Carbonization of coals to produce anisotropic cokes: 3. Evaluation of low-rank bituminous and subbituminous coals by single and co-carbonizations with pitch

Single carbonizations and co-carbonizations of 17 low-rank bituminous and subbituminous coals have been studied to evaluate their suitability as sources of blast furnace coke in terms of pore-wall profile and anisotropic development within the cokes. Co-carbonizations suggest the possible use of low-rank coals which from single carbonizations would not have been considered suitable. To evaluate semi-quantitatively the coke quality, two structural characteristics of the cokes produced by single and co-carbonizations are graded on a scale of 1 to 5. Overall assessments for each coal are plotted against the atomic H/C and 0/C ratios of the original coals. Although there are a few exceptions, coals with similar assessments are located in the same region of the plot, indicating that, to a first approximation, the H/C and 0/C ratios are suitable indicators of the single and co-carbonization properties of a coal. The presence of cations in the coal appears to be an additional factor influencing the carbonization properties and may explain the exceptional behaviour of some coals. Removal of these cations by pretreatment of the coals improves the carbonization properties.     

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.     

Carbonization of coals to produce anisotropic cokes.: 4. Improving co-carbonization behaviour of bituminous and subbituminous coals with pitch by pretreatment coals to remove cations

Several de-ashing pretreatments of selected coals have been examined to establish simple and effective procedures to improve, in terms of anisotropic development, the co-carbonization behaviour of the coals with pitches. Refluxing pretreatments of the coals in 1N HCI containing methanol and in boiling water containing EDTA-2Na (EDTA-2Na/coal = 7/100 byweight) improve the co-carbonization behaviour of Witbank, Miller, Taiheiyo and Wandoan coals, all of which, in their original, untreated form, are modified in terms of anisotropic development only very slightly in co-carbonizations with A240 petroleum pitch. Pretreatment of coals of very low rank appears to be ineffective in co-carbonizations with A240; however, co-carbonization with hydrogenated A240 shows that the pretreatments are effective. Analyses and FT-i.r. spectroscopy of mineral matter suggest that improved behaviour due to the pretreatment is related to the removal of divalent cations and to the modification of the oxygen functionality of the 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 of coals into anisotropic cokes: 6. Formed cokes of high density and optical anisotropy from non-fusible and slightly fusible coals

A procedure for the preparation of solid formed coke of enough adhesion and anisotropic development for use in the blast furnace has been studied, using non-fusible and slightly fusible coals with petroleum cocarbonizing additives. The coke precursor was prepared through the copreheat-treatment of coal and a suitable additive in adequate quantity under stipulated conditions. The desired coke was produced by carbonization after forming with a press. The conditions for the copreheat-treatment have been carefully examined in terms of the temperature, time and heating devices. The behaviour of coals during copreheat-treatment and carbonization were discussed in terms of coal ranks, comparing this behaviour to the liquefaction reactivity and thermal stability of their liquefied product.     

Carbonization of coals to produce anisotropic cokes. 2. Up-grading of modification activities of petroleum process residues and their correlation with structural parameters

Modifying activities of petroleum pitches and up-graded pitches in the co-carbonization with a range of coals have been examined with the object of proposing an effective co-carbonization process for blast-furnace coke production. Up-grading of additives was attempted using thermal, acidic and oxidative reactions. Acidic reactions with aluminium chloride were most effective with lighter petroleum residues of initially poor modifying activity, this being attributed to dealkylation, ring-closure and ring condensation reactions. The relation between modifying activity and structural indices is discussed. The aromaticity (f_a) and the naphthenic ring number in the unit structure T_n,us can be used as appropriate parameters for the activity when the coking yield is taken into account.     

Carbonization of coals into anisotropic cokes: 8. Carbonization of a canadian weathered coal into anisotropic coke

The carbonization properties of a weathered high rank bituminous coal were compared with those of the non-weathered coal. The weathering decreased the fusibility of the coal to leave more basic anisotropy and to diminish the size of the majority of the anisotropy in the resulting coke. On the other hand, more domain and flow domain textures developed. Co-carbonization with a petroleum pitch additive (Ashland A240) was found effective in enhancing the fusibility of the coal and anisotropic development in the coke. Formed coking of the weathered coal by means of copreheat-treatment with the additive, provided an anisotropic, dense and strong coke of uniform size. For the weathered coal, the optimum copreheat-treatment was shorter than that using the non-weathered coal indicating high coking reactivity of the weathered coal. The transferable hydrogens from the additive are rapidly consumed by the oxygen containing groups of the weathered coal.     

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.     

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.     

Correspondence between the composition and plastic properties of British coals and the structural properties and reactivity of the corresponding cokes

The chemical composition and the physico-chemical properties of a suite of British coals, mainly of types 501/2 as defined by the NCB classification, but including some coals of higher and lower rank (NCB classification 204,401/2 and 601/2), were comprehensively investigated. Each coal was subsequently carbonized under controlled conditions of size distribution, bulk density and temperature on the 250 kg scale and the tensile strength, coke structure and coke reactivity were determined. This data highlighted the significance of the atomic ratio of the oxygen and carbon of the coals and the lack of relations between coal properties and coke structure and strength. As regards coke reactivity only complex relations with coal properties could be found, with coal rank, the oxygen/carbon ratio and the chlorine content being of greatest importance.     

Applications of laser Raman microprobe spectroscopy to the characterization of coals and cokes

Optical microscopy is widely used in the characterization of coals and cokes. This Paper shows that the laser Raman microprobe (MOLE) which combines an optical microscope and a Raman spectrometer can provide useful additional information. Three main areas were investigated: identification of minerals in coal and coke; structural characterization of coals and cokes; and the interaction of inorganic additives and coal. Where possible, the results were compared with conventional optical microscopy measurements whereby it was shown that the optical texture and Raman spectra of cokes are not closely related. The Raman spectra of high temperature cokes were used to estimate the size of microcrystalline regions.     

Carbonization and liquid crystal (mesophase) development. 14. Co-carbonization of coals with A240 Ashland petroleum pitch: effects of conditions of carbonization upon optical textures of resultant cokes

This study examines the effect of pitch concentration, rate of heating, soak temperature and time of soak upon the optical texture of cokes prepared from the co-carbonizations of a coal (Oxcroft-Clowne, NCB Rank 802) and three vitrains of NCB Rank 204, 801, 902 with Ashland A240 petroleum pitch. Using the coal (Rank 802) with 10 wt % and 25 wt % additions of pitch caused progressive penetration of the pitch into the coal with a resultant development of a mozaic anisotropy in the coke to replace partially the original coke isotropy. With 50 wt % addition of pitch almost all of the coal particles, 600 to 1100 μm in size, were modified during carbonization. Some pitch coke was formed. For the coal and three vitrains with increasing rates of co-carbonization from 0.5–10 K min^?1 to 1200 K, using 25 wt % of A240 pitch, resultant cokes showed progressively increased extents of modification. For the two vitrains (Rank 801, 902) soaking at temperatures of 650–690 K caused a decrease in the extent of modification of isotropic coke when compared with the coke of HTT 1200 K. Evidently fast heating rates create the conditions of fluidity necessary for the pitch to modify the coal leading to growth of mesophase and anisotropic coke.     

Constitution of tars from the flash pyrolysis of Australian coals: 2. Structural study of Millmerran coal-tar resins by hydrogenolysis

The structures of the acid, base, polyfunctional and neutral resin fractions of Millmerran coal tar have been studied by high-pressure catalytic hydrogenolysis followed by g.c.-m.s. analysis of the volatile products. n-Alkanes from C₉ to C₃₂ constitute 4–24% of the organic products. Each fraction shows a characteristic n-alkane distribution. The alkanes are considered to be an integral part of the coal-tar resin structure. The results show that 40–70% of the coal-tar resin fractions consist of 1- or 2-ring aromatic units substituted or linked by long methylene chains.     

Catalytic carbonization of aromatic hydrocarbons—IX: Carbonization mechanism of heterocyclic sulfur compounds leading to the anisotropic coke

Carbonization mechanisms of three heterocyclic sulfur compounds catalyzed by aluminium chloride were investigated in order to resolve the factors which influence the optical texture of the coke produced from these compounds. The extent and rate of sulfur elimination, the rate of carbonization as measured by the increase of benzene insolubles, the temperature region of fusion, and the intermediate structure were assumed influencial during the carbonization. Thioxanthene, which produced a mosaic coke, showed a similar fused region to that of diphenylene sulfide which formed a needle coke, however the rate of carbonization of the former compound was much faster than that of the latter. Thianthrene, which produced a fine mosaic coke with some isotropic portions, had the narrowest region of fusion. The importance of the intermediate structure in understanding the carbonization mechanisms of the compounds in modifying the carbonization reaction is emphasized. The desulfurization mechanism is also discussed to some extent, relating it to that of carbonization.     

Structural changes and product distribution of typical Xinjiang coals and chars during pyrolysis

This study used micro-Raman spectroscopy, gas chromatography–mass spectrometry (GC–MS), and gas chromatography–flame ionization detector/thermal conductivity detector (GC–FID/TCD) to analyze the structure and pyrolysis reactions of nine typical coals and chars from Xinjiang. The study fitted 10 Gaussian bands of typical Xinjiang coal and investigated the changes in coal structure during coalification and pyrolysis. The results indicated that the reduction degree of CO structures in coal during coalification had a rough linear relationship with the V_daf (dry ash-free volatile matter) content. During coalification, the condensation of aromatic rings is accompanied by a continuous decrease of CO structures, while the contents of cross-linking and substitution structures decrease persistently relative to the large aromatic ring structures. The influence of coal type on char yield for typical Xinjiang coal is within 15 wt.%; the influence on tar yield is within 8.5%, with a greater impact on the yield of alkanes and phenols in tar; the influence on CO yield in pyrolysis gas is within 6.3%. The relative content of large aromatic ring structures in coal is relatively stable during pyrolysis, while the relative content of small aromatic ring structures declines as coal transforms into char. The study inferred that small aromatic rings might decompose and transform into tar after pyrolysis reaction, which also resulted in a high selectivity of phenolic products in tar from most coal pyrolysis above 40%. This study revealed the structural changes and pyrolysis product distribution of nine typical coals and chars from Xinjiang, providing useful information for their utilization.     

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.     

Studies related to the structure and reactivity of coals : 16. The chemical structure of the oil products from reactions of Victorian brown coals

A suite of Victorian brown coals and the guest and host components of the coals obtained by 320 °C extraction have been reacted to obtain oils for analysis by n.m.r. and g.c.-m.s. techniques. Batch autoclave experiments without solvent, but with 10 MPa initial hydrogen pressure in the presence of stannic oxide, were undertaken at 405 °C. Oils derived from the macromolecular host material were highly polar materials and contained mainly phenols, and one- and two-ring aromatic hydrocarbons. They were of similar composition for all Victorian low-sulphur brown coals. In contrast, oils derived from the guest material were mainly a mixture of n-alkanes and terpenoid-derived cyclic hydrocarbons, and the ratio of these two types of compounds varied with the coal.     

Carbonization properties of partially hydrogenated aromatic compounds—II: Factors influencing the coke yield in the carbonization of hydrogenated pyrene

Factors influencing the coke yield in the carbonization of hydrogenated pyrenes were investigated from the view of reactivities of their hydrogens. The amount of hydrogen located at 4 ppm in their proton NMR spectrum was found to be intimately related to the coke yield of hydrogenated pyrenes. Oxidative pretreatment at 150°C significantly increased the coke yield. The structural changes of hydrogenated pyrenes by oxidative pretreatment were investigated by means of GPC, IR and NMR. The scheme of oligomerization as the first step of carbonization is discussed in connection with the reactivities of hydrogens in hydrogenated pyrenes.     

Studies related to the structure and reactivity of coals : 18. The chemical structures of products from reactions of a suite of higher rank Australian coals

The structure of the oils, asphaltenes and residues obtained by the thermal reactions of a suite of Australian higher rank coals under hydrogen or nitrogen have been studied by chemical and spectroscopic methods. The host-guest model that has been used to describe the structure of Australian brown coals cannot be applied directly to the higher rank coals. Evidence is provided that suggests that a modified version of the model may be of use in describing the structure of some subbituminous coals. The methodology has proved to be useful in the understanding of structural features of coals which are often not rank dependent, e.g. Callide coal (ABL2), a subbituminous coal, has been shown to have characteristics of both very high and also low rank coals.     

Carbonization and liquid-crystal (mesophase) development. 18. carbonization of coal-extract solutions (non-hydrogenated): influence of digestion conditions upon optical texture of cokes

Coal-extract solutions have been produced by the dissolution of a prime coking coal in anthracene oil followed by the removal of the undissolved solids. A range of coal-extract solutions prepared under different conditions was carbonized and the optical texture of the polished surfaces of the resultant cokes were assessed. The coal-extract solution prepared with the longest digestion time and at the highest temperature produced a coke with the largest anisotropic domains with some flow structure. Removal of the anthracene oil component of the coal-extract solution by extraction with selected solvents modified the carbonization behaviour such that although the coke yield increased substantially there was a significant decrease in the size of the anisotropic domains of the resultant cokes.