Small Hydrocarbons Research Articles

Impact of PAH photodissociation on the formation of small hydrocarbons in the Orion Bar and the horsehead PDRs

ABSTRACT We study whether polycyclic aromatic hydrocarbons (PAHs) can be a weighty source of small hydrocarbons in photodissociation regions (PDRs). We modelled the evolution of 20 specific PAH molecules in terms of dehydrogenation and destruction of the carbon skeleton under the physical conditions of two well-studied PDRs, the Orion Bar, and the Horsehead nebula that represent prototypical examples of PDRs irradiated by ‘high’ and ‘low’ ultraviolet radiation field. PAHs are described as microcanonical systems. The acetylene molecule is considered as the main carbonaceous fragment of the PAH dissociation, as it follows from laboratory experiments and theory. We estimated the rates of acetylene production in gas phase chemical reactions and compared them with the rates of the acetylene production through the PAH dissociation. It is found that the latter rates can be higher than the former rates in the Orion Bar at AV < 1 and also at AV > 3.5. In the Horsehead nebula, the chemical reactions provide more acetylene than the PAH dissociation. The produced acetylene participate in the reactions of the formation of small hydrocarbons (C2H, C3H, C3H+, C3H2, C4H). Acetylene production via the PAH destruction may increase the abundances of small hydrocarbons produced in gas phase chemical reactions in the Orion Bar only at AV > 3.5. In the Horsehead nebula, the contribution of PAHs to the abundances of the small hydrocarbons is negligible. We conclude that the PAHs are not a major source of small hydrocarbons in both PDRs except some locations in the Orion Bar.

Mass spectra and incident energy resolved spectra after collisions of hydrocarbon ions with fusion-plasma tungsten thin films

We have performed surface-induced dissociation studies of small deuterated hydrocarbon cations i.e. CDx+ with x=2-4, colliding with two types of tungsten-coated surfaces, in the incident energy range between Ein = 0 eV approximately, up to Ein = 100 eV. A 34 nm thick W layer deposited on stainless steel using the Thermionic Vacuum Arc (TVA) method and a small sample of a tile cut from ASDEX-Upgrade tiles, consisting of PlasmaSprayed (PS) tungsten on carbon, are exposed to ion flux in these experiments. A double-focussing reverse geometry BE mass spectrometer, is used under ultra high vacuum conditions. Mass spectra of secondary charged particles are recorded via time-of-flight mass analyser. For comparison, we have performed equivalent study on polished stainless steel under experimental status explained in Section 2 below. At very low energies i.e. below 10 eV, only surface reflected projectiles are seen, whereas most of them are neutralized by surface micro charges. We observed that the fragmentation pattern of the small molecular ions at a given energy is strongly dependent on the surface. The roughness of both of the said thin films and their reflectivity for the projectile ion beam is studied by analysis of the ion yields of the reaction products

Atomic hydrogen interactions with small polycyclic aromatic hydrocarbons cations

When exposed to a thermal beam of hydrogen atoms, gas-phase coronene cations C24H12+ can be sequentially hydrogenated. This process is accompanied by a gradual transition of the electronic structure from aromatic to aliphatic. The planar very stable coronene structure transforms into the significantly weaker corrugated structure, typical for aliphatic molecules. In this study, we have investigated the hydrogenation of 5 smaller polycyclic aromatic hydrocarbon cations using a combination of radiofrequency ion trapping with time-of-flight mass spectrometry. Anthracene (C14H10+), pyrene (C16H10+), triphenylene (C18H12+), tetracene (C18H12+) and 8-9-benzofluoranthene (C20H12+) only cover a small mass range, but differ in carbon/hydrogen ratio, number of outer-edge sites and overall structure. We have observed qualitatively similar initial hydrogenation patterns for all 5 molecular ions, with odd hydrogenation states being dominant. Strong quantitative differences in hydrogenation and in attachment-induced fragmentation were found. For the case of pyrene cations, we have also investigated exposure to atomic D. Clear lines of evidence for HD/D2 abstraction reactions of Eley–Rideal type were found, as previously observed for coronene cations.Graphical abstract

Nickel-loaded zeolite snags small alkynes

When making polymers from lower olefins like ethylene, propylene, and 1,3-butadiene, it’s important to ensure no alkynes are in the mix. These small hydrocarbons—acetylene, propyne, and butyne—are ...

Understanding the blending octane behaviour of unsaturated hydrocarbons: A case study of C4 molecules and comparison with toluene

Octane number (ON) is an important empirical parameter for developing and optimizing internal combustion engine (ICE) for knock resistance. Primary reference fuels (PRF) comprising iso-octane and n-heptane are the simplest gasoline surrogates. C4 hydrocarbons: butane isomers (n-butane and isobutane), butene isomers (1-butene, 2-butene and isobutene) and 1,3-butadiene are the smallest hydrocarbons with isomeric, saturated, unsaturated and conjugated bond structures, which makes them good candidates for understanding the blending octane behavior of saturated and unsaturated hydrocarbons. In this study, the blending octane behaviors of six PRF60 & C4 hydrocarbon mixtures were systematically investigated. A state-of-the-art kinetic models were used by merging the latest KAUST gasoline surrogate model with the AramcoMech 3.0 model. IDTs of stoichiometric fuel/air mixtures were simulated at wide range of pressure (20–50 atm) and temperature (600–1400 K). Three correlation equations were employed from the literature to predict the research octane number (RON) and motor octane number (MON) of all blends based on these calculated IDTs. Compared with the experimentally measured ON, the best correlation conditions and errors were identified. With the highest degree of unsaturation, 1,3-butadiene was found to be the strongest ON enhancer. Moreover, based on a polynomial correlation, a TPRF (PRF + toluene) blend was formulated by matching the RON and MON of PRF plus 1,3-butadiene blend, for a comparative analysis. Finally, the reactants’ consumption profile, flux and sensitivity analysis were simultaneously performed for explaining the chemistry behind the blending octane behavior of the PRF blends with 1,3-butadiene and toluene.

How does successive hydrogen addition to PAH ions impact their unimolecular chemistry?

Hydrogenated polycyclic aromatic hydrocarbons (PAHs) have been proposed to contribute to the formation of interstellar H2 by acting as a surface catalyst for the adsorption of hydrogen atoms and desorption of H2 molecules. In the present study, imaging photoelectron photoion coincidence (iPEPICO) spectroscopy and tandem mass spectrometry were employed to examine the unimolecular chemistry of four hydrogenated polycyclic aromatic hydrocarbon ions: 9,10-dihydroanthracene (DHA+•) and 1,2,3,4,5,6,7,8-octahydroanthracene (OHA+•), having opposite patterns of hydrogenation, and 1,2,3,4-tetrahydrophenanthrene (THP+•) and 1,2,3,4,9,10-hexahydrophenanthrene (HHP+•). DHA+• exhibits the same reactions previously observed for 1,2-dihydronaphthalene and 9,10-dihydrophenanthrene, namely competing loss of H• and CH3•. However, the energy required for H•-loss, as predicted by RRKM modeling of the iPEPICO results, was lower than the latter ions, presumably due to charge delocalization across the central ring upon dehydrogenation. OHA+• behaves similarly to ionized tetralin, displaying losses of H•, CH3•, C2H4 and C3H5• in its collision induced dissociation (CID) mass spectra, but under iPEPICO conditions CH3•-loss is not observed. THP+• and HHP+• have aspects of both DHA+• and OHA+• chemistries, displaying losses of H•, CH3•, C2H4 and C3H5•. RRKM modeling produced minimum energies for all observed reaction channels, which were also computationally explored at the B3LYP/6–31+G(d,p) level of theory. The results indicate that small PAH ions may not be effective surfaces for the catalytic formation of H2 in the ISM, but rather sources of small hydrocarbons.

Analysis of the viscosity reduction of crude oil with nano-Ni catalyst by acoustic cavitation

The present study discusses ultrasound wave and heterogeneous catalysts act synergistically on viscosity reduction of crude oil. The reasons for the possible viscosity reduction were analyzed from the structural changes of asphaltene. This paper presents a systematic and unified approach to analyzing asphaltene clusters structure based on FTIR spectra and XRD patterns. The results reveal that the cavitation effect can be intensified by the addition of metallic nickel particles. The cavitation effect destroys the spatial network structure formed by resin, asphaltene and wax crystals, so that the viscosity of the treated oil sample tends to be stable. With the addition of metallic nickel particles which has a synergistic effect on cavitation, the asphaltene molecules have undergone a cracking reaction and decomposed into small molecular hydrocarbon compounds, contributing to viscosity reduction. However, when added a certain amount of metallic nickel particles, the degree of surface cavitation leads to increasing number of cavitation bubbles, free radicals recombination, and aromatic hydrocarbons polymerizing to form secondary asphaltenes. This leads to a slight rise in viscosity.

Thermal-oxidative aging mechanism of asphalt binder based on isothermal thermal analysis at the SARA level

To better understand the thermal-oxidative aging mechanism of asphalt binder at the component level, a new isothermal agingmethod was developed to discuss thermal behaviors of saturates, aromatics, resins and asphaltenes (SARA) fractions. Volatile constituents released from SARA fractions were identified and the changes in chemical compositions, morphology and elements of SARA fractions were characterized before and after the thermal-oxidative aging. Results indicate that the mass losses of saturates and resins are 2.1% and 0.7%, respectively. However, the aromatics and asphaltenes masses are increased by 2.0% and 5.2%, respectively. Also, endothermic reactions occur in saturates and aromatics, and endothermic and exothermic reactions are basically equivalent in resins, and exothermic reactions occur in asphaltenes. Further, CO, CO2, CH4 and light oxygen-containingcompounds are released during the aging of SARA fractions, and short-chain alkanes are generated in saturates. Low molecular hydrocarbons, CO2, and SO2 are emitted, and more aromatic ring products are generated in aromatics. Carboxylic acids, small molecular unsaturated hydrocarbons and SO2 are volatilized, and fused aromatic rings, alcohols and ethers are produced in resins. Unsaturated hydrocarbons are released, and the molecular polymerization becomes obvious in asphaltenes. Additionally, after the isothermal aging, pores or bulges are left in saturates, and obvious folds and pores appear on aromatics. Cluster whiskers, lumps and disordered lamellar layers are observed on resins, and resins and asphaltenes become loose, dry and rough. C element content is increased, but O element content is decreased. Finally, various volatiles are released from SARA fractions at different aging stages. The thermal-oxidative aging of asphalt binder consists of the volatilization of light components and the oxidation of side chains in benzene methyls and aliphatic hydrocarbons, leading to the content changes of SARA fractions in asphalt binder.

Reconnaissance of the uncharted low energy vibrational motions of acenaphthene

The room-temperature, millimeter-wave rotational spectrum of the small polycyclic aromatic hydrocarbon acenaphthene has been measured between 75 and 110 GHz. Accurate rotational and distortion parameters are presented due to the over 1400 transitions that have been included into a global fit. Besides observing transitions of the ground vibrational state, six vibrationally excited states have been identified: four fundamental modes (ν30,ν41,ν40,ν29), one overtone (2ν30), and one combination band (ν41+ν30). This is the first report of four of these excited states observed in the gas phase as two of the fundamental modes are IR inactive and the intensities of the overtone and combination bands are often too weak to be observed. These excited states reside less than 300 cm−1 above the ground state, and an experimental approximation of their band centers is presented. The rotational constants and line lists can be used to facilitate the search for this polycyclic aromatic hydrocarbon in the interstellar medium.

Molecular dynamics simulation and DFT calculations on the oil-water mixture separation by single-walled carbon nanotubes

The treatment of oily wastewater has drawn much attention due to environmental and human health challenges. Among several techniques and materials developed to mitigate the contamination of oily wastewater, the nanostructured materials for effective adsorption and separation came into the limelight. Owing to their high specific area and nanosized structure, CNTs have demonstrated inclusive utilization as superior materials for selective adsorption. Here, we present molecular origin of oil-water mixture separation by SWCNTs. We used reactive MD simulation to explain scientifically the separation mechanism of considered mixture at molecular scale. It was shown that small hydrocarbons tend to migrate toward the nanotube surface faster than large counterparts do and whole components were adsorbed on the CNT surface up to 0.8 ns of simulation time. This is due to the different hydrophobicity tendency associated with each oil components that has also been addressed by MD simulation. DFT-D3 calculations showed that interaction nature of adsorbed oil molecules onto the nanotube surface was typical for the physisorption. Furthermore, the accuracy of current methods has been validated by experimental and theoretical data. Our simulation findings provide a well-founded understanding for adsorption and separation of oil-water mixture by carbon based nanostructured materials.

Predicting the photoresponse of soot nuclei: Spectroscopic characteristics of aromatic aggregates containing five-membered rings

Establishing the mechanism for soot nucleation will require in situ experimental characterization of the identity and intermolecular interactions of the initial precursors, and electronic spectroscopy methods have the potential to do both. However, the optical response of polycyclic aromatic hydrocarbon (PAH) dimers and complexes differs significantly from that of the constituent monomers, and studies of soot precursor complexes have largely been limited to PAHs containing only six-membered aromatic rings. Hydrocarbons containing unsaturated five-membered rings are also present in high concentration in flames, and the photoresponse of complexes containing five-membered rings has not yet been examined. In this work, we elucidate the spectroscopic properties of small hydrocarbon complexes containing cyclopentadienyl groups or cyclopenta-fused groups, calculating ground- and excited-state binding energies, optimal excited-state geometries, repulsion energies, and fluorescence emission wavelengths. We show that excited-state distortion of cyclopentadienyl groups allows strong binding and low-energy fluorescence emission compared to similar-sized PAHs, and that a cyclopenta-fused group dramatically lowers the absorption and emission energies for acenaphthylene, dominating excited-state noncovalent interactions—findings that could shed light on the complex electronic properties of flames.

Adsorption of small hydrocarbons on pristine, N-doped and vacancy graphene by DFT study

In this paper, the adsorption mechanisms between different species (CH3, CH4, C2H2, C2H4, C2H6, and C6H6) and the carbon-based materials (pristine graphene, N-doped graphene, and vacancy graphene) during the chemical vapor infiltration process were systematically studied using the density functional theory. The optimized adsorption configurations were obtained by using Dmol3 code in Material Studio. The adsorption energies, Mulliken atomic charges, density of states, and charge density differences of the adsorption process were analyzed. It showed that the CH3 is chemisorbed, while the other species (CH4, C2H2, C2H4, C2H6, and C6H6) are weak physisorbed on pristine graphene, N-doped graphene and vacancy graphene. In addition, the introduction of nitrogen dopant and vacancy defect into the pristine graphene does not significantly affect the adsorption mechanisms between small hydrocarbons and graphene.

Effects of n-Butanol Blends on the Formation of Hydrocarbons and PAHs from Fuel-Rich Heptane Combustion in a Micro Flow Reactor with a Controlled Temperature Profile

ABSTRACT The effects of the addition of n-butanol on the formation of hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) of n-heptane combustions were investigated using a micro flow reactor (MFR) with a controlled temperature profile. The concentrations of small and large hydrocarbons, as well as PAHs were measured at a maximum wall temperature of 1,100 K and atmospheric pressure. The values obtained from several mechanisms were compared to the measurement values at equivalence ratios of 2.0–5.0. The CRECK mechanism was in fair agreement with the measurements. The computational results confirmed that the concentration of the PAHs and soot precursors’ decreased, while that of CO and CO2 increased due to the addition of butanol. These trends were also shown by the measurement values. The reaction path and rate of production analyzes were carried out to identify the major reactions contributing toward species concentrations.

Time-of-flight secondary ion tandem mass spectrometry depth profiling of organic light-emitting diode devices for elucidating the degradation process.

Organic light-emitting diode (OLED) products based on display applications have become popular in the past 10 years, and new products are being commercialized with rapid frequency. Despite the many advantages of OLEDs, these devices still have a problem concerning lifetime. To gain an understanding of the degradation process, the authors have investigated the molecular information for deteriorated OLED devices using time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS depth profiling is an indispensable method for evaluating OLED devices. However, the depth profiles of OLEDs are generally difficult due to the mass interference among organic compounds, including degradation products. In this study, the tandem mass spectrometry (MS/MS) depth profiling method was used to characterize OLED devices. After degradation, defects comprised of small hydrocarbons were observed. Within the defect area, the diffusion of all OLED compounds was also observed. It is supposed that the source of the small hydrocarbons derives from decomposition of the OLED compounds and/or contaminants at the ITO interface. The true compound distributions have been determined using MS/MS depth profiling methods. The results suggest that luminance decay is mainly due to the decomposition and diffusion of OLED compounds, and that OLED decomposition may be accelerated by adventitious hydrocarbons present at the ITO surface.

Effect of in-situ and ex-situ injection of steam on staged-gasification for hydrogen production

K modified Ni-based catalysts are used to investigate the effect of in-situ and ex-situ injection of steam (ISI and ESI) on biomass pyrolysis and in-line catalytic steam reforming in a two-stage fixed bed reactor. The results show that 0.5 wt% K is appropriate to modify the Ni-based catalysts for steam reforming of biomass pyrolysis vapor. Compared to the catalytic cracking without steam addition, both ISI and ESI increase the gas yield and the carbon conversion efficiency (Xc) of the pyrolysis vapors. And the ESI is more beneficial to the conversion of pyrolysis vapors to small molecular gases. The maximum hydrogen concentration, hydrogen yield and carbon conversion efficiency (Xc) of staged-gasification can reach 53.8%, 31 mmol/g-bio, and 94.6%, respectively, when both stages are at 700 °C with ex-situ steam injection (S/C = 1.2) and 3 g catalyst loaded in the second stage. Also, the steam is beneficial to removing the depositions of graphitized coke and small molecular polycyclic aromatic hydrocarbon on the catalysts. However, it is yet difficult for steam to react with the highly ordered carbonaceous.

Fuel Oil from Plastic Waste

In Earlier days PLASTIC was a revolutionary invention which brought many changes in industrial & daily activities. But now a days, it has become a major problem as it is increasing the landfills which is leading to more pollution because of its high degradation time and no proper disposable way which is affecting the environment. The global production of plastic has shown an increase from around 1.3 MT in 1950 to 300 MT in 2010 due to the introduction of plastic in various fields. Out of the total consumption of plastic,53 % constitute polyolefins which is a large hydrocarbon. Polyethene is most consumed one i.e. 33% of total due to this it is taken into consideration. To overcome this problem, we used Thermal Cracking i.e. Pyrolysis, it is a process which converts the large hydrocarbon chains in to small hydrocarbon chains by heating the plastic at high temperature (350 – 400℃) & the products obtained are fuel oil and non- condensable fractions. The fuel oil can be used for heating purposes and non-condensable fractions to reduce air pollution. Polythene, Polypropylene are used as they are pure hydro-carbons and burnt completely.

The infrared view of dust and molecules around V4334 Sgr (Sakurai’s object): a 20-yr retrospective

ABSTRACT We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakurai’s object) over an ∼20-yr period, drawing on ground-, airborne-, and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from ∼1200 K in 1998 August to ∼180 K in 2016 July. The dust mass, assuming amorphous carbon, was ∼5 × 10−10 M⊙ in 1998 August, and we estimate that the total dust mass was ∼2 × 10−5 M⊙ by ∼2016. The appearance of a near-infrared excess in 2008 suggests that a new episode of (or renewed) mass-loss began then. We infer lower limits on the bolometric luminosity of the embedded star from that of the dust shell, which rose to ∼16 000 L⊙ before declining to ∼3000 L⊙. There is evidence for weak 6–7 μm absorption, which we attribute to hydrogenated amorphous carbon formed in material ejected by Sakurai’s object during a mass ejection phase that preceded the 1997 event. We detect small hydrocarbon and other molecules in the spectra, and trace the column densities in hydrogen cyanide (HCN) and acetylene (C2H2). We use the former to determine the 12C/13C ratio to be 6.4 ± 0.7, 14 times smaller than the Solar system value.

Confinement of Mg Nanoparticles by Bituminous Coal and Associated Synergistic Hydrogen Storage Effect

Using the coking property of bituminous coal, a nanostructured Mg-C composite hydrogen storage material was developed by ball milling and heat treatment. The heat treatment conditions and hydrogen storage behavior of the composite material were investigated. Results show that when the material is heat-treated at 550 °C under Ar atmosphere, the carbon could react with Mg to irreversibly form Mg2C3. When 1.0 MPa H2 was introduced to the heat treatment at 550 °C, the magnesium does not form Mg2C3. The resulting composite material is shown to have a globular bonded structure by scanning electron microscopy, and the Mg nanoparticles are confined by the bituminous coal. Fourier transform infrared spectroscopy and gas chromatography analysis show that the carbon could combine with hydrogen only in the presence of MgH2 under current experimental conditions. The carbon-bonded hydrogen would be released in the form of small molecule hydrocarbons such as CH4, C2H4 and C2H6. Dynamic tests show that coal carbon and magnesium absorb/desorb hydrogen at similar temperatures, which proves that there is a synergistic hydrogen storage effect between magnesium and coal carbon.

A new model for the synthesis of graphite encapsulated nickel nanoparticles when using organic compounds in an arc-discharge system

Herein we propose a new “three-step” model of synthesizing graphite encapsulated nickel nanoparticles (Ni-GEM), including the pyrolysis reaction of organic compounds which the conventional two-step model ignores. According to the results of XRD, Raman, and TEM, we found that the Ni-GEM synthesized by using both PF resin and benzene vapor as the carbon sources has two favorable characteristics: thicker shells (~5–10 nm) and smaller particle sizes (~30 nm), which are much better than those using only PF resin or PF resin mixed with cyclohexane vapor (thinner shell less than 5 nm and larger particle sizes ~50 nm). Benzene decomposes into large aromatic molecules and tiny graphitic flakes at 1200–3500K, while cyclohexane prefers to decompose and form small hydrocarbon molecules at 1000K. As a result, the two compounds go through two different reaction paths. Benzene will decompose and directly attach onto the surface of Ni nanoparticles, forming smaller sized but thicker shell structured Ni-GEM, while cyclohexane will lead to the formation of amorphous carbon coating on the Ni-GEM. By including the above two distinct hydrocarbon pyrolysis reactions, this study modifies the conventional model and successfully explains the formation processes of Ni-GEM with very different morphologies. Furthermore, the new model may help in controlling the morphologies of other GEM nanoparticles with a number of core-metals.

Determination of ultra-low concentrations of gaseous 14C-bearing hydrocarbons produced during corrosion of irradiated steel using accelerator mass spectrometry.

Compound-specific radiocarbon analysis (CSRA) was developed to identify and quantify gaseous 14C-bearing carbon compounds at the pico- to femtomolar concentration range and employed in a corrosion experiment with small specimens of irradiated steel. The approach is based on gas chromatographic separation of single 14C-bearing carbon compounds, their oxidation to 14CO2, sampling with a custom-made fraction collector and quantification by accelerator mass spectrometry (AMS). In addition to CSRA, a method allowing the quantification of the total 14C content of the gas phase was developed and tested. After validation of the two set-ups with standards, the gaseous 14C-bearing carbon compounds produced during alkaline anoxic corrosion of irradiated steel were quantified. Small hydrocarbons (HCs) like methane (14CH4) and ethane (14C2H6) were the only 14C-bearing compounds identified in the gas phase above the detection limit. 14CH4 was the main species (on average 5.4 × 10-14 mol L-1 gas) and contributed >90% to the total 14C content, whereas the concentration of 14C2H6 was much lower (7.9 × 10-16 mol L-1 gas). To our knowledge, this is the first study reporting CSRA of gaseous 14C-bearing HCs produced during anoxic corrosion of irradiated metallic radioactive waste at ultra-low concentrations.