Catalytic Oligomerization of Methane via Microwave Heating

Catalytic microwave heating has been used as a method for the oligomerization of methane to higher hydrocarbons. Many catalysts were tested in this reaction. Nickel powder, iron powder, and activated carbon were the most active and efficient catalysts for the production of higher hydrocarbons. When helium was used as a diluent gas and the applied power was optimized, the selectivities were controlled to the most desired products. Iron powder was active only at high power (1130 W). At these conditions acetylene was avoided and ethylene and ethane were produced in the same proportion. At low power (378 W) with nickel powder as catalyst and no diluent, ethane was the major C 2 hydrocarbon. The amount of acetylene increased when arcing was observed. The proportion of C 2 products changed from ethane > ethylene > acetylene to ethylene > acetylene > ethane when the power was increased from 378 to 1130 W. The major product was CO when high power (1130 W) was used. Selectivities toward C 3s and C 4s were enhanced to 16 and 18%, respectively, and the major products were propane and methylpropane when He was used as a diluent gas. Activated carbon catalysts and helium diluent led to a product distribution of C 2s of ethylene > acetylene > ethane at low applied power (378 W). At medium power (754 W) as time increases, the selectivities to C 2s decrease and the selectivity to benzene increases to 33%. Some manganese oxides such as OMS-1, OMS-2, and MnO 2 (dielectric constant, ε ≈ 10 4 ) were not active in these reactions. These data suggest that the dielectric constant is not the most important factor in the oligomerization of methane via microwave heating. Conversion and activities of these materials are not proportionally related to the surface area of the catalysts.