Characterization and classification of Rocky Mountain coals by Curie-point pyrolysis mass spectrometry

A set of 102 coal samples from the Rocky Mountain coal province, selected from the Penn State Coal Sample Bank, was analysed by Curie-point pyrolysis mass spectrometry in combination with computerized pattern recognition techniques. The spectra obtained were shown to be quite representative for the coal seams with characteristic differences often present between different seams, fields or regions within the Rocky Mountain Coal province. In general, the spectra were found to be dominated by homologous ion series, e.g., representing dihydroxybenzenes, phenols, naphthalenes, benzenes, alkenes, dienes, alkyl fragments and sulphur compounds with varying degrees of alkyl substitution. The relative abundances of dihydroxybenzenes and naphthalenes were shown to correlate closely with differences in rank, whereas those of phenols, aliphatic hydrocarbons and sulphur compounds appeared to correlate more closely with differences in depositional environment. Different spectra -dominated by aliphatic compound series -were obtained from several samples of a boghead coal (Cannel King seam). Moreover, spectra of two of these boghead coal samples, known to be severely weathered, showed markedly increased CO₂⁺ and C₆H₆⁺ signals, indicating the presence of benzenecarboxylic acids. Factor analysis of pyrolysis m.s. data revealed the two main underlying chemical tendencies to be a shift from heteroatomic compounds to hydrocarbon series with increasing rank and a difference in degree of aromaticity corresponding primarily to differences in depositional environment. The dominant rank-related factor exhibited a clear coalification break between the ASTM hvC bituminous and hvB bituminous ranks and appears to represent a significant shift in coalification mechanisms. It was demonstrated that rank-dependent differences in the pyrolysis mass spectra enable correct classification of the spectra into four ASTM rank classes (subbituminous, hvC, hvB and hvA bituminous) in 90% of all cases. Moreover, the discovery of a marked aliphaticity/aromaticity factor in the data could be useful for the direct measurement of aromaticity (f_a) from pyrolysis mass spectra of whole coals.     

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.     

Influence of coal forced oxidation on technological properties of cokes produced at laboratory scale

The effect of coal oxidation in air at 140 °C on the technological properties of cokes obtained at laboratory scale from two medium volatile bituminous coals has been studied. The proximate and ultimate analyses do not show important changes with coal oxidation time. However oxidation clearly has a strong effect on the plastic properties of the coals in view of the fact that the Gieseler fluidity eventually disappears. From this point variations in plastic properties can still be detected by FSI. Other changes, such as a shortening of the length of the saturated fragments of the aliphatic chains, a decrease in the aliphatic hydrogen content and an increase in the oxygen-containing groups are detected by PA-FTIR. It was also found that the main coke quality indices (mechanical strength and reactivity to CO₂) of both coke series are impaired with coal oxidation. A close relationship between reactivity to CO₂ and the micropore specific surface area of the cokes has been corroborated.     

Influence of coal forced oxidation on technological properties of cokes produced at laboratory scale

The effect of coal oxidation in air at 140 °C on the technological properties of cokes obtained at laboratory scale from two medium volatile bituminous coals has been studied. The proximate and ultimate analyses do not show important changes with coal oxidation time. However oxidation clearly has a strong effect on the plastic properties of the coals in view of the fact that the Gieseler fluidity eventually disappears. From this point variations in plastic properties can still be detected by FSI. Other changes, such as a shortening of the length of the saturated fragments of the aliphatic chains, a decrease in the aliphatic hydrogen content and an increase in the oxygen-containing groups are detected by PA-FTIR. It was also found that the main coke quality indices (mechanical strength and reactivity to CO₂) of both coke series are impaired with coal oxidation. A close relationship between reactivity to CO₂ and the micropore specific surface area of the cokes has been corroborated.     

Study of the relation between the phosphorus content of coal and coke

Established methods for the determination of phosphorus in coal and coke were compared and found to give results in satisfactory agreement. The method for the determination of phosphorus described in BS 1016, ‘Methods for the analysis and testing of coal and coke’, Part 9, 1977 was used to study the relation between the phosphorus content of coals and their corresponding cokes. The cokes were prepared on laboratory, test oven and industrial scales, by the carbonization of various bituminous coals within the range of volatile matter yield of 16–40 wt%. The determined values of the phosphorus contents of these cokes and their parent coals indicated that the phosphorus present in the coal is completely retained in cokes carbonized to temperatures between 900 and 1050 °C. On the basis of these experimental results it is suggested that the phosphorus content of coke can generally be calculated from a knowledge of the phosphorus content of the coal and the coke yield with an accuracy which is sufficient for normal requirements.     

Quantitative aspects of solid state 13C n.m.r. of coals and related materials

The quantitative aspects of cross-polarization (CP), which is used in conjunction with dipolar decoupling and magic-angle rotation to obtain high resolution ¹³C n.m.r. spectra of coals, have been studied using a bituminous coal (82 wt% C, dmmf basis) and asphaltenes from an extract of the same coal. The condition for obtaining reliable quantitative data, that rotating frame ¹H relaxation times (T_1p′ these govern the extent of CP) are much longer than the time required to polarize the carbons present (≈1 ms), was met for the asphaltenes. In contrast, about half the protons in the coal have T_1p5 of ≈ ? 1 ms, these times being too short to allow CP of all the carbons. Although the aromaticities obtained for this coal were fairly constant (≈0.75) using (CP) contact times > 0.5 ms, the total peak intensity decreased markedly as the contact time was increased and was much less than that for the asphaltenes. These results indicate that not all the carbons in bituminous coals are observed by CP and, as a consequence, aromaticities reported in the literature for some bituminous coals appear to be low.     

Determination of oxygen and nitrogen in coal by instrumental neutron activation analysis

The purpose of this study was to measure oxygen and nitrogen in coals using instrumental neutron activation analysis. For six U.S. coals total oxygen ranged from 9.4 to 28.7% and total nitrogen varied from 0.72 to 1.61%. To obtain values of organic oxygen and nitrogen either a low-temperature-ashing method or an acid-treatment method was suitable for bituminous coals. The mean difference of the experimentally determined values (O_dmmf)_LTA ? (O_dmmf)_AT = ?0.82, s = 0.51, was found to be statistically significant at the 95% confidence level, but the comparable difference for nitrogen was not. By the LTA method oxygen and nitrogen on the dmmf basis for bituminous coals showed no statistically significant difference with calculated dmmf values. Nitrogen was detected in all the LTAs varying from 0.38 to 1.67%. Formation of insoluble CaF₂ in the acid-treatment method caused an interference in the nitrogen determination due to the ¹⁹F (n, 2n) ¹⁸F reaction but was correctable. In addition, recoil proton reactions on C and O leading to the formation of ¹³N must be accounted for in all nitrogen determinations in the coal matrix.     

Nuclear magnetic proton relaxation studies of oxidized coals

Coals of NCB rank 301 a (coking), 502 (caking) and 802 (very weakly caking) are oxidized in air at 373 K or 383 K for up to 42 days. Spin-lattice and spin-spin relaxation times, T₁ and T₂ respectively, of oxidized coals are measured using a Bruker SXP 4–100 and FT spectrometer. Free radical concentrations in the coals are obtained using a JES PE e.s.r. spectrometer. Infrared spectra of oxidized coals are obtained and optical textures of cokes from fresh and oxidized coals are assessed by optical microscopy. For two coking coals, decreasing values of T₁, and increasing concentration of free radicals occurred with oxidation at 383 K to 16 and 28 days. Thereupon values of T₁, increased and free radical concentrations decreased with further progressive oxidation. At the point of inflexion in properties, resultant cokes from the coals ceased to shown any anisotropy in their optical textures and became isotropic resembling cokes from low-rank coals. For the caking coals, T₁ increased at all stages of oxidation to 42 days with decreasing concentrations of free radicals. Two values of T₂ were found in each coal corresponding to a rigid and mobile component ((T₂)_r < (T₂)_m). The rigid component (T₂)_r was not affected by oxidation but values of (T₂)_m decreased with increasing duration of oxidation. It is considered that coking and caking coals exhibit different effects of oxidation with perhaps phenols and quinones in caking coals acting as inhibitors to the growth of stable free radicals. Oxidized coking coal may behave like fresh caking coal.     

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.     

Thermogravimetric investigations in prediction of coking behaviour and coke properties derived from inertinite rich coals

The coal quality, temperature, pressure, heating rate, various processes and reactor type affect coking behaviour of coal and resulting coke properties. Several petrographic and chemical methods were proposed earlier for prediction of coking behaviour of coals. Inertinite rich coal samples (I^mmf>30 vol%) having different petrographic compositions were selected for thermogravimetric investigations (DTA, DTG and TGA) and their coking behaviour was studied. The petrographic build up, micro-structural properties (porosity and cell wall thickness) and mechanical strength of the resulted cokes were also investigated. ΔH and ΔH_max (the main endothermic area of heat absorption and fast absorbing main endothermic area, respectively) were distinguished in DTA curves. ΔA and ΔA_max (the main decomposition area and fast disintegrating main decomposition area) under DTG curves were identified. ΔH_max/ΔA_max shows good correlation with Roga's indices (RI, caking properties) as well as with petrographic caking ratio (PCR). The coarse mosaic content of cokes seem to depend on LΔT_max/ΔT_max (ratio of weight loss during fast decomposing main reaction to temperature difference) under DTG. L^mΔT/ΔT (ratio of weight loss during main decomposing reaction to temperature difference) under DTG exhibits correlation with p₁ (mean pore size) and t₁ (mean cell wall thickness) of cokes. ΔA_max/(L^mΔT_max) also indicates good relationship with mechanical strength of cokes. (L^mΔT_A−T_B)/(L^mΔT) (i.e. ratio of weight loss during main endothermic reaction under DTA to weight loss during main decomposing reaction) appears to have relationship with DD (compactness) of cokes. The course of main endothermic reaction/main decomposition reaction under DTA, DTG and TGA seems to govern coking behaviour and the resulting coke strength, which in turn is controlled by microlithotypes.     

Effect of coal weathering on technological properties of cokes produced at different scales

The effect of weathering (natural oxidation) on the technological properties of cokes obtained at three different scales (laboratory, pilot plant and semi-industrial), from two medium volatile bituminous coals stored at INCAR open stockyard for several months, has been studied in this work. The results show that the procedure developed at laboratory scale is useful for studying the evolution of coke quality because the trends of the main quality indexes (mechanical strength and reactivity to CO₂) are in agreement with those of the cokes produced at larger scales. Furthermore, it was found that the total porosity and the micropores specific surface area of the cokes vary with the scale of carbonization, and that they increase as follows: semi-industrial<pilot plant<<laboratory. All of which are related to the evolution of the mechanical strength and reactivity to the CO₂.     

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.     

Steric requirements for coal swelling by amine bases

A set of six coals ranging in rank from lignite to hvA bituminous was swollen with a series of alkyl-substituted pyridines and a smaller set of 4-alkylanilines. The size and branching of the alkyl groups was varied and the effect of this variation on the dissolution of the amines in the coal and the resulting coal swelling was measured volumetrically. In a few cases, substituents which hindered the amine nitrogen were studied. The lignite and subbituminous coal have a much higher tolerance to branched, bulky groups than do the bituminous coals. The presence of tertiary groups in a solute strongly inhibits their dissolution in bituminous coals. Bituminous coals behave as if extensive parallel packing of structures occurs. Often, they can accept very large planar groups but have a low capacity for branched groups.     

Determination of specific heats of coal powders by differential scanning calorimetry

Specific heats (C_p) of bituminous and subbituminous coals were investigated in the temperature range 300–360K by differential scanning calorimetry (DSC). To establish the validity of the procedure, specific heats of glass beads and graphites in powdered and bulk form were determined. Good agreement was obtained with the values for the specific heats of glass and graphites in the literature, and it was established that the specific heats were not dependent on the degree of diminution of these materials. Specific heats of coal samples were found to depend upon mesh size, temperature, rank, moisture content and whether the coal powder was wet- or dry-screened. However, there were only minor differences in C_p between bituminous and subbituminous 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.     

Mutagenicity of eluent by hot water extraction of various coals: Effect of chlorination

Six kinds of powdery coals (two bituminous coals, two sub-bituminous coals, and two lignites) were extracted by hot water, and the eluents obtained were analyzed for total organic carbon (TOC), absorbance at 260 nm (A₂₆₀), and pH. The TOC in the eluents decreased in the order, lignites > sub-bituminous coals > bituminous coals. The eluents of lignite gave high A₂₆₀/TOC values and fairly low pH compared to other coals. Chemical structure of the organic matter eluted from coals was discussed with the aid of FTIR analysis. The coal eluents were analyzed by the Ames mutagenicity assay using Salmonella typhimurium TA100 and TA98 strains, and no mutagenicity was observed for all of the six coals. However, especially for the lignites, chlorination of the eluents produced an appreciable mutagenicity, and the expression of mutagenicity was dependent upon the type of coal. The mutagenicity was extinguished when metabolic activation (rat liver homogenate, +S9) was applied.     

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.     

Reactivity of hydrolysed coals in liquefaction

A hvA bituminous, a subbituminous and a lignite coal have been hydrolysed by 20–30% aqueous caustic solution at 100–300 °C and total pressure from ambient to 8.3 MPa (1200 psi). Reactivity of these pretreated coals toward liquefaction has been examined. The conversion to benzene-soluble material (BS) and oil increases, and the preasphaltene and char residue decreases after pretreatment. Improvement in the conversion to the BS fraction is only marginal for the pretreated bituminous coal, but substantial for the low-rank coals. For the subbituminous coal, the liquefaction reactivity (conversion to BS) increases with the severity of hydrolysis pretreatment. Analyses of chemical compositions, ¹H n.m.r. nuclei distributions and hydroxyl concentrations of the acid-insoluble hydrolysis coal extracts indicate that both O and S are enriched in the extracts with half of the oxygen atoms being in hydroxyl forms. The hydroxyl concentrations of the extracts (acid-insoluble) are ≈2 to 3 times higher than their parent coals. Coal activation by this alkali pretreatment is explained by the hydrolytic attacks on ether C–O linkages, and the removal of some constituents rich in oxygen functional groups which are responsible for poor liquefaction behaviour.     

Structural analysis of quinoline and pyridine extracts of coals

Various ranks of coals were extracted in an autoclave with quinoline at 350–380°C for 1–4 h. More than 50% of bituminous coals were dissolved, and almost 100% of Japanese bituminous coals in particular were dissolved. These quinoline extracts were further extracted by shaking with pyridine at room temperature for 8 h and the extraction yield attained a maximum of 85%. NMR spectra of these extracts were recorded using deuteroquinoline and deuteropyridine as solvent. The structural indices calculated from the observed spectra showed a good agreement between quinoline extracts and pyridine extracts, which indicates that the coal structure is almost homogeneous. The aromatic ring number in structural units varied from 1–2 in younger coals to 5 in coking coals. f_a increased from 0.7 for younger coals to 0.9 for coking coals. The aliphatic carbon number per structural unit increased from younger to older coals, but foreign coals had smaller values than Japanese coals, which corresponds well with higher values of H/C in Japanese coals.     

煤的变质程度对焦炭性质影响的研究

对不同变质程度的5种烟煤进行了5 kg实验焦炉炭化实验.并就单种煤的结焦性与对应焦炭的微晶结构间的关系进行了探讨.结果表明,1/3焦煤焦炭、焦煤焦炭的冷态强度和热态强度较好;X射线衍射(XRD)分析结果表明,肥煤焦炭的炭结构因子(La/Lc)最小,石墨化程度最高.焦炭的真相对密度(TRD)随着La/Lc的增大而减小.