Distinctly different bubble behaviors in a bubble column with pure liquids and alcohol solutions

BACKGROUND: Bubble column reactors are widely used in chemical processes and wastewater processing. The relevant properties of surface tension play important roles in the hydrodynamics and bubble coalescence and breakup. However, the underlying mechanisms are complicated and need further research. In this work, the bubble behaviors were studied in a bubble column of 0.1m i.d. with pure liquids of different surface tension and alcohol solutions varying in concentration and alcohol type. RESULTS: The bubble size and shape were measured by the photographic technique. The gas holdups of small bubbles and large bubbles were measured by dynamic gas disengagement (DGD) experiments. In the pure liquids, the bubble size decreased and the total gas holdup increased with decreasing liquid surface tension. In the alcohol solutions, the liquid surface tension was almost unchanged with a little addition of ethanol to pure water, but the bubble size decreased and the total gas holdup increased significantly. In the ethanol solutions, the gas holdup reached its maximum at a critical ethanol volumetric concentration of about 3%. CONCLUSIONS: The bubble behaviors in pure liquids and alcohol solutions were very different. The coalescence of small bubbles was inhibited more significantly in alcohol solutions than in pure liquids. The dynamic surface tension effect strongly affected the bubble behaviors in the alcohol solutions, and the predicted critical concentration based on this effect agreed well with the experimental value. (C) 2016 Society of Chemical Industry