On the influence of hydrogen on the pyrolysis of ethane and ethylene near 600°.—Part I

It is well known that when ethane is heated to the neighbourhood of 600° in silica apparatus, the equilibrium represented by the equation C2 H6 ⇌ C2 H4 + H2 , is approached very rapidly. We have confirmed this result, and have obtained accurate values for the equilibrium constant at 590° and 610°. As we shall show presently, this reaction is accompanied by other reactions which involve the condensation of both ethane and ethylene independently, with formation of methane and of a product which is mainly benzene, though we are not actually interested in the final product. It appears that though hydrogen takes part in only the ethane-ethylene-hydrogen reaction, it has indirectly a profound influence on the rates at which the other reactions take place. Further, it seems that the silica surface does not act as a catalyst, though, again, the fact that the reaction vessels are of silica, and the pretreatment to which they are subjected, has great influence in determining the course of the reactions. This investigation has been carried out with the object of studying the kinetics of these reactions. II.Method of Investigation . Now, mainly on account of the complex character of the reactions, and also on account of the fact that hydrocarbons are formed which readily condense, it was not possible to adopt the method of measuring the changes of pressure of the gas at constant volume, which is commonly employed for following the course of gaseous reactions. Our method involved the heating of definite quantities of the pure gases in sealed silica tubes to a definite temperature, for varying periods, and making a complete analysis of the contents of each tube.