Comparison of Fixed and Fluidized Bed Reactors in the Steam Reforming of Raw Bio-oil with Nial2o4 Derived Catalyst

Abstract

This work compares the performance of fixed and fluidized bed reactors in the SR of raw bio-oil with a NiAl2O4 spinel derived catalyst, which has high activity and selectivity of H2 in the raw bio-oil reforming. The SR runs have been carried out at 600 ºC, steam/carbon molar ratio (S/C) of 3 and space time of 0.15 gcatalysth/gbio-oil. The results of the fluidized bed reactor evidences lower initial bio-oil conversion and H2 and CO2 yields, due to the less effective gas-solid contact, however its stability is higher. The characterization of deactivated catalysts by Temperature Programed Reduction (TPR), X-Ray Diffraction (XRD), N2 adsorption-desorption and Temperature Programed Oxidation (TPO) evidences that the main deactivation cause is coke deposition, that is noticeably higher in the fixed bed reactor (73 wt%) than in the fluidized bed (17 wt%). The TPO profiles for catalysts used in both reactors show two combustion domains, at low and high temperature. The reactor type does not affect the amount of coke that burns below 500 ºC (coke I, amorphous), but notably affects both the amount and morphology of the coke burning at higher temperature (coke II, more graphitic). The use of fixed bed reactor leads to a noticeable higher formation of coke II, which contains heterogeneous carbon filaments and also carbon spheres, the latter not being formed in the fluidized bed. These differences in the amount and nature of the coke deposited explain the differences in stability of the catalyst in both reactors.