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

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 (Ug) 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 Ug 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 Ug and a decrease in CMC concentration. In the air–water system, kla/αg was found to be independent of Ug and was 0.2 1/s, and a constant liquid-side mass transfer coefficient (kl) 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: kla/αg was not constant and was affected by the superficial gas velocity and CMC concentrations; the interfacial area increased with an increase in Ug and a decrease in CMC concentration; kl increased more significantly with increasing Ug, and no obvious trend was found for the influence of CMC concentration on kl.