| Liquid dispersion efficiency cannot be measured by conventional means in a non-transparent slum. By measuring the conversion of cellulose to glucose using a liquid enzyme as a tracer, this work seeks to determine if the dispersion of a small liquid volume in a high-solids viscous slurry can be quantified. The method is then used to compare the efficiency of a variety of mixing systems, and determines the effects of shear, solids in suspension, and bulk flow in dispersing the liquid.;Enzymatic hydrolysis reactions were carried out in a 3.0 L bioreactor with a working volume of 2.5 liters utilizing a 13 percent sawdust solids concentration and an enzyme concentration equal to 11.5 filter paper units per gram of cellulose. Four impeller configurations were investigated using either two rushton turbines, two marine propellers, or a combination of the two. Two agitation speeds were chosen, one above (300 rpm) and one below (100 rpm) the just suspended speed of the solids. A helical impeller was also investigated for its effectiveness in mixing a higher viscosity slurry.;The reactions were stopped after 24 hours to avoid complicating factors such as viscosity changes and product inhibition. The theoretical maximum production of glucose was determined to be 12.4 g/L by dispersing the enzyme in a pure liquid volume prior to adding the solids. Mixing system power requirements are also considered in the discussion of efficiency. The marine over rushton configuration gives the maximum dispersion on an equivalent power basis, yielding 86 percent of the theoretical maximum conversion. Efficiency comparisons indicate that shear and bulk flow components, plus operating above the just suspended speed of the solids, are all necessary to optimize dispersion of a small liquid volume in a viscous slurry. |
