Kinetics of oxygen absorption in aqueous sodium dithionite solutions

The absorption and reaction of oxygen in aqueous alkaline solutions of sodium dithionite has been experimentally investigated in a novel gas-liquid contactor. The novel gas-lift bubble column contactor was used to study the kinetics over wide ranges of reactant concentrations, temperature, and pH. The oxygen-sodium dithionite reaction was found to be first-order with respect to dithionite in the range of dithionite concentration < 0.1 M, and second-order in the range of dithionite concentration > 0.1 M. The reaction with respect to oxygen was found to be zero-order for all dithionite concentrations. These results and experimental investigations of the effect of solution alkalinity and temperature on the reaction rate are consistent with previous findings obtained in different gas-liquid contactors. The results thus confirm the feasibility of using the gas-lift bubble column for the kinetics of gas-liquid reactions.     

Absorption of oxygen by aqueous sodium sulphite solutions

New data have been reported on the absorption of oxygen by aqueous sodium sulphite solutions with cobalt sulphate as catalyst at 30°C. It is observed that the absorption rate increases up to a critical sulphite concentration beyond which the absorption rate becomes constant and this critical concentration varies with the catalyst concentration. The order of reaction with respect to sulphite and oxygen in the constant absorption rate regime was found to be zero and two respectively. The absorption rate is affected by the total ionic strength (sulphite and sulphate) in addition to the effect of pH and catalyst concentraion. The reported data were also analysed to ascertain the effect of temperature and a relationship has been proposed for prediction of the second order reaction rate constant.     

The oxidation of aqueous sodium sulphite solutions

In this paper new experimental work on the kinetics of the absorption of oxygen in an aqueous solution of sodium sulphite with cobaltous sulphate as a catalyst, has been presented and compared with already published data. It is shown that the reaction of oxygen with sodium sulphite is zero order in sulphite, first order in cobalt and second order in oxygen for 2 × 10⁴ N/m² <p_O2 < 10⁵ N/m², 150°C <T < 60°C, 3 × 10^?6 kmol/m³ <c_Co⁺⁺ < 3 × 10^?3 kmol/m 7.50 < pH < 8.50 and 0.4 kmol/m² <c_SO2-- < 0.8 kmol/m³. The reaction rate constant can be varied by more than two decades by changing the cobalt concentration, pH and temperature.The specific interfacial areas, a, and mass transfer coefficients, k_L, measured by DeWaal and Beek [14, 15] using an incorrect kinetic model of this reaction, are reinterpreted with the results of the present kinetic investigation. It is shown that their values of a and k_L are a factor 2.2 too low and too high, respectively, but that their values of k_La are correct.     

Calculation of the leaching kinetics of sodium borosilicate glasses in aqueous solutions of acids

The kinetics of diffusion interaction of single-phase sodium borosilicate glasses with aqueous solutions of acids is investigated as applied to the preparation of porous glasses. The kinetics of mass transfer in a glass-solution system is calculated with due regard for the delay of diffusion fluxes.     

A study of oxygen absorption kinetics in ionic Cu(I) aqueous solutions

We developed the oxidation reaction of Cu(I) ion in aqueous hydrochloric solution by oxygen in a gas-lift capillary bubble column. The method of gas-liquid absorption with chemical reaction was used. Test data confirmed that the rate constant of the reaction is strongly affected by solution compositions, and that chloride ions induce an inhibition effect. The kinetical orders found are equal to 1 and 2 for oxygen and Cu(I) respectively. The influence of temperature on reaction rate constant showed the existence of a maximum value between 303 and 313K. The effect of gas-liquid of gas-liquid system on the liquid-side mass transfer coefficient k_L was also investigated.     

The transport properties of oxygen in aqueous borate solutions

The solubility and diffusivity of oxygen in borate buffer solutions were studied on a Pt μ electrode under diffusion-controlled conditions. The solubility of oxygen in diluted borate solution is unusually high (4.2 × 10⁻³ M l⁻¹), whereas its diffusion coefficient is lower (5 × 10⁻⁶ cm² s⁻¹) than in other aqueous solutions The decrease in oxygen solubility at higher ionic strengths is due to the salting-out effect. The results are consistent with the formation of “oxygen-borate” complex whereby the stability of BO₃ containing polymeric anions is enhanced.     

Reaction kinetics of sodium bisulfite and dissolved oxygen in seawater and their applications to seawater reverse osmosis

Recently, single-stage seawater reverse osmosis (SWRO) in the Middle East has been developed. In this process, removing dissolved oxygen (DO) from the feed seawater is very important for membrane life. The reaction rate of sodium bisulfite (SBS) and DO in seawater was investigated to apply DO removal system to the SWRO. The reaction in seawater was very fast because the salinity had a positive catalytic effect and the bicarbonate ion kept the pH suitable for the reaction. By applying these results, Toray's PEC-1000 membrane modules have shown excellent performance and long durability.     

The electrochemical behaviour of copper in sodium salicylate aqueous solutions

Cyclic voltammetry has been used to investigate the behaviour of copper surfaces in sodium salicylate aqueous solutions. The observed copper anodic passivation dependence on the presence of salicylate ion in solution is explained. The analysis of the experimental data supports the formation of a complex passivating film formed by a Cu₂O inner layer and a mixed cupric oxide/cupric salicylate outer layer; this film provides a partial passivation of the copper surface and can be completely removed upon excursion to negative potentials values; the composition of the passivating layer depends on the electrolyte nature, i.e. sodium salicylate ion and solution pH, and on the potential programme the copper electrode is subjected to.     

Thermal decomposition of sodium dithionite

The thermal decomposition of sodium dithionite (Na₂S₂O₄) in the solid state was investigated by differential scanning calorimetry and the exothermic heat of decomposition was determined. The effect of isothermal pretreatment at various selected temperatures on the subsequently determined decomposition temperature was studied, together with the effect of sample weight on the decomposition temperature and degree of exothermicity.     

Absorption kinetics of ozone in aqueous O-cresol solutions

The kinetics of ortho-cresol ozonation in water has been studied using the film theory. At most experimental conditions investigated, the kinetic regime of the absorption has been fast pseudo first order with respect to ozone. At 30°C mass transfer plays an important role in controlling the absorption rate of ozone. The selfdecomposition reaction of ozone does not take place because of the great reactivity of o-cresol with ozone. Reaction rate constants have been determined at pH 7 for different temperatures below 30°C. The following Arrhenius equation was obtained: k_T = 2.2 × 10²³ exp(-11784/T), L/mol ? s At temperatures below 30°C there exists an ozone partial pressure value above which the ozone absorption kinetic regime changes to fast second order regardless of experimental conditions.     

Kinetics of the reaction of carbon dioxide with aqueous sodium and potassium carbonate solutions

Kinetics for CO₂ absorption into 5–30 wt-% sodium carbonate solutions and 5–50 wt-% potassium carbonate solutions up to 70 °C were studied in a string of discs apparatus under conditions, in which the reaction of CO₂ could be assumed pseudo-first-order. The experimental data were evaluated based on the use of activities in the reaction rate expressions. The second order kinetic constant for the CO₂ reaction CO₂+OH^??HCO₃^? at infinite dilution is discussed and an expression for it is obtained up to 70 °C.The difference between the activity and concentration based kinetic constants were found to be small at low concentrations, where the apparent Henry’s law constant is close to that at infinite dilution in water. However, at high concentrations (high apparent Henry’s law constants), the difference was bigger. Using the activity based approach, the second order kinetic constant was calculated, compared to the second order kinetic constant in infinite dilution and found to be independent of both carbonate concentration and the cation present in the solution.     

The kinetics of iron dissolution and passivation in solutions containing oxygen

The iron dissolution and passivation was studied in sulphate solution containing different oxygen concentrations and within the range 3 < pH < 6. The measurements were carried out cyclic voltammetrically and under steady-state polarization conditions using a rotating disc electrode of highly pure recrystallized iron. The obtained kinetic data can be explained mainly by the iron dissolution and passivation mechanism proposed previously for oxygen free solutions. This mechanism is characterized by the formation of different oxide intermediates [Fe(OH)_n]_ads, with n = 1,2,3 depending on the pH and the potential. Above a critical pH-value, the diffusion controlled oxygen reduction is the dominating cathodic process, and the anodic iron dissolution and passivation is inhibited by the time-dependent formation of three-dimensional porous oxide layers on the electrode surface. In neutral solutions the iron dissolution and passivation mechanism turns to that encountered in alkaline media.     

Electro-oxidation of sodium lauryl sulfate aqueous solutions

The electro-oxidation of dilute aqueous solutions of sodium lauryl sulfate (LS) was studied in the presence of metal ions and sulfuric acid, in order to achieve the complete destruction of the detergent. An undivided cell and rhodiated titanium electrodes were used. The LS concentration was studied as a function of time, added metal ion, pH, temperature, initial current density and detergent concentration. The results obtained showed that 99% LS destruction can be easily achieved and that complete oxidation occurs. LS depletion rate was found to increase with temperature, current density (up to 2 A dm^–2) and detergent concentration but to decrease with pH. The best results were obtained with iron ions dissolved in the electrolyte, but the process rate was nearly independent of Fe concentration above 0.5 mM.     

The pH dependence of the ozone absorption kinetics in aqueous phenol solutions

Using a wetted wall laboratory absorber, the rate of ozone absorption in aqueous phenol solutions has been measured in the pH range 1.75–12.The phenol concentration was varied in a wide range (7–800 ppM) and the ozone partial pressure over a six-fold range. The temperature and the liquidThe results were interpreted by assuming that the rate determining step of a reaction sequence is different in acid and basic solutions.