Fluidized-bed OCM reaction: A promising Mn2O3-Na2WO4/TiO2 catalyst and a numerical study
The fluidized-bed reactor with excellent heat and mass transfer features has great appeal for application in the oxidative coupling of methane (FB-OCM), whereas qualified fluid catalysts represent a grand challenge. Herein, we report a high-performance Mn 2 O 3 -Na 2 WO 4 /TiO 2 fluid catalyst (5.4 wt% Mn 2 O 3 and 2 wt% Na 2 WO 4 ), which was obtained by the incipient-wetness impregnation method and examined in the OCM reaction in an electric-heating quartz fluidized-bed reactor (i.d., 2 cm). The standard normalization method on the basis of carbon atom was used for calculating the CH 4 conversion and C 2- C 3 selectivity. This catalyst achieves 35.5 % CH 4 conversion, 66 % C 2 -C 3 selectivity and particularly 15.1 % single-pass yield of C 2 H 4 for a feed of CH 4 /O 2 /H 2 O=3/1/1 with a catalyst dosage of 20 mL at 700 °C and a total GHSV of 7200 h −1 . Such catalyst is stable for at least 50 h without signs of deactivation and agglomeration/defluidization. The catalyst particle size is crucial for the FB-OCM reaction with respect to the reaction light-off and catalyst fluidization. The catalyst with preferable particle size of 450–600 μm can not only trigger the OCM reaction at a relatively low temperature of 630 °C but also warrant active bubbling fluidization. Furthermore, thanks to the low amount of Na 2 WO 4 and interpenetrating structure of TiO 2 -nanorod, such catalyst achieves good anti-aggregation and robust mechanical strength (with a low attrition index of 1.9 %). The effects of water-adding amount in feedstock and catalyst particle size distribution on the hydrodynamics behaviour were investigated in a laboratory-scale fluidized-bed OCM reactor by using numerical simulation method.
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