Effect of Acid–Base Pretreatment on Pyrolysis Kinetics of Pine

Biomass represents a significant renewable energy source. Pyrolysis is one method to directly convert biomass into thermochemical energy, with alkali and alkaline earth metals (AAEMs) content potentially improving energy efficiency. In this paper, thermogravimetric experiments were carried out on the samples after acid–base pretreatment, and the kinetics were analyzed using the Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose (KAS), and Kissinger methods at various heating rates. The results show that the KAS method is the most reliable among the four methods. As the conversion rate rose from 0.05 to 0.7, the activation energy of water, acid, alkali, and alkaline acid-treated samples calculated using the KAS method increased by 66.08, 42.20, 88.30, and 52.93 kJ/mol, respectively. Acid treatment can remove AAEMs from biomass, inhibit their initial decomposition, and enhance their subsequent decomposition. Alkali treatment can increase the carboxylate content, resulting in a lower activation energy. Nonetheless, the continuous increase in activation energy due to the breaking and reformation of Char–Na bonds hinders subsequent pyrolysis. Additionally, acid–base treatment alters the structure of biomass, leading to a general decrease in activation energy and facilitating its decomposition.