Phase separation in a salting-out extraction system of ethanol–ammonium sulfate

• The kinetics of phase separation in salting-out extraction system was studied.
• Ethanol–ammonium sulfate salting-out extraction system was used.
• The time required for product distribution and phase equilibrium was investigated.
• Phase separation in salting-out extraction system is fast and stable.

The effects of tie line length, phase volume ratio, phase continuity, degree of mixing and equipment geometry size on the kinetics of phase separation in the ethanol–ammonium sulfate salting-out extraction system were studied with tie line lengths of 42.5%, 51.4% and 56.6% and phase volume ratio in the range of 1:9–9:1. The time for product distribution and phase equilibrium was also investigated. It was found that the rate of phase separation increased as the tie line length increased and the shortest separation time was obtained at the phase inversion point for all the tie lines at a constant phase volume ratio. The phase continuity was determined not only by the phase volume ratio, but also by the degree of mixing. An ambiguity area where gentle vortex produced a top-continuous system and intense mixing produced a bottom-continuous system was observed and its scope was extended as the mixing intensity decreased. Additionally, increasing the cross-sectional area of equipment had a significant effect on the rate of phase separation because the coalescence process determined the separation rate in the salting-out extraction system. By comparing the concentration of target product (butanol) and phase-forming component (ethanol) in the top phase at different time intervals, it was concluded that this system can achieve complete phase equilibrium within 10 min. The knowledge of kinetics of phase separation is important to the deep understanding of this system and beneficial to process scale up for industrialization.