Liquid–solid mass and heat transfer behavior of a concentric tube airlift reactor

Rates of liquid–solid mass transfer and heat transfer (by analogy) at the downcomer of concentric tube airlift reactor were studied by an electrochemical technique which involved measuring the limiting current of the cathodic reduction of ferricyanide ion in a large excess of sodium hydroxide. Variables studied were: superficial air velocity, physical properties of the solution and the effect of surface active agents. The data were correlated by the equation:j=0.096(Re·Fr)-0.14 Surface active agents were found to decrease the rate of mass transfer by an amount ranging from 54% to 84% depending on surfactant concentration. The importance of the present results for the design and operation of cooling jackets used to cool airlift reactors was highlighted. Also the possibility of using airlift reactors as low cost electrochemical and catalytic reactors to conduct liquid–solid diffusion controlled reactions, especially those involving gaseous reactants, was discussed, as in electrochemical air pollution control to remove pollutants such as SO2, Cl2, H2S and nitrogen oxides, in which case the airlift reactor acts simultaneously as a gas scrubber and a reactor.