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ILs + H2O + K3PO4 Ternary Systems
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4.2.2. Phase Diagrams and Tie-Lines
The phase diagram binodals were determined
through the cloud point titration method 69, 70 at 298
K ( 1 K), as shown in Figure 16. The experimental
procedure adopted was validated with the phase
diagram obtained for the [C4mim][Cl] IL + water +
K3PO4 ternary system against literature data 71 .
Aqueous solutions of K3PO4 at 40 w/w % and
aqueous solutions of the different hydrophilic ILs at
variable concentrations were prepared and used for
the phase diagrams binodal determination.
Repetitive drop-wise addition of the aqueous
inorganic salt solution to the aqueous solution of IL was carried until the detection of a
cloudy solution, followed by the drop-wise addition of ultra-pure water until the detection
of a monophasic region (clear and limpid solution). Drop-wise additions were carried
under constant stirring. The ternary system compositions were determined by the weight
quantification of all components added within an uncertainty of 10 -4 g.
The tie-lines (TLs) were determined by a gravimetric method
described by Merchuck et al. 68 . For the TLs determination a
mixture at the biphasic region was prepared, vigorously stirred
and allowed to reach the equilibrium by the separation of both
phases for 24 h at 298 K using small ampoules (ca. 10 mL)
especially designed for the purpose. After the separation step,
both top and bottom phases were weighed. Each individual TL
was determined by application of the lever rule to the
relationship between the top mass phase composition and the overall system composition 68 .
For that purpose the experimental binodal curves were fitted using Eq. 5 68 ,
0.
5 3
BX
Y Aexp
CX
(5)
where Y and X, are respectively, the IL and salt weight percentages, and A, B and C are
constants obtained by the regression.
For the determination of TLs was solved the following system of four equations (Eq. 6, 7,
8 and 9) and four unknown values (YT, YB, XT and XB):
a) b)
Figure 16. Experimental
determination of the binodal curve for
the aqueous systems IL-K3PO4: a)
addition of K3PO4 for the cloud point
detection; b) addition of water for the
clean point detection.
IL-rich phase
K 3PO 4-rich phase
Figure 17. Experimental
determination of the TLs
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