Synergistic effects in the thermal conversion of sawdust-pine needles biomass blend: A comprehensive kinetic approach

Abstract

Biomass utilization for renewable energy is gaining attention for mitigating climate change and reducing fossil fuel dependence. However, limited knowledge exists on the pyrolysis behavior and kinetics of biomass blends. This study assesses the thermal degradation behaviour and kinetic characteristics of biomass blend (BB) of sawdust (S) and pine needles (PN). Under nitrogen atmosphere, experiments were conducted at four different heating rates (10, 50, 75, and 100 °C min⁻¹), with TG-DTG curves revealing that increasing heating rates shift curves towards higher temperatures with increased peak heights. One model-fitting method (Coats-Redfern) and four model-free method (Starink, Friedman, Ozawa-Flynn-Wall, and Kissinger-Akahira-Sunose), are simultaneously used to undertake comprehensive kinetic and thermodynamic evaluations. The study overcame the challenge of reaction mechanism identification through application of Criado analysis using Z-master plots, revealing distinct reaction mechanisms at different conversion stages. At lower conversions (α ≤ 0.5), the BB follows a second-order reaction model (F2), while at higher conversions (α > 0.5), it exhibits nucleation-growth processes (A3/A4), demonstrating genuine synergistic effects rather than simple additive behavior. According to the model-free approaches, the average activation energies were 159.27, 170.25, 160.95, and 158.99 kJ mol⁻¹, respectively. A pronounced synergistic effect was observed in the BB, exhibiting a markedly higher experimental conversion rate (1.7 at α = 0.7) than the individual components. This showcases the enhanced reactivity arising from cross-catalytic interactions by alkali and alkaline earth metals present in sawdust and pine needles. Such synergy suggests improved thermal decomposition behavior of biomass blend.