Continuous alcohol addition in vaporized form and its effect on bubble behavior in a bubble column

This study investigated the effect of alcohol on gas hold-up in two methods to add alcohol into a column. In the first method, a weighed amount of ethanol was poured into the column before the gas hold-up measurement (batch mode). In the second method, we added ethanol continuously in the form of vapor dispersed in the gas phase (continuous mode). The continuous mode was more effective in improving the gas hold-up in a heterogeneous flow regime than the batch mode. On the other hand, it had a negative effect on gas hold-up in a homogeneous flow regime. To investigate these phenomena in more detail, we measured the detachment period, bubble size distribution, and bubble break-up frequency during bubble formation in the continuous mode. When the liquid vapor was highly soluble in the continuous water phase, the detachment period and average bubble size increased and the bubble break-up frequency decreased. On the other hand, when there was little interaction between the liquid vapor and continuous water phase, the effect was negligible. This could be explained by liquid vapor diffusion from the bubble inside into the continuous water phase. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.