Ethanol removal by vacuum-assisted gas stripping: Influence of operating conditions

One way to overcome the inhibitory effects caused by ethanol on yeast cell growth is the use of extractive fermentation, whereby ethanol is removed from the fermentation broth as it is produced. The present work investigates ethanol removal from solution by vacuum-assisted gas stripping, which is a promising method for enhancing performance, compared to conventional gas stripping. Evaluation was made of the effects of carbon dioxide flow rate (ϕ_CO2), temperature (T), and pressure (P) on ethanol removal performance. Bench-scale assays were performed using a 2-L bubble column containing 10 % v/v ethanol solution, with monitoring of the gas and liquid phases by FT-MIR spectroscopy. The ethanol entrainment factor (F_E) increased with ϕ_CO2 and temperature, but decreased at higher pressure. Only ϕ_CO2 had significant and positive effects on the concentration factor (F_C) and selectivity (α_E/W), within the operating ranges of the variables studied. An ethanol removal model was obtained that provided an accurate description of the process behavior, with good agreement between the experimental and simulated data. In addition, the energy requirement for ethanol removal by vacuum-assisted gas stripping in the bioreactor was lower than for the conventional stripping process.