Demixing kinetics of phase systems employed for liquid–liquid extraction and correlation with system properties

The kinetics of phase demixing in liquid–liquid extraction for model systems comprising PEG 4000/potassium phosphate and t-butanol/ammonium sulfate was studied. The kinetics of demixing depicts the entire demixing pattern of phases of the phase system during and after extraction and hence the study is essential prior to design of large scale gravity phase separators. With an increase in composition, both the systems showed increase in demixing rate (decrease in demixing time). At high tie line length (TLL) and phase volume ratio <1, with salt rich phase as continuous phase, both PEG 4000/potassium phosphate and t-butanol/ammonium sulfate systems showed reduction in demixing time by 59% and 50%, respectively as compared to that at low TLL. An empirical equation proposed in the literature for rate of phase demixing was used to correlate the experimental data. The agreement was better for t-butanol/ammonium sulfate system when compared to PEG 4000/potassium phosphate system.

Research highlights▶ Kinetics of phase demixing is studied for model systems. ▶ Phase demixing kinetics is useful for the design of gravity separators. ▶ High phase composition and low phase volume ratios (<1) are favorable for faster separation. ▶ Empherical equations reported in literature could predict the phase demixing kinetics very well. ▶ Phase demixing kinetics of model systems can be extrapolated to that of extraction of biomolecules.