Kinetics and thermodynamics of non-isothermal pyrolysis of Terminalia chebula branches at different heating rates

Non-isothermal thermogravimetric tests of Terminalia chebula (Helikha) were conducted under inert N₂ gas environment for temperatures (25–900°C) at heating rates of 10, 20, 35, and 55°C min⁻¹. Kinetic triplet approximated employing five iso-conversional methods namely, differential Friedman method (DFM), distributed activation method (DAEM), Ozawa–Flynn–Wall (OFW), Kissinger–Akahira–Sunose (KAS), and Starink (STK). Average values of activation energy (kJ mol⁻¹) and frequency factor (min⁻¹) calculated by the five models were 227.11, 2.98 × 10²¹ for DFM; 229.21, 4.63 × 10²¹ for KAS; 227.11, 3.81 × 10²⁰ for OFW; 225.54, 1.15 × 10¹⁸ for STK; and 227.33, 3.02 × 10²⁰ for DAEM respectively over the conversion range up to 0.8. In the kinetics study, correlation coefficient (R²) of greater than 0.97 is noticed in the conversion range of α = 0.1–0.8 for all models. From thermodynamic analysis, average values of ΔH (kJ mol⁻¹), ΔG (kJ mol⁻¹), and ΔS (kJ mol⁻¹ K⁻¹) for DAEM: 221.8, 179.69, and 0.065; for DFM: 236.40, 179.37, and 0.089; for KAS: 221.8, 179.69, and 0.065; for OFW: 220.22, 179.72, and 0.063; and for STK: 222.02, 179.68, and 0.066 were estimated to assess viability and reactivity of the process. Criado's master plots revealed that the data obtained from pyrolysis of selected biomass was followed a multistep reaction pathway.