Fundamental investigation of osmolality, thermo-responsive phase diagram, and water-drawing ability of ionic-liquid-based draw solution for forward osmosis membrane process

• Published in: Journal of membrane science Vol. 570-571; pp. 93 - 102
• Main Authors: Kamio, Eiji, Takenaka, Aki, Takahashi, Tomoki, Matsuyama, Hideto
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2019
• Subjects: aqueous solutions; artificial membranes; chemical structure; Critical aggregation concentration; Draw solution; Forward osmosis membrane process; hydrophilicity; hydrophobicity; Ionic liquid; ionic liquids; molecular weight; osmolality; osmosis; permeability; separation; sodium chloride; temperature; Thermo-responsive phase separation; viscosity; Forward osmosis membrane process; Draw solution; Thermo-responsive phase separation; Critical aggregation concentration; Ionic liquid
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2018.10.004

Thermo-responsive ionic liquids (ILs) were examined as draw solutions in forward osmosis (FO) membrane process. We synthesized several ILs to understand the relationship between the hydrophilicity/hydrophobicity balance of ILs and the osmolality and phase diagram of the IL aqueous solutions. An increase in the hydrophobicity led to a decrease in the osmolality because of the formation of IL-based aggregates in water. At the critical aggregation concentration (CAC), the osmolality was drastically changed. Above the CAC, the water-rich phase appeared after liquid–liquid separation at elevated temperature. The osmolality, phase separation temperature, viscosity, and water-drawing ability of the IL-based draw solution could be controlled by controlling the chemical structure and hydrophilic/hydrophobic balance of ILs. The IL with small molecular weight and low viscosity showed the comparable water permeability as the NaCl aqueous solution and the possibility of repeated use. Prevention of the IL leakage through FO membrane is a future subject. [Display omitted] •Thermo-responsive ionic liquids (ILs) was examined as draw solute.•ILs with various hydrophilicity/hydrophobicity balance were synthesized.•Formation of IL aggregates affected the osmolality and phase separation property.•Design criteria of ILs as a solute of an effective draw solution (DS) was proposed.•Potential of the ILs as DS was evaluated using forward osmosis membrane module.