Analysis of in situ Gas Stripping of Ethanol during Fermentation via Dynamic Modelling and Simulation

Abstract

Ethanol fermentation becomes inhibitory to microbial growth at elevated ethanol concentrations. This problem could be alleviated by continuous removal of ethanol from the broth during fermentation and this could increase productivity and potentially reduce the cost of ethanol recovery during distillation. The use of in situ gas stripping as a means of recovering ethanol from fermentation broth was analysed using a batch fermentation model. The Hinshelwood specific growth rate model and the Luedeking-Piret production model were used to formulate and simulate the fermentation model. The model was simulated to investigate the effect of stripping gas flow rate on the fermentation process. Results of gas stripping analysis showed that increasing the stripping gas flow rate enhanced the stripping of ethanol from the fermentation broth thereby keeping its concentration below inhibitory levels. This ensured that the fermentation could be continued for long periods. Almost 50% ethanol recovery was achieved when a stripping gas flow rate of 80 L/h was used. The maximum water fraction in the gas phase was 1% which was not enough to dilute the gas phase. These results show the possibility of recovering ethanol from fermentation broth by gas stripping.