Autothermal Partial Oxidation Of Methane To Synthesis Gas Catalyzed By Ni Metallic Monolith Catalysts

Synthesis gas is mainly produced by steam reforming of methane, which has several shortages, such as high energy intensity, easy carbon deposition, and higher H2/CO ratios which are not suitable for several important processes. Because of its low investment and low energy consumption with instant reaction rate, partial oxidation of methane has attracted much attention. In the present work, Ni metallic monolith catalysts were prepared with Ni foam and further treated by acid. In order to study the mechanism of the catalytic partial oxidation of methane on Ni metallic monolith catalyst, catalyst length and gas flow rate were varied, and global conversion and selectivity data were correlated with the catalyst temperature profiles. Morever, considering that the Ni metallic monolith is much stable, but has lower activity than supported catalysts, Ni monolith-Ni/MgAl₂O₄ dual bed was studied for the autothermal partial oxidation of methane as well.The results showed that the reaction of methane autothermal partial oxidation on the Ni metallic monolith catalyst proceeded in two stages: initial direct partial oxidation, followed by steam reforming of the methane unconverted. From the inlet to 0.7mm of the catalyst bed was the oxidation zone, in which O2 was completely converted. Further onwards along the catalyst bed, CH4 conversion, H2 and CO selectivities and the temperature of the catalyst bed all increased sharply,and the temperature reached the maximum at the position of 1.5mm. After O2 total conversion, methane conversion continued due to the reforming of the remaining methane with H2O in the second zone, but the conversion rate slowed down significantly; the H2 and CO formation rates also decreased, with the decrease of CO to larger extent than H2; the catalyst temperature also steeply decreased after the maximum as well. The slight increase of CO2 molar flow rate in the steam-reforming zone showed that some water gas shift occurred in the catalyst bed, and no CO2 reforming was observed. The experiments results indicated that the syngas was formed mostly by direct partial oxidation in the oxidation zone, and the contribution of steam reforming to syngas was minor.Result on the catalytic performance of Ni monolith-Ni/MgAl₂O₄ dual bed showed that the activity and selectivities of dual bed were higher than Ni metallic monolith catalyst alone, but close to Ni/MgAl₂O₄. The results showed that the dual bed catalyst can achieve high methane conversion and high selectivities to syngas at the minimum length of Ni/MgAl₂O₄ of 9mm, when the feed flow rate was 1.67 L/min at room temperature, 45% dilution, catalyst diameter was 16mm, and the length of the Ni metallic monolith catalyst was 3mm. When the feed gas was preheated to higher temperatures, the activity and selectivities of dual bed catalysts increased to some extent.