Kinetics of chlorination of zirconia in mixture with petroleum coke by chlorine gas

Studies on the kinetics of carbothermic chlorination of zirconium dioxide in gaseous chlorine were carried out with petroleum coke fines in powder form. The amounts of ZrO₂ chlorinated were found to be directly proportional to the time of chlorination in the temperature range studied (973 to 1273 K). The activation energy values for chlorination of ZrO₂, in mixture with petroleum coke, was found to be 18.3 kJ/mole. The influence of particle size of petroleum coke on the chlorination of ZrO₂ (−38 + 25 μm) was studied, and it was found that the rate of chlorination increased up to the size range of −75 to +53 μm, and the size finer than this produced negligible increase. The amount of petroleum coke in the mixture above 17.41 pct in excess of the stoichiometry resulted in very little increase in the rate. The effect of the partial pressure of chlorine (pCl₂) on the rate of chlorination was found to obey the following relationship, derived from the Langmuir adsorption isotherm:

Kinetics of chlorination of niobium pentoxide by carbon tetrachloride

Kinetics of the chlorination of Nb₂O₅ powder by CCl₄ vapor in mixture with N₂ in a static bed in the temperature range of 698 to 853 K were carried out at different partial pressures of CCl₄ (p _{CCl 4}), varying from 0.10 to 0.75 atm. The fraction of Nb₂O₅ chlorinated R at p _{CCl 4} of 0.6 atm in the temperature range of 698 to 773 K was found to be proportional to time t, and the activation energy E is calculated to be 112 kJ/mole. Results on the effect of p _{CCl 4} (0.4, 0.6, and 0.75 atm) at 723 K suggest that the rate v (R/min) is proportional to p _{CCl 4} ^1.5. However, at p _{CCl 4} of 0.2 atm, R is not linear with t, rather, R ^1/2 is linear with t. Based on these results, two mechanisms, one at low p _{CCl 4} (0.2 atm) and another at higher p _{CCl 4} values, in the temperature range of 698 to 773 K have been suggested. Similar studies in the higher temperature range (793 to 853 K), where p _{CCl 4} used to decompose to elemental chlorine and carbon, were also carried out. At all temperatures and p _{CCl 4} values, R is found to be directly proportional to t. At two higher p _{CCl 4} (0.4 and 0.6 atm), v is proportional to p _{CCl 4} ^1.5, whereas at two lower p _{CCl 4} (0.1 and 0.2 atm) it is proportional to p _{CCl 4} ^1.5. The E values obtained in the temperature range of 793 to 853 K at p _{CCl 4} of 0.6 and 0.2 atm are found to be 57 and 115 kJ/mole, respectively. In this higher temperature range, two different reaction mechanisms have been proposed.     

Studies on the kinetics of carbon tetrachloride chlorination of tantalum pentoxide

Studies on the kinetics of chlorination of tantalum pentoxide powder by carbon tetrachloride vapor in dilution with nitrogen have been carried out by weight-loss measurements in two temperature ranges, i.e., 698 to 773 K and 793 to 853 K. The effect of time, temperature, and partial pressure of CCl₄ on the kinetics of chlorination of the powder Ta₂O₅, (−105+74 μm) has been investigated. In both the temperature ranges, the chlorination results have been found to fit the following relationship during the “initial periods:”

Kinetics of low-temperature chlorination of vanadium pentoxide by carbon tetrachloride vapor

Low-temperature chlorination of vanadium pentoxide by carbon tetrachloride vapor in dilution with nitrogen has been carried out. The effect of time, particle size, partial pressure of CCl₄ vapor (0.1 to 0.6 atm), and temperature (553 to 788 K) on the extent of chlorination of V₂O₅ has been investigated. The extent of chlorination of the oxide is found to increase with a decrease in its particle size. In all cases, the reaction followed a topochemical reaction model, obeying the following relationship:

Kinetics of chlorination and carbochlorination of vanadium pentoxide

Kinetics of chlorination of V₂O₅ with Cl₂-air, C1₂-N₂, and C1₂-CO-N₂ gas mixtures have been studied by nonisothermal and isothermal thermogravimetric measurements. In the temperature range of 500 °C to 570 °C, the chlorination of V₂O₅ with C1₂-N₂ gas mixture is characterized by an apparent activation energy of about 235 kJ/mole. This could be attributed to chemical reaction. Between 570°C and 650 °C, the apparent activation energy is equal to 77 kJ/mole, indicating that the overall reaction rate is controlled by chemical reaction and pore diffusion. The reaction order with respect to chlorine is 0.78. The apparent activation energy of the carbochlorination of V₂O₅ by C1₂-CO-N₂ gas mixture is about 100 kJ/mole in the temperature range of 400 °C to 620 °C. In this case, the chemical reaction is the limiting step. At temperatures higher than 620 °C, an anomaly is observed in the Arrhenius plot, probably due to thermal decomposition of COC1₂ formedin situ and/or transformation of the vanadium oxide physical state. The maximum reaction rate is obtained by using a C1₂-CO-N₂ gas mixture having a C1₂/CO volume ratio equal to about 1. Formerly Graduate Student, Mineral Processing and Environmental Engineering Team. Formerly Graduate Student, Mineral Processing and Engineering Team, Institut National Polytechnique de Lorraine, Vandoeuvre, France.     

Kinetics of MgO chlorination with HCl gas

The kinetics of chlorination of MgO particles with HCl gas in the temperature range from 450 °C to 650 °C were measured and analyzed in terms of the shrinking core model. The MgO particles were produced by the thermal decomposition of MgOHCl manufactured in-house and were found to have a d₅₀ of 510 nanometers. Over 90 pct of the MgO was converted to MgCl₂ within 30 minutes at 650 °C. Analysis of the data indicated that the chlorination process was initially controlled by the kinetics of the chemical reaction between MgO and HCl, but as the thickness of the MgCl₂ product layer increased as the chlorination progressed, the rate of chlorination became controlled by the diffusion of HCl through the MgCl₂ ash layer surrounding a MgO core in the particles. A mathematical model that predicted the shrinkage of the MgO core with time was found to be in good agreement with the measurements over the range of temperatures studied. The ash layer thickness for the onset of the diffusion control regime was found to increase linearly with temperature. The apparent rate constant for chlorination in the initial reaction-controlled regime was well described by the Arrhenius equation: k (m/s)=0.0787 exp (−7596/T).     

Kinetics of chlorination and carbochlorination of pure tantalum and niobium pentoxides

Kinetics of chlorination and carbochlorination of pure Nb₂O₅ and Ta₂O₅ were studied by thermogravimetric analysis between 385 °C and 1000 °C using Cl₂-N₂ and Cl₂-CO-N₂ gas mixtures. Standard free energy changes of the reactions and phase stability diagrams of Nb-O-Cl and Ta-O-Cl systems were calculated. The chlorination reaction order, for both oxides, with respect to Cl₂ in the Cl₂-N₂ gas mixture was 0.82. The apparent activation energies (E _a ) for Nb₂O₅ chlorination were 208 and 86 kJ/mole for temperatures lower and higher than 850 °C, respectively. The experimental data could be described by a shrinking sphere model between 700 °C and 1000 °C. The chlorination mechanism, between 700 °C and 850 °C, was likely controlled by the chemical reaction. For T > 850 °C, the overall Nb₂O₅ chlorination rate was affected by the allotropic transformation of the Nb₂O₅ T form to M form. Between 925 °C and 1000 °C, E _a for Ta₂O₅ chlorination was 246 kJ/mole. In this case, the most appropriate model was also that of shrinking sphere suggesting that the chlorination of Ta₂O₅ was controlled by the chemical reaction. For both oxides, the carbochlorination reaction order with respect to Cl₂+CO partial pressure, in the gas mixture, was about 2. The mathematical analysis of carbochlorination data indicates that Nb₂O₅ and Ta₂O₅ reactions could be described by shrinking sphere or cylinder, respectively. Below 600 °C, the E _a values of Nb₂O₅ and Ta₂O₅ carbochlorination were 74 and 110 kJ/mole, respectively. Chemical reaction was probably the rate controlling step in both cases. An anomaly characterized by a decrease of the reaction rates occurs in the Arrhenius plots between 600 °C and 800 °C. This anomaly could be attributed to the thermal decomposition of COCl₂ formed in situ during the carbochlorination.     

Kinetics of chlorination and microstructural changes of xenotime by carbon tetrachloride

Among the rare earth minerals, fluorides, phosphates, and oxides have received attention from the rare earth industry. Traditional methods of decomposition of these minerals, usually alkaline or acid processes, involve several operations. Another possibility to obtain lanthanide chlorides or oxychlorides is reacting the mineral with chlorinating agents, such as gaseous chlorine, hydrogen chloride, thionyl chloride, and carbon tetrachloride, reducing the operation costs and making the process less complicated. In this context, we investigated the decomposition of xenotime using carbon tetrachloride at temperatures from 873 to 1173 K and kinetic and mechanistic studies have been performed. Powder X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectrometry, ultra-violet/visible spectroscopy, and thermal analysis techniques were used in this study. The results showed that the reaction follows the shrinking-unreacted-core model with formation of a product layer (lanthanide oxychloride), confirmed by powder X-ray diffraction. Moreover, microstructural changes of xenotime grains during the chlorination reaction were verified.     

Kinetics of the chlorination of Cu2S with Cl2 gas

Abstract

When Cu₂S is chlorinated with Cl₂ gas, CuS, CuCl and CuCl₂ are observed at various stages of the reaction. It is proposed that CuCl₂ and CuS are the first products, which then react to produee CuCl and elemental sulphur. The elemental sulphur is then chlorinated to S₂Cl₂, which acts as a liquid bridge for the transport of dissolved sulphur away from the reaction interface. CuCl₂ forms only when all of the sulphide has been eliminated, and the partial pressure of chlorine in the CuCl₂ layer can exceed that for the stability of CuCl. The activation energy proposed for the diffusion of sulphuralong the gradient in a pore filled with S₂Cl₂ is 8.6 ± 0.5 kcal.

Résumé

Quand Cu₂S est chloruré par Cl₂ gaz, on observe CuS, CuCl et CuCl₂ à divers stades de la réaction. L’hypothèse proposée est que le CuCl₂ et le CuS sont les premiers produits formés qui réagiront ensuite pour produire CuCl et S. Le soufre élémentaire est ensuite chloruré en S₂Cl₂, et agit alors comme un pont liquide pour éloigner le S dissout de l’interface de réaction. CuCl₂ se forme quand tout le sulfure a été éliminé, et la pression partielle de Cl₂ dans la couche de CuCl₂ peut excéder celle correspondant àCuCl stable. L’énergie d’activation proposée par la diffusion du soufre dans S₂Cl₂est 8.6 ± 0.5 kcal.     

Kinetics of interaction of tantalum disilicide with tantalum and other metals

The rate of growth of Ta₅Si₃ in the Ta?TaSi₂ system has been measured with good accuracy in the temperature range of 1150° to 1370°C (2100° to 2500°F) using couples consisting of dense wafers of the components. The isothermal growth is shown to be parabolic and the temperature dependence of the growth constant is given byk=5 exp (?77,000/RT) It has been shown that tantalum diffusion is negligible by comparison with silicon diffusion. The Ta₅Si₃ was found to exist in both tetragonal and hexagonal forms. A more limited investigation of silicon loss from TaSi₂ to W, Mo, Nb, Zr, Ti, and Re indicates that none of these is superior to tantalum in limiting the degradation of the tantalum disilicide. In most instances a layer of composition M₅Si₃ forms on the metal side of the couple.     

Kinetics of chlorination of Co and Co-10 At. Pct Pt alloy by reaction with HCI gas

The reaction of alloys with HCI gas is generally more complicated than that of pure metals, and is, typically, a dealloying process. In this work the rates of a model dealloying process, Co(Co-Pt) + 2HC1 → CoCl₂(g) + H₂ were measured in the temperature range 973 to 1273 K. The only reaction product for the HC1/H₂ gas mixtures used in the experiments was gaseous CoCl₂. Weight loss during the reaction was continuously monitored with a recording balance. Experimental variables included gas composition, gas flow rate, and temperature for Co-10 at. pct Pt and for pure Co samples. The rate of the reaction was constant with time and very nearly as high for the alloy as for the pure metal, in spite of the fact that Pt was inert for the conditions. A surface instability occurred for the alloy yielding an open porous structure of ever increasing surface area. Transport of CoCl₂(g) in the gas boundary layer was important for determining the rate of the chlorination reaction for both the alloy and pure metal. Formerly Research Associate, Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802.     

Extraction of tantalum and niobium from tin slags by chlorination and carbochlorination

Chlorination and carbochlorination of tantalum and niobium low-grade concentrate (LGC) and high-grade concentrate (HGC), obtained by leaching of tin slag, were studied using Cl₂ + N₂ and Cl₂ + CO + N₂ gas mixtures. Thermogravimetric analysis and conventional boat experiments were performed between 200 °C and 1000 °C. Chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to characterize the samples and reaction products. Chlorination of LGC led to the recovery of about 95 pct of tantalum and niobium compounds at 1000 °C. However, the tantalum and niobium chlorinated compounds were contaminated by chlorides of Fe, Mn, etc. For HGC, chlorination at 1000 °C allowed the extraction of about 84 and 65 pct of the niobium and tantalum compounds, respectively. The recovered condensates were composed of pure tantalum and niobium chlorinated compounds. The apparent activation energies E _a for the chlorination of LGC and HGC, between 850 °C and 1000 °C, were 166 and 293 kJ/mole, respectively. At temperatures lower than 650 °C, the apparent activation energies for the LGC and HGC carbochlorination were 116 and 103 kJ/mole, respectively. Total extraction of the tantalum and niobium compounds was achieved by the carbochlorination of the LGC at 1000 °C. The generated tantalum and niobium chlorinated compounds were contaminated by the chlorides of Fe, Mn, Al, and Ca. The carbochlorination of the HGC at 500 °C allowed complete extraction and recovery of pure tantalum and niobium compounds. These results confirm the importance of obtaining an HGC from tin slag before its subsequent chlorination. The carbochlorination of such a concentrate could be an efficient process for the recovery of relatively pure tantalum and niobium chlorinated compounds at low temperatures.     

Kinetics and mechanism of the reaction of iron-chromium and iron-chromium-molybdenum alloys with chlorine gas

This report deals with the kinetics and mechanism of the reaction of iron-chromium and iron-chromium-molybdenum alloys (containing 1.25 pct Cr-0.5 pct Mo, 5 pct Cr-0.5 pct Mo, and 12 pct Cr) with low partial pressure chlorine gas in the temperature range 270 to 550 °C. The rate of reaction generally decreases with exposure time and, in the case of alloys containing five pct Cr and higher chromium content, the kinetics follows a parabolic rate law. The reaction kinetics is influenced by surface films containing FeCl₂ and CrCl₃ which have very low vapor pressure in the temperature range studied. The effect of molybdenum on the reaction is negligible. In the case of alloys containing five pct Cr-0.5 pct Mo and 12 pct Cr, the reaction product film consists essentially of CrCl₃ (outer layer) and much smaller concentration of FeCl₂ (inner layer). For these alloys, the observed parabolic kinetics is attributed to kinetic control of the overall reaction by solid-state diffusion through the reaction product surface film. In the case of the 1.25 pct Cr-0.5 pct Mo alloy, the film consists essentially of a mixture of FeCl₂ and CrCl₃. In this case, an outer CrCl₃ film layer is not formed and the overall kinetics is influenced by the rate of formation of volatile FeCl₃ speciesvia the reaction 2 FeCl₂ + Cl₂ (FeCl₃)₂.     

微波场下的钒渣氯化动力学

研究了微波加热条件下（500～800 ℃）,AlCl₃氯化钒渣中有价金属Fe、Mn、V和Cr变温动力学。通过X射线衍射和扫描电镜能谱表征了氯化产物随时间的物相演变和形貌变化,考察了AlCl₃/钒渣的质量比和熔盐配比对氯化提取率的影响。结果表明,AlCl₃/钒渣的质量比为1.5、(NaCl-KCl)/AlCl₃熔盐质量比为1.66∶1时Fe、Mn、V和Cr的提取率最佳,分别为91.66%、92.96%、82.67%、75.82%和63.14%,微波加热30 min,5种元素的提取率达到或者超过常规加热方式6 h的氯化提取效果。通过热力学和动力学分析,橄榄石相优先于尖晶石相发生氯化反应。而且V和Cr的氯化反应速度小于Fe和Mn。Fe和Mn氯化过程为扩散控制,其非等温扩散活化能为17.02和17.10 kJ·mol?1, V和Cr在氯化过程中的限制性环节为界面化学反应,其表观活化能分别为40.00和50.92 kJ·mol?1;微波与熔盐耦合强化氯化反应的机理可以描述为扩散作用增强和局部化学反应增强。      

Kinetics of the vapor phase chlorination of niobium oxychloride by phosgene

The kinetics of the homogeneous gas phase reaction between niobium oxychloride and phosgene was studied between 380° and 450°C in a constant volume reactor. The reaction was found to be essentially irreversible with the only detected reaction products being niobium pentachloride and carbon dioxide. The data obtained were fit by an elementary second-order rate equation. Values of the Arrhenius frequency factor and activation energy were found to be 1.33 × 10⁶ liter per g mol sec and 21.9 kcal per g mol with standard deviations of 0.05 × 10⁶ and 1.4, respectively.     

CuO氯化过程动力学研究

铜渣中含有30 %~40 %的Fe, 对铜渣中的Fe进行回收, 有利于缓解中国依赖进口铁矿石的压力.基于热力学分析氯化除铜的可行性, 在823 K、873 K、923 K、973 K温度下, 通过热重分析研究CuO-FeCl₂体系的氯化过程动力学, 并考察反应温度和Ar气流量对反应的影响: CuO-FeCl₂体系的氯化率随温度的升高而增大, 当Ar流量为50 mL/min时, 氯化率达到最大值为62.46 %.通过推导氯化反应动力学公式, 确定CuO-FeCl₂体系的氯化反应为0级反应, 并且在873 K时由氯化过程动力学区过渡到扩散区, 动力学区的反应速率取决于CuCl₂的挥发速率, 扩散区的反应速率取决于FeCl₂向CuO表面扩散的速率.      

Kinetics of chlorination and carbochlorination of molybdenum trioxide

Kinetics of chlorination of MoO₃ with Cl₂-air, Cl₂-N₂, and Cl₂-CO-N₂ gas mixtures have been studied by nonisothermal and isothermal thermogravimetric measurements, between ambient temperature and 900 °C. Between 500 °C and 700 °C, the chlorination reaction of MoO₃ with Cl₂-N₂ gas mixture has an apparent activation energy of about 165 kJ/mole, reflecting that a chemical reaction is the rate-controlling step. The reaction order with respect to Cl₂ partial pressure is about 0.75. The apparent activation energy for carbochlorination with Cl₂-CO-N₂ gas mixture is about 83 kJ/mole, between 400 °C and 650 °C. The carbochlorination of MoO₃ was controlled by the chemical reaction, probably affected by the pore diffusion regime. The maximum reaction rate is obtained by using a Cl₂-CO-N₂ gas mixture, having a Cl₂/CO volume ratio equal to about 1. The total apparent reaction order with respect to Cl₂ + CO in Cl₂-CO-N₂ gas mixture is about 1.5 for a Cl₂/CO ratio equal to 1. Laboratoire Environnement et Minéralurgie, associated with the Centre National de la Recherche Scientifique, Mineral Processing and Environmental Engineering team.     

Inhalation of chlorine gas

The clinical features of acute chlorine gas inhalation, and its management are reviewed. Current medical views on the chronic effects of an acute overwhelming exposure on lung function (reactive airways dysfunction syndrome), and the more controversial field of lung disease secondary to repeated inhalations of lower concentrations of chlorine gas are discussed.     

Reduction of titania by methane-hydrogen-argon gas mixture

Reduction of titania using methane-containing gas was investigated in a laboratory fixed-bed reactor in the temperature range 1373 to 1773 K. The reduction product is titanium oxycarbide, which is a solid solution of TiC and TiO. At 1373 K, the formation rate of TiC is very slow. The rate and extent of reaction increase with increasing temperature to 1723 K. A further increase in temperature to 1773 K does not affect the reaction rate and extent. An increase in methane concentration to 8 vol pct favors the reduction process. A further increase in methane concentration above 8 vol pct causes excessive carbon deposition, which has a negative effect on the reaction rate. Hydrogen partial pressure should be maintained above 35 vol pct to depress the cracking of methane. Addition of water vapor to the reducing gas strongly retards the reduction reaction, even at low concentrations of 1 to 2 vol pct. Carbon monoxide also depresses the reduction process, but its effect is significant only at higher concentrations, above 10 vol pct.