Non-membrane solvent extraction desalination (SED) technology using solubility-switchable amine

Abstract

Solvent extraction desalination (SED) is one of the liquid-liquid separation techniques that selectively uptake freshwater from high saline water, and then separate the absorbed freshwater from the solvent through temperature swing. This study evaluated the desalination performance of seven different amine solvents. Among these solvents, dipropylamine (DPA) was selected as the best solvent for SED, with higher potential of water recovery and salt removal efficiency in batch screening experiment. A continuous SED process was operated using DPA as the solvent, and its desalination performance, i.e. water recovery and salt removal efficiency, was investigated under varied retention time, mixing intensity, and separation temperature. Increase in mixing time, mixing intensity, and separation temperature led to better efficiency of water recovery. On the other hand, salt removal efficiency tended to depend on the inherent characteristics of the solvent, rather than the operating conditions. When the retention time, mixing intensity, and separation temperature were 30 min, 600 rpm, and 80 °C, respectively, the continuous SED process showed 11.05% of water recovery, and 95.5% of salt removal efficiency. Under these conditions, the total thermal energy consumption was estimated at 5.0-6.9 kW h/m3, which is significantly lower than the evaporation process 14.1-27.3 kW h/m3, and comparable to the membrane process 4.0-6.0 kW h/m3.