Effect of the radical scavenger t-butanol on gas–liquid mass transfer

Abstract

The alcohol t -butanol has been used as a radical scavenger in the studies of ozone reactions in water and has been found to affect the gas–liquid mass transfer rates. An understanding of the effects of t -butanol on mass transfer parameters, including bubble size, gas holdup, mass transfer coefficient and the mass transfer specific surface area, is of key importance to not only improve the knowledge of this particular system but also to gain fundamental understanding about the effects of gas/liquid surface modifiers on the contact between phases and the mass transfer rates. An experimental study has been carried out to investigate the effects of t -butanol concentrations on the physical properties of aqueous solutions, including surface tension and viscosity. It was found that t -butanol reduced both properties-by 4% for surface tension and by a surprising 30% for viscosity. These reductions in the solution physical properties were correlated to enhancement in the mass transfer coefficient, k L . The hydrodynamic behaviour of the system used in this work was characterised by a homogeneous bubbling regime. It was also found that the gas holdup was significantly enhanced by the addition of t -butanol. An equation to predict the gas holdup from the gas flow rate and t -butanol concentration was proposed to describe the experimental data. Moreover, the addition of t -butanol was found to significantly reduce the size of gas bubbles, leading to enhancement in the volumetric mass transfer coefficient, k L a . Bubble mean diameter was predicted using an equation developed by the Radial Basis Function Neural Network architecture obtained from the literature, and the mass transfer coefficient, k L , was predicted using an equation based on the surface coverage ratio model. The ratio was found not to depend either on t -butanol concentration or on gas flow rate. A significant increase in the volumetric mass transfer coefficient, k L a , due to an increase in both k L and a , was obtained following the addition of t- butanol, even at low concentrations.