Mass transfer across liquid—liquid interfaces : Part 2. Calculation of Mass-transfer Coefficients from Experiments with an Automated Falling-drop Apparatus

The mass transfer of 4-methoxy-N,N-dimethylbenzylamine from aqueous drops to cyclohexane was studied by the falling-drop method with computer-controlled equipment. Different contact times were achieved by letting the drop-forming device ascend or descend to previously defined levels in the column containing the continuous phase. The overall mass-transfer coefficient was evaluated from the relationship between contact time and solute concentration in the donating phase. Whether or not the continuous phase must be replaced between the measurements needed to calculate the overall mass-transfer coefficient is discussed in detail. Corrections for the gradually increasing concentration of the transported solute in the receiving phase are proposed and tested. The order of contact times (decreasing or increasing) is shown to be of great importance for these corrections.