(531e) Six-Carbon Amine-Based Solvents for Temperature Swing Solvent Extraction

Desalination of high salinity brines presents a unique challenge. Reverse osmosis (RO) through a semi-permeable polyamide membrane works well for low salinity brines, but it is not effective for high salinity brines. These high salinity brines require operating pressures outside the usable range for RO. High salinity brines can be found in RO concentrate and industrial processes and is two or more times saltier than seawater. Temperature Swing Solvent Extraction (TSSE) is a recently re-discovered technique that could achieve desalination of these high salinity brines. TSSE is performed by adding brine water to a solvent that is typically either amine-based or carboxylic acid-based and manipulating the temperature of the mixture. The temperature changes will cause a shift in the solvent’s ability to hydrogen bond with water so that the solvent will selectively extract water but not salt at one temperature and then phase separate the water out at the other temperature. For amine-based solvents, the solvent will extract water at a low temperature and release water at a higher temperature. Diisopropylamine (DIPA) and dipropylamine (DPA) are the two most commonly used amine-based solvents in literature due to their ability to desalinate and release water. However, these solvents cross-over into the water phase enough to the point where a purification step would be needed afterwards. The goal of this study is to look at isomers of DIPA to study structure-property-performance relationships to find guiding principles for solvent design. Solvents with six carbons other than DIPA and DPA have not been studied in literature; solvents with more carbons have, yet these other solvents do not perform as well as DIPA and DPA. Solvent properties such as viscosity will be reported. TSSE performance evaluation of the solvents will report salt concentration, water uptake, and organic cross-over in the brine and product water phases.