Simulation of Feed Modulation on Dynamic Fixed-Bed Reactor for CO Methanation over Ni-based Catalyst

Abstract

The hydrogénation of CO to produce synthetic natural gas (SNG) is highly exothermic and usually catalyzed by nickel as an active site. These reactions are typically conducted under elevated pressures and low temperatures to shift the reversible reactions to the products. However, conducting reaction under such low temperature is kinetically limited. An alternative method that can be applied to ameliorate this limitation is by conducting a dynamic operation. This study focused on model development and reactor approach for dynamic fixed-bed operation intended for CO methanation. One dimensional pseudo-homogeneous reactor model was developed for a typical laboratory scale by neglecting internal and external diffusion based on Weisz-Prater, Anderson, and Mears criteria. The gas phase model was governed for compounds in the bulk phase. The model consisted of the dynamic term, convective term, diffusive term, and source term. The design criteria involving pressure drop, ratio of the height of catalyst bed to particle diameter (LB/dp), ratio of reactor diameter to particle diameter (dr/dp), ratio of bed length to reactor diameter (LB/dr) and axial dispersion were taken into consideration. A kinetic model to complement the simulation was taken from literature. The reactor model was simulated for steady-state and unsteady-state operation with optimum feed composition. The result of steady-state model simulation was considered as a base case and comparison to judge the reactor performance under unsteady-state operation. Modulating the value of the inlet CO fraction in step function was introduced to the unsteady-state model in order to enhance methane production. The simulation results showed that the highest methane production could be achieved by modulating CO inlet fraction between 0.45 and 0.4 with the overall switching time of 25 s.