Oxygen migration characteristics during bamboo torrefaction process based on the properties of torrefied solid, gaseous, and liquid products

Bamboo is a potentially renewable biomass resource which can be converted into bio-fuels and bio-chemicals by thermochemical conversion technology. Torrefaction deoxygenation pretreatment can effectively upgrade bamboo into high-grade fuels with a lower content of water and higher energy density. Therefore, it is essential to establish the deoxygenation mechanism and oxygen migration characteristics during the bamboo torrefaction process, based on the properties of torrefied solid, gaseous, and liquid products. In this study, these three types of torrefied product (solid, gaseous, and liquid) were produced at different torrefaction temperatures (210, 240, 270 and 300 °C) by the tube furnace, TGA−FTIR, and Py−GC/MS. Results showed that following a series of deoxygenation reactions, the oxygen removal efficiency of bamboo reached a maximum of 28.52% at 300 °C, resulting in the highest HHV of 23.12 MJ kg−1. Oxygen in the torrefied solid product was released in the form of torrefied gaseous components (CO2, H2O and CO) and torrefied liquid oxygen-containing compounds (E.g. acids, phenols, furans and ketones). CO2 was the dominant oxygen carrier in the torrefied gaseous product, with oxygen distribution in the torrefied gaseous components ranked in the order: CO2 (82.1–86.6%) > CO (10.9–13.9%) > H2O (2.4–4.1%). In the torrefied liquid product, oxygen transferred to acids, furans, ketones and aldehydes was favored under lower torrefaction temperatures, while more oxygen was transferred to phenols under higher torrefaction temperatures.