137 research outputs found
First Study of the Pyrolysis of a Halogenated Ester: Methyl Chloroacetate
International audienceThe pyrolysis of a halogenated ester, methyl chloroacetate (MC), under dilute atmosphere and quasi-atmospheric pressure was studied at temperatures from 473 to 1048 K using an alumina tubular reactor. MC was chosen as a surrogate to model the thermal decomposition of ethyl bromoacetate, a chemical warfare agent. A maximum MC conversion of 99.8% was observed at a residence time of 2 s, a temperature of 1048 K, and an inlet mole fraction of 0.01. The following products were quantified: CO, CO2, HCl, methane, ethylene, ethane, propene, chloromethane, dichloromethane, vinyl chloride, chloroethane, and dichloroethane. For the first time, a detailed kinetic model of MC pyrolysis was developed and gave a good prediction of the global reactivity and the formation of most of the major products. Flow rate and sensitivity analyses were made to highlight the different pathways of decomposition during the MC pyrolysis. In a first attempt to extrapolate the results obtained with methyl chloroacetate to ethyl bromoacetate, simulations were run with a modified version of the model developed in this study taking into account the differences in bond dissociation energies induced by the change of the chlorine atom by a bromine one
Experimental and modeling study of the low-temperature oxidation of large alkanes
This paper presents an experimental and modeling study of the oxidation of
large linear akanes (from C10) representative from diesel fuel from low to
intermediate temperature (550-1100 K) including the negative temperature
coefficient (NTC) zone. The experimental study has been performed in a
jet-stirred reactor at atmospheric pressure for n-decane and a
n-decane/n-hexadecane blend. Detailed kinetic mechanisms have been developed
using computer-aided generation (EXGAS) with improved rules for writing
reactions of primary products. These mechanisms have allowed a correct
simulation of the experimental results obtained. Data from the literature for
the oxidation of n-decane, in a jet-stirred reactor at 10 bar and in shock
tubes, and of n-dodecane in a pressurized flow reactor have also been correctly
modeled. A considerable improvement of the prediction of the formation of
products is obtained compared to our previous models. Flow rates and
sensitivity analyses have been performed in order to better understand the
influence of reactions of primary products. A modeling comparison between
linear alkanes for C8 to C16 in terms of ignition delay times and the formation
of light products is also discussed
To better understand the formation of short-chain acids in combustion systems
International audienceOur study aims at a better control and understanding of the transfer of a complex [DNA supercoiled plasmid - dodecyltrimethylammonium surfactant] layer from a liquid-vapour water interface onto a silicon surface without any additional cross-linker. The production of the complexed layer and its transfer from the aqueous subphase to the substrate is achieved with a Langmuir-Blodgett device. The substrate consists of a reconstructed boron doped silicon substrate with a nanometer-scale roughness. Using X-ray photoelectron spectroscopy and atomic force microscopy measurements, it is shown that the DNA complexes are stretched in a disorderly manner throughout a 2-4 nm high net-like structure. The mechanism of transfer of this layer onto the planar surface of the semi-conductor and the parameters of the process are analysed and illustrated by atomic force microscopy snapshots. The molecular layer exhibits the typical characteristics of a spinodal decomposition pattern or dewetting features. Plasmid molecules appear like long flattened fibers covering the surface, forming holes of various shapes and areas. The cluster-cluster aggregation of the complex structure gets very much denser on the substrate edge. The supercoiled DNA plasmids undergo conformational changes and a high degree of condensation and aggregation is observed
Modeling of the formation of short-chain acids in propane flames
International audienceIn order to better understand their potential formation in combustion systems, a detailed kinetic mechanism for the formation of short-chain monocarboxylic acids, formic (HCOOH), acetic (CH3COOH), propionic (C2H5COOH) and propenic (C2H3COOH)) acids, has been developed. Simulations of lean (equivalence ratios from 0.9 to 0.48) laminar premixed flames of propane stabilized at atmospheric pressure with nitrogen as diluent have been performed. It was found that amounts up to 25 ppm of acetic acid, 15 ppm of formic acid and 1 ppm of C3 acid can be formed for some positions in the flames. Simulations showed that the more abundant C3 acid formed is propenic acid. A quite acceptable agreement has been obtained with the scarce results from the literature concerning oxygenated compounds, including aldehydes (CH2O, CH3CHO) and acids. A reaction pathways analysis demonstrated that each acid is mainly derived from the aldehyde of similar structure
A Lean Methane Prelixed Laminar Flame Doped witg Components of Diesel Fuel. Part I: n)Butylbenzene
To better understand the chemistry involved during the combustion of
components of diesel fuel, the structure of a laminar lean premixed methane
flame doped with n-butylbenzene has been investigated. The inlet gases
contained 7.1% (molar) of methane, 36.8% of oxygen and 0.96% of n-butylbenzene
corresponding to an equivalence ratio of 0.74 and a ratio C10H14 / CH4 of
13.5%. The flame has been stabilized on a burner at a pressure of 6.7 kPa using
argon as diluent, with a gas velocity at the burner of 49.2 cm/s at 333 K.
Quantified species included the usual methane C0-C2 combustion products, but
also 16 C3-C5 hydrocarbons, 7 C1-C3 oxygenated compounds, as well as 20
aromatic products, namely benzene, toluene, phenylacetylene, styrene,
ethylbenzene, xylenes, allylbenzene, propylbenzene, cumene, methylstyrenes,
butenylbenzenes, indene, indane, naphthalene, phenol, benzaldehyde, anisole,
benzylalcohol, benzofuran, and isomers of C10H10 (1-methylindene,
dihydronaphtalene, butadienylbenzene). A new mechanism for the oxidation of
n-butylbenzene is proposed whose predictions are in satisfactory agreement with
measured species profiles in flames and flow reactor experiments. The main
reaction pathways of consumption of n butylbenzene have been derived from flow
rate analyses
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