Modulating thermokinetic and thermodynamic insights into the pyrolysis of two wetland weed-based biomass via acetic acid pretreatment

Acetic acid remains underexplored as a biomass pretreatment agent, despite its ability to remove harmful minerals that adversely affect biomass pyrolysis with minimal structural degradation or without generating toxic byproducts, unlike mineral acids. Herein, the effect of acetic acid pretreatment on the kinetics and thermodynamics of Phragmites karka (PK) and Actinoscirpus grossus (AG) devolatilization were elucidated using thermogravimetric analysis integrated with isoconversional and combined kinetics methods. Results reveal catalytic effects of inherent minerals in PK, as pretreatment increased E a and ΔH # from 224.6 to 219.9 kJ·mol⁻¹ to 235.9 and 231.0 kJ·mol⁻¹, respectively. In contrast, AG exhibits high E a and ΔH # associated with simultaneous decompositions of cellulose and hemicellulose (282.1 kJ·mol⁻¹ and 277.2 kJ·mol⁻¹), which are substantially reduced after pretreatment to 232.6 kJ·mol⁻¹ and 227.7 kJ·mol⁻¹, respectively. While pretreatment marginally decreases the ΔS # for PK (75.89 to 57.68 J·mol⁻¹·K⁻¹), a pronounced reduction is observed for AG (211.4 to 75.19 J·mol⁻¹·K⁻¹), indicating significant rearrangement of its internal structure. The increase in ΔG # (from 175.6 to 193.3 kJ·mol⁻¹ for PK and from 146.3 to 185.6 kJ·mol⁻¹ for AG) suggests decreased reaction spontaneity following pretreatment. Master plot analysis indicates that pretreatment modifies biomass devolatilization models, with a stronger effect observed in AG. Changes in thermodynamic parameters with conversion further reveal the influence of pretreatment and the dependence of pyrolysis behaviour on biomass composition. These findings provide kinetic and thermodynamic guidance, further validated by the kinetic compensation effect and entropy–enthalpy compensation, for optimization and design of biomass pyrolysis reactor employing green pretreatment strategies.