Comprehensive investigation on fast pyrolysis of waste Lotus shells to produce valuable products: Pyrolysis characteristics, reaction mechanism and economic analysis

Abstract

Lotus shells (LS) represent an abundant, underutilized renewable resource with significant potential for producing bio-based fuels and chemicals. Pyrolysis emerges as an effective means to maximize the value derived from LS waste. This study assessed the behavior, kinetics of LS pyrolysis for bioenergy production through thermogravimetric analysis (TGA), model-free and model methods. The product distribution resulting from LS fast pyrolysis and the physicochemical properties of the derived products were comprehensively investigated. A plausible reaction mechanism for LS pyrolysis was proposed, followed by an estimation of the associated costs for bioenergy production through pyrolysis. The activation energy (Eα) for LS calculated through Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Friedman (FR) methods was 197.36 kJ/mol, 193.66 kJ/mol, and 197.16 kJ/mol, respectively. The kinetic reaction model for LS pyrolysis was represented by the equation f(α) = α−26.59(1-α)12.35[-ln(1-α)]−27.26, indicating the dominance of a diffusion model and nucleation mechanism in the LS pyrolysis process. Notably, the fast pyrolysis bio-oil derived from LS mainly comprised phenols (34.73 % at 300 °C), acids (42.33 % at 600 °C), and nitrogenous compounds (27.40 % at 800 °C), and the gaseous products primarily consisted of H2, CH4, CxHy, CO, and CO2. Biochar derived from LS exhibited abundant functional groups and mesoporous structure, and its moderate C/N ratio and low H/C ratio indicated potential for soil remediation. Furthermore, the high heating value (21.55–27.01 MJ/kg) of LS biochar exceeded that of Zhaotong lignite, demonstrating its favorable combustion characteristics. This study lays the theoretical foundation for the efficient treatment and high-value utilization of Lotus shells.