Oxidation products methane—oxygen mixtures

A high selectivity of methanol formation is the main feature of the oxidation of rich methane—oxygen mixtures ([Ct J/iOJ = 10—30) at high pressures and moderate temperatures. The other two main liquid products of this process are water and formaldehyde. Although only trace amoimts of formaldehyde, if any, have been detected in a number of studies, it can be argued that this is most likely a result of its subsequent removal in secondary processes, including those on the surface of the reactor or catalyst. 

A comparative study of oxides which were closely related, but had different electrical properties, showed that both n- and p-type semiconduction promoted the oxidation reaction, forming CO as the major carbon-containing product. In a gas mixture which was 30% methane, 5% oxygen, and 65% helium, reacted at 1168 K the coupling reactions were best achieved with the electrolyte Lao.9Sro.1YO 1.5 and the /i-lype semiconductor Lao.sSro MntL A and the lily pe semiconductor LaFeo.sNbo.2O1 a produced CO as the major oxidation product (Alcock et al., 1993). The two semiconductors are non-stoichiometric, and the subscript 3 — x varies in value with the oxygen pressure and temperature. Again, it is quite probable that the surface reactions involve the formation of methyl radicals and O- ions. 

Carbon monoxide may be prepared by several methods. Large scale production is carried out by controlled oxidation of natural gas or by the catalytic steam reforming of methane or light petroleum fractions. The products obtained are mixtures of CO, H2, and CO2. It also is made by gasification of coal and coke with oxygen at about 1,500°C. 

The amount of the products formed over the studied catalysts, in the presence and absence of molecular O2, are listed in Table III. It is evident that the formation of the oxidation products is associated with the gas phase oxygen supply. Then, as the reaction rates in the mixture of reactant and in separate steps differ (19), these data exclude the participation of lattice oxygen in the partial oxidation of methane via a two step redox mechanism as main reaction pathway proving the occurrence of a "concerted mechanism". 

Methane reacts only slowly with oxygen below 400° C. Ethane oxidation was observed by Bone and Hill (S) at 290° to 323° C. Formaldehyde, a reaction product, was found to increase, reach a maximum, and then decrease. Addition in amounts of 1% to a 3 to 1 ethane-oxygen mixture at 316° C. and 720 mm. eliminated the induction period, but other additives such as nitregen dioxide, acetaldehyde, ethyl alcohol, or water, were also more or less effective. 

Complete oxidation of methane to carbon dioxide and water occurs when it is burned in air and controlled combustion is an extremely important source of thermal energy. Methane and O2 also form extremely dangerous mixtures in the gas phase and explosions are easily detonated. Explosions occur under oxygen-deficient conditions and CO is an important and toxic product. 

The fact that ethane has been found to be so much more readily reacted upon by oxygen than methane to yield larger quantities of formaldehyde than is obtainable from methane, makes it seem that some of the high yields reported from methane may have in most part beeu due to ethane admixed in the hydrocarbon gas used, rather than the attainment of unusually productive operating conditions. This is true of data from experiments in which natural gas had been used for oxidation. The pressure oxidation process producing a mixture of methanol, formaldehyde, and acetaldehyde from natural gas utilizes the hydrocarbons higher than methane, and especially ethane. ... 

To understand how coal can be used as a raw material for the production of organic compounds, it is necessary to discuss synthesis gas. Synthesis gas is a mixture of carbon monoxide and hydrogen in varying proportions, depending on the means by which it is manufactured. Synthesis gas is prepared by passing steam over coal. It is also prepared by the partial oxidation of methane by oxygen. 

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