Supporting Information: Membrane-less and Non-Evaporative Desalination of Hypersaline Brines by Temperature Swing Solvent Extraction

Hypersaline brines are of growing environmental importance but are technologically under-served by today’s desalination methods. Temperature swing solvent extraction (TSSE) is a radically different desalination technology that is membrane-less and not based on evaporative phase change. TSSE utilizes low-temperature heat and a low-polarity solvent with temperature-dependent water solubility for the selective extraction of water over salt from saline feeds. This study demonstrates TSSE desalination of high-salinity brines simulated by NaCl solutions with three amine solvents: diisopropylamine (DIPA), N-ethylcyclohexylamine (ECHA), and N,N-dimethylcyclohexylamine (DMCHA). We show that TSSE can desalinate brines with salinities as high as ≈234000 ppm total dissolved solids (i.e., 4.0 M NaCl) and achieve salt removals up to 98.4%. Among the solvents, DIPA exhibited the highest water extraction efficiency whereas ECHA and DMCHA produced water with the lowest salt content and solvent residue content, respectively. Lastly, a high water recovery of >50% was demonstrated for TSSE desalination of 1.5 M NaCl brine using DIPA in semibatch experiments with multiple extraction cycles. This study underscores the unique capabilities of TSSE for the desalination of hypersaline brines

Membrane-less and Non-Evaporative Desalination of Hypersaline Brines by Temperature Swing Solvent Extraction

Hypersaline brines are of growing environmental importance but are technologically under-served by today’s desalination methods. Temperature swing solvent extraction (TSSE) is a radically different desalination technology that is membrane-less and not based on evaporative phase change. TSSE utilizes low-temperature heat and a low-polarity solvent with temperature-dependent water solubility for the selective extraction of water over salt from saline feeds. This study demonstrates TSSE desalination of high-salinity brines simulated by NaCl solutions with three amine solvents: diisopropylamine (DIPA), N-ethylcyclohexylamine (ECHA), and N,N-dimethylcyclohexylamine (DMCHA). We show that TSSE can desalinate brines with salinities as high as ≈234000 ppm total dissolved solids (i.e., 4.0 M NaCl) and achieve salt removals up to 98.4%. Among the solvents, DIPA exhibited the highest water extraction efficiency whereas ECHA and DMCHA produced water with the lowest salt content and solvent residue content, respectively. Lastly, a high water recovery of >50% was demonstrated for TSSE desalination of 1.5 M NaCl brine using DIPA in semibatch experiments with multiple extraction cycles. This study underscores the unique capabilities of TSSE for the desalination of hypersaline brines

Phase equilibria insights into amine-water-NaCl interactions in liquid-liquid biphasic systems for temperature swing solvent extraction desalination

This study sheds light on the fundamental phenomena governing temperature swing solvent extraction (TSSE) desalination by investigating the influence of temperature on the equilibrium partitioning of water, salt, and solvent. The distribution of components across a range of temperatures and feed salinities typical to TSSE hypersaline desalination was examined for two amine solvents. A tradeoff between selectivity and productivity is established, providing a novel framework to assess TSSE performance. Salt was shown to be a key determinant in equilibrium partitioning by diminishing the ability of the solvent to extract water at lowered temperatures and salting-out amines from the aqueous phase. Na+ and Cl− ions consistently partition into the solvent phase in equimolar ratios. Analysis further reveals a linear correlation between the natural logarithms of salt activity coefficients and water contents of the organic phase. The two collaborating results suggest that water-ion interactions are more important than amine-ion interactions in the organic phase, resolving a critical gap in the understanding of salt transport. The findings of this study can provide important insights for the informed development of temperature swing solvent extraction for hypersaline desalination

Drivers, challenges, and emerging technologies for desalination of high-salinity brines: A critical review

Hypersaline brines are of growing environmental concern. While high-salinity desalination and zero liquid discharge (ZLD) are increasingly attractive treatment options, the high salt and scalant contents pose considerable technical difficulties to existing desalination techniques. In this review, we introduce sources of hypersaline brines, examine factors driving high-salinity desalination, and present the thermodynamic minimum energy of hypersaline desalination and ZLD, highlighting effects of mineral precipitation and imperfect salt rejection. We then critically examine prospects and challenges of 10 alternative technologies for hypersaline desalination: electrodialysis, osmotically-mediated reverse osmosis, forward osmosis, membrane distillation, humidification-dehumidification, solvent extraction desalination, supercritical water desalination, freeze desalination, clathrate hydrate desalination, and solar thermal desalination. Although electrodialysis and osmotically-mediated reverse osmosis show promise of having competitive energy efficiencies, these membrane-based techniques are still constrained by concentrate salinity limits. Recovery and reuse of heat will be vital for competitiveness of thermally-driven approaches. Technologies that intrinsically precipitate salts in bulk solution, namely solvent extraction desalination, supercritical water desalination, and humidification-dehumidification, can advantageously avoid mineral scaling. Due to the highly heterogeneous nature of hypersaline streams and the wide array of end-use goals, the high-salinity desalination market will ultimately be best served by a range of different technologies with distinctive capabilities