Methane to ethylene

Methanol to Ethylene. Methanol to ethylene economics track the economics of methane to ethylene. Methanol to gasoline has been flilly developed and, during this development, specific catalysts to produce ethylene were discovered. The economics of this process have been discussed, and a catalyst (Ni/SAPO 34) with almost 95% selectivity to ethylene has been claimed (99). Methanol is converted to dimethyl ether, which decomposes to ethylene and water the method of preparation of the catalyst rather than the active ingredient of the catalyst has made the significant improvement in yield (100). By optimizing the catalyst and process conditions, it is claimed that yields of ethylene, propylene, or both are maximized. This is still in the bench-scale stage. 

Y. Jiang, I.V. Yentekakis, and C.G. Vayenas, Methane to Ethylene with 85% Yield in a Gas-Recycle Electrocatalytic Reactor-separator, Science 264, 1583-1586 (1994). 

Benson A process for converting methane to ethylene, developed by Hydrocarbon Research, CA. 

Methane to Ethylene One target is to achieve an ethylene selectively of 90% at a methane conversion level of 50% in a single pass. Additionally, design of novel recycle reactors or membrane systems (to remove the ethylene produced) remain part of the active research. 

Methane and Toluene to Styrene Basic catalysts in the presence of oxygen and/or air are reported to be attractive catalysts for this reaction. Most research was performed in the late 1980s and early 1990s. The fundamentals resemble the oxidative coupling reaction of methane to ethylene. 

The direct catalytic conversion of methane has been actively pursued for many years. Much of the emphasis has been on the direct production of methanol via selective partial oxidation (8), coupling of methane to ethylene (9), or methane aromatization (10). At this time none of these technologies has been demonstrated commercially due to low yields of desired products due to combustion by-products or low equilibrium conversion at reasonable process temperatures and pressures. The potential benefits of a hypothetical process for the direct partial oxidation of methane to methanol (11) are presented as an example. 

Hess s law can be used to calculate reaction enthalpies for hypothetical processes that can t be carried out in the laboratory. Set up a Hess s law cycle that will let you calculate A H° for the conversion of methane to ethylene ... 

The anaerobic oxidative coupling of methane to ethylene was studied by ARCO Chemical [70b]. The reaction occurs at a very high temperature of 850-900 °C with a Li/B/Mn/Mg/0-Si02 catalyst, a conversion of 22% was achieved with selectivity to C2 compounds of about 60% under anaerobic conditions. Monsanto [71] studied... 

Oligomerization of methane to ethylene 2CH4 + 02 — 2H20 + C2H4... 

Benson A process for converting methane to ethylene. The methane is reacted with chlorine at a high temperature, yielding hydrogen chloride and ethylene. The hydrogen chloride must be reconverted to chlorine or used in another process. Developed by Hydrocarbon Research, CA, but not commercialized. 

Other applications have been proposed but as yet without success, like the direct coupling of methane to ethylene or the direct conversion of methane to methanol. Recently, some disclosures were made on the reaction of methane with alkanes to yield augmented alkanes. ... 

Jiang, Y., Yentekakis, TV., and Vayenas, C.G. 1994. Methane to ethylene with 85 percent yield... 

Methyl radicals formed simultaneously with ethylene can rapidly capture a hydrogen atom from any organic molecule in the gas (first of all, from propane) and transform it into methane. The latter is almost inert under the conditions of propane ODH. This means that methane-to-ethylene ratios close to 1 or above serve as evidence for predominantly homogeneous anaerobic degradation of the C-C-C skeleton. On the other hand, such degradation can also proceed via oxidative paths with the participation of molecular oxygen and/or oxidized (oxidative) intermediates. One of the most probable is an aldehyde route ... 

Thus, a preliminary analysis of olefin production pathways can be performed based on the methane-to-ethylene ratio and on temperature dependence of the (C3 = )-to-(C2 =) ratio. A more detailed elaboration can be reached from experiments with varied oxygen concentration and from the detailed analysis of the product distribution (including hydrogen formation). However, ethylene formation itself is strong evidence for the contribution of the radical route in product formation. The analysis of experimental data about product distribution during propane oxidation (Kondratenko et al, 2005) demonstrates that over rare-earth oxide catalysts radical route is prevailing in olefin formation. On the other hand, over supported Y-containing catalysts, propylene... 

Adsorption complexes of methane at MgO are interesting because they relate to the conversion of methane to ethylene and methanol. In particular, oxidative coupling of methane on metal-oxide catalysts attracted great attention [119]. Usage of methane as a probe to identify and characterize adsorption sites of different acid strength on oxide catalysts is another important aspect. Because CH4 is not easily captured by surfaces of metal oxides, the nature of the interaction of methane with surface sites was little understood until recently. A FTIR spectroscopy investigation of methane on MgO at 173 K revealed adsorbed molecular species preferentially bound at Lewis basic sites CH4 adsorption on a Lewis acid-base pair has also been proposed [120]. 

For the spontaneous conversion of methane to ethylene, for example, the respective empirical oxidation and reduction half-reactions occurring on each membrane surface in these O - conducting materials may be represented as follows ... 

Capabilities of this technique to compress gases were studied both eiqierimentally and theoretically. The experimental results on the pressure change were used to estimate the capabilities of the technology proposed for conversion of methane to ethylene and acetylene. 

The Liquid Compression Reactor seems to be very promising technology for high temperature, high pressme processes. Direct conversion of methane to ethylene and acetylene in the reactor is a one of such processes. 

Figure 1. Each sloped line represents the loci of all possible combinations of average residence times and hydrocarbon partial pressures which are consistent with a fixed pyrolysis yield pattern, i.e., constant pyrolysis selectivity lines. For liquid feedstocks, the methane-to-ethylene ratio found in the pyrolysis reactor effluent has been used as a good overall indicator of pyrolysis reactor selectivity. Low methane-to-ethylene ratios correspond to a high total yield of ethylene, propylene, butadiene and butylenes. Consequently, the yields of methane, ethane, aromatics and fuel oil are reduced. TL refore, each constant pyrolysis selectivity line shown in Figure 1 is identified with a fixed methane-to-ethylene ratio. This specific selectivity chart applies to a Kuwait heavy naphtha which is pyrolyzed to achieve a constant degree of feedstock dehydrogenation, i.e., a constant hydrogen content in the effluent liquid products, which in this case corresponds to the limiting cracking severity.

Recently, it has been reported that Siluria Technologies has developed a nanowire-based catalyst that can convert methane to ethylene more efficiently and at a significantly lower temperature than anything reported previously. This method has not yet been demonstrated beyond the laboratory. 

The direct oxidative addition of methane to ethylene shown in the equation below is a thermodynamically favorable reaction (Gibbs free energy of-69 Kcal/mole). 

Pereira, P., Lee, S.H., Somoijai, G.A., and Heinemann, H. (1990) The Conversion of Methane to Ethylene and Ethane With Near Total Selectivity by Low Temperature (<610" C) Oxydehydrogenation Over a Calcium-Nickel-Potassium Oxide Catalyst, Catalysis Letters 6, 255-62. 

Wan, J.K.S. (1986) Microwave Induced Catalytic Conversion of Methane to Ethylene and Hydrogen, US Patent 4,574,038. 

Figure 27. Process scheme for catalytic oxidative coupling of methane to ethylene [57].

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