Abstract:

The evolution of lignin pyrolysis products and the migration mechanism of oxygen were discussed in depth by ReaxFF-MD simulation, and the pyrolysis reaction mechanism of lignin was emphatically analyzed. The results showed that 2000 K was the turning point of different pyrolysis mechanisms of lignin, and the primary decomposition reaction was dominant at low temperatures, which principally involved the decomposition of lignin macromolecular network structure and the cleavage of weak bridge bonds. Additionally, an increase in temperature facilitated the migration of oxygen into bio-oil and pyrolysis gas. In the higher temperature range, the lignin pyrolysis process included both the initial decomposition reaction and the subsequent secondary reaction of the pyrolysis products at high temperatures. The higher the reaction temperature, the shorter the time of the primary reaction. During the secondary reaction, most of the bio-oil is converted into coke through recombination or polycondensation, and only a small part of the bio-oil is decomposed to generate pyrolysis gas. Oxygen mainly existed in the pyrolysis gas at high temperatures. The production of oxygen-containing gases such as H₂O, CO₂, and CH₂O were related to the abundant hydroxyl, carboxyl, and carbonyl in the lignin structure.

Key words: lignin, pyrolysis, ReaxFF molecular dynamics, pyrolysis mechanism

摘要：

通过ReaxFF-MD反应分子动力学模拟，深入探讨了木质素热解产物的演化规律及氧元素的迁移机制，重点分析了木质素的热解反应机理。结果表明，2000 K是木质素热解不同反应机制的转折点，低温度条件下一次分解反应起主要作用，主要涉及大分子网络结构的分解及弱桥键的断裂。并且温度的升高有助于氧元素向生物油和热解气迁移。高温度条件下木质素热解过程既存在一次分解反应也包含热解产物的二次反应。反应温度越高，一次反应的时间越短。二次反应过程中绝大部分生物油通过重组或缩聚转化为焦炭，仅有小部分生物油分解生成热解气。高温条件下，氧元素主要存在于热解气中，H₂O、CO₂、CH₂O等含氧气体的产生与木质素结构中含有丰富的羟基、羧基、羰基官能团有关。

关键词: 木质素, 热解, 反应分子动力学, 热解机理