Biomass pyrolysis for biochar production: Study of kinetics parameters and effect of temperature on biochar yield and its physicochemical properties

This study investigates the pyrolysis kinetics behaviour and temperature effects on biochar yield and properties during pyrolysis. The kinetic study of biomass was performed using a thermogravimetric analyser at dynamic heating rates (10, 30, and 50 °C min⁻¹) in an inert atmosphere. The kinetic parameters were estimated using Kissinger-Akahira-Sunose (KAS), Distributed Activation Energy Model (DAEM), and Vyazovkin model (VZ). The pyrolysis experiment was performed in a stainless steel semi-batch reactor at 400, 600, and 900 °C, 10 ^oC min^-1 heating rate, 45 min holding time and 100 mL min⁻¹ nitrogen gas flow rate. The produced biochar was characterised using proximate analysis, ultimate analysis, heating value, bulk density, BET surface area analyser, TGA, FTIR, and FE-SEM analysis. The physicochemical results support the candidacy of biomass for biochar and fuel production. Further, the kinetic analysis of MWS using KAS, DAEM, and VZ was found to be 233.39, 238.11, and 224.74 kJ mol⁻¹, respectively. The experimental results reveal that higher temperatures (600 and 900 °C) generally reduce biochar yield (19 %) due to increased devolatilization but enhance the biochar's surface area (17 %) and carbon content (4.84 %). The characterisation results of biochar confirmed higher carbon content (76.02 wt. %), HHV (36.97 MJ kg⁻¹), and significant oxygen content (22.01 %) at 900 °C. Also, the thermal profile and surface morphology of the biochar suggest that biochar derived at 600 and 900 °C can be used for carbon-based applications, whereas biochar derived at 400 °C can be used for soil amendment or fertiliser applications.