木质素慢速热解机理

Mechanism analysis of lignin slow pyrolysis

利用热重考察了不同升温速率下木质素的热解特性,结合红外光谱对木质素热解的不同阶段生成的半焦的表征结果,分析了木质素在慢速升温条件下的热裂解机理,表明:木质素的热解是一个旧键断裂挥发、新键重组的过程。热解过程随着反应时间的推移依次分为水分挥发、支链断裂重组或挥发和芳环缩聚成碳3个阶段。采用Flynn-Wall-Ozawa方法,根据不同升温速率下测得的失重速率变化求算后两个阶段的活化能,结果分别为64kJ.mol-1和132kJ.mol-1,进一步证明了木质素热解的分段特征,并表明芳环缩聚成碳所需活化能远大于与苯环相连的支链断裂所需的能量。

The characteristics of lignin pyrolysis was investigated by TG at different heating rate,combined with FTIR characterization of the chars from different stages of slow pyrolysis of lignin to analyze lignin pyrolysis mechanism at slow heating rate.The results show that pyrolysis of lignin is a process involving breakage of old chemical branched chains and recombination of new branched chains.With time extending i.e.temperature rising,there are three successive stages in process of lignin pyrolysis：dewatering,breakage-recombination-volatilization of branched chains and polymerization of aromatic rings and formation of carbon.Based on the weight loss rate at different heating rates,according to the Flynn-Wall-Ozawa equation,the calculation of kinetic parameters resulted in activation energies of 64 kJ·mol-1 and 132 kJ·mol-1 for the latter two pyrolysis stages,respectively.This indicates further that the pyrolysis of lignin carried out in different stages and the breakage of the branded chains was easier than the polymerization of aromatic rings.