Separation of a CaCl2-HCl Model Mixture on Neutral Nanoporous Hypercrosslinked Polystyrene under Static and Dynamic Conditions

The distribution of CaCl₂ and HCl (separately and in a mixture) between the aqueous and nanoporous hypercrosslinked polystyrene sorbent phases was studied under static conditions. It was shown that virtually the whole pore volume of the sorbent was accessible to HCl, whereas CaCl₂ was largely excluded from small pores. It was found that the distribution isotherms of the electrolytes between the phases changed significantly in going from the pure electrolytes to their mixture. Under dynamic (chromatographic) conditions, the elution profiles of CaCl₂ and HCl (separately and in a mixture) were studied. It was shown that the components of the mixture competed for the pore space of the sorbent: small HCl molecules were displaced from large pores and the interstitial space into small pores inaccessible to CaCl₂. (This is why the retention of HCl in the chromatography column significantly increased as the concentration of the mixture grew; that is, both the efficiency and selectivity of separation increased as the column became loaded heavier.) It was found that the degree of hydration of ions decreased as the concentration of the solution increased.     

The contraction of granules of nanoporous super-cross-linked polystyrene sorbents as a result of the exclusion of large-sized mineral electrolyte ions from the polymer phase

The deformation of neutral super-cross-linked polystyrene sorbents and ionites based on styrene-divinylbenzene gel-type copolymers brought in contact with concentrated solutions of HCl, H₃PO₄, NaOH, NH₄Cl, (NH₄)₂SO₄, and LiCl electrolytes was studied by dilatometry for separate spherical granules. Considerable contraction of super-cross-linked polystyrene matrices swollen in water was observed in concentrated solutions containing large-sized lithium, sulfate, and phosphate ions. Volume compressive strain correlated with the size of excluded hydrated ions. The contraction effect was caused by the difference in the osmotic pressure of water in thin pores and water in concentrated solutions filling large pores. The exclusion effect ignored earlier should also influence the degree of ion exchange and volume deformation of standard ion-exchange resins brought in contact with solutions of various electrolytes. Original Russian Text ? A.V. Pastukhov, V.A. Davankov, M.P. Tsyurupa, Z.K. Blinnikova, N.E. Kavalerskaya, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 541–549.     

Modeling of size-exclusion chromatography of electrolytes on non-ionic nanoporous adsorbents

A dynamic model has been developed for chromatographic separation of mixed electrolyte solutions with non-ionic nanoporous adsorbents. The thermodynamic equilibrium condition at the pore entrance is written in terms of mixing, electrostatic and size-exclusion effects. The model is tested against experimental data measured with three binary mixtures on hypercrosslinked polystyrene and nanoporous carbon. The selectivity of the nanoporous adsorbents can be explained by the size-exclusion of the electrolytes and enrichment of both electrolytes in frontal chromatographic runs can be correlated satisfactorily with the proposed model. The model is also used to demonstrate continuous separation in a simulated moving-bed (SMB) system.     

Selectivity in preparative separations of inorganic electrolytes by size-exclusion chromatography on hypercrosslinked polystyrene and microporous carbons

Preparative-scale separation of concentrated solutions of simplest mineral electrolytes by size-exclusion chromatography was performed on three samples of commercially available microporous hypercrosslinked polystyrene sorbents "Macronet Hypersol" and two experimental samples of activated carbons. Selectivity of separation of a pair of electrolytes was found to be determined by the largest ions in each pair. Fortunately, selectivity rises at higher concentrations of electrolytes, which was explained by exclusion of smaller species from the concentrated solution, i.e., mobile phase, into small pores of the column packing that are inaccessible to large species. The separation of concentrated mixtures revealed another remarkable advantage of the new process - self-concentrating of each of two separated components in the corresponding fractions. Self-concentration is more pronounced for the minor component that occupied less space in the initial mixture. The new method may prove productive in processing pickle bath solutions.     

Sorption equilibrium of methanol on new composite sorbents “CaCl<Subscript>2</Subscript>/silica gel”

This paper presents experimental data on methanol sorption on new composite sorbents which consist of mesoporous silica gels and calcium chloride confined to their pores. Sorption isobars and XRD analysis showed the formation of a solid crystalline solvate CaCl₂⋅2MeOH at low methanol uptake, while at higher uptake the formation of the CaCl₂–methanol solution occurred. The solution confined to the silica pores showed the sorption properties similar to those of the CaCl₂–methanol bulk solution. Calorimetric and isosteric analyses showed that the heat of methanol sorption depends on the methanol uptake, ranging from 38±2 kJ/mol for the solution to 81±4 kJ/mol for the solid crystalline phase CaCl₂⋅2MeOH. The above mentioned characterizations allowed the evaluation of the methanol sorption and the energy storage capacities, clearly showing that the optimal applications of these new composite sorbents are the methanol removal from gaseous mixtures, heat storage and sorption cooling driven by low temperature heat.     

A Study of Concentration Polarization on Ion Exchange Membrane Electrodialysis

The concentration polarization phenomena in ion exchange membrane electrodialysis have been studied with single exchange membrane cell. The limiting current densities of Asahi ion-permselective membranes CK-1 and CK-2, Selemion ion-exchange membranes CMV, AMV, DMV and ASV have been measured with Ag-AgCl reversible electrode in various electrolyte solutions under 25°C and constant flow rate. In sodium chloride solution, the cation exchange membrane is easier to occur concentration polarization than the anion exchange membrane. The limiting current density increases as the concentration of solution increases for the same kind of ion exchange membrane. The experimental limiting current densities of Selemion CMV and AMV in NaCl, KCl, MgCl₂, CaCl₂, BaCl₂, Na₂SO₄, NaOH and HCl aqueous solutions are measured. The results show that the limiting current density increases as the ion mobility and diffusivity increase, and is affected by the transference number of ion. For the mixture of electrolyte solution, there are linear relationship between limiting current density and equivalent fraction of electrolytes.     

Highly concentrated polycarbonate‐based solid polymer electrolytes having extraordinary electrochemical stability

Solid polymer electrolytes (SPEs) are compounds of great interest as safe and flexible alternative ionics materials, particularly suitable for energy storage devices. We study an unusual dependence on the salt concentration of the ionic conductivity in an SPE system based on poly(ethylene carbonate) (PEC). Dielectric relaxation spectroscopy reveals that the ionic conductivity of PEC/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte continues to increase with increasing salt concentration because the segmental motion of the polymer chains is enhanced by the plasticizing effect of the imide anion. Fourier transfer‐infrared (FTIR) spectroscopy suggests that this unusual phenomenon arises because of a relatively loose coordination structure having moderately aggregated ions, in contrast to polyether‐based systems. Comparative FTIR study against PEC/lithium perchlorate (LiClO₄) electrolytes suggests that weak ionic interaction between Li and TFSI ions is also important. Highly concentrated electrolytes with both reasonable conductivity and high lithium transference number (t₊) can be obtained in the PEC/LiTFSI system as a result of the unusual salt concentration dependence of the conductivity and the ionic solvation structure. The resulting concentrated PEC/LiTFSI electrolytes have extraordinary oxidation stability and prevent any Al corrosion reaction in a cyclic voltammetry. These are inherent effects of the highly concentrated salt. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2442–2447     

Hartley–Crank Equations for Coupled Diffusion in Concentrated Mixed Electrolyte Solutions. The CaCl2 + HCl + H2O System

Nernst—Planck equations and ionic conductivities are used to calculate accurate limiting interdiffusion coefficients D _ik ^o for mixed electrolyte solutions. The electrostatic mechanism for coupled electrolyte diffusion is investigated by calculating the electrostatic contribution to each D _ik ^o coefficient to give the flux of each electrolyte driven by the electric field, which is generated by the migration of ions of different mobilities. Ternary diffusion coefficients are measured for dilute aqueous K₂SO₄ + KOH and Li₂SO₄ + LiOH solutions. Because of the different mobilities of K⁺ and Li⁺ ions relative to SO ₄ ^2– ions, diffusing K₂SO₄ drives cocurrent flows of KOH, but diffusing Li₂SO₄ drives counterflows of LiOH. To describe coupled diffusion in concentrated mixed electrolyte solutions, the Hartley–Crank theory is used to correct the limiting D _ik ^o coefficients for nonideal solution behavior, viscosity changes, ionic hydration, and the zero-volume flow constraint. Diffusion coefficients predicted for concentrated aqueous CaCl₂ + HCl solutions are compared with recently reported data. The large amount of HCl cotransported by the diffusing CaCl₂ is attributed to the salting out of HCl by CaCl₂ and to the migration of H⁺ ions in the diffusion-induced electric field, which slows down the Cl^– ions and speeds up the less-mobile Ca²⁺ ions to maintain electroneutrality along the CaCl₂ gradient.     

Transition of TiO2 nanotubes to nanopores for electrolytes with very low water contents

Over the past decade, the electrochemical formation of self-organized nanotube layers in dilute fluoride containing electrolytes has been studied intensively. In the present work, we show that by anodization of Ti in similar electrolytes but containing only very low water contents, the formation of ordered TiO₂ nanoporous structures can be observed. I.e., the water content in the electrolyte is the critical factor that decides whether self-ordered oxide tubes or pores are formed. This supports the concept that tube formation originates from ordered porous oxide by a “pore-wall-splitting” mechanism.     

Effect of free solvent on the solvation of electrolytes and nonelectrolytes

An approach is developed for analyzing hydration of sodium and magnesium sulfate electrolytes over a wide range of concentrations up to 1.8 mol/L at temperatures from 278.15 to 318.15 K. The model of free water (water that does not enter hydrate complexes) is used to analyze the hydration numbers, mean compressibility of water in the hydration sphere, its temperature dependence, and several other solvation parameters that are determined with difficulty. A comparative analysis of the behavior of the β_h V _h = f(h) function is carried out for zwitterions and electrolytes. This function has an identical slope for amino acids, halides, and nitrates; that is, the adiabatic compressibility of water in the hydrate complex of an electrolyte or nonelectrolyte (β_1h V1h) is independent of the solution concentration over a wide range of compositions. This suggests that the clathrate solvation mechanism operates both for a stoichiometric ion mixture and for zwitterions. Aqueous solutions of sodium sulfate and magnesium sulfate behave quite differently: they appreciably deviate from the solutions of the specified systems.     

Water structure and electron trapping in aqueous ionic solutions

The optical absorption spectra observed by pulse radiolysis of alkaline (NaOH, KOH, RbOH), chloride (LiCl, MgCl₂, CaCl₂, NaCl, KCl) and perchloride (NaClO₄) solutions at temperature 298 K are reported. Some measurements were performed at low temperature with aqueous ionic glasses. With increasing concentration of the above solutes a uniform blue-shift of the maximum of the solvated electron (e¯_sol) absorption band is observed. Near infrared (NIR) spectroscopy was so used to examine the properties of water in several concentrated electrolyte solutions. It is shown that some inorganic electrolytes (e.g. NaOH, NaClO₄) substantially change the water structure whereas some others (e.g. LiCl, CaCl₂) influence water structure insignificantly. The correlation between the ability of excess electron trapping in electrolyte solutions and water structure deduced from NIR spectroscopy is discussed.     

Dependences of the osmotic coefficients of aqueous calcium chloride solutions on concentration at different temperatures

A model that considers the contributions from hydration, ion association, and electrostatic interactions to the nonideality of 2?1 electrolyte solutions is substantiated. The parameters of the model’s equations are the mean ion hydration number, the spread of the distribution of hydrated ion stoichiometric coefficients in the standard state, and the number of association. The model is successfully used to describe literature experimental data on the concentration dependence of osmotic coefficients of aqueous CaCl₂ solutions at temperatures ranging from 0 to 100°C. The modeling of the above systems shows that as the temperature rises, the hydration number falls slightly, the distribution of the hydration number broadens, and the ion paring of the salt rises by the first degree.     

Dielectric properties of alcohol electrolyte solutions

Dielectric properties of ethanol and 1-hexanol solutions containing LiCl, CaCl₂·2H₂O and Ca(NO₃)₂·4H₂O, respectively, have been determined. It is found that LiCl reduces the static permittivity in ethanol, but CaCl₂·2H₂O and Ca(NO₃)₂·4H₂O both give an initial increase in _s. All the electrolytes studied increase the mean relaxation time of the ethanol solutions. In 1-hexanol the static permittivity is rather invariant for all studied electrolytes at low concentrations, while the same lengthening of the mean relaxation time is observed. When water is added in addition to the hydration water of the electrotyte, the static permittivity in hexanol is almost unaltered while the relaxation time is drastically shortened. The experimental result is discussed in terms of a formation of ion pairs, solvation sheaths, and kinetic depolarization, a partial release of hydration water and a structuring influence on the alcohol structure by the hydrated cation.     

The effect of counterions on coacervation and solubilization in oil-external and middle-phase microemulsions

The effect of hydrated radii, valency, and concentration of counterions on the coacervation of aqueous petroleum sulfonate solutions and on the solubilization capacity of oil-external and middle-phase microemulsions was investigated. The critical electrolyte concentration (CEC) for coacervation increased with Stokes' hydrated radii of monovalent counterions. The CEC for CaCl₂ was much lower than that predicted by either the Stokes' hydrated radii or the ionic strength. For mixed electrolytes containing NaCl and CaCl₂, it was concluded from the shift in CEC that 1 mole of CaCl₂ is equivalent to 16 to 19 moles of NaCl. The changes in relative concentrations of NaCl and CaCl₂ for coacervation exhibited additive behavior. The maximum solubilization of brine in oil-external microemulsions occurred at a specific salt concentration. For mixed electrolytes containing NaCl and CaCl₂, the shift in electrolyte concentration for maximum solubilization showed that 1 mole of CaCl₂ is equivalent to about 4 moles of NaCl. These results suggest that the equivalence ratio of CaCl₂ to NaCl is strikingly different in aqueous solutions and oil-external microemulsions. For solubilization in middle-phase microemulsion containing mixed NaCl and CaCl₂, it was concluded from the shift in optimal salinity that 1 mole of CaCl₂ is equivalent to about 16 moles of NaCl. Here also the changes in NaCI and CaC1₂ concentrations showed additive behavior. The equivalence ratio of CaCl₂ and NaCl appears to be independent of oil chain length in the present study. As shown by the equivalence ratio of CaCl₂ to NaCl, the formation of middlephase microemulsions appears to be similar to coacervation of aqueous surfactant solutions and quite different from the solubilization of water in oil-external microemulsions.     

Factors influencing the growth behaviour of nanoporous anodic films on iron under galvanostatic anodizing

The growth behaviour of nanoporous anodic films on iron during galvanostatic anodizing in ethylene glycol electrolytes containing NH₄F and H₂O is examined at various current densities, H₂O concentrations in electrolytes and temperatures. The film morphology is mainly controlled by the formation voltage, regardless of anodizing conditions. Relatively regular cylindrical pores are formed at formation voltages less than 50 V, while rather disordered pores are formed above 100 V. The decrease in the H₂O concentration suppresses chemical dissolution of anodic films in addition to the increased growth efficiency, resulting in the formation of anodic films with a steady thickness of ～7 μm. The cell size of the anodic films depends upon the H₂O concentration as well as the formation voltage, but not upon the current density. Findings in this study will be useful for controlled growth of the anodic films on iron.     

Novel pore shape and self-organization effects in n-GaP(111)

n-type GaP(111) has been porosified in HCl, H₂SO₄, HBr, NaBr, and alkaline NaBr in the dark. The pore morphology strongly depends on the electrochemical conditions and on the chemical nature of anions in the electrolyte. Independent of the pH-value of bromide-containing solutions, layers of triangular pores with a defined cross-section were growing under an irregular pore nucleation layer. Optimized conditions led to a regular structure of equally sized triangular pores with a side length of (98 ± 5) nm. The pore walls are determined by (110)-crystal planes of GaP. In other electrolytes such as HCl or H₂SO₄ it was not possible to form triangular pores during the electrochemical etching process.     

Identifying Optimal Zeolitic Sorbents for Sweetening of Highly Sour Natural Gas

Raw natural gas is a complex mixture comprising methane, ethane, other hydrocarbons, hydrogen sulfide, carbon dioxide, nitrogen, and water. For sour gas fields, selective and energy‐efficient removal of H₂S is one of the crucial challenges facing the natural‐gas industry. Separation using nanoporous materials, such as zeolites, can be an alternative to energy‐intensive amine‐based absorption processes. Herein, the adsorption of binary H₂S/CH₄ and H₂S/C₂H₆ mixtures in the all‐silica forms of 386 zeolitic frameworks is investigated using Monte Carlo simulations. Adsorption of a five‐component mixture is utilized to evaluate the performance of the 16 most promising materials under close‐to‐real conditions. It is found that depending on the fractions of CH₄, C₂H₆, and CO₂, different sorbents allow for optimal H₂S removal and hydrocarbon recovery.     

Hydration forces underlie the exclusion of salts and of neutral polar solutes from hydroxypropylcellulose

The distance dependence for the preferential exclusion of several salts and neutral solutes from hydroxypropyl cellulose (HPC) has been measured via the effect of these small molecules on the thermodynamic forces between HPC polymers in ordered arrays. The concentration of salts and neutral solutes decreases exponentially as the spacing between apposing nonpolar HPC surfaces decreases. For all solutes, the spatial decay lengths of this exclusion are remarkably similar to those observed between many macromolecules at close spacings where intermolecular forces have been ascribed to the energetics of water structuring. Exclusion magnitudes depend strongly on the nature and size of the particular salt or solute; for the three potassium salts studied, exclusion follows the anionic Hofmeister series. The change in the number of excess waters associated with HPC polymers is independent of solute concentration suggesting that the dominating interactions are between solutes and the hydrated polymer. These findings further confirm the importance of solvation interactions and reveal an unexpected unity of Hofmeister effects, preferential hydration, and hydration forces.     

Use of the concentration dependences of hydration numbers for calculating the gibbs energies and activities of strong electrolytes

The expression for the Gibbs energy (G) of electrolytes derived in terms of the Debye-Hückel theory is modified so as to describe the experimentally observed dependence of the hydration numbers of electrolyte ions on their concentration by minimizing G. It is shown that the activity coefficients of electrolyte solutions determined from this expression are in good agreement with experimental data over a wide concentration range.     

New electrolytes for n-type InP and electrochemical C-V profiling of a semiconductor optical amplifier device structure

New electrolyte systems for profiling n-type indium phosphide (InP) have been reported and are compared with the conventional HCl electrolyte. Among the new electrolytes, the electrolyte comprising HNO₃-HF-H₂O has better characteristics and is best suited for profiling InP material. Both epitaxial layers and substrate materials have been subjected to electrochemical carrier concentration profiling using the new electrolyte and the estimated concentration values are compared with that of Hall effect measurements. Barrier heights of the new electrolytes have been calculated. For the first time, the dopant profiling of a complete device structure grown by the chemical beam epitaxy technique for the realization of laser and semiconductor optical amplifier structures has been presented. Received: 1 February 1999 / Accepted: 1 April 1999