The roles of vehicle and gaseous hydrogen during short contact time coal liquefaction

The roles of the vehicle and gaseous hydrogen during short contact time liquefaction (SCTL) in microreactors were examined by using a number of synthetic vehicles. The importance of vehicles during SCTL was evaluated on their ability to convert coal to tetrahydrofuran (THF)-soluble products. Reaction conditions were three minutes at 425 °C following a one minute heat-up. Although the consumption of hydrogen (hydrogen donor or gaseous hydrogen) by reactive coal fragments is minimal during the early stages of liquefaction (as in SCTL reactions), hydrogen donors were important and could be ranked according to the extent of conversion to THF-soluble products (tetrahydroquinoline > hydrogenated pyrene > dihydroanthracene = dihydrophenanthrene > tetralin). The importance of gaseous hydrogen was also studied. Gaseous hydrogen was needed if either quality or quantity of hydrogen donor was not adequate in a SCTL reaction. With certain synthetic vehicles, the SCTL stage of an integrated two-stage liquefaction process could be conducted in the absence of hydrogen. Solubility properties that might enhance solubilization of coal-derived products, and therefore the extent of liquefaction, were examined by varying the concentration of certain components (m-cresol and quinoline) of the synthetic vehicle mixtures. Solubility effects were minimal.     

Pyrolysis studies of organic oxygenates: 3. High temperature rearrangement of aryl alkyl ethers

Thermal chemistry pathways of aryl alkyl ethers have been investigated under coal conversion-like conditions. Anisole is a thermally reactive compound having an oxygen functionality found in such coal precursors as lignins. Pyrolysis of anisoles was carried out using small batch autoclaves. Under thermolysis conditions anisole yielded a product distribution strongly dependent upon experimental parameters. Phenol, methane, CO and benzaldehyde are the low molecular weight products and polyphenyls and polyethers are the predominant high molecular weight products. The generation of CO is explained by a high temperature rearrangement of the phenyl group from O- to C- followed by rapid thermal decarbonylation of the benzaldehyde. Carbon monoxide formation from aryl alkyl ethers can thus be an important mechanistic pathway in coal conversion processes. By investigating the rearrangement using para-fluoroanisole it was shown that this rearrangement proceeds via a three-centered intermediate to para-fluorobenzaldehyde. No meta isomer was observed.     

煤颗粒燃烧过程氧化机理及有机氮转化的分子模拟：以宁东红石湾煤为例

煤燃烧是煤炭资源有效利用的重要方式之一。从原子分子水平上识别煤燃烧的机理,系统把握反应条件的影响,揭示含氮污染物迁移转化的路径对于煤炭高效清洁利用具有重要意义。以前期构建的宁东红石湾煤分子结构模型为基础,采用反应分子动力学模拟方法对煤大分子结构聚集态模型进行燃烧反应模拟,考察化学当量比和反应温度对燃烧过程中结构演变、燃烧反应物和产物的影响,探究有机氮转化路径。研究发现,随着反应不断进行,煤结构的断裂变化非常明显。不同化学当量比和不同温度下煤燃烧的结果表明,化学当量比越大、燃烧温度越高时,O₂分子消耗速度越快,CO₂的生成量也越多。对燃煤过程中含氮气体分子数量的分析表明,HCN是重要的含氮中间产物,NO、NO₂是主要含氮气体产物。本研究还建立了煤燃烧过程中有机氮的转化路径,获得了HCN、NO和NO₂的演变过程。     

Coal gasification with water under supercritical conditions

The conversion of an array of coal particles in supercritical water (SCW) was studied in a semibatch reactor at a pressure of 30 MPa, 500–750°C, and a reaction time of 1–12 min. The bulk conversion, surface conversion, and random pore models were used to describe the conversion. The quantitative composition of reaction products was determined, and the dependence of the rate of reaction on the degree of coal conversion, reaction time, and reaction temperature was obtained on the assumption of a first-order reaction and the Arrhenius function (E = 103 kJ/mol; A ₀ = 7.7 × 10⁴ min^?1). It was found that the gasification of coal under SCW conditions without the addition of oxidizing agents is a weakly endothermic process. The addition of CO₂ to SCW decreased the rate of conversion and increased the yield of CO. It was found that, at a 90% conversion of the organic matter of coal (OMC) in a flow of SCW in a time of 2 min, the process power was 26 W/g per gram of OMC.     

Coal liquefaction in lignin-derived liquids under low severity conditions

It is found that lignin-derived liquids when reacted with coal under mild reaction conditions (375 °C and 2.17 × 10⁶ − 3.55 × 10⁶ N m⁻¹) enhance the rate of coal depolymerization. Up to 30% enhancement in coal conversion rate is achieved using lignin-derived liquids. The influence of time of reaction and temperature on the degree of reaction was investigated. The lignin liquid-assisted coal depolymerization products (liquid) are observed to contain a significant amount of the desirable pentane-soluble fraction. Influence of the time of storage of lignin-derived liquids on coal conversion was also determined. Also reported are data on elemental analyses of the solid and liquid products. The liquid product analyses using n.m.r. and s.e.c. techniques are also presented. Based upon the experimental data collected, it is hypothesized that enhancement in coal depolymerization rate can be explained by a reaction pathway involving intermediates formed from lignin-derived lignin liquids. A mathematical model describing the reaction chemistry has been developed. Computed rate constants are also reported. The analysis indicates that the lignin-derived intermediates are short-lived as compared to the time needed for complete coal depolymerization.     

Effect of pressure and temperature on the reaction of coal with alcohol-alkali

The ethanol-NaOH reaction of Taiheiyo coal (C, 77.5; H, 6.3 wt%) was examined under a pressure of 0.1–8 MPa nitrogen or hydrogen, at 300 °C for 1 h. Almost all of the products are extracted with pyridine for the entire pressure range and the extraction yield with ethanol increases with pressure, even under nitrogen. The yield of the products extracted with ethanol is higher when the coal is reacted under hydrogen than when reacted under nitrogen. The explanation for these results is that, under pressure, the hydrogen produced from the reaction of alcohol and NaOH is enclosed for a longer period in the solvent, thus accelerating the hydrogenation reaction of the coal, also under hydrogen pressure, the reaction is particularly accelerated because the hydrogenation takes place with the hydrogen gas. At 300 °C, the ethanol-extraction yield is much higher than the benzene-extraction yield, but the latter increases rapidly and approaches that of the ethanol-extraction yield as the temperature rises to 400 °C. This is because the polar groups, e.g. as hydroxyl groups which are rich in the low-temperature products, decrease with the temperature rise.     

Comprehensive two-dimensional gas chromatography for basic and neutral nitrogen speciation in middle distillates

The molecular knowledge of nitrogen compounds in diesel feedstocks has become a key issue in the development of hydrotreatment processes, especially for ultra-low sulfur diesel production. Indeed, nitrogen species have a strong impact on the hydrodesulfurization (HDS) pathway, since basic nitrogen is known to poison acidic sites of HDS catalysts.Since conventional methods only allow a poor degree of information, the increased separation power of comprehensive two-dimensional gas chromatography (GC × GC-NCD) was used in this study to obtain a detailed overview of nitrogen compounds by type (basic/neutral), by family and by carbon breakdown in diesel and liquefied coal samples. Partially hydrogenated compounds such as tetrahydrocarbazole and tetrahydroquinoline derivatives could even be detected in liquefied coal samples as well as diesel from ebullated bed conversion units. Comparison of GC-NCD with GC × GC-NCD for quantitative determination of nitrogen compounds by family was achieved in a first step. These results demonstrate the superiority of GC × GC to allow for a comprehensive characterization of nitrogen compounds in diesel and related samples in one injection. Furthermore, nitrogen speciation by GC × GC-NCD technique allows identifying most nitrogen species in conventional diesel or liquefied coal samples, with no use of mass spectrometry.GC × GC-NCD was also applied to a wide range of diesel feedstocks obtained from distillation, cokefaction, FCC, ebullated bed hydroconversion units to correlate nitrogen species to the origin of the feedstocks or distillation end points, giving interesting indications on reaction mechanisms involved in the processes.     

Release of nitrogen during thermochemical conversion of Shenhua bituminous coal under Ar,CO2, and air atmospheres

Coal thermochemical conversion processes unavoidably generate gaseous pollutants, endangering the environment or influencing synthetic processes downstream. In order to display the differences in release behaviours of nitrogen among different coal thermochemical conversion stages, the nitrogen release characteristics of Shenhua bituminous coal under Ar, CO₂, and air atmospheres were investigated using X-ray photoelectron spectrum (XPS) and thermogravimetry-mass spectrometry (TG-MS). Results indicate that the reaction atmosphere has an important influence on nitrogen release. The total released mass of nitrogen when using 100 g raw coal in the whole experiment under Ar, CO₂, and air atmospheres is 0.54, 0.64, and 0.75 g, respectively. The organic forms of nitrogen in raw coal and coal char are pyridine nitrogen (N-6), pyrrole nitrogen (N-5), quaternary nitrogen (N-Q), and nitrogen oxide (N-X). While in the coal ash, the sub-peaks of N-Q and N-X disappear entirely, leaving only N-5 and N-6 sub-peaks. The released nitrogen-containing gas consists of NH₃, HCN, NO, and NO₂ during experiments in CO₂ and air atmospheres. However, only NH₃ and HCN are detected during experiments in the Ar atmosphere. The revolution characteristics of NH₃ and HCN under Ar and CO₂ atmospheres are similar.     

Releases of NO and its precursors from coal combustion in a fixed bed

Experiments have been carried out to investigate the emissions of nitrogen species including NO and its precursors during temperature-programmed coal combustion by TG/EGA method. Experimental results show that the conversion ratio of fuel nitrogen to NO is the highest, followed by that of fuel nitrogen to HCN and the conversion ratio to NH₃ is negligibly small. Nitrogen is retained in the char and released mainly as NO at the later stages of coal combustion. HCN and NO are both primary products from coal char oxidation. Coal rank, heating rate, indigenous minerals and external additives are the major influential factors of the nitrogen species release. Higher rank coals with higher fuel ratio have higher NO releases. HCN release decreases as fuel ratio increases for most coals. The fuel nitrogen conversion to NO increases and the fuel nitrogen conversion to HCN decreases with the increase of heating rate, which may imply that the char nitrogen prefers to react with oxygen to form NO instead of HCN while coal char is combusted at higher temperatures. Different metallic additives show different effects on nitrogen species emission and the effects of indigenous minerals on nitrogen release can be qualitatively estimated by ash analyses.     

固体酸催化新疆褐煤直接加氢液化研究

为了实现褐煤温和加氢液化联产高附加值酚类化学品,研制了1种新型固体酸催化剂,可以弥补反应条件缓和带来的褐煤大分子结构单元桥健断裂的裂解性能不足,进行了固体酸催化剂的物性表征和活性评价,考察了催化剂类型对褐煤温和加氢液化性能和产物分布的影响规律,探讨了固体酸催化剂用于褐煤温和加氢液化的可行性,并与传统液化进行了比较。结果表明:固体酸催化剂粒径减小,出现了强酸中心,在430℃和15 MPa反应条件下,转化率和油产率与传统液化相当,低级酚产率增加了1.5%,气产率降低近4%,这种固体酸催化剂有利于实现褐煤加氢液化的节能减排增效和产品结构优化,是一种值得关注和深入研究的煤直接加氢液化催化剂。     

NOx generation from the combustion of Australian brown and subbituminous coals

The formation of NO_x during the combustion of pulverized brown and subbituminous coals from Victoria and Queensland respectively was investigated in an entrainment reactor. As no NO₂ was detected, all the NO_x was present in the form of NO. The brown coals exhibited a significantly greater potential for NO emission under fuel-lean conditions than did the subbituminous coal, even though the latter coal had a higher nitrogen content. However, under fuel-rich conditions the conversion of coal nitrogen to NO for the subbituminous coal was higher than for the brown coals. The differences in conversion efficiency may have been related in part to the nature and reactivity of the volatile nitrogen species. Reactivity differences between the chars produced from the brown and subbituminous coals may also have accounted for different extents of removal of NO. There was a significant reduction in the amount of NO emitted when brown coal was added to a combustion gas stream containing an appreciable quantity of NO before coal injection.     

Synergistic effects between light and heavy solvent components during coal liquefaction

As part of research to examine coal conversion in solvents containing high-boiling-point components, experimental studies were carried out with model compound solvents. The dissolution of bituminous and subbituminous coals was investigated in pyrene-tetralin and 2-methylnaphthalene-tetralin mixtures. The effects of donor level, gas atmosphere, hydrogen pressure and conversion temperature were determined. At 400 °C, in the presence of hydrogen gas, pyrene-tetralin solvent mixtures show synergism in coal conversion. At donor concentrations as low at 15 wt%, the degree of conversion was almost as high as in pure tetralin. This phenomenon was not apparent in 2-methylnaphthalene-tetralin mixtures. The relative ease of reduction of pyrene and its ability to shuttle hydrogen is considered to be a principal reason for this difference in behaviour. Conversion in pure pyrene and in pyrene-tetralin mixtures at low donor concentrations increased with increasing hydrogen pressure. At 427 °C, bituminous coal conversion was higher in a 30 wt% tetralin-70 wt% pyrene mixture than in either pure compound. It was found that in the absence of coal pyrene can be hydrogenated by H-transfer from tetralin as well as by reaction with hydrogen gas. This can provide a means to increase the rate of transfer of hydrogen to the dissolving coal through the formation of a very active donor (dihydropyrene). During coal liquefaction, several pathways appear to be available for hydrogen transfer for a given coal, the optimal route being dependent upon the solvent composition and the conditions of reaction.     

Hydrogen/deuterium transfer in coal liquefaction

Reactions have been made with deuterium-labelled solvent (d₄- and d₁₂-tetralin) and both Powhatan bituminous (Pittsburgh Seam) coal and model compounds under coal liquefaction conditions to study hydrogen transfer mechanisms. Powhatan coal liquefies quickly. Hydrogen transfer from the solvent to the reaction products continues throughout the heating period (up to 60 min). Significant hydrogen/deuterium exchange occurs and this strongly affects the distribution of deuterium in the products and also affects the extent of conversion as measured by the amount of THF-insoluble material. Increased deuteration of the solvent leads to decreased conversion. This exchange is enhanced by heavy aromatic species and by the presence of mineral matter and unconverted coal solids.     

Data on low rank coal liquefaction from DRIFT analysis

A Spanish low rank coal was hydrogenated without solvent in the presence of a molybdenum catalyst. The asphaltenes and derived residues were analysed to obtain an understanding of the behaviour of the coal under hydrogenation conditions and the influence of a previous extraction with chloroform, as well as reaction time and temperature, on the structure of the products obtained. Under the reaction conditions used, with tubing bomb reactors and an initial hydrogen pressure of 7 MPa, the data obtained for this coal show that an increase in temperature from 350 to 400 °C, and of reaction time from 5 to 60 min gives, in general, lower content of organic matter in the residues. The two variables have opposing effects on the aromatic content of the asphaltenes. Increasing reaction time reduces the aromaticity, whereas increasing the temperature will increase aromaticity. Prior extraction of the low molecular weight chloroform-soluble compounds increased conversion, and resulted in asphaltenes with higher content of aromatic- and oxygen-containing groups.     

Coal liquefaction in a fluorocarbon medium. 1. Nitrogen compounds as hydrogen transfer agents

Coal processed in a perfluorocarbon liquid at 250 °C with low concentrations of additives may undergo chemical reactions, but does not dissolve. Under these conditions quinoline has little effect on coal, while 1,2,3,4-tetrahydroquinoline produces marked increases in coal solubility, presumably due to hydrogen donation. While the hydrogen requirements of a bituminous coal are satisfied by tetrahydroquinoline at a tetrahydroquinoline: coal ratio of 0.2, for a lignitic coal, addition of gaseous hydrogen is necessary for substantial solubility increase.     

Hydrogenation of heavy liquids from a direct coal liquefaction residue for improved oil yield

For hydrogenation of heavy liquids in direct coal liquefaction residue (DCLR) within the direct coal liquefaction (DCL) process, heavy liquids in a DCLR derived from a bench-scale Shenhua DCL process using Shenhua coal are evaluated under two conditions. One simulates the coal liquefaction conditions of the Shenhua plant in the presence of a Fe-based Shenhua catalyst; the other one simulates the online hydrotreating conditions in the presence of a NiMo/Al₂O₃ catalyst. The results show that the heavy liquids of DCLR can be hydrogenated under these two conditions yielding less heavy products; hydrogenating the heavy liquids under the online hydrotreating conditions is more effective than that under the coal liquefaction conditions; the preasphaltene fraction is a main problem that yields non-soluble materials under these hydrogenation conditions. The results suggest that hydrogenation of toluene soluble and tetrahydrofuran soluble fractions of the DCLR under the coal liquefaction and online hydrotreating conditions is feasible, but their conversion to lighter products are inapparent under the coal liquefaction conditions, and elimination of the formation of tetrahydrofuran insoluble fraction in the online hydrotreator should be considered.     

Effect of temperature,catalyst and charge gas on the mean chemical structures of the products from hydrogenation of Liddell coal

Liddell coal (New South Wales, Australia) has been hydrogenated at 400, 425 and 450 °C with excess tetralin as vehicle and nitrogen or hydrogen as charge gas for 4 h at reaction temperature. In some experiments a nickel-molybdenum catalyst was used. The structures of the liquid and solid products were investigated by nuclear magnetic resonance spectroscopy, gel permeation chromatography and combustion analysis. Increasing the hydrogenation temperature from 400 to 450 °C decreases the yield of liquid products but increases conversion. At higher temperatures the liquid products are smaller in molecular size and molecular weight and contain a greater proportion of aromatic carbon and hydrogen; the solid residues also contain a greater proportion of aromatic carbon. The changes in variation of yield and structure with temperature are independent of the presence of catalyst under nitrogen and the nature of the charge gas. However, as the reaction system is capable of absorbing more hydrogen than can be supplied by the tetralin, the products from reactions with hydrogen as charge gas contain more hydrogen, some in hydroaromatic groups. Catalyst has little, if any, role in dissolution of the coal when a nitrogen atmosphere is used. When nitrogen is used as charge gas, reactions of coal-derived liquids with the catalyst do not alter the hydrogen, carbon or molecular size distributions in the products. The results show that the changes in composition of the liquid and solid products with increase in hydrogenation temperature are due to pyrolytic reactions and not to increased hydrogenation of aromatic rings.     

Study of coal conversion in polycondensed aromatic compounds

Coal conversions of up to 90 wt% can be obtained in solvents such as pyrene in an inert gas atmosphere. The extent of conversion is strongly dependent on the carbon content of the coal, those coals with 82–88 wt% maf carbon being the most easily converted. Under these conditions, conversion is sensitive to coal preparation and even mild air exposure can be greatly detrimental. In a hydrogen atmosphere, enhanced coal conversions are obtained in pyrene. The degree of enhancement is related to the interaction of pyrene, hydrogen and the coal mineral matter. Analyses of pyrene-coal reaction products showed the presence of hydro- and alkylated pyrenes. Alkylation can be very extensive, accounting for the transfer to pyrene of as many as one in 60 of the carbon atoms in the coal. It appears that dihydropyrene formation is catalysed by coal mineral matter and tends to increase with increasing convertibility of the coal. A mechanism is proposed by which the hydroderivative, formed in-situ by reaction with hydrogen gas, increases conversion. If the catalytic activity for hydrogenation is high and the demand for hydrogen by the coal is sufficiently low the hydroderivative will be fromed at a rate in excess of that required to liquefy coal through a hydrogen-donor mechanism. The properties of pyrene and similar solvents are discussed in relation to the beneficial effects of recycling high-boiling coal liquefaction products in process units.     

Solubilization of Neyveli lignite by oxidative degradation: A potential source of carbochemicals

The recent and possible future shortages of petroleum-derived hydrocarbons for use as starting materials for the synthesis of organic chemicals/products have stimulated renewed interest in the use of coal as raw material for chemical production. Oxidatively solubilized coal and or lignite (OSC) in alcohol is a potential substitute for value added carbo-chemicals of the future. Phenomenal increase in the solubility of lignite in organic solvent consequent on treatment with dilute nitric acid under mild conditions was considered to be an expedient pathway for its direct utilization. The primary requirements for the solubilization are generation of functional groups like free carboxyl groups and size degradation. For the desired product the reaction should also be guided in such a manner, so that the aromatic/hydroaromatic moieties of the coal/lignite are preserved. The present study aims at the selection of the required reaction parameters for the conversion of lignite to such a product. Characterization of the original lignite and the products have been done chemically and spectroscopically. FT-IR, ¹³C (solid state) and ¹H NMR spectra have shown that substances posses both aromatic and aliphatic characteristics. The dominant functional groups which contribute to the reactivity of the substances are phenolic and carboxylic acids.     

Coal liquefaction using indene-tetralin and indene-decalin mixtures as solvent

Indene-tetralin and indene-decalin mixtures were used as the solvent for coal liquefaction. The effect of mixing on conversion for Yallourn coal was observed under nitrogen pressure at 400 and 440 °C. Conversion to benzene-soluble material in an indene-decalin mixture (50:50, wt) at 440 °C for 1 h was 73.0% and was only 9% lower than that in 100% tetralin. The reaction of indene with tetralin or decalin may provide the active species for coal dissolution. Simultaneously, coal radicals may be scavenged by indene.