Determination of intrinsic kinetics parameters for MoO3 chlorination with Cl2 gas between 798 and 873 K (original) (raw)
Related papers
The Journal of Physical Chemistry, 1991
The kinetics of reaction 1, CCI, + O2 + M-CCI3O2 + M, has been investigated in detail as a function of temperature and Over a large pmure range. At low pressure, 0.8-12 Torr, the reaction was investigated by laser photolysis and timeresolved mass spectrometry, while at high pressure (760 Torr), flash photolysis with UV absorption spectrometry was employed. At the low-pressure limit, the rate expression, k,(O) = (1.6 f 0.3) X 10-'(T/298)*6.3fo") cm6 molecule-2 s-' (M = N2), exhibits a quite strong negative temperature coefficient. The obtained strong collision rate expression, 7.0 X T/298y3 cm6 molecule-2 s-I, using either RRKM calculations or Troe's factorized expression, is unable to reproduce the experimental temperature dependence, unless an unreasonably strong temperature dependence is assigned to the collisional efficiency factor: = 0.23(T/298)-2.0 (M = N2). Similar results are obtained for other chlorofluoromethyl radicals. The falloff curves were constructed by using RRKM calculations obtained by adjusting 8, and the transition-state model, in order to reproduce the experimental data. The rate expression at the high-pressure limit was derived from these calculations kl(-) = (3.2 i 0.7) X 10-'2(T/298)-(1.2M.4) cm3 molecule-I s-l. All the parameters to be used in Troe's analytical expression for calculating the bimolecular rate constant at any pressure and temperature are given. The rate constant at the low-pressure limit kl(0) is more than an order of magnitude lower than for the CF, radical. The RRKM calculations show that this arises from a large difference in the CO bond dissociation energies in the corresponding peroxy radicals: 81.9 kJ mol-] for CC1302 instead of-145 kJ mol-' for CF3O2.
Some kinetics aspects of chlorine-solids reactions
Revista de Metalurgia, 2010
The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl 2 +N 2 (chlorination), Cl 2 +O 2 (oxychlorination), and Cl 2 +CO (carbochlorination). Results are presented as effects of various parameters on the reaction rate of these solids with these chlorinating agents. It was observed that the reactivity of these solids towards different chlorinating agents varied widely. Sulfides could be chlorinated at room temperature, while carbochlorination of chromium (III) oxide was possible only above 500°C. The variation of the chlorination rate of these complex materials with respect to gas velocity, composition and temperature enabled us to focus some light on the plausible reaction mechanisms and stoichiometries. The obtained results were used for selective removal of iron from chromite concentrates, extraction of valuable metals from sulfide materials, purification of MgO samples, etc.
Kinetics of the redox reaction between Mo2O42+ and VO2+ in HClO4 medium
Polyhedron, 1991
The kinetics of the oxidation of Mo20d2+ with VOz+ in HC104 medium at 25°C and ionic strength 2 M has been studied by the stopped-flow method. Under conditions of excess V02+, the experimental rate constant is represented by the expression : (1238[H+]+811) 'a" = (5.50 x 10-4+[H+]~0,+]) Wo2+32* This rate law can be interpreted by the following mechanism : D~sDOH+H+ D+VOz ++C+H+ 2 DOH+VOZ++C 3 (I) (II) (III) H++C+V02+~2MoV'+2V'", (IV) where D is MORONS+ and C an intermediate complex. For this mechanism, k2 = 1238 M-' s-', k3K1 = 811 s-' and k_ 3/k4 = 5.00 x 10e4 M'. Limiting values for the individual constants can be estimated and the nature of the intermediate is discussed. The kinetics of the oxidation of molybdenum(V) with different reactants has been the subject of several investigations. L-9 The kinetics of the reaction between VOz+ and molybdenum(V) has already been studied by Issa et al. lo in the highly complexing HCl medium via stopped-flow techniques. These authors worked in the proton concentration range l-O.23 M HCl and ionic strength 1 M (NaCl)
Kinetics of oxychlorination of magnesium oxide
Metallurgical and Materials Transactions B, 1999
The kinetics of oxychlorination of MgO by Cl 2 +O 2 were studied in the temperature range of 850 °C to 1025 °C, using thermogravimetric analysis. The effects of Cl 2 /O 2 ratio, gas velocity, temperature and partial pressure of reactive gases on the reaction rate were investigated. The oxychlorination process was characterized by an apparent activation energy of about 214 kJ/mol. The reaction orders with respect to O 2, Cl 2 and Cl 2 +O 2 at 950 °C were about-0.37, 0.98, and 0.65, respectively. Data concerning oxychlorination of MgO, Cr 2 O 3 and MgCr 2 O 4 contained in chromite were compared. Effectiveness of using oxychlorination to extract iron oxides contained in magnesia was demonstrated. a. Laboratoire Environnement et Minéralurgie, rue du Doyen M.
Kinetics and Reaction Mechanisms of High-Temperature Flash Oxidation of Molybdenite
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2010
The kinetics and reaction mechanism of the flash oxidation of +35/–53 μm molybdenite particles in air, as well as in 25, 50, and 100 pct oxygen higher than 800 K, has been investigated using a stagnant gas reactor and a laminar flow reactor coupled to a fast-response, two-wavelength pyrometer. The changes in the morphology and in the chemical composition of partially reacted particles were also investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal analysis (DTA), and electron microprobe. High-speed photography was also used to characterize the particle combustion phenomena. The effects of oxygen concentration and gas temperature on ignition and peak combustion temperatures were studied. The experimental results indicate that MoS2 goes through a process of ignition/combustion with the formation of gaseous MoO3 and SO2 with no evidence of formation of a molten phase, although the reacting molybdenite particles reach temperatures much higher than their melting temperature. This effect may be a result of the combustion of gaseous sulfur from partial decomposition of molybdenite to Mo2S3 under a high gas temperature and 100 pct oxygen. In some cases, the partial fragmentation and distortion of particles also takes place. The transformation can be approximated to the unreacted core model with chemical control and with activation energy of 104.0 ± 4 kJ/mol at the actual temperature of the reacting particles. The reaction was found to be first order with respect to the oxygen concentration. The rate constant calculated at the actual temperatures of the reacting particles shows a good agreement with kinetic data obtained at lower temperatures. The ignition temperature of molybdenite shows an inverse relationship with the gas temperature and oxygen content, with the lowest ignition temperature of 1120 K for 100 pct oxygen. Increasing the oxygen content from 21 to 100 pct increases the particle combustion temperature from 1600 K to more than 2600 K. A high oxygen content also resulted in a change of the reaction mechanism from relatively constant combustion temperatures in air to much faster transient combustion pulses in pure oxygen.
Chlorination of commercial molybdenite concentrate in a fluidized bed reactor
Metallurgical Transactions B, 1987
Studies on recovery of molybdenum from commercial grade molybdenite using the technique of fluidized bed chlorination in the presence of oxygen are presented. Molybdenum recovery above 99 pct at a chlorine utilization efficiency of 84 pct has been achieved for a fluidizing gas flow-rate of 3 L/min of the gases Clz, 02, and Nz mixed in the proportion of 2: 5 : 23, respectively, at 300 ~ The investigations on kinetics showed that the overall oxychlorination reaction is controlled by chemical reaction and is of first order with respect to particle surface area.
Kinetic study of the chlorination of gallium oxide
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2005
The kinetics of the chlorination of gallium oxide in chlorine atmosphere was studied between 650 °C and 800 °C. The calculations of the Gibbs standard free energy variation with temperature for the reaction Ga2O3(S)+3Cl2 (g)→2GaCl3(g)+1.5O2 (g) show that direct chlorination is favorable above 850 °C. Thermogravimetric experiments were performed under isothermal and nonisothermal conditions. The effect of temperature, gas flow rate, and Cl2 partial pressure were studied. The solids were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The nonisothermal results showed that chlorination of Ga2O3 starts at approximately 650 °C, with a mass loss of 50 pct at 850 °C. The isothermal results between 650 °C and 800 °C indicated that the reaction rate increased with temperature. The correlation of the experimental data with different solid-gas reaction models showed that the results are adequately represented by the model proposed by Shieh and Lee: X=1−{1−b 22[b 21t+e −b 21t−1]}1/(1−γ). From this model, it was found that the rate of reaction for the chlorination of Ga2O3 is of the order 0.68 with respect to Cl2 and the activation energy is 113.23 kJ/mol. On the other hand, the order of the activation rate of the interface surface is 0.111 with respect to Cl2 and its activation energy is 23.81 kJ/mol.
Flow Tube Kinetic Study of Mo and Mo2 Reactivity
The Journal of Physical Chemistry, 1994
The reactivity of molybdenum atoms and dimers with respect to H2, Nz, CH4,02, N20, COZ, CO, C2H4, C3H6 (propene), and NH3 in He buffer gas in the pressure range 0.44-8 Torr at room temperature has been investigated by using a flow tube reactor equipped with a laser vaporization source for production of Mo and MOZ. Detection and monitoring of Mo and M02 is by resonance fluorescence excitation. The performance of the flow tube is investigated over a range of operating conditions by studies of several test reactions of Ti and Cr atoms, for which rate constants have been measured in previous work. Factors that contribute to the uncertainty of rate constants measured by using the laser vaporization flow tube reactor are discussed. Molybdenum atoms and dimers show significant differences in reactivity, in particular with respect to adduct formation reactions with rc-acceptor and Lewis base ligands. The possible origins of these differences in features of the valence electronic structures of Mo and M02 are discussed, and the role of repulsive interactions in controlling reactivity is emphasized. In view of parallels with coinage metal atoms and dimers, generalizations of reactivity differences between transition metal atoms and dimers are suggested. Analysis of kinetic data for Mo + C2H4 and Moz + NH3 association reactions leads to the following estimates for binding energies of the 1:l association complexes: AEa&cal mol-' = 17:: for Mo[C2&] and 14 f 2 for ModNH31.