Compressed liquid density measurements for {methylbenzoate + (cyclohexane or 1-hexanol)} binary systems

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Abstract

Densities of the binary systems {methyl benzoate + (1-hexanol or cyclohexane)} were measured over the full composition range from (278.15 to 358.15) K and pressures up to 60 MPa, as a part of a study on the interactions between MB and organic solvents provided with six atoms of carbon but different functional groups and structures. Experimental data were correlated with temperature and pressure using the TRIDEN-10 parameter equation. From these parameters, isobaric expansivity, isothermal compressibility, and internal pressure were calculated. The complex behavior of the derived excess properties was interpreted in terms of intermolecular interactions and structural effects between the system components.

Research highlights

► (methylbenzoate + cyclohexane/1-hexanol) pressure–temperature –density–behavior. ► PVT data was measured using vibrating tube densimeter. ► Data was correlated using TRIDEN equation. ► Excess properties were analyzed as a function of pressure and temperature.

Introduction

The existence of many industrial processes that involve multi-component solvents requires a better understanding of their thermophysical properties, allowing further development of physical models, and therefore, improving the design of industrial processes, reducing time, cost and pollution of the operations. The experimental determination of thermophysical properties is absolutely necessary to develop industrial processes, new physical models and improve the available ones. Moreover, thermophysical properties allow to infer valuable information about the molecular-level structure of the fluids, as well as about the intermolecular forces and structural factors [1].

Methyl benzoate (MB, CAS 93-58-3) is known to exhibit a specific behavior because of its self-aggregation. Besides it is considered a very useful compound in polymer science and technology; in addition to its dipolar (μ298.15Κ = 1.94 D [2]), hydrophobic and aprotic character, the presence of the polarizable aromatic π-electron system near the dipolar ester group, confers this molecule a highly selective solvent ability. However, despite these promising properties, the scarce existing literature makes convenient a systematic research on its properties. Few studies have been reported on methyl benzoate containing mixtures, with most of them carried out at ambient pressure conditions [3], [4], [5], [6], [7], [8], [9], [10].

This work reports results of the ongoing research carried out by our research group on binary and ternary methyl benzoate-containing mixtures [11], [12], [13], [14], [15], [16], [17], [18], including thermophysical properties study for binary mixtures of methyl benzoate and organic solvents, which are provided with six carbon atoms but different structure and functional groups, as a function of pressure and temperature [19]. Thus, we report the experimental densities and their derived properties for the binary mixtures of MB/1-hexanol and MB/cyclohexane, in the whole composition range from (278.15 to 358.15) K and pressures up to 60 MPa. These solvents were selected to analyze the effects of their geometric structures and the presence of hydroxyl functional group on the mixture thermophysical properties and to provide a deeper insight into the intermolecular interactions.

Section snippets

Solvents and sample preparation

MB (GC purity 0.999), 1-hexanol (GC purity 0.999), and cyclohexane (GC purity 0.999) were obtained from Fluka. They were stored out of light over Fluka Union Carbide 0.4 nm molecular sieves to avoid moisture absorption. Fluids were degassed with ultrasounds before samples’ preparation and used without additional purification. Binary liquid mixtures were prepared by syringing amounts, weighed to Δm = ±1 · 10−5 g with a Mettler AT 261 Delta Range balance, into suitably stoppered bottles. The estimated

Experimental results

Experimental and calculated thermophysical properties of the xMB + (1  x) 1-hexanol and xMB + (1  x) cyclohexane binary systems were obtained in the compressed liquid state from (0.1 to 60) MPa over the (278.15 to 358.15) K temperature range. The density data for each composition were correlated with temperature and pressure according to the TRIDEN 10-parameter equation [23], which combines a modified Rackett equation for saturation densities with Tait’s equation for isothermal compressed densities,

Discussion

A regular behavior is inferred from the analysis of pressure–density–temperature data for all the studied systems, as it may be expected, with increasing density when the temperature decreases and the pressure increases, showing pi the same tendency, but with a more complex behavior (FIGURE 2, FIGURE 3). Also, αp and κT show a regular behavior, increasing with the temperature and decreasing with the pressure. The planar methyl benzoate structure is disrupted by the globular shaped cyclohexane,

Acknowledgments

The financial support by Junta de Castilla y León, Project BU020A07, and Ministerio de Educación y Ciencia, Project CTQ2005-06611/PPQ, (Spain) is gratefully acknowledged.

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