Bed packing configuration and hot-spot utilization for low-temperature CO2 methanation on monolithic reactor

Abstract

The revival of CO2 methanation (Sabatier reaction) as part of the large-scale Power-to-Gas technology has stimulated the development of novel reactor concepts for better heat management due to its exothermic nature. The generation of hot-spots in fixed bed reactors could reduce methane yield, accelerate catalyst deactivation, and potentially cause thermal runaway. However, hot-spots could be utilized to achieve outstanding CO2 methanation performance at low temperatures and high gas flow rate in monolithic reactors, whereas strategic bed packing configurations could boost the performance of low-activity catalytic beds. We prepared NiFe catalysts derived from in-situ grown layered double hydroxides via urea hydrolysis on washcoated cordierite honeycomb substrate with varying activities. Temperature profiles by both experimental and computational fluid dynamic (CFD) studies revealed hot-spot formation along catalytic beds. Hot-spots increased the catalytic beds’ temperature due to high thermal conductivity of cordierite monolith, thus accelerated the reaction. The monolithic reactor with a single-monolith bed exhibited a methane yield of 16.5% at 250 °C, which was significantly increased to 80.4% on the reactor with three-monolith bed of the same catalyst at similar reaction condition with a constant ratio of catalyst mass to gas flow rate. A combined low-high activity monolithic bed was proposed which demonstrated high methane yield and excellent stability. Interestingly, the methane yields were higher at a gas flow rate of 1500 mL/min than that at 500 mL/min, again ascribed to the beneficial effect of hot-spot formation on monolithic reactors. Therefore, strategic bed packing configuration plays an important role in the optimization of monolithic methanation reactors, and hot-spot formation could be exploited to achieve excellent CO2 methanation performance at low temperatures.