Schematic diagram of the fluidized-bed system for fast pyrolysis of biomass. Credit: ACS, Zhang et al. 2009. Click to enlarge.

The conversion of biomass into bio-oil using fast pyrolysis technology is a promising alternative to convert biomass into liquid products—either for direct use or for easier transport and upgrading into higher value products. However, substituting bio-oil for conventional petroleum fuels directly may be problematic because of the high viscosity, high oxygen content, and strong thermal instability of bio-oil.

The focus of the Southeast University research is decreasing the oxygen and polymerization precursor content of bio-oil to improve its thermal stability and heating value. The team conducted catalytic fast pyrolysis of corncob with different percentages (5, 10, 20, and 30% by volume) of fresh fluidized catalytic cracking (FCC) catalyst (FC) and spent FCC catalyst (SC) in bed materials in a fluidized bed.

The team found that a greater catalyst percentage lead to a lower bio-oil yield, while a lower catalyst percentage lead to little change of the composition of the bio-oil. The hydrocarbons increased with the increase of the catalyst percentages, and this contributed to the decrease of the oxygen content of the bio-oil. Multi-stage condensation achieved a good separation of the oil fraction and water.

The best percentages of FC and SC were 10 and 20%, respectively. FC showed more catalytic activation in converting oxygen into CO, CO2, and H₂O than SC, but the oil fraction yield with FC was remarkably lower than that with SC because of more coke formation.

The application of the multi-stage condensation achieved a good separation of the oil fraction and water in the liquid products. The water content of the liquids collected by the first, second, and third condensers were 5.1, 10.5, and 60.3% in the noncatalytic test while about 5-6, 10-12, and 79-82% in the presence of 10% FC or 20% SC. Most of the oil fraction obtained in the catalytic experiment was the light oil fraction collected by the second condenser.

The analysis of the collected liquid in the second condenser showed that the use of the FCC catalyst reduced the contents of multifunctional components of phenols, which are believed as the most likely bio-oil polymerization precursors. Therefore, the stability of the bio-oil should be improved. Moreover, the addition of the FCC catalyst led to a remarkable increase of the hydrocarbon content and contributed to the decrease of the oxygen content of the collected liquid.

—Zhang et al. 2009

Resources

• Huiyan Zhang, Rui Xiao, Denghui Wang, Zhaoping Zhong, Min Song, Qiwen Pan and Guangying He (2009) Catalytic Fast Pyrolysis of Biomass in a Fluidized Bed with Fresh and Spent Fluidized Catalytic Cracking (FCC) Catalysts. Energy Fuels, Article ASAP doi: 10.1021/ef900720m