Yuzo Sanada

Optical mesophase texture and X-ray diffraction pattern of the early-stage carbonization of pitches

Abstract Low temperature carbonization of pitches was studied with polarized-light microscopic method, X-ray diffraction, solvent extraction and density measurements. The nucleation and growth of spherical bodies occur progressively with increase of residence time at a fixed temperature, until the spherical bodies eventually coalesce with each other. Fine irregular particles of insolubles in coal-tar pitch are observed in the region of boundary between spherules and matrix. They play an important role in the mesophase transformation. The typical changes of stacking height of lamellae, interlamellar spacing, weight loss, density and insolubility with residence time show nearly the same tendency at the various temperatures from 390° to 430°C. The time-temperature superposition has been successfully employed. In the master curve for coal-tar pitch reduced at 410°C, the reduced time scale extends from 10−2 to 102 hr. From the relation between the reducing factor of time translation and absolute temperature, the apparent activation energies can be estimated over the range of 35–45 kcal/mole. It seems probable that a model of the rearrangement of C—C bonding together with vaporization of low molecular substances is applicable for the growth of spherical bodies.

Changes of pleochroism and extinction contours in carbonaceous mesophase

Abstract Reflected polarized-light micrography using crossed polarizers with a gypsum plate has been employed to investigate the microstructure of carbonaceous mesophase formed at the early stage carbonization of pitches. It follows from the changes in pleochroism and in isogyres occurring with the stage rotation, that a simple mesophase spherule is optically a uniaxial positive liquid crystal belonging to the hexagonal system with a straight extinction. Observations of changes in pleochroism and in extinction contours for coalesced and for deformed mesophases, permit to distinguish crosses from nodes and by that to identify four types of linear defects in the stacking of the aromatic layer planes. It is explained schematically how the cross and nodal structures are formed in the coalescence of two simple spherules and in the deformation of such coalesced mesophase.

Surface modification and characterization of carbon black with oxygen plasma

Abstract The surface of carbon black was modified with an oxygen plasma treatment. The initial increase and following reduction of carbon black weight due to the treatment were observed as the treatment time increased. The chemical structure of carbon black surfaces formed by the oxidation process has been characterized by X-ray photoelectron spectroscopy (XPS). The XPS O C atomic ratio of the surfaces showed a plateau after an initial increase and saturated at about 0.42 after 120 minutes regardless of the plasma input power. The introduction rate of oxygen-containing functional groups onto the carbon black surfaces increased by increasing the plasma input power. The oxygen plasma was found to cause changes in surface CO or OCO and OCO functionalities, and their concentrations were proved to increase with the treatment time up to about 120 minutes irrespective of the input power.

Nuclear magnetic relaxation studies of coal

Abstract The techniques of both pulsed nuclear magnetic resonance (n.m.r.) and electron spin resonance (e.s.r.) were applied to clarify the nature of coal. The spin-lattice relaxation time (T1n) and the spin-spin relaxation time (T2n) for protons were measured. At room temperature T1n varies with rank of coal and shows a maximum value at about 86% carbon of coal. The values of T1n for the samples selected increase in the order of extraction residue, parent coal and pyridine extract respectively. The variation of T1n during solvent treatment reflects the different circumstances of protons in such a heterogeneous system as coal. From spin-spin relaxation time (T2n) measurements two relaxation regions, that is an immobile region and a relatively free one, are deduced.

Effect of low-temperature oxidation of coal on hydrogen-transfer capability

Abstract Coal oxidation with molecular oxygen at low temperatures is a process that can lead to spontaneous combustion. In this study, four Colombian coals were oxidized in a stove at temperatures between 30 and 150°C. The oxidized samples were heat-treated in an autoclave under nitrogen pressure at 420°C in the presence of anthracene. The main hydrogenated product was 9,10-dihydroanthracene. The amount of hydrogen transferred to the aromatic solvent was drastically reduced by oxidation of the sample and this varies with the coal rank. Fourier transform infra-red analysis, solvent swelling and coal conversion to soluble products in tetrahydrofuran were carried out for all of the samples. The mechanism by which coal reacts with molecular oxygen is strongly dependent on temperature. The initial stage of coal oxidation was apparently the same for all coals studied, i.e. the attack by molecular oxygen on the hydrogen in the α position. However, the path followed thereafter depends on the chemical functionality to which the α CH 2 group is attached. In this way it is possible to differentiate the products from low- and high-rank coals.

Air-blowing reactions of pitch: I. Oxidation of aromatic hydrocarbons

Abstract In order to deepen our understanding of the air-blowing reaction of pitch as a precursor of carbon fiber, aromatic hydrocarbons having 2 to 3 rings were selected as pitch models, and structural analyses of their air-blown products were conducted using FD-MS, GC-MS, NMR, and FT-IR spectroscopies. Alkyl-substituted aromatic compounds polymerized with methylene, biphenyl-type, and ether bonding, leading the methylene to partially change into carbonyl during the air-blowing reaction. Therefore, the pitches containing alkyl-substituted compounds are the most effective source materials for raising the softening point, increasing molecular weight, and suppressing anisotropic texture. The properties of the air-blown products were characterized by, and dependent mainly upon, the crosslinked carbon and the condensed aromatic carbon formed by the air-blowing reaction.

Combination of 13C- and 1H-n.m.r. spectroscopy for structural analyses of neutral, acidic and basic heteroatom compounds in products from coal hydrogenation

Abstract Polar compounds consisting of acidic, basic and neutral nonhydrocarbons were separated from the oil portion derived from coal hydrogenation by means of liquid chromatography. These polar compounds comprised a substantial amount of the oil portion, up to ≈ 60 wt%. Acidic and basic compounds were extracted subsequently by chemical methods, leaving the neutral nonhydrocarbons. The neutral nonhydrocarbons were derived further into eight subfractions, Fr-PP n -1 to-8, using gel permeation chromatography. The fractions were analysed quantitatively using 13 C- and 1 H-n.m.r.. Information on the distribution of functional groups containing heteroatoms, especially oxygen, which were present as phenolic, phenylether or heteroaromatic rings, was provided indirectly by 13 C-n.m.r. spectra, utilizing the chemical shift of the carbon which can be distinguished by an adjacent oxygen. Simultaneous application of 13 C-n.m.r. with 1 H-n.m.r. reduced considerably the number of assumptions required for estimating the average molecular structure of polar compounds.

Analysis of a coal-derived liquid using highpressure liquid chromatography and synchronous fluorescence spectrometry

Abstract Synchronous fluorescence spectra of model polycondensed aromatic hydrocarbon molecules were recorded and used to identify the number of condensed rings in the aromatic molecules. A coal-derived liquid from Yubarishinko coal was initially separated into fractions having different number of condensed aromatic rings, and each fraction was further divided into narrow fractions having different numbers of carbon atoms. These fractions were studied using synchronous fluorescence spectroscopy. Results indicate the potential usefulness of synchronous fluorescence spectroscopy as a method of analysis of complex mixtures as coal-derived liquids despite the limitation of the method that some molecules give only weak peaks. Several components in some fractions were identified by a combination of synchronous fluorescence spectra and conventional excitation and emission fluorescence spectra.

High temperature 1H-NMR study of coal and pitch at the early stages of carbonization

Abstract The temperature dependence of the 1 H-NMR absorption in coals and pitches have been obtained using a pulsed Fourier transform NMR spectrometer with a high temperature probe. The samples as received were heated in the high temperature probe and NMR spectra were obtained simultaneously. With increasing temperature, the value of the line width at half-height (ΔH 1/2 ) of a brown coal decreases and then increases rapidly. On the other hand, tar pitch and the γ component of a coal indicate that the values of ΔH 1/2 remain small over a wide temperature range. It is found that there is an excellent relation between the temperature dependence of ΔH 1/2 and the optical texture of the mesophase.

FT-IR ATR spectroscopy of the edge surface of pyrolytic graphite and its surface/PVC interface

The edge surface of pyrolytic graphite (PG) has been oxidized by electrochemical and oxygen plasma treatments. The structure of the oxidized edge surfaces of PG and the interaction between the oxidized surface and poly(vinyl chloride) (PVC) have been studied by means of Fourier transform — infrared attenuated total reflection (FT-IR ATR) spectroscopy. Phenolic hydroxyl groups and functional groups with a carbonyl group are present on the untreated and all oxidized edge surfaces. For all the surfaces, some of the phenolic hydroxyl groups are linked by hydrogen bonds to each other or functional groups with a carbonyl group, part of the carboxyl groups also being linked by hydrogen bonds to each other. Lactone, carboxyl, and quinone structure moieties are formed on the edge surface by the electrochemical treatment. Among the moieties, quinones are mainly introduced to the edge surface by the severe electrochemical treatment. Quinones are not present on the untreated and the plasma-treated edge surfaces. FT-IR ATR spectra provide evidence for the existence of hydrogen bonds between the > C = O groups present on the edge surface and PVC.