Ethanol removal by stripping with CO2 reduced-size bubbles: Mechanical and thermodynamic entrainments

• Published in: Chemical engineering and processing 2024-11, Vol.205, p.110011, Article 110011
• Main Authors: Pereira, Rauber D., Almeida, Letícia P., Sousa, Marina D.B., Buffo, Mariane M., Veloso, Ivan I.K., Silva, Kaio C.R., Cruz, Antonio J.G., Badino, Alberto C.
• Format: Article
• Language: English
• Subjects: Bubbles; Ethanol; Mechanical entrainment; Stripping; Thermodynamic
• ISSN: 0255-2701
• DOI: 10.1016/j.cep.2024.110011

•Saturation of the gas phase in ethanol and water was experimentally confirmed for microbubbles and coarse bubbles.•Mathematical modeling was proposed to quantify the mechanical and thermodynamic entrainments separately.•Mechanical entrainment was 15 times more concentrated in ethanol than the liquid phase.•Mechanical entrainment intensified the selectivity in ethanol removal by around 64 % more than equilibrium. The efficiency of stripping processes for volatile compounds is governed by mechanical and thermodynamic entrainments, which play crucial roles in ethanol removal during the extractive fermentation process. These mechanisms depend on variables such as bubble diameter, ethanol concentration, liquid volume, pressure, and temperature. However, the quantification of each of them separately and their dependence on bubble diameter have never been addressed. The present study proposes a new methodology to evaluate both mechanical and thermodynamic entrainments, based on experimental data and thermodynamic equilibrium analysis of the bubbles in reactors with working volumes of 10.0 and 50 L, aiming to clarify the role that bubble diameter (microbubbles, fine and coarse bubbles) plays in these mechanisms. The results indicated that thermodynamic equilibrium was reached for any size of bubbles up to 5 mm in diameter, under a wide range of experimental conditions with specific gas flow rates from 0.22 to 10 vvm. Equally important, mechanical entrainment was found to enrich the gas phase in ethanol by a factor of 15, representing a higher concentration factor than for thermodynamic entrainment, which was inconceivable initially. This introduces a new and promising approach to intensify the stripping process of volatile compounds by means of mechanical entrainment. [Display omitted]