The formation of polycyclic aromatic hydrocarbons from the supercritical pyrolysis of 1-methylnaphthalene

In order to better understand the pyrolytic reactions leading to the formation of polycyclic aromatic hydrocarbons (PAH) and carbonaceous solids under supercritical conditions, we have pyrolyzed the model fuel 1-methylnaphthalene (critical temperature, 499 °C; critical pressure, 36 atm) in an isothermal silica-lined stainless-steel reactor coil at 585 °C, 110 atm, and 140 s. Analysis of the reaction products by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection and mass spectrometric detection has led to the identification of 37 individual 2- to 7-ring PAH—fifteen of which have never before been reported as products of 1-methylnaphthalene pyrolysis. The absence, among the reaction products, of single-ring aromatics and acetylene indicates that there is no aromatic ring rupture in this reaction environment, and the structures of each of the 5- to 7-ring PAH products reveal the intactness of the two 2-ring naphthalene units required in their construction. Proposed reaction pathways involving species plentiful in the reaction environment—1-naphthylmethyl radical, methyl radical, 1-methylnaphthalene, naphthalene, and 2-methylnaphthalene—account for the formation of the observed 5- to 7-ring PAH products. These reaction pathways, along with consideration of bond dissociation energies and relative abundances of reactant species, account for the extremely high product selectivity exhibited by the observed product PAH. The detection of seven 8- and 9-ring PAH, each requiring construction from three naphthalene or methylnaphthalene units, provides evidence that the types of reaction mechanisms outlined here—for the combination of two naphthalene entities to form 5- to 7-ring PAH—are also likely to apply to the combination of three and more such entities in the formation of larger-ring-number PAH and eventually carbonaceous solids.     

Polycyclic aromatic hydrocarbons from the co-pyrolysis of catechol and 1,3-butadiene

In order to better understand the reactions responsible for the formation and growth of polycyclic aromatic hydrocarbons (PAH) from solid fuels, we have performed pyrolysis experiments in an isothermal laminar-flow reactor (at temperatures of 600-1000 °C and a fixed residence time of 0.3 s) with catechol, a model fuel representative of the aromatic moieties in coal and biomass fuels; 1,3-butadiene, a major product of biomass pyrolysis; and with catechol and 1,3-butadiene together (in a catechol-to-1,3-butadiene molar ratio of 0.83). No PAH of ?3 rings are produced at temperatures <700 °C, but PAH production becomes significant at temperatures ?800 °C. Analysis of the higher-temperature reaction products by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection has led to the identification of over 100 PAH (ranging in size to 10 fused aromatic rings) - 47 of which have never before been reported as products of any phenol-type fuel. Quantification of the product yields shows that a much higher percentage of fed carbon is converted to PAH in the catechol-only pyrolysis experiments than in the 1,3-butadiene-only pyrolysis experiments - a result attributable to catechol’s relatively labile O-H bond and capacity for generating oxygen-containing radicals, which accelerate both fuel conversion and the pyrolysis reactions leading to 1- and 2-ring aromatics and PAH. When the two fuels are co-pyrolyzed, the percentage of the total fed carbon converting to PAH is more than two times higher than the amount calculated for the hypothetical case of the two fuels together behaving as a linear combination of the two fuels individually. This elevated production of PAH from the co-pyrolysis experiments reflects not only the reaction-accelerating role of the oxygen-containing radicals but also the efficacy, as growth agents, of the C₂ - and especially the C₄ - species abundantly present in the catechol/1,3-butadiene co-pyrolysis environment.     

Dissolved organic matter inhibition of sonochemical degradation of aqueous polycyclic aromatic hydrocarbons

Sonochemical degradation of aqueous polycyclic aromatic hydrocarbons (PAHs) was found to be rapid in the absence of other dissolved compounds (k = 0.006-0.015 s-1). In the presence of 20 mg Cl-1 fulvic acid, first-order PAH degradation rate constants decreased from 2.3- to 3.7-fold. Similar results were obtained with added benzoic acid, a crude analog for fulvic acid. In natural waters, PAH degradation was almost completely inhibited. Analysis of the kinetic behavior and reaction products indicates that PAHs are most likely degraded through a radical cation mechanism. Hydroxyl radical appeared to play an insignificant role in the degradation. Inhibited degradation was probably the result of either altered cavitation processes or isolation of the PAH away from cavitation sites.     

表面增强拉曼光谱技术在多环芳烃检测中的应用

多环芳烃(polycyclic aromatic hydrocarbons,PAHs)是一类致癌性很强的环境污染物.由于PAHs分子不含有能与金属配位或键合的官能团,因此很难利用SERS技术对其进行直接检测.本文综述了近年来表面增强拉曼散射(surface-enhanced Raman scattering,SERS)...     

Aqueous sonolytic decomposition of polycyclic aromatic hydrocarbons in the presence of additional dissolved species

Sonochemical degradation of aqueous polycyclic aromatic hydrocarbons (PAHs) results in a first-order loss of the PAHs (k=0.010–0.027 s⁻¹). When sonication occurred in the presence of other organic compounds, the degradation rate constant was reduced quite dramatically. This reduction is believed to come about through scavenging of radicals by the matrix chemical. When oxygen was bubbled into the PAH solution before sonication, the degradation rate constant was elevated. Nitrogen purging resulted in decreased rate constants. These results indicate that oxygen was an important precursor in the degradation of the PAHs. Organic compounds, including humic acid, benzoic acid, and sodium dodecyl sulfate, decreased PAH degradation rate constants by scavenging oxygen derived reactive transients.     

The influence of the aromatic character in the gas chromatography elution order: the case of polycyclic aromatic hydrocarbons

A link between the aromatic character of polycyclic aromatic hydrocarbons (PAHs) and gas chromatography (GC) elution order in columns with a polysiloxane backbone in the stationary phase is reported for the first time. The aromatic character was calculated using a method that combines the π-Sextet Rule and the Pauling Ring Bond Orders to allow the establishment of the location and migration of aromatic sextets in PAH structures. One GC column with a polysiloxane-like backbone (Rxi-PAH) and three GC columns with a polysiloxane backbone (DB-5, SE-52 and LC-50) were used for the analysis. According to the results of this study, within an isomer group, PAHs that contain a lower number of rings affected by the aromatic sextets tend to elute earlier than PAHs that contain a higher number of rings affected by the aromatic sextets. The PAHs that follow the calculated elution order are 88% in the Rxi-PAH column, 88% in the DB-5 column, 93% in the SE-52 column and 85% in the LC-50 column. It is expected that future analyses with other aromatic compounds in GC columns with a polysiloxane backbone in the stationary phase will follow a GC elution order that agrees with the aromatic character of the molecules.     

多环芳烃在超临界环己烷中的溶解：分子动力学模拟研究

重油中大量存在的多环芳烃会经过缩合反应会形成稠环芳烃,而溶解扩散的限制会导致稠环芳烃之间的聚合从形成残焦,使得对重油的利用率大大降低,所以多环芳烃热解过程的溶解扩散是重油改质的关键因素之一.因此,基于环己烷对烃类良好的溶解性,本文采用分子动力学模拟的方法研究了多环芳烃及其混合物在超临界环己烷中的溶解行为,结果表明在不同温度与密度下超临界环己烷对于具有NAP均具有良好的溶解性,而温度对于Bghip溶解的影响较小.在多环芳烃混合物的油滴溶解过程中,NAP优先溶解到环己烷相中,而Bghip则集中在粒径减小的油滴中.通过计算体系中多环芳烃的径向分配函数与溶剂化自由能发现环己烷与多环芳烃间之间能相互吸引,环己烷在多环芳烃分子周围形成的溶剂壳能抑制多环芳烃分子间的聚合.温度升高以及密度的将降低会导致多环芳烃的内聚能密度降低,增加了多环芳烃与超临界环己烷之间的相互作用.环己烷密度越小以及温度的升高可以促进多环芳烃或多环芳烃混合物在超临界环己烷中的溶解.     

Restricted geometry optimization for estimating stabilization energies of polycyclic aromatic hydrocarbons

At the B3LYP/6‐31G* level, our program of geometry optimization under the restrictions of π‐orbital interactions was applied to five homologous series such as acene‐, phenanthrene, triphenylene, chrysene, benzopyrene series, and seven additional molecules such as tri‐ and tetra‐benzanthracene, benzo‐ and naphtho‐pentaphene, dibenzopentacene and tribenzotetracene, providing each of the 35 polycyclic aromatic hydrocarbons (PAHs) with two types of localized reference geometries: (i) the ‘GL’ geometry where all double bonds are localized and (ii) m different ‘GE‐m’ geometries, where only a specific pair of double bonds are permitted to conjugate and all other bonds are localized.. Each GE‐m resulted from the local π interaction between a pair of double bonds in the GL geometry. The total sum of molecular energy differences, ([E(Ground) ? E(GL)] ? Σ[E(GE‐m) ? E(GL)]), is defined as the extra stabilization energy (ESE) for a PAH. The corrected ESE (CESE) then resulted from considering π interactions between pairs of nonbonded double bonds. In this work, the position, energy and GL sextet rules were developed to ensure that the GL geometry chosen from its candidates as well as the GE‐m geometries is no longer arbitrary. Therefore, it is the GL and GE‐m geometries of the PAH itself, rather than nonaromatic compounds, that serve as reference structures for calculating CESE. As a result, for each of the four homologous series (acene, phenanthrene, triphenylene, and benzopyrene), CESE/π can be fitted as a linear function of the p band frequency . For each of the four isomeric series with molecular formulas of C₁₈H₁₂, C₂₂H₁₄, C₂₆H₁₆, and C₃₀H₁₈, CESE/π can also be fitted as a second‐order polynomial function of the p band frequency as well as of the number of GL sextets. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of surface and solution properties of gemini-conventional surfactant mixtures and their effects on solubilization of polycyclic aromatic hydrocarbons

The aqueous solubility enhancement of the polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene and pyrene by micellar solutions of single gemini surfactant hexanediyl-1,6-bis(dimethylcetylammonium bromide) (G6) and its mixtures with cationic cetyltrimethylammonium bromide (CTAB), anionic sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and nonioinic polyoxyethylene (20) cetyl ether (Brij 58) have been investigated. Above the cmc, maximum solubilization occurs in the Brij 58 surfactant micelles whereas the solubilization is least in presence of AOT. The PAHs are solubilized synergistically in mixed gemini-conventional surfactant solutions, which is attributed to the formation of mixed micelles, their lower cmc values, and the increase of the solvents' molar solubilization ratios or micellar partition coefficients because of the lower polarity of the mixed micelles.     

Selective determination of acenaphthene in mixtures of three-ring polycyclic aromatic hydrocarbons by fluorescence quenching in micellar medium of cetylpyridinium bromide

The interaction of acenaphthene, anthracene, and phenanthrene with cetylpyridinium bromide (CPB) was studied. The CPB acts as a quencher provoking inhibition of fluorescence intensity emitted by these hydrocarbons. The existing differences in the fluorescence inhibition for these PAHs allow us to develop a selective synchronous spectrofluorimetric method for the determination of acenaphthene in a CPB micellar medium, with a detection limit of 9.2 and 10.4 ng ml^-1 for Δλ = 10 and 40 nm, respectively. The method was applied to the selective determination of acenaphthene in mixtures of typical three-ring hydrocarbons, including anthracene, phenanthrene, and fluorene.     

Characterization of polycyclic aromatic hydrocarbons using Raman and surface‐enhanced Raman spectroscopy

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous atmospheric pollutants and food contaminants, which exhibit potent carcinogenicity, mutagenicity, and teratogenicity. Vibrational spectroscopy techniques, especially Raman spectroscopy and surface‐enhanced Raman spectroscopy (SERS), can be potentially used as an alternative technique to liquid and gas chromatography in PAH analysis. However, there is limited information on the intrinsic Raman and SERS fingerprints of PAHs. In this study, we have acquired the Raman and SERS spectra of seven PAH compounds and compared their experimental spectra with theoretical Raman spectra calculated by density function theory (DFT). The vibrational modes corresponding to the Raman peaks have also been assigned using DFT. Characteristic Raman and SERS peaks have been identified for five PAH compounds, and the limits of detection were estimated. Such information could be useful for developing SERS assays for simple and rapid PAH identification. Copyright © 2014 John Wiley & Sons, Ltd.     

In Silico study of carcinogenic o‐Quinone metabolites derived from polycyclic aromatic hydrocarbons (PAHs)

A computational density functional theory study on the structural and electronic properties of several polycyclic aromatic hydrocarbon (PAH) ortho‐quinones was performed and the possible mechanism of DNA‐adduct formation was analyzed to evaluate its thermodynamic viability. Molecular docking techniques were applied to examine the noncovalent interactions developed when a model PAH ortho‐quinone intercalates between the DNA double helix. Quantum‐chemical ONIOM (our Own N‐layer Integrated molecular Orbital molecular Mechanics) calculations within the structure of a DNA fragment were carried out to evaluate the significant steps of noncovalent complex and covalent adduct formation. The solvent effect was also considered by employing a continuum solvation model. The present calculations suggest that initial noncovalent interactions of the PAH o‐quinone within the DNA double helix could determine the feasibility of benzo[a]pyrene‐7,8‐dione‐DNA covalent adduct formation, and that dispersion‐corrected functionals are more suitable for locating the noncovalent complex. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural and electronic properties of potassium-doped 1,2;8,9-dibenzopentacene superconductor: comparing with doped [7]phenacenes

Polycyclic aromatic hydrocarbons doped by metal have exhibited the potential of high temperature superconductivity. Understanding the basic properties of materials is the key to reveal the superconductivity. Here, a systemically theoretical study has been done to explore crystal structures and electronic properties of pristine and potassium-doped 1,2;8,9-dibenzopentacene, compared with [7]phenacenes case. We determined that vdW-DF2 functional is more suitable to describe the non-local interaction in a molecular crystal. Based on this functional, we predicted the crystal structures and investigated in detail the K atomic positions in a system. It was found that the intralayer doping leads to lower total energy. From the calculated formation energy, for each 1,2;8,9-dibenzopentacene molecule, the doping of two electrons is more stable under the relatively K-poor condition while the doping of four electrons is more stable under the K-rich condition. Between these two phases, the three-electron doping phase stabilises in a narrow region of K chemical potential. Combining with the electronic states at Fermi level, we analysed the reasons of superconductivity enhancement in doped 1,2;8,9-dibenzopentacene. This work further deepens the understanding of 1,2;8,9-dibenzopentacene superconductor.     

Oxidized metabolites from cyclopenta‐fused polycyclic aromatic hydrocarbons (CP‐PAHs). A DFT model study of their carbocations formed by epoxide ring opening

A density functional theory (DFT) study aimed at understanding structure–reactivity relationships in the oxidized metabolites of cyclopenta‐fused polycyclic aromatic hydrocarbons (CP‐PAHs) is reported. Epoxidation at various positions was examined in order to identify the most stable epoxide in each class of CP‐PAHs. Relative energies of the carbocations resulting from O‐protonation and epoxide ring opening were analyzed and compared, taking into account the available biological activity data on these compounds. Geometrical, electronic, and conformational issues were considered. Charge delocalization modes in the resulting carbocations were deduced via the natural population analysis (NPA)‐derived changes in charges. Computational results pointed to the importance of the unsaturated cyclopenta ring on the reactivity of these compounds. The reported bioactivity of this highly mutagenic/carcinogenic family of PAHs was observed to parallel their relative carbocation stabilities. A different behavior was observed in crowded non‐planar structures possessing a distorted aromatic system. A covalent adduct formed between a CP‐PAH epoxide and a purine base was computed inside a DNA fragment employing the ONIOM method. Copyright © 2010 John Wiley & Sons, Ltd.     

Trace analysis of polycyclic aromatic hydrocarbons using calixarene layered gold colloid film as substrates for surface‐enhanced Raman scattering

A surface‐enhanced Raman scattering (SERS) active substrate for the detection of polycyclic aromatic hydrocarbons (PAHs) was developed, which used 25, 27‐dimercaptoacetic acid‐26, 28‐dihydroxy‐4‐terbutyl calix[4]arene (DMCX) to functionalize a gold colloid film. This SERS‐active substrate prepared by self‐assembly method exhibits a high sensitivity, especially for the detection of PAHs. With the use of this SERS‐active substrate and with the application of the shifted excitation Raman difference spectroscopy (SERDS) technique, Raman signals of pyrene and anthracene in aqueous solutions at low concentration level (500 pM) can be obtained. Moreover, because PAHs are blocked from being directly adsorbed on gold colloid by DMCX and the photochemical reactions of adsorbates are avoided, the Raman bands of PAHs adsorbed on DMCX‐fuctionalized gold colloid film can be one‐to‐one correspondence with those of solid PAHs, and additionally, this SERS‐active substrate can be easily cleaned and reused. The obtained results demonstrate that the DMCX‐functionalized gold colloid films prepared by self‐assembly method have great potential to be developed to an in situ PAHs detection substrate. Copyright © 2012 John Wiley & Sons, Ltd.     

南极海洋芳香烃低温降解微生物的拉曼光谱分析

激光镊子拉曼光谱技术可以实现在自然状态下对单个细胞或细胞器较长时间的观察研究.应用激光镊子拉曼光谱技术实时观察南极微生物低温降解芳香烃过程中单个南极细菌的细胞生长和胞内生物大分子的动态变化过程,收集、分析其拉曼光谱,结果发现:单细胞的拉曼光谱反映了其细胞内部的生命物质组成,南极动球菌 NJ41 和希瓦氏菌 NJ49 生...     

Functionalisation of graphene by edge-halogenation and radical addition using polycyclic aromatic hydrocarbon models: edge electron density-binding energy relationship

Structures and properties of functionalised graphene were investigated using several derivatives of some small polycyclic aromatic hydrocarbons (PAHs) taken as finite size models employing unrestricted density functional theory. The functionalisation reactions included fluorination or chlorination of all the edge carbon sites, addition of H, F or Cl atom, OH or OOH group at the different sites and addition of OH or OOH group at the different sites of the edge-halogenated PAHs. σ-inductive effects of fluorine and chlorine in the edge-fluorinated and edge-chlorinated PAHs, respectively, were found to affect electron density and molecular electrostatic potential (MEP) distributions significantly. σ-holes were located at the MEP surfaces along the CH and CCl bonds of the unmodified and edge-chlorinated PAHs, respectively. The H and F atoms and the OH group were found to add to all the carbon sites of PAHs exothermically, while addition of the Cl atom and the OOH group was found to be exothermic at a few carbon sites and endothermic at the other carbon sites. Enhanced electron densities at the edge carbon sites of the PAHs and binding energies of adducts of H and F atoms and the OH group at these sites were found to be linearly correlated.     

Dimers and trimers of polycyclic aromatic hydrocarbons as models of graphene bilayers and trilayers: enhanced electron density at the edges

Structures of dimers and trimers of polycyclic aromatic hydrocarbons (PAHs) having zig-zag edges, and continuous electron density and molecular electrostatic potential (MEP) distributions in these systems were studied in gas phase. Dimers of benzene and naphthalene for which high-accuracy results are available were used to test the reliability of four different functionals of density functional theory in combination with the 6-31G(d,p) basis set. The dispersion-corrected WB97XD functional was found to be distinctly superior to the other three functionals used and was employed to study PAH dimers and trimers. Electronic structures and geometries of dimers of a four benzene ring and a nine benzene ring systems and trimers of the four benzene ring system were investigated. The dimers and trimers of PAHs were found to be of parallel-displaced type, as observed experimentally for graphene. The enhanced electron density edge effect found in the PAH monomers earlier is found to exist in the dimers and trimers also.     

Classical trajectory calculations for state-resolved Penning ionisation reactions of polycyclic aromatic hydrocarbon C10H8 in collision with He*(23S)

ABSTRACT

The reaction dynamics of Penning ionisation of a polycyclic aromatic hydrocarbon (PAH), naphthalene C₁₀H₈, in collision with the metastable He*(2³S) atom is studied by classical trajectory calculations using an approximate interaction potential energy surface between He* and the molecule, which is constructed based on ab initio calculations for the isovalent Li?+?C₁₀H₈ system. The ionisation width (rate) around the molecular surface are obtained from overlap integrals of the He 1s orbital and the molecular orbital. The calculated collision energy dependences of partial Penning ionisation cross sections (CEDPICS) in the range 50–500?meV at 300?K have reproduced the experimental results semi-quantitatively. The opacity functions, which represent the reaction probability with respect to the impact parameter b, are discussed in connection with collision energy, interaction with He* and the exterior electron density of molecular orbitals. They indicate that the collisional ionisations of C₁₀H₈ can be classified into three types: π electron ionisations with negative collision energy dependences which are predominantly determined by attractive interaction with He*; σ orbitals ionisations of the hardcore type; σ orbital ionisations which reflect interaction potentials around CH bonds. The critical impact parameters b_c become larger with increasing collision energy due to the centrifugal barrier.