Effects of surface-active substances on gas holdup and gas-liquid mass transfer in bubble column.

Abstract

The effects of surfactants and antifoam agent on the gas holdup s, the liquid-phase mass transfer coefficient kL and the volumetric liquid-phase mass transfer coefficient kLa in a bubble column were studied experimentally. An addition of surfactants such as //-alcohols to water increases s and decreases kL, and an addition of antifoam agent to water decreases e, kL and kLa. However, the degree of reduction of kL value by an addition of surfactant to water is lower for bubble swarms in a bubble column than that for a single bubble in stagnant liquid. Based on these observations, the previous model for estimating kL of a single bubble in aqueous solutions of surface-active substance is modified so as to be applicable to the estimation of kL for bubble swarms in a bubble column.

Effect of scale-up on average shear rates for aerated non-Newtonian liquids in external loop airlift reactors

“…Foam could be controlled either mechanically or chemicallly. Chemical antifoams were avoided in this work due to their known effects of hydrodynamics and mass transfer characteristics of bioreactors (Kawase and Moo-Young, 1987;Koide et al, 1985;Prins and van't Reit, 1987). Therefore, a mechanical antifoam system (variable-speed stirrer) was installed at the top of the downcomer.…”

Studies of Gas Holdup in Bubble Column Reactors

“…Transition gas velocity and corresponding gas holdup can be obtained from the simultaneous solution of Eqs. (1), (5) and (6). For batch operation and gas distributors with orifice diameter less than 1 mm one obtains:…”

Microreactor Mixing-Unit Design for Fast Liquid-Liquid Reactions

“…There are several factors affecting the rate of interphase mass transfer when surfactant is present. For example, the surfactant can reduce the droplet size; however, this can be counteracted by a reduction in the mass transfer coefficient across the film (K org ) due to the known surface immobilization of the interface in liquid-liquid [23] and gas-liquid [24][25][26] systems. The key finding from testing with the surfactant was the ability to eliminate the unstable slug/ drop flow regime observed in the toluene-water system and obtain consistent and repeatable mass transfer coefficients.…”