Phase equilibrium of (water + formic or acetic acid + ethyl heptanoate) ternary liquid systems at different temperatures
Introduction
Formic and acetic acids are very important chemical reagents in chemical industry. Formic acid gets more attention to be used as environmental benign storage and transportation medium for hydrogen [1]. Some researchers also reported that formic acid has the potential to direct power fuel cells for electricity generation and automobiles [2], [3]. Acetic acid is used as a solvent or an additive for producing paints, dyes, soft drink bottles, photographic film, wood glue, and synthetic fiber and fabrics [4]. Formic and acetic acids possesses significant fungicidal activity, and also used as food additives.
Solvent extraction is an efficient method for the recovery of formic and acetic acids from their dilute aqueous solutions, wastewater or fermentation broth. Separation of these acids from water can not only provide economic benefits, but also play an important role in chemical industry and environment protection disciplines. Reliable and accurate liquid–liquid equilibrium data (LLE) are required for design, innovate and choose the optimum solvent and process conditions. In addition, the measurement of LLE data is also valuable for testing and developing of thermodynamic models.
LLE data of formic and acetic acids in systems including various solvents and water are reported in the literature [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]. In this paper, we report the LLE results for the ternary systems of (water + formic acid + ethyl heptanoate) and (water + acetic acid + ethyl heptanoate) at 288.15, 298.15, and 308.15 K and atmospheric pressure, where the phase equilibria of these mixtures have not been reported.
The tie-line data were determined experimentally for the ternary systems including both of formic and acetic acids for each temperature. The distribution coefficients and separation factors were obtained from experimental results and were also reported. The tie-line data were compared with the results predicted by the UNIFAC [35], and correlated by means of UNIQUAC model [36].
Section snippets
Chemicals
Formic acid, acetic acid, and ethyl heptanoate with mass fraction purities higher than 0.98 were purchased from Merck and were used without further purification. Deionised and redistilled water was used throughout all experiments. The purity of the chemicals was checked on the basis of their densities and refractive indexes at 293 ± 0.20 K. Refractive indexes and densities were measured with Anton Paar densimeter (Model DMA 4500) integrated with a refractive index unit (Model RXA 170) both in ±10−5
Results and discussion
The tie-line compositions of the equilibrium phases were tabulated in Table 2, for which xi1 and xi3 refer to the mole fractions of the ith component in the aqueous and solvent phases, respectively. The experimental and predicted tie-lines through UNIFAC and correlated data by UNIQUAC model for the related ternaries were plotted in Fig. 1, Fig. 2, Fig. 3. Referring to Fig. 1, Fig. 2, Fig. 3, the slopes of tie-lines obtained in this work show that acetic acid is more soluble in the solvent-rich
Conclusion
The LLE data for the ternary systems of (water + formic acid + ethyl heptanoate) and (water + acetic acid + ethyl heptanoate) were investigated at 288.15, 298.15, and 308.15 K and atmospheric pressure.
It is concluded that acetic acid is more soluble in the solvent-rich phase than formic acid. The effect of the temperature change on the equilibrium data was found to be insignificant over the investigated temperature range for each of acid. The separation factors, varying between 1.87 and 8.63 for formic,
Acknowledgements
The authors thanks to Prof. J. Gmehling for the opportunity of using Dortmund Data Bank. This work was supported by The Research Fund of Istanbul University. Project number: UDP-26496.
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