Bioethanol is a key renewable energy source that can be used as a gasoline additive, feedstock in synthesizing renewable gasoline, renewable diesel, or sustainable aviation fuel. Annual U.S. production exceeds 16 billion gallons, mostly from fermentation of starch or lignocellulose, with ethanol (EtOH) mass fractions in the broth ranging from 1-15% depending on feedstock, enzymes, and operating conditions. Water is the major broth impurity and must be removed, with significant energy consumption in distillation being a major economic hurdle. State-of-the-art dewatering technology requires 30-60 % of the 29 MJ/kg EtOH combustion heat, depending on the EtOH broth concentration. Here, we describe development of a novel liquid/vapor ultrasound separation based on surface enrichment. The electrically-driven ultrasound transducer generates cavitation bubbles in the liquid, which rise in an ultrasonically-generated fountain, and shatter into fine droplets upon reaching the interface between the bulk liquid and headspace. Compared to distillation, no energy is consumed in effecting a liquid-to-vapor phase change, and second-law losses associated with heat transfer are greatly reduced. This approach also avoids the azeotropic bottleneck of 1-atm distillation, and the separate steps necessary to overcome it. A single-stage separation was used to investigate the effects of partial recycling of large drops (which are less enriched in EtOH than small droplets), as well as the effect of bulk liquid temperature, carrier gas flow rate and inlet pressure, and transducer voltage. A two-stage separation investigated the feasibility of replacing the beer column and rectifier used in conventional distillation. Energy analysis indicates that ultrasound separation in bioethanol purification can significantly reduce energy consumption in dewatering. The potential annual energy reduction is about 470 10<sup>9</sup> MJ for the U.S. and 760 10<sup>9</sup> MJ globally. A carbon-balance analysis shows a potential annual carbon reduction between 125 and 205 million metric tons.

Development of ultrasound-mediated bioethanol purification process

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