Electrically Powered High-Salinity Brine Separation Using Dimethyl Ether

Dewatering highly saline aqueous streams, from mining and geothermal leachates to industrial wastewater, is essential for effective resource recovery and safe disposal. Membraneless water extraction (MWE) uses a low-polarity solvent to separate water from concentrated aqueous solutions. In this study, we design a new MWE that uses dimethyl ether (DME) to selectively extract water from high-salinity brines, leveraging the volatility of DME to achieve rapid solvent recovery. By separating water and dissolved salts at a liquid–liquid interface, MWE minimizes the deleterious effects of scaling on vulnerable membrane and heat exchanger surfaces, reducing the need for extensive pretreatment and expensive materials. We begin by developing a computational framework for a multistage counterflow liquid–liquid contactor, which extracts water into DME, coupled with a multistage solvent regenerator that uses vapor compression to efficiently separate the desalinated water from the DME extractant. Excess Gibbs free energy and equation of state frameworks are used to model fluid phase equilibria in water–DME–sodium chloride (NaCl) mixtures, with interaction parameters estimated from experimental data. Incorporating equilibrium calculations into a system-scale computational model, we examine the performance of MWE using DME for the first time. Our analysis demonstrates that MWE can concentrate seawater desalination brine (>1.0 molNaCl kg–1) to zero-liquid discharge salinities, with an energy consumption of under 50 kW h per m3 of water extracted with a solvent recovery ratio greater than 99.9%. We highlight the importance of staging the vapor compression process to simultaneously minimize energy consumption while enabling brine concentration and product water solvent contamination. The thermodynamic framework developed here allows for the robust evaluation of new MWE solvents and systems for critical brine concentration and fractional precipitation applications

Thermodynamic Properties of the Ni−H Bond in Complexes of the Type [HNi(P₂^RN₂^R‘)₂](BF₄) and Evaluation of Factors That Control Catalytic Activity for Hydrogen Oxidation/Production

Thermodynamic data for hydride complexes of the general formula [HNi(P2RN2R‘)2](BF4), 3, which have been reported previously to function as effective catalysts for the electrochemical oxidation or production of hydrogen, have been determined. Values of ΔG°H+, ΔG°H•, and ΔG°H- have been determined for 3a where R = Cy, R‘ = Bz, for 3b where R = R‘ = Ph, and for the new complex 3c, R = Ph, R‘ = Bz. In addition, the ΔG values for the heterolytic addition of hydrogen to the Ni(II) precursor complexes [Ni(P2RN2R‘)2](BF4)2, 1a−c, have been determined experimentally or calculated. The data are useful for understanding the factors that control the catalytic activities observed for these complexes and for the design of additional catalysts

Density Functional Theory Analysis of the Impact of Steric Interaction on the Function of Switchable Polarity Solvents

A density functional theory (DFT) analysis has been performed to explore the impact of steric interactions on the function of switchable polarity solvents (SPS) and their implications on a quantitative structure–activity relationship (QSAR) model previously proposed for SPS. An X-ray crystal structure of the <i>N</i>,<i>N</i>-dimethylcyclohexylammonium bicarbonate (Hdmcha) salt has been solved as an asymmetric unit containing two cation/anion pairs, with a hydrogen bonding interaction observed between the bicarbonate anions, as well as between the cation and anion in each pair. DFT calculations provide an optimized structure of Hdmcha that closely resembles experimental data and reproduces the cation/anion interaction with the inclusion of a dielectric field. Relaxed potential energy surface (PES) scans have been performed on Hdmcha-based computational model compounds, differing in the size of functional group bonded to the nitrogen center, to assess the steric impact of the group on the relative energy and structural properties of the compound. Results suggest that both the length and amount of branching associated with the substituent impact the energetic limitations on rotation of the group along the N–R bond and NC–R bond, and disrupt the energy minimized position of the hydrogen bonded bicarbonate group. The largest interaction resulted from functional groups that featured five bonds between the ammonium proton and a proton on a functional group with the freedom of rotation to form a pseudo six membered ring which included both protons

Studies of Structural Effects on the Half-Wave Potentials of Mononuclear and Dinuclear Nickel(II) Diphosphine/Dithiolate Complexes

Two series of mononuclear Ni(II) complexes of the formula (PNP)Ni(dithiolate) where PNP = R2PCH2N(CH3)CH2PR2, R = Et and Ph, have been synthesized containing dithiolate ligands that vary from five- to seven-membered chelate rings. Two series of dinuclear Ni(II) complexes of the formula {[(diphosphine)Ni]2(dithiolate)}(X)2 (X = BF4 or PF6) have been synthesized in which the chelate ring size of the dithiolate and diphosphine ligands have been systematically varied. The structures of the alkylated mononuclear complex, [(PNPEt)Ni(SC2H4SMe)]OTf, and the dinuclear complex, [(dppeNi)2(SC3H6S)](BF4)2, have been determined by X-ray diffraction studies. The complexes have been studied by cyclic voltammetry to determine how the half-wave potentials of the Ni(II/I) couples vary with chelate ring size of the ligands. For the mononuclear complexes, this potential becomes more positive as the natural bite angle of the dithiolate ligand increases. However, the potentials of the Ni(II/I) couples of the dinuclear complexes do not show a dependence on the chelate ring size of the ligands. Other aspects of the reduction chemistry of these complexes have been explored

Studies of Structural Effects on the Half-Wave Potentials of Mononuclear and Dinuclear Nickel(II) Diphosphine/Dithiolate Complexes

Two series of mononuclear Ni(II) complexes of the formula (PNP)Ni(dithiolate) where PNP = R2PCH2N(CH3)CH2PR2, R = Et and Ph, have been synthesized containing dithiolate ligands that vary from five- to seven-membered chelate rings. Two series of dinuclear Ni(II) complexes of the formula {[(diphosphine)Ni]2(dithiolate)}(X)2 (X = BF4 or PF6) have been synthesized in which the chelate ring size of the dithiolate and diphosphine ligands have been systematically varied. The structures of the alkylated mononuclear complex, [(PNPEt)Ni(SC2H4SMe)]OTf, and the dinuclear complex, [(dppeNi)2(SC3H6S)](BF4)2, have been determined by X-ray diffraction studies. The complexes have been studied by cyclic voltammetry to determine how the half-wave potentials of the Ni(II/I) couples vary with chelate ring size of the ligands. For the mononuclear complexes, this potential becomes more positive as the natural bite angle of the dithiolate ligand increases. However, the potentials of the Ni(II/I) couples of the dinuclear complexes do not show a dependence on the chelate ring size of the ligands. Other aspects of the reduction chemistry of these complexes have been explored

Thermodynamic Studies of [H₂Rh(diphosphine)₂]⁺ and [HRh(diphosphine)₂(CH₃CN)]²⁺ Complexes in Acetonitrile

Thermodynamic studies of a series of [H2Rh(PP)2]+ and [HRh(PP)2(CH3CN)]2+ complexes have been carried out in acetonitrile. Seven different diphosphine (PP) ligands were selected to allow variation of the electronic properties of the ligand substituents, the cone angles, and the natural bite angles (NBAs). Oxidative addition of H2 to [Rh(PP)2]+ complexes is favored by diphosphine ligands with large NBAs, small cone angles, and electron donating substituents, with the NBA being the dominant factor. Large pKa values for [HRh(PP)2(CH3CN)]2+ complexes are favored by small ligand cone angles, small NBAs, and electron donating substituents with the cone angles playing a major role. The hydride donor abilities of [H2Rh(PP)2]+ complexes increase as the NBAs decrease, the cone angles decrease, and the electron donor abilities of the substituents increase. These results indicate that if solvent coordination is involved in hydride transfer or proton transfer reactions, the observed trends can be understood in terms of a combination of two different steric effects, NBAs and cone angles, and electron-donor effects of the ligand substituents

The Role of the Second Coordination Sphere of [Ni(P^Cy₂N^Bz₂)₂](BF₄)₂ in Reversible Carbon Monoxide Binding

The complex [Ni(PCy2NBz2)2](BF4)2, 1, reacts rapidly and reversibly with carbon monoxide (1 atm) at 25 °C to form [Ni(CO)(PCy2NBz2)2](BF4)2, 2, which has been characterized by spectroscopic data and by an X-ray diffraction study. In contrast, analogous Ni(II) carbonyl adducts were not observed in studies of several other related nickel(II) diphosphine complexes. The unusual reactivity of 1 is attributed to a complex interplay of electronic and structural factors, with an important contribution being the ability of two positioned amines in the second coordination sphere to act in concert to stabilize the CO adduct. The proposed interaction is supported by X-ray diffraction data for 2 which shows that all of the chelate rings of the cyclic ligands are in boat conformations, placing two pendant amines close (3.30 and 3.38 Å) to the carbonyl carbon. Similar close C−N interactions are observed in the crystal structure of the more sterically demanding isocyanide adduct, [Ni(CNCy)(PCy2NBz2)2]2(BF4)2, 4. The data suggest a weak electrostatic interaction between the lone pairs of the nitrogen atoms and the positively charged carbon atom of the carbonyl or isocyanide ligand, and illustrate a novel (non-hydrogen bonding) second coordination sphere effect in controlling reactivity

Iridium Corroles

Iridium Corrole

The Role of the Second Coordination Sphere of [Ni(P^Cy₂N^Bz₂)₂](BF₄)₂ in Reversible Carbon Monoxide Binding

The complex [Ni(PCy2NBz2)2](BF4)2, 1, reacts rapidly and reversibly with carbon monoxide (1 atm) at 25 °C to form [Ni(CO)(PCy2NBz2)2](BF4)2, 2, which has been characterized by spectroscopic data and by an X-ray diffraction study. In contrast, analogous Ni(II) carbonyl adducts were not observed in studies of several other related nickel(II) diphosphine complexes. The unusual reactivity of 1 is attributed to a complex interplay of electronic and structural factors, with an important contribution being the ability of two positioned amines in the second coordination sphere to act in concert to stabilize the CO adduct. The proposed interaction is supported by X-ray diffraction data for 2 which shows that all of the chelate rings of the cyclic ligands are in boat conformations, placing two pendant amines close (3.30 and 3.38 Å) to the carbonyl carbon. Similar close C−N interactions are observed in the crystal structure of the more sterically demanding isocyanide adduct, [Ni(CNCy)(PCy2NBz2)2]2(BF4)2, 4. The data suggest a weak electrostatic interaction between the lone pairs of the nitrogen atoms and the positively charged carbon atom of the carbonyl or isocyanide ligand, and illustrate a novel (non-hydrogen bonding) second coordination sphere effect in controlling reactivity

The Role of the Second Coordination Sphere of [Ni(P^Cy₂N^Bz₂)₂](BF₄)₂ in Reversible Carbon Monoxide Binding

The complex [Ni(PCy2NBz2)2](BF4)2, 1, reacts rapidly and reversibly with carbon monoxide (1 atm) at 25 °C to form [Ni(CO)(PCy2NBz2)2](BF4)2, 2, which has been characterized by spectroscopic data and by an X-ray diffraction study. In contrast, analogous Ni(II) carbonyl adducts were not observed in studies of several other related nickel(II) diphosphine complexes. The unusual reactivity of 1 is attributed to a complex interplay of electronic and structural factors, with an important contribution being the ability of two positioned amines in the second coordination sphere to act in concert to stabilize the CO adduct. The proposed interaction is supported by X-ray diffraction data for 2 which shows that all of the chelate rings of the cyclic ligands are in boat conformations, placing two pendant amines close (3.30 and 3.38 Å) to the carbonyl carbon. Similar close C−N interactions are observed in the crystal structure of the more sterically demanding isocyanide adduct, [Ni(CNCy)(PCy2NBz2)2]2(BF4)2, 4. The data suggest a weak electrostatic interaction between the lone pairs of the nitrogen atoms and the positively charged carbon atom of the carbonyl or isocyanide ligand, and illustrate a novel (non-hydrogen bonding) second coordination sphere effect in controlling reactivity