INTEGRATION OF PERVAPORATION AND CONTINUOUS BUTANOL FERMENTATION WITH IMMOBILIZED CELLS .2. MATHEMATICAL-MODELING AND SIMULATIONS

In alcoholic fermentations substrate conversion is limited by product inhibition, but it can be increased by in situ product recovery. In the present study a model is developed to describe continuous butanol fermentation with immobilized cells coupled to pervaporation for in situ product recovery. The model incorporates linear inhibition kinetics with respect to butanol and the assumption that the pervaporation capacity is proportional to the butanol concentration. Both the predicted values for the alcohol concentration in the broth and the substrate consumption show good agreement with experimental values. Simulations were performed with the model for a hypothetical process. It was shown that a high productivity and a high substrate consumption should be possible, by matching the feed flow rate and the alcohol recovery rate. Furthermore, it is concluded that because of the accumulation of components and byproducts in the medium, the concentration of these components in the broth following the removal of water is of great importance. This concentration effect depends strongly on the operating conditions and the selectivity of the separation.