Kinetic and structural requirements for a CO2 adsorbent in sorption enhanced catalytic reforming of methane – Part I: Reaction kinetics and sorbent capacity

This paper presents a fundamental model-based analysis for the applicability of integration of a highly active Rh/CeαZr1−αO2 catalyst with two candidate CO2 sorbents for pure H2 production in low temperature sorption-enhanced steam reforming of methane. K-promoted hydrotalcite and lithium zirconate solids are considered in the investigation as CO2 sorbents. The process is analyzed using multi-scale modeling levels of a heterogeneous particle-based model, a heterogeneous bulk-scale model, and a homogenous bulk-scale model. The presence of this active catalyst dictates strict requirements on the sorbent in terms of fast adsorption kinetics for an efficient process performance. The maximum CH4 conversion enhancement is determined to be a strong function of sorption kinetics. This enhancement is not affected by a higher sorbent capacity at slow adsorption kinetics. The process is studied using two fixed bed configurations of an integrated dual function particle and an admixture bed of catalyst/sorbent particles. Optimal operating conditions for the hydrotalcite-based system are identified to provide CH4 conversion of 98% with high H2 purity of 99.8% and low CO2 contamination (<250 ppm). The lithium zirconate-based system can provide CH4 conversion and H2 purity of 99.9% at identical conditions. Based on the end application of H2 produced, the process can be tuned to feed gas turbine cycles, fuel cells, or petrochemical plants.