Thermophysical Properties and Liquid–Liquid Equilibria of Pseudoternary Systems {Toluene + n-Heptane + Deep Eutectic Solvents Based on Levulinic Acid}

Abstract

Three deep eutectic solvents (DESs), DES1−DES3, were prepared using levulinic acid and choline chloride with molar ratios of 3:1, 4:1, and 5:1, respectively. Another three DESs, DES4−DES6, were prepared using levulinic acid and acetylcholine chloride with the same molar ratio. The density and viscosity of all six DESs were experimentally measured at temperatures ranging from 293.2 to 323.2 K. Both the density and logarithmic value of viscosity of all DESs follow a linear tendency with respect to temperature and reciprocal temperature, respectively. The liquid−liquid equilibria (LLE) for the pseudobinary systems of both toluene and the DES and n-heptane and the DES were performed over a temperature range from 298.2 to 318.2 K with a 10 K interval. The solubilities of toluene in DESs were higher than those of n-heptane in DESs. The LLE of the pseudoternary systems of toluene, n-heptane, and DESs were obtained over a temperature range of 298.2−318.2 K with a 10 K interval. The distribution coefficient of toluene and selectivity were determined. The values of selectivity of toluene with DESs measured in this study were higher than those of other conventional solvents. Not only the mole fraction of toluene in the raffinate phase and temperature but also the mole ratio between the hydrogen bond acceptor and the hydrogen bond donor plays a role in determining both the distribution coefficient of toluene and selectivity.

Pyridine Ionic Liquid-Based Deep Eutectic Solvents Selectively Separating Toluene from Alkanes

“…At present, organic solvents are used as extractants for the separation of aromatic/alkane mixtures, such as sulfolane, N -methyl pyrrolidine (NMP), N -formyl morpholine (NFM), dimethyl sulfoxide (DMSO), ethylene glycols, or propylene carbonate. − However, the toxicity, volatility, selectivity, and separation performance of organic solvents limit their development. In recent years, ionic liquids (ILs) and deep eutectic solvents (DESs) with designable structures and adjustable properties have become a hot spot for the design and development of new functionalized solvents due to their low volatility, low toxicity, high stability, and so forth. − Among them, DESs have become a potential choice of extractants for aromatic/alkane separation due to the advantages of simple synthesis process, easy availability of raw materials, and so forth. − …”

“…In addition, the CO structure in the HBD can further improve the toluene selectivity due to its π–π interactions with the aromatic ring. Jung et al synthesized DES using choline chloride as the HBA and levulinic acid (LA) as the HBD for the separation of toluene/ n -heptane, and the selectivity of toluene reached 52.9. At present, ammonium/phosphonium salts as HBAs and alcohols/acids as HBDs are mainly used to design and synthesize DESs, which have achieved good extraction effects in the separation of aromatic/alkane. , Nevertheless, it is difficult to further improve the separation performance by adjusting the HBA/HBD structure for common DESs.…”