Separation of lignocellulosic slurries into liquor and solids fractions is a critical but often overlooked step in ethanol production from biomass.  Many dilute-acid pretreatment-based biorefinery configurations require solid-liquid separation at various points throughout the process. For example, higher fermentation yields are achieved when the liquor fraction is separately conditioned at an elevated pH before recombination with the solids.  Separate fermentation of pentose and hexose sugars is another process configuration that requires extraction of xylose-rich liquor from the cellulose solids.  Because the performance of these solid-liquid separation steps directly affects product recovery, the efficacy of this unit operation also influences process economics.

Experiments were performed on bench and pilot scale equipment to determine solid-liquid separation efficiency during co-current washing of dilute-acid pretreated corn stover slurries.   The three separation techniques assessed were pressure filtration, vacuum filtration and centrifugation.  Computer simulations were then developed to simulate multiple stage counter-current washing to determine the impact of staged separation and wash water usage rate on recovery of soluble sugars from pretreated slurries.   Equipment configuration, slurry physical properties, and solids washing techniques were identified as the major factors influencing performance, and these issues will be discussed and recommendations will be provided.