THE ORETICAL STUDY ON PYROLYSIS OF β-O-4 TYPE LIGNIN DIMER MODEL THE ORETICAL STUDY ON PYROLYSIS OF β-O-4 TYPE LIGNIN DIMER MODEL

摘要

Lignin is high molecular polyphenols of natural origin and main by-product of pulp-and-paper industry.It is the obvious candidate to serve as a future aromatic resource for the production of liquid biofuels,biomaterials and green chemicals.In order to understand the pyrolysis mechanism of lignin,2'-methyl(2'-methyl'-phenylethyl)phenyl ether was selected as a lignin dimer model compound of β-O-4-linkage.The pyrolysis of this dimer was investigated by using density functional theory B3LYP methods at 6-31G(d,p)level.Eight possible pyrolysis pathways(mainly the homolytic cleavage of C-O bond)were proposed according to bond dissociation energies of lignin dimer model,then the activation energies for each reaction pathway were calculated.The calculation results show that the bond dissociation energy of Cβ-O is the lowest,and that of C-C is second lowest,and the order of all kinds of bond dissociation energy is Cβ-O ＜Cα –Cβ ＜ Caromatic-O＜ Cα-Caromatic.It could be deduced that the dimer was mainly decomposed through the cleavage of the Cβ-O linkage.And major pyrolytic products of phenol compounds were formed in this process Thus,the optimum pathway1 can be determined based on its kinetic parameters and lowest energy barrier of 44.73KJ/mol..