Tunable Synchrotron Vacuum Ultraviolet Photoionization Research Articles

Production of Aliphatic-Linked Polycyclic Hydrocarbons during Radical-Driven Particle Formation from Propyne and Propene Pyrolysis

We investigated the pyrolysis of propyne and propene using aerosol mass spectrometry coupled with tunable synchrotron vacuum ultraviolet photoionization. The results show that propyne forms particles at pyrolysis temperatures approximately 100 K below the lowest temperature at which propene produces particles. The aerosol mass spectra show that the carbon-to-hydrogen (C/H) ratios of the pyrolysis products from both reactants increase with temperature between the particle onset temperature and 1275 K. In this temperature range, the mass peaks corresponding to species with 18 or more carbon atoms are more saturated (i.e., have lower C/H ratios) than species predicted by the stabilomer grid. The observation of relatively high saturation (low C/H ratios) at temperatures near particle onset is consistent with the presence of aliphatically linked hydrocarbons during the preliminary stages of soot formation. The masses of the species presumed to be aliphatically linked suggest that these linked species are adducts of species smaller than chrysene (C18H12). We performed a comparative analysis of the initial PAH-growth pathways consistent with aerosol mass spectra and associated mass-specific photoionization-efficiency curves. The results from the comparative analysis indicate that the development of PAHs up to the size of acenaphthylene (C12H8) follow similar formation pathways for propyne and propene, but the isomeric composition of species larger than acenaphthylene diverges for the two reactants.

Kinetic insights into plasma-assisted low-temperature oxidation of propane with synchrotron photoionization mass spectrometry

The present study investigates the chemical kinetics of low-temperature oxidation of propane activated by nanosecond pulsed dielectric barrier discharge in a flow reactor. Molecular beam mass spectrometry with tunable synchrotron vacuum ultraviolet photoionization (SVUV-PIMS) is employed for components identification and quantification. A series of hydrocarbons and oxygenated intermediates are observed, including fuel-specific species reported for the first time in this system like propyl hydroperoxide (C3H7OOH), acrolein (C3H4O2), oxetane (-CH2CH2CH2O-), methyloxirane (-CH(CH3)CH2O-), and propanol (n-/i-C3H7OH), which provide original kinetic information in the plasma-assisted low-temperature oxidation of propane. The detection of alkyl hydroperoxide (ROOH) demonstrates the existence of alkyl peroxy (RO2) formed through oxygen addition to alkyl (R) and the detection of cyclic ethers provides evidence for the presence of hydroperoxyl alkyl (QOOH). A kinetic model incorporating plasma chemistry and combustion chemistry is developed for plasma-assisted oxidation of propane. Path fluxes of fuel consumption and oxygenated intermediates formation are provided based on model analysis. Besides H abstractions by the OH radical, reactions activated by plasma involving electron impact dissociation, O(1D)/Ar* quenching dissociation, and ionization contribute much to fuel consumption. The formed propyl (n-/i-C3H7) are exclusively consumed through oxygen addition producing propyl peroxy (n-/i-C3H7O2). Propyl peroxy can participate in self- and cross-reactions yielding various oxygenated intermediates such as aldehydes, ketones, alcohols, and propoxy (n-/i-C3H7O). Discrepancies between simulations and experiments suggest that further kinetic studies on low-temperature mechanisms, including propyl peroxy related reactions for plasma-assisted combustion modeling, are still desired.

Experimental and kinetic study of pyridine oxidation under the fuel-lean condition in a jet-stirred reactor

Pyridine is an important model compound of fuel-nitrogen during the coal combustion process. The lean oxidation of pyridine was studied over 800–1100 K at atmospheric pressure with the equivalence ratio of 0.4 in a jet-stirred reactor. Pyridine and its oxidation products were measured by tunable synchrotron vacuum ultraviolet photoionization molecular-beam mass spectrometry and gas chromatography analyzer. Three-stage consumption phenomenon of pyridine and O2 was observed including a fast consumption stage at 910–920 K, a moderate consumption stage at 920–1000 K, and a slow consumption stage at 1000–1100 K. HCN, N2, N2O, and HNCO are the major nitrogenous oxidation products of pyridine. CO, CO2, HCN, and HNCO are the dominant carbonaceous products. HNCO is uniquely detected in the lean oxidation of pyridine compared with rich oxidation. A new pyridine LTO 2.0 model comprising 210 species and 1349 reactions was proposed, providing a good prediction of pyridine and its major oxidation products against experimental data. N2O emission is larger than NO at 1100 K. HCN is the dominant nitrogenous intermediate under both fuel-lean and fuel-rich conditions. Results of this work provide a detailed analysis of the nitrogen evolution mechanism of pyridine oxidation under the fuel-lean condition, which is close to the real industrial low-temperature coal combustion processes including the MILD combustion, fluidized bed combustion, etc.

Combined experimental and theoretical study on photoionization cross sections of benzonitrile and o/m/p-cyanotoluene

Photoionization cross sections (PICSs) for the products of the reaction from CN with toluene, including benzonitrile and o/m/p-cyanotoluene, were obtained at photon energies ranging from ionization thresholds to 14eV by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Theoretical calculations based on the frozen-core Hartree-Fock approximation and Franck-Condon simulations were carried out to cross-verify the measured PICS. The results show that the photoionization cross sections of benzonitrile and cyanotoluene isomers are similar. The generalized charge decomposition analysis was used to investigate the components of the highest occupied molecular orbital (HOMO) and HOMO-1. It was found that the HOMO and HOMO-1 of benzonitrile and cyanotoluene isomers are dominated by the features of the benzene ring, indicating that the substitution of CN and methyl has a minor influence on the PICS of the studied molecules. The reported PICS on benzonitrile and cyanotoluene isomers in the present work could contribute to the near-threshold PIMS experiments and determine the ionization and dissociation rates in interstellar space for these crucial species. The theoretical analysis on characteristics of molecular orbitals provides clues to estimating the PICS of similar substituted aromatic compounds.

Experimental study of nitropropane pyrolysis with molecular-beam mass spectrometry and tunable synchrotron VUV photoionization. Part II. The flow reactor pyrolysis of 2-nitropropane

An experimental study of 2-nitropropane (2-NP) pyrolysis was performed in a flow reactor at low pressure (4.0 kPa) and in the temperature range of 523–923 K. The pyrolysis species were detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS) techniques. Species from m/z = 15 to 87, such as radicals of CH3, C2H5, C3H5 and C3H7; isomers of C3H4 (allene and propyne), C5H8 (1,3-pentadiene and cyclopentene), were identified from near-threshold photoionization efficiency (PIE) spectra. Four nitrogenous intermediates never reported in the homogeneous pyrolysis of 2-NP (i.e., 2-propen-1-imine, 2-propen-1-amine, acetamide and 2-nitropropene) were identified in this work. The mole fraction profiles of the pyrolysis species were evaluated at different temperatures. Based on the experimental findings, the pyrolysis pathways of 2-NP were discussed.

Experimental study of nitropropane pyrolysis with molecular-beam mass spectrometry and tunable synchrotron VUV photoionization. Part I. The flow reactor pyrolysis of 1-nitropropane

An experimental study of 1-nitropropane (1-NP) pyrolysis was performed in a flow reactor at low pressure (4.0 kPa) in the temperature range of 623–973 K. The pyrolysis species was detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS). Species from m/z = 15–87 were identified from near-threshold photoionization efficiency (PIE) spectra, such as radicals of CH3, C2H5, C3H5 and C3H7; isomers of C2H4O (ethenol and acetaldehyde), C3H6O (acetone and propanal), C4H10 (butane and isobutane), HNC (hydrogen isocyanide), HCN (hydrogen cyanide)), C3H5N (ethyl isocyanide and species with unidentified structure) and C3H5NO (methoxyacetonitrile and species with unidentified structure). Their mole fraction profiles were evaluated at different temperature. Based on the mole fractions of species measured at the minimum temperature of 1-NP pyrolysis, some new channels of 1-NP primary pyrolysis were speculated, such as the channels involving O-transfer from N to C-atoms in different positions, deoxygenation, dehydrogenation and OH-abstraction. Based on the mechanisms proposed in the literature, the species produced from secondary or subsequent reactions were also discussed. These results are valuable to a further quantum mechanical calculation for a better understanding of 1-NP chemistry.

Determination of absolute photoionization cross-sections of some aromatic hydrocarbons.

Aromatic hydrocarbons play an important role in the formation and growth of polycyclic aromatic hydrocarbon (PAH) and soot particles. Measurements of their absolute photoionization cross-sections (PICSs), that benefit the quantitative investigation of mass spectrometry, are still lacking, however. PICSs of some aromatic hydrocarbons were measured with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Nitric oxide and benzene were chosen as standard references for PICS calibration, since their photoionization cross-sections are well documented in the literature. Binary liquid mixtures of the investigated molecules and their specific solvents were used in the measurements. The investigated aromatics include naphthalene, phenanthrene, 1-methylnaphthalene, indene, 2-/3-/4-methylphenylacetylene, 2-methylindene, diphenylacetylene, 1-/2-ethynylnaphthalene and acenaphthylene. Photo-induced fragments from the molecules were also observed with increasing photon energy. Based on our measurements and literature data, PICSs of most aromatic molecules have very similar values beyond their ionization energies. However, molecules that contain the phenylacetylene structure have PICSs higher than other aromatics.

Experimental and kinetic investigation of pyrolysis and oxidation of nitromethane

The pyrolysis and oxidation of nitromethane (NM) were studied in a plug flow reactor over the temperature range of 735–1476 K at 5 Torr and in a jet-stirred reactor over the temperature range of 600–875 K at atmospheric pressure, respectively. Mole fraction profiles of major products and intermediates were identified with tunable synchrotron vacuum ultraviolet photoionization and molecular-beam mass spectrometry. The current study represents the first comprehensive characterization of NM conversion under these conditions. The experimental results were compared to predictions with a detailed chemical kinetic model involving 364 species and 2389 reactions. The rate constants for significant dissociation reactions CH3NO2 = CH3 + NO2 and CH3NO2 = HCNO + H2O were calculated by the RRKM/Master Equation method using Variflex program in this work. The model provided an overall reasonable agreement with the measured data, but for pyrolysis conditions future work is required to improve predictions of some intermediates. Rate-of-production analysis indicates that the primary decomposition pathways of NM are different for pyrolysis and oxidation due to the effects of CN bond fission and roaming mediated isomerization. From the sensitivity analysis, the two pathways mentioned above have promoting effects on NM consumption for all the studied conditions, while the reaction of CH3+NO2CH3O+NO with inhibiting effect at Φ=2.0 shows promoting effects for Φ=0.4 and pyrolysis. This work extends the experimental database and helps to improve the understanding of low temperature chemistry of NM.

Catalytic pyrolysis of xylan over alkali metal salts as revealed by synchrotron vacuum ultraviolet photoionization mass spectrometry

Xylan is the primary hemicellulose polysaccharide found in biomass. In this study, catalytic pyrolysis of xylan with Na2CO3 and K2CO3 was conducted in a homemade tubular furnace at 300 °C. As a result of on-line sampling and the use of tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), the evolution of unstable products, such as 4-hydroxy-5,6-dihydro-pyran-2-one (m/z 114), could be monitored in real time. The obtained photoionization mass spectra were interpreted by statistical analysis and the mechanisms of xylan pyrolysis with alkali metal salts were further discussed. The differences in thermogravimetry curves, photoionization mass spectra and time-evolved profiles revealed the important effects of alkali metal ions on both the decomposition temperature and reaction rates during xylan pyrolysis. Furthermore, we showed that alkali metal ions can promote the formation of char and lighter compounds. This work can provide guidance on the better utilization of hemicellulose resources with the help of alkali metal salts.

Low-temperature gas-phase oxidation of diethyl ether: Fuel reactivity and fuel-specific products

Diethyl ether (DEE) has been recently suggested as a potential biofuel for compression-ignition engines that are known to be significantly controlled by low-temperature (LT) chemistry. However, the LT oxidation of DEE has not fully been understood in term of the formation of LT fuel-specific products. We have thus studied the oxidation of DEE by examining detailed profiles of its oxidation products under LT conditions (400–1100 K). To this end, we have used a dedicated experimental setup including a nearly-atmospheric jet-stirred reactor (JSR) coupled to online gas chromatography (GC). The experiments were complemented by measurements made with a JSR coupled to tunable synchrotron vacuum ultraviolet (SVUV) photoionization (PI) molecular-beam mass spectrometry (MBMS) for a cross-validation of the identification of important LT species.Experimental results indicate that DEE is very reactive; it starts to react around 425 K. DEE exhibits an unusual oxidation behavior with two negative temperature coefficient (NTC) zones in the JSR study. Because of this two-NTC observation, additional experiments were performed with a plug flow reactor (PFR) combined with electron ionization (EI)-MBMS, confirming this behavior in the two types of reactor. Moreover, about 20 oxidation species in C1C4 range were detected with several intermediates containing 2-3 O-atoms. Acetic acid is found to peak at 525 K with a very large amount, suggesting that it is a key species in the early stage of DEE's LT oxidation. Possible DEE-consumption paths leading to acetic acid formation could play an important role in the oxidation mechanism of DEE. A new model is proposed based on the present experimental observations to include new primary LT reaction paths. The model reproduces the experimental phenomena quite well and enhances the understanding of the two-NTC-zone occurrence and of intermediates containing 2-3 O-atoms during the LT oxidation of DEE.

Experimental and Kinetic Modeling Study of Nitroethane Pyrolysis at a Low Pressure: Competition Reactions in the Primary Decomposition

The pyrolysis of nitroethane has been investigated over the temperature range of 682–1423 K in a plug flow reactor at a low pressure. The major species in the pyrolysis process have been identified and quantified using tunable synchrotron vacuum ultraviolet photoionization mass spectrometry and molecular beam sampling techniques. The rate constants for the primary pyrolysis of nitroethane as well as those for the decomposition of the secondary product CH3CHNO2 have been obtained via ab initio calculations. These results have been adopted in a detailed chemical kinetic model, which contains 95 species and 737 reactions. The model was validated against the experimental results with satisfactory agreement for most of the identified and quantified species. Further analysis on the results indicates that both the concerted molecular elimination and C–N bond rupture are significant in the primary pyrolysis of nitroethane, with the latter channel being more important at high temperatures. The adoption of new deco...

Influence of the biofuel isomers diethyl ether and n-butanol on flame structure and pollutant formation in premixed n-butane flames

Diethyl ether (DEE) and its isomer n-butanol are both considered as promising fuel additives or neat biofuels. While some effects of their addition to hydrocarbon fuels under engine conditions have been reported, fundamental studies that aim at understanding the joint reaction pathways of such fuel mixtures remain quite scarce. Here, we have chosen n-butane as a well-studied hydrocarbon base fuel, and we have added these oxygenated isomers individually under identical conditions in premixed low-pressure flames. Different combustion behavior of the respective alkane-biofuel mixtures must then be related to the fuel structure. Analyses were performed in five fuel-rich flames including flames of n-butane, DEE, and n-butanol as well as two flames of n-butane doped with 50% DEE or 50% n-butanol. In this series, the carbon-to-oxygen ratio, argon dilution, pressure, and gas velocity were kept constant. More than 40 species in the range of C0–C8 were identified and quantified in each flame by electron ionization (EI) molecular-beam mass spectrometry (MBMS) coupled with gas chromatography (GC). The experiments were partially complemented by tunable synchrotron vacuum ultraviolet (SVUV) photoionization (PI)-MBMS. To assist in the interpretation of the data, a kinetic model was established by combining different sub-mechanisms for these fuels available in the literature. As expected, the formation of toxic carbonyls, such as formaldehyde and acetaldehyde, increased significantly upon addition of both oxygenated fuels to n-butane. Blending n-butane with DEE noticeably reduces the formation of soot precursors, because primary reactions of DEE mainly release C1–C2 hydrocarbon species to the system. n-Butanol addition, however, shows no significant reduction effects or even higher formation of soot precursors. These trends were observed both in the experiments and model predictions, and the higher ability of n-butanol to form soot precursors compared to DEE indeed results mainly from the differences in the fuel structure.

Experimental and kinetic modeling study of diethyl ether flames

Diethyl ether (DEE, C4H10O) is being considered as a promising biofuel. However, its combustion chemistry has not been well studied. Particularly lacking are quantitative intermediate species profiles in flames that provide a stringent test for kinetic models, and flame speed data at elevated pressures. In the present paper, we obtain species distributions in low-pressure flames and measure flame speeds at elevated pressure to gain insights into high-temperature combustion chemistry of DEE. Specifically, a fuel-rich DEE flame (ϕ∼1.8) with 25% argon dilution at 4kPa was investigated by using a dedicated combination of electron ionization (EI) molecular-beam mass spectrometry (MBMS) with gas chromatography (GC) and tunable synchrotron vacuum ultraviolet (VUV) photoionization (PI) MBMS. High-pressure flame speeds of DEE were measured in a constant-volume cylindrical chamber at an initial temperature of 298K at an equivalence ratio of ϕ=1.4 and pressure up to 507kPa. Moreover, a new detailed kinetic model for DEE combustion was developed, with the most noticeable advances over the solely existing model by Yasunaga et al., 2010 being a more complete description of the reactions of DEE radicals and the use of accurate theoretical methods, i.e. CBS-QB3, to determine the rate constants for important primary reactions. In contrast to the previously published one, the present model includes reactions of DEE radicals that directly involve the formation of ethyl vinyl ether (EVE), an addition supported by identification and quantification of EVE by PI-MBMS in the flame experiment. Finally, the results showed that DEE flames yield low concentrations of aromatic species. However, high acetaldehyde emission was observed, originating from the dominant pathways of DEE consumption via H-abstractions from C-α positions followed by β-scissions.

Pyrolysis study of pectin by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

The thermal decomposition of pectin was studied, and some major products were online analyzed by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). The principal products were furfural, methyl 2-furoate and 5-oxo-tetrahydro-furan-2-carbaldehyde. Some new high molecular weight intermediate products were firstly observed thanks to the soft ionization and MSMS structural analysis of ions. The results demonstrated the variation of the pyrolysis product pool with temperatures, dividing the thermal decomposition process into two stages: the low-temperature stage for the intramolecular pyrolysis of galacturonic acid subunit at the chain ends of polymers and the high-temperature stage for the rupture of α-(1 → 4) glycosidic bond between galacturonic acid subunit. This work reported a new application of SVUV-PIMS in pectin pyrolysis and demonstrated its good performance in product analysis. The formation mechanisms of some major products from pectin pyrolysis were discussed based on the analysis of pyrolysates, which should provide insight into the pyrolysis behavior of pectin.

Site-selective dissociation processes of cationic ethanol conformers: the role of hyperconjugation.

In present report, we explored hyperconjugation effects on the site- and bond-selective dissociation processes of cationic ethanol conformers by the use of theoretical methods (including configuration optimizations, natural bond orbital (NBO) analysis, and density of states (DOS) calculations, etc.) and the tunable synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry. The dissociative mechanism of ethanol cations, in which hyperconjugative interactions and charge-transfer processes were involved, was proposed. The results reveal Cα-H and C-C bonds are selectively weakened, which arise as a result of the hyperconjugative interactions σCα-H → p in the trans-conformer and σC-C → p in gauche-conformer after being ionized. As a result, the selective bond cleavages would occur and different fragments were observed.

Thermal decomposition of polypropylene by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

The application of synchrotron vacuum ultraviolet (VUV) photoionization combined with molecular-beam mass spectrometry, also called synchrotron VUV photoionization mass spectrometry (SVUV-PIMS), in the research of the thermal decomposition of polypropylene (PP) was studied, and some main pyrolysis products formed at different photon energies have been identified. Using SVUV-PIMS, some isomers can be distinguished, which are much helpful for further understanding of the thermal decomposition of PP.

PRIMARY COMBUSTION INTERMEDIATES IN LOW-PRESSURE PREMIXED LAMINAR 2,5-DIMETHYLFURAN/OXYGEN/ARGON FLAMES

Primary combustion intermediates in low-pressure premixed laminar 2,5-dimethylfuran (DMF)/oxygen (O2)/argon (Ar) flames with equivalence ratios of 0.8 and 1.5 were investigated by using tunable synchrotron vacuum ultraviolet photoionization and molecular-beam mass spectrometry. DMF is a promising biofuel, with properties similar to those of gasoline. However, the combustion chemistry of DMF is not well-studied. Possible reaction pathways of DMF and its primary combustion derivatives were proposed based on the combustion intermediates identified in this work. Photoionization efficiency curves (PIEs) of the combustion intermediates in the DMF/O2/Ar flames were recorded. Ionization energies (IEs) were measured from the PIEs. The combustion intermediates were identified by the agreement of the measured IEs with those reported in the literatures or calculated at G3B3 level. H abstraction and the consecutive reaction products were identified, including 5-methylfurfural, (Z)-1-oxo-1,3,4-pentatriene, and 2-ethyl-5-methylfuran, etc. Furan was not observed in the low-pressure DMF flames. H and OH addition products were also identified, including 2-methylfuran, (2Z,3E)-1-oxo-1,3-pentadiene, and 2-oxo-2,3-dihydro-5-methylfuran. The extra methyl side chain may explain the lower laminar burning velocity of DMF relative to that of 2-methylfuran.

Products from the Oxidation of Linear Isomers of Hexene

The experimental study of the oxidation of the three linear isomers of hexene was performed in a quartz isothermal jet-stirred reactor (JSR) at temperatures ranging from 500 to 1100 K including the negative temperature coefficient (NTC) zone, at quasi-atmospheric pressure (1.07 bar), at a residence time of 2 s and with dilute stoichiometric mixtures. The fuel and reaction product mole fractions were measured using online gas chromatography. In the case of 1-hexene, the JSR has also been coupled through a molecular-beam sampling system to a reflectron time-of-flight mass spectrometer combined with tunable synchrotron vacuum ultraviolet photoionization. A difference of reactivity between the three fuels, which varies with the temperature range has been observed and is discussed according to the changes in the possible reaction pathways when the double bond is displaced. An enhanced importance of the reactions via the Waddington mechanism and of those of allylic radicals with HO2 radicals can be noted for 2- and 3-hexenes compared to 1-hexene.

Analysis of Petroleum Aromatics by Laser-Induced Acoustic Desorption/Tunable Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Laser-induced acoustic desorption coupled with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (LIAD/SVUVPI-MS) is employed to analyze aromatics prepared under different conditions from Lungu atmospheric residue (LGAR), i.e., the primary aromatics separated directly from LGAR, and the secondary aromatics after hydrogenation of LGAR and its resins. The mass spectra of the primary aromatics present a bimodal normal distribution in the range of 200–900 Da, in which the relative intensity of the two peaks changes significantly with the SVUV photon energies (9.0, 11.0, and 14.0 eV), indicating that at least two categories of compounds with different ionization energies (IEs) are included, i.e., polycyclic aromatics (IEs < 10.0 eV) in the mass range of 400–900 Da, and aliphatic and alicyclic compounds (IEs close to 11.0 eV) in 200–400 Da. Also detected in the aromatics are metalloporphyrins. Furthermore, the mass spectra of the secondary aromatics separated from LGAR and its resins at different hydrogenation temperatures (390, 400, 410, and 420 °C) are also recorded. The results indicate that the hydrogenation process, especially at higher temperatures, results in removal of alkyl-side and bridge chains in the aromatics, and the secondary aromatics from LGAR resins contain more alkyl side and bridge chains and metal compounds than those from LGAR.

Online Analysis of Volatile Products from Bituminous Coal Pyrolysis with Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Volatile species from pyrolysis of two kinds of bituminous coal, Huainan (HN) and Yima (YM), were investigated online with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Mass spectra of products at different photon energies and temperatures were measured during the pyrolysis process. Some isomeric products can be characterized by the SVUV-PIMS based on their different ionization energies. Aromatic compounds are dominant pyrolysis products of these coal samples, while a number of aliphatic products were also observed. In comparison of these two coals, the HN coal probably has more condensed aromatic structures than YM coal. The different structures of the macromolecular network between HN and YM coals probably lead to different pyrolytic products at the same temperature. This work demonstrates the good performance of SVUV-PIMS in online analysis of complex coal pyrolysis.