Evaluating salt effects on the hydrodynamic and mass transfer of hydrophobic deep eutectic solvent drops in extracting phenol from aqueous phase

• Using a low viscosity DES was feasible for extraction phenol from salty aqueous solutions. • The terminal velocity of circulating drops was aligning with the Grace model. • Overall mass transfer coefficient consists the Hofimester series as MgSO 4 > Na 2 SO 4 > NaCl. • Comparable mass transfer coefficients were revealed for the utilized systems. • Mass transfer data were reproduced using Newman’s equation with an effective diffusivity. Eco-friendly hydrophobic deep eutectic solvents (HDESs) could be designed and utilized for separation of pollutants from aqueous solutions. This study explores the performance of a low viscosity HDES, formulated from dodecanoic and octanoic fatty acids (1:3 molar ratio), in extracting phenol from aqueous phase and in the presence of NaCl, Na 2 SO 4 and MgSO 4 salts. In hydrodynamic study, it was revealed that presence of salts alters the system physical properties, resulting in lower contact time due to larger generated drops from nozzles. HDES drops were in circulating mode and terminal velocities in close alignment with the Grace model. In mass transfer study, amazingly, 54.8%, 103.7% and 142.3% enhancements in the overall mass transfer coefficient were achieved with 0.02 mass fraction of the salts, respectively. These findings align with the Hofmeister series, as the salting-out follows the order of MgSO 4 > Na 2 SO 4 > NaCl, bringing about significant enhancement in the rate of extraction. Modelling of the mass transfer data were established by using the effective diffusion coefficient alongside a modified version of Newman’s equation, revealing a strong concordance between calculated and experimental results with a maximum deviation of only 8.1%. Results underscore the potential application of HDESs in separating pollutants from salty aqueous solutions.