Methane Chemistry in the Hot Supersonic Nozzle

Combination of pyrolysis and expansion to a supersonic molecular beam is shown to be very effective in conversion of pure methane to heavier hydrocarbons. The conversion reaches ∼70% in the supersonic nozzle made of quartz with the diameter of orifice equal 100 μ. The major products are acetylene, benzene and its homologues. Free radicals are also detected in the product distribution. The mechanism consists of the surface generation of the radicals, C−C bond formation, desorption to the gas phase, and expansion to the supersonic beam. It is suggested that relatively short gas−surface contact time (about 50 ms at Tnozzle = 1000 °C) enables simultaneous kinetic and thermodynamic control.