Electrolyte-free System Research Articles

Stability studies of high-stable water-in-oil model emulsions

ABSTRACTDifferent compositions and emulsification protocols were used to prepare stable water-in-oil (w/o) emulsions. Water, mineral oil, and a mixture of Span 80 and Tween 80 surfactants were combined to form emulsions that can be used as reference for electrolyte-free systems. Here, we have proposed emulsions wherein different properties were evaluated. Electrical conductivity measurements indicated that conductivity increases linearly with increasing surfactant content. The emulsions’ flow curves and viscoelastic behaviors were delineated by rheological measurements. Stability studies by centrifugal testing have shown that smaller the surfactant content, lower the stability, for any used stirring speeds. Furthermore, higher the applied mixing rate to make the emulsion, higher the stability, regardless of the amount of surfactant. Electrical field stability analysis showed, for all systems, that critical electric field (CEF) values were dependent on either surfactant amount and emulsion elastic modulus.

Formic acid electro-catalytic oxidation at high temperature in supporting electrolyte free system: Mechanism study and catalyst stability

Abstract As a potential fuel for proton exchange membrane fuel cell, formic acid (FA) is easily decomposed on palladium (Pd) based catalysts, which are also the most effective and commonly used FA electro-oxidation catalysts in the direct formic acid fuel cell (DFAFC). Here we try to study the interaction between these two reactions in a supporting electrolyte free electrochemical cell. Considering the operation condition in the anode of DFAFC, influence of FA decomposition on FA electro-oxidation is detected and confirmed by mechanistic study. By doping platinum (Pt) into Pd, stability of the FA electro-oxidation can be extremely improved at fuel cell operation temperature.

An electrolyte-free system for ozone generation using heavily boron-doped diamond electrodes

An electrolyte-free system for electrochemical ozone generation was developed using boron-doped diamond (BDD) electrodes as the anode and cathodes in combination with Nafion® N117/H+ as the separating membrane. Trials using BDD with various B/C ratios suggested that heavily boron-doped BDD with sp2 impurities yielded high concentration of ozone. Further experiments by replacement of the feedstock solutions with 0.85M Na2SO4 or 0.85M NaCl resulted in no significant difference, suggesting that the use of pure water as the feedstock is the most appropriate method for ozone production. A high efficiency could be achieved by applying water as a feedstock for the anode and the cathode chambers. In addition, comparison with Pt electrodes confirmed that the excellent structural stability of BDD was the main factor contributing to this success.

Solubility of hydrogen sulfide in aqueous solutions of single strong electrolytes sodium nitrate, ammonium nitrate, and sodium hydroxide at temperatures from 313 to 393 K and total pressures up to 10 MPa

New experimental results for the solubility of hydrogen sulfide in aqueous solutions of the single strong electrolytes sodium nitrate, ammonium nitrate, and sodium hydroxide at temperatures from 313 to 393 K and total pressures up to 10 MPa are reported. As in the strong electrolyte-free system, a second — hydrogen sulfide-rich — liquid phase is observed at high hydrogen sulfide concentrations. A thermodynamic model for describing the phase equilibrium is presented. Calculations are compared with the new experimental data.

Application of an extended DLVO theory for the calculation of the interactions between emulsified oil droplets in alcohol solutions

The stability of diluted emulsions (0.1% v/v) of n-dodecane in 1 M methanol, ethanol or propanol was studied. The effective diameter and zeta potential were determined by dynamic light scattering. The parameters were measured 5, 30, 60, 120 min and after 1 day after preparation of the emulsions by mechanical mixing at 10 000 r.p.m. for 3 min. Calculations of the free energy interactions between dodecane droplets were conducted applying van Oss et al.’s extended DLVO theory, in which acid–base interactions involving electron donor and electron acceptor parameters are also accounted for. For this purpose the interfacial tensions of oil–alcohol solutions were taken from the literature. The acid–base interactions were evaluated considering two variants. In the first we assumed a close-packed monolayer of alcohol molecules on the droplet surface, interacting by hydrogen bonds with water as well with alcohol molecules. In the second variant, it was considered that in these electrolyte-free systems (pH close to neutral) the measured zeta potentials were due to the oriented alcohol dipoles on the droplet surface. This would mean that the slipping plane is very close to the droplet surface. Both variants lead to the same conclusion that in these system the dominant role is played by attractive acid–base interactions, which is much bigger than the equally attractive apolar Lifshitz–van der Waals interaction. Repulsive electrostatic interactions play only a minor role.

Effect of sodium chloride on interactions of fulvic acid and fulvate with montmorillonite

The interaction of montmorillonite and fulvic acid has been studied at various values of pH and 1 : 1 electrolyte concentrations. The fulvic acid was prepared from gallic acid by heterogeneous catalysis. The amounts adsorbed were determined from the decrease in solute concentration. The adsorption of fulvic acid on H-montmorillonite at pH of about 2.8 is higher than that of Na-fulvate on Na-montmorillonite at pH of about 7.5 in electrolyte-free systems. At low pH, a small amount of NaCl (10 or 20 mmol dm −3) had virtually the same effect on interaction as an amount of 200 or 500 mmol dm −3 at alkaline pH. The combined effect of the pH and NaCl was interpreted by calculating the surface charge, the potential, and the interaction energy of montmorillonite and humic substance particles by a simple model including the assumption of two widely different, intrinsic dissociation constants of the fulvic acid.

Electrochemiluminescence in liquid crystals

Electrochemiluminescence (ecl) of rubrene was studied in nematic liquid crystal 4-cyano-4′- n-pentylbiphenyl. A thin-layer cell of indium-tin oxide glass with an electrode distance of 5 μm was fabricated with a treatment for molecular aligning of a twisted nematic display of the liquid crystal. In cyclic voltammetric scans up to ± 100 V, a fairly stable emission was observed in the voltage range over ± 50 V. whereas the molecular alignment of the liquid crystal was induced at a usual voltage around ± 5 V. The generation of ecl at such a high voltage was interpreted in terms of electrohydrodynamic convection which was induced under a high electric field in an electrolyte-free system. Other nematic liquid crystals such as phenylcyclohexanes and phenylpyrimidines were examined using rubrene, tris(2,2′-bipyridine)ruthenium ion and p-(9′-anthryl)- N,N-dimethylaniline, as the ecl molecule, but they gave either less stable than 4-cyano-4′- n-pentylbiphenyl, or no emission.

Effect of electrolyte concentration on the interaction of humic acid and humate with montmorillonite

In the present study we examine the dependence of the interaction of montmorillonite with a brown-coal humic acid on the pH and electrolyte concentration. The effects of these two factors were studied separately. The interaction was always measured by decrease of concentration of humic substances in the solution. The adsorption isotherms of humic acid on H-montmorillonite and of Na-humate on Na-montmorillonite were measured. In the electrolyte-free systems, the isotherms run almost together: a pH difference of about 5 units between the two isotherms did not play an essential role. However, the isotherms measured in the presence of neutral electrolyte were very different at low and at around neutral pH values. At low pH a small amount (10 and 20 mmol dm −3) of NaCl had an extremely large effect on the interaction. At around neutral pH the effect of NaCl was less; a significantly greater NaCl concentration (e.g., 500 mmol dm −3) was needed for the same change in the interaction. The effect of the pH on the interaction can only be evaluated if it is considered along with the effect of the neutral electrolytes. To interpret these effects, the surface charge, potential and the interaction energy of montmorillonite and humic substances were calculated on the basis of a simple model concerning two, mostly different, intrinsic dissociation constants. As a result of these calculations, it is most likely that joint coagulation, i.e., coaggregation, of the components takes place.

A simple Na2SO3 feeding method for KLa measurement in large‐scale fermentors

A simple and convenient method for measuring K(L)a in large-scale fermentors was proposed. This method was based on the measurement of the dissolved oxygen concentration under steady state conditions established by an equivalency of the sulfite ion feed and chemical oxidation rates. This method had the following advantages: It was a steady state method, and so it was not necessary to consider the response lag of a dissolved oxygen probe and the response lag due to gas phase mixing in fermentors. The oxygen content of the effluent gas in this measuring system was nearly the same as that of the sparged air. Therefore, it was possible to use the oxygen partial pressure of the sparged air for the calculation of the driving force of oxygen transfer. The detailed information on the kinetics of sulfite oxidation was not necessary, because the dissolved oxygen concentration in steady state was not influenced by sulfite oxidation rates. The K(L)a measurement was finished in as short a period as 150 s, even in a fermentor with a volume of 10 m(3). Since the amount of Na(2)SO(4) accumulation in the test fermentors was very small because of the quick measurement, the K(L)a values obtained by this method were applicable to the electrolyte-free system. Furthermore, we could discharge the used liquid from the fermentors into a drain without any pretreatment due to the low salt concentration.