Fraction Of Coal Tar Pitch Research Articles

Complex research of the components of the coal tar pitch

The composition, structure and morphology of particles of β-and α2-fraction powders of medium-temperature coal tar pitch were studied using the methods of electron microscopy, adsorption porosimetry, NMR, IR-EPR spectroscopy, X-ray diffractometry, thermal analysis, and chromatography-mass spectrometry. The morphology and structure of coke residues were investigated depending on the heating temperature. It has been established that polyaromatic hydrocarbons in the composition of volatile products of thermolysis of coal tar pitch are formed mainly during the decomposition of the β-fraction components. The results obtained are of interest from the point of view of the directions of using the isolated fractions of coal tar pitch as precursors for obtaining functional carbon materials.

Получение графитоподобных материалов из каменноугольного пека

In the research, the study of precursors of graphite-like materials obtained from medium-temperature coal tar pitch was carried out on the individual components of coal tar pitch by separating the multicomponent composition of the pitch into separate fractions. Such approach, to study the physicochemical characteristics of the individual components of coal tar pitch, contributes to both the determination of the contribution of individual pitch components to the process of its structuring during carbonization and the development of new environmentally friendly methods for the synthesis of functional materials for various applications. The β-fraction was precipitated with n-hexane from toluene extract of coal tar pitch. γ-fraction was isolated from n-hexane by solvent evaporation. α2-fraction was isolated from the residue, insoluble in toluene, by quinoline extraction. The composition and structure of the isolated individual fractions of coal tar pitch were studied by physicochemical methods of analysis. The shape and morphology were investigated by electron microscopy. To study the composition and structure, the methods of elemental analysis, infrared spectroscopy, electron-paramagnetic resonance, XRD-analysis, and thermoanalysis were used in combination with methods of derivative analysis, chromatography, and mass spectrometry. The authors of the work propose new approaches to the use of individual fractions of coal tar pitch in order to obtain new graphite-like materials on their basis.

Self-healing and Oxidation Resistance of B-Si Doped Carbon Materials Derived from Modification Coal Tar Pitch

AbstractWith toluene soluble fraction of coal tar pitch, polycarbosilane and pyridine borane as raw materials, the modification coal tar pitch was synthesized by a liquid method. The B-Si-doped carbon materials were obtained by carbonization treatment at 800–1,600 °C for 1 h. The effects of carbonization temperatures on the composition, microstructure and oxidation resistance of the B-Si-doped carbon materials were investigated by XRD, SEM and TG-DSC. The results showed that the B-Si-doped carbon materials were composed of B2O3 and carbon. SiC crystal grains appeared when the carbonization temperatures were over 1,200 °C. The higher the carbonization temperatures were, the larger the SiC grain sizes of B-Si-doped carbon materials became. But oxidation rate of larger grain sizes of SiC was slow during oxidation. It was difficult to form a protective glassy film on the surface of the materials rapidly. Therefore, the B-Si-doped carbon materials obtained by carbonization at 1,200 °C showed better oxidation resistance. Oxidation resistance mechanism of B-Si-doped carbon materials was illustrated. The SiO2 produced by the oxidation of SiC and B2O3 formed protective glassy film, which had self-healing and anti-oxidation synergism.

Synthesis of SiC nanowires via catalyst-free pyrolysis of silicon-containing carbon materials derived from a hybrid precursor

SiC nanowires were successfully synthesized without catalyst by pyrolysis of silicon-containing pitch-derived carbon materials in a closed graphite crucible. These silicon-containing carbon materials were obtained by homogenization and co-carbonization of a hybrid precursor consisting of the toluene soluble fraction of coal tar pitch with polycarbosilane (PCS). The composition, morphology and structure of the nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The influence of pyrolysis temperature on the growth of the nanowires was investigated by Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetry coupled with mass spectroscopy (TG-MS) analysis. The results indicate that the growth of the SiC nanowires starts at around 1200 °C. As the pyrolysis temperature increases to 1300–1500 °C, a large quantity of nanowires are formed on the top surface of the pitch-derived carbon substrate. In addition, increasing the pyrolysis temperature leads to an increase in the average diameter and a change in the typical morphology produced. The synthesized SiC nanowires have single-crystalline structure and are grown along the [111] direction with numerous stacking faults and twins. The vapor-solid (VS) mechanism may be responsible for the growth process of the SiC nanowires.

Structural Characterization of Large Polycyclic Aromatic Hydrocarbons. Part 2: Solvent-Separated Fractions of Coal Tar Pitch and Naphthalene-Derived Pitch

Complex polycyclic aromatic hydrocarbon (PAH) mixtures separated from a coal tar pitch (CP) and naphthalene pitch (NP) by sequential extraction with heptane and toluene were characterized in detail by applying a multiarray analytical approach. Gas chromatography–mass spectrometry (GC-MS), size exclusion chromatography (SEC), laser desorption ionization-time-of-flight mass spectrometry (LDI-TOFMS), and thermogravimetry (TG) were used to relate the volatility and coking yield of pitch components to their solubility and molecular weight distribution. Spectroscopic analysis, including infrared (IR), ultraviolet–visible (UV–vis), and fluorescence spectroscopy, proved to be useful for measuring specific features of aromatic systems, such as the aromatic content, degree of aliphatic substitution, and size distribution of PAHs of different molecular weights. In particular, it has been shown that the spectroscopic analysis is an essential tool for characterizing very large PAH systems concentrated in the pitch tol...

Molecular differences in genotroph forms of common wheat (Triticum aestivum L.) and their initial cultivars

By the modified ISSR-amplification method the comparison of the structural organization of enzyme loci in the initial common wheat cultivars and their genotrophs induced with epimutagens: plant niacin acid and niacin acid and its derivatives produced from β-picoline fraction of coal-tar pitch (niacin acid nitrile, isocinchomeronic and benzoic acids) was carried out. It is shown that niacin acid influence causes in genotrophs specific band appearance in PCR-profiles obtained on the DNA of enzyme loci. All these before mentioned epimutagens induced in limits of each genotroph differently directed changes in number and intensity of bands of PCR-profiles.

Molecular mass ranges of coal tar pitch fractions by mass spectrometry and size‐exclusion chromatography

A coal tar pitch was fractionated by solvent solubility into heptane-solubles, heptane-insoluble/toluene-solubles (asphaltenes), and toluene-insolubles (preasphaltenes). The aim of the work was to compare the mass ranges of the different fractions by several different techniques. Thermogravimetric analysis, size-exclusion chromatography (SEC) and UV-fluorescence spectroscopy showed distinct differences between the three fractions in terms of volatility, molecular size ranges and the aromatic chromophore sizes present. The mass spectrometric methods used were gas chromatography/mass spectrometry (GC/MS), pyrolysis/GC/MS, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) and laser desorption time-of-flight mass spectrometry (LD-TOFMS). The first three techniques gave good mass spectra only for the heptane-soluble fraction. Only LDMS gave signals from the toluene-insolubles, indicating that the molecules were too involatile for GC and too complex to pyrolyze into small molecules during pyrolysis/GC/MS. ESI-FTICRMS gave no signal for toluene-insolubles probably because the fraction was insoluble in the methanol or acetonitrile, water and formic acid mixture used as solvent to the ESI source. LDMS was able to generate ions from each of the fractions. Fractionation of complex samples is necessary to separate smaller molecules to allow the use of higher laser fluences for the larger molecules and suppress the formation of ionized molecular clusters. The upper mass limit of the pitch was determined as between 5000 and 10,000 u. The pitch asphaltenes showed a peak of maximum intensity in the LDMS spectra at around m/z 400, in broad agreement with the estimate from SEC. The mass ranges of the toluene-insoluble fraction found by LDMS and SEC (400-10,000 u with maximum intensity around 2000 u by LDMS and 100-9320 u with maximum intensity around 740 u by SEC) are higher than those for the asphaltene fraction (200-4000 u with maximum intensity around 400 u by LDMS and 100-2680 u with maximum intensity around 286 u by SEC) and greater than values considered appropriate for petroleum asphaltenes (300-1200 u with maximum intensity near 700 u).

03/01727 Structural modification of coal-tar pitch fractions during mild oxidation-relevance to carbonization behavior: Machnikowski, J. et al. Carbon, 2002, 40, (11), 1937–1947

03/01727 Structural modification of coal-tar pitch fractions during mild oxidation-relevance to carbonization behavior: Machnikowski, J. et al. Carbon, 2002, 40, (11), 1937–1947

Structural modification of coal-tar pitch fractions during mild oxidation—relevance to carbonization behavior

Modified pitches with softening points of about 175 °C were prepared by air-blowing at 300 °C of coal-tar pitches from different commercial coke-oven tars. The modifications induced by the mild oxidation were monitored using solvent and extrographic fractionation, elemental analysis, 1H NMR and HPLC. Optical microscopy was used to follow the effect of air-blowing on carbonization behaviour. Low molecular weight cata-condensed PAHs and those with basic nitrogen and hydroxylic functionalities present in extrographic fractions F2 and F4, respectively, are preferentially polymerized pitch constituents. In contrast, peri-condensed PAHs in extrographic fractions F2 and F3, are practically unreactive under the oxidation conditions used. The mild oxidation enhances the tendency of quinoline insoluble (QI) particles to form aggregates in an early stage of thermal treatment, modifying the mode of mesophase development and leading to a non-homogeneous optical texture. The enhanced propensity of QI to aggregation is discussed in terms of structural peculiarities of the parent pitch and possible oxidative polymerization reactions.

Hydrogen-transfer ability of extrographic fractions of coal-tar pitch

Coal-tar pitch was fractionated using extrography into classes of compounds of similar functionality and molecular weight. Hydrogen acceptor and donor abilities of the whole pitch and its extrographic fractions were evaluated by reaction at 360°C with tetralin and anthracene, respectively, and related to structural characteristics by elemental analysis, VPO, 1H NMR and HPLC. Hydrogen acceptor ability (HAA) of the fractions increases markedly with the elution depth. There is a good correlation between HAA and the total oxygen content in the fraction. On the other hand, all extrographic fractions show comparable relatively low hydrogen donor abilities (HDA) in the initial period of reaction with anthracene due to a similar content of hydroaromatic rings and methylene bridges. On further treatment, F2 and F4 are differentiated by a stronger HDA than other fractions. Among the fractions, only in F2 the hydrogen donor ability outweighs over hydrogen acceptor ability. The opposite situation is observed for F5, F6 and F7. In the case of F3 and F4, a comparable amount of hydrogen is transferred from tetralin to fraction and from fraction to anthracene. There is no straight correlation between the observed hydrogen transfer behaviour of fraction and its ability to develop an anisotropic texture in carbonization product. Possible contribution of various fractions to the creation of optical texture of pitch coke is discussed.

Carbonization behavior of coal tar pitch modified with benzoquinone

A soluble fraction of coal tar pitch (CP) in tetrahydrofuran (THF) was reacted with p-benzoquinone (BQ) at 160 and 180°C and followed by carbonization and graphitization. The reaction and carbonization behavior were monitored in-situ by using differential scanning calorimeter, high-temperature 1H NMR and high-temperature ESR. The reactions of CP and BQ resulted in an increase in molecular weight with an increase in BQ concentration. Such molecular weight increases led to the formation of a less ordered structure due to the reduced mobility of the molecules. The relative order of the carbonized materials was determined by using polarized light microscope and X-ray diffraction. The molecular size of the precursor was recognized as an important factor in determining the morphology of carbon materials.

Extraction of Coal Tar Pitch Using a Mixture of Compressed CO2 and Toluene

The removal of low-molecular-weight components from commercial pitches is a critical step in the production of suitable precursors for isotropic carbon fiber formation. A unique extraction process employing a one-phase binary mixture of carbon dioxide and toluene has been developed to remove low-molecular-weight components from coal tar pitch, with an ultimate goal of increasing the softening point of the pitch. The mass fraction of coal tar pitch extracted was determined as a function of extraction temperature (25−75 °C), pressure (8.7−14.9 MPa), and extractive solvent composition (40−70 wt % toluene) using a factorial experimental design. As much as 44 wt % of the coal tar pitch was removed at these extraction conditions, and softening points greater than 250 °C were achieved. The separation is controlled by the temperature and composition of the extractant solvent. This compressed gas/organic solvent extraction process removes low-molecular-weight material from the coal tar pitch using significantly milder solvents and reduced temperatures relative to traditional extractive processes.

98/01014 Composition and structure of fractions of coal-tar pitch as a coking additive for a coal charge: Gladun, T. G. and Gagarin, S. G. Koks Khim., 1997, (1), 26–30. (in Russian)

98/01014 Composition and structure of fractions of coal-tar pitch as a coking additive for a coal charge: Gladun, T. G. and Gagarin, S. G. Koks Khim., 1997, (1), 26–30. (in Russian)

97/00047 Quantitative solid-state 13C n.m.r. measurements on cokes, chars and coal tar pitch fractions

97/00047 Quantitative solid-state 13C n.m.r. measurements on cokes, chars and coal tar pitch fractions

Application of liquid crystal theory to the estimation of mesophase pitch phase-transition behavior

The molecular field treatment developed for analysis of phase equilibria of meson-nonmesogen liquid crystal mixtures was applied to a quantitative description of the phase transition behavior of mesophase pitches, which were prepared by mixing a benzene-soluble fraction with a benzene-insoluble fraction of coal-tar pitch. The result showed that such a simplified theoretical treatment can be used to describe a phase diagram for a mesophase pitch.

Quantitative solid-state 13C n.m.r. measurements on cokes, chars and coal tar pitch fractions

Bloch decay or single pulse excitation (SPE) 13C n.m.r., generally recognized as the best approach to obtain quantitatively reliable aromaticity values and other skeletal parameters for coals, was applied to partly carbonized coal samples, a biomass char and the toluene-insolubles from a coal tar and a corresponding pitch. As found previously for coals, the aromaticities and non-protonated carbon concentrations were generally higher than those estimated by cross-polarization (CP). Furthermore, in terms of accumulation times, the shorter 13C T 1's of low-temperature chars makes SPE a more efficient technique than for coals. The higher concentrations of paramagnetic centres responsible for the shorter 13C T 1's still result in observability of 75% of the carbon in the chars by the SPE technique. The H C ratios derived from the SPE measurements agree well with those obtained from elemental analysis.

96/03773 Characterization of large molecular mass materials in coal tar pitch fractions separated by planar chromatrography

96/03773 Characterization of large molecular mass materials in coal tar pitch fractions separated by planar chromatrography

Fluorescence spectroscopic analysis of benzo[ a]pyrene in coal tar and related products

Direct quantitative fluorescence spectroscopic analysis of benzo[ a]pyrene in coal tar, without sample fractionation, was shown to be valid by analysis of a standard reference coal tar (with certified concentrations for 12 polycyclic aromatic hydrocarbons) and a mixture of 16 polycyclic aromatic hydrocarbons of known concentration. This simple and rapid method was applied to the analysis of benzo[ a]pyrene in coal-tar pitch, a coal-tar-derived heavy residual oil, coal-tar pitch fractions and the volatiles from heat treatment of pitch (both coal-tar and petroleum). However, high values were obtained for the analysis of perylene in the same samples due to the presence of benzo- and dibenzoperylenes with similar spectra to perylene.

Matrix-assisted Laser Desorption/Ionization Mass Spectrometry of Pitch Fractions Separated by Planar Chromatography

Molecular mass distributions of coal-tar pitch fractions separated by planar chromatography (P-C) have been compared by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, carried out in the absence of added matrix. Solvent pairs used in the P-C separation were pyridine–acetonitrile, pyridine–N,N-dimethylformamide and tetrahydrofuran–toluene. Molecular complexity and average molecular masses were found to increase with decreasing mobilities of the fractions. UV-fluorescence spectroscopy showed shifts of peak intensities to longer wavelengths and decreasing quantum yields, suggesting the presence of progressively greater concentrations of large polynuclear aromatic systems with decreasing mobility of samples in P-C. Fractions immobile in pyridine gave MALDI mass spectra of low intensity, indicating that larger molecules are less easily desorbed or ionized. The observed similarity of upper-mass limits of planar-chromatographic fractions of different mobility is thought to suggest the presence of relatively large-molecular mass (MM) materials of variable polarity in coal-tar pitch. The results were consistent with earlier investigations showing the presence of high molecular mass materials in coal-derived liquids. MM-distributions determined by size exclusion chromatography (SEC) were also observed to increase with decreasing mobility of the fractions on P-C plates. This qualitative agreement with results from MALDI-MS indicates that reported shifts of polar molecules to shorter elution times in SEC (i.e. to apparently larger-MMs) were not of a sufficient magnitude to distort the relative ordering of MM-distributions of PC-fractions observed by SEC. A number of problems relating to the refinement of MALDI-MS determinations on complex mixtures are discussed.

95/03584 Structure characterization of coal-tar pitch fractions

95/03584 Structure characterization of coal-tar pitch fractions