Catalytic fast pyrolysis: Influencing bio-oil quality with the catalyst-to-biomass ratio

In situ catalytic fast pyrolysis can be used to produce partially upgraded bio-oils. This process, however, suffers from rapid catalyst deactivation caused by coke formation, which necessitates the use of continuous catalyst regeneration. This can be achieved by using a circulating fluidized-bed reactor. In such a reactor, one key operational variable is the catalyst-to-biomass (C/B) ratio, which influences the extent of the catalytic reactions that take place. In this study, woody biomass is pyrolyzed in a pilot-scale circulating fluidized-bed reactor system using a HZSM-5 zeolite with varying C/B ratios. The C/B ratio influences the overall product distribution, the elemental distribution, and the characteristics of the liquid products. An increase of the C/B ratio enhances the conversion of pyrolysis vapors but this does not result in a continuous improvement in bio-oil quality. The C/B ratio is, nevertheless, a factor that can be used to optimize the catalytic fast pyrolysis process.