Modeling of Concentration Profiles in Yeast Capsules for Efficient Bioethanol Production

Encapsulated yeast can be used for increasing bioethanol production during fermentation of inhibitory lignocellulose hydrolysates. It is useful for decreasing the effect of inhibitors when the substrate through the capsule. It can be considered as a spherical pored catalyst, which contains yeast within the capsule. The capsule has 3 main parts, i.e. capsule membrane, cell pellet and liquid core. Glucose consumption by encapsulated yeast was modeled as a diffusion and reaction process. The diffusion included effects of different diffusivities of the capsule membrane (Dm) and cell pellet (Dc). The reaction was assumed by following Monod kinetics. Comsol Multiphysics was used to simulate mass transfer effect in encapsulated cells using the finite element method. Simulation was set in 2D and geometry was set in axis stmmetry. Steady state concentration profiles were obtained after 24 hours depending on the diffusivity in membrane and cell pellet. Steady state glucose limitation was only apparent if Dc or Dm was ≤ 1% of the diffusivity in water. However, temporary glucose limitation was observed after 1 and 2 hours cultivation in many cases. The internal diffusion is more affect to rate concentration limiting because of cell diffusivity