Fundamental insights into heat and mass transport phenomena in single pellet string reactors based on the exothermic CO₂ methanation reaction

Heat and mass transport phenomena in single pellet string reactors (SPSRs) during the exothermic CO₂ methanation reaction using Ni/Al₂O₃ catalysts are investigated. Kinetic measurements, thermal imaging, and particle-resolved computational fluid dynamics (PRCFD) simulations reveal internal and external heat and mass transfer limitations in the SPSR. Local temperature and concentration profiles indicate significant mass diffusion constraints within the pellets, notably impacting the SPSR performance, particularly at higher gas hourly space velocities, GHSV. Heat removal through the reactor wall, rather than by convective heat transport by the gas, has been identified as the most critical factor for activity measurements in an SPSR. Heat transfer limitations have been observed both within and outside the porous pellets, which directly impact the CO formation. A comprehensive toolbox combining experiments and PRCFD approaches is presented to identify and assess heat and mass transport limitations, which are essential for reliable kinetic measurements.