Pyrolysis of kenaf ( Hibiscus cannabinus L.) biomass: influence of ashless treatment on kinetics and thermal behavior

Recently, ashless pretreatment of lignocellulosic biomass prior to pyrolysis has been used for removing mineral matters to prevent slagging and fouling. The purpose of this study is to fundamentally investigate the pyrolysis characteristics of ashless treated kenaf with torrefaction. The related kinetic parameters and thermal behaviors were examined using non-isothermal thermogravimetric experiments. Thermal degradation experiments were conducted at temperatures ranging from 300 to 900 K at six different heating rates in a N 2 environment. Ashless treatment resulted in a slight increase in hemicellulose and cellulose contents with decreasing lignin, whereas torrefaction of ashless kenaf led the hemicellulose to be decomposed more into cellulose and lignin compared to only ashless treatment. The decrease in the devolatilization index ( D i ) for ashless kenaf (AK) reached approximately 20%, whereas the D i for torrefied ashless kenaf (TAK) increased nearly three times the raw kenaf (RK) value. The distributed activation energy model was used to analyze the kinetics and thermal parameters for pyrolysis. The activation energies of RK, AK, and TAK were estimated as 180.51, 195.32, and 187.15 kJ mol −1 , respectively. Thermodynamic parameters (Δ H , Δ G , Δ S ) and reaction mechanisms were also compared and evaluated. The results indicated that torrefaction can improve the thermal degradation process of AK and can provide useful information for the development and optimization of thermochemical conversion systems using pretreated kenaf as feedstock.