(404e) Dispersion in a Resonating Acoustic Mixer

We previously showed that overcoming mass transfer limitations by using an impeller-less resonating acoustic mixer during enzymatic saccharification of pretreated corn stover slurries maintained glucose release rates and yields despite orders of magnitude increases in viscosity as solids concentrations increased up to 30% w/w.  In this study, dispersion coefficients in the mixing vessel were determined as a function of viscosity in order to quantify the mass transfer improvements and determine if the system was a valid choice for studying reactions in the absence of mass transfer limitations that are typical of highly viscous systems.  Since conventional means of measuring dispersion could not be performed due to the slurry characteristics, a computational fluid dynamics model was developed that simulated motion of the slurries in the mixer.  The model was very well validated by comparing experimentally determined mixing times using an electrolytic tracer with mixing times from the simulations.  Computational and experimental mixing times differed by 2% or less in all cases.  Axial dispersion coefficients were generally 3 to 6 times higher than radial dispersion coefficients.  Despite the high viscosities studied here, up to 25,000 cP, dispersion values were achieved simlar to water flow in a pipe, indicating the system was a valid choice for studying reactions in the absence of mass transfer limitations.