Carbonization of coals into anisotropic cokes: 7. Copreheat-treatment under short contact-time conditions at high temperature

The copreheat-treatment of non-fusible and slightly fusible coals with A240 and hydrogenated A240 under high temperature-short contact-time conditions around 500 °C has been examined in an attempt to produce a formed coke with better anisotropic development. These conditions shortened the copreheat-treatment time and provided better anisotropic development in the resultant coke after carbonization. Effectiveness of short contact-time has been discussed in terms of the extent of depolymerization of coal molecules suitable for anisotropic development, this being related to coal liquefaction under similar conditions.     

Modification of mesophase pitch by blending Part 2 Modification of mesophase pitch fibre precursor with thermoresisting polyphenyleneoxide (PPO)

Polyphenyleneoxide was blended in amounts of 5 or 10 wt% into petroleum-derived mesophase pitch to reinforce the pitch fibre before the oxidative stabilization to achieve better handling properties. Although polyphenyleneoxide was fusible but hardly soluble in the mesophase pitch even at a spinning temperature of 350° C, blended pitch could be smoothly spun into pitch fibre 10m diameter, as could the parent pitch. Fibrous polyphenyleneoxide of less than 1m diameter was homogeneously dispersed in the pitch fibre, being arranged along the fibre axis. Such fibrous polyp henyleneoxide reinforced the pitch fibre considerably. The fibrous substances at the centre of the fibre disappeared in the carbonized fibre at 1300° C after oxidation at 250° C, although some short ones were observed in the skin region of the fibre, suggesting that polyphenyleneoxide was co-carbonized to be assimilated with mesophase pitch at the centre of the fibre, where the effects of oxidation may be rather limited. The oxidation reactivity and its mechanical strength after carbonization were slightly lower in comparison with those of the parent mesophase pitch.     

Carbonization of coals to produce anisotropic cokes. 1. Modifying activities of some additives in the co-carbonization of low-rank coals

Using low-rank coals, the modifying activities of some petroleum, coal tar and aromatic hydrocarbon additives have been examined to find procedures for their utilization in the preparation of blast furnace coke. Petroleum pitch, especially after hydrogenation, exhibited excellent modifying activity even with non-fusible coals. In contrast, the activity of coal tar was very limited with such coals. The napththenic component, revealed by n.m.r. of the additives, appears to be important in the co-carbonization by inducing fusibility and anisotropic development in such coals. Co-carbonization to recover the dehydrogenated additives was attempted. However, there was no development of the anisotropy in the resultant coke by dissolution of the coal particles although the coal particles were firmly fixed in the matrix. Acid-refluxing treatment of non-fusible coals was found to enhance their modification susceptibility, indicating that some of the acid-soluble mineral matter is important in the thermal depolymerization or fusion process of the coal.     

Aspects of gasification and structure in cokes from coals

Cokes were prepared from nine coals of different rank and characterized by surface area measurement, reactivity to carbon dioxide at 1473K and Raman-laser spectroscopy. Rates of gasification of cokes on a unit surlface area basis (K¹ = g m^?2 min^?1) decreased with increasing rank of parent coal based on maximum oil reflectances. However rates of gasification could not be related to coke structure as measured by Raman-laser spectroscopy.     

Liquefaction of subbituminous coals under apparently non-hydrogenative conditions

Reactivities of several coals of different ranks have been examined in degrading extractions with aromatic solvents under apparently non-hydrogenative reaction conditions. Pyrene and A240 pitch liquefied the fusible coals in high yields and the slightly-fusible coals in moderate yields, indicating the importance of fusibility in such liquefaction processes. A240-LS pitch is a powerful solvent for slightly-fusible coals. Considerable amounts of pyridine- or THF-soluble fractions were produced especially with A240-LS pitch. A240 pitch is a better solvent than pyrene for some slightly-fusible coals. However, the extent of depolymerization of liquefied coal, pyridine- or THF-solubility, was definitely inferior. Yields of such fractions are higher for lower-rank coals. The mechanism of coal liquefaction under apparently non-hydrogenative conditions is discussed with emphasis on the stabilization of thermal fragments derived from the coal.     

Modifying ability of Ql-free coal-tar pitch to develop optical anisotropy in co-carbonizations

Carbonization properties of a Ql-free coal-tar pitch (CTP-ASM) prepared by selective precipitation were studied to evaluate it as a source for needle-coke. Its modifying ability for production of needlecoke in co-carbonizations with principal carbonizing substances which gave cokes of mozaic texture in single carbonizations was estimated by changing mixing ratios. The shape and size of the anisotropic optical texture in the co-carbonized coke were measured by point counting. CTP-ASM and Ashland A240, of eight additives, had the highest modifying ability in the co-carbonizations with Khafji vacuum residue. Both contained ca. 6% benzene-insolubles (Bl), and had f_a values of ≈0.9. Other additives of either lower or higher Bl or f_a showed less modifying ability. The modifying susceptibility of principal carbonizing substances varies with their structure and properties. Based on a systematic investigation of co-carbonizations the compatibility between a principal carbonizing substance and an additive is discussed from a viewpoint of their structural parameters.     

Reactivities of Blair Athol and Nang Tong coals in relation to their behavior in PFBC boiler

The combustion reactivities of Blair Athol (BA) and Nang Tong (NT) coals were measured by thermogravimetry to understand their different behaviors in the PFBC boiler. The reactivity of BA was much the same as that of NT coal but their chars showed different characteristics. BA char of higher surface area (25 m²/g) showed slightly higher reactivity than that of NT char of smaller surface area (7 m²/g). BA coal showed heterogeneous ignition even at its particle size of as large as +355 μm while NT coal showed homogeneous ignition at the average particle size over 75 μm heterogenous one occurring with finer particle size (−75 μm). Higher calorific value of BA volatile matter and higher reactivity of its char than those of NT coal causes of its heterogeneous ignition with an intense DTA peak, which may lead to local heating at its combustion and to yield reactive CaO from limestones causing of bed materials agglomeration in the PFBC.     

Interaction among fractions in mesophase pitches derived from AlCl3-modified ethylene tar

The anisotropic development is studied of mesophase pitches prepared from modified ethylene tar (ETP) using AlCl₃, of fractions separated by benzene, tetrahydrofuran (THF) and pyridine, and of mixed fractions, to find structural factors affecting fusibility and optical anisotropy of mesophase pitch. Annealing was carried out at 360° C for 10 min. Each fraction developed a unique optical anisotropy quite different from that of the parent mesophase pitch. The lightest fraction (soluble in benzene) was highly fusible with small numbers of small anisotropic spheres. The heaviest fraction (insoluble in pyridine) was infusible and exhibited a total mosaic anisotropy. In contrast, mixed fractions behaved like the parent mesophase pitch in terms of liquid crystal behaviour. The extent of anisotropy and fusibility after annealing were strongly dependent on the preparatory conditions of the parent mesophase pitch. The fusibility of mixed fractions is ascribed to the dissolving ability of the fusible fraction and the solubility of the infusible fraction at the annealing temperature. Small molecules in the lighter fractions also contribute to anisotropy when they are located in interlayer positions between the larger aromatic molecules which constitute liquid crystals. Such co-operative properties of constituent molecules of the mesophase pitch can be described in terms of a practical compatibility.