Optimization of the in situ recovery of butanol from ABE fermentation broth via membrane pervaporation

Abstract

Butanol produced via the ABE fermentation is plagued with low final concentrations and low yield. The selective removal of butanol from the fermentation broth by integrating a separation process to the fermenter for the in situ recovery of butanol has been proposed by many researchers. In this investigation, the integration of a membrane pervaporation separation process with the continuous ABE fermentation system has been simulated and optimized using a multi-objective genetic algorithm. The ABE fermentation model proposed by Mulchandani and Volesky was used and the multi-objective optimization problem was defined to simultaneously maximize the butanol productivity, the overall butanol concentration and the sugar conversion. The three objective functions, if non-dominated, define the Pareto domain of the optimization problem along with the four decision variables, namely the dilution rate, the feed sugar concentration, the cell retention factor and the membrane surface area. The optimal solutions of the integrated process for two different pervaporation membrane models were compared to the stand-alone continuous fermentation. By adding an in situ separation system to the continuous ABE fermentation, the optimal butanol productivity and overall butanol concentration increased by approximately 250% compared to those of the non-integrated fermenter. Furthermore, the sugar conversion also increased.