Chloride distribution coefficient on strongly basic anion-exchange resin: Dependence on co-ion in alkali fluoride solutions

Summary The dependence of the chloride distribution coefficient on the co-ion of solutions of different alkali fluorides, MF, up to 11M is tested on the strongly basic anion-exchange resin AG1-X10. Under the same experimental conditions the distribution coefficient decreases in the following order for M⁺: Na⁺>K⁺>Rb⁺>Cs⁺. This can be explained by the different co-ion-chloride interactions. The consequence of this interaction for a chromatographic separation of chloride is shown with 5M KF and CsF solutions, used as eluants. Depending on the fluoride concentration, the distribution coefficient passes through a minimum value to increase again at higher electrolyte concentration. The non-exchange electrolyte in the resin phase is responsible for this effect. In addition, the bromide and the iodide distribution coefficients up to 10M KF solutions are determined. One results is that the selectivity coefficient between halide ions increases at higher electrolyte concentrations.     

Study on ion exchange equilibrium for some uni-univalent and uni-divalent reaction systems using strongly basic anion-exchange resin Duolite A-113

The study on thermodynamics of ion exchange equilibrium for uni-univalent Cl⁻/I⁻, Cl⁻/Br⁻, and uni-divalent Cl⁻/SO₄²⁻, Cl⁻/C₂O₄²⁻ reaction systems was carried out using ion-exchange resin Duolite A-113. The equilibrium constant K was calculated by taking into account the activity coefficient of ions both in solution as well as in the resin phase. The K values calculated for uni-univalent and uni-divalent anion exchange reaction systems were observed to increase with rise in temperature, indicating the endothermic exchange reactions having enthalpy values of 17.21, 36.60, 19.50, 18.43 kJ/mol respectively.     

强碱阴离子交换树脂及碱性洗脱剂的离子排阻/阴离子交换色谱法同时测定NH4+ ，NO2-和NO3-（英文）

Ion-exclusion/anion-exchange chromatography(IEC/AEC) on a combination of a strongly basic anion-exchange resin in the OH——form with basic eluent has been developed.The separation mechanism is based on the ion-exclusion/penetration effect for cations and the anion-exchange effect for anions to anion-exchange resin phase.This system is useful for simultaneous separation and determination of ammonium ion(NH+4),nitrite ion(NO-2),and nitrate ion(NO-3) in water samples.The resolution of analyte ions can be manipulated by changing the concentration of base in eluent on a polystyrene-divinylbenzene based strongly basic anion-exchange resin column.In this study,several separation columns,which consisted of different particle sizes,different functional groups and different anion-exchange capacities,were compared.As the results,the separation column with the smaller anion-exchange capacity(TSKgel Super IC-Anion) showed well-resolved separation of cations and anions.In the optimization of the basic eluent,lithium hydroxide(LiOH) was used as the eluent and the optimal concentration was concluded to be 2 mmol/L,considering the resolution of analyte ions and the whole retention times.In the optimal conditions,the relative standard deviations of the peak areas and the retention times of NH+4,NO-2,and NO-3 ranged 1.28%-3.57% and 0.54%-1.55%,respectively.The limits of detection at signal-to-noise of 3 were 4.10 μmol/L for NH+4,1.87 μmol/L for NO-2 and 2.83 μmol/L for NO-3.     

Synthesis and properties of anion-exchange membranes for fuel cells

Approaches to the synthesis of polymeric anion-exchange membranes for fuel cells are summarized. A classification of the synthesized anion-exchange membranes based on the chemical structure of the main polymer chain and the composition of the system is proposed. Some characteristics of the synthesized membranes and of fuel cells using them are presented. The main directions of research in this field are examined.     

Mass transfer mechanism and chemical stability of strongly basic anion-exchange membranes under overlimiting current conditions

The dynamics of changes in overall and partial voltammetric characteristics with respect to chloride and hydroxide ions is studied by the method of rotating membrane disk (RMD) under the conditions of stabilized diffusion layer thickness for the original strongly basic MA-41P and homogeneous AMX membranes and also for the modified heterogeneous MA-41P-M membrane at high current densities. For unmodified anion-exchange membranes at currents exceeding the limiting value, the hydrolysis of fixed ammonium bases produces secondary and ternary amino groups which are catalytically active in the reaction of water molecule dissociation. The hydrolysis of amino groups in the membrane surface layer is the mechanism of degradation of electrochemical characteristics of strongly basic membranes. This results in the increase of transport numbers with respect to hydroxide ions and weakening of mass transfer with respect to salt ions. For the surface-modified heterogeneous anion-exchange membranes, no degradation of electrochemical characteristics is observed. The characteristics of the surface-modified MA-41P-M membrane remain stable: after long-term operation of the energized membrane, the partial currents with respect to hydroxide ions are close to zero and the mass transfer with respect to salt ions is considerably intensified. The dependences of the thickness of the hydrolyzed layer of a strongly basic anion-exchange membrane on the time of its exposure to solutions of high pH are determined. An original method is developed for determination of the hydrolyzed layer thickness for strongly-basic anion-exchange membranes, which is based on the copper ability to form stable complex compounds with weakly basic amino groups of anion-exchange membranes.     

The kinetics and mechanism of bromide ion isotope exchange reaction in strongly basic anion-exchange resin duolite A-162 determined by the radioactive tracer technique

In the present investigation, ⁸²Br radioactive isotope was used as a tracer to study the kinetics and mechanism of exchange reaction between an ion exchange resin and an external bromide ion solution. In an attempt to study the reversible bromide ion isotopic exchange reaction kinetics, it was expected that whether the initial step was the exchange of radioactive bromide ions from the solution into the ion exchange resin (forward reaction) or from the ion exchange resin into the solution (reverse reaction), two ion isotopic exchange reactions should occur simultaneously, which was further confirmed by the experimental specific reaction rates of 0.130 and 0.131 min⁻¹, respectively. The results can be used to standardize process parameters so as to optimize the utilization of ion exchange resins in various industrial applications. The text was submitted by the authors in English.     

Enhanced extraction of cleistanthol from Phyllanthus flexuosus by deep eutectic solvent-modified anion-exchange resin

Anion-exchange resin (AER) and choline chloride-based deep eutectic solvent-modified anion-exchange resin (DES-AER) were prepared, and their performance properties were assessed by Fourier transform infrared spectrometer (FTIR), field emission scanning electron microscopy (FE-SEM), and adsorption experiments. In addition, the separation characteristics on the solid-phase extraction (SPE) cartridges packed with octadecyl silica (ODS), AER, and DES-AER for rapid extraction of cleistanthol from Phyllanthus flexuosus extracts have been evaluated, with recoveries of the materials tested at 72.14, 68.21, and 82.11%, respectively. All results demonstrated that DES-AER not only offered higher adsorption capacity for cleistanthol but also exhibited better extraction efficiency of cleistanthol than those of ODS and AER. In this work, it is the first application of DES in the modification of AER, and the proposed DES-AER showed significant affinity and selectivity toward cleistanthol, which could have potential application for natural product extraction.     

Synthesis of new polyfunctional 2-pyrrolidinones from methyl 2-(carboethoxyhydroxymethyl)acrylate

The synthesis of new polyfunctional 2-pyrrolidinone derivatives from methyl 2-(carboethoxyhydroxymethyl)acrylate is described. These alkenes present an extremely high reactivity upon Michael addition with primary amines leading to a simple, mild, and efficient route to the preparation of new polyfunctional pyrrolidinones.     

Adsorption behavior of various metals on a weakly basic anion-exchange resin in sulfuric acid media

A systematic study is presented on the adsorption behavior of some 20 metals on a weakly basic condensed phenol resin, Amberlite CG-4B, in sulfuric acid media. The distribution coefficients were determined over a sulfuric acid concentration range of 0.005 M to 2 M. The metals adsorbed are similar to those which exhibit strong adsorption on a strongly basic resin, but the magnitudes of the distribution coefficients and the adsorption sequences differ considerably between the two types of the resin. Several two- and three-component separations of analytical interest are possible. A new method for the separation of titanium(IV) is described; this is based on its high adsorption on CG-4B from sulfuric acid media containing hydrogen peroxide.     

An improved extraction chromatographic resin for the separation of uranium from acidic nitrate media

The preparation and characterization of a new extraction chromatographic resin exhibiting extraordinarily strong retention of hexavalent uranyl ion over a wide range of nitric acid concentrations and very high selectivity for U(VI) over Fe(III) and numerous other cations is described. This new material (designated U/TEVA-2) comprises a novel liquid stationary phase consisting of an equimolar mixture of diamyl amylphosphonate (DA[AP]) and Cyanex 923^® (a commercially available trialkyl-phosphine oxide, TRPO) sorbed on silanized silica or Amberchrom CG-71. Cyanex 923 is shown to be preferable to a related TRPO, Cyanex 925^®, due to its lower viscosity and higher selectivity for U(VI) over Fe(III). The retention of uranyl nitrate by the U/TEVA-2 resin, as measured by the k′ values (number of free column values to peak maximum) is >5000 from approximately 0.1 to 8 M HNO₃. The ability of the new resin to strongly and selectively retain U(VI) from such a wide range of acid concentrations, along with its favorable physical properties, make it a good candidate for application in the separation and preconcentration of U(VI) from complex environmental, biological, and nuclear waste samples for subsequent determination.     

Adsorption of phenol from water by N-butylimidazolium functionalized strongly basic anion exchange resin

N-butylimidazolium functionalized strongly basic anion exchange resin with Cl(-) anion (MCl) was prepared by anchoring N-butylimidazole onto chloromethylated macroporous styrene-divinylbenzene (St-DVB) copolymer. The adsorption performances of phenol on MCl were studied using the batch technique at acidic and alkaline pH. The studies showed that phenol can be effectively removed at both acidic and alkaline pH. The maximum adsorption was achieved at about pH 11. The maximum adsorption capacities of phenol on MCl at pH 6.6 and 11.2 were 80.2 and 92.9 mg/g, respectively. The adsorption mechanism was mainly molecular adsorption at acidic pH and anion exchange at alkaline pH. The adsorption of phenol was hindered by the presence of Cl(-) and SO(4)(2-) at alkaline pH due to the competitive anion exchange reaction. The adsorption of molecular phenol species on MCl at acidic pH was exothermic, and the anion exchange of phenolate species by MCl at alkaline pH was endothermic. Desorption of phenol from loaded adsorbent was achieved by using 0.5 mol/L NaOH and 0.5 mol/L NaCl mixed solution. MCl can simultaneously remove phenol and Cr(VI) from their mixtures, which would be of practical value in actual industrial wastewater treatment.     

Sorption of humic substances on a weakly basic anion-exchange resin: Relationship with the adsorbate structure

Adsorption of a broad range of humic substances (HS) of different origins and fractional compositions on a macroporous weakly basic anion-exchange resin is studied. It is found that the nature of the HS has a substantial effect on both the efficiency of sorption and the mechanism of interaction with the adsorbent. The dependence of the determined thermodynamic parameters of sorption on the HS origin, composition, and structure is shown for a broad range of HS. It is concluded that the results can be used to predict the sorption properties of weakly basic anion-exchange resins with respect to HS of known origin and structural group composition.

     

Selective determination of ammonium ions by high-speed ion-exclusion chromatography on a weakly basic anion-exchange resin column

This paper describes an ion-exclusion chromatographic system for the rapid and selective determination of ammonium ion. The optimized ion-exclusion chromatographic system was established with a polymethacrylate-based weakly basic anion-exchange resin column (TSKgel DEAE-5PW) as the separation column, an aqueous solution containing 0.05 mM tetramethylammonium hydroxide (pH 9.10) as eluent with conductimetric detection for the analyte determination. Under the optimum chromatographic conditions, ammonium ion was determined within 2.3 min with a detection limit (S/N=3) better than 0.125 microM. Ammonium ion in rain and river waters was precisely determined using this ion-exclusion chromatographic system.     

Synthesis of phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin and its adsorption properties of uranium(VI)

A new phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin (PS–N–P) was synthesized by P,P-dichlorophenylphosphine oxide modified commercially available ammoniated polystyrene beads, and characterized by Fourier transform infrared spectroscopy and elemental analysis. The adsorption properties of PS–N–P toward U(VI) from aqueous solution were evaluated using batch adsorption method. The effects of the contact time, temperature, pH and initial uranium concentration on uranium(VI) uptake were investigated. The results show that the maximum adsorption capacity (97.60 mg/g) and the maximum adsorption rate (99.72 %) were observed at the pH 5.0 and 318 K with initial U(VI) concentration 100 mg/L and adsorbent dose 1 g/L. Adsorption equilibrium was achieved in approximately 4 h. Adsorption kinetics studied by pseudo second-order model stated that the adsorption was the rate-limiting step (chemisorption). U(VI) adsorption was found to barely decrease with the increase in ionic strength. Equilibrium data were best modeled by the Langmuir isotherm. The thermodynamic parameters such as ?G ₀, ?H ₀ and ?S ₀ were derived to predict the nature of adsorption. Adsorbed U(VI) ions on PS–N–P resin were desorbed effectively (about 99.39 %) by 5 % NaOH–10 % NaCl. The synthesized resin was suitable for repeated use.     

Synthesis of polyfunctional 2-thionicotinonitriles

Reaction of 2-amino-4-arylbuta-1,3-diene-1,1,3-tricarbonitriles with sulfur in benzonitrile affords 4-amino-6-aryl-2-thio-1,2-dihydropyridine-3,5-dicarbonitriles. They also are synthesized by an authentic synthesis from 4-amino-6-aryl-2-bromopyridine-3,5-dicarbonitriles and sodium hydrosulfide.     

Synthesis and properties of new polyfunctional curing agents for epoxy resins based on dimerized fatty acid

The synthesis and properties of a number of devised imino(amino)amide derivatives of dimerized fatty acid are described. It is shown that synthesized products exhibit the properties of plasticized curing agents for epoxy resins.     

Determination of uranium in natural waters after anion-exchange separation

A method is described for the determination of uranium by fluorimetry and spectrophotometry in samples of natural non-saline waters. After acidification with hydrochloric acid, the water sample is filtered and, following the addition of ascorbic acid and potassium thiocyanate, passed through a column of the strongly basic anion-exchange resin Dowex 1-X8 (thiocyanate form). On this exchanger uranium is adsorbed as an anionic thiocyanate complex. After removal of iron and other coadsorbed elements by washing first with a mixture consisting of 50 vol.% tetrahydrofuran, 40 vol.% methyl glycol and 10 vol.% 6 M hydrochloric acid, and then with pure aqueous 6 M hydrochloric acid, the uranium is eluted with 1 M hydrochloric acid. In the eluate, uranium is determined fluorimetrically or by means of the spectrophotometric arsenazo III method. The procedure was used for the routine determination of uranium in water samples collected in Austria.