A theoretical comparison of multifunctional catalyst for sorption-enhanced reforming process

Abstract

This work presents the first side-by-side comparison of the two leading multifunctional catalyst designs reported in the literature today for sorption-enhance reforming processes. Two-dimensional unsteady-state models were developed to compare the performance of a core–shell multifunctional catalyst, consisting of a calcium-based sorbent core enclosed in a porous shell of methane steam reforming or water-gas shift catalyst, against an equivalent case of a uniform-distributed multifunctional design in which catalyst and sorbent materials are uniformly distributed within the particle. Additionally, these two multifunctional catalyst designs were compared against the conventional two-pellet approach, where the capture and catalytic properties are distinguished into separate pellets. Both multifunctional catalyst designs (i.e. core-shell and uniform-distributed) had greater adsorbent utilization and higher H2 outlet concentration up to breakthrough time than the conventional two pellet design. The uniform-distributed multifunctional catalyst design had greater adsorbent utilization up to breakthrough conditions as compared to the core-shell design. This behavior may be attributed to the fact that for the uniform-distributed multifunctional, the active catalyst is constantly producing CO2 next to an adsorbent active site. For the core-shell multifunctional catalyst design, decreasing catalyst-shell thickness resulted in performance approaching the uniform-distributed case. For the case of exothermic water-gas shift reaction coupled with CO2 chemisorption, the core-shell design mitigated local bed hot-spot magnitudes by ~40K.