Liquid–liquid equilibria for ternary systems acetic acid + n-butyl acetate + hydrocarbons at 293.15 K
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,
References (21)
- et al.
Catalysis Today
(1993) - et al.
Journal of Catalysis
(1983) - et al.
Journal of the Taiwan Institute of Chemical Engineers
(2009) - et al.
Chinese Journal of Chemical Engineering
(2012) - et al.
Fluid Phase Equilibria
(2011) - et al.
Fluid Phase Equilibria
(2002) - et al.
Fluid Phase Equilibria
(2012) - et al.
Fluid Phase Equilibria
(1991) - et al.
Fluid Phase Equilibria
(2012) - et al.
Chemistry Letters
(1984)