2024 Theses Doctoral
Structural and application-based insights into temperature swing solvent extraction desalination
High salinity desalination is coming into prominence as pressure on conventional water resources increases. However, high salinity desalination is technologically underserved: the conventional technologies, all of which rely on evaporation of water, are prohibitively energy-intensive and costly. In this work, we examine a promising hypersaline desalination method, temperature swing solvent extraction (TSSE). TSSE uses a switchable solvent to extract water from brine, meaning it can avoid many of the problems faced by conventional evaporation- or membrane-based desalination methods. However, the mechanisms by which water is absorbed and expelled from the switchable solvent, a process that is driven by a change in temperature, are poorly understood. The process by which salts can enter the relatively nonpolar organic phase is likewise mysterious.
In this work, we investigate the nanoscale structuring in the switchable solvent-water-salt mixtures used in TSSE. We identify that the aggregation of water inside the solvent phase is key to explaining many of the macroscopic properties of TSSE. For instance, we find evidence of the directional interactions hypothesized as necessary for the unusual temperature-switchable behavior of the amine-water system that is used most often in TSSE. We further find that ions enter the solvent-rich phase inside nanometer-sized aggregates of water, and that the presence of these aggregates accounts for the unusually high viscosity of the amine-water mixture. These results greatly advance our understanding of TSSE, moving us from macroscopic and bulk properties to a fundamental, molecular-level understanding of the process.
We also demonstrate several new applications of TSSE. Specifically, we show that TSSE is adept at treating hypersaline brine containing trace amounts of the toxic anions selenate and arsenate. TSSE rejected both trace ions at a far higher rate than the majority ion, chloride. To explain this phenomenon, we conduct the first systematic study of the behavior of different ions in TSSE and develop a straightforward model for predicting salt partitioning in TSSE using fundamental ion-specific parameters. Finally, we demonstrate that TSSE is capable of zero liquid discharge operation, in which only a solid waste is produced.
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More About This Work
- Academic Units
- Earth and Environmental Engineering
- Thesis Advisors
- Yip, Ngai Yin
- Degree
- Ph.D., Columbia University
- Published Here
- October 23, 2024