Sulfo Cation Exchanger Research Articles

Percolation effects in metal-cation-exchange membrane nanocomposites

121 Modification of ion exchangers (granules, mem branes, fibers) by an inorganic component (metal, salt, oxide) is used for imparting new properties to the initial matrix or improving the existing ones [1–3]. If a dis perse material in introduced into an ion exchanger, the forming metal–ion exchanger composites have as many as two sorts of spatially separated active sites: metal particles and ionogenic groups of the matrix [3– 5]. The bifunctionality of such materials allows one to use them as catalysts of chemical and electrochemical reactions, electrode sensors, and highly reactive mate rials. The electronic conduction of nanocomposites, which determines their electrochemical activity, is a function of the metal content [6, 7]. In this work, by chemical deposition of a metal (copper, silver) into heterogeneous sulfo cation exchange membrane MK 40, nanocomposites with bulk distribution of metal particles were obtained. Multiple metal redeposition gives rise to a percolation threshold of specific electronic conduction of the composite. The number of deposition cycles necessary for the emergence of the percolation threshold is determined by the nature of the metal. It was shown for the first time that, in the course of the formation of a percolation cluster of metal particles in the ion exchange membrane, the boundary potential of the membrane, which characterizes its ion exchange properties, undergoes a step change. The purpose of this work was to study the depen dence of the electronic conduction and the equilib rium boundary potential of nanocomposites on the content of the metal component. Nanocomposites with different metal (Cu0, Ag0) contents were synthesized by cyclic alternation of ion exchange saturation and chemical reduction of metal ions according to a published procedure [5]. The matrix was heterogeneous styrene–divinylbenzene sulfo cation exchange membrane MK 40. Figure 1 presents scanning electron microscopy images of nanocomposites Cu0 · MK 40 (panel (a)) and Ag0 · MK 40 (panel (b)) after three cycles of metal deposi PHYSICAL CHEMISTRY

The chemical precipitation of nickel on ion exchangers and active carbons

The chemical precipitation of nickel in the form of poorly soluble precipitates in ion exchanger matrices and on active carbons from solutions of nickel chloride and chemical nickel plating electrolytes was studied. The sorption of nickel ions from a solution of nickel chloride occurs most effectively on Purolite D24002 macroporous chelate forming ion exchanger, KU-23-15/100 sulfo cation exchanger, and KU-2-8 gel sulfo cation exchanger. Nickel enters sulfo cation exchangers in the form of counterions, and is adsorbed on Purolite D24002 largely because of complex formation. The subsequent precipitation of nickel in the solid state in matrix pores liberates ionogenic centers, which allows repeated sorption cycles to be performed. After three chemical precipitation cycles under static conditions, the amount of nickel is higher by 170–250% than the ion exchange capacity of the sorbents. The electrolyte of chemical nickel plating contains nickel predominantly in the form of negatively charged and neutral complexes with glycine, which cannot form bonds with the matrices under study. It is therefore reasonable to perform sorption at decreased solution pH values.

Reductive sorption of molecular oxygen from water on silver-KU-23 sulfo-cation exchanger nanocomposites in different ionic forms

It was found that the rate of reductive sorption of molecular oxygen on dispersed silver-KU-23 sulfo-cation exchanger nanocomposites depends substantially on the ionic form (H+, Ag+, Na+ forms) of the nanocomposite. It was established that the observed dependence is due to the influence of the composition of the medium in pores of the ion-exchange matrix, which serve as nanoreactors, on the rate of the chemical reaction between silver nanoparticles and dissolved molecular oxygen.

The process of producing 2-methyl-2-butene by positional isomerization on sulfocation exchangers

The results of determination of composition and strength of the granules of nitrogen-phosphoric fertilizers containing 1.5 to 5.0% of P2O5, obtained by interaction of the mineralized mass of the phosphorites of Central Kyzylkum with the 70–90% solutions of ammonium nitrate at 110°C, are presented.

Processes of synthesis of 1-butene from 2-butene by the positional isomerization on sulfocation exchangers

Obtaining of individual 1-butene and 2-butenes from the butane-butene fractions can be processed sufficiently effectively by combining positional isomerization of alkenes on the sulfocation exchanger catalysts and careful rectification. At 50–60°C is reached the equilibrium with the ratio of the sum of 2-butenes to 1-butene ∼20:1. The relatively high-boiling 2-butenes are enough completely separated by rectification of 1-butene, and isobutane from the harmful impurities (butadiene and isobutene). The reverse isomerization of the purified 2-butene into 1-butene with the continuous distillation of the latter makes it possible to obtain pure 1-butene with a very low prime cost.

The processes of benzene alkylation with n-alkenes on the sulfocation exchangers

The processes of benzene alkylation with n-alkenes C2–C3 on sulfocation exchangers are developed. The processes are deprived of the strong corrosion aggressiveness, characteristic of the industrial processes with use of AlCl3 or BF3, and do not need the periodic burning out of the formed contaminants, that is characteristic of the processes with application of zeolites. Alkylation proceeds in the liquid phase at moderate temperatures: 70–90°C in the case of alkylation with propene and n-butenes, and 130°C for the alkylation with ethylene. With the use of alkane-alkene fractions C2–C3 the conversion of alkenes process exceeds 99%, the alkylbenzene to dialkylbenzenes ratio reaches 20–25%. Peralkylation of dialkylbenzenes it not required.

Theoretical consideration of the sorption of complexones on sulfo cation exchangers in displacement complexation chromatography

A mathematical model is proposed for describing the sorption of complexones (compositions of the solid and liquid phases, the elution order from the zone of sorbed complexone). The sorption of diethylenetriaminepentaacetic acid (DTPA) is considered as an example. In terms of this concept, experimental data reported by some Russian and foreign researchers are interpreted.

H+-Cu2+ ion exchange on a Cu0-KU-23 sulfocation exchanger nanocomposite in solutions with various pH values

The influence of solution pH on H+-Cu2+ exchange equilibrium was studied for the disperse copper- KU-23 (15/100 S) macroporous strongly acid sulfocation exchanger nanocomposite. In dilute solutions of copper(II) sulfate in weakly acid media (pH 3–6), ion exchange limitation is related to the consumption of hydrogen counterions and the formation of copper counterions in a side reaction between copper particles and impurity oxygen. The concentration of hydrogen counterions in the nanocomposite is replenished as pH decreases because of their sorption from solution together with copper ions.

The mutual influence of imino acids and phenylalanine on the dynamic characteristics of sorption on KU-2 × 8 sulfocation exchanger in the H form

The dynamics of sorption of pure imino acids (proline and hydroxyproline) and imino acids in the presence of aromatic amino acid, phenylalanine, on KU-2 × 8 sulfocation exchanger in the H form was studied. Mutual influence of amino acids on the dynamic characteristics of sorption was observed. This influence changed the shape of elution curves and decreased the working exchange capacity. Both competitive and synergistic sorption mechanisms governed sorption of amino acids from binary solutions.

Electroreduction of molecular oxygen on dispersed copper in an ion-exchange matrix

Electrochemical reduction of molecular oxygen was studied on a [dispersed copper]-[macroporous KU-23 15/100S sulfocation exchanger with various metal concentrations] composite electrode. It was found that a high proton concentration in the ion-exchange matrix causes a decrease in the oxygen reaction overvoltage. The nanostructured state of copper particles causes stabilization of the intermediate product, i.e., hydrogen peroxide. Using the rotating disk electrode method, it was detected that the process is limited by external diffusion of oxygen to composite grains. The oxygen reaction is mostly concentrated on the grain surface and surface layers; oxygen is reduced in the bulk due to dispersed copper oxidation.

A wood-based fibrous chemisorbent

A method and the conditions for fabricating a fibrous chemisorbent by graft polymerization of acrylamide on pine wood in the presence of a Fe 2+ —H 2 O 2 redox initiating system were developed. The maximum values of the yield of commercial copolymer (76.79%) and mass fraction of the graft component (53.49%) were attained at a 0.017 wt. % concentration of H 2 O 2 , 1.5% monomer, temperature of 60°C, and process time of 1 h. The process takes place with 97.85% efficiency and insignificant formation of homopolymer (1.4%). The sorption and kinetic properties of the samples with respect to mercury ions were established. It was found that sorbent with a 9.93% nitrogen content extracts 65-64% of Hg(II) ions from dilute and concentrated solutions and is equal to the industrial strongly acid sulfo cation exchanger Ky-2x8. Based on the data from IR spectroscopy and the linear anamorphoses of equilibrium sorption isotherms, the chemisorption mechanism of absorption of mercury(II) ions by wood with graft amide groups was established. Graft polymerization of unsaturated nitrogen-containing monomers, acrylamide (AA) in particular, on different natural matrices, for example, lignin, coconut shells, starch, and especially cellulose [1-4], has been relatively widely treated in scientific publications. However, the studies on synthesis of graft amino copolymers based on wood are limited. Moreover, modification of such lignocellulosic material with chemically active monomers, where it is possible to create fibrous ion exchangers that differ from ordinary sorbents by smaller geometric dimensions and developed external surface which determine their high capacity and kinetic characteristics, is very pressing. We synthesized a graft copolymer of wood and AA (Wd-AA) and studied its sorption properties with respect to mercury(II) ions. Air-dried pine sawdust of the 2 mm screen sizing fraction containing (in wt. %) 48.3% cellulose, 17.6% hemicellulose, 28.6% lignin, 5.0% extractives, 0.52% ash (including 0.48% insoluble and 0.04% water-soluble residue; pH of ash of 4.72) was used for modification. The elemental composition of the wood was (in %): 45.63 C, 6.10 H, 47.40 O, 0.87 N; moisture content of 9.85; dryness coefficient of 0.9015. Graft polymerization was conducted with the Fe 2+ —H 2 O 2 redox initiating system. The wood was held in a solution of Mohr’s salt with a 7.09 mg/liter concentration of Fe 2+ at pH = 5 and after washing off the excess metal ions, immersed in an aqueous solution containing a different amount of monomer and H 2 O 2 . The concentration of Fe 2+ in the polymer matrix was 2.52 mg/g. The product was purified of homopolymer — polyacrylamide (PAA) and unreacted AA with distilled water in a Soxhlet apparatus. The amount of ungrafted polymer was determined gravimetrically after precipitation of PAA from aqueous solution into ethanol or evaporation of the solution at low pressure. The characteristics of the graft copolymer and grafting parameters were: mass content of PAA in modified wood (W), degree of conversion of AA into homo-, graft polymer (C hp , C g ); the total conversion of monomer (C t ), grafting percentage (P g ) and efficiency (G E ) were calculated according to [5, 6]. The content of amide groups in the reaction products (E N ) was determined by titration with an accurate weighed portion of samples in a solution of acetic anhydride with 0.1 N solution of HClO 4 in glacial acetic acid. The amount of iron ions adsorbed in the polymer phase was established by atomic-absorption analysis and the nitrogen content in the graft copolymers was determined chromatographically. Sorption of Hg(II) was conducted in static conditions from 20 ml of a solution of Hg(NO 3 ) 2 ⋅2H 2 O (analytically pure) with copolymer weighing 0.05 g. The initial and equilibrium concentrations of metal ions in the solution was determined by

The stabilization of nanodisperse silver in a sulfo cation exchanger

Silver-ion exchanger (electron ion exchanger, EI) composites with equivalent silver and hydrogen counterion contents were prepared by chemical deposition. Microscopic and X-ray data showed that silver nanoparticles and their ensembles isolated from each other and stabilized by a polymeric matrix were formed. Contact of Ag0-EI in the H+ form with solutions of silver salts caused the occurrence of two processes, ion exchange and metal recrystallization. These processes were interrelated because they involved one common particle, the silver counterion. Recrystallization proceeded by the electron-ion mechanism, but, because of matrix isolation of silver particles, electron transfer occurred inside separate structural elements (ensembles of particles) rather than over the whole composite volume. The transfer of silver ions largely occurred over ionogenic matrix centers, which substantially decreased their mobility. The low electronic conductivity of the composite and limited mobility of counterions were charge stabilization factors, which hindered recrystallization and, along with matrix stabilization, contributed to the retention of nanosized silver particles.

Metal-ion-exchanger nanocomposites in redox sorption processes

Metal‐ion-exchanger nanocomposites were produced by redox sorption. For the first time, conditions were substantiated for the stabilization of metal (Ag, Cu) particles by an ion-exchange matrix through the limitation of recrystallization via matrix isolation of particles and reduction of the mobility of metal counterions. A model was proposed for the redox sorption of molecular oxygen from water in the nanocomposites, given a metal particle size distribution function. This model was used to calculate the particle size at which the kinetic control of the process is replaced by the optimal control by internal diffusion. Metal‐ion-exchanger nanocomposites are nanostructured heterogeneous systems consisting of particles of a metal or its slightly soluble compounds that are distributed throughout the bulk of an ion-exchange polymer matrix. Owing to the excess Gibbs energy of nanodispersed metal particles and the ability of the matrix to exchange ions, the nanocomposites can be used as highly efficient catalysts, sorbents, and chemical reagents. The kinetics of metal deposition into the ion exchanger, the chemical activity of the obtained nanocomposites with respect to molecular oxygen dissolved in water, and the laws of reaching quasi-equilibrium were studied previously [1‐3]. The creation and use of nanocomposites as reagents include the same processes, namely, ion-exchange or molecular sorption and redox reaction. The overall process involving simultaneous reaction steps can be called redox sorption. The specific feature of this process for the metal‐ion-exchanger nanocomposites is that the redox reaction is particle-size-dependent [4]. To develop the concepts of particle-size-dependent processes, it is important to determine the conditions for the aggregation stability of metal particles in the ionexchange matrix and to investigate the effect of the particle size on the kinetic laws of processes involving nanocomposites. The purpose of this work was to reveal the role of the ion-exchange matrix in maintaining the aggregation stability of metal nanoparticles and determine the effect of their size on the macrokinetics of redox sorption of molecular oxygen from water. Metal (Ag, Cu) is deposited into macroporous and gel sulfo cation exchange matrices (KU-23 and KU-2). A metal salt solution is brought into contact with the ion exchanger under static or dynamic conditions. Metal ions enter the matrix by an ion-exchange mechanism and are held as counterions near charged ionogenic groups; e.g.,

Stability of Ultradisperse Copper in a Sulfo Cation Exchanger Matrix

The recrystallization of ultradisperse copper chemically deposited onto a sulfo cation exchanger matrix was studied by the potentiometric method. The stationary value of the electrode potential of the copper-sulfo cation exchanger composite was established during a long period of time, which depended on the ionic form of the composite (H+, Cu2+, or Na+), solution composition (CuSO4, H2SO4, and Na2SO4), and solution concentration. Recrystallization was favored by copper(II) counterions, which entered the composite as a result of ion exchange, nonexchange absorption of copper sulfate, or preliminary composite transformation into the Cu2+ form. In the quasi-equilibrium state, the concentration of copper(II) counterions was maintained at a high level by the Donnan interfacial potential. At all the copper(II) sulfate concentrations used, the potential of the Cu2+/Cu ion—metal pair in the ion-exchange matrix remained at virtually the same level, which was indicative of the stable state of copper particles. In the absence of an external source of copper ions, recrystallization was significantly hindered; therefore, the potential exhibited only a slight drift. Copper ions formed in the solution of small crystals were localized in the vicinity of ionogenic matrix centers, which decreased the mobility of these particles as counterions; therefore, the dispersity of particles remained unchanged.

Interpretation of hypsochromic and bathochromic shifts of vibrational frequencies of a cation exchanger

Structures of a representative fragment of a sulfocation exchanger in the form of alkali metal salts were optimized using the Gaussian-03 program package. Frequencies of stretching vibrations of the sulfo group were calculated for structures of the contact ion and hydrate-separated ion pairs. A comparison of the calculated and experimental values of hypsochromic (bathochromic) shifts of the frequencies of stretching vibrations of the sulfo group due to the cation field suggests that the ion pair in the studied systems dissociates. The calculated IR spectra of the representative fragment of the sulfocation exchanger can be used as calculated benchmarks in analyzing substances using expert systems.

Dependence of equilibrium and kinetic parameters of erythromycin a sorption on the structural characteristics of the biosorbent

The use of special synthetic sorbents with surface carboxyl groups allowed us to increase fourfold the effective diffusion coefficient for erythromycin. The maximum sorption capacity for the antibiotic exceeded twofold that observed in experiments with a macroporous sulfocation exchanger MN-500. The sorption of the antibiotic was completely reversible upon treatment with a combined eluant that competitively interacts with the sorbent and does not impair the structural characteristics of erythromycin.

Ionic and molecular Self-Diffusion in Ion-Exchange materials for fuel energetics studied by pulsed field gradient NMR

Pulsed field gradient nuclear magnetic resonance technique was applied to investigate the self-diffusion mechanism of water, alcohol molecules and Li− counterions in sulfocation exchangers with different structures of the polymeric matrix. It was shown that in the homogeneous perfluorinated sulfocation exchange membranes the ionic and water translation motions are controled by the hydrogen bond network forming in ionogenic channels at the high water content. At the low solvent content, the self-diffusion coefficients of methanol and ethanol are higher than the water self-diffusion coefficients. The influence of non-ion-exchange sorbed electrolyte on Li+ self-diffusion coefficients was observed in the heterogeneous sulfocation exchanger KU-23.

Effect of Chromium Ions on Degradation of Fiban K-1 Fibrous Sulfocation-Exchanger

It was shown that the mechanism of thermostabilization of the substituted chromium form of the fibrous sulfo cation-exchanger Fiban K-1 is due to the formation of chromium complexes and polystyrene sulfonicacid and then sulfates.

Computer Simulation of Cation-Exchange Membrane Structure: An Elementary Act of Hydrated Ion Transport

A fragment of the structure of a sulfo cation exchanger, which is the basis of most cation-exchange membranes, is calculated by an ab initio method. An analysis of interatomic bonds in the structure shows that, to detach a mobile ion from a fixed ion, it is necessary to break the hydrogen bond between hydration water molecules of the counterion in addition to overcoming the electrostatic attraction. As the hydrogen bond cleavage work for simple hydrated ions is ten times the electrostatic attraction energy, an elementary act of ion transport in a cation-exchange membrane is considered mostly as the hydrogen bond transfer reaction.

Oily Acid Tars as Feedstock for Manufacture of Cation Exchangers

Resin–asphaltene concentrates were obtained by the redox reaction of acid tar and naphtha deasphalting residue and used for fabrication of sulfo–cation exchangers. The strongly acid powdered sulfo cation exchanger with a static exchange capacity of 3.8 meq/g and mechanical strength of 92% is characterized by elevated thermohydrolytic stability and radiation stability. Based on its properties, it can be used in metal–gauze–asbestos gravity filters at atomic power plants for preliminary treatment of water.