Kinetic and thermodynamic study of pyrolysis of the hydrolyzed residue of rice straw and husk by subcritical water process using thermogravimetric analysis

Abstract

The use of hydrolyzed rice straw (HRS) and hydrolyzed rice husk (HRH) as feedstock for pyrolysis was evaluated through kinetic and thermodynamic studies. HRS and HRH were obtained from subcritical water hydrolysis (SWH) at different temperatures (180, 220, and 260°C). The Coats‐Redfern method was used to analyze the thermal behavior through thermogravimetry (TG) and derivative thermogravimetry (DTG) curves. TG profiles showed higher decomposition in the range of 250–400°C, especially for rice straw (RS) and HRS (80 wt %). The pyrolysis curves were well predicted by a first‐order reaction model. The kinetic analysis showed a variation in activation energy (EA) between 24.3 to 41.3 kJ mol−1 and 40.4 to 54.7 kJ mol−1 for RS/HRS and rice husk (RH)/HRH, respectively. The enthalpy (ΔH), Gibbs free energy (ΔG), and entropy (ΔS) varied from 25.9 to 39.6 kJ mol−1, 35.4 to 69.6 kJ mol−1, and −64.1 to −6.7 J mol−1 K−1, respectively, for RS/HRS, and 35 to 49.8 kJ mol−1, 43.2 to 79.3 kJ mol−1, and −53.5 to −10.2 J mol−1 K−1, respectively, for RH/HRH. These results showed that the pyrolysis reactivity using HRS is higher than HRH, which indicates the pyrolysis of HRS is more advantageous than HRH.