Kinetics of phase separation for polyethylene glycol–phosphate two‐phase systems

Phase separation times for polyethylene glycol (PEG)‐4000–phosphate aqueous two‐phase systems were studied, for small scale (5‐g) and large scale (1300‐g) systems, as a ‐function of the stability ratio. Profiles of dispersion height for both large and small scale systems were represented as a fraction of the initial height and were found to be independent of the geometrical dimensions of the separator. Furthermore, by plotting time as a fraction of the initial height the total time of separation can be calculated for a given height of system at a particular stability ratio. This generalization is important for the design of large scale aqueous two‐phase separators. Phase separation times were also found to be dependent on which of the phases is continuous. A characteristic change in phase separation time was also observed at the phase inversion point (i.e., where the dispersed phase changes to a continuous phase and vice versa) and this point tends toward higher volume ratios as the tie‐line length (TLL) is increased. Furthermore, the phase inversion point at each TLL corresponds to a fixed phosphate concentration. © 1995 John Wiley & Sons, Inc.