Method of controlling pyrolysis temperature

A method of controlling temperature during pyrolysis of methane wherein the predominant reactions are endothermic and the reaction is rapidly quenched to obtain at least one intermediate reaction product selected from the group consisting of acetylene and ethylene comprising the sequential steps of:

• (a) introducing hydrogen and substantially pure oxygen into a combustion zone, said hydrogen being present in an amount in excess of that required to react with all of the oxygen, and combusting them to produce a hot gas stream comprising steam and a minor amount of unreacted hydrogen, having a temperature of from 2000.degree.-3500.degree. C. and a pressure of at least three atmospheres;
• (b) passing the hot gas stream through a converging-diverging nozzle, said nozzle having an expansion ratio sufficient to accelerate the hot gas stream to a velocity of at least mach 2.0 along with a corresponding reduction in pressure and temperature, the reduced temperature being in the range of 1500.degree.-2000.degree. C. and the reduced pressure being subatmospheric;
• (c) injecting the methane to be pyrolyzed into the hot gas stream to produce a reaction mixture flowing at supersonic velocity and initiate the endothermic pyrolysis reactions;
• (d) reducing the velocity of the reaction mixture over a predetermined reaction time to convert the kinetic energy of the reaction mixture to thermal energy in an amount sufficient to substantially offset the effects of the endothermic reactions taking place to convert at least about 60% of the methane to the selected intermediate products and produce enhanced yields of the selected intermediate reaction produce while maintaining supersonic flow;
• (e) reducing the velocity of the reaction mixture to subsonic flow and concurrently quenching the reaction;
• and
• recovering the selected intermediate reaction products.