Pyrolysis Of Toluene Research Articles

Spectral signatures (0.2–5 μm) of soot initiation in the pyrolysis of toluene near 2000 K

The spectral and temporal distributions for optical absorption and radiation occurring in the formation of soot have been investigated for pyrolysis of 1.5% toluene/98.5% argon near 2000 K and 0.8 atm in a shock tube. The experiments employed four concurrent spectrally resolved optical diagnostics: ultraviolet absorption (200–400 nm); absolute emission in the visible (400–700 nm); HeNe laser extinction (632.8 nm); and absolute infrared emission (2–5 μm). The measurements show clearly the progression from parent fuel to increasingly complex species and finally to soot particles. In the earlier phase of the reaction, the measurements reflect molecular absorption and emission signatures of species formed prior to the appearance of soot particles, and exhibit nearly continuous spectral behavior due to extensive overlap between bands. At later times, the spectral signature in all channels is controlled by soot particles. In particular, infared emission at 3–5 μm provides a reliable quantitative monitor of soot particles in pyrolysis. This technique has been employed to determine a working value for the soot extinction cross section at the HeNe laser wavelength (632.8 nm), thus quantifying that diagnostic for a limited set of experimental conditions.

Soot particle size and soot yield in shock tube studies

The size of soot particles formed during the shock tube pyrolysis of toluene was measured by laser Doppler velocimetry. The particle size appeared to be of the order of a micron, i.e. about an order of magnitude higher than previously reported in the literature. This result indicates that (a) agglomeration of the primary soot spheres takes place prior to the onset of cooling and (b) the use of the Rayleigh limit of the Mie scattering theory for the determination of absolute soot yield may be invalid and may lead to an overestimation of the conversion of hydrocarbon to soot.

X-ray diffraction studies on the arrangement of atoms in carbon blacks. I. Results of radial distribution analysis

Radial distribution analysis studies by X-ray diffraction of carbon blacks obtained by pyrolysis of benzene C6H6, toluene, C7H8, and sucrose, C12H22O11, and samples of ultracarbon of the medicinal variety have been carried out. Bonding distances, coordination numbers and the layer dimensions have been determined. It has been observed that the carbon blacks have turbostratic structures. The C-C distances in the carbon layers lie in the range of that for aromatic rings and double bonds. Ultracarbon has the C-C bonding distance corresponding to graphite.

Apparatus to study the electron spin resonance of fluids under high pressure flowing at high temperature

An electron spin resonance (ESR) system is described in which a fluid sample is pressurized and flowed through a fused silica capillary that traverses the microwave cavity of an ESR spectrometer. The capillary is heated to a high temperature, and well-resolved spectra of short-lived free radicals may be seen at steady-state concentration during pyrolysis. The system operates to 20.7 MPa and 700 °C. High-pressure hydrogen may be injected prior to pyrolysis. A spectrum of benzyl during pyrolysis of toluene at 20.7 MPa and 680 °C is shown.

ChemInform Abstract: A DIRECT MASS SPECTROMETRIC STUDY OF THE MECHANISM OF TOLUENE PYROLYSIS AT HIGH TEMPERATURES

The detailed mechanism of the high-temperature pyrolysis of toluene has been studied over a large range of pressures and temperatures by using mass spectrometric techniques. The vapors leaving a high-temperature Knudsen cell equipped with a gas inlet line were examined by using modulated molecular beam mass spectrometric techniques. The pyrolysis products from both quartz and tungsten Knudsen cells were examined over a pressure range of 10/sup -5/ to 1 torr and temperatures up to 1800/sup 0/C. At the lower pressures, only products with molecular weights lower than C/sub 7/H/sub 8/ were observed, including CH/sub 3/, C/sub 2/H/sub 2/, C/sub 3/H/sub 3/, C/sub 4/H/sub 2/, C/sub 4/H/sub 3/, C/sub 4/H/sub 4/, C/sub 5/H/sub 5/, C/sub 6/H/sub 6/, and C/sub 7/H/sub 7/. At higher pressure, these products undergo bimolecular processes to form heavier compounds, up to at least C/sub 20/H/sub 12/. To help define the reaction mechanism, the pyrolyses of C/sub 6/H/sub 5//sup 13/CH/sub 3/ and C/sub 6/H/sub 5/CD/sub 3/ were also studied, as well as toluene in the presence of H/sub 2/, C/sub 2/H/sub 2/, and C/sub 6/H/sub 6/. These studies allowed an unambiguous determination of most of the major processes occurring during toluene pyrolysis. 7 figures, 6 tables.

A direct mass spectrometric study of the mechanism of toluene pyrolysis at high temperatures

ADVERTISEMENT RETURN TO ISSUEArticleNEXTA direct mass spectrometric study of the mechanism of toluene pyrolysis at high temperaturesRichard D. SmithCite this: J. Phys. Chem. 1979, 83, 12, 1553–1563Publication Date (Print):June 1, 1979Publication History Published online1 May 2002Published inissue 1 June 1979https://doi.org/10.1021/j100475a001RIGHTS & PERMISSIONSArticle Views260Altmetric-Citations82LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Formation of radicals and complex organic compounds by high-temperature pyrolysis: The pyrolysis of toluene

A high-temperature Knudsen cell equipped with a gas inlet and modulated molecular-beam mass-spectrometric detection has been constructed to study the high-temperature pyrolysis of model fuel compounds. The high-temperature pyrolysis of toluene has been examined at temperatures of up to 1900°C and over a pressure range of approximately 10 −3–10 N/m 2 (10 −5–10 −1 torr). The pyrolysis of toluene has been found to produce a number of higher-molecular-weight species (including radicals, polycyclic aromatic compounds, and polyacetylenes) efficiently at temperatures of 1200–1500°C. At temperatures of 1200–1400°C, C 3H 4, C 4H 2, C 4H 3, C 5H 3, C 5H 5, C 6H 4, C 6H 5, C 7H 5, C 7H 6, and C 7H 7 species were observed to have maxima in their concentrations as a function of pressure, suggesting a role in the formation of higher-molecular-weight compounds. At higher temperatures, the major products were C 2H 2, C 2H 3, C 2H 4, C 4H 2, C 6H 2, and C 6H 6; species containing even numbers of carbon atoms dominate the reaction products.

A study of the pyrolysis of toluene and phenols at low pressure

Pyrolyses of o-cresol, 2,4-xylenol and toluene have been carried out at 10 −6 torr. In addition to the products previously obtained in pyrolysis at atmospheric pressure and under high pressure, unexpected compounds, such as ketones from phenols and hydrogenated products from toluene, have been obtained. Possible reaction mechanisms are discussed.

Pyrolysis of toluene using a static system

The pyrolysis of toluene was investigated in the temperature range 920–970 K and the effect of hydrogen sensitization was studied at temperatures around 820 K. The unsensitized reaction is autocatalytic and the gaseous products, methane and hydrogen, are formed with different energies of activation (E(H2)= 74 kcal/mol; E(CH4)= 89.4 kcal/mol). Hydrogen accelerates the reaction and the overall reaction rate is determined by the relationship d[CH4]/dt= 1011.44 exp (–58 800/RT)[H2][C6H5CH3]½1. mol–1 s–1. The rate k1 of initiation is given by k1= 1015.96 exp(–88 900/RT) s–1 and an estimate of k12= 109.45 exp(–14,500/RT) 1. mol–1 s–1 is made of the rate constant for the reaction, C6H5CH2+ H2= C6H5CH3+ H. (12)

The high‐temperature degradation of poly(2,6‐dimethyl‐1,4‐phenylene ether)

AbstractThe thermal degradation of poly(2,6‐dimethyl‐1,4‐phenylene ether) has been investigated to 1000°C in an inert atmosphere. X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were employed to study the physical changes in the polymer, and vapor‐phase chromatography, infrared spectroscopy, and mass spectrometric thermal analysis were used to elucidate the chemical aspects of the degradation process. It was found that degradation occurs in two steps: (1) a rapid exothermic process occurs between 430 and 500°C, leading to the evolution of phenolic products, water, and a black, highly crosslinked residue, and (2) a slower, char‐forming process occurs above 500°C, characterized by the evolution of methane, carbon monoxide, and hydrogen. The chars formed in process 2 were found by x‐ray analysis to be amorphous. The infrared spectrum of a sample heated to 510°C is nearly identical with that of the starting polymer, indicating that oxidative reactions are not important in the first process. The data for the low‐temperature process are consistent with a thermal degradation scheme based on the radical‐redistribution reaction of polyphenylene ethers and/or the degradation of o‐benzylphenols formed by the thermal rearrangement of o‐methyl diphenyl ethers. The char‐forming process is best explained by simultaneous operation of the Szwarc mechanism of toluene pyrolysis, producing hydrogen and methane and reactions that cleave the aromatic rings and produce carbon monoxide.

Kinetic Study of Pyrolysis of Toluene-d5

Abstract Reaction mechanism of pyrolysis of toluene was studied with toluene-d5 of high isotopic purity. The rate constant of pyrolysis of toluene-d5 in gas phase was determined to be k=1011.5±0.3×exp(−70±1 kcal/mol) (sec−1) and compared with that of toluene. Hydrogen isotope mixtures produced in the pyrolysis of toluene-d5 were collected and analyzed by mass spectrometer. Formation of some amount of D2 is confirmed, and it is concluded that the fission of ring C–D bond is involved to some extent in the pyrolytic reaction of toluene-d5 at high reaction temperatures. The ratio of rate constants of abstraction type (kD–H⁄kH–H) is also determined, and the difference of the activation energies between kD–H and kH–H is found to be approximately 14 kcal/mol.

A Study of the Pyrolysis of Toluene Using 14C as a Tracer

Abstract The pyrolysis of toluene-1-14C was carried out by means of the semi-flow method at 800 and at 1000°C in the presence of the registers of porcelain, and the distributions of the radioactive carbon in gaseous products and that of the deposited carbon were determined. The molar c.p.m. of methane and that of a mixture of C2-compounds were about 1/20 of and twice the molar c.p.m. of the original toluene respectively, while the c.p.m. per gram-atom of the deposited carbon was about twice that of toluene, when the temperature of reaction was 800°C. In the case of the reaction at 1000°C, the c.p.m. per gram-atom of carbon of each product was found to be practically equal to that of the original toluene. It was proposed that methane is formed by the removal of the methyl group of toluene, and that the main source of the carbon of C2-compounds and the deposited carbon is the 1-carbon of toluene. The equalization of the radioactive carbon in every product at a high temperature was interpreted by assuming that the tropyl radical is formed as an intermediate after the formation of the phenyl radical in the initial stage of the reaction.

Errors in Determining the Rate Constant of a First-order Gaseous Reaction by the Flow Method

The rate constant of a gaseous reaction calculated from data obtained by the conventional flow method is subject to errors arising from departures from piston flow and thermal equilibrium in the reaction tube. An approximate theoretical analysis of the errors is given for the first-order pyrolysis or isomerization of an organic vapour. In the case of a reaction occurring near 1000�K in a tube 2 cm in diameter, it is shown that for the measured value of the rate constant to be accurate within about 10% the experimental conditions should be such that z > tc/p > 0.5, where p cmHg is the total pressure and tc sec the average contact time. The upper limit (z) of tc/p increases from 3 under conditions of 50% conversion to 10 at 25% and ∞ at 0%. The analysis is applied to measurements of the rate of pyrolysis of toluene. Lack of thermal equilibrium could be at least partly responsible for the observed effect of contact time on the rate constant but does not account for the effect of pressure. The error incurred by assuming piston flow in an isothermal reactor when in fact viscous flow is occurring is discussed in the Appendix.

THE PYROLYSIS OF TOLUENE

The pyrolysis of toluene has been studied in a flow system from 913 to 1143 °K. First-order rate constants are independent of the toluene concentration but decrease approximately 9% when the contact time is reduced from 1.0 to 0.41 second. Increasing the contact time from 1.0 second to 2.07 seconds does not affect the rate constant. The overall rate has been resolved into homogeneous and heterogeneous components. It is suggested that the activation energy of the homogeneous process, 85 kcal/mole, may be associated with D(C6H5CH2—H).

Pyrolysis of Organic Compounds. I. Kinetic Study of the Pyrolysis of Toluene

Abstract Pyrolysis of toluene by the flow technique was carried out under various conditions, and the velocity was measured over the wide temperature range 737∼953°C at contact time 0.02∼0.3 sec. The relation of logk versus 1/T appears to be linear, but the more precise analysis shows a slight concave nature, and therefore activation energy tends to increase, as the reaction temperature is raised. Detailed investigation on its cause was made, and it is presumed that such an increase of activation energy with rise of temperature is mainly brought about by some competitive reaction, but not by experimental conditions. The present author considers that the involvement of ring-hydrogen reaction may compete with the reaction of fission of C–H bond of the methyl group, and such competitive reaction may modify the activation energy of the fission of the methyl bond of toluene, if the experiment is carried out over the wide reaction temperature range.

Pyrolysis of Organic Compounds. II. Pyrolysis of Toluene-3-d and Toluene-4-d

Abstract In order to elucidate the mechanism of the pyrolysis of toluene, pyrolysis of toluene-3-d and -4-d was carried out by the flow method in the temperature range 830∼955°C, and the mole ratios D2: HD : H2 and CH3D : CH4 were determined by mass spectrometry. The involvement of the reaction of ring-hydrogen in the pyrolysis has been confirmed from the formation of HD and CH3D. As there was not any distinct difference in the mole ratios between the reactions of toluene-3-d nor -4-d, it is concluded that the reactivities of m- and p-hydrogens of toluene are of the same order. Considering these results, the possible elementary processes involving ring-hydrogen are discussed.

THE KINETICS OF THE PYROLYSIS OF TOLUENE

The pyrolysis of toluene has been studied in an attempt to verify the findings of Szwarc (2). The major products have been confirmed but styrene and isomeric dimethyl diphenyls have also been detected. First order rate constants for the decomposition have been found to depend on the condition of the surface of the reactor, the contact time, and, to a lesser degree, on the pressure. Some preliminary studies on the mechanism of the formation of the dimethyl diphenyls are also recorded.

The C–H Bond Energy in Toluene and Xylenes

The pyrolysis of toluene and the xylenes was investigated by a new technique, which made it possible to study these reactions for degree of decomposition ranging from 0.01 percent up to a few percent. It was shown that these reactions are homogeneous, unimolecular reactions. It was found that the weakest bond in these molecules is the C–H bond in the methyl group. The bond energy of that C–H bond was found to be 77.5 kcal. for toluene and meta-xylene, 75 kcal. for para-xylene and 74 kcal. for ortho-xylene. These data indicate that the resonance energy of the benzyl radical is 24.5 kcal. and that the hyper-conjugation in para-xylene decreases the C–H bond energy in the methyl group of this molecule by 2.5–3 kcal.

The C—H Bond Energy in Toluene and Xylenes

The pyrolysis of toluene and of the three xylenes has been investigated by a flow method in a silica reaction vessel with a technique permitting the measurement of the rate of the reaction for decompositions ranging from 0.01 per cent up to a few per cent. The reactions were shown to be homogeneous gas reactions of the first order, the first-order constant remaining the same when the time of contact and the pressure of the hydrocarbons were varied.

The Reactions of Methyl Radicals with Benzene, Toluene, Diphenyl Methane and Propylene

The reactions of methyl radicals with benzene, toluene, diphenyl methane and propylene to yield methane have been studied in the temperature range of 100–260°C. With toluene the activation energy is 5.6 kcal. and with propylene 3 kcal. Diphenyl methane shows a reactivity corresponding to these low values while the experiments with benzene, as well as earlier work with ethylene, indicate much higher activation energies of methane formation. The activation energies obtained have been correlated with earlier data on reactions with saturated hydrocarbons, with thermal data indicative of the strength of individual C – H bonds, with similar data from the interaction of atomic sodium with halide compounds, with concepts of the organic chemist on bond strengths and with some experimental data on pyrolysis of toluene. It is concluded that, contrary to accepted views, there may be marked differences in C – C and C – H bond strengths among the various hydrocarbons studied.