Mixing analysis of PCS slurries in a horizontal scraped surface bioreactor

Horizontal rotating reactors offer many advantages for enzymatic hydrolysis of viscous biomass slurries; however, they do not provide homogenous mixtures since motion is only in the angular direction. Multi-directional mixing is important for dispersing enzymes and carrying products away from reaction sites. The objective here was to experimentally quantify mixing times and axial dispersion coefficients in a horizontal rotating bioreactor. Mixing times were of the same order as reaction times, indicating that enzymatic hydrolysis could be as much controlled by diffusion and mixing effects as by the complex reaction mechanism. The dispersion coefficient for the highest solids slurry was 20× less than the lowest solids slurry, which is indicative of the difference in free water and the magnitude change of viscosity with relatively small addition of solids. The slow mixing times and low dispersion may be an acceptable tradeoff with significantly lower power requirements compared to a conventional vertical reactor.