Elsevier

Fluid Phase Equilibria

Volume 258, Issue 2, 15 September 2007, Pages 115-124
Fluid Phase Equilibria

Measurement of the thermodynamic properties for the reactive system ethylene glycol–acetic acid

https://doi.org/10.1016/j.fluid.2007.05.030Get rights and content

Abstract

Isothermal vapor–liquid equilibria for eight binary systems of the reactive system ethylene glycol–acetic acid have been measured using a static VLE-equipment. Furthermore, excess enthalpies were determined with the help of an isothermal flow-calorimeter. Additionally, vapor pressure and density measurements of the monoacetylated ethylene glycol were carried out.

Introduction

The esterification of ethylene glycol with acetic acid is a reversible and consecutive nucleophilic second order substitution reaction whose mechanism is well known (Fig. 1). It is an interesting example for a reaction capable to be used for reactive distillation.

Although the monoacetylated as well as the diacetylated ethylene glycol is considered as an organic solvent and non-polluting fuel-additive, only a very small amount of thermodynamic data is published. Information of some applications is available in literature [1], [2].

Reliable pure component and mixture data of the components involved is a precondition for the design and optimization of reactive rectification processes and other applications of industrial interest.

This work is part of our studies concerning the description of the reaction kinetics of the heterogeneous catalyzed esterification of ethylene glycol with acetic acid. In order to describe the reaction kinetics by means of activities one has to know the activity coefficients. These coefficients can be calculated with the help of GE-models, such as UNIQUAC [3], whose parameters are fitted to experimental data. Up till now sufficient thermodynamic properties are only available for the systems water–acetic acid and water–ethylene glycol. Therefore, the measurement of vapor–liquid equilibria and excess enthalpies of 8 of the 10 possible binary systems had to be carried out as well as the measurement of pure component properties like vapor pressure and density data for ethylene glycol monoacetate. The investigated binary systems are given in Table 1.

Section snippets

Chemicals and purities

Ethylene glycol and acetic acid were purchased from Sigma–Aldrich, ethylene glycol diacetate from Acros Organics. Ethylene glycol monoacetate was synthesized and purified in our laboratory. In order to obtain ethylene glycol monoacetate with a sufficient purity, the reaction of ethylene glycol with acetic acid catalyzed with the acid ion-exchange resin Amberlyst 36 from Rohm and Haas was carried out in a 2 l flask. After neutralization ethylene glycol monoacetate was extracted from the reaction

Results

The experimental vapor pressures, densities, VLE and heats of mixing data are given in Table 3, Table 4, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10, Table 11, Table 12, Table 13, Table 14, Table 15, Table 16, Table 17, Table 18, Table 19, Table 20, Table 21.

The new experimental vapor pressure data were used to fit the parameters A, B and C of the Antoine equationlog10PiS[kPa]=ABC+ϑusing the experimental data under minimizing the following objective function:F=(|Pi,expSPi,calcS|)/

Conclusion

In this work, besides vapor pressure data and densities for monoacetylated ethylene glycol isothermal VLE and HE-data for eight of the ten possible binary systems of the reactive system ethylene glycol–acetic acid have been measured to fill the gaps in the database. Since ethylene glycol monoacetate could not be purchased with the required purity a procedure for the production had to be developed to produce the ester with a sufficient purity for the measurement of the pure component properties

Acknowledgements

The technical assistance of R. Bölts is gratefully acknowledged. The authors thank the Arbeitsgemeinschaft Industrieller Forschungsvereinigungen (AiF) for the financial support of the project “Anfahren von Reaktivrektifikationsprozessen” (No. 14183).

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