Effect of torrefaction on yield, reactivity and physicochemical properties of pyrolyzed char from three major biomass constituents

Torrefaction is an efficient pretreatment technology for large-scale and high-value utilization of biomass fuel. To understand the effects of torrefaction pretreatment on the physicochemical characteristics of the pyrolyzed char from the three major constituents of lignocellulosic biomass (cellulose, xylan-representative of hemicelluloses, and lignin), torrefied samples were produced at 200, 260, 320, and 380 ℃, and then pyrolyzed at 1028 ℃ with a heating rate of 65 ℃/s and 0.25 ℃/s, respectively. The experimental results demonstrate that the torrefaction temperature strongly influences the pyrolyzed char’s yields, oxidative reactivities, and physicochemical structure. The sensitivity of the accumulated char yield and char reactivity to the torrefaction temperature differed with varied constituents. Accurate modeling of accumulated char yield is achieved through a weighted summative law, showing a decreasing deviation from 2.4 wt% to 0.6 wt% as torrefaction temperatures increase. Raman spectra indicate that there is a strong correlation between the relative amount of small and large aromatic rings and the accumulated char yield of torrefied samples, with the determination coefficient R2 of 0.98, 0.88, and 0.77 for cellulose, xylan, and lignin, respectively.