Morpholine derivatives as thermoresponsive draw solutes for forward osmosis desalination

To develop a forward osmosis (FO) process, selection of draw solutes (DSs) is a critical factor in determining water permeability of the process. In this search for novel high-performance DSs, various morpholine derivatives were investigated for their thermoresponsive potential. 4-Butylmorpholine (BuMP) showed a preferable minimum lower critical solution temperature for the FO process (31.7 °C). The dilute phase of BuMP after phase separation at 70 °C showed a low concentration (3.3 wt %) and low osmotic pressure (3.16 bar). In the FO flux test, the water permeability and reverse solute flux of BuMP (55.0 wt %, 28 bar) against water were J_w 2.09 L m^-2 h^-1 and J_s 14.0 g m^-2 h^-1, respectively. Using 0.6 M NaCl (model seawater) as feed solution, BuMP (94.6 wt %) could extract water from this model seawater (J_w 0.56 L m^-2 h^-1). These results indicate a high potential for MP derivatives as DSs and provide new guidance for their development for FO desalination.