PYROLYSIS OF METHANE INTO HIGHER HYDROCARBONS ON CARBON-FIBER IN A THIN FLAT TUBE OF QUARTZ HEATED BY AN INFRARED IMAGE FURNACE

Pyrolysis of methane over pitch-based carbon fiber (CF) was studied, using a thin flat quartz tube reactor heated in an infrared (IR) image furnace. The pyrolysis produced ethane as the dominant product when the conversion was below 1%. Increasing conversion by additional CF or lower flow rate increased the selectivity for ethylene first, and then acetylene and pyrolytic carbon. C3 and C4+, principally C4, hydrocarbons were always minor products, indicating the consecutive nature of the reaction. The maximum yields of C2 and C2-C4+ hydrocarbons were 7.5 and 9.2%, respectively, at a conversion of 10%. The conversion stayed constant with increasing concentration of methane, indicating a first order reaction in methane; however selectivity varied with the concentration, suggesting that bimolecular reactions govern the product selectivity. It should be noted that there was no production of tar or carbon on the reactor wall in the present pyrolysis. The CF surface may initiate the C-H fission of methane and assist the termination of chain reactions to produce C2-C4 hydrocarbons at rather high selectivity.