7-04: Flow of biomass undergoing enzymatic hydrolysis

The rheological properties of cellulosic biomass suspensions undergoing hydrolysis are influenced by many factors including particle size, shape and concentration. We performed magnetic resonance flow imaging to characterize velocity profiles and rheograms for lignocellulosic and delignified fibers. Depending on the concentration and flow rate many flow phenomena are observed that include turbulence, laminar symmetric and asymmetric velocity profiles and settling. Symmetric, laminar velocity profiles that are well described by generalized Newtonian models only occur at certain ranges of concentration and flow rate. Rheograms obtained during hydrolysis of delignified fibers having different average fiber lengths suggest that crowding numbers computed using length-averaged lengths can be used to predict yield stresses of suspensions where particle aspect ratio undergo rapid changes. In experiments with wheat straw at 5% solids loading the initial velocity profiles were flat, with apparent wall slip. As hydrolysis progressed the profiles changed to a concentric flow with a central plug surrounded by an annular region moving at a non-zero velocity. Later in the hydrolisis the suspensions displayed shear thinning behavior with continuous velocity profiles amenable to obtaining rheograms. Also observed for wheat straw slurries was an increase over time in resistance to flow before any addition of enzymes which is attributed to "swelling" or hydration of the fibers.