I.S. Pap

Kinetics of γ-alumina chlorination by carbon tetrachloride

Abstract The kinetics of the reaction between γ-Al2O3 and gaseous CCl4 has been studied by isothermal TG measurements in the temperature range 700—1123 K. The reaction starts with a weight gain which can be attributed to the chemisorption of the reactive gas. The weight loss vs. time curves at relatively high temperatures can be described by the contracting cylinder equation and at relatively low temperatures by first-order kinetics. The dependence of the initial reaction rate on the CCl4 partial pressure follows the Langmuir—Hinshelwood rate expression. At 700—723 K, chemical control is thought to be predominant and an apparent activation energy of 212 kJ mole−1 is found for the chlorination process.

Kinetics of γ-alumina chlorination by phosgene

Abstract The kinetics of the reaction between γ-Al2O3 and COCl2 have been studied by isothermal TG measurements in the temperature range 585–1085 K. The influence of the partial pressure of COCl2 on the reaction rate was investigated at 648, 673 and 698 K in the 104–105 Pa range, using N2 as a diluting gas. The reaction seems to proceed in the chemical control region below 675 K. Above this temperature, however, diffusional processes and decomposition of COCl2 are considered to affect the reaction rate. In the chemical control region an apparent order of reaction of 0.75 in respect of COCl2 and an apparent activation energy of 128–135 kJ mole−1 were found for the chlorination process.

Kinetic study of the carbonyl sulphide synthesis from carbon dioxide and carbon disulphide on alumina catalysts

Abstract The kinetics of the CO 2 +CS2=2COS reaction over new and used alumina catalysts was studied at 523–623 K. The adsorption of the reaction components was measured at the temperature of the catalytic tests by volumetric and thermogravimetric methods. The number and energetics of the acidic and basic sites were investigated with a combined volumetric-microcalorimetric method using NH 3 and CO 2 as probe molecules. The equilibrium constants of the main reaction and several assumed side reactions have also been calculated. Closely zero order and first order behaviour were observed for CO 2 and CS 2 , respectively. The loss of catalytic activity upon long term loading was roughly proportional to the loss of the surface basic sites whereas the number of the acidic centers moderately increased. On all catalysts, very likely by the removal of basic OH and 0 2 -sites, carbon tetrachloride immediately caused an ultimate cession of the catalytic activity. As CS 2 also reacts with the surface OH groups, leading to H 2 S and side products, under steady state conditions the rate-determining step is considered to be the reaction of strongly adsorbed CO 2 (presumably in a bidentate or a bridging carbonate form) with physisorbed or gas-phase CS 2 . Efforts to regenerate the aged catalysts by treatments with oxygen at 573 K or by leaching with liquid phase CS 2 have failed.

Tg studies on the reactions of hematite, magnetite and wüstite with COC12 and CO+Cl2

Abstract The chlorination of hematite, magnetite and wustite with COCl 2 and CO+Cl 2 were studied by thermogravimetry and X-ray diffraction. The equilibrium compositions of the gas- and solid-phases were determined by computer assisted thermodynamic calculations. During the chlorination of wustite, as an intermediate product, FeCl 2 (s) was detected. A simulteneous transformation of wustite was observed first into magnetite, and at higher temperatures, into hematite. In the case of the chlorination of magnetite with COCl 2 , hematite and FeCl 2 (s) were formed as intermediate products. The reaction of wustite with CO+Cl 2 , started at very low temperatures and took place via the formation of FeCl 2 (s), FeCl 3 (s) and FeOCl(s).

Comparative thermogravimetric study of chlorinations of hematite and wustite

The reactions of hematite and wustite with Cl2, COCl2, CO+Cl2 and gaseous CCl4 were studied by thermogravimetry, X-ray diffraction and computer-assisted thermodynamic calculations. During the chlorination of hematite, only gaseous products were formed. The apparent activation energies were calculated from the isothermal TG curves. The chlorination of wustite involves the formation and transformation of a series of solid chloride products. FeCl2(s), FeCl3(s) and FeOCl(s) were found as intermediates during chlorination with Cl2 or Cl2+CO, while only FeCl2(s) was detected in reactions with COCl2 oe CCl4. The chlorinations of the iron oxides with various agents were compared, and the differences in reactivity sequences were established.ZusammenfassungDie Reaktionen von HÄmatit und Wustit mit Cl2, COCl2, CO+Cl2 and gasförmigen CCl4 wurden thermogravimetrisch und röntgendiffraktometrisch untersucht. Thermodynamische Berechnungen wurden mit Computern ausgeführt. Bei der Chlorierung von HÄmatit entstehen nur gasförmige Reaktionsprodukte. Die scheinbaren Aktivierungsenergien wurden aus isothermen TG-Kurven berechnet. Bei der Chlorierung von Wustit wird eine Reihe von festen Chloriden gebildet. FeCl2(s), FeCl3(s) und FeOCl(s) treten bei der Chlorierung mit Cl2 oder Cl2 + CO als intermediÄre Produkte auf, wÄhrend bei Reaktionen mit COCl2 oder CCl4 nur FeCl2(s) nachgewiesen wurde. Die verschiedenen Chlorierungsmittel wurden hinsichtlich ihrer Wirksamkeit miteinander verglichen und in einer entsprechenden Reihenfolge eingeordnet.РЕжУМЕРЕАкцИИ гЕМАтИтА И ВУ стИтА с Cl2, COCl2, CO+Cl2 И гАжООБРАжНыМ CCl24 Бы лИ ИжУЧЕНы с пОМОЩьУ тЕРМОгРАВИ МЕтРИИ, РЕНтгЕНОстРУ ктУРНОгО АНАлИжА И тЕРМОДИНАМ ИЧЕскИх РАсЧЕтОВ, пРОВЕДЕННых с ЁВМ. пРИ хлОРИРОВАНИИ гЕМАтИ тА ОБРАжУУтсь тОлькО гА жООБРАжНыЕ пРОДУкты. НА ОсНОВЕ кРИВых ИжОт ЕРМИЧЕскОИ тг БылИ Вы ЧИслЕНы кАжУЩИЕсь ЁНЕРгИИ Ак тИВАцИИ. хлОРИРОВАНИЕ ВУстИт А ВклУЧАЕт ОБРАжОВАН ИЕ И пРЕВРАЩЕНИЕ РьДА тВЕ РДых пРОДУктОВ. пРИ ВжАИМОДЕИстВИИ с Cl2 Ил И Cl2 + CO БылИ ИДЕНтИФИцИРОВАНы тА кИЕ пРОМЕжУтОЧНыЕ пР ОДУкты, кАк FeCl2, FeCl3 И FeOCl, тОгДА кАк В Р ЕАкцИИ с COCl2 CCl4 — тОлькО ОДИН FeCl2. сОпОстАВлЕНы РЕАкцИ И хлОРИРОВАНИь РАжлИ ЧНыМИ АгЕНтАМИ ОкИслОВ жЕл ЕжА И УстАНОВлЕНы РАжлИЧИь В Их РЕАкцИО ННОИ спОсОБНОстИ.

TG studies on the reactions of hematite, magnetite and wustite with CCl4

Abstract The chlorination of hematite, magnetite and wustite with gaseous CCl4 were studied by thermogravimetry. The equilibrium compositions of the gas- and solid phases were determined by computer assisted thermodynamic calculations. In the case of hematite a reaction order of 0.5 was found with an apparent activation energy of 125 kJ.mol−1. During the chlorination of wustite solid FeCl2/s/ was detected as intermediate product. A simultaneous transformation of wustite was observed, first into magnetite, at higher temperatures, into hematite. Similarly, FeCl2 and hematite were formed as intermediate products during the chlorination of magnetite. Temperature and partial pressure dependence of the FeCl2/s/ formation and volatilization were also studied.

Kinetics of γ-alumina chlorination by tetrachloroethylene

Abstract The kinetics of the reaction between γ-Al 2 O 3 and gaseous C 2 Cl 4 have been studied by anisothermal and isothermal TG measurements in the temperature range 298–1123 K. The weight loss due to chlorination becomes measurable above 933 K. Supposing dissociative adsorption the initial reaction rate can be described by a Langmuir—Hinshelwood type of rate expression in the partial pressure range investigated (0–2 x 10 3 Pa C 2 Cl 4 . The apparent activation energy calculated from the initial reaction rates (141 kJ mole −1 ) is in good agreement with that calculated from the rate constants of the Langmuir—Hinshelwood expression (133 kJ mole −1 ). The characteristic temperature dependence observed earlier in the γ-Al 2 O 3 + CCl 4 system can be interpreted by the results obtained in this work.

Thermogravimetric, mass spectrometric and XPS investigation on the chlorination reactions of V2O5 AND TiO2

Abstract Comparative studies on the kinetics and mechanism of the chlorination of V 2 O 5 and TiO 2 /anatase/ with CCl 4 have been performed. The chlorination of V 2 O 5 occurred to be O.5 order in CCl 4 , whereas in case of TiO 2 closely first order kinetics was observed with apparent activation energies of 77 ± 5 and 118 ± 7 kJ.mol −1 , resp. In both cases a dissociative adsorption of CCl 4 is considered to precede the reaction and the transformation of CCl 4 to CO 2 is assumed to occur via the formation of adsorbed COCl 2 intermediate. In case of V 2 O 5 , phosgene is less reactive than CCl 4 , so during the chlorination of V 2 O 5 by CCl 4 the gas phase concentration of COCl 2 might achieve a considerable level, while in the TiO 2 CCl 4 system only trace quantities of phosgene are observable. At the beginning of the reactions step by step exchange of surface O by Cl occurs, and the surface intermediates of the chlorination are V and Ti ions of lowered valence state, as it has been characterized by ESCA.

TG Studies on Chlorination Reactions of γ-Al2O3

Kinetics of the reactions of γ-Al2O3 with COCl2, CO+Cl2 and CCl4 was studied by performing anisothermal and isothermal TG measurements from room temperature up to 1123 K and at partial pressures up to 105 Pa, using a Mettler semimicro recording balance coupled with a fused silica reactor designed specially for this purpose. From the anisothermal measurements performed at linear heating rate the temperature ranges of adsorption and of chemisorption and the starting temperatures of the reactions were determined. The isothermal weight loss curves could be well fitted by the first order kinetics at temperatures where chemical control was predominant and by the contracting cylinder model above these temperatures. The Langmuir-Hinshelwood rate expression could be used to describe the reaction rate vs reactive gas concentration. The apparent activation energies were calculated by the Arrhenius plots in temperature ranges where the reactions were controlled by the chemical kinetics. It is shown that the technique and the procedure developed enable to determine the characteristic kinetic parameters of the different phases of these reactions.

TG study on the reaction of γ-Al2O3 by CCl4. Part I. Kinetic model for the chlorination process

Abstract Thermogravimetric (TG) measurements were carried out to study the chlorination of γ-alumina by gaseous CCl 4 in the temperature range 650–1123 K at 10 2 –10 4 Pa CCl 4 partial pressure. Experimental results indicate that the reaction involves two main steps: the substitution of oxygen atoms on the surface by chlorine leading to a mass gain and the volatilization of the main gaseous product, aluminium chloride, with a mass loss of the sample. These processes take place simultaneously during the course of the reaction. A kinetic model is proposed to describe these two steps providing a simple method for linearization of the initial part of the isothermal TG curves. Temperature and partial pressure dependence of the reaction rate and of the steady-state surface coverage are discussed on the basis of the proposed kinetic model. Activation energies and reaction orders are calculated for these two steps.