Toshiyuki Obara

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.

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.

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.

Carbonization behaviour of pitch in the presence of inert material

The influence of silica gel (< 45 μm) as an inert additive on the carbonization reactions of A240 pitch was investigated by optical microscopy, measurements of transferable hydrogen, high-temperature e.s.r. and high-temperature 1H n.m.r. Additions of silica gel have the effect of reducing the size of the optical texture of mesophase which appears in the early stages of carbonization. The higher the concentration of silica gel, the smaller is the amount of transferable hydrogen. The spin concentration of pitch increases with increasing silica gel content. Measured values of ΔH12, using high-temperature 1H n.m.r., suggest that the molecular motions in the pitch become restricted on addition of silica gel. The effect of silica gel on the physical properties and chemical reactivity of carbonizing pitch is discussed.

In-situ monitoring of hydrogen transfer in carbonization reaction by well resolved high-temperature 1H NMR

Abstract By means of a well resolved high-temperature 1H NMR technique, the carbonization process of acenaphthylene as well as the hydrogen transfer from some model compounds and decant oil to anthracene and/or acenaphthylene have been studied. The hydrogen transfer reaction was found to take place in the liquid phase at temperatures above 630 K for the decant oil/anthracene system.

Chemical structure and kinetic properties of hydroaromatic compounds

The precise co-ordinates of alicyclic compounds have been determined by means of the force field method. Using the co-ordinates thus obtained, the binding energy of the compounds and their radicals were calculated from approximate theory by the INDO method and were correlated to the ease of their dehydrogenation. The order of ease of dehydrogenation is decalin < tetralin < 1,2-dihydronaphthalene < 1,4-dihydronaphthalene. The variation of hydrogen evolution with temperature for the compounds above described was measured by using g.l.c. and the results were analysed kinetically. The rate at decomposition of these compounds showed a similar trend to that of thermochemical binding energy.

CHARACTERIZATION OF SELENIUM CATALYST FOR COAL LIQUEFACTION IN TERMS OF HYDROGENATION AND CRACKING ABILITY

ABSTRACT The activities of selenium and zinc chloride catalysts upon transferable hydrogen in coal have been investigated by IH-NMR. Se is more active than ZnCl2 for hydrogen transfer in the coal/anthracene system. The change of radical concentration was monitored by high temperature ESR. It was confirmed that radical concentration in the coal/Se system is greater than that in the coal/ZnCl2 system at the early stage of pyrolysis. It was concluded that Se has a higher cracking activity as well as hydrogen transfer ability and there is the potential for the use of Se as a catalyst for coal liquefaction.

Stability test of SRC II distillates by ESR

The stability of distillates derived from the SRC II coal liquefaction process has been investigated by means of electron spin resonance (E.S.R.). The samples were prepared by storing at room temperature for 8 days in air or in vacuo. The lighter fraction of distillate deteriorated more easily via oxidation than the heavier fraction.

Effect of H2S on hydrodenitrogenation of SRC-II heavy distillate.

Hydrotreatment of SRC-II heavy distillate was investigated over presulfided CoMo/Al2O3 catalyst at 390°C, 10MPa both in H2 flow and in 5%H2S/H2 flow. Elemental analysis, 1H-NMR, FT-IR and column chromatography were used for characterization of pro-duct oils. It was observed that hydrotreatment over presulfided catalyst decreased both nitrogen and sulfur contents. It was also found that gas phase addition of H2S promoted HDN reaction and inhibited HDS reaction. In order to clarify the promoting effect of H2S on HDN reaction, product oils were separated into base components by column chromatography and investigated in detail. Hydrotreatment in H2S/H2 flow removed 80% of base component of reactant. Compar-ing with the reaction in H2 flow, removal of strong base was especially promoted in the presence of H2S/H2 and removal of very weak base was conversely inhibited. 1H-NMR results of strong base component showed that hydrogen aromaticity of feed markedly decreased in H2 S/H2 flow but no difference was observed between Ha in H2 flow and that in H2S/H2 flow. Pro-moting effect of H2S on HDN reaction was thus ascribed to a improvement of catalytic cracking ability for C-N bond.

Carbonization of hydrogenated ethylene tar pitch; study of the pitch molecular compactness factor and coke optical texture

Compactness factors of aromatic molecules in hydrogenated ethylene tar pitch were calculated as a parameter to relate to properties of mesophase of the carbonization system. Compactness factors, φ, derived from structural analyses of hydrogenated ethylene tar pitch were also related to the size and shape of optical textures of resultant cokes. Hydrogenated ethylene tar pitches having values of φ 〉 0.5 gave cokes with flow type anisotropy and relate to formation of peri-condensed structures. The spin-lattice relaxation times, T1, for the cokes derived from hydrogenated ethylene tar pitch, are related to their optical texture.