Objectives. In comparison with methyl tert-butyl ether (MTBE) and methanol mixtures, the separation of MTBE and tert-butanol (tert-butyl alcohol, TBA) mixtures represents a relevant challenge in chemical technology due to limited research in this area. Our aim was to evaluate the potential and efficiency of using choline chloride-based deep eutectic solvents (DESs) as green extractants for the separation of the MTBE–TBA system via liquid–liquid extraction (LLE).

Methods. DESs were prepared by mixing and heating a hydrogen bond acceptor (choline chloride, ChCl) with hydrogen bond donors (HBDs) as follows: malonic acid (1 : 1 molar ratio), glutaric acid (1 : 1), urea (1 : 2), and glycerol (1 : 2). Liquid–liquid phase equilibrium was experimentally studied in four ternary systems containing MTBE, TBA, and DES at temperatures of 293.15 and 313.15 K and atmospheric pressure. The compositions of the equilibrium liquid phases were determined using 1H nuclear magnetic resonance spectroscopy (500 MHz, dimethyl sulfoxide-d6).

Results. The experimental data allowed the key extraction parameters to be calculated: distribution coefficients for TBA and selectivity for MTBE–TBA separation for each investigated DES. A comparative analysis of the extraction capacity of the synthesized solvents toward the separated components was performed. The experimental phase equilibrium data confirm the fundamental possibility of using the ChCl-based DESs under study as extractants for separating the MTBE–TBA system. The calculated selectivity and distribution coefficient values allow the efficiency of various HBDs within the DES composition to be evaluated for solving this separation task. The comparative analysis of the DES extraction capacity showed a dependence of selectivity on the HBD and a slight dependence of selectivity on temperature. The highest selectivity values were observed for DESs based on ChCl/glycerol (1 : 2) and ChCl/urea (1 : 2) systems.

Conclusions. The feasibility of using DESs based on choline chloride with malonic acid, glutaric acid, urea, and glycerol as extractants for separating the MTBE–TBA mixture by LLE method has been experimentally confirmed. The calculated distribution coefficients and selectivity values enable a quantitative assessment and comparison of the efficiency of different DESs for this task, identifying the most promising compositions. The results obtained can be used as the basis for further development and optimization of the LLE process for MTBE and TBA using promising green solvents.