Effect Of Surface Active Additives On Mass Transfer In Newtonian Or Non-Newtonian Fluids In An Internal Loop Airlift Reactor

In the present work, hydrodynamic and mass transfer characteristics of gas-liquid system containing Newtonian fluid (water) or non-Newtonian fluid (aqueous solution of sodium carboxymethylcellulose, CMC) as the liquid phase respectively in an Internal Loop Airlift Reactor (ILAR) are investigated experimentally in the presence of small amounts of surface active components as additives. Thereafter, the experimental results are interpreted based on theoretical considerations.The experimental results of air-water system in ILAR show that the addition of alcohols (ethanol, tertiary butanol, pentaerythritol) into water results in a significant increase in the oxygen transfer coefficient, which is mainly due to the change of gas-liquid interfacial properties and subsequent inhibition of bubble coalescence process. However, the intensification of gas-liquid mass transfer occurs in a certain concentration range. Beyond a limiting concentration value, the liquid phase volumetric mass transfer coefficient of oxygen decreases slightly. Gas holdups in both the water and aqueous solutions of alcohols increase significantly with the increase in gas superficial velocity, however, the latter is much higher at the same gas superficial velocity. In addition, an increase in the measured liquid phase volumetric mass transfer coefficient is also found when minute quantities of electrolyte are present in the water, which can be analyzed on the basis of ionic strength.The experimental results with respect to aqueous solutions of CMC reveal that gas-liquid mass transfer performance is inferior to that of Newtonian fluid. Meanwhile, an increase in the viscosity of non-Newtonian fluid will cause a further decrease in the oxygen transfer rate, showing that in such case bubbles are possibly more easier to coalescence because the increasing viscosity tends to stabilize the wake flow behind Taylor bubble and consequently reduces the turbulence level there. Also, the addition of alcohol into the non-Newtonian fluid has some certain influence on the gas-liquid mass transfer behavior in such system. However, this influence varies with the concentrations of CMC polymer in the aqueous solutions. That is, the addition of minute quantities of alcohol will increase mass transfer rate at low CMC concentrations while at high CMC concentrations the contrary trend is observed. As there are small amounts of electrolyte in the CMC solutions, the measured liquid phase volumetric mass transfer coefficients are always higher than those of CMC solutions of different concentrationswithout such electrolyte. When the viscosity of the non-Newtonian fluid increases, the gas holdup in the riser is found to change slightly while that in the downcomer increases.