95 / 2021-06-30 21:14:49

Pyrolysis of Phragmites australis pretreated by gas-pressurized torrefaction: investigation of pyrolysis kinetics, and characterization of biochar and bio-oil

Biomass; Torrefaction; Gas-pressurized; Pyrolysis; Kinetic; Biochar

Torrefaction have been proven to be an advantageous method for the pretreatment of biomass for its further thermochemical processes. In this study, an atmospheric (AP) and a gas-pressurized (GP) torrefaction of Phragmites australis (PAS) were carried out in a rotary tube furnace and a gas-pressurized autoclave, respectively, aiming to evaluate the effects of torrefaction pressure on pyrolysis behaviors and kinetics (Friedman, KAS and Coats-Redfern methods) of torrefied PAS, and on properties of biochar and bio-oil derived from torrefied PAS. Results showed that the TG weight loss decreased, and maximum DTG range enlarged for GP torrefied PAS when compared to AP torrefied PAS. The activation energy (E) of GP torrefied PAS was significantly higher than that of AP torrefied PAS, indicating that the pyrolysis of GP torrefied PAS had more stability and safety than AP torrefied PAS. The organic matter species of bio-oils included esters, alcohols, naphthalenes, ketones, phenols, furans, and pyridines. Compared with AP bio-oils, GP bio-oils contained higher contents of ketones and pyridines, suggesting that GP torrefaction could increase the potential for pyrolysis of PAS to produce more valuable organic matter. The GP biochars contained higher H/C ratio and pore diameter than AP biochars. The specific surface area of the raw biochar was 307.579 m²/g, and the maximum specific surface area in AP biochars was 350.855 m²/g, while it in GP biochars was only 5.239 m²/g, indicating that AP torrefaction could be beneficial to improve the specific surface area of PAS biochar, while the GP torrefaction had the opposite effect. These results were satisfactory, and seem to have a promising potential for novel torrefaction and pyrolysis applications.