Directional valorization of eucalyptus waste into value-added chemicals by a novel two-staged controllable pyrolysis process

Abstract

Fast pyrolysis is a promising way to convert biomass waste into value-added chemicals, but current approaches give poor yield and selectivity for the desired chemicals (e.g. anhydrosugars). This study reported a novel two-staged controllable pyrolysis process consisting of torrefaction of H2SO4-impregnated eucalyptus waste and subsequent fast pyrolysis for achieving directional valorization of eucalyptus waste. Under different torrefaction temperature and holding time, the performance of two-staged controllable pyrolysis of 0.5%H2SO4-impregnated eucalyptus waste was evaluated. The highest total yield of levoglucosan (82.4%, based on cellulose) was obtained by torrefaction at 300 °C with a holding time of 240 s followed by fast pyrolysis at 550 °C, while the highest total yield of xylosan (17.0%, based on hemicellulose) was obtained from torrefaction at 280 °C with a holding time of 20 s combined with subsequent fast pyrolysis at 550 °C. It is demonstrated that H2SO4 impregnation can achieve the directional valorization of holocellulose into anhydrosugars during torrefaction at low temperature, while evidently inhibiting the degradation of lignin and the formation of non-condensable gas and C1-C4 light oxygenates. The unreacted holocellulose and lignin in torrefied eucalyptus waste can be further converted into anhydrosugars and phenols via subsequent fast pyrolysis. This study provides a very simple and efficient strategy to achieve staged and directional valorization of holocellulose and lignin in biomass waste into value-added chemicals.