Gas holdup, bubble behavior and mass transfer in a 5 m high internal-loop airlift reactor with non-Newtonian fluid

Abstract

Gas holdup, bubble behavior, interfacial area and gas–liquid mass transfer in a 5 m internal-loop airlift reactor with non-Newtonian fluid were studied in the superficial gas velocity ( U g) range of 2–12 cm/s. Air and aqueous CMC solutions of 0–0.45 wt% were used as the gas and liquid phases, respectively. It was found that increased U g or CMC concentration led to a wider bubble size distribution and an increase in the bubble Sauter diameter. The volumetric mass transfer coefficient increased with an increase in U g and a decrease in CMC concentration. In the air–water system, k l a/ α g was found to be independent of U g and was 0.2 1/s, and a constant liquid-side mass transfer coefficient ( k l) was found in the heterogeneous regime. However, in the air–CMC solution system, the influences of the superficial gas velocity and liquid viscosity were much more complicated: k l a/ α g was not constant and was affected by the superficial gas velocity and CMC concentrations; the interfacial area increased with an increase in U g and a decrease in CMC concentration; k l increased more significantly with increasing U g, and no obvious trend was found for the influence of CMC concentration on k l.