Monoaromatic Compounds Research Articles

Biodegradation of phenol and phenol-related compounds by psychrophilic and cold-tolerant alpine yeasts

We characterized 32 cold-adapted, psychrophilic and cold-tolerant, yeast strains isolated from alpine habitats with regard to their taxonomy, growth temperature profile, and ability to degrade phenol and 18 phenol-related mono-aromatic compounds at 10 °C. Twenty of the strains were identified by sequencing of the ribosomal ITS region as seven species of the basidiomycota: Cryptococcus terreus (three strains), Cryptococcus terricola (one strain), Rhodosporidium lusitaniae (two strains), Rhodotorula creatinivora (10 strains), Rhodotorula ingeniosa (one strain), Mastigobasidium intermedium (one strain), and Sporobolomyces roseus (two strains). Twelve strains sharing closely related ITS sequences could not be identified to the species level; according to their ITS sequence they are included in the Microbotryomycetidae. These 12 strains were psychrophilic (no growth at temperatures above 20 °C); one-third of these strains did not grow above 15 °C. None of the 32 strains utilized any of the highly volatile mono-aromatic compounds (benzene, toluene, ethylbenzene, nitrobenzene, o-xylene, m-xylene, and p-xylene) as the sole carbon source. Non/low volatile aromatic compounds were degraded in the following order: phenol > hydroquinone > resorcinol > benzoate > catechol > salicylate ≫ p-cresol > m-cresol. o-Cresol, guaiacol, p-nitrophenol, or p-nitrotoluene were not utilized for growth. R. creatinivora strains degraded up to seven compounds, whereas C. terricola and S. roseus strains degraded only two compounds. The toxicity of the compounds was determined via growth inhibition in the presence of toxicants and nutrients at 10 °C. R. creatinivora strains were characterized by higher IC 50 values than other species, S. roseus was the most sensitive species. The most toxic compounds were the xylene isomers, ethylbenzene, p-nitrophenol, and m-cresol. There was a relation between the chemical structure of the compounds and their toxicity, whereas a relation between the toxicity of the compounds and the ability of the yeasts strains to utilize these compounds for growth was only detected in some cases.

Group-type characterisation of mineral oil samples by two-dimensional comprehensive normal-phase liquid chromatography–gas chromatography with time-of-flight mass spectrometric detection

Normal-phase liquid chromatography (NPLC) and capillary gas chromatography (GC) are complementary techniques, which makes them ideally suited for hyphenated and comprehensive coupling. In this work, an LC and a GC equipped with a time-of-flight mass spectrometer were on-line and comprehensively coupled (LC × GC–ToF MS) for the analysis of mineral oil samples. Classes of compounds present in the oil like paraffins, mono-aromatic and multi-aromatic compounds were separated by normal-phase LC, with a subsequent boiling-point separation within each class by means of GC. Sub-groups present in each class of compounds were distinguished by selecting their unique masses.

Group-type characterisation of mineral oil samples by two-dimensional comprehensive normal-phase liquid chromatography–gas chromatography with time-of-flight mass spectrometric detection

Normal-phase liquid chromatography (NPLC) and capillary gas chromatography (GC) are complementary techniques, which makes them ideally suited for hyphenated and comprehensive coupling. In this work, an LC and a GC equipped with a time-of-flight mass spectrometer were on-line and comprehensively coupled (LC × GC–ToF MS) for the analysis of mineral oil samples. Classes of compounds present in the oil like paraffins, mono-aromatic and multi-aromatic compounds were separated by normal-phase LC, with a subsequent boiling-point separation within each class by means of GC. Sub-groups present in each class of compounds were distinguished by selecting their unique masses.

Anaerobic degradation of monoaromatic hydrocarbons.

Over the last two decades significant advances have been made in our understanding of the anaerobic biodegradability of monoaromatic hydrocarbons. It is now known that compounds such as benzene, toluene, ethylbenzene, and all three xylene isomers can be biodegraded in the absence of oxygen by a broad diversity of organisms. These compounds have been shown to serve as carbon and energy sources for bacteria growing phototrophically, or respiratorily with nitrate, manganese, ferric iron, sulfate, or carbon dioxide as the sole electron acceptor. In addition, it has also been recently shown that complete degradation of monoaromatic hydrocarbons can also be coupled to the respiration of oxyanions of chlorine such as perchlorate or chlorate, or to the reduction of the quinone moieties of humic substances. Many pure cultures of hydrocarbon-degrading anaerobes now exist and some novel biochemical and genetic pathways have been identified. In general, a fumarate addition reaction is used as the initial activation step of the catabolic process of the corresponding monoaromatic hydrocarbon compounds. However, other reactions may alternatively be involved depending on the electron acceptor utilized or the compound being degraded. In the case of toluene, fumarate addition to the methyl group mediated by benzylsuccinate synthase appears to be the universal mechanism of activation and is now known to be utilized by anoxygenic phototrophs, nitrate-reducing, Fe(III)-reducing, sulfate-reducing, and methanogenic cultures. Many of these biochemical pathways produce unique extracellular intermediates that can be utilized as biomarkers for the monitoring of hydrocarbon degradation in anaerobic natural environments.

Characterization of a Gas Oil Fraction and Its Hydrotreated Products

In this work we explore the chemistry of a gas oil fraction in the mid-boiling range (433–483°C) and its products after hydrotreating at 375, 385, and 400°C. Each sample was fractionated by high performance liquid chromatography (HPLC) based on the elution times for saturate, mono-, di-, and poly-aromatic standards. The HPLC saturate fraction is practically free of aromatic components. The nominal mono- and di-aromatics fractions differ in that the former has a higher molecular weight and H/C ratio cbut lower aromaticity and heteroatom content. The H/C atomic ratios, aromaticities, and average structural parameters of the HPLC poly-aromatic subfractions are virtually the same. Regardless of their structural resemblances they differ substantially in their HPLC elution behavior. This can be attributed to the differences in their oxygen and, especially, nitrogen contents. Hydrogenation produced a significantly greater amount of saturate material having a higher H/C ratio than the original feed. A large part of this increase must result from dealkylation, saturation, or opening of aromatic molecules. This mechanism also produced nominally mono-aromatic compounds from the poly-aromatic species originally present. The effect of hydrogenation on heteroatoms was mixed. While the overall amount of nitrogen was reduced, its concentration in the poly-aromatic fractions actually increased. Overall, oxygen concentration in the product was not much affected by hydrogenation, except that its distribution became skewed towards the more easily eluted HPLC front-fractions. Both thiophenic and sulphide sulphur were significantly reduced in all of the separated fractions.

Optimization of a Thermal Desorption Method for a Mixture of Volatile Organic Compounds (C1–C10): Comparison of Two Types of Cold‐Traps

This study concerns the optimization of the desorption of 42 volatile organic compounds (nonhalogenated and halogenated aliphatic hydrocarbons, alkylated and chlorinated monoaromatic compounds, and terpenes) from a sorbent trap that contains 140 mg of Tenax‐GR and 60 mg of Chromosorb‐106. Gaseous standards were used for this purpose and were prepared using the packed column injector method. Generation conditions were optimized by means of a centered factorial experimental design and fixed at 125°C of injector temperature, 50 mL/min of carrier gas flow rate, and 40 sec of injection time. After tube desorption, analytes were focused on a cold‐trap. The type of cold‐trap determines the load of analytes on the system and, therefore, the method sensitivity. The influence of some variables (times, flows, and temperatures of desorption for tube and cold‐trap) on the whole desorption process was studied using two types of traps: a standard packed cold‐trap, and a low‐flow one. In the case of the standard cold‐trap, no variables have a significant effect on the process, and therefore, tube desorption was carried out at 190°C for 4 min with a helium flow of 100 mL/min. For cold‐trap desorption, values were 275°C, 3 min, and 3.9 mL/min. But in the case of the low‐flow trap, the flow that desorbs adsorption tube and cold‐trap was significant and was classically optimized. The final values were 190°C, 4 min, and 60 mL/min of desorb flow for tube desorption and 275°C, 3 min, and 1 mL/min of outlet split flow for cold‐trap desorption. An important improvement (ca 50%) on method detection limits was observed using the low‐flow cold‐trap.

Pyrolysis of virgin and waste polypropylene and its mixtures with waste polyethylene and polystyrene

A comparison of waste and virgin polypropylene (PP) plastics under slow pyrolysis conditions is presented. Moreover, mixtures of waste PP with wastes of polyethylene (PE) and polystyrene (PS) were pyrolyzed under the same operating conditions. Not only the impact of waste on degradation products but also impacts of the variations in the mixing ratio were investigated. The thermogravimetric weight loss curves and their derivatives of virgin and waste PP showed differences due to the impurities which are dirt and food residues. The liquid yield distribution concerning the aliphatic, mono-aromatic and poly-aromatic compounds varies as the ratio of PP waste increases in the waste plastic mixtures. In addition to this, the alkene/alkane ratio of gas products shows variations depending on the mixing ratio of wastes.

Avoiding Hydrolysis of Fuel Ether Oxygenates during Static Headspace Analysis

The determination of fuel ether oxygenates in groundwater was found to be problematic when samples are preserved at pH < 2 and then analyzed using heated headspace sampling. Acid catalyzed the hydrolysis of tert-amyl methyl ether, ethyl tert-butyl ether, and methyl tert-butyl ether during headspace sampling when aqueous samples were heated at 80 degrees C, a typical temperature used for heated headspace sampling. Hydrochloric acid at pH 2 did not cause hydrolysis of oxygenate ethers in samples stored for 28 d at 4 degrees C. When trisodium phosphate was used to preserve the sample or to adjust the pH of samples preserved with acid before headspace sampling, the recovery of spiked ethers was excellent. The heated headspace method was also applicable for the determination of other fuel oxygenates including ethanol, tert-butyl alcohol (TBA), tert-amyl alcohol (TAA), isopropyl alcohol (IPA), acetone, and monoaromatic compounds found in gasoline including benzene, toluene, ethylbenzene, xylenes, and trimethylbenzenes. The method detection limits range from 0.1 to 0.2 microg/L for the ethers and aromatics. For alcohols and acetone, the method detection limits were 0.8 microg/L for TBA, 18 microg/L for ethanol, 1.2 microg/L for TAA, 5.5 microg/L for IPA, and 3.3 microg/L for acetone. The heated headspace method yielded accurate results for ether oxygenates in samples containing a wide range of gasoline concentrations (2500-100000 microg/L).

Anaerobic biodegradation of BTEX using Mn(IV) and Fe(III) as alternative electron acceptors

Anaerobic BTEX biodegradation was tested in batch experiments using an anaerobic sediment as inoculum under Fe(III) and Mn(IV) reducing conditions. All BTEX were degraded under the conditions tested, specially under Mn(IV) reducing conditions, where benzene was degraded at a rate of 0.8 micromol l(-1) d(-1), significantly much faster than Fe(III) reducing conditions. Under Fe(III) reducing conditions, ethylbenzene was the compound that degraded at the faster rate of 0.19 micromol l(-1) d(-1). Mn(IV) reducing conditions are energetically more favourable than Fe(III), therefore, BTEX were more rapidly degraded under Mn(IV) reducing conditions. These results represent the first report of the degradation of benzene with Mn(IV) as the final electron acceptor. Amorphous manganese oxide is a natural widely distributed metal in groundwater, where it can be microbiologically reduced, leading to the degradation of monoaromatic compounds.

Evidence of poly-condensed aromatic rings in a Victorian brown coal

An attempt was made for obtaining UV/VIS absorption and fluorescence spectra of a whole Victorian brown coal and then examining the presence of aromatic ring systems (ARSs) with poly-condensed rings in the coal. Loy Yang brown coal was subjected to an alkali-promoted depolymerization in an aqueous solution of sodium hydroxide at 473 K and then dissolved nearly completely into the solution. The solution of the solubilized coal was analyzed by UV/VIS absorption and fluorescence spectroscopies. The spectra of the solubilized coal were compared with those of a tar that was produced from the rapid pyrolysis of the coal in a wire-mesh reactor. Absorbance of the solubilized coal per unit molar concentration of aromatic carbon and unit light path length was averaged over 50 nm wavelength intervals in a range from 250 to 600 nm. The averaged absorbance of the solubilized coal was much greater than those of mono-aromatic compounds and lignin at intervals from 400 to 600 nm while comparable to those of tetra- to hexa-aromatic compounds, suggesting that the coal is abundant of ARSs with poly-condensed rings. The fluorescence spectra of the solubilized coal also give indication of the presence of ARSs with three to six condensed rings. Furthermore, the presence of even larger ARSs is evidenced from appreciable difference in apparent quantum yield of the solubilized coal and that of the tar. By comparing the absorption and fluorescence spectra of the solubilized coal with those of the tar, it was revealed that the tar is richer in relatively small poly-ARSs than the solubilized coal while the larger poly-ARSs are abundant in the solubilized coal. Smaller poly-ARSs were thus released from the coal preferentially to larger poly-ARSs during the pyrolysis.

Resolving the unresolved complex mixture in petroleum-contaminated sediments.

Comprehensive two-dimensional gas chromatography (GC x GC) was used to investigate the chemical composition of the unresolved complex mixture (UCM) of hydrocarbons in petroleum-contaminated marine sediments. The UCM hydrocarbons were extracted and separated with silica and silver-impregnated silica gel chromatography to yield four fractions (branched alkanes and cycloalkanes, monoaromatics, naphthalenes, and multi-ring PAHs) prior to GC x GC analysis. GC x GC separations used a poly-(dimethylsiloxane) stationary phase for volatility selectivity on the first dimension and a 14% cyanopropylphenyl polysiloxane phase for polarity selectivity on the second dimension to fully resolve monoaromatic, naphthalene, and multi-ring PAH compounds from the UCM. A chiral gamma-cyclodextrin phase was used for shape selectivity on the second GC x GC dimension to resolve individual branched alkanes and cycloalkanes in the saturates fraction of the UCM. The ability of GC x GC to resolve thousands of individual chemical components from the UCM will facilitate an understanding of the sources, weathering, and toxicity of UCM hydrocarbons.

Detection of the gasoline components methyl tert-butyl ether, benzene, toluene, and m-xylene using ion mobility spectrometers with a radioactive and UV ionization source.

For the first time, ion mobility spectrometers (IMS) with radioactive and UV ionization sources in combination with multicapillary columns (MCCs) have been used to determine methyl tert-butyl ether (MTBE), a gasoline additive, in water and nitrogen as well as the monoaromatic compounds benzene, toluene, and m-xylene (BTX). A membrane extraction unit was set up to extract the substances from water, which is simple, effective, and easy to automate for further applications. Thus, the detection of MTBE and BTX of gasoline vapors was accomplished after a preliminary silicone membrane extraction. Two-dimensional data analyses of IMS-chromatograms allow us to separate these substances clearly according to their different retention and drift times. Method detection limits for MTBE were 2 microg/L (UV) and 30 pg/L (63Ni) in nitrogen and 20 mg/L (UV) and 1 microg/L (63Ni) in water. Rather a good reproducibility was achieved with relative standard deviations of between 2.9 and 9%. The method presented in this article has been proven to be suitable for nearly real-time monitoring as the total analysis time is less than 90 s. As an example of application, the detection of MTBE and BTX in a mixture of volatile organic compounds of pure gasoline using the 2-D IMS-chromatogram is presented.

Computational chemical investigation into isorenieratene cyclisation

In sediments, the diaromatic carotenoid isorenieratene can undergo a wide range of molecular transformations, including cyclisation reactions via a Diels–Alder mechanism resulting in either mono- and diaromatic compounds or tetracyclic isorenieratene derivatives. To study these complex diagenetic pathways, we have used molecular dynamics simulations, in concert with a newly developed reactive hydrocarbon force field (ReaxFF). This allows us to simulate the entire cyclisation pathway, including both stable intermediates as well as energy barriers related to transition states. Our simulations indicate that the formation of tetracyclic isorenieratene derivatives is likely to occur via an A-ring initiated reaction mechanism, as the reaction product resulting from A-ring closure is more stable than that derived from B-ring closure. Furthermore, the A-ring initiated tetracyclisation pathways contain one fewer high-energy hydrogen shift step than their B-ring initiated counterparts, indicating that B-ring initiated cyclisation is more likely to result in the formation of monoaromatic compounds. These observations are in excellent agreement with observed distributions of isorenieratene derivatives in sediments and provide a better understanding of the complex diagenetic pathways of isorenieratene.

Monoaromatic complexity in urban air and gasoline assessed using comprehensive GC and fast GC-TOF/MS

Abstract Two state-of-the-art analytical techniques have been used to assess monoaromatic complexity in gasoline, gasoline vapours and urban air. A comparison of comprehensive gas chromatography (GC×GC) and fast gas chromatography—time-of-flight mass spectrometry (GC-TOF/MS) has been made, with emphasis on the ability of each technique to speciate at high isomeric complexity. The high spectral acquisition rates from TOF/MS gave improved peak deconvolution of overlapping analytes when compared to standard quadrupole configurations, with 89 monoaromatic isomers isolated in gasoline during a 200 s GC separation. Higher analytical resolution for gasoline was obtained using GC×GC, isolating 130 monoaromatics, using combined column retention behaviour for analyte identification. Analysis of urban air using GC×GC indicated the presence of 147 monoaromatic species with up to 8 carbon substituents on the ring. In conventional separations such as single column GC-FID, heartcut GC and GC/MS these compounds are hidden by the constant co-elutions occurring in low volatility regions. The vast number of low concentration species in the higher boiling point range make it impossible to completely speciate all analytes present using single column methodologies. Comparison of 2D GC×GC chromatograms for air and gasoline vapours demonstrated visually the impact of evaporative emission sources in urban environments. The potential contribution of larger monoaromatic compounds as precursors to both photochemical ozone and secondary organic aerosol is discussed along with the implications on modelling OH chemistry in polluted air.

Molecular-Level Investigation of Monoaromatic Compound Sorption to Suspended Soil Particles by Deuterium Nuclear Magnetic Resonance

Molecular-Level Investigation of Monoaromatic Compound Sorption to Suspended Soil Particles by Deuterium Nuclear Magnetic Resonance

Conversion of Acetone to Aromatic Chemicals with HZSM-5

Monoaromatic compounds are important chemicals as raw material for many petrochemical industries. Conventionally, these compounds are obtained from fossil resources by petroleum refining processes. In order to reduce the dependency on this resource, a new route with the utilization of biomass as starting material for the production aromatic chemicals is considered to establish a sustainable system of chemical industry. The route is that acetone could be produced selectively by catalytic reaction from biomass-derived oil. From this point, therefore, this study is to explore a catalytic conversion of acetone toward aromatic chemicals with HZSM-5. The reaction is carried out by continuous flow reactor at an atmospheric pressure to examine the activity and selectivity of HZSM-5. Some parameters such as temperature, space velocity, effect of water have been investigated. The results show that HZSM-5 exhibited a high active and a shape-selective catalyst for the formation of monoaromatic chemicals. The favourable condition for acetone aromatization is found i.e. at 673K with space velocity of 4h-1, the acetone conversion is close to 100% and monoaromatic selectivity is approximately 71%. The low selectivity of carbon oxides (less than 5%) was obtained, and it could be contributed significantly for this catalytic reaction on realization toward sustainable development of chemical industry in the future. There is no effect of water existence in the acetone feed on the aromatization reaction process, making the process will be simplified.

Molecular-level investigation of monoaromatic compound sorption to suspended soil particles by deuterium nuclear magnetic resonance.

Molecular-level sorption behavior of monoaromatic compounds in suspensions of water-dispersable clay components was studied by measuring 2H nuclear magnetic resonance (NMR) spin-spin relaxation times (T2). In general, decreased T2 values indicate stronger solute-sorbent interactions and increased sorption of the solute. A decreasing trend for T2 values in the order benzene > fluorobenzene > toluene (-C6D5 moiety) was observed, which was probably caused by the hydrophobic effect. The T2 values for benzene and the -C6D5 moiety of toluene increased with increasing pH, whereas the trend with pH was much weaker and less consistent for fluorobenzene and the methyl group of toluene. Conversely, no clear relationship was found between T2 values and pH for dichloromethane. These contrasting results cannot be explained by the pH-dependent self-assembly and hydrophobicity of humics. Instead, directed specific forces, including hydrogen bonding, cation-pi interactions, and aromatic-aromatic interactions, are proposed between the benzene ring of monoaromatic solutes and soil organic matter (SOM). Substituents of benzene affect these interactions by varying the pi electron density. When the soil fraction was treated with NaOH to remove humic and fulvic acids, T2 values for the different monoaromatic solutes were surprisingly lower compared with those for the untreated soil fraction. This result is probably caused by the increased ratio of solutes adsorbed to "hard" or "glassy" SOM components, which leads to less mobile sorbed solute molecules, after removing NaOH-extractable humics that contain more "soft" or "rubbery" SOM components.

Liquid-Phase Hydrogenation Kinetics of Multicomponent Aromatic Mixtures on Ni/Al2O3

The hydrogenation reactivity of some aromatic compounds used to model diesel fractions was examined under sulfur-free conditions. Reactions of toluene, 1,2,3,4-tetrahydronaphthalene (tetralin), and naphthalene, separately and as mixtures, were studied using a commercial Ni/Al2O3 catalyst. The reactivity decreased in the following order: naphthalene ≫ tetralin > toluene. Because of competitive adsorption and subsequent inhibition, naphthalene severely reduced the other hydrogenation rates in mixtures, whereas the hydrogenation rate of naphthalene was little affected by the concentration of toluene or tetralin. A kinetic model based on the general form of the Langmuir−Hinshelwood equation was developed. The activation energies of toluene, tetralin, and naphthalene were found to be 52.9, 40.4, and 58.7 kJ/mol, respectively, and the reaction orders of the monoaromatic and diaromatic compounds were about 1.4 and 2.1, respectively. Furthermore, simulations showed that the reaction kinetics in mixtures can be s...

Brazilian Oil Spills Chemical Characterization—Case Studies

In the last decade, PETROBRAS has experienced some significant oil spills cases and the PETROBRAS Research Center has played an important role in the company emergency response program by characterizing the spilled oil, monitoring the affected ecosystem, determining the fate of the oil in the environment, and, subsequently, helping the company in assessing the environmental damage. This paper presents the use of advanced chemical analytical techniques (GC/FID, P&T/GC/PID and GC/MS) in some Brazilian oil spill studies in order to determine fractions and individual petroleum hydrocarbons in different matrices such as water, groundwater, sediment, sand, fish and the spilled oil itself. The spill studies encompassed crude and fuel oil releases on land and coastal ecosystems, related to the incidents in Guanabara Bay (Rio de Janeiro), Barigui and Iguassu Rivers (Parana) and Sao Sebastiao Channel (Sao Paulo). Total petroleum hydrocarbons (TPH), n -alkanes, isoprenoids, unresolved complex mixtures (UCM), volatile monoaromatic compounds—benzene, toluene, ethylbenzene and xylenes (BTEX), parent and alkylated homologues polycyclic aromatic hydrocarbons (PAH), and terpanes and steranes were characterized for determining correlation to the spilled oil and other known oil sources and environmental assessment. Some of the acute ecotoxicity data for water and sediment samples is also presented.

Review of Natural Attenuation of BTEX and MTBE in Groundwater

Monitored natural attenuation has become accepted as an appropriate “technology” for treating petroleum hydrocarbon-contaminated groundwater. Commonly, the monoaromatic compounds benzene, toluene, ethylbenzene, and xylenes (BTEX) and oxygenated additives, e.g., methyl tert-butyl ether (MTBE), are the major constituents of regulatory importance. Although a variety of naturally occurring attenuation mechanisms may reduce BTEX and MTBE concentrations, intrinsic biodegradation is the primary destructive mechanism. Attenuation by anaerobic biodegradation is important for BTEX compounds because of the relative abundance of anaerobic electron acceptors as compared with dissolved oxygen. Field studies indicate that MTBE is also biodegradable in shallow aquifers, but at a slower rate relative to BTEX compounds; thus, dispersion and dilution may also be important MTBE attenuation mechanisms. To demonstrate that natural attenuation is occurring, it is critical to document the proposed natural attenuation processes in the field. These processes often cause measurable “footprints.” At a large number of petroleum-hydrocarbon release sites, natural attenuation processes have been observed and documented and found to control the extent of migration of BTEX contaminants. Although the presence of MTBE may compromise the use of natural attenuation at some sites due to the greater mobility and persistence of MTBE compared to BTEX, some data indicate that MTBE plumes do eventually stabilize.