Substituent Effects on the Desalination Performance of Six-Carbon Amines in Temperature Swing Solvent Extraction

Most current desalination technologies cannot process the high levels of total dissolved solids in hypersaline brines or are very energy-intensive. Temperature swing solvent extraction (TSSE) is a method that can circumvent these challenges by utilizing a solvent’s ability to intake water at one temperature and release the water at a different temperature. Two secondary (2°) six-carbon amines, diisopropylamine (DIPA) and dipropylamine (DPA), are the leading solvents for the TSSE process. However, they require an extra purification step due to solvent crossover into the final product water phase. In this study, we investigated six-carbon amines (most of which are constitutional isomers) to understand what aspects of the molecular configuration allow DIPA and DPA to be the leading TSSE solvents. Ethylbutylamine desalinated close to the levels of DIPA and DPA, but it had a higher level of solvent crossover and did not produce as much water. Based on our results, the symmetry and branching of DIPA and DPA are important driving factors in their desalination abilities.