Light aromatics from the hydropyrolysis of coal

The hydropyrolysis of British coals was studied at hydrogen pressures of 5–15 MPa using heating rates of up to 30 K s^?1. In a single-stage reactor, hydropyrolysis of a high-volatile coal gave a maximum yield of 4.5 Wt % of single-ring aromatics. The results suggested that the evolution of volatiles and their cracking to benzene, toluene and xylenes were sequential reactions. This was confirmed using a two-stage reactor in which the coal was heated in one zone and the volatiles cracked in a separate, isothermally heated zone. Yields of up to 12 wt % benzene were then obtained from a high-volatile bituminous coal in hydrogen at 15 MPa, both the cracking temperature and the vapour residence time being separately optimized. Hydropyrolysis of model compounds showed that benzene was a major product of the cracking of polynuclear aromatics under hydrogen pressure.     

Steady-state conversion of methane to aromatics in high yields using an integrated recycle reaction system

Methane can be converted in high yields to aromatic products using an integrated recycle system containing both an oxidative coupling (OCM) reactor at 800°C, for conversion of CH₄ to C₂H₄, and a secondary reactor containing Ga/ZSM-5 at 520°C for subsequent conversion of ethylene to aromatics. Using this system, aromatic product yields of >70% at CH₄ conversions of ~100%, based on total CH₄ added, can be obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of pressure on the hydropyrolysis of Manvers coal

Manvers weakly-coking coal was pyrolysed to 500 °C in a stirred autoclave under varying pressures of hydrogen and nitrogen. As expected the major changes produced by increase in nitrogen pressure were a decrease in tar yield accompanied by increases in gas and, to a smaller extent, in coke yields. Total pressures and hydrogen :coal ratios were altered to obtain maximum yields of tar, gases and liquor. All products were investigated. Tar fractions, separated into neutral, phenolic and basic components, were analysed by g.c.-m.s. Short-chain hydrocarbons were detected in the gas sample. Methanol densities and micropore surface areas the cokes were related to the conditions of pyrolysis. At the relatively low rates of heating employed, pressure had effects on tar composition similar to increasing the temperature of pyrolysis.     

Fixed-bed pyrolysis and hydropyrolysis of sunflower bagasse: Product yields and compositions

Pyrolysis and hydropyrolysis experiments at different temperatures, heating rates and pressures have been conducted on a sample of sunflower pressed bagasse to investigate the effect of particle size, sweep gas velocity, and hydrogen pressure on the product yields and characteristics. In contrast to coal and oil shales, char and oil yields from sunflower pressed bagasse were found to be largely independent of particle size and sweep gas velocity in a Heinze retort with the oil yield of ≈ 40% w/w being the same as that from a well-swept fixed-bed reactor in which a much smaller sample size was used. The use of high hydrogen pressure ( > 50 bar) increased the oil yields by up to ≈ 10% w/w but these increases are much greater when expressed on a carbon basis due to the reduced oxygen contents of the oils. Even at low pressure, it has been estimated that ≈ 40% of the carbon aromatized during pyrolysis.     

The effect of coal rank on flash hydropyrolysis of Chinese coal

Fourteen kinds of Chinese coal were flash hydropyrolysed in a small entrained reactor at 750°C and hydrogen atmosphere. The results indicated that carbon content and yields of liquid hydrocarbon, H/C and yields of gaseous hydrocarbon, oxygen content and yields of CO, CO₂ and H₂O show better corresponding relations. The correlations between yields of CH₄, C₂ and C₂H₆ and H/C can be expressed as Y_CH4=−42.2+100(H/C)(0.51<0.59), Y_CH4=15.8+1.67(H/C)(0.59<1.11), Y_C2=0.347+4.78(H/C), Y_C2H6=0.352+4.74(H/C); The correlations between yields of CO₂ and water and oxygen content can be expressed as: Y_CO2=−0.0437+0.0355(O); Y_H2O=0.726+0.467(O). The cutoff points of flash hydropyrolysis for coal are that H/C is 0.6 and carbon content is 85%. The coal which H/C is lower than 0.6 and carbon content is higher than 85% is usually not good for flash hydropyrolysis. It is found that influence of coal rank on yields of liquid, gas product and total yields of product in flash hydropyrolysis can be expressed as of H/C in coal.     

Modeling the process of producing hydrogen from methane

Using the chemical reactions that accompany the production of syngas via the steam reforming of methane as a basis, the differential material balance equations were derived and solved for all conversion products on an aluminum/nickel catalyst. For the following stage of hydrogen synthesis on an iron/chromium catalyst, the system of two differential equations of the material balance of the direct and reverse reactions of steam carbon monoxide conversion was obtained and solved. The analytical solutions were compared with the experiment.     

The effect of bisphenol monomer structure on the gas permeability of aromatic polycarbonates

Permeability measurements for oxygen and, to a lesser extent, carbon dioxide were carried out on a series of 24 structurally different aromatic polycarbonates. Polymers were prepared from bisphenols bearing substituents on the aromatic rings and/or the central aliphatic carbon atom. A strong correlation between monomer structure and polymer permeability was found, with gas transport rates varying by over two orders of magnitude between the most and the least permeable materials. In addition, a semilogarithmic relationship was found between oxygen transmission rates and monomer composition for two series of copolycarbonates. Of several methods explored, an excess free volume model was found best able to relate the experimental permeability values to the polymer molecular structure.     

The effect of molecular structure on the gas transmission rates of aromatic polyimides

A series of high-molecular weight condensation polyimides was evaluated to determine the effect of polymer molecular structure on the transmission rate of oxygen, carbon dioxide, and water vapor. The polyimide films were prepared from either 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) or pyromellitic dianhydride (PMDA) with various diamines. The study shows that molecular structure had a strong influence on gas transmission rates with results for some films varying three orders of magnitude from that of other polyimide films. In general, the BTDA series of polyimides had overall lower gas transmission rates than the PMDA-derived series. Polymers prepared with meta-oriented diamines characteristically displayed lower gas transmission than those prepared with para-oriented diamines.     

Relation between formation rates of methane and hydrogen on pyrolysis of coal under pressure

In an earlier paper¹ it became clear that secondary-methane formation occurs under certain experimental conditions during pyrolysis of coal. In order to study this more deeply, the evolution rates of methane and hydrogen were measured simultaneously for an anthracite and a lignite. The secondary-methane formation was accompanied by a corresponding decrease in hydrogen formation. It is suggested that secondary-methane formation occurs according to the equation C + 2H₂ = CH₄ on an average and is proportional to the partial pressure of evolved hydrogen.     

Direct post-cracking of volatiles from coal hydropyrolysis: 2. Influence of pressure

Direct post-cracking of volatile material produced by hydropyrolysis of bituminous coal at 580 °C under hydrogen pressure 1–5 MPa has been investigated at 700 °C under constant hydrogen pressure with 0.1 and 1 s residence times. Results show that pressure promotes the formation of benzene, toluene and xylenes (BTX) and naphthalenes during post-cracking, while phenol, cresols and xylenols (PCX) are not affected. The transformation of heavy Ohenols into PCX is not influenced by the hydrogen pressure. During post-cracking the BTX yield can be more than doyble that reached in simple hydropyrolysis. Post-cracking applied to high oil yield hydropyrolysis processes will be a valuable BTX source.     

Y型分子筛应用于双环芳烃加氢裂化多产轻芳烃过程研究进展

催化柴油富含双环芳烃,可通过加氢裂化过程选择性多产高价值轻质芳烃（BTX）产物,现有研究已对此过程所需的工艺条件和催化剂性质进行了大量考察。工业应用中催化剂的酸性组分以Y型分子筛为主,研究分子筛性质和反应结果的关系成为重点内容。本文主要介绍了双环芳烃多产BTX产物经历加氢饱和、开环、断侧链等主要反应过程,金属组分及其与分子筛的协同作用;总结了Y型分子筛的性质如孔道性质、小晶粒、酸性质、核壳结构等因素对上述反应过程的影响。初步表明分子筛孔性质、酸性质直接影响目标反应选择性,通过对分子筛性质进行调变,可以达到促进反应物有效转化及提高BTX产物收率的目的。     

甲烷转化制芳烃技术工艺进展及工业前景分析

综述了甲烷转化制芳烃技术工艺进展,对甲烷有氧制芳烃、甲烷无氧制芳烃、甲烷溴化制芳烃、甲烷活化从木质素转化中制芳烃、甲烷乙醇低温制芳烃进行了讨论,并对这些技术的工业前景进行了分析,提出了相应的建议,对甲烷的工业化利用及增加轻质芳烃来源途径具有重要意义。     

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.     

Effect of environmental hydrogen pressure on the hydrogen yield from x-irradiated polyethylenes

An experimental assembly incorporating a capacitance-type, differential pressure transducer, which provides resolutions of 3 × 10^?4 torr at pressures extending to 30 torr, has been employed to monitor the effect of hydrogen environmental pressure on the hydrogen yield from x-irradiated polyethylenes. Contrary to the observations of previous investigators, the hydrogen yield is found to be independent of hydrogen environmental pressures extending over the critical range up to at least 30 torr. It is demonstrated that neglecting the temperature and density gradients inherent in closed-volume irradiation assemblies employing cryogenic traps to separate liberated gases into condensable and noncondensable fractions may lead to erroneous conclusions with respect to gas yields arising from the irradiation of materials. A homogeneous, variable-plate separation ion chamber consisting of a polyethylene body and utilizing flowing ethylene as the cavity gas was employed to obtain total volatile G values of 3.6 ± 0.4, 3.8 ± 0.4, and 4.0 ± 0.4 molecules/100 e.v., for Marlex 6002, Dow Ziegler (Q 917.5), and DuPont A-1410 polyethylenes, respectively. A hydrogen contribution of approximately 98 mole-% was obtained with this experimental method.     

The effect of temperature and ventilation condition on the toxic product yields from burning polymers

A major cause of death or permanent injury in fires is inhalation of toxic gases. Moreover, every fire is unique, and the range of products, highly dependant on fire conditions, produces a wide variety of toxic and irritant species responsible for the most fire fatalities. Therefore, to fully understand each contribution to the toxicity it is necessary to quantify the decomposition products of the material under the test. Fires can be divided into a number of stages from smouldering combustion to early well‐ventilated flaming through to fully developed under‐ventilated flaming. These stages can be replicated by certain bench‐scale physical fire models using different fuel‐to‐oxygen ratios, controlled by the primary air flow, and expressed in terms of the equivalence ratio (the actual fuel/air ratio divided by the stoichiometric fuel/air ratio). This work presents combustion product yields generated using a small‐scale fire model. The Purser Furnace apparatus (BS7990 and ISO TS 19700) enables different fire stages to be created. Identification and quantification of combustion gases and particularly their toxic components from different fire scenarios were undertaken by continuous Fourier transform infrared spectroscopy. The relationship between type of the fire particularly the temperature and ventilation conditions and the toxic product yields for four bulk polymers, low‐density polyethylene, polystyrene (PS), Nylon 6.6 and polyvinyl chloride (PVC) is reported. For all the polymers tested, except PVC, there is a dramatic increase in the yield of products of incomplete combustion (CO and hydrocarbons) with increase in equivalence ratio, as might be expected. For PVC there is a consistently high level of products of incomplete combustion arising both from flame inhibition by HCl and oxygen depletion. There is a low sensitivity to furnace temperature over the range 650–850°C, except that at 650°C PS shows an unexpectedly high yield of CO under well‐ventilated conditions and PVC shows a slightly higher hydrocarbon yield. This demonstrates the dependence of toxic product yields on the equivalence ratio, and the lack of dependence on furnace temperature, within this range. Copyright © 2007 John Wiley & Sons, Ltd.     

The catalytic combustion of methane and hydrogen sulphide

The odorous components of sewage gas consist mainly of ca. 15–40 ppm hydrogen sulphide. The gas may also contain methane. The catalytic combustion of hydrogen sulphide and methane has been studied using palladium- and platinum-based monolithic catalysts. Platinum-based catalysts perform better in the presence of hydrogen sulphide and kinetic equations have been derived. The relationships were used to design an industrial converter, which has operated satisfactorily for two years.     

On additivity of the yields of ethylene formed from methane and naphtha by an integrated process

A heat-effective ‘integrated’ process carried out in one reactor, composed of exothermic oxidative coupling of CH₄ over the catalyst fixed bed and endothermic pyrolysis of naphtha injected from the outside to the stream of gaseous coupling products in the hot oxygen-free postcatalytic zone, has been studied. An additivity of the yields of ethylene formed in both component processes was examined under varied operating conditions (type of naphtha fraction, flow rate of reagents and temperature of pyrolysis). A very high degree of additivity of the yields of ethylene and its main coproducts was observed, independently of the relative contribution of the component processes to the integrated process and of applied variations in the process conditions. Evidently, the mutual interactions between the component processes and products were negligible under experimental conditions. © 1998 Society of Chemical Industry     

A two-stage fixed-bed reactor for direct hydrotreatment of volatiles from the hydropyrolysis of biomass: effect of catalyst temperature, pressure and catalyst ageing time on product characteristics

This investigation involved the hydropyrolysis of biomass (eucalyptus globulus) and the immediate catalytic hydrocracking of pyrolytic oils in the second stage of the reactor. The effects of temperature, pressure and the catalyst ageing time on the final product tar have been studied using the catalyst Zeolite H-ZSM5. The catalytically hydrocracked tar/oil products were characterised and compared with the hydropyrolysis product from the first stage of the reactor to determine the effect of catalytic hydrocracking. The carbon deposition on the catalyst has been examined using thermogravimetric analysis. The tar yields after catalytic hydrocracking decreased with increasing pressure and temperature of the cracking stage. The tar yields at 10 bar pressure were greater than those at 40 bar pressure. The fresh zeolite catalyst trapped more than 40% of the product from the hydropyrolysis stage and TGA evidence indicated that this was not as carbon deposition but as volatiles trapped in the zeolite matrix. Reuse of the catalyst resulted in little more uptake of volatiles; however, extended use of the catalyst did not result in increased yields of liquid products but in increased production of light volatiles or gas. The H-ZSM5 catalyst appeared to act as a more active cracking catalyst rather than to promote hydrogenation or deoxygenation of the liquids produced in the hydropyrolysis stage. Characterisation of the liquids by SEC and UV fluoresence indicated that structural changes were relatively minor despite the significant changes in yields of liquids with process conditions. Available reaction routes do not appear to allow specific deoxygenation pathways to predominate without disintegration of parent molecules to lighter volatiles, under the conditions used here.     

Separation of hydrogen from methane by asymmetric PEI membranes

Hydrogen is anticipated to play an inevitable role as one of the promising sources of energy in the future. Recovery of hydrogen from flare gases is an economical and environmental policy of Marun Petrochemical Company. The asymmetric polyetherimide (PEI) membrane was synthesized and sorption and permeation of CH₄ and H₂ were studied. The influence of pressure and temperature as operating variables were investigated. Results showed that permeance was enhanced by temperature. The pressure increase caused a decline in H₂ permeance, whereas CH₄ permeance increased due to the Flory–Huggins sorption mechanism and ideal H₂/CH₄ selectivity reduction. The effect of different non-solvents as coagulants of the phase inversion technique in membrane morphology and behavior were explained by precipitation time. Water as a non-solvent makes membrane structures denser than others, while isopropanol leads to a porous sponge-like morphology. Lower coagulation bath temperature makes the membrane denser. Finally, a selectivity of 27.8 was achieved for the separation of H₂ from CH₄.     

C8芳烃临氢异构化催化剂研究进展

从分子筛酸性组元方面综述了国内外C₈芳烃异构化催化剂的研究进展,并对C₈芳烃异构化催化剂酸性组元沸石分子筛的发展提出了建议。认为C₈芳烃异构化催化剂的研究方向应集中在新型分子筛的制备和改性研究上。