5 research outputs found
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Advancing the Productivity-Selectivity Trade-off of Temperature Swing Solvent Extraction Desalination with Intermediate-Step Release
Temperature swing solvent extraction (TSSE) offers a membrane-less and nonevaporative approach to hypersaline desalination, but performance of conventional TSSE operation is restricted by an inherent trade-off between water recovery yield and salt rejection. This study presents enhanced desalination capability of TSSE with a novel intermediate release step (TSSE-IR) over a conventional (c-TSSE) single-step operation. TSSE-IR demonstrated superior performance in the hypersaline desalination of 1.0 M NaCl brines for three amines with distinct water and salt partitioning behaviors: diisopropylamine, triethylamine, and tert-octylamine. The astute introduction of the intermediate temperature step in TSSE-IR dramatically improves salt rejection while minimizing the sacrifices in water recovery yields. We show that the intermediate step does not introduce additional solvent loss compared with c-TSSE operations with the same extraction temperature for any of the three solvents examined. TSSE-IR is demonstrated to advance the productivity-selectivity trade-off that constrains c-TSSE. Finally, Hunter–Nash analysis conducted on diisopropylamine–H2O–NaCl ternary diagrams exhibits good agreement with experimental TSSE-IR results, offering a reliable platform for modeling intermediate-step release performance and informing process design. This study establishes the potential of TSSE-IR to expand the spectrum of viable solvents for hypersaline desalination to include greener chemicals that exhibit high water recovery yields but low selectivities in c-TSSE
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Zero Liquid Discharge of Ultrahigh-Salinity Brines with Temperature Swing Solvent Extraction
Zero liquid discharge (ZLD) of hypersaline brines is technically and energetically challenging. This study demonstrates ZLD of ultrahigh-salinity brines using temperature swing solvent extraction (TSSE), a membrane-less and nonevaporative desalination technology. TSSE utilizes a low-polarity solvent to extract water from brine and then releases the water as a product with the application of low-temperature heat. Complete extraction of water from a hypersaline feed, simulated by 5.0 M NaCl solution (≈292 g/L TDS), was achieved using diisopropylamine solvent. Practically all of the salt is precipitated as mineral solid waste and the product water contains <5% of NaCl relative to the hypersaline feed brine. Consistent ZLD performance of high salt removals and product water quality was maintained in three repeated semibatch TSSE cycles, highlighting recyclability of the solvent. The practical applicability of the technique for actual field samples was demonstrated by ZLD of an irrigation drainage water concentrate. This study establishes the potential of TSSE as a more sustainable alternative to current thermal evaporation methods for zero liquid discharge of ultrahigh-salinity brines
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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
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Thermomorphic Hydrophilicity Base-Induced Precipitation for Effective Descaling of Hypersaline Brines
This study presents a novel technology, termed thermomorphic hydrophilicity base-induced precipitation (THBIP), for the effective removal of hardness ions from hypersaline brines with high-scaling propensity. THBIP utilizes thermoresponsive amine bases for the controlled precipitation of scaling constituents in alkaline conditions and subsequently uses low-temperature heat to trigger the phase separation of amine from aqueous solution, thus enabling reuse of the base. Three amines exhibiting distinct water solubility and basicity, specifically, diisopropylamine (DIPA), N-ethylcyclohexylamine (ECHA), and N,N-dimethylisopropylamine (DMIPA), were examined to identify the key parameters affecting THBIP performance. The amine bases were added to solutions containing hardness ions, Mg2+ or Ca2+, to induce the precipitation of hydroxide minerals (i.e., Mg(OH)2(s) and Ca(OH)2(s)). All three amines are effective in increasing solution pH, leading to high Mg2+ removals of over 90%. But because Ca(OH)2(s) is relatively more soluble, only DIPA, which is both highly miscible in water and also the strongest base, obtained significant removal of Ca2+ ions (>33%). The observed precipitation and hardness removal are quantitatively consistent with the principles of aqueous chemistry. Using a simulated hypersaline feedwater (240 g/L total dissolved solids) of high-scaling propensity, THBIP with DIPA achieved ∼80% hardness removal. Subsequent elevation of the temperature from 15 to 70 °C triggered demixing of the thermoresponsive base from the aqueous solution, to enable liquid–liquid separation for amine reuse. The study demonstrates the proof-of-concept of using thermomorphic hydrophilicity bases as an alternative strategy to effectively reduce the scaling potential of hypersaline brines
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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