The effect of carbonaceous deposits on product selectivity in alkane hydrogenolysis

The hydrogenolysis of propane and of n-butane on Pt/Al₂O₃ and Pt-Re/Al₂O₃ catalysts has been studied using a stepwise temperature programme which reveals clearly the effects of carbonaceous deposits on both rate and product selectivities. On Pt/Al₂O₃ catalysts, deposits formed during the reaction of n-butane suppress C₂H₆ formation and enhance C₃H₈ formation, due solely to a decrease in the probability of central C-C bond fission. On Pt-Re/Al₂O₃, such deposits have little or no effect on product selectivities.Presented at the Royal Society-U.S.S.R. Academy Workshop on Surfaces and Catalysis, Oxford, 8–10 April 1989.     

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.     

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.     

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.     

High temperature hydrogenolysis of bibenzyl

Bibenzyl was pyrolysed in the gas phase, in the presence of a large excess of hydrogen at 600–850 °C. Products formed were benzene, toluene, ethylbenzene and styrene; no stilbene or phenanthrene were formed. The yield of toluene decreased with increasing temperature, that of benzene increased, that of ethylbenzene dropped to zero and that of styrene slowly decreased. The decrease in toluene plus ethylbenzene yield was roughly equal to the increase in benzene yield. The apparent pseudo first order ‘activation energy’ for loss of bibenzyl under these conditions is 10.2 ± 0.8 kcal mol^?1. The nature of products formed, their variation with increasing temperature and the low activation energy can be interpreted in terms of a radical chain mechanism in which the chain carrier is the hydrogen atom.     

煤化工产品为烯烃原料生产重烷基苯的研究

以煤化工产品为烯烃原料,通过与苯的烷基化反应,并在氢氟酸催化剂的作用下合成了重烷基苯。考察反应温度、压力和时间、苯烯摩尔比及催化剂用量对反应的影响。结果表明,在反应温度90℃,压力0.5 MPa,反应3.5 h,苯烯摩尔比8.33,催化剂用量9%条件下,液体收率84.3%,重烷基苯、饱和烷烃和副产物的产率分别为96.2%,17.4%和5.8%,82.4%的苯回收率说明苯可以循环利用。由此证明以煤化工产品为烯烃替代原料,与苯通过烷基化生成重烷基苯反应的可行性。     

煤化工产品为烯烃原料生产重烷基苯的研究

以煤化工产品为烯烃原料,通过与苯的烷基化反应,并在氢氟酸催化剂的作用下合成了重烷基苯。考察反应温度、压力和时间、苯烯摩尔比及催化剂用量对反应的影响。结果表明,在反应温度90℃,压力0.5 MPa,反应3.5 h,苯烯摩尔比8.33,催化剂用量9%条件下,液体收率84.3%,重烷基苯、饱和烷烃和副产物的产率分别为96.2%,17.4%和5.8%,82.4%的苯回收率说明苯可以循环利用。由此证明以煤化工产品为烯烃替代原料,与苯通过烷基化生成重烷基苯反应的可行性。     

煤化学结构模型研究进展及应用

为了解煤结构与反应性之间的关系,论述了褐煤、次烟煤、烟煤、无烟煤的典型化学结构模型,分析了煤的化学结构模型在煤热解、煤气化、煤液化、煤自燃及煤的溶剂溶胀性中的应用。煤的化学结构模型有助于在分子水平上研究煤反应过程中的反应路径和反应机理。煤结构模拟的方法能够有效捕获煤热解过程中化学键的生成和断裂行为,解释煤气化反应机理,有效检测或捕获煤液化时生成的不稳定自由基,从微观方面分析影响煤自燃的因素,达到预防煤炭自燃的目的。     

化学药剂对粉煤灰改性作用的研究

用CaO,Na2CO3,NaOH等物质对粉煤灰进行干、湿法联合改性,并引入热冲击程序,通过XRD衍射分析粉煤灰改性前后的物相变化,研究其改性效果。结果表明：加CaO焚烧-硫酸浸泡和加Na2CO3焚烧所得样品的衍射峰较多;而在加CaO焚烧-酸浸泡中引入热冲击则出现了更多紧密的衍射峰,最终确定用加有CaO高温焙烧,经热冲击后用（1＋4）酸浸泡得到的改性粉煤灰吸附性能较好。     

Effect of preheating on chemical structure and infrared spectra of Yanzhou coal

The results of thermosolvolysis experiments performed on a high volatile bituminous coal from Yanzhou, China are described. The coal was preheated in a vacuum at temperatures between 250 and 400 °C, after which the soluble materials were extracted with chloroform, l.r. spectra of the preheated coal, the chloroform extract, and the residue after extraction were measured and compared. The extraction yield passed through a maximum for a preheating temperature near the plastic softening point of the coal. As the preheating temperature was increased, the aromaticity of the coal and its residue after extraction increased markedly. The aromaticity of the extract appeared to increase slightly and the methylene-methyl ratio of the extract dropped significantly near the softening temperature. The ester content of the extract was reduced to almost zero on preheating the coal, presumably because of decarboxylation during preheating.     

Relation of the chemical structure of coal to its hydropyrolysis

The hydropyrolysis of Illinois No. 6 coal has been studied in a batch reactor, in which the reactions were initiated by explosion of $\text{H}{}_2\text{O}{}_2$ mixtures. The ratio of H₂ to O₂ was kept at 8, while the total pressure of the gas mixture was changed to vary the reaction temperature. The heating rate was ≈ 50 000 °C s^?1, and the reaction time was < 50 ms. The conversion of the feed coal increased from 19% at 620 °C to 81%at ? 1500 °C. At conversions < 50%, the gaseous product consisted of mainly CH₄ and CO in almost equal proportions, and at conversions ? 60% the concentration of CO increased. Comparison with results from a large flow reactor revealed that comparable conversions were obtained in the present batch reactor, although product distributions were markedly different from each other. The dissimilar product distribution is attributed to different reacting media: preburning of H₂ and O₂ in the flow reactor versus in situ burning of the mixture in the batch reactor. The H/C ratios of solid residues after the hydropyrolysis decreased linearly as the conversion increased, revealing that the portions of coal having high H/C ratios were preferentially gasified. This observation was substantiated by a high H/C ratio, 1.74 of the first portion of coal gasified, and by a sharp decrease in H/C ratio in subsequent gasified portions. These data indicated that aliphatic side chains (or linkages) and single-ring aromatic clusters in the feed coal were gasified first, followed by larger aromatic clusters. Semi-quantitative determination of the distribution of different aromatic clusters showed good agreement with current structural information on coal. Thus, the effects of reaction variables were explained in terms of the structural features of coal, and the ratelimiting steps in the hydropyrolysis process were identified.     

合理配煤入洗 提高经济效益

介绍了南下庄选煤厂为适应市场需求 ,调整产品结构 ,采取配煤入洗 ,使精煤产品种由 1 3焦煤改变为低硫肥煤 ,取得了较好的经济效益和社会效益     

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.     

风化煤的化学氧化及产物的抗蒸腾生理效应

对过氧化氢氧化风化煤获得黄腐酸及其抗旱生理活性进行7研究。考察7过氧化氢浓度、氧化处理时间和液煤比对黄腐酸溶液浓度的影响，得出了获得高浓度黄腐酸的最佳氧化条件。初步的抗蒸腾生理活性实验数据显示：喷施lOOmg／L的黄腐酸能使小麦的蒸腾速率降低，这表明过氧化氢氧化风化煤获得的黄腐酸具有抗蒸腾作用，但喷施黄腐酸后的第七天黄腐酸的抗蒸腾效应消失。     

Organic emissions in coal combustion in relation to coal structure and combustion temperature

The pulsed combustion of coal has been studied in a small fluidized-bed reactor. The effect of combustion temperature and coal rank on the organic composition of the off-gas was investigated. Results are presented for the combustion of an anthracite, a medium-volatile bituminous coal and a high-volatile bituminous coal at 700, 800 and 900°C. The analytical techniques used include on-line FT-i.r., O₂ monitoring, FID and off-line g.c.-m.s. using Tenax as adsorbent. About 120 hydrocarbons were found, of which over 80% have been identified. Overall combustion characteristics such as oxygen consumption, total amount of unburned hydrocarbons and swelling properties of the coal have been related to the composition of the organic substances in the off-gas. The distribution of the polycyclic aromatics, from benzene to chrysene, and of alkylated derivatives is discussed in detail. Oxygen-containing compounds have also been analysed, although detailed discussion would be premature.     

Effect of different oxidation treatments on the chemical structure and properties of commercial coal tar pitch

Different oxidation treatment was used for the increase of the softening point of a commercial coal tar pitch. H₂SO₄, HNO₃, H₂O₂ and air are selected as treatment reagents. These preliminary investigations show that the oxidation treatment of commercial coal tar pitch with different reagents at 160 °C and heat treatment to 250 °C causes considerable changes in the chemical composition of obtained pitches. This leads to increase of TI and QI fraction, and results in considerable increase in the softening point of the pitches. The yield of modified pitches is considerable in the case of treatment with H₂SO₄, H₂O₂, and HNO₃ and lesser in the case of air blowing. The data obtained also indicate some differences in the composition and softening point of pitches obtained after modification with different reagents. These differences could influence the applicability of the obtained pitches in the various areas of carbon material production.     

Aniline hydrogenolysis on nickel: effects of surface hydrogen and surface structure

Fluorescence yield near-edge spectroscopy (FYNES) above the carbon K edge and temperature programmed reaction spectroscopy (TPRS) have been used as the methods for characterizing the reactivity and structure of adsorbed aniline and aniline derived species on the Ni(100) and Ni(111) surfaces over an extended range of temperatures and hydrogen pressures. The Ni(100) surface shows appreciably higher hydrogenolysis activity towards adsorbed aniline than the Ni(111) surface. Hydrogenolysis of aniline on the Ni(100) surface results in benzene formation at 470 K, both in reactive hydrogen atmospheres and in vacuum. External hydrogen significantly enhances the hydrogenolysis activity for aniline on the Ni(100) surface. Based on spectroscopic evidence, we believe that the dominant aniline hydrogenolysis reaction is preceded by partial hydrogenation of the aromatic ring of aniline in the presence of 0.001 Torr of external hydrogen on the (100) surface. In contrast, very little adsorbed aniline undergoes hydrogen induced C-N bond activation on the Ni(111) surface for hydrogen pressures as high as 10^–7 Torr below 500 K. Thermal dehydrogenation of aniline dominates with increasing temperature on the Ni(111) surface, resulting in the formation of a previously observed polymeric layer which is stable up to 820 K. Aniline is adsorbed at a smaller angle relative to the Ni(111) surface than the Ni(100) surface at temperatures below the hydrogenolysis temperature. We believe that the proximity and strong -interaction between the aromatic ring of the aniline and the surface is one major factor which controls the competition between dehydrogenation and hydrogen addition. In this case the result is a substantial enhancement of aniline dehydrogenation relative to hydrogenation on the Ni(111) surface.     

藻类与煤低温共炭化对低温煤焦油的影响

将不同配比的藻类与煤以低温干馏的方法进行低温共炭化,研究煤焦油的变化.结果表明,煤焦油中轻质油含量增加29.55％,萘类化合物含量增加9.15％,酚类化合物含量增加23.93％,实现一定程度的轻质化.