Directional solvent extraction (DSE) is a relatively new alternative to membrane-based desalination technologies for freshwater production. Process costs are considerably lower as the comparatively low operation temperatures required can be supplied by the consumption of waste heat or unconcentrated solar energy. The efficiency of the DSE approach has been further enhanced by University of Notre Dame researchers with the use of ionic liquids to boost water yield.

An ionic liquid based on ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Tf2N), was observed to deliver a freshwater yield 10 times that of the decanoic acid currently used in DSE systems. When tested at a sodium chloride salinity of up to 3.8 wt%, Tf2N achieved ion rejection rates of up to 98.3% and lowered the salt content below the drinking water standard of 500 ppm. The ionic liquid also proved effective in treating highly saline water with 10.8 wt% aqueous sodium chloride solution, achieving an ion rejection rate of 96%.

The researchers will next focus on reducing the cost of the ionic liquid, increasing its production and designing a continuous system to scale up from the original experiments.

A paper on this research is published in Nature Communications.