Methane conversion processes partial oxidation

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). 

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

As an alternate to LNG, natural gas can be chemically converted to methanol, chemical feedstocks (such as ethylene), gasoline, or diesel fuel. Most processes start with the conversion of methane to synthesis gas, a mixture of carbon monoxide and hydrogen. This can be done partial oxidation, an exothermic reaction ... 

The other two main processes for conversion of methane into synthesis gas are partial oxidation and CO2 reforming. In the 1940s, Prettre et al. (3) first reported the formation of synthesis gas by the catalytic partial oxidation of CH4... 

Hydrogen production by partial oxidation is similar to production by catalytic steam reforming. The process basically involves the conversion of steam, oxygen and hydrocarbons to hydrogen and carbon oxides. The process proceeds at moderately high pressures with or without a catalyst depending on the feedstock and process selected. The catalytic POX, which occurs at about 865 K, will work with feedstock ranging from methane to naphtha. The non-catalytic POX, which occurs... 

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. 

The current two-step industrial route for the synthesis of methanol, from coal or methane to synthesis gas and then from synthesis gas to methanol, has certain drawbacks. The economic viability of the whole process depends on the first step, which is highly endothermic. Thus a substantial amount of the carbon source is burned to provide the heat for the reaction. It would be highly desirable, therefore, to replace this technology with a technically simpler, single-step process. This could be the direct partial oxidation of methane to methanol, allowing an excellent way to utilize the vast natural-gas resources. Although various catalysts, some with reasonable selectivity, have been found to catalyze this reaction (see Sections 9.1.1 and 9.6.1), the very low methane conversion does not make this process economically feasible at present. 

In the petrochemical industry it is of interest to develop processes that convert a gaseous fuel, such as methane, to a liquid fuel, such as methanol or formaldehyde, by partial oxidation. It has proved difficult, however, to identify reaction conditions with a sufficient yield of CH2O from CH4. The problem is that the rate of CH2O oxidation is large compared to the rate of methane oxidation, and for this reason it is difficult to avoid subsequent conversion of CH2O to CO in the oxidative process. 

It is of interest to assess the process potential of methanol production by a direct partial oxidation of methane. This way the steam reformer and the shift reactor can be saved, and the catalytic methanol reactor can be replaced by a noncatalytic partial oxidation reactor. It is estimated that direct partial oxidation is competitive if a conversion of methane of at least 5.5% can be obtained with a methanol selectivity of at least 80%. 

The auto-thermic conversion of methane to H2 occurs at 850°C, where a partial oxidation process is combined to a catalytic steam reforming process (Damen et al., 2006). A 60-65% methane conversion could be attained with a selectivity of 80% towards hydrogen production. According to the mechanism of consecutive... 

Partial oxidation of methane (or hydrocarbons) is another option to produce syngas [4], This process, which runs without a catalyst, needs high temperatures for high CH4 conversion and to suppress soot formation. The process can handle other feedstocks, such as heavy oil factions and biomass, and yields syngas with a H2/CO ratio of about 2. The process is eminently suitable for large-scale production of syngas (e.g. for gas-to-liquids [GTL] plants). 

A catalytic version of partial oxidation (CPO) exists as well [5, 6]. It is based on short-contact time conversion of methane, hydrocarbons, or biomass on, for example, rhodium catalysts. This process is suitable for small-scale applications. 

The ITM Syngas process involves the direct conversion of methane to synthesis gas (see Fig. 22.7). The process utilizes a mixed, conducting ceramic membrane and partial oxidation to produce the synthesis gas.40 The goal of this advanced reformer technology is to reduce the cost of hydrogen production by over 25 percent.59,79... 

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