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. 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.     

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.     

Carbonization and liquid-crystal (mesophase) development. 17. Co-carbonization of a solvent-refined coal with petroleum pitches and hydrogenated coal-extract solution

This study characterizes the optical textures of cokes prepared by the carbonization of Ashland petroleum pitches, of non-hydrogenated and hydrogenated coal-extract solutions (CES) and of blends of non-hydrogenated CES materials with the petroleum pitches and hydrogenated CES materials. At an HTT of 823 K petroleum pitches produce cokes with large sized optical texture of flow-type anisotropy characteristic of needle-cokes. The non-hydrogenated CES materials produce cokes with optical textures of mozaics, 2–10 μm. However, following hydrogenation the CES materials carbonized to cokes all of which possess considerable large sized optical textures which for some materials resemble that of needle-cokes by possessing strong flow-type anisotropy, > 100 μm. Hydrogenation of the CES materials evidently facilitates the physical and chemical requirements for growth and coalescence of lamellar nematic liquid-crystals and mesophase from the fluid phase of carbonization leading to anisotropic carbon. Co-carbonizations of the non-hydrogenated and hydrogenated CES materials exhibit the dominant partner effect and are comparable in behaviour with Ashland petroleum pitches which are known to produce needle-cokes on carbonization.     

Carbonization and liquid-crystal (mesophase) development. 9. The co-carbonization of vitrains with Ashland A200 petroleum pitch

Vitrains from a wide range of ranks of coals were carbonized singly and also co-carbonized (HTT 1273 K) with 25% of Ashland A200 petroleum pitch. Polished surfaces of the resultant cokes were examined for optical texture in a polarizing-light optical microscope using a half-wave retarder plate to produce interference colours. For the anthracites, there is no modification of either component during co-carbonization. The growth of optical texture from the A200 pitch is not affected. For all caking vitrains the optical texture of coke from the blend system is extensively modified when compared to the optical texture of coke from the vitrain. For the low-rank non-caking vitrains the isotropic coke becomes totally or partially anisotropic in co-carbonization. The mechanism of modification of the optical texture of resultant cokes is related to the formation of nematic liquid crystals, mesophase and the semi-coke. It is not considered that the chemistry of pyrolysis is modified on cocarbonization of the vitrain and pitch.     

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.     

Carbonization and liquid-crystal (mesophase) development: Part 1. The significance of the mesophase during carbonization of coking coals

Recent concepts of the growth processes of liquid-crystal structures, also called mesophase systems, during the carbonization of pitch substances is extended to coal carbonization. A basic model is formulated to explain the coal and coal-blend carbonization processes leading to metallurgical coke. This model explains the differences observed by optical microscopy in the size and shape of anisotropic structures seen in cokes in terms of liquid-crystal growth processes. These processes are considered to be restricted by chemical heterogeneity within the plastic phase, or to be influenced by the presence of solid surfaces (inerts) within the carbonizing system.     

Carbonization and liquid-crystal (mesophase) development. 13. Kinetic considerations of the co-carbonizations of coals with organic additives

Five coals, of rank from an anthracite to a non-caking coal, have been carbonized singly and also cocarbonized with decacyclene, mixing ratio 7:3, in the temperature range 648 K to 823 K, heating at 10 K min^?1, with various soak times. The objective of the study is to derive the basic factors which influence the kinetics of formation of mesophase and anisotropic coke. Accordingly, resultant cokes were polished and surfaces examined by reflected polarized light in an optical microscope. The size, shape and extent of anisotropic development is discussed in terms of the conditions of carbonization and the rank of coal. In these systems a somewhat larger optical texture results in cokes produced at the higher carbonization temperatures. The temperature of onset of growth of anisotropic carbon in co-carbonizations was below that of either the coal or the decacyclene. Reactivities are evidently modified. The origins, growth and coalescence of growth units of anisotropic carbon in these cocarbonizations of coals with decacyclene are demonstrated.     

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.     

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. 20. Co-carbonization of a high-volatile caking coal with several petroleum pitches

A high-volatile caking coal and five petroleum pitches were carbonized singly and coal/pitch systems were co-carbonized to 1273 K in the ratio of 75 wt% coal and 25 wt% pitch. Optical textures of cokes from the single carbonizations and co-carbonizations are assessed in terms of modification to the coalcoke by the pitch and unmodified pitch-coke using a point-counting technique. The pitches differ considerably in their carbonization behaviour. Each pitch can be placed into one of three groups defined in terms of their interaction with the high-volatile caking coal. A passive pitch does not modify the coalcoke but apparently carbonizes independently of the coal. An active pitch modifies some of the coalcoke. No pitch-coke can be detected. A super-active pitch modifies the coal-coke extensively beyond the extent expected from a 25% addition. No pitch-coke can be detected. The effects are related to the ability of the pitch to cause depolymerization of the coal. Quinoline-insoluble material in pitch may inhibit modification.     

Carbonization and liquid-crystal (mesophase) development. 21. Replacement of low-volatile caking coal by petroleum pitch in coal blends for metallurgical coke

Cokes were prepared in a 7 kg oven from blends of high-volatile and low-volatile caking coals, using ratios of 1:1 and 3:7. To the 1:1 blend was added 7.5% of either Ashland A240 or A170 petroleum pitch or SFBP petroleum pitch 1. Micum m₃₀ and m₁₀ indices were determined on cokes from the 7 kg oven, using the $\text{1}\text{5}$ Micum drum. Optical textures were assessed using polarized light microscopy of polished surfaces of cokes. The effect of additive is to increase the strength of cokes. The pitch can be an effective replacement of low-volatile caking coal. The analysis by optical microscopy shows that with the stronger cokes from the 7 kg oven there has occurred an interaction between the coal and pitch at the interface of coal particles to produce a solution or fluid phase which carbonizes to a coke with an optical texture of fine-grained mozaics. This material could be responsible for the enhancement of coke strength, being associated with pore wall material rather than with a change in porosity. The results agree with previous work using cokes prepared in the laboratory on a small scale.     

Carbonization and liquid-crystal (mesophase) development. 15. A common stage in mechanisms of coal liquefaction and of coal blends for coke making

This paper discusses the processes of coal liquefaction and co-carbonization of coal/pitch blends in terms of physical and chemical properties of the fluid phases found in both pyrolysis systems. Mechanisms of development of thermal plasticity in coals are outlined. In coal liqudfaction the importance is stressed of hydrogen-donor vehicles interacting with the products of thermal depolymerization of coal. The concept of variations in the facility of solvation and solvolysis of additives in co-carbonizations can explain the variations observed in degrees of interaction of a single coal with several additives. Possibly, the hydrogen-donor facility of an additive may be as important in assessments of modifying ability as an average molecular structure. The possibility exists of using an analysis of optical texture of cokes resulting from the fluid coal/solvent pyrolysis systems to characterize the effectiveness of solvents in coal liquefaction systems as distinct from coal blending co-carbonization studies.     

Carbonization and liquid-crystal (mesophase) development. 7. Optical textures of cokes from acenaphthylene and decacyclene

Optical textures of cokes prepared by carbonizing acenaphthylene, decacyclene and mixtures thereof at selected values of heat-treatment temperatures and soak time have been compared. Optical textures are assessed using polished surfaces and reflected-polarized-light microscopy in conjunction with a half-wave plate. The acenaphthylene is chemically more reactive than the decacyclene which is itself formed during the carbonization of acenaphthylene. Products of carbonization of acenaphthylene can influence rates of carbonization of the decacyclene. Similar optical textures in cokes cannot be formed by compensating low heat-treatment temperatures with long soak periods. In addition to chemical rate-controlling processes, the physical properties of the system must be acknowledged, in particular the viscosity. Very large non-coalesced growth units of mesophase (800 μm diameter) have been observed. Pre-alignment of growth units of mesophase may occur prior to coalescence.     

Carbonization and liquid-crystal (mesophase) development. 6. Effect of pre-oxidation of vitrinites upon coking properties

The effects of atmospheric oxidation at 378 K upon the carbonization of a coking and a caking vitrinite have been examined in terms of the origins and extents of development of anisotropic material. The vitrinites, oxidized from 1 to 40 days, were carbonized to temperatures between 618 and 878 K, in open boats under nitrogen at atmospheric pressure, and in sealed gold tubes at maximum pressures of 140 to 310 MPa. Optical microscopy was used to observe, qualitatively, changes in reflectance and in shape and size of the anisotropic material of the carbonized product; morphological changes were monitored by scanning electron microscopy. For both vitrinites, whereas one day of oxidation destroyed coking properties and almost all of the anisotropic development in the open-boat carbonizations, the pressure carbonizations were not significantly affected until after five days of oxidation. Anisotropy still developed by mesophase growth from the plastic phase of carbonization, to produce the shaped, botryoidal material characteristic of pressure carbonizations. Thereafter, although in the pressure carbonizations the particles of coking vitrinite only fused slightly at interfaces to form a coherent product, marked increases occurred in reflectance and in observed anisotropy, showing maxima at nine days of oxidation. Results are interpreted on the assumption that oxidation cross-links the macromolecular structure of the vitrinite substance. The effect of high pressure during carbonization after five days of oxidation is to preserve and perfect the original basic anisotropy of the vitrinites initially stabilized by the cross-linkage of oxygen atoms.     

Carbonization and liquid-crystal (mesophase) development. 16. Carbonizations of soluble and insoluble fractions of coal-extract solution

A coal-extract solution prepared by extraction of a coking coal (CRC 301a) with anthracene oil by the National Coal Board is separated into fractions using solvents of increasing solvent power. These fractions are carbonized to 823 K and the optical textures of resultant cokes are assessed. The objective of the study is to examine the role of the molecular components of the coal-extract solution including the residual anthracene oil in mechanisms of formation of the optical texture of the anisotropic coke. Generally, the low-molecular-weight fractions of the coal-extract solution produce cokes with larger sized optical textures than the coke from the parent coal-extract solution. The higher-molecular-weight fractions produce cokes with smaller sized optical textures. Isotropic coke is produced from material which is not soluble in benzene and tetrahydrofuran. Within this parent-coal-extract solution it would appear that the dominant partner effect is influential over the size of the optical texture of coke from the coal-extraction solution, that is the minor component of smaller molecules controls the necessary growth of liquid crystals. Also, the presence of anthracene oil augments the size of optical texture of resultant cokes by providing the necessary physical fluidity of the system and possibly some chemical stability.     

Carbonization and liquid-crystal (mesophase) development. 22. Micro-strength and optical textures of cokes from coal-pitch co-carbonizations

This study examines the micro-strength and optical textures of a laboratory coke from a base-blend of Freyming and Pocahontas coal (wt ratio, 1:1) and of cokes from the co-carbonization of the blend, with each of five petroleum pitches in various proportions. Coke pieces, 212–600 μm, from the micro-strength test are assessed in terms of origin and propagation of cracks induced by the test. Always, the addition of pitch to the base-blend improves the strength of the resultant cokes, the pitches behaving differently. A qualitative, subjective appraisal of results indicates that increases in coke strength are associated with relative abilities of pitches to interact with the coals to produce a fluid phase, of solution of coal in pitch, which gives an ‘intermediate’ coke with an optical texture of mozaics. This intermediate coke strengthens the bonding at interfaces. Cracks originate predominantly from the shrinkage cracks in the domains of Pocahontas coke. Mozaic structures tend to resist crack propagation. The coal/pitch system may flow around coal particles so containing incipient crack formation in resultant coke particles.     

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. 5. Importance of eutectic zones formed from nematic liquid crystals

The development of anisotropy in carbons arises from growth of nematic liquid crystals from the plastic phase of carbonization systems. Mixed, nematic liquid crystals form eutectic zones stable at lower temperatures than the single components. This phenomenon may have relevance to co-carbonization of mixtures of organic compounds and to coal blending procedures. A lowering of the temperature of onset of anisotropy may be beneficial to both graphite and coke quality. In the co-carbonization of carbazole and pyromellitic dianhydride to form anisotropic carbons, such a concept may be relevant. However, in the co-carbonization of two coals, although some lowering occurred in the temperature of formation of anisotropy, other interfacial phenomena are observed.     

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.