Thermodynamic modeling of CO2 solubility in aqueous solutions of NaCl and Na2SO4

A thermodynamic model based on the electrolyte NRTL activity coefficient equation and PC-SAFT equation-of-state is developed for CO₂ solubility in aqueous solutions of NaCl and Na₂SO₄ with temperature up to 473.15 K, pressure up to 150 MPa, and salt concentrations up to saturation. The Henry's constant parameters of CO₂ in H₂O and the characteristic volume parameters for CO₂ required for pressure correction of Henry's constant are identified from fitting the experimental gas solubility of CO₂ in pure water with temperature up to 473.15 K and pressure up to 150 MPa. The NRTL binary parameters for the CO₂-(Na⁺, Cl⁻) pair and the CO₂-(Na⁺, SO₄²⁻) pair are regressed against the experimental VLE data for the CO₂-NaCl-H₂O ternary system up to 373.15 K and 20 MPa and the CO₂-Na₂SO₄-H₂O ternary system up to 433.15 K and 13 MPa, respectively. Model calculations on solubility and heat of solution of CO₂ in pure water and aqueous solutions of NaCl and Na₂SO₄ are compared to the available experimental data of the CO₂-H₂O binary, CO₂-NaCl-H₂O ternary and CO₂-Na₂SO₄-H₂O ternary systems with excellent results.     

Activity coefficients of Na2O in molten NaCl,Na2SO4, and Na2CO3

Measurements of the cell

have been used to determine activity coefficients of Na₂O in molten NaCl, Na₂SO₄ and Na₂CO₃. Extreme negative deviations from Raoult's law were observed (γ < 10^?3). In NaCl and Na₂SO₄, γ is independent of concentration below 1 m/o Na₂O, but in Na₂CO₃, the activity is nearly independent of concentration, probably because the oxide reacts with dissolved O₂ to form superoxide (O^?₂).     

Solubility of Na2SO4, Na2CO3 and their mixture in supercritical water

The solubility of many salts in water decreases dramatically with temperature in the vicinity of the critical point of pure water. Examples of these salts are sulfates of sodium, potassium, lithium and sodium carbonate. These salts are usually produced during supercritical water oxidation (SCWO) and contribute to fouling. The solubility of Na₂CO₃ and Na₂SO₄ has been determined in pure form and in the presence of each other, for the temperature range relevant to SCWO. The experimental procedure was to pass the salt solution through a tube at constant temperature. After a brief initiation period during which no salt sticks to the tube, the salt above the solubility limit deposited on the tube surface. The solution leaving the section was thus at the solubility limit. A rapid decrease in the salt solubility was observed just above the pseudo-critical temperature. For supercritical conditions, the solubility of each salt in the form of a mixture was quite close to the solubility of pure salt. At the highest fluid density considered (480 kg/m³) the presence of Na₂CO₃ reduces the solubility of Na₂SO₄, as might be expected from the “common-ion effect”.     

Effect of the addition of NH4F on anodic behaviors of DSA-type electrodes in H2SO4-(NH4)2SO4 solutions

The effect of NH₄F addition on the high-anodic behaviors of various DSA-type electrodes was investigated in a mixture of sulfuric acid and ammonium sulfate. The pronounced effect of NH₄ addition was observed on DSA-type Ti/RuO₂, Ti/IrO₂?TiO₂ electrodes, but not observed on the other electrodes studied. The close relationship was found between the increment of the electrode potential caused by the NH₄ addition and the quantity of F^? adsorbed on the electrode surface. The effect of NH₄F addition was considered to be resulted from the adsorption of F^? on the electrode surface, and the presence of adsorbed F^? was directly proved.     

Self-organized porous titanium oxide prepared in Na2SO4/NaF electrolytes

The anodic formation of nanoporous TiO₂ on titanium was investigated in Na₂SO₄ electrolytes containing low concentrations of NaF (0.1-1 wt.%). It was found that under optimized electrolyte conditions and extended polarization, a self-organized nanostructure consisting of porous TiO₂ is obtained. The porous structure is arranged in sections of arrays with single pore diameters of typically 100 nm and an average spacing of 150 nm. The pores are open at the top and covered by oxide at the bottom. Compared with earlier work, we show that using a neutral NaF electrolyte significantly thicker porous layers can be obtained than in acidic solutions.     

Anodic oxidation of bismuth in H2SO4 solutions

Anodic charging curves have been measured on polycrystalline Bi in H₂SO₄ solutions (0·01–6·0 N) at 30°C. The effect of various experimental procedures, eg electrode treatment and stirring, has been established. The anodic behaviour of Bi depends markedly on the acid concentration. In the high range, the results indicate dissolution which follows a Tafel relation. However, in dilute solutions, growth of oxide film occurs, and the potential rises rapidly with time, reaching over 100 V at high cds. Sparking and oxide breakdown start at about 150 V. Oxide growth follows the high field ionic conduction. The reciprocal capacitance is linearly related to the logarithm of cd. The constants of the exponential law, the half-barrier width, and the field strength have been calculated The last lies between 1 and 3 × 10⁶ V/cm at 1 mA/cm². The effect of F⁻ and Cl⁻ ions on oxide growth in H₂SO₄ has been also investigated.     

Hot corrosion and protection of Ti2AlC against Na2SO4 salt in air

The hot corrosion behavior of Na₂SO₄-coated Ti₂AlC was investigated by means of thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy/energy dispersive spectroscopy. This carbide displays good hot corrosion resistance below the melting point of Na₂SO₄ while the corrosion attacks become virulent when the salt is molten. A protectively continuous Al₂O₃ layer forms and imparts good corrosion resistance, and consequently, the corrosion kinetics is generally parabolic at 850 °C. However, porous oxide scales fail to protect the Ti₂AlC substrate at 900 and 1000 °C. The segregation of sulfur at the corrosion scale/substrate interface accelerates the corrosion of Ti₂AlC. Furthermore, a convenient and efficient pre-oxidation method is proposed to improve the high-temperature hot corrosion resistance of Ti₂AlC. An Al₂O₃ scale formed during pre-oxidation treatment can remarkably restrain the infiltration of the molten salt into the substrate and prevent the substrate from severe corrosion attacks.     

A study on mechanism of charging/discharging at amorphous manganese oxide electrode in 0.1 M Na2SO4 solution

In the present work, the mechanism of charging/discharging at the amorphous manganese oxide electrode was investigated in 0.1 M Na₂SO₄ solution with respect to amount of hydrates and valence (oxidation) states of manganese using a.c.-impedance spectroscopy, anodic current transient technique and cyclic voltammetry. For this purpose, first the amorphous manganese oxide film was potentiostatically electrodeposited, followed by heat-treatment at 25–400 °C to prepare the electrode specimen with different amounts of hydrates and oxidation states of manganese. For as-electrodeposited electrode with the most hydrates, the anodic current transient clearly exhibited a linear relationship between the logarithm of current density and the logarithm of time, with a slope of −0.5, indicating that the charging/discharging is purely limited by Na⁺/H⁺ ion diffusion. From the analyses of the impedance spectra combined with anodic current transients measured on the hydrated electrode heat-treated at 25–150 °C, it was found that as the amount of hydrates decreases, the depth of cation diffusion in the electrode becomes shallower and the ratio of charge-transfer resistance to diffusion resistance also increases. This suggests that a transition occurs of pure diffusion control to a mixed diffusion and charge-transfer reaction control. For the dehydrated electrode heat-treated at 200–400 °C, the charging/discharging purely proceeds by the charge-transfer reaction. The reversibility of the redox reaction increases with increasing amount of hydrates and oxidation states of manganese, which provides us the higher power density. On the other hand, the pseudocapacitance decreases in value with increasing heat-treatment temperature, thus causing the lower energy density.     

The mechanism of the anodic formation of S2O2−8 ions on a Ti-supported IrO2 electrode in mixed aqueous solutions of H2SO4, (NH4)4SO4 and NH4F

The mechanism for the anodic formation of peroxydisulfate ion on a Ti-supported IrO₂ electrode was investigated in mixed aqueous solutions of H₂SO₄, (NH₄)SO₄ and NH₄F.Peroxydisulfate ion can be formed in higher yield at lower overpotential on the Ti-supported IrO₂ electrode, compared with smooth Pt electrode. The most probable mechanism under Langmuir conditions of intermediate adsorption was proposed as

     

Inactivation of Escherichia coli in Na2SO4 electrolyte using boron-doped diamond anode

Electrochemical disinfection in chloride-free electrolyte has attracted more and more attention due to advantages of no production of disinfection byproducts (DBPs), and boron-doped diamond (BDD) anode with several unique properties has shown great potential in this field. In this study, inactivation of Escherichia coli (E. coli) was investigated in Na₂SO₄ electrolyte using BDD anode. Firstly, disinfection tests were carried on at different current density. The inactivation rate of E. coli and also the concentration of hydroxyl radical (OH) increased with the current density, which indicated the major role of OH in the disinfection process. At 20 mA cm⁻² the energy consumption was the lowest to reach an equal inactivation. Moreover, it was found that inactivation rate of E. coli rose with the increasing Na₂SO₄ concentration and they were inactivated more faster in Na₂SO₄ than in NaH₂PO₄ or NaNO₃ electrolyte even in the presence of OH scavenger, which could be attributed to the oxidants produced in the electrolysis of SO₄²⁻, such as peroxodisulfate (S₂O₈²⁻). And the role of S₂O₈²⁻ was proved in the disinfection experiments. These results demonstrated that, besides hydroxyl radical and its consecutive products, oxidants produced in SO₄²⁻ electrolysis at BDD anode played a role in electrochemical disinfection in Na₂SO₄ electrolyte.     

Electrosorption of tert-butyl compounds on Hg from aqueous Na2SO4 solution: tert-butylamine

The adsorption of tert-butylamine (TBUNH₂) at the Hg/0.5 M aqueous Na₂SO₄ polarized interface has been studied by means of electrocapillary measurements. Adsorption has been found to follow a Frumkin isotherm with interaction parameter corresponding to particle-particle attraction. Adsorption is congruent neither with respect to charge nor with respect to potential, but the model of two capacitors in parallel is much better approached, especially at positive rational potentials. The positive value of the interaction parameter is explained in terms of unfavourable solvent-adsorbate surface interactions, slightly dependent on the electric field. The fundamental adsorption parameter of TBUNH₂ are compared with data previously obtained for TBUOH. The behaviour of TBUNH₂ at the air-solution interface seems to exclude any specific interaction between the Hg surface and NH₂ group; the differences between TBUNH₂ and TBUOH are probably to be related to the different nature of the particle-particle interactions.     

Durability of hydrated portland cement with copper slag addition in NaCl + Na2SO4 medium

The reactivity of hydrated portland cement pastes containing up to a 30% of a Spanish ground copper slag (CuGS) in an aggressive solution (Cl⁻ + SO₄⁼) has been studied in order to evaluate the changes in microstructural and mechanical properties of the composite material. Flexural strength data were related to microstructural parameters, studied by means X-ray diffraction as well as porosity and pore-size distribution analyses.     

用Na2SO4提高牛眼透明质酸回收率的研究

通过NaCl和Na     

Removal of methyl orange dye and Na2SO4 salt from synthetic waste water using reverse osmosis

The efficiency of reverse osmosis (RO) membranes used for treatment of colored water effluents can be affected by the presence of both salt and dyes. Concentration polarization of each of the dye and the salt and the possibility of a dynamic membrane formed by the concentrated dye can affect the performance of the RO membrane. The objective of the current work was to study the effect of varying the Na₂SO₄ salt and methyl orange (MO) dye concentrations on the performance of a spiral wound polyamide membrane. The work also involved the development of a theoretical model based on the solution diffusion (SD) mass transport theory that takes into consideration a pressure dependent dynamic membrane resistance as well as both salt and dye concentration polarizations. Control tests were performed using distilled water, dye/water and salt/water feeds to determine the parameters for the model. The experimental results showed that increasing the dye concentration from 500 to 1000 ppm resulted in a decrease in the salt rejection at all of the operating pressures and for both feed salt concentrations of 5000 and 10,000 ppm. Increasing the salt concentration from 5000 to 10,000 ppm resulted in a slight decrease in the percent dye removal. The model’s results agreed well with these general trends.     

The Au/O2 electrode in 1 M H2SO4

Open circuit dependence of potential on oxygen partial pressure as well as potentiostatic behavior in O₂- and He-saturated solution were determined. Stable hydrogen-oxygen species were formed, but potential-determining reversbility was found only in the potential range from 0·64–0·70 V (nhe). This equilibrium could be reasonably explained by an O₂/H₂O₂ exchange. Oxygen, H₂O₂, or other hydrogen-oxygen species may affect open circuit potentials and potentiostatic behavior, but analysis of data assuming reversibility or quasi-equilibrium kinetic theory may be justified only between 0·64 and 0·70 V.     

Diffusion and electromigration in solid Na2WO4

The differential equation for the case of one-dimensional diffusion/electromigration of silver ions in solid Na₂WO₄ is solved for the case of galvanostatic electrolysis of the cell system Ag/Na₂WO₄/Ag. Galvanostatic pulse measurements and silver ion concentration profile measurements (by microscan analysis) of sectioned electrolyzed Ag/Na₂WO₄/Ag cell arrangements were performed. The theory is not in quantitative accordance with the experiments, the reasons of which are discussed. According to the present study, the diffusion of Ag⁺ in ∝-Na₂ WO₄ (high temperature phase, 589–694°C) can be given by:

     

Electrochemical behaviour of titanium in H2SO4-MnSO4 electrolytes

The corrosion of titanium in H₂SO₄ electrolytes (0.001-1.0 M) at temperatures from ambient to 98 °C has been investigated using steady-state polarization measurements. Four distinct regions of behaviour were identified, namely active corrosion, the active-passive transition, passive region and the dielectric breakdown region. The active corrosion and active-passive transition were characterized by anodic peak current (i_m) and voltage (E_m), which in turn were found to vary with the experimental conditions, i.e., d(log?(im))/dpH=−0.8±0.1 and dE_m/dpH which was −71 mV at 98 °C, −58 mV at 80 °C and −28 mV at 60 °C. The activation energy for titanium corrosion, determined from temperature studies, was found to be 67.7 kJ mol⁻¹ in 0.1 M H₂SO₄ and 56.7 kJ mol⁻¹ in 1.0 M H₂SO₄. The dielectric breakdown voltage (E_d) of the passive TiO₂ film was found to vary depending on how much TiO₂ was present. The inclusion of Mn²⁺ into the H₂SO₄ electrolyte, as is done during the commercial electrodeposition of manganese dioxide, resulted in a decrease in titanium corrosion current, possibly due to Mn²⁺ adsorption limiting electrolyte access to the substrate.     

Pt-Co/C nanoparticles as electrocatalysts for oxygen reduction in H2SO4 and H2SO4/CH3OH electrolytes

The oxygen reduction reaction (ORR) was studied on carbon dispersed Pt and Pt-Co alloyed nanocatalysts with high contents of Co in H₂SO₄ and H₂SO₄/CH₃OH solutions. The characterization techniques considered were transmission electron microscopy (TEM), X-ray diffraction (XRD) and in situ X-ray absorption near edge structure (XANES). The electrochemical activity for the ORR was evaluated from steady state polarization measurements, which were carried out in an ultra thin layer rotating disk electrode. The results showed that with the increase of Co content, the nanoparticle size distributions become sharper and the mean particle diameters become smaller. XRD indicated low degree of alloy formation but significant phase segregation of Co was observed only for Pt-Co/C 1:3 and 1:5 (Pt:Co atomic ratios). The electrochemical measurements indicated that the four-electrons mechanism is mainly followed for the ORR on all materials and the electrocatalytic activities per gram of Pt is higher for the catalysts with higher Co contents. This was explained based on the XANES results which evidenced a decrease of the coverage of oxygenated Pt adsorbates due to the presence of Co. In the methanol-containing electrolyte, the Pt-Co/C 1:5 catalyst showed the highest performance. This was attributed to its low activity for the methanol oxidation due to the smaller probability for presenting three Pt neighboring Pt active sites.     

Fluxing reactions of sulphate and carbonates in cement clinkering. I. Systems CaSO4-K2SO4 and K2SO4-CaCO3

Phase equilibria and thermodynamics have been used to determine compatabilities in the systems CaSO₄-K₂SO₄ and K₂SO₄-CaCO₃. In the CaSO₄-K₂SO₄ system, a polymorphic inversion at 200°C is encountered in K₂Ca₂(SO₄)₃. Thermodynamic calculation of the reciprocal salt system K₂SO₄-CaCO₃-CaSO₄-K₂CO₃ discloses that the join K₂SO₄-CaCO₃ constitutes a stable binary: experiments in flowing CO₂ at 1 bar pressure confirm this. A noteworthy feature of the system is the solid solution of CaCO₃ in K₂SO₄, reaching 20% mol % CaCO₃. The eutectic, located at 880°C and 43 mol % CaCO₃, is attainable without significant decomposition. The possible consequences to clinkering reactions are discussed.     

Electrochemical behavior of LiCoO2 in a saturated aqueous Li2SO4 solution

The electrochemical behavior of a commercial LiCoO₂ with spherical shape in a saturated Li₂SO₄ aqueous solution was investigated with cyclic voltammetry and electrochemical impedance spectroscopy. Three redox couples at E_SCE = 0.87/0.71, 0.95/0.90 and 1.06/1.01 V corresponding to those found at ELi/Li⁺=4.08/3.83, 4.13/4.03 and 4.21/4.14 V in organic electrolyte solutions were observed. The diffusion coefficient of lithium ions is 1.649 × 10⁻¹⁰ cm² s⁻¹, close to the value in organic electrolyte solutions. The results indicate that the intercalation and deintercalation behavior of lithium ions in the Li₂SO₄ solution is similar to that in the organic electrolyte solutions. However, due to the higher ionic conductivity of the aqueous solution, current response and reversibility of redox behavior in the aqueous solution are better than in the organic electrolyte solutions, suggesting that the aqueous solution is favorable for high rate capability. The charge transfer resistance, the exchange current and the capacitance of the double layer vary with the charge voltage during the deintercalation process. At the peak of the oxidation (0.87 V), the charge transfer resistance is the lowest. These fundamental results provide a good base for exploring new safe power sources for large scale energy storage.