Large Aromatic Hydrocarbons Research Articles

Impact of molecular composition on viscosity of heavy oil: Machine learning based on semi-quantitative analysis results from high-resolution mass spectrometry

The primary impediment to the recovery of heavy oil lies in its high viscosity, which necessitates a deeper understanding of the molecular mechanisms governing its dynamic behavior for enhanced oil recovery. However, there remains a dearth of understanding regarding the complex molecular composition inherent to heavy oil. In this study, we employed high-resolution mass spectrometry in conjunction with various chemical derivatization and ionization methods to obtain semi-quantitative results of molecular group compositions of 35 heavy oils. The gradient boosting (GB) model has been further used to acquire the feature importance rank (FIR). A feature is an independently observable property of the observed object. Feature importance can measure the contribution of each input feature to the model prediction result, indicate the degree of correlation between the feature and the target, unveil which features are indicative of certain predictions. We have developed a framework for utilizing physical insights into the impact of molecular group compositions on viscosity. The results of machine learning (ML) conducted by GB show that the viscosity of heavy oils is primarily influenced by light components, specifically small molecular hydrocarbons with low condensation degrees, as well as petroleum acids composed of acidic oxygen groups and neutral nitrogen groups. Additionally, large molecular aromatic hydrocarbons and sulfoxides also play significant roles in determine the viscosity.

Development of a practical soot model for diesel surrogate fuels and oxygenated fuels with specific soot precursor tracking and uniform model structure

Soot formation and oxidation involve several complex processes, which are driven by gas-phase chemistry and soot particle dynamics. An effective soot model for diesel surrogate and practical oxygenated fuels is necessary for predicting the soot emissions to meet the emission regulations in engines. To develop a practical and universal soot model for various fuels without tuning any model parameters under wide operating conditions, it is important to reproduce the soot behaviors for different fuels with distinct molecular structures. In this work, a practical soot model was developed to describe the soot behaviors for diesel surrogate fuels comprising large n-alkane, isoalkane, cycloparaffin, and aromatic hydrocarbon, as well as oxygenated fuels including alcohol and ether. The influence of the fuel molecular structures on the soot behaviors was emphasized by utilizing the specific reaction pathways of polycyclic aromatic hydrocarbon (PAH) production and the specific reaction channels of the soot formation including soot nucleation and PAH condensation for different fuels. An efficient method named the moment projection method (MPM) was employed to describe the soot particle dynamics by directly solving the moment transport equations and track the number of soot particles. By coupling a reduced chemical reaction model for describing the fuel oxidation chemistry and PAH formation, it is found that the soot volume fraction and number density are well predicted for iso-octane, n-heptane, toluene, methanol, n-butanol, dimethyl ether, their mixtures, and diesel surrogate in shock tubes and laminar premixed flames without tuning any model parameters. The effects of equivalence ratio, temperature, and fuel type on soot production are analyzed through the rates of soot nucleation, surface growth, PAH condensation, and oxidation. The computational results indicate that the present model can satisfactorily reproduce the soot characteristics of different fuels with distinct soot formation and oxidation processes.

Exploring the reaction chemistry of biomass upgrading over HZSM-5 catalyst through model compounds

The catalytic fast pyrolysis of 17 biomass-derived model compounds over HZSM-5 was conducted in double microfixed-bed reactors (DFBRs) at 500 °C. Our single photoionization mass spectrometer (SPI-MS) allows the real-time monitoring the dynamics of volatiles formation as a function of catalyst deactivation, which provides interesting information on reaction chemistry of biomass catalytic upgrading. The roles of some important intermediates (e.g., benzofurans, benzaldehydes, benzenediols etc.) and their conversion in biomass upgrading are comprehensively discussed. The network of reaction pathways for the conversion of chosen model compounds is also proposed based on the release trend of different products. Strikingly, the favorite formation pathways of large aromatic hydrocarbons in catalytic upgrading are considered to be different between carbohydrate- and lignin-derived model compounds. The level of HZSM-5 deactivation is closely associated with their ability to remove the number of oxygen atoms in feeding model compounds. Besides, the impact fact on the catalyst deactivation in the upgrading of lignin model compounds is discussed. Overall, the performance of commercial HZSM-5 in biomass upgrading is unsatisfactory and has limited relevance to the type of model compounds except for oxygen-free intermediates.

Supramolecular Cages Based on a Silver Complex as Adaptable Hosts for Poly-Aromatic Hydrocarbons.

In this work, an L-shaped silver complex, AgLClO4 (L = 2,3-bis[3-(pyridin-2-yl)-1H-pyrazol-1-yl·methyl]quinoxaline), M, is found to be adaptable enough to host a range of medium and large aromatic hydrocarbons including several polycyclic aromatic hydrocarbons (PAHs). The transformation of M from as-synthesized closed (nonporous) crystalline to at least three types of open phase structures in the presence of different aromatic hydrocarbons enables the adaptable binding of M to these aromatics. In essence, M can rearrange its cavities to fit the different sizes and shapes of the guest molecules in the manner that is infeasible with cage compounds or coordination networks. Single-crystal and powder X-ray diffraction confirm the adaptable structures of the resulting host-guest complexes, M·nG (G= guest, n= 0.5 or 0.75). Detailed 1D and 2D nuclear magnetic resonance spectra, along with the fluorescence spectroscopy, reveal that the host-guest complexes feature similar chemical compositions in the solution, but are in the states of rapid exchange in and outside the cages. Such an adaptability of M provides insights into the strength of host-guest interactions and enables a new class of adsorptive molecular materials that can bind a large number of aromatics, specifically PAHs.

Large Aromatic Hydrocarbon Radical Cation with Global Aromaticity and State-Associated Magnetic Activity

The stable radical cation of large aromatic hydrocarbons remains a challenge, due to the recessive aromatic character and high reactivity. Here we report the design, synthesis, and characterization...

Coriolis interaction of small and large aromatic hydrocarbons

Energy shifts by Coriolis interaction between the degenerate levels are discussed for aromatic hydrocarbons with D6h symmetry, benzene and coronene. The degenerate vibrations of e symmetry (the second-order irreducible representation) necessarily exist in a molecule with the n-fold symmetry axis (n⩾3), of which the rotational levels are expressed by the oblate symmetric-top model. The high-resolution spectrum was accurately analyzed by applying the theoretical model of Coriolis interaction, which significantly shifts the vibrational and rotational levels. The Coriolis interaction enhances intramolecular vibrational energy redistribution (IVR) at high vibrational levels in the electronic excited state. A rapid decrease in the fluorescence quantum yield at the vibrational levels above 3000 cm−1 in the S1 state of benzene (Channel 3) is shown to be mainly due to level mixing by Coriolis interaction.

Determination of heavy polycyclic aromatic hydrocarbons by non-aqueous reversed phase liquid chromatography: Application and limitation in refining streams

The heavy polycyclic aromatic hydrocarbons (HPAHs) cause detrimental effects to hydrocracker operations by deactivating the catalysts and depositing in the downstream of the reactor/ exchangers. Therefore, it is essential to continuously monitor the accumulation of HPAHs in a hydrocracker unit. To accurately measure the concentration of HPAHs, the development of a fast and reliable analytical method is inevitable. In this work, an analytical method based on non-aqueous reversed phase chromatography in combination with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was developed. As a first step, five different types of stationary phases were evaluated for the separation of HPAHs in non-aqueous mode and the best suited phase was further used for the fractionation of HPAHs in a fractionator bottom sample obtained from a refinery hydrocracker unit. The eight major fractions or peaks obtained from the separation were further characterized by UV spectroscopy and FT-ICR MS and the compounds in the fractions were tentatively confirmed as benzoperylene, coronene, methylcoronene, naphthenocoronene, benzocoronene, dibenzoperylene, naphthocoronene and ovalene. The developed liquid chromatography method can be easily adapted in a refinery laboratory for the quantitation of HPAHs in hydrocracking products. The method was further tested to check the interference of sulfur aromatics and/or large alkylated aromatic hydrocarbons on the determination of HPAHs in hydrocracking products.

ChemInform Abstract: One‐Pot Synthesis of Sterically Congested Large Aromatic Hydrocarbons via 1,4‐Diphenyl‐2,3‐triphenylyne.

AbstractThe preparation of 3 novel polycyclic aromatic hydrocarbons is carried out starting from triphenylene (III).

One-pot synthesis of sterically congested large aromatic hydrocarbons via 1,4-diphenyl-2,3-triphenylyne

Large polyarenes with unusually complex structures can be obtained in a straightforward manner from commercially available starting materials, by means of aryne chemistry. This approach involves a sequence of tandem reactions that can be performed in one pot to give sterically congested chiral aromatic hydrocarbons that adopt highly twisted conformations.

Suppression of Grain Boundaries in Graphene Growth on Superstructured Mn-Cu(111) Surface

As undesirable defects, grain boundaries (GBs) are widespread in epitaxial graphene using existing growth methods on metal substrates. Employing density functional theory calculations, we first identify that the misorientations of carbon islands nucleated on a Cu(111) surface lead to the formation of GBs as the islands coalesce. We then propose a two-step kinetic pathway to effectively suppress the formation of GBs. In the first step, large aromatic hydrocarbon molecules are deposited onto a sqrt[3]×sqrt[3] superstructured Cu-Mn alloyed surface to seed the initial carbon clusters of a single orientation; in the second step, the seeded islands are enlarged through normal chemical vapor deposition of methane to form a complete graphene sheet. The present approach promises to overcome a standing obstacle in large scale single-crystal graphene fabrication.

Facile air-oxidation of large aromatic hydrocarbon bay regions to bay region quinones: predicted oxygen-sensitivity of hydrogen-terminated carbon nanotubes

Dimesitylbisanthene (1) oxidizes to the corresponding bay region quinone (2) on standing in solutions exposed to air and ambient light. It is anticipated that hydrogen-terminated carbon nanotubes with bay regions on the rim are likely to exhibit even greater sensitivity toward air oxidation.

Near infrared optical materials from polymeric amorphous carbon synthesized by collisional plasma process

The synthesis of polymerlike amorphous carbon (a-C:H) thin-films by microwave excited collisional hydrocarbon plasma process is reported. Stable and highly aromatic a-C:H were obtained containing significant inclusions of poly(p-phenylene vinylene) (PPV). PPV confers universal optoelectronic properties to the synthesized material. That is a-C:H with tailor-made refractive index are capable of becoming absorption-free in visible (red)-near infrared wavelength range. Production of large aromatic hydrocarbon including phenyl clusters and/or particles is attributed to enhanced coagulation of elemental plasma species under collisional plasma conditions. Detailed structural and morphological changes that occur in a-C:H during the plasma synthesis are also described.

A thermal decomposition study of polymers by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

The thermal decomposition of polymers (poly(vinyl chloride) (PVC) and polystyrene (PS)) has been studied with synchrotron VUV photoionization mass spectrometry at low pressure. Pyrolysis products formed at different temperatures have been identified by the measurement of photoionization mass spectra at different photon energies. The experimental results demonstrate the variation of the pyrolysis product pool of PVC at different temperatures, dividing the thermal decomposition process into two stages: the low-temperature stage to form HCl and benzene, and the high-temperature stage to form numerous large aromatic hydrocarbons. For the thermal decomposition of PS, four reaction categories are determined. This work reports a new application of synchrotron VUV photoionization mass spectrometry in the study of the thermal decomposition of polymers, and demonstrates its good performance in product analysis, which is expected to help understand the thermal decomposition mechanism of PVC, PS and other synthesized polymers.

The role of surface vanadia species in butane dehydrogenation over VO x/Al 2O 3

A series of θ-Al 2O 3 supported VO x catalysts, of different vanadium loadings, have been characterised and employed for the selective dehydrogenation of n-butane. Characterisation of the unreacted catalysts has been carried out by solid-state NMR ( 51V MAS NMR, 27Al MAS NMR and 27Al 3Q-MAS NMR), and FT-IR spectroscopies, with reference to previously acquired Raman and UV–vis spectroscopy data. As vanadium loading increases, so does the domain size of the supported vanadate units with significant quantities of V 2O 5 observed at the highest loadings. The influence of calcination, pre-reduction, reaction and regeneration on the structure of the catalysts has been studied by NMR, FT-IR, EPR, microanalysis and TEOM. Calcination disperses crystalline vanadate units, and at high loadings AlVO 4 formation is observed. Pre-reduction reduces the vanadium oxidation state from 5+ to 3+, while regeneration results in the formation of highly crystalline V 5+ species. From these data it is possible to determine structure–activity relationships, with polymeric vanadia clusters favouring the formation of butenes and butadienes, while more isolated species are highly active towards the formation of polynuclear aromatic hydrocarbons retained on the catalyst surface post-reaction. These large polynuclear aromatic hydrocarbons are however not the principle cause of catalyst deactivation in this reaction.

Empirically corrected ab initio calculation of proton NMR chemical shifts of antiaromatic hydrocarbons

Rablen and co-workers have developed an ab-initio based protocol for calculating proton NMR chemical shifts drawn from a wide range of molecules (80 molecules, 161 shifts) with a standard deviation of 0.15 ppm. When the Rablen model was applied to the protons of a set of five relatively large aromatic hydrocarbons, the fit was excellent ( Φ=0.05 ppm), but when it was applied to the protons of a set of antiaromatic hydrocarbons, it failed badly (Φ=0.73 ppm). The failure is identified with the well known too-small HOMO–LUMO gap arising from the B3LYP procedure employed in the Rablen model and the intrinsically small HOMO–LUMO gaps of antiaromatic species. Five empirical fixes for the failure are developed. Each markedly improves the fit of the antiaromatic NMR proton shifts. The best of them, based on graph theory, gives a standard deviation of only 0.10 ppm for the 16 antiaromatic proton shifts, a standard deviation of 0.05 ppm for the 19 aromatic proton shifts, and a standard deviation of 0.14 ppm for the combined set of 196 proton shifts.

Colorimetric Signaling of Large Aromatic Hydrocarbons via the Enhancement of Aggregation Processes

[graph: see text] In this paper, the use of aggregation processes in squaraine derivatives as signaling protocols in the development of colorimetric probes for certain neutral guest (aromatic hydrocarbons) has been studied.

The optical and charge transport properties of discotic materials with large aromatic hydrocarbon cores.

The optical absorption and charge transport properties of a series of discotic molecules consisting of peripherally alkyl-substituted polycyclic aromatic cores have been investigated for core sizes, n, of 24, 42, 60, 78, 96, and 132 carbon atoms. In dilute solution, the wavelength maximum of the first absorption band increases linearly with n according to lambda(max) = 280 + 2n and the spectral features become increasingly broadened. The two smallest core compounds display a slight red-shift and increased spectral broadening in spin-coated films. For derivatives with n = 24, 42, 60, and 96, the one-dimensional, intracolumnar charge mobility, Sigma mu(1D), was determined using the pulse-radiolysis time-resolved microwave conductivity technique. For the compounds which were crystalline solids at room temperature, Sigma mu(1D) lay within the range 0.4-1.0 cm(2)/Vs. In the discotic mesophases at ca. 100 degrees C, Sigma mu(1D) was somewhat lower and varied from 0.08 to 0.38 cm(2)/Vs. The mobility values in both phases are considerably larger than the maximum values found previously for discotic triphenylene derivatives. However, the recently proposed trend toward increasing mobility with increasing core size is not substantiated by the results on the present series of increasingly large aromatic core compounds.

Estimation of C−C Bond Dissociation Enthalpies of Large Aromatic Hydrocarbon Compounds Using DFT Methods

Four density-functional methods (B3LYP, B3PW91, MPW1PW91, and B3P86) are employed to compute the C−C homolytic bond dissociation enthalpies (BDE) of a set of aromatic hydrocarbons related to coal structures with aliphatic linkages. In comparison with the available experimental data, the B3P86 method can provide reasonably reliable BDE values for these model compounds. The BDE values for large aromatic hydrocarbon systems of interest are computed, and the substituent effects are discussed.

A kinetic model for the formation of aromatic hydrocarbons in premixed laminar flames

A detailed chemical kinetic mechanism, including 340 elementary steps and 90 species, has been developed to simulate the formation of aromatic compounds in rich premixed flames of aliphatic hydrocarbons. The mechanism can reproduce the concentration profiles and net rates of benzene and larger aromatic hydrocarbons (two- and three-ring polycyclic aromatic hydrocarbons [PAHs]) in a wide range of temperatures for a slightly sooting, premixed ethylene-oxygen flames. Key sequences of reactions in the formation of aromatics are the combination of resonantly stabilized radicals, whereas the alternative mechanism that involves acetylene addition does not seem to be fast enough to explain the observed formation rates of aromatics in the flames examined. The main routes involved in the formation of the first aromatic ring are the propargyl self-combination and its addition to 1-methylallenyl radicals. Cyclopentadienyl radical combination, propargyl addition to benzyl radicals, and the sequential addition of propargyl radicals to aromatic rings are the controlling steps for the formation of larger aromatic species. The predicted concentration and formation rate of larger aromatics are higher than those of PAHs identified by gas chromatography but similar to those of total aromatic species collected in flames, namely, soot and tar-like material. This result suggests that tar-like material can be considered as the result of a fast reactive coagulation of two- and three-ring PAHs, which form structures with aromatic compounds, eventually connected by aliphatic bonding. Soot inception may be the result of an internal rearrangement of tar without significant contribution of light hydrocarbons, at least in the conditions examined. The model has been used to explore the effect of C/O ratio and temperature on the formation rate and concentration of aromatic hydrocarbons. The net formation rate of aromatics increases monotonically with C/O ratio, and at a fixed C/O ratio, it passes through a maximum as temperature is increased. A comparison with the “bell-shaped” concentration profile of soot collected in flames at different temperatures supports the hypothesis that the formation of two- and three-ring structures may be the rate-determining step in soot formation for slightly sooting regimes.

The effect of metal ions on the fluorescence of sewage wastewater

Fluorescence spectroscopy has the potential to be used in real-time monitoring of sewage strength for process control in sewage treatment works. However, unpredictable pollution incidents may contribute to a large variation in the metal ion content of sewage. These ions, particularly Cu2+ and Ni2+, have been found to quench the fluorescence of sewage by as much as 40% at a concentration of 0.2 mg/l. The quenching is not pronounced for the fluorescence of the final effluent from sewage plants. The results are explained in terms of possible chelating of the metal ions with the large aromatic hydrocarbons in humic or fulvic substances.