Oxide ion concentration dependence of the potential of stabilized zirconia-air electrode in a molten LiF-KF system

This paper describes oxide ion concentration dependence of the potential of stabilized zirconia-air electrode in a molten LiF-KF eutectic system at 823–973 K. Experimental results can be explained well by the theoretical equation of the zirconia-air electrode potential,

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derived by the authors.

As an example of the application of the equation, solubility product of Al₂O₃ in a molten LiF-KF eutectic system has been determined to be (1.0–3.0) × 10⁻¹⁷ at 823 K, by the use of the zirconia-air electrode.     

Solid solution of ettringites part I: incorporation of OH and CO3 in 3CaOA12O332H2O

Solid solutions of ettringites containing SO₄^2-, OH⁻ and CO₃^2- were investigated. The compositions of the solid solutions are represented by:

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The properties of the different solid solution series are given. By X-ray measurements it is possible to distinguish between the different solid solutions of ettringites.     

Adsorption and electrokinetics of glucose reduction

The kinetics of cathodic reduction of glucose were studied by a rotating disk electrode at rotation speeds from 500 to 6000 rpm and zero to 2.0 M concentration of glucose. Sodium sulfite was used as the supporting electrolyte as well as the reducing mediator. Both the experimental results and the theoretical analysis indicated that several reaction steps occurred for the cathodic reduction of glucose. The results also revealed that the adsorption of glucose on a cathode played an important role during the electrolysis. The reaction mechanism was proposed and a mathematical model was developed. The model correlated well with the experimental results. The rate determining step was found to be the cathodic reduction of the sodium cation. The rate current of the electroreduction of glucose can be expressed as

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The effects of pH on the molecular distribution of water soluble ruthenium(II) hydrides and its consequences on the selectivity of the catalytic hydrogenation of unsaturated aldehydes

The effect of pH on the formation and equilibrium distribution of the water soluble ruthenium hydrides [HRuCl(TPPMS)₂]₂, [HRuCl(TPPMS)₃] and [H₂Ru(TPPMS)₄] (TPPMS=(3-sulfonatophenyl)diphenylphosphine sodium salt) was studied in aqueous solution by pH-potentiometric and

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and

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NMR methods. Depending on the pH, [RuCl₂(TPPMS)₂]₂ and its hydrido-derivatives hydrolyse extensively, giving rise to formation of hydroxo-ruthenium complexes. It was established that at pH≤3.3 the dominant ruthenium(II) species was [HRuCl(TPPMS)₃], while at pH≥7 it was [H₂Ru(TPPMS)₄]. While [HRuCl(TPPMS)₃] catalyzed the slow, selective hydrogenation of the C=C bond in trans-cinnamaldehyde, [H₂Ru(TPPMS)₄] was found an active and selective catalyst for C=O reduction. Consequently, the selectivity of the hydrogenation of trans-cinnamaldehyde could be completely inverted by minor changes in the solution pH, shifting the equilibrium between [HRuCl(TPPMS)₃] and [H₂Ru(TPPMS)₄].     

The application of chronoamperometry to the study of the kinetic parameters of electron-donor-acceptor (EDA) complexes. The N,N,N′,N′-tetramethyl-p-phenylenediamine-m-dinitro-benzene complex in acetonitrile

The kinetic parameters of the Electron-Donor-Acceptor (EDA) complex between N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) and m-dinitrobenzene (MDB) in acetonitrile have been determined by chronoamperometry. The CE_rev system studied and represented by

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was chosen as a model to test the applicability of this electrochemical technique to determine k_f and k_b. Three different methods of calculation are proposed and their scope is discussed. The values of k_f and k_b obtained, although relatively large, are well below diffusion control values. The calculated activation parameters allowed to presume an entropic control for the association process and suggest that the formation of this EDA complex may require a preferred orientation of the donor and acceptor. Moreover, solvation effects seem to play an important role for the dissociation process. The results obtained with this model allowed to consider that chronoamperometry may be a very valuable technique for this type of studies, with the condition that the lifetimes of complexation are within the time constant of the technique.     

Epoxide–tertiary amine combinations as efficient catalysts for methanol carbonylation into methyl formate in the presence of carbon dioxide

The influence of CO₂ on the carbonylation of methanol into methyl formate was investigated with two classes of catalytic systems: MeO⁻ and epoxide–amine combinations. In the absence of CO₂, NaOMe is the more active, but its efficiency is rapidly destroyed by CO₂. On the other hand, the epoxide–amine system is much less sensitive to the presence of CO₂. Different classes of amines and epoxides have been tested. Tertiary alkyl amines and terminal epoxides are the most efficient. Phosphines associated with an epoxide have also been found to be able to catalyse this reaction. On the basis of

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NMR studies, a plausible mechanism which can also be applied to amines is proposed for the reaction.     

Palladium(0) allylic alkylation in a two-phase system or with a supported aqueous phase catalyst

The reaction of allylic carbonates with various acyclic and cyclic carbonucleophiles is catalyzed by the system Pd(OAc)₂ and P(C₆H₄-m-SO₃Na)₃ (or tppts) in a two-phase liquid medium H₂O-nitrile, the activity of the catalyst depending mainly on the nature of the nitrile, the temperature of the reaction and the ratio palladium/tppts. The same system Pd(OAc)₂ and P(C₆H₄-m-SO₃Na)₃ supported on silica catalyzes also this reaction. The formation of the active palladium species in the two cases is followed by

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NMR spectroscopy and discussed.     

Recent developments in photoinitiators

A new photoinitiator, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (1), has been developed for industrial applications. The absorption of this bisacylphosphine oxide (BAPO) compound in the near UV-Vis range is significantly higher than that of hitherto known photoinitiators for UV curing. Investigation of the photochemistry of 1 revealed the efficient formation of four radicals, which can all initiate polymerization. Since the photoreaction is accompanied by the destruction of the chromophore responsible for absorption in the near UV-Vis, photobleaching of the long wavelength absorption is observed and the photoinitiator does not impart yellowing in the cured lacquer. Studies using FTIR and RTIR techniques showed that these features result in a higher conversion of acrylic double bonds than obtained with other photoinitiators in formulations containing a high loading of rutile type titanium dioxide pigments. These findings were confirmed by application tests in different white pigmented coatings. Further, the new photoinitiator allows the fast curing of thick pigmented layers, which makes it suitable for use in pigmented furniture coating. This new class of high performance photoinitiators is expected to promote the development of UV curable white coatings of high opacity and other applications where light in the near UV-Vis range is essential for curing. A liquid containing 25 parts of the BAPO photoinitiator 1 and 75 parts of 2-hydroxy-2-methyl-l-phenyl-propan-l-one (2) is an excellent technical and economical solution for most applications.

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Catalytic dehydrofluorination of CF3CH3(HFC143a) into CF2CH2(HFC1132a)

The catalytic dehydrofluorination of CF₃CH₃ was studied over various metal phosphate catalysts in a fixed-bed reactor. The Mg₂P₂O₇ catalyst exhibited the moderate activity and high selectivity of CF₂CH₂, and it is the most suitable catalyst for the dehydrofluorination of CF₃CH₃. Deactivation did not take place during the 100 h reaction over the Mg₂P₂O₇ catalyst, and XRD patterns of the catalyst were unchanged after 100 h reaction. However, small amounts of F⁻ ions were present on the surface of the catalyst from results of XPS. The active sites for CF₂CH₂ formation are weak acid sites of the catalysts, and carbon deposition and/or polymerization take place on strong acid sites. Results of CF₃CH₃-TPD indicated that the dehydrofluorination proceeds through a

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carbonium-ion mechanism over Mg₂P₂O₇ catalyst, and the rate-determining step is the cleavage of the C–F bond.     

Reduction eletrochimique de l'oxygene en eau oxygenee. Etablissement de l'equation de la courbe de polarisation: application au calcul des parametres thermodynamiques et cinetiques des etapes elementaires

The theoretical equation for the current/potential curve is determined for oxygen reduction in hydrogen peroxide in acidic and alkaline media on a mercury or graphite electrode.

By comparing these theoretical results with experimental data, the standard potentials and the rate constants of the two elementary electrochemical reactions are deduced, and as well as the rate constants and the pK of the chemical reaction

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The values determined by this way are different from those generally obtained by most authors.

Zusammenfassung

Die theoretische Gleichung fur die Reduktionsstromstärke/Reduktionspotential-Kurve wird für Sauerstoff in Wasserstoffsuperoxyd in sauren und alkalischen medien mit einer Quecksilber oder Graphit-Electrode aufgestellt.

Wenn man die theoretischen Ergebniise mit den experimentellen Werten vergleicht, so ergeben sich die Normalpotentiale und die Geschwindigkeits-Konstanten der beiden elementaren elektrochemischen Reaktionen und sowie die Geschwindigkeits-Konstanten und der pK der chemischen Reaktion Die so gefundenen Werte sind ziemlich verschieden von denen, die allgemeine von den meisten Autoren anerkannt werden.     

Structures of H3PO4/SiO2 catalysts and catalytic performance in the hydration of ethene

The hydration of ethene was carried out over H₃PO₄/SiO₂ having various amounts of H₃PO₄. The rate of the ethanol formation increased markedly with the increasing H₃PO₄ loadings, in particular above 60–70 wt%. By X-ray diffraction (XRD), and

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and

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MAS NMR methods, it was revealed that various silicon phosphates were produced in the preparation of the catalysts. The structures of the phosphates depended on the H₃PO₄ loadings. It was suggested that Si(HPO₄)₂·H₂O species which formed at higher H₃PO₄ loadings were hydrolyzed to H₃PO₄ and SiO₂ during the course of the reaction, yielding the catalysts with high performance. The bulk phase of the H₃PO₄ was involved in the reaction.     

Determination of optimized membrane area from long-term flux decline data

Due to membrane fouling, long-term flux decline follows a general trend: it starts with a steep decline followed by a gradual decrease and approaches its final value asymptotically. Coupled with the concentration effect, our data indicate that this flux behavior can be represented with the equation F = f(t) (k₁ 1n r + k₂) with f(t) = a₀ + exp [a₁ + a₂t + a₃t²] where t is time, a₀, a₁, a₂, a₃, k₁, and k₂ are constants and r is the concentration ratio.

To take advantage of early high flux, ultrafiltration is usually discontinued after a period of time t_u, to be replaced by membrane cleaning period of time t_c. Only then the ultrafiltration cycle is repeated. The total membrane area required for multistage ultrafiltration can be shown as

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where Q₀ is the ultrafiltration capacity, n is the number of stages, and rr_i is the concentration ratio at stage i. An optimization method can be utilized to determine minimum value of A_T. Results will be presented for the case of ultrafiltration of palm oil mill effluent.     

Kinetic study of the photocatalytic recovery of Pt from aqueous solution by TiO2, in a closed-loop reactor

The photocatalytic recovery of platinum

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ions from aqueous solution by TiO₂ (anatase) at conditions met in hydrometallurgical practice (low platinum concentration, low pH values and high chloride concentration) was studied. A continuous flow system with recirculation of the TiO₂ suspension through an illuminated column was applied. The addition of methanol as a “hole scavenger” was proved essential for the reaction to proceed. The influence of various parameters, such as initial platinum and methanol concentration, TiO₂ concentration, pH and flow rate, on the recovery rate was studied. The rate determining stage was found to be the adsorption of methanol molecules on the particles surface. The process seems to be effective and recovery yields up to 95% were achieved.     

Photocatalytic reactors: Reaction kinetics in a flat plate solar simulator

The kinetics of the photocatalytic decomposition of low concentrations of trichloroethylene (TCE) in water was modeled and the reaction parameters have been evaluated for different catalyst loadings. The employed reactor is a flat plate configuration irradiated by tubular lamps that have emission in the 300–400 nm wavelength range.

The mass conservation model is two-dimensional while the developed radiation model is two-dimensional in space and two directional in radiation propagation. The performance of the photoreactor with this reaction can be properly represented employing only two lumped kinetic constants that can be derived from a 12 steps, complete reaction sequence. The deduced kinetic model has explicit functional dependencies for the local volumetric rate of photon absorption (LVRPA) and the effect of the catalyst concentration:

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. Values of the kinetic constants are: =1.94×10⁻⁹ mol g^1/2 cm⁻² s^−1/2 einstein^−1/2 and ₃=5.52×10⁶ cm³ mol⁻¹. As derived from the reaction sequence and validated with experiments, it was observed that the reaction rate is proportional to the square root of the LVRPA. The dependence on the catalyst loading, well described by the model, is more complex due to its characteristic effect on the light distribution inside the reaction space.     

NO reduction by H2 over perovskite-like mixed oxides

Perovskite-like mixed oxides

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(A′=Ce or Eu; B=Mn or Co) and La_0.8Sr_0.2BO_3+δ (B=Mn, Fe, Co or Ni) prepared by the amorphous citrate method were used as catalysts for NO reduction by hydrogen. XRD patterns showed a fully crystalline perovskitic structure only in the case of Ce- and Eu-substituted samples. The results suggest that the presence of structural defects is important for the activity of these catalysts, as shown by pretreatment under different atmospheres (He and O₂). La_0.9Ce_0.1CoO_3+δ was the most active of the mixed oxide catalysts investigated and its activity was influenced by the presence of both anion vacancies and Co²⁺ species. La_0.8Sr_0.2NiO_3+δ showed a particular catalytic behaviour, attributed to surface Ni reduction.     

Sulfonic acid functionalized periodic mesostructured organosilica as heterogeneous catalyst

Periodic mesostructured organosilicas (PMO) were first synthesized using 1,2-bis(triethoxysilyl)ethylene (BTENE) under acidic conditions using Pluronic 123 as surfactant. The ethylene bridges were then arylated with benzene using AlCl₃ as catalyst. These materials were further treated with sulfuric acid for the sulfonation of the phenyl moieties yielding a new preparation of sulfonic acid functionalized PMO. Ordered hexagonal mesostructures with surface areas up to 440 m²/g and narrow pore size distribution (around 5.3 nm) were obtained. This work thus provides a new example of chemical modification for the conception of functionalized PMO catalysts. Liquid phase self-condensation of heptanal was performed at 75 °C in the presence of these catalysts and the results were compared with those obtained with several other heterogeneous acid catalysts.

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Case study: Optimization of an industrial fluidized bed drying process for large Geldart Type D nylon particles

With an aim to conduct performance rating and optimization of an industrial-scale fluidized bed dryer, a decision tree has been devised to aid selection of the most appropriate mathematical model. The operating fluidization regime is first identified and a theoretical criterion using a cross flow factor is used to decide between using the Class 1 model based on plug flow or the Class 3 model based on the Davidson bubble. In this case-study, this approach is applied on an existing multi-stage dryer for large Geldart Type D nylon particles. The optimization study was carried out using the Class 3 model, which applies the two-phase fluidization theory to determine the transport of moisture between the dense and the bubble phases. An iterative numerical solution has been used to reduce computational time by avoiding the need to solve complex coupled heat and mass balance equations. Changes in bubble size and wall effects along the bed height are taken into account to improve model accuracy. The sensitivity of operating conditions (temperature, weir height, fluidization velocity) and recommendations for optimal operation are presented.

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In-bed char combustion of Australian coals in PFBC. 3. Secondary fragmentation

Secondary fragmentation occurs during the char combustion stage of coal combustion in fluidised beds and was investigated at pressure in a bench-scale PFBC rig for five Australian black coals. The critical diameter of char particles above which secondary fragmentation occurred was 2 mm for all the coals studied. In contrast with previous work [1 and 2] at atmospheric pressure, secondary fragmentation was found to occur during the early stage of char combustion, explaining its influence on char burnout and in-bed char loading in PFBC.

Two normal distribution functions were found to describe the secondary fragmentation behaviour in PFBC. The first determined randomly which particle broke up, and the second predicted the size distribution of fragments. Neither char properties nor oxygen concentration significantly affected the parameters in these two statistical functions. However, the rank of the parent coal correlated with the ratio of maximum number of char fragments to initial number of char particles. This secondary fragmentation behaviour should be included in mathematical modelling of char combustion in PFBC to predict the char burnout correctly.     

Mie scattering of electromagnetic radiation by a sphere: A computer program

A computer program for calculating the Mie scattering of electromagnetic radiation by a sphere is described. The program will evaluate, amongst other parameters, the Mie scattering functions a_m and b_m, the extinction, scattering, back-scattering, absorption and radiation pressure efficiencies, the intensity functions, I₁ and I₂ and the polarisation ratios

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. The program can be made available to other users and computations can be commissioned on a repayment basis. A library of results is being established.     

Theoretical prediction of the minimum stirrer speed in mechanically agitated suspensions

The objective of this article is to derive theoretical equations for the minimum stirrer speed in vessels containing suspensions. There are a variety of equations for the prediction of this stirrer speed (Zwietering, Chem. Eng. Sci. 8 (1958) 244–253; Kneule and Weinspach, Verfahrenstechnik 1 (12) (1967) 531–540; Nienow, Chem. Eng. Sci. 23 (1968) 1453–1459; Einenkel, VDI-Forschungsheft Nr. 595, Düsseldorf, 1979; Einenkel and Mersmann, vt-Verfahrenstechnik 11 (2) (1977) 90–94; Niesmak, Thesis TU Braunschweig, 1982; Molerus and Latzel, Chem. Eng. Sci. 42 (6) (1987) 1423–1437; Zehner, Chem. Ing. Technol. 58 (10) (1986) 830–831). However, nearly all of them are derived from experimental results obtained in a limited range of vessel size and suspension properties [1, 2, 3]. Some relationships based on experiments carried out in small vessels are contradictory and not useful for scale-up. Reliable models are necessary not only for the design of stirred vessels but also for the reduction of power consumption. It is important to distinguish between two decisive processes: the ‘avoidance of settling’ and ‘off-bottom lifting’.