Two-ring Aromatics Research Articles

Bottom-up synthesis of pyridinic nitrogen-containing carbon materials with C–H groups next to pyridinic nitrogen from two-ring aromatics

Carbon materials containing pyridinic nitrogen are expected to be effective for electrodes and catalysts. However, it is challenging to selectively and simultaneously introduce both pyridinic nitrogen and C–H groups next to the pyridinic nitrogen at a high content, which has been reported to work as an active site for oxygen reduction reaction, in the absence of catalysts. In this work, among six relatively inexpensive precursors with pyridinic N and two-fused rings, 1,5-naphthyridine showed the highest percentage of pyridinic nitrogen (80%) and the highest pyridinic-nitrogen content (12.4 at%) after carbonization in an ampoule at 873 K. Unlike carbon materials prepared from precursors with three- or more-fused rings, C–H groups next to pyridinic nitrogen remained in carbonized 1,5-naphthyridine with two-fused rings. Carbonization mechanisms of precursors with two-fused rings were quite different from those of precursors with three- or more-fused rings because of the low thermal stability of the precursors with two-fused rings as results of energy calculation and ReaxFF. The highest percentage and content of pyridinic nitrogen were attained using 1,5-naphthyridine because 1,5-naphthyridine had the highest thermal stability of C–N bonds and the low probability to form tertiary nitrogen among precursors with two-fused rings.

Prenucleation chemistry of aromatics: A two-ring precursor?

Prenucleation reaction chemistry of polycyclic aromatic hydrocarbons was examined in detailed, site-specific kinetic Monte-Carlo simulations, tracking a single aromatic structure evolving from naphthalene in soot environments of two laminar premixed flames. The numerical results offer a possible reconciliation of a recent flame-based suggestion that one- or two-ring aromatics are the precursors to soot with the otherwise accumulating evidence that soot nucleation begins with mid-size aromatics. The resolution rests in the numerical observation of rapid destruction of the two-ring aromatic molecule, naphthalene, and its replacement with cyclopenta-added derivative structures. The analysis of the reaction events identified important contributions to aromatics evolution from methyl addition to edge five-membered rings. The computed curvature of the growing aromatics exhibited a similar dependence on the molecular size in two substantially different flame environments, thus raising a possibility of universality in aromatic-structure evolution.

Bottom-Up Synthesis of Pyridinic Nitrogen-Containing Carbon Materials with Reactive C-H from Two-Ring Aromatics

Bottom-Up Synthesis of Pyridinic Nitrogen-Containing Carbon Materials with Reactive C-H from Two-Ring Aromatics

Formation of Two-Ring Aromatics in Hexylbenzene Pyrolysis

The formation of two-ring aromatics in hexylbenzene pyrolysis is used in this work as a model system toward understanding the underlying chemistry of coke formation during crude oil upgrading processes. In this work, batch reactor experiments were performed at 55 bar and 450 °C to study the pyrolysis of hexylbenzene utilizing two dimensional gas chromatography mass spectrometry (GC×GC–qMS) as an analysis tool. This work finds many different classes of aromatic species with more than one ring, including bridged two-ring aromatics, nonfully aromatized fused two-ring aromatics, fully aromatized fused two-ring aromatics, and >2-ring species. A kinetic model detailed with elementary chemical reactions is constructed using the reaction mechanism generator, with thermodynamic and kinetic parameters calculated by the CBS-QB3 quantum chemistry method. The results of the generated model were compared to batch reactor experiments. For many compounds, the predicted selectivities agree with the data within a factor of 2. The formation pathways of previously less-understood species were clarified based on evidence of intermediates predicted by the model and measured in this work’s experiments. Despite these advances, there are larger model-versus-data discrepancies in the selectivities of some species, and also, the overall conversion rate is underestimated, indicating the need for future work to further improve thermochemical and kinetics data of alkylaromatics.

Hydrocarbons Extracted from Advanced Pyrolysis Bio-Oils: Characterization and Refining

Catalytic fast pyrolysis (CFP) and tail-gas reactive pyrolysis (TGRP) of biomass produce partially deoxygenated bio-oils (10–20 wt % O) which allow for subsequent separation into phenolic and hydrocarbon fractions. The hydrocarbon fraction, while low in oxygen (<2 wt %), still requires further upgrading to become a finished fuel blendstock. In particular, the hydrogen deficiency, molecular weight distribution, and benzene content require further treatment. Specific biomass feedstocks like guayule carry over significant amounts of sulfur (∼500 ppm) even after catalytic hydrodeoxygenation. Our strategy was to fractionate the hydrocarbon fraction using distillation and then upgrade each fraction according to its needed product changes, including desulfurization. For each hydrocarbon fraction, sulfur levels ranged from 80–700 ppm, increasing with respect to decreasing volatility. Light fractions contained primarily one-ring aromatics, with heavy fractions increasing to two-ring aromatics. The lightest fractio...

Study on the product distribution and thermal behavior of coal, extract and extracted residue over FeCl3

Catalytic depolymerization of lignite for improving tar yield has been proved feasible in our previous work. While the correlation between coal structure and catalyst was not clear owing to the heterogeneous nature and complicated compositions of coal, along with the multiple reactions during coal pyrolysis. In this study, two coals were extracted by tetrahydrofuran to afford residues and extracts. The thermal behavior and product distribution of coals, residues and extracts with/without FeCl3 were studied by Gray-King assay reactor and thermogravimetry coupled with mass spectrometry. The results showed that the catalyst not only affects the cleavage of chain aliphatic hydrocarbons at lower temperature, but also facilitates the cracking of oxygen-containing functional groups, leading to the variation of liquid products generation and gaseous products evolution. With the FeCl3 catalyst addition, tar yields of all samples (coals and residues) increased, meanwhile, the conversion of residues enlarged in comparison with that of corresponding raw coals. The composition of tars obtained from coals and residues with catalyst addition varied greatly, especially for phenols and two-ring aromatics. With the catalyst addition, the conversion of extracts increased, and the temperature at which the residual yield kept nearly unchanged was decreased. The extracts act as hydrogen donors to stabilize the radical fragments in the catalytic depolymerization of lignite.

Polycyclic aromatic hydrocarbons formation and growth during the supercritical pyrolysis of 1-octene

To better understand the roles of larger 1-alkenes in reactions leading to the production of polycyclic aromatic hydrocarbons (PAH) and solids in the supercritical pre-combustion environments of future-high-speed-aircraft fuels, supercritical pyrolysis experiments have been conducted with the model fuel 1-octene, a representative 1-alkene product of supercritical n-alkane-fuel pyrolysis. The 1-octene pyrolysis experiments are performed in an isothermal, silica-lined stainless-steel flow reactor at 94.6 atm, 133 s, and ten temperatures in the range 440–535 °C. Straight-chain aliphatics—particularly n-alkanes, 1-alkenes, and 2-alkenes—are the highest-yield products at all temperatures. At temperatures ≤500 °C, high yields of the C8 product 2-octene and the C16 product 6-hexadecene evidence 1-octene's facile formation of the resonance-stabilized alkylallylic radical 1-octen-3-yl, whose resonance structure 2-octen-1-yl not only abstracts H to produce 2-octene but also reacts with 1-octene to produce, with high selectivity, 6-hexadecene—establishing that, at low temperatures, a long-chain alkene with an interior CC double bond can result from alkylallyl-radical addition to a 1-alkene. Gas-chromatographic analyses of 1-octene's aromatic products show that one- and two-ring aromatics are produced at temperatures ≥ 475 °C. High-pressure-liquid-chromatographic analyses reveal the identities of 180 three- to nine-ring PAH products—178 of which have never before been identified as pyrolysis products of a large 1-alkene and all of which are produced from supercritical n-decane pyrolysis as well. As in the case for n-decane, the high levels of methyl-substituted PAH in the 1-octene products provide a ready source for resonance-stabilized arylmethyl radicals and (after reaction with ethylene) phenalenyl-type radicals. Reactions of these arylmethyl and phenalenyl-type radicals with C2C4 1-alkenes lead to the sequential PAH growth that accounts for 1-octene's production of PAH as large as nine rings at temperatures as low as 500 °C and the dramatic increases in the PAH-product yields as temperature approaches 535°C, 1-octene's temperature of incipient solids formation.

Catalytic depolymerization of a typical lignite for improving tar yield by Co and Zn catalyst

A novel process for improving tar yield through catalytic depolymerization of a typical lignite was put forward. The catalytic depolymerization of the lignite over CoCl2 and ZnCl2 catalyst in different concentrations were investigated by a Gray-King apparatus. The optimal catalyst concentrations of CoCl2 and ZnCl2 catalyst that could obtain the highest tar yield was achieved, by which the tar yield increased about 20.3% and 6.6% compared with that of the raw coal, respectively. Different with the traditional catalytic pyrolysis process for which the tar yield decreased, more tar was produced by the catalytic depolymerization method. The GC × GC-MS analysis showed that the components of alkanes and two-ring aromatics in tar increased dramatically with the addition of the optimal CoCl2 and ZnCl2 catalyst. The Raman measurement revealed that more large aromatic ring systems ( > 6 rings) were formed in the char from depolymerization with catalyst and the elemental analysis showed that the hydrogen content decreased slightly. The gas products analysis reflected the contents of methane showed an obvious decrease. All of this reflects that more fragments and small free radicals cracked were enhanced by catalysis in the catalytic depolymerization process, thereby leading to an enhancement of the tar formation possibilities.

A Semi-Empirical Formula of the Dependence of the Fluorescence Intensity of Naphthalene on Temperature and the Oxygen Concentration

Two-ring aromatics, such as naphthalene, are important fluorescent components of kerosene in the planar laser-induced fluorescent (PLIF) technique. Quantifying measurements of kerosene vapor concentrations by PLIF require a prior knowledge of the fluorescence intensity of naphthalene over a wide temperature and oxygen concentration range. To promote the application of PLIF, a semi-empirical formula based on the collision theory and experimental data at the laser wavelength of 266 nm and a pressure of 0.1 MPa is established to predict the fluorescence intensity of naphthalene at different temperatures and oxygen concentrations. This formula takes vibrational states, temperature, and oxygen quenching into account. Verified by published experimental data, the formula can predict the fluorescence intensity of naphthalene with an error less than 9%.

Low-pressure effective fluorescence lifetimes and photo-physical rate constants of one- and two-ring aromatics

One- and two-ring aromatics such as toluene and naphthalene are frequently used molecular tracer species in laser-induced fluorescence (LIF) imaging diagnostics. Quantifying LIF signal intensities requires knowledge of the photo-physical processes that determine the fluorescence quantum yield. Collision-induced and intramolecular energy transfer processes in the excited electronic state closely interact under practical conditions. They can be separated through experiments at variable low pressures. Effective fluorescence lifetimes of gaseous toluene, 1,2,4-trimethylbenzene, anisole, naphthalene, and 1-methylnaphthalene diluted in CO2 were measured after picosecond laser excitation at 266 nm and time-resolved detection of fluorescence intensities. Measurements in an optically accessible externally heated cell between 296 and 475 K and 0.010–1 bar showed that effective fluorescence lifetimes generally decrease with temperature, while the influence of the bath-gas pressure depends on the respective target species and temperature. The results provide non-radiative and fluorescence rate constants and experimentally validate the effect of photo-induced cooling.

The Effects of Temperature on the Yields of the Major Aliphatic and Aromatic Products of Supercritical n-Decane Pyrolysis

To investigate the effects of pyrolysis temperature on the production of polycyclic aromatic hydrocarbons (PAH), precursors to solids, in the precombustion environment of fuels for future high-speed aircraft, we have conducted supercritical pyrolysis experiments with the model fuel n-decane, an alkane component of jet fuels. The experiments are performed in an isothermal, isobaric, silica-lined stainless-steel flow reactor at 94.6 atm, 133 s, and at six temperatures in the range of 530–570 °C, over which n-decane conversion rises from 57% to 92%. The products from the experiments have been analyzed by gas chromatography with flame-ionization and mass-spectrometric detection as well as by high-pressure liquid chromatography with diode-array ultraviolet–visible absorption and mass-spectrometric detection, and the experimentally measured product yields are reported, as functions of pyrolysis temperature, for 20 major aliphatic products (mostly C1–C9 n-alkanes and C2–C9 1-alkenes), 27 one- and two-ring aromatics, and 117 PAH of three to nine aromatic rings. The yield-temperature data of 11 of the one- and two-ring aromatics and all 117 of the PAH products are each found to conform well to the first-order global-kinetic rate expression dY/dt = kapp(1 – X), where Y is the measured aromatic-product yield, X is n-decane conversion, and kapp is the global first-order rate constant, kapp = Aappexp[−Eapp/(RT)]. The derived values of Eapp generally increase with increasing aromatic product size from 68.26 kcal/mol for benzene, to 188.96 kcal/mol for the four-ring PAH pyrene, to 351.94 kcal/mol for the eight-ring PAH benzo[pqr]naphtho[8,1,2-bcd]perylene. In addition to all of the values of Eapp and Aapp determined for the individual product PAH, linear relationships for Eapp and ln Aapp as functions of carbon number have been determined, providing a means of modeling the production of PAH of a given carbon number in a generic way.

Oils and Phenols-and-Water-Free Tars Produced in Pyrolysis of 23 Chinese Coals in Consecutive Temperature Ranges

Coal pyrolysis has been widely studied, and the overall tar yield has been reported frequently in the literatures. It is recognized that the yield and composition of the tar vary with the coal rank and pyrolysis temperature, but detailed information is limited, especially for the oil fraction defined as the hexane-soluble matter. In this work, 23 Chinese coals of different rank with carbon content of 73.7–89.1% are pyrolized in a fixed-bed reactor, and the liquid products collected in the temperature ranges of 110–300, 300–400, 400–500, 500–600, and 600–800 °C are extracted by n-hexane. The yields of phenols-and-water-free tars and oils are estimated, and the oil fractions are analyzed by HPLC. It is found that the total yields of the phenols-and-water-free tar are generally greater than 10 wt % of the coals (dry and ash-free), and 30–60 wt % of the tars are soluble in n-hexane. Generally, about 50 wt % of the phenols-and-water-free tars and oils are produced in the temperature range of 400–500 °C. The HPLC analysis indicates that the oils from the coals with carbon contents of less than 80 wt % are dominated by aliphatic hydrocarbons, whereas those from the coals with carbon contents of greater than 80 wt % are dominated by one- and two-ring aromatics. Aliphatic hydrocarbons appear in all the oil fractions regardless of the pyrolysis temperature and coal rank, whereas the one-ring aromatics are found only in oils produced at 400–500 °C.

Effects of Acetylene Addition on Yields of the C1−C10Hydrocarbon Products of Catechol Pyrolysis

To better understand the role of C2 species in the formation of polycyclic aromatic hydrocarbons (PAH) from complex solid fuels, we have performed pyrolysis experiments with the model fuel catechol (ortho-dihydroxybenzene)—a phenol-type compound representative of structural entities in coal, wood, and biomass—in an isothermal laminar-flow reactor, with acetylene added as a dopant. The catechol pyrolysis experiments are conducted at a residence time of 0.3 s, at temperatures of 500−1000 °C, and at a fixed catechol-to-acetylene molar feed ratio of 0.785. The pyrolysis products are analyzed by high-pressure liquid chromatography with ultraviolet–visible absorbance detection and by gas chromatography with flame-ionization and mass spectrometric detection. Product quantification reveals that acetylene addition to the catechol pyrolysis environment does not change catechol conversion or the yields of most C1−C5 hydrocarbon products. Acetylene addition does, however, increase the yields of the C3 products and facilitate consumption of the C4 products. As for the one- and two-ring aromatics, acetylene addition brings about increases in the yields of benzene, toluene, phenylacetylene, and indene. Except for the highest temperature (1000 °C), however, the yields of naphthalene are unaffected by the addition of acetylene. The experimental results show consistency with acetylene addition to a benzyl radical being the dominant pathway for indene formation and with cyclopentadienyl radical self-addition being the dominant reaction pathway for naphthalene formation. Since the C1−C10 products are participants in reactions leading to PAH, the observed effects of acetylene addition are relevant to the mechanisms of PAH formation and growth.

The effects of oxygen on the yields of polycyclic aromatic hydrocarbons formed during the pyrolysis and fuel-rich oxidation of catechol

To better understand the effects of oxygen on the formation and destruction of polycyclic aromatic hydrocarbons (PAH) during the burning of complex solid fuels, we have performed pyrolysis and fuel-rich oxidation experiments in an isothermal laminar-flow reactor, using the model fuel catechol ( ortho-dihydroxybenzene), a phenol-type compound representative of structural entities in coal, wood, and biomass. The catechol pyrolysis experiments are conducted at a fixed residence time of 0.3 s, at nine temperatures spanning the range of 500–1000 °C, and under varying oxygen ratios ranging from 0 (pure pyrolysis) to 0.92 (near stoichiometric oxidation). The PAH products, ranging in size from two to nine fused aromatic rings, have been analyzed by gas chromatography with flame-ionization and mass spectrometric detection, and by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection. The quantified PAH products fall into six structural classes: benzenoid PAH, indene benzologues, fluoranthene benzologues, cyclopenta-fused PAH, ethynyl-substituted PAH, and methyl-substituted PAH. A comparison of product yields from pyrolysis and fuel-rich oxidation of catechol reveals that at temperatures <800 °C, where only two-ring PAH are produced in significant quantities, increases in oxygen concentration bring about increases in yields of the two-ring aromatics indene and naphthalene. At temperatures >800 °C, increases in oxygen concentration bring about dramatic decreases in the yields of all PAH products, due to oxidative destruction reactions. The smaller-ring-number PAH are produced in higher abundance under all conditions studied, and the oxygen-induced decreases in the yields of PAH are increasingly more pronounced as the PAH ring number is increased. These observations regarding PAH ring number, from the fuel-rich oxidation experiments with catechol, fully support our finding from catechol pyrolysis in the absence of oxygen: that PAH formation and growth occur by successive ring-buildup reactions involving the C 1–C 5 and single-ring aromatic products of catechol’s thermal decomposition. The yield/temperature data reported here represent one of the most extensive quantifications of the effects of oxygen on PAH produced during the pyrolysis of any fuel.

Improved sooting tendency measurements for aromatic hydrocarbons and their implications for naphthalene formation pathways

Sooting tendencies have been determined for aromatic hydrocarbons using a new definition: the maximum soot volume fraction f v , max measured in a coflow methane/air nonpremixed flame whose fuel is doped with 400 ppm of the test hydrocarbon. These f v , max were converted into apparatus-independent yield sooting indices (YSIs) by the equation YSI = C × f v , max + D , where C and D are apparatus-specific parameters chosen so that YSI-benzene = 30 and YSI-1,2-dihydronaphthalene = 100. The dopants were added to the fuel mixture with a syringe pump and f v , max was measured with laser-induced incandescence. YSI was determined for 6 cycloaliphatics and for 62 aromatics, which included 28 alkylbenzenes, 10 alkenylbenzenes, 10 alkynylbenzenes, 25 multiply substituted benzenes, 6 two-ring aromatics, and 6 substituted benzenes with heteroatoms in the side chains. The YSIs correlate well with literature values of threshold sooting index (TSI), which is a more traditional sooting tendency based on the height of pure-fuelled flames at the smoke point. This agreement indicates that f v , max and smoke height are equivalent measures of sooting tendency and that YSI is largely apparatus-independent. However, the YSIs have a total uncertainty of ± 3 % , which is substantially better than the TSIs, and the number of aromatic YSIs reported here is more than double the number of aromatic TSIs in the literature. The YSIs depend strongly on molecular structure; thus they provide information about the chemical kinetic reaction mechanisms responsible for fuel decomposition and hydrocarbon growth from a broad cross section of one-ring aromatics. Important naphthalene formation pathways appear to include acetylene addition to ethynylphenyl, propargyl addition to benzyl, and methyl addition to indenyl. This last pathway is particularly significant because it converts indene quantitatively to naphthalene and because the side chains in many alkenylbenzenes and alkynylbenzenes cyclize to form five-membered rings.

Hyper-coal process to produce the ash-free coal

Research and process development to produce the ash-free coal (Hyper-coal, HPC) has been carrying out since 1999. A new cost-effective process (Hyper-coal process) by the application of the solvent de-ashing technology can be adopted for the Hyper-coal process. Coal extraction rate achieved almost 70 wt.%daf (based on dry and ash-free coal) from some kinds of coals using two-ring aromatics as the recycle solvent. A gravity settling effectively removed insoluble residue from the solution. A flash separator recovered the solvent completely and produced Hyper-coal as a spherical fine particle, which containing several hundred PPM of ash. It was estimated that the calorie base cost of Hyper-coal would be competitive to a general coal price including its ash disposal cost in Japan.

UV-visible spectroscopy of organic carbon particulate sampled from ethylene/air flames

A systematic comparison of spectra obtained with extra and in situ diagnostics in the soot preinception region of rich, premixed ethylene air flames suggests that combustion generated organic carbon (OC) particulate can be extracted from flames and isolated from other flame material for further chemical analysis. Both the trend with height above the burner and the form of UV fluorescence and absorption spectra from extra situ sampled material captured in water agree with those measured in situ. These results show that the OC particulate formed in flames is partially water soluble. However, the collection efficiency can be increased using less polar solvents, like acetonitrile and dichloromethane. The fluorescence spectra from the water samples are comprised both a naphthalene-like component and a broad band UV fluorescence component similar to that observed in situ which is attributed to flame generated OC particulate. The broad band UV fluorescence centered around 320 nm is also observed very early in flames and does not change considerably with increasing flame residence time. These results support previous hypotheses that the UV broad band fluorescence is from carbonaceous material comprised two-ring aromatics, formed earlier than soot in the flame, and is still present along with soot at higher heights or flame residence times.

Solubilization of Naphthalene and Methyl-Substituted Naphthalenes from Crude Oil Using Biosurfactants

Glycolipids produced by Rhodococcus species H13-A and a representative synthetic surfactant Tween-80 (polyoxyethylene sorbitan monooleate) were used to demonstrate enhanced substrate “solubility” (aqueous-plus-micellar phase) in the presence of surfactants. Nascent concentrations of naphthalene and its methyl-substituted derivatives in crude oil were used as representative polycyclic aromatic hydrocarbons for the study. Both biosurfactant glycolipids from H13-A and Tween-80 lowered the surface tension of aqueous solutions from 72 to ∼30 dyn/cm. The two-ring aromatics showed a substantial increase in their apparent solubilities in the presence of surfactants; the increase being significantly greater for the biosurfactant as compared to the synthetic surfactant. The aqueous phase solubility enhancement was greater for the highly substituted derivatives as compared to the lesser substituted compounds. Higher toxicity levels, as seen by the lower EC50 values, of the surfactant mixtures indicated enhanced part...

Coal hydrogenation: Quality of start-up solvents and partially process-derived recycle solvents

The performance of three sets of start-up solvents and one set of partially process-derived recycle solvents was studied in small autoclave coal hydrogenation tests. The start-up solvents were obtained by catalytically hydrotreating anthracene oils or creosote oils. It is shown that this preparation procedure converts polynuclear aromatics and two-ring aromatics to hydroaromatics and, ultimately, to alicyclics. Coal conversions using start-up solvents are found to reach a maximum at intermediate degrees of solvent hydrogenation which is believed to correspond to a maximal abundance of hydroaromatic solvent hydrogen donors. A solvent hydrogen donor index (SHDI), simply derived from 1H n.m.r. spectral data, was devised and is found to successfully correlate coal conversions obtained using different start-up solvents, especially where N 2 gas rather than H 2 gas is employed in the autoclave tests. A set of partially process-derived recycle solvents were produced in multiple cycle continuous coal hydrogenation experiments. These were tested under relatively severe hydrogenation conditions in the presence of hydrogen gas, using the small autoclave unit. Substantial donation of solvent hydrogen was found to occur and coal conversions to hexane — and toluene-soluble products are found to be a smooth function of the solvent hydrogen donor index. It is concluded that the hydrogen donor capacity of a solvent is a major factor governing coal conversion, especially when the demand for solvent hydrogen is high. The SHDI parameter is useful in rationalizing the behaviour of start-up solvents. Also, at least in the first few cycles of a continuous two stage coal hydrogenation process, the SHDI parameter allows solvent quality to be monitored, and consequently optimized.

Suspended Load and Solubility Affect Sedimentation of Petroleum Hydrocarbons in Controlled Estuarine Ecosystems

The concentrations of No. 2 fuel oil and a suite of hydrocarbons with varying chemical properties (perhydrofluorene, pristane, biphenyl, 1-methylnaphthalene, 9-methylanthracene, and pyrene) were measured over time in the water column, on suspended particles, and in the sediments of two controlled microcosms receiving different amounts of mixing energy. The initial aqueous concentrations of the No. 2 fuel oil and other hydrocarbons were 330–500 μg/L and 0.80–10.8 μg/L, respectively. The levels of suspended particles were 3–5 mg/L in the control microcosm and up to 160 mg/L in the highly mixed system. The simulated storm made no major difference in the overall fate of the hydrocarbons. The concentration on particles collected in sediment traps was considerably lower in the tank with high suspended loads, and roughly equal amounts of hydrocarbons were eventually measured in the sediments of each microcosm. The percentage sedimented and residence time in the sediment varied with the lipophilicity and degradability of each hydrocarbon. Fifty percent or more of the least soluble hydrocarbons (aromatics with three or more rings, and saturates) were transported to the sediments. Most of the saturates were more persistent in the sediment than the two-ring aromatics. Aromatics of this class with additional substituent aliphatic groups showed increases in their degrees of sorption and sedimentary residence times in a regular manner. Three- and four-ringed aromatics were similar to the saturates in their sedimentary behavior. After 23 wk, the sediments contained a reduced but still significant fraction (~1/7) of the added petroleum hydrocarbons, enriched in branched and cyclic saturates and high molecular weight aromatics.