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 240s 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 20s 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.

快速热解是将生物质废物转化为高附加值化学品的一种有前途的方法，但是当前的方法对所需化学品（例如脱水糖）的收率和选择性差。这项研究报告了一种新颖的两阶段可控热解过程，该过程包括对H ₂ SO ₄浸渍的桉木废料进行焙干和随后的快速热解，以实现桉木废料的定向增值。在不同的焙烧温度和保温时间下，0.5％H ₂ SO ₄的两步可控热解性能评价了浸渍的桉树废料。左旋葡聚糖的最高总收率（82.4％，基于纤维素）是通过在300°C的烘烤条件下保持240s，然后在550°C的快速热解而获得的，而木聚糖的最高总收率（17.0％，基于纤维素） （半纤维素）是通过在280°C的烘烤下保持20s的时间以及随后在550°C的快速热解而获得的。证明了H ₂ SO ₄浸渍可在低温下烘焙期间实现全纤维素向脱水糖的定向增值，同时明显抑制木质素的降解以及不可冷凝气体和C1-C4轻质含氧化合物的形成。烘焙的桉树废料中未反应的全纤维素和木质素可通过随后的快速热解进一步转化为脱水糖和酚。这项研究提供了一种非常简单有效的策略，可以实现生物量废物中的纤维素和木质素的阶段性和定向增值，成为增值化学品。