(345g) Simulation and Optimal Operation Strategy for Continuous Biobutanol Production

Biobutanol is considered to be a promising renewable energy source, especially as a gasoline substitute, owing to its high energy content, low volatility, and low water solubility. However, the volumetric productivity of biobutanol in batch fermentation is limited by the toxicity of butanol: the microorganism’s cell growth gets inhibited when its concentration in the fermentation broth reaches a certain critical level. For this reason, produced biobutanol needs to be removed from the fermentation broth during the operation, in order to achieve a high level of volumetric productivity needed for commercialization. In this study, a continuous extractive fermentation process integrated with an ex-situ adsorption recovery process is investigated as a way to overcome this limitation. The spatial segregation of the adsorption system and the fermentation process enables continuous biobutanol production without the need to stop the fermentation, and can maintain the concentration of butanol in the fermentor below the threshold of toxicity thanks to removal of biobutanol in the adsorption column. Since the adsorption column has to be switched periodically due to the limited capacity of the adsorbent, the overall operation follows a cyclic pattern and the proposed continuous extractive fermentation process shows a cyclic steady state behavior. A dynamic model for the integrated process is developed and used for simulating the concentration profiles at cyclic steady state. Finally, major operating variables are optimized based on the cyclic steady state behavior in order to design an optimal operation strategy that satisfies given requirements.