Energy Transfer Effects during Chemically Activated Decomposition of Larger Aromatic Compounds (original) (raw)
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Mechanisms and kinetics of thermal reactions of aromatic hydrocarbons from pyrolysis of solid fuels
The kinetics of the thermal conversion of aromatic hydrocarbons in the presence of hydrogen and steam were studied, using anphthalene, toluene and benzene as model compounds. The experiments were performed in a tubular flow reactor at a total pressure of 160 KPa, temperatures of 700-14OO"C, residence times of 0.3-2s and different gas-phase concentrations of hydrogen, steam and the aromatics. The mechanisms of primary and consecutive reactions are presented as reaction schemes that are supported by kinetic calculations. The following order of reactivity is obtained: toluene >> naphthalene > benzene. Besides gaseous organic cracking products such as methane and ethene, condensed products and a carbonaceous residue (soot) is formed, principally from naphthalene. Soot formation is strongly inhibited by hydrogen. Steam has only a little influence on the conversion of the aromatics. Under the given reaction conditions, neither the soot primarily formed nor the organic cracking products such as methane are completely converted by steam to carbon monoxide and hydrogen, even at the highest temperature investigated (1400°C). Copyright 0 1996 Elsevier Science Ltd.
Physical Chemistry Chemical Physics, 2002
Kinetic modeling is becoming a powerful tool for the quantitative description of combustion processes covering different fuels and large ranges of temperature, pressure and equivalence ratio. In the present work, a reaction mechanism which was developed initially for benzene oxidation, and included the formation of polycyclic aromatic hydrocarbons was extended and tested for the combustion of acetylene and ethylene. Thermodynamic and kinetic property data were updated. If available, data were taken from the recent literature. In addition, density functional theory as well as ab initio computations on a CBS-Q and CBS-RAD level, partially published previously, were carried out. Quantum Rice-Ramsperger-Kassel analysis was conducted in order to determine pressure-dependent rate constants of chemically activated reactions. The model was developed and tested using species concentration profiles reported in the literature from molecular beam mass-spectrometry measurements in four unidimensional laminar premixed low-pressure ethylene, acetylene and benzene flames at equivalence ratios (f) of 0.75 and 1.9 (C 2 H 4 ), 2.4 (C 2 H 2 ) and 1.8 (C 6 H 6 ). Predictive capabilities of the model were found to be at least fair and often good to excellent for the consumption of the reactants, the formation of the main combustion products as well as the formation and depletion of major intermediates including radicals. Selfcombination of propargyl (C 3 H 3 ) followed by ring closure and rearrangement was the dominant benzene formation pathway in both rich acetylene and ethylene flames. In addition, reaction between vinylacetylene (C 4 H 4 ) and vinyl radical (C 2 H 3 ) contributed to benzene formation in the f ¼ 1.9 ethylene flame. Propargyl formation and consumption pathways which involve reactions between acetylene, allene, propyne and singlet and triplet methylene were assessed. Significant overpredictions of phenoxy radicals indicate the necessity of further investigation of the pressure and temperature dependence and the product distribution of phenyl oxidation. The possible formation of benzoquinones, the ratio of the ortho and para isomers and their degradation pathways are of particular interest.
A Kinetic Modeling Study of the Oxidation and Combustion of Aromatic Species
The aim of this work is to further validate a general and detailed kinetic model on very recent experimental data of the oxidation and combustion of aromatic compounds and also in the case of their blends with n-alkanes, both studied in a jet-stirred reactor. The comparisons between new experimental data and model predictions further confirm the validity and the broad applicability of the kinetic model.
Thermal reactions of aromatic hydrocarbons in the pyrolysis of ethane and propane
2002
The influence of aromatics on the pyrolysis of ethane and propane was studied using benzene, toluene, α-methylnaphthalene and anthracene as model compounds. The experiments were performed in a tubular flow reactor at ordinary pressure, temperatures of 700-850°C, residence times between 0.1-1s and low concentration of aromatics (1-6%mole). Aromatic hydrocarbons inhibited the pyrolysis rate of ethane and propane and the following order of inhibitory effectwhich decreases with the increase of temperature-was found: toluene > α-methylnaphthalene > benzene > anthracene. The C 1-C 4 composition of the effluent was only slightly influenced by the presence of aromatics, which were found to suffer an appreciable transformation to alkylated derivatives, depending on their structure and despite their thermal stability when highly diluted with N 2 at the same temperatures. The transformation of the aromatic hydrocarbons was explained by the interference of the main chain propagators (·H, ·CH 3 , ·C 2 H 3 , ·C 2 H 5) with the aromatic and benzyl type radicals. Benzene has only a small contribution to soot formation, a phenomenon which however was found to increase when alkylaromatic and polycyclic hydrocarbons are present in the feed.
Kinetic and products of C3H3 and C4H2 reaction: theoretical and computational study
Jurnal Teknik Kimia Indonesia, 2018
The formation of first aromatic ring was suggested to be a crucial step of the PAHs and soot growth mechanism. In general, four-, five-, six-, or seven-membered ring molecules could be formed by the addition reaction of two hydrocarbon molecules resulted from many different pathways. Small hydrocarbon molecules with numerous concentrations during combustion/pyrolysis are suspected to play an important role. Propargyl radical (•C3H3) and butadiene (C4H2) have been chosen as the initial reactants in this discussion, since they are found at relatively high concentrations in flame experiments to examine the above particular reaction. Following initial addition mechanisms, their adduct intermediate can form a ring molecule and undergo subsequent rearrangement. All possible molecular structures were considered and the viability of each channel was assessed through a “RRKM + master equation” kinetic study. This study is an attemp and example to develop and apply molecular computational met...
Reassessment of the Kinetic Influence of Toluene on n Alkane Pyrolysis
Energy & Fuels, 2010
The inhibition effect of toluene on the kinetics of n-alkane pyrolysis has been well-known for a long time. However, most studies were performed at high-temperature-low-pressure conditions. The present study investigates a wider range of experimental pressures and temperatures (from 0.001 to 700 bar and from 350 to 600°C). To account for those, a kinetic model based on free-radical reactions was developed. This model was tested against available literature data for the low-pressure range and against new experiments for the high-pressure range. Whatever the temperature and pressure, it arises that toluene has indeed an inhibitive effect on the pyrolysis of n-octane. This effect is explained by the formation of benzyl radicals stabilized by resonance, via hydrogen-transfer reactions, that leads to new termination reactions. However, this inhibition will be significantly modulated as a function of the pressure, temperature, and reaction progress, from strong to very weak. Our paper describes the mechanistic reasons for this change in the extent of the inhibition effect and proposes an integrated model for the kinetic effects of monoaromatic hydrocarbons on n-alkanes during pyrolysis.