Petroleum-derived Pitch Research Articles

In situ characterization of phase transformations in petroleum pitch by high temperature X-ray diffraction

The phase transformation from isotropic to mesophase of a petroleum-derived pitch was monitored by in situ X-ray diffraction at 410 °C. The kinetics of the transformation were characterized by monitoring the growth of a broad peak at 2θ∼24° and could be described by Avrami’s equation. The volatilization of low molecular weight components originally present in the pitch, or produced during the condensation reaction, was assessed by thermal gravimetry analysis, following the same thermal history. Ex situ characterizations of the pitch precursor before and after thermal treatment provided insight into the evolution of the molecular structure associated with mesophase generation (optical polarized microscopy, molecular weight distribution by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, X-ray photoelectron spectroscopy, Auger spectroscopy, and thermal stability). This investigation demonstrates the value of using complementary in situ and ex situ experimental techniques to characterize complex mechanisms during the processing of organic materials.

Impact of spinning conditions on the diameter and tensile properties of mesophase petroleum pitch carbon fibers using design of experiments

The structure of a mesophase pitch carbon fiber evolves in spinning and is perfected through stabilization and carbonization. Thus, it is crucial to control extrusion variables to form standard carbon fibers. Design of experiments was employed in melt spinning to investigate the influence of three process variables on the diameter of petroleum-derived pitch filaments. Optimized conditions were validated in an experiment that produced filaments with average diameter of 14 μm. Pitch filaments with different thickness were thermally treated to verify structure discrepancies and quantify the relation between mechanical properties and fiber’s diameters. Diameters smaller than 45 μm could be stabilized in air. Thinner fibers reached average strength of 1.4 GPa and 150 GPa modulus, thicker fibers only supported 120 MPa with 65 GPa modulus.

Investigation on chemical and structural properties of coal- and petroleum-derived pitches and implications on physico-chemical properties (solubility, softening and coking)

The structural properties and composition of pitches are particularly important for the optimization of pitch processing to high-value products and practical application. Because of their complexity, pitch analysis requires both chemical and spectroscopic tools, as those applied in the present work to coal and petroleum-derived pitch samples. In particular, a large variety of methods, including chromatography, elemental analysis, thermogravimetry, mass spectrometry, UV–Visible and FTIR spectroscopy, was applied for evidencing the different characteristics of commercial solid pitch derived from petroleum and coal. The interrelation among some pitch properties was investigated by analyzing petroleum and coal-derived pitches having different softening points and volatility. It was observed that properties as the softening point and the coking yield are mainly related to the pitch volatility rather than on the pitch source (coal or petroleum), whereas some other features as the solubility and the oxidation reactivity of coke produced appeared correlated with the source characteristics.

Composition and Structural Characterization of the Extractive Pitches as Compared with the Commercial Reference Pitches of Different Origins

The chemical and group composition, the empirical properties and the molecular structural characteristics of the extractive pitches produced by thermal dissolution of three medium-ranked coals were studied in comparison with the reference commercial pitches including typical coal-tar pitch, petroleum-derived pitch and the pitch sample derived from the blended mixture of coal tar with petroleum feedstock. The structural parameters of the average pitch molecules have been compared based on the 1H and 13C NMR spectra. It was shown that, in terms of chemical composition and empirical properties including carcinogen content, the extractive pitches resemble blended pitch sample, the structural parameters being close to commercial coal-tar pitch sample. The average pitch molecule of extractive pitches was composed of predominantly aromatic nuclei with rather pericondensed structure.

Comparative Study of the Properties of the Coal Extractive and Commercial Pitches

Three extractive pitches were produced by using thermal dissolution of the medium-ranked coals at 380 °C in anthracene oil. The empirical properties such as the chemical composition, solubility in quinoline and toluene, softening point, and content of carcinogenic polycyclic hydrocarbons, and also molecular and structural parameters of the extractive pitches were characterized in comparison with three commercially available pitches, including typical coal-tar pitch, petroleum-derived pitch, and blended pitch derived from the mixture of coal tar with petroleum feedstock. The molecular and structural properties of pitches were studied using FTIR, 1H and 13C NMR, and XRD techniques. It was shown that the average molecule of the extractive pitches was composed of predominantly aromatic rarely substituted pericondensed nuclei, such as that in coal-tar pitch. The spatial structures of both the extractive and reference pitches consisted of predominantly disordered carbon matter with a small amount of rather ordered nanosized “graphite-like” stacks. In terms of the technical specifications, the extractive pitches irrespective of the coal used met the requirements for the pitch binder and resembled commercial blended petro-coal-tar pitch. A remarkable merit of the extractive pitches compared to coal-tar pitch was low carcinogenicity (two to three times as low).

Development of Petroleum-Based Carbon Composite Materials Containing Graphite/silicon Particles and Their Application to Lithium Ion Battery Anodes

ABSTRACT: Herein, a novel preparation method of highly homogeneous carbon-silicon composite materials waspresented. In contrast to conventional solvent evaporation method, a milled silicon-graphite or itsoxidized material were directly reacted with petroleum-derived pitch precursor. After thermal reactionunder high pressure, pitch-graphite-silicon composite was prepared. Carbon-graphite-silicon compositewere prepared by an air-oxidization and following carbonization. From energy dispersive spectroscopy,it was observed that small Si particles were highly embedded within carbon, which was confirmedby disappearance of Si peaks in Raman spectra. Furthermore, X-ray diffraction and Raman spectrarevealed that carbon crystallinity decreased when the strongly oxidized silicon-graphite was added,which was probably due to oxygen-induced cross-linking. From the anode application in lithiumion batteries, carbon-graphite-silicon composite anode displayed a high capacity (565 mAh g − 1 ), agood initial efficiency (68%) and an good cyclability (88% retention at 50 cycles), which wereattributed to the high dispersion of Si particles within cabon. In case of the strongly oxidized silicon-graphite addtion, a decrease of reversible capacity was observed due to its low crystallinity.Keywords : Pitch-graphite-Si composite, Petroleum pitch, Anode in lithium ion batteries

Characteristics and carbonization behaviors of coal extracts

N-methyl pyrrolidone (NMP) raw coal extract (EXT), hydrogenated coal extract (HEXT) and the blend of EXT and HEXT in NMP (BLD), from two bituminous coals, were studied. The extracts were carbonized in both tube-bomb and a temperature programmable furnace. Elemental analysis, FTIR spectroscopy and optical microscopy techniques were employed to characterize the extracts and the carbonization residues. It was found that the extracts resembled petroleum-derived pitches in the hydrogen content and (C/H) atomic ratio. Higher oxygen and nitrogen contents differentiated the coal extracts from commercial petroleum pitch. More carbon and hydrogen, and lesser oxygen and sulfur differentiated HEXT from EXT. The ratios of integrated IR band intensity for aromatic and aliphatic CH stretching indicate that the relative content of aliphatic hydrogen in EXT is higher than in HEXT. HEXT contains comparatively more aromatic hydrogen, a feature necessary for thermal stability and fluidity during carbonization. BLD materials are at a place somewhere in between. Kinetic modeling of the aliphatic hydrogen change during carbonization reveals that EXT has high carbonization rate and low apparent activation energy. This can be related to the optical texture size of carbonization residues. The residues made from EXTs exhibited fine mosaic optical texture and limited mesophase development. HEXTs were readily converted into highly anisotropic coke. BLDs produced carbonization residues with intermediate properties. Extracts with similar activation energies produced similar residues in the same coal series. The degree or extent of anisotropy displayed by the carbonization residues was found to be dependent on the relative distribution of aromatic and aliphatic hydrogen.

Effects of hydrogenation of petroleum pitch on mesophase formation

The effects of hydrogenation of petroleum pitch on mesophase formation have been studied in terms of the hydrogen donor (Da) and acceptor (Aa) abilities of starting pitch, the temperature dependence of mesophase content, the thermal properties of the resultant mesophase pitches with differential scanning calorimetry (DSC), and 13C-NMR spectra of the mesophase pitches in the liquid and solid states. Hydrogenation of petroleum-derived pitch causes a significant increase of (Da) and a clear shift of the mesophase generation temperature to the hightemperature side. Measurement of the characteristics of molecular size for mesophase pitches using DSC has been successfully accomplished. The increase of Da due to hydrogenation cause the production of mesophase having a smaller average molecular size and a more homogeneous molecular size distribution. The decrease of molecular size in the mesophase seems to cause the narrowing of the characteristic peak for mesophase around 180 p.p.m. in 13C-NMR spectra in the liquid state.

In-situ monitoring for mesophase formation processes of various pitches by means of high-temperature 13C-NMR

High-temperature heating processes for coal-tar-derived pitch (pitch A), petroleum-derived pitch (pitch B), and hydrogenated petroleum-derived pitch (pitch C) have been studied by in-situ hightemperature 13C-NMR. Mesophase formation processes have been successfully monitored for all three kinds of pitches. The times required for appearance of mesophase in pitches A and B are similar and shorter than that in pitch C at 430°C. Time intervals from mesophase appearance to finishing mesophase transformation in pitches B and C are nearly the same and shorter than that in pitch A at 430°C. There may be a critical region of aliphatic carbon content for mesophase appearance of petroleum-derived pitch. Completion of mesophase development correlates to the line-width of characteristic peak of 180 ppm assigned as carbon in stacked aromatic layer molecules. Aliphatic carbons of molecules in mesophase seem to cause an increase of mesophase mobility and a narrowing of the characteristic peak for mesophase around 180 ppm.

The optical properties of carbonaceous mesophase

The optical constants of carbonaceous mesophase and anisotropic carbons from petroleum-derived pitches have been measured over a wide range of wavelengths and heat-treatment temperatures by interferometry and by reflected and transmitted spectrophotometry. The optical properties differ substantially from those of conventional nematic liquid crystals. The intrinsic birefringence Δn measured by polarized interferometry is only 0.02–0.03 and depends weakly on wavelength; the anisotropy of absorption coefficients is of the order of ~0.1 with k ⊥ = 0.03 and k ⊥ = 0.10 ( at T HT = 450° C) and has strong wavelength dependence with a maximum at 560–590 nm (symbols∥ and ⊥ denote that the electric vector of the incident light lies along the optical axis, or perpendicular to it, respectively). The anisotropy of reflectivities ΔR at normal incidence is of the order of ~0.1 with R ⊥ = 0.13 and R ∥ = 0.04 (at T HT = 450° C); ΔR increases with increasing temperature of heat-treatment. To explain the features of optical properties, a theory of light reflection is developed based on a model of carbonaceous mesophase that consists of graphite-like disc-shaped particles having a nematic-like packing. From the reflectivity values the dimensions and the concentration of these particles have been evaluated. The nature and formation of carbonaceous liquid crystals are discussed.