Binary mixtures of choline chloride-based deep eutectic solvents as green extractants for the extraction of benzene from n-hexane

Abstract

A suitable green solvent for extraction of aromatics from aliphatics must possess good solvation and physicochemical properties, a rare occurrence in a single deep eutectic solvent (DES). Mixture of DESs could enable synergy and provide a good candidate extractant. In this study, DESs of glyceline, ethaline, and reline were synthesized and their binary mixtures (glyceline/ethaline, reline/ethaline, and glyceline/reline) produced by blending in various volume proportions. Twelve of such mixed solvents were prepared and their extraction efficiency for separating benzene from n-hexane investigated in a batch equilibrium process. Liquid–liquid equilibria (LLE) data for the pseudo-ternary systems of n-hexane + benzene + mixed DESs were measured at 303 K and 101.3 kPa. The distribution coefficient (D) and selectivity (S) of each pseudo-ternary system were determined to elicit extraction efficiency. The physicochemical properties of the mixed DESs were also measured. The results show that generally the distribution coefficients, selectivities, and physicochemical properties of the mixed DESs lie between the corresponding values for the constituent DES. The best performance was given by the mixed solvent of glyceline and ethaline in the 80:20 volume ratio, respectively, with D = 0.75 and S = 422.485. This assertion was further corroborated by higher percent recovery of benzene obtained from the said mixed DES (57.88%) relative to other mixed DESs (≤ 49.11%) examined in this study. Furthermore, its separation efficiency is superior to sulfolane but lower than glyceline, though there was a 9.4% reduction in its viscosity relative to glyceline.

Evaluation of hybrid solvents featuring choline chloride-based deep eutectic solvents and ethanol as extractants for the liquid–liquid extraction of benzene from n-hexane: towards a green and sustainable paradigm

“…This signifies selectivity becomes insensitive to EtOH addition when the composition of benzene in the extract phase goes above 10%. Similar trend occurred in the extraction of benzene from n -hexane using a binary mixed DES (glyceline/ethaline) as extractant [ 21 ]. Generally, selectivity tends to unity as the tie line tends toward the plait point, where the distribution coefficient of solute and other components of the ternary mixture becomes unity.…”

“…The quaternary ammonium salt (choline chloride) was used as the hydrogen bond acceptor while urea, glycerol and ethylene glycol serve as the hydrogen bond donors in the molar ratio 1:2, respectively. The detailed protocol for preparing these DESs is explained in our previous articles [ 19 , 21 ]. The hybrid solvents of these DESs were then prepared by mixing each DES with ethanol in varying volume proportion and named appropriately.…”

“…The 61 solvents were each investigated for their extraction capacity; each was used as an extractant in the separation of n -hexane + benzene mixture. The extraction process was done on a bench scale as described in our articles [ 19 , 21 ]. Measured volume of n -hexane + benzene mixture (feed) was contacted with hybrid solvent or solvent in 250 ml beaker.…”

“…In a related study using ASPEN simulation, Usman et al [ 20 ] reported higher values of selectivity for glyceline ( S max = 378.283) and ethaline ( S max = 77.364) compared to sulfolane ( S max = 55.371) in the extraction of aromatics (benzene–toluene–xylene) from waste tire pyrolysis gasoline at 303.15 K and 1 atm. Further, using a mixture of glyceline and ethaline in the volume ratio 80:20, respectively, as extractant for separating benzene from n -hexane, Usman et al [ 21 ] reported the selectivity value of 422.485. These studies eloquently speak to the superiority of DESs to sulfolane in terms of thermodynamic properties.…”

“…However, the undesirable transport property (high viscosity) of DESs is a huge challenge to its industrial application. For example, the viscosities of glyceline, ethaline, reline and sulfolane are 342.12 cP, 38.52 cP, 667.28 cP [ 21 ], and 10.35 cP [ 27 ] at 303.15 K, respectively. Zheng et al [ 28 ] posited that mixing of DESs with molecular solvents (volatile organic solvents) can help overcome the drawbacks of neat DESs and thus extend the practical or industrial application of DESs.…”