| Biomass energy is the fourth largest energy source in the world,followed by coal,fossil oil and gas.It has the characteristics of abundant in production,renewable,and non-pollution,which can be seen as an ideal clean energy resource,and its efficient usage has become one of the important subjects to the researchers.Lignin is the second most abundant biomass resource in the world,whose development and utilization has paid numbers of scholars' attention.It can be seen from former researches' that the liquefaction with hydrogenation can effectively promote the breakage of the lignin's chemical bond,and efficiently improve the quality of liquefaction products as well.Thus,it has been considered as a high efficient pathway in degrading lignin.Therefore,the study on liquefaction mechanism is helpful to understand the liquefaction characteristics and the formation process of the products,so as to find the efficient way of transformation.In this paper,the possibility of liquefaction path of lignin model compounds which is in supercritical methanol has been studied by means of quantum chemical calculation in molecular simulation.The reaction of hydrogenated liquefaction and alcoholysis of lignin model compounds dihydrobenzofuran in supercritical methanol has been studied by density functional B3LYP/6-31G++(d,p)method.As the result showed,the heterocyclic fracture of dihydrobenzofuran is relatively easy under the action of active hydrogen,and the main hydrogenation product is 2-ethylphenol.2-ethylphenol may further undergo two reaction paths including alcoholysis and hydrodeoxygenation.Every remaining position on the benzene ring has the possibility to be alcoholysised,especially 2-ethyl-6-methyl phenol which is easiest to be produced by energy comparison.The hydrogenation process in the hydrodeoxygenation process is better than the hydrogenolysis process,and the C-O bond on the aliphatic ring is easier to be breaked than the C-O bond on the benzene ring.The reaction of hydrogenated liquefaction of lignin model compounds guaiacol in supercritical methanol has been studied by density functional B3LYP/6-31G++(d,p)method.Four possible reaction pathways has been eproposed.It was found that the presence of active hydrogen can reduce the rupture energy of guaiacol oxygen functional groups.Under the induction of active hydrogen,guaiacol forms veratridine and catechol,which tend to break the bond to form phenol and anisole for subsequent liquefaction experiments.Path2,Path3 and Path4 were used to compare the degree of hydrodeoxygenation of guaiacol,phenol and anisole under the action of active hydrogen.When the reactants and products are the same,the total energy change is the same.The difference lies in the energy barrier to be overcome in the whole process.After the hydrogenation of guaiacol,the hydroxyl removal is preferentially removed and the methoxy group is removed to form cyclohexane.When the guaiacol is hydrogenated,the hydroxylation of phenol is preferentially removed to carry out the subsequent hydrodeoxygenation reaction.Anisole is easier to form cyclohexane than phenol,and the cleavage of the C-O bond in the aliphatic ring is easier than that of C-O bond attached to the benzene ring.By studying the alcoholysis of guaiacol,phenol,and anisole in supercritical methanol,it was found that the energy barrier of the alcoholic products of guaiacol is not big difference.Phenol and anisole give priority to the formation of ortho-substituted products,and the steric hindrance of methoxy would affect the monovalent substituted products,so that the activation energy of alcoholysis increased.The hydrodeoxygenation energy of the three alcoholic products was compared.From the results,it can be concluded that the hydroxyl group was easily be dissociated when the hydrogenation reaction was carried out under the induction of hydrogen.Under the absence of hydrogen condition,the methoxy group is easier to be dissociated than the hydroxyl group,but the cleavage of the C-O bond in the aliphatic ring is still easier. |
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