Analyze and control on the membrane ethanol fermentation process with periodic exogenous signals

Abstract

Bio-ethanol production by continuous fermentation reactor would generate self-oscillatory dynamics at high substrate concentrations, which exacerbates the control problem. Andronov-Hopf bifurcation analysis of the process model indicates that the self-oscillatory dynamics is caused by ethanol inhibition, and an ethanol selective membrane is assembled to the fermentation reactor for in-situ product removal (ISPR). The simulation results show that the membrane reactor eliminates the self-oscillatory dynamics effectively, but considering the operational cost for the membrane reactor is substantial, periodic operation and on/off control of the sweeping stream in the membrane separator is adopted, and it is interesting to find that when the ethanol content follow fine designed periodic trajectories, the corresponding control actions become regular and square waveform is formulated, which is beneficial from real-time operational perspective. This result could aid periodic operation and control of the fermentation reactor at high ethanol concentrations.