Effects of various concentrations (0–5 ppm) of anionic (sodium dodecyl sulfate, SDS) and non-ionic (Tween-80 and Triton X-405) surfactants on gas hold-up and gas–liquid mass transfer in a split-cylinder airlift reactor are reported for air–water. Surfactants were found to strongly enhance gas hold-up. Non-ionic surfactants were more effective in enhancing gas hold-up compared to the anionic surfactant SDS. An enhanced gas hold-up and a visually reduced bubble size in the presence of surfactants implied an enhanced gas–liquid interfacial area for mass transfer. Nevertheless, the overall gas–liquid volumetric mass transfer coefficient was reduced in the presence of surfactants, suggesting that surfactants greatly reduced the true liquid film mass transfer coefficient and this reduction outweighed the interfacial area enhancing effect. Presence of surfactants did not substantially affect the induced liquid circulation rate in the airlift vessel.
