Steam reforming of raw bio-oil over Ni/La2O3-αAl2O3: Influence of temperature on product yields and catalyst deactivation

Abstract

The hydrogen production by steam reforming (SR) of raw bio-oil (obtained by fast pyrolysis of pine sawdust) has been studied in a continuous two-step process, which consists of a thermal treatment at 500 °C, followed by SR in a fluidized bed reactor with Ni/La2O3-αAl2O3 catalyst. The effect of SR temperature on bio-oil conversion, product yields and catalyst deactivation was evaluated in the 550–700 °C range. The bio-oil conversion and H2 yield were significantly enhanced by increasing temperature. A H2 yield of around 88% and low catalyst deactivation were achieved at temperatures above 650 °C, for a S/C (steam/carbon) ratio of 6 and space-time of 0.10 gcatalysth/gbio-oil. The influence temperature has on product yields and catalyst deactivation was explained by the different nature of the coke deposited. The temperature-programmed oxidation (TPO) curves of coke combustion allow identifying two fractions: i) Coke I, which is the main responsible for deactivation (by encapsulating the Ni sites), whose formation depends on the concentration of bio-oil oxygenates; ii) Coke II, which has filamentous nature and CO and CH4 as main precursors. The effect of temperature on the formation of both types of coke depends on the space–time. Thus, for low values (0.04 gcatalysth/gbio-oil) there is significant formation of both types of coke, with their content increasing with temperature. For higher values (0.38 gcatalysth/gbio-oil), the increase in reaction temperature promotes the removal of coke I, and therefore this is the prevailing fraction at 550 °C and is negligible at 700 °C. This fact is of special relevance for attenuating the Ni/La2O3-αAl2O3 catalyst deactivation.