木质素热解中CO和CO2形成机理的理论研究

采用密度泛函理论方法(B3LYP)对含苯基的各种木质素模型化合物的脱羰基反应和脱羧基反应进行了理论研究。设计了8种模型化合物 R1-R8的8条脱羰基反应路径(1)-(8)和8种模型化合物 R9-R16的8条脱羧基反应路径(9)-(16)。计算了不同温度下各热解反应途径的标准热力学和动力学参数。计算结果表明,反应路径(1)-(4)的脱羰基反应能垒明显高于反应路径(5)-(8),CO 更可能通过苯基(对羟苯基、愈创木基和紫丁香基)乙醛的脱羰基反应而形成；反应路径(9)-(12)的脱羧基反应能垒低于反应路径(13)-(16),CO2的形成更可能通过苯基(对羟苯基、愈创木基和紫丁香基)甲酸的脱羧基反应而完成。

Theoretical Studies on Formation Mechanism of CO and CO2 in Pyrolysis of Lignin

The decarbonylation and decarboxylation reactions of lignin model compounds were theoretically studied by using density functional theory methods at B3LYP/6-31G++(d,p) level. Eight decarbonylation reaction pathways (1)-(8) and eight decarboxylation reaction pathways (9)-(16) were designed. The standard thermodynamic and kinetic parameters of every reaction pathway in different temperature ranges were calculated. The calculation results showed that energy barriers of decarbonylation reaction pathways (1)-(4) were apparently higher than those of decarbonylation reaction pathways (5)-(8), and then CO was formed more easily through decarbonylation of phenyl(p-hydroxyphenyl, guaiacyl and syringyl) acetaldehyde; energy barriers of decarboxylation reaction pathways (9)-(12) were lower than those of decarboxylation reaction pathways (13)-(16), and then CO₂ was formed more easily through decarboxylation of phenyl (p-hydroxyphenyl, guaiacyl and syringyl) formic acid.