Properties of oxidatively torrefied Chinese fir residue: Color dimension, pyrolysis kinetics, and storage behavior

Abstract

Chinese fir residue, as an important bioenergy, was torrefied at 240–270 °C in 0–9% O2 atmosphere to improve its utilization. By using colorimetry, the good relationships between mass loss during oxidative torrefaction (R2 > 0.91), proximate analysis (R2 > 0.96), elemental analysis (R2 > 0.82) and color coordinates have been established. Based on thermogravimetric analysis, the increased O2 (0–9%) in the torrefaction system significantly affected the peak temperature, peak height, T50, and R50 of the torrefied samples, especially the samples torrefied at 270 °C. Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Friedman, and Coats-Redfern methods can satisfactorily estimate the apparent activation energies of the samples. As temperature and O2 concentration in the torrefaction system increased, the fragmentation of lignocellulose accelerated, and the apparent activation energy of the raw sample was estimated to decrease from 121.7–135.4 to 66.0–116.6 kJ mol−1. During the 30 days of storage, the increased hydrophobicity and composition change reduced the loss of dry matter, color change, and aldehyde/ketone emission of the torrefied sample from 7.37%, 3.6, and 16.69 μg g−1 to 1.52%, 0.1, and 2.65 μg g−1, respectively. In this work, efficient ways to accelerate the properties evaluation, improve the pyrolysis behavior of Chinese fir residue, and simultaneously control its aldehyde/ketone formation during storage were proposed.