(466d) Molecular Design of Solvents for Temperature Swing Solvent Extraction

Desalinating or purifying high salinity brine water presents a unique challenge. While reverse osmosis (RO) through a semi-permeable polyamide membrane has shown positive results for low salinity brine water and seawater, it is not effective to treat high salinity brine waters where the high osmotic pressure requires unreasonable operating pressures. High salinity brine is found in industrial processes and RO concentrate and is multiple times saltier than sea water. Temperature Swing Solvent Extraction (TSSE) is a recently re-discovered technique that could achieve desalination of these high salinity brines. TSSE is done by adding brine water to an amine-based or carboxylic acid-based solvent and manipulating the temperature of that mixture. The solvent’s polarity is temperature dependent, such that by changing the temperature of the solution, the solvent will extract water from the brine at one temperature and then phase separate the water out at a different location when that temperature is changed. In the case of amine-based solvents, the solvent will dissolve water at a lower temperature and, by increasing the temperature, the water solubility in the solvent will decrease. The goal of this study is a rational molecular design process driven by experiments and computations by which to discover and assess optimal systematically-varied solvents that can improve the efficiency of the TSSE process. For each solvent, the efficiency was measured in terms of the amount of water the solvent extracted and released, the salinity of the brine phase after contact with the solvent, the salinity of the released product water, and the amount of solvent in the water phase at the low and high temperatures. Initial results have shown that certain amine compounds appear more favorable for solubilizing water while others appear to be more water soluble.