Elsevier

Fluid Phase Equilibria

Volume 356, 25 October 2013, Pages 264-270
Fluid Phase Equilibria

Liquid–liquid equilibria for ternary systems acetic acid + n-butyl acetate + hydrocarbons at 293.15 K

https://doi.org/10.1016/j.fluid.2013.07.032Get rights and content

Highlights

  • Ternary systems acetic acid + n-butyl acetate + hydrocarbon have been studied.

  • Influence of hydrocarbon chain length has been investigated.

  • Consistency of tie-line data was shown with several correlations.

  • Experimental data can be well represented with an UNIQUAC model.

  • Asymmetric binary interaction parameters were determined.

Abstract

Liquid–liquid equilibrium data for acetic acid + n-butyl acetate + hydrocarbons ternary systems at T = 293.15 K are reported in this work. The effect of hydrocarbon chain length on liquid–liquid equilibrium is determined and discussed. Aliphatic hydrocarbons such as hexadecane, dodecane and decane were particularly investigated. The organic chemicals (esters and hydrocarbons) were quantified by gas chromatography using a flame ionization detector while acetic acid was quantified by titration with sodium hydroxide. Experimental tie-line data for the ternary mixtures were correlated using Othmer–Tobias, Bachman and Hand correlations in order to show the reliability of the experimental results. Finally, these experimental data were correlated with the UNIQUAC model. It appeared that this model provides a good correlation of the solubility curve with these three hydrocarbons.

Introduction

Low molecular weight esters are most commonly synthesized by direct esterification of carboxylic acids with alcohols in presence of acid catalysts by either a batch or a continuous process [1], [2], [3], [4]. Esters are essential for the fragrance and flavouring industry. n-butyl acetate (BA) is a widely known ester used as a solvent in the production of lacquers for example, but more commonly as a synthetic apple flavouring used in food industry [5]. Production of BA increased in the last decade because its low toxicity and low environmental impact compared with other esters [6].

Industrially, the most commonly used separation processes for such equilibrium-limited reversible reactions is reactive distillation [7], [8]. Nevertheless, in the case of butyl acetate, distillation is high-energy consuming due to low relative volatilities between the carboxylic acid and the ester. Indeed, the boiling points of acetic acid (118 °C) and butyl acetate (126 °C) are relatively close, and thus separation by distillation require a higher number of stage and reflux ratio in comparison to other esters. With the increasing price of energy, alternative separation techniques have to be considered, in order to reduce the energy consumption associated with the separation of the components. In this study, we focus on liquid–liquid extraction of the principal product, n-butyl acetate (BA) from the remaining reactant, acetic acid (AA), these mixture being a single homogeneous phase. This technique is of considerable economic importance in the chemical industry and may be considered either at the end of the reaction or during the reaction in order to shift the equilibrium. The nature of solvent naturally influences the equilibrium characteristics of BA extraction from AA solutions. Previous works give some data on phase equilibrium for systems such as acetic acid and butan-1-ol [9] or ternary systems with acetic acid, water and esters [10] or alcohols [11], [12], [13]. In this study, aliphatic hydrocarbons (HCs), from hexane (C6) to hexadecane (C16), were used as organic solvent. Some liquid–liquid equilibrium (LLE) data for such ternary systems AA–BA–HC were obtained at T = 293.15 K, under atmospheric pressure.

First of all, mutual solubility of AA and HCs were studied in order to determine suitable solvents for liquid–liquid extraction of BA in excess of AA. LLE results for the ternary systems AA + BA + HC presenting a biphasic area are given in this work. Moreover, to show the consistency of our experimental results, tie-line data were correlated using Othmer–Tobias, Bachman and Hand correlations. Finally, experimental ternary diagrams were compared with data calculated with the UNIQUAC model. This model may provide a good correlation of the solubility curve with the hydrocarbons of interest.

Section snippets

Materials

All chemicals (n-butyl acetate, glacial acetic acid, hexane C6, octane C8, decane C10, dodecane C12 and hexadecane C16) were purchased from Sigma–Aldrich. They were of guaranteed reagent grade and their purities are reported by the supplier to be higher than 99%. They were used without any further purification as no impurities were detected using gas chromatography with a flame ionization detector (GC-FID). The amount of water in acetic acid was determined using a Karl–Fisher apparatus (831 KF

LLE experimental results

First of all, miscibility of acetic acid with hydrocarbons was determined. It was noticed that AA and hexane were miscible in all proportions whereas AA and all the other hydrocarbons present an incomplete mutual solubility. The results are reported in Table 1 (lines with a butyl acetate mass fraction wBA equal to zero) and represented in Fig. 1. It is experimentally shown that the biphasic area is larger when the hydrocarbon chain length increases. Concerning the system AA + BA + C8, as it can be

Conclusion

Liquid–liquid equilibrium (LLE) data for the systems acetic acid + n-butyl acetate + hydrocarbons were determined at 293.15 K and atmospheric pressure. As it was shown that hexane and acetic acid were miscible in all proportions, ternary mixtures were not feasible. Nevertheless, all the other investigated systems from octane to hexadecane formed a type-I phase diagram of LLE. The two-phase region increased with increasing the hydrocarbon chain length for the ternary systems studied. Moreover,

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