Model verification of limiting concentration by electrodialysis of an electrolyte solution

The concentration of LiCl in brine and brine volume are obtained as functions of current density by the method of limiting concentration by electrodialysis. These relationships are used for model calculations of current efficiency, the diffusion, osmotic, and electroosmotic permeability of an MK-40/MA-40 membrane pair, and also salt hydration numbers. These theoretical values of water transport numbers and LiCl hydration numbers are compared with corresponding experimental and literature data. It is shown that the model adequately describes the phenomena of the mass electrotransport occurring in electrodialyzers with noncirculating concentration compartments, and it can be successfully applied in calculating the technological parameters of the process, finding the transport properties of ion-exchange membranes, and determining salt hydration numbers in aqueous electrolyte solutions.     

Numerical study of two-dimensional multi-layer spacer designs for minimum drag and maximum mass transfer

Based on the insights gained from previous published works, a series of multi-layer spacer designs for use in spiral wound membrane modules are proposed and evaluated via computational fluid dynamics simulations. The filament diameter to channel height ratio of traditional cylindrical filaments is reduced from 0.6 to 0.4 and 0.3, and one or two layers of elliptical filaments with various attack angles are introduced in the middle region of the channel. The mass transport equations are solved in conjunction with the momentum and continuity equations for a solute with Schmidt number of 600, and the hydraulic Reynolds number is varied from 50 up to 800. Spacer performance is evaluated via a basic permeate processing cost analysis. The proposed designs did not lower processing costs when operating at hydraulic Reynolds numbers above 200, but showed potential for reducing costs in the steady laminar flow regime, at hydraulic Reynolds numbers equal to or less than 200. Implications for design improvements of spacer meshes, such as extra layers of spacer filaments to direct the bulk flow towards the membrane walls, and changes to the filament profiles to reduce form drag are discussed.     

Influence of multivalent ions on power production from mixing salt and fresh water with a reverse electrodialysis system

Reverse electrodialysis is a membrane-based technique for production of sustainable electricity from controlled mixing of a diluted electrolyte solution (e.g., river water) and a concentrated electrolyte solution (e.g., sea water). Reverse electrodialysis has been investigated with pure sodium chloride solutions. In practice, however, in most cases also other ions are present in both feed solutions. In the present paper, the effect of multivalent ions on the performance of a reverse electrodialysis stack was investigated. Results show that, besides a higher stack resistance in presence of multivalent ions, especially the presence of multivalent ions in the dilute solution has a lowering effect on the stack voltage. This can be explained by an observed transport of these ions from the diluted electrolyte solution to the concentrated electrolyte solution. In order to prevent or hamper this transport against the activity gradient, monovalent-selective membranes can be used. This shows indeed better results with respect to the stack voltage. Therefore, it would be beneficial to use monovalent-selective membranes in reverse electrodialysis, especially in the case of a relatively high content of multivalent ions in the dilute (i.e., in the first stages of the installation where the sodium chloride content in the dilute is still relatively low).     

Current progress in membranes for fuel cells and reverse electrodialysis

The deterioration of the environmental situation has led to the need to restructure the world’s power industry, and clean renewable power sources are coming to the forefront. This review deals with recent advances in the development of promising ion-exchange membrane materials for two types of application that have been intensely developing recently, namely, hydrogen energy and reverse electrodialysis. Special attention is paid to the comparison of two properties of membranes, conductivity and selectivity, that are competing but fundamentally important in both areas. Perfluorinated sulfonic acid membranes now play a dominant role in hydrogen power engineering, as they provide not only high proton conductivity but also chemical stability and low gas permeability. The review also covers other types of membrane materials, including anion exchange membranes, polybenzimidazoles and hybrid membranes containing inorganic nanoparticles that have been actively developed in recent years. The milder operating conditions of membranes in reverse electrodialysis units allow one to use less expensive non-perfluorinated membranes, including grafted ones. It is of note that in devices of this type, the selectivity of membranes to the transfer of oppositely charged ions is a more important parameter.     

Reducing power losses caused by ionic shortcut currents in reverse electrodialysis stacks by a validated model

Both in electrodialysis and in reverse electrodialysis ionic shortcut currents through feed and drain channels cause a considerable loss in efficiency. Model calculations based on an equivalent electric system of a reverse electrodialysis stack reveal that the effect of these salt bridges could be reduced via a proper stack design. The critical parameters which are to be optimized are ρ/r and R/r, where ρ is the lateral resistance along the spacers, R is the resistance of the feed and drain channels between two adjacent cells, and r is the internal resistance of a cell. Because these two parameters are dimensionless, different stacks can be easily compared. The model is validated with two experimental stacks differing in membrane type and spacer thickness, one with large ionic shortcut currents and one where this effect is less. The loss in efficiency decreased from 25 to 5% for a well-designed stack. The loss of efficiency in reverse electrodialysis and in electrodialysis can be reduced with the aid of the design parameters presented in this paper.     

The conjugation of ionic flows in the diffusion layers of electrodialysis systems

Fundamental regularities of the ion interference in diffusion layers of electrodialysis systems are revealed, as well as their effect on the electrical field strength, through which the ionic flows in their turn affect each other.     

Permselectivity between two anions in anion exchange membranes crosslinked with various diamines in electrodialysis

A membranous copolymer crosslinked with divinylbenzene reacted with N,N,N′,N′-tetra-methylethylenediamine, N,N,N′,N′-tetramethyl-1,3-propanediamine, and N,N,N′,N′-tetramethyl-1,6-hexanediamine to prepare highly crosslinked anion exchange membranes. More than 80% of both tertiary amino groups of the diamines reacted with chloromethyl groups of the membrane to form crosslinkage. After formation of the high crosslinkage of the membrane was confirmed with dialysis of a neutral molecule, electrochemical properties of the obtained membranes (mainly, relative transport number between two anions in electrodialysis) were evaluated: nitrate ions to chloride ions, sulfate ions to chloride ions, fluoride ions to chloride ions, and bromide ions to chloride ions. Though larger anions, in general, were difficult to permeate through the membranes due to high crosslinkage, the number of methylene groups of the diamines (which means the increase in hydrophobicity of anion exchange groups) also affected the relative transport number between two anions. The lower the hydration of anions, the higher the relative transport number of the anions through the membranes with the hydrophobic anion exchange groups. © 1996 John Wiley & Sons, Inc.     

Irreversible dissociation of water molecules on the ion-exchange membrane-electrolyte solution interface in electrodialysis

The fluxes of hydrogen ions through the cation-exchange membrane and hydroxyl ions through the anion-exchange membrane in the electrodialysis were measured using the method of selective polarization. The experiments, which were conducted in a wide range of current densities, enabled us to obtain the results of ionic transport different from the literature data and to explain them on the basis of chemical reactions proceeding in the system. It is shown that a decrease in the hydration of ionogenic groups intensifies the ionic fluxes of the medium in the electrodialysis.     

Improved preparative electrochromatography column design

Improved chromatography column fittings were developed for the efficient and reliable application of an electric field to a preparative chromatography column (a process termed electrochromatography). The improved fittings contained electrodes in close proximity to the column packing media and allowed uniform electric fields to be applied. Membranes in the fittings prevented mixing of the electrode and the column eluent buffers. The membranes prevented gases and electrolytic products generated in the electrode chamber from entering the column eluent buffer. An electrode buffer solution was pumped through the electrode chamber to a large external container. The circulation of buffer through the electrode chamber removed the gases and electrolytic products and ensured a uniform electric field by helping to maintain a constant buffer composition. The membranes prevented macromolecules being separated on the column from coming in contact with the electrodes.     

Adsorption and thermodynamic properties of dissymmetric gemini imidazolium surfactants with different spacer length

A series of dissymmetric gemini imidazolium surfactants with different spacer length ([C_mC_sC_nim]Br₂, m + n = 24, m = 12, 14, 16, 18; s = 2, 4, 6) were synthesized and characterized by ¹H NMR and ESI-MS spectroscopy. Their adsorption and thermodynamic properties were investigated by the surface tension and electrical conductivity methods. Consequently, the surface activity parameters (cmc, γ_cmc, π_cmc, pC₂₀, cmc/C₂₀, Γ_max, A_min) and thermodynamic parameters (ΔG_m^θ, ΔH_m^θ, ΔS_m^θ) were obtained. The effects of the dissymmetry (m/n) and the spacer length (s) on the surface activity and micellization process of surfactants have been discussed in detail.     

Application of horizontal staircase electrophoresis in agarose minigels to the random intergenic spacer analysis of clinical samples

The random intergenic spacer analysis is a recently developed technique for the study of microbial populations. The bacterial intergenic spacer (ITS) is located between 16S rRNA and 23S rRNA genes and presents different length and sequence among bacterial species. Therefore, the amplicons can be separated by electrophoresis commonly performed at low voltage during several hours. Although this technique is especially useful for unculturable microorganisms, it has not been applied before to clinical sample analysis. As these samples have a limited number of bacterial species, the size of the gels may be reduced to facilitate their handling and to reduce the running time. To obtain maximum separation among the ITS bands, we analysed in this work different electrophoretical conditions including staircase electrophoresis, a technique based on the application of several voltage steps. The results obtained showed a different behaviour of the electrical resistance during the performance of submarine horizontal and vertical staircase electrophoresis. In the first case the resistance decreased during most of the running time whereas in the second case it increased. Here, we show that the performance of horizontal staircase electrophoresis reduces the running time more than 80% with respect to conventional electrophoresis at low voltages. This procedure was applied to the separation of ITS bands from bacterial DNA present in a tissue from a vocal cord biopsy. The sequencing of these bands allowed their identification. This new procedure may be very useful in the rapid diagnosis of bacteria present in human, animal and plant tissues.     

Investigation of the mass transfer processes during the desalination of water containing phenol and sodium chloride by electrodialysis

Oxidation processes are used in wastewater treatment when conventional processes are not effective due to the presence of recalcitrant organic contaminants, like phenol. However, the presence of ionic compounds associated with organic pollutants may retard the oxidation. In this work the transport of species contained in an aqueous solution of phenol containing sodium chloride was evaluated in an electrodialysis (ED) system. An experimental study was carried out in which the influence of the process variables on the phenol loss and sodium chloride removal was investigated. Experiments were also performed without current, in order to determine the phenol transfer due to diffusion. The phenol and salt concentration variations in the ED compartments were measured over time, using dedicated procedures and an experimental design to determine the global characteristic parameters. A phenomenological approach was used to relate the phenol, salt and water fluxes with the driving forces (concentration and electric potential gradients). Under ED conditions, two contributions were pointed out for the phenol transport, i.e. diffusion and convection, this latter coming from the water flux due to electroosmosis related to the migration of salts. The fitting of the parameters of the transport equations resulted in good agreement with the experimental results over the range of conditions investigated.     

Fluorimetric determination of histamine in wine and cider by using an anion-exchange column-FIA system and factorial design study

A study has been performed of the conditions for the reaction of histamine with o-phthaldehyde in a flow injection analysis system employing three channels, using an anion-exchange column to eliminate sample matrix interferences. Factorial design was used to determine which operational parameters should be included in the optimization and their optimal values were found. The method developed shows good selectivity for histamine determination in alcoholic beverages. A linear response of up to 2.0 mg l⁻¹ was observed and the detection and quantification limits were 30 and 101 μg l⁻¹, respectively. The repeatability, measured by the R.S.D. for 10 replicate injections, was 0.84 and 0.52% for histamine solutions of 0.20 and 2.0 mg l⁻¹, respectively. The recoveries obtained in wine and cider samples were close to 100% and a sample frequency of 24 samples per hour was achieved.     

Design,synthesis, and characterisation of symmetrical bent-core liquid crystalline dimers with diacetylene spacer

Two new symmetrical bent-core liquid crystalline dimers (B-DA4 and B-DA12) bearing diacetylenes spacer and different terminal alkyl chains were successfully synthesised via Sonagashira coupling reaction. The molecular structures of these dimers were confirmed by ¹H nuclear magnetic resonance (NMR), Fourier transform-infrared spectroscopy (FT-IR), Raman spectroscopy, mass spectrometry, and elemental analysis. Their thermal stability and liquid crystalline properties were characterised by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarised light microscopy (PLM), and small-angle X-ray scattering (SAXS). Results showed that the diacetylene group may be thermal polymerised at about 260°C far from thermal decomposition. The dimers exhibited monotropic phase behaviour and typical layered-structure phase with long-range order on a length scale of about 6.3 nm was observed. The results mentioned above offer a promising opportunity to design polydiacetylene nanowires by thermal, UV irradiation, or scanning tunnelling microscope (STM) tip-induced polymerisation.     

Concentration and purification of malate ion from a beverage industry waste water using electrodialysis with homopolar membranes

Recovery of l-malate from a by-product of fermentation industry was investigated in order to decrease its polluting content as well as to ensure a better valorisation. Environmental-friendly process could consist in a first homopolar electrodialysis step to purify and concentrate malate and a subsequent electrodialysis step involving bipolar membranes in order to recover malic acid. The feasibility of the first step was assessed. Purification experiments on a two-compartment pilot device operated batch-wise with different homopolar membranes showed that the non-ionised impurities (sugars, alcohols) were retained better than 96% in the diluate stream and that the colour of the purified stream changed from dark brown to very pale yellow. More than 84% malate could be recovered with current efficiencies better than 90%. An additional purification effect was observed with the retention of a part of citrate, calcium and magnesium ions. The best flux conditions observed (316 g h⁻¹ m⁻²) corresponded to the Neosepta CMX-Sb/AXE 01 arrangement. Moreover, membrane arrangement using a monoselective cation-exchange membrane (Neosepta CMX-S) proved very efficient in removing divalent cations from the purified stream. Concentration was undertaken through a series of ten consecutive batches, allowing a malate concentration of 130 g L⁻¹ (i.e. approximately 2 equiv. L⁻¹) to be reached which complies with criteria for a subsequent bipolar electrodialysis step. According to these results, it was shown that a malate concentration as high as 300 g L⁻¹ could be expected in industrial operating conditions.     

Syntheses and properties of ethoxylated double‐tail trisiloxane surfactants containing a propanetrioxy spacer

A new type of ethoxylated double‐tail trisiloxane surfactants containing a propanetrioxy spacer of the general formula ROCH₂CH(OR)CH₂O(CH₂CH₂O)_xCH₃ [R = Me₃SiOSiMe(CH₂)₃OSiMe₃, x = 8.4, 12.9, 22] has been synthesized. Their structures were characterized by ¹H‐NMR, ¹³C‐NMR and ²⁹Si‐NMR spectroscopy. The critical micelle concentration (CMC) values of these double‐tail trisiloxane surfactants were at the level of 10⁻⁵ mol l⁻¹, and the surface tension values of their aqueous solutions at CMC were in the range of 21‐24.9 mN m⁻¹. Only the double‐tail trisiloxane surfactant with average ethoxy units of 8.4 ( 1P ) possesseda good spreading ability (SA) value. Its SA values of aqueous solutions (5.0 × 10⁻³ mol l⁻¹) on parafilm and Ficus microcarpa leaf surfaces were more than 15 (within 10 min) and 13 (within 3 min), respectively. The trisiloxane surfactant 1P was also found to have the strongest hydrolysis resistant ability among all of the double‐tail trisiloxane surfactants prepared. Its aqueous solutions were stable for 130 days in an acidic environment (pH 4.0) and 59 days in an alkaline environment (pH 10.0) with surface tension values less than 23 mN m⁻¹. It is suggested that this surfactant can be used as a wetting agent or spreading agent in certain extreme pH environments. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel polyimides bearing a side chain composed of stilbene mesogen and undecyl spacer and the alignment ability of nematic liquid-crystal molecules

Four different polyimides with side chains containing undecyl spacers and 4-fluorostilbene mesogen end groups were prepared, and their structures and the controllability of the liquid-crystal (LC) alignment with rubbing were investigated. From X-ray scattering and differential scanning calorimetry data, pyromellitic dianhydride (PMDA)-, benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA)-, and 4,4′-oxydi(phthalic anhydride) (ODPA)-based polyimides were shown to have layered structures and short-range ordering. Pretilt angles of LCs on the rubbed surfaces were 1–9°, depending on the rubbing density and backbone. In particular, the long undecyl spacers caused the mesogenic stilbene end groups to lie next to the main chain, resulting in a reduction in the pretilt angles. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1800–1809, 2001     

Liquid crystalline non-linear S-shaped oligomers consisting of azobenzene and biphenylene units: synthesis,characterisation and influence of central spacer

A series of non-linear S-shaped liquid crystal oligomers wherein the molecule consists of biphenylene moiety as a central core unit and two symmetrical side arms azobenzene moieties joined to catechol as a linkage group have been successfully synthesised and characterised. The members in this series possess different inner spacer with carbon number n ranging from 4 to 9 while the outer spacer length located in azobenzene moieties are remains unaltered. The members with even parity exhibit monotropic phase, whereas homologues with odd parity display enantiotropic phase. The appearance of nematic, smectic A and smectic B phases was validated with texture observation under polarised light and X-ray diffraction (XRD). The XRD study on the S-shaped oligomer indicates that the arrangement of smectic phase exists as an intercalated structure. The S-shaped oligomer shows photoisomerisation properties in solution whereby the trans to cis isomerisation for this molecule is accomplished 1140 s, whereas reverse process under thermal back reaction occurred in 4620 min.     

Synthesis and characterization of novel ferroelectric liquid crystal polysiloxane containing undecanoyloxy spacer (I)

A novel side-chain liquid crystal polysiloxane and its corresponding monomer were synthesized by the standard method. We ensured their structures were as expected and their purities were high by ¹H nuclear magnetic resonance and infrared measurements. They were studied by differential scanning calorimetry (DSC) for their thermal analysis and polarizing optical microscopy (POM) with hot stage for their textures and transition temperatures. The results showed good liquid crystal properties and low transition temperatures of the mesophase. X-ray diffractions were done to research their layer structure and SmA and SmC^* phases were assured, in good agreement with the results of the POM and DSC measurements. The optical rotation degree was also measured.     

Rational design of platinum-group-metal-free electrocatalysts for oxygen reduction reaction

Platinum-group-metal (PGM)-free materials have been promised as potential replacement for Pt as the cathodic catalyst in proton exchange membrane fuel cells. Critical design criteria of the PGM-free catalyst reside on the high active site density to compensate its generally lower turn-over frequency and improved mass-charge transfers during the electrocatalysis. This short review summarizes the research activities in recent years from our team at Argonne National Laboratory in preparing highly active oxygen reduction reaction (ORR) catalysts using rationally designed porous organic precursors, as reported in the First Telluride Science Research Center (TSRC) Workshop on PGM-free Electrocatalysis in 2019. More recent studies by others are also discussed.