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The range of temperature used by Lur’e and Mikhno [6] (20–3208C) for the investigation of the kinetics of oxidation of graphitized soot by NO2 (using a circulating-flow set-up) is more relevant for NO2-regenerative technologies. A mechanism for the interaction between NO2 and carbon based on the formation and decomposition of an intermediate species was proposed and the activation energy found for the reaction of NO2 consumption by soot material was 50 kJ mol21 in the temperature range 180– 3508C. A strong variation of the reaction order with respect to NO2 inlet concentration was noticed without any explanation. Moreover the combustion behavior was found to be different for the two temperature ranges 20–1808C and 180–3208C, meaning that the results obtained for the atmospheric chemistry (at low temperature) cannot be used for the moderate temperature range (200–5008C). For a quite similar temperature range 150–3508C, the investigation of adsorption and reaction of NO2 on activated carbon was performed gravimetrically by Gray and Do [7]. The extracted activation energy (86.2 kJ mol21) was smaller than that for O2, H2O and CO2 while NO2 was the most reactive for the temperature range used.
0008-6223 / 02 / $ – see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(01)00103-8
336
F. Jacquot et al. / Carbon 40 (2002) 335 –343
Laboratoire Gestion des Risques et Environnement, Universite´ de Haute-Alsace 25, rue de Chemnitz, 68200 Mulhouse, France Received 4 December 2000; accepted 3 April 2001
Carbon 40 (2002) 335–343
Kinetics of the oxidation of carbon black by NO2 Influence of the presence of water and oxygen
F. Jacquot, V. Logie, J.F. Brilhac*, P. Gilot
In the literature, only little attention has been paid to the reaction of carbon with NO2 at moderate temperature (100–5008C). Most of the publications are in relation with the chemistry of the atmosphere [3–5] for which the oxidation reaction of soot ຫໍສະໝຸດ Baiduith NO2 was extensively
Some papers deal with catalytic soot filters or with soot particulates containing metal additives [10,11]. The effect of the presence of SO2 was also investigated [12].
Most of the investigations published regarding the NO2regenerative technologies were devoted to the flow characterization within the particulate filter [8] for its design optimization but the combustion of soot material was not accounted for in these studies. The behavior of the soot combustion in the CRT system was however investigated by Cooper and Thoss [9] on a test bench. Orders of reaction with respect to NO2 inlet concentration and soot weight were found equal to 1. The benefit of the presence of water in the feed gas for soot oxidation was mentioned by Cooper and Thoss [9] and Cooper et al. [2]. But no kinetic data for the reaction between carbon and NO2 accounting for the presence of H2O in the gas phase were proposed.
Keywords: A. Carbon black; B. Oxidation; D. Reaction kinetics
1. Introduction
The need to meet projected future standards for exhaust emissions from diesel engines will require the application of after-treatment devices such as wall-flow particulate filters [1]. The NO2-regenerative technologies [2] are based on the continuous oxidation of the soot collected in a particulate filter by NO2 in the temperature range 200– 5008C. In this system NO2 is produced by the oxidation of the engine exhaust NO in a catalytic upstream monolithic converter. NO2 is known to be more reactive than the other oxidizing species (O2, H2O and CO2) at low temperature. The rate of carbon consumption by NO2 is sufficient to ensure an equilibrium in the particulate filter between the weight of soot produced by the engine and that consumed by the reaction.
*Corresponding author. Tel.: 133-3-8932-7666; fax: 133-38932-7661.
E-mail address: jf.brilhac@uha.fr (J.F. Brilhac).
studied by different techniques (infrared spectroscopy, thermogravimetry, . . . ) but, for lower temperature (below 1008C).
Abstract
In a fixed bed reactor, the rate of carbon black oxidation by NO2 is significant for temperatures above 3008C, leading to NO, CO and CO2 formation. The presence of O2 in the feed gas increases the rate of oxidation, as well as the presence of water. A cumulative effect is observed when both water and oxygen are present. An oxygen balance shows that oxygen atoms of water molecules are not consumed. Water acts as a catalyst for the C–NO2 reaction. A kinetic mechanism in which intermediate nitro-oxygenated species are formed in the presence of NO2 during an initial step is in agreement with all these observations. Oxygen and NO2 are able to react with these species at 3008C. A parametric study of the effects of the temperature, NO2, O2 and H2O concentrations was performed. With a one-dimensional model of NO2 consumption along the thickness of the carbon black bed, kinetic constants were derived and a phenomenological law was proposed, accounting for the effect of the presence of oxygen and water. © 2002 Elsevier Science Ltd. All rights reserved.
0008-6223 / 02 / $ – see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(01)00103-8
336
F. Jacquot et al. / Carbon 40 (2002) 335 –343
Laboratoire Gestion des Risques et Environnement, Universite´ de Haute-Alsace 25, rue de Chemnitz, 68200 Mulhouse, France Received 4 December 2000; accepted 3 April 2001
Carbon 40 (2002) 335–343
Kinetics of the oxidation of carbon black by NO2 Influence of the presence of water and oxygen
F. Jacquot, V. Logie, J.F. Brilhac*, P. Gilot
In the literature, only little attention has been paid to the reaction of carbon with NO2 at moderate temperature (100–5008C). Most of the publications are in relation with the chemistry of the atmosphere [3–5] for which the oxidation reaction of soot ຫໍສະໝຸດ Baiduith NO2 was extensively
Some papers deal with catalytic soot filters or with soot particulates containing metal additives [10,11]. The effect of the presence of SO2 was also investigated [12].
Most of the investigations published regarding the NO2regenerative technologies were devoted to the flow characterization within the particulate filter [8] for its design optimization but the combustion of soot material was not accounted for in these studies. The behavior of the soot combustion in the CRT system was however investigated by Cooper and Thoss [9] on a test bench. Orders of reaction with respect to NO2 inlet concentration and soot weight were found equal to 1. The benefit of the presence of water in the feed gas for soot oxidation was mentioned by Cooper and Thoss [9] and Cooper et al. [2]. But no kinetic data for the reaction between carbon and NO2 accounting for the presence of H2O in the gas phase were proposed.
Keywords: A. Carbon black; B. Oxidation; D. Reaction kinetics
1. Introduction
The need to meet projected future standards for exhaust emissions from diesel engines will require the application of after-treatment devices such as wall-flow particulate filters [1]. The NO2-regenerative technologies [2] are based on the continuous oxidation of the soot collected in a particulate filter by NO2 in the temperature range 200– 5008C. In this system NO2 is produced by the oxidation of the engine exhaust NO in a catalytic upstream monolithic converter. NO2 is known to be more reactive than the other oxidizing species (O2, H2O and CO2) at low temperature. The rate of carbon consumption by NO2 is sufficient to ensure an equilibrium in the particulate filter between the weight of soot produced by the engine and that consumed by the reaction.
*Corresponding author. Tel.: 133-3-8932-7666; fax: 133-38932-7661.
E-mail address: jf.brilhac@uha.fr (J.F. Brilhac).
studied by different techniques (infrared spectroscopy, thermogravimetry, . . . ) but, for lower temperature (below 1008C).
Abstract
In a fixed bed reactor, the rate of carbon black oxidation by NO2 is significant for temperatures above 3008C, leading to NO, CO and CO2 formation. The presence of O2 in the feed gas increases the rate of oxidation, as well as the presence of water. A cumulative effect is observed when both water and oxygen are present. An oxygen balance shows that oxygen atoms of water molecules are not consumed. Water acts as a catalyst for the C–NO2 reaction. A kinetic mechanism in which intermediate nitro-oxygenated species are formed in the presence of NO2 during an initial step is in agreement with all these observations. Oxygen and NO2 are able to react with these species at 3008C. A parametric study of the effects of the temperature, NO2, O2 and H2O concentrations was performed. With a one-dimensional model of NO2 consumption along the thickness of the carbon black bed, kinetic constants were derived and a phenomenological law was proposed, accounting for the effect of the presence of oxygen and water. © 2002 Elsevier Science Ltd. All rights reserved.