Solid−liquid phase diagram of the system water/ propionic acid was achieved using two methods, the differential scanning calorimetry and a synthetic method. The liquidus curve is a simple eutectic diagram (89 wt % at 243 K) with an "S-shaped" form due to an inflection point (occurring at around 30% in weight of propionic acid), characteristic of a metastable liquid−liquid phase separation. The experimental data were modeled using experimental activity coefficients of the same system reported in the literature. The results are coherent, although the working temperature domains are different. The obtained phase diagram shows that ice is in equilibrium with the solution in a large composition domain; this is favorable for our further application of freeze wastewater treatment.
This work aims to study an industrial wastewater treatment process by melt crystallization on a cold wall. A binary solution of water/acetone was chosen as model effluent. A parametric study of the wastewater treatment process was performed by means of an experimental design. The process was conducted in a static mode and the impurity concentration in the ice was analyzed after each freezing cycle. The process required applying very precise conditions and the ice concentration mainly depended on the initial solution concentration and on the applied cooling rate. The ice microstructure was also characterized by optical microscopy in a cold chamber and gave insights into the mechanism of impurity incorporation: the liquid inclusions were localized under the form of solution pockets at low growth rate or between the polycrystals at higher growth rate.
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