Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films

Amorebieta, V. T.; Colussi, A. J.

doi:10.1002/kin.550170806

Cited by 26 publications

(7 citation statements)

References 22 publications

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“…Heterogeneous reactions play an important role in the chemistry of chlorinated hydrocarbons, especially in the ini-tiation which is influenced by soot deposition on the walls [8]. We have observed that wall conditions also have an effect on byproduct formation.…”

Section: Benzene 1l-dichloroethanementioning

confidence: 81%

Mechanisms of By‐Product Formation in the Dehydrochlorination of 1,2‐Dichloroethane

Schneider

Wolfrum

1986

Ber Bunsenges Phys Chem

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The decomposition of 1,2‐dichloroethane (DCE) to vinyl chloride (VC) was studied in the temperature range 620–750 K at DCE partial pressures of 50–450 Torr. Initiation of the radical chain reaction by a XeCl laser allowed controlled degree of conversion which had a strong influence on the formation of the major by‐products acetylene and 2‐chlorobutadiene. Both compounds are formed via abstraction of olefinic hydrogen from vinyl chloride by Cl atoms. Analysis of the product distribution combined with calculations yielded kinetic data of these side reactions. The mechanism was confirmed by adding HCl and vinyl chloride to the substrate. Formation of other byproducts by homogeneous processes and the photolysis of vinyl chloride are discussed.

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Section: Benzene 1l-dichloroethanementioning

confidence: 81%

Mechanisms of By‐Product Formation in the Dehydrochlorination of 1,2‐Dichloroethane

Schneider

Wolfrum

1986

Ber Bunsenges Phys Chem

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“…At this stage the atmospheric relevance of present results must be limited to the preliminary statement that carbonaceous surfaces are indeed very active for the decomposition of C1,CF to an extent hardly predictable on the basis of its chemical inertness. Several questions remain to be explored, such as : (1) the similarity between the charcoal material used here and the undefined and necessarily variable properties of atmospheric carbon particles, and (2) the synergism or antagonism of other more abundant and reactive, albeit more lightly bound, pollutants. '' Although both aspects certainly deserve further study they can not be expected to be easily answered, since alternatives to present experiments should involve lower temperatures and the addition of NO,, 0, and hydrocarbons better to simulate actual atmospheric conditions.…”

Section: Resultsmentioning

confidence: 99%

Heterogeneous decomposition of trichlorofluoromethane on carbonaceous surfaces

Colussi¹,

Amorebieta²

1987

J. Chem. Soc., Faraday Trans. 1

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The interaction of trichlorofluoromethane with activated charcoal has been investigated by dynamic mass spectrometry up to 750 K. Prior physical adsorption, revealed in programmed desorption experiments, is followed by irreversible first-order decay with formation of nearly equimolar amounts of HCl above 550 K. This unexpectedly fast process has an apparent activation energy of only 59.4 kJ mol-' and is demonstrably catalytic. The mechanism of C1,CF decomposition on carbon surfaces and its possible impact on atmospheric chemistry are discussed.We have recently presented direct evidence showing that carbon surfaces efficiently catalyse the atomization of molecular chlorine and the breakdown of polychlorinated methanes.' Such results are particularly relevant to the free-radical mechanisms underlying the synthesis and decomposition of chlorocarbons and, moreover, provide a rationalisation for the erratic kinetic behaviour often observed in such systems.2 Early reports had already identified charcoal as a catalyst in thermal chlorination^.^ Since carbon is the most abundant element associated with pollution particulates,* and considering that the collision frequency between gas molecules and particles in highly contaminated urban environments can reach up to ca. 1 s -' ,~ and that current estimates of the tropospheric lifetime of chlorofluorocarbons span the wide range 30-150 years, we decided to undertake studies on the decay of C1,CF with the specific goal of assessing the likelihood of its decomposition on atmospheric carbonaceous surfaces. Clearly we face one of those rare kinetic problems which require one to explore chemical change over long, rather than short, time period^.^ The results reported in this paper confirm the remarkable activity of carbonaceous surfaces towards chlorocarbon decomposition and, in conjunction with simple considerations, suggest the possibility of an active role for soot as a tropospheric sink for such species. ExperimentalKinetic studies were performed in a 300 cm3 heated Pyrex reactor coupled to an analytical mass spectrometer (EMBA 11, Extranuclear Laboratories) via a molecular leak for continuous monitoring of reactants and pr0ducts.l It was verified that C1,CF (Freon 11, Matheson) is perfectly stable in the gas phase below 750 K, as expected from kinetic and thermochemical considerations." On the other hand the addition of small amounts (0.5-1.0 g) of activated carbon (Mallinckrodt, 0.5 O h ash, specific area 684 m2 g-l, as determined by nitrogen adsorption B.E.T. measurements) dispersed on glass wool to minimize mass-transfer artifacts, led to the rapid first-order decay of C1,CF at pressures between 0.02 and 0.1 1 Torr in the range 555-750 K. The most intense ion signal in the mass spectrum of the reactant at m / z = 101 (C1,CF') was used for this purpose. Moreover, rates were found to be proportional to the amount of carbon added, confirming the catalytic nature of a process which leads to the formation of nearly equimolar amounts of HCl as the sole gaseous product. The last...

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“…It has been demonstrated of gaseous ZrCl 4 through further chlorination of ZrCl 2 is that on carbon surface at high temperature, the chlorine thermodynamically most feasible. This is suggested to be molecule dissociates into atoms [20] that are highly reactive. kinetically fast.…”

Section: Mechanism Of the Chlorinationmentioning

confidence: 97%

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

Jena

Brocchi

Reis

1999

Metall Mater Trans B

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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 ZrO 2 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 ZrO 2 , 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 ZrO 2 (Ϫ38 ϩ 25 m) was studied, and it was found that the rate of chlorination increased up to the size range of Ϫ75 to ϩ53 m, 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 ( pCl 2 ) on the rate of chlorination was found to obey the following relationship, derived from the Langmuir adsorption isotherm: v ϭ k и K и pCl 2

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Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films

Cited by 26 publications

References 22 publications

Mechanisms of By‐Product Formation in the Dehydrochlorination of 1,2‐Dichloroethane

Mechanisms of By‐Product Formation in the Dehydrochlorination of 1,2‐Dichloroethane

Heterogeneous decomposition of trichlorofluoromethane on carbonaceous surfaces

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

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