Citric acid-based deep eutectic solvents: Physical properties and their use as cosolvents in sulphuric acid-catalysed ethanolysis of oleic acid

Abstract

Deep eutectic solvents (DESs) are noted to be green ionic liquid (IL) analogues, and their many favourable properties made them interesting for the scientific community. In this study, two novel DESs of citric acid with the monosaccharides D-glucose or D-fructose (1:1 molar ratio) were prepared and characterized. At the atmospheric pressure, the density, the dynamic viscosity, and the electrical conductivity of these eutectic solvents were measured and analysed as the function of temperature in the practical temperature range of 293.15-363.15 K. Arrhenius theory was employed for understanding the transport phenomena in these DESs. By using the experimental data, some important properties were calculated such as molecular volume, lattice energy, heat capacity, molar Gibbs energy, enthalpy and entropy of activation of viscous flow for the synthesized DESs. The fractional Walden rule was employed to establish the relationship between molar conductivity and viscosity, which proved an excellent linear behaviour.Finally, these DESs were tested as cosolvents in oleic acid (oA) ethanolysis. The investigated DESs possess many desirable properties, such as low vapour pressure, inflammability, biodegradability, and can be obtained from available renewable resources. These DESs showed to have the potential to be utilized for several industrial applications, like processing and separation of food constituents, pharmaceutical applications, and mediums for chemical reactions.

The perspectives of natural deep eutectic solvents in agri-food sector

“…Shear flow behavior of NADES Flowability of NADES under varied shear rates depend on the apparent viscosity indicating their expected field of application and uses (Elhamarnah et al 2019). The flow behavior of NADES at room temperature has advantages over traditional solvents, so that they can be more easily used and operated in different industrial conditions (Troter et al 2016;Paiva, Matias, and Duarte 2018). The rheological behavior of different mixtures of NADES at room temperature is showing a universal trend depending on the detailed microstructure of the HBD and HBA.…”

“…However, NADES may behave as Newtonian fluids as well, independently of shear rate (Elhamarnah et al 2019;R€ uther et al 2013;Cao et al 2016;Aroso et al 2017). Troter et al (2016) reported a shear-thinning behavior of citric acid:glucose and choline chloride:citric acid at 1:1 molar ratios in the temperature range of 293.15-363.15 K at atmospheric pressure within the shear rate of 0.1-1000 s À1 . Sheer thinning behavior of choline chloride:lactic acid, choline chloride:citric acid, choline chloride:malic acid, choline chloride:lactic acid and choline chloride:fructose NADES was also observed by Altamash et al (2017) at 25 C under a shear rate domain of 0.01-1000 s À1 at atmospheric pressure.…”

The extraction of quercetin from waste onion (Allium cepa L.): Tunic by the aqueous solutions of different deep eutectic solvents

“…The properties of the prepared DESs at room temperature are given in Table 1. The physical and thermodynamic properties of the ChCland citric acid-based DESs can be found elsewhere [6,20].…”

Effects of temperature on physicochemical properties of the lecithin based deep eutectic solvents and their use in the CaO-catalyzed transesterification

“…In addition, density values can be used to calculate values of thermal expansion or compressibility coefficients that are valuable liquid structure and interactions data. When a DES system is heated, the molecules move faster, increasing the molar volume and, thus, decreasing the density [34]. Although high density of a DES is a problem for handling or mixing in chemical processes, it may be desirable in extraction processes since a relatively large difference in density between the raffinate and extract phases is required to guarantee more efficient phase separation [26].…”