Designed synthesis of porous carbons for the separation of light hydrocarbons

The separation of light hydrocarbon mixtures (C₁-C₃) generated from petrochemical industry is vital and challenging process for obtaining valuable pure chemical feedstocks. In comparison to the energy intensive conventional separation technologies (cryogenic distillation, absorption and hydrogenation), the adsorptive separation is considered as a low energy cost and high efficiency process. Porous carbons have been demonstrated as excellent adsorbents for the separation of light hydrocarbons, owing to their designable structure and tailorable properties. This review summarizes the recent advances of using porous carbons as adsorbents for the separation of light hydrocarbons, including methane/nitrogen, methane/alkane, methane/carbon dioxide, ethylene/ethane and propylene/propane. We discuss the separation mechanisms and highlight the material features including pore structure, surface chemistry and target molecular properties that determine the separation performance. Furthermore, the challenges and development direction associated with carbonaceous adsorbents for light hydrocarbon separation are discussed, meanwhile the guidelines for the design of porous carbons are proposed.     

Effect of ethane addition on propane pyrolysis

Pyrolysis of propane/argon mixture in the presence of trace quantities (0.1% and 0.9%) of ethane was investigated at reflected shock wave temperatures between 1200 and 2000K. Traces of ethane accelerated propane decomposition at high temperature. However, increase in the quantity of ethane added to propane/argon mixture did not result in the same increase of its accelerating influence. Ethylene, methane and acetylene were the main hydrocarbon reaction products, with small quantities of propylene and ethane detected only at lower temperatures. Below 1500K, addition of ethane slightly enhanced the yields of ethylene and methane at the expense of propylene and ethane respectively. The selectivity for acetylene increased with increasing temperature and with the decline of those for the other products. For none of the products, did the presence of ethane alter the relationship between product formation rates and temperature. The influence of ethane addition on propane pyrolysis at high temperatures was explained in terms of increased radical concentrations, especially hydrogen atoms and vinyl radicals, formed at high conversions. These accounted for the rapid acceleration of propane decomposition and the high yield of acetylene at high temperatures.     

Evaluation of the use of different hydrocarbon fuels for gas reburning

Gas reburning is a NO_x reduction technique that has been demonstrated to be efficient in different combustion systems. An experimental study of gas reburning performance in the low temperature range (at and under 1100°C) has been carried out. An evaluation of the use of different hydrocarbon fuels, such as natural gas, methane, ethane, ethylene and acetylene was performed and the influence of the temperature and stoichiometry is considered. The results show that the reburning process is effective under appropriate conditions at the low temperatures used in this work. However, as the temperature diminishes, the influence of the reburn fuel becomes more marked and the use of acetylene or ethane and ethylene leads to better performance than natural gas or methane, the classical reburn fuels for high temperature applications.     

金属有机骨架材料（MOFs）用于气态轻烃的高效分离研究进展

气态轻烃（C₁～C₃）如甲烷、乙烯、丙烯分别作为应用最广的清洁燃料和大宗化工产品，在国民经济中占据重要的地位。然而，在其生产过程中广泛存在着分离与提纯能耗较高的问题。金属有机骨架材料（MOFs）作为第三代新型多孔材料，近年来在轻烃分离领域显示出巨大的应用潜力。本文综述了MOFs用于气态轻烃分离的现状和机理，总结了本文作者课题组针对不同轻烃产物的分离要求，对MOFs进行了精确的孔径调控、配体功能化修饰、构筑吸附位点、调变柔性结构“开口压力”等，实现了多种气态轻烃组分的高效分离。最后，针对低碳烃工业分离过程中存在的关键问题，对MOFs材料的吸附分离机理进行了深入分析，以及MOFs工业化应用所面临的结构稳定性与分离工艺匹配等进行了展望。     

高效分离乙烷/乙烯的烷烃选择性吸附剂研究进展

乙烯是石油化学工业的基础原材料,聚合级乙烯工业纯化的关键挑战是去除其中的乙烷杂质,这一步骤难度大、能耗高。近年来,以乙烷选择性吸附剂为核心的吸附分离纯化技术快速发展,并得到学术界和工业界的关注。该技术可在温和工况下高选择性分离出乙烯中的乙烷杂质,显现出巨大潜力。本文总结了近年来乙烷选择性吸附剂（特别是乙烷选择性MOFs）的研究进展,并归纳阐释其选择性吸附机理。同时,在前人研究成果的基础上,总结可行的乙烷选择性吸附剂的设计策略,指出当前开发高效乙烷选择性吸附剂面临的挑战和未来的研究方向。     

高效分离乙烷/乙烯的烷烃选择性吸附剂研究进展

乙烯是石油化学工业的基础原材料,聚合级乙烯工业纯化的关键挑战是去除其中的乙烷杂质,这一步骤难度大、能耗高。近年来,以乙烷选择性吸附剂为核心的吸附分离纯化技术快速发展,并得到学术界和工业界的关注。该技术可在温和工况下高选择性分离出乙烯中的乙烷杂质,显现出巨大潜力。本文总结了近年来乙烷选择性吸附剂（特别是乙烷选择性MOFs）的研究进展,并归纳阐释其选择性吸附机理。同时,在前人研究成果的基础上,总结可行的乙烷选择性吸附剂的设计策略,指出当前开发高效乙烷选择性吸附剂面临的挑战和未来的研究方向。     

Light olefins synthesis from С1-С2 paraffins via oxychlorination processes

A two-step process was employed to convert methane or ethane to light olefins via the formation of an intermediate monoalkyl halide. A novel K₄RuOCl₁₀/TiO₂ catalyst was tested for the oxidative chlorination of methane and ethane. The catalyst had high selectivity for methyl and ethyl chlorides, 80% and 90%, respectively. During the oxychlorination of ethane at T≥250°C, the formation of ethylene as a reaction product along with ethyl chloride was observed. In situ Fourier transform infrared studies showed that the key intermediate for monoalkyl chloride and ethylene formation is the alkoxy group. The reaction mechanism for the oxidative chlorination of methane and ethane over the Ru-oxychloride catalyst was proposed. The novel fiber glass catalyst was also tested for the dehydrochlorination of alkyl chlorides to ethylene and propylene. Very high selectivities (up to 94%–98%) for ethylene and propylene formation as well as high stability were demonstrated.     

锆基MOF次级结构单元调控及轻烃吸附分离性能增强

从天然气中回收C₂/C₃轻烃组分具有重要的工业价值,吸附分离技术可在常温常压下实现轻烃的回收。对MOF材料进行次级结构单元（SBU）调控,可在继承其晶体结构和发达孔道的同时,优化孔道化学微环境并引入新的吸附位点。使用三嗪（TZ）取代Zr-TBAPy(NU-1000)SBU中的配位水分子,在其孔道内构筑对轻烃吸附质具有更强限域作用的碱性表面化学微环境,得到了高选择性的新型TZ@Zr-TBAPy吸附剂。TZ的引入在分子尺度上提高了孔道的表面粗糙度,同时强化对轻烃吸附质的限域作用,提高材料对烷烃的吸附容量和选择性。常温常压下,TZ@Zr-TBAPy对丙烷和乙烷的吸附容量分别为10.08和4.19 mmol?g^-1,比Zr-TBAPy提高了27%和9%,是目前国际上已报道的丙烷吸附容量最高的吸附剂之一。此外,丙烷/甲烷的IAST选择性为1518,是原材料的6.27倍;乙烷/甲烷的IAST选择性为11.7,比原材料提高了22%。更为重要的是,以TZ@Zr-TBAPy吸附剂为核心的固定床吸附过程可实现在常温常压天然气中乙烷和丙烷的一步分离回收。     

Adsorption of Methane,Ethane, Ethylene,and Carbon Dioxide on High Silica Pentasil Zeolites and Zeolite-like Materials Using Gas Chromatography Pulse Technique

Abstract

Adsorption of methane, ethane, ethylene, and carbon dioxide in H-ZSM-5, Na-ZSM-5, H-ZSM-8, Na-ZSM-8, Silicalite, and ALPO-5 at 303–473 K has been investigated using a gas chromatography pulse technique. The zeolites have been compared for the heat of adsorption of the adsorbates at near zero adsorbate loading and also for the specific retention volume (or thermodynamic adsorption equilibrium constant) of ethane, ethylene, and carbon dioxide relative to that of methane. Among the zeolites, ALPO-5 has a high potential for the separation of methane, ethane, ethylene, and carbon dioxide from their mixture.     

Analysis of products of high-temperature pyrolysis of various hydrocarbons

Ethane, ethylene, acetylene, propane and neopentane have been pyrolyzed at 1173 K, and methane at 1372 K in a flow system, and the volatile pyrolysis products analyzed. Eleven aromatic hydrocarbons, containing 14 or fewer carbon atoms, accounted for 98 + % of the liquid products recovered in each case. Benzene was the main product, followed by naphthalene. No compounds with branched chains or multiple substituents were present, and compounds containing even numbers of carbons comprised 93–99% of each mixture. Acetylene was a major component of the gaseous effluent from each of the initial hydrocarbons. The effect of temperature on the composition of the gaseous effluent during pyrolysis of methane, ethane and ethylene was determined. Carbon film deposition from methane commenced at about 1273 K; from ethane at 1015 K and from ethylene at 1100 K, in each instance coinciding with the appearance of acetylene in the effluent. As the temperature was raised, at first the increase in the rate of carbon deposition closely followed the increase in the concentration of acetylene in the effluent. It is proposed that acetylene may be a common factor in the pyrolysis of aliphatic hydrocarbons, perhaps acting as the precursor of both surface carbon and aromatic hydrocarbons by a process of head-to-tail linkage of two-carbon units at active surface sites to form chains that then undergo dehydrogenation to carbon or cyclization and desorption as aromatic species.     

天然气轻烃回收工艺设计及操作参数的优化

以廉价天然气中的乙烷和丙烷为原料的乙烯成本仅是石脑油等重质原料成本的30%,高压管输天然气进入城市门站分输需调压,调压过程中有大量压力能可利用。本文以某段高压管输天然气为原料,提出了处理量60×10⁴m³/h的轻烃分离回收工艺流程,综合考虑轻烃回收率、系统功耗、CO₂冻堵、冷箱传热温差等因素,优化操作参数,完成了系统能量的高效集成,实现了轻烃分离工艺的节能降耗。该方案C₂回收率达90%以上,可为乙烯装置提供优质的乙烷等轻烃原料50.75万吨/年,有利于解决乙烯工业发展的原料瓶颈,提高天然气、乙烯工业的整体经济效益。     

The oxidative coupling of methane in a fluidised-bed reactor

A small fluidised-bed reactor has been used by the CSIRO Division of Coal Technology to study the oxidative coupling of methane to higher hydrocarbons. Methane conversions of 9.6 to 13.5% were obtained in preliminary experiments using a lithium-promoted magnesium oxide catalyst at 850°C and with feed gases containing 5.6 to 10.7% v/v oxygen. Total hydrocarbon selectivity declined from 82 to 72% with increasing methane conversion. When operating with ethane in the feed at concentrations found in natural ethylene, the fluidised-bed reactor converted the ethane with good selectivity to ethylene, a key result in the context of using oxidative coupling for natural gas conversion. In view of these promising results, current work is directed towards increasing methane conversion and hydrocarbon selectivity in fluidised-bed reactors by development of more active and selective catalysts.     

THE MECHANISM OF THE SELECTIVE OXIDATION OF ETHYLENE TO ETHYLENE OXIDE

The modern petrochemical industry relies on several hydrocarbon raw materials: methane, ethylene, propylene, butene, higher olefins, and the aromatics. Some of the most important processes that such raw materials are initially subjected to are oxidation reactions[1]; for example, methane is converted to acetylene, ethylene to ethylene oxide, and propylene to acrolein, acrylic acid, or acrylonitrile. The complete oxidation of any of the hydrocarbons being favored thermodynamically, all partial oxidation reactions are kinetically limited, the nature of the products being determined mechanistically. In heterogeneous catalytic oxidations the mechanism essentially involves interaction between a hydrocarbon and surface oxygen species. In the case of the oxidation of ethylene to ethylene oxide, carbon dioxide, and water, silver is unique in giving a high selectivity to ethylene oxide. We believe it is the type of adsorbed oxygen species involved in the interaction that determines the course of the reaction and hence the selectivity.     

Selective ethylene adsorbent composed of copper(I) chloride and polystyrene resin having tertiary amino groups

Selective adsorbent for ethylene is prepared from copper(I) chloride and a macroreticular type polystyrene resin having tertiary amino groups. The adsorbent rapidly adsorbs ethylene at 20°C under 1 atm. The adsorbed ethylene is readily desorbed by subjecting the adsorbent to a reduced pressure (3 mm Hg) at 20°C. The ethylene adsorbing capacity of the adsorbent is 5.5 times as large as the adsorbing capacity for ethane. The present adsorbent exhibits no measurable adsorptions of nitrogen and hydrogen at 20°C under 1 atm, and thus is applicable to selective separation of ethylene from mixtures containing these gases and ethane.     

Radiochemical studies of chemisorption and catalysis: XIII. A mass-spectrometric study of the interaction of acetylene and carbon monoxide with a rhodium-on-silica catalyst

Mass spectrometry and thermal desorption studies have shown that when acetylene, at pressures of a few Torr at 18 °C, interacts with a Rh-SiO₂ catalyst the principal reaction occurring is self-hydrogenation to ethylene and ethane, with ethane as main product. Species which could be thermally desorbed from the surface in the range 36–186 °C included benzene, methane, ethylene, ethane, C₃- and C₄-hydrocarbons. Carbon monoxide had the effect of inhibiting self hydrogenation. C₁- to C₆-hydrocarbons could still be recovered by thermal desorption from the surface. Hydrogen, as a probe for surface species, brought ethane into the gas phase after exposure of Rh-SiO₂ to acetylene. Small amounts of C₃-hydrocarbons represented the only other species. A reaction scheme is presented.     

Moisture stability of ethane-selective Ni(II), Fe(III), Zr(IV)-based metal–organic frameworks

Metal–organic frameworks (MOFs) combined with selective adsorption capacity of ethane over ethylene and good moisture stability are highly urged by adsorption industrial community. Here, the moisture stability mechanism of Zr-bptc, UiO-66, PCN-245, and Ni(bdc)(ted)_0.5 were investigated by moisture stability experiments, and computational simulation of metal node-linker breaking energy caused by water. Results show that the moisture stability follows the order of Zr-bptc > UiO-66 > PCN-245 > Ni(bdc)(ted)_0.5. The different moisture stability for these MOFs is likely attributed to the bond strength between metal center and ligands, the coordination number of metal center, the hydrophobicity of framework, as well as the degree of interpenetrated framework. Additionally, comparing with ethylene-selective MOFs, ethane-selective MOFs have fewer coordinatively unsaturated metal sites. Breakthrough experiments indicated that Zr-bptc is the promising material for ethane/ethylene separation.     

Pyrolysis of propane at reflected shock-wave temperatures from 1300 to 2700 K

Shock tube pyrolysis of propane at temperatures between 1300 K and 2700 K at reflected shock pressures of 500 to 1500 kN/m² has been investigated. The reaction is of 1st order with a rate constant K = 1.79 × 10⁸ exp (-176.2 kJ/RT) s^?1. The major reaction products were acetylene, ethylene and methane, while traces of propylene and ethane were only detected at temperatures below 1500 K. At higher temperatures, propane conversion to acetylene increased at the expense of the other products. Optimum conversions to ethylene and methane, in contrast to that to acetylene, were more sensitive to changes in temperature than to variations in reaction time. However, at reaction pressures above 550 kN/m², extension of reaction time beyond 0.5 ms did not favour the formation of acetylene. A simple kinetic model which confirmed the experimental optimum product selectivity conditions is put forward.     

Reverse selectivity of zeolites and metal-organic frameworks in the ethane/ethylene separation by adsorption

Major advances in the ethane/ethylene separation will be related with the discovery of adsorbents that present preferential adsorption of ethane over ethylene. Metal-organic frameworks (MOFs) are crystalline materials consisting of metal ions, or ion clusters, and organic ligands. Gas chromatography (GC) is most informative for materials screening for the ethane/ethylene separation since it needs only few mg of sample and gives selectivity results at various temperatures. This is illustrated by the methodology presented in this work where materials from two types of families (zeolites and MOFs) were used to show the reversed selectivity that can be found towards the ethane/ethylene separation.     

碳氢燃料空气混合物爆轰性能的研究

用一维模型对含有四种特征官能团的碳氢燃料甲烷、乙烯、乙炔和环氧丙烷的爆轰参数进行了计算,并分析了官能团对碳氢燃料与空气混合物爆轰特性的影响,得出FAE燃料中利用烃类燃料代替环氧烷烃类可以相应地提高爆压和爆温,增加FAE（Fuel-Air-Explosive)武器的威力。     

Hydrogen production by decomposition of ethane-containing methane over carbon black catalysts

Mixtures of methane and small amounts of ethane were decomposed in the presence of carbon black (CB) catalysts at 1,073–1,223 K for hydrogen production. Although most of the added ethane was first decomposed to ethylene and hydrogen predominantly by non-catalytic reaction, subsequent decomposition of ethylene was effectively facilitated by the CB catalysts. Because some methane was produced from ethane, the net methane conversion decreased as the added ethane increased. The rate of hydrogen production from methane was decreased by the added ethane. A reason for this is that adsorption of methane on the active sites is inhibited by more easily adsorbing ethylene. In spite of this, the hydrogen yield increased with an increase of the added ethane because the contribution of ethane and ethylene decomposition to the hydrogen production was dominant over methane decomposition. A higher hydrogen yield was obtained in the presence of a higher-surface-area CB catalyst.