Carbonization and liquid-crystal (mesophase) development. 8. The co-carbonization of coals with acenaphthylene and decacyclene

Several coals of different rank have been carbonized singly and also co-carbonized with acenaphthylene and decacyclene. The resultant cokes were mounted in resin and polished surfaces were examined for optical texture using a polarized-light optical microscope fitted with a half-wave retarder plate. The optical texture can be assessed qualitatively (visually) or quantitatively by a point-counting technique in terms of size and shape of constituent isochromatic anisotropic units. Some cokes from coals were Isotropic. Acenaphthylene was only able to exert a smaller influence than decacyclene on the optical texture of the resultant cokes from co-carbonizations. Decacyclene was able to modify the optical texture for both the low-rank non-fusible and the caking coals. The effects of changing the proportions of coal to additive were examined. Results are interpreted in terms of ‘depolymerization’ of the coal by the action of the additive (as solvent) and also by the action of the additive in modifying the processes of formation of semi-coke via nematic liquid crystals.     

Carbonization and liquid-crystal (mesophase) development. Part 4. Carbonization of coal-tar pitches and coals of increasing rank

Coal-tar pitches, from coals of different rank and with various quinoline-insoluble contents, were carbonized under pressure (67 to 200 MN m⁻²) to maximum temperatures of 923 K. The resultant cokes were examined by optical and scanning electron microscopy in terms of size and shape of anisotropic structures within the coke. Natural quinoline-insolubles and carbon blacks both destroyed growth of the mesophase and development of anisotropy. Graphite particles (<10 μm) promoted growth and coalescence of the mesophase. Fourteen coals, of carbon content 77 to 91 wt%, VM 41 to 26%, were similarly carbonized under pressure. In the lower-rank coals no microscopically resolvable anisotropic mesophase was produced, but at a carbon content of 85% anisotropic units 1–2 μm in diameter were detected, increasing in size at a carbon content of 90% to 5 μm diameter. Results are discussed in terms of the origins of anisotropic mosaics observed in cokes, their variation in size with coal rank, and their significance in the carbonization of coal.     

The co-carbonization of oxidized coals with pitches and decacyclene

Coals of rank (NCB) 701, 401 and 204 were oxidized in air at 371 K for up to 15 days. The changes in optical texture of cokes from these coals were monitored by optical microscopy and point counting. The oxidized coals were cocarbonized to 1273 K with up to 30% of A240 petroleum pitch, a hydrogenated coal extract and decacyclene, and the resultant cokes were reassessed. The increase in isotropy in cokes caused by the oxidation treatment was never completely removed by use of the additives, but significant improvements existed for the less extensively oxidized coals. The possibility exists of using co-carbonization of oxidized coals with additives in coke making. Additives with good hydrogen donor ability, as with the coal extract, appear to be the most suitable.     

Structure in cokes from coals of different rank

A range of bituminous coals has been carbonized to 1273 K. Polished surfaces of the solid products, carbons or cokes, are examined for optical texture by optical microscopy. Fracture surfaces of the carbons are examined by scanning electron microscopy (SEM). The carbon from the lowest rank coal (NCB Code No. 702) is isotropic and fracture surfaces are featureless. Carbons from coals of ranks 602, 502 are optically isotropic but fracture surfaces are granular (size 0.1–0.2 μm), indicating small growth units of mesophase. In the carbon/coke from a 401 coal, the anisotropic optical texture and grain size are both ≈0.5–10 μm diameter. Coke from a coking coal (301a, 301b) has a layered structure extending in units of at least 20 μm diameter with sub-structures ~ 1.5 μm within the layers, indicating perhaps that the bedding anisotropy of these coals is not totally lost in the fluid phase of carbonization. The carbons from the higher rank coals have the bedding anisotropy of the parent coal. The combined techniques of optical microscopy and SEM (both before and after etching of the fracture surfaces of coke in chromic acid solution) reveal useful detail of structure in carbons/cokes and of the mechanism of carbonization of coking coals.     

Carbonization and liquid-crystal (mesophase) development. 10. The co-carbonization of coals with solvent-refined coals and coal extracts

Coals (NCB rank 102 to 902) were co-carbonized with solvent-refined coals and coal extracts, mixing ratio of 7:3, to 873 K, heating at 10 K min^?1 with a soak period of 1 h. Resultant cokes were examined in polished section using reflected polarized-light microscopy and optical textures were recorded photographically. These optical textures were compared to assess the ability of the additive pitch to modify both the size and extent of optical texture of resultant cokes. The objective of the study is to provide a fundamental understanding of the use of pitch materials in co-carbonizations of lower-rank coals to make metallurgical coke. A Gulf SRC was able to modify the optical texture of cokes from all coals except the anthracite. Soluble fractions of this Gulf SRC were less effective than the parent SRC. A coal extract (NCB D112) modified coke optical texture, the extent being enhanced as the rank of coal being extracted was increased. Hydrogenation of the coal extract increased the penetration of the pitch into the coal particles but simultaneously reduced the size of the optical texture relative to the non-hydrogenated pitch. This indicates a positive interaction of pitch with coal in the co-carbonization process. The optical texture of the cokes from the hydrogenated coal extract in single carbonizations was larger than that from the non-hydrogenated material. Mechanisms explaining these effects are briefly described.     

Carbonization of coal blends: mesophase formation and coke properties

Laboratory investigations of strength of cokes from blends of coals incorporating pitch were supported by 7 kg trials. The stronger cokes showed a greater interaction between coal and pitch to produce an interface component of anisotropic mozaics which is relatively resistant to crack propagation. The process whereby coal is transformed into coke includes the formation of a fluid zone in which develop nematic liquid crystals and anisotropic carbon which is an essential component of metallurgical coke. Strength, thermal and oxidation resistance of coke can be discussed in terms of the size and shape of the anisotropic carbon which constitutes the optical texture of pore-wall material of coke. Coals of different rank form cokes with different optical textures. Blending procedures of non-caking, caking and coking coals involve the interactions of components of the blend to form mesophase and optical texture. Petroleum pitches used as additives are effective in modifying the carbonization process because of an ability to participate in hydrogen transfer reactions.     

Catalytic graphitization of cokes by indigeneous mineral matter

Indigeneous mineral matter in coals acts catalytically towards graphitization during heat treatment of coals to 2273 K. Nineteen coals of a wide range of rank were demineralized by acid extraction. Original and demineralized coals were carbonized in the range 1073–2273 K, and the resulting cokes examined by optical microscopy, X-ray diffraction and phase-contrast high resolution electron microscopy. Optical microscopy indicated the extent of formation of anisotropic carbon in the resultant cokes. The (002) X-ray diffraction profiles indicated three types of catalytic effect, for which electron microscopy demonstrated different crystallite structures and interrelations. The importance of catalytic graphitization in metallurgical cokes in relation to their strength and reactivity is discussed.     

Carbonization and liquid-crystal (mesophase) development. 12. Mechanisms of the co-carbonization of coals with organic additives

In industrial situations, coals interact with solvents or additives to produce liquid fuels, solvent-refined coal, coal extract and metallurgical coke. In these processes there occurs a wide variation in effects or modifications of the coal by these additives. This paper describes the modifications which can occur, using a wide range of rank of coal, when these coals interact and are co-carbonized with a wide range of additives of different chemical properties. The optical texture of the resultant cokes is given special attention. The objective of the paper is to summarize the current state of knowledge of the mechanisms of these interactions. Possible mechanisms of interactions are summarized, kinetic and chemical structural aspects of reactions are outlined, the importance is mentioned of the formation of liquid phases enabling anisotropic optical textures in modified cokes to be created, and the industrial relevance of its possible development is discussed.     

Co-carbonization of hard coals and coal extracts 1. The co-carbonization of low rank coals with extracts

Studies on the influence of an additive derived from coal on the coking properties of lower-rank coals and on the structure of cokes obtained from blends have been undertaken in our laboratory since 1978. The two coal extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The results indicate that the blends prepared from low-rank coals — flame coal (Int. Class. 900), gas-flame coal (Int. Class. 721) and the extracts possess better coking properties in comparison to the parent coals. The optical texture and the degree of structure ordering of the cokes obtained from blends is related to the amount of extract in the blend. With increasing extract content in the blend, increases were observed in the amount of optically anisotropic areas in cokes from low-rank coal/extract blends and the crystallite height (L_c) of cokes from the blends. The isotropic optical texture of cokes from low-rank coals can be modified by coal extracts to an anisotropic optical texture. The non-fusible coal is the most difficult to modify. An explanation of the observed phenomena is given.     

Carbonization and liquid—crystal (mesophase) development. 19. Co-carbonization of oxidized coals with model organic compounds

This study examines further the phenomena of the modification of coal carbonizations by organic additives. Anthracene, pyrene and chrysene modify the carbonization in a closed system of coking coals as observed from increases in the size of optical textures of resultant cokes. Weakly caking coals are unaffected. Chrysene is the most efficient modifier probably because of its lowest calculated free valence. The co-additives tetralin and hydrogenated anthracene oil further enhance the modification processes so obviating the necessity to use hydrogenated additives. Co-carbonizations of oxidized coking and caking coals with decacyclene are effective in removing the effects of mild oxidation. Increased rates of carbonization enhance the sizes of optical textures of resultant cokes.     

Carbonization and liquid-crystal (mesophase) development. 11. The co-carbonization of low-rank coals with modified petroleum pitches

Coals of rank ranging from medium quality coking to non-caking, non-fusible, have been co-carbonized with Ashland petroleum pitches A170, A240 and A200 as well as pitches modified by heat-treatment with aluminium chloride using A170, and by reductive hydrogenation of the A200. The mixing ratio was 7:3, the final HTT was 873 K, heating at 10 K min^?1 with a soak time of 1 h. The optical texture of the resultant cokes is assessed using polished surfaces and a polarized-light microscope using reflected light and a half-wave plate. The changes in optical texture are studied from the point of view of using coals of low rank in the making of metallurgical coke. The optical texture of resultant cokes is modified by co-carbonization and the mechanism involves a solution or solvolysis of the non-fusible coals followed by the formation of nematic liquid crystals and mesophase in the resultant plastic phase. The modified A170 pitch is more effective in modifying optical texture than the A170 because of an increase in molecular weight. The hydrogenated A200 is a very reactive additive probably because of an increased concentration of naphthenic hydrogen. The hydrogenated A200 can modify the optical texture of cokes from the organic inerts of coals and from oxidized, non-fusible coals.     

Structure of cokes from coking coal vitrites

The coking process of vitrites and thermobitumens separated from vitrites was examined; structural X-ray and microscopic examinations of the cokes obtained were carried out. A correlation between reflectance distribution of vitrites and microscopic structure of their cokes was found.An increase in the structural ordering of the cokes from vitrites, passing from cokes of gas coal to cokes of orthocoking coals, is observed. It is accompanied by an increase of the optical anisotropy of the resultant cokes; this anisotropy first appears in coke from gas-coaking coal.The cokes from the thermobitumens are lower ordered than the cokes from parent vitrites but all these cokes are partially or entirely optically anisotropic.Total removal of the thermobitumens from coals deprives the cokes from the residues after the extraction of any optical anisotropy.     

Structure of the cokes obtained from the group components separated from coking coal vitrites by selective thermosolvolysis

The examination of the structure of cokes obtained from extracts separated from preheated vitrites of coking coals by progressive and continuous extraction with chloroform was carried out. The structural ordering (interplanar spacing and crystallite dimensions) of the cokes depends on the rank of the parent vitrites but it does not depend on the degree of extraction. The occurrence of optical anisotropy in cokes from the extracts is connected with both the rank of the parent vitrite and the degree of extraction. In the formation of the optical anisotropic structure during the carbonization of coking coal vitrites, the part of the extract which is of small size, which partially undergoes decomposition, is an important factor.     

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.     

Development of optical anisotropy in vitrains during carbonization

The purpose of this work was to examine the possible significance in the formation of metallurgical coke of the anisotropic spherical mesophase exemplified by that found during the carbonization of pitch-like materials, and to ascertain if the various types of optical anisotropy found in coke could form a basis for the characterization of cokes produced from different coals. Vitrains from a wide range of coals were carbonized at temperatures from 370 to 1000 °C and the types and amounts of optical anisotropy in the resulting semi-cokes and cokes were determined from microscopic examination, the anisotropic components being classified according to grain size of the granular mosaics and appearance. The anisotropy developed directly from the isotropic phase, appearing initially as a fine-grained mosaic. With increasing carbonization temperature, this fine-grained mosaic was transformed into progressively coarser-grained anisotropy, the extent of this transformation depending on the rank of the vitrain. It is therefore concluded that the formation, growth and coalescence of anisotropic spherical bodies, such as occurs during the carbonization of pitch, is not a necessary precursor of the mosaic anisotropy in coke. The type and amount of anisotropy developed provide a quantitative means of characterising different cokes.     

Co-carbonization of hard coals and coal extracts 2. The co-carbonization of medium- and high-rank coals with extracts

Studies on the influence of anthracene coal extracts on the carbonization process of medium- and high-rank coals were undertaken. Extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The blends prepared from the examined coals and the extracts exhibited better coking properties than the parent coals. The addition of extract to the coals gave an increase in the microstrength of the resultant cokes. The effects of co-carbonization of coking coals with extracts were increases in the size of the optical texture as well as in the degree of structural ordering of cokes. In the co-carbonization of semicoking coal with addition of coal extracts, a reduction in the size of the anisotropic units and a decrease in the crystallite height of cokes were observed. No modification of the basic anisotropy of coke from anthracite by coal extract was observed. With increasing extract content in anthracite/extract blends there was an increase in the degree of structural ordering of co-carbonization products. Extract addition was unable to modify the behaviour of fusinite. Based on the results of investigation of the influence of coal extracts on the carbonization of different-rank coals, a division of coals according to the modification of the optical texture of coke is given.     

Carbonization and liquid-crystal (mesophase) development. Part 3. Co-carbonization of aromatic and heterocyclic compounds containing oxygen, nitrogen and sulphur

A detailed investigation is reported of the effects upon size and shape of anisotropic mesophase structures in resultant semi-cokes of co-carbonizing eighteen oxygen-, nitrogen- or sulphur-containing compounds with fluorene, carbazole and acenaphthylene. Carbonizations were carried out under pressures of 130 to 320 MN m⁻² to a maximum heat-treatment temperature of 873 K, the mesophases being examined by optical and scanning electron microscopy. Additions of phthalimide, phthalic anhydride or pyromellitic dianhydride to fluorene and carbazole caused development of anisotropic carbon where none was formed on carbonization of the single compounds, or enhanced existing mesophase growth processes. Improvements in mesophase growth result in improved graphitizability of the semi-coke. Of the oxygen-containing compounds, the polycyclics with quinone groupings, or monocyclic molecules with several functional oxygen groupings, assist the growth of anisotropy. Phenol severely retards mesophase growth. Reasons are advanced which incorporate mechanisms of liquid-crystal formation. The implication for coal carbonization is that as the oxygen content in coals, on coalification, becomes increasingly attached to aromatic systems, then the oxygen in prime coking coals may actually enhance the growth of the mesophase during its carbonization. Nitrogen- and sulphur-containing compounds on co-carbonization with acenaphthylene at nitrogen or sulphur contents greater than 3% by weight may cause deterioration of mesophase growth. Such compounds do not significantly affect the carbonization of prime coking coals, but may contribute to the smallness of anisotropic structures in the carbons from coals of lower rank.     

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.     

Temperature-dependence of propagation velocity of ultrasonic wave in coals

To study the characteristics of the change of rheological properties of coals on heating, the propagation velocity of an ultrasonic wave of 100 KHz was determined for 27 coals of different rank (C, 71.2–94.5%) in the temperature range 77–523 K. It was difficult to establish a clear relationship between absolute values of the velocity and rank of coals, but the temperature-dependence of the velocity appears to be a function of the carbon content of the coals, similar to the well-known correlation between hardness and rank of coals. The change of propagation velocity in 17 coals was determined continuously while the coals were heated from room temperature up to 673 K at 0.5 Kmin⁻¹. At temperatures below 523 K the velocity decreased almost linearly with increasing temperature; however it was observed that the velocity suddenly decreased at a certain temperature above 523 K, which was specific for each individual coal. This specific temperature was found for both caking coals and non-caking coals and was significantly lower than the initial softening temperature detectable by the conventional plastometer or dilatometer.     

水煤浆气化原料的成浆性研究

在实验室条件下研究了从低煤化度烟煤到高煤化度无烟煤,以及石油焦等不同气化原料煤的成浆性.为提高低煤化度烟煤的成浆浓度,在保证其混合原料灰熔融特征温度满足液态排渣前提下,将低煤化度烟煤与一种或两种煤化度较高的煤或者石油焦配比,考察了它们的成浆性.结果表明,煤化度适中的QD煤单独制浆浓度达到70%,黏度536mPa.s,流动性为A;通过不同煤种的级配,三种原料配合的料浆浓度为62%时,黏度在340mPa.s～550mPa.s之间,可以获得符合液态排渣气化要求的混合料水煤浆,扩大了气化原料来源.