气相色谱QSRR研究在质谱谱库检索定性中的应用

对质谱谱图相似的多取代烷基苯各位置异构体,根据一种从苯、单取代烷基苯及双取代烷基苯保留指数预测相关多取代烷基苯保留指数的方法,测定了基础化合物在OV－1毛细管柱上的保留指数,预测了相关多取代烷基苯在OV－1上的保留指数。利用该保留数据,结合质谱,给予了正确定性,从而解决了质谱谱库检索定性时对于各位置异构体难于定性的困难。     

Unraveling chemical structure of laminar premixed tetralin flames at low pressure with photoionization mass spectrometry and kinetic modeling

This work reports an investigation on laminar premixed flames of tetralin at 30 Torr and equivalence ratios of 0.7 and 1.7. Measurements of the chemical structure including identification and mole fraction measurements of free radicals, isomers, and polycyclic aromatic hydrocarbons (PAHs) were performed using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV‐PIMS). A kinetic model with 296 species and 1 577 reactions was developed and validated against the flame chemical structure data measured in this work. Modeling analysis reveals the key reaction pathways in tetralin decomposition and PAHs formation. The H‐atom abstraction reactions by H, O, and OH are found to control the consumption of tetralin in the lean flame, while those by H play the dominant role in the rich flame. Indene and naphthalene have very high concentration levels in the rich tetralin flame due to the existence of direct formation pathways from the decomposition of tetralin. The two bicyclic PAHs and their radicals play significant roles in the PAHs growth process of tetralin combustion, which results in the high sooting tendency of tetralin compared to those of alkylbenzenes with smaller or same carbon atom numbers.     

A Global Model of Chemical Vapor Deposition of Silicon Dioxide by Direct-Current Corona Discharges in Dry Air Containing Octamethylcyclotetrasiloxane Vapor

A model of the electron distribution in direct current corona plasmas is combined with a global chemistry model and a two-dimensional transport model to predict the rate of chemical vapor deposition of silicon dioxide on the discharge wire in both positive and negative discharges in dry air containing octamethylcyclotetrasiloxane. The gas-phase chemistry includes reactions to form atomic oxygen (O) and additional global reactions to form gaseous silicon dioxide precursors by the impact reactions of electrons and atomic oxygen with silicone molecules. Surface chemistry is approximated by a single step global reaction from gaseous to solid silicon dioxide. The rate coefficient between atomic oxygen and octamethylcyclotetrasiloxane is estimated from prior experiments to be on the order of 10^–12 cm³/molecule-s. The effects of discharge polarity, current, wire radius and air velocity (Peclet number for mass transfer) on the deposition rate are considered. Deposition rates can be minimized by using positive coronas instead of negative coronas for Peclet number less than 18.5. At higher Peclet numbers, the deposition rate is slightly higher in positive corona discharges, but devices used indoors should continue to use the positive corona in order to minimize the production of ozone. The deposition rate in the positive corona is relatively insensitive to air velocity for velocities from 0.044 to 10 m/s^–1 . However,it may be minimized by operating the corona with the lowest current that provides adequate performance (e.g., particle charging) and the smallest wire that provides adequate mechanical strength.     

Synthesis and flame retardant potential of polyols based on bisphenol‐S

Polyether polyols based on bisphenol‐S were prepared by alkoxylation and compared with analogs based on bisphenol‐A, as well as standard aromatic polyester, and polyether polyols for viscosity and temperature stability. Thermo‐oxidative stability was determined by thermo‐gravimetric analysis, pyrolysis gas chromatography/mass spectroscopy, and evolved gas analysis mass spectroscopy. Incorporation of the sulfone moiety was found to dramatically improve the thermo‐oxidative stability of the neat polyol. Significant char formation was observed with gas phase evolution of flame retardant SO₂ and aromatic sulfone only apparent at about 600 °C. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2102–2108     

Conventional and microwave induced pyrolysis of coffee hulls for the production of a hydrogen rich fuel gas

This paper describes the conventional and microwave-assisted pyrolysis of coffee hulls at 500, 800 and 1000 °C. The influence of the pyrolysis method and temperature on the product yields and on the characteristics of the pyrolysis products is discussed. It was found that the pyrolysis of this particular residue gives rise to a larger yield of the gas fraction compared to the other fractions, even at relatively low temperatures. A comparison of microwave-assisted pyrolysis and conventional pyrolysis showed that microwave treatment produces more gas and less oil than conventional pyrolysis. In addition, the gas from the microwave has much higher H₂ and syngas (H₂ + CO) contents (up to 40 and 72 vol.%, respectively) than those obtained by conventional pyrolysis (up to 30 and 53 vol.%, respectively), in an electric furnace, at similar temperatures. From the pyrolysis fraction yields and their higher heating values it was found that the energy distribution in the pyrolysis products decreases as follows: gas > solid > oil. Moreover, the energy accumulated in the gas increases with the pyrolysis temperature. By contrast, the energy accumulated in the char decreases with the temperature. This effect is enhanced when microwave pyrolysis is used.     

Nitric oxide-assisted atmospheric pressure corona discharge ionization for the analysis of automobile hydrocarbon emission species

Nitric oxide reagent gas has been found to improve the sensitivty and robustness of the atmospheric pressure corona discharge ionization (APCDI) process. Sensitivity has been increased by a factor of 20-100, depending on the compound, over APCDI without nitric oxide. The robustness (defined as the sensitivity to matrix interferences) of APCDI in the presence of water has been improved by a factor of 3 over normal APCDI. These improvements are due in part to a modification of the commercial inlet system and ionization chamber that allows the chamber and sample gases to be heated to 100 and 350 °C, respectively. Nitric oxide was chosen as the reagent gas because of the variety and selectivity of its interaction with hydrocarbons with differing functional groups. Product ions of nitric oxide ionization and their subsequent tandem mass spectra are presented and discussed for selected alkanes, alkenes, alkylbenzenes, alcohols, aldehydes, and an ether. A tandem mass spectrometry (unique parent ion-daughter ion transition) method was developed to quantify componds of specific interest in vehicle emissions. The absolute sensitivty for these compounds, under ideal conditions, was determined and ranges from 0.006 ppb for xylene (most sensitive) to 80 ppb for C₈ (or larger) normal alkanes. Routine sensitivity for real-world samples was in the single parts per billion range for aromatic and olefinic species. Potential applications include the real-time, on-line monitoring of selected hydrocarbons in automobile exhaust.     

Oxidation of Acetylene in Atmospheric Pressure Pulsed Corona Discharge Cell Working in the Nanosecond Regime

Combined experimental and modeling studies of acetylene oxidation in pulsed corona discharges working in the nanosecond regime are presented. The corona cell was characterized in term of power deposition to provide input data for the model. The concentrations of ozone, CO, CO₂ and residual acetylene were systematically measured for model validation purposes. The model used allows describing the detailed chemistry in the discharge and the mass transfer between the microdischarges and the discharge free regions in the corona cell. Results showed that the model allows a satisfactory prediction of the acetylene residual fraction, CO and CO₂ yields and O₃ concentration for a wide range of conditions. They enabled a precise identification of the product distribution and confirmed the central role of O-atom in the oxidation process. They also revealed that ketene, H₂CCO, plays an important role in the oxidation mechanism and allowed drawing some conclusions on the optimization of the oxidation process.     

Overview of Atmospheric Pressure Discharges Producing Nonthermal Plasma

Recently, much attention has been paid to gas discharges producing nonthermal plasma because of many potential benefits in industrial applications. Historically, past work focused on Dielectric Barrier (silent) Discharges (DBD) and pulse-periodical corona discharges. Recently, a number of new different discharge techniques succeeded in producing stable gas discharge at atmospheric pressure. Among these are repetitively pulsed glow discharge; continuous glow discharge in a gas flow; hollow-cathode atmospheric pressure discharge; RF and microwave (MW) discharges. Several new variants of the DBD have been demonstrated over a rather wide range of frequencies. All these forms of gas discharge are characterized by a strong nonequilibrium plasma state. We attempt to classify these discharges with respect to their properties, and an overview of possible applications is made. Conditions for the existence of homogenous and filamentary forms of each of the discharge types are discussed.     

Kinetic Modelling of Atmospheric Pressure Corona Discharges in Humid Air

Corona discharge is a self-sustained discharge of gaseous medium in inhomogeneous electric fields, which often occurs on transmission lines and has some adverse effect on the power transmission system. In this paper, a kinetic model of corona discharges is presented to simulate the evolution process of charged particles and neutral species in humid air. To investigate the effect of humidity, our model consists of 69 species and 393 chemical reactions which consider important reactions containing H₂O molecules and hydrates. In addition, CO₂ molecules are also included to improve the integrity of reaction database. A temporal evolution of reduced electric field strengths E/N, which are typical experimental values of corona discharges, is used as input. The simulation results show that H₃O⁺ is one of the dominant positive ions which is in qualitative agreement with previous experimental results. The effect of humidity and pulse width on the plasma chemistry is also discussed. It is found that the humidity affects the maximum density and life time of the specific species. Meanwhile, the plasma chemistry could be affected by different pulse widths of the input electric field.

     

Preparation of highly efficient flame retardant unsaturated polyester resin by exerting the fire resistant effect in gaseous and condensed phase simultaneously

The unsaturated polyester resins (UPR) were usually applied in electronic equipment, but the intrinsic flammability severely retrained their application. A mono‐component flame retardant poly (piperazine methylphosphonic acid neopentylglycol ester) (PPMPNG) made in our lab was selected and applied to improve their flame retardant performance. The UPR thermosets achieved UL‐94 V‐0 grade during vertical burning tests and the limiting oxygen index was as high as 32.1% when 15 wt% PPMPNG was incorporated. PPMPNG promoted the decomposition and carbonization of UPR materials in advance during heating process, and the residual mass was effectively enhanced at high temperature. The flame retardant mechanism of UPR/PPMPNG thermosets was investigated by pyrolysis‐gas chromatography/mass spectrometry tests, and the measurement of the morphologies and chemical components of the char residue. The phosphine oxygen radical was generated and then quenched the active free radicals in gas phase. Moreover, the av‐EHC of FR‐UPR was declined from 15.8 MJ kg^?1 of pure UPR to 8 9 MJ kg^?1 corresponding a reduction of 43.6%, which also verified the flame retardant effect in gas phase. The compact, integrated, and graphitized char layer was produced on materials surface and then exerted excellent barrier effect in condensed phase. Thus, the UPR/PPMPNG composites were conferred superior flame retardant properties.     

Ozone Production in the Positive DC Corona Discharge: Model and Comparison to Experiments

A numerical model of ozone generation in clean, dry air by positive DC corona discharges from a thin wire is presented. The model combines the physical processes in the corona discharge with the chemistry of ozone formation and destruction in the air stream. The distributions of ozone and nitrogen oxides are obtained in the neighborhood of the corona discharge wire. The model is validated with previously published experimental data. About 80% of the ozone produced is attributed to the presence of excited nitrogen and oxygen molecules. A parametric study reveals the effects of linear current density (0.1–100 A/cm of wire), wire radius (10–1000 m), temperature (300–800 K) and air velocity (0.05–2 m/s) on the production of ozone. The rate of ozone production increases with increasing current and wire size and decreases with increasing temperature. The air velocity affects the distribution of ozone, but does not affect the rate of production.     

Universal and discriminative detection using a miniaturized pulsed discharge detector in comprehensive two-dimensional GC

A miniaturized pulsed discharge detector (Mini-PDD) has been successfully demonstrated for comprehensive 2-D GC (GC x GC) analysis of pyrolysis gasoline and the pyrolysis GC x GC analysis of a polyethylene copolymer. The detector cell volume of the Mini-PDD is reduced to 25% of the Valco plug-in PDD D-3. An n-C11 peak width at base is 96 ms for the Mini-PDD, about 23% larger than a peak width of 78 ms detected by a flame ionization detector (FID). The Mini-PDD has sufficient response time for most GC x GC applications. When Mini-PDD is operated in helium photoionization mode (Mini He-PDD), it is a universal detector for both inorganic and organic compounds. This is especially useful when detection of water is needed in GC x GC applications. When krypton is doped in the helium discharge gas (Mini Kr-PDD), it can suppress signals of compounds having higher ionization potentials and enhance relative signal intensities of aromatic compounds. The determination of aliphatic to aromatic hydrocarbon ratios is essential to the operation of petroleum crackers. Comparison of the signal from two modes of the Mini-PDD is a simple and fast way to verify the location of aromatics in comprehensive 2-D gas chromatograms.     

Analysis of BTEX, PAHs and metals in the oilfield produced water in the State of Sergipe, Brazil

During oil and gas exploitation, large amounts of produced water are generated. This water has to be analyzed with relation to the chemical composition to deduce the environmental impact of its discharge after a treatment process. Therefore, a study was carried out to evaluate preliminarily the BTEX (benzene, toluene, ethylbenzene and xylenes), polycyclic aromatic hydrocarbons (PAHs) and metals contents in produced water samples taken from effluents of the Bonsucesso treatment plant located in the city of Carmópolis, the most important oil and gas producer in the State of Sergipe, North-east of Brazil. Three methods were optimized to determine the target compounds. Polycyclic aromatic hydrocarbons were determined by gas chromatography with mass spectrometric detection (GC/MS), volatile aromatic hydrocarbons (BTEX) by gas chromatography with photoionization detector (GC/PID) and metals were analyzed by flame atomic absorption spectrometry (FAAS). The results showed that concentrations of the target compounds in these samples ranged from 96.7 to 1397 μg L^− 1 for BTEX, from 0.9 to 10.3 μg L^− 1 for PAHs and from 0.003 to 4540 mg L^− 1 for metals.     

Pyrolysis-GC-FTIR for structural elucidation of aquatic humic substances

Substructure components of various aquatic humic substances were investigated by a coupled pyrolysis — gas chromatography — Fourier-transform infrared spectroscopy (Py-GC-FTIR) procedure. The humic substances studied gave similar pyrolysis products, but in varying proportions. Many of the pyrolysis products (e.g. methanol, acetone, alkylbenzenes, cyclopentane, aliphatic and aromatic organic acids, acetamide, pyrrole and phenols) could be identified by their FTIR spectra using a digital library for automatic comparison. Some of the compounds are related to lignin fragments which form a large part of the humic substances investigated. Other products give hints to the involvement of tetrapyrroles, fatty acids, furanoses and amino compounds in the structure of humic macromolecules.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Comparison of gasification and pyrolysis of thermal pre-treated wood board waste

The second step of a two-step process of thermo-chemical conversion of wood board waste is discussed in this paper. GC-TCD and FTIR analyses of the gas product enable to compare the two proposed way: pyrolysis and gasification of the pre-treated and virgin wood board sample between 800 and 1000 °C. The effect of the first step of the process (low-temperature pyrolysis which aims to remove nitrogen initially present in wood board waste) has shown to be really efficient as the production of ammonia observed during the second step decreases by a factor 6–8 jointly to a slight decrease of the energy recovery. The first step also prevents the production of hydrogen cyanide and is therefore essential. Concerning pre-treated samples, the best results have been obtained at 1000 °C with samples pre-treated at 250 °C. The way of gasification has been shown to be more efficient in term of energy recovery but leads to a production of ammonia larger than in the case of the pyrolysis way. The conversion of the pyrolysis residual char into an activated char must be considered since it presents a potential economic interest.     

Pyrolysis of waste tyres: The influence of USY catalyst/tyre ratio on products

In this paper, an ultrastable Y-type (USY) zeolite was investigated with two-staged pyrolysis–catalysis of waste tyres. Waste tyres were pyrolysed in a fixed bed reactor and the evolved pyrolysis gases were passed through a secondary catalytic reactor. The main objective of this paper was to obtain high concentration of certain aromatic hydrocarbons suitable to be used as a chemical feedstock rather than a liquid fuel, and the influence of catalyst/tyre ratio on the product yield and composition of derived oils. The light fraction (boiling point < 220 °C) was distilled from the derived oil prior to be analyzed with gas chromatography/mass spectrometry (GC/MS). It showed that the increase of catalyst/tyre ratio resulted in high yield of gas at the expense of the oil yield. The high catalyst/tyre ratio favored to increase the concentration of light fraction (<220 °C) in oil. Increasing the catalyst/tyre ratio resulted in significant changed in the concentration of benzene, toluene, xylenes and the alkyl aromatic compounds. For benzene and toluene, the highest concentration was obtained at the catalyst/tyre ratio of 0.5. The concentration of xylenes increased with the increasing of catalyst/tyre ratio.     

Application of pyrolysis-capillary gas chromatography with NPD detection in thermal degradation of polyphosphazenes study

Polyphosphazenes represent a unique class of polymers with a backbone composed of alternating phosphorous and nitrogen atoms. The thermal behaviour and decomposition of a variety of polyphosphazenes depends on the type of side groups present. Especially those that bear aryloxy side groups, possess a high temperature stability as well as excellent flame resistance. Pyrolysis-capillary gas chromatography has been used in a study of three polyphosphazene samples for thermal stability characterisation. Degradation products were detected with three single detectors for flame ionisation (FID), nitrogen-phosphorous sensitivity (NPD) and mass spectrometry (MSD) at different pyrolysis temperatures ranging from 300°C up to 800°C. The NPD responses for phosphorous or nitrogen fragments of polyphosphazenes have been used for the construction of degradation product schemes and the examination of the thermal stability of the polyphosphazene’s backbone. Partial identification of the degradation products present in the gaseous phase was achieved by MSD. The polyphosphazenes thermal degradation conversion rates were at a maximum at 450–500°C. At various pyrolysis temperatures, the calculated N/P peak area ratio is a function of the degree of polyphosphazene-N=P-chain degradation, and reflective of the nitrogen — phosphorous detector sensitivity. NPD proved to be suitable tool for characterization of polyphospazene thermal stability.     

Variable high-pressure and concentration study of cyclohexane pyrolysis at high temperatures

A high-pressure and temperature cyclohexane pyrolysis shock tube study was completed with the goal of extending the experimental cyclohexane pyrolysis data to pressures relevant to current and future combustors and to investigate whether ring contraction products observed in high-pressure, supercritical phase cyclohexane and cycloalkane pyrolysis experiments can form at matching, and higher, pressures in the gas phase. The experiments in the current work were completed over a range of 950–1650 K and at nominal pressures of 40, 100, and 200 bar. No alkylcyclopentanes, possible ring contraction products, were observed to form under the conditions of the current study. The production of methylenecyclopentane and 1,3-cyclopentadiene, and the other three cyclic species quantified: cyclohexene, benzene, and toluene, increased significantly with a substantial increase in the initial fuel concentration. Two sets of experimental data obtained at 200 bar were compared with a literature and laboratory-generated model. Both models had difficulty capturing the propadiene and propyne profiles, and the literature model significantly overestimated the benzene observed in the set of experiments completed with the more dilute fuel mixture. The literature model was able to better predict propadiene, propyne, and benzene product profiles in the 200 bar set of experiments, which used a higher concentration of fuel in the test gas. These results suggest that despite both cyclohexane and benzene being well-studied and important species in combustion chemistry, their reaction pathways and reaction rates would benefit from further refinement.     

Photochemical and discharge-driven pathways to aromatic products from 1,3-butadiene

A detailed study of the photochemical and discharge-driven pathways taken by gas-phase 1,3-butadiene has been carried out. Photolysis or discharge excitation was initiated inside a short reaction tube attached to the outlet of a pulsed valve. Bath gas temperatures near 100 K were achieved in the reaction tube by the constrained expansion of the gas mixture into the tube, simulating temperatures of relevance in Titan's atmosphere. Photolysis of 1,3-butadiene was initiated at 218 nm with a laser pulse that counter-propagated the reaction tube. Discharge excitation was carried out using discharge electrodes imbedded in the reaction tube walls, enabling the study of the photochemical and discharge products under similar conditions. Products were detected using either single-photon VUV photoionization (118 nm = 10.5 eV) or resonant two-photon ionization (R(2)PI) spectroscopy in a time-of-flight mass spectrometer. Emphasis was placed on characterization of the aromatic products formed, since these may be of particular relevance to Titan's atmosphere, where benzene has been positively identified and 1,3-butadiene is projected as the principle pathway to its formation. Consistent with previous studies of the photodissociation of 1,3-butadiene, C(3)H(3) + CH(3) is the dominant primary product formed. Under the temperature-pressure conditions present in the reaction tube (T approximately 75-100 K, P = 50 mbar), C(6)H(6) is the dominant secondary photochemical product formed. A 1:1 C(4)H(6):C(4)D(6) mixture was used to prove that the C(6)H(6) product was formed by recombination of two C(3)H(3) radicals; however, a careful search for benzene revealed none, indicating that less than 1% of the C(6)H(6) formed in the reaction tube is benzene. This is consistent with expectations for these temperatures and pressures based on previous modeling of propargyl recombination. Two aromatic products were observed from the photochemistry: ethylbenzene and 3-phenylpropyne. Plausible pathways leading to these products are proposed. In the discharge, C(3)H(3) + CH(3) are also identified as significant primary neutral products and C(6)H(6) as a dominant higher-mass product. In this case, the C(6)H(6) was identified as benzene via its R2PI spectrum, appearing with intensity about 10 times larger than any other aromatic formed in the discharge. R2PI spectra of a total of about 15 aromatic products were recorded from the 1,3-butadiene discharge, among them toluene; styrene; phenylacetylene; o-, m-, and p-xylene; ethylbenzene; indane; indene; beta-methylstyrene; and naphthalene. Previously unidentified spectra in the m/z 142 and 144 mass channels were positively identified as the 1,3- and 1,4-isomers of phenylcyclopentadiene and the analogous 1-phenylcyclopentene.     

Compositional elucidation of heavy petroleum base oil by GC × GC‐EI/PI/CI/FI‐TOFMS

Comprehensive two‐dimensional gas chromatography (GC × GC) coupled to time‐of‐flight mass spectrometry is a powerful separation tool for complex petroleum product analysis. However, the most commonly used electron ionization (EI) technique often makes the identification of the majority of hydrocarbons impossible due to the exhaustive fragmentation and lack of molecular ion preservation, prompting the need of soft‐ionization energies. In this study, three different soft‐ionization techniques including photo ionization (PI), chemical ionization (CI), and field ionization (FI) were compared against EI to elucidate their relative capabilities to reveal different base oil hydrocarbon classes. Compared with EI (70 eV), PI (10.8 eV) retained significant molecular ion (M^+·) information for a large number of isomeric species including branched‐alkanes and saturated monocyclic hydrocarbons along with unique fragmentation patterns. However, for bicyclic/polycyclic naphthenic and aromatic compounds, EI played upper hand by retaining molecular as well as fragment ions to identify the species, whereas PI exhibited mainly molecular ion signals. On the other hand, CI revealed selectivity towards different base oil groups, particularly for steranes, sulfur‐containing thiophenes, and esters, yielding protonated molecular ions (M + H)⁺ for unsaturated and hydride abstracted ions (M‐H⁺) for saturated hydrocarbons. FI, as expected, generated intact molecular ions (M^+·) irrespective to the base oil chemical classes. It allowed elemental composition by TOFMS with a mass resolving power up to 8000 (FWHM) and a mass accuracy of 1 mDa, leading to the calculation of heteroatomic content, double bond equivalency, and carbon number of the compounds. The qualitative and quantitative results presented herein offer a unique perspective into the detailed comparison of different ionization techniques corresponding to several hydrocarbon classes.