Excess properties and vapour pressure of 2-diethylaminoethylamine + cyclohexane

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Abstract

The vapour pressures of liquid (2-diethylaminoethylamine (2-DEEA) + cyclohexane) mixtures were measured by a static method between (T = 273.15 and T = 363.15) K at 10 K intervals. The excess molar enthalpies HE at 303.15 K were also measured. The molar excess Gibbs energies GE were obtained with Barker’s method and fitted to the Redlich–Kister equation. The Wilson equation was also used. Deviations between experimental and predicted GE and HE, by using DISQUAC model, were evaluated. The proximity effect of N atoms produces a decrease of the interactional parameters.

Highlights

Vapor pressures for 2-diethylaminoethylamine + cyclohexane mixtures were measured. ► The excess molar enthalpies HE at 303.15 K were measured by C80 calorimeter. ► The data obtained are examined on the basis of Disquac model. ► The influence of the proximity effect of N atoms on HE and GE was investigated. ► The calculated values of GE and HE agree well with the experimental values.

Introduction

Diamines are an important class of compounds used in different fields of industry [1], [2], [3] and represent a particularly interesting family of molecules for the purpose of testing group-contribution models, and analyse of the intramolecular effects, especially the proximity effect. Previous studies, [4], [5], [6], [7], have shown that the occurrence of a functional group in a cycle ring and/or the proximity of another group may change considerably the interaction parameters.

(Vapour + liquid phase) equilibria measurements are important in thermodynamics for their direct use in process design, and for their testing and extending solution theories to more complex mixtures.

Following our systematic study of the thermodynamic properties of mixtures of symmetric diamines with n-alkanes, or cyclohexane [8], [9], [10], [11], [12], [13], and linear or aromatic diamines with polyaromatics [14], [15], [16], we present in this paper experimental data of vapour pressures for (2-diethylaminoethylamine + cyclohexane) mixture, at ten temperatures between (T = 273.15 and T = 363.15) K as well as the excess molar enthalpies HE at 303.15 K.

The excess properties of these mixtures GE and HE are also studied in terms of DISQUAC model [17], [18], [19], [20], this to examine the influence of the intramolecular effect (steric effect and proximity effect of N atoms) on these thermodynamic properties.

Section snippets

Materials

Cyclohexane (Merck, purity greater than 99 mol%) is fractionally distilled on a 40-plate column and its vapor pressures agree to within 2% with literature values [21]. The diamine (Aldrich) was also distilled under nitrogen with the presence of sodium, the purity (99.8 mol%) was checked by GC.

Apparatus and procedure

The total vapour pressure measurements were obtained by a static method whose experimental details and procedure have been described elsewhere [22], [23], [24]. The static apparatus allows reliable

Results and discussion

Data reduction for the binary mixture was done by Barker’s method [26]. The nonideality of the vapor phase was taken into account with the virial equation of state, truncated in the second term. Table 1 shows the molar volumes of the pure compounds (2-DEEA and cyclohexane) estimated with the Rackett correlation using the literature data for acentric factor and critical properties [27] and the mixed virial coefficients together with the vapour pressures. The virial coefficients of the diamine

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