Three-ring Aromatics Research Articles

Preparation and characterization of char supported Ni[sbnd]Cu nanoalloy catalyst for biomass tar cracking together with syngas-rich gas production

In order to realize the efficient biomass tar cracking into syngas-rich gases, several Aspen wood char (ASC) supported metal catalysts, including the Ni/ASC, Cu/ASC and bimetallic Ni-Cu/ASC catalysts, were synthesized with the method of one-step pyrolysis. The structure of the NiCu/ASC catalyst with NiCu nanoalloy encapsulated in carbon nanofibers (CNFs) was observed on the basis of the XRD, SEM and TEM analysis. The catalytic performances of the prepared catalysts on tar cracking were assessed in a two-stage fixed-bed pyrolysis-cracking/reforming device at the catalytic cracking temperatures of 600-800 °C. In a comparison to the single metal catalysts, the bimetallic Ni-Cu/ASC catalyst exerted a better performance on tar removal and possessed a higher selectivity to H2 and CO. The tar conversion efficiency and syngas (H2 + CO) yield, over the NiCu/ASC catalyst at 800 °C, reached up to 93.2% and 581.07 ml/g with the total volumetric content of 72.2% together with H2/CO of 1.1, respectively. The Ni-Cu/ASC catalyst resulted in the lowest contents of two-ring and three-ring aromatics accompanied with highest contents of one-ring aromatics in tar. The Ni-Cu/ASC catalyst was reasonably stable because of its good resistance to sintering and carbon deposition.

Spatially resolved measurements of soot and gaseous precursors in ethylene counterflow diffusion flames up to 32 atm

We investigate the effect of pressure on both flame structure and soot formation in nitrogen diluted counterflow diffusion flames of ethylene in the 8–32atm pressure range. Capillary-probe gas sampling is performed to resolve spatially the profiles of gaseous species up to three-ring aromatics by GC/MS analysis and multi-color pyrometry is used to quantify the soot volume fraction and dispersion exponent. Self-similarity of flames is preserved by keeping constant mixture fraction and strain rate, so that profiles of concentrations and temperature, normalized with respect to their peak values, are unaffected by changes in pressure, once the axial coordinate is nondimensionalized with respect to the pressure-dependent diffusion length scale. When conditions are chosen so that the overall soot loading is approximately constant and compatible with the diagnostics, it is found that both the soot volume fraction and the profiles of key aromatics in the high-temperature nucleation region are virtually invariant. For it to happen, a twofold increase in pressure must be compensated by a ∼100 K decrease in peak flame temperature and, therefore, in the temperature across the soot forming region. The implication is that from the perspective of the chemical kinetics of soot formation these two actions counterbalance each other. As pressure increases (and temperature decreases) the peak production rate of the high-temperature soot mechanism decreases and, further downstream, towards the particle stagnation plane, a low-temperature soot mechanism sets in, yielding an increase in soot H/C content. This mechanism is enhanced as the pressure is raised, causing a higher overall soot volume production rate in the 16atm flame and, especially, in the 32atm one. The role of C4/C2 species in the formation of C6H6 increases with increasing pressure and dominates over the recombination of propargyl radical at sufficiently high pressures. A comprehensive database is established for soot models at high pressures of relevance to applications.

Reaction behaviour of light and heavy components of bio-oil in methanol and in water

The main components in bio-oil behave differently during the thermal treatment in water or in methanol. Water cannot stabilize the aromatics in bio-oil. Consumption of the aromatics with mono-ring and two fused benzene rings and the formation of the aromatics with three or more fused benzene ring aromatics were observed during the thermal treatment in water. In methanol, the fluorescence intensities of the mono-ring, the aromatics with the two fused ring structures and three-ring aromatics increased. Methanol could stabilize the aromatics and retain them in the reaction medium. The conversion of mono-ring phenolics in thermal treatment of bio-oil in water and their formation in methanol was further confirmed with GC–MS measurement. In addition, it was found that the effects of acetic acid and formic acid on the conversion of the aromatics in bio-oil were negligible. This was probably due to the relative weak acidities of acetic acid and formic acid or the presence of the internal heavy carboxylic acids in bio-oil. However, the conversion of the aromatics in bio-oil was significantly promoted by the strong acids such as Amberlyst 70.

The relation between polyaromatic hydrocarbon concentration in sewage sludge and its uptake by plants: Phragmites communis, Polygonum persicaria and Bidens tripartita.

The aim of the study was to define the relationship between the concentration of PAHs in sewage sludge at a particular location and their amount in various plant materials growing on it. The credibility of the results is enhanced by the fact that sewage sludge from two separate sewage-treatment plants were selected for their influence on the content of PAHs in three plant species growing on them. The investigations were carried out for a period of three years. The results demonstrated unequivocally that the uptake of PAHs by a plant depended on polyaromatic hydrocarbon concentration in the sewage sludge. The correlation between accumulation coefficient of PAH in a plant and the content of the same PAH in the sewage sludge had for three-, four- and five-ring hydrocarbons an exponential character and for six-ring hydrocarbons was of a linear character. The accumulation coefficients calculated for three-ring aromatics were several times higher than for four-ring PAHs; further the coefficient values calculated for five-ring PAHs were several times lower than for four-ring hydrocarbons. Finally, the accumulation coefficient values of six-ring PAHs were the lowest in the series of studied polyaromatic hydrocarbons.

Modeling of two- and three-ring aromatics formation in the pyrolysis of toluene

A detailed chemical kinetic model for the pyrolysis of toluene and subsequent formation of polycyclic aromatic hydrocarbons (PAHs) was constructed for the low pressure (∼10Torr) experimental condition of Shukla et al. [J. Phys. Chem. A 11 (1) (2007) 8308–8324; J. Phys. Chem. A 112 (2008) 2362–2369]. The kinetic model for PAHs formation in premixed flames proposed by Richter et al. [Proc. Combust. Inst. 30 (2005) 1397–1405] was used as a starting-point model and was revised for a number of reactions. Computational and empirical estimates of the rate constants were performed for important reactions involving resonance stabilized hydrocarbon radicals. The resultant model consists of 289 species and 947 reactions. The numerical simulation with the proposed model satisfactory reproduced the formation of two- and three-ring aromatic hydrocarbons observed in the mass spectrometric experiments for the low-pressure flow-reactor pyrolysis of toluene and toluene/acetylene and toluene/benzene mixtures at temperatures 1136–1507K by Shukla et al. The sensitivity and flux analyses indicated the importance of the reactions of resonance stabilized radicals such as benzyl, fulvenallenyl and propargyl radicals for the PAHs formation processes.

Addition Effect of Model Compounds of Coal Extract on Coke Strength

Eight polyaromatic hydrocarbons that are model compounds of coal extract were added to coal blends to clarify the mechanism of the effects of coal extract (HyperCoal) on coke strength. Addition of large aromatic-ring compounds (coronene, perylene, naphtho[2,3-a]pyrene) greatly enhanced coke strength, whereas three-ring aromatics (anthracene, phenanthrene) had no significant effect on coke strength. Because large polyaromatic compounds have greater affinity for coal molecules, they co-fused with the coal particles. As a result, formation of large pores during coking was suppressed, leading to increased coke strength.

Examination of the Sooting Tendency of Three-Ring Aromatic Hydrocarbons and Their Saturated Counterparts

Hydrotreating of a 1:1 blend of coal-derived refined chemical oil (RCO), with petroleum-derived light cycle oil (LCO), has been identified as a strategy for the production of an advanced coal-based jet fuel, JP-900. The conversion of the jet fuel section of a conventional refinery for the production of coal-based JP-900 would impact the quantity and quality of the other refinery products, such as diesel. The physical and chemical properties of refinery streams may be perturbed by the introduction of coal components into the refinery, including the sooting tendency. A coal-derived diesel cut was chemically analyzed via gas chromatography−mass spectrometry (GC−MS). The results showed that two- and three-ring aromatics and their hydrogenated derivatives comprised the bulk of the cut. Phenanthrene and its hydrogenated derivatives were chosen as representative compounds of this cut. Existing sooting tendency correlations and soot formation indicators in the literature apply to some two-ring aromatic compounds, but little or no information is available about how to predict the sooting tendency of aromatics with three or more rings. The present study provides an analysis of the effects of three-ring aromatic hydrocarbons on soot formation and evaluated how their saturated counterparts contribute to the reduction of the sooting tendency. This research also generated a consistent set of data for smoke point and threshold sooting index (TSI), a parameter proposed for evaluating the onset of soot formation, for three-ring compounds, which have not been reported previously. It was found that the sooting tendency of aromatics is more accurately estimated by investigating their effect on hydrocarbon mixtures rather than as pure compounds. When adding aromatic compounds with the same number of carbon atoms to a reference mixture of 35% (v/v) toluene and 65% (v/v) n-heptane, the most saturated compounds showed the lowest sooting tendency. At small concentrations, three-ring saturated hydrocarbons in fuel blends did not improve the sooting tendency, in contrast to two-ring saturated compounds, which are good hydrogen donors and have low sooting tendency. Finally, the calculated TSI of the mixtures was used to estimate the TSI and smoke points of the individual three-ring compounds contained in the blend using mixing rules.

Modeling of particulate formation in combustion and pyrolysis

We use a detailed chemical kinetic mechanism to explore the effects of C/O ratio, temperature and pressure on the formation of high molecular weight aromatic species in premixed flames and shock tubes in a wide range of operating conditions. Key sequences of reactions in the formation of aromatics are the addition of acetylene to smaller aromatics, activated by H-atom abstraction and the combination of resonantly stabilized radicals, including cyclopentadienyl radical combination, propargyl addition to benzyl radicals and the sequential addition of propargyl radicals to aromatic rings. The modeling results are compared with those obtained by considering only the H-abstraction acetylene addition (HACA) route for aromatic formation to identify the controlling steps in different combustion regimes and to assess the viability of the HACA and resonantly stabilized radical (RSR) pathways to model aromatic growth. The full model is able to predict the concentration and formation rate of total organic carbon collected in slightly sooting rich flames at different temperatures and pressures. On the contrary, the HACA model predicts concentrations and formation rates more than one order of magnitude lower than those measured in experiments. This result indicates that a combination of resonantly stabilized radicals are the controlling steps in the formation of aromatics in flames. The oxidative environment is pivotal in the formation of aromatics to activate the pathways involving the resonantly stabilized radicals in the aromatic growth process. Since the model simulates only the formation of two- and three-ring aromatics, it can be hypothesized that total organic material collected in flames, i.e. a mass quantity much larger than the chromatographable polycyclic aromatic hydrocarbons, is the result of a fast reactive coagulation of small aromatics, forming structures of high molecular mass. Results indicate that reactions leading to the formation of two- and three-ring aromatics are rate-limiting, and combination reactions involving these aromatics control soot formation in oxidative or slightly sooting regimes. In very fuel-rich and pure pyrolysis conditions, the two models predict the same amount and formation rate of aromatics; this indicates that the HACA route controls formation in these conditions since the RSR pathways are activated only in oxidative environments.

Fabrication of a Portable Large-Volume Water Sampling System To Support Oil Spill Nrda Efforts

ABSTRACT A field-portable water-sampling system was designed and fabricated for collecting adequate volumes of seawater to meet the quantitation requirements to support Natural Resource Damage Assessment (NRDA) toxicity determinations and modeling efforts following an oil spill. This system is a significant improvement to conventional water sampling equipment and includes the ability to filter water samples at the time of collection, thereby providing critical differentiation between truly dissolved constituents and dispersed oil droplets. The system can be quickly and easily deployed from shoreline structures (piers and breakwaters) and/or vessels of opportunity to provide essential data during the early stages of a spill. Likewise, data collected with the system can be used to document dispersant effectiveness and provide information relating to seafood exposure, tainting, and toxicity issues. In many oil-spill NRDA efforts, water-column effects from dissolved components and dispersed oil droplets have not been adequately quantified or documented because: (1) samples are not obtained early enough after the spill event; (2) insufficient volumes are collected; and (3) the wrong constituents are analyzed. Generally, EPA hazardous-materials sampling approaches are followed, leading to inadequate sample sizes (e.g., 40 mL for volatile component analyses and 1-L samples for dissolved/dispersed constituents). Analytically, EPA semivolatile gas chromatography/mass spectrometry (GC/MS) SW-846 Method 8270 is often specified for polynuclear aromatic hydrocarbons (PAH). These sample sizes are not large enough to meet the detection limits required for most marine hydrocarbon analyses (de Lappe et al., 1980; Payne, 1997 and references therein), and the EPA PAH target analyte list does not include the majority of alkyl-substituted one-, two-, and three-ring aromatics that are the primary dissolved constituents actually present in the water column following an oil spill (Sauer and Boehm, 1991). As a result, water column effects are often written off as being short-lived or insignificant. Alternatively, impacts are often assessed by computer modeling efforts with limited field validation. In either event, there is inadequate profiling of the extent and duration of petroleum hydrocarbon exposure to marine organisms. Furthermore, when adequate volumes of water have been collected and the proper target analytes have been specified, provisions have not been taken to differentiate between truly dissolved components and dispersed oil droplets. Consequently, later data analyses are unreliable in their ability to reflect conditions as they actually existed during the early stages of the spill. For example, PAH analyses of unfiltered water samples are confounded by the facts that: (1) a significant, but unknown fraction of discrete oil droplets in the water column will rise to the surface with time; (2) high levels of dispersed oil droplets will raise detection limits of dissolved PAH; and (3) it is impossible to determine how much of the PAH is in the truly dissolved state where it will persist as a toxic fraction to exposed organisms and how much is simply associated with slightly less toxic oil droplets that are subject to relatively rapid removal by resurfacing. The equipment and field implementation approach described in this paper can provide samples that are not subject to the aforementioned problems.

Spatial, Vertical Distribution and Budget of Polycyclic Aromatic Hydrocarbons in the Western Mediterranean Seawater

Polycyclic aromatic hydrocarbons (PAHs) were determined in the suspended particulate matter (SPM) (21 surface and 6 vertical profiles) and in the dissolved phase (DP) (7 sampling sites) of the western Mediterranean seawater. Terrigenous inputs were recognized by the co-occurrence of perylene (SPM) and trimethyl-1,2,3,4-tetrahydrochrysenes (SPM and DP) collected at the major river plumes. The PAH patterns in the SPM (>0.7 μm) and DP (<0.7 μm) phases were dominated by the three-ring aromatics (i.e., phenanthrene, dibenzothiophene, and their alkylated derivatives), reflecting a predominant contribution of fossil hydrocarbon inputs. Only the DP collected at the continental shelf and slope (fluoranthene), presumably of pyrolytic origin, predominated. PAHs associated with SPM were evenly distributed in subsurficial waters, and their concentrations ranged from 200 to 750 pg L-1, respectively, maximizing at the Gibraltar and Sicilian Straits and at a frontal zone located midway between the Iberian Peninsula and the Balearic Islands. Vertical PAH profiles associated with the SPM exhibited a surface-enrichment depth-depletion distribution where the concentration maxima were located at the 20−30 m depth concurrently with fluorescence attributable to biomass uptake or adsorption to organic rich detritus. An enrichment in PAHs in the deeper samples of vertical profiles was found in stations collected near submarine canyons and at the sewage disposal zone attributable to advective transport of particles. Concurrently, a higher depletion of the three-ring aromatic PAHs in comparison with the four−five-ring aromatics according to depth was ubiquitously found. Budget of PAHs in the SPM and DP was estimated according to a three-box model to be 335 and 372 t, respectively, and their residence time in the continental shelf and in the open sea were 0.95 and 6.5 yr, respectively.

Selective synchronous spectrofluorimetric detection of acenaphthene in mixtures of three-ring aromatic compounds based on complexation with cyclomaltoheptaose (β-cyclodextrin) in the presence of iodide ion as quencher

Acenaphthene in a three-ring aromatic compound mixture can be selectively detected in a dimethyl sulfoxide–water (1 + 4) medium containing both cyclomaltoheptaose (β-cyclodextrin, β-CDx) and potassium iodide by synchronous fluorescence spectrometry. In this medium, synchronous fluorescence of acenaphthene was hardly quenched by iodide ion because of the inclusion complexation with β-CDx. According to Ksv values calculated from the simple Stern–Volmer plots, the fluorescence sensitivity to acenaphthene in the iodide-quenching state increased 364-fold in the presence of β-CDx, whereas those to other three-ring aromatics increased only 2–3-fold. Acenaphthene could be characterized by the double peaks at 322 and 328 nm in the synchronous fluorescence spectrum measured with Δλ= 7 nm. The method was applied directly to the selective detection of acenaphthene in mixtures of typical three-ring compounds, including dibenzofuran, fluorene, dibenzothiophene, carbazole, phenanthrene and anthracene, and in commercially available dibenzofuran.

Rapid group-type analysis of crude oils using high-performance liquid chromatography and gas chromatography

A simple, effective and rapid high-performance liquid chromatographic (HPLC) method was developed for the separation of crude oils into different group types. The method can be used to separate crude oils, kerosenes, gasolines, middle distillates, fuel oils, etc., into various classes of aliphatics (such as straight-chain, branched and cyclic), one-, two- and three-ring aromatics, polar compounds, resins and asphaltenes. A discussion of the experimental details and data from several samples is presented.

Biodegradation in South Texas Eocene oils — Effects on aromatics and biomarkers

The Eocene oil producing trend in South Texas provides an excellent area for studying sequential effects of biodegradation on crude oil composition. Many small fields contain oils of a common genetic type which exhibit a broad range of biodegration stages. Gas chromatograms of 26 oils from Eocene Jackson reservoirs in Duval County, Texas, show that n-paraffins are missing in 23 oils, while the other three appear to be undegraded. Among the degraded samples, a progressive increase in degradation is indicated by first a gradual disappearance of isoprenoids, then by disappearance of other prominent peaks in the C 13–C 17 range. Gas chromatography-mass spectrometry analyses were on nine oils, selected on the basis of their gas chromatograms to represent various biodegradation stages. Changes in distributions of geochemically important compound types, including the more common biomarkers, were related to extent of biodegradation. Significant observations include: (1) two- and three-ring aromatics, including benzo- and dibenzothiophenes show selectivity in degradation and disappear during adjacent degradation stages; (2) a series of adamantanes is unaffected; (3) steranes and aromatized steroid hydrocarbons remain undegraded; (4) tricyclic and tetracyclic terpanes are not degraded, but ammong pentacyclic triterpanes, a a slight decrease in C 29 and C 30 hopanes can be seen; and (5) bicyclic and diterpanes are degraded irregularly and less rapidly than aromatics. Aside from an early loss of straight-chain and branched-chain paraffins, biodegradation may follow quite different routes at different locations, particularly with regard to aromatics. Therefore, criteria for correlating biodegraded oils and assessing biodegradation stages on the basis of aromatic hydrocarbon distributions must be carefully selected.

Polycyclic aromatic hydrocarbons in rock oysters: a baseline study.

Coral-rock oysters were collected in September 1982 from six locations in the area of Mermaid Sound in North-Western Australia. Analysis was carried out by digestion of the samples, followed by solvent extraction and analysis of the extracts using HPLC-UVF and GC-MS. The levels of two- and three-ring aromatics ranged from very low for the site outside Mermaid Sound and for one site within the Sound, to low for the four other sites within the Sound. The PAH values at the latter four sites are attributed to occasional petroleum release episodes related to small boat activities and large-scale salt and iron ore shipping and general cargo activities of the Port of Dampier. The levels of PAHs with four or more rings were found to be low or very low at all sites; in fact, in most cases values measured for specific PAHs were below the limits of detection of even the very sensitive methods used in this study. Samples from sites within Mermaid Sound closest to the town and port of Dampier showed noticeably higher levels than those from outside; the present study does not allow the source of the PAHs to be determined. It is interesting to note, however, that the parent PAHs appear to form a greater proportion of the total PAH assemblage in these cases, indicating contributions from material which has been subjected to high temperature processing prior to release into the Sound.

Application of gas chromatography on glass capillary columns to the analysis of hydrocarbon pollutants from the Amoco Cadiz oil spill

About 230,000 tons oil spilled when the Amoco Cadiz sank in 1978 and heavily polluted the northern Brittany coasts. During a 9-month period, the composition of oil on beaches near the wreck site was studied by high-performance gas chromatography (HPGC). Simultaneously, levels of aliphatic and aromatic hydrocarbons in flat and Japanese oysters were measured. Quantification was effected by means of perdeuterated hydrocarbons which were totally resolved from the natural compounds by HPGC. Much attention has been paid to the input and fate of polyaromatic hydrocarbons in oysters. They were characterized as three-ring aromatics by gas chromatography-mass spectrometry and separation by normal-phase high-performance liquid chromatography on LiChrosorb-NH 2- Di- and trimethyldibenzothiophenes appeared to be the major persistent hydrocarbons in the environment.

Stratigraphic Distribution of Some Residual Organic Compounds in Upper Jurassic

Examination of some residual organic substances in Upper Jurassic rocks has shown several relationships between rock types and organic constituents. The organic carbon and nitrogen content as well as the residual amino acids and carbohydrates of these samples were discussed earlier (Palacas et al., 1960; Swain, 1961). The nearshore marine and non-marine Jurassic rocks have relatively more of the organic nitrogen represented by amino acids or amines, while the basinal and neritic samples have more of the organic nitrogen in the heterocyclic form or in humic complexes. Both the presumed saturated and aromatic hydrocarbon residues, extracted from littoral and neritic non-reservoir Jurassic rocks and separated chromatographically, are roughly equal in amount and are similar to modern occurrences. In basinal Jurassic rocks the aromatics tend to exceed the saturates, although exceptions occur. Several possible polycyclic aromatic hydrocarbons were detected in the basinal and some neritic, but less definitely in littoral samples. Residual asphaltenes in the Jurassic rocks are much less in amount than in Recent equivalents, probably because of post-depositional changes. Trace amounts of probably aromatic and heteroaromatic substances are widespread in the Jurassic samples studied. Among the substances possibly represented are: anthracene, naphthalene, pyridines, quinolinic acid, pyrazine, aniline, pyrimidine, purine, and several possible polycyclic aromatic hydrocarbons. Of these, anthracene and the pyridines occur most commonly, and also have been recognized in samples of other ages. The basinal marine Jurassic samples tend to have a predominance of one-ring residual aromatics, whereas the neritic and littoral samples seem to have relatively more two- and three-ring aromatics and porphyrins. No relation was found between the larger fossil remains and organic residues in the samples studied; the nannofossils may contribute to the organic residues but no quantitative relationship was found. Conclusions by others that air and surface water temperatures were higher in central North America during the Jurassic than at present are supported by the present study. Such contributing factors as organic productivity, preservation of organic residues, redox potentials, mineralogy, and color of sediments are discussed in relation to the residual organic matter.