Conventional Aqueous Media Research Articles

Real-Time Monitoring for Electrochemical Analysis in Molten LiCl-KCl Eutectic Salt

Molten salts are one of the promising alternative classes of new materials for electrochemical processing. They have high chemical stability and offer much wider electrochemical window than conventional aqueous media. This enables various electrochemical reactions to be conducted without decomposing background media. In addition, the high operation temperature of molten salt boosts the mass transfer of reactant of electrochemical reaction, so that the processing time is shortened. Owing to such advantages, the molten salt media have intensively dealt with the electrowinning of metal and electrochemical separation processes. However, knowing the chemical behavior of electrodes during such processes is crucial to understanding the mechanism of electrochemical reactions that occur during the process. One of the most powerful methods of examining the system is to monitor the visual status of electrodes in real time while the electrochemical process is running. However, due to some practical limitations, it has rarely been applied to the molten salt electrochemical system.In the present work, the real-time monitoring system for molten LiCl-KCl eutectic salt medium is set up. Instead of an optically opaque ceramic crucible, a cylindrical quartz tube is chosen for the electrochemical cell of our experimental system. With four optically accessible quartz windows mounted on the electrical furnace, a commercially available CMOS camera can be installed externally to monitor the molten salt system without any special modifications.Real-time monitoring was carried out to investigate the electrode behavior in various electrochemical systems. First, the deposition behavior of cobalt in molten CoCl2-LiCl-KCl system (1wt% CoCl2) is compared on a tungsten working electrode. As shown in Figure 1, there is a clear morphological structural difference in the cobalt deposit between the galvanostatic and the potentiostatic electrodeposition. While the metallic cobalt was deposited evenly on the surface of the working electrode by galvanostatic electrodeposition, rapid growth of the dendritic structure was observed using the potentiostatic electrodeposition. This suggests that the structural properties of deposits can vary significantly due to the nature of the electrodeposition methods.In electrochemical experiments in molten salt system that do not produce solid phase products, it is difficult to elaborately understand the behavior of chemical species during the experiment. However, real-time monitoring enables noteworthy observation from these experiments. During the galvanostatic lithium reduction in the molten LiCl-KCl system, the liquefied metallic lithium formed the oval bulge on the surface of the tungsten working electrode. At the same time, the unknown indigo-colored flow was observed on the surface of the deposited metallic lithium. The clear mechanism remains to be explored, but it appears to be related to the re-oxidization of metallic lithium to Li(I) ions. In the molten ZrCl4-LiCl-KCl system (1wt% ZrCl4) with tungsten working electrode, the reduction of Zr(IV) ions to Zr(III) ions during the potentiostatic electroreduction was visualized and identified by the formation of brown-colored flow near the surface of the working electrode. This confirms the result of our previous work and suggests that Zr(IV) is reduced to Zr(III) with a brown color in the first step of CV [1].Furthermore, with the video signal from the CMOS camera to the PC that controls the potentiostat, the visual changes can be synced with the measured current or potential during the experiment. This enables us to compare the visualized morphological properties on the surface of the working electrode under different applied potential conditions during the CV experiment (Figure 2).[1] H. L. Cha, J.-I. Yun, Electrochem. Commun. 84, 86 (2017) Figure 1

Single step peroxidase extraction and oxidation of highly concentrated ethanol and phenol aqueous solutions using supercritical carbon dioxide

Extraction of peroxidase from raw vegetables using supercritical carbon dioxide (scCO2) and its simultaneous application for oxidation of organics in wastewater in the presence of hydrogen peroxide has been demonstrated. Ethanol and phenol were used as the model organic contaminants and potato and cabbage were employed as the sources of peroxidase. The extractions were carried out at 10MPa for 2h over a temperature range of 25°C to 60°C. Oxidation of ethanol increased by 330% when the treatment was carried out in the scCO2 medium compared to conventional aqueous medium when cabbage was employed, while use of potato as the enzyme source resulted in an increase of 85%. In the case of phenol, scCO2 exhibited a huge increase of 400% in presence of cabbage and 140% in presence of potato. Comparison of vegetable extracts with commercial horseradish peroxidase indicated the feasibility, importance and advantage of employing vegetables as a peroxidase source. This work presents the simultaneous extraction of enzymes and its application for oxidation of organics and opens up new opportunities for recovery of resources from unwanted/discarded plant materials and their use for environmental remediation in a single step.

Dyeing Procedures of Polyester Fiber in Supercritical Carbon Dioxide Using a Special Dyeing Frame

Supercritical CO2 fluid dyeing, a new type of anhydrous dyeing technology, has the advantage of high uptake rate, short dyeing process, recycling of dyes and CO2, and zero discharge. This study investigated a dyeing technique of loose fibers using supercritical CO2 as solvent to replace water. Based on the existing characteristics of the self-developed supercritical CO2 dyeing equipment, a special dyeing frame of loose fibers was designed. Using the dyeing frame and inner and outer dyeing processes, polyester fibers were dyed with disperse red 153# maternal dyes at temperatures of 80–140?, pressures of 17–29MPa and time of 20–80min, respectively. The experimental results revealed that the dyeing performance of fibers was good on the dyeing frame, as well as with a favorably increased temperature, pressure and time. Dyeing temperature had a strong influence on the color yield. The dyeing results were compared with those of polyester fibers dyed with disperse red 153# dyes. With the special dyeing frame of loose fibers, color fastness to washing and artificial light was generally similar to conventional aqueous medium methods.

Voltammetric Study on the Behaviour of Refractory Metals in ((BMP)(TFSA)) Ionic Liquid.

Electrochemical studies of tantalum fluoride and zirconium fluoride in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([BMP][TFSA]) ionic liquid were carried out in presence of lithium fluoride using cyclic voltammetry technique. The electrochemical behaviour of Ta(V) and Zr(IV) on gold and platinum substrates was investigated in the temperature range from R.T. to 200 °C at different values of scan rate and different potential windows. Special attention was paid to the mechanism of cathodic reduction. Cyclic voltammetries exhibit well-defined peaks attributed to the formation of metallic deposits on the substrates. The knowledge of electrode and chemical reactions based on the experimental results of the refractory metals considered allow us to propose a possible reaction path for the oxidation/reduction processes. The mechanisms of electrochemical reduction of Tantalum(V) depends strongly on the composition of the bath; using TaF5 as metal salt, two cathodic peaks due to Ta(V)/Ta(III) and Ta(III)/Ta reduction were observed. The cyclic voltammograms recorded at different values of scan rate have shown that the Ta(III)/Ta reduction process is mainly controlled by diffusion of the electroactive species to the electrode surface. It has been proposed that the mechanism for reduction of zirconium ions occurs in a one step process exchanging four electrons and controlled by the zirconium ions diffusion in the ionic liquid. The electrochemistry of refractory metals (IVB, VB and VIB groups) has been widely studied in molten salts to optimize the cathodic deposition process of these metals. Due to their properties, such as high strength and high corrosion resistance, refractory metals are widely used in electronics, optics, sensors, automotive, nuclear and aerospace industries. Conventional aqueous media cannot be always used as electrolytes due to the narrow electrochemical windows, low thermal stability and evaporation (Simka et al., 2009). The mechanism of the electrodeposition of refractory metals is not yet fully elucidated. Senderoff and Mellors (1966) developed a general process for the electrodeposition of eight of the nine refractory metals of groups IVB, VB and VIB as dense coherent deposits by using a solution of the refractory metal in a molten alkali-fluoride eutectic mixture from 680 °C to 800 °C. They concluded that an irreversible metal-producing step is a necessary (though not sufficient) condition for the deposition of coherent deposits from molten salts. The mechanical properties of refractory metals, such as the excellent corrosion resistance and the nuclear properties of some, make them particular interesting as coatings. Inman and White (1978) have summarized in a review the electrochemistry of refractory metals in molten salts electrolytes. The authors have reported that the recovery of a primary metal is ensured by using, as solvent, a melt having a much larger decomposition voltage than that of the solute and an inert cathode; controlling the electrodeposition of metal by rate processes other than mass transfer, will lead to coherent deposits. Few years later, Girginov et al. (1995) have presented a selective review of the anodic and cathodic processes of Ti, Zr, Nb and Ta from molten salts-based electrolytes in order to investigate the optimization of cathodic deposition of these metals highlighting that the two main types of electrolyte employed in the electrodeposition of refractory metals were chloride and fluoride based. The Ta(V) reduction has been studied in a wide range of melts, such as chlorine or fluorine melts. In FLINAK-K2TaF7 DOI: 10.3303/CET1441017

Catalytic effect of CTAB reverse micelles on the kinetics of dissociation of bis(2,4,6–tripyridyl-s-triazine) iron(II)

The kinetics of dissociation of bis(2,4,6–tripyridyl-s-triazine) iron(II), ([Fe(TPTZ)2]2+) has been studied in CTAB/chloroform/hexane reverse micellar medium. In the absence of acid, the reaction is immeasurably slow and does not go to completion in conventional aqueous medium but is markedly accelerated and takes place with a rate constant equal to 55.3 × 10−3 s−1 and goes to completion in reverse micelles. The significant increase in rate is attributed to the special properties of the water pool in the reverse micelles like low dielectric constant, nucleophilic effect of Br- ion, and favorable partitioning of TPTZ in the organic phase. The rate of the reaction decreases with increase in W (=[H2O]/[CTAB]) at constant CTAB concentration and remains constant with increase in CTAB at fixed W. The results are compared with other closely related systems.

Export of intracellular Monascus pigments by two-stage microbial fermentation in nonionic surfactant micelle aqueous solution

Microbial fermentation of intracellular product is usually limited by high intracellular product concentration inhibition and complex downstream product processing. Perstractive fermentation of intracellular Monascus pigments in the nonionic surfactant Triton X-100 aqueous solution was studied in the present work, in which the intracellular product was exported from the intracellular to the extracellular aqueous solution and consecutively extracted into the nonionic surfactant micelles. After the second stage perstractive fermentation in the two-stage operation mode, biomass increased from 5 to 24g/l DCW. The corresponding extracellular concentrations of yellow, orange, and red pigments were 60, 49 and 26AU. The increase of cell density and the final pigment concentration were difficult to occur in a conventional aqueous medium using the two-stage fermentation. This positive effect of perstractive fermentation was ascribed to low intracellular pigment density, which eliminated the product inhibition and prevented the product from further degradation. The high efficiency of perstractive fermentation was further confirmed by fed-batch operation mode, in which the final biomass reached 28g/l DCW and the corresponding extracellular concentrations of yellow, orange, and red pigments were 130, 84 and 47AU.

Exploring the large voltage range of carbon/carbon supercapacitors in aqueous lithium sulfate electrolyte

This study investigates the large voltage range of symmetric carbon/carbon capacitors in environmentally friendly aqueous lithium sulfate electrolyte. A high over-potential related to the hydrogen sorption mechanism at the negative electrode contributes usefully to enhance the operating voltage up to 1.9 V with an excellent stability during 10 000 charge/discharge cycles. Such a voltage value is two times higher than the values generally demonstrated with symmetric carbon/carbon capacitors in conventional aqueous media, while avoiding the disadvantages of the corrosive properties of acidic and basic electrolytes. Temperature programmed desorption analysis of the electrodes after long-term cycling gives the evidence that the maximum voltage is essentially limited by an irreversible electro-oxidation process at the positive electrode. If the potential of the positive electrode goes beyond a given value during cell operation, a massive electro-oxidation of carbon leads to a further deleterious increase of the maximum potential of the electrode and an increase of electrode resistance resulting in a decrease of capacitance. Inconvenience can be sidestepped by performing a controlled chemical oxidation of the carbon surface using hydrogen peroxide. As a consequence, the maximum potential of the electrode remains stable during operation of the cell at 1.9 V, and the system can be charged/discharged during 10 000 cycles with very moderate loss of capacitance or increase of resistance.

Kinetics of oxidation of iodide by vanadium (V): Catalysis by the water pools of CTAB reverse micelles

The kinetic study of the oxidation of iodide ion by V(V) has been carried out in the water pools of cetyl trimethyl ammonium bromide(CTAB) reverse micelles in a mixture of chloroform-hexane (3 : 2). The study of the effect of concentration of V(V) and I− on rate show that the reaction obeys first order kinetics with each of the reactants. A plot of k′ (pseudo first order rate constant) versus [H+] is linear with a positive intercept at constant concentrations of iodide and bromide. The rate of the reaction is markedly increased in the reverse micellar medium compared to conventional aqueous medium under identical conditions. The pronounced acceleration in reverse micelles has been accounted for by the concentration effect in the water pool which have an effect on kinetics.

Preparation of SAPO-5 and Its Catalytic Synthesis of p-Aminophenol

Abstract Silicoaluminophosphate molecular sieves (SAPO-5) were synthesized by hydrothermal crystallization using both a conventional aqueous medium and a HF medium. The SAPO-5 samples were characterized by X-ray diffraction, scanning electron microscopy, solid state NMR, Fourier transform infrared reflectance spectroscopy, and temperature-programmed desorption of adsorbed NH3. The effect of Si content and presence of HF in the initial gel on the structure of the SAPO-5 synthesized and the manner of Si incorporation into the framework were investigated. Their acidity and catalytic activity for phenylhydroxylamine (PHA) rearrangement in the synthesis of p-aminophenol (PAP) from nitrobenzene were studied. The incorporation of Si in the samples prepared in the presence of HF was mainly by the SM3 mechanism and patches of Si(4Si) were predominant. This resulted in a decrease in the acid amount and increase in acid strength. The presence of HF during synthesis increased the integrity of the SAPO-5 crystal and helped incorporate more Si in the SAPO-5 structure by inhibiting the polymerization of Si species to a reticulated silica gel. The samples prepared in the HF medium exhibited better catalytic performance for PHA rearrangement in the synthesis of PAP, and a PAP yield of 53.2% could be obtained.

Characterization and hydroisomerization performance of SAPO-11 molecular sieves synthesized in different media

Abstract Silicoaluminophosphates SAPO-11 molecular sieves were synthesized from a conventional aqueous medium, a two-liquid phase medium and a HF medium, respectively, and were characterized by various methods such as XRD, SEM, pyridine-FT-IR, NH 3 -TPD, 29 Si MAS-NMR. The morphologies of the SAPO-11 molecular sieves obtained from the conventional aqueous medium and the two liquid-phase media exhibit pseudo-spherical aggregates ranging from 7 to 10 μm assembled from cubic plate microcrystallites, whereas the SAPO-11 molecular sieves synthesized from the HF medium exhibit hexagonal prismatic aggregates of about 1–3 μm length. The synthesis media used highly influenced the number and the strength of SAPO-11 acid sites. Compared to SAPO-11 obtained from conventional aqueous medium, SAPO-11 prepared from two-liquid phase media possessed a similar number of BrOnsted acid sites but a much larger number of Lewis acid sites, whereas the SAPO-11 synthesized from HF medium had a similar number of Lewis acid sites but a much lower number of BrOnsted acid sites. The 29 Si MAS-NMR spectra showed that the HF could change the manner of Si incorporation into the SAPO-11 framework. The hydroisomerization of n -hexadecane on Pt/SAPO-11 samples showed that Pt/SAPO-11 obtained from the two-liquid phase media had the largest yield of isomers. The conversion activity of n- hexadecane was dependent on the amount of BrOnsted acid of SAPO-11 molecular sieves, while its hydrocracking activity was related to the strong acid sites of SAPO-11.

Noble metal catalysed aerial oxidation of alcohols to aldehydes in supercritical carbon dioxide

Platinum and palladium supported on carbons are shown to be excellent catalysts for selective oxidation of organic alcohols to aldehydes (>99%) at high yields using dioxygen as an oxidant in supercritical CO2 fluid medium. There is no detectable over-oxidation of the product to acid and no metal leaching that are commonly encountered in the conventional aqueous medium. It is also found that the hydrophobicity/hydrophilicity of the catalyst surface relative to the CO2 solvent plays a crucial role in the resulting catalytic activity and stability. Adding 1% Teflon onto the noble metal–carbon catalysts dramatically enhances the activity and lifetime of the catalysts during the aerial oxidation of fine chemicals in scCO2 fluid.

Continuous enzymatic production of peptide precursor in aqueous/organic biphasic medium

N-(benzyloxycarbonyl)-L-aspartic acid (Z-L-Asp) has generally been used as a carboxyl substrate for the enzymatic synthesis of a precursor of aspartame (synthetic sweetener); however, alternative inexpensive protection groups have been in demand for lowering the total cost of its industrial-scale production. A formyl group (F-) was found to be a more desirable protecting group for the N-terminus of amino acid derivatives due to its low cost of preparation, introduction, and removal. The yield of F-AspPheOMe (N-formyl-L-aspartyl-L-phe- nylalanine methylester), however, was found to be <10% in a conventional aqueous medium. We found that F-L-Asp and L-PheOMe were partitioned mainly to the aqueous phase in an aqueous/organic biphasic medium, whereas F-AspPheOMe partitioned to the organic phase, especially when some extracting agents were added. In this study, simultaneous operation of an enzymatic reaction and a product separation by liquid–liquid extraction was thus applied to the F-AspPheOMe synthesis. We succeeded in synthesizing F-AspPheOMe continuously in an aqueous/tributylphosphate (TBP) biphasic medium with >95% yield, which was about tenfold higher than that in an aqueous monophasic medium. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 69: 57–65, 2000.

Continuous enzymatic production of peptide precursor in aqueous/organic biphasic medium

N-(benzyloxycarbonyl)-L-aspartic acid (Z-L-Asp) has generally been used as a carboxyl substrate for the enzymatic synthesis of a precursor of aspartame (synthetic sweetener); however, alternative inexpensive protection groups have been in demand for lowering the total cost of its industrial-scale production. A formyl group (F-) was found to be a more desirable protecting group for the N-terminus of amino acid derivatives due to its low cost of preparation, introduction, and removal. The yield of F-AspPheOMe (N-formyl-L-aspartyl-L-phe- nylalanine methylester), however, was found to be <10% in a conventional aqueous medium. We found that F-L-Asp and L-PheOMe were partitioned mainly to the aqueous phase in an aqueous/organic biphasic medium, whereas F-AspPheOMe partitioned to the organic phase, especially when some extracting agents were added. In this study, simultaneous operation of an enzymatic reaction and a product separation by liquid-liquid extraction was thus applied to the F-AspPheOMe synthesis. We succeeded in synthesizing F-AspPheOMe continuously in an aqueous/tributylphosphate (TBP) biphasic medium with >95% yield, which was about tenfold higher than that in an aqueous monophasic medium.

Abnormal mineral composition of osteogenesis imperfecta bone as determined by electron probe X-ray microanalysis on conventional and cryosections.

Osteogenesis imperfecta (OI) is a genetic disorder of the connective tissue characterized by frequent bone fractures. The cause of bone fragility is still unknown even though substantial work on collagen has been done. We measured the calcium to phosphorus ratio (Ca/P) of bone mineral from 35 OI bone samples and 25 age- and site-matched control specimens, using electron probe X-ray microanalysis in the transmission electron microscope. Ultra-thin cryosections and conventionally prepared resin sections were used. Cryo-ultramicrotomy avoids any possible artifactual demineralization that may occur in conventional aqueous media. The Ca/P ratio obtained by these two methods was compared and there was no statistical difference between them. The results were differentiated according to the clinical types of OI for the first time. The Ca/P ratio of OI bone mineral was lower than normal in both resin and cryosections, and mirrored the severity of the disease. OI type II had the lowest ratio (Ca/P = 1.49) compared with normal age- and site-matched controls (Ca/P = 1.69). This abnormal mineral composition in OI type II could be a contributory factor to bone fragility in OI bone.

Effects of organised media on the generation of volatile species for atomic spectrometry

The use of surfactant-based organised assemblies, such as micelles and vesicles, to improve the characteristics of room temperature chemical generation of volatile species of metals and semi-metals (e.g. hydride generation, cold mercury vapour or alkylcompound generation), as a means to further enhance sample introduction efficiency/kinetics for atomic techniques, is reviewed. The complex influence of different organised media (including cationic, anionic, non-ionic and zwitter-ionic micelles and cationic and anionic vesicles) on the hydride generation of the elements As, Pb and Cd and on Hg 0 cold vapour generation have been revised and compared with organised media effects on alkylmetals generation of Se, Pb, Cd and Sn. Enhancements in efficiency/transport of volatile species formed in the surfactant-based media, increases in the reaction kinetics, stabilization of some room temperature unstable species and also changes in the observed selectivity of reactions taking place in conventional aqueous media are some of the discussed effects. Possible mechanisms and analytical potential and usefulness of this enhancement by surfactants of the generation of volatile species for atomic detection methodologies are summarized and illustrated with the determination of low levels of arsenic, lead, cadmium, tin, selenium and mercury.

Kinetic analysis of enzymes in situ determined with a real-time image analysis system.

Department of Anatomy and Physiology, University of Dundee Peter J. Stoward Many enzymes diffuse out of sections of unfixed tissue when they are incubated in conventional aqueous media. This invalidates their quantitative assay by microdensitometry. The quantitative effectiveness of three methods for overcoming this problem are reviewed. The methods utilise semipermeable membranes, polyvinyl alcohol-containing media, and agarose gel films. Unfortunately, most applications of these techniques reported to date have given data that do not meet criteria of validity. A new approach based on the gel film technique for the kinetic analysis of a soluble enzyme in situ by computer-assisted image analysis is described in detail.

Alterations to the catalytic properties of polyphenoloxidase in detergentless microemulsions and ternary water-organic solvent mixtures

The catalytic properties of mushroom polyphenoloxidase could be substantially altered by entrapment into hexane- and toluene-based microemulsions stabilized with isopropanol. The fast irreversible inactivation and drastic substrate inhibition of the enzyme were significantly reduced in detergentless microemulsions in comparison to conventional aqueous media. Similar changes in the catalytic behavior of polyphenoloxidase were observed in the normal ternary solutions of hexane-(toluene)-isopropanol-water, and in the H-bonded aggregates of isopropanol and water in toluene, but not in hexane.

Kinetics of the oxidation of iodide by persulphate in AOT–oil–water microemulsions

The oxidation of iodide by persulphate has been studied in different sodium bis-2-ethylhexylsulphosuccinate (aerosol-OT or AOT)–oil–water microemulsions at 298 K. The rate of this reaction is appreciably higher in a microemulsion than when it takes place in a conventional aqueous medium. The dependence of the rate constant on the surfactant concentration as well as on the molar ratio R(=[H2O]/[AOT]) has been examined. The results are interpreted on the basis of the anionic nature of the reactants and the surfactant itself, and the high concentrations of sodium cations inside the aqueous cores. The dependence of the rate constant on the nature of the organic phase present in the system has also been investigated.

Development of a supported molten-salt Wacker catalyst for the oxidation of ethylene to acetaldehyde

A modified supported molten-salt Wacker catalyst involving palladium chloride/copper chloride is developed by replacing the conventional aqueous reaction medium (H 2O + HCl) with a eutectic melt of cuprous chloride and potassium chloride and supporting it on a porous support. Experimental studies for the oxidation of ethylene to acetaldehyde over the supported molten-salt catalyst (SMSC) show the kinetics to be similar to the aqueous-phase Wacker process and the SMSC diffusion-reaction characteristics to be well predicted by the theoretical model of R. Datta and R. G. Rinker ( J. Catal. 95, 181 (1985)). The SMS catalyst was found to be extremely stable owing to the essentially nonvolatile nature of the molten salt whereas the aqueous-phase supported liquid-phase catalyst deactivated rapidly due to the evaporation of the solvent. The developed supported molten-salt catalyst appears to have substantial advantages over the commen⌝cal liquid-phase Wacker process. Further, the SMSC technique utilized here should prove to be useful in developing efficient catalysts for many other processes.

Advantages of floating lipiodol as a further testfor voiding efficiency

Summary A further radiographic method forthe determination of voiding efficiency was tested. The findings suggested that to increase the sensitivity of any standardized cystogram the addition of floating Lipiodol may provide: (1) a more delicate evaluation of borderline vesical detrusor function in the pediatric patient who cannot void on command, as determined by the presence or absence of floating Lipiodol within the urinary tract after 24 hours; (2) superiority over the conventional aqueous contrast medium for the radiographic determination of residual urine; (3) a diagnostic aid in the determination of the segment of the urinary tract which retains urine; and (4) the elimination of repeated traumatic catheterizations, especially in children. This additional cystographic technique has proved most valuable in the field of pediatric urology.