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The production of acetylene from methane by partial oxidation Watt, Leonard John

Abstract

Acetylene may be produced from methane in any process which raises the methane to a high temperature for a very short period followed by rapid cooling. There are three processes which accomplish these critical conditions of temperature and reaction time: A. By electric discharge through the gas B. By supplying heat from an auxilliary fuel either in direct heat exchange or in a regenerative type furnace C. By simultaneously burning some of the feed gas by the admixture of some oxygen The last of these processes was studied in this project in a flow type reactor. The process was studied at temperatures of 1000°C to 1300°C and reaction times of .01 to .03 seconds. An attempt was made to derive the mechanism for this process. A quartz reactor of special design was used in this study. It consisted of three zones: namely, the preheat zone where the oxygen, and methane were separately preheated, the reaction zone where the oxygen and methane were mixed and burned, and finally the quench zone where the reaction products were rapidly cooled and the reaction halted. The products were then analyzed for acetylene, carbon dioxide, carbon monoxide, hydrogen and methane. The mechanism for the partial oxidation of methane is believed to follow the following reactions. First there are the initial rapid oxidation reactions which supply the necessary heat to crack methane: CH₄ + ½O₂ → CO + 2H₂ ; CH₄ + 2O₂ → CO₂+ 2H₂O ; CH4 + O₂ → C + 2H₂O After the oxygen has been used up, methane decomposes into ethane, ethylene, acetylene, carbon and hydrogen by the following reactions: CH₄ ⇌ CH₂ + H₂ ; CH₄ + CH₂ ⇌ C₂H₆ ; C₂H₆ ⇌ C₂H₄ + H₂ ; C₂H₄ ⇌ C₂H₂ + H₂ ; C₂H₂ ⇌ 2C + H₂ The rate of formation of acetylene was found to depend upon the square of the methane concentration while the rate of decomposition of acetylene depended upon the concentration of the acetylene. As the reaction progresses the concentration of acetylene rises to a maximum and then decreases to zero. This was explained to occur because the methane concentration decreased with time. Further reaction follows between the products of combustion and the products of decomposition of methane. The most important of these is the water gas reaction: C + H2Q ⇌ CO + H₂ It was proven by stoichiometric considerations that this reaction takes place, and is the most important of the side reactions. The following reactions also take place to a small extent: C + CO₂ ⇌ 2CO ; CO + H₂O ⇌ C0₂ + H₂

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