Methane conversion processes oxidative coupling

Figure 11 Schematic of a flow diagram of an integrated plant, showing the main processes involved in methane conversion by oxidative coupling.

Fig. 1. Process concept for methane conversion by oxidative coupling.

The industrially important direct methane conversion processes comprise oxidative coupling, reductive coupling including pyrolysis reactions, partial oxidation, halogenation and oxyhalogenation,26 and ammoxidation. Other direct conversions include alkylation, electrophilic substitution, and C-H bond activation over various complex and super acid catalysts. Several of these direct conversion technologies remain to be exploited to achieve their full commercial potentials. 

The partial introduction of lead as cations in the hydroxyapatites shifts the methane conversion process to favour oxidative coupling products (Fig. 2). 

The production of higher hydrocarbons directly from methane by catalytic oxidative coupling is a novel methane conversion process which warrants further study. When combined with an ethylene oligomerisation step it is a potential alternative to conventional processes, based on synthesis gas, for producing liquid fuels from methane. However, further research is necessary to provide the information required to assess the commercial prospects for this route. 

The application of heterogeneous catalysts to the methane conversion process has recently been examined by Lunsford (ref. 9) with MgO and Mo/Si02, Somorjai (ref. 10) with Mo/Si0 2 and V/SiO2 and Sofranko (ref. 11), the latter of whom has examined various supported oxides for the oxidative coupling of methane. 

Peil KP, Marcehn G, Goodwin JG, Jr, The role of lattice oxygen in the oxidative coupling of methane, in Wolf EE (ed.). Methane Conversion by Oxidative Processes-Fundamental and Engineering Aspects, Van Nostrand Reinhold, New York, pp. 139-145, 1992. 

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. 

Methane-based commercial production of ethylene via oxidative coupling has been investigated, but to date the lower per pass conversions required for acceptable ethylene selectivities combined with purified oxygen costs make this process noncompetitive with thermal cracking of ethane from natural gas liquids. 

Industry experts today suggest conversions of 40-50 percent and selectivities above 80 percent based on methane and oxygen as the minimum needed for commercial consideration after fixed and variable costs are added. Nonetheless, methane oxidative coupling holds the most promising combination of process simplicity, product slate versatility and low cost, and worldwide raw material availability not offered now by practiced fuel and chemical feedstock technologies. 

To promote both the conversion of reactants and the selectivity to partial oxidation products, many kinds of metal compounds are used to create catalytically active sites in different oxidation reaction processes [4]. The most well-known oxidation of lower alkanes is the selective oxidation of n-butane to maleic anhydride, which has been successfully demonstrated using crystalline V-P-O complex oxide catalysts [5] and the process has been commercialized. The selective conversions of methane to methanol, formaldehyde, and higher hydrocarbons (by oxidative coupling of methane [OCM]) are also widely investigated [6-8]. The oxidative dehydrogenation of ethane has also received attention [9,10],... 

Earlier and continuing work from our laboratories has shown that the introduction of small quantities of tetrachloromethane (TCM) into the feedstream for methane partial oxidation or oxidative coupling produces benefrcial increases in the selectivides to hydrocarbons, particularly ethylene, with many heterogeneous catalysts [19]. Consequently it is of interest to examine the effect of this additive with other oxidation processes, such as the conversion of CO to COj. 

Performance of catalytic properties of reagent catalyst in the processes such as methane oxidative coupling and hydrogen production by methane conversion... 

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