Kinetics of the photochemical reactions of gas mixtures of methane and water and the effects of added oxygen

Abstract

A kinetic study of the photolysis of methane and water mixtures has been performed. Major products are ethane, methanol, hydrogen and hydrogen peroxide. Ethane is produced in the highest yield (71%) followed by methane (17%). Hydrogen abstraction from methane by hydroxyl radicals is the rate-determining step in ethane and methanol formation. The activation energy for methanol and ethane formation is estimated to be 4.9 kcal mol −1. The quantum yield φ of the photolysis of water is given by φ = φ(CH 3OH) + 1 2 φ(C 2H 6) + φ(H 2) + φ(H 2O 2) and is calculated to be 0.62 at 100 °C. The addition of oxygen enhances the formation of CH 3OH, CH 2O, HCOOH and CO 2, but decreases the formation of C 2H 6 and H 2. The quantum yield in the presence of oxygen is a function of the concentration of oxygen. The value extrapolated to O 2 = 0 is in good agreement with that obtained in the absence of oxygen.