Heavy media separation of SRC-II feedstocks: 1. Effect on coal properties

The objectives of this investigation were to determine the effects of coal preparation on the properties of Run-of-Mine (ROM) and washed Powhatan and Ireland Mine coals and to assess the potential effects on SRC-II liquefaction yields. The effect of washing on the two coals was found to be quite similar. For both coals, the properties were altered more significantly by changes in separation media gravity than by changes in the coal size. The elemental composition of the Powhatan and Ireland washed coals was correlated with carbon content. It was shown that both the hydrogen and oxygen levels increased linearly with the carbon content of the coal samples. However, the $\text{H}\text{C}$ and $\text{O}\text{C}$ ratios were not changed significantly by coal cleaning. Only small variations in the nitrogen and organic sulphur levels were observed while the sulphate sulphur and chlorine levels were not affected by coal cleaning. The major impact of the coal cleaning was to reduce the pyritic sulphur (and hence the total sulphur) content of the coals. Most of the pyritic sulphur was shifted into the middling coal and refuse fractions while the clean coals had much lower contents and the pyritic sulphur level decreased with increasing carbon content. Coal cleaning did not significantly alter the maceral contents of vitrinite, exinite, total reactive macerals (TRM), or the reflectance of vitrinite; all these parameters varied over a very narrow range, probably within the precision of the measurement technique.     

Liquefaction of partially dried and oxidized coals: 3. Liquefaction results

Samples of partially dried and oxidized Belle Ayr subbituminous coal were liquefied in a recycle donor solvent (SRC-ll heavy distillate) to observe the effect of coal pretreatment on conversion. Because subbituminous coals have moisture contents typically > 25%, it would appear useful to dry these coals prior to liquefaction; however, the drying of Belle Ayr coal, either in nitrogen or oxygen-containing gases, resulted in a significant decrease in yields of liquefied coal products. The liquefaction residues recovered from these runs were examined by optical microscopy and were found to contain high levels of coke. This coke appeared to have formed by polymerization of coal-derived liquid products.     

Combustion and Pollutant Emission Characteristics of Lignite Dried by Low Temperature Air

Lignite is a kind of coal that has high moisture content and needs to be dried before being utilized. In this article, a Chinese lignite was dried in air at 120–180°C and the changes in its physical and chemical structures after drying were investigated. The results showed that the pore volume and specific surface area of the lignite decreased after drying. Some of the methylene and methyl groups were oxidized by the oxygen in the drying air, resulting in an increase in oxygen functional groups. The combustion characteristics of the dried coals and parent coal (dry basis) were studied via thermogravimetric analysis. The total volatile yields of the dried coals increased compared to the parent coal. The burnout temperatures of the dried coals were higher than the parent coal, whereas the ignition temperatures stayed almost unchanged. An entrained flow system was set up to study the release of nitrogenous gas products during rapid pyrolysis and combustion. The HCN yields of the dried coals during pyrolysis were higher than that of the parent coal, and a similar trend was found for the NO yield during combustion. The mechanism changes of combustion and pollutant emission characteristics were discussed according to the results of the physical and chemical structure analyses.     

Comparison of sulphur in HNO3-extracted and physically cleaned coals

The sulphur contents of eight bituminous and subbituminous coals, after extraction with nitric acid, are compared with the sulphur contents of physically cleaned samples of the coals. Samples of −60 mesh (250 μm) coal were extracted with boiling 2 M HNO₃, which removes essentially all mineral sulphur. After washing and drying, the extracted samples were analysed for moisture, ash, and total sulphur. The dry, ash-free (daf) sulphur values for the eight coals obtained by this method show excellent agreement with the daf sulphur values for physically cleaned samples of the coals. The physically cleaned samples were prepared by float/sink separation of −60 mesh coal in 1.30 specific gravity media, followed by milling the float coal to particle sizes less than 10 μm and subsequent float/sink-centrifugation cleaning. The daf sulphur values determined in the HNO₃-extracted and physically cleaned samples were less than those obtained using ASTM Method D 2492 and differed by as much as 1.3%.     

Hydrogen transferring liquefaction of some bituminous coals with hydrogenated fluoranthene under high temperature-short contact time conditions

Hydrogen transferring liquefaction using hydrogenated fluoranthene at high temperatures was very effective for three Japanese bituminous coals, with a total yield of oil and asphaltene > 85 wt%. The high temperature-short contact time conditions (480 °C for 10 min or 510 °C for 2.5 min) resulted in a total yield of > 90 wt% from the coal of lowest rank, with low consumption of hydrogenated fluoranthene. The oil yields were as high as 75 and 68 wt% at 480 °C and 510 °C, respectively. In contrast, the lower temperature of 450 °C appeared more effective in diminishing preasphaltene formation with the highest rank coal providing oil and asphaltene yields of 47 and 38 wt%, respectively. Longer times or higher temperature increased the oil yield but without reducing the preasphaltene. Higher temperature was found favourable for the formation of asphaltene of lower molecular weight. The reactivity of butiminous coals of different rank is discussed from the viewpoint of their structure.     

Free radicals in coal and coal conversions. 8. Experimental determination of conversion in hydroliquefaction

The results of conversion determinations on the products from Powhatan No.5 coal liquefied in an autoclave and in a high-pressure, high-temperature e.s.r. cavity are reported. Oil, asphaltene and preasphaltene yields, and overall conversion have been determined for Powhatan No.5 coal samples liquefied in tetralin, SRC-11 heavy distillate, and naphthalene at temperatures from 400 to 480 ° C in both reactor systems. The concept of reaction severity is introduced and used to formalize the relation between the effect of temperature and reaction time on oil yield and conversion. Oil is the predominant product in liquefaction in tetralin or naphthalene, asphaltene is the major product of liquefaction in SRC-II heavy distillate. Retrogressive reaction (THF-insoluble product formation) becomes severe when SRC-II heavy distillate is the liquefaction solvent and residence time of >10 min are used at temperatures >450 °C. Preasphaltenes appear to be the only intermediate species in Powhatan No.5 liquefaction.     

Hydroliquefaction of Wyodak coal using bottoms recycle

Wyodak coal has been liquefied using recycle solvents consisting of blends of Wyodak coal-derived distillates and SRC or SRC oils, asphaltenes and oils plus asphaltenes. Whilst the quality of the distillate portion of the bottoms recycle is maintained by hydrogenation and distillation in the Exxon Donor Solvent (EDS) process, no reported efforts have been made to hydrogenate the nondistillable portion of the EDS bottoms recycle solvent nor the bottoms recycle solvent in the SRC-II process. As hydrogenation of the distillate portion of the recycle solvent in the EDS process increased Wyodak coal distillate yields, this study was initiated to determine whether hydrogenation of the nondistillable portions of Wyodak coal-derived bottoms recycle solvent would show similar beneficial effects. Results suggest that distillable liquid yields in the range of 55–60 wt% of dry Wyodak coal can be obtained using mildly hydrogenated SRC or SRC oils plus asphaltenes as a bottoms recycle solvent component. This result can be compared to distillable liquid yields of 40 wt% of dry, Wyodak coal obtained from the EDS process using bottoms recycle. Further, the unhydrogenated, SRC-derived oil and asphaltene portions of the recycle solvent also appear to be effective solvent components. However, the most effective solvents were obtained using hydrogenated SRC or SRC-derived oils plus asphaltenes.     

Supercritical gas extraction of Victorian brown coals: The effect of coal properties

A selection of fifteen Victorian brown coals, which varied in lithotype but only slightly in rank, were subjected to supercritical gas extraction with toluene. Seven of these coals were also extracted with 5% tetralin/toluene under the same conditions of temperature and pressure (400 °C and 10 MPa). The overall conversion, the extract yield and the yield of toluene solubles (oil and asphaltene) were correlated with more easily obtained coal properties using simple linear regression analysis. Good correlations were obtained between the total conversions and the volatile matter content of the coals, and for the toluene extractions between both the extract yield and the yield of toluene solubles and the H/C atomic ratio. For the toluene solubles from the toluene extractions, the aromaticity decreased and the molecular weight increased as the H/C atomic ratio of the coal increased. Inorganic constituents of the coals did not appear to have a marked effect on total conversion and liquid yields. Removal of the cations from two coals increased conversion and liquid yields in one case and decreased these in the other, but in both instances the changes were not large.     

Liquefaction characteristics of selected vitrinite- and liptinite-rich coals from British Columbia,Canada

Four coals from British Columbia, Canada are described micropetrographically, and their liquefaction potential was tested in a rocking autoclave system. Rank was determined by measuring vitrinite reflectances and was found to range from subbituminous C to high volatile A bituminous. Composition was determined by maceral analysis. All four coals were found to be extremely high in the reactive maceral groups vitrinite and liptinite (> 97%) and were thus considered to be susceptible for liquefaction.Results of the liquefaction experiments indicate that in fact all four coals were converted easily into liquid and gaseous products. Overall conversion was found to be >90% and liquid yields (THF solubles) were beyond 80%. Alginite-rich coals from southeastern British Columbia were found to produce greater amounts of gases, indicating that temperatures used in the experiments might have been excessive for liquefaction of alginite-rich coals. Higher liquid yields and less gaseous products were obtained from the vitrinite-rich coals from northeastern British Columbia, indicating that these coals might have the optimum blend of vitrinite/liptinite macerals.     

Stability of some coal and tar sands syncrude fractions

Three fractions from a SRC-II coal liquefaction process, two naphthas from Illinois No. 6 coal and Wyodak coal using the Exxon Donor Solvent liquefaction process, and three fractions from tar sands extract were characterized for physical and chemical properties. Selected samples of syncrudes were stored at 43 °C for 32 weeks in air. The tar sands materials more closely resembled the properties of present petroleum-based materials, whereas the coal-derived liquids from the SRC-II process demonstrated the need for considerable upgrading. Heavier fractions seemed to undergo polymerization to produce gums, whereas lighter fractions deteriorated via oxidation.     

Rapid pyrolysis of Canadian coals in a miniature spouted bed reactor

A 25 mm diameter bench scale pyrolyser unit was constructed to study atmospheric pressure rapid pyrolysis of coal. Coals with particle size below 250 microns were injected continuously into a bed of sand spouted with nitrogen. Gas, liquid and char yields were determined as functions of temperature, coal feed rate and particle size. Gas compositions, tar yield and solvent fractionation results, and char proximate analyses are presented for six coals as functions of the pyrolysis temperature. Pyrolysis liquids from low rank coals contained significant amounts of water and were high in hexane solubles. Hexane and benzene soluble fractions are dependent on coal type and pyrolysis conditions.     

Liquefaction of subbituminous coals under apparently non-hydrogenative conditions

Reactivities of several coals of different ranks have been examined in degrading extractions with aromatic solvents under apparently non-hydrogenative reaction conditions. Pyrene and A240 pitch liquefied the fusible coals in high yields and the slightly-fusible coals in moderate yields, indicating the importance of fusibility in such liquefaction processes. A240-LS pitch is a powerful solvent for slightly-fusible coals. Considerable amounts of pyridine- or THF-soluble fractions were produced especially with A240-LS pitch. A240 pitch is a better solvent than pyrene for some slightly-fusible coals. However, the extent of depolymerization of liquefied coal, pyridine- or THF-solubility, was definitely inferior. Yields of such fractions are higher for lower-rank coals. The mechanism of coal liquefaction under apparently non-hydrogenative conditions is discussed with emphasis on the stabilization of thermal fragments derived from the coal.     

Re-examination of the phenolic hydroxyl contents of coals

In connection with studies of the dependence of liquefaction behaviour on coal characteristics, parameters were needed that might effectively characterize the organic chemical structures. Accordingly, the phenolic hydroxyl contents of 37 coals from three geological provinces of the USA have been determined, by acetylation with ¹⁴C-labelled acetic anhydride. The results, when expressed as fractions of the total organic matter in the coals, showed a good inverse correlation with the carbon contents (dmmf). However, application of a stepwise multiple regression analysis to the data developed a linear equation relating hydroxyl content to the vitrinite reflectance, calorific value and vitrinite content, the fraction of variance explained being 92%. When the hydroxyl contents were expressed in the alternative manner, as fractions of the total oxygen content, no correlation could be seen with carbon content. However, in the wide scatter of points on the graph, the data are seen to fall into three reasonably distinct populations such that at the same level of rank, hydroxyl contents typically decrease for coals from the three provinces in the order Interior > Eastern > Rocky Mountain, implying that coals from these areas differ in structure as a result of differing antecedents. Statistical analyses showed that $\text{OH}\text{O}$ has some significance in determining liquefaction behaviour, but it is not among the coal properties found most significant.     

Effect of oxidation on the chemical nature and distribution of low-temperature pyrolysis products from bituminous coal

Two bituminous coals, a high volatile Eastern Canadian and a medium volatile Western Canadian, were used to investigate the effect of oxidation on yields and chemical composition of gases, liquids and chars produced during coal pyrolysis. Pyrolysis experiments were performed at 500 °C using the Fischer assay method. Mild oxidation of coals resulted in a decrease of liquid hydrocarbon yields. Further coal oxidation increased the proportion of aromatic carbon in liquid products as determined by n.m.r., and also increased the content of oxygen in liquid products. The content of oxygen in chars was markedly lower than in corresponding coals. An attempt is made to explain reactions occurring during oxidation and subsequent pyrolysis of coal on the basis of differences in chemical composition of gases, liquids and chars.     

Composition of an SRC-II coal-derived liquid: Changes in composition resulting from hydrotreatment at different levels of severity

An SRC-II coal-derived liquid fuel and eight upgraded coal liquids derived from it were separated into chemical class-type fractions by preparative liquid chromatography. Mass and infrared spectroscopy, gas chromatography and non-aqueous titration were used, together with the mass balance data from the l.c. separations, to describe changes in composition of the liquids as a function of severity of hydrotreating conditions. The relative abundance of the following classes of compounds was determined in each of the liquids : saturates, monoaromatics, diaromatics, polyaromatics, total acids, total bases, hydroxyarenes, strong acids, pyrrolic benzologs, carbonyl compounds (amides), basic diarylamines, basic monoarylamines, azaarenes, and strong bases. The results are discussed in the light of known reaction pathways for aromatic ring saturation and heteroatom removal.     

Liquefaction of coal by SRC-II process: Part III: Reactivity of liquefaction products

Data from experimental studies of the reactivities of SRC-II liquefaction products, in the absence of coal, are analyzed. A general quantitative validation of the new kinetic model for SRC-II coal liquefaction (Singh et al., 1981 a) is obtained by very good agreement between model predicted and measured yields. This shows that the new kinetic model provides a reasonable representation of the overall intrinsic process of SRC-II coal liquefaction and hence, it can be used to explore the regions of process conditions far away from those obtained under normal SRC-II operations.     

Analyses of mild hydrogenation products of coals treated with zinc and butyl iodide

Butylation using zinc and butyl iodide under mild conditions (130 °C and atmospheric pressure) is an effective method to convert solid coals to soluble products in poor solvents such as hexane and benzene. Because of mild conditions and high solubility, the butylation of coals is found to be applicable for estimating coal structures. Until now, two typical coals, Taiheiyo and Yubari coals, were converted to hexane soluble products significantly. However they were too heavy to obtain much information on the structure of the original coals. In order to analyze the structural features of the coals butylated with zinc and butyl iodide, the polar mixture (PM) fractions separated from hexane soluble products (HS) from butylated Yubari and Taiheiyo coals were hydrogenated using Adkins catalyst. The HS products of hydrogenated PM fractions were fractionated by gel permeation chromatography (GPC), and the GPC fractions were further analyzed. After hydrogenation, structural parameters of HS products separated from PM fractions did not change so much, but molecular weight decreased. The GPC fractions (Fr.1–Fr.7) from both coals had similar high σal (degree of aliphatic chain substitution) as well as low fa (aromaticity) to the original PM fractions. These results indicated that the GPC fractions were highly butylated. Many structural parameters of GPC fractions except for Fr.7 were similar with each other. For Taiheiyo coal, the ring sizes of GPC fractions were 1–2, and similar to those from pyridine soluble products. For Yubari coal they were 2–3, and smaller than those from pyridine soluble product, 4 due to reductive butylation. The ring sizes of the Fr.7 from both coals were as small as one. Because the solvent soluble products were subject to reductive butylation, the naphthenic rings of the fractions seemed to be ruptured by hydrogenation. These findings suggest that high hexane extractability of the coals butylated with zinc and butyl iodide was caused by reductive butylation.     

Concentration and distribution of sixty-one elements in coals from DPR Korea

Fifty coal samples (28 anthracite and 22 lignites) were collected from both main and small coal mines in DPR Korea prioritized by resource distribution and coal production. The concentrations of 61 elements in 50 coal samples were determined by several multielement and element-specific techniques, including inductively coupled plasma atomic emission spectrometry (ICP-AES), and inductively coupled plasma mass spectrometry (ICP-MS), ion chromatogram (IC), cold-vapor atomic absorption spectrometry (CV-AAS), and hydride generation atomic absorption spectrometry (HGAAS). The ranges, arithmetic means and geometric means of concentrations of these elements are presented. A comparison with crustal abundances (Clarke values) shows that some potentially hazardous elements in the coals of DPR Korea are highly enriched Li, B, S, Cl, Zn, As, Se, Cd, Sn, Sb, W, Te, Hg, Ag, Pb, and La, Ce, Dy, Tm, Ge, Mo, Cs, Tl, Bi, Th and U are moderately enriched. A comparison of ranges and means of elemental concentrations in DPR Korea, Chinese, and world coals shows the ranges of most elements in DPR Korea coals are very close to the ranges of world coals. Arithmetic means of most elements in DPR Korea coals are close to that of American coals. Most elements arithmetic means are higher in Jurassic and Paleogene coals than coals of other ages. In DPR Korea coals, only seven elements in early Permian coals are higher than other periods: Li, Zn, Se, Cd, Hg, Pb, and Bi. Only five elements B, As, Sr, Mo, W in Neogene coals have arithmetic means higher than others. SiO₂ and Al₂O₃ in ashes are more than 70% except six samples. The correlation between ash yields and major elements from high to low is in the order of Si>Al>Ti>K>Mg>Fe>Na>Ca>P>S. Most elements have high positive correlation with ash (r>0.5) and show high inorganic affinity.     

The effect of preswelling and/or pretreatment of some Turkish coals on the supercritical fluid extract yield

The effects of preswelling, and/or pretreatment with 1N HCl of four Turkish coals (Bolu-Göynük, Seyitömer, Tunçbilek and Soma-Merkez) on the supercritical toluene extract yields have been investigated. Methanol, 1,4-dioxane, THF (tetrahydrofuran), pyridine and EDA (ethylenediamine) were used as swelling agents. Solvent swelling and pretreatment with 1N HCl of coals significantly enhanced the liquid yields. The effectiveness of the swelling solvents in enhancing the liquid yield is in the same order as their swelling ratios. Swelling in EDA and pyridine were more effective for the extraction of coals. The highest improved liquid yields in supercritical toluene for each coal was obtained by the combined effects of pretreatment and preswelling of coals. No simple trend in reactivity increment with properties of coals was observed.     

Low-temperature air oxidation of caking coals. 2. Effect on swelling and softening properties

Three highly swelling bituminous coals (< 75 um > 63 um size) were pre-oxidized to various levels of weight gain and then their plastic properties monitored during carbonization. Additions of relatively small amounts of oxygen (<1–2% by wt) cause marked changes in swelling and softening properties. In general, oxidation causes: substantial reductions in volume changes, increases in softening and dilation temperatures, and a slight reduction in resolidification temperatures. For coals which exhibit high fluidities, slight oxidation results in an increase in expansion prior to destruction of swelling properties. For a given level of weight gain, reduction in plastic behaviour of a coal becomes more severe as the temperature of pre-oxidation is increased. Weathering studies indicate that exposure of an hvA bituminous coal to moist air at ambient temperature has more effect on subsequent swelling and softening properties than exposure to dry air. Fine coal particles stored for extended periods of time in atmospheres with even slight oxygen concentrations show definite signs of weathering. The plastic properties of an oxidized coal may be partially resotred by grinding to expose new surface.