1767. ---------------. [KING, J. G.] Synthesis of Methane. Gas World, vol. 122, 1945, pp. 196-200, 209; Gas Times, vol. 42, Supp., 1945, pp. 1-4; Chem. Abs., vol. 39, 1945, p. 2189.

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Literature Abstracts

Review of research and a discussion of the reactions involved in synthesizing CH₄ from water gas and the application of these reactions to the production of city gas. With a high H₂:CO ratio and when the main reaction at a low temperature and atmospheric pressure is CO+3H₂=CH₄+H₂O, (1), the water-gas-shift reaction must be satisfied: CO+H₂O=CO₂+H₂ (4).

If the H₂:CO ratio is reduced, reaction (4) becomes more effective and more CO₂ appears in the final gas. When the ratio reaches unity, the reaction is: 2CO+2H₂=CH₄+CO₂ (2).

The effect of increase of temperature is to favor the water-gas reaction (4) at a high ratio and the CH₄ reaction (1) at a low ratio. A constant CO₂:CH₄ ratio independent of the H₂:CO ratio is suggested at a temperature of about 750° C. The effect of pressure up to 25 atm. is nil at 300° but reduces the effect of increasing temperature. AT 300° and 1 atm., the percentage of CH₄ obtainable in the dry CO₂-free gas rises from 83 to 98% as the H₂:CO ratio falls from 3:1. With increase of temperature the % of CH₄ falls until it is less than 10% at 700°; a gas containing 50% CH₄ is obtained at 500° when the pressure is 1 atm. and at 700° when the pressure is 25 atm. In operating a technical process, assuming the use of a catalyst active enough to bring reactions (1) and (4) to completion at a high space velocity, the most favorable conditions for obtaining a gas of high CH₄ content would be low temperature and atmospheric pressure whatever the H₂:CO ratio. At a higher temperature, however, the CH₄ content would be maintained and catalyst activity preserved only by increasing the working pressure. Care must be taken to prevent deterioration of the catalyst by surface overheating and bringing on reaction:

2CO=CO₂+C (5)

The deposition of C can be suppressed by using a high H₂:CO ratio, which favors reaction (1). To obtain a ratio of 3:1, it may be necessary to treat part of the water gas with steam

H₂+CO+H₂O=CO₂+2H₂(6)

and to remove the CO₂ by washing under pressure, thus increasing the H₂ content of the original gas to the desired figure. Ni catalysts have been developed that can be operated at a high space velocity and that have an initial activity many times greater than is necessary to carry the main reactions to equilibrium. The reactions have been subjected to close study, and the knowledge collected is being applied to the control of the reaction on a larger scale looking towards the development of a pilot plant to operate under the proved conditions.