Methane inflammation limit

Fig. 12.—Effect of initial pressure on inflammability limits of methane-air mixtures. Data of Bolte and Newitt. [Compare Berl and Werner, Z. anyno. Chem. 40, 24S-S0 (1927).]...

The theoretical air required for the oxidation of toluene to benzoic add, 1.5 mols of oxygen per mol of tolnene, amounts to about 30 cn. ft. of air measured at 20° C. (6S° F.) and one atmosphere, per pound of toluene oxidized. Similarly, the theoretical air for oxidation to bcnzalcle-hyde amounts to 20 cu. ft. per pound of tolnene oxidized. The explosive limits of toluene at ordinary pressures and temperatures as measured in narrow tubes or small vessels are lower limit, 0.003375 lbs. toluene per cu. ft. air (296.5 cu. ft. air per lb. toluene) and upper limit, 0.01927 lbs. toluene per cu. ft. air (52 cu. ft. air per lb. toluene).1151 In the case of the lower aliphatic hydrocarbons as methane and ethane it is well known that the explosive or inflammability limits widen with rise in temperature so that it could well be expected that mixtures of toluene and air leaner than the one given for the lower limit and richer than the one for the upper limit would become inflammable as the temperature becomes higher. The same is true for increase in size of the explosion chamber. Hence, although theoretical mixtures of toluene and air for formation of benzaldehyde and benzoic acid lie on the rich side of the inflammable range,... 

It is only in a few cases that the limits of inflammability of a vapour mixture can be calculated, thanks to the limits of inflammability of the components in the pure state of a mixture. In fact, Le Chatelier s law only applies to mixtures of saturated aliphatic hydrocarbons and to two or three other mixtures of inorganic substances (CO, H2) alone or with methane. 

Class III safety explosives must be safe in a 9% methane-air mixture when fired with the maximum number of cartridges that can be placed in a row in the 2 m long groove of the angle-shot mortar. The experiment starts with 1800 g charge. It is increased by 200 g increments. The charge limit is determined this should not give any inflammation in five consecutive shots. 

Amongst the earliest experiments carried out with a view to the quantitative determination of the limits of inflammability of combustible gases were those of Davy with fire damp, wfliich is mainly methane, CH4. Owing to the importance of this gas m connection with gob fires and explosions in coal mines, several other workers have also investigated it. The value of the results, however, is restricted by the fact that firedamp, like most natural products, is subject to very considerable variation in composition.3 Even Davy recognised that it was not pure methane indeed, perfectly pure methane is not easy to prepare in quantity. The gas, as obtained from sodium acetate, may contain as much as 8 per cent, of hydrogen, as well as ethylene.4 No doubt this variation m composition is one contributory cause of the very varied results listed in the table on p. 93. 

Lower Limit or Inflammation of Methane in Air. (Burgess and Wheeler, 1911.)... 

The value obtained for the lower limit of inflammation of methane when mixed with air is 5-6. The calorific value of methane is 189T. Substituting m the above equation a value of 1059 is obtained for k, and the relative values for L for other gases can then be calculated. 

Influence of Pressure.—Both the lower and the upper limits of inflammation are raised by increase of pressure. Hence the total effect upon the limits of inflammability is the algebraic sum of these two. In the case of methane the data 3 are as follow ... 

The effect of pressure upon the limits of inflammability of saturated gaseous hydrocarbons is similar to that shown by Figure 12 for methane. 

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