Synthesis of Methane

The synthesis of methane from its elements at high temperature was first announced by Bone and Jerdan in 1897, but was questioned by Berthelot, Pring and Hutton, and Mayer and

Altmayer, Bone and Coward, however, reaffirmed the synthesis in 1908, and obtained 73 per cent, of the theoretical yield of methane by heating less than 0.1 gramme of highly purified sugar-charcoal to 1150° C. in a current of pure dry hydrogen. These conclusions were subsequently upheld by Pring; and in 1910 Bone and Coward obtained over 95 per cent, of the theoretical yield of methane by heating the sugar-charcoal in specially prepared porcelain tubes through which hydrogen was passed.

In the paper above referred to Mayer and Altmayer studied the equilibrium in the presence of a catalyst between carbon, hydrogen, and methane represented by the equation:

C + 2H₂ ⇔ CH₄

and expressed it as follows:

KT = -18,507 + 5.9934 T logT + 0.002936T² + RT log

where T = abs. temp., P_CH4 and P_H2 are the partial pressures of methane and hydrogen respectively, and K = 21.1. Their conclusion that methane cannot be formed from its elements at 1200° C. is not, however, in accordance with the facts established by Bone, Jerdan, and Coward. The synthesis of hydrocarbons at high temperatures and the methane equilibrium "have been investigated by Pring and Fairlie, who find that under special conditions at 1200° C. and under 10 to 60 c.m. pressure of hydrogen the ratio methane to ethylene produced is as 100:1, but that at 1400° C. it is as 10:1. When hydrogen is heated with carbon under a pressure of 30 to 50 atmospheres, equilibrium is reached in two hours at 1200°-1300° C., and in fifteen minutes above 1400° C. No saturated hydrocarbon but methane is formed between 1100° C. and 2100° C., and with a range of pressure up to 200 atmospheres; and the relative amount of methane produced increases with pressure according to the law of mass action as applied to the equation C + 2H₂ = CH₄. In accordance with these facts methane might be conveniently prepared by synthesis on a large scale by arranging suitable conditions.

1. Methane is generally prepared for laboratory use by heating an acetate with caustic alkali, when the following reaction takes place:
   
   CH₃COOM + MOH = CH₄ + M₂CO₃.
   
   It is usual to employ a mixture of anhydrous sodium acetate and soda-lime; to heat the mixture in a tube of hard glass or iron, or in a copper flask, and to collect the gas over water. Calcium acetate, also, may be heated with lime or baryta. The gas thus prepared may contain as much as 8 per cent, of hydrogen, as well as ethylene.
2. Methane also results from the putrefactive hydrolysis of calcium acetate, thus:
   
   (C₂H₃O₂)₂Ca + 2H₂O = (CO3H)₂Ca + 2CH₄,
   
   and
3. from the decomposition by sunlight of acetone in acetic acid solution:
   
   CH₃COCH₃ + H₂O = CH₃COOH + CH₄.
4. Methane may be prepared by the reduction of chloroform (CHCl₃) and carbon tetrachloride (CCl₄). This may be effected by passing their vapours together with excess of hydrogen through a red-hot tube, by heating the chlorine compound with copper, potassium iodide, and water in a tube, or by reducing it with potassium amalgam in alcoholic solution.
5. Methane is obtained by passing the vapour of carbon disulphide mixed with water-vapour or hydrogen sulphide over red-hot iron or copper:
   
   CS₂ + 2H₂O + 6Cu = CH₄ + 2Cu₂S + 2CuO
   CS₂ + 2H₂S + 8Cu = CH₄ + 4Cu₂S,
   
   and by reducing carbon disulphide at 120° to 140° C. with phosphonium iodide.
6. Carbon monoxide and hydrogen yield methane and water when submitted to the silent electric discharge:
   
   CO + 3H₂ = CH₄ + H₂O.
   
   A similar action takes place at 250° C. under the catalytic influence of reduced nickel, and at 350° C. carbon dioxide is reduced in the same way:
   
   CO₂ + 4H₂ = CH₄ + 2H₂O.
7. Pure methane results from the action of water on zinc methyl, thus
   
   Zn(CH₃)₂ + 2H₂O = Zn(OH)₂ + 2CH₄,
   
   as well as upon magnesium methyl iodide prepared by Grignard: CH₃-Mg-I + H₂O = CH₄ + MgIOH.
8. Methane is also obtained by the action of a metallic couple on methyl iodide in alcoholic solution. Gladstone and Tribe employed a zinc-copper couple, but Bone and Wheeler found that an aluminium- mercury couple is more efficient. The reaction is essentially
   
   CH₃I + 2H = CH₄ + HI;
   
   the methane, however, always contains a little hydrogen, which can be got rid of by passing the gas through a layer of oxidised palladium black at 100° C., or by cooling to the temperature of liquid air, when methane condenses, but not hydrogen.
9. Still another method of obtaining methane is by the action of water on metallic carbides. Aluminium carbide, for example, reacts as follows:
   
   Al₄C₃ + 12H₂O = 4Al(OH)₃ + 3CH₄.

Campbell and Parker have shown that methane prepared by this reaction contains a little hydrogen, which can be removed by mixing the gas with a slight excess of oxygen and passing the mixture over palladium-black. After removal of the remaining oxygen by alkaline pyrogallol solution, no impurity could be detected in the methane.

Other carbides, such as those of glucinum, thorium, and uranium, yield methane mixed with other hydrocarbons.