Experimental and kinetic studies on the intrinsic reactivities of rice husk char

In this study, the intrinsic reactivities of chars prepared from rice husk under fast pyrolysis conditions at 700–900 °C in a micro quartz reactor were characterized. The physicochemical structures of collected chars were investigated through scanning electron microscope, energy dispersive spectrometer, and Raman microscope. The intrinsic reaction rates between the pyrolyzed char and CO₂ or O₂ were measured by a thermogravimetric analyzer, and the influences of reaction temperature and gas pressure on the intrinsic rates were quantified to obtain the kinetic parameters. It was observed that the destruction and melting of char became serious when the rice husk was pyrolyzed at 900 °C. As the pyrolysis temperature increased from 700 °C to 900 °C, the concentration ratio of O/C and the graphitization degree of char decreased. For the char-CO₂ reaction, the intrinsic kinetic constants varied within the ranges of 230.74–235.68 kJ/mol for activation energy, 0.309–0.368 for reaction order, and 6.118 × 10⁵–5.710 × 10⁵ 1/s·Pa^m for pre-exponential factor, respectively. For the char-O₂ reaction, the corresponding kinetic parameters were within the ranges of 120.97–124.71 kJ/mol, 1.431–1.981, and 2.591–0.024 1/s·Pa^m, respectively.