Selective Exchange Research Articles

Preparation and characterisation of anion exchangers with dihydroxy-containing alkyl substitutes in the quaternary ammonium functional groups

Novel poly(styrene-divinylbenzene) (PS-DVB) based anion exchangers having one and two (2,3-dihydroxypropyl) substitutes in the quaternary ammonium functional groups are prepared and characterised by ion chromatography (IC). The introduction of bulky and hydrophilic substitutes to the anion-exchange groups allows the elimination of non-ionic interactions between the polarisable anions and the aromatic rings from the matrix and the improvement of separation selectivity as compared with the traditional trimethylammonium (TMA) functionalised ion exchangers. The synthesis of the ion exchangers includes acylation of PS-DVB particles with acetic anhydride followed by reductive amination either with methylamine hydrochloride or dimethylamine and further alkylation with oxiranes under varied conditions. The ion exchange selectivity and separation efficiency of nine adsorbents having different structure of bonded groups, ion exchange capacity (9–98μequiv.g−1) or particle size is studied for model mixture of inorganic anions (F−, Cl−, NO2−, Br−, NO3−, HPO42− and SO42−) using carbonate and hydroxide eluents. The adsorbents with more hydrophilic substitutes provided superior columns efficiencies and better peak symmetry as compared with analogues having hydrophobic functional groups. The calculated values of column efficiencies for polarisable NO3− and HPO42− are 18,500 and 29,000N/m, respectively, for anion-exchanger, having N-methyl-N′,N″-di-(2,3-dihydroxypropyl)ammonium groups which is significantly higher than 1800 and 12,000N/m obtained for these anions with anion exchanger bearing TMA functional groups.

Membrane-free electrodeionization for high purity water production

High purity water can be produced either by ion exchange or through electrodeionization. The latter deionization technology is superior to the former in many aspects, including no chemicals required, environmental friendliness, and easy operation. However, it usually needs the assistance of selective ion exchange membrane, causing a series of problems, such as high cost, difficulty in repairing, and membrane fouling. In this work, a new process called as membrane-free electrodeionization has been proposed and tested for high purity water production. It was operated in a batch countercurrent mode, alternating with a long service step and a short regeneration step. A total of 20 operational cycles were examined. The effluent conductivity was 0.056–0.059μS/cm only. The Na+ and Ca2+ concentrations, conductivity and pH value of the concentrate, as well as the voltage required were examined systematically during regeneration. The conductivity of the concentrate varied from 217μS/cm to 150μS/cm, the average pH value of the concentrate was 7.9, and the average voltage was 730V. Effective regeneration was achieved, and the resins after repeated regeneration still remained their good efficacy for deionization.

Condensation of diphenylguanidine and hexamethylenediamine

Reaction of condensation of diphenylguanidine with hexamethylenediamine was performed. It is shown that the resulting condensate is a selective ion exchanger.

Methods of increasing the stability of the catalytic effect of MFI type zeolites and the total service life of catalysts based on them

Increasing the operational stability of MFI-type zeolite catalysts is topical for the creation of highly efficient catalysts for the conversion of methanol or C2-C4 hydrocarbon gases into aromatic hydrocarbons, i.e., important industrial processes. This study proposes three new approaches to increasing the stability of zeolite catalysts: selective dealumination on the outer surface of MFI zeolite crystals, structurally selective ion exchange on the outer surface of crystals, and the application of an isothermal (multitube) reactor. The effect of selective dealumination and structurally selective ion exchange conditions on the SiO2/Al2O3 molar ratio in the zeolite on the interregeneration period duration in the conversion of methanol into hydrocarbons has been studied. It has been established that the selective dealumination of the outer surface increased the interregeneration period duration by 3–5 times. Structurally selective ion exchange on the outer surface of zeolite crystals allows us to increase the interregeneration period duration by 2–4 times and to decrease the regeneration temperature and duration due to the change of the properties of deposited coke. The application of a multitube reactor facilitates the procedure of regeneration in comparison with an adiabatic reactor due to the formation of less condensed coke depositions.

Studies on separation of Cs/Ba and Zn/Cu binary mixtures on zirconium antimonate as ion exchanger

Zirconium antimonate (ZrSb) ion exchanger was prepared. Distribution coefficients of metal ions on ZrSb ion exchanger in solutions of various acids (hydrochloric, nitric, acetic, citric, ascorbic) and salts (sodium chloride and sodium nitrate) were determined to evaluate the ion exchange behavior and selectivity to specific ions. ZrSb, as compared to other inorganic ion exchangers, showed increased thermal and chemical stability. ZrSb is an efficient and promising ion exchanger for preparation of 137Cs/137mBa and 62Zn/62Cu radioisotope generators.

Highly selective ion sorption and exchange by crystalline zinc complexes of unsymmetrical angular ligand 3-hydroxy-2-quinoxalinecarboxylic acid

With the motivation of searching for highly selective ion sorbents, two new supramolecular complexes, [Zn(qc)2(H2O)2]·H2O·CH3OH (1) and [Zn(qc)2(4,4′-bpy)]n (2) have been synthesized and structurally characterized by assembly of 3-hydroxy-2-quinoxalinecarboxylic acid (Hqc) with Zn(II) at ambient conditions. Complex 1 has a discrete mononuclear moiety, whereas 2 possesses a 1-D polymeric chain structure. Interestingly, complex 1 exhibits highly selective ion sorption and exchange capacity for Cd2+ and Cu2+ over Co2+ and Ni2+ ions in the crystalline solid state when the crystals of 1 is immersed in the aqueous solutions of the perchlorate salts of Cd2+, Cu2+, Co2+ and Ni2+ ions, respectively, which indicates that ion sorption and central Zn(II) ion exchange might be considered as being dominated by the coordination ability of metal ions to free functional groups, ionic radii of adsorbed metal ions, and the solution concentration of adsorbed metal salts. Thermal stabilities and solid state fluorescent properties of the title complexes have been studied.

Quaternized Poly(Styrene Ethylene Butylene Poly Styrene)/Multiwalled Carbon Nanotube Composites for Alkaline Fuel Cell Applications

The present study is aimed at synthesizing a novel anion exchange composite membrane from quaternized polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene [QPSEBS] and functionalized multi walled carbon nanotubes (f-MWCNT) by solution casting method. The characteristic properties of the QPSEBS/f-MWCNT composite membranes were investigated using Fourier transform infrared (FTIR), UV-Visible spectroscopy, thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD) studies and Raman spectroscopy. The water uptake, ion exchange capacity, ionic conductivity, methanol permeability and selectivity ratio of the membranes were also studied. The prepared composite membranes were tested in an in-house fabricated alkaline membrane fuel cell (AMFC) set up using Pt/C as the common anode catalyst and three different cathode catalysts namely Pt/C, Pd-Ni/C and Ag/C. Among all the three cathode catalysts, Pt/C for QPSEBS/5% f-MWCNT is found to show the maximum power density and open circuit voltage (OCV) of 187 mW cm(-2) and 0.73 V respectively. For direct methanol alkaline membrane fuel cells (DMAMFC), the OCV of QPSEBS/5% f-MWCNT is found to be 0.76 V and the maximum power density of 59.5 mW cm(-2) is achieved at a current density of 175 mA cm(-2).

The removal of cesium ion with natural Itaya zeolite and the ion exchange characteristics

AbstractBACKGROUNDThe large Itaya zeolite deposit in Yonezawa, Japan produces good quality, natural zeolite. Its properties as an adsorbent and a functional carrier were assessed and the ion exchange characteristics examined. Natural zeolite has a useful high cation exchange capacity, but has a disadvantage in scattering of the powder. In this study a nonwoven fabric containing zeolite was tested for the removal of cesium.RESULTSThe X‐ray diffraction (XRD) peak pattern confirmed that Itaya zeolite is mainly clinoptilolite and contains some mordenite. Ion exchange selectivity of the natural zeolite was Ag+ > Pb2+ > Cu2+ > Zn2+ > Cd2+ > Cr3+ > Ni2+ with almost 100% removal of Ag+ and Pb2+ ions.The cation exchange capacity (CEC) of Itaya zeolite was 131 cmol kg‐1. Low concentrations of Cs+ were removed effectively from the solution with natural zeolite. Cesium ions were removed by ion exchange with potassium and sodium. Cs+ was desorbed from the zeolite with ammonium salt solutions. Elution of Cs+ was influenced by the coordination ability of counter anions.CONCLUSIONSatisfactory results were obtained using zeolite‐containing nonwoven fabric for the removal of cesium ions. © 2013 Society of Chemical Industry

Tunable Selectivity of Lanthanide Ion Exchange within a Coordination Polymer

The exchange of lanthanide(III) ions (Ln(3+)) between a solution and a coordination polymer (CP) formed by cerium(III) or samarium(III) ion and an organophosphorous ligand has been studied. The CPs exhibit distinctive Ln(3+) affinity that varies with a small change in its framework, depending on the central Ln(3+).

Modeling of power generation from the mixing of simulated saline and freshwater with a reverse electrodialysis system: The effect of monovalent and multivalent ions

A reverse electrodialysis (RED) system utilizes the transport of cations and anions from controlled mixing of saline water (e.g., seawater) and freshwater (e.g., river water) through selective ion exchange membranes for power generation. Sodium chloride alone has been widely used to create power via salinity gradients in lab-scale RED systems. In an effort to simulate realistic salinity conditions in the natural water environment, in this study a new RED model was developed to quantify the power generation with coexisting monovalent and multivalent salt ions. The effects of different flow rate ratios (saline water flow, ØS, over freshwater flow, ØF) and intermembrane distance ratios on power density (amount of power per unit membrane area) were investigated. Our results indicated that magnesium sulfate, sodium sulfate, and magnesium chloride in the feed solutions of the RED system led to a 9–20% lower power density than when sodium chloride was the single ion source, largely because of the higher internal stack resistance of the multivalent ions. Higher power densities could be achieved with higher flow rates in the saline water compartment and shorter intermembrane distances in the freshwater compartment. For example, the power density increased by approximately 11% when the flow rate ratio was 5 compared with 1; similarly, an intermembrane distance ratio of 8 yielded an approximately 85% increase in power density compared with a ratio of 1. The goal of the present work is to advance our understanding of RED systems working in realistic salinity environments.

Low-cost glass fiber composites with enhanced alkali resistance tailored towards concrete reinforcement

Glass fiber reinforced polymer (GFRP) composites were modified through introduction of ion-exchangers in order to enhance their longevity in the alkaline environment of concrete. Glass fiber composites offer a desired balance of performance and cost for replacement of corrosion-prone steel reinforcement in concrete; their rapid deterioration in the alkaline environment of concrete is, however, a major drawback. Ion exchangers are insoluble solids carrying cations (or anions) which can be exchanged with ions of the same sign. Cation exchangers of hydrogen form replace alkali metal cations (e.g., K+ in alkaline solutions diffusing into the polymer matrix) with H+. This exchange of cations neutralizes aggressive alkaline solutions by converting K+ OH− (and Na+ OH−, etc.) into H2O. Fine weak-acid cation exchangers, when introduced as coating on glass fiber composite bars (applied immediately after pultrusion and before curing of polymer matrix) proved to be compatible with the industrial-scale pultrusion process of composite bars without any need to modify the curing process. Thorough laboratory investigations and industrial-scale pultrusion efforts, were undertaken, which successfully demonstrated that introduction of selected ion exchangers into the polymer matrix (or a surface layer of matrix) does not interfere with the pultrusion process, and yields significant gains in the alkali resistance of glass fiber composites. The durability characteristics of glass fiber composite bars modified with weak-acid cation exchanger coating were investigated under two different accelerated aging conditions. The modified composite bars provided desirable durability attributes under these two different accelerated aging effects, including exposure to the alkaline pore solution of concrete and salt solution. The mechanical characteristics of modified glass fiber composite bars (with weak-acid cation exchanger coating) were investigated by conducting compression, flexure, and shear tests. The results indicated that the modification of pultruded bars did not alter their mechanical performance.

Ion-exchange and hydrophobic interactions affecting selectivity for neutral and charged solutes on three structurally similar agglomerated ion-exchange and mixed-mode stationary phases

The nature and extent of mixed-mode retention mechanisms evident for three structurally related, agglomerated, particle-based stationary phases were evaluated. These three agglomerated phases were Thermo Fisher ScientificIon PacAS11-HC – strong anion exchange, Thermo Fisher Scientific IonPac CS10 – strong cation-exchange PS-DVB, and the Thermo Fisher Scientific Acclaim Trinity P1silica-based substrate, which is commercially marketed as a mixed-mode stationary phase. All studied phases can exhibit zwitterionic and hydrophobic properties, which contribute to the retention of charged organic analytes. A systematic approach was devised to investigate the relative ion-exchange capacities and hydrophobicities for each of the three phases, together with the effect of eluent pH upon selectivity, using a specifically selected range of anionic, cationic and neutral aromatic compounds. Investigation of the strong anion-exchange column and the Trinity P1 mixed-mode substrate, in relation to ion-exchange capacity and pH effects, demonstrated similar retention behaviour for both the anionic and ampholytic solutes, as expected from the structurally related phases. Further evaluation revealed that the ion-exchange selectivity of the mixed-mode phase exhibited properties similar to that of the strong anion-exchange column, with secondary cation-exchange selectivity, albeit with medium to high anion-exchange and cation-exchange capacities, allowing selective retention for each of the anionic, cationic and ampholytic solutes. Observed mixed-mode retention upon the examined phases was found to be a sum of anion- and cation-exchange interactions, secondary ion-exchange and hydrophobic interactions, with possible additional hydrogen bonding. Hydrophobic evaluation of the three phases revealed logP values of 0.38–0.48, suggesting low to medium hydrophobicity. These stationary phases were also benchmarked against traditional reversed-phase substrates namely, octadecylsilica YMC-Pac Pro C18 and neutral μPS-DVB resin IonPac NS1-5u, yielding logP values of 0.57 and 0.52, respectively.

Underground water area rehabilitation project in Hungary financed by the Hungarian government to save the environment of the river Sió's using membrane technology

This article is a case study about a real environmental project in Hungary that is financed by the Hungarian Government. The main task of the project is to re-cultivate the area of an old leather factory in the town of Simontornya, including soil exchange and underground water rehabilitation. This article itself mainly gives detailed technological information about the underground water treatment process, but also basic information about the recultivation parts of the whole project. The basic question of the underground water treatment project was how to withdraw 168,000 m3 of highly polluted underground water, remove the very heavily polluted metals and salts (arsenic, boron, chrome, ammonia, nitrate, chloride) and infiltrate the treated water back into the ground, all over a period of 2 years. The solution implemented is an integrated membrane system (NF; RO) including conventional physical and chemical pre-treatment and softening, with a selective ion exchange process for post-treatment. One further key aspect of the technology applied was to minimise the waste created during the whole process.

An innovative integrated system for boron removal from geothermal water using RO process and ion exchange-ultrafiltration hybrid method

In this study, removal of boron from the geothermal water was investigated by an integrated process coupling reverse osmosis (RO) with ion exchange-ultrafiltration hybrid method. Desalination tests were performed by using a mini-pilot scale brackish water reverse osmosis (BWRO) system which was installed at Yenikale Geothermal Heating Center, Izmir. Boron selective chelating ion exchange resin Dowex (XUS 43594.00) with a particle size of 20μm was employed for removal of boron from BWRO permeate of geothermal water. A submerged hollow fiber type ultrafiltration membrane module (ZW-1) was used for filtration. Effect of such process variables as resin concentration in the suspension, flow rates of fresh and saturated ion exchange resins, and flow rate of permeate on the efficiency of the hybrid process for boron removal from RO permeate of geothermal water was studied.

NH3CH3]4[In4SbS9SH]: a novel methylamine-directed indium thioantimonate with Rb+ion-exchange property

The protonated methylamine was successfully used to direct the formation of one novel indium thioantimonate compound, namely, [NH3CH3]4[In4SbS9SH] (1), whose structure features a three-dimensionally microporous framework based on the linkage of a T2 {In4S9SH} cluster and a {SbS3} pyramid. Detailed ion-exchange reactions performed on the sample of 1 demonstrated its high selectivity for Rb+ ion adsorption, as well as the significant role of the pore size directed by the organic amine cation on ion-exchange selectivity. Under the time-dependent Rb+-exchange treatments, compound 1 exhibited framework flexibility, in which the increasing exchange yields accompanied the gradual contraction of its unit cell.

Selectivity of ion exchangers in extracting cesium and rubidium from alkaline solutions

We compare the ion exchange selectivity of phenol-type sorbents based on phenol formaldehyde resins, products of condensation of diatomic phenols with formaldehyde, and crosslinked polymer based on C-phenyl[4]resorcinarene resin, for cesium and rubidium ions. It is shown that phenol formaldehyde sorbents are the ones most selective. The interaction of alkali metal cations with the anion of calix[4]arene is investigated via quantum-chemical modeling. It is shown that the selectivity toward cesium and rubidium ions in ion exchangers of the phenolic type is not due to specific interactions of ions with phenolic groups.

Modification of the radioactive wastewater treatment technology in the Hungarian PWR

This paper describes the results of a joint research program of Budapest University of Technology and Economics and the Paks Nuclear Power Plant to modify the radioactive wastewater treatment technology for the evaporator bottom residue contained in tanks in the NPP. The main characteristics of the modified technology were that we first removed all the long life radioactive isotopes with underwater plasma torch reactor (UPTR), micro and ultrafiltration and a cesium selective ion exchanger stable at pH~12–13. After the separation of precipitated borate crystals, the remaining liquid was released as chemical waste.

Modeling of fixed bed column studies for removal of boron from geothermal water by selective chelating ion exchange resins

The efficiency of boron removal from geothermal water was investigated using boron selective ion exchange resins Diaion CRB 02 and Dowex (XUS 43594.00) in a fixed-bed column. The effect of pH and feed flow rate on boron removal from geothermal water was additionally tested using Dowex (XUS 43594.00) resin. Yoon–Nelson and Thomas models were applied to the experimental data to predict the breakthrough curves and model parameters such as rate constants and breakthrough times. The results showed that the models describe the breakthrough curves quite well compared with the all experimental data. Similarly, the model predictions for qo obtained both by Yoon–Nelson and Thomas models greatly fit with the experimental results for all conditions and for both boron selective ion exchange resins.

From 1D Chain to 3D Framework Uranyl Diphosphonates: Syntheses, Crystal Structures, and Selective Ion Exchange

In this work, we demonstrate a family of new inorganic-organic hybrid uranyl diphosphonates based on 1-hydroxyethylidenediphosphonic acid (H(4)L) linker by using hydrothermal method. These compounds, (Hbpi)[(UO(2))(H(2)O)(HL)]·H(2)O (UP-1), represents 1D structure, (Hbpi)[(UO(2))(H(2)O)(HL)] (UP-2), (H(2)dib)(0.5)[(UO(2))(H(2)O)(HL)] (UP-3), and [(UO(2))(H(2)O)(H(2)L)]·2H(2)O (UP-4) feature 2D architectures, (H(2)bipy){[(UO(2))(H(2)O)](2)[(UO(2))(H(2)O)(2)](L)(2)}·2H(2)O (UP-5), and (H(3)O)(2){[(UO(2))(H(2)O)](3)(L)(2)}·2H(2)O (UP-6) adopt 3D networks (bpi: 1-(biphenyl-4-yl)-1H-imidazole, dib: 1,4-di(1H-imidazol-1-yl)benzene, bipy: 2,2'-bipyridine). Among them, UP-1, UP-2, UP-3, and UP-4 possess the same structural building unit but with different structures. UP-5 and UP-6 feature the same UO(2)/L ratio of 3:2 but a different structural building unit. Photoluminescence studies reveal that UP-5 displays characteristic emissions of uranyl cations. Ion-exchange experiments demonstrate that the H(3)O(+) in UP-6 can be easily and selectively exchanged by monovalent cations including Na(+), K(+), Cs(+), and Ag(+) cations, whereas the framework retains identical as confirmed by single-crystal X-ray diffractions.

CFD analysis of the fluid flow behavior in a reverse electrodialysis stack

Abstract Salinity Gradient Power by Reverse Electrodialysis (SGP-RE) technology allows the production of electricity from the different chemical potentials of two differently concentrated salty solutions flowing in alternate channels suitably separated by selective ion exchange membranes. In SGP-RE, as well as in conventional ElectroDialysis (ED) technology, the process performance dramatically depends on the stack geometry and the internal fluid dynamics conditions: optimizing the system geometry in order to guarantee lower pressure drops (ΔP) and uniform flow rates distribution within the channels is a topic of primary importance. Although literature studies on Computational Fluid Dynamics (CFD) analysis and optimization of spacer-filled channels have been recently increasing in number and range of applications, only a few efforts have been focused on the analysis of the overall performance of the process. In particular, the proper attention should be devoted to verify whether the spacer geometry optimization really represents the main factor affecting the overall process performance. In the present work, realized within the EU-FP7 funded REAPower project, CFD simulations were carried out in order to assess the effects of different parameters on the global process efficiency, such as the choice of spacer material and morphology, and the optimization of feed and blowdown distribution systems. Spacer material and morphology can affect the fluid dynamics inside each channel. In particular, the appropriate choice of net spacer material can influence the slip/no-slip condition of the flow on the spacer wires, thus significantly affecting the channel fluid dynamics in terms of pressure drops. A Unit Cell approach was adopted to investigate the effect of the different choices on the fluid flow along the channel. Also, the possibility of choosing a porous medium to substitute the net spacer was theoretically addressed. Such investigation focused on the porosity and the fiber radius required to respect the process constrains of pressure drops and mechanical stability. On the other hand, the overall pressure drops of a SGP-RE or ED stack can be considered as resulting from different contributions: the pressure drop relevant to the feed distributor, the pressure drop inside the channel, and the pressure drop in the discharging collector. The choice of the optimal stack geometry is, therefore, strongly related to the need of both minimizing each of the above terms and obtaining the most uniform feed streams distribution among the stack channels. In order to investigate such aspects, simulations were performed on a simplified ideal planar stack with either 50 spacer-less or 50 spacer-filled channels. The effect of the distribution/collector channel thickness and geometry on single-channel flow rates and overall pressure drops in the system was analyzed and a significant influence of distributor layout and size on the overall process performance was found.