Diffusion-Adsorption Measurements of Solutes in Cellulose Fiber Beds Using Magnetic Resonance Imaging

Effective mixing and transport of cellulosic suspensions for enzymatic conversion to glucose is an important biofuels process bottleneck. Most recent literature studies have highlighted the lack of efficient mixing strategies available for combining substrate and enzymes at the initial stages of high solids enzymatic hydrolysis. Design of new energy efficient mixers requires quantitative information about rheology and diffusion in concentrated slurries. We investigated diffusion and adsorption of cellulose suspensions using magnetic resonance imaging. MRI allows for spatially resolved measurements of concentration distributions in highly concentrated suspensions. Paramagnetic tracers of various molecular sizes were used as diffusing solutes in suspensions of various fiber types. Effective diffusion coefficients are compared with predictions of a simple diffusion-adsorption model which accounts for the system porosity, tortuosity, and adsorption.