Solid–liquid equilibria and purity determination for binary n-alkane + naphthalene systems

doi:10.1016/j.tca.2006.03.011

Thermochimica Acta

Volume 444, Issue 2, 15 May 2006, Pages 166-172

https://doi.org/10.1016/j.tca.2006.03.011 Get rights and content

Abstract

Mixtures of heavy aromatics with high aliphatics are important in the formation of asphaltenes in the oil industry.

This work reports binary solid–liquid equilibria for naphtalene + eicosane, +pentacosane, +hexatriacontane mixtures by differential scanning calorimetry. Results are compared with those from modified UNIFAC (Larsen and Gmehling versions) and ideal predictions. Finally, we determine the purity according to van’t Hoff equation. Results are in good agreement with values given by ultraviolet spectrophotometry.

Introduction

Solid –liquid phase equilibria form the basis for crystallization processes, which are used in chemical and petrochemical industry for separation of mixtures. Mixtures of high normal long-chain alkanes and polyaromatics are important in the flocculation of asphaltenes, and their codeposition constitutes a major problem during the exploitation, transport, and storage of crude oil.

The experimental determination of thermodynamic and structural properties of pure long-chain n-alkanes and phase diagrams of their molecular alloys have been the subject of many investigations in the literature [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. Some data concerning solid–liquid equilibria of normal long-chain alkanes + organic compounds have been reported [11], [12], [13], [14], [15], [16], [17].

Following a systematic study of the thermodynamic properties of mixtures containing organic molecules [18], [19], we present in this paper data on solid–liquid equilibria (SLE) of naphthalene + eicosane, +pentacosane, +hexatriacontane systems which represent a particularly interesting family of molecules for testing theories and can be helpful to understand the phase behavior of heavy oils. Results obtained are compared with those given by modified UNIFAC (Larsen and Gmehling versions) and ideal models [20], [21]. The experimental results were also exploited in the determination of purity [22], [23], [24], [25].

Section snippets

Materials and methods

Naphthalene, n-eicosane, n-pentacosane and n-hexatriacontane were purchased from Fluka (purity greater than 99 mol%) and by gas chromatography have a purity >99.5%. They were used without further purification.

A series of heavy alkane–naphthalene binary mixtures were prepared by heating very slowly in a glass cell near the melting temperature of the major component.

With continuous stirring, the liquefied sample was quenched in liquid nitrogen, ground and powdered in a clean agate mortar with as

Solid–liquid equilibria

Typical DSC curves obtained are shown in Fig. 1, Fig. 2, Fig. 3. The thermodynamic properties of the pure compounds (Table 1) are in good agreement with literature data [1], [11], [26], [27], [28], [29], [30], [31]. Table 2, Table 3, Table 4 list the experimental results of each system. Plots of the eutectic heat ΔH_e and fusion heat ΔH_m versus naphthalene mole fractions (Fig. 4, Fig. 5, Fig. 6) illustrate that naphthalene (1) + n-eicosane (2), naphthalene (1) + n-pentacosane (2) and naphthalene (1) +

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Solid–liquid equilibria and purity determination for binary n-alkane + naphthalene systems

Abstract

Introduction

Section snippets

Materials and methods

Solid–liquid equilibria

J. Chem. Thermodyn.

Thermochim. Acta

Polymer

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Fluid Phase Equilib.

Fluid Phase Equilib.

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J. Pharm. Sci.

Chem. Eng. Sci.

Fluid Phase Equilib.

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Chem. Phys. Lett.

J. Mol. Struct.

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