Mechanism of high-pressure hydrogenolysis of Hokkaido coals (Japan) 3. Chemical structure changes in coal asphaltenes during hydrogenolysis

Asphaltenes produced by hydrogenolysis of coal were further hydrogenated in a batch autoclave at 400°C and 22 MPa hydrogen pressure. Red-mud was used as a catalyst and sulfur as promoter. The hydrogen content of the residual asphaltene increases and the fraction of aromatic carbon and the fraction of protons bound to aromatic carbons decrease as the reaction proceeds, indicating that hydrogenation of aromatic rings occurs. Aromatic ring systems of more than 2 rings are relatively easily hydrogenated to 2 rings. However, 2 ring systems are not easily hydrogenated. The heteroatoms-to-carbon ratios are similar for both the oil and the residual asphaltene, but less than that of the original asphaltene. The main differences in the chemical structure between the oil and the residual asphaltene are the hydrogen-to-carbon ratio, the fraction of aromatic carbon, the molecular weights and the average degrees of crosslinking. The residual asphaltene is composed of trimers and/or oligomers of unit structures of two or more condensed aromatic rings bound together by crosslinks. The size and composition of the condensed ring systems varies about the average properties measured in these experiments. Cleavage of the crosslinks by hydrogenation and heteroatom removal produces oil, composed for the most part of monomers of unit structures of two condensed aromatic rings. Coals of different rank show similar behavior although the magnitude of the changes depends on rank.     

Reaction mechanism for the hydrogenolysis of coal-derived preasphaltene

Preasphaltene, prepared in advance from hydrogenation of Akabira coal, was further hydrogenated at 385 °C with a hydrogen initial pressure of 9.8 MPa for various reaction times. According to the structural analysis and the variation of the inert oxygen content of the remaining preasphaltene and the benzenesoluble product, it is concluded that the conversion of preasphaltene to asphaltene plus oil is principally the reaction of the splitting of ether linkages which reduces the polymerization degree and the saturation of the aromatic rings with hydrogen which increases the solubility in benzene.     

Mechanism of hydrogenation of coal-derived asphaltene

Use of asphaltene instead of the parent coal as the starting material for hydrogenolysis makes it easier to discuss the reaction mechanism, because the mean chemical structures of both reactant and products can be deduced from structural analysis. In this study asphaltene from Japanese Akabira coal was hydrogenated at 400 or 370 °C under initial pressures of 9.8 or 10.4 MPa using red-mud and sulphur catalyst. The structures of the products (oil and remaining asphaltene) and of the original asphaltene were analysed statistically by n.m.r. data. Most of the conversion of asphaltene to oil was caused by saturation of aromatic rings, decomposition of naphthenic rings, dehydroxylation and the decrease of inert (O + N + S) elements resulting from the opening of hetero-rings; the splitting of linkages between unit structures did not contribute to the conversion.     

Hydrogenation of Liddell coal. Yields and mean chemical structures of the products

The products from the hydrogenation of an Australian medium-volatile bituminous coal (Liddell) in batch autoclaves have been investigated. Tetralin was used as a vehicle and Cyanamid HDS-3A as catalyst. The influences of temperature (315–400 °C), hydrogen pressure (3.4–17.2 MPa) and reaction time (0–4 h) on the yields of pre-asphaltene, asphaltene, oil and pitch were studied. The chemical compositions of these materials were investigated by nuclear magnetic resonance and infrared spectrometry, and high-pressure liquid chromatography. Higher temperatures (400 °C) and pressures (17.2 MPa) favour the formation of products with lower average molecular size, lower aromatic carbon and aromatic proton contents and smaller average aromatic fused-ring number. N.m.r. evidence is presented which shows that increasing the temperature from 370 °C to 400 °C or pressure to 17.2 MPa assists reactions which bring about hydrogenation and cleavage of aryl rings. Longer reaction times (4 h) promote reactions by which the oxygen content of the product is decreased and by which polymethylene becomes cleaved from other functional groups. The results show that asphaltenes are true intermediates in the formation of oil from coal.     

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.     

Pressure and temperature effects on the hydrogenation of coal-derived asphaltene

Pressure and temperature effects on hydrogenation reactions were examined using coal-derived asphaltene at 390,420 and 450 °C, under 3 and 10 MPa of hydrogen partial pressure. Higher conversion was obtained at higher reaction temperatures. Benzene-insoluble material (Bl) was formed at higher temperatures especially at low hydrogen pressure, this Bl being one-third of the reaction product at 450 °C. From structural analysis of unreacted asphaltenes and product oils, at 390 °C, it was concluded that smaller molecular components convert to oil initially and the larger molecules remain as unreacted asphaltene. Under higher hydrogen pressure for all temperatures carbon aromaticity (f_a) and number of aromatic ring per structural unit (R_aus) in unreacted asphaltenes were lower than those under lower hydrogen pressure suggesting that hydrogenation of the aromatic nucleus was promoted by higher pressure. At lower hydrogen pressure, R_aus for asphaltenes at higher temperature is larger than that at lower temperature. This suggests that at lower hydrogen pressure, dehydrogenation or condensation reactions occur more easily. A large effect at higher hydrogen pressure was a reduction in the extent of condensation reactions. Higher reaction temperatures contribute to splitting of bridged linkages so reducing molecular size and degree of aromatization.     

The effect of hydrogen pressure and aromatic structure on methane yields from the hydropyrolysis of aromatics

The chemistry of the formation of methane from the hydrogasification of naphthalene, substituted naphthalenes and toluene has been investigated using a flow tube. Temperatures were varied between 650–1050 °C (depending on the aromatic) and pressures ranged over 0.5–2 MPa. The results show that methane yields increase with increasing hydrogen pressure. For naphthalene the methane yield increases linearly with temperature for a given pressure. Methyl substituents are lost from aromatic rings, in a reaction which is insensitive to hydrogen pressure, to form 1 mole of methane and the parent aromatic. At these hydrogen pressures the phenolic group in 1-naphthol is removed predominately as H₂O to form naphthalene and the methane yields from this species parallel those from naphthalene. Analyses of the condensed products demonstrate that increased hydrogen pressure results in a reduction in the amounts of high molecular weight condensation products resulting in increased yields of methane.     

干馏终温对油砂油化学结构的影响

引言随着全球石油资源的日益短缺和石油需求的不断增加,油砂作为非常规油气资源中的一种,因其储量丰富、开采成本不断降低而越来越受到资源需求者的极大关注。世界上有70多个国家蕴藏油砂资源,主要油砂资源国有加拿大、俄罗斯、委内瑞拉、尼日利亚和美国[1]。据统计,全球油砂可采资源量约为891×108 t,占世界油气资源可采总量的32%[2]。油砂又称沥青砂或焦油砂,是一种含有沥     

Chemistry of methane formation in hydrogasification of aromatics. 2. Aromatics with aliphatic groups

The chemistry of the formation of methane in hydrogasification of such methyl-substituted and methylene-bridged aromatics as toluene, 1- and 2-methylnaphthalene, diphenylmethane, fluorene and 9,10-dihydroanthracene was studied using a flow tube. Temperatures varied between 600 and 1000 °C. Gases and benzene were analysed by on-line gas chromatography, the tar products being analysed by mass spectrometry. Methane formation from aliphatic groups, not in cyclic systems, is decisively favoured compared with the formation from aromatic rings. The splitting off of aliphatic groups does not influence cleavage of attached aromatic rings. Splitting off of hydrogen from the aliphatic groups weakens aromatic rings. This primary step is important for methylene bridges in five membered rings only.     

Influence of chemical structure of isophthaloyl dichloride and aliphatic,cycloaliphatic, and aromatic diamine compound polyamides on their chlorine resistance

The influence of the chemical structures of the polyamides on chlorine resistance was studied by measuring their chlorine uptake rates. They were prepared from isophthaloyl dichloride and aliphatic, cycloaliphatic, or aromatic diamines by the solution or interfacial polycondensation method. This study showed that the chlorine resistance was dependent on the chemical structures of the diamine compounds used in the synthesis of the polyamides. We concluded that the polyamides comprising the diamine components with the following chemical structures had higher chlorine resistance: aliphatic or cycloaliphatic diamine compounds with a secondary amino group, aliphatic or cycloaliphatic diamine compounds with a shorter methylene chain length between end amino groups, and aromatic diamine compounds with methyl or chlorine substituents at the ortho position of the amino groups. Chlorine resistance is related to the basicity of the aliphatic and aromatic diamines used. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 201–207, 2000     

利用GC-MS与NMR技术研究干馏终温对桦甸页岩油组成性质的影响

通过控制桦甸油页岩干馏终温,得到5个不同终温下页岩油样品,对各页岩油样按沸点300℃进行切割,其中轻质油馏分(<300℃)进行GC-MS检测,对产物分类统计,分析页岩油组成成分随干馏终温变化规律;重质油馏分(>300℃)进行了¹H和¹³C核磁共振波谱分析,对谱图积分获得其氢、碳分布情况,研究了干馏终温对页岩油化学结构的影响。结果显示,轻质油组成中脂肪族化合物占绝大部分,其中正构烷烃、α-烯烃和正构醛、醇三者具有同源性,均由烷基自由基生成。随着干馏终温的升高,长链烷烃分解,支链烷烃侧链断裂,使轻质油脂肪烃碳链长度变短,重质油直链脂肪烃增多,页岩油发生更多的芳环缩合反应导致轻质油与重质油芳香环数量均增多,同时轻质油中芳环缩合程度加深。     

霍林河褐煤化学结构特性的13C NMR与FTIR对比分析

采用¹³C NMR及FTIR对霍林河褐煤的化学结构特性进行深入分析,通过¹³C NMR计算得到霍林河褐煤包含34.32%的脂肪族碳、61.25%的芳香族碳以及4.43%的羰基碳。平均每个芳环团簇包含1~2个芳香环,每个芳香环中平均碳原子取代数为3~4。平均亚甲基碳链数为1.4,烷链支化度为25.47%,说明脂肪族多以短链分支形式存在。通过对霍林河褐煤红外光谱进行分峰拟合,计算得到煤的FTIR结构参数（平均亚甲基碳链数、芳香环取代度、烷链支化度）与¹³C NMR计算结果相吻合。虽然芳碳率（f_ar-F=55.37%）与¹³C NMR计算结果存在一定的偏差,但是FTIR很大程度上仍然可以反映煤的碳骨架结构特性。     

Experimental and Kinetics Studies of Aromatic Hydrogenation in a Two‐Stage Hydrotreating Process using NiMo/Al2O3 and NiW/Al2O3 Catalysts

In this work, hydrogenation of aromatic compounds in light gas oil derived from Athabasca bitumen was carried out using a single‐ and two‐stage hydrotreating processes. Experiments were performed in a trickle‐bed reactor using two catalysts namely NiMo/Al₂O₃ and NiW/Al₂O₃. NiMo/Al₂O₃ was used in the first stage for nitrogen and sulphur containing heteroatoms removal whereas NiW/Al₂O₃ was used in the second stage for saturation of the aromatic rings in the hydrocarbon species. Temperature and liquid hourly space velocity (LHSV) were varied from 350‐390°C and 1.0‐1.5 h^?1, respectively, while pressure was maintained constant at 11.0 MPa for all experiments. Results from single‐stage were compared with those from two‐stage process on the basis of reaction time. Kinetic analysis of the single‐stage hydrotreating process showed that HDA and HDS activities were retarded by the presence of hydrogen sulphide that is produced as a by‐product of the HDS process. However, with inter‐stage removal of hydrogen sulphide in the two‐stage process, significant improvement of the HDA and HDS activities were observed.     

The chemistry and physics of coking

The causes of coke formation during petroleum refining are only now beginning to be understood. They are closely related to the mechanism of the thermal decomposition of the petroleum Constituents and to changes in the character of the liquid medium. It was formerly believed that coke formation was, a polymerization reaction whereupon the chemical precursors to coke immediately formed macromolecules when subject to the processing temperatures. This is not so. And it is the initial stages of the thermal decomposition which determine the ultimate path of the reaction. Coke formation is a complex process involving both chemical reactions and thermodynamic behavior. Reactions that contribute to this process are cracking of side chains from aromatic groups, dehydrogenation of naphthenes to form aromatics, condensation of aliphatic structures to form aromatics, condensation of aromatics to form higher fused-ring aromatics, and dimerization or oligomerization reactions. Loss of side chains always accompanies thermal cracking, and dehydrogenation and condensation reactions are favored by hydrogen deficient conditions.     

Chemical transformations during pyrolysis of Rundle oil shale

Rundle shale (Queensland, Australia) was pyrolysed at 12.5 K min⁻¹ to 350–500 °C for 10–240 min. The structures of the liquid products and pyrolysis residues were investigated by a number of n.m.r. spectroscopic techniques including cross-polarization and dipolar dephasing. N.m.r. provided a simple method for detecting nitrile carbon and measuring terminal and internal olefinic hydrogen in shale oil. It was found that the ratio of terminal olefinic hydrogen to internal olefinic hydrogen in shale oil increases by a factor of three over the range 350–500 °C. Moreover, the results suggest that aromatic rings in Rundle shale residues are not highly substituted and hence that aromatic ring condensation reactions are not important during pyrolysis. From elemental, yield and n.m.r. data, the conversion of aliphatic carbon to aromatic carbon during pyrolysis was found to be as high as 25% at 500 °C.     

Mesophase from electrode-binder coal-tar pitch: An appraisal of structural techniques

An electrode-binder coal-tar pitch containing mesophase and resulting from combined mild thermal treatment under nitrogen and hot filtration (to remove ash, etc.) has been examined by solvent analysis and magnetic resonance (high-resolution ¹H-nuclear-magnetic and electron-spin resonance) spectroscopy, X-ray diffraction and polarised light microscopy. At ambient temperature, residues and filtrates with higher mesophase contents tend to exhibit higher concentrations of unpaired electrons and higher stacks in crystalline regions. Room-temperature 100 MHz ¹H-n.m.r. spectra of solvent extracts of the treated pitch fractions confirm the predominance of aromatic over aliphatic hydrogen in all samples; heat-treated samples have lower content of hydrogen α to the rings but greater amounts of methylene and methyl hydrogen more remote from the rings than before the heat treatment.     

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.     

Preparation of carbon fibers with excellent mechanical properties from isotropic pitches

A novel isotropic pitch composed of linear methylene chains of polycondensed aromatic molecules was synthesized from naphtha-cracked oil through bromination and subsequent dehydrobromination (NB). Isotropic pitch-based carbon fiber obtained from the prepared NB yielded an unprecedentedly high tensile strength and elongation at break of 1500 MPa and 3.2%, respectively, following carbonization at only 800 °C for 5 min. The aromatic components of NB were primarily condensed cyclic compounds containing three and four aromatic rings. In contrast, a pitch prepared by simple distillation (ND), was composed of compounds containing three to six aromatic rings, which carried the tensile strength of carbon fiber by only 700 MPa with the similar fiber diameter. Interestingly, TOF-Mass analysis indicated that the molecular weight of the NB was higher than that of the ND. ¹³C-NMR analyses revealed that the NB pitch contained up to 18.8% aliphatic and naphthenic components compared to the 2.8% found in the ND pitch. Both isotropic pitches exhibited Bingham behavior above their softening temperatures. However, the linear chains of the NB pitch resulted in a higher degree of shear-thinning than was observed with the nonlinear ND pitch. This could result in a greater degree of molecular orientation during spinning.     

Modification of poly(vinyl alcohol) with aliphatic and aromatic epoxides in the molten phase

A new method for improving the processability and thermal stability of commercially available poly(vinyl alcohol) is presented involving the reaction of the hydroxyl group on the polymer backbone with long-chain aliphatic, cycloaliphatic, and aromatic epoxides. The reaction was performed in the molten phase using a laboratory-scale thermostated reactor. As expected, the extent of the reaction varied with the chemical structure of the epoxide, the properties of polymers obtained being dependent on the amount of the incorporated side group. Specifically, the reactivity of long aliphatic chain epoxides was low and the polymers obtained exhibited a small decrease in the melting points, being directly proportional to the length of the aliphatic chain. They displayed, however, improvement in thermal stability compared to the parent polymer. Cyclohexene oxide was appreciably more reactive and it exhibited a larger melting point reduction and satisfactory thermal stability. Polymers functionalized with aromatic rings and prepared under the same conditions were mostly amorphous, not showing melting point transition or improvement in their thermal stability. Finally, the reactions with aliphatic epoxides were catalyzed with phoshoric acid and the modified polymer exhibited a large decrease in the melting point but not a concomitant improvement in thermal stability. © 1996 John Wiley & Sons, Inc.     

Rapid Hydrogenation of Aromatic Nitro Compounds in Supercritical Carbon Dioxide: Mechanistic Implications via Experimental and Theoretical Investigations

An exceptionally rapid hydrogenation of nitrobenzene to aniline [TOF=252,000 h⁻¹] over palladium containing MCM‐41 (Pd/MCM‐41) with excellent yield of >99% can be achieved in supercritical carbon dioxide at 50 °C and a hydrogen pressure of 2.5 MPa. It has been observed that this promising method preferred a single phase between liquid substrate and carbon dioxide‐hydrogen system. The ascendancy of the supercritical carbon dioxide medium is established in comparison with the conventional organic solvent and solvent‐less conditions. Changes in the reaction parameters such as carbon dioxide and hydrogen pressure, temperature and the reaction time do not affect the selectivity. A combined experimental and theoretical study has elucidated the mechanism under the studied reaction condition because experimental observations revealed a direct conversion of nitrobenzene to aniline. However, density functional theory (DFT) calculation shows that the direct conversion is energetically unfavourable; hence, a stepwise mechanism has been proposed. Theoretical predictions and experimental observations suggested that the rate‐limiting step of nitrobenzene conversion is different from that of the liquid phase hydrogenation. This catalytic process can also be successfully extended to the hydrogenation of other aromatic nitro compounds with different substituents. Easy separation of the liquid product from catalyst and the use of an environmentally friendly solvent make this procedure a viable and an attractive green chemical process.