Removal of tributyl phosphate from aqueous stream in a pilot scale combined air-lift mixer-settler unit: Process intensification studies

• Mass transfer studies in combined air-lift mixer-settler unit (CAL-MSU).
• Effect of phase flow ratios on steady state, number of stages and mass transfer coefficient.
• Describes optimization of operating parameters for the removal of TBP in CAL-MSU.
• Energy input for 10-stage CAL-MSU and 10-stage pump-mix mixer-settler is reported.

This work reports the removal of tributyl phosphate (TBP) from aqueous stream using organic solvent in an industrial scale combined air-lift mixer-settler unit (CAL-MSU) having 10 stages. The solute i.e., TBP is transferred from aqueous continuous (0.3 M HNO3 saturated with TBP) to organic dispersed phase i.e., normal paraffin hydrocarbon (NPH). Effect of phase flow ratios on steady state, number of stages as well as mass transfer coefficient on TBP removal and mass transfer coefficient, is observed. The maximum TBP extraction efficiency of about 96% (201 ppm to 8 ppm) and maximum overall volumetric mass transfer coefficient of 13.3 × 10−5 s−1 was observed at continuous phase flowrate 36 LPH and dispersed phase flowrate 24 LPH. For optimized operating parameters, the energy input per unit volume for 10-stage CAL-MSU and similar configuration 10-stage pump-mix mixer-settler are found to be 37.0 kJ/m3 and 77.7 kJ/m3, respectively.