratory
Sievers, D. A., National Renewable Energy Laboratory
Crawford, N. C., National Renewable Energy Laboratory

The biochemical conversion of lignocellulosic biomass to ethanol is able utilize robust microorganisms that tolerate residual solids and moderate concentrations of soluble inhibitory species. However, many potential hydrolysis-based conversion pathways to hydrocarbon fuels are highly sensitive to the composition of the hydrolyzate slurries. Removal of the insoluble solids from the slurry is a requisite first step before additional aqueous species fractionation or concentration steps may occur.

Here we present the development of a solid-liquid separation process for pretreated and enzymatically hydrolyzed corn stover slurries. The separation of the insoluble lignin residues from these slurries is challenging due to the high concentration of solids (5-10 wt%) and the fact that the solids are relatively small (23 μm mean diameter) and deformable. The focus of the work is vacuum-driven bulk filtration aided by flocculation. Without flocculation, the solids form a compressible cake with low permeability. Conversely, adding low doses of a cationic polyacrylamide flocculant generated large flocs (1 mm target size) which formed highly permeable cakes under low applied differential pressures.  In general, flocculation greatly increased the overall capacity of vacuum filtration for the slurries tested, but this comes at the expense of increased wash water, where washing is used to remove residual sugars from the cake bed. Finally, we show that a polishing filtration step may be avoided when using flocculants, depending on the requirements of the subsequent upgrading process.