Coal liquefaction by in-situ hydrogen generation.: 1. Zinc-water-coal reaction

Liquefaction of coal was carried out in a zinc—water—solvent system to give a product with high concentration of pyridine and benzene solubles. In this system the metal reacts with water to produce the corresponding metal oxide and hydrogen. This hydrogen was used for in-situ hydrogenation of coal. The effects of reaction time, temperature, type of solvent, the quantity of metal used and the rank of coal were investigated. The solvent has a very marked effect on the conversion of coal to benzene-soluble materials, especially at short reaction times. A maximum benzene conversion of 96% for Taiheiyo coal was obtained when it was treated at 445 °C for 1 h using wash oil as solvent. With regard to the influence of coal rank it was found that low rank coals were more reactive than high rank coals. The amount of preasphaltene is only slightly influenced by coal rank but depends on the temperature and the type of solvent used.     

Effect of air oxidation on coal hydrogenation

Japanese Taiheiyo coal (75.9%C) was oxidized with air at 250 °C for 3–40 h and at 300 °C for 3–10 h. The weight decreased from 16.3 to 46.5% at 250 °C and from 21.7 to 41.3% at 300 °C. Carbon loss and yield of NaOH soluble were obtained. The resultant oxidation products were hydrogenated at 370 °C for 1 h under 10 MPa hydrogen pressure using red mud with sulphur as catalyst and wash oil as solvent. Conversion to pyridine, benzene and n-hexane soluble fraction shows a minimum for the coal oxidized 10 h at 250 °C and for the coal oxidized for 3 h at 300 °C. Initial oxidation makes a network structure which contributes to a reduction in conversion, but in later stages of oxidation, splitting of bridge linkages and/or ring opening of aromatic structures, contribute to increases in conversion.     

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.     

Reaction of coals in hot acidic phenol at constant acid concentration

Previous work showed that the efficient ‘depolymerization’ of bituminous coals in hot phenol containing p-toluenesulphonic acid failed to occur and that the acid was destroyed during the reaction. Four coals varying in rank from lignite to low volatile bituminous were treated with refluxing phenol containing p-toluenesulphonic acid with the acid concentration held constant. The amount of colloidal material, of pyridine-soluble material, of benzene—ethanol solubles, and the number average molecular weight of the pyridine extractables were measured as a function of time. Although the reaction proceeds better with the lower rank coals, a large portion of the products is colloidal material. Treatment of coals with hot acidic phenol does not lead to their complete depolymerization. Treatment of Bruceton coal with refluxing phenol saturated with BF₃ also failed to give complete depolymerization. The formation of colloidal suspensions during investigations employing spectral and other physical measurements may lead to results that are susceptible to misinterpretation.     

Increase in extractability of bituminous coals caused by Friedel-Crafts acylation

Four bituminous coals of different rank were acylated with aliphatic acyl chlorides using Friedel-Crafts catalysts. A dry steam coal and a coking coal showed particularly good reactivity, five acyl groups being inserted per 100 carbon atoms. Compared with the initial coal, the acylated coals were distinguished by considerably higher amounts soluble in pyridine and other solvents. 85% of the coking and dry steam coal substance became soluble when acylated with lauric acid chloride or acyl chlorides having still longer chains. The extractability of the coals after acylation depends on the chain length of the inserted acyl groups. To all appearances, the extracts are dispersed in the solution in the form of molecules. It is supposed that the good extractability of acylated coals is mainly due to depolymerization of the coal substance during acylation, disappearance of hydrogen bridges by esterification of the phenolic OH groups, and neutralization of inter-molecular forces between the aromatic structures by insertion of long-chain substituents.     

Effect of coal particle size on the coal hydrogenation reaction — In relation to the plasticity of coal

The effect of coal particle size on the catalytic hydrogenation of dry coal was investigated for three Hokkaido coals (Japan) of different ranks. It was found that the effect of coal particle size on conversion is dependent on coal rank. A greater difference in conversion with respect to coal particle size is noticed for coals of lower carbon content. The physical appearance of the products in the autoclave after the reaction suggests that the effect of particle size on conversion is dependent on the plastic properties of the heated coal sample. When the reaction proceeds with coal in the plastic state, the effect of particle size is small. As indicated by the product distribution, the plastic properties of a coal sample are related to the yield of asphaltene (hexane insoluble/benzene solubles) and/or the structural parts of original coal which yield asphaltene.     

Pyrolysis—gas chromatography of Australian coals. 2. Bituminous coals

Pyrolysis—gas chromatography (Py—g.c.) was used to characterize quantitatively a series of high- to low-volatile bituminous Permian Australian coals. The levels of n-alkanes, n-alkenes and triterpenoids released by pyrolysis all decrease as a function of increasing rank and thus, the coal samples can be classified into three distinct groups. Carbon Preference Indices (CPI's) for alkanes and alkene/alkane ratios also decrease as a function of rank. The triterpenoids have exclusively the hopane skeleton. The hopane isomeric distributions exemplify the geological maturity of bituminous coals relative to brown coal (lignite). A significant correlation has been established between the level of n-alkanes and n-alkenes released under Py-g.c. conditions and the predicted oil yield by pyrolysis of these coals. Further development and application of the techniqueshould enable much to be learnt relating to the quality and yield of flash pyrolysis tars as well as the original coal macromolecular structure.     

Flash hydrogenation of coal. 3. A sample of US coals

The susceptibility of a group of US coals to the production of light gaseous and liquid hydrocarbons during flash hydrogenation is examined. Eight coals ranging from lignite to high-volatile A bituminous and representing five provinces, have been flash heated in 101.3 MPa of flowing hydrogen using a bench scale reactor. A 0.6 s gas phase residence time was provided to hydrocrack the vapour products. Temperatures ranged from 750 to 850°C, where maximum yields of ethane and BTX (benzene+toluene + xylene) are found. The carbon conversion decreased with increasing rank at fixed reaction conditions. Methane yields are highest for lignite. Peak ethane yields range from 6.4 to 9% carbon conversion. BTX yields have a shallow maximum at intermediate ranks, decreasing towards high and low rank coals. Total liquid yields range from 14 to 43%. Although a definite variation of yield with rank is evident, the trends, especially total liquid yields, are attended by considerable scatter. Rank is not the only, and indeed may not be the most significant variable in determining the yield of individual species in flash hydrogenation. To establish the significant variables a stepwise regression procedure was applied to the experimental data using information from the elemental, proximate and petrographic compositions of the coals as independent variables. Two variables are adequate in all cases to correlate species yield and coal properties. Exinite appears to be capable of increasing the amount of liquid obtained from other macerals.     

A study by density measurement of changes in pore structures of coals with heat treatment: Part 1. Macropore structure

Changes in the pore structures of six Japanese coals with heat treatment up to 1200 °C were followed both by measurement of densities in mercury and in n-hexane and by mercury porosimetry. Pore volumes deduced from the difference between the reciprocals of densities measured in mercury and in n-hexane were almost equal to pore volumes deduced from mercury penetration for all the coals heat-treated. This suggests that, for all the coals, transitional pores and micropores whose entrance diameter is larger than the diameter of the n-hexane molecule were not developed or produced by heat treatment. For caking coals, the pore volume changed sharply in the plastic stage of carbonization, with a maximum at ≈400 °C that was probably due to the appearance and disappearance of bubble structure, whereas for non-caking coal it did not show any appreciable change in the range of heat treatment temperature (HTT) studied. It is suggested that the macropore structure of carbonized coals is related to the hardness, or the binding energy between their molecules.     

Chemical structure of the high-molecular-weight hydrogenation products of coal from the Zashulanskoe field

The results of experimental studies on the determination of the chemical structure of asphaltenes and preasphaltenes in the liquid products of the hydrogenation of coal from the Zashulanskoe field in the Chita oblast. It was found that, in the preasphaltenes, the value of f _a and the concentrations of oxygen groups (OH, COOH, and C=O) were greater and the concentrations of CH₂ and CH₃ groups were smaller that those in the asphaltenes. The highest concentration of CH₂ groups was found in substances soluble in n-hexane (oils). It is likely that the change in the character of high-molecular-weight hydrogenation products formed from the structural fragments of the organic matter of coal (OMC) largely depended on reaction conditions, namely, the rate of heating and the isothermal exposure time.     

Differential scanning calorimetry studies on coal. 2. Hydrogenation of coals

Results of exothermic heats involved during hydrogenation of twenty U.S. raw coals of varying rank at 5 · 6 MPa (gauge) and temperatures up to 570 °C are reported. The heat evolved during hydrogenation up to 570 °C decreases with increase in coal rank. A part of the total heat released during hydrogenation of coals appears to be due to the exothermic reaction between H₂ and surface carbon-oxygen complexes removed during the reaction. The transition temperature, that is the temperature corresponding to the onset of exotherms, is markedly dependent on coal rank. A sharp increase in the transition temperature occurs for coals having a carbon content, on a dry-ash-free basis, in the 75–80% range. Demineralization of coals lower in rank than HVA bituminous decreases the heat of hydrogenation; in the case of higher-rank coals, exothermic heats increase upon demineralization. The presence of pyrite has a beneficial catalytic effect on coal hydrogenation.     

The estimation of char reactivity from coal reflectogram

Measurements of the intrinsic reactivity of chars to oxygen are increasingly being sought as an indicator of the combustion potential of fuels. The coal reflectogram has been used to characterize the chemical properties of coal and its resultant char structure. In this study, six Australian coals varying in rank were separated using density separation technique to obtain vitrinite and inertinite rich fractions. Chars were obtained from these density fraction samples in a Drop Tube Furnace (DTF) at 1673 K. The reactivity of the chars was measured non-isothermally in a Thermal Gravimetric Analysis (TGA) in the temperature range of 573–1073 K. The results suggested that with the increase in the coal rank, the maximum reactivity of chars derived from vitrinite rich fractions decreases, while the reactivity of chars derived from inertinite rich fractions decreases with the increase in the inertinite content in samples and has no obvious relationship with rank. The kinetic parameters were derived using data from non-isothermal TGA after accounting for changing in surface area with conversion. The frequency factor is found to decrease with increasing coal FMR, defined as the summation of each reflectance value multiplied by its frequency, for a constant activation energy (E=146 kJ/mol). This suggests that the behavior of a maceral is characterized primarily by its reflectance distribution instead of the type of its parent coal.     

Reaction mechanism of coal hydrogenation. 3. Effect of coal type

Seven coals have been hydrogenated in naphthalene and phenanthrene under 10 MPa (initial pressure) of hydrogen with a stabilized niekel catalyst at 400°C for 15 min. Preasphaltene, asphaltene and oil conversions and solvent conversion were measured. The amounts of hydrogen absorbed by coal and by solvent were calculated. Coal conversion and the amount of hydrogen absorbed by coal decreased, while the amount of hydrogen absorbed by solvent increased, with increase in coal rank. The ratio of the amounts of hydrogen absorbed by coal and by solvent showed a good correlation with conversion to benzene- and n-hexanesoluble materials. Naphthalene and phenanthrene gave similar results, suggesting that the coal was hydrogenated directly by gaseous hydrogen.     

Chemical structure of coals as indicated by reductive alkylation

Reduction with potassium in tetrahydrofuran in the presence of naphthalene, and alkylation of the ‘coal anion’, were applied to coals of different rank. The reduction reaction alone increases the dissolution of the coals in benzene only to a very small extent. However, the reduction process in conjunction with alkylation of the ‘coal anion’ leads to products readily soluble in benzene. The solubilization of alkylated coals depends on the type of coal, the degree of its substitution with alkyl groups, and the length of the substituent alkyl chain. The number-average molecular weights of benzene extracts from the lowest-rank coal ranged from 500 to 800, whereas the higher-rank coals consist essentially of structural units characterized by number-average molecular weights ranging from 1300 to 2000.     

A reactivity study of chars obtained at different temperatures in relation to their petrographic characteristics

This study reports on the reactivity of chars obtained at 1000°C and 1300°C (within the range of temperatures reached by coal particles in the near-burner zone of pulverised fuel boilers) from three different coals. The coals were selected according to petrographic criteria: two of them are high volatile bituminous coals differing in maceral composition and the third one is a vitrinite-rich low volatile bituminous coal.The morphology and optical texture of the chars were studied by optical microscopy. The kinetic parameters for the combustion of the high temperature chars under Regime I (combustion controlled by chemical kinetics) have been obtained and related to the optical texture and reflectance of the chars. The intrinsic reactivity of the high temperature chars was found to be lower than that of the low temperature chars, whereas the enhanced porosity observed in the high temperature chars had a positive effect on their combustion reactivity under Regime II (combustion controlled by oxygen pore diffusion). The intrinsic reactivities of the chars decreased following the sequence: vitrinite-rich low rank char>inertinite-rich char>vitrinite-rich high rank char. As the combustion temperature increases, the reactivity of the inertinite-rich char approaches that of the low rank vitrinite-rich char, which justifies the good performance observed for high volatile bituminous inertinite-rich coals in power plants.     

Coal microlithotype response to froth flotation in selected Western Kentucky coals

Seven coals representing four western Kentucky coal seams and the coal rank range from high volatile C to high volatile A bituminous were selected for bench-scale froth flotation processing. Each coal was represented by two splits of the run-of-mine coal: a 12.7 mm × 0 fraction (crushed to 28 mesh × 0) and a 28 mesh × 0 fraction. The original 28 mesh × 0 split was found to be higher in the inertinite macerals fusinite and semifusinite than the coarser fraction. The separation of the inertinite macerals, expressed as the microlithotype inertite, from the vitrinite-rich vitrite and clarite microlithotypes proved to be markedly rank dependent. In the higher rank coals vitrite and clarite were concentrated in the clean coal while inertite was concentrated in the clean product in the high volatile C coals. Whereas in gravity-based coal cleaning only the finest pyrite usually remains in the clean coal, in this study no consistent trend in pyrite-size or pyrite-quantity partitioning was noted.     

New chemical structural features of coal. The structure of coal products

The object of this paper is to demonstrate the usefulness of the transalkylation reaction for determining chemical structural features of products derived from coal. For example, the method is applied to derivatized coals, coals modified by thermolysis, and materials physically or chemically separated from coals. Data are presented for the pyridine soluble and insoluble parts of two coals, an O-methylated coal, a Birch reduced coal, a solvent refined coal, and a coke. Similarities and differences in chemical make-up of these materials are discussed.     

Reactivities of 34 coals under steam gasification

The reactivities of 34 coal chars of varying rank with H₂O have been determined to examine the effect of coal rank on the gasification rate of coal char. The reactivities of chars derived from caking coals and anthracites (carbon content > 78 wt%, daf) were very small compared with those from non-caking (lower-rank) coals. The reactivities of low-rank chars do not correlate with the carbon content of the parent coals. To clarify which factor is more important in determining the reactivity, the evolution of CO and CO₂ from char, the moisture content of char and the amount of exchangeable cations were determined for these low-rank coals or their chars. These values were considered to represent the amount of active carbon sties, the porosity and the catalysis by inherent mineral matters, respectively. It was concluded that the amount of surface active sites and/or the amount of exchangeable Ca and Na control the reactivity of low-rank chars in H₂O.     

不同煤阶煤的CS2-NMP萃取率及与煤性质的关联

对6种不同变质程度煤(包括气煤、弱黏煤、肥煤、焦煤和瘦煤)常温常压下用CS2-NMP混合溶剂进行了萃取实验.结果表明,挥发分(Vdaf)为35%左右的煤具有最高的萃取率,达到43.05%,不同煤阶煤的萃取率与其奥压膨胀度及塑性温度区间近似呈线性关系.通过对原煤、萃取残渣和生成焦粒的红外对比分析表明,不同变质程度煤经过萃取后,残渣中脂肪烃和脂环烃含量有所减少,矿物质大都在残渣中,氢键缔合峰的强弱随不同煤种表现不同,肥煤和气煤氢键缔合的极性键都位于煤中的大分子上,而焦煤和弱黏煤中的极性键大都在小分子化合物上.     

Reactivity of heat-treated coals in air at 500 °C

Twenty one US coals, of widely ranging rank, have been carbonized under controlled conditions to 1000 °C, and the reactivity in air at 500 °C of the resulting chars or cokes has been measured by a gravimetric method. The reactivities lie within a well-defined band when plotted against rank of the parent coal. The lower-rank coal chars are more reactive than those prepared from high-rank coals. In extreme cases, the reactivity found for a Montana lignite char is some 100 times as great as that obtained for a char produced from a Pennsylvania low-volatile coal. Variation of reactivity with heat-treatment temperature (600 to 1000 °C) has been studied for three coals. As heat-treatment temperature increases, there is a decrease in reactivity. Some results are reported on the effects which mineral matter and pore structure have on the reactivity parameter. Chars containing high concentrations of magnesium and calcium impurities are most reactive. The amount of macro and transitional porosity in a char has a marked influence on reactivity.