Stable free radicals are the long-lived macromolecule radicals formed in pyrolysis, and their reactions play an essential role in biochar formation. The alkali and alkaline earth metals (AAEMs) in biomass might be involved in the radical reactions during pyrolysis. Figuring out the effect of AAEMs on the reactions of stable free radicals can further understand the radical reaction mechanism and the formation of biochar in pyrolysis. In this paper, the in-situ electron paramagnetic resonance (EPR) spectroscopy was used to detect the stable free radicals in cocoanut pyrolysis, and the effect of AAEMs was analysed by the comparative experiments. The results indicate that the stable free radicals in nascent chars, which are generated from the thermal decomposition of biomass, could react and couple with each other. The AAEMs in biomass improve the activity of stable free radicals and promote the radical-radical coupling during high-temperature pyrolysis above 400 °C, which inhibits the condensation of aromatic structure and generates more weak bonds in hot nascent char. After stopping the heating, the weak bonds will be broken by cooling stress, thus inducing radical reactions and further changing the char structure.

稳定的自由基是热解中形成的长寿命的大分子自由基，它们的反应在生物炭的形成中起着至关重要的作用。生物质中的碱金属和碱土金属（AAEM）可能参与热解过程中的自由基反应。弄清楚AAEMs对稳定自由基反应的影响可以进一步了解自由基反应机理和热解中生物炭的形成。本文采用原位电子顺磁共振（EPR）光谱技术检测椰子热解过程中的稳定自由基，并通过对比实验分析AAEMs的作用。结果表明，生物质热分解产生的初生焦中的稳定自由基可以发生反应并相互耦合。生物质中的AAEM提高了稳定自由基的活性，并在400℃以上的高温热解过程中促进自由基-自由基耦合，从而抑制芳香结构的缩合并在热初生焦中生成更多的弱键。停止加热后，弱键会因冷却应力而断裂，从而引发自由基反应，进一步改变焦结构。