Pyrolysis kinetics and mechanism of pore formation during the pyrolysis of biomass sawdust impregnated with phosphoric acid

Abstract

The precise regulation of the pore structure in bio-based activated carbon derived from industrial waste remains a significant challenge, which has impeded the controlled synthesis of high-quality and cost-effective industrial carbon materials. To facilitate the effective resolution of this critical issue, this work studied the pyrolysis kinetics mechanism and pore formation mechanism during pyrolysis of phosphoric acid-impregnated industrial waste biomass sawdust (BP). Results showed that the thermal decomposition of BP proceeded in four stages as follows: stage 1 was the phase boundary chemical reaction mechanism, a power-law diffusion mechanism and a phase boundary chemical reaction mechanism for stage 2, the power-law diffusion mechanism and a three-dimensional diffusion mechanism for stage 3; the stochastic nucleation and growth mechanism for stage 4. The formation mechanisms of pores were: (a) the reactions between H₃PO₄ and its derived P₂O₅ with biomas sawdust; (b) the reaction between small molecule gases such as H₂O, H₂, and CO₂ with the biomass sawdust. With increase of H₃PO₄ amount, H₃PO₄ and P₂O₅ mainly reacted with biomas sawdust. This process removed large amounts of oxygen and carbon of biomass, meanwhile formed lots of vacancies, accompanying generation of developed mesoporous structure (1.38 cm³/g). These findings provide valuable theoretical guidance for the production of high-quality industrial activated carbon with a tunable pore structure.