Thermal degradation of kenaf (Hibiscus cannabinus L.): Impact of torrefaction on pyrolysis kinetics and thermal behavior

Pre-treatment of biomass has garnered significant research attention to facilitate biomass utilization. This study examines the effect of torrefaction on the pyrolysis characteristics of kenaf (Hibiscus cannabinus L.), which grows in South Korea and has a relatively short life cycle as well as a low production cost among herbaceous biomass. In this study, raw kenaf (RK) and torrefied kenaf (TK) were prepared in an inert atmosphere. Torrefaction was carried out in a bed reactor for 30 min at 503, 523 and 553 K, and pyrolysis was performed at six heating rates and analyzed using thermogravimetric analysis. The results showed that the optimal temperature for RK torrefaction based on the energy-mass co-benefit index was 523 K, owing to a higher energy density and low volume. The torrefaction and a higher heating rate resulted in the weight loss and decomposition rate (derivative thermogravimetric) curves moving to a higher temperature region, and improvement in the devolatilization index of the TK. The activation energy was calculated using three methods (Kissinger, Flynn–Wall–Ozawa, and Kissinger–Akahira–Sunose), with all indicating that the activation energy of the TK was greater than that of RK. Additionally, in terms of thermodynamic parameters, the TK had a higher frequency factor, higher enthalpy, slightly lower Gibbs free energy, and higher entropy than those of RK. These kinetic and thermal behavior results are useful for designing pyrolysis processes wherein TK is used as a feedstock; moreover, they provide a useful reference for TK heat conversion applications.

Abstract licence: CC BY-NC-ND

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