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On the kinetics of phase separation in aqueous two-phase systems
M H Salamanca1, J C Merchuk, B A Andrews
1Centre for Biochemical Engineering and Biotechnology, Department of Chemical Engineering, University of Chile, Santiago.
Summary
Phase separation kinetics in PEG/salt aqueous two-phase systems (ATPS) depend on tie-line location. Faster separation occurs with a continuous bottom phase, while a continuous top phase shows slower kinetics influenced by phase volume ratio and Bacillus subtilis extract.
Area of Science:
- Chemical Engineering
- Separation Science
Background:
- Aqueous two-phase systems (ATPS) are widely used for bioseparation.
- Understanding phase separation kinetics is crucial for optimizing ATPS processes.
Purpose of the Study:
- To investigate the effect of tie-line location (phase volume ratio) on phase separation kinetics in batch PEG/salt ATPS.
- To evaluate the influence of Bacillus subtilis extract on phase separation.
Main Methods:
- Batch studies using PEG/sulphate systems with varying stability ratios and relative tie-line lengths.
- Design and testing of a continuous settler with different inlet geometries.
- Analysis of phase separation behavior in both batch and continuous systems.
Main Results:
- Phase separation is significantly faster when the bottom phase is continuous.
- When the top phase is continuous, larger phase volume ratios (R and rd) lead to slower separation.
- Bacillus subtilis extract generally slows down the phase separation process, especially at higher volume ratios.
- Three distinct settling regions (coalescence, drop movement, drop queuing) were observed at large volume ratios.
Conclusions:
- Tie-line location and phase volume ratio are critical parameters affecting ATPS phase separation kinetics.
- The presence of Bacillus subtilis extract impacts separation efficiency, necessitating process adjustments.
- A modified correlation accounting for tie-line location and volume ratio was developed and validated.