Oxidative Coupling of Methane to Higher Hydrocarbons

Natural gas is an abundant resource in various parts of the world. Methane is the major component of natural gas, often comprising over 90 mol% of the hydrocarbon fraction of the gas. Methane itself is primarily used as a fuel, while the nonmethane components can be separated and used as feedstocks for the production of chemicals or liquid fuels. In many cases, however, natural gas reserves are found in locations distant from their place of utilization. Since it is not generally economical to transport liquefied natural gas, efficient methods are needed to convert methane into transportable liquid products. A possible route is oxidative dimerization of methane followed by oligomer-ization of the C₂ products.     

甲烷催化转化制高碳烃技术进展

甲烷的化学性质很不活泼,首先得转化为中间体然后才能将其转变成高附加值的化工产品:以钼、锰、锌和铁等金属催化剂及分子筛负载下,甲烷无氧催化脱氢芳构化可得苯及其衍生物,后者是重要的基础化工原料;而用等离子体法转化CH_4可以直接获得C_2以上烷烃、烯烃、炔烃甚至芳烃,具有潜在和巨大的应用前景。     

Higher Hydrocarbon Production through Oxidative Coupling of Methane Combined with Hydrogenation of Carbon Oxides

In the production of higher hydrocarbons, combining oxidative coupling of methane (OCM) with hydrogenation of the formed carbon oxides in a separate reactor provides an alternative to the currently applied methane conversion to syngas followed by Fischer‐Tropsch synthesis. The effects of CH₄:O₂ feed ratio in the OCM reactor and partial pressures of H₂ or/and H₂O in the hydrogenation reactor were analyzed to maximize production of C₂₊ hydrocarbons and reduce CO_x formation. The highest C₂₊ yield was achieved with low CH₄:O₂ feed ratio for OCM and removal of the formed water before entering the hydrogenation reactor.     

Thermal Reaction Analysis of Oxidative Coupling of Methane

For more than three decades, the oxidative coupling of methane (OCM) process has been investigated as a promising alternative approach for ethylene production. Simulations of different sets of surface mechanisms over the Na₂WO₄/Mn/SiO₂ catalyst and the gas phase reactions that come along with the OCM reaction were analyzed in a fixed‐bed, membrane, and fluidized‐bed reactor. The results were compared with the experimental data generated in an OCM mini‐plant. It was observed that the gas phase reactions are crucial in reducing the overall selectivity, especially in the fluidized‐bed reactor.     

甲烷氧化偶联制乙烯工艺研究进展

甲烷氧化偶联(OCM)途径是通过一步法获取乙烯,是现有乙烯生产中最为简捷的工艺。本文综述了该工艺催化剂系统、反应机理、工艺开发研究的新进展,并探讨了OCM过程面临的关键问题有催化剂的选择、反应器和反应流程的设计和反应温度的控制。     

Bismuth-Containing Oxides as Catalysts for Oxidative Coupling of Hydrocarbons

Some bismuth-containing oxides, such as bismuth molybdates, are known to be effective catalysts for so-called allylic oxidation of C₃-C₄ olefins including partial oxidation to unsaturated aldehyde, oxidative dehydrogenation to diolefin, and ammoxidation to corresponding nitrile. This type of catalyst is well studied and repeatedly reviewed [1-3]. Its high effectiveness can be interpreted within a dual-site concept according to which hydrocarbon adsorbs on an active site associated with one of the metal oxide components while oxygen adsorbs on an active site associated with another metal oxide component. For instance, the authors [4, 5] assume a bismuth center to be responsible for the hydrocarbon conversion to an allylic species which then reacts further at a molybdenum site to produce aldehyde.     

Oxidative Coupling of Methane in Small Scale Parallel Reactors

In this work the testing of high temperature reactions in small scale parallel reactors is explored using the oxidative coupling of methane as an example. The advantages of small scale reactors for this very exothermic and complex reaction are discussed. The data generated in this study is explored making use of response surface models derived from statistically designed experiments. Methane conversion has been explored over a Mn-promoted Na₂WO₄/SiO₂ catalyst over the temperature range 755–875 °C, pressure range 0.2–8.4 barg and GHSV range 4,000–36,000 h⁻¹ using air as oxidant. Methane to oxygen stoichiometries of 4–8 have been explored. The highest C2 yield (16 %) is obtained at at low pressure.

     

甲烷氧化偶联制C_2催化剂的研究进展(一)

本文话细地介绍了甲烷氧化偶联制备C_2的催化剂研究概况,并着重分析了催化剂的种类及其特性。     

Oxidative Coupling of Methane in Small Scale Parallel Reactors

In this work the testing of high temperature reactions in small scale parallel reactors is explored using the oxidative coupling of methane as an example. The advantages of small scale reactors for this very exothermic and complex reaction are discussed. The data generated in this study is explored making use of response surface models derived from statistically designed experiments. Methane conversion has been explored over a Mn-promoted Na₂WO₄/SiO₂ catalyst over the temperature range 755–875 °C, pressure range 0.2–8.4 barg and GHSV range 4,000–36,000 h^?1 using air as oxidant. Methane to oxygen stoichiometries of 4–8 have been explored. The highest C2 yield (16 %) is obtained at at low pressure.     

Controlled Oxidative Coupling of Methane by Ionic Conducting Ceramic Membrane

Oxidative coupling of methane was performed on a tubular dense membrane reactor made of catalytically active fluorite-structured Bi_1.5Y_0.3Sm_0.2O_3-. Methane and air were separately fed to the tube and shell side of the membrane. The tubular dense membrane reactor gives 35% one-pass C₂ (C₂H₄+C₂H₆) yield for oxidative coupling of methane with a C₂ selectivity of 54% at 900 °C.     

Combined Single-pass Conversion of Methane Via Oxidative Coupling and Dehydro-aromatization

A single-pass process with the combination of oxidative coupling (OCM) and dehydro-aromatization (MDA) for the direct conversion of methane is carried out. With the assistance of the OCM reaction over the SrO–La₂O₃/CaO catalyst loaded on top of the catalyst bed, the duration of the dehydro-aromatization reaction catalyzed by a 6Mo/HMCM-49 catalyst shows a significant improvement, and. the initial deactivation rate constant of the overall process revealed about 1.5×10⁻⁶ s⁻¹. Up to 72 h on stream, the yield of aromatics was still maintained at 5.0% with a methane conversion of 9.6%, which is obviously higher than that reported for the conventional MDA process with single catalyst. Upon the TPR results, this wonderful enhancement would be attributed to an in-situ formation of CO₂ and H₂O through the OCM reaction, which serves as a scavenger for actively removing the coke formed during the MDA reaction via a reverse Boudouard reaction and the water gas reaction as well.     

Combined Single-Pass Conversion of Methane Via Oxidative Coupling and Dehydroaromatization

A new reaction mode, i.e., the combined single-pass conversion of methane via oxidative coupling (OCM) over mixed metal oxide (SLC) catalysts and dehydroaromatization (MDA) over Mo/HZSM-5 catalysts, is reported. With the assistance of an OCM reaction over SLC catalysts in the top layer of the reactor, the deactivation resistance of Mo/HZSM-5 catalysts is remarkably enhanced. Under the selected reaction conditions, the CH₄ conversion decreased from 18 to 1% and the aromatics yield decreased from 12.8 to 0.1%, respectively, after running the reaction for 960min on both 6Mo/HZSM-5 and SLC-6Mo/HZSM-5 catalyst system without O₂ in the feed. On the other hand, for the SLC-6Mo/HZSM-5 catalyst system with O₂ in the feed, the deactivation was improved greatly, and after 960min onstream the CH₄ conversion and aromatics yield were still as high as 12.0 and 8.0%, respectively. The promotion effect mainly appears to be associated with in situ formation of CO₂ in the OCM layer, which reacts with coke via the reverse Boudouard reaction.     

Modeling of Methane Oxidative Coupling under Periodic Operation by Neural Network

A set of feed forward multilayer neural network models have been proposed to predict CH₄ conversion, C₂ and ethylene selectivity of methane oxidative coupling under periodic operation. These parameters predicted by the proposed neural network are based on cycle period, cycle split, and CH₄ and O₂ mole fractions in the first and second part of the period. Due to the dynamic nature of periodic operation and the kinetic complexity of the investigated reactions, the proposed approach is an effective tool to model the system. The agreement between model predictions and experimental data was quite satisfactory. The models could be employed to optimize the experimental conditions in order to get better output from the catalytic reaction. It is concluded that the neural network is an effective tool for modeling catalytic chemical reactions under periodic operation.     

氧泵型反应器及在甲烷氧联反应中的应用

本文介绍了氧泵型反应器构造、原理和固体氧离子电解质的性能表征.通过对催化剂、氧泵的作用、催化膜制备方法及反应历程几方面近期来研究的叙述和总结,分析了氧泵型甲烷氧化偶联的研究现状,介绍了NEMCA效应及其研究手段和主要结论.对氧泵型反应器甲烷氧化偶联存在的问题和今后的研究方向提出了看法.     

Li-doped MgO From Different Preparative Routes for the Oxidative Coupling of Methane

Li-doped MgO was prepared on different preparative routes and with different loadings. The catalytic activity was found to decay for all catalysts for 40 h time on stream. A detailed structural analysis of 0.5 wt% Li-doped MgO showed heavy losses of Li, reduced surface area and grain growth. A correlation between these factors and the deactivation could not be found. The reaction temperature and the flow rate were found to be the main deactivation parameters.     

Oxidant Activation Over Structural Defects of Oxide Catalysts in Oxidative Methane Coupling

Different aspects concerning the process of direct methane conversion to oxygen-containing products developed during more than half a century have been considered in previous reviews [1-3]. In particular, Gesser et al. [13 paid most attention to the homogeneous stages in methane conversion, while Foster [2] and Pitchai and Klier [3] examined the effect of different catalysts on methanol and formaldehyde formation. At present the main product of the homogeneous methane oxidation process with oxygen is shown to be methanol formed according to a chain-branching mechanism. In the presence of homogeneous initiators [4] (benzene, 2,2,4- trimethylpentane, etc.) or heterogeneous catalysts [2,3,5,6], formaldehyde is formed together with CH30H. However, the yield of the desirable products is low and does not exceed 8-10%. Charged atomic oxygen forms are considered to take part in the process of catalytic methane oxidation.     

介质阻挡放电常压低温等离子体转化甲烷制C2及高碳烃的研究

对介质阻挡放电(DBD)反应器用于甲烷常压低温等离子体转化过程,分别就停留时间、输入功率、内电极材料及温度、介质厚度等对反应的影响进行了研究。实验结果表明,甲烷转化率随停留时间、输入功率的增加而增加,但增加的幅度逐渐减小。内电极材料对反应积炭有很大的影响。紫铜和紫铜(镀银)材料能够有效地抑制积炭的产生,从而可以增加反应寿命,还对甲烷转化率有很大的影响。较低的内电极温度可以抑制积炭,但是甲烷转化率有所降低,同时液态高碳烃选择性增加。在甲烷流量较低时介质厚度对反应的影响很小,但随着甲烷流量的提高会逐渐增大,并且介质厚度越小,甲烷转化率越高。