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Nitrates are a potential class of substances as cetane improvers of diesel fuel and are critical raw materials for some military explosives. Thus, an in-depth investigation of the thermal decomposition mechanism of nitrates is important for further improving their effects. Herein, a combination of experimental and computational studies was performed for the pyrolysis of n -pentyl nitrate in the temperature range of 400‒900 K. Using synchrotron radiation vacuum ultraviolet photoionization, some intermediates and products, such as ethylene, formaldehyde, propene, ethenol, pentanal, NO 2 , and HONO, were identified according to their photoionization efficiency curves. Quantum chemical calculations at the CBS-QB3 level were conducted to elucidate the overall reaction mechanism of n -pentyl nitrate pyrolysis. Along the direct bond fission of n -pentyl nitrate, primary products, C 5 H 11 O• radical and NO 2 , and butyl radical and CH 2 ONO 2 , can further dissociate into many products, in which formaldehyde is the most dominant. In addition, two hydrogen-atom migration channels followed by decomposition are verified for the decomposition of n -pentyl nitrate according to the observation of trans -HONO, pentanal, and 1-pentene. These evidences highlight that both bond fission and hydrogen migration play comparable roles as potential driving forces in the pyrolysis of n -pentyl nitrate at low pressure. This thermal decomposition mechanism of n- pentyl nitrate provides some useful clues for developing combustion models of long chain nitrates in future. [ABSTRACT FROM AUTHOR]

Furan-based derivatives are promising biomass fuels that may be used directly in internal combustion engines as alternative fuels or as additives to fossil fuels. In this work, the experimental studies of 2-acetylfuran (AF2) pyrolysis were carried out in a jet-stirred reactor in the temperature range of 770 – 1130 K and at the pressure of 760 Torr, using synchrotron vacuum ultraviolet photo-ionization mass spectrometry, coupled with gas chromatography. Key pyrolysis intermediates such as methane, ethylene, acetylene, ketene, vinylacetylene, cyclopentadiene, ethynylketene, 2-methylfuran, furfural, carbon monoxide and isomers such as allene/propyne, furan/vinylketene, benzene/fulvene, etc., were identified and quantified. The potential energy surfaces of AF2 unimolecular decomposition reactions were calculated at CBS-QB3 level. The temperature- and pressure-dependent rate constants of the relevant reactions were calculated by solving the master equation based on Rice-Ramsperger-Kassel-Marcus theory. A detailed pyrolysis kinetics of AF2 was developed based on the previous combustion models of 2-methylfuran and was validated against the current experimental results. Rate of production and sensitivity analysis showed that the main consumption pathways of AF2 pyrolysis under atmospheric pressure are unimolecular decomposition reactions, leading to 2-furyl + acetyl and furoyl + methyl, and hydrogen atom-addition reaction to C(5), leading to 2,3-dihydro-5-acetyl-3-furyl, accounting at 1070 K for 25.1%, 13.2% and 20.7% of AF2 consumption, respectively (the remaining 41.0% are due to minor reaction channels contributing < 10% each). At this temperature, the total AF2 consumption is 73%. The contributions of ipso -substitution reactions by methyl and by hydrogen atom to AF2 consumption were comparable. [ABSTRACT FROM AUTHOR]

The pyrolysis of 1-heptene was studied in a flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry at 0.04 and 1 atm and in a jet-stirred reactor using gas chromatography at 1 atm. Flow reactor pyrolysis products, including the allyl radical, cycloalkenes and aromatics, were identified and quantified. Alkenes are found to be the dominant product family, among which ethylene is the most abundant product. A detailed intermediate-to-high temperature model of 1-heptene was developed and validated against the new pyrolysis data in this work, as well as previous data of 1-heptene combustion in literature over a wide range of pressures, temperatures and equivalence ratios. Rate of production analysis and sensitivity analysis were performed to reveal the key pathways in fuel decomposition and product formation. The allylic C C bond dissociation reaction is concluded as the most important pathway in 1-heptene decomposition. Reactions of allyl, propargyl and cyclopentadienyl radicals play important roles in the formation of cycloalkenes and aromatics. Furthermore, comparative pyrolysis experiments of 1-hexene and n-heptane were also performed in the jet-stirred reactor at 1 atm using gas chromatography to explore fuel molecular structure effects on pyrolysis reactivity and product distributions among 1-alkene and n-alkane fuels. The comparison between 1-heptene and 1-hexene pyrolysis demonstrates that similar fuel molecular structure results in the similarities in primary fuel decomposition pathways and pyrolysis reactivity. Ethylene is the most abundant product in both 1-alkene pyrolysis, and the feature in 1-heptene molecular structure leads to enhanced formation of ethylene in its pyrolysis. The abundant formation of ethyl and methyl radicals leads to higher production of 1-pentene and 1-butene in 1-heptene and 1-hexene pyrolysis, respectively. The comparison between 1-heptene and n-heptane pyrolysis reveals that the existence of C C double bond enhances the pyrolysis reactivity of 1-heptene. Different from 1-heptene consumption, n-heptane consumption is dominantly controlled by H abstraction reactions instead of unimolecular decomposition reactions. Propene and 1-butene are prone to be produced in 1-heptene pyrolysis, while 1-hexene has higher mole fractions in n-heptane pyrolysis. [ABSTRACT FROM AUTHOR]

Biodiesels are promising renewable fuels that can aid in the transition to carbon neutrality. The high molecular weight and complex composition of real biodiesel fuels complicate development of compact kinetic models needed for engine simulations. Our group previously proposed the functional group approach (FGMech) to model real-fuel combustion based on the identification of intrinsic relationships between fuel molecular structure and model parameters. Establishing these relationships requires a database consisting of the model parameters of pure fuels for training. In this work, we selected five fatty acid methyl esters (FAMEs) as target fuels, including methyl pentanoate (MPE), methyl hexanoate (MHX), methyl heptanoate (MHP), methyl octanoate (MO) and methyl nonanoate (MN). To facilitate development of an FGMech reaction scheme, a decoupling model approach is adopted here for model construction. Lumped reaction mechanisms are developed to describe the (oxidative) pyrolysis of fuels while a detailed model is used for describing the conversion of pyrolysis intermediates. To validate the present model, pyrolysis experiments for these FAMEs are conducted in a jet-stirred reactor (JSR) at 1 atm and over 790–1120 K. Both the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC)/GC–MS are applied for measuring pyrolysis intermediates. The fuels, primary hydrocarbon and oxygenated products, secondary products including various aromatic compounds, are identified and quantified for model validation. The present model well-predicts the temperature window of fuel decomposition, and reasonably predicts the yields of most pyrolysis products under both present atmospheric conditions and high pressure conditions in literature. The agreement between the measured and predicted results indicates that the present decoupling methodology can accurately describe fuel decomposition and the evolution of intermediates under pyrolysis conditions. In addition, it is found that increasing alkyl CH 2 groups in C 6 to C 10 FAMEs has little influence on the yields of primary oxygenated products; however, increasing yields of hydrocarbon products with increasing alkyl CH 2 groups indicates that alkane chemistry becomes more important moving from MPE to MN. [ABSTRACT FROM AUTHOR]

The pyrolysis of 2-ethylfuran (EF2) in a flow reactor was studied by using synchrotron vacuum ultraviolet photoionization mass spectrometry at 846 – 1319 K and at 30 and 760 Torr. Over 20 pyrolysis products were detected and measured. A detailed kinetic model was constructed by extending the reported comprehensive 2,5-dimethylfuran model to describe the pyrolysis of EF2 and validated against the current experimental results, including methyl, 2-furylmethyl, propargyl, acetylene, ethylene, propene, ketene, 2-vinylfuran, furan/vinylketene and benzene, etc. Rate of production analysis and sensitivity analysis indicate that the main reaction pathways of EF2 pyrolysis are H-abstraction reactions forming 1-(2-furyl)ethyl and 2-(2-furyl)ethyl, unimolecular decomposition reactions forming 2-furylmethyl, and H-addition reactions forming furan and vinylketene. The corresponding products, 2-vinylfuran, 2-furylmethyl and vinylketene, etc., are indicated to be the most key products in EF2 pyrolysis. Comparisons of the formation of aromatic hydrocarbons in the pyrolysis of EF2, 2-methylfuran and 2,5-dimethylfuran show that EF2 had a lower tendency to produce aromatic soot precursors. [ABSTRACT FROM AUTHOR]

Pyrolysis experiments of dimethyl methylphosphonate (DMMP) were carried out in a jet stirred reactor (JSR) coupled to synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) at 1 atm, from 900 to 1200 K, to quantitatively measure the mole fraction profiles of DMMP and its pyrolysis products. Furthermore, theoretical calculations were carried out. Geometry optimization and vibrational frequency analysis were conducted for DMMP unimolecular and isomerization reactions at the MN15/6-311+G(2df,2p) level of theory, and kinetic calculations were performed using the kinetic code of MESS. The results show that DMMP mainly undergoes isomerization channels to form its isomers before decomposing into pyrolysis products. This is different from the DMMP decomposition channels adopted in the literature models. The kinetic model of DMMP in the literature was modified and improved by adding newly calculated reactions and their rate constants and updating the rate constants of unimolecular reactions for DMMP as well based on computations. Some rate tuning of reactions by 5 or 10 factors has been tried in model development to better describe the experimental measurements. Finally, the model developed by this work showed much better prediction of DMMP consumption and major species production than the prediction by literature models. In addition, the updated model was validated against various previous experimental data (CO mole fraction distributions in the shock tube, the flame speed and species mole fraction distributions in the premixed flame), and the satisfactory validation results indicate the reliability of the DMMP model that was improved in this work. This preliminary work laid a foundation to further study the combustion properties and to develop the kinetic model of organophosphorus compounds. [ABSTRACT FROM AUTHOR]

As an important component of organic solid wastes, disposal of plastic wastes (PWs) has always been a thorny issue. Thermochemical conversion is an efficient method. In-depth research on the influence of structural differences on their pyrolysis behavior is beneficial to promote the development of thermal treatment and conversion technology of PWs. The differences in the chemical structure of different polyolefin plastics at the molecule level are mainly reflected in their side chains. Herein, a series of typical polyolefin plastics with similar backbone structure and different side chain structures, including high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyvinyl alcohol (PVA) and ethylene-vinyl acetate copolymer (EVA), were selected for comprehensive pyrolysis characterization in this work. Advanced experimental analysis methods such as in-situ DRIFT and 2D-PCIS were adopted to investigate the evolution of two weak oxygen-containing side chains during pyrolysis of PVA and EVA, respectively. Besides, typical product distribution of six samples were systematically studied by combining SVUV-PIMS and GC/MS. Spectral analysis showed that OH side chain in macromolecular structure of PVA had the weakest thermal stability, and its oxidation reaction occurred earlier than dissociation and dehydration, while the acetoxy side chain in EVA polymers could not only be directly dissociated via deacetoxylation, but also be transformed into OH side chain via deacetylation that occurred simultaneously with deacetoxylation. Further combined with SVUV-PIMS and GC/MS, the distribution characteristics of pyrolysis products of polyolefin plastics and the rules of generation and release of typical products with temperature were obtained in detail. It was found that the release of typical oxygen-containing products was earlier or slightly earlier than the release of hydrocarbons in pyrolysis of PVA or EVA. However, the release of all hydrocarbons was almost simultaneous during the respective pyrolysis process of HDPE, PP and PS, suggesting that the evolution of oxygen-containing side chains with weak thermal stability occurred earlier under the drive of temperature. Based on the characterization results, the main evolution pathways of different side chains were proposed to explain the influence mechanism of different side chain structures on the pyrolysis behavior of polyolefin plastics. The cleavage of C C bonds mainly occurred in HDPE, PP and PS, while the evolution of side chains occurred first in PVC, PVA and EVA, and exerted different influence on the degradation of carbon skeleton. [ABSTRACT FROM AUTHOR]

Pyrrole is a typical fuel nitrogen model compound of coal and it is the precursor of fuel-NO x. The mechanism and kinetics of pyrrole pyrolysis were studied in a jet-stirred reactor coupled with a synchrotron vacuum ultraviolet molecular beam mass spectrometer and a gas chromometer over the temperature range of 940–1240 K at atmospheric pressure. Two sets of new data of pyrrole pyrolysis were provided. Based on the photoionization efficiency analysis, nitrogenous products are mainly produced in the form of nitriles and dinitriles. Of the pyrrole pyrolysis products, six nitriles were newly identified including methyl isocyanide (C 2 H 3 N), cyanogen (NCCN), isocyanogen (CNCN), propionitrile (C 3 H 5 N), propanedinitrile (C 3 H 2 N 2), butanedinitrile (C 4 H 4 N 2). Mole fractions of pyridine (C 5 H 5 N), C 3 H 2 N 2 , cyanovinylacetylene (C 5 H 3 N), and benzonitrile (C 7 H 5 N) were also quantified. HCN is the dominant nitrogenous product of pyrrole pyrolysis. C 2 H 2 and CH 4 are the major carbonaceous products. An updated pyrrole kinetic model was proposed comprising 196 species and 2939 reactions. The production of pyridine and several nitriles during pyrrole pyrolysis could be reasonably predicted using the current model. C 3 H 2 N 2 is mainly produced by the reaction between CH 2 CN and other nitriles, and it is converted into CH 2 CN and CH 3 CN. The reaction between CH 3 and C 3 H 2 N 2 is the most sensitive reaction for promoting the consumption of C 3 H 2 N 2. Results of this work confirm the importance of dinitriles and nitriles during the pyrolysis of pyrrole as an important fuel-NO x model compound of coal and other nitrogen-containing fuels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The pyrolysis of isopropylamine (IPA) was studied in a jet-stirred reactor at 1 atm within 670–1100 K. Pyrolysis products and intermediates were identified and quantified with both synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography analysis. Propiolonitrile, propanenitrile, 1-methylethenylamine, 3-butenenitrile, pyridine and benzonitrile were newly identified compared with previous studies of amines. HCN and 1-methylethenylamine were found to be the dominant N-containing species in IPA pyrolysis. The peak mole fractions and temperatures of C 1 -C 2 hydrocarbons are generally higher than C 3 -C 4 ones. The peak temperatures tend to rise with the increase of degree of unsaturation for hydrocarbons with the same C numbers. Based on the observations, a detailed kinetic model consisting of 429 species and 2407 reactions was developed with reasonable predictions against the measured data. Rate-of-production analysis indicates that IPA is mainly consumed by the H-abstraction at the Cα atom: (CH 3) 2 CHNH 2 + H = (CH 3) 2 CNH 2 +H 2. Sensitivity analysis shows that the unimolecular decomposition via C C bond cleavage and H-abstraction at the Cα atom play promoting roles. The H-abstraction of propene by H-atom yielding allyl radical and self-combination of methyl radicals forming ethane exhibit inhibiting effects. Compared to the pyrolysis of n-propylamine (NPA), more amine- or imine-like species were generated during NPA pyrolysis while more nitriles were detected in IPA pyrolysis. Moreover, the peak temperatures of hydrocarbons in both NPA and IPA pyrolysis shift to higher values with the increase of degree of unsaturation. The results will enrich the understanding of IPA for further combustion kinetic studies of low sooting fuels. [ABSTRACT FROM AUTHOR]

Pyrolysis of norbornadiene (NBD) was investigated in a jet-stirred reactor at 760 torr and within the temperature range of 560 to 1100 K. 37 products and intermediates ranging from m/z = 26 to 178 were identified and quantified by using synchrotron radiation photoionization molecular-beam mass spectrometry accompanied by gas chromatography. The C 7 H 8 isomers, including NBD, cycloheptatriene (CHT) and toluene (A1CH 3), were differentiated. Acetylene (C 2 H 2), cyclopentadiene (C 5 H 6), C 7 H 8 isomers and other aromatics are abundant during the pyrolysis process. A detailed kinetic model was developed with reasonable predictions against the measured results, involving 264 species and 1259 reactions, which is helpful to understand the kinetic and heat features of initial consumption as well as the synergistic effect of C 2 H 2 , C 5 H 6 and A1CH 3 to the formation of aromatics. Rate-of-production analysis shows that the pyrolysis of NBD experiences two stages. The first stage involves the isomerization and decomposition of NBD, yielding A1CH 3 , CHT, C 5 H 6 and C 2 H 2. Branching ratio analysis shows that C 5 H 6 and C 2 H 2 are dominant products in the first stage. Heat release analysis indicates that the first stage is endothermic. The second stage involves the pyrolysis and interactions of first-stage products to produce light hydrocarbons and polycyclic aromatic hydrocarbons like indene, naphthalene, acenaphthylene, fluorene and phenanthrene. Three routes dominate the formation of indene, including C 5 H 6 + C 5 H 5 , benzyl radical + C 2 H 2 and cycloheptatrienyl radical + C 2 H 2 , the last one of which has been scarcely considered in the previous investigation. Sensitivity analysis indicates the reactions in the first stage exhibit strong promoting effects for the consumption of NBD, while the second-stage reactions play minor roles in NBD consumption. This work would enrich the understanding of NBD consumption, PAH formation and heat release. [ABSTRACT FROM AUTHOR]