The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions: A kinetic study

The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions was studied in a standard stirred reactor. Each test was carried out at constant pH and under stable hydrodynamic conditions. The effect of stirring speed, solution volume, temperature, pH, oxygen partial pressure, chloride and copper ion concentration of the solution were evaluated.The oxidation of Cu(I) followed linear kinetics up to 85% of the copper ions in the cupric state. The experimental results were interpreted by using the film theory of mass transfer with chemical reaction. In the linear range, the chemical reaction was found to be first order with respect to oxygen concentration. The kinetic constant is given. The flux equation was specific of a fast reaction regime and the overall reaction rate was independent of the mass transfer coefficient k_L up to a k_L-value of about 10^?2 cm/sec. A parallel study of the oxidation of SO₃^2? by oxygen gas was carried out in the same reactor. The effects of stirring speed and solution volume were similar for both systems.     

Mass transfer and kinetics study on the sulfite forced oxidation with manganese ion catalyst

Wet limestone scrubbing is the most common flue gas desulfurization process (FGD) for control of sulfur dioxide emissions from the combustion of fossil fuels. Forced oxidation, which controls the overall reaction of the sulfur dioxide absorption, is the key path of the process. Manganese which comes from the coal is one of the catalysts during the forced oxidation process. In the present work, the two-film theory was used to analyze the sulfite forced oxidation reaction with an image boundary recognition technique, and the oxidation rate was experimentally studied by contacting pure oxygen with a sodium sulfite solution. There was a critical sulfite concentration 0.328 mol/L without catalyst or at a constant catalyst concentration value. The kinetics study focused on the active energy of the reaction and the reaction constant k; furthermore, we obtained the order with respect to the sulfite and Mn²⁺ concentrations. When the Mn²⁺ catalyst concentration was kept unchanged, the sulfite oxidation reaction rate was controlled by dual film and the reaction kinetics was first order with respect to sulfite while SO₃²⁻ concentration was below 0.328 mol/L; the sulfite oxidation reaction rate was controlled by gas film only and the reaction kinetics was zero order with respect to sulfite while SO₃²⁻ concentration over 0.328 mol/L. When SO₃²⁻ concentration was kept unchanged, the sulfite oxidation reaction rate depended on gas-liquid mass transfer and the reaction kinetics was different in various stages with respect to Mn²⁺ concentrations. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Effect of Alkanediyl-α,ω-Type Cationic Dimeric (Gemini) Surfactants on the Reaction Rate of Ninhydrin with [Cu(II)-Gly-Tyr]+ Complex

The effect of gemini (16‐s‐16, s = 4, 5, 6) surfactants on the reaction rate of ninhydrin with [Cu(II)‐Gly‐Tyr]⁺ complex was determined using a spectrophotometric technique. The ninhydrin concentration was kept in excess in order to maintain pseudo‐first‐order conditions. The reaction followed irreversible first‐ and fractional‐order kinetics with respect to [Cu(II)‐Gly‐Tyr]⁺ and [ninhydrin], respectively. It is found that gemini surfactants effectively catalyze the reaction. The rate constants (k_ψ) first increase and then become relatively constant with increasing gemini surfactant concentration similar to conventional cetyltrimethylammonium bromide. At higher gemini surfactant concentration a third region of increasing k_ψ is observed. The unusual third region is ascribed to changes in micellar morphology. The kinetic data has been analyzed using a micellar pseudo‐phase model.     

Kinetic study of photocatalytic decolorization of C.I. Basic Blue 3 solution on immobilized titanium dioxide nanoparticles

The photocatalytic decolorization of C.I. Basic Blue 3 (BB3) solution on immobilized TiO₂ nanoparticles was carried out in a rectangular flat-plate photoreactor. The investigated TiO₂ was Millennium PC-500 (anatase, average crystallite size 8 nm, surface area 320.76 m² g⁻¹) immobilized on non-woven paper. A new kinetic model was proposed on the basis of intrinsic element reactions. The proposed kinetic model fairly resembled the classic Langmuir–Hinshelwood (L–H) equation from its expression. It was found that both k_obs (the reaction rate constant) and K_R (the adsorption rate constant) were linearly proportional to the light intensity in a rather large intensity range.     

A new approach to the mechanism of heterogeneously catalysed reactions: the oxydehydrogenation of ammonia at a Cu(111) surface

The oxydehydrogenation of ammonia at a Cu(111) surface is a highly efficient process at 295 K, with the selectivity sensitive to the dioxygen-ammonia ratio. However, there is no evidence from either XPS or HREELS for surface oxygen being present during the reaction and, in effect, catalysis occurs at a clean Cu(111) surface. The rate of NH _x (a) formation is indistinguishable from the rate of the dissociative chemisorption of oxygen at close to zero coverage suggesting that the reactive oxygen species are the hot transients O-(s). The chemisorbed oxygen overlayer, the O^2-(a)-like species are, by comparison, unreactive. The reaction is, therefore, not characteristic of either Eley-Rideal or Langmuir-Hinshelwood mechanisms but involves the interaction of rapidly diffusing ammonia molecules and hot transient O-(s)-like species. Models for this type of reaction have been discussed previously, while very recent studies by scanning tunnelling microscopy have provided further evidence for such oxygen transients.     

Absorption of carbon dioxide into glycidyl methacrylate solution containing the triethylamine immobilized ionic liquid on MCM-41 catalyst

An ionic liquid (TEA-MS41), triethylamine-immobilized on chloropropyl-functionalized MCM-41, was synthesized by a grafting technique through a co-condensation method and used as a catalyst in the reaction of carbon dioxide with glycidyl methacrylate (GMA). CO₂ was absorbed into the heterogeneous system of the GMA solution and dispersed with solid particles of the catalyst in a batch stirred tank with a plane gas-liquid interface at 101.3 kPa. The absorption of CO₂ was analyzed by using mass transfer accompanied by chemical reactions based on film theory. The proposed model fits the measured data of the enhancement factor to obtain the reaction rate constants. Solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidinone, and dimethyl sulfoxide influenced the reaction rate constants.     

Structure sensitivity of dimethylamine deep oxidation over Pt/Al2O3 catalysts

The deep oxidation of dimethylamine (DMA) was studied over Pt/Al₂O₃ catalysts with small (1 nm) and large (7.8–15.5 nm) Pt crystallite sizes. The turnover frequency (TOF) was higher for the large than for the small Pt crystallites, indicating that the reaction is structure sensitive. Two kinetic models were used to interpret the obtained results, i.e., the Mars van Krevelen and a mechanism based on the adsorption of oxygen and adsorption of dimethylamine on different active sites were employed. Both models showed that the activation energy for the oxygen chemisorption rate constant (k_o) decreased with increasing of Pt crystallite size and that the activation energy for the surface reaction rate constant (k_i) was independent of the Pt crystallite size. The structure sensitivity may be explained by differences in the reactivity of the oxygen adsorbed on these Pt crystallites.The Mars van Krevelen model fits the TOF values very well at concentrations of DMA higher than 1500 ppm, while in the lower concentrations region, the model under predicts the experimental data. The model based on the adsorption of oxygen and DMA on different active sites fits the experimental data quite well over the whole temperature and concentration range. The fitted values of the Henry adsorption constant are independent of the Pt crystallite size.     

A Two-Step Reaction Mechanism of Oxygen Release from Pd/CeO2: Mathematical Modelling Based on Step Gas Concentration Experiments

A mathematical model has been developed to study the transient release of oxygen from a 1wt% Pd/CeO₂ catalyst in the 450–550 °C range based on alternate step concentration switches between CO and O₂. A two-step reaction mechanism that involves the reaction of gaseous CO with the oxygen species of PdO and of the back-spillover of oxygen from ceria to the oxygen vacant sites of surface PdO has been proven to better describe the CO and CO₂ transient response curves. The proposed mathematical model allows the estimation of the transient rates of the CO oxidation reaction and of the back-spillover of oxygen process. It also allows the calculation of the intrinsic rate constant k ₁ (s^–1) of the Eley–Rideal step for the reaction of gaseous CO with surface oxygen species of PdO to form CO₂. An activation energy of 10.1 kJ/mol was estimated for this elementary reaction step. In addition, an apparent rate constant k ₂ ^app (s^–1) was estimated for the process of back-spillover of oxygen.     

Mechanism transition of mixed diffusion and charge transfer-controlled to diffusion-controlled oxygen reduction at Pt-dispersed carbon electrode by Pt loading, Nafion content and temperature

The mechanism transition in the oxygen reduction reaction at the Pt-dispersed carbon (Pt/C) electrode was investigated in an oxygen-saturated 0.5 M H₂SO₄ solution. The reaction was monitored by acquiring data for Pt loading, Nafion content and temperature by analyses of the rotating disk voltammograms and potentiostatic current transients (PCTs). From the shape of the cathodic PCTs and the dependence of the initial current density on the potential drop, it is suggested that oxygen reduction at the Pt/C electrode is controlled by the charge transfer at the electrode surface mixed with the oxygen diffusion in the solution below the value of the potential drop, ΔE_tr, needed for the occurrence of the mechanism transition, whereas oxygen reduction is purely governed by the oxygen diffusion in the solution above ΔE_tr. In particular, it was noted that the value of ΔE_tr remained nearly constant irrespective of the Pt loading and Nafion content. On the other hand, the value of ΔE_tr decreased as temperature increased, which is ascribed to the fact that the contribution of the Cottrell current enhanced by temperature rise to the fall in ΔE_tr is overwhelmed by that contribution of the Butler-Volmer current increased. Consequently, it is concluded that it strongly depends upon the extrinsic parameters such as Pt loading, Nafion content and temperature as well as the intrinsic parameters such as rate constant for interfacial reaction and oxygen diffusivity in the solution, which mechanism of the overall oxygen reduction reaction is operative.     

The kinetics of the Cu/Cu redox couple in deep eutectic solvents

Kinetics of electron transfer of the Cu(I)/Cu(II) redox couple at a platinum electrode has been studied with chronoamperometry, cyclic voltammetry and impedance spectroscopy in a deep eutectic solvent consisting of choline chloride and ethylene glycol. At 25 °C, the reaction was found to be quasi-reversible with a relatively high rate constant k⁰ of 9.5 ± 2 × 10⁻⁴ cm s⁻¹, and a charge transfer coefficient α of 0.25 ± 0.05. Diffusion coefficients for the Cu(I) and Cu(II) complexes were determined to be 2.7 ± 0.1 × 10⁻⁷ and 1.5 ± 0.1 × 10⁻⁷ cm² s⁻¹, respectively. The viscosity of the electrolyte was 41 ± 3 mPa s. The temperature dependency was also investigated. The activation energy of mass transfer was found to be 27.7 ± 1 kJ mol⁻¹ and that of electron transfer 39 ± 7 kJ mol⁻¹. Speciation of the Cu(I) and Cu(II) complexes was determined using UV–VIS spectroscopy, and the prevailing Cu(I) complex was found to be [CuCl₃]²⁻ and that of Cu(II) [CuCl₄]²⁻.     

Absorption of Carbon Dioxide into Aqueous Solution of Sodium Glycinate

Abstract

Carbon dioxide was absorbed into aqueous solution of sodium glycinate (SG) at different SG concentrations, CO₂ partial pressures, and temperatures in the range of 0.5–3.0 kmol/m³, 25–101.3 kPa, and 298–318 K, respectively, using a stirred semi-batch vessel with a planar gas-liquid interface. Both the reaction order and rate constant are determined from gas absorption rates under the fast reaction regime. The reaction was found to be first order with respect to both CO₂ and SG. The activation energy for the CO₂-SG reaction has been found to be 59.8 kJ/mol. The second-order reaction rate constants were used to obtain the theoretical values of absorption rate based on the film theory.     

Chemical absorption of carbon dioxide into oxirane solution containing ID-CP-MS41 catalyst

CP-MS41 was synthesized by hydrolysis of tetraorthosilicate, as a silicon source, with 3-chloropropyltriethoxysilane as an organosilane using cetyltrimethylammonium bromide as a template. ID-CP-MS41 was synthesized by immobilization of imidazole on the CP-MS41 and was dispersed in organic liquid as a mesoporous catalyst for the reaction between carbon dioxide and oxirane. Phenyl glycidyl ether and glycidyl methacrylate were used as oxiranes. Carbon dioxide was absorbed into the oxirane solution in a stirred batch tank with a planar gas-liquid interface within a range of 0–2.0 kmol/m³ of oxirane and 333–363 K at 101.3 kPa. The measured values of absorption rate were analyzed to obtain the reaction kinetics using the mass transfer mechanism associated with the chemical reactions based on the film theory. The overall reaction of CO₂ with oxirane, which is assumed to consist of two steps-i) a reversible reaction between oxirane (B) and catalyst of ID-CP-MS41 (QX) to form an intermediate complex (C₁), and ii) irreversible reaction between C₁ and CO₂ to form QX and five-membered cyclic carbonate (C)-was used to obtain the reaction kinetics through the pseudo-first-order reaction model. Polar solvents such as N, N-dimethylacetamide, Nmethyl-2-pyrrolidinone, and dimethyl sulfoxide affected the reaction rate constants.     

Cathodic reaction kinetics and its implication on flow-assisted corrosion of aluminum alloy in aqueous ethylene glycol solution

The cathodic reaction kinetics and anodic behavior of Al alloy 3003 in aerated ethylene glycol–water solution, under well-controlled hydrodynamic conditions, were investigated by various measurements using a rotating disk electrode (RDE). The transport and electrochemical parameters for cathodic oxygen reduction were fitted and determined. The results demonstrate that the cathodic reaction is a purely diffusion-controlled process within a certain potential region. The experimentally fitted value of diffusion coefficient of oxygen is 3.0 × 10⁻⁸ cm² s⁻¹. The dependence of cathodic current on rotation speed was in quantitative agreement with Levich equation. At potentials more positive than the diffusion controlled region, the cathodic process was controlled by both diffusion and electrochemical kinetics. The electrochemical reaction rate constant, k ₀, was determined to be 1.1 × 10⁻⁹ cm s⁻¹. There is little effect of electrode rotation on anodic behavior of Al alloy during stable pitting. However, fluid hydrodynamics play a significant role in formation of the oxide film and the Al alloy passivity. An enhanced electrode rotation would increase the mass-transfer rate of solution, and thus the oxygen diffusion towards the electrode surface for reduction reaction. The generated hydroxide ions are favorable to the formation of Al oxide film on electrode surface.     

Thermal degradation of aliphatic–aromatic polyamides: Kinetics of N,N′-Dihexylisophthalamide neat and in presence of copper lodide

An experimental study to determine the effect of copper (I) iodide (Cul) on the rate and product distribution of degradation of a model of an aliphatic–aromatic polyamide was carried out. N,N′-Dihexylisophthalamide (DHI) was reacted in both an inert argon atmosphere and a pure oxygen environment at 350°C with CuI added in amounts ranging from 0 to 20% by weight. The rate of disappearance of DHI was enhanced by an order of magnitude when 0.5% by weight of CuI was added and was an increasing function of increasing CuI loading. Reaction in pure O₂ increased the rate of DHI degradation by two orders of magnitude over that for neat DHI pyrolysis. The rate of disappearance of DHI in O₂ was relatively unchanged when 5% CuI by weight was added. The transformations of DHI and its products are organized in terms of a set of reaction rules. This “reaction operator” formalism allowed computer generation of the reaction network and facilitated estimation of kinetic parameters. © 1995 John Wiley & Sons, Inc.     

Mass transfer characteristics of a novel gas-evolving electrochemical reactor

Mass transfer coefficients were measured for the deposition of copper from acidified copper sulphate solution at a vertical-plate cathode stirred by the oxygen evolved at a coplanar, vertical-plate lead anode placed upstream from the cathode. The variables studied were: oxygen discharge rate, electrolyte concentration and height of the cathode. The cathodic mass transfer coefficient was increased by a factor of the order of 2 to 5 over the natural convection value depending on the rate of oxygen discharge at the lead anode. The relationship between the mass transfer coefficient and the oxygen discharge rate was found to be logK=a+0.296 logV.The mass transfer coefficient was found to decrease initially with increasing electrode height, but then reached a constant value independent of further change in electrode height. A new, modified parallelplate reactor stirred by the counter electrode gases is described. The advantage of the design is that it offers more efficient stirring with no added power consumption. Details of the design are discussed.Nomenclature C concentration of CuS0₄ (mol cm^–3) - F Faraday's constant - h electrode height (cm) - K mass transfer coefficient (cm s^–1) - l _L limiting current density (A cm^–2) - V gas discharge rate (cm s^–1) - z number of electrons involved in the reaction On leave from the Department of Chemical Engineering, Faculty of Engineering, Alexandria University, Alexandria Egypt.     

Redox and transport behaviors of Cu(I) ions in TMHA-Tf<Subscript>2</Subscript>N ionic liquid solution

The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf₂N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf₂N containing 12 mmol dm⁻³ Cu(I) ions was 1.2 × 10⁻⁶ cm² s⁻¹ and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I ⁻/I ₃⁻ at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10⁻⁵ cm² s⁻¹ at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO₄ solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol⁻¹ in the ionic liquid solution.     

Aqueous meta-Chloronitrobenzene Degradation by Ozonation and Its Kinetics

The kinetics and degradation process of meta-Chloronitrobenzene by ozonation in aqueous solution were investigated. Compared to para-chlorobenzoic acid, the rate constant of meta-Chloronitrobenzene with O₃ was 0.59 L/(mol·s), while that of the reaction with ^?OH was 2.07 × 10⁹ L/(mol·s). The main intermediate products were chloronitrophenols and some carboxylic acids. Neither chlorophenols nor nitrophenols was detected. The five-day biochemical oxygen demand and chemical oxygen demand were determined. The ratio of the former to the latter was above 0.3 at 20 min. It was feasible to perform a continuous biotreatment step after 20 min of ozonation.     

Adsorption of methyl iodide on reduced silver-functionalized silica aerogel: Kinetics and modeling

The low concentration methyl iodide (CH₃I) adsorption process on reduced silver-functionalized silica aerogel (Ag⁰-Aerogel) was studied. The kinetic data were acquired using a continuous flow adsorption system. Because the corresponding physical process was observed, the shrinking core model (SCM) was modified and applied. An average CH₃I pore diffusivity was calculated, the CH₃I-Ag⁰-Aerogel reaction was identified as a 1.40 order reaction instead of first order reaction, and the n^th order reaction rate constant was determined. This modified SCM significantly increases the accuracy of adsorption behavior prediction at low adsorbate concentration. Modeling results indicate that the overall adsorption process is controlled by the pore diffusion. However, at low adsorbate concentration (ppbv level), the CH₃I adsorption is limited to the surface reaction due to the low uptake rate in a predictable time period.     

Photocatalytic decolorization of Basic Blue 41 using TiO2-Fe3O4-bentonite coating applied to ceramic in continuous system

Abstract

Photocatalytic degradation/decolorization of Basic Blue 41 dye assisted by UV radiation has been studied over TiO₂-Fe₃O₄ supported by bentonite. In this experiment, photocatalytic decolorization process was performed continuously; where dye feed solution was supplied to a coated-ceramic vessel. The influence of the initial concentration, pH, and flow rate of the dye feed solution on the degradation efficiency process was examined in this study. The results showed that the increase in the dye concentration and flow rate reduces decolorization efficiency. The highest decolorization efficiency was at pH of 5.5. The kinetic study of this photo-decolorization indicated that under the experimental condition, the photocatalytic kinetic process followed first-order kinetics on the basis of Langmuir–Hinshelwood heterogeneous reaction mechanism, where the reaction rate constant, namely k_r, is 0.7707 and the adsorption rate constant, namely K, is 0.01298.     

Chemical Absorption of Carbon Dioxide into Aqueous Solution of Potassium Threonate

Carbon dioxide was absorbed into aqueous solution of potassium threonate (PT) at different concentrations of PT and CO₂, and temperatures in the range of 0.1–1.0 kmol/m³, 10.1–101.3 kPa, and 293-313 K, respectively, using a stirred semi-batch vessel with a planar gas-liquid interface. Both the reaction order and rate constant were determined from gas absorption rates under the fast pseudo-first-reaction regime. The reaction was found to be first order with respect to both CO₂ and PT, and its activation energy has been found to be 40.6 kJ/mol. From a comparison of the reaction kinetics by the overall reaction scheme with those by the elementary reaction scheme based on the zwitterions mechanism, the overall reaction between CO₂ and PT has been found to be equivalent to the formation of zwitterions.