Fast pyrolysis with fractional condensation of lignin-rich digested stillage from second-generation bioethanol production

Poplar-derived lignin-rich feedstock (i.e. stillage) obtained from bioethanol production was subjected to fast pyrolysis in a modified fluidised bed reactor at 430 °C, 480 °C, and 530 °C. The stillage was pretreated by enzymatic digestion prior to fast pyrolysis. Pyrolysis vapors were collected by fractional condensation to separate the heavy organic and aqueous phase liquids. The intention of this study was to assess the potential utilization of lignin-rich digested stillage as a fast pyrolysis feedstock. Heavy organic and aqueous phase pyrolysis liquids were obtained in yields ranging from 15.1–18.1 wt.% and 9.7–13.4 wt.% respectively. The rest of the feedstock material was converted to char (37.1–44.7 wt.%) and non-condensable gases (27.1–31.5 wt.%). Detailed liquid analysis indicated that the heavy organic phase fractions contain compounds arising from the degradation of lignin, residual microbial biomass and remaining polysaccharides. Fast pyrolysis adds 26.8 wt.% to the conversion of this otherwise recalcitrant feedstock material, thereby reducing waste generation and enhancing the value of second-generation bioethanol production.