Katelyn Wendt

Chemistry and Biochemistry

Faculty Advisor: Brandon Ashfeld

Task Specific Ionic Liquids Increase Efficiency in Water Desalination Processes

This work in the Ashfeld lab focuses on the design and synthesis of new heterocycle-based ionic liquids (ILs) as environmentally benign, non-toxic fluids in an energy efficient directional solvent extraction (DSE) process for the desalination of industrial and residential water resources. The ability to desalinate high salinity water is critical to addressing the ongoing global water shortage crisis. To be able to do this through the use of minimal energy on a production level scale is necessary for impacting industrial waste streams and rendering current polluted water to potable levels of saline content. While current methods for saltwater purification (e.g., reverse osmosis, etc.) are effective at treating hypersaline on small scale, these techniques are inefficient due to the need for a large enough membrane and high temperatures. A recent study by the Ashfeld lab, in collaboration with Prof. Tengfei Luo, has demonstrated that task-specific ILs can improve the energy efficiency of current desalination techniques by eliminating the need for a membrane and overcoming the temperature barrier, which also allows for improved operational capabilities (Guo, J.; Tucker, Z. D.; Wang, Y.; Ashfeld, B. L.; Luo, T. “Ionic liquid enables highly efficient low temperature desalination by directional solvent extraction.” Nat. Commun. 2021, 12 (437), https://doi.org/10.1038/s41467-020-20706-y). The use of ILs for DSE have the potential to substantially reduce the operating costs relative to current water purification methods. However, it is difficult to identify and synthesize new and more efficient ILs due to the slight differences in their solubilities. When an effective ionic liquid solvent is discovered, it often has the potential to increase freshwater yields by 10x in comparison to current solvents used for directional solvent extraction while also allowing for a decrease in cost and energy.

The acceptable amount of NaCl in drinking water is 500 ppm according to the Secondary Drinking Water Standards developed by the EPA, and one of the ILs reported by Ashfeld and Luo was able to produce a higher yield of freshwater below that met this standard (NaCl concentration < 500 ppm). This project will design and synthesize a collection of ILs aimed at enabling the energy efficient desalination of hyper salinity water. By employing the synthetic methods for heterocycle construction, a diverse array of architecturally variable IL candidates for evaluation as DSE solvents will be assessed. The objective is to identify a specific fluid that will improve upon the existing salt rejection rate and freshwater yield exhibiting by the IL identified by Ashfeld and Luo in a DSE system. Additionally, there will be focus on those IL frameworks derived from naturally occurring substances, such as amino acid and sugar scaffolds, to address potential issues of environmental toxicity.