Towards Understanding Catalyst Diffusion in Biomass

The diffusion of blue dextran (BD) in milled biomass was studied by analysis of residence time distributions of solutes flowing through packed beds of the biomass. A step input of BD dissolved in water was applied to a column packed with the biomass, and BD concentration at the bottom of the column was monitored in order to construct an elution curve. Irreversible binding of BD to biomass was observed, resulting in irreproducible elution curves. This irreversible binding was controlled by using 2% (w/v) sodium dodecyl sulfate in water as the carrier solvent, leading to consistent results. The elution curves were fitted to a mass transfer model that accounts for advection, dispersion, and reversible mass transfer between the bulk fluid and the surface of the biomass. This fitting procedure allowed the calculation of important physical properties of the biomass slurries such as void fraction, as well as the dispersion coefficients of BD at different flow velocities. This method represents an effective approach to studying the transport properties of biological macromolecules in biomass slurries. Thus, the transport properties of proteins in biomass can be studied in order to obtain a better understanding the diffusion of enzyme catalysts used for enzymatic hydrolysis of lignocellulosic biomass to fermentable sugars.