Distributions
of Hydrochloric Acid between Water and
Organic Solutions of Tri‑<i>n</i>‑octylphosphine
Oxide: Thermodynamic Modeling
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Abstract
Tri<i>n</i>-octylphosphine
oxide (TOPO) is a widely used
extractant because of its high extractive ability. However, there
is no systematic research on the thermodynamics of TOPO/<i>n</i>-dodecane in the separation of hydrochloric acid (HCl) from aqueous
solution. In this study, the liquid–liquid equilibrium (LLE)
system (water + <i>n</i>-dodecane + TOPO + HCl) was investigated.
Both the equimolar series and slope methods were used to determine
the composition of the complex formed in the equilibrated organic
phase. The form of the water molecules in the equilibrated organic
phase was first investigated by the thermodynamic method. The thermodynamic
model was established with the Pitzer equation for aqueous phase and
both Margules and organic Pitzer equations for the organic phase.
Two chemical equilibrium constants and their corresponding interaction
parameters were regressed from experimental LLE data. The correlated
results were in good agreement with the experimental data. Furthermore,
this model can also be used to predict the organic phase composition
for this system. This confirmed that the thermodynamic model chosen
was suitable for the extraction system