Influence of 1–alkyl–3–methylimidazolium based ionic liquids on the thermodynamic and transport properties of L(+)–lactic acid in aqueous solutions of polyethylene glycol

doi:10.1016/j.fluid.2017.02.019

Fluid Phase Equilibria

Volume 440, 25 May 2017, Pages 77-86

https://doi.org/10.1016/j.fluid.2017.02.019 Get rights and content

Highlights

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Effect of ionic liquids on the volumetric properties of lactic acid in aqueous PEG solutions has been investigated.
•
Effect of ionic liquids on the viscometric properties of lactic acid in aqueous PEG solutions has been investigated.
•
The solute–solvent interactions were decreased by increasing concentration and length of alkyl group of ionic liquid.
•
The solute–solvent interactions were decreased by increasing temperature.

Abstract

In this study, effect of some ionic liquids on the thermodynamic and transport properties of L(+)–lactic acid in aqueous polyethylene glycol solutions have been investigated. Density, speed of sound and viscosity of L(+)–lactic acid in the aqueous solutions of polyethylene glycol, (polyethylene glycol + 1–hexyl–3–methylimidazolium bromide) and (polyethylene glycol + 1–octyl–3–methylimidazolium bromide) were measured at temperatures 288.15–318.15 K. Apparent molar volumes, transfer apparent molar volume, apparent molar isentropic compressibility and viscosity B–coefficient of L(+)–lactic acid were calculated by using experimental data and were discussed in terms of solute–solute and solute–solvent interactions. The results reveal that solute–solvent interactions were decreased by increasing concentration of ionic liquid, length of alkyl group of ionic liquid and temperature.

Introduction

L(+)–lactic acid (LaH), as an industrially important organic acid, has widespread applications in the pharmaceutical, food, chemical, leather, and cosmetic industries [1]. It is produced both chemical synthesis and fermentation processes. The efficiency of the processes mainly depends on the separation and purification of L(+)–lactic acid. As a result, researches in this area have been focused on effective and economical reaction mixture to recover LaH from the fermentation broth lately or synthesis method. The recovery process of LaH has been made with use of several techniques such as ion exchange resins, direct distillation, adsorption, electrodialysis, and liquid–liquid extraction [2], [3], [4]. Liquid–liquid extraction based on aqueous biphasic systems (ABS) as a method has been used widely for separation and purification processes of biological materials [5], [6]. In recent years, a new type of ABS based on ionic liquids (ILs)-polymer has been reported [7], [8], [9], [10], [11]. Polyethylene glycol (PEG) as an effective and useful polymer in these types of ABS is extensively used due to its low melting points, low cost, hydrophilic nature and low toxicity [12], [13]. Recently, IL–based ABS have been used extensively for many processes in industry and academia as green solvent due to their unique properties such as; low vapor pressure, high thermal stability, non–flammability, low toxicity, and high electrical conductivity [14], [15], [16], [17], [18]. Thereby, these properties caused ionic liquids to have many attractive applications in biotechnology for separation and purification of organic acids. Extraction of LaH has been studied by using the ionic liquids in recent years [19], [20], [21], [22]. Jan Martak et al. have investigated extraction of lactic acid by phosphonium ionic liquids [23]. Solvent extraction of organic acids with ionic liquids was also investigated by Huddleston [24]. Oliveira et al. investigated extraction of L–lactic, L–malic, and succinic acid from aqueous solutions by using hydrophobic ILs [25]. Despite abundant applications of ionic liquids in the ABS process, there is no report with regard to their thermodynamic and transport properties of LaH in the presence of ionic liquids. Therefore, to design and optimization of the extraction process using ABS method and selection of the proper ionic liquid, information about the thermodynamic and transfer properties of aqueous (LaH + IL + polymer) systems in order to understand better solute–solvent interactions between components are necessary. On the other hand, knowledge of volumetric, acoustical and viscometric properties are useful technique to evaluating the solute–solute and solute–solvent interactions which occur in these solutions. In the present work, volumetric and transport properties of lactic acid in aqueous solution of (PEG + ILs) were investigated at different temperatures to provide the information about the nature of interactions LaH in aqueous solutions of (PEG + ILs). The apparent molar volume $(V_{ϕ})$ , the infinite dilution apparent molar volumes $(V_{ϕ}^{0})$ , transfer volume $(Δ_{t r} V_{ϕ}^{0})$ , the apparent molar isentropic compressibility $(κ_{ϕ})$ and the viscosity B–coefficients were used to interpret the solute–solute and solute–solvent interactions of LaH in the aqueous solutions of (PEG + ILs).

Section snippets

Chemicals

The names, CAS numbers, abbreviations, purity in mass fraction of the used chemicals and analysis method used in this work are listed in Table 1. The doubly distilled water was used for preparation of the solutions.

Synthesis of ionic liquids

The ionic liquids, 1–Alkyl–3–methylimidazolium bromide, ([C_nmim]Br, n = 6 and 8) were synthesized as described in the literature by direct alkylation of N-methylimidazole with an excess amount of 1-haloalkane in a round bottom flask about at T = 353 K for 72 h under an argon

Apparent molar volume

The experimental density (ρ) and speed of sound (u) for LaH in water, the aqueous solutions of PEG and in the aqueous solutions of (PEG + ILs) (contain of w_PEG = 0.020 of polyethylene glycol and w_IL = 0.010, w_IL = 0.015, and w_IL = 0.020 of ionic liquids) at T = (288.15, 298.15, 308.15, and 318.15) K are reported in Table 2. In order to study the influence of ILs on the volumetric properties of LaH in aqueous solution of PEG, the apparent molar volume of lactic acid were calculated by following

Conclusions

In this work volumetric and viscometric properties of LaH in the aqueous solutions of PEG and in the aqueous solutions of (PEG + ILs) were investigated. The calculated infinite dilution apparent molar volume $V_{ϕ}^{0}$ , transfer volumes, the limiting value of apparent molar isentropic compressibility $κ_{ϕ}^{0}$ and B-coefficient viscosity reveal that solute–solvent interaction were decreased by increasing temperature, concentration ionic liquids and alkyl chain length of ionic liquids.

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Citation Excerpt :
Therefore, solute–solvent interactions were decreased by increasing concentration of PEG as well as temperature. However, the values of κϕo for LaH in aqueous solutions of PEG are smaller than those of LaH in pure water which reported in literature [18]. This behavior may be due to interactions of water molecules and PEG.
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View full text

Influence of 1–alkyl–3–methylimidazolium based ionic liquids on the thermodynamic and transport properties of L(+)–lactic acid in aqueous solutions of polyethylene glycol

Highlights

Abstract

Introduction

Section snippets

Chemicals

Synthesis of ionic liquids

Apparent molar volume

Conclusions

J. Chem. Thermodyn.

J. Chem. Thermodyn.

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Sep. Purif. Technol.

Sep. Purif. Technol.

Sep. Purif. Technol.

J. Chem. Thermodyn.

Thermochim. Acta

Fluid Phase Equilib.

J. Chem. Thermodyn.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Mol. Liq.

Fluid Phase Equilib.

Thermochim. Acta

Korean J. Chem. Eng.

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