The phase diagrams and compositions
of coexisting phases have been
determined and correlated for poly(ethylene glycol) (PEG) 3000 + trisodium
citrate aqueous two-phase systems (ATPS’s) at 25 °C and
different pH values (6.1, 7.5, and 9.0). It was found that an increase
in pH caused the binodal curve to be displaced downward and also the
expansion of the two-phase region. The experimental binodal data of
the mentioned system has been successfully correlated with Bleasdale
equations (high R
2 and low AARD). Furthermore,
the viscosities, densities, electrical conductivity, and refractive
index of binary (PEG 3000 + water; trisodium citrate + water) and
ternary (PEG 3000 + trisodium citrate + water) systems at the above
pH value have been measured and correlated. The density data show
a linear variation with mass fraction of the polymer and also the
salt. The viscosity data of PEG 3000 solutions were correlated as
a function of mass fraction, using a nonlinear equation. The effect
of tie line lengths on density and viscosity of the aqueous two-phase
systems has also been represented.
The present work reports the liquid–liquid
equilibrium (LLE) measurements and
the construction of binodal curves for polyethylene glycols (PEG)
+ zinc sulfate/ammonium sulfate + water at three different temperatures
(298.15, 303.15, and 308.15 K) and pH values (3.00, 4.70, and 5.21).
PEGs with different molecular weights of 2000 g·mol–1 (PEG 2000), 3000 g·mol–1 (PEG 3000), and
8000 g·mol–1 (PEG 8000) were chosen for this
study. The phase composition was obtained by measuring the refractive
index (n
D) and density (ρ) and was
further used to obtain the tie-line length (TLL) and the slope of
tie-line (STL). The tie-lines are reported at different polymer lengths,
pH values, and temperatures. The values of the effective excluded
volume (EEV) were employed to analyze the effect of the parameters
on the binodal curves. Moreover, the impact of those parameters on
the TLL and STL and plait point are discussed and compared with the
results of the literature. Furthermore, the binodal curves data and
the tie-lines’ ends were fitted using some semiempirical equations
with satisfactory results. Finally, the UNIFAC is used to calculate
the LLE data of the above system and the adjusted binary group interaction
parameters of the model were reported.
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