(640b) Ex-Situ Catalytic Cracking of Biomass Pyrolysis Vapors over Montmorillonite K10-Supported Iron (III) Oxide
In this study, catalytic cracking of biomass pyrolysis vapor over montmorillonite K10 (MMT) supported iron catalyst was investigated in a fixed bed lab scale reactor. Iron loadings of 0%, 5%, and 10% Fe (weight basis) were prepared by wet impregnation and calcined catalysts were characterized by several methods. Fast pyrolysis was carried out in an inductively heated reactor at 600 °C under 1.25 L min-1 nitrogen flow, and the vapors were passed over a heated catalyst bed (360 °C, 1.5 catalyst-to-biomass ratio) prior to condensation by a cold trap and electrostatic precipitator. Non-catalytic pyrolysis was also carried out for comparison.
Char yield remained constant for all runs (18.1+/-0.9) as pyrolysis conditions were kept the same. Compared to non-catalytic pyrolysis, catalytic upgrading resulted in lesser liquid yield and greater non-condensable gas yield, due to catalytic cracking. Liquid yields from upgrading were found to be 17.8, 14.0, and 17.5% for pyrolysis over 0, 5, and 10% Fe/MMT, respectively, compared to 53.6% liquid yield for non-catalytic pyrolysis. Water yield in the bio-oil increased with increasing Fe content, indicating promotion of dehydration reactions over catalysts with greater Fe. Non-condensable gas yields were 54.3, 57.0, and 51.3% for 0, 5, and 10% Fe/MMT, respectively, while non-catalytic pyrolysis gas yields were 27.5%.
As a result of upgrading, yields of polyaromatics in the bio-oil were found to decrease indicating occurrence of cracking reactions over the catalysts studied. Upgraded bio-oil is composed of mainly phenols, aromatic and aliphatic ketones, and furans/pyrans. Non-upgraded bio-oil contains phenols as well, but also contains less stable molecules such as carboxylic acids and aldehydes. On average, the non-condensable gas produced from catalytic pyrolysis is composed of 15.2% CH4, 51.9% CO, 18.5% CO2, 4.7% H2, and 5.7% C2-C6. According to the carbon balance, we saw 50% carbon conversion to the gas fraction as a result of upgrading compared to 30% conversion for non-catalytic pyrolysis. Energy balance revealed greater gas higher heating values of 160 MJ/kg (dry biomass basis) compared to that of non-catalytic pyrolysis gas (90 MJ/kg, dry biomass basis). Carbon conversion to coke decreased from 1.4% on pure montmorillonite K10 catalyst to 0.4% for 10% Fe catalyst.