A study of liquid-fluidized reactors for the enzymatic hydrolysis of biomass

The use of liquid-fluidized beds for the enzymatic hydrolysis of aspen wood chips was investigated using a laboratory-scale, fluidized bed reactor. The effects of intraparticle diffusion and interphase mass transport resistance on reaction rate were investigated. Interphase mass transport resistance was found to be negligible under fluidized conditions. Additionally, the reaction rate was found to be similar for each of the three size classes of aspen wood chips tested, thereby indicating that intraparticle diffusion does not limit the hydrolysis rate, at least for wood chips less than about 1/4" "effective" diameter.; The incipient fluidization behavior of unreacted aspen woodchip beds was found to be dominated by flow maldistribution. This behavior was most marked for smaller particles with narrow size distributions. Prehydrolyzed and enzymatically hydrolyzed woodchip beds were less prone to this behavior. The bed expansion data were fit to the Richardson-Zaki equation. The value of the resultant exponent varied from 6 to 9. Bed expansion at a given liquid velocity was found to increase with extent of enzymatic hydrolysis. This effect was attributed to a reduction in particle density. Particle segregation with axial location (i.e., larger particles concentrating at the bottom of the bed, and smaller particles at the top) was found to be prominent for the aspen wood chips.; Liquid and solid phase axial dispersion in liquid-fluidized beds were investigated for both porous (i.e., aspen wood chips) and nonporous (i.e., 4.4 mm diameter acrylic spheres) beds. The effects of column misalignment or "tilt" on liquid and solid phase dispersion were also investigated. Solid phase mobility was observed to increase with column misalignment, resulting in the formation of secondary recirculation flow patterns for both the porous and nonporous solids. Liquid phase dispersion in nonporous beds was unaffected by column inclination. However, column "tilt" had a strong effect on the "effective" liquid phase axial dispersion in the porous particle beds. This effect is due to interphase transport of tracer, combined with the increased solid phase mobility resulting from column "tilt." This conclusion was also confirmed by numerical analysis.