Chemical effects of a high frequency electric discharge in acetylene and ethylene

The reactions of methane, ethane, ethylene and acetylene when subjected to various activating influences have been studied in many researches. The activating agencies used have been alpha-rays, activated hydrogen, activated mercury, light, heat and electric discharges. Of these, only thermal means and electric discharges offer possibilities for an industrial utilization since they afford the means for the large energy input that would be required for the production of large quantities of material. The reactions of the hydrocarbons have been studied in the ozonizer, the arc and the silent electric discharge but, as yet, very little study has been made with a high frequency discharge. In the hope that new and fundamental information would be revealed, it was decided to undertake a study of the reactions of these substances in high frequency discharges. The frequencies that were to be used were such that the distance that an ion would travel before having its direction reversed by the alternating field was of the same order of magnitude as the mean free path of the molecules. The frequencies chosen were in the range of 6 x 10⁶ to 1.5 x 10⁷ cycles per second which correspond to wave lengths of 50 to 20 meters. Electrical discharges in hydrocarbons produce acetylenic, ethylenic and saturated hydrocarbons, solid and liquid condensation products, carbon and hydrogen. Even for the simple compound methane, the reactions are exceedingly complex. The electric discharge can be operated under a wide range of conditions of current, pressure, rate of flow and wave length, each of which affects, in some manner, the character and the extent of the reactions. The great complexity of the reaction products demands an analytical procedure which, if it must be exact, presents a very complex problem. Consider, for example, any experiment performed with ethylene in which there are formed acetylene, unsaturated hydrocarbons containing from three to six carbon atoms, various saturated hydrocarbons and a solid condensation product. Since these reactions can only be carried out at low pressures, the individual experiments would require much time of operation in order to obtain a sufficiently large sample for a complete analysis. Such a procedure would be very expensive from the standpoint of materials, power and time. The micro analysis of gases has been developed in this laboratory sufficiently to handle partial analyses of hydrocarbons. The physical measurements on the discharge are equally simple on macro and micro scales. A study of the reactions could be carried out most expediently upon an amount of material which was just sufficiently large enough for accurate analysis. The procedure finally adopted enabled individual experiments to be carried out in three to five minutes on 10-15 c.c. of the gaseous material. As will be revealed in the following pages, the analytical procedure grouped the reaction products into several logical groups and then studied the reactions in terms of these groups. The fact that many of the compounds that are actually found to be present represent mere chance, or side reactions, rather than main reactions makes such a grouping sufficiently adequate for the interpretation of the data obtained. Two years ago, Mr. Frank and the writer began an investigation of the reactions of methane in the high frequency discharge. Somewhat later this study was extended to acetylene and ethylene since they were formed from methane and these studies were needed in an interpretation of the results obtained from methane