Biomass to hydrogen-rich gas via steam reforming of raw bio-oil over Ni/La2O3-αAl2O3 catalyst: Effect of space-time and steam-to-carbon ratio

Abstract

Hydrogen-rich gas production by steam reforming (SR) of the raw bio-oil was studied in a continuous two-step system, with the first unit of thermal treatment (at 500 °C) used for retaining the pyrolytic lignin. The remaining volatile stream was reformed in the second unit (fluidized bed reactor) over a Ni/La2O3-αAl2O3 catalyst at 700 °C. The effect of space-time (0.04–0.38 gcatalysth/gbio-oil) and steam-to-carbon ratio (S/C) (1.5–6) on bio-oil conversion and product yields was assessed. Temperature programmed oxidation (TPO) was used to analyze the coke deposited on the Ni/La2O3-αAl2O3 catalyst. It was found that a raise in both the space-time and the S/C ratio contribute to increasing the H2 yield and to decreasing that of CO, CH4 and C2-C4 hydrocarbons. Catalyst deactivation is highly attenuated by raising space-time because of the lower deposition of encapsulating coke, which is directly related to the concentration of bio-oil oxygenates in the reaction medium. Space-time does not affect the formation of filamentous coke (less responsible for deactivation). The S/C ratio has less influence on total coke content than space time. For 700 °C, 0.38 gcatalysth/gbio-oil and S/C = 6, a hydrogen-rich gaseous stream (66 vol% H2) is obtained, with the H2 yield being 93% based on the bio-oil entering the catalytic reactor (or 87% based on the raw bio-oil fed into the two-step system), which decreases to 70% after 7 h time on stream as a consequence of the low catalyst deactivation.