Composition, structure, and properties of coal from the 2.2 Ulug bed of the Elegestsk deposit in Ulug-Khemsk coal basin

Coal from the 2.2 Ulug bed of the Elegestsk deposit in Ulug-Khemsk coal basin is investigated in terms of international quality certification. According to State Standard GOST 25543-88, the coal is of rank Zh and technological group 2Zh. The coal’s code according to the international system and State Standard GOST 30313-95 is 08 0 01 8 38 05 04 36. Attention is paid to the composition and structure of the coal, which are associated with elevated clinkering properties at high vitrinite reflectance, as well as maximum yield and fluidity of thermostable liquid products in the coal’s plastic mass. These features indicate that the coal’s organic mass contains considerable quantities of thermally unstable hydroaromatic and aliphatic structures. On account of the low oxygen content in the organic mass of coal from the Ulug bed, with high quantities of carbon and hydrogen, much of the hydrogen formed on thermal destruction reacts with the radicals formed, which prevents their polycondensation, and considerable quantities of relatively low-molecular liquid products of the plastic mass are produced. The mineral component is characterized by low content of silicon and aluminum oxides (51.65%) and relatively high content of iron oxide (15.96%) and calcium oxide (15.07%). Accordingly, the base/acid ratio I _b and basicity index B _b are high: 0.692 and 6.29, respectively. The Donets Basin has no counterparts of this coal. Coal from the 2.2 Ulug bed of the Elegestsk deposit in Ulug-Khemsk coal basin may be regarded as a valuable component of coal batch.     

Comparison of the chemical structure of coal hydrogenation products,athabasca tar sand bitumen and Green River shale oil

Coal hydrogenation products, Athabasca tar sand bitumen, and Green River shale oil produced by retorting were analyzed by the Brown—Ladner method and the Takeya et al. method on the basis of elemental analysis and ¹H-NMR data, by ¹³C-NMR spectroscopy and by FT-IR spectroscopy. Structural characteristics were compared.The results show that the chemical structure of oils from Green River shale oil and Athabasca tar sand bitumen, and the oils produced in the initial stage of hydrogenation of Taiheiyo coal and Clear Creek, Utah, coal is characterized as monomers consisting of units of one aromatic ring substituted highly with C_3–6 aliphatic chains and heteroatom-containing functional groups. The chemical structure of asphaltenes from Green River shale oil and Athabasca tar sand bitumen is characterized by oligomers consisting of units of 1–2 aromatic rings substituted highly with C_3–5 aliphatic chains and heteroatom-containing functional groups. The chemical structure of asphaltenes from coal hydrogenation is characterized by dimers and/or trimers of unit structures of 2 to 5 condensed aromatic rings, substituted moderately with C_2–5 aliphatic chains and heteroatom-containing functional groups.The close agreement between fa(¹H-NMR) and fa(¹³C-NMR) for Green River shale oil derivatives and Athabasca tar sand derivatives indicates that the assumption of 2 for the atomic H/C ratio of aliphatic structures is reasonable. For coal hydrogenation products, a value of 1.6–1.7 for the H/C ratio of aliphatic structures would be more reasonable.     

13C, 2H, 1H n.m.r. and gpc study of structural evolution of a subbituminous coal during treatment with tetralin at 427 °C

Subbituminous Kaiparowitz coal was treated with 1,1-d₂-tetralin or tetralin in sealed tubes at 427 °C and 500 °C for varying periods of time and rates of temperature rise (15 °C/s, 3 °C/s, and 1 °C/s). The time dependence of yields, average molecular weights, molecular-weight distributions and changes in hydroxyl-group content and elemental composition were determined. Deuterium FT n.m.r. was used to monitor the incorporation of deuterium from 1,1-dideuteriotetralin into aliphatic and aromatic structures in the fractionated products. The exchange of ²H with phenol in the presence of the coal was examined to aid in the interpretation of ²H n.m.r. results. ¹³C and ¹H FT n.m.r. and i.r. spectroscopy were used to monitor the fractionated products over time. The ultimate obtainable yields of THF-soluble product were not significantly altered by the shorter temperature-rise times. The highoxygen-containing subbituminous coal undergoes an extremely rapid loss of about 20% of its oxygen by dehydration, and was found to enhance the rate of reduction of acetophenone and the scrambling of deuterium label in tetralin. The growth of benzylic aliphatic hydrogen at the expense of β (ArCH₂C$\text{H}$₂) hydrogen was rapid in the early stages of reaction. In spite of apparently labile aliphatic structures, the preasphaltenes exhibited products above MW 1200 that were stable for more than 2 h at 500 °C.     

Linear alkane chains in coals

The products of coals oxidized with 40% aqueous nitric acid at 60 °C include a homologous series of linear aliphatic diacids starting with succinic acid (C₄). These diacids are stable under the conditions of oxidation so that their amounts and lengths measure the amounts and lengths of the saturated components of linear aliphatic chains in the coals. In one coal (PSOC-155) they account for 38% of the carbon and members of the series up to C₂₃ were detected. Evidence is presented indicating that these chains are integral parts of the coal structure and not interspersed contaminants.     

Chemical characterization of coal. 3. Qualitative and quantitative aspects of the reductive methylation of coal

The treatment of coal with solvated electrons (formed as a blue solution by treating potassium with the dimethyl ether of ethyleneglycol) followed by solvolysis of the polyanionic coal with dimethylsulphate allows coal derivatives to be prepared, 85 wt% (daf) of which can be extracted with pyridine. Detailed investigations of these products, and of analogous deuterium-labelled derivatives, show that an average of 7 methyl groups per 100 C atoms have been introduced in a single treatment. This value can be increased by a second treatment, l.r. structure-element analysis shows, in addition, that 35% of the hydrogen so introduced forms hydroaromatic species and takes part in the degradation of aromatic structures. The site of the reaction is studied by comparing the results from the deuteromethylation of coal and of model compounds: it is suggested that the marked increase in extractability results from the cleavage of aliphatic bridges of the type ArCH₂CH₂Ar' giving ethyl-substituted aromatics and related products. A method is described which determines increments from quantitative i.r. measurements for model compounds and allows a rapid determination of the Cl_3-content of a deuterated coal.     

Combustion of carbonized coal residue in water–oxygen supercritical fluid

The autothermal regime of partial oxidation of carbonized coal residue in a stream of water-oxygen fluid at 923 K and 30 MPa is implemented for the first time. It is revealed that the oxidation of coal residue and the formation of combustible gases (hydrogen content in the products is increased by 26% with respect to its amount in the original sample) occur simultaneously and are caused by the participation of the H₂O molecules in the redox reactions.     

Low temperature oxidation of coals of different rank and different sulphur content

Five coals of different rank and of different content of sulphur were subjected to oxidation by peroxyacetic acid (PAA), 5% nitric acid, by oxygen in 0.5N Na₂CO₃ aqueous solution and the air oxidation for 7 days at 125 °C. The processes of oxidation were carried out for coal samples demineralised by the Radmacher method, and additionally for the pyrite-free coal samples. Proximate, elemental and spectral analyses of the initial coals and the products obtained from them were made. The most effective oxidising agents were 5% HNO₃ and PAA. As a result of oxidation, a significant part of the organic components of coal is converted into acid soluble products. Depending on the oxidising agent, the loss of sulphur in the solid oxidation products was different and the highest for the coal samples oxidised with HNO₃ and PAA. Formation of oxidised sulphur species (SO and -SO₂) was detected by IR spectroscopy. FTIR data also provide useful information on evolution of the molecular structure of different rank coals on oxidation, in particular in the carbonyl and aliphatic ranges (1800-1500 and 3500-2800 cm⁻¹).     

Coal structure change by ionic liquid pretreatment for enhancement of fixed-bed gasification with steam and CO<Subscript>2</Subscript>

An innovative pretreatment of Indonesian low-rank coal (ILRC) by 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) ionic liquid (IL) was conducted. The obtained IL pretreated coal had a loose and porous structure. Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) analysis showed that pretreated ILRC had a stronger absorption ability and an increased average pore size (from 23.6 to 51.8 nm). Steam-coal gasification was conducted to explore the effect of coal pretreatment. The result showed that 1.63-times more hydrogen was generated from pretreated coal compared to original (i.e., untreated) coal, and carbon conversion (X _c ) increased from 89.03 to 97.25%. During CO₂ coal gasification, IL pretreated coal had a greater CO₂ consumption potential and generated more CO. The chemical exergy of syngas of the pretreated coal gasification was higher than that of the untreated coal gasification with CO₂ at 900 °C. In addition, pretreated coal emitted less CO₂ than untreated coal at 900 °C.     

酸洗脱灰后平顶山煤镜质组分的结构变化

利用傅立叶红外光谱(FTIR)技术对平顶山矿区的原生结构煤、糜棱煤和三级酸(HCl-HF-HCl)脱灰处理后的煤镜质组分差异进行了分析,运用origin9.1软件对不同类型煤的红外光谱曲线进行了分段分峰拟合,并计算了红外光谱结构参数。结果表明,经过三级酸脱灰后,灰分脱除率达96%;脱灰后原生结构煤对称的CH2相对含量减少,不对称的CH2增加,糜棱煤呈现相反的趋势,说明脱灰处理对煤的脂肪结构有一定的影响;原生结构煤的结构参数I1(脂肪结构)值、I2(芳香结构)值和A(生烃潜能)值均比较大,说明其含有大量的脂肪烃并具有良好的生烃潜能;芳香烃CC含量较高且脱灰前后变化不明显,说明煤有机键的主要部分为CC,且结构相对稳定;糜棱煤的五取代芳环含量和I1值低于原生结构煤,说明原生结构煤在构造应力作用下发生脂肪侧链脱落,缩合程度增加,导致糜棱煤具有超前演化的特征。     

Correlation of coal volatile yield with oxygen and aliphatic hydrogen

An interesting correlation has been observed between the volatile yield for three coal conversion processes and the oxygen and aliphatic hydrogen (H_al) content of the coal. The three processes are: (1) rapid pyrolysis in vacuum, (2) hydropyrolysis at ≈10 MPa hydrogen, and (3) liquefaction with tetralin at 400 °C. The volatile yield for the first two processes and for low sulphur coals studied in the third process may be predicted with the equation: Yield≈0.8 O_T+15 H_al where: O_T, the organic oxygen concentration measured by ultimate analysis; and H_al is the aliphatic hydrogen concentration determined from Fourier Transform infrared (FTIR) measurements. The similarity of yields for these processes suggests that they are basically controlled by thermal decomposition. Justification for the above equation is offered by considering a recently developed model for thermal decomposition of coal. The correlation does not fit a group of high sulphur coals studied in the liquefaction programme. These coals have extremely high volatile yields which may be a result of catalytic activity.     

Study of the preasphaltenes of coal liquefaction and its hydro-conversion kinetics catalyzed by SO4/ZrO2

The investigation of hydro-conversion behavior of the heavy intermediate products derived from coal direct liquefaction is advantageous to optimize the technological conditions of direct coal liquefaction and improve the oil yield. In this paper, the hydro-conversion of preasphaltenes catalyzed by SO₄²⁻/ZrO₂ solid acid was investigated based on the structural characterization of preasphaltenes and its hydro-conversion products, and the determination of products distribution and the kinetics of preasphaltenes hydro-conversion. The results indicated that the content of condensed aromatic rings increased, and the contents of hydrogen, oxygen and aliphatic side chains of preasphaltenes decreased with the increase of coal liquefaction temperature. The preasphaltenes showed higher hydro-conversion reactivity while SO₄²⁻/ZrO₂ solid acid was used as catalyst. Higher temperature and longer time were in favor of increasing the conversion and the oil + gas yield. The conversion of preasphaltenes hydro-conversion under 425 °C, for 40 min reached 81.3% with 51.2% oil + gas yield. SO₄²⁻/ZrO₂ solid acid was in favor of the catalytic cracking rather than the catalytic hydrogenation in the hydro-conversion of preasphaltenes. The activation energy of preasphaltenes conversion into asphaltenes was 72 kJ/mol. The regressive reactions were only observed at a higher temperature.     

Oxidations of coal by aqueous sodium hypochlorite

Oxidations of Illinois No. 6 coal, mostly as insoluble residues of pyridine extractions, by aqueous NaOCl at 30 °C have yielded several products. They range from black, bicarbonate-soluble acids of molecular weight as high as 1000 to nearly colourless, water-soluble acids with molecular weights near 300. Most of the products have a higher ratio of aliphatic/aromatic content than the original coal. The product mix depends mostly on the pH during oxidation and on the state of subdivision of the coal. At pH 13, 96% of the coal introduced is dissolved and 80% of the carbon dissolving is found as the high-molecular-weight acids, which present a promising soluble material for investigation of coal structure. At lower pH, more of the coal structure is destroyed; simple, oxidation-resistant benzene and aliphatic carboxylic acids then become the principal organic products.     

Characteristics and carbonization behaviors of coal extracts

N-methyl pyrrolidone (NMP) raw coal extract (EXT), hydrogenated coal extract (HEXT) and the blend of EXT and HEXT in NMP (BLD), from two bituminous coals, were studied. The extracts were carbonized in both tube-bomb and a temperature programmable furnace. Elemental analysis, FTIR spectroscopy and optical microscopy techniques were employed to characterize the extracts and the carbonization residues. It was found that the extracts resembled petroleum-derived pitches in the hydrogen content and (C/H)_atomic ratio. Higher oxygen and nitrogen contents differentiated the coal extracts from commercial petroleum pitch. More carbon and hydrogen, and lesser oxygen and sulfur differentiated HEXT from EXT. The ratios of integrated IR band intensity for aromatic and aliphatic CH stretching indicate that the relative content of aliphatic hydrogen in EXT is higher than in HEXT. HEXT contains comparatively more aromatic hydrogen, a feature necessary for thermal stability and fluidity during carbonization. BLD materials are at a place somewhere in between. Kinetic modeling of the aliphatic hydrogen change during carbonization reveals that EXT has high carbonization rate and low apparent activation energy. This can be related to the optical texture size of carbonization residues. The residues made from EXTs exhibited fine mosaic optical texture and limited mesophase development. HEXTs were readily converted into highly anisotropic coke. BLDs produced carbonization residues with intermediate properties. Extracts with similar activation energies produced similar residues in the same coal series. The degree or extent of anisotropy displayed by the carbonization residues was found to be dependent on the relative distribution of aromatic and aliphatic hydrogen.     

Hydroliquefaction of low-sulfur coals using iron carbonyl complexes—Sulfur as catalysts

Hydroliquefaction of low-sulfur Australian coals (Wandoan and Yallourn) was studied using iron carbonyl complexes as catalyst. The addition of Fe(CO)₅ (2.8 wt% Fe of coal) increased coal conversion from 48.6 to 85.2% for Wandoan coal, and from 36.7 to 69.7% for Yallourn coal in 1-methylnaphthalene at 425°C under an initial hydrogen pressure of 50 kg cm^?2. When molecular sulfur was added to iron carbonyls (Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂), higher coal converions ( > 92%) and higher oil yields (>46%) were obtained, along with an increase in the amount of hydrogen transferred to coal from the gas phase (0.2 to 2.8%, d.a.f. coal basis). In the liquefaction studies using a hydrogen donor solvent, tetralin, Fe(CO)₅S catalyst increased the amount of hydrogen absorbed from the gaseous phase and decreased the amount of naphthalene dehydrogenated from tetralin. The direct hydrogen transfer reaction from molecular hydrogen to coal fragment radicals seems to be a major reaction pathway. Organic sulfur compounds, dimethyldisulfide and benzothiophene, and inorganic FeS₂ and NiS were found to be good sulfur sources to Fe(CO)₅. From X-ray diffraction analyses of liquefaction residues, it is concluded that Fe(CO)₅ was converted into pyrrhotite (Fe_1?xS) when sulfur was present, but into Fe₃O₄ in the absence of sulfur.     

Non-isothermal liquefaction of liptobiolith coal in supercritical water flow and effect of zinc additives

The liquefaction of liptobiolith coal in water vapor and supercritical water (SCW) flow at uniform increase in temperature from 300 up to 470 °C and in SCW flow at 400 °C (30 MPa) with addition of zinc shavings to coal has been investigated. Temperature dependences of the yield of liquid and volatile products and kinetic parameters of the process have been obtained. The yields of oil, resin, asphaltene and volatile products in relation to the coal organic matter (COM) are 23.2, 16.1, 5.1 and 14.1%, respectively. CO₂, CO, H₂S and C₁–C₄ alkanes prevail in the composition of volatile products. The generation of oil, resin and asphaltene are found to have occurred in terms of the simultaneous chemical reactions of cleavage of the COM aliphatic CC bonds, while the volatile products result from the consecutive transformations of the COM components in the bulk and SCW solution. Participation of H₂O molecules in thermochemical transformations of COM leads to increase in the oxygen amount in the conversion products and residue by 13.2%. Hydrogen and heat evolution during zinc oxidation by SCW provides for the hydrogenation of COM in situ. Addition of zinc to coal results in increase in the volatile products yield up to 48.6% and decrease in the conversion residue yield up to 20.8%. Under these conditions the yield of resin does not change, while the yields of oil and asphaltene decrease up to 21.2 and 2.5%, respectively. Based on the sulfur balance it is revealed that ≈40% of sulfur atoms pass into ZnS owing to the reactions of H₂S with Zn and ZnO resulting in the removal of H₂S from the volatile conversion products.     

The characterization of coal macerals by diffuse reflectance infrared spectroscopy

Diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was applied to study the structure of vitrinites, liptinites and fusinites isolated from different rank coals (77.0-91.5%C) using a centrifugal float-sink procedure. Among the macerals separated from a given coal, liptinites are characterized by the highest proportion of aliphatic CH groups, occurring principally as CH₂, and fusinites by the most aromatic structure. Macerals separated from the low rank coals show comparable content of hydroxyl groups that occur as free OH or form similar types of hydrogen bonds. Carbonyl groups appear not only as conjugated ketones and quinones in vitrinites, but also as carboxylic groups in liptinites and low rank fusinites. CH_ar/CH_al ratio does not vary with carbon content in liptinites, but increases in vitrinites and fusinites. In the case of liptinites and vitrinites, a linear relationship between CH_ar/CH_al and reflectance is observed up to vitrinite R₀ value of 1.80%. For all macerals, the ratio CH_ar/CC increases with reflectance, but at different rates. Structural parameters CH_ar/CH_al and CH_ar/CC calculated from DRIFT spectra are very helpful in monitoring the differences among macerals of given coal and following structural rearrangement occurring with rank.     

Superacid coal chemistry: 1. HF:BF3 catalysed depolymerization—ionic hydroliquefaction of coals under mild conditions

HF:BF₃:H₂ catalysed depolymerization and hydroliquefaction of coal was studied. This superacidic system was found to be extremely effective for low temperature liquefaction of coal. Illinois No. 6 coal could be solubilized in pyridine to the extent of > 90% by treating it at ≈ 105 °C for 4 h. Under somewhat more elevated temperature (150–170 °C) cyclohexane extractabilities of up to 22% and distillability of up to 28% is achieved. A hydrogen donor solvent such as isopentane is shown to improve the efficiency of the superacidic catalyst for the conversion of coal to cyclohexane soluble products.     

Alcohols as H-donor media in coal conversion. 1. Base-promoted H-donation to coal by isopropyl alcohol

Isopropyl alcohol can act as a hydrogen donor to coal, as can tetralin. In contrast to tetralin, however, the transfer of hydrogen by the alcohol can be promoted by the presence of either potassium isopropoxide or KOH. Acetone is formed from the alcohol in quantities that accord with the amounts of hydrogen transferred to the coal. In runs at 335 °C for 90 min, coal was converted with isopropyl alcohol in the presence of either the alkoxide or KOH to a fully pyridine-soluble product with $\text{H}\text{C}$ ratios from 0.88 to 1.13, in contrast to coal (0.79). The organic sulphur content of the coal was reduced from 2.1% to 1%. Model-compound studies with anthracene and diphenyl ether showed that the anthracene was reduced in the system to 9,10-dihydroanthracene, but the ether was recovered unchanged. The coal products from the alcohol/base treatment are very rich in aliphatic hydrogen and have number-average molecular weights in the 450–500 range. The scheme suggested to explain the conversion at 335 °C includes initial hydrogenation of anthracene-like structures in the coal, followed by thermolysis of the dihydro-intermediate.     

Investigation of aqueous sodium dichromate oxidation for coal structural studies

To determine optimum conditions, the aqueous Na₂Cr₂O₇ oxidation as applied to coals, coal products, model compounds and polymers was investigated in detail. It was found that this oxidation preferentially attacks aliphatic and alicyclic methylene linkages with minimum degradation of most aromatic ring systems, as suggested earlier. However, aliphatic-rich macromolecules, probably related to exinites, were found to be selectively oxidized and isolated as long-chain aliphatic dicarboxylic acids under buffer-controlled oxidation conditions.