Pyrolysis Of Toluene Research Articles

An extended mechanism including high pressure conditions (700 bar) for toluene pyrolysis

Toluene pyrolysis was studied between 350 °C and 400 °C under 700 bar pressure using confined pyrolysis (gold cells). A detailed kinetic model consisting of 30 free-radical reactions was developed to describe the thermal cracking of toluene at low conversion. The mechanism considered is consistent with the experimental results concerning conversion as well as formation of the main products (benzene, methane, biaromatic compounds). This study shows that high pressure and low temperature are favorable to bimolecular reactions. Thus, additions of benzyl radicals to aromatic rings lead to the formation of biaromatic compounds. Yet, the most important conclusions concern the initiation reactions for which a bimolecular mechanism (or RRD: reverse radical disproportionation) needed to be considered. The relative importance of the monomolecular vs. bimolecular initiation mechanism changes as a function of temperature and pressure. The extension of the published mechanisms by our results allows to significantly increase the temperature–pressure domain for the modeling of toluene pyrolysis.

Synthesis of Carbon Nanotubes on Zeolite Substrate of Type ZSM-5

The present work deals with the synthesis of carbon nanotube-zeolite composites using as method the catalytic liquid spray pyrolysis. The nanotubes were formed after pyrolysis of toluene on the surface of a zeolite of type ZSM-5, which was used as a catalytic substrate. ZSM-5 zeolite was synthesized using the autoclave process and full characterized. Prior to the pyrolyses, the catalytic substrates were produced by mixing a certain amount of zeolite with a solution of Fe(NO3)3•9H2O of specific concentration. The obtained materials from the spray pyrolysis were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry-differential analysis (TG-DTA).

Role of Methyl Radicals in the Growth of PAHs

The role of methyl radicals in the networking of sp(2) carbons has been explored through kinetic analysis of mass spectra of the gas-phase products of the pyrolysis of toluene and toluene/acetone mixtures. Pyrolytic reactions were performed in a flow tube reactor at temperatures of 1140-1320 K and a constant total pressure of 10.38 Torr with a residence time of 0.585 s. On addition of acetone, methyl substituted products and their derivatives were enhanced. Mass peaks were observed in several sequences at an interval of 14 mass units; these ions correspond to methyl substituted products formed as a result of hydrogen abstraction (-H) followed by methyl radical addition (+CH(3)). Each major peak was usually preceded by a peak at two mass units lower, which was likely produced through dehydrogenation/dehydrocyclization (-H(2)) of methyl substituted products. Detected species include a large number of alkyl, cyclotetrafused (CT), cyclopentafused (CP) mono-, di-, and polycyclic aromatic hydrocarbons (PAHs) along with primary PAHs. The analysis showed that MAC (methyl addition/cyclization) has a unique capacity to induce the sequential growth of hexagonal networks of sp(2) carbons from all fusing sites of a PAH. Moreover, MAC was found capable of answering an important question in PAH growth, which is expansion of the CT --> CP --> hexagonal network for which other reported mechanisms are inefficient.

Dendritic carbon architectures formed by nanotube core-directed diffusion-limited aggregation of nanoparticles

A regular array of fractal patterns with macroscopic dendritic carbon architecture was prepared by catalytic chemical vapor deposition (CVD). The dendritic carbon architectures have micrometre-sized stems and hyperbranches evolved by lateral growth, and they are formed by diffusion-limited aggregation of carbon-encapsulated iron nanoparticle building blocks generated from catalytic pyrolysis of toluene, which is directed by carbon nanotube cores, and followed by subsequent restructuring from surface to bulk. Incorporation of such proposed processes in Monte Carlo simulations generates dendritic architectures similar to the morphologies observed from the experiments. The findings provide direct information to the time resolved evolution of the morphology and microstructure of the dendritic carbon architecture, which mimic the nature behavior as snowflake attaching on the tree branches. Those will be important to understand the growth of vapor grown carbon fibers and carbon filamentous structures, and further possibility to control branching out of vapor grown carbon fibers.

In‐Situ Deposition of Nickel Nanoparticles on Carbon Nanotubes by Spray Pyrolysis

Nickel nanoparticles have been deposited on carbon nanotubes by spray pyrolysis of toluene as carbon source and nickelocene as catalyst at different temperatures. The optimum temperature to produce well‐grown Ni/carbon nanotubes was found to be 850°C. The carbon nanotubes were characterized by SEM, TEM, XRD, Raman spectroscopy and TGA‐DTA. The microscopy studies show that the produced carbon nanotubes have disorder morphologies with diameters between 60 and 100 nm and lengths of a few hundred microns. Ni particles of 40 nm are well dispersed along the carbon nanotubes. XRD patterns show the crystalline planes corresponding to graphite and metallic Ni. The TGA‐DTA results indicate a Ni loading of 20wt%. Raman spectroscopy reveals that the grown carbon nanotubes are graphitized, showing both the D and G bands at 1330 cm−1 and 1590 cm−1, respectively. The corresponding intensity ratio of these bands (ID/IG) varies with respect to synthesis temperature and catalyst concentration.

An experimental and theoretical study of toluene pyrolysis with tunable synchrotron VUV photoionization and molecular-beam mass spectrometry

An experimental study of toluene pyrolysis (1.24 vol.% toluene in argon) was performed at low pressure (1.33 kPa) in the temperature range of 1200–1800 K. The pyrolysis process was detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS). Species up to m/ z = 202 (C 16H 10), containing many radicals (CH 3, C 3H 3, C 5H 3, C 5H 5, C 7H 5, C 7H 7, C 9H 7, C 11H 7 and C 13H 9) and isomers, such as C 3H 4 (propyne and allene), C 4H 4 (vinylacetylene and 1,2,3-butatriene), C 5H 5 (cyclopentadienyl radical and pent-1-en-4-yn-3-yl radical), C 6H 4 (3-hexene-1,5-diyne and benzyne), C 6H 6 (benzene and fulvene), C 7H 8 (toluene and 5-methylene-1,3-cyclohexadiene) and so on, were identified from near-threshold measurements of photoionization mass spectra, and the mole fraction profiles of the pyrolysis products were evaluated from measurements of temperature scan. Experimental results indicate that the reaction C 7H 8 → C 7H 7 and the subsequent reactions are dominant at comparatively low temperature (<1440 K), while the reaction C 7H 8 → C 6H 5 and subsequent reactions gradually become competitive and important with increasing temperature. Furthermore the barriers of the decomposition pathways of toluene and benzyl radical determined by quantum mechanical calculation are in good agreement with the initial formation temperatures of the species. Based on the mole fractions and formation temperatures of the detected pyrolysis species, a simple reaction network is deduced. At relatively high temperatures, H-abstraction is prevalent and the mole fraction of C 2H 2 is so high that many aromatics are formed through the hydrogen-abstraction/C 2H 2-addition (HACA) mechanism. Moreover the reactions of benzyl with toluene/benzyl/phenyl/propargyl radicals to directly produce larger aromatics should play an influential role in PAH formation. Meanwhile the five-member-ring recombination mechanism also plays an indispensable role in the aromatics growth, as cyclopentadienyl radical (C 5H 5) was determined to be a major product of the decomposition of toluene.

Analyzing the effects of temperature on soot formation with a joint volume-surface-hydrogen model

The intent of the current work is to present and further validate a new tri-variate model for the formation of soot particles, to apply this model in analyzing the effects of temperature on the formation and growth of soot, and to compare the findings with the present understanding derived from numerous experimental studies. In this novel model, a particle is represented as a fractal shaped aggregate and is described by three independent quantities: the volume, the surface area, and the number of hydrogenated sites (or active sites) on the surface. The introduction of this third variable allows for a better description of the surface reactivity at high temperatures. This approach is extended by a model for the total carbon-to-hydrogen (C/H) ratio of the particle. The model is validated first in high temperature premixed ethylene flames, premixed benzene flames, an acetylene counterflow diffusion flame, and toluene pyrolysis in shock-tubes. Then, the soot volume fraction is computed for a series of atmospheric laminar ethylene premixed flames with varying flame temperatures. The soot model is shown to reproduce the well known bell-shaped temperature dependence of soot volume fraction, which was found in many experiments. It is observed that nucleation is the largest contributor to soot volume fraction at low temperatures while growth by surface reactions is more important at higher temperatures. The surface reactivity and the volumetric carbon-to-hydrogen ratio (C/H) are also computed as a function of temperature. The surface reactivity is found to depend not only on the temperature but also on the particle size and the residence time in the flame. Finally, as observed experimentally, the C/H ratio is found to be essentially constant and close to unity for low temperature flames and increases with residence time in high temperature flames.

The negative effects of alcohols on carbon nanotube synthesis in a nebulised spray pyrolysis process

Multi-walled carbon nanotubes were synthesized by the nebulised spray pyrolysis (frequency 1.6 MHz) of toluene and toluene–alcohol mixtures with ferrocene as the catalyst precursor. The CNTs produced were characterized by TEM, SEM, Laser-Raman spectroscopy and TGA. The results show that the presence of ethanol, 2-propanol and octanol in the reaction mixture reduces the CNT yield, growth rate and produces CNTs that are less well graphitized and less resistant to oxidation. The data suggests that the exposure of the alcohol-containing mixture to ultrasound irradiation results in the production of radicals that inhibit CNT formation.

Synthesis of Multi-Walled Carbon Nanotubes by Spray-Pyrolysis Using a New Iron Organometallic Complex as Catalytic Agent

An organometallic catalytic agent ([(Hexyl)4N]3FeCl3Br3) has been synthesized through the reaction of tetrahexylammonium bromide ((Hexyl)4NBr) and iron chloride (FeCl3) aqueous solutions. Multi-walled carbon nanotubes (MWCNTs) were obtained by spray pyrolysis of toluene (carbon source) using the new organometallic compound as catalyst. The synthesized catalytic agent was characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and thermal analysis (TA) techniques. Spectroscopic results indicated that the new iron organometallic compound has suitable characteristics to grow MWCNTs by spray pyrolysis. The MWCNTs were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The MWCNTs grow in a disordered way without orientation with diameters ranging from 20 to 50 nanometers. XRD patterns exhibit the 2-H graphite characteristics peaks of the MWCNTs.

Role of Phenyl Radicals in the Growth of Polycyclic Aromatic Hydrocarbons

To investigate the role of phenyl radical in the growth of PAHs (polycyclic aromatic hydrocarbons), pyrolysis of toluene with and without benzene has been studied by using a heatable tubular reactor couple with an in-situ sampling vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometer (TOFMS) at temperatures 1155-1467 K and a pressure of 10.02 Torr with 0.56 s residence time. When benzene was added, a significant increase of phenyl addition products (biphenyl, terphenyl, and triphenylene) was observed and the mass spectra showed a clear regular sequence with an interval of approximately 74 mass number, corresponding to the phenyl addition (+C6H5) followed by H-elimination (-H) and cyclization (-H2). The analysis showed that the PAC (phenyl addition/cylization) mechanism is efficient for the growth of PAHs without a triple fusing site, for which the HACA (hydrogen abstraction/C2H2 addition) step is inefficient, and produces PAHs with five-membered rings. The PAC process was also suggested to be efficient in the subsequent growth of PAHs with five-membered rings. The role of the PAC mechanism in combustion conditions is discussed in relation to the importance of disordered five-membered ring structure in fullerene or soot core.

Pyrolysis of spill oils adsorbed on zeolites with product oils recycling

Experimentally, a feasibility study for adsorption and catalytic pyrolysis of spill oils on Cu/ZSM-5 for recycling of light oils has been conducted in the present work. The adsorption and pyrolysis of model compounds such as heptane, toluene, and diesel (to stimulate the spill oils) on Cu/ZSM-5 have been investigated on a continuous fixed-bed reactor. By component fitted X-ray absorption near edge structural (XANES) spectroscopy, catalytic active species such as metallic copper (Cu) (77–84%) and Cu 2O (6–7%) are found in the channels of ZSM-5 during pyrolysis of heptane or toluene. Pyrolysis of diesel effected by Cu/ZSM-5 yields gas (C 1–C 5) (32%) and light oil (68%) that can be used as auxiliary fuels.

Scattering/extinction measurements of soot formation in a shock tube

The understanding of the mechanism of soot formation and growth in combustion systems is a challenging task. Although many works are found in literature concerning experimental measurements and modelling development, efforts are still required to have a deep knowledge of soot formation mechanisms. Tanks to the application of optical diagnostics techniques, experiments in shock tube give important contribution to this. This work is focused on the development and application of the laser extinction/scattering technique in shock tube experiments. Emphasis is given to the scattering optical arrangement for the determination of soot size growth. Results concerning the induction delay time, the soot yield and the particle diameter growth are presented for the pyrolysis of ethylene and toluene at pressure about 500 kPa and for a wide range of temperature.

Synergetic effect of Fe and S on toluene pyrolysis products

Different carbon products were obtained by the pyrolysis of toluene using ferrocene as catalyst precursor and thiophene as promoter.The effect of catalyst and promoter on the morphologies and microstructure produced were investigated by TEM and XRD.The pyrolysis product consisted of spherical carbon nanoparticles when no catalyst or promoter was used.Some nanoparticles in the product were linked together into chain-like structures.When ferrocene was used alone,Fe-encapsulated carbon nanoparticles were the main product.When ferrocene and thiophene were used together,the product morphologies were related to the thiophene content.The above results suggest that the coexistence of Fe and S has a large synergetic effect on the pyrolysis reaction and the product formation process.

In Situ Direct Sampling Mass Spectrometric Study on Formation of Polycyclic Aromatic Hydrocarbons in Toluene Pyrolysis

The gas-phase reaction products of toluene pyrolysis with and without acetylene addition produced in a flow tube reactor at pressures of 8.15-15.11 Torr and temperatures of 1136-1507 K with constant residence time (0.56 s) have been detected in an in situ direct sampling mass spectrometric study by using a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry technique. Those products range from methyl radical to large polycyclic aromatic hydrocarbons (PAHs) of mass 522 amu (C(42)H(18)) including smaller species, radicals, polyynes, and PAHs, together with ethynyl, methyl, and phenyl PAHs. On the basis of observed mass spectra, the chemical kinetic mechanisms of the formation of products are discussed. Especially, acetylene is mixed with toluene to understand the effect of the hydrogen abstraction and acetylene addition (HACA) mechanism on the formation pathways of products in toluene pyrolysis. The most prominent outputs of this work are the direct detection of large PAHs and new reaction pathways for the formation of PAHs with the major role of cyclopenta-fused radicals. The basis of this new reaction route is the appearance of different sequences of mass spectra that well explain the major role of aromatic radicals mainly cyclopenta fused radicals of PAHs resulting from their corresponding methyl PAHs, with active participation of c-C(5)H(5), C(6)H(5), C(6)H(5)CH(2) ,and C(9)H(7) in the formation of large PAHs. The role of the HACA only seemed important for the formation of stable condensed PAHs from unstable primary PAHs with zigzag structure (having triple fusing sites) in one step by ring growth with two carbon atoms.

Production and Characterization of Coaxial Nanotube Junctions and Networks of CNx/CNT

Novel coaxial structures consisting of nitrogen-doped carbon nanotube (MWNTs-CNx) cores with external concentric shells of pure carbon were produced by the pyrolysis of toluene over Fe-coated MWNTs-CNx. These materials were thoroughly characterized by SEM, HRTEM, X-ray diffraction, and TGA; a possible growth scenario for their formation is also proposed. In addition, these coaxial structures were able to form 2D and 3D covalent networks that mainly exhibited T-, Y-, and on-type morphologies. The two-step technique presented here could be further developed to fully control the growth of these new coaxial structures, study of individual junctions, and it could be used to create periodic nanotube networks, in which the heterocable structure could find applications in nanoelectronics.

Graphite-like carbon-encapsulated iron nanoparticle self-assembly into macroscopic microtube structures

We report the self-assembly of graphite-like carbon-encapsulated iron nanoparticles into macroscopic microtube structures by using a floating catalytic chemical vapor deposition method. The microtubes have a hollow tubular architecture with a diameter of several tens of microns, and several are up to ten centimetres in length. The walls of the microtubes are formed by aggregation of graphite-like carbon-encapsulated iron nanoparticle building blocks generated from catalytic pyrolysis of toluene and the wall thickness is several microns. The microtubes combining the tubular geometry with nanoparticle morphology and properties are constructed by self-assembly of graphite-like carbon-encapsulated iron nanoparticles induced by anisotropic particle mutual interactions. This unusual carbon-capsulated iron nanoparticle tubular superstructure provides spatially distributed nucleation sites, which can induce the construction of two dimensional (2D) and 3D carbon nanotube networks with various types of multi-terminal junctions. More generally, we believe that the catalytic approach with spatially distributed nucleation sites for 1D nanomaterials can be readily expanded to create other 1D nanomaterial network structures.

Reaction Mechanisms Governing the Formation of Polycyclic Aromatic Hydrocarbons in the Supercritical Pyrolysis of Toluene: C28H14Isomers

Reaction pathways for the formation of C28H14 polycyclic aromatic hydrocarbons (PAH)of which there are eight benzenoid isomersduring the supercritical pyrolysis of toluene are described in detail. These reaction mechanisms involve the addition of benzyl, methyl, and/or phenyl radicals to smaller PAH products in three specific reactions: (A) addition of methyl and benzyl, usually to a position adjacent to a bay region; (B) addition of phenyl to a bay region; and (C) addition of two methyls to a bay region. Using these three types of reactions, we are able to explain why the five identified C28H14 PAH−benzo[a]coronene, phenanthro[5,4,3,2-efghi]perylene, benzo[cd]naphtho[3,2,1,8-pqra]perylene, benzo[ghi]naphtho[8,1,2-bcd]perylene, and benzo[pqr]naphtho[8,1,2-bcd]perylene−are present in our product mixture and why bisanthene, a C28H14 isomer that we know is not present from UV spectral data, is not formed. We then determine reaction pathways for the remaining two C28H14 benzenoid isomers, naphthaceno[3,4,5,6,7-defghij]naphthacene and tribenzo[cd,ghi,lm]perylene, to deduce that the sixth C28H14 PAH detected in our product mixture by HPLC/MS is most likely tribenzo[cd,ghi,lm]perylene.

Identification of a new C 28H 14 polycyclic aromatic hydrocarbon as a product of supercritical fuel pyrolysis: Tribenzo[ cd,ghi,lm]perylene

Tribenzo[ cd,ghi,lm]perylene has been identified as a product of the supercritical pyrolysis of both toluene and Fischer–Tropsch synthetic jet fuel. This identification is based on HPLC/UV/MS data, which show that compound I, eluting immediately after five other C 28H 14 isomers, is also a C 28H 14 PAH. The UV spectrum of compound I has features of a benzenoid PAH, of which there are only eight C 28H 14 isomers. Four of these isomers – benzo[ a]coronene, phenanthro[5,4,3,2- efghi]perylene, benzo[ cd]naphtho[3,2,1,8- pqra]perylene, and benzo[ pqr]naphtho[8,1,2- bcd]perylene – have already been identified as supercritical pyrolysis products by matching their UV spectra with those of respective reference standards. A fifth C 28H 14 PAH – benzo[ ghi]naphtho[8,1,2- bcd]perylene, which does not have a reference standard – has also been recently identified through MS and UV data, use of annellation theory to predict UV spectral characteristics, and length-to-breadth ratio/retention time data. Of the remaining three isomers, bisanthene (IUPAC name phenanthro[1,10,9,8- opqra]perylene) has been determined not to be present in our product mixture, as its UV spectrum does not match that of any of our product PAH. Using annellation theory, we predict the UV spectral characteristics of the two remaining C 28H 14 benzenoid isomers, for which there are no reference standards (tribenzo[ cd,ghi,lm]perylene and naphthaceno[3,4,5,6,7- defghij]naphthacene). Results from this analysis show that the predicted UV spectral features of tribenzo[ cd,ghi,lm]perylene match those of compound I—and that those of naphthaceno[3,4,5,6,7- defghij]naphthacene are inconsistent with those of compound I. The length-to-breadth ratio of tribenzo[ cd,ghi,lm]perylene also agrees with compound I's HPLC elution behavior. This is the first time that tribenzo[ cd,ghi,lm]perylene (IUPAC name phenanthro[2,1,10,9,8,7- pqrstuv]pentaphene) has been identified as a product of fuel pyrolysis or combustion.

Characterization of adsorbed species on soot formed behind reflected shock waves

The present work addresses the soot formation parameters behind reflected shock waves and the identification of adsorbed species on their surface. Soot induction delay times and yields have been experimentally determined in the case of toluene pyrolysis highly diluted in argon for the following conditions: the initial carbon atoms concentration was kept constant around 1 × 10 18 C atoms cm −3, reflected shock pressure and temperature ranges of 1135–1600 kPa and 1470–2230 K, respectively. The decrease of the induction time, as the temperature is raised, was described using an Arrhenius type expression while, for the bell-shaped evolution of the soot yield versus the temperature, a modified Gaussian expression was derived. Using TEM analysis, the mean particle diameter was found to decrease from 35 to 20 nm as the temperature is raised from 1475 to 2135 K. The micro-texture of the soot sample was found to vary as the temperature is raised, leading to a more organised structure. The adsorbed species on these soot were characterized using laser desorption/ionization time of flight mass spectrometer. Results indicate that for temperatures below 1600 K, PAHs in the 178–572 atomic mass units (amu) range were identified. PAHs range was limited to 178–374 amu above 1900 K and they were of benzenoid type above 1600 K. The amount of species adsorbed on the soot surface was found to be inversely proportional to the soot yield with a maximum for the lower temperature domain.

Detailed kinetic modeling of soot formation in shock tube pyrolysis and oxidation of toluene and n-heptane

A new detailed kinetic model of soot formation in shock tube pyrolysis and oxidation of aliphatic and aromatic hydrocarbons is proposed. The model is based on the comprehensive kinetic model of PAH formation and growth [H. Richter, J.B. Howard, Phys. Chem. Chem. Phys. 4 (2002) 2038–2055; H. Richter, S. Granata, W.H. Green, J.B. Howard, Proc. Combust. Inst. 30 (2005) 1397–1405; J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122–136; M. Frenklach, D.W. Clary, T. Yuan, W.C. Gardiner, Jr., S.E. Stein, Combust. Sci. Tech. 50 (1986) 79–115; M. Frenklach, J. Warnatz, Combust. Sci. Tech. 51 (1987) 265–283; M.S. Skjøth-Rasmussen, P. Glarborg, M. Østberg, J.T. Johannessen, H. Livbjerg, A.D. Jensen, T.S. Christensen, Combust. Flame 136 (2004) 91–128], on the new concepts of soot particle nucleation [A. Violi, Combust. Flame 139 (2004) 279–287; A. Violi, A.F. Sarofim, G.A. Voth, Combust. Sci. Tech. 176 (2004) 991–1005; A. D’Alessio, A. D’Anna, P. Minutolo, L.A. Sgro, A. Violi, Proc. Combust. Inst. 28 (2000) 2547–2554; A. D’Anna, A. Violi, A.D’Alessio, A.F. Sarofim, Combust. Flame 127 (2001) 1995–2003] and the traditional H-abstraction/C 2H 2-addition (HACA) route of PAH and soot particles surface growth [H. Wang, M. Frenklach, Combust. Flame 110 (1997) 173–221; J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122–136]. The gas-phase kinetic scheme was validated against the experimentally measured concentration profiles of the main gas-phase species formed during toluene pyrolysis and H and OH radicals during benzene and phenol pyrolysis and toluene oxidation behind reflected shock waves. The model describes the main characteristics of soot formation in pyrolysis and oxidation of toluene and n-heptane oxidation under conditions typical of shock tube experiments. Both hydrocarbons have the same number of carbon atoms but different structures, which causes different behavior of the systems. The discrete Galerkin technique was applied for direct counting of the mean number of active sites formed on the surface of soot precursors and soot particles in reactions of activation, deactivation, and surface growth.