Theoretical Studies on Formation Mechanism of CO and CO_2 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.