Solute displacement in the aqueous phase of water-NaCl-organic ternary mixtures relevant to solvent-driven water treatment

Extraction and Separation of Natural Products from Microalgae and Other Natural Sources Using Liquefied Dimethyl Ether, a Green Solvent: A Review

Microalgae are a sustainable source for the production of biofuels and bioactive compounds. This review discusses significant research on innovative extraction techniques using dimethyl ether (DME) as a green subcritical fluid. DME, which is characterized by its low boiling point and safety as an organic solvent, exhibits remarkable properties that enable high extraction rates of various active compounds, including lipids and bioactive compounds, from high-water-content microalgae without the need for drying. In this review, the superiority of liquefied DME extraction technology for microalgae over conventional methods is discussed in detail. In addition, we elucidate the extraction mechanism of this technology and address its safety for human health and the environment. This review also covers aspects related to extraction equipment, various applications of different extraction processes, and the estimation and trend analysis of the Hansen solubility parameters. In addition, we anticipate a promising trajectory for the expansion of this technology for the extraction of various resources.

Modeling Henry's law and phase separations of water-NaCl-organic mixtures with solvation and ion-pairing

Empirical measurements of solution vapor pressure of ternary acetonitrile (MeCN) H2O-NaCl-MeCN mixtures were recorded, with NaCl concentrations ranging from zero to the saturation limit, and MeCN concentrations ranging from zero to an absolute mole fraction of 0.64. After accounting for speciation, the variability of the Henry's law coefficient at vapor-liquid equilibrium (VLE) of MeCN ternary mixtures decreased from 107% to 5.1%. Solute speciation was modeled using a mass action solution model that incorporates solute solvation and ion-pairing phenomena. Two empirically determined equilibrium constants corresponding to solute dissociation and ion pairing were utilized for each solute. When speciation effects were considered, the solid-liquid equilibrium of H2O-NaCl-MeCN mixtures appear to be governed by a simple saturation equilibrium constant that is consistent with the binary H2O-NaCl saturation coefficient. Further, our results indicate that the precipitation of NaCl in the MeCN ternary mixtures was not governed by changes in the dielectric constant. Our model indicates that the compositions of the salt-induced liquid-liquid equilibrium (LLE) boundary of the H2O-NaCl-MeCN mixture correspond to the binary plateau activity of MeCN, a range of concentrations over which the activity remains largely invariant in the binary water-MeCN system. Broader comparisons with other ternary miscible organic solvent (MOS) mixtures suggest that salt-induced liquid-liquid equilibrium exists if: (1) the solution displays a positive deviation from the ideal limits governed by Raoult's law; and (2) the minimum of the mixing free energy profile for the binary water-MOS system is organic-rich. This work is one of the first applications of speciation-based solution models to a ternary system, and the first that includes an organic solute.

Sustainable Lithium Recovery from Hypersaline Salt-Lakes by Selective Electrodialysis: Transport and Thermodynamics

Evaporative technology for lithium mining from salt-lakes exacerbates freshwater scarcity and wetland destruction, and suffers from protracted production cycles. Electrodialysis (ED) offers an environmentally benign alternative for continuous lithium extraction and is amenable to renewable energy usage. Salt-lake brines, however, are hypersaline multicomponent mixtures, and the impact of the complex brine-membrane interactions remains poorly understood. Here, we quantify the influence of the solution composition, salinity, and acidity on the counterion selectivity and thermodynamic efficiency of electrodialysis, leveraging 1250 original measurements with salt-lake brines that span four feed salinities, three pH levels, and five current densities. Our experiments reveal that commonly used binary cation solutions, which neglect Na+ and K+ transport, may overestimate the Li+/Mg2+ selectivity by 250% and underpredict the specific energy consumption (SEC) by a factor of 54.8. As a result of the hypersaline conditions, exposure to salt-lake brine weakens the efficacy of Donnan exclusion, amplifying Mg2+ leakage. Higher current densities enhance the Donnan potential across the solution-membrane interface and ameliorate the selectivity degradation with hypersaline brines. However, a steep trade-off between counterion selectivity and thermodynamic efficiency governs ED's performance: a 6.25 times enhancement in Li+/Mg2+ selectivity is accompanied by a 71.6% increase in the SEC. Lastly, our analysis suggests that an industrial-scale ED module can meet existing salt-lake production capacities, while being powered by a photovoltaic farm that utilizes <1% of the salt-flat area.

Cryoprotective Mechanism of DMSO Induced by the Inhibitory Effect on Eutectic NaCl Crystallization

Cryopreservation is a critical procedure in autologous hematopoietic stem cell transplantation. Dimethyl sulfoxide (DMSO) is the cryoprotectant of choice. Optimization of the cryopreservation protocol in the past revealed a dramatic loss of cell viability associated with a reduction of the DMSO concentration below 2 vol % in the freezing medium. The cryoprotective mechanism of DMSO is usually ascribed to the ability to suppress ice formation and reduce the adverse effects of the freeze-concentrated solution. This work proposes an alternative hypothesis considering the detrimental impact of NaCl eutectic crystallization on cell viability. Thermoanalytical and microstructural analysis of the DMSO effect on eutectic phase transformation of cryoprotective mixtures revealed a correlation between the loss of cell viability and eutectic NaCl crystallization. DMSO inhibits the eutectic crystallization of NaCl and preserves cell viability. Thermodynamic description of the inhibitory action and possible mechanism of cryoinjury are provided.

1-Propyl-4(5)-Methylimidazole Isomers for Temperature Swing Solvent Extraction

Temperature swing solvent extraction (TSSE) utilizes an amine solvent with temperature-dependent water solubility to dissolve water at a lower temperature to concentrate or crystallize the brine and the phases are separated. Then, the water in solvent mixture is heated to reduce water solubility and cause phase separation between the solvent and water. The solvent and de-salted water phases are separated, and the regenerated solvent can be recycled. Issues with current TSSE solvents include the high solvent in water solubility and the high solvent volatility. This project used the highly tunable platform molecule imidazole to create two 1-butylimidazole isomers, specifically 1-propyl-4(5)-methylimidazole, to test their effectiveness for TSSE. The imidazoles take in more water than their current state-of-the-art counterparts, but do not desalinate the product water and dissolve in water at higher concentrations. Thus, while imidazoles make intriguing candidates for TSSE, further work is needed to understand how to design imidazoles that will be useful for TSSE applications.

Solvent-driven fractional crystallization for atom-efficient separation of metal salts from permanent magnet leachates

This work reports a dimethyl ether-driven fractional crystallization process for separating rare earth elements and transition metals. The process has been successfully applied in the treatment of rare earth element-bearing permanent magnet leachates as an atom-efficient, reagent-free separation method. Using ~5 bar pressure, the solvent was dissolved into the aqueous system to displace the contained metal salts as solid precipitates. Treatments at distinct temperatures ranging from 20–31 °C enable crystallization of either lanthanide-rich or transition metal-rich products, with single-stage solute recovery of up to 95.9% and a separation factor as high as 704. Separation factors increase with solution purity, suggesting feasibility for eco-friendly solution treatments in series and parallel to purify aqueous material streams. Staged treatments are demonstrated as capable of further improving the separation factor and purity of crystallized products. Upon completion of a crystallization, the solvent can be recovered with high efficiency at ambient pressure. This separation process involves low energy and reagent requirements and does not contribute to waste generation.

Rare earth elements are essential to electrified infrastructure and clean energy production. Here, authors show reagent- and energy-efficient separation of lanthanides from secondary feedstock using dimethyl ether-driven fractional crystallization.

Mass action model of solution activity via speciation by solvation and ion pairing equilibria

Solutes and their concentrations influence many natural and anthropogenic solution processes. Electrolyte and solution models are used to quantify and predict such behavior. Here we present a mechanistic solution model based on mass action equilibria. Solvation and ion pairing are used to model speciated solute and solvent concentrations such that they correlate to a solution's vapor pressure (solvent activity) according to Raoult's law from dilute conditions to saturation. This model introduces a hydration equilibrium constant (K_ha) that is used with either an ion dissociation constant (K_id) or a hydration modifier (m) with an experimentally determined ion dissociation constant, as adjustable parameters to fit vapor-liquid equilibrium data. The modeled solvation equilibria are accompanied by molecular dynamics (MD) studies that support a decline in the observed degree of solvation with increased concentration. MD calculations indicate this finding is a combination of a solvent that solvates multiple solutes, and changes in a solute's solvation sphere, with the dominant factor changing with concentration. This speciation-based solution model is lateral to established electrostatics-based electrolyte theories. With its basis in mass action, the model can directly relate experimental data to the modeled solute and solvent speciated concentrations and structures.