Comparison of the NiAl2O4 derived catalyst deactivation in the steam reforming and sorption enhanced steam reforming of raw bio-oil in packed and fluidized-bed reactors

Abstract

The choice of appropriate reactors and reforming strategies is key to make progresses on scaling up H2 production processes from raw bio-oil. This work compares the performance (conversion, product yields and deactivation) of packed-bed and fluidized-bed reactors (PBR and FBR, respectively) using a NiAl2O4 spinel derived catalyst for the H2 production from raw bio-oil via steam reforming (SR) and sorption enhanced SR (SESR, with dolomite to capture CO2). The experiments were carried out at 600 °C; steam/carbon ratio, 3.4; space time, 0.15 h; time on stream, 5 h; dolomite/catalyst ratio, 10 (SESR runs); and with prior thermal separation of the pyrolytic lignin from the raw bio-oil. The initial H2 yields are 80 % and 69 % in the SR runs with PBR and FBR, respectively, and 99 % and 92 % in the CO2 capture period (of 30 min duration) of the SESR runs in the PBR and FBR, respectively. The lower H2 yield in the FBR is due to the less efficient gas–solid contact (bubbling or slugging phenomena). Based on the analysis of the spent catalysts with varied techniques the catalyst deactivation is related to the coke deposition, whose quantity and nature (amorphous or structured) depends on the reactor type and reforming strategy. The catalyst deactivation is slower in the FBR due to the rejuvenation of the catalyst surface by the moving particles that favor external coke gasification. The presence of dolomite prolongs the period of stable catalyst activity in both reactors with different effects on the coke quantity and nature. The results are of interest to advance on scaling up the SESR process that would require a FBR integrated with a regeneration unit for the catalyst and sorbent.