Thermodynamic study of 1,1,2,2-tetrachloroethane + hydrocarbon mixtures: I. Excess and solvation enthalpies

doi:10.1016/j.fluid.2006.10.013

Fluid Phase Equilibria

Volume 250, Issues 1–2, 20 December 2006, Pages 105-115

https://doi.org/10.1016/j.fluid.2006.10.013 Get rights and content

Abstract

The excess enthalpies, H^E, at 298.15 K for binary mixtures of 1,1,2,2-tetrachloroethane (TCE) + an hydrocarbon (n-heptane, cyclohexane, benzene, toluene, ethyl-, n-propyl-, iso-propyl-, n-butyl-, sec-butyl-, and tert-butylbenzene) have been measured by flow microcalorimetry. All mixtures containing an aromatic hydrocarbon as second constituent exhibit negative H^E, while mixtures with n-heptane or cyclohexane are endothermic. The H^E data have been analysed in terms of the DISQUAC model. Using a limited number of adjusted interchange energy parameters, C, taken as structure dependent, the model provides a fairly consistent description of H^E as a function of concentration. The enthalpies of solvation, ΔH°, of hydrocarbons in TCE, as obtained from heats of solution at infinite dilution and known vaporization enthalpies, have been described using an additive scheme of surface interactions. The effects of aromatic ring, chain lengthening, branching, and cyclization on both H^E and ΔH° have been discussed.

Introduction

In continuation of our studies [1], [2], [3], [4], [5], [6], [7] on the excess thermodynamic properties H^E, G^E, and V^E [4] of chloroalkanes (tetrachloromethane [1], [2], [3], [4], [6], chloroform [7], dichloromethane [5], 1,2-dichloroethane [7], 1-chlorobutane [5]) mixed with organic compounds (alkanes, cycloalkanes, alkenes, alcohols, ethers, aldehydes, ketones), we have started a similar investigation on binary mixtures containing 1,1,2,2-tetrachloroethane (TCE).

As the first results, in this paper we report excess enthalpies H^E for TCE + an aromatic hydrocarbon (benzene, toluene, ethyl-, n-propyl-, iso-propyl-, n-butyl-, sec-butyl-, and tert-butyl-benzene). Measurements of H^E have been carried out also for TCE + a linear alkane (n-heptane) and + a cyclic alkane (cyclohexane). Among the examined systems, heats of mixing are reported in the literature only for TCE + cyclohexane [8], +benzene [8], [9], and +toluene [10]. For this latter they have erroneous large values.

The dispersive–quasi-chemical model DISQUAC [11] has been applied to examined mixtures with the aim of reproducing H^E curves and of characterizing the interchange energy between chlorine atoms of TCE and π-electrons of aromatic hydrocarbons. The model, that for different surface contacts generates two sets of parameters, dispersive and quasi-chemical, has been successfully employed to analyse the excess properties of many classes of polar + non-polar systems [11], [12], [13], [14], [15].

From partial molar enthalpies at infinite dilution and from the known enthalpies of vaporization, the enthalpies of solvation ΔH° have been evaluated either for hydrocarbons in TCE and TCE in hydrocarbons. An additive scheme of surface interactions is presented to estimate different group (CH₃, CH₂, CH, C, cy-CH₂, CH_ar, C_ar, OH) contributions to ΔH°.

The interchange energy parameters C_sv obtained from H^E together with group contributions B_j to ΔH° have been analysed, and the effects of chemical structure (benzene ring, chain lengthening, branching, and cyclization) on both H^E and ΔH° have been discussed.

Section snippets

Instrumentation

Heats of mixing were determined by means of a flow micro-calorimeter (model 2277, LKB-producer AB, Bromma, Sweden). The apparatus and the experimental procedure are described in detail elsewhere [16]. Fully automatic burets (ABU80, Radiometer, Copenhagen) were used to pump the liquid into the LKB unit. The molar flow rate m_i (mol s⁻¹), of component i flowing into the mixing cell is given by $m_{i} = \frac{Φ_{i} ρ_{i}}{M_{i}}$ where Φ_i is the volumetric flow rate, ρ_i the density and M_i is the molar mass. The necessary

Results

The experimental H^E data are collected in Table 2 and plotted in Fig. 1, Fig. 2, Fig. 3 for almost all systems examined. The H^E values were fitted to the smoothing Redlich–Kister equation: $H^{E} = x_{1} x_{2} \sum_{j = 0}^{n - 1} a_{j} {(x_{1} - x_{2})}^{j}$ where x₁ is the mole fraction of TCE and n is the number of coefficients. As objective function, the ratio H^E/x₁x₂ has been chosen instead of H^E to evaluate a_js. This ratio tends to emphasise the dilute regions, whilst fitting to H^E may result in large relative errors on H^E of the

The DISQUAC model

DISQUAC is an extended quasi-chemical group-contribution model based on Guggenheim's lattice theory [11], [26]. In the classical model [27], molecules are assumed to possess one of several types of contacts s or v and occupy the sites of a lattice with coordination number z. The type of lattice and the assignment of contact points are arbitrary and irrelevant in applications to liquid mixtures and can be avoided by using the group–surface interaction version of the theory [28]. In the classical

Acknowledgement

We are grateful to Dr. H.V. Kehiaian for helpful suggestions and comments.

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Thermodynamic study of 1,1,2,2-tetrachloroethane + hydrocarbon mixtures: I. Excess and solvation enthalpies

Abstract

Introduction

Section snippets

Instrumentation

Results

The DISQUAC model

Acknowledgement

Fluid Phase Equilib.

Fluid Phase Equilib.

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J. Chem. Thermodyn.

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Fluid Phase Equilib.

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Thermochim. Acta

Fluid Phase Equilib.

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Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

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J. Sol. Chem.