Determining Dispersion in High-Solids Biomass Slurries

Conversion of lignocellulosic biomass to fuels can be made more cost-effective by operating at high-solids conditions. However, little is known about the transport properties in these systems. A thorough understanding of convection and diffusion in high-solids biomass slurries is necessary in order to properly develop predictive models for the degradation of biomass in reactor systems. In this work, packed-beds of pretreated biomass were prepared in preparative chromatography columns. Step inputs of tracer molecule solutions of varying size and type were passed through the packed beds. Initial residence-time-distribution analyses were performed to determine the extra-particle porosity of the packed beds and to determine apparent pore volume accessibility of the biomass. Secondly, an advection-diffusion-adsorption model was used to distinguish the effects of dispersion and adsorption of tracer molecules, and to measure parameters for the adsorption and diffusion. The relationship between dispersion and flow rate was examined, and diffusion parameters for a given bed were estimated. These diffusion parameters were then related to tortuosity factors, and the relationship between tortuosity and packing density was examined.