Toluene Carbon Research Articles

Catalytic fast pyrolysis of duckweed: Effects of pyrolysis parameters and optimization of aromatic production

Catalytic fast pyrolysis (CFP) of duckweed is a potential source for biorenewable gasoline and diesel fuel production, but its ability to produce aromatics has not been investigated in detail. In this study, we employed a micro-pyrolyzer coupled with gas chromatograph–mass spectrometer, flame ionization detector, and a thermal conductivity detector to conduct CFP of duckweed (Lemna minor) with HZSM-5 catalyst and obtained promising yields of total aromatic hydrocarbon (TAH) and benzene, toluene, and xylene (BTX). In the operating conditions studied, pyrolysis temperatures and catalyst-to-biomass ratios (CBR) had significant effects on product yields and distributions. Duckweed CFP can be optimized to maximize either the TAH yield or the output of the BTX components. Optimal operating conditions were determined based on response surface methodology (RSM) with a 4×5 full factorial design (FFD). The RSM predicted optimal TAH and xylene carbon yields to be 27.2mol% and 6.2mol% at 736°C and 662°C, respectively, with CBR of 16:1. Optimal benzene and toluene carbon yields of 5.5mol% and 8.0mol%, respectively, were obtained at 750°C and CBR of 20:1.

Gas-phase hydrodeoxygenation of guaiacol over iron-based catalysts. Effect of gases composition, iron load and supports (silica and activated carbon)

Fe/SiO2 is shown to be a selective catalyst for guaiacol hydrodeoxygenation (HDO). Guaiacol is used as a model compound to study the conversion of lignin pyrolysis vapours into aromatics (benzene, phenols). The effect of each individual gas present in a pyrolysis gas (H2, CO, CO2, H2O, CH4) on the selectivity of a 10wt% Fe/SiO2 catalyst is studied (673K, atmospheric pressure, 50mol% H2, 1/WHSV=0.6gcath/ggua). The speciation of the iron phase (metallic (α-Fe), carbide (Fe5C2), oxide (Fe3O4), and super-paramagnetic) in spent catalysts is revealed by XRD and Mössbauer spectroscopy as a function of gases composition. At least 3 types of carbonaceous deposit were evidenced by TPO analysis. TEM observations showed that iron particles size is not markedly affected by the reaction and that carbon deposit mainly occurs in the vicinity of iron particles. When all the gases except methane (Guaiacol+H2+CO+CO2+H2O) are simultaneously in the feed stream, the conditions are still sufficiently reducing to maintain the activity of the catalyst (66% of benzene and toluene carbon yield, 7.5gcath/ggua). The effects of support (silica or activated carbon-AC) and iron loading (5, 10, 15wt% Fe/SiO2) were also studied. 10wt% Fe/AC has a higher selectivity in phenol and cresols production than Fe/SiO2. Active sites and reaction mechanisms are discussed.

An Investigation of the Effect of Pre-swelling on the Extraction Yield of Two Different Ranked Turkish Coals

In this article, the effect of pre-swelling on the extraction yield of two Turkish coals was investigated. Supercritical toluene extraction and carbon disulfide/N-methyl-2-pyrrolidinone mixed solvent extraction at room temperature were the extraction methods employed. Ten different solvents were used to study the swelling behaviors of the coals. The swelling ratios were found dependent on the coal type, solvent basicity, and steric effect of the solvent used. The best swelling solvent identified was ethylenediamine for two coal samples. Pre-swelling enhanced the conversion and oil yield in supercritical toluene extraction. However, when using the mixed solvent extraction, the effect of pre-swelling was dependent on coal rank. Pre-swelling with ethylenediamine enhanced the extraction yield of Soma lignite while it decreased that of Nasifoglu coal.

Synthesis of Multi-Walled Carbon Nanotubes by Spray-Pyrolysis Using a New Iron Organometallic Complex as Catalytic Agent

An organometallic catalytic agent ([(Hexyl)4N]3FeCl3Br3) has been synthesized through the reaction of tetrahexylammonium bromide ((Hexyl)4NBr) and iron chloride (FeCl3) aqueous solutions. Multi-walled carbon nanotubes (MWCNTs) were obtained by spray pyrolysis of toluene (carbon source) using the new organometallic compound as catalyst. The synthesized catalytic agent was characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and thermal analysis (TA) techniques. Spectroscopic results indicated that the new iron organometallic compound has suitable characteristics to grow MWCNTs by spray pyrolysis. The MWCNTs were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The MWCNTs grow in a disordered way without orientation with diameters ranging from 20 to 50 nanometers. XRD patterns exhibit the 2-H graphite characteristics peaks of the MWCNTs.

The use of isotopic and lipid analysis techniques linking toluene degradation to specific microorganisms: applications and limitations

Phospholipid fatty acid (PLFA) analysis combined with 13C-labeled tracers has been used recently as an environmental forensics tool to demonstrate microbial degradation of pollutants. This study investigated the effectiveness and limitations of this approach, applied to the biodegradation of toluene by five reference strains that express different aerobic toluene degradation pathways: Pseudomonas putida mt-2, P. putida F1, Burkholderia cepacia G4, B. pickettii PKO1, and P. mendocina KR1. The five strains were grown on mineral salts base medium amended with either 10 mM natural or [ 13C-ring]-labeled toluene. PLFA analysis showed that all five strains incorporated the toluene carbon into membrane fatty acids, as demonstrated by increases in the mass of fatty acids and their mass-spectrometry fragments for cells grown on 13C-labeled toluene. Because of its ubiquitous presence and high abundance in bacteria, C16:0 fatty acid might be a useful biomarker for tracking contaminant degradation and 13C flow. On the other hand, the 13C-label (which was supplied at relatively high concentrations) generally exerted an inhibitory effect on fatty acid biosynthesis. Differences in fatty acid concentrations between cells grown on natural versus 13C-labeled toluene would affect the interpretation of lipid profiles for microbial community analysis as indicated by principal component analysis of fatty acids. Therefore, caution should be exercised in linking lipid data with microbial population shifts in biodegradation experiments with 13C-labeled tracers.

The use of isotopic and lipid analysis techniques linking toluene degradation to specific microorganisms: applications and limitations

Phospholipid fatty acid (PLFA) analysis combined with 13C-labeled tracers has been used recently as an environmental forensics tool to demonstrate microbial degradation of pollutants. This study investigated the effectiveness and limitations of this approach, applied to the biodegradation of toluene by five reference strains that express different aerobic toluene degradation pathways: Pseudomonas putida mt-2, P. putida F1, Burkholderia cepacia G4, B. pickettii PKO1, and P. mendocina KR1. The five strains were grown on mineral salts base medium amended with either 10 mM natural or [13C-ring]-labeled toluene. PLFA analysis showed that all five strains incorporated the toluene carbon into membrane fatty acids, as demonstrated by increases in the mass of fatty acids and their mass-spectrometry fragments for cells grown on 13C-labeled toluene. Because of its ubiquitous presence and high abundance in bacteria, C16:0 fatty acid might be a useful biomarker for tracking contaminant degradation and 13C flow. On the other hand, the 13C-label (which was supplied at relatively high concentrations) generally exerted an inhibitory effect on fatty acid biosynthesis. Differences in fatty acid concentrations between cells grown on natural versus 13C-labeled toluene would affect the interpretation of lipid profiles for microbial community analysis as indicated by principal component analysis of fatty acids. Therefore, caution should be exercised in linking lipid data with microbial population shifts in biodegradation experiments with 13C-labeled tracers.

HPTLC method for determination of nevirapine in pharmaceutical dosage form

A sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic method of analysis of nevirapine both as a bulk drug and in formulations was developed and validated. The solvent system consisted of toluene–carbon tetrachloride–methanol–acetone–ammonia (3.5:3.5:2.0:1.0:0.05, v/v/v/v/v). Densitometric analysis of nevirapine was carried out in the absorbance mode at 289 nm. This system was found to give compact spots for nevirapine ( R f value of 0.44±0.02). Nevirapine was subjected to acid and alkali hydrolysis, oxidation, dry heat and wet heat treatment and photodegradation. The drug undergoes degradation under acidic, basic conditions and oxidation. Also the degraded products were well resolved from the pure drug with significantly different R f values. Linearity was found to be in the range of 30–1000 ng/spot with significantly high value of correlation coefficient. The linear regression analysis data for the calibration plots showed good linear relationship with r 2=0.998±0.002 in the working concentration range of 300 ng/spot to 1000 ng/spot. The mean value of slope and intercept were 0.073±0.005 and 36.78±1.50, respectively. The method was validated for precision, robustness and recovery. The limit of detection and quantitation were 5 and 10 ng/spot, respectively. As the method could effectively separate the drug from its degradation products, it can be employed as a stability indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of acid degradation process. Arrhenius plot was constructed and activation energy was calculated.

Assimilation of toluene carbon along a bacteria–protist food chain determined by 13C-enrichment of biomarker fatty acids

A food chain consisting of toluene, toluene-degrading Pseudomonas sp. PS+ and a bacterivorous flagellated amoebae Vahlkampfia sp. was established in a batch culture. This culture was amended with [U- 13C]toluene and served as a model system to elucidate the flux of carbon in the food chain by quantifying bacterial biovolumes and 13C enrichment of phospholipid fatty acid (PLFA) biomarkers of the bacteria and the heterotrophic protists. Major PLFA detected in the batch co-culture included those derived from Pseudomonas sp. PS+ (16:1ω7c and 18:1ω7c) and Vahlkampfia sp. (20:4ω6c and 20:3ω6c). A numerical model including consumption of toluene by the bacteria and predation of the bacteria by the heterotrophic protists was adjsuted to the measured toluene carbon, bacterial carbon and δ 13C values of bacterial and protist biomass. Using this model, we estimated that 28±7% of the consumed toluene carbon was transformed into bacterial biomass, and 12±4% of the predated bacterial carbon was incorporated into heterotrophic protist biomass. Our study showed that the 13C enrichment of PLFA biomarkers coupled to biomass determination via biovolume calculations is a suitable method to trace carbon fluxes in protist-inclusive microbial food chains because it does not require the separation of protist cells from bacterial cells and soil particles.

Theoretical Study of Toluene Adsorbed on Zeolites X and Y: Calculation of 13C NMR Parameters

The adsorption of toluene on basic faujasite-type zeolites with different Si/Al ratio and charge compensating interstitial alkali metal cations, M−X and M−Y (M = Li+, Na+, K+, Rb+, and Cs+) has been investigated with molecular mechanics and quantum chemical methods. The Monte Carlo docking method was used to find energetically favorable positions of the toluene molecule within the zeolitic void space. Subsequently, density functional calculations of geometries, Mulliken partial charges, adsorption energies, and 13C NMR chemical shift parameters of clusters representing the adsorption site were performed. The polarization of the toluene carbon atoms is held to be a decisive step in the zeolite-catalyzed alkylation reaction and will therefore influence the outcome of this reaction in terms of the preference between ring and side-chain alkylation. Both the Lewis acidity of the alkali metal cations and, to a lesser extent, the basicity of the zeolite, which is governed by the nature of these interstitial cations and by the amount of aluminum atoms in the framework, simultaneously influence the electron distribution within the toluene molecule. Key geometric parameters, the Mulliken partial charges of the toluene carbon atoms, adsorption energies, and the chemical shift parameters are presented as a function both of the alkali cation and of the Al/Si ratio of the zeolite. As a general result, the 13C NMR chemical shift parameters δ11, δ22, δ33, δaniso, and η of the toluene carbon atoms are sensitive to the changes in composition mentioned above, while δiso hardly shows any sensitivity. Our results are in accord with experimental findings and indicate that adsorption on a single alkali cation site in zeolite X or Y does not result in the activation of toluene for alkylation. We expect our results to be useful in improving and interpreting data from MAS NMR experiments.

Isolation and characterization of a novel toluene-degrading, sulfate-reducing bacterium.

A novel sulfate-reducing bacterium isolated from fuel-contaminated subsurface soil, strain PRTOL1, mineralizes toluene as the sole electron donor and carbon source under strictly anaerobic conditions. The mineralization of 80% of toluene carbon to CO2 was demonstrated in experiments with [ring-U-14C]toluene; 15% of toluene carbon was converted to biomass and nonvolatile metabolic by-products, primarily the former. The observed stoichiometric ratio of moles of sulfate consumed per mole of toluene consumed was consistent with the theoretical ratio for mineralization of toluene coupled with the reduction of sulfate to hydrogen sulfide. Strain PRTOL1 also transforms o- and p-xylene to metabolic products when grown with toluene. However, xylene transformation by PRTOL1 is slow relative to toluene degradation and cannot be sustained over time. Stable isotope-labeled substrates were used in conjunction with gas chromatography-mass spectrometry to investigate the by-products of toluene and xylene metabolism. The predominant by-products from toluene, o-xylene, and p-xylene were benzylsuccinic acid, (2-methylbenzyl)succinic acid, and 4-methylbenzoic acid (or p-toluic acid), respectively. Metabolic by-products accounted for nearly all of the o-xylene consumed. Enzyme assays indicated that acetyl coenzyme A oxidation proceeded via the carbon monoxide dehydrogenase pathway. Compared with the only other reported toluene-degrading, sulfate-reducing bacterium, strain PRTOL1 is distinct in that it has a novel 16S rRNA gene sequence and was derived from a freshwater rather than marine environment.

Benzylfumaric, benzylmaleic, and Z- and E-phenylitaconic acids: synthesis, characterization, and correlation with a metabolite generated by Azoarcus tolulyticus Tol-4 during anaerobic toluene degradation.

E-Phenylitaconic acid has been isolated as a metabolite generated by Azoarcus tolulyticus Tol-4 along with benzylsuccinic acid during anaerobic degradation of toluene. Strain Tol-4 converted 1 to 2% of toluene carbon to E-phenylitaconate and benzylsuccinate (10:1). The identification of E-phenylitaconic acid was based on 1H nuclear magnetic resonance (NMR) characterization of degradation products derived from 13C-labeled toluene followed by comparison of spectroscopic and chromatographic data for the isolated, unlabeled metabolite with those for chemically synthesized benzylfumaric acid, benzylmaleic acid, E-phenylitaconic acid, and Z-phenylitaconic acid. Spectroscopic comparisons included 1H NMR, 13C NMR, and nuclear overhauser effect correlations. High-pressure liquid chromatography (HPLC) retention times and HPLC coinjections with synthetic dioic acids provided another reliable line of evidence for structure assignment. The formation of E-phenylitaconic acid differs from previous reports of benzylfumaric acid generation along with benzylsuccinic acid during anaerobic microbial degradation of toluene. This has important implications relevant to elaboration of the metabolic route for anaerobic toluene degradation by strain Tol-4 and related organisms. Similar amounts of E-phenylitaconic acid were also produced by seven other strains of A. tolulyticus.

Kinetic study of the anaerobic degradation of toluene by a mixed culture

AbstractToluene was anaerobically degraded by an enriched mixed culture under methanogenic conditions. The mixed culture was originally developed from cow‐dung and sludge from a laboratory reactor, in which benzene was anerobically degraded by sulphate‐reducing bacteria. First the mixed culture was enriched on toluene over a year with and without the use of sulphate in the medium. For the evaluation of growth‐kinetic and maintenance parameters, namely μmax, Ks, kd and Y, the anaerobic degradation of toluene was carried out in batch as well as in continous reactors systems. The gas volume and the methane content in the produced gas was somewhat lover than the theoretical value expected, indicating an incomplete degradation of some of the complex intermediates of the toluene degradation pathway. However, the mixed culture was able to transform 41.3% of the toluene carbon into methane.

Initial reactions in the anaerobic oxidation of toluene and m-xylene by denitrifying bacteria

Pseudomonas sp. strain T and Pseudomonas sp. strain K172 grow with toluene under denitrifying conditions. We demonstrated that anaerobic degradation of toluene was initiated by direct oxidation of the methyl group. Benzaldehyde and benzoate accumulated sequentially after toluene was added when cell suspensions were incubated at 5 degrees C. Strain T also grows anaerobically with m-xylene, and we demonstrated that degradation was initiated by oxidation of one methyl group. In cell suspensions incubated at 5 degrees C 3-methylbenzaldehyde and 3-methylbenzoate accumulated after m-xylene was added. Toluene- or m-xylene-grown strain T cells were induced to the same extent for oxidation of both hydrocarbons. In addition, the methyl group-oxidizing enzyme system of strain T also catalyzed the oxidation of each isomer of the chloro- and fluorotoluenes to the corresponding halogenated benzoate derivatives. In contrast, strain K172 only oxidized 4-fluorotoluene to 4-fluorobenzoate, probably because of the narrow substrate specificity of the methyl group-oxidizing enzymatic system. During anaerobic growth with toluene strains T and K172 produced two transformation products, benzylsuccinate and benzylfumarate. About 0.5% of the toluene carbon was converted to these products.

Metabolic by-products of anaerobic toluene degradation by sulfate-reducing enrichment cultures.

Two dead-end metabolites of anaerobic toluene transformation, benzylsuccinic acid and benzylfumaric acid, accumulated in sulfate-reducing enrichment cultures that were fed toluene as the sole carbon source. Stable isotope-labeled toluene and gas chromatography-mass spectrometry were used to confirm that the compounds resulted from toluene metabolism. The two metabolites constituted less than 10% of the toluene carbon (over 80% was mineralized to carbon dioxide, according to a previous study). This study demonstrates that the novel nonproductive pathway proposed by Evans and coworkers (P. J. Evans, W. Ling, B. Goldschmidt, E. R. Ritter, and L. Y. Young, Appl. Environ. Microbiol. 58:496-501, 1992) for a denitrifying pure culture applies to disparate anaerobic bacteria.

Anaerobic degradation of toluene by a denitrifying bacterium

A denitrifying bacterium, designated strain T1, that grew with toluene as the sole source of carbon under anaerobic conditions was isolated. The type of agar used in solid media and the toxicity of toluene were determinative factors in the successful isolation of strain T1. Greater than 50% of the toluene carbon was oxidized to CO2, and 29% was assimilated into biomass. The oxidation of toluene to CO2 was stoichiometrically coupled to nitrate reduction and denitrification. Strain T1 was tolerant of and grew on 3 mM toluene after a lag phase. The rate of toluene degradation was 1.8 mumol min-1 liter-1 (56 nmol min-1 mg of protein-1) in a cell suspension. Strain T1 was distinct from other bacteria that oxidize toluene anaerobically, but it may utilize a similar biochemical pathway of oxidation. In addition, o-xylene was transformed to a metabolite in the presence of toluene but did not serve as the sole source of carbon for growth of strain T1. This transformation was dependent on the degradation of toluene.

Stimulated raman scattering of fuel droplets

The strong stimulated Raman scattering (SRS) from diesel fuel droplets has the potential of providing the relative concentration of multicomponent fuel and the absolute size of individual droplets. The morphology-dependent resonances (MDRs) of a sphere cause the droplet to act as an optical resonator which greatly lowers the SRS threshold. The number density, quality factor, and frequency shift of several MDRs are calculated as a function of the ratio of the index of refraction of the liquid and the surrounding gas, which approaches unity at the thermodynamic critical condition for the fuel spray. The SRS spectra of monodispersed droplets of toluene, pentane, Exxon-Aromatic-150, and Mobil D-2 are presented. The exponential growth region of the SRS intensity I 1S as a function of the input laser intensity I input is investigated for the toluene carbon ring breathing mode v 2 and the pentane C-H stretching region. The I 1S ratio of toluene and pentane is measured as a function of the ratio of the toluene and pentane concentration for monodispersed droplets. The reduced fluctuation in I 1S when I input is changed from multimode to single-mode is displayed as a histogram of the I 1S of the v 2 mode of toluene droplets.

C14Study of Relative Fuel-to-Soot Carbon Conversion in Premixed Flames

Abstract Three 1,fC-!abeled fuels were burned as premixed flames: (a) 72 percent methanol in toluene; (b) 62 percent acetone in toluene; (c) 54 percent cyclohexane in toluene. These compositions correspond to 1:1 cofuel carbon:toluene carbon ratios. Soot, sampled from the yellow flame zone and collected on a glass-fiber filter, was assayed for 1,(C-activity. Results were analysed in terms of R, the relative probability of toluene carbon xofuel carbon conversion. R values of 2 and 50 were determined for cyclohexane and methanol respectively. Studies were carried out at 4:1 Na:02 composition and fuel:oxygen equivalence ratios of 1.6, 1.8 and 2.0. Fuel:oxygen equivalence ratio had minor impact on relative fuel-to-soot conversion.

Substituent effects in α-substituted carbanions

The para13C shifts of benzylcarbanions PhCH–X (VI) in Me2SO, acidities of toluene carbon acids PhCH2X (I) in Me2SO, and gas-phase acidities of methane carbon acids CH3X (VIII) are submitted to mono- and bi-parametric substituent treatment using previously defined sets of σc–, σIB, and σR– constants. It is confirmed that these scales are appropriate for describing interactions between contiguous functionalities, as opposed to literature values which account for remote interactions. Gas-phase acidities respond excellently to substituent effect treatment, while solution data show deviations for the SO2R and CN substituents. Such deviances are accounted for as a manifestation of SSSAR (Stabilization due to Specific Solvent Assisted Resonance) for groups which exhibit extensive charge transfer from the carbanionic carbon to the π-accepting substituent (COR, CO2R, CONMe2, NO2, etc.). The mesomeric component of substituent effects is about three times more important than the polar–inductive one in governing the acidities of carbon acids in Me2SO solution and in affecting the chemical shift of the para monitor in PhCH–X. Relative to the gas phase, the solvent enhances by a factor of 2 the sensitivity of acidities of carbon acids to the mesomeric components of substituent effects. The sensitivity of the para monitor in PhCH–X to polar–inductive components of substituent effects shows, relative to the neutral precursor PhCH2X (I), a three-fold increase and, relative to the PhNHX family, a two-fold increase. The sensitivity of the para monitor in PhCH–X to mesomeric components of substituent effects shows a three-fold increase relative to the PhNHX family.

Contiguous interactions in α-substituted nitrogen acids and conjugate nitroanions: the role of mesomeric and polar components.

1 H, 19F, and 13C n.m.r. parameters of α-substituted sodium phenyl amides PhN–X (VIII) are obtained in Me2SO solution to study the interactions of the variable substituent X with the contiguous negatively charged nitrogen atom. Results probe the considerable structural reorganization undergone by the precusor nitrogen acids PhNHX (IV) upon deprotonation: the effect on 13C shifts exerted by the [2.2.1] cryptand provides evidence for ion pairing and/or aggregation of the salts. Correlative analyses with the n.m.r. data probe the effect of the substituent in PhN–X: in addition to the monoparametric treatment in terms of the σC– constants, DSP analysis with the σ1B and σR– constants reveals that charge transfer from the nitrogen atom to the phenyl ring is dominated by the mesomeric component of the effects exerted by the substituent X. Unlike the analogous acid–base pair of toluene carbon acids PhCH2X and of benzyl carbanions PhCH–X, no correlation whatsoever is found between C(p) of PhN–X (VII) and Bordwell's acidities of PhNHX (IV) in Me2SO. The DSP treatment of parent α-substituted nitrogen acids NH2X and of their phenyl homologues reveals that the energetics of the deprotonation process is dominated by the polar–inductive component of the effect exerted by the substituent. The different sensitivities of charge release from nitrogen in nitroanions and of acidities of nitrogen acids are accounted for on plausible structural arrangements in these species. The pKa of ammonia is extrapolated from the intersystem correlation between acidities of NH2X and of PhNHX: the value (35.8) is in excellent accord with the value obtained (36.6) from the DSP treatment of NH2X acidities.

Sound Velocities in Binary Liquid Mixtures

AbstractThe velocity of sound in five binary liquid mixtures of Toluene–Carbon tetrachloride, Benzene–Hexane, Cyclo hexane–Carbon tetrachloride, Hexane‐Toluene and Benzene–Carbon tetrachloride at various concentrations has been measured by the Debye Sear's diffraction method. It is found that the velocity and compressibility vary approximately linearly with concentration. Comparison between experimental and theoretical results shows fairly good agreement between them.