Tetsuro Yokono

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.

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.

Characterization of carbonization reaction of petroleum residues by means of high-temperature ESR and transferable hydrogen

Abstract An attempt has been made to characterize the carbonization reaction of petroleum residues through measurements of high temperature ESR, hydrogen donor ability and optical texture of resultant cokes. Good correlations were found between hydrogen donor ability and change in spin concentration. Residues forming cokes with large sizes of optical texture have a high ability as a hydrogen donor and show a low spin concentration at high temperatures. Similar results were obtained also for some model compounds. A model for the mechanism of carbonization is proposed on the basis of these observations.

Nuclear magnetic proton relaxation studies of oxidized coals

Coals of NCB rank 301 a (coking), 502 (caking) and 802 (very weakly caking) are oxidized in air at 373 K or 383 K for up to 42 days. Spin-lattice and spin-spin relaxation times, T1 and T2 respectively, of oxidized coals are measured using a Bruker SXP 4–100 and FT spectrometer. Free radical concentrations in the coals are obtained using a JES PE e.s.r. spectrometer. Infrared spectra of oxidized coals are obtained and optical textures of cokes from fresh and oxidized coals are assessed by optical microscopy. For two coking coals, decreasing values of T1, and increasing concentration of free radicals occurred with oxidation at 383 K to 16 and 28 days. Thereupon values of T1, increased and free radical concentrations decreased with further progressive oxidation. At the point of inflexion in properties, resultant cokes from the coals ceased to shown any anisotropy in their optical textures and became isotropic resembling cokes from low-rank coals. For the caking coals, T1 increased at all stages of oxidation to 42 days with decreasing concentrations of free radicals. Two values of T2 were found in each coal corresponding to a rigid and mobile component ((T2)r < (T2)m). The rigid component (T2)r was not affected by oxidation but values of (T2)m decreased with increasing duration of oxidation. It is considered that coking and caking coals exhibit different effects of oxidation with perhaps phenols and quinones in caking coals acting as inhibitors to the growth of stable free radicals. Oxidized coking coal may behave like fresh caking coal.

Studies on the early stage of carbonization of petroleum pitch by means of high-temperature 1H-NMR and ESR

Abstract The early stage of carbonization of petroleum pitches has been studied by in-situ, hightemperature 1 H-NMR and ESR techniques. Well-resolved 1 H-NMR spectra were found to provide detailed information about the mesophase formation in the course of pyrolysis. The process of mesophase generation during cooling was clarified by using an ESR spin probe. The nucleation of mesophase embryos in these processes was clearly observed in the both spectra. It was found that the mesophase transformation occurs at nearly the same level of aromatic hydrogen fraction or spin concentration.

Carbonization behavior of hydrogenated ethylene tar pitch

Abstract Carbonization behavior of ethylene tar pitch has been studied with respect to mesophase formation by means of modification of the chemical composition of the starting materials. The hydrogen treatment of ethylene tar pitch has been carried out over the temperature range from 473 to 673 K under a pressure of 10 MPa without catalyst. Then, the hydrogenated ethylene tar pitches were carbonized at 723 K and the optical texture of the resultant cokes were assesed by optical microscopy. It was revealed that the carbonization of the ethylene tar pitch hydrogenated at 673 K gives a coke of optical texture with enlarged flow-domain. The hydrogen-transfer ability of the ethylene tar pitches during the temperature range of mesophase formation was estimated by the method of 9,10 dihydroanthracene (DHA) formation through co-carbonization of the pitch with anthracene. It was recognized that the larger the amount of conversion of DHA, the better is the development of optical texture.

Aromaticity of coal extract by 1H and 13C pulsed n.m.r. methods

Abstract High-resolution gated decoupling 13 C spectra of soluble materials such as coal extracts have been analysed to evaluate the carbon aromaticity ( f a ). A correlation was found between f a and the reciprocal of the square of the shorter component in spin—spin relaxation time ( T 2 ), which was obtained by pulsed 1 H n.m.r. in the solid state at low temperature. Values of carbon aromaticity for several coals as received were estimated by using the above correlation and compared with those by van Krevelens densimetric method.

Relationships between hydrogen donor abilities and chemical structure of aromatic compounds in terms of coal liquefaction

To obtain fundamental information about hydrogen transfer, the relationships between hydrogen donor ability and chemical structure of model compounds representing donor solvents is studied using gas chromatography,1H n.m.r. and computing calculation methods. The order of the model compounds in terms of the ability as donor solvent to release hydrogen is: decalin < tetralin < 1,2-dihydronaphthalene < < 1,4-dihydronaphthalene. This trend closely correlates with the difference in binding energies of the hydroaromatic compounds and their radicals, determined by intermediate neglect of differential overlap (INDO) calculation. Electron spin resonance spectroscopy (e.s.r.) confirms that radical species are created after heat-treatment of the donor compounds. The ability of model compounds representing coal to accept hydrogen is assessed from a comparison of the1H n.m.r. spectra. It is established that donor and acceptor efficacies are dependent upon chemical structure.

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

Abstract 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 13 C-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.

Development of anisotropic texture in co-carbonization of low rank coal with pitch-evaluation from hydrogen donor and acceptor abilities of coal and pitch

The extent of development of anisotropic texture in cokes prepared from various coals or blended coals in co-carbonization systems was assessed by using the ratio of hydrogen donor ability to acceptor ability. A parameter D/A, corresponding to the amount of hydrogen transfer during carbonization in the system of blended coal and pitch additive has been proposed to give a measure of the aforesaid development of anisotropic texture in resultant cokes. In pitch A/non-caking coal systems, blending the pitch A with coal to a value of D/A − 0.22, D/A − 0.28 and D/A − 0.40 gives mainly fine-granted mosaics, medium-grained mosaics and coarse-grained mosaics, respectively. The Gieseler plastometry and high-temperature 1H-NMR were also used to obtain informations about the mobility of the co-carbonization system. A good relation was found between D/A, and the solidification temperature determined by the Gieseler plastometry. Such an approach based on the concept of D/A parameter provides a guideline for selecting pitch as a modifier for low rank coal carbonization.