(640b) Ex-Situ Catalytic Cracking of Biomass Pyrolysis Vapors over Montmorillonite K10-Supported Iron (III) Oxide

Authors: 
Ellison, C., National Energy Technology Lab (ORISE)
Boldor, D., Louisiana State University
Bio-oil produced from biomass pyrolysis exhibit low stability, corrosiveness, high viscosity, and low calorific value. Pyrolysis vapor upgrading can improve the stability and other properties of bio-oils to facilitate storage, transport, and drop in use as fuels and chemical feedstocks in existing petroleum refining infrastructure. Synthetic acid zeolites, in particular HZSM-5, have shown good catalytic cracking results for pyrolysis vapors, however, synthesis cost and catalyst deactivation due to susceptibility to coking limit its application for pyrolysis upgrading. A naturally occurring catalyst material with mesoporous structure could reduce costs and prolong catalyst use by reducing deactivation by coking.

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.