Self‐concentration effects in preparative SEC of mineral electrolytes using nanoporous neutral polymeric sorbents

Separation of mineral electrolytes according to size exclusion mechanism using neutral nanoporous polystyrene sorbents and carbonaceous materials has been examined in detail on hand of HCl and CaCl₂ solutions, taken separately and in the mixture. Phase distribution coefficients of the above electrolytes have been measured under static conditions at different concentrations. The k‐values and their dependence on the concentration were correlated with the elution curves of the components from a chromatographic column. Both the static and dynamic data suggest a strong dependence of the hydration number and effective size of ions on the concentration. Self‐concentration of HCl in small pores and that of CaCl₂ outside of small pores exhibits itself in both static and chromatographic experiments and results from the relocation of the components largely within the volume of the initial mixture. Additional apparent “retention” of HCl in the porous volume of the sorbent in concentrated electrolyte mixtures was shown to be caused by the competition between all ions of the system for hydration water. Increased separation selectivity and enhanced self‐concentration effects for more concentrated mixtures point to preparative and industrial perspectives of size exclusion chromatography (SEC) of complex electrolyte mixtures on nanoporous neutral sorbents.     

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.     

High-molecular-weight poly(p-phenyleneterephthalamide) by CaCl2 promoted direct polycondensation with thionyl chloride in N-methylpyrrolidone

The direct polycondensation of terephthalic acid and p-phenylenediamine hydrochloride (PPD.2HCl) with thionyl chloride was found to be significantly promoted in N-methylpyrrolidone (NMP) by dissolved CaCl₂ and tertiary amines. The inherent viscosity of the polymer obtained varied with the amount of CaCl₂ and tertiary amines added. The reaction, when effectively promoted by CaCl₂, proceeded homogeneously in the early state of polycondensation, and then resulted in a highly swollen gel. CaCl₂ had to be present in the PPD.2HCl/tertiary amines/NMP solution as well as in the TPA/SOCl₂/NMP mixture for the polycondensation to proceed to high molecular weight. Complexes of CaCl₂, PPD.2HCl, and tertiary amines in NMP similar to the well known complex, CaCl₂ · nNH₃ (n = 2, 4, 8) was proposed to facilitate the polycondensation.     

Effect of hypercrosslinking conditions on pore size distribution and efficiency of monolithic stationary phases

Three dihalogenic solvents differing in the length of alkyl chain (1,2‐dichloroethane, 1,4‐dichlorobutane, and 1,6‐dichlorohexane) with three Friedel–Crafts alkylation catalysts varying in reactivity (AlCl₃, FeCl₃, and SnCl₄) have been used to prepare hypercrosslinked poly(styrene‐co‐vinylbenzyl chloride‐co‐divinylbenzene) columns. Hydrodynamic characteristics as well as column efficiency and mass transfer resistance were tuned by the combination of swelling solvent and alkylation reaction catalyst in the modification mixture. The column swelled in 1,6‐dichlorohexane and hypercrosslinked in the presence of AlCl₃ provided the highest column efficiency and enabled fast isocratic separations of small molecules in a RP mode. To uncover factors controlling the efficiency of hypercrosslinked monolithic columns, we have studied pore volume distribution of prepared columns. We found that column efficiency increases with the higher pore volume of pores smaller than 2 nm.     

Porous Proton- and Chloride-Ion Conducting Layers Based on Ethanolamine Derivatives of PVC on the Surfaces of Fabrics

Materials are produced with porous layers based on ethanolamine derivatives of PVC or compounds of active carbon with hydroxyethylcyclam derivatives of PVC with aqua complexes of chloride hydrogen cross-linked with the surface of cellulose or asbestos fabric. Their capacity for sorption with respect to hexane and benzene in the saturated vapor and liquid phases is determined. The dependences of current on voltage in a circuit are determined for bridges composed of these materials in air, and in the vapor and liquid phases of benzene and hexane between 3 M HCl solutions and 3 M HCl solutions containing 3 M CaCl₂. It is established that only H⁺ ions migrate along the bridges between the HCl solutions, and H⁺ and Cl^– ions were the only species that moved along the bridges between the HCl solutions containing CaCl₂. The voltages at which the movement of ions starts are determined, and constants characterizing the conductivity of the layers are found. It is shown that these parameters depend on the structure of a layer, the nature of the fabric, and the medium surrounding a bridge.

     

Preparation and characterization of double metal-silica sorbent for gas filtration

This paper presents the preparation of a porous (Mg, Ca) silicate structure, which could be employed as sorbent filter media. The sorbents have been prepared using sodium silicate precipitated with various ratios of magnesium and calcium salts. The sorbents obtained were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen physisorption isotherm. Further, the applicability and performance of the sorbent impregnate with potassium hydroxide for removal of sulphur dioxide (SO₂) has been demonstrated. From the isotherms, specific surface area, pore diameter and volume of pores were estimated. Results show that the chemical composition and textural properties of the resultant sorbents were highly dependent on Mg/Ca molar ratio. It was found that sorbents made with 68 mol% Mg and 32 mol% Ca (PSS-MgCa-68/32); and 75 mol% Mg and 25 mol% Ca (PSS-MgCa-75/25) exhibited even higher specific surface area and pore volume than the sorbents containing a single metal. The Mg/Ca-silica sorbents obtained contains interconnected bimodal porosity with large portions being mesopores of varied sizes. The pore size distribution (PSD) results further indicate that PSS-MgCa-68/32 sorbent exhibits wide PSD of interconnected pores in the size range of 1 to 32 nm while PSS-MgCa-50/50 and PSS-MgCa-75/25 exhibits narrow PSD of 1 to 5 nm. Using SO₂ as model contaminate gas, it was shown that the dynamic adsorption performance of the PSS-MgCa-sorbents impregnated with 8 wt% KOH exhibits SO₂ uptake, with impregnated PSS-MgCa-68/32 showing better performance. This shows that the materials prepared can be used as adsorbent for gas filtration.     

Influence of chemical dealumination on the properties of USY zeolite

Three series of dealuminated Y zeolites have been prepared by chemical extraction ofhydrothermally dealuminated Y zeolite(USY)with H_2Na_2EDTA,HCl and H_4EDTA.The unitcell constant,mesopore distribution,acidity and extraframework aluminum(EFAL)of thezeolites were studied with XRD,chemical analyses,adsorption,IR and NH_3-TPD techniques.It was shown that H_2Na_2EDTA only removed EFAL species deposited in the pores of USY,by contrast,HCl and H_4EDTA extract both extraframework and framework aluminum,andmake the zeolite framework further dealuminated.Adsorption tests gave evidence that a second-ary pore system exists in these dealuminated zeolites.H_2Na_2EDTA extraction increased bothmicropore and mesopore volumes,but after HCl and H_4EDTA treatments,new mesopores formedand the micropore volume was decreased.The pyridine-IR and NH_3-TPD measurements demon-strated that EFAL had no evident contribution to the zeolite acidity.     

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.     

Selective Water Sorbents for Multiple Applications. 11. CaCl2 Confined to Expanded Vermiculite

This paper presents the water sorption properties of a new selective water sorbent based on expanded vermiculite as a host matrix and calcium chloride as a hygroscopic salt. Sorption isobars, isosters and isotherms at T = 30–150°C and vapor partial pressure 8.2–42.0 mbar clearly show that at low water contents crystalline hydrates with 0.33, 1 and 2 molecules of water per 1 molecule of CaCl₂ are formed in the pores. These hydrates are stable over a temperature change of 20–30°C and exhibit kinetically slow transformations. At higher water uptake, the vapor absorption leads to the formation of a CaCl₂ aqueous solution inside the pores, which properties are close to those in the bulk. Isosteric sorption heat was found to depend on water sorption and change from 76.3 kJ/mol for solid hydrates to 39.1–46.6 kJ/mol.     

Preliminary Study on Indirect Polymerization with Electrolytically-Generated Redox Initiators—A New Method of Polymerization

FeCl₃, CrCl₃, CH₃NH₂·HCl and H₃NNH₂·2HCl were used as the electrolytes which were dissolved in water, methanol or DMF. The redox initiators which composed of oxidizing agent and reducing agent were produced in the anode and cathode chamber respectively through electrolysis. It was found that the redox initiators obtained by using organic electrolytes of CH₃NH₂·HCl and H₂NNH₂·2HCl have much better polymerization yield of MMA than those of using inorganic electrolytes such as CrCl₃, FeCl₃. The reasons of different yields with different electrolytes are also discussed.     

Synthesis and characterization of ammonium molybdophosphate–silica nano-composite (AMP–SiO2) as a prospective sorbent for the separation of 137Cs from nuclear waste

The ammonium molybdophosphate–silica (AMP–SiO₂) nano-composites were prepared by sol–gel method. The material synthesized was nanocrystalline, with average crystallite size of primary particles in the range of 10–25 nm. Small angle X-ray scattering showed presence of mass fractal aggregates made of small particles with rough pore boundaries. To realize the scope of using AMP–SiO₂ nano-composites sorbent for removal of ¹³⁷Cs from nuclear waste solutions, its adsorption characteristics for cesium were evaluated. It was found that the AMP–SiO₂ nanocomposites were amenable for column operation, have high affinity for Cs, and possess very high adsorption capacity for Cs. From the perspective of separation of ¹³⁷Cs from acidic radioactive waste solution, AMP–SiO₂ nanocomposite holds significant promise.     

Distribution of elements in the surface layer of plasma-electrolytic coatings formed on titanium in electrolytes with MnO<Subscript>2</Subscript> particles

The influence of electrolytes (aqueous solutions of H₂SO₄, Na₂SO₃, and K₂B₄O₇ (group I) and Na₂SiO₃ (group II)), as well as the effects of pores and ridges around them, on the element composition of oxide coatings was studied. The addition of MnO₂ particles to electrolytes initiated the formation of large pores. The pores had increased titanium and decreased oxygen contents. Coatings I contained, on average, up to 1 at % Mn, and coatings II had up to 8 at % Mn; in the pores of II, the Mn concentration was increased to 18 at %. The coatings contained 7–28 at % carbon, which was concentrated in pores in I and on the surface of the oxide coating in II.     

Composite Water Sorbents of the Salt in Silica Gel Pores Type: The Effect of the Interaction between the Salt and the Silica Gel Surface on the Chemical and Phase Compositions and Sorption Properties

The influence of the inorganic salt-silica gel surface interaction on the chemical and phase compositions and sorption properties of composites of the salt in silica gel pores type is studied. Two possible interaction mechanisms are considered: (1) the ion-exchange adsorption of metal cations on the silica gel surface from a solution of a salt (CaCl₂, CuSO₄, MgSO₄, Na₂SO₄, and LiBr) and (2) the solid-phase spreading of a salt (CaCl₂) over the silica gel surface. The adsorption of metal cations on the silica gel surface in the impregnation step affords ≡Si-OM ⁿ⁺¹ surface complexes in the composites. As a result, two salt phases are formed in silica gel pores at the composite drying stage, namely, an amorphous phase on the surface and a crystalline phase in the bulk. The sorption equilibrium between the CaCl₂/SiO₂ system and water vapor depends on the ratio of the crystalline phase to the amorphous phase in the composite.     

Diffusion of Aqueous Solutions of CoCl2, Co(NO3)2, and Cu(NO3)2 in Porous Glass Membranes

Diffusion coefficients of CoCl₂, Co(NO₃)₂, and Cu(NO₃)₂ salts, characterizing permeation of their aqueous solutions across glass membranes with predominant pore radius in the range from 70 to 4.5 nm are determined. With pores in the membranes becoming narrower, the diffusion mobility of the electrolytes decreases.     

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.     

Influence of ion-background changes on the aquation rate of [CrCl3(H2O)3)]

The influence of change in ion background on the aquation rate constants of [CrCl₃(H₂O)₃)] was studied spectrophotometrically at 25°C over a broad range of ionic strengths (up to several moles/liter). The electrolytes KBr, KCl, NaClO₄, NaCl, NaBr, NaNO₃, HClO₄, HCl, LiClO₄, CaCl₂, LaCl₃, and ethanol were used. It is shown that the rate constant decreases with increasing electrolyte concentration in the electrolytic media (to 0.3 log unit in some of them), while increasing in ethanol media with increasing content of the alcohol.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2695–2699, December, 1992.     

Retention profile and selective separation of 90Y from 89Sr using zirconium-vanadate gel packed column

A low cost and selective method has been developed for the separation of trace concentrations of ⁹⁰Y³⁺ from its parent ⁸⁹Sr²⁺. The proposed procedure is based upon complete retention of ⁹⁰Y³⁺ onto zirconium-vanadate (Zr-V) gel ion exchanger packed column from aqueous solutions containing HCl (1.0 × 10^?5mol dm^?3). Under these conditions, ⁸⁹Sr²⁺ species were not retained onto Zr-V sorbent. The retained ⁹⁰Y³⁺ species were then recovered with HCl. The performance of Zr-V sorbent packed column was determined via the height equivalent to the theoretical plates (HETP) and the number of plates (N). Validation of the developed method was checked by calculating the radionuclidic purity in terms of purification factor (P _f = A/A₀) and radiochemical purity of the eluted ⁹⁰Y from the column. Zr-V sorbent packed column offers unique advantages of retention and quantitative separation of ⁹⁰Y from retention over conventional solid sorbents in rapid and effective separation of trace concentration of ⁹⁰Y³⁺ from ⁸⁹Sr²⁺ in their aqueous equilibrium media.     

Estimation of the kinetic characteristics of sorption of an organic ion on a heterogeneous crosslinked polymer sorbent within the framework of a bidisperse model

For the sorption of rubomycin, an antitumor athracycline-type antibiotic, on BDM-12 carboxyl-containing heterogeneous crosslinked polymer sorbent, it was shown that the measured time dependences of the extent of process are determined by two characteristic times: τ₁ (in the range of short times) and τ₂ (at long times). A phenomenological theory of the kinetics of sorption on the heterogeneous sorbent was developed on the basis of a biporous sorbent model. The dependences of the characteristic times τ₁ and τ₂ on the sorbent grain radius were obtained. It was concluded that the theory makes predictions in good agreement with experimental data and allows calculating the most important kinetic parameters of sorption of organic ions on polymer sorbents: the time of diffusion of the sorbate into microgranules, the diffusion coefficient of the sorbate in transport pores, the effective coefficient of the sorbate diffusion into the heterogeneous sorbent, etc.     

Porous microsphere of magnesium oxide as an effective sorbent for removal of volatile iodine from off-gas stream

Porous microspheres of magnesium oxide were synthesized by calcination of precursor obtained via hydrothermal method. A sample of microsphere was characterized by transmission electron microscopy, scanning electron microscopy–energy dispersion spectroscopy, X-ray diffraction, thermogravimetric analysis, N₂ adsorption–desorption isotherms, and BET surface area. The average pore size and surface area of the microsphere were found to be 9.0 nm and 83.1 m² g^?1, respectively. The performance of sorbent was investigated in a continuous adsorption system. Iodine adsorption on sorbent was studied by varying temperature of adsorption column, sorbent calcination temperature and initial concentration of iodine. The capacity of sorbent increased by ~25 % when calcination temperature was raised from 350 to 500 °C. The maximum iodine adsorption capacity of sorbent was found to be 196 mg g^?1 using Langmuir isotherm. These results indicate the microspherical form of MgO to be effective sorbent to capture iodine vapor from off-gas stream.     

Nano/subnano-tuning of porous ceramic membranes for molecular separation

In sol–gel processing, porous ceramic membranes can be prepared by sol-coating porous substrates and drying for gelling, followed by a firing process. Ceramic membranes prepared by sol–gel processing can be categorized into amorphous materials such as silica, and crystalline materials such as alumina and titania. Amorphous silica networks, which can be prepared by the polymeric sol route, have ultra-microporous pores that allow small molecules such as helium and hydrogen to permeate. On the other hand, crystalline materials, which are mostly prepared by the colloidal sol route, have nano-sized pores in the range of one to several nanometers. In this article, sol–gel derived SiO₂ and TiO₂ membranes with controlled pore sizes in the range of sub-nano to nanometers will be reviewed with respect to membrane preparation and to their application in the separation of the gas and liquid phases. Ceramic membranes with high performance can be obtained by precise control of membrane structures (pore size, pore size distribution, thickness, pore shape, etc.) and membrane materials (SiO₂, TiO₂, composite oxide, hybrid materials, etc.). Nano/subnano-tuning of porous ceramic membranes is quite important for the improvement of membrane permeability and selectivity.