A variety of processes have been proposed for the conversion of lignocellulosic biomass to chemicals and fuels. A common step in all of these processes is heating the biomass to high temperature (110-230'C), where a desired reaction takes place. The costs of such processes constitute a significant fraction of the overall cost of biorefining, and these costs can be decreased by reducing the amount of water in the biomass. Unfortunately, concentrated biomass is a rheologically-complex material, which is challenging to transport, mix with reagents, and heat and cool.
In this seminar, several vignettes of our research will be presented. These research projects are all aimed at understanding and controlling the rheological and mass transfer properties of concentrated biomass.
First, the challenges of measuring rheological properties of highly concentrated biomass will be described. We will show shortcomings of conventional methods such as parallel disk and vane rheometry, and illustrate how torque rheometry can be used to extract rheological properties.
Second, we will show how various rheological modifiers can be employed to control the rheological properties of biomass. For many situations, high molecular weight water-soluble polymers function well in this role, at relatively low concentrations (a few wt% based on the dry weight of the biomass). We will illustrate the dependence of rheological properties on such properties as modifier molecular weight, composition, temperature, pH, and solids concentration. We will also describe recent experiments in which rheological modifiers are exploited to facilitate extrusion of biomass at high solids concentrations with aggressive mixing.
Third, we will show how rheological properties can also be probed using fiber-level simulations. Fibers are modeled as linked rigid bodies that deform and interact during flow. Rheological properties obtained from these simulations agree qualitatively with experimental data, and offer methods for probing phenomena that are not accessible by experimental methods.
Finally, we will describe more recent efforts to understand and predict mass transfer behavior in biomass using these simulations. We have found anomalously large mass transfer rates for suspensions of deformed fibers, which can be traced to unexpected cross-streamline migration of fibers in shear flow.