Effect of flow rate on the partial oxidation of methane and ethane

The partial oxidation of CH4 over rhodium coated monoliths and C2H6 over platinum coated monoliths was examined in the fuel rich regime at: space velocities up to 4 x 10(6) h(-1) (similar to 200 mu s), a variation by a factor of 50. For CH4, the conversion drops from 90% at 5 x 10(4) h(-1) to 20% at 1 x 10(6) h(-1), while for C2H6, the conversion and the selectivity to C2H4 remain nearly constant up to 4 x 10(6) h(-1). For CH4, the O-2 conversion drops below 100% at 5 x 10(5) h(-1) but remains complete in the oxidation of C2H6. AS the space velocity increases in CH4 oxidation, the temperature of the leading edge of the monolith decreases from 900 degrees C at 1 x 10(5) h(-1) to 60 degrees C at 1 x 10(6) h(-1). The cool region of the monolith promotes the formation of total oxidation and also the production of CH3 radicals which lead to the formation of C-2 coupling products in the gas phase. A maximum in coupling selectivity of 10% is observed at 5.5 x 10(5) h(-1) and 270 degrees C preheat. (C) 1996 Academic Press, Inc.