Pyrolysis Of Benzene Research Articles

Two-route formation of soot nuclei: experimental and modeling evidence

The results of shock-tube measurements of acetylene concentration and characteristics of the ensemble of soot particles during the pyrolysis of benzene, ethylene, ethylene–methane and ethylene–propane diluted with argon are compared with the predictions of the unified kinetic model of soot formation implemented in the MACRON program based on the Galerkin method. The simulation results demonstrate good agreement with experimental data for the pyrolysis of ethylene alone and with the specified additives, thereby confirming the two route mechanism of soot nuclei formation. The agreement for benzene pyrolysis is less satisfactory.

Experimental and kinetic modeling investigation on the co-pyrolysis of benzene, acetylene, and dimethyl ether: Insights into the fuel component interactions

The addition of dimethyl ether (DME) to hydrocarbons is proposed to be a feasible strategy to reduce carbon dioxide emissions in engines. In order to unravel the interaction between hydrocarbons and oxygenated fuels, the co-pyrolysis of benzene, acetylene, and dimethyl ether (DME) is investigated in a flow reactor at 880–1250 K and 1 atm using gas chromatography in this work. Additionally, pyrolysis of pure benzene and co-pyrolysis of benzene and acetylene are also performed. It is observed that the pyrolysis of pure hydrocarbon components and co-pyrolysis of benzene and acetylene can hardly happen in the investigated temperature region, while the addition of DME to the pyrolysis of benzene and acetylene significantly accelerate their decompositions and enhance the formation of key aromatics, such as toluene and indene, showing remarkable synergistic effects on pyrolysis reactivity and aromatics growth. A kinetic model describing the combustion of the three components is developed and used to perform numerical investigation on fuel decomposition and PAH formation. Modeling analysis shows that the addition of DME can effectively activate the pyrolysis system through fast C-O bond dissociation reactions, thereby reducing the decomposition temperatures of benzene and acetylene. The phenyl radical produced from the H-abstraction of benzene can react with acetylene to produce phenylacetylene, while phenylacetylene can further combine with another phenyl radical to form b-phenyl-a-styryl radical which can readily convert to phenanthrene. The addition of DME also generates abundant methyl radical, which further reacts with benzene or other aromatics to form large aromatics such as toluene and methylated PAHs.

The elusive phenylethynyl radical and its cation: synthesis, electronic structure, and reactivity.

Alkynyl radicals and cations are crucial reactive intermediates in chemistry, but often evade direct detection. Herein, we report the direct observation of the phenylethynyl radical (C6H5CC˙) and its cation (C6H5CC+), which are two of the most reactive intermediates in organic chemistry. The radical is generated via pyrolysis of (bromoethynyl)benzene at temperatures above 1500 K and is characterized by photoion mass-selected threshold photoelectron spectroscopy (ms-TPES). Photoionization of the phenylethynyl radical yields the phenylethynyl cation, which has never been synthesized due to its extreme electrophilicity. Vibrationally-resolved ms-TPES assisted by ab initio calculations unveiled the complex electronic structure of the phenylethynyl cation, which appears at an adiabatic ionization energy (AIE) of 8.90 ± 0.05 eV and exhibits an uncommon triplet (3B1) ground state, while the closed-shell singlet (1A1) state lies just 2.8 kcal mol-1 (0.12 eV) higher in energy. The reactive phenylethynyl radical abstracts hydrogen to form ethynylbenzene (C6H5CCH) but also isomerizes via H-shift to the o-, m-, and p-ethynylphenyl isomers (C6H4CCH). These radicals are very reactive and undergo ring-opening followed by H-loss to form a mixture of C8H4 triynes, along with low yields of cyclic 3- and 4-ethynylbenzynes (C6H3CCH). At higher temperatures, dehydrogenation from the unbranched C8H4 triynes forms the linear tetraacetylene (C8H2), an astrochemically relevant polyyne.

Experimental coalescence characteristic time of carbon nanoparticle produced from ethylene or benzene pyrolysis

The coalescence behavior of soot and carbon black has not been so much discussed. The coalescence rate was obtained from the previous experimental results which measured the decrease in mobility diameter by re-heating with tandem differential mobility analyzer. Employing the rate expression used for sintering metallic and inorganic nanoparticles, it was found that the ease of coalescence varied with particle size. It was also suggested that the mechanism of coalescence may differ depending on the temperature. A model of coalescence kinetics based on crystallinity could not represent experimental coalescence kinetics.

Effect of Biphenyl, Acetylene and Carbon Dioxide on Benzene Pyrolysis at Intermediate Temperatures

ABSTRACT Benzene pyrolysis chemical kinetic mechanism has been of interest as benzene and phenyl radicals are important species for polycyclic aromatic hydrocarbons (PAHs) growth. Also, valuable industrial species such as biphenyl can be produced from benzene pyrolysis. This work aims to study the effect of additives (biphenyl and acetylene) on benzene pyrolysis at intermediate temperatures (900–1250 K). However, significant soot was noticed at high temperatures (1200–1250 K), which may affect the measurements. Nitrogen and a blend of nitrogen and carbon dioxide were used for dilution. The experiments were performed using a jet-stirred reactor (JSR) coupled with gas chromatography (GC) at atmospheric pressure. A residence time of 3 s was considered, as a long residence time is needed to collect enough samples at intermediate temperatures. The concentration-temperature profiles from the experimental measurements were compared with three selected models, Hamadi et al., Ranzi et al. and Sun et al. models. In general, Sun et al. model performs better than the other two models, especially for the prediction of light hydrocarbon concentrations. The results show an apparent influence of additives on benzene pyrolysis. The experiments and Sun et al. model illustrate a noticeable formation of methane and ethylene. Hamadi et al. and Ranzi et al. models demonstrate minor formation of light hydrocarbons under our experimental conditions. Sensitivity analyses of benzene, biphenyl, methane and ethylene were conducted at 1175 K using Sun et al. model.

Insight into the pyrolysis of benzene via a novel ultra-high temperature pyrolysis photoionization mass spectrometry

It is extremely challenging to explore pyrolysis reactions in-situ at high temperatures over 2000 K. Here we present a new method that integrates ultra-high temperature graphite tube pyrolysis (UT-GTP) chemical reactor with photoionization time of flight mass spectrometer (PI-TOFMS) along with pyrolysis chemistry. The ultra-high temperature pyrolysis photoionization time of flight mass spectrometer (UT-Py-PI-TOFMS) allows in-situ detection and identification of pyrolysis products at a maximum temperature of 2370 K with a mass resolving power of ∼ 4000 at m/z = 28, and a sensitivity of benzene is better than 64 ppb. This methodology is employed to reveal the pyrolysis mechanism of benzene at 5 kPa and temperature range between 1000 K and 2370 K. A series of pyrolysis products, including radicals, carbyne, and polycyclic aromatic hydrocarbons (PAHs) with high molecular weight are observed. Compared with previous work, we observed some unreported products such as carbyne (C8H2, C10H2), naphthalyne (C10H6), phenanthryne (C14H8) in the pyrolysis of benzene by UT-Py-PI-TOFMS. A plausible pyrolysis mechanism is presented based on the experimental data obtained by UT-Py-PI-TOFMS, and the results can be used for future research on accurately simulating the formation of PAHs. Furthermore, this results provide a practical analytical method for the study of ultra-high temperature pyrolysis reactions.

Pyrolysis and oxidation of benzene and cyclopentadiene by NOx: a ReaxFF molecular dynamics study.

Benzene (C6H6) and 1,3-cyclopentadiene (c-C5H6) are critical intermediate species in the combustion of fossil fuel and the formation of polycyclic aromatic hydrocarbons (PAHs). This study investigates the underlying mechanisms of pyrolysis and oxidation of C6H6 and c-C5H6 in the presence of O2, NO and NO2, respectively, under combustion conditions via ReaxFF molecular dynamics simulations. The size growth in the pyrolysis system is accompanied by an amorphous nature as well as an increase in the C/H ratio. In the oxidation sytems, NO2 is the most effective in the oxidation of both C6H6 and c-C5H6, followed by NO and O2. In the presence of NOx, O and N radicals generated in the high-temperature decomposition reactions of NO and NO2 are actively involved in the addition and H-abstraction reactions of C6H6 and c-C5H6. Remarkably, the decomposition of NO2 dramatically increases the number of O radicals in the system, which significantly accelerates the ring-opening of C6H6 and c-C5H6 by O-addition and forms linear-C6H6O and C5H6O species, respectively. Afterwards, the formation of -CH2- by H-transfer plays an essential role in the decomposition of linear-C6H6O and -C5H6O. Reaction pathways of O and N radicals with C6H6 and c-C5H6 are reported in detail. The O and N-addition of C6H6 facilitate the decomposition to resonance-stabilized cyclopentadienyl radicals after the restructuring of the C-C bond.

Shock-tube study of the influence of oxygenated additives on benzene pyrolysis: Measurement of optical densities, soot inception times and comparison with simulations

The influence of the addition of oxygenated hydrocarbons (methanol, ethanol, and n-butanol) and ethers (diethyl ether, dimethoxymethane, furan, and tetrahydrofuran) on soot formation from benzene pyrolysis was studied. The pyrolysis process was investigated behind reflected shock waves at pressures around 1.4 bar and in the temperature range of 1670–2680 K. Extinction was measured at 633 nm to determine soot optical densities and soot-inception times. For extinction measurements, the studied gas mixtures contain 2.00 mol% C6H6 and 0.75 mol% additives diluted in argon. Since particle-inception times strongly depend on temperature and the reactive system cannot be considered isothermal because of the high reactant concentration in the shock tube, the temperature was measured as a function of time by two-color infrared absorption based on CO using two quantum-cascade lasers. For this purpose, 0.80 mol% CO and 5.00 mol% He were added to the studied gas mixtures as thermometry target species and enhancing species for vibrational relaxation, respectively. Both, temperature and measured optical densities were compared to simulations based on a detailed chemical kinetics mechanism from the CRECK Modeling Group. Additionally, simulations with a new mechanism composed of the CRECK mechanism (Pejpichestakul et al. 2009) and the recent PAH sub-mechanism of Sun et al. (2021) were performed. The agreement of experiments and simulations of the optical density were considerably improved using the aforementioned merged mechanism.

Anti-Coking Performance of Ethyl Benzene Pyrolysis of Silicon-Based Films Prepared through Plasma-Enhanced Chemical Vapour Deposition

Anti-Coking Performance of Ethyl Benzene Pyrolysis of Silicon-Based Films Prepared through Plasma-Enhanced Chemical Vapour Deposition

An experimental and kinetic modeling study of benzene pyrolysis with C2−C3 unsaturated hydrocarbons

A combined experimental and kinetic modeling study is carried out to explore the influences of added acetylene, ethylene, propylene, and propyne on the reaction schemes of benzene pyrolysis. Pyrolysis of benzene with and without the presence of the C2- or C3- unsaturated hydrocarbons (HCs) is conducted in a single pulse shock tube coupled to gas chromatography-mass spectrometry technique. A minimum of 30 species is detected in each reaction system, and their mole fraction profiles are obtained over the temperature range 1030–1800 K at a nominal pressure of 20 bar and a nominal reaction time of 4 ms. With updates based on recent theoretical studies, our ongoing detailed kinetic model with 552 species and 4958 reactions can successfully reproduce the decomposition reactivity of the fuels, formation of decomposition products, and the growth of aromatics in the pyrolysis of different fuel mixtures. Various considerations apply to all studied binary mixtures. The addition of C2- and C3- HCs to the reaction system leads to C2H2 formation, and consequently promotes the HACA mechanism starting from phenyl radical (C6H5) at relatively low temperatures. The resulted phenylacetylene, formed through C6H5+C2H2 reaction, promotes the addition-elimination reaction C6H5C2H + C6H5 leading to the enhanced and early formation of all C14H10 PAH isomers including ethynyl biphenyl, methylene-fluorene, diphenylacetylene, phenanthrene, and anthracene. It is also noteworthy that the existence of C2H2 as fuel or its production from C2H4, C3H6, and C3H4-P decomposition results in numerous compounds with ethynyl branches such as ethynyl biphenyl, diethynyl naphthalene, and ethynyl acenaphthylene. Considering the specific features of the different fuel mixtures, the addition of acetylene intensifies the HACA route leading to greater acenaphthylene formation, while naphthalene formation remains similar to the pure benzene case due to the limited H-atoms. Differently, in benzene-C2H4 co-pyrolysis, naphthalene and acenaphthylene are mainly formed through reactions between PAH radicals (phenylacetylene radical and naphthyl radical, respectively) and ethylene. Concerning benzene-C3 co-pyrolysis, indene is the major C9 species resulting from the reaction of benzene/phenyl with C3 fuels. This is an important theoretical pathway to indene which is experimentally probed here for the first time. The high concentration of indene leads to the enhanced formation of naphthalene and acenaphthylene through the reactions of indenyl radical with methyl and propargyl (C3H3) radicals, respectively. Afterwards, the naphthyl radicals participate in the formation of several larger C11–13 PAHs such as methylnaphthalene, ethynylnaphthalene and fluorene through their reactions with CH3, C2H2 and C3H4-P/C3H3, respectively.

PAH formation in the pyrolysis of benzene and dimethyl ether mixtures behind shock waves

In this work the laser-induced fluorescence (LIF) method was used to study the formation of polyaromatic hydrocarbons (PAHs) in the pyrolysis of benzene C6H6 and dimethyl ether C2H6O (DME) mixtures diluted with argon behind reflected shock waves within a temperature range of 1300–2000 K and pressures of 3.5–5.7 bar. To monitor the volume fraction of the condensed phase, laser extinction at a wavelength of 633 nm at the temperature range 1600–2500 K was measured. The LIF spectra of PAHs formed at varying temperatures and at different times relative to the onset of the pyrolysis process were recorded. It was found that the LIF spectra shift toward longer wavelengths with increasing temperature and reaction time. It has been shown that PAHs with four or more aromatic rings are the precursors of the appearance of the condensed phase. In mixtures with DME, greater amounts of small aromatics (consisting of one-two rings and fewer larger PAHs) were detected relative to benzene pyrolysis. Besides, the DME presence significantly reduced the optical density of the mixture at 633 nm, indicating a decrease in the soot yield. Modeling of PAHs and soot growth for the conditions of experiments using the modern sectional kinetic mechanism was carried out. The simulation results have demonstrated a change in PAH formation pathways that depend on fuel composition and temperature. The effect of DME on the growth of PAHs in benzene pyrolysis is both a decrease in temperature due to heat consumption during the decomposition of DME and the appearance of additional pathways for small PAHs formation and, at the same time, a decrease in the yield of heavier compounds consisting of four or more aromatic rings.

Probing PAH formation chemical kinetics from benzene and toluene pyrolysis in a single-pulse shock tube

Benzene and toluene were pyrolyzed under highly argon-diluted conditions at a nominal pressure of 20 bar in a single-pulse shock tube coupled to gas chromatography/gas chromatography–mass spectrometry (GC/GC–MS) diagnostics. Concentration evolutions of polycyclic aromatic hydrocarbon (PAH) intermediates were measured in a temperature range of 1100–1800 K by analyzing the post-shock gas mixtures. Different PAH speciation behaviors, regarding types, concentrations and formation temperature windows, were observed in the two reaction systems. A kinetic model was proposed to predict and interpret the measurements. Through a combination of experimental and modeling efforts, PAH formation patterns from species pools of benzene and toluene pyrolysis were illustrated. In both cases, channels leading to PAHs basically originate from the respective fuel radicals, phenyl and benzyl. Due to the higher thermal stability of benzene, the production of phenyl, and thus most PAH species, occur in higher temperature windows, in comparison to the case of toluene. In benzene pyrolysis, benzyne participates in the formation of crucial PAH species such as naphthalene and acenaphthylene. Phenyl self-recombination takes considerable carbon flux into biphenyl, which serves as an important intermediate leading to acenaphthylene through hydrogen loss and ring closure. The resonantly-stabilized benzyl is abundant in toluene pyrolysis, and its decomposition further produces other resonantly-stabilized radicals such as fulvenallenyl and propargyl. Barrierless addition reactions among these radicals are found to be important sources of PAHs. Fuel-specific pathways have pronounced effects on PAH speciation behaviors, particularly at lower temperatures where fuel depletion is not completed within the reaction time of 4.0 ms. Contributions from the commonly existing Hydrogen-Abstraction-Carbon-Addition (HACA) routes increase with the temperature in both cases.

Fractal description and adsorption-desorption behaviour of coke treated by benzene pyrolysis carbons

Fractal description and adsorption-desorption behaviour of coke treated by benzene pyrolysis carbons

Study on PAHs and PM Formed by Benzene Pyrolysis

<div class="section abstract"><div class="htmlview paragraph">The main component of PM (particulate matter) formed in the combustion field is soot. Soot is formed by pyrolysis, polymerization and partial oxidation of hydrocarbon fuel. In this experimental research, the effects of temperature and oxygen on PAHs (polycyclic aromatic hydrocarbons) and PM formed from benzene-oxygen mixture were investigated by independent control of temperature (<i>T<sub>f</sub></i> = 1,073 K, 1,173 K, 1,273 K, and 1,338 K) and oxygen concentration (<i>ϕ</i> = ∞, 6.2, and 2.8). In order to investigate the growth processes of PAHs, mass concentrations of naphthalene, biphenyl, phenanthrene, anthracene, and pyrene were measured. As the result, it was found that mass concentration of biphenyl (two-ring PAH, <i>n<sub>C</sub></i> = 12) was higher than naphthalene (two-ring PAH, <i>n<sub>C</sub></i> = 10) under benzene-N<sub>2</sub> mixture condition (without oxygen condition:<i>ϕ</i> = ∞). Mass concentrations of biphenyl and naphthalene were almost same levels under <i>ϕ</i> = 6.2 condition. Furthermore, under <i>ϕ</i> = 2.8 condition, mass concentration of naphthalene was higher than that of biphenyl. Biphenyl and naphthalene concentration change was obvious at 1,250±20 K. Under low temperature condition of 1,190 K, small amount of PM was formed from benzene pyrolysis without oxygen and PM concentration increased with an addition of oxygen. When the temperature increased over 1,310 K, much of PM was formed and it had no difference in with and without oxygen.</div></div>

Fractal description and adsorption-desorption behaviour of coke treated by benzene pyrolysis carbons

For explaining why benzene pyrolysis carbons could inhibit coke deterioration in blast furnace, the adsorption-desorption data of coke sample treated by benzene pyrolysis carbons were obtained to establish adsorption-desorption isotherms and to fit fractal description model with Frenkel-Halsey-Hill equation. The SEM photographs of coke revealed that the pores of the infiltrated coke were almost filled with pyrolysis carbon particles. The fitted curves showed that the types of isotherms were similar to 'type II' of IUPAC classification, and the hysteresis loops belonged to type H3 which represents a typical multilayer adsorption. Model tests indicated that the pore structure of the coke samples have obvious fractal feature and the fractal dimensions of coke sample treated by benzene pyrolysis carbons were smaller than that of original coke sample. So, it explained that benzene pyrolysis carbons can effectively inhibit coke deterioration by infiltrating into the pore structure of coke and reducing pore roughness.

Oxygen effect on PAH and PM formation in low temperature benzene pyrolysis

Carbonaceous particulate matter (PM) is formed by combustion of hydrocarbon fuel. PM contains SOF (soluble organic fraction) and vapor phase hydrocarbons, and the main component of PM is soot. Soot formation process is considered to start from pyrolysis of the fuel, but needs more detail analysis. Then, formation processes of PAHs (polycyclic aromatic hydrocarbons) and PM in a benzene-oxygen-nitrogen mixture were experimentally investigated using a flow reactor. The effects of temperature, especially low temperature, and oxygen on these processes were analyzed by independent control of them. To analyze growth processes from single-ring aromatics to PAHs, mass concentrations of naphthalene, biphenyl, phenanthrene, anthracene, and pyrene were measured by GC-FID. Furthermore, the total mass concentrations of single-, two-, three-, and four-ring aromatics were evaluated to clarify temperature and oxygen effects on these processes. Experimental results showed that concentration of biphenyl formed from benzene pyrolysis with no oxygen was higher than the naphthalene concentration, however concentration of naphthalene formed from benzene pyrolysis with oxygen was higher than the biphenyl concentration. As for the PM formation, small fraction of PM was formed under lower temperature than 1173 K even though the mixture contained no oxygen. Its formation ratio increased with oxygen addition. Temperature of 1280 K was a valley where yield PM showed the minimum. Beyond this temperature, much of PM than in low temperature pyrolysis was formed. However, the low concentration PM valley did not appear under ϕ = 2.80 and 1.83 conditions. At lower temperature than 1170 K, PM mass concentration increased with the addition of oxygen. On the other hand, at higher temperature than 1300 K, PM mass concentration decreased with the addition of oxygen. Under low temperature condition, it suggested that PM formation mechanisms was different depending on the without- and with oxygen.

Toluene pyrolysis in an electric ARC: Products analysis

Toluene pyrolysis in a submerged carbon arc produced at least 72 different molecular species as detected by gas-chromatography coupled with mass spectrometry (GC-MS). The most abundant products found were bibenzyl (1,2-diphenylethane), naphthalene and biphenylene. Furthermore, also diethynylbenzene isomers, fluorene, diphenymethane, indene and biphenyl were produced in appreciable amounts. The formation mechanisms of these and other minor products are discussed mainly in the light of the benzyl radical and its decay into other products. Among polyynes, only 1,3,5,7-octatetrayne was produced above 1% relative yield. The results are discussed in comparison to the products detected in toluene pyrolysis under other experimental conditions, such as shock tube pyrolysis and toluene flames. Furthermore, a comparison with the products obtained from the benzene pyrolysis is reported.

Experimental study of polyaromatic hydrocarbons growth during the pyrolysis of benzene behind shock waves

Experimental study of polyaromatic hydrocarbons growth during the pyrolysis of benzene behind shock waves

Self-assembly of the Ag deposited ZnO/carbon nanospheres: A resourceful photocatalyst for efficient photocatalytic degradation of methylene blue dye in water

Carbon nanospheres (CNSs) are synthesized by pyrolysis of benzene at 1000 °C. Various UV-light photocatalysts of ZnO/CNSs and Ag-ZnO/CNSs (AZCN) composites are synthesized on the surface of CNSs using a facile chemical precipitation method. Morphological and optical properties of the as-synthesized photocatalysts are characterized by scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, UV-Vis spectroscopy, photoluminescence and Raman spectroscopy. Photocatalytic degradation efficiency of methylene blue dye is investigated to examine the photocatalytic activity of synthesized photocatalysts. It is found that as-synthesized ZnO/CNSs composite can degrade higher methylene blue dye (∼85.6%) after 25 min of UV irradiation in comparison with that of CNSs. A prominent improvement in the photodegradation is attained by depositing metal (Ag) particles on the surface of ZnO/CNSs composite. AZCN composite displays the enhanced photocatalytic degradation performance (∼95% after 15 min of UV light) in high concentration of methylene blue dye. Furthermore, stability performance is studied by recycling the AZCN composite photocatalyst. It is found that the photocatalytic activity of AZCN composite is only slightly decreased even after five cycles. Present work demonstrates that AZCN composite show a great potential in the treatment of organic pollutants for wastewater treatment.

Soot formation in shock-wave-induced pyrolysis of acetylene and benzene with H2, O2, and CH4 addition

Experiments on the pyrolysis of C2H2/Ar and C6H6/Ar mixtures with addition of H2, O2, and CH4 have been carried out behind reflected shock waves at temperatures ranging from 1400 to 2600 K. Soot formation was measured by laser extinction at 633 nm. Time-resolved temperature measurements were performed via two-color CO absorption on the P(8) and R(21) lines at 2111.54 and 2191.50 cm-1 using quantum-cascade lasers. For this purpose, 0.5–0.8% CO was added to the gas mixtures. The measured temperature dependence of soot formation in experiments with added O2, and CH4 was corrected for the temperature effect caused by the thermochemistry of either endothermic pyrolysis or exothermic oxidation or reactions that cause time-dependent deviation from the initial frozen-shock temperatures. In all mixtures, the addition of H2 resulted in a noticeable decrease of the soot yield. A considerable increase in the soot yield was found with addition of methane to acetylene mixtures. In contrast, in benzene mixtures, the addition of methane caused a decrease of the soot yield. The qualitative analysis of the kinetics of the gas-phase stage of the pyrolysis reactions elucidated the influence of all investigated additives on the change in the key routes of initial stages of PAH and soot formation. We observed that the addition of H2 to acetylene inhibits the initial stages of the pyrolysis reaction, while the addition of CH4 and O2 opens up new ways for the formation of benzene and phenyl and following growth of pyrene. In contrast to that, in benzene all the additives studied lead to the suppression of the kinetics pathways for the formation of pyrene and the subsequent growth of soot.