Chemistry Reference
In-Depth Information
1.3
Two phases
0.65
hree phases
0
0
1.5
3
[HNO
3
]
org
/[DMDBTDMA]
FIGURe 7.10
Pseudo-binary phase diagram of the water, HNO
3
/DMDBTDMA, dodecane
system to identify the third-phase limit. Experimental points (circles) and theory (lines)
obtained from Baxter sticky hard-sphere approach. The theoretical line is obtained with
the experimental determination of the linear variation of the stickiness parameter τ
-1
ver-
sus [HNO
3
]/[DMDBTDMA]. The different lines illustrate the impact of the error in this τ
-1
experimental linear law. (From C. Erlinger, L. Belloni, T. Zemb, and C. Madic,
Langmuir
, 15:
2290-2300, 1999. With permission).
demonstrated that it is possible to reproduce the re-entrant, nonmonotonic path of the
phase limit on the binary pseudo-phase diagram ([DMDBTDMA], [HNO
3
]).
This approach proves that a phase diagram can be modeled when the solution
microstructure is known (i.e., aggregation number and micellar aggregate number per
unit volume) together with an experimental determination of the potential between
aggregates. If the variation of the potential versus various parameters (metal salt in
the organic phase) can be obtained experimentally, the limits of the phase separation
can be reliably correlated with theory.
Despite this important step toward a model of the phase diagram in liquid/liquid
extraction, no other models using this approach are described in the literature for
other conditions or other extractant systems. It is likely that a model of third-phase
formation in liquid/liquid extraction could be obtained by considering the aggregates
in solution. However, a Baxter approximation would not work if the polar cores of
the micelles are nonspherical on average or connected. Thus, the determination of
the phase diagram could be obtained if the large diversity of structure of aggregates
and a complex potential are considered instead of simply spherical reverse micelle
with sticky hard-sphere potential. To our knowledge, such an approach was not pre-
sented in the literature until now.
7.2.5.2 Flory-Huggins Description
There are some similarities between third-phase formation in liquid/liquid extrac-
tion and the critical phenomenon of “cloud points” in aqueous solutions of nonionic
polyethoxylated surfactants (
12, 91
). When a nonionic micellar solution is heated to
a certain temperature, it becomes turbid, and by further increasing the temperature,
