Oxidative coupling, of methane

There are large reserves of natural gas throughout the world in America alone, the Energy Information Administration (EIA) estimates that there are 1190.62 Tcf of technically recoverable natural gas. Natural gas is a combustible mixture of hydrocarbon gases, formed primarily of 

Oxidative coupling of methane (OCM) to C2 products (C2H4 and C2H4) represents one of the most effective ways to convert natural gas to more useful products  

Membrane Reactor configuration Temperature (°C) Main results Ref. 

sFeQ 203 5 Disk coated with La-Sr/CaO catalyst 950 Yc2=18% 5c2 65% [68] 

sFeQ 203 5 Tube, no catalyst, or packed with 800-900 82 2 = 62% or [70] 

DENSE CERAMIC OXYGEN-PERMEABLE MEMBRANE REACTORS 

The oxidative coupling of methane (OCM) to ethane and ethylene is a very attractive reaction for the conversion of natural and biogas, see Equation (32). However, the reaction suffers from severe drawbacks, such as high reaction temperatures, lack of stable and selective catalysts, and an extremely complex reaction mechanism. 

In a detailed academic study, the application potential of Li-doped MgO, prepared via different synthetic routes and with different loadings of Li, was investigated [11], Catalysts were prepared via decomposition of single source precursors, wet impregnation, precipitation, and mixed milling. The materials were sieved to a particle size 200 pm to avoid mass transfer limitations. Certain preparations (e.g. precipitation) result in very fluffy materials in such cases, the catalysts were pressed in advance of sieving. 

In Equation (35), an estimation of the mass transfer with the Weisz-Prater criterion is given. By taking always reasonable estimations or overestimated values, one obtains a good conclusion if mass transfer is present or not. For the characteristic length, 200 pm as particle diameter is used. The reaction order usually has the value of 1 to 4 a value of 4 would therefore be a worst case scenario. The catalyst density can be measured, or the common estimation of 1.3 kg/m3 can be used, which should not be too erroneous for Li-doped MgO. The observed reaction rate re is calculated from the concentration of CH4 at the inlet of the reaction cch4 0 multiplied with the highest observed conversion of 25% (the highest initial value for all tested catalysts), divided by the inverse flow rate, corrected by the reactor temperature. The calculation of re is shown in Equation (33)  

The concentration cch4 0 is obtained via the ideal gas law to f - For the diffusion of gases, the two most important cases are molecular diffusion (diffusion in the gas phase) and Knudsen diffusion (diffusion through pores, while the number of collisions between the pore wall is larger than the number of collisions between the gas 

Moreover, for high temperatures as applied in the OCM, the diffusion coefficients can be expected to be even higher. 

In the past 10 years there has been a renewed interest in finding new utilization methods for the conversion of methane due to the global excess of natural gas reserves and highly unpredictable market for petroleum. Most of natural gas reserves are located in remote areas of op ation and due to the lack of an infrastructure it is not cost-effective to transport these gaseous fuels to customers therefore intensive effort has been devoted to the research fOT methods to convert methane to more valuable chemicals. 

The interest in the oxidative coupling reaction was initiated 10 years ago by the pioneering work conducted by Keller and Bhasin. Since then hundreds of papers have been published including review papers (references 2-4 to cite a few), proceedings from several synqx sia on the subject, and a recent book which summarizes the state of research in several leading laboratories around the world. The objective of this survey is not to review the literature of methane coupling but rather to appraise certain aspects of methane dimerization that in the opinion of the authors are critical for the better understanding of the methane dimerization reacticm. As a result, the review is focused on selected topics and does not include many aspects which otherwise would have been included in broader literature review. The topics selected are as follows  

There is agreement among the researchers that the first and most fundamental part of the methane activation reaction is hydrogen abstraction from the CH molecule to form methyl radicals consequently, it is appropriate to start this overview with a section devoted to the formation and reaction of these species. The most comprehensive studies on this subject have been conducted by the group of Lunsford and coworkers whose objective was to establish a relation between methane conversion, surface-assisted generation of methyl radicals (CHj ), and the formation of C2 hydrocarbons. Direct measurement of the methyl radical production was 

In order to resolve the issue of the possible adsorption of methyl radicals on the surface of the MgO-based catalysts Campbell and Lunsford conducted an MIESR experiment with an additional layer of magnesium oxide placed downstream from the Li/MgO catalyst It was expected that, if methyl radicals were adsorbed by the MgO surface, a significant decrease in the CH3 signal would have been observed. The results of this experiment conducted at 700 °C showed that tire presence of magnesium oxide increased production of methyl radicals, suggesting that no ads(Hption of methyl radicals occurs at this tonperature. Furthermore, it was concluded that no coupling of CH3 radicals takes place on the MgO catalyst 

Additional results on sodium-carbonate-promoted Ce02 catalyst showed that die presence of Na2C03 decreased the combustion ability of cerium oxide. It is believed, however, that the active t iase (or phases) does not involve Ce02 which in this case serves as a su x t to sodium carbonate. Without presenting conclusive evidence, the authors proposed sodium peroxide, Na202, as the active phase responsible fw methane activation on this catalyst 

The scope of the present contribution is to describe and analyze the developments made over the last 10 years in oxidative transformations of methane into value-added products over heterogeneous catalysts. Particularly, we focus on (i) reaction engineering concepts for the OCM reaction (ii) mechanistic aspects of direct methane oxidation to methanol, its derivatives, and acetic acid and (iii) novel approaches for designing OCM catalysts. 

The present contribution analyzes new ideas and concepts on OCM published after 2008 with the focus on 

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There are two types of the OTM reactor for OCM that with or without 

So far, there are only a few reports of perovskite hollow fiber membrane reactors in the oxidative coupling of methane. Tan and Li studied the catalytic perovskite Lao.6Sro.4Coo.2Feo.8G3 (LSCF) hollow fiber membrane as 

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The direct methane conversion technology, which has received the most research attention, involves the oxidative coupling of methane to produce higher hydrocarbons (qv) such as ethylene (qv). These olefinic products may be upgraded to Hquid fuels via catalytic oligomerization processes. 

Generally, the most developed processes involve oxidative coupling of methane to higher hydrocarbons. Oxidative coupling converts methane to ethane and ethylene by... 

Although ethylene is produced by various methods as follows, only a few are commercially proven thermal cracking of hydrocarbons, catalytic pyrolysis, membrane dehydrogenation of ethane, oxydehydrogenation of ethane, oxidative coupling of methane, methanol to ethylene, dehydration of ethanol, ethylene from coal, disproportionation of propylene, and ethylene as a by-product. 

S. Seimanides, P. Tsiakaras, X.E. Verykios, and C.G. Vayenas, Oxidative Coupling of Methane over Yttria-doped Zirconia Solid Electrolyte, Appl. Catal. 68, 41-53 (1991). 

Oxidative Coupling of Methane to Ethylene with 85% Yield in a Gas Recycle Electrocatalytic or Catalytic Reactor-Separator... 

Two conqiletely different behaviors of oxidative transformation of methane, namely the Oxidative Coupling of Methane to C2 Hydrocarbons(OCM) and the Partial Oxidation of Methane to Syngas(POM), were performed and related over the nickel-based catalysts due to different modification and different supports. It is concluded that the acidic property favors keeping the reduced nickel and the reduced nickel is necessary for POM reaction, and the bade property frvors keeping the oxidized nickel and the oxidized mckel is necessary for OCM reaction. POM and OCM reactions proceed at different active sites caused by different... 

Thompson, W. J., Microreactor system for hydrogen generation and oxidative coupling of methane, in Proceedings of the 4th International Conference on Microreaction Technology, IMRET 4, pp. 351-357 (5-9 March 2000), AIChE Topical Conf Proc., Atlanta, USA. 

Oxidative coupling of methane to yield C2 and higher hydrocarbons... 

The oxidative coupling of methane has been studied by several authors. The most elusive transformation has been the oxidative coupling of methane into C2 hydrocarbons (ethene, ethane), because the reaction is more endothermic than other transformations [2]. The application of fast and efficient microwave heating to endothermic reactions is particular interest. 

Oxidative coupling of methane has also been examined by other authors [2, 68-70], who have used different catalysts. 

Oxidative coupling of methane to yield C2 and higher hydrocarbons 358 Direct partial oxidation of methane to produce methanol and other oxygenates 360... 

IFP Oxypyrolysis Also called NGOP. A process for converting natural gas to gasoline, based on the oxidative coupling of methane to ethane in a fixed-bed reactor. Developed in 1991 by the Institut Frangais du Petrole. 

In the 1980s, the oxidative coupling of methane to give ethylene and ethane was reported by Keller and Bhasin (8), whose discovery prompted numerous attempts to convert methane directly—and not only to ethylene and ethane (8), but also to methanol and formaldehyde (9) (Table I). Research on oxidative coupling of methane was motivated by results showing that the methane was... 

Omata, K., S. Hashimito, H. Tominaga and K. Fujimoto. 1989. Oxidative coupling of methane using a membrane reactor. Appl. Catal. 52(L1). 

Roos, J. A., S. J. Korf, J. J. P. Bicrmann, J. G. van Ommen and J. R. H. Ross. 1989. Oxidative coupling of methane, the effect of gas composition and process conditions. Proc. 2nd Europ. Workshop Meeting, New Developments in Selective Oxidation. Rimini, Italy. 

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