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 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.     

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.     

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.     

Bonding of solid additives in cokes from coals: a microscopy study

Cortonwood Silkstone (NCB class 401) and Betteshanger (NCB class 301 a/204) coals were co-carbonized with solid additives such as anthracite, coke breeze, green and calcined petroleum cokes. The resultant carbonization products (cokes) were examined by optical microscopy and SEM was used to investigate polished surfaces etched by chromic acid and fracture surfaces. For both coals only the anthracite and green petroleum coke become bonded to the coal cokes. This probably results from softening and interaction of interfaces of the anthracite and green coke with the fluid coal via a mechanism of hydrogenating solvolysis during the carbonization process. The coke breeze and calcined petroleum cokes were interlocked into the matrix of coal coke.     

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. 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.     

Effects of additions of petroleum coke in coals upon strengths of resultant cokes

Coals of NCB rank 301, 401 and 502 were co-carbonized with pitch-coke breeze pre-carbonized to temperatures between 900–1200 K, in the ratio 9:1. The objective was to provide fundamental information concerning the effect of inert components upon strength of metallurgical coke; these inert components occur naturally in coals and may also be added to coking blends as coke breeze. Polished surfaces of resultant cokes were examined by optical microscopy and fracture surfaces were examined by SEM to investigate the coal-coke/pitch-coke interface for bonding between components and fissure propagation across the interface. Strengths of cokes were measured using a micro-strength apparatus. For three coals, pitch-coke breeze (900 K and highest volatile content) bonded best to the surrounding coal-coke. The interface became increasingly fissured with increasing pre-carbonization temperature of pitch-coke.     

Carbonizations under pressure of chloroformsoluble material of coking vitrinite

Chloroform-soluble material from a Polish coking coal was prepared by extracting the coal after heating it initially to 673 K for 15 min. The soluble material was carbonized in sealed gold tubes to 800 K and 873 K at 200 MPa pressure and to 800 K, 1000 K and 1200 K at atmospheric pressure. Coke morphology was assessed by SEM with optical texture (micro-texture) being assessed by polarizedlight microscopy of polished surfaces. Cokes from the pressure carbonizations (100 wt % yield) showed coalescing spherule morphology, 10 to 20 μm diameter, and are totally anisotropic. The material normally lost as volatiles thus contributes totally to the formation of mesophase and anisotropic coke. Coke from the carbonization of the soluble material at one atmospheric pressure (41 wt % yield) is composed mainly of anisotropic fine-grained mozaics in the range 1–5 μm. Carbonization under pressure extends the range of sizes of optical texture in cokes from this chloroform-soluble material. Applications may exist in graphite manufacture.     

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. 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 behavior of hydrogenated ethylene tar pitch

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.     

Modification of petroleum coke by different additives and the impact on anode properties

Anodes, which provide the carbon required for aluminum production, are made from dry aggregates (petroleum coke, rejected anodes, and butts) with coal tar pitch as the binder. Good quality anodes require good interaction between coke and pitch, and this relies on good wetting properties. The objectives of this work are to analyze the wetting properties of four different cokes with and without modification using an additive and to test the effect of the modified coke on anode properties. A FTIR study was done to identify functional groups in non‐modified and modified coke samples since they play an important role on coke‐pitch interactions. The wetting tests were done using the sessile‐drop method to measure the contact angle between coke and pitch. The results showed that the additive improved the wettability of all four cokes by pitch. The least wettable coke was chosen to produce anodes. For anode production, the entire dry aggregate is modified. The additive was mixed with the dry aggregate using two different approaches (one day earlier and 5 min before mixing). The anodes were characterized before and after baking. The early treatment with the additive was found to be better for the modification of dry aggregate.

     

Microscopy study of bonding in co-carbonizations between coke grist from coal-extract solution and coal-tar binder

Optical microscopy and SEM examine coke composites from the co-carbonization at 673 K of coke grist (60%) from a coal-extract solution with Orgreave lean coal-tar pitch (40%) to study binding mechanisms. The coke grist was prepared at heating rates of 5–300 K h^?1 to HTT of 800 K (one coke to 1200 K). It was found that the bonding was weak or non-existent using coke grist of heating rates 5 and 15 K h^?1, but was significant using coke grist of heating rates 75, 150 and 300 K h^?1 (except for coke of HTT 1200 K which showed poor bonding). These effects are discussed in terms of surface structure of the coke grist, possible influences of free-radicals (free-spins) and wettability associated with porosity.     

The influence of oxidation upon strength and structure of a needle-coke and a coal extract coke

Calcined commercial needle-cokes and coal extract coke are characterised by optical microscopy of polished surfaces. The needle-coke has an optical texture of coarse-grained mosaic, flow domain and a acicular flow domain; the coal extract coke has an optical texture of medium- and coarse-grained mosaics. The cokes are oxidised in air to 1–25% wt. loss. The microstrengths of original and oxidised cokes are measured. For the needle-cokes, a 1% wt. loss significantly reduces the microstrength values whereas for the coal extract coke the microstrength begins to decrease only after 15% wt. loss. SEM examination of original and oxidised surfaces indicates that oxidation of the needle-coke proceeds by the development of microfissures within the flow domain and by pitting of surfaces of the basal planes of the acicular flow domains. The surfaces of the coal extract coke were uniformly pitted. The decline of microstrength values of needle-cokes is associated with internal oxidation of the coke particles.     

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.     

芳香族硝基化合物改性煤沥青研究

以煤沥青为原料,通过添加不同含量的芳香族硝基化合物对煤沥青进行改性处理,采用TG、CO2反应性、XRD和SEM对改性沥青焦进行表征。结果表明,芳香族硝基化合物有效地促进了煤沥青在炭化过程中的焦化缩聚,使产物沥青焦结构更加致密,并在一定程度上改变了沥青焦的氧化行为,从而显著提高了沥青黏结焦的抗氧化性能。     

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.     

The strength of industrial cokes: Part 4. The influence of carbonizing conditions on the tensile strength

The objective of this study was to ascertain if the observed differences in strength behaviour of blast-furnace and foundry cokes could be attributed to the different carbonizing conditions used in their production. Two coal blends, one being representative for blast-furnace coke production and the other for foundry coke production, were carbonized in a small-scale test oven using a wide range of heating conditions which included those used in the industrial production of the two types of coke. Coke tensile strengths were determined by the diametrical-compression test and a small-scale drum test was used to derive strength indices comparable to standard micum indices. The tensile strengths and material constants obtained by Weibull statistical analysis, when related to those drum-test indices which assess the resistance of coke to attrition and to corresponding data for equivalent commercial cokes, demonstrated that the cokes fell into two distinct sets according to the coal blend used. It was concluded that changes in coke strength caused by different carbonizing conditions could not account for the different strength behaviour of blast-furnace and foundry cokes. The alternative hypothesis that the nature of the coal blend is the predominant factor is supported by the correlations established for each of the coal blends.