Tetrabutylammonium 2,4,6-trimethylbenzenesulfonate as an effective and regenerable thermo-responsive ionic liquid drawing agent in forward osmosis for seawater desalination

Efficient drawing agents are essential in forward osmosis (FO) for clean water production. Monomeric thermo-responsive ionic liquid (IL) [N4444]2,4,6-ManSO(3) was thoroughly investigated as a drawing agent in FO. The IL can be safely employed due to its thermal stability and low cytotoxicity. It has a van's Hoff factor i = 1.21, with sufficient ionic strength to generate osmotic pressure similar to 58.92 bars (2 M). FO operations especially under PRO mode demonstrate that 2 M [N4444]2,4,6-ManSO(3) can induce competitive water flux J(v) similar to 12.3 L M-2 h(-1) with remarkably low reverse solute flux J(s) < 0.006 mol M-2 h(-1) and specific reverse solute flux J(s)/J(v) similar to 4.5 x 10(-4) mol L-1. Using 0.6 M NaCl as feed demonstrates its consistency in desalinating seawater (J(v) similar to 3.72 L M-2 h(-1), J(s) similar to 0.004 mol M(-2 )h(-1), and J(s)/J(v) similar to 0.91 x 10(-3) mol L-1). After FO, [N4444] 2,4,6-ManSO(3) can be effectively retrieved (similar to 98%) through thermal precipitation at 60 degrees C, above its cloud point temperature (57 degrees C). Meanwhile, > 99% of the remaining 2% can be recovered through reverse osmosis or membrane distillation to produce water effluents with non-toxic IL concentrations (<< 100 mg L-1). Results indicate that thermo-responsive [N4444]2,4,6-ManSO(3) is a promising alternative reusable drawing agent in FO process.