Pyrolysis kinetics of Poplar fluff bio-char produced at high carbonization temperature: A mechanistic study and isothermal life-time prediction

Abstract

This paper provides insights into understanding the physical and chemical changes that take place during reheating process of Poplar fluff bio-char derived by carbonization at high operating temperature (850 ?C). Biochar re-heating experiments were performed by simultaneous TGA-DTG-DSC techniques in N2 atmosphere at 5, 10, 15 and 20 ?C min- 1. Kinetic modeling of the process was done through implementation of model-free and model-based approaches. It was identified that re-heating process contains two stages. The first was described by single consecutive reaction step (up to 200 ?C) which is attributed to removal of physisorbed moisture at surface and in pores of carbonized material, while second was described by multiple reactions, including one consecutive step and two competitive steps. In the last, consecutive pathway includes reduction of PAH compounds (400?600 ?C) into smaller ones, changing degree of condensation of carbon structure continuously. Competitive steps encompass competition between C10H8 (naphthalene) (700?780 ?C) and C9H8 (indene) (700?750 ?C) molecules decomposition. It was found that used heating rates have great influence on regulating the amount of gaseous (combustible) products from these reactions. It was established that internal heat and mass transfer processes control the release of products. Changing the pyrolysis mechanism with temperature of carbonized biochar is the main factor for occurrence of true kinetic compensation effect, which is also discussed by applied isothermal life-time analysis.