Determination of the Solid–Liquid Phase Diagram of the Binary System Propionic Acid/Water

Abstract

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.

Carboxylic acid recovery from Fischer–Tropsch aqueous product by fractional freezing

“…The experimentally determined data were in reasonable agreement with the data of Faucon [7] and Htira et al [9] for the solid-liquid equilibrium of propionic acid and water. The values shown in Fig.…”

“…The eutectic points reported by Faucon [7] were − 27 °C for acetic acid, − 29.4 °C for propionic acid and − 13.4 °C for butyric acid. The eutectic point for propionic acid reported by Htira et al [9] was − 30 °C. The intervals with which the temperature was decreased varied depending on the acid and its solid-liquid equilibrium response and temperature intervals were between − 1 and − 5 °C.…”

“…The values shown in Fig. 3 from the study by Htira, et al [9] were those obtained using dynamic cooling and heating a of bulk solution at a rate of 1 °C/h. They also reported values determined by differential scanning calorimetry, which used the temperature at maximum energy flow found at different cooling rates to determine the temperature of solid-liquid equilibrium.…”

“…The solid-liquid equilibrium acid concentration measurements are shown in Fig. 3, and are compared with the values from literature [7,9].…”

“…In the first part, solid-liquid equilibrium data were collected for aqueous solutions of acetic acid (ethanoic acid), propionic acid (propanoic acid), and butyric acid (butanoic acid). The experimental solid-liquid equilibrium data were compared with equilibrium data available in literature [7,9]. In the second part, a synthetic mixture was prepared to represent the carboxylic acid distribution in Fischer-Tropsch acid water.…”