Alkylaromatic Hydrocarbons Research Articles

Polarizability and Spin Density Correlate with the Relative Anaerobic Biodegradability of Alkylaromatic Hydrocarbons

Polarizability ((alpha) and spin density (SD) of benzyl radical intermediates calculated using Gaussian O3 were correlated with the extent of anaerobic biodegradation for 17 C1 to C4 parent alkylbenzenes. The percent anaerobic biodegradation of the hydrocarbon series was determined in a previous study using an inoculum from a gas condensate-contaminated aquifer incubated under sulfate-reducing conditions. Many of the parent compounds are known to be biodegraded in the absence of oxygen by fumarate addition reactions. Percent biodegradation over a 100 day incubation (predicted) = -1.044 <alpha> + 908.271SD - 586.197 (R2 = 0.839; all p-values < or = 0.058). This correlation suggests that compounds forming more stable alkylbenzyl radical intermediates biodegrade by fumarate addition more slowly than their counterparts forming less stable radicals. More highly substituted molecules including isopropylbenzene, 1-ethyl-2,6-dimethylbenzene and 1-ethyl-3,4-dimethylbenzene did not fit the model. The assumption of biodegradation by fumarate addition reaction was independently verified with several substrates. These findings help form a basis for predicting the relative rate of alkylbenzene metabolism in anaerobic environments.

Comparative catalytic studies on alkylaromatics transformations over [Al]MCM-22 and boron-substituted [Al, B]MCM-22

The catalytic performance of [Al]MCM-22 and boron-containing [Al, B]MCM-22 was compared in the conversion of four alkyl aromatic hydrocarbons in view of the impact of their cage/channel pore structure. The contribution of the pore geometry to the observed molecular-sieve effects is discussed on the basis of the XRD, thermal analysis (TGA) of template and coke removal, N 2 adsorption, 11B-MAS NMR and the catalytic test reactions. It was found that the reaction products distribution is thermodynamically or selectively controlled, depending on the type of the pores to which the different feed molecules and reaction intermediates have an access, and on the presence or absence of boron in the framework. The geometric constraints caused by the introduction of framework boron and the framework Al- and B-atoms positioning regulate the product selectivity in these transformations.

Effect of surfactants on liquid-phase oxidation of hydrocarbons and lipids

A review is presented compiling new data on liquid-phase oxidation of hydrocarbons and plant oils in microheterogeneous environment formed by the addition of surfactants. Cationic surfactants catalyze the decomposition of the primary oxidation products, hydroperoxides, into free radicals thus accelerating the oxidation process. Anionic surfactants catalyze the heterolystic decomposition of hydroperoxides and therefore are excellent antioxidants for ethylbenzene, cumene, and other alkylaromatic hydrocarbons.

New developments in catalysts at AZKiOS Co. and their introduction in production

Data on new developments in catalysts at AZKiOS Co. for the petroleum, oil refining, and nitrogen industry are generalized. The results of using the catalysts in processes are briefly analyzed: hydrotreating of diesel fuel and gasolines, hydrodealkylation of alkylaromatic hydrocarbons, treatment of hydrocarbon gases, steam reforming of hydrocarbon gases, and steam conversion of carbon monoxide.

Supramolecular catalytic systems in biomimetic oxidation

Oxidation of alkylaromatic hydrocarbons and benzene with hydrogen peroxide was studied under homogeneous and heterophase conditions. The catalytic systems contained the transition metal complex and salt along with the phase-transfer catalysts of different nature (micelle-forming surfactants, compounds containing a substrate in the polymer globule, macromolecules capable of forming host—guest complexes) and cosolvents. This substantially enhanced the yield of the oxidation product and selectivity of the process compared to the classical systems of hydrocarbon oxidation with hydrogen peroxide.

Selective catalytic oxidation of alkylaromatic molecules by nanosize water droplets containing Co2+ species in supercritical carbon dioxide fluid

Stabilized nano-sized water droplet carrying water-soluble Co2+ species is employed as a new catalyst system for the oxidation of the alkyl aromatics in the presence of a fluorinated surfactant. This stable system contains no labile C--H structure and can facilitate excellent mixing of catalytic Co(II)/NaBr species, hydrocarbon substrates and oxygen in supercritical carbon dioxide fluid, which is demonstrated to be an excellent alternative solvent system to acetic acid or nitric acid for air oxidation of a number of alkyl aromatic hydrocarbons using Co(II) species at mild conditions. As a result, potential advantages of this ‘greener’ catalytic method including safer operation, easier separation and purification, higher catalytic activity with selectivity and without using corrosive or oxidation unstable solvent are therefore envisaged.

In situ1H MAS NMR investigations of the H/D exchange of alkylaromatic hydrocarbons on zeolites H-Y, La,Na-Y, and H-ZSM-5

In situ 1H MAS NMR spectroscopy was used to investigate the H/D exchange behavior of benzene- d 6, ethylbenzene- d 10, toluene- d 8, and p-xylene- d 10 with Brønsted acid sites in different zeolite catalysts. In the temperature range of 303 to 393 K, the H/D exchange takes place exclusively between zeolitic bridging OH groups and deuterons bound to the aromatic rings of adsorbed compounds. The activation energies E a of the H/D exchange of same deuterated aromatics adsorbed on different zeolites have the sequence: H-Y ⩾ La,Na-Y > H-ZSM-5. The decrease of the E a values correlates well with the increase of the strength of Brønsted acid sites determined via the low-field shift of the 1H MAS NMR signal of bridging OH groups upon adsorption of deuterated acetonitrile (CD 3CN). The E a values determined for the different deuterated aromatic hydrocarbons adsorbed on the zeolites under study show the sequence: benzene ( E a = 46–76 kJ/mol) > ethylbenzene ( E a = 29–41 kJ/mol) > toluene ( E a = 25–32 kJ/mol) > p-xylene ( E a = 20–27 kJ/mol). Generally, this sequence demonstrates the electron donation effect of alkyl groups bound to the aromatic rings (+I effect). The larger E a value of ethylbenzene in comparison with that of toluene indicates an interaction of ethylbenzene with the zeolite framework via its ethyl group leading to a lower electron density and a decrease of the +I effect of this alkyl group towards the aromatic ring.

A New Oxidation Catalyst System using Fluorous Cobalt(II) Species in Water-supercritical Carbon dioxide (C–H free environment)

Stabilized water droplet dispersed in supercritical carbon dioxide fluid is demonstrated to be an excellent alternative solvent system to acetic acid for air oxidation of a number of alkyl aromatic hydrocarbons using Co(II) species at mild conditions.

Effects and impact of early-stage anaerobic biodegradation on Kuparuk River Field, Alaska

Abstract Anaerobic processes have only recently been recognized as an important mechanism in the biodegradation of crude oils. They are normally invoked to explain extensively biodegraded oils with little or no possibility of contact by oxygenated waters from an active aquifer. This work with Kuparuk Field indicates that early stages of anaerobic biodegradation can be subtle and easily missed, yet have economic impact. Kuparuk River Field, North Slope of Alaska, comprises two reservoir intervals: vertically stratified and imbricated lower shoreface sandstones (A sands), and overlying shallow marine sandstones with complex permeability structure (C sands). The vertical and lateral distribution of viscous oil (less than 20° API) shows a strong relationship to structure and faulting in the Kuparuk Field. Multiple mechanisms for the origin of tars and viscous oils can be proposed, including early aerobic biodegradation, anaerobic biodegradation, inorganic oxidation and gas deasphalting. This geochemical study, integrated with stratigraphic, structural and production data, was undertaken to help understand the origin and distribution of tar and viscous oil in the field. Obvious depletion of n -alkanes and other paraffins, classically regarded as indicative of early biodegradation, is not observed in examined samples. However, Kuparuk viscous oils show slight to extreme selective depletion in long-chain alkyl aromatic (LCAA) hydrocarbon families (e.g. alkylbenzenes and alkyltoluenes). This is interpreted as indicative of an early stage of anaerobic microbial degradation that likely destabilized the oil to promote subsequent precipitation of asphaltenes as tar. Depletions in LCAAs in core samples in the field are linked to decreased hydrocarbon/nonhydrocarbon ratio and to an increase in the high molecular weight (&gt;C 50+ ) components of Rock-Eval 6 pyrolysates. Using a calibration curve constructed from oil Rock-Eval 6 pyrolysis, the API gravity of core oil plus bitumen can be estimated. Tar-plugged formations with depleted LCAAs have estimated API gravities &lt;8°. Portions of the Kuparuk reservoir with higher iron content tend to show greater depletions in LCAA. Anaerobic biodegradation is likely mediated by dissimilatory iron-reducing bacteria. Biodegradation likely destabilizes the oil with respect to asphaltene precipitation such that later arrival of petroleum leads to tar in the reservoir. Increased tar and depleted LCAAS correspond to intervals with lower productivity indices, thus indicating a significant impact on petroleum producibility.

Fingerprinting of Gasoline and Coal Tar NAPL Volatile Hydrocarbons Dissolved in Groundwater

Accidental spills and chronic leaks of fuel oil or other hydrocarbon material (e.g., coal tar) often result in subsurface accumulation of nonaqueous phase liquid (NAPL), which can be a subsequent source of contamination in groundwater. Linking hydrocarbons in groundwater to a source NAPL has been difficult when using standard target analytes (e.g., BTEX) because of differences in partitioning properties of the analytes between the source NAPL and groundwater. Because aqueous solubility is predicted to be the controlling influence in the partitioning of hydrocarbons from NAPL to groundwater, a solubility-based approach to matching dissolved hydrocarbons in groundwater to their source NAPL has been developed and validated for two sites with commonly encountered types of NAPL contamination. Specifically, a gasoline LNAPL and a coal tar DNAPL from two separate sites (West Virginia and California) and groundwater interfaced with these NAPLs were analyzed for approximately 50 gasoline-range hydrocarbons consisting of paraffin, isoparaffin, (mono-) aromatic, naphthene, and olefin compounds (PIANO). Solubility characteristics of selected alkyl aromatic hydrocarbons from the PIANO analysis were used to identify a set of diagnostic hydrocarbons, expressed as hydrocarbon ratios, which were found to be useful in distinguishing the source(s) of hydrocarbons in groundwater. At the West Virginia site, the diagnostic ratios in a downgradient groundwater sample were similar to those of a gasoline NAPL at that site, indicating the source of hydrocarbons to the groundwater was the upgradient gasoline NAPL. The diagnostic ratios of the groundwater in contact with the gasoline NAPL and the remote groundwater were also similar, providing evidence that the diagnostic ratios were retained during transport in the aquifer. At the California site, diagnostic ratios in a cross-gradient groundwater sample differed from those of the coal tar NAPL at that site, indicating that the remote groundwater hydrocarbons did not originate from the coal tar contamination. Environmental factors such as selective degradation of specific isomers and various geological conditions (e.g., soil mineralogy, and organic content) may confound the application of this solubility-based fingerprinting approach. Thus, it is recommended that multiple diagnostic pairs be simultaneously evaluated when considering this fingerprinting approach for specific sites and product types.

The Effect of 1- and 2-(1-Hydroperoxy-1-methylethyl)naphthalenes on the Liquid-Phase Oxidation of Alkylaromatic Hydrocarbons

The properties of 1- and 2-(1-hydroperoxy-1-methylethyl)naphthalenes as initiators were studied in the liquid-phase free-radical oxidation of hydrocarbons with oxygen. 2-(1-Hydroperoxy-1-methylethyl)naphthalene was found to initiate the reaction, whereas unexpectedly, 1-(1-hydroperoxy-1-methylethyl)naphthalene was found to inhibit the reaction. The products of decomposition of the studied hydroperoxides were found to exhibit essential differences. Thermal decomposition of 1-(1-hydroperoxy-1-methylethyl)naphthalene was found to yield hydroxyaromatic compounds active as oxidation inhibitors. This fact explains the oft-reported lack of reaction in long-term oxidation of 1-isopropylnaphthalene and its disfavourable effect on the oxidation of 2-isopropylnaphthalene.

Detection of anaerobic metabolites of saturated and aromatic hydrocarbons in petroleum-contaminated aquifers.

Recent investigations have demonstrated that several classes of petroleum hydrocarbons are susceptible to anaerobic decay, including alkanes and mono- and polycyclic aromatic compounds. In previous work, benzylsuccinates were shown to be useful indicators of in situ anaerobic alkylbenzene metabolism. In the present study, we sought to determine whether metabolites of alkanes and naphthalenes could similarly be used as indicators of the intrinsic decomposition of these compounds in petroleum-contaminated aquifers. Such metabolites include succinate derivatives of n-alkanes, cyclic alkanes, and alkylaromatic hydrocarbons as well as naphthoic acids. Using gas chromatography-mass spectrometry (GC-MS), we analyzed trimethylsilyl-derivatized organic extracts from six hydrocarbon-contaminated groundwaters for MS fragment ions indicative of such anaerobic metabolites. Geochemical indicators in these aquifers suggested the prevalence of anaerobic processes. In the groundwaters of the contaminated sites, we found compounds whose MS profiles suggested that they were indeed alkylsuccinic acids, ranging from C3 to C11 succinates. Propyl-, hexyl-, octyl-, and decylsuccinic acids were positively identified in the groundwaters by GC-MS matches with chemical or biologically produced standards. In two of the aquifers, we also detected components whose MS profiles matched with authentic standards of naphthoic acids and tetrahydronaphthoic acids. Metabolites were detected in nanomolar concentrations. The finding of these putative anaerobic metabolites of alkanes and naphthalenes signifies the in situ biodegradation of these hydrocarbons and attests to their value as indicators of intrinsic bioremediation.

High molecular weight organic matter in martian meteorites

We have performed an investigation to detect high molecular weight organic matter in martian meteorites. Solvent-extracted samples of two Antarctic finds (ALH 84001, sub-sample 106 and EET A79001, sub-sample 351) and one non-Antarctic fall (Nakhla) were analysed by flash pyrolysis–gas chromatography–mass spectrometry. Results suggest that our sub-sample of ALH 84001 contains no pyrolysable organic matter. In contrast, our samples of EET A79001 and Nakhla contain organic matter of high molecular weight, which releases aromatic and alkylaromatic hydrocarbons, phenol and benzonitrile as major compounds upon pyrolysis. The detection of similar pyrolysis products from Nakhla and EET A79001 indicates that these martian meteorites may have a common high molecular weight organic phase. Carbon isotopic measurements of individual molecules in the Nakhla pyrolysate, by flash pyrolysis–gas chromatography–isotope ratio mass spectrometry, reveal that this high molecular weight organic matter has some similarities to that found in carbonaceous chondrites. At this point, an origin by terrestrial contamination cannot be unequivocally ruled out, but the data seem to support proposals that martian samples contain organic matter originating from meteoritic infall on Mars. The results suggest that a wider, pyrolysis-based study of martian meteorites would be a justifiable use of these precious samples.

Thermal reactions of aromatic hydrocarbons in the pyrolysis of ethane and propane

The influence of aromatics on the pyrolysis of ethane and propane was studied using benzene, toluene, α-methylnaphthalene and anthracene as model compounds. The experiments were performed in a tubular flow reactor at ordinary pressure, temperatures of 700-850°C, residence times between 0.1-1s and low concentration of aromatics (1-6%mole). Aromatic hydrocarbons inhibited the pyrolysis rate of ethane and propane and the following order of inhibitory effect - which decreases with the increase of temperature - was found: toluene > α-methylnaphthalene > benzene > anthracene. The C1-C4 composition of the effluent was only slightly influenced by the presence of aromatics, which were found to suffer an appreciable transformation to alkylated derivatives, depending on their structure and despite their thermal stability when highly diluted with N2 at the same temperatures. The transformation of the aromatic hydrocarbons was explained by the interference of the main chain propagators (·H, ·CH3, ·C2H3, ·C2H5) with the aromatic and benzyl type radicals. Benzene has only a small contribution to soot formation, a phenomenon which however was found to increase when alkylaromatic and polycyclic hydrocarbons are present in the feed.

Chain and monomolecular decomposition of hexogen in solutions

The decomposition of hexogen dissolved in alkylaromatic hydrocarbons, alcohols, ketones, ethers, chloroform, and some other solvents occurs via the chain mechanism. This mechanism is supported by slowing down of the reaction when inhibitors are added, the solvent deuterium kinetic isotope effect, and the dependence of the rate on the reactivity of the C—H bond in solvents. The chain reaction propagates through the transfer of a free valence from the primary N-radicals formed by N—NO2 bond dissociation to the C-centered radicals of the solvent. The solvents are inert when the N—H bond dissociation energy is >380 or <200 kJ mol–1, and hexogen decomposition in such solvents is monomolecular.

Effects of white spirits on rat brain 5-HT receptor functions and synaptic remodeling

Previously, inhalation exposure to different types of white spirit (i.e. complex mixtures of aliphatic, aromatic, alkyl aromatic, and naphthenic hydrocarbons) has been shown to induce neurochemical effects in rat brains. Especially, the serotonergic system was involved at the global, regional, and subcellular levels. This study investigates the effects of two types of white spirit on 5-hydroxytryptamine (5-HT) transporters (5-HTT), 5-HT 2A and 5-HT 4 receptor expression in forebrain, and on neural cell adhesion molecule (NCAM) and 25-kDa synaptosomal associated protein (SNAP-25) concentrations when applied as indices for synaptic remodeling in forebrain, hippocampus, and entorhinal cortex. Male Wistar rats were exposed to 0, 400, or 800 ppm of aromatic (20 vol.% aromatic hydrocarbons) or dearomatized white spirit (catalytically hydrogenated white spirit) in the inhaled air for 6 h/day, 7 days/week for 3 weeks. The 5-HTT B max and K d were not affected. Both types of white spirit at 800 ppm decreased B max for the 5-HT 2A receptor. The aromatic type decreased the K d of the 5-HT 2A and 5-HT 4 receptors at 800 ppm. Aromatic white spirit did not affect NCAM or SNAP-25 concentrations or NCAM/SNAP-25 ratio in forebrain, whereas NCAM increased in hippocampus and the NCAM/SNAP-25 ratio decreased in entorhinal cortex. Dearomatized white spirit did not affect NCAM, SNAP-25, or NCAM/SNAP-25 ratio in any brain region. The affected 5-HT receptor expression and synaptic plasticity marker proteins indicate that inhalation exposure to high concentrations of white spirit may be neurotoxic to rats, especially the aromatic white spirit type.

Alkylation of Alkyl Aromatic Hydrocarbons over Metal Oxide–Alkali Metal Superbasic Catalysts

The alkylation of toluene, ethylbenzene, cumene, and xylenes with ethene, propene, and 1,2-diphenylethylene was investigated over superbasic MgO–K and γ-Al2O3–K catalysts and over model systems of the EDA complex type. Metal oxide–alkali metal solid superbases as well as MgO–K polyaromatic hydrocarbon systems exhibited high activity in the transformations carried out under atmospheric and elevated pressure at low temperature. The reaction kinetics, the results of ESR investigations of adsorbed intermediates, and the effects of poisoning using radicals trap TEMPO enabled the identification of Fs+ sites as catalytically active centres. The proposal of a radical pathway of the reaction was confirmed and illustrated.

Ubiquitous occurrence of high molecular weight hydrocarbons in crude oils

For many years the presence of waxes in crude oils has been associated with organic matter derived from terrigenous sources. High temperature gas chromatography (HTGC) has been used to establish the ubiquitous presence of high molecular weight (HMW) hydrocarbons, extending as high as C120, in crude oils. HMW hydrocarbons (>C40+) have been observed in crude oils derived from terrigenous, lacustrine, and marine source materials. Modified extraction techniques have also led to the detection of HMW hydrocarbons in source rock extracts. The fractions of HMW hydrocarbons are complex mixtures of long-chain aliphatic and alkyl-aromatic hydrocarbons, and can represent up to 8% of a whole oil. The carbon preference index (CPI) of HMW alkylcyclopentanes in the C42–C46 range provides useful information on the characteristics of the original depositional environment. Age, maturity, and degree of biodegradation do not appear to affect the CPI of alkylcyclopentanes used for evaluating depositional environments. Differences in the distributions of the HMW hydrocarbons between the source rock extracts and the crude oils in the reservoirs may reflect changes occurring due to migration.

Partition coefficients of alkyl aromatic hydrocarbons and esters in a hexane–acetonitrile system

Partition coefficients ( K p) in a heterogeneous system consisting of two immiscible organic solvents can be successfully used for a supplementary identification parameter in qualitative GC and GC–MS analysis of organic compounds. For rapid addition to database of K p values, calculation methods based on the well-known ‘retention–structure relationships’ approach can be used. This paper reports the experimentally determined and calculated K p values for 252 compounds including alkyl aromatic hydrocarbons and esters. It is shown that for group identification of components it is desirable to use not the K p values themselves but the parameter j which is a combination of K p and gas chromatographic retention indices: j= kI−log K p.

Characterization and role of tbuX in utilization of toluene by Ralstonia pickettii PKO1.

The tbu regulon of Ralstonia pickettii PKO1 encodes enzymes involved in the catabolism of toluene, benzene, and related alkylaromatic hydrocarbons. The first operon in this regulon contains genes that encode the tbu pathway's initial catabolic enzyme, toluene-3-monooxygenase, as well as TbuT, the NtrC-like transcriptional activator for the entire regulon. It has been previously shown that the organization of tbuT, which is located immediately downstream of tbuA1UBVA2C, and the associated promoter (PtbuA1) is unique in that it results in a cascade type of up-regulation of tbuT in response to a variety of effector compounds. In our efforts to further characterize this unusual mode of gene regulation, we discovered another open reading frame, encoded on the strand opposite that of tbuT, 63 bp downstream of the tbuT stop codon. The 1,374-bp open reading frame, encoding a 458-amino-acid peptide, was designated tbuX. The predicted amino acid sequence of TbuX exhibited significant similarity to several putative outer membrane proteins from aromatic hydrocarbon-degrading bacteria, as well as to FadL, an outer membrane protein needed for uptake of long-chain fatty acids in Escherichia coli. Based on sequence analysis, transcriptional and expression studies, and deletion analysis, TbuX seems to play an important role in the catabolism of toluene in R. pickettii PKO1. In addition, the expression of tbuX appears to be regulated in a manner such that low levels of TbuX are always present within the cell, whereas upon toluene exposure these levels dramatically increase, even more than those of toluene-3-monooxygenase. This expression pattern may relate to the possible role of TbuX as a facilitator of toluene entry into the cell.