Formation Of Major Products Research Articles

UV-induced reactive species dynamics and product formation by chlorite

Chlorite (ClO2-) is a regulated byproduct of chlorine dioxide water treatment processes. The transformation of chlorite under UV irradiation into chloride (Cl-) and chlorate (ClO3-) involves reactive species chain reactions that could enhance chlorine dioxide water treatment efficiency while reducing residual chlorite levels. This study conducted a mechanistic investigation of chlorite phototransformation by analyzing reaction intermediates and stable end products, including chlorine dioxide (ClO2), free chlorine (HOCl/OCl-), hydroxyl‑radical (•OH), Cl-, and ClO3- through combined experimental and modeling approaches. Experiments were performed at UV254 irradiation in pure buffered water within the pH range of 6 to 8. Results indicated that the apparent quantum yields for chlorite phototransformation increased from 0.86 to 1.45, and steady-state •OH concentrations at 1 mM initial chlorite concentration rose from 8.16 × 10–14 M – 16.1 × 10–14 M with decreasing pH values. It was observed that under UV irradiation, chlorite acts as both a significant producer and consumer of reactive species through three distinct reaction pathways. The developed kinetic model, which incorporates optimized intrinsic chlorite quantum yields Φchloritein ranging from 0.33 to 0.39, effectively simulated the loss of oxidants and the formation of major products. It also accurately predicted steady-state concentrations of various species, including •OH, •ClO, Cl• and O3. For the first time, this study provides a comprehensive transformation pathway scheme for chlorite phototransformation. The findings offer important insights into the mechanistic aspects of product and oxidizing species formation during chlorite phototransformation.

Ab Initio Chemical Kinetics for Oxidation of CH3OH by N2O4: Elucidation of the Mechanism for Major Product Formation and Its Relevancy to Tropospheric Chemistry.

Next to CH4, CH3OH is the most abundant C1 organics in the troposphere. The redox reaction of CH3OH with N2O4 had been shown experimentally to produce CH3ONO, instead of CH3ONO2. The mechanism for the reaction remains unknown to date. We have investigated the reaction by ab initio MO calculations at the UCCSD(T)/6-311+G(3df,2p)//UB3LYP/6-311+G(3df,2p) level. The result indicates that the reaction takes place primarily by the isomerization of N2O4 to ONONO2 through a very loose transition state within the N2O4-CH3OH collision complex with a 14.3 kcal/mol barrier, followed by the rapid attack of ONONO2 at CH3OH producing CH3ONO and HNO3. The predicted mechanism for the redox reaction compares closely with the hydrolysis of N2O4. The computed rate constant, k1 = 1.43 × 10-8 T1.96 exp (-9092/T) (200-2000 K) cm3molecule-1s-1, for the formation of CH3ONO and HNO3 agrees reasonably with available low-temperature kinetic data and is found to be similar to that of the isoelectronic N2O4 + CH3NH2 reaction. We have also estimated the kinetics for the termolecular reaction, 2 NO2 + CH3OH, and compared it with the direct bimolecular process; the latter was found to be 4.4 × 105 times faster under the troposphere condition. On the basis of the known pollution levels of NO2, N2O4, and CH3OH, both processes were estimated to be of negligible importance to tropospheric chemistry, however.

Mechanistic Insight and Intersystem Crossing Dynamics of the C(3P) + H2CO/D2CO Reaction

The reaction of atomic carbon, C(3P), with H2CO has been investigated using the direct dynamics trajectory surface hopping (DDTSH) method with Tully's fewest switches algorithm. The lowest lying ground triplet and single states are considered for the dynamics study at a reagent collision energy of 8.0 kcal/mol. From the trajectory calculations, we observed that CH2 + CO and H + HCCO are the two major product channels for the title reaction. The insertion mechanism of the C(3P) + H2CO reaction is rather complex and is followed by three distinct intermediates with no entrance channel barrier to the reaction on the B3LYP/6-31G(d,p) potential energy surfaces. The triplet insertion complexes are formed by three different approaches; "Sideways", "End-on" and "Head-on" attack of the triplet carbon atom toward H2CO molecule. Our dynamics calculations predict a new product channel (H + HCCO(X 2A'')) with a contribution of ∼46% of the overall products formation via ketocarbene intermediate through "Head-on" approach. Despite the weak spin-orbit coupling (SOC) interactions, intersystem crossing (ISC) via a ketocarbene intermediate has a small but significant contribution, about 2.3%, for the CH2 + CO channel. To understand the kinetic isotope effects on the reaction dynamics, we have extended our study for the C(3P) + D2CO reaction. It is seen that isotopic substitution of both the H atoms has a small reduction in the extent of ISC dynamics for the carbene formation. Our results, certainly, reveal the importance of the ketocarbene intermediate and the H + HCCO products channel as one of the major product formation channels in the title reaction, which was not reported earlier.

Experimental and Kinetic Study on the Gas-Phase Pyrolysis of Syringol

Syringyl (3,5-dimethoxy-4-hydroxyphenyl) units are abundant in hardwood lignin, which explains the large amount of syringol present in bio-oils derived from these feeds. To improve understanding of the decomposition chemistry of these syringyl units, the gas-phase pyrolysis kinetics of syringol have been studied experimentally and theoretically under typical fast pyrolysis conditions. The experiments were performed at 673–923 K in a micropyrolyzer unit hyphenated with a gas chromatography (GC) × gas chromatography-flame ionization detection/time-of-flight mass spectrometry and a customized gas chromatograph, which allows to detect and quantify products with boiling points up to 823 K next to permanent gases and water. New obtained experimental data show that 2,3-dihydroxybenzaldehyde is the most important phenolic product, and a large amount of pyrolytic water was formed. The proposed decomposition pathways of syringol to these two products show two new features: (1) 2,3-dihydroxybenzaldehyde is formed from a unimolecular decomposition of syringol without any stable intermediates and (2) both pathways leading to 2,3-dihydroxybenzaldehyde and water involve one more H-atom migration step to form the more stable radicals. Potential energy surface calculations at the CBS-QB3 level of theory indicate that the new features are kinetically favorable. Furthermore, a detailed kinetic model for syringol pyrolysis including 361 reactions and 93 species was constructed. Thermodynamic data for important species and kinetics for crucial reactions were determined with ab initio calculations at the CBS-QB3 level of theory. The model predicts well the conversion of syringol and the formation of major products. A rate of production analysis shows that the new proposed pathway is the major decomposition pathway of syringol. These findings shed new light on the pyrolysis and oxidation chemistry of syringyl species.

N‐coordinated Aluminum Complexes Catalyze the Hydrostannation of Alkynes

AbstractThe effective catalytic activity of hydrostannation of internal and terminal alkynes has been developed by using aluminum complexes. A novel aluminum complex L1AlMe2 was synthesized and characterized. N‐coordinated aluminum complex LAlH2 was chosen to be the most desirable catalyst. Under relatively mild and solvent‐free conditions, excellent yields, regio‐ and stereoselectivities have been achieved. Possible mechanistic pathways for the formation of major products by hydrostannation of alkynes with HSnBu3 were proposed.

A Reaction Kinetics Study on Benzene Oxidation in the Claus Process by Sulfur Monoxide

The Claus process is used in natural gas processing plants to treat H2S-rich acid gas to recover sulfur, but the process suffers from catalytic deactivation when aromatic contaminants such as benzene, toluene, ethylbenzene, and xylene isomers (collectively called as BTEX) are present in the acid gas feed. To safeguard the catalytic reactors, it is desired to oxidize aromatic contaminants in the furnace that are present upstream of the catalytic reactors in the process by oxidants present in it. This work develops a reaction mechanism and evaluates the reaction kinetics for the oxidation of phenyl radical by SO using CBS-QBS for reaction energetics and RRKM and transition state theory for reaction kinetics. The mechanism explores the possible products that are formed from the barrierless addition of SO on phenyl through the O atom as well as through the S atom. The exothermicity of the addition reaction is higher when the addition of SO on the aromatic structure takes place through the S atom. The major products formed from phenyl oxidation by SO are cyclopentadienyl, cyclopentadienethiol and thiopyran radicals. A remarkable similarity between the pathways for phenyl radical oxidation by O2 and its oxidation by SO at high temperatures is observed. The proposed reactions and their rate constants are used to conduct reactor simulations to determine the important reactions that contribute to the formation of major products during phenyl-SO reactions and the temperatures suitable for benzene oxidation by SO under process conditions similar to the Claus furnace.

Deep reaction network exploration at a heterogeneous catalytic interface

Characterizing the reaction energies and barriers of reaction networks is central to catalyst development. However, heterogeneous catalytic surfaces pose several unique challenges to automatic reaction network characterization, including large sizes and open-ended reactant sets, that make ad hoc network construction the current state-of-the-art. Here, we show how automated network exploration algorithms can be adapted to the constraints of heterogeneous systems using ethylene oligomerization on silica-supported single-site Ga3+ as a model system. Using only graph-based rules for exploring the network and elementary constraints based on activation energy and size for identifying network terminations, a comprehensive reaction network is generated and validated against standard methods. The algorithm (re)discovers the Ga-alkyl-centered Cossee-Arlman mechanism that is hypothesized to drive major product formation while also predicting several new pathways for producing alkanes and coke precursors. These results demonstrate that automated reaction exploration algorithms are rapidly maturing towards general purpose capability for exploratory catalytic applications.

Experimental and kinetic model studies on the pyrolysis of 2-furfuryl alcohol at two reactors: Flow reactor and jet-stirred reactor

2-Furfuryl alcohol, derived from non-edible biomass, is the significant component of bio-oil in the pyrolysis of lignocellulose biomass and a potential alternative fuel or fuel additive. To better optimize the pyrolysis model of lignocellulose to improve the properties of pyrolysis bio-oil and further understand the combustion characteristics of 2-furfuryl alcohol, the pyrolysis experiments were performed in a flow reactor at 30 Torr for T = 1006 – 1339 K and 760 Torr for T = 850 – 1131 K, and in a jet-stirred reactor at 760 Torr for T = 750 – 1050 K. The pyrolysis products, including radicals (methyl, propargyl, allyl, and cyclopentadienyl), isomers (furfural/2-ethyl furan, furan/vinyl ketene, and allene/propyne), and aromatics (benzene, toluene, indene, etc.) were identified and measured using synchrotron vacuum ultraviolet photoionization mass spectrometry. A comprehensive kinetic model for 2-furfuryl alcohol pyrolysis was developed and was validated against the experimental data in the present and previous work. Rate of production analysis indicated that the C–O bond dissociation reaction, H-abstraction reactions on the hydroxymethyl group, and the H-addition reactions on the furan-ring controlled the consumption of 2-furfuryl alcohol and the formation of primary pyrolysis products like 2-methyl furan, 2-ethyl furan, furfural, and furan. In addition, the OH-addition reaction on the furan-ring had a certain contribution to the consumption of 2-furfuryl alcohol, while the contribution of H-shift reactions was negligible. The present work systematically compared the effects of methyl, ethyl, and hydroxymethyl groups on the decomposition of furanic fuels and the formation of major products. The results showed that the substituent groups can reduce the decomposition temperature of the fuels, especially the ethyl and hydroxymethyl groups. The alkyl substituent group can promote the formation of small hydrocarbons, of which the mole fraction increased with the length of the carbon chain increasing. The hydroxymethyl group facilitated the formation of oxygenated products.

Experimental and kinetic modeling study of the homogeneous chemistry of NH3 and NOx with CH4 at the diluted conditions

Homogeneous oxidation of CH4/NH3/NO/NO2 mixtures in the temperature range from 600 to 1200 K was investigated in this work. Seven gas mixtures were designed to reveal the influence of CH4 and NO/NO2 ratio during the reaction process. The experiments were carried out in a laminar flow reactor at atmospheric pressure. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used to achieve comprehensive detection of major products and critical hydrocarbon, carbonyl and nitrogenous intermediates. An improved kinetic model, which incorporates a detailed C1-C2/NOx/NH3 sub-mechanism was developed to complement the experiments. In general, the experimental results are in good agreement with prediction of the kinetic model. Rate of production analysis and sensitivity analysis were performed to interpret the experimental observations. The results show that in the oxidation of NH3/NOx mixtures, the NO/NO2 ratio can affect the conversion of NO through the reaction NH2 + NO2 = H2NO + NO. In the presence of CH4, the oxidation reactivity of NH3/NOx mixture is significantly promoted. As the added amount of CH4 increases, the production of H2O is enhanced while N2 formation is inhibited. Beside, the addition of CH4 also promotes the production of carbonyl and nitrogenous species. In the oxidation of CH4/NH3/NOx mixtures, the change of NO2/NO ratios only has little effect on the formation of major products and intermediates.

Photolysis of Chlorine Dioxide under UVA Irradiation: Radical Formation, Application in Treating Micropollutants, Formation of Disinfection Byproducts, and Toxicity under Scenarios Relevant to Potable Reuse and Drinking Water.

Conversion of potable reuse water utilities and drinking water utilities from a low-pressure UV/H2O2 (LPUV/H2O2) advanced oxidation process (AOP) to alternative AOPs in which oxidants can effectively absorb photons and rapidly generate radicals has attracted great interest. Herein, we propose a novel UVA/ClO2 AOP for different water treatment scenarios because of reduced photon absorption by the background matrix and high molar absorptivity for ClO2 at UVA wavelengths. While the photolysis of ClO2 produces •Cl + O2 or •ClO + O(3P) via distinct product channels, we determined the parameters needed to accurately model the loss of oxidants and the formation of byproducts and combined a kinetic model with experimental data to determine quantum yields (Φ). Modeling incorporating the optimized Φ simultaneously predicted oxidant loss and the formation of major products -HOCl, Cl-, and ClO3-. We also systematically investigated the removal of three contaminants exhibiting different radical reactivities, the formation of 35 regulated and unregulated halogenated disinfection byproducts (DBPs), DBP-associated toxicity, and N-acetylcysteine thiol reactivity in synthetic or authentic RO permeates/surface waters treated by different AOPs. The kinetic model developed in this study was used to optimize operating conditions to control undesired products and improve contaminant removal efficiency. The results indicate that UVA/ClO2 can outperform LPUV/H2O2 in terms of electrical energy per order of contaminant degradation, disinfection byproduct formation, and toxicity indices.

5-(R)BENZYLIDENE-2,2-DIMETHYL-1,3-DIOXANE-4,6-DIONES IN SYNTHESIS OF AROMATIC OXIMES, THIOSEMICARBAZONES AND HYDRAZONES

The behavior of some derivatives of Meldrum's acid, namely, 5-(R)benzylidene-2,2-dimethyl-1,3-dioxane-4,6-diones (a well-known synthetic platform) was studied with mono- and biazanucleophiles (hydrochloric hydroxylamine, thiosemicarbazide, hydrazine hydrate). The reaction of the reagents was carried out in acetic acid in a 1:1 molar ratio at 75 °C for 6-8 h, which resulted in aromatic oximes, thiosemicarbazones and hydrazones. The synthesis of (E)-4-chlorobenzaldoxime, (E)-N-(4-nitrobenzylidene) hydroxylammonium chloride, (E)-2-(4-chloro)- and (E)-2-(4-nitrobenzylidene) hydrazine-1-carbothioamides is probably accompanied by the formation of the Michael β-adduct with the subsequent elimination of Meldrum's acid. The interaction of nitrobenzylidene dioxanedione with hydrazine hydrate occurs to form a mixture of (E)-N-(4-nitrobenzylidene) acetohydrazide, (E)-(4-nitrobenzylidene) hydrazine and acetate of the latter in a ratio of 17:3:1, found from the integral signal intensity in the 1Н NMR spectrum (the ratio of similar products was 6:2:1 for chlorobenzylidene dioxanedione). It has been shown that during the reaction the studied substrates are attacked by two hydrazine molecules at the arylidene fragment and the carboxyl group of the opened dioxane cycle of Meldrum's acid. Further, the intermediates are recondensed to form hydrazones and acetylhydrazides. The latters interact with the aromatic aldehydes arising under these conditions as a result of the Knoevenagel retro-reaction of the substrates, with the formation of major products, mixtures of (E)-N-(4-chloro)- or (E)-N-(4-nitrobenzylidene) acetohydrazides. Thus, under the selected conditions, in contrast to the common mechanism presented in the periodicals, no formation of N-heterocyclic systems is observed. The structure of the compounds obtained was confirmed on the basis of 1H, 13C NMR spectroscopy data, as well as elemental analysis. Methods of two-dimensional heteronuclear correlation spectroscopy (HSQC) were also used for more reliable identification of the signals of the products (the components of mixtures).

A density functional theory study of the mechanism and onset potentials for the major products of NO electroreduction on transition metal catalysts

Electrocatalytic reduction of nitrate (NO3−) and other NOx species is a potential solution to reactive nitrogen pollution. Various products are possible in the electroreduction reaction, however, the mechanisms toward each product are not yet well understood. Herein we explore possible mechanisms from NO toward the formation of major products, NH4+, H3NOH+, and N2O, on planar transition metal catalysts, using density functional theory; the majority of metals studied produce NH4+via an NOH intermediate, while for H3NOH+ both NOH and HNO are key intermediates. Onset potentials, scaling relations, and limiting potential volcanoes have been calculated for NH4+ and H3NOH+; it is found that the onset potential of NO reduction is not strongly influenced by the energy of N binding. For N2O formation, two mechanisms were found to be plausible: a Langmuir–Hinshelwood mechanism, possible on Ag, Au, and Cu, and an Eley–Rideal mechanism, possible on all of the metals studied.

A detailed chemical kinetic model for the supercritical water oxidation of methylamine: The importance of imine formation

AbstractA detailed chemical kinetic model has been developed for supercritical water oxidation (SCWO) of methylamine, CH3NH2, providing insight into the intermediates and final products formed in this process as well as the dominant reaction pathways. The model was adapted from previous mechanisms, with a revision of the peroxyl radical chemistry to include imine formation, which has recently been identified as the dominant gas‐phase pathway in amine oxidation. The developed model can reproduce previous experimental data on methylamine consumption and major product formation to reasonable accuracy, although with deficiencies in describing the induction time. Our simulations indicate that oxidation of the •CH2NH2 radical to methanimine, CH2NH, is the major channel in methylamine SCWO, with subsequent hydrolysis of CH2NH providing the experimentally observed reaction products ammonia and formaldehyde. Integral‐averaged reaction rates were used to identify major reaction pathways, and a first‐order sensitivity analysis indicated that the concentration of CH3NH2 is most sensitive to OH radical kinetics. Overall, this work clarifies the importance of imine chemistry in the oxidation of nitrogen‐containing compounds and indicates that they are necessary to model these compounds in SCWO processes.

Thermal decomposition of model compound of algal biomass

AbstractThis contribution investigates thermal decomposition of leucine, as a representative model compound for amino acids in algal biomass. We map out potential energy surface for a wide array of unimolecular and self‐condensation reactions operating in the decomposition of leucine. Decarboxylation and dehydration of leucine ensues by eliminating CO2 and –OH, respectively, from the –COOH group attached to the α‐carbon. The molecular channel for deamination involves cleavage of NH2 from α‐carbon of leucine. The activation energies for direct elimination of CO2, NH3, and H2O from a leucine molecule lie within 20.7 kJ/mol of each other. Activation energies for these decomposition pathways reside below the bond dissociation enthalpy of H–C(α) of 323.1 kJ/mol. The decarboxylation, deamination, and dehydration pathways, via radical‐prompted pathways, systematically require lower energy barriers, in reference to closed‐shell reaction corridors. Detailed computations at the CBS‐QB3 level provide the Arrhenius rate parameters for the unimolecular and bimolecular reactions, and standard enthalpies of formation, standard entropies, and heat capacities for all the products and intermediates. A kinetic analysis of gas‐phase reactions, within the context of a plug‐flow reactor model, accounts qualitatively for the formation of major products observed experimentally in the thermal degradation of the condensed‐phase leucine. Among notable N‐containing species, the model predicts the prevailing of NH3 over HCN and HNCO, in addition to corresponding appreciable concentrations of amines, imines, and nitriles. Our detailed kinetic investigation illustrates a negligible contribution of the self‐condensation reactions of leucine in the gas phase.

Application of High-Resolution NMR and GC-MS to Study Hydrocarbon Oils Derived from Noncatalytic Thermal Transformation of e-Waste Plastics.

The increases in the volumes of electronic waste have become an aggravating environmental, economic, and social health issue in recent times. This study investigates the conversion of e-waste plastics into hydrocarbon oils via noncatalytic thermal transformation followed by an in-depth characterization of these oils using diverse analytical techniques such as gas chromatography–mass spectrometry (GC–MS), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. In particular, NMR spectroscopy is a key analytical tool utilized in this study to gain a comprehensive insight into the chemical nature of the resultant oils along with a semiquantitative investigation of the changes in their composition over a temperature range of 800–1200 °C. The one-dimensional (1D) 1H and two-dimensional (2D) heteronuclear single-quantum correlation spectra were acquired for the oils, wherein the 2D NMR spectrum provided improved resolution of peaks to address the overlaps encountered in the 1D spectrum. The experimental results obtained from GC–MS, FTIR spectroscopy, and NMR spectroscopy were found to align well with each other. The oils produced in this study have a high calorific value of 38.27 MJ/kg and thus may find use in several applications. A detailed mechanism for the thermal degradation of styrene acrylonitrile plastics and the formation of major products is elucidated in this study.

Kinetic Modeling of Cellulose Fractional Pyrolysis

The kinetics of cellulose fractional pyrolysis was studied for the first time in the temperature range of 200–900 °C, with 25 °C increment under nitrogen atmosphere. A detailed analysis of the major and minor pyrolysis products was performed using a System for Thermal Diagnostic Studies (STDS) and FTIR techniques. A semiglobal kinetic model was proposed, with products grouped into kinetic lumps, based on their formation profile similarity. Kinetic parameters (pre-exponential factor A and activation energy Ea) for formation of major products grouped into heavy volatiles 1 lump (levoglucosan and anhydrosugars) and light volatiles 2 lump (furans and carbonyls) were obtained based on the performed experimental studies. The final model accurately predicts not only the weight loss, the temperature-distribution of major lumped products, and the total yields of tar and gases from the fractional pyrolysis of cellulose but also shows a good performance toward literature data for experimental studies of others.

Stereoselective and Regioselective Synthesis of Heterocycles via Copper-Catalyzed Additions of Amine Derivatives and Alcohols to Alkenes.

This Perspective describes the development of a family of copper(II)-catalyzed alkene difunctionalization reactions that enable stereoselective addition of amine derivatives and alcohols onto pendant unactivated alkenes to provide a range of valuable saturated nitrogen and oxygen heterocycles. 2-Vinylanilines and related substrates undergo alternative oxidative amination or allylic amination pathways, and these reactions will also be discussed. The involvement of both polar and radical steps in the reaction mechanisms have been implicated. Major product formation is a function of the lowest energy pathway, which in turn is a function of structural aspects of the various reaction components.

Molecular Products and Fundamentally Based Reaction Pathways in the Gas-Phase Pyrolysis of the Lignin Model Compound p-Coumaryl Alcohol.

The fractional pyrolysis of lignin model compound para-coumaryl alcohol (p-CMA) containing a propanoid side chain and a phenolic OH group was studied using the System for Thermal Diagnostic Studies at temperatures from 200 to 900 °C, in order to gain mechanistic insight into the role of large substituents in high-lignin feedstocks pyrolysis. Phenol and its simple derivatives p-cresol, ethyl-, propenyl-, and propyl-phenols were found to be the major products predominantly formed at low pyrolysis temperatures (<500 °C). A cryogenic trapping technique was employed combined with EPR spectroscopy to identify the open-shell intermediates registered at pyrolysis temperatures above 500 °C. These were characterized as radical mixtures primarily consisting of oxygen-linked conjugated radicals. A comprehensive potential energy surface analysis of p-CMA and p-CMA + H atom systems was performed using various DFT protocols to examine the possible role of concerted molecular eliminations and free-radical mechanisms in the formation of major products. Other significant unimolecular concerted reactions along with formation and decomposition of primary radicals are also described and evaluated. The calculations suggest that a set of the chemically activated secondary radical channels is relevant to the low temperature product formation under fractional pyrolysis conditions.

Experimental and kinetic modeling study of butene isomer pyrolysis: Part II. Isobutene

The pyrolysis of isobutene was investigated using a tubular flow reactor at an absolute pressure of ∼0.82atm over a temperature range of 610–860°C with residence times ranging from ∼0.5 to ∼2.4s. The initial concentration of the fuel ranged from 5 to 50mol%. These data were compared to the predictions of a fundamentally based detailed kinetic model. The model accurately predicted the observed fuel conversion, production of light products, and the formation of several important molecular weight growth species. The primary pathways that lead to the fuel decay and the formation of major products are discussed. In particular, H-atom abstraction from isobutene results in the formation of the 2-methyl allyl radical, which undergoes a β-scission reaction to form allene plus methyl. The subsequent addition reaction of 2-methyl allyl to allene is energetically favored and provides a route to the formation of stable molecular weight growth products that are readily converted to benzene and toluene. The potential energy surface for this reaction was derived from CBS-QB3 calculations and the corresponding temperature and pressure dependent rate constants are obtained. The model predictions were also compared and generally are in good agreement with multiple published isobutene pyrolysis data sets that were measured under significantly different conditions.

Experimental and kinetic modeling study of butene isomer pyrolysis: Part I. 1- and 2-Butene

1- and 2-Butene pyrolysis experiments were performed using a tubular flow reactor at an absolute pressure of ∼0.82atm over a temperature range of 535–810°C with residence times ranging from ∼0.5–∼2.4s. The initial concentration of the fuel ranged from 5 to 50mol%. These data were compared to the predictions of a fundamentally based detailed kinetic model. For both sets of experiments, the model accurately predicts the observed fuel conversion, production of light products, and the formation of several important molecular weight growth species. The primary pathways that lead to the fuel decay and major product formation are discussed. One of the important kinetic features of 1- and 2-butene pyrolysis is that significant amounts of 1,3-butadiene are produced. The addition reactions of vinyl, allyl, and methyl allyl radicals to 1,3-butadiene are all energetically favorable, leading to substantial production of higher molecular weight species. The model was also applied to published pyrolysis and oxidation data for 1- and 2-butene that were collected under significantly different conditions. The comparison to the latter data sets illustrate that, even under oxidation conditions, it is important to properly account for the pyrolysis kinetics.