Mathematical modelling of sequential DRM and catalyst regeneration in a fixed-bed reactor

Abstract

Dry reforming of methane is an attractive route for syngas production because it enables the simultaneous utilisation of methane and carbon dioxide. However, its practical application is limited by high energy demand, catalyst deactivation and, in particular, carbon deposition on the catalyst surface. In this work, a mathematical model of sequential dry reforming of methane and CO₂-assisted catalyst regeneration in a fixed-bed reactor is proposed. The carbon formed during the reforming stage is treated not only as a deactivating deposit, but also as a reactive intermediate that can be converted into carbon monoxide during the subsequent regeneration step. The axial distribution of carbon obtained from the DRM model is used as the initial condition for the transient regeneration model. To avoid dependence of the total carbon mass on the spatial discretisation adopted for regeneration, the carbon distribution from the DRM stage is recalculated into the mass of carbon assigned to reactor intervals Δ_mC, and then transferred to the regeneration grid using a local linear carbon-mass density reconstructed by cubic spline interpolation and integrated numerically over the new grid intervals. The regeneration model describes transient changes in CO₂ and CO concentrations and in the local mass of deposited carbon along the reactor. A thermodynamic constraint based on the reaction quotient and the equilibrium constant of the reverse Boudouard reaction is introduced to limit carbon gasification to conditions favourable for CO formation. The resulting system ofmequations is solved numerically using the method of lines and a stiff ODE solver. The influence of spatial grid discretisation is analysed, and a discretisation level is selected to strike a balance between numerical accuracy and computational cost. Regeneration simulations are performed over a temperature range of 973 to 1270 K. The results show that the proposed model enables the local course of catalyst regeneration to be followed, preserves the carbon mass balance when the regeneration grid is changed, and provides a basis for assessing CO₂-assisted regeneration as part of cyclic DRM–regeneration operation.