F. Baronnet

Characterization of emissions during the heating of tyre contaminated scrap

In order to characterize the compounds (type and quantities) emitted during melting of organic contaminated scrap and to investigate the mechanism of their formation, an experimental set-up has been designed and built to study precisely the influence of temperature and gas atmosphere in the conditions of an electric arc furnace. These experiments lead to the determination of mass balances (C, H, O, S) and to the quantification of unburnt compounds (tars, carbon monoxide, volatile organic compounds (VOCs), benzene, toluene, ethylbenzene and xylenes (BTEX), polyaromatic compounds (PAHs)). Degradation conditions (gas atmosphere and temperature) corresponding to different areas in the electric furnace have also been investigated. Such experiments lead to a better understanding of degradation mechanisms; this interpretation is not possible from investigations performed in an industrial furnace since there are many uncontrolled parameters (large dispersion of the results).

Thermal decomposition of chloropicrin, diphosgene and phosgene between 100 and 530°C

Abstract The gas-phase pyrolysis of chloropicrin, diphosgene and phosgene has been investigated in a static reactor at temperatures between 100 and 530°C, at an initial pressure of 25 torr and for reaction times ranging from 10 to 120 min. Phosgene is the main carbon containing reaction product of the pyrolyses of chloropicrin and diphosgene and its decomposition leads to the formation of carbon monoxide and chlorine. A kinetic scheme for the decomposition of phosgene has been proposed and has permitted satisfactory modelling of the experimental results obtained. The study clearly shows the possible industrial use of this process to destroy chemical weapons and a first range of temperatures and reaction times has been selected for future reactor design.

Detailed mechanism of the oxidative coupling of methane

To determine the relative importance of gas-phase and surface reactions in the oxidative coupling of methane (OCM), experimental investigations were performed. Our experimental results were compared to simulated values derived from a kinetic model taking into account heterogeneous and gas-phase reactions. We propose an original approach derived from Bensons techniques to estimate the kinetic parameters of surface reactions.

Kinetic study of the Chddative Coupling of Methane in a Catalytic Jet Stirred Reactor

It is now well-established that the oxidative coupling of methane is a homogeneous-heterogeneous reaction. Lunsford [1] has been a pioneer in this field, showing that methyl radicals are produced on the surface of the catalyst, released and coupled in the gas phase. However, the question of interaction between the homogeneous and heterogeneous processes is not completely understood. In order to obtain more information on this reaction, a new type of reactor was developed, which contains a large well-stirred gas phase volume in contact with catalyst pellets laid on the bottom of the reactor. The chosen catalyst is lanthanum oxide because it has a high stability and activity. This reactor permits an investigation of the influence of the usual parameters: space time, temperature, ratio of reactants, dilution, …; it also makes possible the modification of the relative importance of the gas phase and surface reactions by varying the number of catalyst pellets (i. e. the active catalyst surface) with a fixed gas phase volume. It is also possible to choose different operating temperatures for the catalyst and for the gas phase. The effect of these new parameters has been investigated at low conversion for the major part of this study, in order to limit as far as possible any change in the reaction due to the consumption of reactants.

Competition between the gas and surface reactions for the oxidative coupling of methane: 1. ‘Non-isothermal’ results in catalytic jet-stirred reactor

Abstract A catalytic jet-stirred reactor (CJS reactor) has been developed to investigate the interaction between gas-phase and surface reactions for the oxidative coupling of methane. This reactor allows the modification of the number of catalyst pellets (La2O3) for a fixed gas-phase volume. It permits also to set different temperatures for the gas-phase volume and the catalyst. The results of these ‘nonisothermal’ experiments are presented; they suggest that the contribution of the gas-phase reactions is rather significant and that the C2+ selectivity is improved by an increase of the gas-phase temperature up to 850°C.

Comparative modelling study on the inhibiting effect of TAME, ETBE and MTBE at low temperature

The oxidation of tert-amyl methyl ether (TAME) at low temperature and low pressure is investigated computationally in a static reactor. The results are compared to measurements. The observed satisfactory agreement between the model predictions and the experimental data confirms the validity of the proposed reaction scheme. The results for TAME oxidation are related to those for ethyl tert-butyl ether (ETBE) and methyl tert-butyl ether (MTBE), previously obtained in the literature. For all three ethers, it is found that their addition to n-pentane increases the induction period of the first cool flame of the latter. The calculations indicate that the amount of alkene production which can form resonance-stabilized ‘‘dead radicals’’ correlates with the efficiency of octane boosters.

Competition between gas and surface reactions in the oxidative coupling of methane 2. Isothermal experiments in a catalytic jet-stirred gas phase reactor

Abstract The oxidative coupling of methane over a La2O3 catalyst was investigated by means of a continuous flow reactor with a perfectly mixed gas phase and a variable number of catalyst pellets. Experiments were carried out isothermally, i.e. at the same temperature for the gas phase and the catalyst, under the following conditions: total pressure equal to 1.05 bar, inlet mixture CH4:O2:He = 13.9:2.8:83.3 (mol), temperatures from 650 to 950°C, gas space times ranging from 0.6 to 6 s and pseudo catalytic contact times from 0 to 60 mg s cm-3. Complementary experiments were performed on carbon monoxide oxidation. Our results are in favour of a reaction mechanism involving, besides gas phase free radical elementary reactions, surface initiation reactions CH4→·CH3C2H6→·C2H5C2H4→·C2H3and surface oxidation reactions.·CH3→CO2

Chemical kinetic modeling of n-hexane pyrolysis of ACUCHEM, CHEMKIN and MORSE software packages

The chemistry of the thermal reactions of complex hydrocarbons is of fundamental importance in steam-cracking operations. The difference in the product distribution observed when various feeds are cracked could in theory be accounted for by a detailed analysis of the initial feedstock (the distribution of the various hydrocarbons in feedstock can explain the variations of the output of the industrial units, especially from the point of view of the yields of the light olefins), but such a method would be very difficult and would require lengthy and complicated calculations

Products of the gas-phase pyrolysis of 1,4-dioxane

Abstract The gas-phase pyrolysis of 1,4-dioxane has been studied in a static reactor at 510 and 550°C below 25 mbar, at reaction times ranging from 1 to 10 minutes, corresponding to conversion rates between 1 and 25%. The main reaction products are CO, H 2 , C 2 H 4 , HCHO, the minor products include C 2 H 6 , CH 2 =CH-CHO, CH 3 -CHO, CH 4 and CH 3 -CH=CH 2 . This reaction is markedly inhibited by the addition of toluene, which observation permits us to propose a free radical chain mechanism to account for the experimental results.

Mechanistic modeling of the pyrolysis of n-hexane

A mechanistic model of the thermal decomposition reactions of n-hexane at low conversion ( < 5%) using as a basis a complex free radical chain mechanism and taking into account H abstraction from propene has been adjusted and compared to the observed product distribution. A reasonably good agreement is found between the computed curves and the experimental results obtained at 693 K and 133 mbar.