Ultrasonic Separation in Bioethanol Refining

Ultrasonic separation opens new possibilities for liquid-liquid separation due to its high energy efficiency and lack of phase equilibrium constraints, but some challenges need to be overcome before it can be commercialized.

Greenhouse gas (GHG) emissions and other environmental consequences of fossil-fuel use have prompted the exploration of renewable energy sources. In the U.S., the transportation sector accounts for about 25% of total GHG emissions (1). Bioethanol not only serves to reduce GHG emissions when blended with gasoline but also can be used with vegetable oil or fats to produce biodiesel. In addition, ethanol can be used as a feedstock to produce sustainable aviation fuels (2–4).

Annual bioethanol production in the U.S. is about 15 billion gallons (5), mainly by fermentation of corn starch and other lignocellulose biomass (6). The ethanol mass fraction (w_EtOH) of the fermentation broth can vary from 0.01 to 0.14 (7, 8), depending on feedstock, pretreatment methods, operating conditions, etc. However, to be used as a fuel additive, the ethanol content must be greater than 99 wt% (w_EtOH > 0.99) (9). Thus, purification of the fermentation broth, which accounts for 50–80% of the total energy consumption in bioethanol production, is critical to successful process design.

This article discusses the use of ultrasonic separation for the purification of bioethanol fermentation broth. It reviews standard methods of bioethanol purification, and identifies the advantages and challenges of the intensified ultrasonic process...