Effect of functional groups on hydrogenolysis of lignin model compounds

Lignin is a future feedstock for the production of low molecular weight aromatics, and hydrogenolysis is probably the most promising process for lignin depolymerization. Effect of the benzylic alcohol group, aromatic methoxyl and phenolic hydroxyl groups on the hydrogenolysis of β-O-4 bonds in lignin model compounds was investigated in Pd/C hydrogenolysis system. It was found that the β-O-4 bonds in compounds with no a benzylic alcohol group were cleaved directly and quickly to form two aromatic monomers in near-quantitative yield. However, both dehydrogenation and dehydroxylation occurred for the model compounds containing a benzylic alcohol group, and resulted in more complicated products distribution. The dehydrogenation of a benzylic alcohol group hindered the cleavage of β-O-4 bonds to form aromatic monomer products. The results also indicated that both the aromatic methoxyl and phenolic hydroxyl groups had no impact on products distribution. The aromatic methoxyl group in non-phenolic and phenolic compounds promoted the cleavage of β-O-4 bonds, while the phenolic hydroxyl group had a slightly negative impact on cleavage of β-O-4 bonds.