Experimental investigation of the effect of ethyl alcohol surfactant on oxygen mass transfer and bubble size distribution in an air-water multiphase Taylor-Couette vortex bioreactor

Volumetric liquid side mass transfer, bubble size distribution, and bubble shape were measured in a vertically oriented semi-batch gas-liquid Taylor-Couette vortex reactor with an aspect ratio of Gamma = h/(r(o) - r(i)) = 40 and radius ratio of eta = r(i)/r(o) = 0.75. Azimuthal Reynolds number, Axial Reynolds number and Capillary number were varied between 0 to 3.8 x 10(4), 7 to 99, and 6.1 x 10(-6) to 76.0 x 10(-6), respectively. Power law correlations based on these data were presented for dimensionless Sauter mean diameter and Sherwood number in terms of the dimensionless parameters. Presence of ethanol as surfactant in the liquid was shown to inhibit bubble coalescence, which in addition to lowering interfacial surface tension causes a generally smaller bubble size at higher concentrations of surfactant. It was also shown that the mass transfer coefficient generally increases with higher concentrations of surfactant. Both the bubble diameter and mass transfer are influenced more at lower concentrations of surfactant, and the introduction of higher amount of ethanol causes a decrease in both parameters. (C) 2017 Elsevier B.V. All rights reserved.