Walnut shell oil-bath torrefaction coupled with fast pyrolysis: Effect of torrefaction heating modes

Lignocellulosic biomass, renewable with short growth cycle and diverse sources, can be substituted fossil fuel. However, low effective hydrogen-to-carbon ratio (H/C_eff) limits its applications. Torrefaction and co-pyrolysis with high H/C_eff feedstocks are promising technology. This paper investigated the effect of heating modes on oil-bath torrefaction of walnut shells, followed by fast co-pyrolysis. Six heating modes during oil-bath torrefaction were evaluated. Com1 (Microwave 67 %, Lightwave 33 %) yielded the lowest residual yield 84 wt%, while the highest gas production 495.47 mL/g which mainly composed of CO and CO₂. Torrefied feedstock under Com1 had the highest H/C_eff. Decarboxylation and decarbonylation reactions dominated among oil-bath torrefaction. Com1 produced the most hydrocarbons and least oxygen-containing compounds. As microwave ratio decreased, the content of olefins, acids and phenols decreased, monocyclic aromatic hydrocarbons and alcohols was showed opposite tend. This study offers new ideas for microwave and lightwave torrefaction and promoting hydrocarbon production from lignocellulosic biomass.