11-36: The effect of mixing on the liquefaction and saccharification of cellulose fibers

During the digestion of biomass by enzymatic hydrolysis, drastic changes in the mechanical properties of the cellulosic slurry cause a transition from a solid-like material to a pumpable liquid. Mixing of enzymes and substrate to facilitate liquefaction and saccharification is an important step. To assess the effect of mixing quality on the rate of liquefaction and saccharification, cellulases were added to static cellulosic fiber beds in vials with different initial enzyme concentration distributions. The first condition represented a well-mixed slurry, with a homogeneous enzyme concentration distribution throughout the suspension. The opposite extreme condition was addition of a thin layer of enzymes on one end of the vial, representing a completely unmixed enzyme. Samples were then incubated at 50C without any additional agitation. The state of liquefaction of the fiber beds was assessed using a cylindrical penetrometer test and magnetic resonance imaging (MRI) and soluble sugar release was quantified by HPLC. MRI was used to measure average signal intensity, which correlates with the water state in cellulose suspensions. Both MRI and penetrometer measurements indicated the strong benefits of centimeter-scale homogenization on the rates of liquefaction and saccharification. Order of magnitude differences in the rate of glucose production were seen between mixed and unmixed samples. Results highlight the importance of cm-scale mixing on both the rate of liquefaction and rate of release of soluble sugars during reaction. The potential of using MRI and penetrometer to monitor liquefaction and saccharification are discussed.