Biomass to hydrogen-rich gas via steam reforming of raw bio-oil over Ni/La2O3-alpha Al2O3 catalyst: Effect of space-time and steam-to-carbon ratio

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 degrees C) used for retaining the pyrolytic lignin. The remaining volatile stream was reformed in the second unit (fluidized bed reactor) over a Ni/La2O3-alpha Al2O3 catalyst at 700 degrees 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-alpha Al2O3 catalyst. It was found that a raise in both the space-time and the S/C ratio contribute to increasing the H-2 yield and to decreasing that of CO, CH4 and C-2-C-4 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 degrees C, 0.38 gcatalysth/gbio-oil and S/C = 6, a hydrogen-rich gaseous stream (66 vol% H-2) is obtained, with the H-2 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.