Production during methane oxidation

Dihydroxydiphenylmethanes are readily prepared using a slight adaptation of Pearl s method. He observed the formation of diguaiacyl-methane as a by-product during the oxidation of vanillin to vanillic acid 21). 

The cooperative effects observed during methane oxidation over a binary oxide-metal system are due to the formation of active intermediates (free methyl radicals) over the oxide component, their escape from the grains of oxide, and transformation into the final products (including CO and H2) over the metal component, which proceeds in a non-steady-state oscillatory regime. 

These data predict more methanol than formaldehyde in the product stream during methane oxidation this clearly is not the case. 

Replacing one or several of the hydrogen atoms in methane by one or several other atoms than hydrogen automatically creates secondary or tertiary C-H bonds. Secondary and tertiary C-H bonds are more reactive than a primary C-H bond. During oxidation reactions, this leads to an easier oxidation of the reaction products than methane, and consequently to a low(er) reaction selectivity. Such reactions therefore produce complicated reactant mixmres that require costly... 

Bartholomew and co-workers also measured the loss of catalytic activity with time of Ni and Co bimetallics (157, 194), Ni-molybdenum oxide (23, 113), and borided Ni and Co catalysts (161) during methanation in the presence of 10 ppm H2S. Typical activity versus time plots are shown in Figs. 25 and 26. Activity is defined as the ratio of the mass-based rate of methane production at any time t divided by the initial rate. The activitytime curves are generally characteristic of exponential decay some catalysts decay more slowly than others, but all catalysts suffer at least two orders of magnitude loss in activity within a period of 100-150 hr. Accordingly, it does not appear that other metals or metal oxides in conjunction with Ni significantly change the sulfur tolerance defined in terms of steady-state activity of Ni. These materials can, however, influence the rate at which the... 

The ultimate products of the oxidation of any hydrocarbon are carbon dioxide and water vapour, but there are many relatively stable partially oxidised organic species such as aldehydes, ketones and carbon monoxide that are produced as intermediate products during this process, with ozone produced as a by-product of the oxidation process. Figure 10 shows a schematie representation of the free radical catalysed oxidation of methane, whieh is analogous to that of a hydrocarbon. As previously discussed, the oxidation is initiated by reaction of the hydrocarbon with OH and follows a mechanism in with the alkoxy and peroxy radicals are chain propagators and OH is effectively catalytic, viz... 

Fig. 15. The influence of the pic d arret on product forrhation during the oxidation of propane. Initial temperature = 430 °C initial pressure of propane = 90 torr initial pressure of oxygen = 210 torr volume of reaction vessel = 30 cm , (b) Left ordinate +, methyl alcohol. Right ordinate x, isopropyl alcohol , ethyl alcohol o, n-propyl alcohol 1, allyl alcohol, (c) Left ordinate +, hydrogen peroxide , formaldehyde. Right ordinate x, total aldehydes, (d) +, propene i, methane , ethylene x ethane. (From ref. 147.)...

Aldehydes are often intermediates in the oxidation of other fuels [1—4, 29], and the ease with which they themselves oxidize and give rise to peroxidic materials or active radicals means that their role in these systems is likely to be important. For example, formaldehyde is produced during the oxidation of most hydrocarbons, and is known to behave as a branching intermediate during the high temperature combustion of methane [1—6], However, in certain systems, and particularly at lower temperatures, formaldehyde may behave as a retarder [7—9, 57]. Acetaldehyde is an intermediate in the oxidation of propene [10] and other olefins [11, 12], and its addition to these systems reduces the induction period or enhances the maximum rate. Many other examples are known both of the occurrence of aldehydes amongst the combustion products and of the ability of aldehydes to influence the oxidation of systems in which they occur [1, 13—19]. 

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... 

In trying to confirm their theory in regard to the intermediate formation of oxygenated products during combustion, Bone 9 and his co-workers carried out extensive researches and from their work has come the present hydroxylation theory. According to Bone the oxidation of methane takes place in steps, methanol, formaldehyde, formic acid, and carbonic acid being formed in the order named. These various steps are indicated below. The double arrows point out the mam course of reaction, while the single arrows show how the intermediate compounds may decompose. 

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