Intrinsic oxidation kinetics examined with thermogravimetric analysis: Mass transfer limitations and kinetic modelling

Abstract

Mass‐transfer limitations frequently pose a significant challenge for the accurate determination of apparent kinetic parameters. To address this, we employed thermogravimetric analysis (TGA) to systematically evaluate the effects of particle size, sample mass, and gas flow rate on mass‐transfer limitation during the oxidation of bamboo char, bituminous coal char, and carbon black. A comparative analysis revealed that bamboo char exhibited superior mass‐transfer characteristics: its threshold sample mass (6 mg) was higher than those of bituminous coal char and carbon black char (2 mg), while its threshold flow rate (150 mL/min) was lower than that of the latter two (180 mL/min). The critical particle‐size range to overcome mass‐transfer limitations was 50–75 μm for bamboo char, compared to a threshold of ≤75 μm required for bituminous coal char. Under these optimized conditions, oxidation data were further analyzed using three classic kinetic models: volume model (VM), shrinking‐core model (SCM), and random pore model (RPM). RPM reproduced the behaviour of bamboo and coal chars most accurately and yielded activation energies consistent with iso‐conversional (model‐free) estimates, whereas all three models showed significant deviations for carbon black. This study highlights the high mass transfer efficiency of bamboo char and provides a crucial reference for selecting operating parameters based on material characteristics in kinetic studies to minimize the mass transfer effect.