Methane partial oxidation over phthalocyanine catalyst

The partial oxidation reaction of methane over a zeolite-supported ruthenium phthalocyanine catalyst is studied in a packed bed reactor. The investigation of such reaction is desirable because partial oxidation of methane yields a synthesis gas that can be upgraded to liquid chemicals and fuels. Reactants of this study are He-diluted CH4 and O2. The effluent includes unreacted CH4 and O2, He, CO, CO2, H2, and H2O vapor. Thermal conductivity gas chromatography is applied to identify the mole fractions of reactants and products. System pressure is maintained at 50 psig. Experiments are run at 250, 275, 300, 325, 350, and 375°C. For each temperature, the feed molar ratio of CH4/O2 is varied from 0.5 to 5.0. Although reaction temperature is more than 200°C lower than that of common catalytic methane partial oxidation, conversion of methane is obvious. Product analysis indicates that the highest conversion is 80.4% at 375°C, CH4/O2=0.5. Conversion of methane increases with increasing temperature, but it decreases with increasing molar ratio CH4/O2. Selectivities of both H2 and CO increase with the increasing temperature or molar ratio CH4/O2. But selectivity of CO2 decreases with the increasing temperature or molar ratio CH4/O2. Based on a differential packed bed reactor model, the global rate of CH4 reaction shows first order dependencies on each of O2 and CH4. The overall reaction rate is a second-order reaction. The reaction rate constant k for each temperature was also determined. An Arrhenius plot of the global rate constants suggest that the reaction is limited by reaction kinetics between 250-300°C, and limited by mass transfer between 300-375°C. Equilibrium calculations are also made for all cases in this study. The result shows that products selectivities of equilibrium calculation are significantly different from that of catalytic reactions, which emphasizes the effective catalytic actions of the zeolite-supported ruthenium phthalocyanine