Hot microbubble air stripping of dilute ethanol–water mixtures

Product inhibition and the cost of downstream separations are two main barriers in using lignocellulosic biomass for bioethanol production. If bioethanol can be continuously removed from fermentation broth without affecting the fermentation process, significant gains can be achieved with bioethanol yields and process efficiency. Hot microbubble clouds generated by energy efficient means have been used to remove ethanol from dilute ethanol–water mixtures (∼4% [v/v]) maintained at 60 °C, and the effect of key operating parameters on the stripping rate has been studied. Numerical simulations of a hot microbubble rising in a dilute ethanol–water mixture were also performed to understand the instantaneous concentrations within the gas phase. Increasing the inlet gas temperature from 90 to 150 °C and decreasing the liquid height in the unit from 50 to 5 mm both increased the ethanol stripping rate. However, the benefit of increasing the gas temperature for maximum ethanol removal depended on the liquid height in the unit. Under all operating conditions, ethanol concentration was reduced below ∼2% [v/v] within ∼25 min of operation, demonstrating the potential of hot microbubble stripping for product removal from lignocellulosic fermenters. Implemented effectively in a fermenter, this technology could intensify the bioethanol production process and improve process economics.