THE DIRECT PARTIAL OXIDATION OF METHANE TO LIQUID HYDROCARBONS OVER HZSM-5 ZEOLITE CATALYST

The direct partial oxidation (DPO) of CH4 with O2 in the presence of a C3 additive over HZSM-5 zeolite catalyst at 960 psig produced C5+ liquid hydrocarbons at the expense of the initially formed CH30H. Previous experiments with pure CH4 and Oz feed and with a sand-packed reactor conclusively showed the need for both the C3 additive and the zeolite in the system to produce C5+ liquids. Evidence of CH4 incorporation into the liquid products was given by selectivity calculations which indicated the C3 alone could not account for the CS hydrocarbons. CH4 incorporation has been conclusively confirmed by mass spectral analyses of tetramethylbenzene produced in a run with 13CH4 under identical conditions which show significant 13C enrichment in the C9H11+ and C6H5+ fragments. While CH4 undergoes DPO to CH30H in the system, two possible reaction mechanisms can explain the role of C3; one involves initiation of methanol conversion to gasoline (MTG) by alkenes and the second involves C3 aromatization followed by aromatics alkylation with CH30H. Studies on this system with HZSM-5 catalysts having varying Al contents indicate a sensitivity to zeolite acidity except at high Al concentrations. © 1992.